Plastic Injection Molding 101: Water Basics

Plastic Injection Molding 101: Water Basics

Injection molding is a complicated process, but that doesn't mean we don't use basic elements. One of the essential requirements for plastic injection molding is proper cooling, and for that we primarily use water. Chilled water is most often the cooling agent of choice because it's low-cost, has excellent thermal transfer properties, and is readily available.

Read on for some interesting facts about water cooling here at HTI Plastics:

Water used for cooling our injection molding machines must be chemically treated to prevent bacterial growth, scaling build-up, or contamination of the entire system.

- HTI Plastics uses two methods of water treatment:  The first being a tower system which maintains a water temperature around 70o – 90o F.  This system is used to keep the machines at a safe operating temperature.  The machines must be cooled to maintain a maximum oil temperature and to reduce the feed throat temperature. The feed throat is where the plastic is fed into the heated barrel, and temperature control is required to prevent it from melting too early as it's being transformed from a solid to melted plastic.

  

- The second is a Chilled Water System which is maintained at a more consistent temp of 50o F.  This system is used to cool the tooling. Chilled water is channeled through the molds and tooling to remove heat as quickly as possible from the injected plastic. Cooling is most often the longest part of the production cycle, so any reduction in wait time is beneficial. In most cases, we're trying to take the plastic from a temperature around 500o F down to 100 o F to 140 o F as quickly as possible.

- In 2018 HTI added a new 120 ton chiller system to improve the distribution of cold water throughout our facility. This system helps maintain a consistent 50o F water temperature distribution throughout the facility to our tooling where required.

  

- In order to achieve optimum mold temperature - which may be above the chilled water supply temperature - we use thermolators, which can raise the water temperature in a small closed loop system that pumps it through the tooling. Using these, we can run different temperatures at each machine location. Each thermolator has a separate valve to let in a little chilled water and release some of the hot water to maintain a stable temperature.

  

- Process water temperature is different for every mold we create, and it's determined by a large number of variables. The wall thickness of the part, dimensional requirements, the type of resin used, and size factors in the mold design all affect process water temperature.

- Extreme conditions sometimes require temperatures too high to safely use running water. In these cases, we will use hot oil thermolators and in turn use the chilled water to maintain the temperatures in these oil units through a heat exchanger.

  

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