Any technology has its own bottleneck, and the cap industry is no exception. Art analyzes and contrasts this issue. The so-called cavity filling imbalance means that the speed of molten plastic entering each mold cavity is inconsistent. In the injection molding process, from the moment the injection molding machine screw advances, the molten plastic cap will enter each mold cavity, because of hot runner processing deviation, cold runner processing deviation, deviation of each cavity venting groove, deviation of the discharge processing of the glue inlet, the various factors such as uneven plastic flow shear rate are superimposed, which may result in inconsistent glue speeds in each mold cavity.

Some of the cavities have been filled, and some cavities are only filled to about 80%. The injection molding process is divided into injection section and holding section. The injection speed is usually very fast, and the cavity filled quickly is likely to explode. Filling a slow cavity is likely to lack glue even if pressure is applied, the problem of filling imbalance also causes the deviation of the weight of the cap to be large, the dimensional stability of the cap is poor, and the injection molding into the rubber port is small, the inlet of the cap product is usually only 1 mm at most, which is very easy to be blocked by debris and the product is lack of glue.

The compression molding dies are all independent. After the granules come out from the nozzles, they are directly entered into each mold in sequence. All the granules are cut into the mold bowl after the cutter is evenly cut, and there is no problem of filling the balance rate, the compression molding process is also extremely simple. Usually, only the screw extrusion frequency can be adjusted to obtain a stable product quality. Unlike the injection molding process, complicated molding parameters such as injection and pressure holding, and returning and pumping are required.

Moreover, the size of the compression molding nozzle is above 10 mm, and the clogging problem frequently occurring on the injection molding does not occur, the production efficiency is higher, the product weight on the compression molding process is more uniform, and the bottle cap size is more stable. The filling balance problem that has plagued the injection cap industry for more than 20 years has been solved perfectly in the compression molding process, which is one of the advantages that the injection molding process can't match. More and more cap manufacturers tend to choose the compression molding process when adding new production lines. The compression molding process has gradually become the mainstream of the cap production industry, which is an irreversible development trend.