Plastic profile technology

The molding process of plastic profiles is divided into three stages:

The first stage is the plasticization of raw materials, that is, through the heating and mixing of the extruder, the solid raw materials become uniform viscous fluid;

The second stage is molding, that is, under the action of extruder extrusion parts, the molten material is continuously passed through the molding head at a certain pressure and speed, so as to obtain a certain section shape;

The third stage is cooling shaping, that is, through different cooling methods, the molten material will be fixed down the shape that has been obtained, and become a solid state.

It can be seen that there are many factors that affect the quality of products, including a series of factors such as materials, extruders, extrusion molds, and tractors. Common plastic profile quality defects include uneven wall thickness, bending, uneven surface, surface scratches, profile vibration, decomposition line, etc. The following quality defects are analyzed one by one, and corresponding solutions are given.

1. Uneven wall thickness

1. Incorrect positioning of the mouth template

Due to the inaccurate positioning of the template in the die head, the gap between the die and the mouth is uneven, which causes the degree of Barras effect to be different, and the wall thickness of the product is uneven after cooling.

Countermeasures: Correct the positioning pins between the templates and adjust the gap between the die.

2, the molding length of the mouth die is short

Determining the forming length of the die is the key to the design of the profile extruder head. For different products, the molding length is not the same, the resistance of the wall thickness is small, the flow rate is fast; The resistance of thin walls is large and the flow rate is slow. The molding length of the wall thickness product should be longer than that of the wall thin product, and the molding length should be used to adjust the speed so that the material flow at the exit is uniform. Otherwise, the product will appear uneven thickness and wrinkles

Countermeasures: Refer to the relevant manual, appropriately extend the mouth die molding length.

3, die head heating uneven

Due to the uneven heating temperature of the heating plate or heating ring of the die head, the viscosity of the polymer melt in the die head is inconsistent, and the wall thickness is uneven after cooling and shrinking.

Countermeasure: Adjust the temperature of the heating plate or heating ring.

4, die wear is not uniform

The die is a part of the surface of the molded profile, which is in direct contact with the material and will cause wear and corrosion. The uneven wear of the die is caused by the different flow rate, flow rate, wall pressure and resistance of the material in different parts of the inner wall of the die and the diverter cone. The plastic can get a certain shape and size after passing through the mouth mold. Therefore, die wear will directly lead to uneven thickness.

Countermeasures: Using the method of "throttling and open source" to repair the gap of the port template or the Angle of the shunt cone.

5, the material contains impurities to block the flow path