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FILE NAME Brakes BRK DATE 1977 May DOC BRK168 DOCUMENT DESCRIPTION Trade Journal Article - The Search for Asbestos Substitutes THE SEARCH FOR ASBESTOS SUBSTITUTES BY K. GREEN & M. PTE The authors of this article are associated with the Fulmer Research Institute Ltd. Ltd. Stoke Poges Slough England and have recently produced a booklet entitled Asbestos Characteristics Applications and Alternatives which includes an examination of the substitute materials commercially available for the major applications of asbestos and asbestos products The Fulmer Research Institute is a profit research organization specializing in materials technology] SUMMARY This article examines in some depth the materials available as alternatives to asbestos for two of its major applications- asbestos and friction materials Asbestos is used in a wide range of applications and the most successful approach to its replacement is to examine each application individually is noted that it is not always possible to replace asbestos on technical grounds and where replacement is possible penalties are frequently involved INTRODUCTION Asbestos is a material which makes a great contribution to human safety through a number of its applications but it can also constitute a health hazard to those who are exposed to its fine airborne fibers In several countries around the world great concern at present exists over the use of asbestos products and attempts are underway to minimize the risks of asbestos exposure by examining the safety precautions taken when carrying out potentially dangerous producing operations with asbestos products machining delagging demolition etc ) and also by exploring the possible use of suitable alternative materials A considerable volume of research has been directed in recent years to finding substitutes for asbestos the major effort being concentrated in areas that use large quantities of the Page 6 ASBESTOS 1977 mc Skve eet ^' Cn Pie Cote SN _ e+ee aan J a havin , ; { : Pot i: L f+ a ake Retina ody dy sbhailmpparpeniancetete sowagis wee tee eSmy Ba te whReOt Ae tea ae ee Pea Soe me wile a tne Dee ihe Ee - a a es we ee ee ae is. "OPN eA 1-4 Tye al Tae thy Pd Na ete, ro ~ OT eee Foe . antl ht Aer : oti ee ho moms a a co peee eee Kad men pnpeemmenatning. + de ke ee . watt te me pm a em means = ~ pais ed ee . - eee a Keeton sole mt ny - ww Rr ew : , Ce el we . * le ce tee ae ene ee oe 2 @ &% ' ee om Fu wa : . a ae _ee _ = ae -. oma which which asbestos has tech- Two prominent asbestos cement friction which respec- respec- and tively accounted 1974. % total States asbestos asbestos 1974. properties asbestos which make it tt consumption consumption these applications applications considered consideredconsidered the following following with properties materials ASBESTOS-CEMENT PRODUCTS make make modulus latter a aspect one the of factors -length determines This This latter composite the asbestos systems The asbestos tant. roofing tensile strength pressure pressure be used for properties purposes as such this latter application as asbestos fibers is application impor- asbestos particularly sumed. this reason used in asbestos Crocidolite Blue con- superior pipes due Chrysotile superior compared strength more more Chrysotile more applications examplewith which it combined % combined this In application in example more of used Crocidolite United United States initial into used Nthe United the initial stages mixin The The initial asbestocsement into and fibers shapes tionally properties properties the asbestos pipes drainage Sheets properties sheets the produced mix enabling relatively relatively cement propipescess Similar similar similar that usedprouducsedepdapapper er making a andnfld exiblfelexible process The making flexibility inherent cinherntoinherentmbination inherent combination combinationfibers confers confers strength properties properties properties asbestos boards boards strength shapes such the green Th Thus complex complex as Page & Us comple x ASBESTOS MAY 1977 ASBESTOS nyY4 1977 Se Denali te a re Far r tet abe oe Ne Yeehate Miwreega tue wa ve . te hOiEghaey AGE eras A7einake wer a ae ~~ Viana ae popes 4 a path OT ta oe As Pr ww ae red . "Veet . ES a ects rane At ita as wre ee ns . we na alte, eb 7 i . he ef hepe . t ~ fe ie kee phi | leah as Qi ahaa ee ie DN ad Lonel Mind! + a en ates tensME oh, te $ de et ~ antoo n. p=e) er et es at ps 4 i a te tet oe os st at on ee 7 . Roe te ~~ SmoneeteD lo eyda Vacs wy'M l 