Metal treatment – Process of modifying or maintaining internal physical... – Processes of coating utilizing a reactive composition which...
Patent
1999-06-11
2000-12-12
Sheehan, John
Metal treatment
Process of modifying or maintaining internal physical...
Processes of coating utilizing a reactive composition which...
148276, 148284, 148712, 148687, C23C 2800
Patent
active
061593079
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF INVENTION
The invention relates to a process to anneal non-ferrous metal objects in an adhesion-free manner, that is to say, to avoid so-called adhesions during the annealing procedure, especially in a bell-type furnace.
Non-ferrous metals such as, for instance, bronze wires or bronze strips undergo a homogenizing annealing step after the casting and shaping. Subsequently, additional shaping measures such as rolling or drawing are taken and re-crystallization annealing steps are carried out.
The annealing temperatures lie between 300.degree. C. and 700.degree. C. [572.degree. F. and 1292.degree. F] The annealing is conducted in continuous furnaces, a relatively complex approach in view of the fact that the objects usually have a small cross section.
When annealing coils, which can be done, for example, in bell-type furnaces, local diffusion welds, so-called adhesions, occur at the contact sites of the objects, for example, between individual windings of the wound-up wire or strip, due to diffusion mechanisms. Upon further processing, that is, during winding, these adhesions cause cracks on the surface of the material, thereby giving rise to surface defects. As a consequence, of course, adhesions are highly undesirable on annealed non-ferrous metal objects.
In this context, the term non-ferrous metals refers to alloys whose main components are copper, tin, aluminum and lead, whereby many other components are also possible such as, for instance, magnesium, nickel, etc.
In order to avoid adhesions when annealing steel strips, DE 4207394 discloses the approach of changing the water-gas equilibrium in a targeted manner in the presence of H.sub.2, CO.sub.2, CO and H.sub.2 O in the protective-gas atmosphere in such a way that a totally oxidizing atmosphere is available at the end of the holding phase, while a totally reducing atmosphere is available in the cooling phase. This approach, however, cannot be used for non-ferrous metals due to the much lower temperatures that are found at times, for instance, 400.degree. C. [752.degree. F.], and due to the detrimental effect on the part of the reaction products, such as CO and H.sub.2 O, on the oxidation mechanism.
SUMMARY OF INVENTION
The invention is based on the objective of creating a process with which it is possible to avoid adhesions during the annealing of non-ferrous metal objects, especially non-ferrous metal coils, in bell-type furnaces.
In accordance with the invention the material being annealed is exposed to an inert or oxidizing protective-gas atmosphere. As a result, a thin layer is formed during this time on the surface of the material being annealed and/or an oxide layer that was previously present was maintained thus preventing the non-ferrous metal objects from adhering together.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be explained in greater detail below with reference to the example of an embodiment in conjunction with a drawing, whereby
FIG. 1 shows a state diagram of copper-tin;
FIG. 2 shows the course of the temperature over time and the composition of a protective-gas atmosphere used for the adhesion-free treatment of bronze wire.
DETAILED DESCRIPTION
First of all, the example of a copper-tin alloy (bronze) is employed to illustrate the problem of the adhesion of individual windings during the annealing of non-ferrous metal coils.
Due to their large solidification interval, copper-tin alloys tend to form zone crystals when they are cast. These solidification intervals are one of the reasons for the reverse block segregation associated with pronounced differences in concentration throughout the cross section. This can be accompanied by exudation on the surface. These concentration differences are the reason why a heterogeneous structure can already form at low tin contents in the cast state. The extent of segregation depends on the cooling conditions. The faster the cooling takes place, the lower the tin contents are at which the theoretical boundary of the homogeneous area lies.
FIG. 1 depicts a state diag
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Messer Griesheim GmbH
Oltmans Andrew L.
Sheehan John
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