Non-Structural Applications of Copper and Copper Alloy Powders

Although the major applications of copper and copper alloy powders are in structural components, significant quantities of the powders are employed in nonstructural applications. These range from the strictly utilitarian to the purely ornamental. As the advantages of using these powders to improve the properties of nonmetallic materials become more apparent, new applications continue to develop. Currently, copper and copper alloy powders are used in paints, coatings and inks, plastics-metal combinations, brazing pastes and in a variety of other applications.

Paints, Coatings and Inks

Pigments are made by flaking copper, copper-zinc or copper-zinc-aluminum alloy powder in ball mills. Colors range from copper red through pink to various shades of gold. Additional color modifications can be achieved by adding such elements as nickel or tin to the alloys or by heating under controlled conditions. The alloy pigments are generally known as "gold bronze."

To produce a highly metallic luster on a surface, the flakes must float to the surface of the film and orient themselves to form a continuous metal film, a phenomenon known as leafing. The coverage of the coating and the gloss generally depend on the particle size and shape.

The leafing properties depend on the formulation of the base material. Metallic coated paper, for example, is produced by applying flake powder in a thin film to paper stock coated usually with a casein or pyroxylin coating. This paper is used for menus, greeting cards, tags, box wrapping and other printed pieces.

Dusting is a process used to put "gold" rims on labels. The area to be bronzed is printed with an ink of tacky consistency, bronze powder is dusted on the surface and adheres to the inked areas, and the excess is shaken off.

Bronze powder is used also in printing wall paper; in silk screening to apply designs to paper, glass, cloth or leather; in hot stamping, a process of roll transfer of flakes to produce stamped or embossed impressions; and in paints.

A major application of gold bronze pigments is in the printing industry. These metallic printing inks are used for both rotogravure and letterpress printing.

Copper powder and cuprous oxide are used in the formulation of vinyl paints for use in marine applications to prevent or delay the fouling of metal ships and buoys by marine organisms. Copper-filled epoxy paint is used in similar applications.

Metallizing guns are fed with copper or bronze powder to form a corrosion resistant coating on the workpiece. A recent development is the use of copper and tin powder to produce coatings by plasma spraying.

Mechanical (peen) plating is a process of depositing a metal coating on a metal surface without the use of electricity. The process consists of tumbling the parts to be plated in a rubber-lined barrel containing a slurry of metal powder, glass beads and a promoter chemical. During the operation, the powders are peened flat and cold welded to the surfaces of the parts. The process is used to plate small ferrous parts such as stampings, fasteners and washers with various soft metals, including brass and copper. As an example, copper powder is mechanically plated on parts which are to be brazed.

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Plastics-Metal Combinations

The use of copper and copper alloy powders in combination with various plastics is growing in importance. A large quantity of bronze powder is used with vinyl resins for floor and wall tile. Similar powder is added to acetyls or nylon to produce thermally or electrically conductive moldings that can be plated if desired. These bronzes are also used with polyethylene, styrene and other plastics in extrusion and injection molding applications for decorative effects.

Epoxy resins filled with copper or bronze powder are used as repair and patching pastes for brass and bronze castings and stampings. Bronze-filled epoxy pastes have been used for years to repair condenser tubes.

Epoxy resins, highly filled with copper or bronze powder, are used to cast forming tools. Ornamental statuettes and other decorative pieces are also cast of filled plastics.

Copper-polyethylene mixtures have been developed for self-lubricating bearing applications. A composition containing 76% copper powder and 24% high molecular weight, high density polyethylene has exhibited good bearing properties. 1

The addition of bronze powder to PTFE (polytetrafluoroethylene) increases the hardness and compressive strength, improves dimensional stability, and lowers cold flow, creep and wear. Improvements are progressive up to a maximum of about 70% bronze. However, the addition of bronze makes the PTFE unsuitable for electrical applications and for applications in environments that are corrosive to bronze. Bronze-fortified PTFE is used for self-lubricating bearings, compression rings, cup seals, rod seals, valve seats and liners.

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Copper and copper alloy powders in paste form are used as filler metals for brazing steel and copper alloy parts. A brazing alloy paste consists of copper or copper alloy powder (55-90%) and a neutral binder (10-35%). It may or may not contain a flux (up to 10%). Fluxing is not required, for example, in certain controlled-atmosphere brazing operations. Pastes range in consistency from those that can be sprayed to those resembling putty.

The major advantage of using a paste in furnace brazing is the ability to deposit a controlled quantity of the paste in the area desired with automatic or manual applicators. If a flux is required, it is combined with the paste, speeding preparation of the assembly and reducing labor costs. Paste alloys can also be dispensed in irregular shapes, an advantage over preforms.

The major use of copper brazing paste is in the furnace brazing of carbon and alloy steel parts. They can be brazed in a variety of reducing atmospheres or in vacuum using fluxless paste. Stainless steels can also be brazed in hydrogen or vacuum with fluxless pastes. Pastes containing fluxes can be used for brazing of low carbon, low alloy and stainless steels in inert gas atmospheres.

Brazing with copper requires temperatures on the order of 2050 F (1130 C). Copper alloy powders can be used where a lower temperature is desirable for brazing. Copper-tin (90Cu-10Sn) bronze pastes can be used at 1925 F (1150 C) for brazing steel parts and copper-nickel alloys. Copper-zinc-tin (59.25Cu-40Zn-0.75Sn) can be used at about 1700 F (925 C) for brazing steels, copper base and nickel-base alloys. However, fluxes are required with the copper-zinc-tin alloy.

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Chemical Applications

Copper powder is used as a catalyst in various chemical operations. In one process, the addition of activated copper powder to solutions containing cyanides and tartrates causes the precipitation of lead, bismuth, tin, cadmium and silver but zinc, cobalt, nickel, copper and aluminum remain in solution.

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Other Applications

Advantage is taken of the excellent electrical conductivity of copper powder to prepare some printed circuits for use in radio and television applications.

Copper powder confers nonsparking and fungicidal properties to oxychloride cements.

A compound containing copper, lead and zinc powders is used to coat the threads of petroleum drilling pipe to aid in breaking the threads when the equipment is dismantled.

Brass powder is added to the compound used in making poker chips to increase the weight of the chips.

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  1. P.M. Kamath, S. Stregeusky and C.A. Sprang, "Development of Applications for Copper Plastic Combinations," Summary Report to International Copper Research Association, 1966.