Up-keeping of rubber items - Indian Railway · 2019. 10. 17. · Oxidation is a chemical reaction and as in any chemical reaction, the rate of reaction is enhanced by rise in temperature

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CAMTECH/E/13-14/Rubber Item/1.0

November, 2013

dsoy dk;Zky;hu mi;ksx gsrq (For Official Use Only)

Handbook on Up-Keeping of Rubber Items of

Pneumatic Valves of Electric Locomotives

TARGET GROUP: Electric Loco Maintenance Staff

QUALITY POLICY

“To develop safe, modern and cost

effective Railway Technology

complying with Statutory and

Regulatory requirements, through

excellence in Research, Designs and

Standards and Continual

improvements in Quality Management

System to cater to growing demand of

passenger and freight traffic on the

railways”.

Handbook on Up-Keeping of Rubber Items of Pneumatic Valves of Electric Locomotives

FOREWORD

The physical properties of most rubber products change in

unfavorable storage conditions or with improper handling. They can become unusable/ unserviceable due to excessive hardening, softening, cracking, crazing or other surface degradation. The deleterious effects of these factors may however be minimized by careful monitoring of the storage conditions.

CAMTECH has prepared this handbook on “Up-Keeping of Rubber Items of Pneumatic Valves of Electric Locomotives” to improve the storage conditions and create awareness on the subject.

I hope this handbook will prove to be useful for the maintenance personnel working in Electric loco sheds, workshops, trip sheds etc.

CAMTECH, Gwalior A.R.Tupe Date:26.11.2013 Executive Director

PREFACE

The properties of rubber products which are properly stored and handled are almost unchanged over long periods. The changes in the properties of rubber items are caused by many factor for instance, oxygen, ozone, heat, light, moisture, solvents or by storage under tension.

This handbook on “Up-Keeping of Rubber Items of Pneumatic Valves of Electric Locomotives” has been prepared by CAMTECH with the objective of making our maintenance personnel aware of storage conditions of rubber items.

It is clarified that this handbook does not supersede any existing provisions laid down by RDSO, Railway Board or Zonal Railways. This handbook is for guidance only and it is not a statutory document.

I am sincerely thankful to all field personnel who helped us in preparing this handbook.

Technological up-gradation & learning is a continuous process. Please feel free to write to us for any addition/ modification in this handbook. We shall highly appreciate your contribution in this direction.

CAMTECH, Gwalior (Peeyoosh Gupta) Date: 26.11.2013 Jt. Director Electrical e - mail id : [email protected]

CONTENTS

Sr.No. Description Page No.

Foreword iii Preface iv Contents v Correction Slip vi

1. INTRODUCTION 01

2. WHAT IS RUBBER 01 3. CLASSIFICATION OF RUBBER TYPES ACCORDING TO THEIR SUSCEPTIBILITY TO DETERIORATION 02 4. PROPERTIES AND APPLICABILITY OF

ELASTOMERIC MATERIALS 05 5. SHELF LIFE AND STORAGE OF RUBBER

COMPONENTS 07

5.1 Shelf Life 08

5.2 Storage Conditions 09 6. CHECKS BEFORE USE 14 7. PERIOD OF SHELF LIFE 15 8. GENERAL GUIDELINES FOR PACKAGING 16 REFERENCES 17

ISSUE OF CORRECTION SLIP

The correction slips to be issued in future for this handbook will be numbered as follows:

CAMTECH/E/13-14/Rubber Item/1.0/ C.S. # XX date---

Where “XX” is the serial number of the concerned correction slip (starting from 01 onwards).

CORRECTION SLIPS ISSUED

Sr. No. Date of issue

Page no. and Item no. modified

Remarks


Handbook on Up-Keeping of Rubber Items of Pneumatic Valves November, 2013 of Electric Locomotives

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1. INTRODUCTION Railways use more than 500 different rubber

components in the rolling stock, track, brake system and other railway equipment. Most common examples of the many are the heat and oil resistant gaskets, grommets, washers, oil seals, O-rings, oil hoses, diaphragms, shaft sealing rings, elastic rubber block, radiator support, rubber bush etc.

Knowledge about storage conditions of rubber items

will be useful to avoid premature failure.

