Bronze-filled PTFE

The highest yields of monomers such as TFE, HFP and C-C4F8 of aronnd 90 wt% were obtained at pyrolysis temperatures of between 645 and 600° C. Formation of oligomeric PTFE waxes can be explained by repolymerization of TFE in the cooling steps where the steam is condensed. The same phenomena occnr dnring indnstrial production of TFE. Carbon black and glass fibres have nearly no inflnence on the prodnct composition (compare Table 24.9). For the bronze-filled PTFE the yields of TFE, HFP and C-C4F8 were... 

Confirmation of chain scission and, at least, liberation of a radical species arises from degradation studies achieved using filled PTFE. By electron spin resonance spectroscopy, Fock [31] found that the carbon black used in carbon-filled PTFE contained large numbers of unpaired electrons and that pyrolysis of carbon-filled PTFE showed vastly different decomposition rates to neat and bronze-filled PTFE. He concluded that the difference in degradation behavior is due to radical intermediates being stabilized by the unpaired carbon black electrons. 

Figure 2.12 The effect of moisture content of gas on the wear of 25% glass-filled and bronze-filled PTFE [9].

Other experiments were carried out with filled PTFE material, using steam as fluidizing gas. Fillers were carbon black, glass fibres, and bronze. Important parameters are listed in Table 24.10. In the first three experiments, the inflnence of the temperatnre was investigated, in the following were other fillers nsed. 

Polytetrafluoroethylene has excellent chemical resistance properties. The effect of incorporation of additives on chemical properties depends on the t) e of the filler and the specific chemicals. In general, chemical properties of filled PTFE compounds are not as good as those of the unfilled resin. Table 3.21 shows the effect of a number of chemicals on car-bon/graphite, glass, and bronze compounds. 

Compounds containing fillers are usually more sensitive to thermal decomposition due to the acceleration of thermo-oxidative reactions by a number of additives at elevated temperatures. Fillers could allow sintering compounds at lower temperatures due to an increase in the conductivity of the part. For example, a metal-filled PTFE compound (steel, lead, or bronze) has a significantly higher thermal conductivity than PTFE, which leads to rapid heating of the part. 

Hostaflmi . [Hoechst Celanese Hoechst UK] PTFE, some glass, carbon, graphite or bronze filled for extrusion, compr. molding, coatings. 

PTFE, 60% bronze filled High speed bearings, wear pads, piston rings ... 

In many applications it may not be feasible to employ the fused spray coatings because of the relatively high temperature (700° F) necessary to fuse the PTFE. Phenolic-bonded PTFE, PTFE-filled porous bronze, and PTFE glass-filled tape are among the other products that may be considered for sliding surfaces. The phenolic-bonded PTFE can be applied with cure temperatures as low as 300 F. The PTFE-filled porous bronze is available in sheets that can be formed to various shapes and mechanically pressed or clamped into retainers. The PTFE tape containing about 25 per cent glass fiber was molded and had one surface etched so that it could be applied to metal surfaces with adhesives. 

Some other bearing materials find extensive use for which production volume is less well defined. Filled plastics such as nylon, acetal resin, PTFE, and phenolics are formed and molded into bearings in a wide variety of mechanical structures. Tin, lead, and bronze alloys are used for oil-film bearings in heavy industrial and power generating equipment, frequently in custom bearings manufactured directly as machine components. 

A mild steel backed porous bronze bearing material in which the pores are filled with PTFE. The brotize layer being approximately 0.010 in. thick with an 0.0005 in. thick overlayer of PTFE. (GLACIER DP.)... 

Reply bv the Authors The upper limit of temperature of self-lubricating dry rubbing compound bearings made of a steel backing with a porous bronze layer filled with a PTFE/solid lubricant mixture corresponds with the lowest upper temperature limit of one of the components of the bearings (bronze, PTFE, M0S2, or lead etc). 

The pure resins are limited to light loads and low draft velocities because of cold-flow problems and low thermal conductivity values (k). Therefore, various fillers are added such as glass, graphite, bronze, and These resins and the filled compounds have a pressure-velocity limit of 8000-10,000 psi fpm. Unfilled PTFE has a static p = 0.05-0.08, and a dynamic p = 0.10-0.13. The p values are larger with fillers ranging from 0.08 up to 0.50. The coefficient of friction, p decreased with pressure under dynamic conditions. 

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