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2008:221 CIV
M A S T E R ' S T H E S I S
New type of slewing bearingfor ship crane
John Lovén Tommy Nordin
Luleå University of Technology
MSc Programmes in Engineering Mechanical Engineering
Department of Applied Physics and Mechanical EngineeringDivision of Machine Elements
2008:221 CIV - ISSN: 1402-1617 - ISRN: LTU-EX--08/221--SE
Abstract MacGREGOR (SWE) AB Crane division, located in Örnsköldsvik, Sweden, is part of the
Cargotec Corporation. MacGREGOR develops and manufactures cranes for shipboard
cargo handling. A typical MacGREGOR ship crane consists of four main modules, the
pedestal, the foundation, the crane house and the jib. The slewing bearing connects the
crane house to the foundation, allowing the crane to rotate around its vertical axis. If the
bearing should fail and split, the crane house will fall down which is a safety issue. The
current slewing bearing design requires a narrow flatness tolerance of the foundations top
surface which complicates the assembly process.
The purpose of this project was to investigate the possibility to use a double slewing
bearing design in order to create a safer and more easily assembled crane. Initially, a
problem analysis was performed in order to understand the scope of the project. A series
of ideas were developed through brainstorming sessions and discussions with handpicked
personnel at MacGREGOR. The ideas were narrowed down and refined into concepts.
The concepts were evaluated and ranked by predetermined criteria derived from the
needfinding process. Two of the concepts were chosen to be further investigated in the
detail design phase, where it was found through numerical calculations that due to the
stiffness of the top bearing, not enough moment could be distributed to the lower bearing
for the design to be feasible. Therefore, finite element analyses were made of the stay
connecting the bearings in order to find a stiffer design, however the results only
confirmed the numerical calculations.
When it became clear that the moment distribution to the lower bearing was insufficient
an alternative design was examined in order to solve the safety issue with a more
effective approach. A safety hook concept was discarded earlier in the project since it fell
outside the delimitations. However, since it now seemed as a realistic alternative it was
investigated in order to remedy the safety issue.
An internal safety hook design was produced. Finite element analysis and numerical
calculations suggested that the design would have to be rather robust. The weight of the
hooks implied that the assembly could be difficult. It is therefore recommended to design
an external safety hook solution.
Glossary
Pedestal
Foundation
Slewing-
bearing
Crane house
Jib
Outreach
Crane house bottom plate
Slewing-
bearing
Blank
Sheet casing
Ring
Cone
Foundation
bottom plate
Table of Contents 1 Introduction ................................................................................................................. 5
1.1 Background ......................................................................................................... 5
1.2 Company description .......................................................................................... 5 1.3 Purpose ................................................................................................................ 6 1.4 Goal ..................................................................................................................... 6 1.5 Delimitations ....................................................................................................... 6
2 Methods used .............................................................................................................. 7
2.1 SIRIUS Masterplan ............................................................................................. 7 2.2 Planning .............................................................................................................. 7 2.3 Problem analysis ................................................................................................. 7
2.3.1 Needfinding..................................................................................................... 7 2.3.2 Benchmarking ................................................................................................. 9 2.3.3 Related technology.......................................................................................... 9 2.3.4 Scope ............................................................................................................... 9
2.4 Product characteristics ........................................................................................ 9 2.5 Concept generation ........................................................................................... 10
2.6 Concept evaluation and selection...................................................................... 10 2.7 Detail design ..................................................................................................... 13
2.7.1 Software ........................................................................................................ 13
2.7.2 Stress analysis ............................................................................................... 14 2.7.3 Bearing design .............................................................................................. 14
3 Current solution ........................................................................................................ 17
3.1 The existing design ........................................................................................... 17
3.1.1 MacGREGOR Crane GL4528 ...................................................................... 17 3.1.2 Slewing bearing ............................................................................................ 18
3.2 Manufacturing and assembly ............................................................................ 18 4 Implementation and results ....................................................................................... 21
4.1 Product development ........................................................................................ 21
4.2 Planning ............................................................................................................ 21 4.3 Problem analysis ............................................................................................... 22
4.3.1 Needfinding................................................................................................... 22
4.3.2 Benchmarking ............................................................................................... 26 4.3.3 Related technology........................................................................................ 28
4.4 Product characteristics ...................................................................................... 30
4.5 Concept generation ........................................................................................... 30 4.6 Concept evaluation and selection...................................................................... 32 4.7 Detail design ..................................................................................................... 35
4.7.1 Numerical analysis ........................................................................................ 35
4.7.2 Finite element analysis .................................................................................. 39 5 Final results ............................................................................................................... 44 6 Discussion ................................................................................................................. 45 7 Recommendations ..................................................................................................... 47 8 References ................................................................................................................. 52 Appendix ........................................................................................................................... 54
5
1 Introduction This project was performed as a master thesis work in the Master of Science program in
mechanical engineering, mechanical design at Luleå University of Technology. The
project was assigned by MacGREGOR (SWE) AB Crane Division, located in
Örnsköldsvik, Sweden, where the project also was performed during the period of mid
August to December 2008.
1.1 Background
The typical MacGREGOR ship crane consists of four main parts; the pedestal, the
foundation, the crane house and the jib. Between the crane house and the foundation the
slewing bearing is mounted, allowing the crane to turn around its vertical axis by a
hydraulically powered slewing gear unit. The bearing is designed to withstand the axial
and radial loads as well as the tilting moment generated by the maximum load at
maximum outreach. It is crucial for the slewing bearing to have a long service life. If the
bearing should fail and split, the crane house will fall down.
The current solution craves a narrow tolerance regarding the flatness of the blank’s top
surface which the bearing is bolted onto; otherwise the bearing will become distorted
when mounted. Before shipyard assembly, the blank is welded onto the top of the
foundation and machined to its final shape. The heat generated in the welding process,
when the foundation and pedestal are assembled at the shipyard, causes the blank to
deform leading to difficulties staying within the range of tolerable flatness thus
complicating the assembly process. If the welding instructions provided by
MacGREGOR are followed, the risk of blank deformation is minimized. (1)
1.2 Company description
MacGREGOR Group is part of the Cargotec Corporation and is the global market leader
in providing marine cargo handling solutions. Cargotec Corporation offers handling
systems and related services for the loading and unloading of goods on land and sea.
Cargotec Corporation includes MacGREGOR Group, Kalmar and HIAB, operates in
close to 160 countries and has 11,000 employees. (2) MacGREGOR Group offers cargo
flow solutions including hatch covers, lashing systems, solutions for passenger and
rolling cargo, dry bulk handling, offshore handling solutions, port and terminal solutions
and cranes. MacGREGOR Group operates in 50 countries and has just over 2200
employees in 2007. (3)
MacGREGOR (SWE) AB Crane Division, from here on referred to as MacGREGOR,
develops and manufactures a wide range of cranes for shipboard cargo handling. The
development and design office is located in Örnsköldsvik, Sweden. Production takes
place near major shipyards by long-term partners in Poland, Croatia, China and Korea.
MacGREGOR supplies basis and components from all over the world to the production
partners through the logistic-centers in Nantong, China and Hamburg, Germany. The
production partners manufacture the steel design, assemblies the components, finishes
and tests the product according to instructions given by MacGREGOR (1)
6
Established 1937 in Whitley Bay, England, MacGREGOR & Company offered a
revolutionary steel hatch cover for cargo transportation at sea. In 1983, after a merger
with Navire, MacGREGOR-Navire was formed. (2) (3)
Hägglund & Söner started out in 1899 as a carpentry shop and grew to be one of the
biggest machine shops in the north of Sweden, manufacturing, amongst other things,
buses, mechanical loaders and airplanes. The company was bought by ASEA in 1972 and
in 1991 by Incentive AB. (4) Hägglunds & Söner was divided into divisions and in 1993
the Marine division was merged with acquired MacGREGOR-Navire and today’s
MacGREGOR Group was formed. (2) Cargotec Corporation, which acquired
MacGREGOR Group in 2005, was formed after a demerger from KONE Corporation the
same year (2).
