Material Selection

When selecting materials for a product it is essential to have a clear understanding of the functional requirements for each of the individual components within the design of the product. In order to define the functional parameters required for this type of component, we first identified a product where this component could be used. Initial research identified this component as a cast iron companion flange which is used in the design of heavy duty pumping equipment. An example of this can be seen in the Warman AH slurry pump. The team have used this product as a case study to help us to understand the functional requirements of the companion flange by analysing the service conditions which this type of pump may be used within. (Amadeal) (Concordmetalsinc)

The image to the left shows the Warman AH slurry pump which we are using to identify functional requirements for the cast iron companion flange component.

Slurry pumps can be used widely throughout the beneficiation sector of the mining industry where the majority of plants use wet separation processes. The systems used in these mining applications usually move large volumes of slurry through the process.

The Warman slurry pumps are also widely used for the disposal of ash from fossil fuel power plants. Other areas of use also include manufacture of fertilizers, land

reclamation, mining by dredges, and the long distance transportation of coal and minerals. These areas of use help to define an extensive list of functional requirements.

Functional Requirements

The defining of functional requirements requires the need for the team to define an application for the cast iron companion flange which will consequently lead to the listing of some design constraints. There are several design constraints which should be considered within the design requirements for any component used within a slurry pump.

Abrasion – The image to the right shows the three main modes of abrasive wear. Abrasive wear occurs when hard particles are forced against and move relative to a solid surface.

Erosion – Erosion is the next design constraint to consider. This is the most dominant mode of wear. This form of wear involves the loss of surface material by the action of particles entrained in the fluid. Erosion in this component will involve a transfer of kinetic energy from the particle, from the slurry, to the surface of the component.

The transfer of kinetic energy from the particle to the surface of the companion flange would result in a high contact stress. The overall contact pressure at each particle site would be small, however, the specific contact pressure is high because of the irregular shape of the particles.

Corrosion – There are many different types of corrosion, e.g. uniform, galvanic, crevice, pitting, intergranular, selective leaching, stress and erosion corrosion. Erosion/corrosion is the most applicable in slurry applications and results from the constant abrading of an oxide layer that forms on the interior surface of the pump liquid end.

Chemical resistance is a broad term used to describe the deterioration of materials when they are immersed in either a static or dynamic fluid. This is an important constraint within this component as any wear on the surface of the companion flange may result in the need to replace the component when the pump is being used in extreme conditions, which are common during the slurry application process.

Solids Concentration – The adverse effects on pump performance caused by solids in slurry are due to:

• Slip between the fluid and the solid particles during acceleration and deceleration of the slurry while entering and leaving the impeller. This slip of solids, and the associated energy loss, increases as the settling velocity of the particles in the slurry increases.

• Increased friction losses in the pump. These losses increase with the density of the slurry.

A rise in solids concentration also reduces the pump efficiency considerably. It becomes more pronounced with an increase in the size of the particles being pumped. This therefore highlights that the properties of the slurry have a direct relationship to the type of materials chosen for the required companion flange.

Volume/Flow Rate – The volume/flow rate relates to the volume of slurry being transported, this must be determined before defining a slurry pump application which in turn defines some of the functional characteristics for the companion flange component.

The volume (or flow rate) is determined by correlation between three factors:

• The solids specific gravity • The tonnage of solids required to be pumped • The concentration of these solids within the slurry mixture.

