In the plastics industry, in order to save costs, many companies will consider the production of hollow products by large-scale blow molding process, which will greatly reduce the cost compared with injection molding, so the method of blow molding processing has also been developed rapidly. The scope of application of blow molding products is also very wide, such as the toy industry, packaging industry, electrical industry and other industries.
For large blow mold products, the big issue of raw materials is very important! Therefore, the selection of suitable raw materials is also an indispensable reason for the extrusion blow molding process factors. The selection of raw materials depends on the performance and processing performance of the raw materials, and must meet the conditions and use requirements of blow-molded products.
(1) HDPE: High-density polyethylene, one of the most commonly used materials in blow molding products. This plastic is suitable for the production of various products, heavy metals, glass, wrapping paper, coolers, fuel tanks, industrial barrels, etc. It is very versatile. Its material is translucent, has good stretchability, strong plasticity, non-toxic, and is also a relatively safe material.
(2) PP: Polypropylene is also a commonly used resin, suitable for high temperature, its texture and HDPE are translucent, high hardness, low density, but also has certain advantages, commonly used in medical equipment, chemical containers, pharmaceuticals, etc. .
(3) PET: polyethylene terephthalate, a common resin in life, has good physical and mechanical properties, suitable for various bottles, such as cola bottles, etc., and can also be used as electrical parts, etc., with many colors It is milky white or light yellow, and the surface is smooth and shiny.
(4) LDPE: high pressure low density polyethylene, which is the lightest variety of polyethylene resins. Has good transparency and softness. Commonly used in clothing, food seasonings, etc., the most commonly used is blown plastic bag film.
Factors such as the position of mold separation (parting line), product slope, product layout, inflation ratio, rounded corners, and modified appearance involved in the blow molding process must be considered by mold engineers and blow molding engineers. The specific analysis is as follows:
(1) The position of the parting line. Before opening the mold, the mold engineer needs to carefully consider how to split the mold, which will affect the ejection of the subsequent products and the appearance of the product.
(2) Product slope. All surfaces parallel to the moving direction of the mold must have a certain slope, and the slope should be such that the mold can be easily opened and the blow-molded product can be taken out.
(3) Check all used functions. When used as a product, the fewer parts and the less assembly work the better, because the cost of the product can be reduced.
(4) Inflation ratio. During inflation, pay attention to areas that cause extremely thin wall thickness geometries, which may be convex or concave, and can be aided by vacuum forming if the width to depth ratio is too large.
(5) Radius principle. Avoid sharp edges, corners, sudden changes in surface, sudden changes in product diameter or wall thickness.
(6) The location of inserts, vent slots, intake pins, ejector pin holes, lettering and labels must be carefully considered.
Controlling the temperature of the extruder is the most important factor in the extrusion molding process! The adjustment of extrusion temperature is related to blow molding raw materials. The extrusion temperature will affect the quality of the product. When the extrusion temperature is too high, the surface wall thickness of the blow mold product will be uneven. When the extrusion temperature is too low, the surface of the parison will be rough. Therefore, when manufacturing large-scale blow molding products, it is mainly to prevent the parison from sagging, and the temperature can be low. When making small blow molded parts, the temperature is higher!