Blow molding is the process used for manufacturing hollow, typically plastic parts. Some common examples of blow molded products are small plastic bottles and containers for consumer products like water, shampoo, or milk. Blow molding can also be applied to larger, industrial jobs, like storage tanks or big plastic drums. In short, the process is focused around creating a lot of single-piece, thin-walled containers for cheap.
What we typically refer to as blow molding is actually called extrusion blow molding (EBM). First, plastic is melted down, and formed (extruded) into what is called a parison. This small tube has an opening for air, and once secured into a mold, air is forced into it. This expands the plastic into the shape of the mold, and once the melted plastic cools, the mold is opened up and the product is removed. There are variations to this technique, but this is the basic process.
Blow molds are most often made of beryllium-copper alloys due to their good heat conductivity and resistance to wear and tear.
What is the Difference Between Extrusion Blow & Injection Molding?
Extrusion blow molding is the most common type of molding today, with injection molding typically reserved for very small glass or plastic bottles. In injection blow molding (IBM), the plastic is melted and molded onto what’s called a core pin. This melted plastic isn’t called a parison like the EBM process, rather a preform. This preform is transferred to a molding station to be inflated, then cooled in a pre-chilled blow mold. Finally, the finished product is ejected and the process repeats.
Injection molding is extremely precise, resulting in more accurate production, but as we mentioned, it’s only suitable for comparatively tiny bottles as a result.
What About Injection Stretch Blow Molding?
Of course! Injection Stretch Blow Molding (ISBM) is similar to IBM, but the preform is stretched in length, as well as width. This makes the walls of the containers stronger and lighter, and suitable for larger volume containers.
When Was Blow Molding Invented?
If you’re at all familiar with glassblowing, you might have already noticed some similarities between it and the plastic blow molding we’ve discussed so far. In fact, that’s how the inventors of blow molding came up with the idea! In 1938, two enterprising inventors developed a mass manufacturing technique for blow molding, patented it, and sold it to Hartford Empire Company.
One bottleneck for the growth of the blow molding industry was the availability of appropriate materials. Variable density plastics came around relatively late in the technology’s emergence, but changed the game forever. Today, three of the most common polymers (plastics) used in blow molding are high and low density polyethylene (HDPE & LDPE), polypropylene (PP), and co-polyester.
When the American soft drink industry began taking off in the mid 1970’s, it marked a turning point resulting in billions of blown products over the next 20 years. Since then, many billions more have been blown, and the industry shows no signs of slowing.
What Should I Look for in a Blow Molding Company?
If you’re on the hunt for a company with blow molding expertise, Blow Molded Products in Southern California provides exemplary customer service, state-of-the-art facilities, and unmatched quality assurance from start to finish of project. If you aren’t ready to take our word for it, our team put together a few recommendations of what you should look for in your blow molding provider.
Ask is about our capabilities and limitations. Not all designs that are intended for blow molding can be blow molded, however, in many cases small changes to the design can make a project much more successful.
It’s always good to know how much your can grow with your manufacturing vendor. At our facility, we produce 433,000 pieces a month across 18 machines. We produce parts from 5 grams up-to 15 pounds and have at least 2 machines for each weight range.
Available Processes (Blow/Injection)
Our facility focuses on EBM manufacturing with future expansion into ISBM for a wider range of capabilities. We also work with local injection molds to help create turnkey projects.
Majority of our projects us HDPE, LDPE, PP and PETG materials. There are also several TPU’s we can process. In the coming months, we will be trying to expand our material selection with PVC and Polycarbonate options.