Mechanical Seal – This is the main functional requirement of the companion flange, to provide a mechanical flange between components within the pump. Limited reliability is common within this component and costs can be relatively high. (pumping handbook)

Application Determination and Specific Functional Requirements

To summarise the findings determining which characteristics will affect material selection we have determined a service use for the companion flange. The industrial application this component will be used in is the slurry pumping applications used within the mining industry. The specific application of use we have decided upon requires the following characterisitics:

• Flow capacities o Up to 22,000 gpm (5,000 m3/hr)

• Head requirements o Up to 240 ft (73 m)

• Pressures o Up to 300 psi (2,020 kPa)(weirs)

• Smooth operation, small vibration and low noise • Ability to deliver high concentration and high viscosity(kehuabest) • Quantity batch size – 250,000 parts per month • Size – The volume of the cylinder is approximately 613839 mm3. The maximum dimensions

are diameter 125mm and height 50mm. • Weight – The weight will very much depend on the material chosen for the part. A

suggested material taken from the manufacturing drawing is cast iron. This material has a density of around 7860 kg/m3, meaning this would be a heavy component if made from this material. As this part is mainly used within the oil and gas, minerals and power and industrial sectors as a key component of the pumps used within these industries then weight saving will be less of an importance than a component which is used in the automotive or aerospace industries. The substitution of materials for weight saving purposes is a major factor within the design of this part. The density plays a significant role in the strength-to-weight ratio and the stiffness-to-weight ratio of materials and structures. Consequently this will affect the yield and tensile strength of the material.

• Complexity of Part – The part complexity is quite high with several features being located on different planes of the part.

• Dimensional and Geometric accuracy required – The geometric tolerancing required has been discussed at length previously and this differs from feature to feature, however the

highest geometric accuracy required from this piece is -0.01. The material selected must be capable of achieving this high dimensional accuracy.

• Surface finish required – One feature within the design of this part has specified a surface finish of 0.1. This is the highest level of surface finish and the material chosen must be capable of achieving this.

• Manufacturability of material – The manufacturability of the material must be high in order to achieve the high tolerances and surface finishes required from the part. There are also many features which require additional machining. It must be able to be machined quickly and easily to the high volume required from the production specification.

As previously mentioned, the particle size of the slurry being pumped has a huge effect on the material selection for the components within the pump design as this table shows:

(metso slurry pumps)

This table illustrates that the material required for the service application we have determined for this component is a hard iron material. With this in mind the team consulted the material tables on the following page.

(pumping handbook)

The materials highlighted in the tables above are Ductile Grey Iron (SG Iron) and Cast Iron. The material properties of each of these materials are explored below:

Ductile Grey Iron – Ductile Grey Iron in the above table is given the reference figure of D21. This material is a ductile alloy grade of grey iron which is primarily used where higher physical properties and greater shock resistance are required compared to G01.

Cast Iron – Cast Iron in the table above is classed as G01. This is the standard grade of grey iron. (pumping handbook) These two potential materials were identified with respect to their potential suitability for use within the component. Upon researching for more detailed information on the structure and physical and mechanical characteristics of these materials, a third grade of cast iron was also identified and all materials are explored in more detail in the table below.

Grey Iron Standard Specifications

• ASTM A48: gray iron castings • ASTM A74: cast iron soil

Characteristics

Several strength grades; vibration damping;

Applications

heads; manifolds for internal combustion

& pipe fittings • ASTM A126: gray iron castings for valves, flanges & pipe fittings • ASTM A159: automotive gray iron castings • SAE J431: automotive gray iron castings • ASTM A278 & ASME SA278: gray iron castings for pressure-containing parts for temperatures up to 650F (343C) • ASTM A319: gray iron castings for elevated temperatures for non-pressure-containing parts • ASTM A823: statically cast permanent mold castings • ASTM A834: common requirements for iron castings for general industrial use

low rate of thermal expansion & resistance to thermal fatigue; lubrication retention; and good machinability.

engines; gas burners; machine tool bases; dimensionally stable tooling subjected to temperature variations, such as gear blanks & forming die covers; cylinder liners for internal combustion engines; intake manifolds; soil pipes; counterweights; and enclosures & housings.

