Handbook en Hydraulics

8/10/2019 Handbook en Hydraulics

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Teaching and

Training in the

action oriented

methodology

Teacher training for the metal sector

P h a s e I I I

H a n d b o o k

Teaching and Training in Hydraulics


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Table of contents page

Preface 3

The set-up of the handbook 6

1. Energy transmission 8

2. Comparison of hydraulics and pneumatics .9

3. Hydraulic circuits with main components 10

4. Projects 11


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PrefaceThe objective of the teachers training of phase III is to improve the quality of the

teaching and learning process in the metal sector and here in phase III in the

field of hydraulics.

Didactic materials for teachers and learners were prepared to facilitate theimplementation of the module hydraulics in the current and future curriculum

of the metal sector.

1. The simulation demo-shareware of FESTO _FluidSim_ is used to design, to simulate and to

evaluate applied hydraulic circuits.

2. Materials in form of animated pictures, technical documents and proposed projects support the

workshop in an interactive learning and partly self-learning process, applying the method of

action-oriented teaching.

3. Problem solving is always in the focus of the learning process.

4. The workshop hydraulics is based on the methodology of the previous teachers training of

phase II pneumatics.

Simulation

The simulation of interactive designed circuits with the help of the FluidSim software of

FESTO was already applied in the previous workshop of pneumatics. Hydraulics and

pneumatics are related subjects and the software is familiar to the participants.

Interactive Learning

Although the use of the computers facilitates the individual learning process, however, there

are times when a skill or concept has been developed in the classroom and practice is

needed for complete understanding and proficiency .

Problem Solving

In the centre of the action-oriented learning is the problem to be solved.

A problem in its easiest form might be presented in form of a task but in modern teaching we

understand a problem rather as a project we give the students to solve.


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Methodology

The methodology of action-oriented learning is not necessarily bound to a certain form of a

curriculum. Action-oriented learning can be practiced even in a very po0rly equipped learning

environment limited to paper, scissors and clue sticks.

In the first phase of the teachers training in September 2007 the methodology of action-

oriented learning was introduced.

In phase II the methodology was applied in the workshop Pneumatics

(February 2008 in Podgorica).

The methodology will be intensified and applied in depth during this workshop.

Expected results of the workshop

The participants are already familiar with the FESTO Software FluidSim of pneumatics,

which is similar to the software FluidSim of hydraulics.

In this workshop same projects will be demonstrated in motion with the help of the CAD

software Solid Works which will bridge this workshop to the next teachers training in

phase IV CAD.

Teachers learn how to develop worksheets effectively using animated pictures, capturing

sequences and selecting contents relevant and helpful for the preparation of learning

materials.

Teachers are able to improve the quality of lessons through the integration of interactive

learning materials in form of the design and simulation-software FluidSim to enable the

students to achieve practical skills in the classroom, where not sufficient or adequate

workshop equipment is available.

The manipulation of the software FluidSim must not be exercised. The software is already

known from the previous training in pneumatics.

In hydraulics accident prevention and safety are to be handled even more seriously than inother subjects, where life-threatening pressures and forces occur and poisonous substances

are to be handled.

Dangerous and hazardous situations can not be simulated in training.

Just therefore the students have to be made aware of those risks while working with or

working in the environment of hydraulic systems.


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watch/listen read/study think & discuss do some work

To simplify the differentiation of the four steps of instruction (watch, study, think, work) in

action-oriented training of hydraulics, the four icons of our Doggie will indicate the respective

phase of instruction.

The set-up of the handbook

Before the action-oriented method of a given problem (in form of a project) followed by the

planning phase, the solution and the evaluation (in form of the simulation) takes place, the

students must have some important knowledge about Power, Energy, Pressure and Force

which arise in hydraulic circuits, devices and installations.

The basic knowledge of chapter 1 energy transmission, chapter 2 comparison of

pneumatics and hydraulics and chapter 3 force, pressure, speed and power should be

taught together with a sequence of safety and security, before the practical applications ofproject work are started.

The design and the simulation of the hydraulic circuits of chapter 4 are realized with the help

of the demo-software FluidSim of Festo.

A variety of practical applications in form of projects is given in chapter 5 and will be

demonstrated in operation with the help of the CAD-software Solid Works. These projectsmay be helpful to work out teaching materials for the students and to give teachers examples

of best practice of applied projects.

The demonstration of Solid Works in hydraulics will give an insight to the application of the

CAD program for further teachers training in the field of CAD.


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The handbook for the teachers training is built up as follows:

Didactic hints are given where required and pedagogical aspects are mentioned. Alternatives of didactical approaches are proposed.

Explanations and representations of basic physical and pneumatic laws are treated inchapter 1, 2.

Explanation and application of the most used components in hydraulic circuits can be studiedin chapter 3.

