Blow molding(blow moulding), or plastic blow molding, is a fabricating process that manufacturers use to create hollow plastic parts and products.
Manufacturers use the blow molding process in order to form a smooth, airtight, uniform product that does not need to be assembled. Also, blow molded products are capable of holding a variety of substances such as herbicides, pesticides, cosmetics, and automotive oil. Some of the many industries that use blow molded plastics include: automotive manufacturing, food and beverage, lawn and garden, waste collection and recycling, storage and transportation, organization, office, healthcare and more.
Typical blow air pressures around 25 to 150 psi. There are three methods in which blow molded plastic products can be produced: extrusion blow molding, injection blow molding, and stretch blow molding. An overview of each process is outlined below:
Injection Blow Molding
Injection blow moulding is used in the production of large quantities of hollow plastic objects. The process starts with the injection moulding of a polymer onto a core pin which is then rotated to a blow moulding station to be inflated and cooled. Typically used to make small medical and single serving bottles, injection blow moulding is the least-used of all blow moulding processes.
Stretch Blow Molding
Stretch blow molding is divided into two different methods: injection stretch blow molding (ISBM) and reheat and blow molding (RHB). These processes are often used to manufacture bottles for beverages such as water and juice.
ISBM (injection stretch blow molding) involves injection molding a preform, and then moving it to the next station to be blow-molded. ISBM is a costly process, and is used to manufacture liquor bottles, water bottles, and peanut butter jars.
RHB (reheat and blow molding) involves purchasing a preform from another vendor who has already injection-molded the material. The preform is reheated to prepare it for the blow-molding process. RHB is much more cost-effective than ISBM, because it eliminates the need for injection molding equipment and provides access to various pre-made preforms.
Extrusion Blow Molding
The molten polymer is led through a right angle and through a die to emerge as a hollow (usually circular) pipe section called a parison.
When the parison has reached a sufficient length a hollow mould is closed around it. The mould mates closely at its bottom edge thus forming a seal. The parison is cut at the top by a knife prior to the mould being moved sideways to a second position where air is blown into the parison to inflate it to the shape of the mould.
After a cooling period the mould is opened and the final article is ejected.To speed production several identical moulds may be fed in cycle by the same extruder unit. The process is not unlike that used for producing glass bottles, in that the molten material is forced into a mould under air pressure.