[Science stickers] Common problems and solutions in the production of PVC pipes

Serial number

Abnormal phenomenon

the reason

Solution

Remarks

1

Surface discoloration

The temperature of the barrel or head is too high, causing the material to decompose

Cool down

The material is not stable enough and decomposes

Check whether the PVC resin or stabilizer causes insufficient stability, replace the resin or stabilizer, or increase the number of stabilizers.

Temperature instrument control failure, decomposition caused by over-temperature

Adjust and repair the instrument

2

There are yellow-brown stripes or colored spots on the surface of the pipe

There are dead corners in the mold or the shunt shuttle or cause stagnation and paste, resulting in local decomposition streaks

Clean up

Local paste, dead corners and increased friction on the surface of the pipe will decompose and form streaks

Uneven mixing or impurities in the material can cause partial decomposition and form surface color spots

Determine the specific reasons, improve the mixing process or replace the problematic raw materials

3

Matte appearance

Low die temperature

Increase the die temperature and increase the amount of ACR to increase the shear

Bright ACR processing aid can significantly improve surface finish even at lower temperatures

Shear rate is too high, melt fracture

Properly increase the material temperature, increase the amount of ACR or reduce the traction speed

The temperature of the die is too high or the inner surface finish is poor

Cool down, reduce roughness

Poor plasticization

Increase temperature, increase processing aids

The external lubricant content is too low

Under the premise of ensuring the plasticization of materials, add external lubricants appropriately

There are too few external cuts, which makes the material easy to bond to the metal surface and affects the surface smoothness.

The particle size of CaC03 is too large or the particle size distribution is too wide

Replace the applicable calcium carbonate

4

Wrinkles on the pipe surface

Uneven temperature around the die

Check the heating ring

Poor cooling

And increase the cooling water or reduce the cooling water decline

Towing is too slow

Speed ​​up traction

Impurities in the material

Exchange of raw materials

Core touch temperature is too low

Increase core mold temperature

Body temperature is too low

Increase the body temperature

Towing speed is too fast

slow down

5

Rough inner wall

Core touch temperature is too low

Increase the core temperature or add work aids

Low temperature causes poor plasticization, and the inner wall is difficult to heat up at the die, so roughness occurs

The barrel temperature is too low, and the plasticization is not good

increase temperature

When raising the temperature makes it difficult to control the temperature in the subsequent stage, you can increase the ACR processing aid without raising the temperature, and the same effect can be obtained

The temperature of the money rod is too high

Enhanced screw cooling

6

Bubbles on the tube wall

Overwhelming

dry

The vacuum at the vacuum exhaust hole after the second section of the barrel is too low or blocked

Check the working condition of the pump, whether the pipeline is blocked (caused by pumping powder))

Decomposition (head temperature is too high)

Reduce the temperature

7

Sentences with uneven wall thickness

Mouth touch, core selection, different hearts

Modulation

The temperature of the machine head is uneven, and the output is fast or slow

Check the heating ring, check the screw for pulsation

Unsteady traction speed

Check and repair tractor

The vacuum of the vacuum tank fluctuates

Check the vacuum pump and its pipeline

8

Uneven inner wall

Screw temperature is too high

Decrease screw temperature

The screw speed is too fast, causing melt rupture

Sim Speed

9

Pipe droop

Uneven wall thickness

Same as 7

Uneven temperature around the nose

Check the heating coil

The fuselage, sizing groove, and traction are not on the same axis

Adjust to an axis

The cooling holes at both ends are not in a straight line

Adjust to an axis

Uneven water output from cooling tank nozzle

Adjust and replace the nozzle

10

Bubbles in section

Material high moisture

Dry or change nozzle

The mixing temperature is low, and the water is not discharged

Increase mixing temperature

Exhaust hole vacuum is low or pipeline is blocked

Check the vacuum pump and its pipeline

The temperature of the fuselage or horizontal head is too high

Reduce the temperature

Poor thermal stability of mixed ingredients

Check and modify the formula

11

The impact strength of the pipe is not fully qualified

Low processing temperature

Increase the processing temperature or increase the ACR processing aid

Poor quality of the original paving

Replace raw materials

Low back pressure

Change process conditions

If the back pressure is low due to the mold, and the process cannot be adjusted, the mold can only be repaired

Poor formula

Improve formula

High processing temperature (plasticization, excessive or decomposition)

Lower Wenqian

When using CPE impact modification, the screw speed is too fast and the shear rate is too high, so that the CPE is unevenly dispersed and is in a piled state, which reduces the impact resistance.

Reduce screw cuff speed

Reducing the screw speed will reduce the production capacity. Switch to ACR as the best solution for the impact modifier. The ACR temperature and shear rate have good adaptability.

11

The impact strength of the pipe is not fully qualified

Low processing temperature

Increase the processing temperature or increase the ACR processing aid

Poor quality of the original paving

Replace raw materials

Low back pressure

Change process conditions

If the back pressure is low due to the mold, and the process cannot be adjusted, the mold can only be repaired

Poor formula

Improve formula

High processing temperature (plasticization, excessive or decomposition)

Reduce the temperature

When using CPE impact modification, the speed of the rod is too fast, and the shear rate is too high, so that the CPE is unevenly dispersed, and it is in a piled state, and the impact resistance is reduced.

Reduce screw speed

Reducing the screw speed will reduce the production capacity. Switch to ACR as the best solution for the impact modifier. ACR has good adaptability to temperature and shear rate.

Cooling water temperature is too low (mostly in winter), excessive internal stress due to sudden cooling

Adjust the cooling water temperature

Poor exhaust, causing pores in the pipe

Adjust the vacuum degree of the exhaust hole, and eliminate it when there is blockage

Defective particles, forming micro-cracks in the pipe wall, reducing the impact strength of the pipe

The sluggish particles may come from impurities, agglomerated CaCO3, slip agent, unplasticized PVC particles, etc., according to specific reasons, take measures, such as sieving the dry mixture

Defective particles refer to the particles that are larger and affect the material. Defective particles will also make the pipe hydraulic test unqualified.

12

The pipe pressure test is not suitable

Poor plasticization and reduced tensile strength

Increase or increase the number of processing aids

The quality of PVC resin is not good, the poly content is low, or the molecular weight distribution is too wide, or the molecular structure is trapped

Replace PVC

The modifier has low tensile strength, which reduces the tensile strength of the pipe.

Replace the impact modifier with higher tensile strength. For ACR and CPE, the impact on the tensile strength of the pipe is much smaller.

The factors in Article 11 will also cause low tensile strength of the pipe, which will make the hydraulic test unqualified.

13

Dichloromethane immersion test is not qualified

Poor plasticization

Increase processing temperature or increase ACR processing aid

For formulas with high filling components such as calcium carbonate and carbon black, it is often difficult to increase the degree of plasticization by increasing the processing temperature. At this time, it is necessary to add ACR processing aids.

14

Unqualified longitudinal retraction rate

The composition of high-resistance substances such as elastic rubber body is too high, such as CPE

Replace the components in the formula that have too high a recovery rate

The extrusion speed does not match the index speed, and the traction speed is too fast

Reduce traction speed

Poor cooling

Decrease the temperature of the cooling water or increase the amount of cooling water

The head temperature is too high

Reduce the temperature