Abnormal Phenomena in Production of PVC Compound

1. Production processes of cable compound.

Single screw extruder production process flow

Raw materials – ingredients —- high speed kneader – single screw extruder – air cooling – screening magnetic separation – metering – packaging.

Single screw double step extruder production process flow

Raw materials – ingredients – high-speed kneading machine – single screw double order granulator – cooling and drying, screening magnetic separation – measurement – packing.

Twin screw extruder production process flow

Raw materials — ingredients — high speed kneader — twin screw extruder — air cooling — screening and magnetic separation — metering — packaging.

Roller press granulation production process

Raw materials – ingredients – high-speed kneading machine – mixer – double roller mixing mill – cooling water tank – drying – granulator – screening magnetic separation – measurement – packing.

2. Abnormal phenomena and possible causes in production of PVC compound

Phenomenon 1: Particles gathering (in regular shape)

Possible causes:

The material is not evenly mixed, the plastcizer wrapped the PVC resin.

When mixing different batches of material, the cylinder is not cleaned up, and the residual material is over-gelatinized.

Temperature is not high enough, gelatinization is bad, so particles occurs. We can add a filter to improve the back pressure, so that PVC with poor gelatinization could reflux.

Phenomenon 2: Impurity particles (in Irregularly shaped, angular particles)

Possible causes:

The impurities mainly come from CCR and CaCO3 in raw materials.The impurity from the stabilizer is very small: less in the calcium zinc series and more in the lead series.

Phenomenon 3: Agglomeration

Possible causes:

Extrusion temperature is too high, air cooler cooling efficiency is low, resulting in agglomeration;

If the extrusion temperature is normal, the appearance of agglomeration is generally related to the stabilizer in the raw material. Agglomeration is operationally related and can be avoided by controlling the temperature.

Phenomenon 4: Color Difference

Possible causes:

Human factor: color matching

Material related: The stabilizer is poor quality. During the color matching process, the PVC deteriorates and turns yellow when being stirred and heated.

Phenomenon 5: Pores

Possible causes: 

Human factor: High processing temperature and insufficient lubricant lead to gasification of low molecular weight materials.

Machine: the air entrained by the material is extruded, and bad engine exhaust caused small pores.

Phenomenon 6: Rough appearance

Possible causes:

The particle size of CaCO3 is large.

The proportion of lubricant is low.