4 Da * . ee ae sx r epee Sey ME weesew ye . mm eT Slag w . a a Se e - ~ e te Sah > aero gtr - wt. ag wen s ~~ -. be ct . a ae _ ree . an ee we Looe SEARCH FOR SUBSTITUTES t corrugated boards may be produced by molding the wet material The main attractions of asbestos products to the end user are durability resistance to weathering attack and effectiveness The noncombustibility of the products is nificant but is often of secondary importance cost sig- SUBSTITUTES FOR C PRODUCTS . Various currently available materials are used as substitutes for asbestos cement in many of its diverse applications Cladding panels are frequently manufactured from Reinforced Plastic GRP or various thermoplastics although these materials do not possess the fire resistance of asbestos cement and their combustion can lead to the evolution of toxic fumes Metals notably aluminum are also widely used in this application GRP or wound concrete pipes are often suitable for use in corrosive environments and the traditional cast iron sewage pipe performs satisfactorily Most of these materials are more expensive than asbestos products although certain thermoplastics may be competitive in specific applications In general however none of these materials can be fairly considered to be a universal replacement for asbestos cement and the most promising route to achieve this objective at present is the development of reinforced cement technology Conventional glass fiber which is commonly used in glass inforced plastics cannot be used in conjunction with cement since the severely alkaline conditions produced during the setting of conventional Portland cement degrade the fibers and the resultant composite material rapidly loses its favorable mechanical properties However within the last ten years a highzirconia resistant glass fiber has been developed at the Building Research Establishment Garston England This fiber is marketed by Pilkington Brothers Ltd. of St Helens England under the name Cem for cement reinforcement purposes reinforced cement usually contains between % and % of fibers and typically one would expect a material containing % of fibers to have a modulus of rupture similar to that which would be expected from asbestos cement containing 15 of fibers about 35 MN Additionally the reinforced cement is considerably more impact resistant than asbestos Page 10 ASBESTOS 1977 coe ~ , se td 7 wee RO EE Riis Rafer a - ice Mabetale . o Fe a . - tes Pa . s A ae ce ayes . re aS . Carere ant e ey? tard te teas! oe, wt gn nore ween ~ Cate a - ~ a e ae me = 4 dante oe 8 eeeenen et yee xs ad Y tetentre acs Ramee senanltan Leas gt pli ween gf pte o aah Aerrercbeanee db eetented mettle aK Me ~ TF Oe : e ee me em eee peek ne me weee ee ee ee ee Deed . gett ee OT Ft ON PT . OTM Pao. ee f wre FL a nk 44 sf age s, SEARCH FOR SUBSTITUTES i cement of comparable strength The green boards have wet strength and can be molded and large bore pressure pipes can be produced The final products perform adequately in pre- venting fire penetration However several drawbacks exist in the use of this material ; | ) The fiber is approximately times as expensive as the asbestos used in cement products and this coupled with the less favorable economics of the production process results in a price for reinforced cement some % greater than asbestos cement even allowing for the smaller fiber content 2 The drainage characteristics of a cement fiber mix are poor and do not permit the manufacturing process for asbestos cement to be used in an unmodified form Glass- reinforced cement is usually made by a process referred to as spray suction In this process a special spray head sprays a mixture of chopped glass fiber bundles a few centimeters long with a fine cement slurry onto a porous bed When spraying is complete a vacuum is applied to the underside of the bed to remove excess water A similar procedure is used to make pipes the spray head being directed onto the inside of a rotating tubular form with the excess water being similarly removed Conse- quently the manufacture of reinforced cement is relatively costly and requires a high capital investment However the manufacturers of reinforced cement are expending considerable effort on attempts to make the material on minimally asbestos cement plants The impetus for this effort was the result of Japanese legislation about two years ago whereby asbestos was placed in the dangerous chemical category of materials Consequently severe restrictions apply to any product sold in Japan