1.3 Purpose
The purpose with the project is to design a safer slewing bearing solution preventing the
crane house to fall down if the bearing should fail. Also a more admissible flatness
deviation is desired to simplify the assembly process. (1)
1.4 Goal
To design a cost efficient slewing bearing solution which allows more flatness deviation
and prevents the crane house to fall down if the bearing should fail. (1)
1.5 Delimitations
This project does not consider a general MacGREGOR crane but a specific model with
predetermined load cases applied on a particular slewing bearing designed by Rothe Erde.
Because of the limited time schedule no extensive benchmarking is made regarding
competitor products, only a brief literature study is performed. No prototype will be
manufactured thereby all testing of the design will be restricted to computer simulation.
The cost of the design is estimated by the physical weight of the structure using data
supplied by the manufacturing partners.
7
2 Methods used Methods used incorporate the theory involved in methods described in literature and
procedures used by MacGREGOR.
2.1 SIRIUS Masterplan
SIRIUS Masterplan, appendix 1, is a guide to be used during creative product
development. It is developed by Luleå University of Technology and is used in the final
year course named SIRIUS for students graduating with a Master of Science degree in
Mechanical Engineering, Mechanical Design. In this course, the students practice
creative product development in projects running over the whole academic year with real
companies as sponsors.
2.2 Planning
Planning is crucial in order to cover all aspects of the project and finish on time. SIRIUS
Masterplan suggests what needs to be done in the planning phase. Team roles need to be
defined so that responsibilities can be delegated and clarified within the group. Individual
and group goals need to be discussed to clarify expectations and goals and thereby
avoiding misunderstandings. The coaching role needs to be understood by the members
of the group and the coaches themselves. Therefore, the group members and coaches
need to discuss the preferred coaching strategy. To estimate costs, a budget should be
created and continuously updated. A Gantt chart should be produced and continuously
updated throughout the project showing phases and milestones in relation to the overall
plan. SIRIUS Masterplan also points out that planning is a continuous activity which
needs to be revised and updated along the way.
The Gantt chart, according to Johannesson et al. (5), is used to visualize the time
consumption and start/finish points for the main activities in a project. The method is
usually used in an early stage of a project; it is a purely informative method and is
therefore not suited for follow-up or process control. The Gantt chart can be visualized in
a coordinate system where the activities are denoted on the y-axis and the x-axis
represents time. Each activity is constituted by a horizontal line where the length
corresponds to the estimated time consumption of the activity.
2.3 Problem analysis
Problem analysis is necessary in order to solve the correct problem and satisfy the needs
at hand and thereby achieving the best possible results and outcome. In SIRIUS
Masterplan this phase is called Design Space Exploration. It consists of four phases;
Needfinding, Benchmarking, Related Technology and Scoping.
2.3.1 Needfinding
Needfinding is about finding the actual needs that the project has to satisfy in order to be
successful. When a product satisfies needs, it offers perceived benefits to the customer
which is a condition for making it a successful product (6). Ulrich and Eppinger have
developed a method where needfinding is a part of the product development process. This
method is based on close interaction between those who have detail control of the product
8
and the customers. This method is suitable for development of new as well as refinement
of old products. Some of the goals of this method are to (6):
- Focusing the product on customer needs. - Identify needs; hidden, latent or explicit. - Act as fact basis for the product characteristics. - Making sure that no critical needs are missed.
(After Ulrich and Eppinger (6))
Ulrich and Eppinger’s method consists of five steps (6):
1. Gather raw data from customers. 2. Interpret the raw data in terms of customer needs. 3. Organize the needs into a hierarchy of primary, secondary, and (if necessary)
tertiary needs.
4. Establish the relative importance of the needs. 5. Reflect on the results and the process.
(Ulrich and Eppinger (6))
Step one, gathering raw data from customers, can be performed by conducting interviews,
using focus groups and observing the product in use. Written surveys are not
recommended at this early stage in the needfinding process. By interpreting the raw data,
need statements can be written. From the same raw material, e.g. interview notes,
different interpretations can lead to different need statements. Therefore, it is useful to
have more than one team member writing statements. There are a few guidelines to keep
in mind when writing need statements. It is important how the need is expressed; the
language should not imply how the product might achieve something, only what it must
achieve. It is important to express the needs at the same level as the raw data and to avoid
leaving out information. Also, the needs should be expressed as an attribute of the
product in order to ensure consistency and simplify translation into product
characteristics. Furthermore, positive phrasing is preferred over negative and wording
that applies a level of importance should be avoided. (6)
Step three in the needfinding process is organizing the needs into a hierarchy. In most
cases the hierarchy has two levels; primary and secondary needs. However, if needed a
third level, tertiary needs, can be added. The needs should be grouped in a way that is
consistent with the customer’s way of thinking. (6)
In step four, the relative importance of the needs is established. This can be achieved
either by performing customer surveys which is more accurate, or by the development
team which is faster and less costly. The customer surveys can be limited to needs that
give rise to major difficulties or costs. (6)
The final step in the process is reflecting on the results and the process. The results need
to be challenged and the group should reflect whether or not some areas need further
investigation or not. (6)
9
2.3.2 Benchmarking
Benchmarking is finding out more about your competition. Knowing what you have to
compete against is of great importance in order to gain commercial success (6). This
knowledge is also critical when determining details of the product specification which in
turn determines the product’s market position (6). Stuart Pugh (7) suggests various
formats such as catalogues and trade information journals where such information can be
found. This can also be achieved by purchasing, testing and examining competitor
products (6).
2.3.3 Related technology
In the phase related technology, inspiration and lessons are gathered from other market
areas and other types of products. This is important in the early stages of concept
generation since new ideas might aspire from unexpected sources. Ulrich and Eppinger
suggest finding information through online directories and also points out that this is a
task requiring persistent and resourceful work (6).
2.3.4 Scope
Needfinding, Benchmarking and Related Technology works as basis when determining
the scope of the project. The scope limits the design space which defines which problem
or problems that are to be solved. Defining a suitable scope helps prepare for the next
step in the process where a mission statement and product characteristics are defined.
2.4 Product characteristics
The product characteristics document is defined using the knowledge gained in the
problem analysis phase. Here the criteria that the product will have to fulfill are stated.
The specification is enhanced during the course of the project, while a technical solution
and a product concept are developed. As Ulrich and Eppinger (6) points out, product
characteristics can be established several times throughout a project. There are a few
fundamental guidelines to keep in mind when forming a product characteristics document
according to Johannesson et al. (5).
Selection If the specification is too extensive the most important criteria and
functions should be selected.
Grouping If a smaller amount of criteria or functions cannot be selected they can be
grouped to be more manageable; for example they can be grouped in
levels or subject areas.
Formulation The criteria and functions should be carefully formulated in order not to be
misinterpreted. The formulation should not state technical solutions such
as “drill holes” in comparison to “make holes”.
Verification It is important to describe the limits and boundaries of the criteria and
functions. Make the criteria measurable and verifiable.
Importance The selected criteria’s importance should be stated for respective function.
This can also be implemented on groups of criteria.
(After Johannessson et al. (5))
10
2.5 Concept generation
Brainstorming is a commonly used method for concept generation. The method is best
suited for a group of 5-15 individuals supervised by a leader. The purpose with the
brainstorming session is for the group to generate as many ideas as possible without
analyzing generated results. There are four fundamental rules according to Johannesson
et al. (5) in brainstorming;
Criticism is not allowed Give no comments what so ever concerning others ideas, not
positive nor negative. The same thing goes for your own
ideas; try to think spontaneous without judging the value of
the idea. Your idea could trigger another participant to a better
idea.
Strive for quantity It is important to generate many ideas since this increases the
chance that one of them might be really good. One
fundamental thought of the method is that a less successful
idea could lead to a more successful one.
Think outside the box Unconventional ideas are welcome. It has proven itself that an
odd and unusual idea can be modified into a perfect solution
to the problem. Just because a solution is unconventional does
not necessarily mean it is not right.
Combine ideas Combine and complement thought up ideas. Listen to other
participants ideas and associate your own from them. New
solutions can be found by merging two different ideas.
