Blow molding, also known as hollow blow molding, is a rapidly developing method of plastic processing. The blow molding process began to produce low density polyethylene vials during the Second World War. In the late 1950s, with the birth of high-density polyethylene and the development of blow molding machines, blow molding technology has been widely used.
Injection Molding is a method of producing shapes for industrial products. Products are usually injection molded from rubber and plastic. The following is a small series of Jiuzhi.com to tell you about the differences between blow molding and
injection molding. There are three main points:
1. The process is different, the blow molding is injection + blowing; the injection molding is injection + pressure; the rotational molding is extrusion + pressure; the blow molding must have the head left by the extraction of the gas pipe, and the injection molding must have a gate section. Rotomolding must be cut without clipping.
2. Generally speaking, the injection molding is a solid core, and the blow molding and rotomolding are hollow cores. The surface of the injection molded parts is bright, and the surface of the blow molding and the rotomolding is uneven. The blow molding and the rotomolding are at least blow molding. There is a blowing mouth. This is a general comparison.
3. Plastic shrinkage and its influencing factors The characteristics of thermoplastics are that they expand after heating, shrink after cooling, and of course the volume will shrink after pressurization. In the injection molding process, the molten plastic is first injected into the mold cavity, and after the filling is completed, the melt is cooled and solidified, and shrinkage occurs when the plastic part is taken out from the mold, and the shrinkage is called forming shrinkage. The size of the plastic part will still change slightly from the time the mold is removed to the stable state. One change is to continue shrinking. This shrinkage is called back shrinkage. Another variation is that some hygroscopic plastics swell due to moisture absorption. For example, when the water content of the nylon 610 is 3%, the dimensional increase is 2%; and when the water content of the glass fiber reinforced nylon 66 is 40%, the dimensional increase is 0.3%. But the main role is the forming shrinkage.
Jiuzhi Plastics Network
May 12, 2022