Hard chrome-plated mold

The shrinkage of the material being processed is taken into account when dimensioning the components in the cavity areas. Hard chrome-plated molds, which consist of individual segments, are designed and manufactured so that the individual mold parts are compensated for their chromium layer thickness. A self-contained chromium layer has to remain for any adjustment work. Unplated areas should be avoided in any case to prevent a separation of the hard chromed plating from the mold steel. 

All mold components contacted by the molding compound—runners, gates, and cavities—should be made of hardened steel, hardened to 65-68 on Rockwell scale, highly polished, and hard chrome plated. 

TS molds are usually hard-chrome-plated on areas that are exposed to the molding compound during the molding process, such as the plunger, pot. 

Heated steel molds, preferably hard chrome plated, are used, which may be of multicavity design. Tooling costs are higher than for compression moulding since appropriate gates and runners must be included in the mould. 

Machines and molds may cost between several hundred thousand and a million dollars, depending on the throughput rates and accessories. Molds for blow molding are made from beryllium copper and aluminum because of the excellent thermal conductivity of these materials. Stainless steel and hard chrome-plated tool steels are also common. 

For reasons mentioned previously, the molds are made of case hardened steel or a fully coated material with a hardened or refined surface and tough core. All components that do not have molding surfaces and are exposed to wear are made of steel with strengths from 600 to 700 N/mm. Hard chrome plating or a corrosion-resistant material has to be selected to protect the finish and the molding surfaces against wear caused by friction and chemical attack. 

On the one hand, high chromium steel polished surfaces can be used as a surface protection. On the other hand, hard chrome plating with a thickness of approx. 0.005 mm is used as the most common and least expensive coating for elastomer molds. Currently, a coating based on chromium nitride is increasingly used. In addition to these coatings, numerous other options can be considered, such as ceramic coatings or titanium-based surfaces. 

In the case of hard chrome plating, after preliminary cleaning (electrolytic or hot degreasing, flushing, etc.), further activation in the bath is required to improve layer adhesion. A roughened mold surface finish is achieved by anodic connection. The steel surface is etched, and it is possible for impurities (e.g. sulfides, oxides) in the steel, or residue from previous operations (EDM, polishing, etc.) to be released, and cause perforation. 

Molding of CSM requires some special care in the type of metal due to the acidic nature of CSM even with the presence of an acid acceptor. A hard surface (minimum 45 Rockwell C), abrasion and corrosion resistant and non-porous steel needs to be employed. A hard chrome plate at least 0.1 mm thick is recommended. Stainless steel is a more expensive but more effective alternative. Lower mold temperatures reduce mold fouling and corrosion if economics will allow. Molds need to be cleaned at least weekly with an alkali solution with ultrasonic vibration. 

Injection Mold Steels Injection mold steels for SPS can be produced with common mold steels used in the mold-building industry. P20 steel can be used, and tool life can be extended by applying hard chrome flash plating. For tooling that creates very thin wall plastic applications, such as electronics and electrical connections, the use of H-13 and/or S-7 tool steels for improved strength and wear capabilities is recommended [7],... 

Construct the mold from stainless steel with a minimum chromium content of 13%, preferably 16% the Rockwell C hardness must be at least 55. A full range of surface finishes is possible, on UPVC moldings, from high gloss to textured. Hardened steel molds may be protected by chrome plating. 

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