(After Johannesson et al. (5))
2.6 Concept evaluation and selection
Selecting one or more concepts for development is a process achieved through evaluation
against customer needs and relative comparison. This is an iterative process where the
number of concept alternatives may increase temporarily through combination and
improvement of various concepts. (6)
There are several methods for selecting concepts. Use of decision matrices provides a
structured and objective method for concept selection. Objectivity is important since
concept selection should be based on rational decisions, influence of organizational,
personal and arbitrary factors are unwanted. Ulrich and Eppinger also points out other
benefits when using a structured method: The result is likely to become more competitive
and customer focused, to have improved manufacturability, help the organization in
improving product development in general and also to be documented for future use. (6)
11
Ulrich and Eppinger (6) describe a two stage process for concept selection based on
decision matrices, the stages have different purposes and each stage consists of six steps:
1. Prepare the selection matrix. 2. Rate the concepts. 3. Rank the concepts. 4. Combine and improve the concepts. 5. Select one or more concepts. 6. Reflect on the results and the process.
(Ulrich and Eppinger (6))
The first stage, concept screening, narrows the number of alternatives quickly and uses a
Pugh matrix developed by Stuart Pugh (7). The decision matrix is prepared by stating
selection criteria in the first column and the different concepts along the first row, an
example is shown in Table 2.1. The selection criteria are chosen from the identified
customer needs. There should be about 5 to 10 different criteria covering both customer
and organizational needs without being too detailed. A reference concept is chosen to
which all of the other concepts are compared against. This can be an existing or
competitor product as well as one of the available concepts.
Next step is to rate the concepts. The reference concept is given the value zero for all
criteria. The other concepts are now compared against this reference by giving a relative
score for each criterion; “better than”, “same as” or “worse than”, expressed as +, 0 or -.
Scoring should be performed by working through one criterion at a time. However, when
having a large number of concepts it can be easier to rate one concept at a time.
When having rated the concepts, ranking is performed by summing up the number of
“better than”, “same as” and “worse than”. After making sure that the results are valid
possible improvement or combination of concepts should be investigated. Ulrich and
Eppinger points out two issues to consider:
- Is there a generally good concept which is degraded by one bad feature? - Are there two concepts which can be combined to preserve the “better than”
qualities while annulling the “worse than” qualities?
12
Table 2.1 Example of a Pugh matrix
Concepts
Selection criteria Concept A Concept B Concept C Concept D
Criterion A - 0 + +
Criterion B + 0 - +
Criterion C 0 0 - 0
Criterion D + 0 - +
Sum +'s 2 0 2 3
Sum 0's 1 4 0 1
Sum -'s 1 0 3 0
Net score 1 0 -1 3
Rank 2 3 4 1
Continue? Yes No No Yes
If new concepts arise, these are added to the matrix and rated the same way as before.
The new concepts can be named so their origin can be traced, for example a combination
of concept A and concept B can be called AB. If a concept is refined a + sign is added as
a suffix. For instance, concept A becomes A+ when refined. Based on previous steps, the
appropriate concepts are selected for further development. Also, decisions should be
made determining whether another round of concept screening or the more detailed
process of concept scoring should be applied. The final step is reflecting on the results
and the process. If not all team members agree on the outcome this can be a sign of
forgotten or unclear criteria. Group consensus also increases commitment of individual
group members and reduces the likelihood of making mistakes. (6)
The second stage, concept scoring, provides a higher resolution of the results due to the
more complicated matrix used. Here the concept selection process is based on the same
six steps as concept screening with some modification. Similar to previously described
matrix preparation, a reference concept is chosen. The criteria, or needs, can be expressed
in more detail than in concept screening through the use of secondary or tertiary needs,
described in section 2.3.1. The criteria are also weighted, which can be achieved through
various methods. In order for the results to be reliable, it is important to weight the
criteria as objectively as possible. In order to avoid subjective influence, Johannesson
et.al suggests a method with pair wise comparison (5). The criteria are put in the top
column and the first row of a matrix, see Table 2.2 Pair wise comparison of criteria When
comparing, the criteria get to share a value of 1. If one criterion is more important than
the other, it is given the entire value of 1 and the less important gets the value 0. If two
criteria are considered to be equally important, a value of 0,5 is given to each. The
diagonal squares are left empty since criteria are not compared against themselves. The
values are then added for each row resulting in a criteria sum. The criteria sum is divided
with a total sum which results in criteria weights.
13
Table 2.2 Pair wise comparison of criteria
Criteria weighting by pairwise comparison
A B C D E F G Sum Weight
A -
B -
C -
D -
E -
F -
G -
Total sum
A different scale for scoring, ranging from 1 to 5 is recommended to give higher
resolution. Also, it may be appropriate not to have one concept as reference for all criteria.
Having a concept as reference which is the best in one area may lead to what Ulrich and
Eppinger call “scale compression”. Ranking of the concepts is achieved by multiplying
the rating with the weight and then sum all weighted ratings resulting in a total score. As
in the concept screening, the team members should still try to find possible ways to
combine and improve the concepts. The final selection of concept or concepts for further
development should be performed carefully. A sensitivity analysis can be performed
where ratings and weights are varied to determine the impact on the final score. The
uncertainty surrounding a concept can also play a role in its perceived feasibility and
likelihood to be selected. When reflecting on the results and outcome, the team should
feel that the concept with most potential was chosen and that no important issue has been
left uninvestigated. (6)
2.7 Detail design
During detail design, both tools and methods are used. The softwares provided by
MacGREGOR are the main tools used and the methods are stress analysis and bearing
design.
2.7.1 Software
I-deas 12 is a computer aided design, manufacturing and engineering analysis software
released by UGS in 2006 (8). This is the software currently used by MacGREGOR for
part modeling, assembly and drafting. In this project, I-deas is used mainly in the detail
design process where the chosen concept is modeled and refined. Simulation and strength
analysis is also performed with the use of I-deas.
Matrix Navigator, provided by MatrixOne Inc., is a PLM (Product Lifecycle
Management) software used by MacGREGOR mainly for handling order specifications
and drawings. Internally it is called MacARK and is integrated with I-deas for creating
drawings.
14
2.7.2 Stress analysis
To analyze the structures involved in this project in terms of stress and deformation, the
finite element method (FEM) has been used. This is a well known tool which is often
used and is incorporated into I-deas. In this project it is used in the detail design phase to
confirm numerical analysis and also to get an idea on how structures behave when
exposed to stress.
2.7.3 Bearing design
The process of bearing selection requires collaboration between the customer and the
manufacturer. The customer in this case is MacGREGOR and the manufacturer Rothe
Erde. Rothe Erde has been a long time supplier of slewing bearings for MacGREGOR
which have resulted in a close relationship between the two.
As on other parts of the crane, MacGREGOR’s module design philosophy is applied on
the slewing bearing as well. A limited amount of bearings are available, each covering a
range of crane types and capacities. The module philosophy renders it possible for
MacGREGOR to have limited amount bearings available which reduces costs and
simplifies the process of bearing selection for a particular order.
The slewing bearings that MacGREGOR use are developed together with Rothe Erde to
fit the needs at hand. The development of a bearing is an iterative process which includes
communication of various formats between MacGREGOR and Rothe Erde. The slewing
bearings used by MacGREGOR are attached to the companion structures with the use of
high-strength prestressed bolts. The focus for MacGREGOR during the development
process is on the bolts sizes and the bearing diameter. The raceway and sealing design is
entirely up to Rothe Erde.
Rothe Erde has developed a method were the bearing selection and development of
surrounding structures is a joint task with the responsibility spread between themselves
and the customer. Previously, analysis has only been made by the manufacturer or the
customer. Experience has shown that such methods where the manufacturer has to gain
knowledge about the customers’ companion structures or the customers has to get
information to be able to correctly model the bearing, are time consuming. With this in
mind, as well as other criteria, the current method based on finite element analysis (FEA)
was developed.
