Mr.GiridharBosch Rexroth (India) LimitedA Drive & Control Company

Cylinder Presentation

Introduction

Good Morning Ladies & Gentlemen,We spend the next hour in understanding the Hydraulic Actuator –Cylinder.I am sure, during the lecture clause on basic principles of Hydraulics, you have already gathered that, there are reasons and advantages to use a Hydraulic System in designing industrial / mobile machines.The source of power such as an electric motor or an engine drives – an hydraulic pump which delivers fluid under pressure. This fluid under pressure is used to create the necessary movements in the machine, linear, rotary or reciprocating. The movement is the desired end function to lift, press, shift or move hold / clamp, orient, turn etc.,

Hydraulic cylinder is the device to which, we supply the pressure oil from the pump and obtain linear movement to push, press, shift, clamp any load.

Eg: Coal stacker reclaimerPusher in a furnace in a steel shop.The boom of an exlavatorThe Dozer blade of a bull dozerThe jacks of a water well rig pressing against the groundThe telescopic cylinder of a rear dumper.The double ended cylinder in a surface grinding machine etc.,

Topics :-1. Brief on hydraulic systems2. The need for a device – linear actuating high forces, compact size3. Where do we use it ? Applications4. How does it work ?5. What is it made of ? Design aspects 6. Materials of construction7. How to size it for a specific applications – calculations, selection

criteria – column strength, stop tube8. Types of cylinders9. Mounting configurations / special features 10.Cushioning – Need, design and variations for it11.Seals – types, materials, selection criteria12.Performance criteria, what to test ? Test procedure13.Trouble shooting / servicing aspects14.Working medium – Hydraulic oil, fire resistant fluids, synthetics,

water, water glycol etc.,

Hydraulic cylinders - Principles

Tie rod type cylinder

Mill type cylinder (Heavy duty cylinder)

Tandem cylinder

Double acting rapid traverse cylinder

Single acting telescopic cylinder

Double acting telescopic cylinder

End position cushioning mechanism in cylinder

The two most relevant formulae used in determining the column strength of piston rod are:

�Euler’s formula:

Pc = r x � ² x E x a = r x � ² x E x I--------------- ---------------(L / r) ² L²

�Johnson’s parabolic formula:

Pc = a x �y x [1- �y x (L / r²) ]-------------------

4 x � x � ² x E

Procedure for determining the safe piston rod calculation :

Pc = Critical or Buckling load, Kgf� = Coefficient of end condition E = Young’s modulus of the material of piston rod, Kgf/mm²a = Area of C/S of piston rod, mm²L = Column length, mmr = Least radius of gyration of piston rod, mm�y = Yield stress of the material of piston rod, Kgf/mm²I = Moment of inertia of piston rod section, mm4

Cylinder wall thickness calculation:

T = 1.143 x d x p for C1 = ±125%------------------

200 x k / s - 2 x p

C1= The tolerance on wall thickness S = Factor of safety (1.5 to 4 can be used)k = Yield strength (minimum) 36 kg/mm² for SE52d = Inside diameter of tube, mmp = Pressure, kg/cm²

EXERCISES :-

1 What is the difference between a single-acting and a double acting hydraulic cylinder ?

2 Name four different types of Hydraulic Cylinder mountings ?3 What is a cylinder cushion ? What is its purpose ?4 What is a double-rod cylinder ? When would it normally be used

?5 What is a telescoping – rod cylinder ? When would it normally

be used ?6 Why does the rod of a double-acting cylinder retract at a greater

velocity than it extends for the same input flow-rate ?

7 How are single-acting cylinders retracted ?8 An 8 cm diameter hydraulic cylinder has a 4 cm diameter rod, if

the cylinder receives flow at 100 lpm and 12 MPa, find the a) Extension and retraction speeds b) Extension and retraction loadcarrying capacities.

9 A 3 in diameter hydraulic cylinder has a 1.5 in diameter road, find the flow rate leaving the cylinder when it is extending by an entering flow rate of 8 gpm