Many rubber products and components are stored for a period before being put into service and thus it is important that they are stored in condition that minimize unwanted changes in properties. Such changes may result from degradation in which case they may include excessive hardening, softening, cracking, crazing and other surface effects. Other changes may be because of deformation, contamination or mechanical damage.

2. WHAT IS RUBBER

In a single word Rubber is a kind of Polymer. There are mainly two kinds of Polymers, Thermoplastics and Thermosets. Rubber falls under Thermosets Polymers group. There are mainly two grades of rubber, Natural & Synthetic. Depending upon application condition the proper rubber is chosen.


November, 2013 Handbook on Up-Keeping of Rubber Items of Pneumatic valves of Electric Locomotives

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Rubber alone cannot be used in any engineering application But when mixed with various chemicals like reinforcing fillers, anti-oxidants, anti-ozonants etc. and vulcanized then it becomes a stable product. This stable material is called Vulcanized Rubber Product, which has many versatile engineering applications.

3. CLASSIFICATION OF RUBBER TYPES ACCORDING

TO THEIR SUSCEPTIBILITY TO DETERIORATION (Ref: IS 6713:1996)

Group ‘A’: Rubber with moderate susceptibility to deterioration by ageing. The following additional rubbers shall be classified as Group ‘A’:

i. All new rubbers until their storage capabilities have been established.

ii. All thermoplastic rubbers until their storage capabilities have been established.

iii. Any products that can not be classified.

Group ‘A’ rubbers

Abbreviation Chemical name Common name

NR Isoprene rubber, natural Natural rubber

IR Isoprene rubber, synthetic Polyisoprene

BR Butadiene rubber Polybutadiene

AU Polyester urethane rubber Polyurehtane

EU Polyether urethane rubber Polyurehtane

SBR Styrene-butadiene rubber SBR



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Group ‘B’: Rubbers with low susceptibility to deterioration by ageing.

Group ‘B’ rubbers


NBR Acrylonitrile butadiene rubber Nitrile

NBR/ PVC Blend or acrylonitrile butadiene rubber and polyvinylchloride

Nitrile PVC

CO Polychloromethyloxiran Epichlorhydrin

ACM Copolymer or ethyl acrylate (or other acrylates) and a small amount of a monomer which facilitates vulcanization

Polyacrylate

CR Chloroprene rubber Neoprene

IIR Isobutene-Isoprene rubber Butyl

XNBR Carboxylic–acrylonitrile-butadiene rubbers

Carboxylated nitrile

BIIR Bromo-isobutene-isoprene rubbers

Bromobutyl

CIIR Chloro-isobutene-isoprene rubber

Chlorobutyl



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Group ‘C’: Rubbers which are highly resistance to deterioration by ageing.

Group ‘C’ rubbers


CM Chloropolyethylene Chlorinated polyethylene

CSM Chlorosulphonylpolyethylene Chlorosulphonated polyethylene

EPM Ethylene propylene copolymers EPM, EPR

EPDM Terpolymer of ethylene propylene and a diene with the residual unsaturated portion of the diene in the side chain.

EDPM

FPM Rubber having fluoro and fluoroalkyl or fluoroalkoxy substituent groups on the polymer chain

Fluorocarbon

Q Group Silicon rubber

FMQ Silicon rubber having both methyl and fluorine substituent groups on the polymer chain

PMQ Silicon rubber having both methyl and phenyl substituent groups on the polymer chain

PVMQ Silicon rubber having methyl, phenyl and vinyl substituent groups on the polymer chain

MQ Silicon rubber having only methyl substituent groups on the polymer chain, such as dimethyl polysiloxane

Silicon

VMQ Silicon rubber having both methyl and vinyl substituent groups on the polymer chain



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4. PROPERTIES AND APPLICABILITY OF ELASTOMERIC MATERIALS (Ref: ESA/FSA publication No. 009/98)

Butyl rubber (IIR, also known as isobutylene, isoprene)

An elastomer offering good resistance to ozone and gas permeation. Suitable for mild acids, alkalis and esters, but little resistance to oils and fuels.

Chlorosulphonated polyethylene

(CSM)

An elastomer with excellent chemical resistance against acids and alkalis. Good oil resistance. Outstanding fire protection properties.

Ethylene propylenediene (EPDM)

Elastomer which offers good resistance to ozone, steam, strong acids and alkalis, but is not suitable for solvents and aromatic hydrocarbons.

