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What is the difference between blow molding and injection molding?

Are you manufacturing a product that requires molded plastic parts? A variety of processes are available. Injection molding and blow molding are two of the most popular methods for producing high-quality, cost-effective plastic parts and products, but they are used for different purposes and have different processing conditions and raw material conditions. Do you know the difference between them? Which one is better? Here we introduce in detail the relevant information about plastic molding and blow molding.

What is blow molding?

Blow molding, also known as hollow blow molding, is a rapidly developing plastic processing method. The tubular plastic parison obtained by extrusion or injection molding of thermoplastic resin is placed in the opposite open mold while it is hot (or heated to a softened state). After the mold is closed, compressed air is injected into the parison immediately, so that the plastic parison expands and clings to the inner wall of the mold. Cooling and demoulding to obtain various hollow products.

The advantages of blow molding include:

  • The cost of the blow mold is low, and the production cost of the product is low.In blow molding, the parison is formed at low pressure through the die head, and the parison is inflated at low pressure. Therefore, the product has small residual stress, high tensile, impact, bending, environmental and other strain properties, and good performance.
  • Blow molding grade plastics have a higher relative molecular weight. Therefore, the blow-molded article has high impact toughness and high environmental stress cracking resistance, and is suitable for producing containers or barrels for packaging or transporting detergents and chemical reagents.
  • Because the blow mold is only composed of the female mold, the wall thickness of the product can be changed only by adjusting the mold gap or the extrusion conditions, which is beneficial to the product whose required wall thickness cannot be accurately calculated in advance.
  • Blow molding can produce products with very small wall thicknesses.
injection molding

What is injection molding?

Injection molding, a molding method for industrial products. The products are usually made by rubber injection molding and plastic injection molding. Injection molding can be divided into injection molding technology and die-casting method. Injection molding machine is the main molding equipment that makes thermoplastic or thermosetting materials into various shapes of plastic products through plastic molding molds. Injection molding is achieved by injection molding machine and mold.

Advantages of injection molding include:Accurately and cost-effectively produce large quantities of small parts.More efficient use of materials with little scrap or waste.Fine, highly engineered tooling with multi-cavity mold options.Flexibility to change the type of material or color being used.

What is the difference between blow molding and injection molding?

Product differentiation

Plastic blow molding is the use of gas molding products, the need for injection molding, generally used to make thicker products. Blow molding is different, because the product is thinner and more transparent, and slight defects are obvious. Therefore, the requirements are higher, and blow molding has certain requirements for the toughness and tensile properties of raw materials. The products for processing injection molds are thicker, and the requirements for raw materials are relatively low.

Structural differences

Blow molding can only be used for products with simple structure, such as seats that can not be adjusted in any part, and removable seats are basically blow molded. Injection molding process can be used to produce safety seats with complex structure, such as adjustable head support and two side wings, adjustable sitting, lying, folding and other functions.

Texture difference

Blow molding products are hollow, and the color is mostly black, because black can cover up the defects such as burrs and rough surface caused by blow molding process. Because the blow molding port is hollow, the weight is light. The surface of injection molding products is smooth, the texture is better than that of blow molding products, and the flexibility and compression resistance of injection molding products are better than that of blow molding products. Of course, the cost is also high, the price of injection molding products is higher than that of blow molding products.

Process differences

The blow molding process begins by heating the plastic feedstock to a temperature of 350-420 degrees Fahrenheit. The material is then extruded from the head of the machine into a hollow tube, which is the parison. The mold is closed around the parison and about 80 PS I is blown into the parison, causing it to expand and form the shape of the mold. The mold is then cooled to allow the plastic to “set.”. Once the set time is reached, the mold is opened and the product is produced. The part then goes through a degating process that allows access to the inside of the part.

The process of injection molding is to melt the plastic material and then inject it into the film cavity. Once the molten plastic enters the mold, it is cooled and molded into the desired shape according to the mold cavity. The final shape is usually the final product and does not require additional processing prior to installation or use as the final product. In addition, during the injection molding process, many details, such as bumps, ribs, and threads, can be molded in a single operation of injection molding.

If you want to know more about injection molding desktop injection molding machine, please contact Timswell.