Getting the Heat Out
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| JOINED WITH NICKEL Metal components brazed with nickel alloys emerge from a vacuum furnace |
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Nickel brazing solves heat transfer challenges in the injection molding industry
Nickel magazine, Mar. 02 -- An innovative approach using nickel brazing and vacuum heat
treating is helping companies in the burgeoning plastic injection molding industry solve heat transfer
challenges. This, in turn, is resulting in improved productivity.
Fused Metals Inc., a metal treatment specialist based in Georgetown, Ontario, Canada uses an approach that
involves brazing cooling channels found in the various components of a mold including the cavity, core,
wedges and stripper rings. Cooling channels are used to remove the heat from the components of the mold as
molten plastic fills the form. When the heat is removed, the plastic cools and solidifies and the cast object
is dropped from the mold. The time it takes to complete this process is known as the cycle time.
The main benefit of brazing, however, is that heat extraction from the cooling channel is maximized and the cycle time is reduced, thereby improving the productivity of the operation. By vacuum brazing the cooling channels with nickel alloys, the channels also become watertight and corrosion resistant.
The company brazes heating elements into manifolds to ensure the molten plastic remains at the correct temperature until the plastic reaches the mold. Because nickel alloys are used to braze the element in place, Fused Metals can ensure that the entire element is in contact with the manifold and the molten plastic remains at a consistent and uniform temperature. This is critical to the process as variations in temperature can affect the integrity of the plastic. Should hot spots develop in the manifold, the plastic could degrade or burn. Similarly, if the plastic were too cool in places, it could become sluggish and flow improperly.
If a heater element burns out, a replacement element can be rebrazed into the manifold without affecting the existing assembly. This is accomplished by rebrazing using a different nickel alloy braze with a lower melting point. The rebrazing process will not affect the tempered conditions or dimensions of the manifold.
Elsewhere in the manifold, copper plugs are brazed with nickel alloys to seal machined channels used to deliver the molten plastic from the manifold to the nozzle. The advantage of using brazed plugs lies in the strength of the seal. While welded plugs or metal screws could be used, the brazed plugs are capable of withstanding pressures up to 40,000 psi. Fused Metals is looking to see if this application can be transferred to other industries with similar heat transfer challenges. Between 80% and 90% of the nickel brazing completed at Fused Metals is for applications in the plastics industry. Brazing is also done for other industries such as the electronics, automotive and power generation industries. Nickel brazing at Fused Metals is performed in vacuum furnaces up to 90 centimetres (cm) in diameter and up to 120 cm deep. The inner elements of the furnace are composed of pure molybdenum because of the extreme maximum operating temperatures up to 1,350°C. The outer layers of the furnaces are made from S30400 stainless steels, however, more experimental furnaces use S40300 stainless steel.
Vacuum brazing is the process of joining two materials, usually metals, in a vacuum using a filler metal of a third composition which has a lower metal point than the base materials, but above 450°C. The base metals do not melt, but the filler metal diffuses more or less into the base metals, and may give a joint strength higher than the base metal. Vacuum brazing can be used to join two compositionally different metals, including joining alloys together that could not be otherwise joined. Unlike welding, vacuum brazing is done in a clean environment, with the filler metal flowing over clean, contaminant-free surfaces, and leaving a joint free of porosity, trapped fluxes and oxide inclusions.
Photo: FUSED METALS
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Grant Robinson B.Sc. |