When using this method, the model is divided into three separate part models; the upper
and lower companion structure and the bearing. The customer creates separate finite
element models for the upper and lower companion structure. Instructions from Rothe
Erde are then given on how to adjust the models so that a problem-free combination with
the finite element model of the bearing is possible. (9)
The process starts with MacGREGOR performing a slewing ring calculation based on
loadcases which form the basis for the bearing design. The loadcases are determined by
classification societies and Rothe Erde. The loadcases defined by classification societies
focuses on the design of the bolt joints meanwhile Rothe Erde needs loadcases for the
15
design of the rolling elements and raceways. The input values in these calculations
depend on the crane type and the situation the crane is to be used in, e.g. SWL, outreach,
type of cargo etc.
A drawing is also created which describes proposed bolt sizes and general dimensions of
the bearing. Here, assembly, maintenance, available space and other criteria play a crucial
role in determining the design space available for Rothe Erde.
When MacGREGOR and Rothe Erde has come to agree on a general design, the process
continues with MacGREGOR developing models that Rothe Erde can use when
developing the bearing itself. These models of the companion structures, i.e. the crane
house and foundation, are created according to instructions given by Rothe Erde.
According to the strength analyst (10) at MacGREGOR, the models of the crane house
and foundation are created as follows:
- A Cartesian coordinate system is used where the Z-axis of the model is coincident with the Z-axis of the bearing and is directed vertically upwards.
- On the flange surfaces of the crane house and foundation, as many nodes as there are bolts are created. The nodes are evenly placed around the bolt circle
each having six degrees of freedom. These nodes are referred to as interface
nodes.
- The first interface node is placed in the XZ-plane, see Figure 2.1. - A node in the centre of the node-circle, with X=0 and Y=0 and the same
global Z-coordinate as the other nodes, is also created.
- The nodes are numbered, increasing around the Z-axis in a positive direction, beginning at the position where X=0 and finishing in the centre node. The
final model does not include nodes with a higher number than the centre node.
Figure 2.1 Nodes created on the flange surface of the bearing
- The interface nodes that act as bolts have to be joined to the surrounding elements in a way that allows them to transfer translations and rotations in all
directions. When using a structure made of shell elements, the nodes can be
directly joined to that structure with the required six degrees of freedom. If a
solid element structure is used, the nodes have to be joined using rigid
16
elements. Otherwise, the nodes will only be able to translate translational
movements.
- The nodes on the lower edge of the pedestal are attached to the centre node with rigid elements. Normally, these nodes are constrained globally to the
coordinate system.
- The interface nodes on the crane house are locked, constraining all translations and rotations.
- The calculated loads are applied on the model and the results are evaluated. If unexpected deformations occur near the interface nodes on the flanges, the
structure can be stiffened with the help of rigid elements.
- When the results are satisfying, i.e. the model has correct tension concentrations and levels, they are written to a universal file (.unv). This file
is later used by Rothe Erde as basis for the load vector in the bearing
calculation.
- In order for the stiffness matrices to be written in required format, data set 612, and also for the mass and stiffness matrices to be written in separate files,
denoted M.unv and S.unv, a file substruc.prg in I-DEAS has to be replaced.
The replacement file is provided by Rothe Erde.
- A Master Dof Set in I-DEAS is created restricting degrees of freedom for the interface nodes.
- The stiffness matrices are reduced by using Guyan’s method so that a small file is created which can be sent to Rothe Erde. This is a process of static
condensation which reduces the stiffness matrices created to the degrees of
freedom of the connecting nodes.
- An email is sent to Rothe Erde with files containing loads and stiffness matrices for the upper and lower companion structures.
With the three files, Rothe Erde performs calculations and determines whether the by
MacGREGOR proposed design works or not. Rothe Erde sends the results through email
in the form of universal files containing Restraint Sets which describes deformations in
the nodes. The model of the crane house and foundation is written into a universal file
into which the Restraint Set from Rothe Erde is incorporated. This file is saved and
imported into I-deas. After checking that the Restraint Set from Rothe Erde is
incorporated, i.e. nodes have constraints, the model can be solved regarding stress and
deformation. (10)
When MacGREGOR and Rothe Erde have come to agree on a final design, the bearing is
included in the list of available bearings, meaning it can be used for a range of crane
types. During 2008, MacGREGOR is in the process of replacing their available slewing
bearings with newly developed ones. These new slewing bearings have a different design
and form a whole new set of modules.
17
3 Current solution The current solution is the design of the components as well as the manufacturing and
assembly involved.
3.1 The existing design
The existing design consists of the GL4528 crane in general and more specific, the
currently used slewing bearing.
3.1.1 MacGREGOR Crane GL4528
This project is based on the MacGREGOR electro-hydraulic deck crane type GL with a
hoisting capacity of 25-100 tons at a jib radius of 20-42 meters with a hoisting speed of
24-44 m/min. The GL crane is designed as a cargo handling crane for container ships,
bulk carriers and cargo ships. The particular order of which the project refers to is
designed to handle a SWL of 45 ton at 28 meters outreach and a 40 ton SWL at 30 meters
outreach. By designing the crane for a specific SWL at a specific outreach instead of the
overall maximum SWL at the maximum outreach the crane can have a slimmer design
and is thereby more cost efficient.
The GL crane is modularly based in order to achieve a stable design with high quality and
a stable production by having common components for many different crane types. This
also leads to shorter lead times for the design and production as well as a reduction of the
number of spare parts. Some of the modules can be seen in Figure 3.1 below.
Figure 3.1 Some modules included in the GL crane assembly
18
Most of the equipment and components are assembled inside the crane house making
inspections and maintenance of the machinery easier and weather independent. An
exception is made for the oil cooler which is located on the top of the crane house in
order to be kept away from dusty environments and to provide a more efficient cooling.
3.1.2 Slewing bearing
For a crane of type GL4528, a three-row roller bearing from Rothe Erde is used, which
internally is called RE16, see Figure 3.2. RE16 replaces a similar bearing called RE6. On
crane types with smaller capacities single-row ball bearings are used.
The bearing consists of an outer [1] and inner [2] ring, the outer attached to the crane
house [3] and the inner to the blank [4] in the foundation [5]. The rings are attached with
the use of high-strength prestressed bolts [6] in bolt circles evenly spread around the
flanges of the bearing. The outer ring is larger in diameter and sits outside the inner ring.
The outer ring is divided horizontally in order for assembly of the slewing bearing to be
possible [7]. The bearing has internal gears [8] placed on the inner ring. In the interface
between the outer and inner ring there are three rolling elements [9], transmitting axial
and radial forces, making it possible for the crane to slew around its own axis. Two seals
[10] keep unwanted material from entering the raceways. Grease nipples [11] are placed
around the inner ring, for lubrication of the raceways.
Figure 3.2 Slewing bearing RE16
3.2 Manufacturing and assembly
MacGREGOR cranes are manufactured by production partners in China, Korea, Poland
and Croatia thus offering logistical benefits for ship owners and shipyards. MacGREGOR
provides the design, key components, continuous production supervision, quality control
and testing. At the partner’s manufacturing plants the crane modules such as the crane
19
house, jib and foundation are welded. The bottom plate of the crane house is machined
with a horizontal boring mill in order to achieve the tolerance required by the slewing
bearing considering planarity. The result of the machining can be seen in Figure 3.3
below, where the crane house is lying on the side with the bottom plate facing the camera
showing the machined outer ring surface prepared for the slewing bearing and four
circular holes prepared for the slewing gears.
Figure 3.3 Machined crane house
The slewing bearing is one of the many modules included in the crane’s design. It is
bolted to the crane house bottom plate through the outer ring of the bearing and to the
flange on top of the foundation through the bearing’s inner ring. In Figure 3.4 below the
bottom plate of the crane can be seen with the slewing bearing bolted onto it.
Figure 3.4 Slewing bearing mounted on crane house
20
The forged top flange i.e. the blank is preheated to 150° C to avoid faulty eccentric
running when welded onto the foundation where it is machined to fulfill the required
flatness tolerance. The crane house is completely assembled with all components and
equipment mounted inside at the manufacturing plant. The crane house, jib and
foundation are then transported to the shipyard where the pedestal has been
manufactured.