Ductile Iron

Standard Specifications

• ASTM A395 & ASME SA395: ferritic ductile iron pressure-retaining castings for use at elevated temperatures • ASTM A439: austenitic ductile iron castings • ASTM A476 & ASME SA476: ductile iron castings for paper mill dryer rolls • ASTM A536 & SAE J434: ductile iron castings • ASTM A571 & ASME SA571: austenitic ductile iron castings for pressure-containing parts suitable for low-temperature service • ASTM A874: ferritic ductile iron castings suitable for low-temperature

Characteristics

Several grades for both strength & ductility; high strength, ductility & wear resistance; contact fatigue resistance; ability to withstand thermal cycling; and production of fracture critical components.

Applications

Steering knuckles; plow shares; gears; automotive & truck suspension components; brake components; valves; pumps; linkages; hydraulic components; and wind turbine housings.

service • ASTM A897: austempered ductile iron castings

Malleable Iron

Standard Specifications

• ASTM A47 & ASME SA47: ferritic malleable iron castings • ASTM A197: cupola malleable iron • ASTM A220: pearlitic malleable iron • ASTM A338: malleable iron flanges, pipe fittings & valve parts for railroad, marine & other heavy-duty service up to 650F (343C) • ASTM A602 & SAE J158: automotive malleable iron castings

Characteristics

Soft & extremely ductile.

Applications

Chains; sprockets; tool parts & hardware; connecting rods; drive train & axle components; and spring suspensions.

(foundry source)

From the table above the two most suitable materials were identified as ductile iron and grey iron. They have been selected from the list due to their good strength capability, wear resistance, contact fatigue resistance and also resistance to thermal fatigue, all of which are characteristics which comply with the functional requirements which were previously outlined. To make a final material selection more information was sought on the materials in question.

Gray Iron Properties

Gray iron’s high damping capacity, combined with its excellent machinability and high hardness, is unique to this material and makes it ideally suited for machine bases and supports, engine cylinder blocks and brake components. Excessive vibration causes inaccuracies in precision machinery and excessive wear on gear teeth and bearings. The damping capacity of gray iron is considerably greater than that of steel and other iron types. For example, if gray iron, CGI and ductile iron have a similar composition, the relative damping capacity of gray iron is 1, CGI is 0.35 and ductile iron is 0.14. The damping capacity of gray iron is about 20-25 times higher than steel. For comparison, aluminum’s damping capacity is one-tenth that of steel.

Gray iron’s compressive strength is typically three to four times more than its tensile strength. The lack of graphite-associated volume changes allows for a similar Poisson’s ratio to other engineering metals but different tension properties. Poisson’s ratio remains constant at 0.25 over a large compressive stress range and increases at higher stress levels.

To classify gray iron in accordance to its tensile strength, ASTM Standard A48 and Society of Automotive Engineers (SAE) Standard J431 provide the best details. The two specifications approach the task from different standpoints, but the concept essentially remains the same. For example, the number in a Class 30 gray iron refers to the minimum tensile strength in ksi. In ASTM A48, a standard size test bar is added to the class. Class 30A indicates that the iron must have a minimum 30 ksi (207 MPa) tensile strength in an “A” bar (0.875-in. as-cast diameter).

In SAE Standard J431, tensile strength is not required, but hardness and a minimum tensile strength to hardness ratio are required. The class then is identified as a grade. A Class 30B iron for ASTM A48 would be comparable to a grade G3000 in SAE Standard J431. The other gray iron specifications build off of these two primary specifications.

Table 3. Property Comparisons for Gray Iron Classes

Property Class 25 (as-cast)

Class 30 (as-cast)

Class 30 (annealed)

Class 35 (as-cast)

Class 40 (as-cast)

Brinell Hardness

187 207 109 212 235

Tensile Strength 29.9 ksi (206

MPa) 33.7 ksi (232

MPa) 20.6 ksi (142

MPa) 34.8 ksi (240

MPa) 41.9 ksi (289

MPa) Modulus of Elasticity

16.6 Msi (114 GPa)

17.0 Msi (117 GPa)

14.5 Msi (100 GPa)

18.0 Msi (124 GPa)

18.2 Msi (126 GPa)

Tensile Poisson’s Ratio

0.29 0.19 0.21 0.22 0.24

Compression Poisson’s Ratio

0.27 0.28 0.26 0.28 0.23

Compression-to-Tensile

Strength Ratio 3.68 3.84 4.05 3.63 3.71

Ductile Iron Properties

Five grades of ductile iron are classified by their tensile properties in ASTM Standard A536 (Table 4). SAE Standard J434c (for automotive castings and similar applications) identifies these five grades of ductile iron only by Brinell hardness. However, the appropriate microstructure for the indicated hardness also is a requirement.

