2.2.4 Wear of Working Parts
In Basics Section 2.2.3.2, we discussed the effects of pin wear. When a chain is operating, the outer surface of the pin and inner surface of the bushing rub against one another, wearing little by little.
When a chain is operating, obviously other parts are also moving and wearing. For example, the outer surface of the bushing and inner surface of the roller move against one another. In the case of transmission chain, the roller and bushing wear is less than that of the pin and the inner surface of the bushing because the chance of rubbing is generally smaller. Also, it is easier to apply lubrication between the bushing and roller.
The progress of pin-bushing wear is shown in Figure 2.20, in which the horizontal axis is the working hours and the vertical axis is the wear elongation (percent of chain length).
Figure 2.20 Pin-Bushing Wear During Operation
In Figure 2.20, O-A is called "initial wear." At first the wear progresses rapidly, but its ratio is less than 0.1 percent and usually it will cease within 20 hours of continuous operation. A-B is "normal wear." Its progress is slow. B-C is "extreme wear." The limit of "allowable wear" (the end of its useful life) will be reached during this stage (1.5 to 2.0 percent).
The solid line reflects a case of using chain with working parts that were lubricated in the factory, but were not lubricated again. If you lubricate regularly, the pin and the bushing continue to exhibit normal wear (reflected by the dotted line), and eventually run out their useful life.
If you remove all the lubricants with solvents, the wear progresses along a nearly straight line, and the life of the chain is shortened. This is shown by the dashed line.
The factors that affect chain wear are very complicated. There are many considerations, such as lubrication, assembly accuracy, condition of produced parts, and the method of producing parts; therefore, wear value can't be greatly improved by merely changing one factor.
In transmission chain, JIS B 1801-1990 regulates the surface hardness of the pin, the bushing, and the roller (as shown in Table 2.2) to meet the multiple requirements for wear resistance and shock resistance.
| Component | HV | HRC |
|---|---|---|
| Pin | 450 or greater | 45 or greater |
| Bushing | 450 or greater | 45 or greater |
| Roller | 390 or greater | 40 or greater |