The narrow flatness tolerance required by the slewing bearing demands a careful welding
procedure when the foundation is welded to the pedestal. There is no gap allowed
between the foundation and the column before welding, nor is it allowed to push or pull
the foundation to make it fit. The welding procedure is then carried out by two welders
working simultaneously on opposite sides of the welding zone. The flatness of the top
flange of the foundation is then checked and must be within tolerance otherwise it is
necessary to machine the surface in place or cut down the foundation and reweld it. The
permissible gap is only 0,20 mm for a Ø2500-4000 mm top flange.
21
4 Implementation and results Implementation and results documents how the methods described in section 2 were used
and what results were gained. The final conclusions will be described in section 5.
4.1 Product development
The methodology used in this project is developed to fit the problem at hand where
SIRIUS Masterplan functions as a guide, inspiration and reference. See appendix 1.
Stage one in SIRIUS Masterplan, describing the planning phase is used with the
exception of creation of a budget. Team roles, group and individual goals, coaching
strategy and a Gantt chart are discussed and defined. Here, discussions also lead to the
chosen methodology and SIRIUS Masterplan is modified to fit the situation.
In this project, phase two called design space exploration is redefined and renamed and is
called problem analysis. This is done since an extensive benchmarking process is not
possible to carry out. For instance, no competitor cranes can be tested or evaluated. Also,
since the problem is already known and this project is about evaluating a double bearing
solution, part of the scope is already defined. As a whole, the design space is well known
and the work in the problem analysis phase focuses on gaining knowledge surrounding
the current solution.
The roadmap phase is used to some extent; a mission statement is not produced since a
similar one already is defined in the project description. The results from the problem
analysis phase form the product characteristics, which are defined with measurable
criteria. The product characteristics are updated throughout the project.
Concept generation, evaluation and selection, which constitute the concept design and
prototyping phase, is work based on various methods and extensive discussion using
experience both from students and MacGREGOR. Here, some of the methods used
originate from the suggestions given in SIRIUS Masterplan. Also, suitable literature
provides detailed information about various methods for generating, evaluating and
selecting concepts.
Detail design and manufacturing constitutes the final phase for this project. No
prototyping or manufacturing of concepts is made. Instead the final design is delivered as
3D models and drawings.
4.2 Planning
First, a general project plan, appendix 2, is developed describing team roles, goals,
coaching strategy and what work that needs to be done in the major phases of the project.
The phases are specified with SIRIUS Masterplan functioning as basis and the content of
each phase defined by the group members. Responsibility over different aspects of the
project is divided between the group members which clarifies the team roles. The
individual and group goals are also defined and a coaching strategy is developed. With
the support of the general plan, a Gantt chart is created showing a timeline from the
22
project’s start to finish, appendix 3. The project plan is approved by coaches before work
proceed.
4.3 Problem analysis
In order to analyze the current situation correctly and thereby understanding the problems
at hand, and doing this without leaving out any crucial information, the work is divided
into three different areas; needfinding, benchmarking and related technology.
The needfinding is carried out as a combination of individual research and interviews
with various resources within MacGREGOR. The individual research is focused on
online resources and suitable literature. Interviews are in the form of casual meetings
with experts in different fields as welding, manufacturing, service, design, strength
analysis, slewing bearing selection etc. Due to difficulties with closely inspecting and
evaluating competitor products, only information provided by the manufacturers
themselves is used for benchmarking. This gives an overview of what manufacturers that
exist on the market today and it also gives a general idea of their design. Work in related
technology is focused on online resources. The idea here is not to closely investigate
other types of technology but to get inspiration and ideas for concept generation.
4.3.1 Needfinding
The new solution has to match or exceed the current solution’s performance and at the
same time motivate any increase in costs. The current solution’s level of performance in
some areas is also the reason why this project came to be. In order to know how and in
what areas the new solution has to perform, the needs involved in this project are
investigated. The needfinding process described by Ulrich and Eppinger (6) provides
support and is used throughout this phase of the project.
The first step in the method described in section 2.3.1 about needfinding, is gathering raw
data. Since interviewing customers and end users of ship cranes is not feasible for this
project, resources at MacGREGOR are used instead. Here, service engineers and experts
with close relationships with customers and end users are informally interviewed on
various occasions. Also, besides doing interviews, individual research focusing on
examining the current solution is performed.
By learning about the current solution’s advantages and drawbacks, needs that are to be
met within the scope of this project can be determined. Therefore, the analysis of the
current solution, presented in section 3, and the needfinding process are combined and
carried out simultaneously.
The raw material is documented as notes from interviews and knowledge gathered
throughout the process. A document describing the needs is created which is
continuously updated as needs are added, refined or revised. The gathered knowledge and
raw data are translated into customer needs, which is step two in the needfinding process
described by Ulrich and Eppinger (6). For example, it is realized that the ship crew needs
to be able to enter and exit the cabin from the ship deck without having to climb on the
outside of the crane itself. This is then translated into a need statement saying that the
23
new solution needs to allow entry and exit through the crane house floor. Step three in the
process is organizing the needs. Similar needs are gathered under one primary need
creating a hierarchy of two levels. This simplifies further use of the needs when creating
criteria for the concept evaluation phase. The relative importance of the needs, step four
in the process, are not determined at this stage in the project. This will be done when
weighting criteria for the concept evaluation process. This process is iterative, and every
loop improves the needfinding’s accuracy. It is also realized that not all needs can be
determined at once at an early stage in the project. Therefore, the needs are continuously
updated as knowledge increase throughout the project.
The needs this project has to fulfill are presented, explained and analyzed below. The
needs are arranged, beginning with safety, manufacturing, assembly and costs which are
central to this project. These are followed by crane house design, pedestal design, jib
parking and space requirements which are more connected to design issues. Entry and
exit, inspection and maintenance are more towards end user needs. Mechanical needs are
separate and constitute a category of its own. These needs are summarized in a document
called “Needfinding Criteria” for easier use later in the project, see appendix 4.
Safety
One of the major reasons why this project was initiated was the wish for increased safety.
In the past, due to poor maintenance, slewing bearings have broken down causing the
crane to fall down from the foundation. This have so far only happened on single row ball
bearings. Also, cracks beneath the blank on the foundation have led to similar
consequences in cases where the crane has been exposed to considerable overload. By
having a design with two bearing positions, failure of one bearing or crack development
would not have such disastrous consequences. Therefore, the solution should not allow
the crane house to fall down if one of the bearings should fail or a crack near the flange
develops.
Manufacturing
The slewing bearing that is to be replaced is manufactured by Rothe Erde and delivered
to a MacGREGOR production partner for assembly on the crane house. The companion
structures are manufactured by the production partner, which will also have to be the case
for the new solution.
Assembly
Due to a combination of low tolerable flatness deviation of the companion structures and
complicated weld joints, the yard mounting of the crane house is an expensive and
demanding procedure. The tolerated out of flatness, given by Rothe Erde, for each of the
machined contact surfaces is 0.2 millimeters. For MacGREGOR, these surfaces are the
bottom of the crane house and the blank on the foundation. The bottom of the crane
house is machined after all welding is done and it is therefore not an issue to clear the
maximum tolerated out of flatness. The foundation however, is machined and then
welded in the yard onto the pedestal which is usually constructed by the yard themselves.
This means that the tolerated out of flatness on the blank when welding the foundation
onto the pedestal, is often less than 0.2 millimeters.
24
The new solution should simplify assembly either by decreasing the effect allowable
flatness deviation has on the assembly or by increasing the tolerable out of flatness itself
given by the bearing manufacturer.
Bolt tightening is performed with a hydraulic tension cylinder. This tool requires space
depending on the bolt size chosen. This has to be taken into account when determining
the size of the surfaces on which the bolts are to be placed. Experience has also shown
that due to inaccuracy when rolling the circular walls and needed accessibility for bolt
tightening the bolt circle diameter has to be placed an extra eight millimeters from the
nearest wall.
