Document evXpGJbKgR4v1Ka943V2vDeL9

FILE NAME: Phenolic Resins (PHR) DATE: 1977 DOC#: PHR004 DOCUMENT DESCRIPTION: Trade Journal Article - The Search for Asbestos Substitutes THE SEARCH FOR ASBESTOS SUBSTITUTES w asysMmmsat [The authors of this article are associated with the Fulmer Research Institute Ltd . Stoke Poges. Slough, England, and have recently pro duced a booklet entitled "Asbestos, Characteristics, Applications and Alternatives" which includes an examination ot the substitute materials commercially available tor the major applications ot asbestos and asbestos products. The Fulmer Research Institute is a non-prolit research organization specializing in materials technology ] This article examines in some depth the materials available as alternatives to asbestos for two of Its major applications-- asbestos-cement 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 It is noted that it is not always possible to replace asbestos on tech nical grounds and where replacement is possible, cost-penalties are frequently involved. ` J a V jro * r te Ep 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 (hose 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 ex posure by examining the safety precautions taken when carrying out potentially dangerous dust-producing operations with as bestos 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 ASU ESTO S--M A Y 1977 ' f -'V 1 ^ , ,, * * * . *-v ' - A1 V-'' ' ^ . : v,"> ' , - j .. w^ 1-41- *> -V f \ `m V-, ' >` ' V / >v.\ ' v . kf .- . ' - .. v ' - i*. * t ,* >' * , f V ` *4,, * *. * *J - . ,, c' , ?"' v .v ;. V - .. > , <,i` *$,, Y* -v. |n ,>< K'*'* ' I i *CH MR SUBSmuifs^o*TlNUfO b ? V " ' " 1" " t o i1'CMtTS'w has lech. J ir r ^ - , high tensile s tre n g ^o M h ^6 p,pes ,n purpses as </ *s. ( m h p m h I m m h w the mixing 0f wSa<ter0Sr 0, asbeslos-cement m 'eadSyi'nio mfs s ^ ^ n d f f l n 0T " , Ufacture involve 4 9ni ! ^ ,w i 9ee" toa'as^ - Pt % ^ r i /V7; lik'.' r "J':'."* -Wr l^/Cfi*1^ r>^Yiw , \'-:v 7 * r ' ^ y fr*v * <-* - ^ ^ "4 ?** *. * - i `* - ,.- < > , y V * v ,-'I*y> ' ^ v r * v . . :V'- ^ v * y ' ^?' ' *' /*; - r - '- * y *v ' ' S.4 .r . t-7v V St \* ^ `* ' . * ' ' * ' * "'* s'l-f-'i- \ r, -, - :# & :z:j ;*** . s -' - * **rr^V *' '? * * * 1 - . -* V A R C H FOR SUBSTITUTES--CONTINUED corrugated boards may be produced by molding the wet material. The mam attractions ol asbestos-cement products to the end user are durability, resistance to weathering attack and cost effectiveness. The noncombustibility of the products is sig nificant, but is often of secondary importance. SUBSTITUTES FOR A-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 Glass-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 GRP-wound concrete pipes are often suitable for use m cor rosive environments and the traditional cast iron sewage pipe performs satisfactorily. Most of these materials are more expen sive than asbestos-cement products, although certain thermo plastics may be cost-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 obiective at present is the development of glass-reinforced cement technology Con ventional E-glass fiber (which is commonly used in glass-re inforced plastics) cannot be used in conjunction with cement since the severely alkaline conditions produced during the setting m of conventional Portland cement degrade the fibers and the resultant composite material rapidly loses its favorable mechan ical properties. However, within the last ten years a highzirconia, alkali-resistant glass fiber has been developed at the 10 mBuairldkientgedRebsyeParilckhinEgtsotanblBisrhomtheenrst, GLtadrs,toonf , SEtngHlaenledn. sT.hiEsnfgiblaenr dis, under the name "Cem-FIL" for cement reinforcement purposes. Glass-reinforced cement usually contains between 3% and 7% of fibers, and typically one would expect a material containing 5% of fibers to have a modulus of rupture similar to that which would be expected from asbestos cement containing 15% of fibers (about 35 M N/m 2). Additionally, the glass-reinforced cement is considerably more impact resistant than asbestos Page 10 ASB ESTO S--M A Y 1977 t */* ' * it.W' ' ; - ' HL ` v' *_* V ' X-,. ir.* 'V \ :1 V. - -V ':"-. r l ^ V - N h '- v,,V , : , , . / ' f ,V,\v Vi ,V ; . ... 1 :-yr> fv 4P if i, i ' 1 ------------ L- ' 'v -- " T- ^jL SEARCH K SUBSTITUTES-- CONTINUE!) K' 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. * 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 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 re move 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 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,erial on minimally-modified 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 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 asbestos fibers 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 com pletely and this has been achieved by suitable plant modifi cations. It is likely that this equipment will shortly become avail able in the United Kingdom, eliminating one of the principal drawbacks to the use of glass-reinforced cement. Page 12 A SB E ST O S--M A Y 1977 ` v-V*,'v ^ !* ' ' v' * 4 > ` -,/ _V *. ' *'"**** v `L*-* --.?*y" * \ llip ...l.|lj|l.