FRICTION DUST

Property Modifiers. Property modifiers can, in general, be divided into two classes nonabrasive and abrasive, and the nonabrasive modifiers can be further classified as high friction or low friction. The most frequently used nonabrasive modifier is a cured resinous friction dust derived from cashew nutshell Hquid (see Nuts). Ground mbber is used in particle sizes similar to or slightly coarser than those of the cashew friction dusts for noise, wear, and abrasion control. Carbon black (qv), petroleum coke flour, natural and synthetic graphite, or other carbonaceous materials (see Carbon) are used to control the friction and improve wear, when abrasives are used, or to reduce noise. The above mentioned modifiers are primarily used in organic and semimetallic materials, except for graphite which is used in all friction materials. 

This is used in manufacture of brake linings and is a polymer based on cashew nutshell liquid admixed with formaldehyde or furfuraldehyde and other ingredients. The polymerised resin mixture is cast into 8 cm thick slabs and then ground finely to produce the friction dust. Several fires have been experienced during bulk storage of the dust, attributed to autoxidation of the still partially unsaturated resin compound. Previously, linseed oil was used in place of the nutshell liquid, but fires were then more frequent. 

Friction dusts are cured coarse powders composed of polymerized cashew nut shell liquids. These materials are added to friction materials to confer friction stability, resiliency, and noise damping. Rubber and abrasive modified friction dusts are also available. Friction dusts tend to absorb solvents, causing the friction material to spring back after forming. This limits the use of cashew friction dusts to dry mixes or solvent-free wet mixes. 

Historically the main interest in cardanol, in the form of the semisynthetic, technical cashew nutshell liquid, obtained by thermal decarboxylation of natural cashew nutshell liquid, has been in a wide range of technological applications such as in friction dusts and in polymer chemistry many of which have been described in a number of reviews [1,2,11]. Remarkably, very new biological applications have been found for this versatile raw material. 

The phenolic lipids of Anacardieum occidentale have been commercially exploited (ref. 174) and those in Rhus vernicifera to a lesser extent. Most of the technical cashew nut shell liquid (CNSL) which results from industrial processing is and has been employed as a phenolic source for formaldehyde polymerisation the products from which in compounded form have been the basis for friction dusts widely used throughout the world in vehicle brake and clutch linings (ref.175). Urushiol has had use over many centuries in the art of Japanese lacquering (ref. 176) and in more recent years has been sometimes supplemented with CNSL. Chemical uses are referred to later. 

The primary objective in cashew processing has been to recover the desirable kernel. The by-product, technical cashew nut-shell liquid, later became of interest as a raw material for friction dusts with superior properties to previous materials which were based on composites of phenol/formaldehyde resins with highly unsaturated glyceride oils. Because of its intractability the cashew nut has been termed in Mozambique, the devil s nut Most CNSL world-wide is now extracted or cracked by an automated process (refs. 170, 177), the hot CNSL bath method, developed comparatively recently, in which raw humidified cashew nuts are submerged in technical CNSL on a slowly-travelling conveyer belt and heated to... 

CNSL used in polymerisation with formaldehyde as for example in friction dusts may not require elaborate analysis. Nevertheless interest in the industrial chemical uses of phenolic lipids has led to a study of quantitative methods of analysis by a variety of chromatographic methods. For cashew phenols these were first based on GLC. Thus the (15 3), (15 2), (15 1) and (15 0) constituents of methyl anacardate, cardol and cardanol have been separated by GLC on PEGA columns (ref.206), the free phenols (anacardic acid as methyl anacardate) by GLC on SE30 (ref207) and the hydrogenated anf fully methylated phenols on Dexsil and PEGA columns (ref.208). A further number of stationary phases have been investigated... 

The resins in the friction dust area tend to be rigid and the flexibility and plasticity associated with the long alkyl chain of phenolic lipids have been used in natural rubber vulcanisation by for example incorporating crosslinking with phosphorylated cardanol (ref. 252). Unpolymerised CNSL phenols have been used in natural or diene rubber compositions for tyre treads to give an improved dynamic elastic modulus but with the same hardness as formulations without the phenolic addition (ref. 253). 

Due to the friction of dust or free snow blowing past the conductors. 

LVHV hose inside diameters are usually recommended to be in the range 2.0-3.5 cm (1-1.5 inches).Hose lengths should be limited to about 2 m (8-10 feet), if possible. If greater lengths are necessary, then the hose inside diameter must be enlarged to reduce friction losses, but not so large as to fail to transport dust to the duct system. It is advisable to obtain accurate hose friction loss data from manufacturers. 

Bearing type temperature temperature friction humid dust vibration... 

On the dusted track the diminished adhesion friction component is clearly apparent for all three rabbers when comparing them with the master curves on the clean track The friction plateau observed for the rubbers filled with 50 pphr black which is typical for tire tread compounds is observed for most rubbers, as shown in Figure 26.5. 

FIGURE 26.4 Master curves on smooth, wavy glass, on a sihcon carbide track dusted with magnesium oxide and on a clean silicon carbide track of three acrylate-butadiene rubber (ABR) compounds as gum rubber, filled with 20 pphr carbon black and 50 pphr, respectively. (From Grosch, K.A., Sliding Friction and Abrasion of Rubbers, PhD thesis, University of London, London 1963.)... 

FIGURE 26.8 The friction master curves of the acrylate-hutadiene rubber (ABR) gum mbber on (a) dry glass, (b) dry clean silicon carbide 180, (c) dry silicon carbide dusted with MgO powder, (d) Alumina 180 wetted with distilled water, and (e) wetted with water +5% detergent. 

---