Daily Archives: 6. September 2018

Jilian Mold – China Plastic Handle Manufacturers Is A Good Choice

Signs of Pet Preform burnt stripes:
. Stripes appear periodically
. Stripes appear in the mold in a narrow cross section (cutting point) or behind the shape edge
. Melt temperature is close to the upper processing limit
. Reduce injection speed has a positive impact on defects
. Lowering melt temperature has a positive effect on defects
. Long residence time in the space in front of the plasticizing unit or screw (due to, for example, cyclic interruptions or low injection volumes)
. High recovery content, or some materials have been melted several times before
. The mold is equipped with a hot runner
. The mold is equipped with a closing nozzle
Signs of moisture streaks:
. Materials tend to absorb moisture (eg, PA, ABS, CA, PBTB, PC, PMMA, SAN)
. When the melt is removed, blisters and/or steam may appear
. The solidification front of some fillers shows a crater-like structure
. The moisture content of the material before processing is high
. The moisture content in the environment is very high (especially in combination with cold and cold particles)
Signs of air streaks:
. As the degree of decompression decreases, the defect becomes smaller
. As the injection speed decreases, the defect becomes smaller
. Blisters in the injected material are visible
. The solidification front flow of some fillers shows a crater-like structure
Physical reasons:
Burn streaks are caused by thermal damage to the melt. The result may be a decrease in the length of the molecular chain (silver discoloration) or a change in macromolecules (brown discoloration).
Possible causes of thermal damage:
. Excessive temperature or excessive residence time during pre-drying
. Melt temperature is too high
. The shear in the plasticizing unit is too high (for example, the screw speed is too high)
. The residence time in the plasticizing unit is too long
. The shear in the mold is too high (for example, the injection rate is too high)
Note:
Remove material to check melt temperature. The temperature is measured with a needle thermometer.
Thermal degradation of plastics has a negative impact on its mechanical properties, even if the surface does not see damage.
Is the melt temperature higher than the processing range? If yes, then
Lower the melt temperature:
(1) Change the cylinder temperature ( – )
(2) change the screw speed (-)
(3) reduce back pressure
Is the melt residence time within the critical range? If yes, then
(1) shorten cycle time
(2) increase the plasticization time delay
(3) use a smaller plasticizing unit
(4) Reduce the recycling part
After the cleaning, the burning stripes will appear periodically or be visible? If yes, then
(1) Avoid dead spots and flow obstruction areas in gate systems and plasticizing units
(2) Check if the plasticizing unit is worn
(3) Check the particle condition
Burnt stripes near the gate? If yes, then
(1) lower injection rate (injection curve slow-fast)
(2) Check the hot runner system
(3) Avoid sharp edges in the gate system
If not, then
(1) lower injection rate
(2) avoid sharp edges
(3) Avoid small chutes * 1 (using rheological mold design)
(4) Check the gate and gate system (using rheological mold design)
(5) Check the nozzle cross section
(6) Check the function of closing the nozzle
(7) Check the pre-drying of the material (may cause thermal damage due to excessive length or thermal drying process)
(8) reduce the recycling part
(9) using a molding compound or coloring agent having high thermal stability
In the whole process of mold making, there will be various problems, and in various situations, if you want to continue and smoothly make molds, choose a more professional China Plastic Handle Manufacturers can solve more problems for you, and Jilian mold is your good choice.

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