Iron-based brazing filler metals

Abstract

A plurality of parts is brazed using an iron-based brazing filler metal. The parts generally include stainless steel, and the brazed assembly forms a heat exchanger characterized by effective corrosion resistance and low rates of leaching of nickel into fluids passing therethrough. The heat exchanger is especially suited for use in processing items intended to be ingested by humans or animals.

Description

BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The present invention relates to brazing of metal parts, and more particularly, to a homogeneous, ductile iron-based brazing material useful in brazing stainless steels, and a method for brazing stainless steel components to form articles of manufacture, wherein the brazed stainless steel components reduce the propensity of nickel to leach from such articles in water. [0003] 2. Description of the Prior Art [0004] Brazing is a process for joining metal parts, often of dissimilar composition, to each other. Typically, a filler metal that has a melting point lower than that of the metal parts to be joined together is interposed between the metal parts to form an assembly. The assembly is then heated to a temperature sufficient to melt the filler metal. Upon cooling, a strong, leak-tight joint is formed. The assembled parts may either constitute a finished article of manufacture or may form a sub-component for use in a ...

AI Technical Summary

Benefits of technology

[0013] The present invention provides a method to fabricate heat exchangers and other articles of manufacture by brazing components thereof with an iron-based brazing filler metal composition. Brazed assemblies advantageously exhibit effective general corrosion resistance and low rates of leaching of nickel into fluids passing through either side of the heat exchanger. As a result, the heat exchanger is highly suited for exposure to items intended for ingestion by humans or animals.

[0014] In a first aspect, the present invention provides a method to manufacture assemblies, especially assemblies which include parts comprising stainless steels. Such assemblies comprise parts joined using iron-based brazing filler metals. When manufactured, the assemblies are characterized by general corrosion resistance and by low leaching rates of nickel. The method comprises: juxtaposing at least two parts to define one or more joints therebetween; supplying to the one or more joints an iron-based brazing filler metal composition that is a ductile, amorphous brazing foil; heating the juxtaposed parts and the brazing filler metal to cause melting of the iron-based brazing filler metal; and cooling the melted iron-based brazing filler metal to produce a brazed joint that minimizes an amount of nickel leaching into a fluid contacting the brazed joint. The heating and cooling operations are generally carried out either in a protective gas atmosphere or in a vacuum.

Problems solved by technology

However, brazing manufacturing processes carried out at high temperatures may also adversely affect the propensity of the stainless steels to leach.

However, the corrosion resistance of heat exchangers having components brazed using copper as the brazing filler metal is poor.

Typically, such heat exchangers required frequent replacement, resulting in significant costs for the replacement device and the associated labor, as well as economic losses resulting from manufacturing downtime.

Unfortunately, it was also found that when such nickel-based brazing filler metals were used, an undesirably high amount of nickel often leached into water or other fluids flowing through such assemblies.

Not surprisingly, governmental regulations in some countries have imposed strict limitations on the amount of nickel which may be leached into fluids for human ingestion or consumption.

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