injection molding

Plastics are as much a part of our lives as food since so much of what we own, what we use, and what we eat with are made from plastic materials. Plastic is one of the best inventions of the last 100 years. However, there is a big downside to plastic: it takes hundreds of years for plastic to breakdown, creating a huge problem with trash.

Luckily, plastic recycling companies, such as KW Plastics, buys scrap plastic and then turns that plastic into plastic resin pellets, which are then sold and reused by manufacturers for their plastic needs. This sustainable process helps our planet and helps plastic manufacturers as well. In this blog post, we’ll take a close look at injection molding. Contact us today for your plastic scrap needs!


Injection molding is one of the most popular forms of making plastic objects, including automotive parts, toys, cell phone cases, and the like. Easily automated and extremely efficient and quick, injection molding is chosen by a lot of recycled plastic manufacturers for their plastic parts needs. In essence, injection molding injects molten material into a mold, where it hardens and produces replicable products. Let’s take a closer look at the steps in the injection molding process.


  1. Plastic materials (often plastic resin pellets, such as those sold by KW Plastics) are fed into the injection machine via a hopper.
  2. These plastic materials are then melted until they become liquefied.
  3. Extra steps such as drying the plastic to remove moisture may be performed.
  4. The plastic is fed through a vacuum into the heated injection barrel to avoid air from getting in.
  5. This melted plastic is then injected under pressure into the chosen mold cavity where it hardens.
  6. Once the plastic has hardened, the plastic component is ejected and then repeated.

As you can see, this is a very efficient and quick way to create identical parts. While the injection molding process may seem easy, it’s actually quite complex. Pressure is a key factor in the injection molding process, and too much or too little pressure can result in a rejected product. Furthermore, while the process itself is great, getting the process going takes time and precision in order to not waste product. Designing the part you want made and then making the molds can become quite complicated and needs to be precise and detailed before you mass produce the plastic part. Hence, the cost of entry is high, but as soon as production begins, economies of scale kick in and the price of production plummets.



Injection molding is very similar to blow molding, the main difference being that blow molding makes hollow objects, such as bottles, whereas injection molding makes solid objects, such as plastic toys. Furthermore, blow molding relies on air to form the mold; injection molding uses no air, and, in fact, tries to keep air out because air bubbles inside a solid object can result in a loss of structural integrity.

The process of making the mold varies vastly between the two as well. Blow molding relies on temperature of the plastic, the type of plastic used, pressure, and speed it is molded. Injection molding spends most of the time making the mold in the first place.

Injection molding can be used to make many items we use everyday:

  • Toys
  • Plumbing pipes
  • Packaging
  • Construction components
  • Automotive parts
  • Medical parts
  • Aerospace parts
  • Bottle caps
  • Combs
  • Musical instrument parts
  • Mechanical parts, such as gears
  • And so much more!


Injection molding has come a long way since its inception in 1872. After World War II, an American inventor named James Hendry built the first screw injection machine to meet the demand for inexpensive, mass-produced products. The technology has continued to progress, allowing for colored plastic to be produced and allowing for single cavity or multiple cavity molds. Plastic production has continued to grow, with more plastic being produced every year than steel. As technology continues to grow, you can expect more efficiencies and innovative processes, including more recycled plastic use, to be developed for injection molding.

KW Plastics is a plastic recycling company that buys plastic scraps and then turns those into plastic resin pellets, which we then sell to recycled plastic manufacturers. We boast the industry’s largest capacity for blow molding, injection molding, extrusion, and blown film. We are proud to partner with companies who use our recycled plastic pellets as part of their plastic manufacturing needs. We are passionate about our community and about supporting community recycling programs. If everyone did their part by recycling the plastic they use at home and while out and about, the plastic in our landfills and environment would significantly diminish. Contact us today to get started!