Electronic parts tooling, plastic mold making service, injection molding

Electronic parts tooling, plastic mold making service, injection molding

Service Details:

  • Brand:Kayou
  • Serial Number: M-0178
  • Country of Origin:Shenzhen, China
  • Certificate:ISO9001

Payment & Shipping Terms:

  • Price Quote:Negotiable
  • Minimum Order: 1
  • Average Delivery Time:25 days
  • Payment Method:T/T
  • Package Details:Wooden Case
  • Ability to Supply:5 Set/per month
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Electronic parts tooling, plastic mold making service, injection molding

Description

Electronic parts tooling, plastic mold making service, injection molding

Processing Properties of Thermoplastics

In addition to thermodynamic properties, crystallinity and orientation, the technological properties of thermoplastics include shrinkage, fluidity, heat sensitivity, water sensitivity, hygroscopicity and compatibility.

Shrinkable plastics are usually formed by filling the cavity of the mould at high temperature. When the plastic parts are cooled from the mould to room temperature, their size will be smaller than the original size in the mould. This property is called shrinkage. It can be expressed as a percentage of shrinkage per unit length of plastic parts, i. e. shrinkage rate (S).

Because this shrinkage is not only caused by the thermal expansion and cold contraction of the plastic parts themselves, but also related to various forming process conditions and die factors, the shrinkage of the plastic parts after forming is called forming shrinkage. By adjusting the process parameters or modifying the die structure, the change of the size of the plastic parts can be reduced or changed.

Molding shrinkage can be classified into two types: size shrinkage and post-shrinkage, and both of them have directionality.

Dimensional shrinkage of plastic parts is caused by thermal expansion and cold contraction of plastic parts and physical and chemical changes inside plastic parts, which leads to the phenomenon of dimension shrinkage of plastic parts after demoulding cooling to room temperature. Therefore, when designing the moulding parts of the mould, it must be considered to compensate them by design so as to avoid the overshoot of the size of plastic parts.

During the POST-SHRINKAGE forming of plastic parts, a series of stresses are produced due to the internal physical, chemical and mechanical changes. Residual stresses exist after the plastic parts are solidified. After the plastic parts are demoulded, the size of plastic parts will be reduced again due to the effect of various residual stresses. Usually, the POST-SHRINKAGE of plastic parts is larger within 10 hours after demoulding, and basically finalizes after 48 hours, but it takes a long time to reach the final finalization. The POST-SHRINKAGE of thermoplastic parts is larger than that of thermosetting plastics. The shrinkage of injection and injection moulding parts is larger than that of compression moulding parts.

In order to reduce the internal stress of plastic parts and stabilize the size of plastic parts after forming, sometimes according to the performance and technological requirements of plastics, plastic parts need to be heat treated after forming, and the size of plastic parts will shrink after heat treatment, which is called post-processing shrinkage. The post-treatment process of plastic parts includes annealing and humidification.

Errors caused by POST-SHRINKAGE and post-processing shrinkage should be compensated in die design of high precision plastic parts.

Orientation effect of polymer along flow direction will lead to anisotropy of plastic parts in the process of plastic parts shrinkage. The shrinkage of plastic parts will inevitably vary with different directions. Usually, the contraction along the direction of the material flow is large and the strength is high, while the contraction perpendicular to the material flow is small and the strength is low. At the same time, due to the uneven distribution of additives and density in all parts of the plastic parts, the shrinkage is not uniform, resulting in poor shrinkage of the plastic parts, which is easy to cause warping, deformation and even cracking of the plastic parts.

 

 

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Electronic parts tooling, plastic mold making service, injection molding

 

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