Six common problems affecting the quality of PVC foamed sheet, their causes and Solutions
1. yellowing. Extrusion temperature is too high or insufficient stability, the solution, lower processing temperature, if not improved can be adjusted formula, appropriate increase stabilizer and lubricant, can be changed one by one, easy to quickly find the problem, the fastest speed to solve the problem;
2. yellowing in the middle. The main reason is the barrel core temperature mold temperature, the amount of lubricant is also relevant, again and white foaming agent has a certain relationship;
3. Plate Bending. Uneven material flow or cooling is not in place, resulting in uneven material flow is generally a large fluctuation in traction, or the formula is not balanced between internal and external lubrication, machine factors can be easily ruled out Formula adjustment generally in the premise of external lubrication as little as possible to adjust internal lubrication will be very good, while ensuring the cooling uniform in place.
4. Bubbles appear in the Cross section or layer by layer. Can Be attributed to a point, is not enough melt strength, melt strength is not enough because 1. Excessive foaming agent or foam regulator insufficient or the ratio of the two does not coordinate, or foam regulator quality problems 2. Poor plasticizing, low processing temperature or excessive lubrication
Foaming plastic cross-section of the bubble or WEAR BUBBLE TWO FACTORS:
A, because the local strength of the melt itself is too low, the bubble is formed from the outside in;
B, because the pressure around the melt is small, local bubble occurred expansion, strength weakened, bubble is formed from inside to outside. In production practice, there is no obvious difference between the two effects, and most of the broken holes are caused by the decrease of melt strength after non-uniform expansion. Melt strength is too low and melt pressure around the smaller many factors, summarized, mainly in the following aspects.
Uneven thickness of plate surface. Uneven material discharge, adjustable die lip opening, if the flow rate is too large can be adjusted choke bar, formula adjustment, generally more than the middle of the lubrication, lubrication on both sides of the material faster
6. The change of the thickness and the grain of the sheet which is easy to appear during the shift. The main reason is related to the mixing. After mixing in the first shift, the mixing time is long after the next shift, the mixing barrel is cooled well, the first batch of mixing is preplasticized well, and the mixture is different from the previous batch Other conditions are constant, easy to undulate, can adjust the traction, processing temperature or through management.
Test Methods for PVC foamed sheet products:
(1) side of the board: Smooth Incision, fine pores, no Pinhole, no thick hole, no serious powder drop, no hole, open fiber from off, do not jump mouth. Note: The occurrence of the above-mentioned situation to pay attention to, after the sequence of finished product process trouble.
(2) plate surface: feel smooth and even, mechanical texture is not obvious, surface color no color, milky white, surface without stains, no obvious small pits, no Pinhole, no coarse holes, cracks. Note: non-milky White Foam Board into the recycling waste board, does not belong to Environmental Protection Board, Environmental Protection Board does not contain lead (the content is less than European and American standards) .
(3) DENSITY ALGORITHM: Density Weight (G) / Length * Width * Thickness (cm).
(4) Plate Weight Algorithm: Weight (G) length * Width * Thickness (cm) * Density.
(5) thickness measurement: Caliper stand surface, close contact seamless, left to right thickness uniformity, left to right measurement, deviation is very large, thickness deviation plus or minus 0.2 mm is normal.