Analysis and Countermeasures of Common Problems in Plastic Pipe Extrusion

 Today, I will share you some problems often encountered in the extrusion process of plastic pipes and give you some corresponding solutions.

I. Uneven wall thickness

1.Inaccurate positioning of die plate

Due to the inaccurate positioning of the die plate in the die head, the gap between the die and the die is uneven, which leads to different degrees of balas effect and uneven wall thickness of the pipe after cooling.

Countermeasures: correct the positioning pin between the plates and adjust the gap between the dies.

2.The forming length of the die is short

The determination of the forming length of the die is the key to the design of the extruder head. For different pipes, the forming length is used to adjust the speed to make the material flow uniform at the outlet. Otherwise, the pipe will appear uneven thickness and wrinkles.

Countermeasures: according to the relevant manual, appropriately lengthen the molding length of the die.

3.Uneven heating of die head

Due to the uneven heating temperature of the heating plate or heating ring of the die head, the viscosity of the polymer solution in the die head is inconsistent. After cooling and shrinkage, the uneven wall thickness will be produced.

Countermeasures: adjust the temperature of heating plate or heating ring.

4.Uneven wear of die

The die is a part on the surface of the pipe, which will be worn and corroded when it is in direct contact with the material. The uneven wear of the die is caused by the different material flow velocity, flow rate, wall pressure and resistance between the inner wall of the die and the different parts of the splitter cone. The plastic can get a certain shape and size after passing through the die. Therefore, die wear will directly lead to uneven thickness.

Countermeasures: adopt the method of "throttle and open source" to repair the gap of die plate or the angle of splitter cone.

5.The material contains impurities to block the flow channel

The blockage of the flow channel makes the flow velocity at the exit of the die uneven and the material unstable, which leads to the uneven wall thickness of the pipe.

Countermeasures: pay attention to the cleaning of raw materials and clean up the impurities in the die channel.

II. Bending

1.Uneven wall thickness

The uneven wall thickness naturally causes the bending of the pipe after cooling. The causes of uneven wall thickness and the countermeasures are shown in section 1 above.

2.Uneven or inadequate cooling

The melt flow extruded from the die is heat exchanged and cooled in the setting die through cooling and vacuum adsorption. If the cooling of each part of the pipe is inconsistent, the pipe will be bent due to the different cooling shrinkage speed of each part; Or the local temperature of the pipe is still high after it is out of the mold and water tank, and it is not completely cooled. When it continues to cool, the local shrinkage of the pipe will still cause the bending of the pipe.

Countermeasures: reduce the temperature of cooling water, check whether the cooling water path is smooth, adjust the flow of cooling water, increase or block the water hole.

3.Uneven distribution of resistance of setting die

Due to the cooling shrinkage of the molten material in the setting die, there will be a certain resistance. If the resistance distribution is quite different, the local resistance will lead to the inconsistent state of the pipe in the setting die, resulting in the bending of the pipe.

Countermeasures: repair the setting die, increase or decrease the resistance.

3.Inconsistent traction speed

The asynchronous and unsteady speed of the tractor makes the molten material uneven in thickness and fineness, and causes bending after cooling shrinkage.

Countermeasures: repair the tractor and adjust the traction speed.

III. Uneven surface

1.Insufficient cooling

Due to the insufficient cooling of each part of the pipe, the cooling rate of each part is inconsistent, and some parts are formed after shaping, resulting in uneven surface of the product.

Countermeasures: dredge the waterway, increase the water hole, and increase the flow.

2.Insufficient vacuum degree

The geometric shape and dimensional accuracy of plastic pipe are controlled by setting die. After leaving the die head, the pipe deforms seriously under the action of self weight. After entering the setting die, the pipe can fit with the setting die cavity under the action of vacuum adsorption force. If the vacuum degree is not enough, the material does not completely match the cavity, which will lead to uneven pipe surface.

Countermeasures: check the tightness, dredge the airway and improve the vacuum degree.

3.The traction speed is too fast

If the traction speed is too fast, it is inconsistent with the extrusion speed, the traction ratio is too large, and the surface is uneven after cooling.

Countermeasures: adjust the traction speed properly.

IV. Surface scratch

1.The roughness of setting die is not enough

Countermeasures: polishing the inner cavity of the mold.

2.The indirect seam of each plate of setting die is not smooth

Countermeasures: polish each plate of setting die.

Therefore, the failure of plastic pipe extrusion die is not necessarily single, it may be several defects existed at the same time, so it should be analyzed and considered as a unified whole.

The above are the problems often encountered in the extrusion process of plastic pipes, and the corresponding solutions are given. If you need more information, you are welcome to contact us for consultation. Ningbo Fangli Technology Co., Ltd., as a manufacturer with nearly 30 years’ experience of extruder production line equipment, we have a lot of equipment manufacturing experience, and we can provide you with professional technical guidance and equipment procurement suggestions.