Projects are worked out as examples of best practice in chapter 4.

The problem to be solved in these projects is to design, to calculate, to draw and to document the

hydraulic devices of:

a boring device a lifting table

In the following chapters of the handbook the basic knowledge, the necessary skills and didactical

aspects are presented.

In each chapter recommendations are indicated by our icon Doggie to watch, to read, to think or

to work with the materials.

In each chapter the acquired competences are named.


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1. Energy transmission

Hydraulics Pneumatics Electricity Mechanics

Energy source Hydraulic oil under pressure

Compressedair

Electrons Solid matter

Energy

transmission

Metal pipes,

hose pipes

Metal pipes,

hose pipes

Electric cables Shafts, levers,

chains, belts..

Actuator,

Drive

Electric motor with

pump

or combustionengine

Electric motor

and

compressor

Electric drive Electric motor

or combustion

engine

Power density

High,

high pressure

big forces

Small because

of low

pressure

For high

performance heavy

electric motor

required

High, but

construction and

volume

unfavourable

Infinitely

variable

speed control

Very accurate

through pressure

and pumped oil

Good Good .very good in

case of electronic

controls

Poor

Accuracy in

positioning

Accurate because

oil is nearly

incompressible

Poor, because

air is

compressible

Accurate Very accurate

through gears

or indexing

Movement type Linear throughhydraulic cylinders

and rotary through

hydro motors

Linear androtary

Mainly rotary,

but also linear

induction motor

Mainly rotary butalso linear

motion through

crankshafts

Competence: The main characteristics of hydraulics are understood.


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2. Comparison of hydraulics and pneumatics

Features of pneumatics Features of hydraulics

Central compressed air supply required Separate power supply for each unit required

Exhaust air released into the atmosphere Closed hydraulic oil circuit; return pipe required

Compressed air is environmentally friendly Hydraulic oil leakages may cause environmental

problems

Air pressure appr. 7 bars causes little hazards High fluid pressure, 300 bars 1000 bars

involves dangers of accidents

Generation and transmission of small to medium

forces

Generation and transmission of very high forces

through the use of comparatively small unitsPneumatic cylinders start with little force as the air

is compressible and pressure must build up

Hydraulic cylinders and hydraulic motors permit

starting from rest with maximum torque

Drip oil must be added to the compressed air

supply for lubrication of the pneumatic elements

Hydraulic equipment is self lubricating therefore

little wear

No slow and accurate movements are possible

because of compressibility of the compressed air

Hydraulic equipment is suitable for fast as well as

extremely slow movements

No accurate feeds are possible Highly accurate feeds are possible

No overload protection is required in the circuit Overload protection achieved through pressure

relief valve

Sometimes jerky movements especially when

flow-control valve is placed in the feeding pipe

Smooth and uniform movements are achieved

Competence: the features of hydraulics can be compared to those of pneumatics.


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3. Hydraulic circuits with main components

This chapter represents the knowledge and skills of the hydraulic circuits.

To understand the hydraulics the materials must be read, well reflected and exercised.

Each component which is presented is not only to be studied on paper but rather it has to be worked

with. To understand each component in operation, the different parameters are to be selected and

checked.

Each component of this chapter should be designed and placed in a simple circuit of the simulation

software FluidSim and should be experienced through simulation and parameterisation.

This chapter can be conducted in self-learning methodology.

Even the state diagrams can be inserted to study the function of the components.

The state diagram helps

to understand the

function of the

components.


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4. Projects

The four following projects are examples which may be introduced as projects in action-

oriented training.

The expected solutions are shown here in the teachers handbook.

a boring device a lifting table

4.1 Lifting platform - Project 1

4.1.1 Lifting table, hydraulically controlled

This lifting platform works hydraulically

with a folding grille and one double-

acting cylinder.

The designer has to select a suitable

hydraulic cylinder for the given

maximum table weight and an oil

pressure which is adjusted and

controlled by the pressure relief valve.


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Conclusion: The forces acting on the cylinder in the lower positions are higher than in theupper positions!

Competence: the student is able to calculate the acting forces of a hydraulic system.

Calculation of the cylinder force:

50 mm

tan = ----------- = 0,2 11,53 250mm =====

force in strut:

3000N 3000N

sin = ------------ x = ----------- = 15000N x 0,2 =======

horizontal force = cylinder force F 2

3000N 3000N 3000N

tan = --------- x = ------------ = ------------- x tan 0,2035

x = 14742 N

==========


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Calculation of mechanical work

The required force on the cylinder can also be calculated with consideration of the

mechanical work to be done by lifting the weight over a given height on the table. Based on

the fact that work done by the table is equal to the work done by the hydraulic cylinder the

following equations can be used to determine the cylinder force required:

Lifting work: W = F G * h W = work (N*m)

