China Manufacturer Directory >>Blow Molding Companies

About Blow Molding and Blow Molding Services Including: Blow Molded Cases, Blow Molded Plastics,Blow Molders, Plastic Blow Molding & Plastic Bottles.

Blow molded plastic is any hollow plastic product, the most common being bottles, that results from the blow molding process. Blow molding uses a continuously running extruder to which a tuned die head is attached, forming a parison. The hot, hollow thermoplastic tube, which is either extruded or reheated, is set within the cavity of a mold and held in place with clamps. Using a blow pin, air pressure is introduced through the inside of the parison, forcing it to assume the shape of the mold. The end product is cooled by conduction or the evaporation of volatile fluids in the container. The purpose of blow molding services is to form a uniform finished product that does not need to be joined together in any way. 
 
Blow molding services use three basic methods for producing blow molded plastic: extrusion, injection and stretch blow molding. Extrusion blow molding is the simplest type that allows for a wide variety of container shapes, sizes and neck openings, along with handleware of many kinds. The parison is dropped from an extruder and captured in a water-cooled mold where it is blown against the mold and frozen into shape. Shuttle and reciprocating extrusion machines are used for small to high volume production, while wheel extrusion machines are the most efficient for huge volume production of certain resins. Injection blow molding is a hybrid of the injection molding and blow molding services and is suitable for smaller containers but not for handleware of any kind. In this process, hot plastic material is injected into a cavity. A neck is created as the material encircles the blow stem, which also establishes the gram weight. The injected material is moved to the next station on the machine where it is subjected to the extrusion blow molding process.
 
Two types of stretch blow molding are injection stretch blow molding (ISBM) and reheat and blow (RHB) molding, both of which are typically used to manufacture P.E.T bottles for juice, water, etc. In the ISBM process, a preform is injection molded and then transferred to another station on the machine, where it is blown. It is then ejected. Because ISBM is so costly, it generally requires extremely high volume (in the multi-millions) runs and is used for items such as wide-mouth peanut butter jars, narrow mouth water bottles, liquor bottles and more. In RHB, a preform is purchased from a vendor that has already put it through an injection molding process. It is then reheated in a relatively simple machine in order to prepare it for blowing. RHB is advantageous because the purchaser does not have to invest in expensive injection molding machinery but still has access to a large catalog of existing preforms.
 
Distinct advantages exist for choosing the blow molding process over other plastic manufacturing processes. It is the most well-suited method for forming hollow plastic parts. It has much lower mold costs than injection molding. Blow molding has a faster cycle time than that of rotational molding. In many cases, one blow molded plastic piece can take the place of many individual parts. However, the scattering of mold thickness is present, due to swell and drawdown. Swell refers to the rapid increase of the thickness of the parison as the polymer melts leave the die and are released into the air. In drawdown, the parison is stretched by its weight, reducing its thickness.