The Role of Temperature in Plastic Injection Molding

Plastic injection molding is one of the most common methods of manufacturing today, and it requires precise monitoring and quality control to produce multiple flawless copies of a single part. Understanding the importance of temperature’s effect on product quality is essential to achieving the desired result.

Thermoplastics are substances that become plastic when heat is applied and harden when cooled. They can go through this cycle multiple times making them very versatile and recyclable. Exacting standards must be met for a product to be aesthetically pleasing and structurally sound. These standards include pressure, time and temperature.

Temperature must be properly managed at every step of the entire injection molding process. As thermoplastics enter the barrel of the machine, temperatures must be high enough to melt the plastic but not cause burning. Sophisticated heating bands around the barrel cause gradient heating and a smooth transaction from solid to liquid and finally the finished product. The actual temperatures depend on the material, size and shape of the part. The common range is between 149º and 426º C or 300º and 800º F.

The mold temperature is maintained at a lower setting so the plastics can cool. This setting is usually between 65º and 17º C or 150º and 350º F. Temperatures that are too low or too high can result in a flawed finished product and might also damage the plastic injection equipment itself.

Here are some examples of what can occur if temperatures are incorrect. If the temperature of the barrel is too high during the melting process, material can burn and manifest as small black pieces in the finished product. High temperatures at this point can also degrade the polymer and produce products that are structurally unsound. High temperatures can also lead to stringing when a remnant from the previous shot is transferred to the next piece. If the temperature is too low during the injection process, wavy lines and flow marks will appear on the manufactured part.

A mold temperature maintained below the ideal temperature can result in something called knit lines. These are an area behind the protruding part of the mold where the melting plastic meets but does not uniformly merge. Low molding temperature can result in a portion of the part sinking or hardening of the plastic before the entire part is completed. Mold temperatures that are too high can result in blistering of the plastic.

At The Toolroom, anything less than a perfect finished product is not an option. We utilize the latest technology and follow rigid protocols to guarantee the desirable outcome for your order. For one part or thousands of parts, our award winning service and design has been helping companies in Missouri and nationwide with state-of-the-art technology and exceptional service. Find out how we can meet your plastic injection molding needs today by calling 573-437-4154 today.