Injection mould of household product, high quality precision plastic mold

Injection mould of household product, high quality precision plastic mold

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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Injection mould of household product, high quality precision plastic mold

Description

Injection mould of household product, high quality precision plastic mold

Residual stress can be defined as local stress existing in any part of the body without external force. The resultant force or moment generated by residual stress must be zero, and the distribution of residual stress should be uniform to avoid warping of the product due to the effect of stress.

Residual stresses in injection parts arise from two aspects:

The stress and shear stress produced by the flow of hot melt polymer in injection and holding stage under non-isothermal conditions in the die cavity are residual flow stress in the cooling and solidification stage of the product.

When the viscoelastic polymer is cooled and passed through the glass transition temperature, the uneven density change and uneven cooling form will produce residual stress.

Flow residual stress

The flow stress is mainly manifested in the filling stage of the cavity, and the holding stage is the maintenance and supplement of the flow stress. In the process of injection, the high pressure strain rate of plastic melt causes shear stress. At the same time, the melt is also subjected to tensile stress. Therefore, the stress is caused by external force, which is the most typical external stress, because the orientation, also known as orientation stress, is formed at this time.

The orientation stress is also affected by the process parameters which affect the orientation of macromolecules. The temperature of injection melt has the greatest influence on orientation stress and degree of orientation. Increasing melt temperature decreases melt viscosity and shear stress and degree of orientation. At the same time, the relaxation degree of orientation stress increases at high melt temperature, and if the melt temperature is lower, the melt viscosity is higher. The higher pressure must be selected for filling, which will increase the shear rate and the orientation force.

Mold temperature is directly related to the cooling rate of melt entering the cavity, which has a significant effect on the dissociation orientation of oriented macromolecules after the melt stops. Increasing die temperature and slowing down the cooling rate of melt are beneficial to the dissociation orientation of macromolecules.

Increasing the injection pressure and prolonging the holding time will increase the orientation stress due to the increase of shear stress and shear rate until the holding time stops with the freezing of the gate. In addition, the orientation stress is related to the wall thickness of the products, and the orientation stress of the thick-walled products is smaller.

Thermal residual stress

Because the cooling of each part of the cavity is not uniform, resulting in temperature difference, resulting in uneven contraction, resulting in stress, known as temperature stress or thermal residual stress. When injection moulding thick-walled products, the high temperature melt enters the cavity, the temperature difference between the melt and the cavity is large. Because of the large heat capacity of the plastic and the small thermal conductivity, the melt near the mould rapidly cooles to form a solidified surface, which will hinder the free shrinkage of the product when it continues to cool. As a result, the internal stress of the product is generated.

The larger the ratio of surface area to volume, the faster the surface cooling, the higher the orientation stress and temperature stress. Besides flow stress and thermal residual stress, there are volume unbalance stress and deformation stress. These stresses are often not the main aspects of stress, and the impact on the physical and mechanical properties of products is not the main.

 

 

 

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injection mould of household product, high quality precision plastic mold

 

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FAX :
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