Process cooling and the plastics industry

October 4, 2019 by Susan Paige

One of the most important and largest industries in the world is that of the global plastic industry. It affects almost all aspects of our day-to-day lives, from aerospace and entertainment to medicine and food. It is a durable yet flexible material that has numerous applications.

Injection molding

The overwhelming bulk of plastic components are produced via the injection molding process. This is an efficient way to manufacture large quantities of the same components with minimal wastage. It works by heating up tiny plastic pieces until they melt enough to be injected into a mold where the plastic cools.

This cooling process is very time consuming with more than 80% of the entire plastic manufacturing process being dedicated to this process. An injection molding chiller works to dramatically reduce this cooling time as well as preserve the standard of the products.

What are the temperatures involved?

Temperatures within the whole injection molding process are highly important. In order for the tiny plastic particles to turn molten and go into the mold they must first be heated to 350 Fahrenheit for Polypropylene, 400 – 420 Fahrenheit for ABS, and 550 Fahrenheit for Polycarbonate.

Following the injection the cooling process must immediately begin. Time is money with injection molding so the longer that it takes to cool down the more time, and thus money that is lost. An efficient process cooling solution is a must for any plastics manufacturers.

Injection molding cooling solutions

Depending on the type of plastic being used, its thickness, and its size, then a variety of different cooling processes can be used. One option is a water / fluid cooled injection molding chiller that works to cool the cavity within the mold. This not the duration of the cooling process but also improves the integrity of the plastic this is produced.

If not cooled correctly the plastic that is inside the mold can become deofrmed and even warp upon its ejection from the mold, and thus will be rendered useless.

Chillers used in the plastics industry

When looking at the type of chillers that can be used for plastic products there are two main categories. These are:

  •     Vapor compression – These are the most common types and include water / fluid chiller and air chillers. They use an electric driven mechanism to push a refrigerant through a system.
  •     Vapor absorption – These work by using heat to push a refrigerant around a system.

As previously stated, vapor compression chillers are the most common types used within the plastic industry and are placed into two categories. These are:

  •     Water / fluid chillers industrial liquid coolers work by removing heat via pumping water, or another fluid, through a condenser and dispersing it through a cooling tower. These types of chillers are more efficient than air cooled ones. Thanks to water’s high heat capacity, the process of using water evaporation to dissipate heat is far less energy intensive than blowing cold air across a hot surface. Traditionally, these types of chillers last longer than air chillers.
  •     Air chillers – There work by using air to get rid of heat. Fans blast cold air across the tubes of the condenser to cool it. This method is much more energy intensive than the water cooling method but these types of chillers are ideal for when it comes to static cooling. They are really easy to install and can even go on the outside of a building, saving space inside. However, they are more likely to experience recirculation issues and blockages than water / fluid chillers.

Despite their differences, they each are made up of the same components, which include an expansion valve, a compressor, an evaporator, and a condenser. Further to this, the mechanics of the two types of chillers are also extremely similar.

The compressor is where the refrigeration cycle starts and works to push a refrigerant through the condenser. During this process the low temperature and low pressure refrigerant is compressed into a high temperature and high pressure gas. Whilst in the condenser air or water / fluid flows over the coils and removes heat from the refrigerant. The refrigerant condenses as it loses heat to the point that it turns into a liquid. After leaving the condenser, the refrigerant goes through the expansion valve where its flow is restricted. Once through the valve it goes into the evaporator where the refrigerant begins evaporating back into a gas. During this process it gets very cold and absorbs large amounts of heat. This heat is removed from the fluid and transferred to the refrigerant. This will then enter the compressor again and the cycle starts all over again.

Depending on what type of compressor the chiller utilizes, they are subcategorized. These include:

  •     Scroll compressor chillers – These are used in both water / fluid chillers and air chillers and work by utilizing one rotating plate and a stationary plate to compress the refrigerant.
  •     Reciprocating chillers – These types of compressors work by a chamber and pistons to compress the refrigerant.
  •     Centrifugal chillers – It is mostly water / fluid chillers that utilize this technology. It is rare to find such a system within an air chiller. They are predominantly used for large and medium cooling loads that are between 150 – 6,000 tons and work by using rotating blades to compress the refrigerant and push it through the chiller. These types of compressors provide high cooling capacity in a compact design.
  •     Screw driven chillers – These are used in air chillers and water / fluid chillers and are ideal for medium to small sized cooling loads. This type of compressor works by utilizing a couple of helical rotors that interlock to compress the refrigerant. They come as units that weigh anywhere between 70 – 600 tons.

What are the benefits of an injection molding cooling solution?

Not only does an effective injection molding cooling solution save time and thus lower operational costs, but it also saves water and energy, and improves the quality of the finished product. Such a solution is easy and simple to install.

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