Design Drawing

When using engineering plastics, designers must first refer to the material properties of the raw materials before designing. They cannot treat them completely like metal.

The material that matches the engineering plastic parts is preferably metal. If it is necessary to use plastic versus plastic, choose two materials with different softness and hardness, such as POM versus NYLON 6A, and consider supplying coolant.

Engineering plastics have a higher thermal expansion rate than metals and have problems with water absorption (NYLON). Therefore, when setting tolerances, they should always be wider than metal parts. POM should be considered first, or the supplier should be asked to provide modified engineering plastics.

If the load and speed do not cause the material to overheat, there is no need to use lubricants. At most, plastics containing solid lubricants (such as graphite or molybdenum disulfide) can be used. However, if the machine parts are not constantly moving, it is not advisable to mix graphite, because in the presence of moisture, graphite has a galvanic corrosion effect on metals. However, the use of lubricants can extend the life of engineering plastics.

Plastics all have creep properties, that is, they will produce some permanent deformation under long-term continuous load. This is also the reason why engineering plastics cannot achieve press fit and shrink fit like metal under heavy load, especially under temperature differences. It is more difficult to achieve under a wide range of operating conditions. Because of these conditions, gears or bearings must be keyed, pinned, or riveted in place. However, in terms of creep properties, POM is the smallest among commonly used engineering plastics, and its rigidity is also the largest, most like metal. Generally speaking, deformation will begin to occur within 36 to 48 hours after the machine part is installed. Therefore, it is best to do a low-speed running inspection 48 hours after the machine part is installed. If there is no problem, you can preliminarily conclude that the machine part is faulty. There will be no problems with future operations.

When designing engineering plastic parts, sharp corners should be avoided regardless of whether they are external or internal corners. If parts with sharp edges are used, the impact strength will be greatly reduced. In order to maintain maximum impact strength and reduce stress concentration, the outer corners and edges should be rounded, and the outer diameter (R) of the inner corners should also be enlarged as much as possible.

Although engineering plastics have higher heat resistance than ordinary plastics, plastics have poor heat conductivity and are prone to heat accumulation. Therefore, when designing, attention should be paid to the fact that such parts cannot be used near high temperatures or fire sources. Otherwise, cooling should be considered. liquid. As for the plastics themselves, due to their good thermal insulation and high thermal expansion rate, their cross-sections should be made as thin as possible during design. Otherwise, overheating will occur at high speeds or high loads, and the parts will naturally be more susceptible to damage. Moreover, a thinner section can also reduce material expenditures.