To boost life and reliability, don't skimp on seals

Seals are among the least expensive components of a hydraulic system. Yet they are expected to perform flawlessly under a wide range of pressures, speeds, temperatures,and other adverse conditions. When seals do become excessively worn or damaged, they leak. To replace a rod or piston seal, the hydraulic system must be shut down, which leads to production down time.

Therefore, by improving the life of a seal, a company can decrease downtime and thereby lower manufacturing costs. Off-the-shelf seals and other components tend to be made from materials that will hold up under typical operating conditions, but may rapidly degrade under extreme conditions — such as high heat.

Because injection molded plastics involve high pressures and temperatures, seals must be able to withstand these adverse conditions.

A maker of fishing equipment found that it had to shut down its highheat injection molding operation down frequently to replace an off-theshelfrod seal that would deteriorate after every few weeks. The seal, part of a cylinder mechanism consisting of a 11/2-in. bore cylinder, 3/4-in. rod with 12-in. stroke, was supposed to keep two sections of the mold clamped together and had to hold back 1500 psi at a fluid temperature higher than 200° F. An off-the-shelf seal made of a standard loaded U-cup had worked effectively on 80% of the company's equipment, but couldn't work on this mold operation because of the high heat. In this case, customization involved analyzing the system pressure and temperature and identifying pressure spikes and shock loading to determine the appropriate high heatresistant material.

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