Steels Used For Plastic Injection Molding

Steels Used for Plastic Injection Molding

By Carter Kho

What are the types of steel used for Plastic Injection Molding?

  1. P-20 (Class 4 and 5)
  2. 420 Stainless Steel (Class 1 and 2)
  3. H-13 (Class 1 and 2)
  4. S136H (Class 3)
  5. 718H (Class 3)


Plastic injection molding has become one of the most effective and innovative manufacturing processes across all industries, providing efficiency like no other. This manufacturing efficiency has helped produce high-quality plastic products in a short amount of time, without compromising the quality.

At the center of plastic manufacturing is the plastic injection molds, which helps create plastic products made by injecting molten plastic. These molds are specially designed and crafted to shape various plastic products and to withstand the rigors of mass production. This makes steel the ideal material to use in plastic manufacturing, as their positive qualities, such as high durability and temperature resistance are qualities needed to produce the best products.


Classes of Plastic Injection Molds

Classes Of Plastic Injection Molds

Plastic injection molds can be divided into different classes, each requiring different types of steel to manufacture products effectively. Each class allows for the development of different kinds of steel products, which means that each steel type must be able to handle various manufacturing demands. Here are the classes of plastic injection molds used in the plastic injection molding industry.


Class 1 and 2

This class of plastic injection mold requires mold steel that can be hardened for higher durability, as other steel types might crack under immense pressure. High heat resistance is also needed, as most of these molds are subject to extreme temperatures during the manufacturing process. These qualities make them great for mass-production purposes.


Class 3

Class 3 requires steel molds that have been pre-hardened. This makes it durable enough to withstand the rigors of manufacturing. Pre-hardened steel is mainly used as general-purpose steel and is a popular steel molding tool.


Class 4 and 5

Class 4 and 5 is another set of classes that utilize general-purpose steel. Mainly used to create cavities in the molding base, some steel types in this class are utilized to create molds with low requirements, making them inexpensive and easy to maintain and replace.


Types of Steel Used in Plastic Injection Molding

Types Of Steel Used In Plastic Injection Molding

Steel has become the main material used in various industries, and that includes the plastic injection molding industry. Being one of the most durable and versatile materials around, steel is able to be molded and shaped into various forms, and withstand the strains and demands of mass production. Here are some of the most common steel types found in the plastic injection molding industry:


P-20 (Class 4 and 5)

This is the most common type of steel used in plastic injection molding, P20 is a general-purpose steel that is used for rubber compression molds, plastic injection molds, prototype molds, transfer molds, and holder blocks. This type of steel is pre-hardened, making it a strong and sturdy material to use. For those looking for a versatile steel type that can be used in various applications and forms, this is one of the best types around.


420 Stainless Steel (Class 1 and 2)

Another common type of steel used for plastic injection molds, 420 stainless steel has a strong resistance to corrosion and wear. These qualities make it great for manufacturing plastic parts for food processing, electronics, and medical products, all of which require plastic types that are durable and resistant to high temperatures and strong substances.


H-13 (Class 1 and 2)

H-13 is a type of air-hardening steel used in die-cast molds which has high-temperature resistance and durability. This makes it a great material to use to create plastic mold cavities, which are subjected to extreme temperatures during the manufacturing process.


S136H (Class 3)

Another type of pre-hardened steel, the S136H is a type of steel that is highly resistant to acidic substances and is suitable for humid environments, like tropical areas where rain is constant. This makes it a good material for plastic injection molds, as it has high corrosion resistance and durability, making it ideal in manufacturing plastic products such as disposable utensils, camera parts, sunglasses, and types of lab equipment. Like the 420 stainless steel, the S136H is an ideal type of steel for the medical and food industry, where temperature and resistance to chemical substances are important.


718H (Class 3)

This type of steel is hardened and tempered before being used for plastic injection molding, which helps give it high durability that makes it a very efficient material used in plastic manufacturing. This helps shorten the cycle time, providing a more cost-effective manufacturing solution that can create more high-quality products. For producing items in bulk, this steel type provides strength and high resistance.


Key Takeaway

Steel is a crucial material in the plastic injection molding industry. By identifying each type of steel and mold class, you can determine what kind of products will be created and which manufacturing processes are involved for various items.