Analysis the problems of plastic granulation-hollowness, overflowing, bridging flocculation.

June 25, 2019

Analysis the problems of plastic granulation-hollowness, overflowing, bridging flocculation.

 

 

Hollowness problem

1. Exhaust (or steam) is not smooth
Due to natural exhaust or vacuum exhaustion (may be too heavy in the material itself, it may also be decomposed by additives such as flame retardants, there may be vacuum blockage or vacuum is too small or air leaks or vacuum gaskets are too high) , the presence of gas (vapor) in the particles, forming a hollow material.
2. Poor plasticization
The processing temperature is low, the material is not completely plasticized, the light (small hole) causes the particles to be hollow, and the heavy one (large hole) causes the broken strip.

There are too many low melting point auxiliaries (including EBS or PETS). In the case of weak shearing of the screw, the hollow material is formed due to poor plasticization of the material.

3. The water temperature is too low
The cooling water temperature is too low, the material shrinks with water, causing shrinkage pores. This kind of phenomenon is mainly for crystalline plastics; in general, crystalline plastics (such as PP, PA, PBT, etc.) should use low water temperature, non-crystalline plastics (such as ABS, PC/ABS, HIPS, etc.) use high water temperature.

 

 

Overflowing problem

1. Natural exhaust venting
The feed speed does not match the host speed, and the feed speed is reduced or the host speed is increased.
The temperature in the area from the feeding section to the natural exhaust port is too low, the material is not plasticized, and under the action of the screw extrusion, the raw material is generated.
The temperature near the natural exhaust port is too high, and the viscosity of the material is seriously degraded. In this section, the screw slips and the material cannot be transported to the front section in time, and the clinker is generated under the subsequent crushing action of the stream.
The natural exhaust port position of the screw does not match the position of the natural exhaust port of the barrel, causing a flue. Generally speaking, the reverse conveying element or the reverse meshing block is not provided here, and the pressure of the natural exhaust port groove cannot be reduced, and the material is caused to be generated by the subsequent flow extrusion.

2. Vacuum port material
The vacuum pumping force is too large, and the material is sucked into the vacuum pipe to cause the material to be thrown.
There is no reverse conveying element or reverse meshing block in the screw vacuum position, which can not reduce the pressure of the vacuum section screw groove, and cause the material to be discharged under the action of vacuuming.
The temperature of the vacuum section is too high, and the viscosity of the material is seriously degraded. The screw of this section is slippery, and the material cannot be transported to the front section in time, and the material is caused by vacuum suction.
The extrusion processing temperature is too low, the material is not plasticized or the flame retardant and the like are not sufficiently dispersed in the resin, and under the action of vacuum suction, the material is caused to be a waste.
The pressure on the machine head is too large (the reasons include: blockage of the die, too much filter net, too low temperature of the machine head, etc.), causing an increase in backflow, causing a flue under the action of vacuum pumping.

Bridging problem
Filler
Too much filler, moisture absorption, agglomeration, resulting in increased friction between the mixture and the hopper wall, adding a white lubricant such as "white oil" to reduce the friction between the mixture and the hopper wall and the mixture, can solve this problem.

2. Agglomeration
Mixing agglomerates (including high temperature agglomerates and liquid additives added too much to agglomerate), reducing drying temperature or high mixing time, reducing the amount of liquid additives added, adding powdery resin that absorbs "oily" substances Or additives (such as high-glue powder, AS powder, PP powder, etc.) can solve this problem.

 

3.Bridging problem
1. Filler.

Too much filler, moisture absorption, agglomeration, resulting in increased friction between the mixture and the hopper wall, adding a white lubricant such as "white oil" to reduce the friction between the mixture and the hopper wall and the mixture, can solve this problem.

2. Agglomeration

Mixing agglomerates (including high temperature agglomerates and liquid additives added too much to agglomerate), reducing drying temperature or high mixing time, reducing the amount of liquid additives added, adding powdery resin that absorbs "oily" substances Or additives (such as high-glue powder, AS powder, PP powder, etc.) can solve this problem.

3.Bridging at the feed opening

Sometimes the bridging problem can occur in the feed opening. This is mainly because the melting point of some processing aids is too low, the processing temperature in the first and second zones is too high, and the material softens at the bottom of the feed silo and adheres to the equipment wall. This will solve the problem by causing difficulties in subsequent material feeding and appropriately reducing the processing temperature in the first and second zones.

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