Document 50rJK86JE3xKdRObOxkD1y65e

exposure ot asbestos bom vaiious sources. Added to these are the many international and state regulations, and the regulatory sit uation is certainly challenging. Another disadvantage ol asbestos is its scar city. Compared to oil. the U.S. is more com pletely dependent on foreign sources tor as bestos than it is lor petroleum. Although gen eral asbestos supplies seem adequate, the long grades such as number 4 and 5 liber lengths used extensively for gasket materials have been in lighl supply lot the past lour years. The final disadvantage ol asbestos Is that it does not always solve alt the problems that it is asked lo solve In shod, belter heat resis tance sealabilily and crush resistance are often requited. Asbestos has served us well and will continue to do so but there are more and more demands lot better solutions. At present, the majority ol gaskets in the U.S. do contain asbestos. Most ot them contain 80% asbestos in their composition with the rest being polymer binder systems and tillers. The problem ol replacing asbestos Is ot very large magnitude. However, before we get into reviewing what is being done to replace as bestos, we should probably consider what the asbestos suppliers are currently saying about the situation. They stale very simply, lhat once the material reaches the consumer, the asbestos is locked-in by the various pro cesses used in manulacture. Granted, this may be true, but it is very difficult tor most gasket suppliers to verily that this condition continues throughout the use ol the product when they consider the asbestos-contained material is typically sheared, torn, calender ed, scraped, sanded, punched, burned, form ed. compressed, and ground in its further manufacture and use as a gasket. Because cl the disadvantages mentioned and Ihe tack ol technical verification of the safety Of the mateiial when processed and used as gasketing, several major domestic users have embarked upon programs to eliminate asbes tos gaskets Irom their product lines. Let's ex amine what asbestos-free materials will have lo do when they replace asbestos pioducts in gaskets. Replacement materials will have to have high-heat resistance, excellent crush re sistance, dimenlional stability, and homogen eity. As another reference point, we should examine those products currently available in the marketplace. These are cellulose, anaerobics, RTV. and rubber-coaled steel. A number of companies have eliminated as bestos gasketing, and gaskets in general, Irom their current assemblies. The General Motors Corporate V-6 has only two gasket ap plications in the engine: the cylinder head gasket and the intake manifold gasket. Both ol these applications are with asbestos con taining materials. Many transmission manulactuiers are also eliminating gaskets from theii assemblies and replacing them with li quid sealant lo reduce the tolerances requir ed lor assembly. This permits them to develop quieter-running transmissions and gear boxes -- another upcoming regulation. Asbestos seems to be used in the majority ot cylinder head applications and intake mani fold applications, exhaust manilotd applica tions. and a large number ol extremely heavi ly loaded flanges. However, the critical re quirements ol these various applications are not the same Irom application lo application. Cylinder head and intake manifold applica tions require materials having good homogen eity and the resulting conlormabHily lhat per mits a good fluid seal. Exhaust manifold appli cations require the high-heat resistance char acteristics ot asbestos and heavily loaded tlanges require the crush and extrusion resis tance of asbestos. So it is possible to replace asbestos in different ways lor different ap plications. More importantly, it appears that it we could improve certain properties in certain applications, we could present design engi neers and the marketplace with an impioved product with greater appeal. For years gasket material producers and de signers have allempted to Improve Ihe binder systems In gaskets. This work was done be cause Ihe binder system appeared to be the limiting Ingredient in gasket functional design. Little was done to improve the liber charac teristics and to obtain increased functional characteristics through this method. We are now looking at that 80% ol the gasket which represents the fiber to see what can be dona in replacing asbestos to improve its lunclional characteristics. However, lo do this, one quickly linds lhat no single man-made fiber or Other high temperature material approaches asbestos in its crucial physical properties. It is therefore necessary to blend materials to obtain the desired properties. The types ot materials blended are mainly various libers and fillers, although rubber coaled sleel is also considered an alternative. Clay is one such tiller. )l is inexpensive, com pressible in bulk, and fills the voids between the larger libers of glass, nylon, or aramid. Clays are easily dispersed in mixtures of water. From a sealing point ot view, the clay reduces the spring rale ol the facing, and im proves the load bearing capabilities. Temper ature resistance is above 3000 F (1649 C). Clay, when added to most materials, in creases the surface area lo the magnitude ol asbestos. Clay has better contormabtlity pro perties than asbesetos. Mica is basically a tiller, also, and has been used lor years in the paper industry. Vermiculiie is the thermal or chemically expanded form ol mica which Is very economical, has high surlace area, and good temperature re sistance (above 2000 F). It has relatively low strength, but good slip characteristics, caus ed by the low coeflicienl ot friction ol the par ticle. Mica has better torque and heat resis tant properties than asbestos. Graphite has the highest heat resistance ot the materials presently under consideration with Ihe tensile strength increasing until 4000 F and heal resistant above 5000 F. Thp mater ial is very costly but can be used in layers. The unique low frictional characteristics ot the platelets help where motion is a problem. Glass fiber is another candidate. It normally endures heal to 1100 F, where softening and fusing takes place. However, it has good strength and Ihe thinnest diameter or highest surlace area ol any man-made liber. II will be used to reinlorce mica, clay or barytes based compounds in Ihe same way as aramids and nylons will be used. In some applications cellulose liber may be favored. Bui it is used very sparingly, if at alt, in materials requiring high temperature resis tance because ol its low charring tempera ture. In applications where heat is not above 300 F. however, Ihe liber can be used as a successful carrier web or matrix lor a variety of fillers. VPD-J 42-0002634