Пластиковые цилиндрические шестерни со стальным сердечником

Описание

Plastic gears are commonly used inside various machines such as food processing machines, home appliances, chemical-related machines, toys, and medical equipment.

Commonly used materials for plastic gears are engineering plastic polyoxymethylene (POM), polyamide MC nylon, U-PE, PEEK, etc.

In addition, when using plastic gears, if the ambient temperature changes significantly, the gear hole diameter is large, and the keyway load is large, S45C or stainless steel hubs are generally used. When using S45C or stainless steel hubs, the teeth and the hub are typically fixed with bolts. However, when the bolts cannot be repaired, spur gears use a fusion method to improve the teeth and the corner. HZPT's fused spur gears (steel core plastic spur gears) are designed to have more vital fused parts than the teeth of the gears.

Plastic gears have many advantages, such as being lightweight, no rust, and high quietness. In addition, there are many advantages, such as mass production can be achieved by injection molding, and no lubrication can be achieved by pairing with metal gears. On the other hand, plastic gears have shortcomings, such as low strength, ease of heat, and significant dimensional changes such as tooth clearance compared with metal gears. However, the degree of dimensional change easily caused by plastic gears varies depending on the material's resistance to temperature changes, water absorption, and chemical resistance.

Metal Inserts

Injection-molded metal inserts are used in plastic gears for a variety of reasons:

1. To avoid an extra finishing operation.

2. To achieve more excellent dimensional stability because the metal will shrink less and is not sensitive to moisture;

it is also a better heat sink.

3. To provide greater load-carrying capacity.

4. To provide increased rigidity.

5. To permit repeated assembly and disassembly.

6. To provide a more precise bore to shaft fit.

7. As durable support for fasteners, such as set screws to affix the gear to the shaft.

Inserts can be molded into the part or subsequently assembled. In the case of subsequent assembly, stress concentrations may be present and lead to cracking of the components. The interference limits for press fits must be obeyed depending on the material used; also, proper minimum wall thicknesses around the inserts must be observed. The insertion of inserts may be accomplished by ultrasonically driving in the insert. In this case, the material melts into the knurling at the insert periphery.

Inserts are usually produced by screw machines and made of aluminum or brass. It is advantageous to attempt to match the coefficient of thermal expansion of the plastic to the materials used for inserts. This will reduce the residual stresses in the plastic part of the gear during a contraction while cooling after molding.

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