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The steels for plastic injection mold
- Jun 14, 2018 -

Due to the enormous diversity of plastic materials and the widely varied requirements for plastic products, various requirements for the performance of plastic injection mold steel have been laid down. Therefore, many industrially developed countries have created an extensive range of plastic mold steel series, including carbon steel, carburized plastic mold steel, aging hardening plastic mold steel, corrosion resistant plastic mold steel, free machining plastic mold steel, through-hardening plastic mold steel, maraging plastic mold steel and mirror polishing plastic mold steel, etc.

 

Plastic injection Molds can be classified into 5 classes by service cycle, and they impose the following requirements on steel materials:

 

According to the length of mold life, molds can be classified into 5 classes. Class 1 mold runs 1 million or more shots, class 2 mold runs 0.5 – 1 million shots, class 3 mold runs 0.3 – 0.5 million shots, class 4 mold runs 0.1 – 0.3 million shots, and class 5 mold runs less than 0.1 million shots.

 

Class 1 and class 2 molds require the steel materials that can be harden up, with a hardness around HRC50, or the molds will wear easily, leading to out-of-tolerance injection molded products. As a result, the selected steel materials need to possess good heat treatment properties and machinability despite the high hardness. Of course, there are some other considerations, too.

 

Usually, the steel choices include Swedish 8407 and S136; American 420 and H13; European 2316, 2344 and 2083 and Japanese SKD61. For strongly corrosive plastics, S136, 2316 and 420 steels are normally chosen. In addition to S136, 2316 and 420 steels, low corrosion plastics can also choose SKD61, NAK80, PAK90 and 718M steels. Product appearance also has a great influence on the mold materials. S136, 2316, 718S, NAK80, PAK90 and 420 steel materials are suitable for transparent and mirror polishing products, while highly transparent products should primarily select the S136, and secondarily the 420 steel materials.

 

Class 3 molds mostly use pre-hardened steels, such as S136H, 2316H, 718H and 083H, with a hardness ranging from HB270 to 340.

 

Class 4 and class 5 molds usually use the P20, 718, 738, 618, 2311 and 2711 steel materials. For molds with extremely low requirements, S50C and 45# steels may be used, i.e. creating a cavity directly in the mold base