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Plastic Blow Molding: The Creation of Plastics Used Daily

Simply put, plastic blow molding is a manufacturing process by which hollow plastic parts are created. It’s a process typically used to form plastics normally used on a day-to-day basis, such as:

  • Dairy containers
  • Shampoo bottles
  • Hoses
  • Pipes
  • Drums

However, blow molding machines can be used to create any desired hollow plastic part, depending on the clients’ needs and the capabilities of plastic blow molding companies. The types of plastics most commonly used in this process are polythene, PVC and polypropylene. In some cases, blow molding is used to create glass molds, but most products are designed as plastic parts.

The Plastic Blow Molding Process

The step-by-step process of making plastic molds is quite simple. The following is an outline of the steps it takes to create a plastic bottle:

  1. The plastic, which is in a granulated, powdery form, is fed into a hopper that stores it.
  2. A motor on the machine turns a large thread which pulls the granules through a heated section.
  3. While in the heated section, the granules melt, become a liquid and flow into a mold.
  4. Air is forced into the mold which pushes the plastic to the sides, forming the shape of the bottle.
  5. After the plastic cools, it is removed from the mold as a brand new bottle.

This type of blow molding method is known as extrusion blow molding and is most often used to create simpler, more day-to-day plastic products. Another blow molding method known as stretch blow molding is a process that involves heating preforms and stretching them with a core rod. The main products designed for this process are jars and other glass-like containers.

Blow Molding vs. Injection Molding

These two processes are easily mixed up as they are similar in what they do and produce. Blow molding and injection molding are both important processes because they each create specific products that we need to function in our everyday lives. Take a look at the following table to view the main differences between blow and injection molding:

Blow Molding Injection Molding
Makes hollow parts  Makes Solid Parts
 Thermoplastic is pushed into mold by air  Thermoplastic is injected into mold
 50% of time is needed for making mold  90% of time is needed for making mold
 Air is needed to expand the plastic  Minimizing air in the plastic is crucial
 Thickness in the part will differ in places  Thickness is determined by mold and core
 Parts tend to be containers like bottles  Parts tend to be used for things like cars


Each process plays a different role in designing parts that provide widespread value to individuals and companies everywhere. Knowing the difference between blow molding and injection molding enables potential customers of molding manufacturers to know what to expect when requesting help mass producing a specific product.

Streamline Plastics Offers Custom Blow Molding Services

As one of the few molding manufacturers in the Greater Salt Lake area, Streamline Plastics is dedicated to providing top-notch service for your plastic blow molding needs.  Whether it’s blowing molding or injection blow molding, we are fully equipped to provide you with expert service for every step of the production process, or for just part of the process, depending on your needs. We are your turn-key solution for mold building and design. Contact a Streamline Plastics representative today for a price quote.