Cashew Nuts Improve Braking Performance
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IN iecent years close attention has I been directed to the production o' moulded clutch and brake facings, consisting essentially of asbestos fibres and various fillers. These are bonded under heat and pressure with a powdered thermosetting resin. Modifications of this process have comprised the use of a binder resin in the form of a solution, and the extrusion of the resultant mixture. These methods have broadened ihe range of friction-modifying agents which • can be incorporated, including metallic particles andjor various dust fillers.
The most successful of these dusts have been based on resins produced from cashew nutshell liquid. This liquid is the acrid juice found within the double rind Which encloses the kernel of the cashew nut. It is a corrosive poison similar to carbolic acid, and is used in a variety of processes, including the manufacture of insulating materials, plastics, varnishes and insecticides.
n10 Although the nut produces a quantity of edible kernel in addition to CNSL (cashew nut shell liquid), the demand for CNSL resin is so great that business enterprise is concentrating on the second product. This can be obtained with relatively little labour and risk.
Friction dusts for brake and clutch facings are usually obtained by grinding the fully cured product of. CNSL.
polymer with an aldehyde. Marked increase in performance, particularly in reducing wear at high temperatures, is obtained when 5-15 per cent. of CNSL friction dusts is included.
Binder resins of both solid and liquid types have also been produced from the reaction of CNSL phenol mixtures with formaldehyde, and these give compoSilions which mould excellently and have high frictional values. They are now in wide use, although the manufacturers of facing materials are still reticent about them.
Cashew resins in solution are used
for impregnating woven asbestos facings, and as binders in the wet-mix process. In powder form, cashew resins are employed as binders, and as friction dusts in the making of moulded brake facings by the dry-mix process. The incorporation of friction dusts intomoulded brake facings smooths out irregularities in friction co-efficients.
As the cashew-nutshell resin is a naturally occurring phenolic body obtained from the tropics, it is particularly useful in these regions. because of its resistance to termite attack. Vehicle manufacturers use cashew resin for protective coverings for metal components, as well as for clutch and brake facings.
Other miscellaneous applications are also being considered. These include wetting agents, anti-sludge agents for lubricating oils, extreme-pressure additives for lubricating oils, petroleum antioxidants, and non-bituminous coatings for underground structures exposed to corrosive soils.