containing more than % asbestos which includes standard asbestos products It was found that the standard asbestos cement plant could produce a good quality board from a cement slurry containing both glass and asbestos fibers in suitable proportions so as to keep the asbestos content below % thus producing reinforced asbestos cement known as GRAC The research effort is presently concentrated on eliminating the asbestos content com- pletely and this has been achieved by suitable plant modifi- cations It is likely that this equipment will shortly become available in the United Kingdom eliminating one of the principal drawbacks to the use of reinforced cement Page 12 ASBESTOS 1977 ay ee 2 we ae mote ea gla gery +4, FS Peete m tae ate: eek md seit! at Gee, peerers We bene OADM Ae BS oat me Ld web sf Kew PN : tae: * Mya eye, Ene * teres ead tee . _ was . wads tan. ae , i ve nw. oe . ' i 6%, . god s RT a ve 1 eee yet, a Tow . walk %> Be wo, aw se, ss ee be GO mee . ALT ee . 7 a > fo, * it ate ghee aged 7. sate alg at wen eet en eee ey tee ee BE ie WE Hge AE SEARCH FOR SUBSTITUTES { 3 Some attack of the glass fiber by the setting cement is necessary to achieve good fiber bonding and this requirement has raised doubts concerning the term durability of glassreinforced cement The product is too new for really term data to be available but manufacturers findings for a seven period indicate that the strength of reinforced cement when wet stored the worst situation drops to half its initial value in approximately two years and then stays constant An additional safety factor of 3 is recommended i.e. the quality control initial strength should be at least six times the design working stress Most existing uses of reinforced cement have been restricted to bearing components eg eg cladding but the more demanding structural applications are gradually being attempted as knowledge of and confidence in the material grows it is likely that the uses for reinforced cement will increase since it allows interesting concepts that are impractical with asbestos cement A good example is the use of continuous glass fiber roving to filament wind large diameter pipes that are much lighter due to the thinner wall required than a steel- reinforced concrete pressure pipe of comparable strength and price FRICTION MATERIALS Asbestos brake and clutch linings are in widespread use particularly but not exclusively in the automotive field The asbestos performs a complex function in these applications which is not completely understood Chrysotile asbestos is used exclusively and stiffens and strengthens the filled phenolic resin matrix The fibers maintain these properties at the high temperatures generated during for example braking and clutch slipping The friction and wear characteristics of the asbestos fibers and their thermal decomposition product forsterite are thought to be responsible for the good braking efficiency and service life properties of these materials Forsterite is a fibrous silicate and is not thought to constitute a health hazard Investigations have established that the dust produced from the wear of asbestos friction materials does in fact contain only % to % of asbestos fibers Repeated exposure to this dust is a potential hazard for personnel such as garage mechanics While this wear debris is not thought to constitute a significant health hazard for the general public much effort has been concentrated in searching for substitutes for asbestos in this application Page 14 ASBESTOS 1977 OD oNS . ONfD ryen- | oe dl a ee eS oag' pavelonr serve oa, SNae e toe? we oe ay Vitae.a poe Ms seta T>? oc Sosa "ete ey cit Ae oF ATR: a PR E rg -Ten ES aad ae me *- ined te . oeRAEgineem Re ~% > ae ye me tev Liat anyPe Tita OE Deer SEARCH FOR SUBSTITUTES 1 Various substitute materials have been investigated but they all have drawbacks Sintered metals ceramics and metallized bonded products have been available for many years However the high thermal conductivity of these materials creates a risk of boiling brake fluid which can cause erratic performance Carbon carbon composite brakes have been used successfully on " racing cars and aircraft such as the Concorde They perform better than asbestos materials under the high service temperatures in these applications but are so expensive that their use can only be justified in specialized circumstances A considerable volume of work is currently underway on using the existing asbestos manufacturing technology and incorporating either steel or glass fibers