Document M4x020eNnwbo7Zkzzg9BGnBNM

FILE NAME: Z< DATE: D DOC#: Z< DOCUMENT DESCRIPTION d:Zd^ZZ ^ THE SEARCH FOR ASBESTOS SUBSTITUTES IT: ... K. GRUN .. A. M. 'T( [The authors of this article are assocla~d with the Fulmer Research Institute lid . Stoke Poges. Slough, England. and have recently produced a booklet entitled "Asbestos, Characteristics. Apphcatlo.,s and Alternatives" which includes an examination of the substitute materials commerClal:y available for the malor applications of asbestos and asbestos produ(;ts. The Fulmer Research Instltule IS a non-profit research orgamzatlOn speCialIZIng In materials technology) SUMMARY This article examines In some depth the materials available as alternaltves to asbestos for two of its major applicatlonsasbestos-cement and friction materials Asbestos IS used 10 a wide range of applications and the most successful approach to its replacement IS to examine eath application indiVidually It IS noted that it IS not always pOSSible to replace asbestos on technical grounds and where replacement is possible, cost-penalties are frequently Involved. INTRODUCTION Asbestos IS a material which makes a great contribution to human saf"!ty through a number of ItS applications but It can also constitute a health hazard to those who are exposed to ItS Itne, airborne Ilbers. In St'veral countries around the wortd great concern at present eXists over the use of asbestos products and attempts are underway to minimize the risks of asbestos exposure by examtntng the salety precaultons taken when carrying out potentially dangerous dust-prodUCing operations with asbestos products (machining, detagging, demolition, etc ) and also by explOring the pOSSible use of sUltabte alternative materials. A conSiderable volume of research has been directed In recent years to ftnding substitutes for asbestos, the major effort being concentrated in areas that use large quanlltles of the P<lg~ 6 ASBESTOS-MA Y 1977 r i' - '!l m&.. .20 ;0-.2 , , ,.. f 4:n= -'wc" -"t. ~':1'1- ; ':'..; .J.'~', '. ,.1 .~.o:,~. 'T ~ " 'r'~-.tI!!!:- ~ -, :"'Jp ~ ',,- .... ,. . ~.:~\; ,. ,~.':-~'I, . . :." ,.' r :... '!, cr fmr1'i-! .. .,t- ' ... ," SEARCH fOIl SU8STlTUTE5-<OHTlNUED material and in those applications for w'. hich asbestos has tech- nIcal advantages m addition to its low cost. Two promment e-<amples which will be discUssed here are aSbestos-cement prOducts and aSbestos-based friction materials, which respec_ ",elyaccOU",ed 10, 38% and g% 01 ""aI UMed Slates asbeslos consumption In 1974. The propertIes of asbestos Which make It uselul ;n Ihese apphcahons w,1I be conSOde'ed ;n Ihe 101l0w'ng Sections and will be Compared With the properlies of materials wh'ch have been Suggested as sUbstllutes. ~BESTOS-CEMENT PRODUC!! The primary function of the asbestos in asbestos-cement prOducts IS to act as a reinforCing flber The prope'lies that make ;1 Uselul ;n Ih" mle "e h;9h I;be, st'englh and mOdulus and a '''ge a'p.cl ""0 (,at;o OI.lenglh 10 d"melen Th;s lalle, parameter IS one of the factors that determines the reInforce_ ment effICiency of flbers in compOSite systems. The asbestos "be" P'Oduco usclul lenSOle a"d lIe,U'" p'ope",es '" lhe asbestos cement, enab/mg It to be Used for such purposes as roofing sheets and preSSure Pipes In thIS lalter applIcatIon the hIgh tensile strength of the asbestos Ilbers is particularly Importanl. For thIS rea$on most of the CrOcldolite (SIue) aSbestos COnSUmed IS used in aSbestos-cement PIpes due to its Supenor strength, compared to the more widety Used Chryso"'e asbestos WIth wh,ch it is combined in this appllcallon. In 1974, for Setxaatmesplew,enmtoirnetothPaInPin9g0%ap0p1lIcthaetIoCnrsO. Cldol/te used In the United The m,llal stages 01 aSbestOs-cement manufacture inVOlve the miXing of water, cement and libers into a Slurry. The IIbers miX readily into this Slurry. This affinIty for water IS thought to be a consequence of the porous nature 01 the fibers and It has been suggested that the individual asbestos fIbrils are hollow. Addl- I,onally lhe "be,s