COPPER BRAZING ALLOYS HEAT METHODS
HEATING METHODS AND ATMOSPHERES
Copper brazing 
is usually limited to furnace heating because of the atmosphere requirements. Heating may be electric, gas, or oil as long as the atmosphere can be maintained within desired limits. In some special cases, other means such as induction or resistance heating can be used, but only for highly specialized brazing of relatively small parts.
is usually limited to furnace heating because of the atmosphere requirements. Heating may be electric, gas, or oil as long as the atmosphere can be maintained within desired limits. In some special cases, other means such as induction or resistance heating can be used, but only for highly specialized brazing of relatively small parts.An atmosphere of combusted gas (containing not more than 20 grains sulfur per 100 cu ft) is satisfactory for MONEL alloy 400 and Nickel 200 but not INCONEL alloy 600. Dissociated ammonia can be used with alloy 400 and Nickel 200 and also for INCONEL alloy 600 if the dew point is low (-800F or lower).
Procedure
Copper brazing materials rapidly alloy with MONEL alloy 400 and Nickel 200. The braze metal should be placed as closely adjacent to the joint as possible. There should be sufficient metal to fill the joint. Excessive copper braze metal, however, can create excessive alloying with the nickel-chromium base metals.
Depth of alloying (penetration) is a function of brazing-alloy
flow, quantity of brazing alloy, and time at temperature. When copper flows over the base metal, it can erode the surface. On heavy sections this effect may not be significant. However, when joining thin sections even shallow penetration may be serious. This problem can be partially overcome by limiting the amount of brazing alloy and reducing brazing time.Excessive oxygen and moisture in the brazing atmosphere will impede or prevent flow
of the copper brazing alloy. The surface of the part will appear dark and oxidized rather than bright. A positive pressure should be maintained in the furnace to prevent air from entering. Improper drying of the combustion gas before it enters the furnace can result in excessive oxidation.COPPER BRAZING ALLOYS
Commercially pure grades of copper are commonly used as brazing filler metals. Tough-pitch copper containing as much as 0.04% oxygen is used. However, it is generally believed that oxygen-free copper will produce joints having somewhat greater strength and ductility. Alloys may be pre-placed in the form of wire, strips, slugs, plating, or powder. Powder may be applied as a slurry. The vehicles or binders most frequently used are methyl cellulose and acrylic resins whose products of combustion are gases that will not interfere with the brazing operation. They are preferred to such binders as machine oil, glycerin, and varnish, which leave a carbonaceous residue. A fairly thin mix will be required for dipping, brushing, or spraying. A stiffer mix may be used in a grease-gun-like manner.
may be pre-placed in the form of wire, strips, slugs, plating, or powder. Powder may be applied as a slurry. The vehicles or binders most frequently used are methyl cellulose and acrylic resins whose products of combustion are gases that will not interfere with the brazing operation. They are preferred to such binders as machine oil, glycerin, and varnish, which leave a carbonaceous residue. A fairly thin mix will be required for dipping, brushing, or spraying. A stiffer mix may be used in a grease-gun-like manner.Fluxes
Fluxes for brazing with copper filler metals are similar to those used for oxy-fuel welding. Mixtures of chloride salts (calcium, sodium, and barium) and fluoride salts (barium) in an appropriate binder are suitable. The addition of hematite and wetting agents may be required for brazing the age hardenable alloys. The flux mixture will become glass-like after cooling and is insoluble in water. Common methods of removal are abrasive blasting, chipping, and grinding.
Joint Designs
Joint designs for copper-brazing nickel alloys are similar to those used for steel. Tolerances for assembly range from a light press fit to 0.002 in. maximum clearance. Butt-brazed joints will have strengths approaching those of annealed wrought alloy products.
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nickel alloys are similar to those used for steel. Tolerances for assembly range from a light press fit to 0.002 in. maximum clearance. Butt-brazed joints will have strengths approaching those of annealed wrought alloy products.by online welding courses – welding training online
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