Corrosion-resistant plastic mold steels

Type Corrosion resistant plastic mold steel (good machinable) Tempered mold steel Tempered and hardened mold steel (highly polishable and etchable)... 

Corrosion-resistant plastic mold steels e.g. for PVC processing, pre-hardened to approximately 30 HRC for standard applications, up to 53 HRC for high levels of wear, with hardening after (pre-)machining... 

FIGURE 3.9 Abrasive wear resistance as a function of carbide size and of the carbide content of the corrosion-resistant plastic mold steels compared to through-hardening... 

The material 1.2738 is the material most often used for larger molds. For best graining results, this steel was further developed and is now available as 2738 mod. TS. Other quenched and tempered steels are 1.2311,1.2711, and 1.2316 as a corrosion resistant material. For small molds or as mold inserts with high hardness, through hardened plastic mold steels such as 1.2343,1.2344, and 1.2767 can be used. 1.2083 is available as a corrosion-resistant variant. 

Coinjection Molding A hybrid technology, also known as multimaterial injection molding, that creates composite pieces made of plastic and metal parts locked together via injection molding or extrusion. The process combines the strength of steel with the corrosion-resistant properties of plastic. Overall weight is reduced, the need for exterior paint is eliminated and assembly and labor costs are slashed due to more efficient use of machinery. 

Materials used in the mold must resist corrosion. This makes stainless steel and copper alloys the materials of choice for water injection molds. The mold is designed with an overflow to provide positive control material flow at the opposite end of the cavity. When the main cavity has been filled, the valve to the overflow is opened and the injection of the secondary material takes place. At this point in the cycle, a gas (typically nitrogen) might be injected to core out the hollow feature and force the displaced plastic into the overflow. If a gas is used, then water injection follows. If not, water injection only occurs. Following water injection, another gas or even plain air is used to discharge the water from the part. 

The shape of the 1910 canteen also became the standard that is still represented by today s molded polyethylene 1-quart (0.95-1) canteen, NSN 8465-00-889-3744 (Fig. 14.3). The 1910 1-qnart shape went through material changes thronghout its life cycle. Aluminum, corrosion-resistant steel, plastic and porcelain were used at different periods of the canteen s history. During World War II, aluminum was... 

Plastic top plates are made from several different types of thermoplastics. Many are molded from acetal or low-friction acetal. Low-friction acetal is a blend of acetal with another plastic with a very low coefficient of friction. The plastic used must have good corrosion resistance and the plastic must also have good wear resistance in conditions where there is little or no lubrication. The barrels of the top plates must be molded very accurately, for the same reasons that the barrels of steel top plates must be curled very accurately. 

For plastics processing, both alloyed and corrosion resistant and nitriding and hardening steels can be used. In general, temperature ranges from 10 to 200 °C in exceptional cases, temperatures 200 °C are required in the injection molding process. 

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