1. PC material can not be used after melting
After the end of the melting glue, the back cable is lifted, the screw moves back, and the air will be pumped into the nozzle and mixed with the high-temperature PC material. Due to the reason that PC material is easy to absorbs moisture, a small amount of water in the air can make the injection parts produce silver rays.
In a similar situation, transparent PVC glue can not be poured. Because transparent PVC is very easy to burn glue, it will immediately cause a chemical reaction when it encounters air, resulting in yellow spots in injection molded parts, and even many black spots that burn glue.
Therefore, when injection molding PC material, or transparent PVC material, do not reverse the cable after melting. If the back pressure needs to be increased because of the process, and when the nozzle spits out glue, it can only be poured a little, and the spits can be eliminated. No more, no more air in the nozzle.
2. How to eliminate the gas marks at the water inlet of PC parts
Among many transparent materials, such as GPPS, K material, transparent ABS, and PC material, PC parts are very easy to produce gas lines in the water position, and it is very difficult to eliminate.
Because of the fluidity of the PC material, it is relatively poor in these materials, and fast injection glue must be used when injection molding, otherwise it is easy to go uneven or produce jarring marks. The result of rapid injection is the slight trapped gas caused by the rebound of the melt glue after rapid injection to the surface of the cavity at the inlet position. And the thicker the injection parts, the larger the trapped air area. Due to the high material temperature, the surface of the molten glue in the trapped gas position is oxidized, and a gas film is formed here, which separates the molten glue from the surface of the mold, so that the surface of the injection part forms a subchromatic gas pattern, affecting the transparency of the injection part.
The liquidity of other transparent materials is much better. Therefore, it is easier to fill the mold, and it is not easy to produce jarring. Therefore, the ejection speed can be relatively low, and the trapped gas at the inlet position is very slight even if it exists, so it is not easy to form subchromatic gas lines. Even if gas lines are produced, they are easier to remove than glue. We only need to reduce the injection speed and pressure a little to solve it, and there will be no jarring or missing material problems. The PC material to reduce the speed can not be done, not the vibration is the lack of material.
Therefore, the problem of water inlet breath pattern of PC material can be said to be very difficult to eliminate in a commonly used transparent material, which can be called an injection molding problem, and some measures and adjusting skills must be taken to solve it.
3. How to solve the problem of brittle PC parts and white fog
A few years ago, we rarely saw the problem of PC injection molding parts becoming brittle. That’s because the PC material brands used at that time were relatively few, usually only the Japanese PC7025A and 1250Y two brands. Nowadays, there are more and more manufacturers producing PC materials, and there are naturally many brands and grades.
The problem then arises. Because various grades of PC injection molding technology processes are not the same, and the strictest degree of process requirements are different, the use of the same injection molding process of PC7025A and 1250Y to produce other grades of PC materials, it is inevitable that there will be problems, and it is often seen that PC injection molding parts sometimes can not withstand the brittleness of the impact.
After careful study, we found that due to the different heat resistance and physical characteristics of various grades of PC materials, the melting temperature, and even the drying temperature and drying time will have a significant impact on the impact resistance of injection parts.
Usually in the production of PC7025A and 1250Y materials, the melt temperature is generally adjusted to 290 to 310 degrees. When producing some grades of PC material, and then using this temperature for injection molding, the injection molding parts will become very brittle. Therefore, for this kind of PC material, the injection temperature is recommended not to exceed 290 degrees, and some may be even lower to solve the brittleness problem. Therefore, as long as the fluidity of the melt is sufficient to fill the mold, it is recommended to use a lower temperature to produce, to prevent the injection parts from becoming brittle and causing strength instability.
The second is the influence of drying temperature. The PC7025A and 1250Y can usually be baked to 110 to 120 degrees for more than 4 hours. But some brands of PC material can not exceed 100 degrees, otherwise, the injection parts will become very brittle, and also white fog, affecting the appearance and transparency.
What is not easy to attract people’s attention, and what is easy to go wrong, is the drying time. Usually when injection molding PC7025A and 1250Y materials, fill the 50kg drying hopper, as long as there is no water vapor, slowly producing six or seven hours will not be any problem.
However, if some PC materials are baked in the drying hopper for more than 4 hours, the injection molded parts will not only produce obvious white fog, but even become very brittle, and the longer the time, the more brittle, the more white fog, the beer becomes cloudy. At this time, if a bucket of material is enough to produce 6 hours, it can only add half a bucket of material, if the injection parts have water and gas production, as long as a little more and a little more often, the problem will not happen again.
Sometimes, there will be a few times of white fog, which should be a few raw materials stuck in the drying hopper for a long time to bake, and then from time to time a few materials flow out of the barrel and are shot into the mold.
This is an important reason for the brittleness and white fog of PC injection parts in production. Therefore, to produce various grades of PC injection parts, we must pay attention to the characteristics and requirements of the injection molding process of various grades of raw materials. Of course, due to the different performance of the various brands themselves, the strength and impact resistance will be different, and some brands’ impact resistance is really poor.
Therefore, in future production, if the PC injection parts suddenly appear brittle problems and lack transparency, we can prioritize the melting temperature and drying temperature and time to consider, so that people can take a lot of detours.
4. Extending the cross runner can reduce the jet and vibration of PC parts
Sometimes because the flow path is too long, the melt in front of the cooling is too much, which leads to the injection parts producing jet and vibration, and PC material in this respect is particularly prominent, followed by transparent PVC.
This is why sometimes the melt temperature has risen very high, injection parts still do not eliminate the shoot or jarring reason.
At this time, if the two ends of the cross-runner are extended by a few centimeters each, the low-temperature melt that has cooled in front can flow into the extended cross-runner, and will not flow into the cavity, and the defect will be well improved. It is believed that this method will also have an improving effect on other plastics, and the improvement of PC and PVC materials will be more obvious.
Therefore, when no matter how you adjust the machine can not solve the jet or seismic marks, you may want to try this method.