Costs
Any increase in cost the new solution will result in has to be motivated by increased
advantages in other areas, e.g. manufacturing or assembly. A more thorough evaluation
of this issue can be seen in appendix 5.
Crane house design
The current slewing bearing solution is compact, which is an advantage when all
components need to fit inside the crane house. No components are placed below the
slewing joint, i.e. the slewing bearing, meaning that no complicated rotatable joints need
to be involved. Also, it means that a complete crane with foundation can be delivered to
the shipyard and be ready for assembly. The new solution should strive to keep current
placement of components. However, if considered necessary because of other advantages,
modification of the crane house can be motivated.
Pedestal design
There are mainly three types of foundations used depending on the design of the pedestal.
Type A foundation has a circular bottom end with a smaller diameter than the upper
flange. This gives it a conical design. A foundation of type B is circular with the same
diameter through the whole length. A foundation of type C is circular near the top flange
and quadratic at the bottom end. Each of these three fits onto different types of pedestals
and for a GL crane, type C is most common. The solution should be valid for all types of
pedestals
Jib parking
Jib parking arrangements vary and are individually designed for each specific crane
delivered. If the crane jib is sea stowed using a cable parking arrangement, the jib’s
slewing movement is locked by features attached to the foundation. If the crane jib is
locked using jib support features, these can be placed on another crane’s foundation. The
conclusion is that the design has to allow for attachment of jib support or slewing lock
features.
Space requirements
The crane’s space requirement on the ship should not increase since this would affect the
ship’s loading capacity.
25
Entry and exit
The new solution has to allow the crew to enter and exit through the floor of the crane
house from inside the pedestal.
Inspection
At the factory, after mounting the slewing bearing on the crane house and before shipping
it to the yard, the gear backlash is measured. This procedure requires access to the gear
teeth with a thickness gauge.
After the crane is mounted, and final inspections are made, the slewing bearing play is
measured. This is done in order for the ship crew to keep a record over the slewing
bearing wear. Measurements should be taken every six months and if the play exceeds a
certain value, the slewing bearing should be replaced. The solution should allow for
bearing wear to be measured.
It should also be possible to discover cracks or any other damage on the crane
components. Therefore, the design should not hide or cover critical areas where such
cracks or damage can arise.
Maintenance
Maintenance has to be easy to perform. Therefore, items such as lubrication nipples have
to be easily accessed. Grease sampling, which is performed every twelve months in order
to check the bearing’s condition, demands access to the slewing bearing seal on the inside
of the crane.
Mechanical
According to the scope of this project, the new solution is meant to replace the current
design involving a specific crane type and slewing bearing. Therefore it is assumed that
the mechanical specifications will be the same as today. These specifications form a basis
which determines what components that needs to be used and how they have to perform.
The specifications that affect the slewing bearing design are in the form of loadcases. The
loadcases used in this project are the same as used for development of slewing bearing
RE16.
Beside the loadcases, the crane must have an unlimited slewing range. This means that no
features or components can restrict its movement. The solution will be designed to fit
current conditions when pedestals of type A, B and C are used. If needed, this issue can
be discussed and the decision revised.
26
4.3.2 Benchmarking
Benchmarking is work consisting of finding competitor products and more specifically,
investigate the slewing bearing solution.
Neuenfelder Maschinenfabrik
NMF, short for Neuenfelder Maschinenfabrik, founded in 1970 and located in Hamburg,
Germany, produces cranes and hydraulic equipment. NMF currently offers heavy-lift
cranes with maximum rated loads of up to 1000 tons. The DK II, seen in Figure 4.1,
which has the highest production volume, is a general purpose cargo crane that is offered
for loads from 20 up to 80 tons with a jib radius of 16 to 35 meters. The DK II Heavy
model has capacities from 100 to 600 tons with a jib radius from 14 to 35 meters. (11)
Figure 4.1 NMF DKII crane
Liebherr
In 1949 the Liebherr family business was founded by Hans Liebherr. The Liebherr Group
is still owned by the family and is divided into independent company units. Liebherr offer
ship cranes of various types where the CBB wire-luffing crane, seen in Figure 4.2, is a
container and multi-purpose handling deck crane. It is offered for loads between 25-45
tons with a jib radius of 24 to 32 meters. (12)
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Figure 4.2 CBB 45(40)36/25(28)31crane
IHI – Japan
Ishikawajima-Harima Heavy Industries Co., Ltd, founded in 1853, manufactures IHI
deck cranes. (13) Products include single and double deck cranes, four-rope grab cranes,
hose handling and gantry cranes. (14)
TTS/LMG
TTS-LMG is part of the TTS Marine Cranes Division after LMG being taken over by
TTS Marine ASA in 2004 (15). Three different types of wire luffing cargo cranes are
offered; KL, KS and K which offer SWL’s from 30 to 45 tons and maximum outreaches
up to 32 meters. (16)
Tsuji Heavy Industries Co., Ltd
Tsuji Heavy Industries Co., Ltd is based in Japan and offers through their marine
equipment division offer deck cranes of various types with lifting capacities up to 400
tons. The HD series has capacities from 30 to 40 tons with maximum jib radiuses from 20
to 30 meters. (17)
Kawasaki Precision Machinery, Ltd
Kawasaki Precision Machinery Ltd (KMP), based in Japan, was established in 2002 when
separating from Kawasaki Heavy Industries Group. KPM offers single, twin, semi-slim
and hose handling cranes where the single type cranes have capacities from 150 to 500
tons. (18)
Mitsubishi Heavy Industries, Ltd
Mitsubishi Heavy Industries, Ltd (MHI), established in 1950, developed their first
electro-hydraulic deck crane in 1972 and has since then delivered approximately 4000
units worldwide. (19)
28
Huisman-Itrec
The heavy lift mast cranes, see Figure 4.3, offered by Huisman-Itrec have capacities from
200 to 7500 tons. These cranes have a fixed welded steel mast attached to the vessel. The
slewing platform, which the jib is attached to, pivots together with the masthead. The
winches are fixed below the mast foot in the ship’s hull which limits the slewing range to
450 degrees. The lower bearing is because of the welded mast structure not a limiting
design item. (20)
Figure 4.3 Huisman-Itrec heavy lift mast crane
Summary MacGREGOR’s major competitors have cranes with a single slewing bearing solution.
An exception is Huisman-Itrec which has a completely different design. These cranes
however, are mainly used for heavy lift situations and cannot be seen as competitors to
MacGREGOR cranes. However, as inspiration for a double bearing solution they are
interesting.
4.3.3 Related technology
Interesting products in other markets have been investigated where efforts have been
focused on how slewing bearings are used.
Excavator
The excavator generally consists of an articulated arm with a bucket and an operator’s
cabin mounted on a pivot on top of the tracks or wheels of the machine as shown in
Figure 4.4. The pivot consists of a slewing bearing with an internal gear allowing the
excavator to rotate. The slewing bearing experiences both axial and radial loads as well
as a tilting moment as the arm of the excavator operates. (21)
29
Figure 4.4 Excavator with red marker indicating location of slewing bearing, cross section of slewing
bearing is shown in lower left corner
Rudder propellers
The rudder propeller, seen in Figure 4.5, is mounted on a vertical shaft allowing the
propeller unit to rotate perpendicular to the propeller’s propulsion direction thus
eliminating the need of an actual rudder. The load created by the propeller’s thrust results
in radial and axial loads as well as a tilting moment on the slewing bearing supporting the
rudder shaft. The weight of the propeller unit also generates an axial load in the pivotally
suspended slewing bearing. (21)
Figure 4.5 Stern rudder propeller with red marker indicating location of slewing bearing, cross
section of slewing bearing is shown in lower left corner
Wind energy turbines
The turbine housing, seen in Figure 4.6, is pivotally mounted to a slewing bearing on top
of the column allowing the housing to rotate into a favorable angle relative the direction
of the wind. The slewing bearing is designed to withstand the axial and radial loads in
addition to the tilting moment generated by the rotor. (21)
30
Figure 4.6 In the mid lower part of the figure the mentioned slewing bearing can be seen along with
two cross section images of a single row respectively a double row ball bearing configuration
4.4 Product characteristics
The product characteristics are developed from the needfinding criteria described in
section 4.3.1. The criteria are modified into measurable demands which the product has
to meet in order to be successful. Final decision regarding each of the product
characteristics are discussed with resources from MacGREGOR and the bearing
manufacturer.
