Processing problems and solutions for PVC transparent profiles extrusion production

August 2, 2019

 

Processing problems and solutions for PVC transparent profiles extrusion production
 

PVC transparent extrusion progfile is one of the main varieties of rigid PVC. Usually, it is produced by cone-type twin-screw extrusion when it is directly produced with pvc resin powder. It is generally produced by single-screw extrusion using pvc compounds/granules/pellets. Common problems encountered in the production process are: bubbles, more crystal points, yellowing of the sheet and other issues.

 

1. Yellowing color problem
The causes and solutions are:
First, PVC itself is stable and poor
If it is a new PVC resin manufacturer, it may be that the PVC itself is stable and can be changed for PVC. However, even the brand PVC that has been used for a long time may be caused by the PVC resin itself, because even if the PVC produced by the same manufacturer has different batches, the quality may be different.

 

Second, insufficient stabilizer
 

Third, the temperature controller has a problem
The display temperature is lower than the actual temperature. If the temperature is too high, the PVC will decompose and yellow. At this time, it is necessary to re-examine the temperature controller. The method is very simple, and the mercury thermometer is used for calibration. In actual production, due to the looseness of the thermocouple and the adhesion of materials, the temperature controller will show a difference between the temperature and the actual temperature. It is also recommended to use a high quality temperature controller.
 
2. The bubbles problem
Causes:
1). Excessive moisture in PVC raw materials: If it is rainy in summer, the raw materials are damp, that is, the water may not be fully discharged in the barrel, heated to expand, and then bubbles are formed in the sheet.
2). Other additives may also have too high moisture content.
In summary, the solution can be adopted: appropriately prolong the mixing time of the hot mixer and use a cooling mixer. The moisture of the raw material can be effectively removed.
 
3. The number of crystal points in the sheet exceeds the standard, also known as fisheye

 

A common cause of crystal lattice generation is that some PVC resin particles are not plasticized or poorly plasticized. The reasons for the formation are: the quality of the PVC resin itself is not good. Under the condition that PVC resin is not replaced, the solution is:
 

First, properly extend the mixing time and increase the mixing temperature to promote the absorption of additives. And the use of high-quality mixing units, the pre-plasticizing effect of the mixing unit on the material is irreplaceable.
 

Second, the mixed raw materials can be placed for half a day or one day, and allowed to mature and then used.
 

Third, the set temperature of the barrel can be appropriately increased, the screw speed can be increased, and the head pressure can be increased to further improve the plasticizing performance.
 

Fourth, in terms of formula, we must carefully select suitable additives and additives. At present, the additive market is more chaotic, and the product quality is very different. We must carefully select and find a better balance between price and performance. .
 

In summary, we must consider the above various reasons and choose the optimal solution. Some solutions have contradictory relationships. For example, raising the temperature may cause the sheet to yellow, and adding more stabilizers may cause the cost to rise. Only in practice will explore the way forward.
 

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