Fluoroelastomer

(FPM)

A fluorinated hydrocarbon which offers excellent resistance to acids, aliphatic hydrocarbons, oils and many corrosive applications. Not suitable for amines, esters, ketones or steam.

Natural rubber (NR)

Excellent for recovery properties. Good resistance to most inorganic salts, mild acids and alkalis. Not recommended for oils and solvents, or where exposure to ozone, oxygen or sunlight is prominent.



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Neoprene (chloroprene, CR)

Excellent resistance to oils, ozone and weathering. Suitable for moderate acids, alkalis, salt solutions, petroleum solvents, oils and fuels. It is not recommended for strong acids or hydrocarbons.

Nitrile (NBR) Improved chemical resistance and temperature capabilities over neoprene. Good resistance to hydrocarbons and oils. Not suitable for chlorinated hydrocarbons, esters, ketones and oxidizing agents.

Silicon (Q Group) Excellent temperature properties, and unaffected by ozone and sunlight. Not suitable for many hydrocarbons and steam.

Styrene butadiene (SBR)

Suitable for use with weak organic acids and moderate chemicals. Not suitable for strong acids, most hydrocarbons or ozone.



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5. SHELF LIFE AND STORAGE OF RUBBER COMPONENTS

Ageing during storage is called Shelf ageing. It is the most universal type of ageing in rubber articles.

Oxygen in the atmosphere diffuses through to the interior of the rubber and the oxidative degradation takes place throughout the bulk of the article. The effect is loss of tensile strength, elongation at break and elasticity in natural rubbers and hardening in case of both natural and synthetic rubbers. This is a long-term process and to judge the effect, accelerated ageing tests are used.

Oxidation is a chemical reaction and as in any chemical reaction, the rate of reaction is enhanced by rise in temperature.

For natural rubber , the temperature coefficient of oxidation, as judged by stress strain study, is about 2.7 per 10 °C between room temperature and 70°C, i.e for every 10°C rise in temperature, the reaction rate increases 2.7 times.

For styrene butadiene (SBR) the coefficient is 2.2.

Therefore, it is possible to judge the long time effects in short time by carrying out the oxidations at higher temperature. However, too high temperature should not be used as heat degradation effects also occur along with the normal oxidation.

The rubbers whether under storage or in use

continue to deteriorate, and ultimately may become unserviceable. The deterioration may be the result of one particular factor or a combination of factors, viz, the action of oxygen, ozone, light, heat, humidity etc.



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The storage life of a rubber product is influenced by its shape and size as well as its composition, with thick products usually undergoing less change due to degradation than thinner ones. (Ref: IS 6713 – 1996)

The deleterious effects of these factors may, however, be minimized by adopting appropriate conditions of storing and duration of storage.

A simple example can be a rubber band; when a

rubber band is unused for prolonged period and if it is stretched suddenly then it normally tends to crack. This simple logic is applicable for most of the rubber based products.

5.1 Shelf Life

Shelf life is a period, which covers the life of an article between its date of manufacture and its being put into service.

Shelf life in Indian Railways context is defined as the time for which under specified conditions, a rubber component can be stored without affecting its performance for a particular application.

While even in specified conditions the rubber may deteriorate every moment, the rate of deterioration is such that when used within shelf life, the component can be used without any appreciable effect on expected or designed performance.

These guidelines of storage provides following suitable conditions for the storage of rubber in all forms.



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5.2 Storage Conditions

Most rubbers change in physical properties during storage and ultimately become unserviceable, due to excessive hardening, softening, cracking, crazing, or other surface degradation. These changes may be the result of one particular factor or a combination of factors, such as the action of oxygen, ozone, light, heat, humidity or oils and solvents. The deleterious effects of these factors may, however, be minimized by careful choice of storage conditions.

To optimize or reduce the deterioration to minimum

possible rate following storage conditions are highly recommended:

(i) Temperature

The rubber components should be stored in a cool place and packed condition as far as practicable, preferably below 25°C (preferably between 15°C to 25°C) because at higher temperatures deterioration occurs more rapidly. Sources of heat in storage rooms if any should be so arranged that the temperature of stored articles never exceeds 25°C (Ref.: IS 6713 – 1996).