conl';bule '''O''ble and Conlmllable d";nage propertIes to the nI/X, enabling the asbestos-cement PIpes and SshImeielalsr 1t0o btehaPt'Oudsuecdooinbpyaap,eerlamt"aekliyng".mple and lIe,;ble P'ccess The comb;nat;on 01 USelully long I,bc, lenglhS and lIe"b""y ;nhe'enl ;" asbestos I;bc" conle" wel st,englh and moldab,h'Y propeflies On the "green" boards. Thus complex shapes SUch as ASBESTOS_MA Y 1977 . - _.s__ ... ---- .. '. $lARCH FOR SUBSTlTUTES-COHTlNU[O corrugated boards may be produced by molding the wet material. The main attractions of asbestos-cement products to the end user are durability. resistance to weathering alta.:k and cost effecliveness. The noncombustlbill!y of the products is significant. bl!t IS often of secondary Importance. SUBSTITUTES FOR AC PRODUCTS Various currently available materials are used as substitutes for asbestns cement m many of Its diverse applications Cladding panels are frequently manufactured from Glass-Remforced Plastic (GRP) or various thermoplastiCS although these materials do not possess the fire resistance of asbestos cement and their combuslion can lead to the evolution of tOXIC fumes Metals. notably alummum. are also Widely used m thiS application. GRP or GRP-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-cement products. although certain thermoplastiCS may be cost-competllive in speCifiC applications. In general. rowever. none of these materials can be falfly conSidered to be a universal replacement for asbestos cement and the most promismg route to achieve thiS obJective at present is the development of glass-remforced cement technology Conventional E-glass flber (which IS commonly used In glass-reinforced plastics) cannot be used m conJunction '....Ith cement since the severely alkalme conditions produced during the setting of conven:lonal Portland cement degrade the libers and the resultant composite matertal rapidly loses its favorable mechanical properti%. However. wllhin the last ten years a highzirconia. alkali-resistant glass liber has been developed at the BUlldlnQ Research Establishment. Garston. England. This fiber is marketed by Pllkmgton Brothers Lld . of St Helens. England. under the name "Cem-FIL" for cement reinforcement purposes. Glass-reinforced cement usually contains between 3% and 7% of flbers. and tYPically one would expect a mdteflal containing 5% of flbers to have a modulus of rupture similar to that which would be expected from asbestos cement con taming 15% of fibers (about 35 MN/m2). Additionally. the glass-remforced cement IS conSiderably more impact resistant than asbestos Page 10 ASBESTOS-MA Y /977 ! , ,af .. .".'',"' - -' . , ~' ... - _.; .. .' ; -: , f " a ---.... b ',' . ....., ~ '. -. .. ;1 " 1 ~. . , - - - -'. - . - -.--- - - ..~-!:.,;.'- - ,-..,. .- r ...... SURCH FOR SU8STIlUTE~ONTINUEO cement of comparable strength. The "green" boards have wet strength and can be molded, and large bore pressure pipes can be produce::l. The final products perform adequately in pre- venting fire penetration. However, several drawbacks eXist in the use of this material. I 1) The fiber is approximately four' times as expensive as the asbestos used In cement-based products and thiS, coupled with the less favorable economics of the production process results in a price for glass-reinforced cement some 70% greater than asbestos cement even allowing for the smaller fiber content. 2) The drainage characteristiCS of a cement-water-glass fiber mix are poor and do not permit the manufacturing process for asbestos cement to be used In an unmodified form. Glassreinforced cement is usually made by a process referred to as "spray suction." In this process, a special spray ~ead sprays a mixture of chopped glass IIber bundles a few centlmeters long with 8 fir.e 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 bemg Similarly removed Consequently, the manufacture of glass-reinforced cement IS relatively costly and requires a high capital investment. However, the manufacturers of glass-reinforced cement are expending considerable