Directly after finishing the needfinding phase, a first version of the product
characteristics was developed and discussed with the project supervisor. Some issues
could not be decided upon, such as costs and possible modifications. These were later
revised as the project proceeded. The final version of the product characteristics can be
seen in appendix 6.
4.5 Concept generation
The concept generation process of this project was conducted at MacGREGOR during
two brainstorming sessions and complementary work throughout the period of week 38.
With the support of various colleagues at the company a series of sketches were created
according to the description below.
First session
The first brainstorming session was performed on Monday the 15th of September, in
cooperation with handpicked recourses from various departments at MacGREGOR.
Initially the participants were briefly informed of the conditions of the project, regarding
the double slewing bearing application. All participants had prior to the meeting received
a document, enclosed in appendix 7, containing information about the first session. The
given information was deliberately restricted with the intention to obtain fresh ideas, not
influenced by prior knowledge of the project. The participants were then given sketching
materials and asked to denote as many concept drawings of a double slewing bearing
31
solution as they could, without communicating with each other. These sketches were then
collected and shown to the group, one at a time, for the participants to explain them to
each other, aiming to associate to new ideas.
After the meeting, the sketches were compiled in to the following three categories,
enclosed in appendix 8; Dual bearing similar size, Dual bearing variable size and Outside
the box. A fourth category with Safety Hook solutions was compiled and laid aside.
These compilations along with a document of information, enclosed in appendix 7, were
sent to the participants prior to the second meeting.
Second session
The second brainstorming session held on Thursday the 18th of September, aimed to
further develop the previously generated ideas and narrow them down to more thought
trough concepts. The meeting also aimed to discuss the assembly problem regarding the
narrow tolerance of flatness of the foundation’s top surface. However the meeting came
to be more about discussing current problems rather than discussing innovative designs
meant to solve them. Nevertheless this resulted in further information regarding the
problems of the current design solution of the slewing bearing’s ambient structures. It
was therefore decided to enhance the previously produced concept sketches through
discussions within the project group.
Summary
The discussions lead to five refined concepts, shown below in Figure 4.7 and enclosed in
appendix 9, that emerged from the sketches created in the first brainstorming session.
These concepts were then brought to the next phase, the concept evaluation.
Figure 4.7 Refined concepts
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4.6 Concept evaluation and selection
The concept evaluation process was performed in cooperation with handpicked personnel
at MacGREGOR. The group involved in the concept generation phase were invited to
participate since they were already aware of the background of the project and the
previously generated concepts.
Prior to the meeting an evaluation matrix was created in order to compare the concepts
relative to each other regarding a set of predetermined criteria. The criteria originated
from the needfinding results and the product characteristics document. The criteria were
weighted by pair wise comparison, seen in Table 4.1, in order to find the decisive design
factors. Scores were set, comparing the importance of a row relative a column in the
matrix, according to; much more important=1, equally important=0,5 and much less
important =0. The criteria implemented in the matrix were as follows:
Manufacturing Machining complexity affecting time required for the
manufacturing process.
Assembly Time needed (both at partner manufacturing plant and shipyard)
for bolt tightening, welding etc.
Safety Effects of bearing failure.
Maintenance Accessibility for performing bearing lubrication and grease
sampling.
Inspection Accessibility for measuring gear backlash and bearing wear.
Entry & Exit Ease of entering and exiting the crane through the pedestal and
foundation assuming that existing regulations are fulfilled.
Modifications needed Modifications needed in order to incorporate solution into existing
design and component placement regarding pedestal and
foundation.
Table 4.1 Criteria weighting by pair wise comparison
Manufacturing Assembly Safety Maintenance Inspection Entry&Exit Mod. Needed Sum Weight
Manufacturing - 0,5 0 0,5 1 1 1 4 0,19
Assembly 0,5 - 0 0,5 1 1 1 4 0,19
Safety 1 1 - 1 1 1 1 6 0,29
Maintenance 0,5 0,5 0 - 0,5 1 1 3,5 0,17
Inspection 0 0 0 0,5 - 1 1 2,5 0,12
Entry & Exit 0 0 0 0 0 - 1 1 0,05
Mod. needed 0 0 0 0 0 0 - 0 0,00
Total sum 21 1,00
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The results of the criteria weighting demonstrated in Table 4.1, shows that safety is the
single most important design criteria, which reflects the purpose of the project; to prevent
the crane house from falling down in case of a bearing failure. Ranking at number two,
manufacturing and assembly are judged to be equally important, derived from the fact
that the two are closely dependent of each other. A thorough manufacturing process is
required in order to attain accurate components, which simplifies the assembly process.
Furthermore, it is of equal importance to perform the assembly in a scrupulous manner,
otherwise the thorough manufacturing is pointless. Maintenance, ranking at number three,
has as well as inspection, ranking fourth, an impact on the safety of the construction. In
order to attain a long service life the structure must be regularly maintained and inspected
to prevent premature failure. The entry & exit criteria proved to have little importance
compared to the other criteria as long as all the existing regulations were followed.
Ranking a total weight of zero, thus ending up last, the criteria modifications needed will
have no impact in the concept evaluation. This since MacGREGOR saw no problems in
redesigning their product in order to fulfill the other criteria.
For each criterion in the concept evaluation matrix in Table 4.2, a concept was chosen to
serve as a reference to which the other concepts would be compared. The chosen
reference concept was assumed to have an average score regarding that specific criterion
therefore it was given the average score of three. The scoring was done according to;
much worse than =1, worse than =2, same as =3, better than =4, much better than =5. The
reference concept for each criterion is marked by a filled box in the concept evaluation
matrix below. The current solution is represented in the RE16 column. The concept C+++,
seen in appendix 9, F1 and F2 was developed during the sessions and added to the matrix.
Table 4.2 Concept evaluation matrix
RE16 A++ B++ C++ H+ C+D+ C+++ F1 F2
Manufacturing 4 3 3 1 2 1 2 4 4
Assembly 4 3 3 2 3 1 4 4 4
Safety 1 3 3 2 3 2 5 3 3
Maintenance 4 4 4 4 3 3 2 4 4
Inspection 5 4 4 2 3 2 2 5 4
Entry & Exit 5 4 4 5 3 4 5 5 4
Mod. needed 5 4 4 3 3 2 3 5 4
The weight calculated in Error! Reference source not found. was then multiplied by the
scores presented in Table 4.2 resulting in the final scoring matrix shown in Table 4.3.
34
Table 4.3 Weighted concept evaluation matrix
Weight RE16 A++ B++ C++ H+ C+D+ C+++ F1 F2
Manufacturing 0,19 0,76 0,57 0,57 0,19 0,38 0,19 0,38 0,76 0,76
Assembly 0,19 0,76 0,57 0,57 0,38 0,57 0,19 0,76 0,76 0,76
Safety 0,29 0,29 0,86 0,86 0,57 0,86 0,57 1,43 0,86 0,86
Maintenance 0,17 0,67 0,67 0,67 0,67 0,50 0,50 0,33 0,67 0,67
Inspection 0,12 0,60 0,48 0,48 0,24 0,36 0,24 0,24 0,60 0,48
Entry & Exit 0,05 0,24 0,19 0,19 0,24 0,14 0,19 0,24 0,24 0,19
Mod. needed 0,00 0,00 0,00 0,00 0,00 0,00 0,00 0,00 0,00 0,00
Total score
3,31 3,33 3,33 2,29 2,81 1,88 3,38 3,88 3,71
The results from the weighted concept evaluation matrix were then compiled in
descending order from the highest total score in Table 4.4 below.
