Analysis of the quality problem of PVC hose extrusion molding

Analysis of the quality problem of PVC hose extrusion molding

1. the surface of the tube is not smooth and has wrinkles

The process temperature of the extruder is too high or the temperature distribution is unreasonable, and the process condition of the temperature rising from the feeding segment to the molding die is not reached. The temperature control mode should be adjusted appropriately.

The temperature of each part of the module is not uniform. There may be local heating elements not working. Proper improvement of heating arrangement should be made.

2. tube diameter is not round

The temperature of the melting material is high and the process temperature of the mould and cylinder should be reduced properly.

The cooling rate of the tube billet extruded from the molding mold is not uniform. The cooling method should be properly adjusted so that the circumference of the tube can be cooled evenly.

The diameter of the diameter is not round and should be checked and repaired.

3. the diameter of the diameter of the pipe is large

The rotation of the screw is unstable, making the extrusion flow unstable. Check the belt drive in the transmission system, and there may be a belt work slip, which should be adjusted or replaced.

The running of the tractor is not stable, which causes the drawing ratio of the tube billet to the extrusion die is not fixed, which affects the longitudinal dimension precision of the pipe. Adjust the drive system of control or overhaul.

The feeding at the mouth of the cylinder is not uniform, and it should check whether there is any material “bridging” in the hopper.

In the case of the inner pressure of the tube billet, it is possible that the air leakage phenomenon or compressed air input should not be stable and should be inspected and repaired.

4. the thickness of the pipe circumference is uneven

The machining precision of parts and the concentricity of the parts in the mold are not equal to the quality requirement. The result is that the flow of the molten material in the inner cavity of the mould is not uniform. The machining quality of each part should be checked and the accuracy of the concentricity after assembly should be checked. The machining should be redesigned when necessary.

The accuracy of the concentricity adjustment of the die and mandrel is not in place, and the circular clearance between the mouth mould and the core rod is not uniform. The gap between die flow should be adjusted.

5. surface roughness of the tube surface

The inner diameter or outer diameter of the die or mandrel is poor, rough and uneven. The roughness of the working face should not be greater than 0.32 mu m.

The process temperature control of mold forming section is unreasonable, and it is easy to be high or low. Attention should be paid to the temperature regulation control here.

The process temperature of machine tube is low and the raw material is not fully plasticized. The heating temperature of the cylinder should be raised appropriately.

6. there are black spots or yellow stripes on the surface of the pipe

The cylinder or screw is badly worn, and the melting material stays in the cylinder for too long. The assembly clearance of the cylinder and screw should be checked and replaced when necessary.

The flow of molten material in molding mould is not smooth, and there is a diap-retarded area, which causes partial decomposition. Respond to die repair, replace the precision parts.

The divergence cone Angle is large, which has great resistance to material flow. The mould structure should be modified.

The composition of raw materials is unreasonable and the heat stability of raw materials is poor. The use of stabilizer in raw materials should be adjusted.

The lubricating oil of the bearing part of the rear screw is too large, and the flow direction is mixed with the raw material. Note the amount of grease used here.