Alloys or metallic compositions – Copper base – Tin containing
Reexamination Certificate
2000-06-15
2002-02-12
Yee, Deborah (Department: 1742)
Alloys or metallic compositions
Copper base
Tin containing
C420S473000, C148S433000
Reexamination Certificate
active
06346215
ABSTRACT:
FIELD OF THE INVENTION
The present invention is directed to copper-tin alloys which are especially suitable for use in the manufacture of structural parts which are joined together through the use of heat.
BACKGROUND OF THE INVENTION
Copper-tin alloys have, due to their high mechanical strength and great resistance to sliding stress or wear and corrosion, been utilized for many different mechanical structural parts and preformed articles that are to be manufactured into semifinished products by mechanical working. Copper-tin alloys also have been used as casting materials and as wrought materials. Phosphor bronzes are also widely used due to their ready availability and low cost and have the physical properties of a high mechanical strength and ductility. Additionally, they offer a high corrosion resistance in many different environments.
Workable copper-tin materials are particularly attractive for use in the manufacture of structural parts having small dimensions and complicated geometries. For example, in DIN 17662, a wide variety of uses for 4 to 8% bronze is disclosed, which in addition to up to 8.5% tin, also contains phosphorus in an amount of from 0.01 to 0.35%, iron in an amount of up to 0.1%, nickel in an amount of up to 0.3%, zinc in an amount of up to 0.3% and lead in an amount of up to 0.05%. Improvements in these materials have been desired with respect to electrical conductivity and suitability for electromechanical structural parts.
WO 9/20176 and WO 98/48068 are concerned with the improvement of electrical conductivity and relaxation resistance of traditional copper-tin materials. However, these improvements have little bearing on the suitability of the use of copper-tin alloys in machine- and apparatus-building industries, and precision-mechanics and jewelry industries. In these particular industries, classic phosphorus-bronzes are still exclusively used due to the fact that these materials can be used in a wide variety of manners due to the characteristics which are obtained through cold-working. However, these classic phosphorus-bronzes also have their deficiencies.
Due to the manufacture of functional parts, it is often necessary to join different structural elements. Welding and hard soldering methods are typically utilized to join these structural elements or parts. However, due to the heat entering into the structural parts to be joined, losses in strength result in the parts of the metal exposed to the heat due to conservation and recrystalization. This is especially true when using fusion-welding and hard-soldering methods. In order to keep the loss in strength as small as possible, hard-soldering instead of welding is used as often as possible. With solders having operating temperatures typically starting at about 450° C., the joining of the structural elements can be performed but this requires a compromise between high strength and good loading capacity.
Since solder serves as a filler metal, the strength of the solder plays a role in the mechanical stability of the joined structure. As such, high strength solders are desirable. However, high strength solders, as a rule, have higher melting temperatures. This results in an increase in the heat applied to the joined parts and an attendant loss in strength in the areas adjacent the soldered junction. As such, there is a need for materials which resist softening during soldering operations.
In the eyeglass industry, nickel-free materials have been developed as materials having a higher resistance to softening. Many different copper-aluminum and copper-titanium alloys have been formulated. These alloys offer better spring characteristics and resistance to softening than phosphor bronze alloys typically utilized for the bows of glasses. However, during the use of these nickel-free alloys, it has been found that hard soldering under a protective gas creates problems in that these materials also react with an oxygen-deficient atmosphere and thereby significantly hinder the wetability of the surfaces of the structural part with the solder. Good processability during hard soldering is only possible through the use of aggressive flux agents. However, these aggressive flux agents have problems with respect to work safety and environmental contamination and also may cause a color change and leave residues on the joined structural parts. This requires that cleaning be performed in utilities where appearance is important. Moreover, independent of the flux agent, copper-tin alloys also have a tendency to change color during heating which also requires a cleaning of the joined structural parts. These cleaning operations are expensive and highly undesirable.
As discussed above, copper-tin wrought alloys containing about 8 wt. % tin are easily formed and especially suitable for the manufacture of complex functional parts. These alloys are used as friction bearings and gearings, springs and for parts which are stressed by ocean water, such as chains, armatures, etc. When utilized as structural parts which are subjected to very high mechanical stresses, such as gears, copper-tin cast alloys with tin contents above 10% by weight are preferred. These cast bronzes are increased in mechanical strength through the increased tin content. However, the increased tin-content results in brittle phases being formed in the primary structure during the solidification in common casting. These phases are not removed, even through a thermal after-treatment, without pores or imperfections remaining in the materials, which also in turn influence reforming.
Therefore, there exists a need for material which combines the chemical and mechanical characteristics of casting bronzes with the processing characteristics of wrought materials having a cold-working ability and guarantee of a high mechanical strength and hardness. In order to meet this need, an alloy has been proposed which is a copper-tin alloy containing tin in an amount of from 12 to 20 wt. % to enhance the strength of the material with the remainder being copper. This alloy can be formed by spray compacting or band casting and then quickly cooled from the molten state to suppress precipitation. This results in the primary structure of the alloy at room temperature being free of microscopic precipitation and the preforms manufactured from these alloys can be hot or cold formed in an excellent manner.
Even though the copper-tin alloy disclosed above has advantageous properties, deficiencies still remain with the alloy. As in a case of conventional low tin content copper-tin wrought alloys, there is a need to deoxidize the melt. Elements having an affinity for oxygen, such as phosphorus, are added to the melt as with conventional alloys. Due to the high affinity for oxygen, these added elements have a tendency to burn off and form slag during melting and casting which requires a complicated post treatment in order to maintain the desired concentrations. Additionally, the oxides of the deoxidation media influences the melt in general and the melt viscosity in particular and thus can have an influence on the forming process, such as spray compacting. Oxides from the oxygen affinity added mixtures can also be created during the hot-forming of the copper-tin alloys and these oxides worsen the surface quality of the formed goods and result in contamination of the tool and shortens the life of the tool. The presence of these oxides in the formed material are also undesirable during cutting or chipping since, due to their hardness, they contribute to an increased wear of the tool.
As such, there is a need for materials, which are at least equal to the high tin content copper-tin alloys in mechanical strength, formability and corrosion resistance and yet can be handled in a simplified manner during manufacture and processing. There also is a need for materials, which on the one hand meet the requirements regarding strength and softening characteristics for alloys used in the manufacture of components which are joined by a heat treatment and yet offer the advantages of hard-solderable tin
Boegel Andreas
Hansmann Stephan
Hofmann Uwe
Mueller Hilmar R.
Riedle Joachim
Wieland-Werke AG
Yee Deborah
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