Mould for household product, plastic mold making, tooling manufacture

Mould for household product, plastic mold making, tooling manufacture

Service Details:

  • Brand:Kayou
  • Serial Number: M-0163
  • 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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Mould for household product, plastic mold making, tooling manufacture

Description

Mould for household product, plastic mold making, tooling manufacture

Shrinkage of plastic parts is usually expressed by shrinkage rate. Measuring shrinkage rate generally refers to the size change within 24 hours. After demoulding of injection moulded products, the shrinkage produced in 6 hours accounted for 90% of the total shrinkage rate, and the remaining shrinkage occurred in 10 days. However, the POST-SHRINKAGE of products is different. Some products take months or longer.

Influencing factors of contraction

The factors affecting the shrinkage of injection moulded products include the characteristics of plastics, the temperature of barrel, the temperature of mould, the injection pressure and pressure, the holding time, the thickness of parts, the size of gate, etc.

The shrinkage of amorphous plastics is greater than that of semi-crystalline and crystalline plastics. The higher the crystallinity, the greater the shrinkage. If the shrinkage of amorphous plastic polystyrene is 0.5%~0.6%, polyvinyl chloride is 0.4%~0.5%, while the shrinkage of crystalline plastic polypropylene is 1.8%~2.1%. For the same plastics, the shrinkage of plastics with relatively high relative molecular mass and wide relative molecular mass distribution is larger. The shrinkage rate of plastics with inorganic filler and reinforcing agent is smaller.

Due to the orientation of filling, the shrinkage of HDPE plastics in the direction of material flow is larger than that in the direction of flow due to molecular relaxation. For example, the shrinkage of HDPE plastics in the direction of flow is 2.8%~3.2% and that in the direction of flow is 1.8%~2%.

Increasing the barrel temperature increases the injection temperature, reduces the specific volume change of the material, increases the density of the product and reduces the shrinkage rate.

The effect of die temperature and die temperature on shrinkage rate is reflected in the fact that die temperature determines the cooling rate of melt. For crystalline and amorphous plastics, the larger the cooling rate, the smaller the shrinkage rate.

Injection pressure and packing pressure have the most significant effect on shrinkage. Increasing injection pressure and packing pressure can make the product compact and shrinkage small. For complex products, the difference of shrinkage can be reduced. The shrinkage in the die can be compensated by increasing the holding pressure.

The longer the holding time is, the better the filling material will be and the smaller the shrinkage will be.

The thicker the workpiece is, the larger the shrinkage is. As shown in Figure 10-15, the position and size of the gate will affect the flow characteristics of melt in the die cavity, shrinkage and deformation of the product. When the gate position is set in the center of flat products, warpage deformation is easy to occur due to different shrinkage rates along each vertical direction. Large gate size is favorable for pressure transmission and strong feeding.

Controlling of Forming Shrinkage

To control the shrinkage rate of products more accurately, we can start from the following aspects.

process control

The precise control of die temperature should not cause too large deviation in the control of die temperature.

Material temperature should be appropriately high, not too high.

Appropriate increase of injection pressure.

Increase injection speed

Extending Pressure Holding Time

Material aspect

Molding materials should be uniform in size.

Choose materials with good fluidity.

To control the moisture content of materials, some materials must be dried when they are processed.

Reinforcement material or inorganic filling material can be selected.

Mold aspect

Appropriate increase of gate section area under possible conditions

Shorten the shunt as much as possible

Temperature control system is better in order to control accurately.

 

 

 

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Mould for household product, plastic mold making, tooling manufacture

 

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