Table 4. Property Comparisons for Ductile Iron Grades (ASTM A536)

Grade Heat

Treatment Tensile

Strength Yield

Strength

% Elongation (min. 2 in.)

Brinell Hardness

Poisson’s Ratio

Tensile Elastic

Modulus 60-40-

18 1

60,000 psi (413 MPa)

40,000 psi (276 MPa)

18 130-170 0.28 24.5 Msi

(169 GPa) 65-45-

12 2

65,000 psi (448 MPa)

45,000 psi (310 MPa)

12 150-220 0.28 24.5 Msi

(169 GPa) 80-50-

06 2

80,000 psi (551 MPa)

55,000 psi (379 MPa)

6 170-250 0.28 24.5 Msi

(169 GPa) 100-70-

03 3

100,000 psi (689 MPa)

70,000 psi (482 MPa)

3 241-300 0.28 25.5 Msi

(176 GPa) 120-90-

02 4

120,000 psi (827 MPa)

90,000 psi (620 MPa)

2 240-300 0.28 25.5 Msi (176 Gpa)

(foundry source)

(symcyclo)

In order to help make a final decision on the material chosen for the manufacture of the companion flange, the team used the following questions to help inform their decision on the material to be chosen:

• Do the materials selected have the appropriate manufacturing characteristics? • Can some of the materials be replaced by others that are less expensive? • Do the materials under consideration have properties that meet minimum requirements and

specifications? • Are the raw materials specified available in standard shapes, dimensions, tolerances, and

surface characteristics? • Is the supplier of the materials reliable? Can the materials be delivered in the required

quantities within the required time frame? Are there likely to be significant price increases or fluctuations?

• Does the material present any environmental hazards or concerns?

The chosen material for the manufacture of this component is Grey Iron. With regards to the manufacturing characteristics present within the material, both grey iron and ductile iron suitably possessed the necessary characteristics to be used within the manufacture of this component, however, the team decided upon using Grey Iron due to its extra characteristics of vibration damping, lubrication retention and good machinability. These characteristics were important as their presence in the material provided the extra ability within the component to provide the smooth operation of the product with low vibration and no noise. The good machinability property within the material will also allow for the surface finish required of the component. This characteristic will make it easier to achieve the high standard required within this functional characteristic.

Reliability of material suppliers and cost – The following chart shows the fluctuation in price of iron ore, which directly affects the price of grey iron. (cranebsu)

It is clear to see that the price is set on a monthly basis depending on the price of

iron ore. The price of this raw material can depend on supply and demand or complex geopolitics. (Manufacturing Engineering and Technology) The price of both ductile iron and grey iron would therefore be affected by the price of iron ore. The cheaper material option was grey iron which is relatively cheap for production and when considering the number of components required per month (250,000) then this material represents a large cost saving over the ductile iron material.

The supply of raw material will be reliable as this is a large industry sector on a global scale. One company which could be used to supply the material has been identified. The company is called Stemcor, which specialises in steel supply but does supply many other materials. The company is a reputable company with many offices all over the world, including 18 in the UK, with one of the UK based offices being situated in Glasgow. (Stemcor)

Quality Control

Quality control will test for surface, geometric, material property, internal integrity, durability, reliability, robustness, cost, serviceability, perceived quality.

Quality Control Management

Quality management within an industrial setting has two important management techniques which should be considered to ensure the smooth running of the quality control and assurance procedures within the manufacturing process.