effort on attempts to make the ma.enal on minimally-modified asbestos cement plants The Impetus for thiS effort v.as 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 5% asbestos, which includes standard asbestos-cement products. It was found that the standard asbestos cement plant could produce a good quality board from a cement slurry containing both glass and asbasto$ libers in suitable proportions. so as to keep the asbestos content below 5%, thus producing glass-reinforced asbestos cement (known as "GRAC"). The research effort IS presently concentrated on eliminating the asbestos content completely and thiS has been achieved by SUitable plant modifications. It is likely that this equipment will shortly become available in the UOiled Kingdom, eliminating one of the pflnClpal drawbacks to the use of glass-reinforced cement. Page 12 ASBESTOS-MAY 1977 Wi'rtz, , ms -'rir' 4 ... ,' or !ftt , ' .... " :.<a I" bS" . te :J;:';~;{;\,;Wl;~~~T' .' ... f'., .......:. ~. f " .. '. ~ ....... ' i . " :. ~ <.. ' t# ~: ..- ; 1, " , ,,' ( , ;' : ~ ,', -........... - , :...~.... , -. ..~- ... _... - . ... , -_ .... "-~-'----'- k+e- .r ..-: ~;\~~Li'"~ __ '~___~_~.__~_''' ,_ '""-':." t SlARCH fOIl SU8STlTUHS~ONTIHUEO 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 long-term durability of glass- reinforced cement. The product IS too new for really long-term data to be available but manufacturers( findings for a seven-year period Indicate that the strength of glass-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 ~ IS recommended. I.e. the quality control initial strength should be at least SIX times the deSign working stress. Most eXisting uses of glass-retnforced cement have been re- stncted to non-load-bearing components (e g. cladding) but the more demanding structural applications are gradually being attempte"d as knowledge of. and confidence 10. the material grows It IS likely that the uses for glass-reinforced cement Will Increase since It allows Interesting concepts that are impractical with asbE";tos cement A good example IS the use of continuous glass flber roving to filament wtnd large diameter pipes that are much ilgrter. due to the thinner wall required. than a steet- reinforced concrete pressure pipe of comparable strength and price. - FRICTION MATERIALS Asbestos-based 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. Chrysotlle asbestos IS used exclUSively and stiffens and strengthens the filled phenoliC resin matm The IIbers maintain these properties at the high temperatures gnnerated during. for example. braking and clutch slipping. The friction and wear characteristiCS of the asbestos fibers and their thermal decompOSition product. forstente. ar~ thought to be responsible for the good braktng efficiency and service life properheS of these materials Forsterlte is a non-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 1% to 2% of asbestos libers. 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 subshtutes for asbestos in thiS appllcallon. ASBESTOS-MA Y 1977 , i<',~ ~ ...~ . ..'.'. .. "."". '.1.. " ~~. ;.~. ~ ....... ..' ~~. . , J'. . ....'. " " ----" . ;1:":'- .... ..-..;. '''''1'.'~- .. .......... . -.\ ~.... _ . :~ 't . " ' . .; \ , ...' ; , ... ~\ .... SEARCH FOR SUBSTlTlJTB-{ONTlNUEO Various substitute materials have been investigated but they all have drawbacks. Smtered metals. ceramics and metalhzed bonded products have been available lor many years. However. the high thermal conductivity 01 these materials creates a risk of boiling brake f:uld which can cause erratic performance Carbon Ilber Icalbon composite brakes have been used successfully on racIng cars and aircraft such as the "Concorde" They perform better than asbestos matenals 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 wor\( IS currently underway on uSing the eXisting asbestos-based manufacturing technology and incorporating either steel or glass IIbers into the mix to replace the asbestos. '. i ,f h Vehicle trials are underway In the United States with these products and It