Common problems of PVC sheets

The vertical thickness deviation of PVC sheet is large
① The temperature control of the barrel is unstable, resulting in unstable melt flow rate. The temperature of the barrel should be adjusted to stabilize it.
② The unstable screw speed leads to unstable extrusion volume. The process parameters of the extruder should be adjusted to ensure stable extrusion.
③ The roller speed in the three roller calender is unstable. The speed of the three roller calender should be adjusted.
④ The traction speed is unstable, fluctuating fast and slow. The traction speed should be adjusted to ensure smooth operation.

Uneven lateral thickness of PVC sheet
① The design of the molding mold is unreasonable, and the fabric flow in the cross-section is uneven. The mold should be modified to ensure even discharge from the mouth mold.
② The adjustment of the gap between the mold lips is unreasonable and uneven. The middle gap should be slightly smaller than the gap on both sides.
③ The gap deviation between the three rollers of the three roller calender is relatively large, and the gap between the three rollers should be made even.
④ The height selection and processing of the three rollers are unreasonable. The height of the roller surface should be appropriately adjusted.

The surface of PVC sheet is rough and lacks luster
① Rough or sticky material on the three roll working surface. The working surface of the three rollers should be cleaned and polished to achieve a smooth surface.
② The roller temperature of the calender is too low, and the temperature of the three rollers should be appropriately increased.
③ The surface of the mold lip is not smooth and should be cleaned.
④ The filter screen is broken and should be replaced with a new one.
 

The surface of the board has horizontal lines

① Uneven mixing of materials causes fluctuations in extrusion volume. It is necessary to switch to uniformly mixed materials and adjust the process parameters of the extruder to ensure good plasticization of the materials and even extrusion volume.
② The barrel temperature fluctuates significantly. The temperature control system of the machine barrel should be checked and adjusted to ensure the accuracy of temperature control.
③ The speed of the three rollers is unstable or there are scratches on the roller surface. The speed of the three rollers should be adjusted to ensure smooth operation; Replace the damaged roller or repair the surface of the roller.
④ The traction speed is unstable or the traction roller pressure is insufficient. The traction speed and tension of the traction roller should be adjusted to ensure smooth traction of the sheet metal.

Longitudinal lines on the surface of the board

① The extrusion temperature is too low, resulting in poor plasticization of the melt. The body and nose temperature should be appropriately increased The gap between the mold lips is too small. It should be appropriately increased.

②The opening of the mold lip is generally equal to or slightly smaller than the thickness of the sheet, which is expanded after extrusion and stretched to the required thickness.

③ The traction speed is too fast. It should be slowed down appropriately. The traction speed should be slightly faster than the extrusion speed.
 

Warping unevenness

① Improper control of roller temperature in the calender, especially when the temperature of the middle and lower rollers is too low. The roller temperature should be controlled within an appropriate range.
② The contact surface between the two ends of the board and the air is too large, and the cooling speed is too fast. The cooling speed is also fast at the thinner parts of the board. When forming, the board bends towards the part that cools first, generating internal stress. In order to reduce internal stress during molding, it is necessary to cool as evenly as possible and reduce stretching.

bubble
①: The raw materials are damp and the moisture content exceeds the standard. The material should be kept low in moisture, and the body and nose temperatures should be too high, causing material decomposition. The processing temperature should be appropriately reduced.

Surface black or discolored stripes and spots

① The temperature of the machine head is too high, causing the material to overheat and decompose. The head temperature should be appropriately reduced.

②There are dead corners inside the nose of the machine, causing the decomposition of stagnant materials. The machine head should be cleaned to eliminate dead corners.

③ There are impurities blocking the nose of the machine, causing stagnation