F G = force of weight H = lifting height

Example: FG = 3000N ; lifting height = 300mm

W = 3000N * 0,3m = 900 N *m

========


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Average force on the cylinder:

W = 900 N*m; cylinder stroke h = 60mm

Calculation of cylinder cross-sectional area and cylinder diameter:

Maximum cylinder force assumed F cyl = 50000 N

Maximum oil pressure p e = 250 bar (1bar = 10 N/cm 2; 250 bar = 2500N/cm 2)

Efficienc y factor = 0,85

F 50000N cm 2

Cylinder force : Fcyl = p e * A * ACyl = ------------ = ----------------------

pe * 2500N * 0,85

A = 23,529 cm 2

============

Calculation of cylinder diameter:

4 * A 4 * 23,529 cm 2

Dcyl = ----------------- D cyl = ---------------------- = 5,473 cm = 54,73 mm ========

W 900 N*mFzyl = ----------- = ---------------- = 15000N H 0,060 m =======

(Note: This calculation does not include Friction in bearings etc.and it is an average value)


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Competences:

The student designs hydraulic circuits derived and developed from agiven task.

The student is able to check the operation of the circuit throughsimulation, measurements and estimated calculations.

Circuit design

Select the hydraulic components from

the FluidSim library and design the

circuit as shown. Adjust the pressure

on the pressure relief valve to

250bar.

Name the components with their

designation numbers.

Measure the pressures p e1 , p e2 and

pe3 on lifting and lowering the

platform.


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4.1.2 Lifting table hydraulically controlled with filter, lifting speed control and

pilot operated check valve

In order to keep a cylinder under load in its position for a longer duration a simpleway-valve does not serve the purpose. Due to leakage the platform may sink downslowly. To prevent this unwanted lowering of the platform a pilot operated check valvemay be inserted.

Functional principle of the pilot-operated check valve

For the lowering of the platform the hydraulicoil must flow into the piston rod chamber ofthe cylinder and the oil pressure (p e3 ) rises.The control inlet (Z) of the pilot-operatedcheck valve is connected to the inflow pipe ofthe piston rod chamber.Once the appropriate control pressure hasbeen reached, the pilot-operated check valve

opens and the load can be lowered.

Please modify the previous circuit and insertfilter, flow control valve for lifting speed controland the pilot-operated check valve.


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Advanced Task of the Project Lifting platformManually actuated hydraulic valves are very common for applications in the area of mobile

hydraulics. For the control of machine-tool slides or related applications electrically

controlled hydraulic valves are more suitable. It would however go beyond the scope of this

workshop to include electric control in detail, therefore only a simple electric control circuit

with push-button operation has been added. More details about electric and electronic

controls may be reserved for future seminars.

In the given circuit the buttons of the electric switches must be held pressed down foractuating the cylinder.

Competences:The student is able to alter existing circuits and to modify the circuit dueto the demands of the client.


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Description of the circuit

When actuating the 4/3 way-valve(1V1) the clamping cylinder (1A1)moves forward and clamps the sheet

metal. On reaching the clampingpressure in the inflow pipe thesequence valve (1V2) opens the wayfrom P-T and the bending cylinder(2A2) moves forward and bends thesheet metal.

When switching back the 4/3 way-

valve (1V1) into position (b), both

cylinders move back simultaneously.

Competence:

The student is able to develop and test a hydraulic circuit from thedescription of the operation of the device.


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4. 3 Boring device with two double acting cylinders

1A1

2A1 Description of operation

This circuit has been designed toclamp a job safely for the drilling

operation. Contrary to the bending

device (6.2) the clamping cylinder

(1A1) must remain in its outward

position during the downward

movement of the drilling cylinder

(2A1) as well as the upward

movement (retracting the drill from

the job).

Only after the drilling cylinder

(2A1) has moved fully back, the

clamping cylinder (1A1) may

move in and the job can be

removed from the vice.

Tasks:

Please design the circuit withthe FluidSim software and testit.

Try out different feeds byselecting various settings forthe flow control valve (2V2).

Describe which design featurehas been added to achieve thesequential movement of thecylinders.


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4.4 Car Lift

Description of the Car Lift Design

Car lifts are usually constructed as 2-post platforms for passenger cars or

four post platforms for trucks or heavy vehicles.

The load to be lifted may not always be evenly distributed on the car lift. The

effect of it will lead to different pressures in the two hydraulic cylinders and

as a consequence to different lifting speeds, as the cylinder with the lowerpressure tends to have the higher volume flow rate and therefore moves

faster than the cylinder with the higher pressure.

This fact may lead to the problem of tilting and damage to guide ways and

perhaps also the hydraulic cylinders.

A special circuit design, called Graetz-circuit ensures constant volume flow

rate to both hydraulic cylinders even at asymmetric load distribution.


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Documents

Handbook en Hydraulics