Injection Blow Molding
Injection blow molding, as its name would suggest, is a combination of plastic injection molding and blow molding that creates hollow, thin-walled plastic containers that are smaller and do not have handleware. It is faster than extrusion blow molding and offers higher precision. Parts may have a threaded neck for screw-on lids, thin yet strong walls, and safety enclosures like those on pill bottles.
Quick links to Injection Blow Molding Information
Applications of Injection Blow Molding
Injection blow molding is a two step process that uses a mandrel to form the preform and then a blow molding machine to form it into a plastic container. Pop bottles are most often made by this process because the design is not limited to uniform thickness. Thicker bottoms and middles are possible by increasing the cavity around the mandrel in the second step of the injection blow molding process. They are also able to handle the pressure generated from holding carbonated beverages. Injection blow molded products are usually made in high volumes to offset the higher cost of setting up two different molds for one process.
Materials Used in Injection Blow Molding
These thermoplastics are often used in injection blow molding to produce containers:
- High density and low density polyethylene
- Polyvinyl Chloride
- Polyethylene Terephthalate
Process of Injection Blow Molding
Since it is essentially two forming processes combined into one, injection blow molding involves more steps than other forms of blow molding. First, a parison made of plastic is formed when a thermoplastic preform is heated to molten form and injected around a hollow mandrel called a blow stem. Once semi-cured but still soft and formable, the newly formed parison, which is still around the stem, is placed into the blow molding chamber. The steel blow stem then extends, forcing the plastic to elongate to the desired size of the product, which will also increase its overall strength. Then, compressed air is injected through the hollow blow stem and into the parison. The almost-molten plastic inflates like a balloon and is blown against the walls of the mold cavity, taking its shape. After it cools and hardens, the newly formed plastic container is ejected from the mold. It exhibits a seamless design and does not need to be trimmed. Injection blow molding machines use multiple mandrels and may form up to 12 containers at one time.
Benefits of Using Injection Blow Molding
Injection blow molding companies have been discovering ways to make their facilities more "green," and the innovations that are now being utilized have been impressive. Businesses do more than just simple recycling programs. These companies have added water chillers in the injection process, which causes drastic savings in the energy costs of the manufacturing procedures. Also, many companies acknowledge that plastic products are a big contributor to overall pollution, so manufacturers are designing new models that use less plastic. For example, in the water bottle industry, there are innovations in the water bottle design that utilize a thinner wall layer. Water bottle manufacturers also engineer new bottles that will bio-degrade at a faster rate than bottles made five years ago.