As per ESA/ FSA publication No. 009/98 also, it should be below 25°C (77°F).

As per RDSO letter no. SD.DEV.RBC dtd. 28.08.2007 it should be as far as practicable preferably below 30°.

The effects of low temperature are not permanently deleterious to rubber articles but they may become stiffer if stored at low temperatures. When articles are



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taken from low temperature storage for immediate use, their temperature should be raised to approximately 30°C throughout their mass before they are put into service. (Leave it at room temperature).

(ii) Light

They should be kept away from direct sunlight preferably in a dark place. Direct sunlight causes much faster degradation of the rubber components. Rubbers should be protected from light, in particular direct sunlight and strong artificial light with a high ultra-violet content.

It is advisable to cover windows of storage rooms with a red or orange coating or screen. (Ref.: IS 6713 – 1996)

It is also advisable to avoid windows in storage room if possible.

(iii) Humidity

The relative humidity of the storage condition should not be more than 70% so that condensation of moisture does not take place on the surface of the components. Very moist or very dry conditions should be avoided. Where ventilation is necessary it should be kept to a minimum.(Ref: Rubber book issued by RDSO).

(iv) Oxygen & Ozone

Where possible, rubber should be protected from circulating air by wrapping, storage in airtight containers or by other suitable means. As ozone is particularly deleterious, storage rooms should not contain any equipment that is capable of generating



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ozone, such as mercury vapour lamps, high voltage electrical equipment giving rise to electric sparks or silent electrical discharges.

In the vicinity of rubber components, any loose electrical connections should be avoided, as the arcing due to loose connections causes production of ozone, which adversely affects rubber. Ozone is particularly damaging, and causes a "scission" of the carbon backbone polymer chain into smaller chains.

Combustion gases and organic vapour shall be excluded from storage rooms as they may give rise to ozone via photochemical processes.

(v) Contact with metals

They should be stored away from contact with certain metals and their alloys containing copper and manganese or materials impregnated with their compounds (except when bonded to them) which act as poisoning agents resulting in their faster degradation.

They shall be protected by wrapping or by separation with a layer of suitable material for example paper or polyethylene.

(vi) Deformation

Under no circumstances rubber components should be stressed during storage. The portions under stress undergo deformations with permanent set and leading to degradation. The material should be stacked in such a way so that any super-imposed stresses are substantially avoided.



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Rubbers should, wherever possible, be stored in a relaxed condition free from tension, compression or other deformation. Large O-rings and seals shall not be suspended on pegs as this will lead to severe deterioration.

(vii) Contact with liquid or semi solid materials:

Any contact with grease or oil should be avoided as these cause swelling, softening and deterioration of rubbers. Even people handling rubber should ensure that their hands are oil/grease free.

Rubbers should not be allowed to come into contact with solvents, oil, greases or any other semi-solid materials at any time during storage, unless so packed by the manufacturer.

(viii) Contact with dusting powder

A small amount of French chalk or soapstone or mica may be applied on the surface of rubber components for the packaging in order to prevent blocking. In such instances the minimum quantity of powder to prevent adhesion shall be used.

Note: Any powder used shall be free from any constituent

having a deleterious effect on the rubber or the subsequent applications of rubber.

(ix) Radiation Precautions shall be taken to protect stored articles from all sources of ionizing radiation likely to cause damage to stored articles.



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(x) Contact between different rubber Contact between rubbers of different composition and colour shall be avoided.

(xi) Article with rubber to metal bonds

The metal parts of bonded metal items shall not come into contact with the rubber of others articles. Any preservative used on the metal shall be such that it will not affect the rubber or the bond to such an extent that it does not comply with the product specification.

(xii) Rotation of stocks

Great care is to be exercised so that the material is used in the order of their receipt in the stores i.e. first-in-first-out basis (FIFO). The rubbers whether under storage or in use continue to deteriorate. The only difference is that under service condition deterioration is much faster.

Every moment of storing is at the cost of useful life and prolonged storage of the material may render it unserviceable due to progressive deterioration.