IS estimated that asbestos substitutes are available for about 30% of !tie fnction products market. the exception being in the heavier-duty applications such as disc brake pads where high temperature surface conditions are encountered Sleel flbers were first used In fncttOn materials In Germany. prior to and during World-War 11. due to dlfllculhes in obtaining asbestos flber. It was found the brakes worked well with little loss of effiCiency when wet. but the wear debns was abraSive and severely damaged the counterface Glass flber-based frichon 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. undeslrabla loss 01 fnctlon since the sliding surfaces can be effectively lubricated by the molten glass Both steel and glass flber-based materials tend Ii to be conSiderably nOISier in vehicle braking applications than their asbestos counterparts. Both glass and steel IIbers can be I; . . incorporated Into Inclion materials uSing standard processing. but steel flbers have been found easier to handle. The steel flber IS usually of the fine steel wool type and IS about four times more expensive than the asbestos used In frlchon matenals Convent:onal E-glass flber is approximately half the poce 01 th~ steel wool Non-asoestos-based materials use proportions of flber comparable to the conventional product and are hence more expensive. ThuS. altncugh aSbestos-based friction materials are technlcall! and ecco;c"nlcally preferable at present for the m3Jonty of applications. It seems probable that these may eventually be replaced by the non-asbestos-based materials as a result of concern over the health hazards Involved With asbestos Page 16 ASBESTOS-JfA Y 1977 - - - - -- -_ .\. . - -.-.-- _--..--,.. - .-... --- . .-.-. - ~-- .. .. _--,,"~... ;rft' ,,"'.,-' ~'''l~ ';"-! .... ~'r_ .--lLf.. _.t."'~"\J ~4': ~-. " I " ~', , . ~ 'f ~.~ ;. , ': .. ,.;" .. . ..... ... .. _ . _ _ _ r _ . . . . _ _ _ _ _ 0 _ _ _ _ _ _ _ _ _ _ - _ SlARCH fOR SUaSTlTUTES-eONTlNUED CONCLUSIONS It is apparent in the two applications which have been con- sidered that one factor common to both is that substl!ute mate/lals will be more expenSive than the asbestos product It IS deSired to replace. The two case histories, however, highlight notable discrepancies: I 1) The health hazards Involved in the handling of asbestoscement products dUring machining and demolition operations are greater than those associated with the handling of friction matenals, where the dangers are confined to manufacture and the cleaning of brake drums and linings. 2) Research has led to the development of technically acceptable substitutes for aSbestos-cement products. whilst Intendr products are likely to be accepted as substitutes for friction matenals. The arguments put forward here therefore r1illgate against a total ban upon the use of asbestos products and would suggest that In some cases it would be preferable to ensure the observation of adequate safety precautions dUring their manufacture and maintenance than to accept ir1lenor products. In addition, the potenltal health hazards involved With the use of alternative fibrous materials, including glass, should not be overlooked COPIES STILL AVAILABLE! . RECOMMENDED WORK PRACTICES-Five manuals published by the Asbestos Information Assoclallon/North Amenca Include "Recommended Work Practices for the Fabricallon and Use of Asbestos Paper Products," "Shop and Field Fabncatlon of As- bestos Sh~et Products," "Moldmg and Fabflcation of Asbestos Containing Plasllc Products," "Fabrication and USE' of Asbestos Fnctlon Materials," and "Use and Handling of Asbestos Textile Products." [SI 35 each plus postage, order from AIA/NA or through ASBESTOS Magazine] NEXT ISSUE-FELTS FOR Ale PRODUCTION Pag~ 18 ASBESTOS-MAY 1977 r h r ,.. L_diet. 1 c If *m dd' lane j i I f ,:' ..... ~ -'... ,I , t! ~ * .... .1 ..:..-....,; __ ... ~...~_... _ _ _~.--t._~ . ..:.-_~ _ _ t _ _ ~:-~ _.... . , ..-" ~I ~ " ' f ' .~~. COP Y ., 0 R K INITIALS DATE BOX NUMBER 5 I <6 ~ SEGMENT NO. NOT E S REOUESTING PARTY f}ft~te 'f C;ts TL6-?7,*tJ