Friction and Lubrication in Mechanical Design Episode 1 Part 8 pdf

Thermal Considerations in Tribology 155

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siderable difference between the film and solid temperatures. Figure 5.27

represents the case of a metallic solid with an insulative surface layer in

contact with another layered solid having an opposite combination of ther￾mal properties. It can be seen from the figure that the heat partition is highly

dependent on the ratio Hd/H,, where

h02 + ho1 Hd = h2 -hol and H,, =- 2

The latter is kept constant to show the main influence of the difference in

surface layer thicknesses. The existence of surface layers strongly deviated

the heat partition from the dry sliding condition. This phenomenon could be

explained by the cooling mechanism in the contact zone by a shallow region

near the surface, which mainly incorporates the layer thickness. Figure 5.27

also demonstrates the possibilities for equalizing the heat partition between

the moving solids by controlling both thermal properties and thicknesses of

surface layers. Negligible sliding is assumed in this case.

Figure 5.28 shows the variation in the maximum temperature rise in the

contact zone and the solid surfaces with respect to Hd/Haw. The contact

I I I I I I I I I 1 1

Film

Slower Surface

Fader Surface

----

-..-.--.

8 10 12 14 16 18 20

P, (1 0' psi)

Figure 5.26 Maximum temperature rise versus maximum pressure for 50% slid￾ing (steel-oil-steel, rolling velocity = 400 in./sec, RI = R2 = 1 in.).

0.4

0.3

-1 .o -0.5 0.0 0.5 1 .o

Ha ' H,

Figure 5.27 Heat partition versus Hd/H,,,, (rolling velocity = 2000 in./sec,

1=.02 in., K~=K~~, K~~=K*=.I K~, H,,,=~o~ in.).