ABS PC plastic part mold, plastic injection mold,CNC lather

ABS PC plastic part mold, plastic injection mold,CNC lather

Service Details:

  • Brand:Kayou
  • Serial Number: M-0038
  • 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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ABS PC plastic part mold, plastic injection mold,CNC lather

Description

ABS PC plastic part mold, plastic injection mold,CNC lather

Filling Flow Behavior of Polymer Melt

In the process of plastics processing, the fluidity of polymer melt mainly shows the change of its viscosity. Therefore, the viscosity of polymer melt and its change are the most important variables in plastic processing, and also the main basis for die design. The viscous flow behavior of polymer melt can be measured by capillary rheometer. In industrial production, multi-functional Brabender torque rheometer and Haake Buchler rheometer are mostly used to measure.

The flow and deformation of polymer liquids are realized under stress. The important stresses are shear, tension and compression. Among them, shear stress is the most important for plastic forming, because the pressure drop of polymer melt or dispersion flowing in equipment or die, the required power and the quality of products are all restricted by it. Filling flow filling of polymer melt during injection, also known as filling, means that polymer melt passes through under injection pressure. Flow and forming process in low temperature die cavity after runner and gate. There are many factors affecting the filling flow of polymer melt, which are not only related to various injection molding process parameters, but also affected by the structure of the mould. Among many influencing factors, whether the filling movement is stable and continuous will directly affect the physical changes such as orientation, crystallization, surface quality, shape, dimensional accuracy and mechanical properties of products. Therefore, whether from the production point of view or from the theoretical research, we must discuss the filling movement.

Orientation and Crystallization of Polymers

Molecular orientation is an inevitable phenomenon accompanied by the shear flow of polymer oriented chain molecules during the filling process. When the melt with higher temperature enters the die cavity, it contacts with the cold die cavity wall first. Its viscosity increases rapidly and solidifies, forming a non-flowing solidification layer. However, the melt close to the solidification layer does not solidify quickly because of the insulation effect of the solidification layer, and is still flowing forward. As a result, the molecular chains at the edge of the two layers are stretched, and the length of the chain is arranged along the flowing direction, which is the molecular orientation. With the cooling of the melt, the solidification layer increases and the orientation layer develops towards the center. Generally speaking, the cortex near the cavity wall of the injection part has no orientation, the orientation near the cortex is the largest, the orientation near the center layer is the smallest, and the orientation near the gate of the whole plastic part (plastic part for short) is the largest.

The result of orientation on plastic parts is anisotropy of mechanical properties and shrinkage. The plastic parts with too large orientation are prone to crack because of the large internal stress, and the shape and size stability are poor. Orientation also makes the thermal conductivity of plastic parts different in different directions. For optical plastic parts, orientation will make the refractive index of plastic parts different in different directions.

There are many factors affecting orientation. It is related to the types and properties of plastics, the sensitivity to shear rate and the wall thickness of plastic parts. In addition, the location, number and section size of the gate in the die design have a significant impact on the orientation direction, orientation degree and orientation distribution of the parts. Therefore, it has a great influence on the mechanical properties, some physical properties, shrinkage and uniformity of plastic parts. It is one of the important issues that must be carefully considered in die design.

In addition to the orientation of molecular chains, the crystallization of molecular chains still exists in polymer crystalline plastics during injection moulding. When the melt is cooled below the melting point in the cavity, the molecular chain begins to crystallize. The crystallization of polymers is an orderly arrangement of molecular chains in space. The degree of crystallization of molecular chains in injection moulding depends first on the crystallization ability of materials. The orderly arrangement of molecules requires a certain amount of energy and time, so the temperature environment has a significant impact on the crystallization. There is a maximum crystallization rate temperature between melting point and glass transition temperature for any crystalline plastics. If the mould temperature is controlled near this temperature, it will undoubtedly be beneficial to obtain the plastic parts with the largest crystallinity; if the mould temperature is low, the plastic parts with smaller crystallinity can only be obtained when the melt is rapidly cooled. Some additives, such as pigments and lubricants, can act as nucleating agents and increase the crystallization center, which can produce finer grains and change the crystallization rate of plastic parts. These additives create favorable conditions for continuous crystallization after heat treatment of plastic parts, and change the grain size and crystallinity of plastic parts. The crystallization of plastics will reduce the volume of plastic parts, increase the shrinkage rate, and decrease the friction coefficient and transparency.

 

 

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FAX :
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