Total quality management – quality circle – consists of regular meetings by groups of employees who discuss how to improve and maintain product quality at all stages of the manufacturing operation.

Taguchi methods – robustness – taguchi loss function, equation to calculate losses on parts that meet the design specification

The manufacturing process for the companion flange will take both of these management methods into consideration, along with important British Safety Standards for quality control:

ISO 9000 Standard – quality management and quality assurance standards

ISO 14000 Standard – environmental management system

Statistical methods of quality control

Issue with tooling must be taken into consideration when trying to assess and control the quality within a manufactured product. Some of the main issues causing problems for quality control are:

• Cutting tools, dies, and moulds are subject to wear; thus, part dimensions and surface characteristics vary over time

• Machinery performs differently depending on its quality, age, condition, and maintenance; thus, older machines tend to chatter and vibrate, are difficult to adjust, and do not maintain tolerances as well as new machines. Cast iron wears out tools very quickly.

• The effectiveness of metal working fluids declines as they degrade; thus tool and die life, surface finish and surface integrity of the workpiece, and forces and energy requirements are affected

• Environmental conditions, such as temperature, humidity and air quality in the plant, may change from one hour to the next, affecting the performance of machines and workers

Quality Assurance Checks

The following procedures will be carried out during the manufacturing process, at different stages in the process, to ensure the quality of the product is kept throughout the manufacturing process:

o Acceptance sampling and control – a few random samples from a lot and inspecting them to judge whether the entire lot is acceptable or whether it should be rejected or reworked

o Liquid penetrants – fluids are applied to the surface of the part and allowed to penetrate into cracks, seams and pores. Can detect a variety of surface defects. The equipment is easy to use, can be portable, less costly to operate than other methods. Can only detect defects that are open to the surface or external

Quality Control

At the end of the manufacturing process there is a need for more detailed checks on the geometric features of the part, as outlined at the start of this section. Some of the process which could be used to carry out an inspection of 1 in every 500, or 5 from every batch of components produced if batch manufacturing is used, finished parts have been explained briefly below:

o Ultrasonic inspection – an ultrasonic beam travels through the part detecting internal flaws. This method has a high penetrating power and sensitivity. Can be used in various directions to inspect flaws in large parts. Requires experienced personnel.

o Acoustic methods – The acoustic-emission technique detects signals generated by the workpiece itself during plastic deformation, crack initiation and propogation, phase transformation, and abrupt reorientation of grain boundaries. This method is usually performed by elastically stressing the part or structure, such as bending a beam, applying torque to a shaft, or internally pressurizing a vessel. Sensors typically consisting of piezoelectric ceramic elements detect acoustic emissions.

o Thermal inspection – use of contact or non-contact heat sensing devices. Detects defects in the workpiece such as cracks, de-bonded regions in laminated structures, and poor joints.

o Holography – creates a 3 dimensional image of the part by utilizing an optical system. Generally used on simple shapes and highly polished surfaces

The quality control procedure chosen for use by the team was holography. Due to the complex shape and the close nature of tolerances and the very high specified surface finish

which the component must have we thought it would be best carried out robotically for greater accuracy and speed.

Holography works much in the same way as a 3D printer, except the output, the 3-dimensional shape, will be a hologram of the finish component instead of a physical component. The part will be scanned using a laser technique so that every coordinate of the part has been mapped. (A coordinate measuring machine) This will be transferred to a computer programme where the image of the finished component will be built in layers to a high level of accuracy. The specialised 3D printer will then print a hologram of the finished item. Information on tolerances and surface finish, and any other appropriate geometric feature, can be obtained from the computer programme and the identified on the hologram.

Importance of quality control and cost issues

Quality control is important in reducing the likelihood of human error. It ensures that all components are produced at the same high standard and reduces cost issues associated with the need to remanufacture components and batches which were found to be unsuitable.

http://www.cranebsu.com/mailers/201010/201010_u.html

http://www.stemcor.com/western-europe.aspx