Canadian Plastics

Moldmakers give specialty steels high marks

ApplicationIt has long been a truism among veteran moldmakers that the quality of the mold begins with the steel. If anything, the observation is even more critical today as customers, some of whom ma...

March 1, 1999   Canadian Plastics



Application

It has long been a truism among veteran moldmakers that the quality of the mold begins with the steel. If anything, the observation is even more critical today as customers, some of whom may be paying up to one-half million dollars or more for a large mold, expect value-added features that will enhance a mold’s performance and lifetime in production.

Buderus’ P20 premium steel, BMP-Thruhard Extra (51, Tool Steel Service, Inc.), has scored points with a number of Canadian moldmakers who have found the steel’s uniform, through-hardened properties ideal for larger molds. The steel, which was introduced to the Canadian market last year, is heat treated to 290/325 BHN (Average, 31 HRc) with virtually no hardness drop-off towards the center.

Andy Moorehead, engineering manager at Accurate Mould Co. (Rexdale, Ont.), says the company used BMP-Thruhard Extra for the first time to build the mold for a large “jeep riding-toy.”

“We found the steel very satisfactory,” says Moorhead. “It cuts nicely and, unlike conventional P20, there is no drop off in hardness in the core of the block.”

Reko Tool & Mould’s Dennis Humen, purchasing manager, says the company’s selection of BMP-thruhard extra was influenced by its requirements for uniform hardness, cleanliness and excellent polishing. BMP-Thruhard Extra is an advantage in large automotive molds, such as molds for fascias, in which half of the block is being removed, notes Humen. Uniform hardness provided by the steel also improves the cooling characteristics of the mold during injection, says Humen.

Uddeholm has recently introduced Corrax (52), a stainless mold steel it says is highly resistant to corrosive plastics. Corrax is supplied at a hardness of 32 HRc, although for more severe applications the hardness can be increased up to 50 HRc through a relatively simple aging process, according to the company.

Corrax is ideal for injection molds making medical parts, parts made of PVC or rubber, or for molds used in clean room environments, the company says. Other specific plastics-related applications for the steel include parts for tools and machinery used in the food and medical industries, dies for extrusion and feed screws in injection molding and extrusion machines.

Thyssen Marathon Canada’s new 15-5 RMQ stainless mold steel (53) possesses good weldability and corrosion resistance, according to Don Cook, vice-president of operations. The steel chemistry is controlled through remelting, which provides superior transverse toughness and ductility, and reduces banding. The clean, uniform microstructure combined with high hardness provides excellent polishability.


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