Reducing Impact Forces

Many machines and items of equipment are designed with parts that strike forcefully against other parts, producing noise. Often, this striking action or impact is essential to the machine's function. A familiar example is the typewriter—its keys must strike the ribbon and paper to leave an inked impression. But the force of the key also produces noise as the impact falls on the ribbon, paper, and platen.

Several steps can reduce noise from impact forces. The particular remedy is determined by the nature of the machine. Not all of the following steps are practical for every machine and every impact-produced noise. However, applying even one suggested measure can often reduce the noise appreciably.

Some of the more obvious design modifications follow. Figure 6.6.1 shows the application of some of these measures.

Reduce the weight, size, or height of fall of the impacting mass.

Cushion the impact by inserting a layer of shock-absorbing material between the impacting surfaces. (For ex ample, insert several sheets of paper in the typewriter behind the top sheet to absorb some of the noise-producing impact of the keys.) In some situations, inserting a layer of shock-absorbing material behind each of the impacting heads or objects reduces the transmission of impact energy to other parts of the machine. Whenever practical, one of the impact heads or surfaces should be made of nonmetallic material to reduce resonance (ringing) of the heads. Substitute the application of a small impact force over a long time period for a large force over a short period to achieve the same result. Smooth out the acceleration of moving parts by applying accelerating forces gradually. Avoid high, jerky acceleration or jerky motion. Minimize overshoot, backlash, and loose play in cams, followers, gears, linkages, and other parts. To achieve this measure, reduce the operational speed of the machine, make better adjustments, or use spring-loaded restraints or guides. Machines that are well made, with parts machined to close tolerances, generally produce a minimum of impact noise.

0 0

Post a comment