|l,lll. lin, I , fmmaamamBmasmvmsrsm i r. .'v> \ \ > -- i J v 1 *+ < i;'- ,' V . . > ' . ' / i " -, VV . , .1 1 ^< v 4 7*' >* . ' ,_ u ', , . . . V 1 * -s V v . ` .* - J :>%< v ^ ; v > x '* , \ ' ~ ' - ^ 7 # ^ ......'' . ..... ; ", '. : i ; . V ,Vt **' ' * 1 i ' ' - t y(. . . \ , * .,lt. _ , ; ' V '. jZ ..........' 7 V f` '> * r .................................. '."4 *<, : ' ' .' .- */ >;..v /-, ' f ^ ^ III, , . ... J 1 ' c . . v*;- " r ./: ' aV>X` - % >*, * SEARCH FOR SUBSTITUTES--CONTINUtO 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 manufactured 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 3 is recommended, i.e. the quality control initial strength should be at least six times the design working stress. Most existing uses of glass-reinforced cement have been re stricted to non-load-bearing components (e g. 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 glass-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 iighter, due to the thinner wall required, than a steel- 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 a1complex function m 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 tempera tures 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 non-fibrous silicate and ts 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 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 searctvng for substitutes for asbestos in this application. Page 14 A SB E STO S--M A Y 1977 - : ufi -i y ,o , -..A ! Vk .,y. , . -- , y ,, v f j. ^' * **, * II * -, . ' d. i, . . . * . * * ' 'V . V A. ` ^.*^4 c;Jk%*. `<y. .tve'1-''-1 - . . . .o' r,' y f .v. Ci-e- A.*, ; ' ", vv - f "" " -- v"* * . * r ii a A R C H fOR SUBSTITUTES--CONTINUED I 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 fiber/caibon 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 tempera tures 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-based 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 avail able for about 30% of th'e friction products market, the exception being in the heavier-duty applications such as disc brake pads where high temperature surface conditions are encountered S'eel fibers were first used in friction materials in Germany, prior to and during World'War 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 fiber-based friction materials also produce a very abrasive wear debris, with corres ponding 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 fiber-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 Con ventional E-glass fiber is approximately half the pnce of the steel wool Non-asbestos-based materials use proportions of fiber comparable to the conventional product and are hence more expensive. Thus, altncugh asbestos-based friction materials are tech nically and eccncmically preferable at present for the majority of applications, it seems probable that these may eventually be re placed by the non-asbestos-based materials as a result of concern over the health hazards involved with asbestos Page 16 ASBESTO S--SIA Y 1977 , t .* * \.v - 'V'-; V * t'* ' hSSMteh hmuuImm 111 1 fit i? t & f;.*- ' X-\ t, ,V,..<', , , U *.- \W -V . . ('.* > . V . " ..... * *- '*. . r . ' . -'i/';. V*-` - v u V 'j r >.-y 'y ; _ ' 'r ' ' . C Y V ** *> ' '"'' a b .r - - \t\- " ,\V- . Jl . - *v A R C H fOR SUBSTITUTES--CONTINUED CONCLUSIONS i sidered Ih P f'n n i'V P f `W aPP|,catl0ns which have been con- SS S S SsceC "cJie ,wo" ,"" ,, 1) The health hazards involved in the handlino of ashPctnc ggreSaterr 'Ptthh0aannUCtthhnods,pe ,nap9ssmoacciaht,eind'n9waitnhddtheemohliatinodnhnoqperoaftiofnrisctiaorne materials, where the dangers are confined to manufacture and the cleaning of brake drums and linings. . . . 2 ). Fle,search ^as led ,0 development of technically c ep,able substitutes for asbestos-cement products whilst a s : r , s . a,e l,k9ly ,o be a" ep,M -S u te fii: tntair K !n r9Ume,K,S put forward here therefore mitigate against a total ban upon the use of asbestos products and would suggest that in some cases it would be preferable to ensure the obse?va- ma^ntlndequa(h Sa,ety Precau,|ons during their manufacture and maintenance than to accept irtfenor products. In addition the potential health hazards involved with the use of alternative fibrous materials, including glass, should not be overlooked COPIES STILL AVAILABLE! ' * E MM.ENP E WORK PRACTICES-Fw manuals published by the Asbestos Information Association/North America include Achp,mmo nded,,Work N o tic e s for the Fabrication and Use of htncQShPapDr PJ oduci?'" "Shop and Field Fabrication of AsrcntPS SheD pr,ody,c,s' "Molding and Fabrication of Asbestos Containing Plastic Products," "Fabrication and Use of Asbestos P oducnts^?iiec % anh VSe and Handlin9 of Asbestos Textil? ******** th(ob ghSASBlsTOSeMagaz?ne]P Sla^e AIA,NA 0r j* f . * vJ| NEXT ISSUE--FELTS FOR A/C PRODUCTION m Page 18 A S B E S T O S -M A Y 1977 in in.. Mi,,n u I,... .. -*. '* * * 'W.hf-.-V'Vp' iM.f'*i*v>* *; *..t+ ' ' I aeaa tfK ^M M M iB M ^. \ W . - >< ; v. * ' ; "f-. ,v;f, , y* - > -- mmm . - i r - ' i ' t ' v - - * _ V' " .*s'>4 - ^ * ''V * - ' ' > s . t v ' i - v . i i - ' ? - *>: 4' ** M x-.v!- > \ *. v si COPT FORM BOX NUMBER 5 /f> SEGMENT NO. NOTES INITIALS DATE REQUESTING PARTY ft / y fs -r c & jk t