Table 4.4 Concepts ranked concerning score received in the weighted concept evaluation
Rank Concept Total score
1 F1 3,88
2 F2 3,71
3 C+++ 3,38
4 A++ 3,33
5 B++ 3,33
6 RE16 3,31
7 H+ 2,81
8 C++ 2,29
9 C+D+ 1,88
The two highest ranking concepts were conceived during a concept evaluation meeting,
and fell under the category Safety Hook. They were still evaluated as a reference to the
other concepts but not further developed since they fell outside the delimitations of the
project. The two lowest ranking concepts were left out from further analysis due to their
low scores in the ranking and for individual scarcity. In the case of C++ there was an
improved version C+++, which was developed in an evaluation meeting, see appendix 9.
The C+D+ concept was predicted to be too complex to manufacture and assemble from
an economical point of view. Furthermore, both required an additional foundation
mounted below to make the transition from the circular cross section of the slewing
bearing to the square cross section of the pedestal.
The remaining four concepts were divided into two categories, depending on the size and
location of the slewing bearings; category one, containing concepts A++ and B++;
category two, containing concepts C+++ and H+. This was done in order to simplify the
concept selection by pairing up the concepts in consideration of their properties. The pros
and cons of the categories were then taken in consideration to determine which category
would be best suited for further development in the detail design phase. It was estimated
that category two would bring difficulties concerning the circular tolerance needed at the
flanges when mounting the bearings. The tolerance would be hard to keep when welding
35
the sheet casings to the flanges, since the heat generated in the welding process would
cause the flanges to distort. Also the pair wise assembly of the bearings linked by the
sheet plate cylinders would result in tolerances in the vertical plane. These tolerances
would complicate the assembly. Furthermore the rotating outer casing of the foundation
of C+++ would complicate the placing of jib parking structures.
Category one on the other hand presented some important advantages, such as being
applicable on all three MacGREGOR foundation types, as well as inclined pedestals
without adding unnecessary height as would be the case of category two foundations. In
addition the component costs would be held down due to the smaller lower bearing and
the fact that less steel is required. Additionally the lower slewing bearing becomes
weather independent since it is mounted inside the foundation, making inspections and
maintenance easier. Category one presents yet another important advantage being safe
even if fissuring in the weld between the foundation and the blank causes fractures,
leading to separation between the two. The structure is in such cases supported by the
stay anchored in the lower bearing position. Supported by the previous mentioned facts,
category one was chosen to be brought into detail design.
4.7 Detail design
Category one including conceps A++ and B++ were, as previously described in the
concept evaluation and selection section of this report, chosen to be further developed
and investigated in the detail design phase of this project. Initially in the detail design
phase a numerical analysis was performed in order to learn the moment distribution
between the two bearings, it was also to be used to confirm the results of the finite
element analysis. Here follows a description of the work perfomed during the detail
design phase.
4.7.1 Numerical analysis
In order to understand the interaction between the two bearings, regarding the moment
distribution, a numerical analysis was performed. The moment distributed to the lower
bearing is directly dependent of the deformation of the top bearing and the stay
connecting the bearings.
The bearing play increases with time due to wear. This causes the bottom plate of the
crane house to tilt relatively the bottom plate of the foundation, thus deforming the stay
connecting the two surfaces. According to Rothe Erde the maximum permissible increase
of bearing clerance in a single row ball bearing is 3 millimeters, as shown in Figure 4.8.
The initial play is approximetly 0,7 millimeters. (22)
36
Figure 4.8 Measurement of bearing play (The stay is excluded in this figure)
The force distributed to the lower bearing by the stay due to the relative incline of the two
bottom plates can be calculated from the inclination angle δ, where
(4.1)
. (4.2)
The force needed to deform the stay the given angle δ, shown in Figure 4.9, can be
derived from the elementary cantilever beam equation
, (4.3)
thus assuming that the stay is rigidly clamped to the bottom plate of the crane house and
that the applied load causes the stay to deform as much as the relative incline suggests.
The stay is defined as a massive cylindrical steel beam with moment of inertia according
to:
(4.4)
37
Figure 4.9 Reaction force acting on the deformed stay
By combining the elementary case equation (4.3) with the moment of inertia equation
(4.4), the reaction force acting on the stay can be expressed according to;
(4.5)
Numerically, the reaction force F in the initial unworn condition is given by
, (4.6)
and with the maximum permissible bearing play,
. (4.7)
In addition to the bearing play, the deformation of the pedestal and foundation contributes
to the deformation of the stay as well, as seen in Figure 4.10. The relative incline between
the bottom plates increases with increased load. The relative incline can be derived from
the elementary cantilever beam equation:
. (4.8)
The pedestal and foundation is approximated by a cylindrical shell of uniform diameter
equivalent to the flange of the foundation, with moment of inertia according to
, (4.9)
where r2, is the radius of the pedestal and T, is the plate thickness.
38
Figure 4.10 Deformation of pedestal and foundation causing relative incline of bottom plates
By combining the elementary case equation (4.8) with the moment of inertia equation
(6.9), the relative incline can be expressed according to
. (4.10)
Numerically the relative incline of the two plates is given by
. (4.11)
The reaction force acting on the stay due to this inclination is given by equation (4.5),
numerically this gives,
(4.12)
39
The total reaction force acting on the stay in the case of a new bearing is given by adding
the results of equations (4.6) and (4.12),
. (4.13)
For the worn bearing the corresponding results are given by equations (4.7) and (4.12),
. (4.14)
The reaction force F acting on the stay, shown in Figure 4.11, is known, hence the
moment about the stay can be calculated in order to learn the distribution between the
two bearings. Using the numerical results from equation (4.13) respectivelly (4.14) the
corresponding moment distributed to the lower bearing in the initial respectivelly the
worn scenario can be calculated according to,
(4.15)
. (4.16)
Figure 4.11 Moment equilibrium about the stay, forces acting on lower bearing
4.7.2 Finite element analysis
To get an idea of how a concept from category one would work in practice, simulations
were made using an existing 3D model of a type GL crane. The model did not represent
the crane involved in our project, it was of the same type but had a lifting capacity of 32
tons at an outreach of 37,2 meters.
The 3D model was developed by Johan Lif, a student performing his thesis work at
MacGREGOR in the fall of 2008 (23). The model was created in I-deas as a surface
model with simplified geometry used to investigate stress propagation in the foundation.
The applied load was equivalent to lifting 32 tons in addition to the weight of the crane
arm. The whole model was meshed using surface elements with corresponding thickness
to each individual plate. The bearing was represented by 100 solid beam elements with a
diameter of 36 mm connecting the bottom plate of the crane house with the flange of the
40
foundation. This can be seen in Figure 4.12 below. These beam elements act as the 100
bolts connected to each of the two rings of the real bearing. The beam elements are
placed at the actual bolt locations thereby translating the stresses into the foundation in a
realistic way. Concept B++ was incorporated into the model by simply connecting the
bottom plate of the crane house with the bottom plate of the foundation with four beams
as seen in Figure 4.12.
Figure 4.12 Four beams acting as a stay between the two bearing positions. Foundation removed in
this view
On the bottom plate of the crane house, the beam elements were each connected to a
centre node of a circular rigid element positioned near the bolt circle. In the bottom plate
of the foundation, all four beams were connected to the same node. This node was in turn
coincident with and connected to a centre node of a circular rigid element. The
connection between these two nodes was of type coupled DOF. By using a coupled DOF
connection the degrees of freedom between these two nodes could easily be controlled.
The main reason to use a coupled DOF was however to be able to determine the forces
acting on the lower bearing, by simply requesting to list constraint forces as one of the
results.
The simulation was set up as linear static. Boundary conditions consisted of a restraint set
and a constraint set. The restraint set locked all movements of the bottom edge of the
pedestal. The constraint set was the coupled DOF acting as the lower bearing. The
coupled DOF was set to allow translation along and rotation around the Z axis due to the
natural behavior of a bearing only translating radial forces. Simulations were also made
41
with all degrees of freedom locked, these showed however that forces along the Z axis
were small and had no impact on the resulting force.
Simulations with beams of five different cross sectional areas were performed. The
results are displayed in Figure 4.13 below. This figure shows the resulting force on the
node as a function of beam type. The re
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