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6. CHECKS BEFORE USE

i) Visual check

It is recommended to carry out visual inspection of gaskets/ o-rings etc. for hardening &. Inspect each of the items or components in the representative sample for the following: Permanent distortions, such as creases or flats. Mechanical damage, such as cuts, tears etc. Surface cracking when viewed under a magnification of x 10. Changes in surface condition such as discoloration, hardening softening, deformation etc.

ii) Remove/ clean French chalk/ soap stone powder softly

from rubber item before use. iii) Rubber should be lightly greased before assembly in the

equipment if recommended by the OEM. Grease is to be in strict accordance with the recommendation of OEM. Care must be taken to avoid excess grease. Rubber components once greased, must be assembled immediately in order to avoid dust accumulation.

iv) Wherever manufacturer recommends use of special tool

for assembly of rubber items, same should be used.



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7. PERIOD OF SHELF LIFE (Ref: RDSO book “Rubber in Railways-2006 & RDSO L.No. SD/DEV/RBC dt. 28.02.2007)

Shelf life of rubber components when stored as per

the guidelines mentioned earlier is quantitatively recommended as under:

1. Natural rubber or SBR = 1 year

2. Other synthetic Elastomers such as nitrile, polychloropene etc. or blend thereof = 2 years

3. Shelf life of diaphragms is expected to be one year.

For EPDM, fluorocarbon and silicone rubbers the shelf life shall be considered as 3 years. But the rubber component with very thin layer such as diaphragm would be expected to have shorter shelf life. It is recommended that the shelf life of these components be taken half of the original shelf life.

It is to be noted that more the storage life less will

be the service life. Hence quick consumption of rubber product is appreciated.

NOTE: Shelf life of rubber components supplied by a RDSO

approved supplier shall be as per the life mentioned in their QAP approved by RDSO/ Lucknow if any.



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8. GENERAL GUIDELINES FOR PACKAGING (Ref.: IS 6713: 1996)

• Unless otherwise specified in the appropriate product

specification, vulcanized rubber of rubber products shall be enclosed.

(a) Either in individual sealed envelopes or

(b) In individual sealed pockets in a multiple envelope provided that they can be removed without affecting the sealing of the remainder of the items in the package or;

(c) If it is not possible to possible to package the items in this manner, they shall be suitably enclosed or wrapped so as to prevent free access of air.

• The packaging shall be carried out in an atmosphere in

which the relative humidity is not greater than 65%. Contamination by dust, oil, grease, etc. shall be avoided.

• If it is necessary for rubber components to be packed

in assembly sets, the components shall be retained in their original identifying envelopes within the main package.

• No part shall be tied or tagged in such a way as to

cause damage.



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REFERENCES

1. Book titled “Rubber in Railway – 2006” issued by M & C Directorate , RDSO, Lucknow.

2. Indian standard “Code of Practice for Packaging and Storage of Vulcanized Rubber” – IS 6713: 1996 (Reaffirmed 2001) issued by Bureau of Indian Standards, New Delhi.

3. International Standard “Rubber Products-Guidelines for Storage” , ISO 2230: 2002 (E)

4. European Sealing Association (ESA)/ Fluid Sealing Association (FSA) publication No. 009/ 98 on “Guidelines for Safe Seal Uses – Flanges and Gaskets – Part 1 – Guidelines for Maintenance Operators/ Engineers/ Fitters.

5. RDSO letter no. SD.DEV.RBC dtd. 28.02.2007 on subject Shelf life of rubber components used in brake valves of diesel and electric locos.



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6.

If you have any suggestions and specific comments please write to us.

Contact person Director Electrical

Postal address Indian Railways

Centre for Advanced Maintenance Technology, Maharajpur, Gwalior,

Pin Code - 474 005

Phone 0751 – 2470740

Fax

E-mail

0751 – 2470841

[email protected]

OUR OBJECTIVE

To upgrade maintenance technologies and methodologies and achieve improvement

in productivity and performance of all Railway assets and manpower which

inter-alia would cover reliability, availability, utilisation and efficiency.



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Always use a good quality rubber item

from a reputed approved supplier,

because the cost of a rubber item is

insignificant when compared to the cost of traffic block due to a loco failure on line.

INDIAN RAILWAY

Centre for Advanced maintenance Technology Maharajpur, Gwalior - 474005

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Documents

Up-keeping of rubber items - Indian Railway · 2019. 10. 17. · Oxidation is a chemical reaction and as in any chemical reaction, the rate of reaction is enhanced by rise in temperature