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PVC Foaming sheet and WPC production

- Jul 06, 2018 -

1.Production process  Moulding technology and equipment

1). Mixing and feeding  

Wood fiber is the strong water imbibition.The water content is about 15% or more commonly, inorganic filler(CaCo3) is around 5%.The water content affects production stability and product quality. such as foaming ratio, the bibulous rate of products, cell structure,the deformation and  weather resistance and other physical properties.So water content is best kept within 1%.

Reasonable control the moisture content of fiber and packing:

A:Adding Wood powder,CaCo3 to high speed mixer.  

B: Mixing to 100 degrees

C: Adding a little coupling agent and mixed to 110-115 degrees.

D:Turn off the motor and keep mixer open 2-3 minutes

E:Add PVC, stabilizer and mix to 80 degrees.

F: Add lubricant additives and others to 100 degrees

G: Add processing aids,Foaming agent to 120-125 degrees and then discharge powder.

H:After unloading the motor and open the cover for 2-3 minutes and then mix the next lot of material (best mix five Lot and then clean the mixer)

I:Cooling the mixed compound to 40 degree and feed to the extruders.

Please pay attention to the mixing temperature and time. Low-speed mixing takes about 20 to 25 minutes and high-speed mixing takes 12 to 15 minutes ( Set temperature 125 degrees).

If the mixing Process is not good. It easily caused the  "bridging" and "holding rod" problems.

 

2.Mold temperature

A:Extrusion process:

Pay attention to the following points:

The key to setting the temperature for each section is the compression section, measuring section and mould. It affects the foaming rate and color. Foaming is mainly the setting of the temperature at compression section and the measurement section, the molding is mainly affected by the mold temperature.

B. The normal operation of each fan section.

C. The current size and stability of the host. If the current fluctuation of the host machine is large, it indicates that CaCo3,Lubricants,processing aid is not evenly distributed with the wood powder and PVC.

D. The speed of the host must remain the same, because the speed will affect the foaming rate,color,glossness.

Please pay attention:Under the condition of full plasticization, low temperature extrusion should be better performance.It can ensure the bubble hole has good shape and small diameter.Feeding zone temperature should be controlled under 165 ℃, compression and homogenization between 160 ~ 180 ℃, the nose and mouth mold in under 160 ℃.

3.The screw rotation speed

The effect of screw rotation speed of the foam is mainly embodied in the following aspects:

A:It impacts the extrusion stress, the higher the speed, the higher pressure in the extruder. The more bubble holes and foaming rate. 

B: However, the pressure can not be too high. The higher the rotating speed of the screw, the stronger shear action, when the shear is too strong, it is easy to cause the bubble hole to merge or break, which affects the quality of the foaming.

C:the screw rotation speed is too high or too low, so that the residence time is too short or too long, it is easy to occur in advance foaming or insufficient foaming agent decomposition and other phenomena, which is not conducive to the formation of uniform and dense bubble hole structure.

Please pay attention: The screw speed is generally between 12 and 18r/min.

 

4.Extrusion pressure

If the extrusion pressure is insufficient,it will cause product surface roughness and low strength. However,the high extrusion pressure is not good for the growth of bubble holes. The proper nose pressure can be obtained by adjusting screw speed, head temperature and die shape.

 

5.Molding equipment

The single screw extruder mainly uses friction to transport materials, and the mixing effect is poor. The wood powder stays in the cylinder for a long time and is easy to scorch. In order to improve the mixing effect of PVC/wood plastic, used for PVC/wood plastic processing of single screw mixing zone should be set up, or granulation first, and then use aggregate extrusion molding, but the process consumes additives, reduces the performance of PVC.

 

 

5、FREQUENTLY ASKED QUESTIONS(FAQ)

 

No.

Abnormality

Reason

Solution

1

Yellow color

Lack of stabilizer

Adding more stabilizer

Lack of external lubricant, more friction and resulting in material decomposition

Adding more external lubricant

Too high temperature setting

Lower temperature setting

2

The middle of the surface is yellowed

 

Mold  temperature setting is high

 

Lower temperature

Lack of external lubricant

Adding more external lubricant

The temperature of zone 5 is high

 

Lower temperature

3

uneven thickness

 

The gap between the die lips is not reasonable

Adjust the die lip thickness

Improper adjustment of choke block

 

Adjust the block

external lubricant too much

Lower external lubricant

Lack of inernal lubricant

Adding more internal lubricant

The mold temperature setting is not reasonable

 

Adjust the mold

4

 Brittle performance

The temperature of the extruder is set too high

 

Decrease temperature

The temperature of the extruder is set too low

Increase temperature

Unreasonable formula

Formula adjustment 

5

The surface of the board is not smooth

 

Lack of external lubricant

Adding more external lubricant

Lack of processing aid

Adding more processing aid

Insufficient dispersion of fillers or additives

 

Adjust adding dosage

 

Mold temperature setting is too low

 

Increase  mold temperature

The temperature setting of extruder and mould is too high

 

Decrease temperature

6

Fishbone pattern

The viscosity Foaming regulator is too high

 

Change Foaming regulator

The temperature setting of the extruder is too low

 

Increase  temperature

The Mold temperature setting is too low

Increase  mold temperature

Hauling speed is too fast

Lower the hauling speed

7

There are big bubbles in the board

 

The melt strength is not strong enough

 

Increase  Foaming regulator dosage

The temperature in zone 5 of the extruder is too high

 

Decrease temperature

The Mold temperature setting is too high

Decrease temperature

Impurity

Pay attention to material impurities

 

Large particle size of recycled PVC

Grinding again

 

 


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