into the mix to replace the asbestos Vehicle trials are underway in the United States with these products and it is estimated that asbestos substitutes are available for about 30 of the friction products market the exception being in the heavier applications such as disc brake pads where high temperature surface conditions are encountered | Steel fibers were first used in friction materials in Germany prior to and during World II due to difficulties in obtaining asbestos fiber It was found the brakes worked well with little loss of efficiency when wet but the wear debris was abrasive and severely damaged the counterface Glass based friction materials also produce a very abrasive wear debris with corresponding damage problems Further at high temperatures the glass can melt This can produce a sudden undesirable loss of friction since the sliding surfaces can be effectively lubricated by the molten glass Both steel and glass based materials tend to be considerably noisier in vehicle braking applications than their asbestos counterparts Both glass and steel fibers can be incorporated into friction materials using standard processing but steel fibers have been found easier to handle The steel fiber is usually of the fine steel wool type and is about four times more expensive than the asbestos used in friction materials Conventional glass fiber is approximately half the price of the steel wool asbestos materials use proportions of liber comparable to the conventional product and are hence more expensive Thus although asbestos friction materials are technically and economically preferable at present for the majority of applications it seems probable that these may eventually be replaced by the asbestos materials as a result of concern over the health hazards involved with asbestos Page 16 ASBESTOS 1977 t . me 1 : s . a $ i? el: Hind APR mm wh ne A semis, saute ern Y vas ~ a 7, : TOTS poeEne an eae ; i oN ce eB ane put *& e eee e ee ee ee re ee ee ats A ty ey Tate, 5 ee er - yee * a Ff whet na, ne Tyee . OD, ne bias Se 8 e > ' wee 7 : ise ek pe oe . a: wa ae ~- : a7 wena at ra . . - i oe SEARCH FOR SUBSTITUTES i CONCLUSIONS CONCLUSIONS t substitute It is apparent in the two applications which have been con- sidered that one factor common to both is that materials will be more expensive than the asbestos product it is desired to replace The two case histories however highlight notable discrepancies 1 cement 1 The health hazards involved in the handling of asbestos- products during machining and demolition operations are greater than those associated with the handling of friction materials where the dangers are confined to manufacture and the cleaning of brake drums and linings 2 Research has led to the development of acceptable substitutes for asbestos technically inferior products are products whilst likely to be accepted as substitutes for friction materials The arguments put forward here therefore mitigate against a total ban upon the use of asbestos products and would that in some cases it would be preferable to ensure the suggest tion of adequate safety precautions during their observamanufacture and maintenance than to accept inferior products In addition the potential health hazards involved with the use of alternative fibrous materials including glass should not be overlooked Peete Beate tae ef EeC S nae EP ote 2 i LIA, a i i ; L 4 | a sonaun batt we pit Ste ey: eeSs OdRtOsaSee rel eeent : ro -: tay er re cee ae ~ rae _ Pirate Sati anaes! K- a \@ ie at Neng Ue, . canned ~ sagSate nk =we mae ee t COPIES STILL AVAILABLE i i - RECOMMENDED WORK PRACTICES manuals published by the Asbestos Information Association America include Recommended Work Practices for the Fabrication and Use of Asbestos Paper Products Shop and Field Fabrication of Asbestos Sheet Products Molding and Fabrication of " Asbestos Containing Plastic Products Fabrication and Use of Asbestos Friction Materials and Use and Handling of Asbestos Textile Products $ 35 each plus postage order from AIA or through ASBESTOS Magazine t Moo te? oe ge res Sa ng Be be 1 ek RE Cf lech a Nagi he leo cot Pe gE plant ee OE DY SEE ~: ee Bow aver tet a ae . v. 3 te OH on ena SO ak Bon 43 ~, en isgte OP RY NEXT Page 18 = FELTS FOR hah i C PRODUCTION ASBESTOS 1977 . . es 7 ae pele, aa ha. ae : nee fE mE RES anes ore oe ea to. 4 fue fe afhe ae 7 . , Egy Peer ey ad een ae He ays ve Bfeeon re COOiNos gt ieh a on fone Yan jc ' as. a. p soe : Me a aol r * rd vf? Actas! 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