Hot/cold cycle blow mold injection technology can greatly improve the appearance and texture of injection molded parts. The most outstanding part is the use of amorphous resin processing parts. The resin types included are: PC resin, PC/ABS compound, PC/ PBT mix. When the surface temperature of the blow mold is higher than the Tg of an amorphous resin, the resin melt will not form a skin during injection, and the melt can move freely. The result is that the melt does not freeze when it hits the surface of the blow mold, which is different from traditional injection molding techniques.
When filling the mold, a thin layer of polymer melt escapes and remains on the outer surface of the pad template, thereby increasing the gloss of the part and reducing the surface roughness. The Blow molding machine research results show that if the gloss of the part is increased by 50% to 90%, the surface roughness index -Rmax can be increased by 70% for glass fiber reinforced materials, and the index for unfilled materials can be increased by 20%. Hot/cold blow mold injection skills have a positive effect on improving weld line width and visibility. The processing comparison test of 3 different materials has been carried out in the same blow mold, and the results show that the product processed by traditional injection molding technology has a weld line width of about 6 to 13 microns on the surface. The product injection molded on the cold blow mold has no weld lines at all, and its width cannot be detected. This infinite advantage can save the secondary processing steps such as painting, which is especially suitable for some special occasions. Residual injection molding stresses in the product can cause part warpage and even shorten part life.
Traditionally injection-molded parts have high internal stresses. Carbon tetrachloride is classified as a solvent known to cause stress cracking in plastic parts. The internal stress of plastic parts processed by the hot/cold cycle blow molding mold is low, and the use of this solvent will not cause stress cracking of the parts, and then the annealing treatment process that needs to be performed before the parts are used can be omitted.
The key to the second blow mold design The factors that determine the success of the hot/cold cycle blow mold injection technology in the entire cycle processing cycle are not only related to the processing raw materials, but also related to the design style and layout of the blow mold. The time required to heat and cool the blow mold depends on the thickness of the steel. For the heat exchange cycle, it is best to minimize the thickness Z of the steel. The cavity and the core can be inlaid and assembled, which is better than the method of cutting and excavating on the formwork, so that the thickness of the formwork can be reduced. To reduce heat loss and improve thermal efficiency, these inserts can be fabricated using air gaps and barrier materials as much as possible on the cavity and core pallets.
In addition to the need to reduce the amount of steel used in the blow mold, it is also necessary to consider the impact of the replacement of cold and heat in the blow mold. The raw materials used in the production of the blow mold need to have a high thermal conductivity, such as copper beryllium alloy or other high thermal conductivity. alloy material to shorten the time required to heat and cool the surface of the blow mold. In addition, the cooling water channel is designed to be close to the surface of the blow mold, and then the response time is accelerated. However, in most cases this is limited by the geometry of the plastic product. It is very reasonable and effective to describe the method of using conformal cooling, that is, the placement of cooling water pipes is described according to the appearance of plastic parts.
In order to effectively control the process, it is necessary to install multiple thermocouples on the outer surface of the blow mold to monitor the temperature. Blow molds, injection molding machines, and heat/cold control equipment must require intelligent connection to achieve the stability of the processing process. During the initial period of the injection molding cycle, steam or superheated water circulates to heat the surface of the blow mold, so that the mold temperature is about 10°C to 30°C higher than the glass transition temperature of the resin. When the set temperature is reached, the injection molding machine obtains a signal and writes the plastic melt into the mold cavity. After the mold cavity is filled, the injection is completed, and the cooling water circulates into the blow mold to quickly cool the plastic parts to shape, and then eject the product. Equipped with a valve switch, it can alternately pass into steam or superheated water, or cooling water. After the part has cooled, the blow mold is opened and the part is ejected, and the system switch is switched back to the blow mold heating period.
