Polypropylene continues to gain popularity in the injection mold industry. With a low-density consistency and chemical resistant design, it is often used to produce items such as medical devices and automotive parts. While polypropylene resins offer a number of benefits, it is important to monitor the temperature threshold during the smelting and printing process. Here are the top 10 tips for injection molding polypropylene resins.
1) Make sure you have the right molding equipment
The road to successful injection moulding starts with the right molding equipment. Fortunately, polypropylene can be printed accurately using unchanged one-stage thread molding equipment.
2) Consider pre-drying ONLY if you use certain polypropylene resins
“In most plastic processing factories, resin dryers are standard equipment. An important exception to this is facilities that exclusively process polyolefins such as polyethylene and polypropylene. These are some polymer families which do not require drying because this material family is not hygroscopic. “
Unlike most commercial polymers that are highly polar, polypropylene is a non-polar substance, allowing you to pass the pre-drying process. The only resin that may require pre-drying is some filled polypropylene resin. This advantage allows you to save time during the injection moulding process.
3) Use a melting temperature range of 400 ° F to 500 ° F
Using melting temperatures higher than 500 ° F can cause flashing, warpage, shrinking and burning. Temperatures lower than 400 ° F, on the other hand, can produce poor quality flow and surface markings. When you set your melting temperature, try to reach a melting temperature that is 25-50 ° F higher than the minimum filling temperature.
4) Strives for an injection pressure range of 800 to 1,500 psi
Injection pressure is another variable that can help control common injection moulding problems with polypropylene molding. While the injection pressure you set must reflect the construction and size of the item. In general, the pressure should be able to fill about 99% of the parts to prevent problems with flashing and stickiness.
5) Don’t rush the injection process
Be prepared for the injection process to consume the majority of each whole cycle. While injection time does not significantly affect the warpage, patience with the injection process is important because the accurate injection is a major factor in controlling shrinkage.
6) Choose a mold temperature around 50-150 ° F
The mold temperature must be carefully regulated to reduce stress and surface imperfections. A mold temperature of 50-150 ° F helps prevent this trap. In addition, ensure that the mold is uniformly cooled to facilitate the removal of components from the mold.
7) Never rush time
Hold time plays an important role in preventing warpage and shrinkage. Therefore resist the urge to remove parts of the mold before it is cool enough. Allowing the part to cool to around 130 ° F is recommended to produce satisfactory results.
8) Use minimal back pressure to increase your cycle time
The ideal backpressure for polypropylene injection mold is usually between 50 and 100 psi. Backpressure in this range can help increase your cycle time. Exceptions to this rule of thumb are cases that require mixing pigments.
9) Adjust your mold or polypropylene level if sticking occurs
Sticking is not common with polypropylene because it has exceptional release properties. However, if minor adhesions occur, you can easily improve the attachment by making minor changes to the mold or using a grade of polypropylene that has been lubricated internally.
10) Seek support from trained industry professionals
The only best way to ensure your satisfaction with polypropylene resin injection molds is to seek guidance from a leader in the injection mold industry. We invite you to contact us for further injection mold tips. With almost years of industry experience, we have the resources and expertise to help you develop the unlimited injection moulding process. We look forward to hearing from you!