Mechanical parts tooling, mould making, injection moulding production

Mechanical parts tooling, mould making, injection moulding production

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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Mechanical parts tooling, mould making, injection moulding production


Mechanical parts tooling, mould making, injection moulding production

Causes of Forming Shrinkage

Heat shrinkage high temperature plastic melt is cooled and shaped as plastic products in injection mould. Most plastic materials follow the physical law of thermal expansion and contraction. The shrinkage phenomenon at this time is called heat shrinkage.

Crystallization shrinkage for crystalline plastics, during the cooling process of forming, there will be a certain crystallization phenomenon in the material of plastic parts, and the degree of crystallization is affected by the cooling conditions. Crystallization changes the composition of plastic macromolecule from random coil to regular and tightly arranged, so the volume of the product will shrink and the shape and size of the product will be reduced relatively. Among the shrinkage values of crystalline plastics, crystalline shrinkage is the main part.

Orientation shrinkage in the pouring process, due to injection pressure, plastics materials along the direction of the molecular chain have a certain orientation effect, melt in the pouring system, flow will produce a very significant orientation structure, orientation effect on the shrinkage of plastics has a certain impact, the shrinkage caused by orientation is called orientation shrinkage. Orientation shrinkage is related to orientation orientation and degree of orientation. Orientation shrinkage is usually significant along orientation orientation, but smaller in orientation perpendicular to orientation. In addition, the number of orientation shrinkage is generally related to degree of orientation.

Negative shrinkage of some kinds of plastics after demoulding will cause the phenomenon of elastic volume expansion due to the sudden disappearance of cavity pressure. The volume compressibility of plastic products is opposite to the volume elastic expansion, so the elastic effect can be called negative shrinkage. Negative shrinkage is related to the variety of plastics, forming temperature and various pressure factors such as injection pressure and cavity pressure.

Characteristics of contraction formation

The shrinkage of injection products during cooling is generally carried out in three stages. The first and second stages are carried out in the injection mould, from the beginning of filling to the time of demoulding. The third stage is called POST-SHRINKAGE after demoulding until the product is cooled to the ambient temperature.

The shrinkage of the first stage mainly depends on the pressure in the die, and can be compensated by compaction process to a large extent. During the holding period, the temperature of the material decreases and the density increases. After the initial volume shrinkage of the material entering the die cavity, different degrees of compensation can be obtained under the appropriate holding pressure and holding time. The second stage of shrinkage begins after the plastic outside the gate solidifies and continues until the product is demoulded.

In the second stage, the holding pressure can not be transferred to the cavity. In this case, the shrinkage of amorphous plastics is based on the volume expansion coefficient. The shrinkage depends on the cooling rate. The lower the die temperature, the smaller the shrinkage. Crystalline plastics are accompanied by the crystallization process at this time. As the size of the injection products decreases a lot, the higher the mold temperature, the more complete the crystallization, and the larger the shrinkage caused by crystallization.

The shrinkage of the third stage has been transformed into free shrinkage stage. At this time, the product has been completely demoulded. At this time, the volume of Y reduction depends on the temperature difference between the product and the environment, and also depends on the coefficient of thermal expansion.




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Mechanical parts tooling, mould making, injection moulding production


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