RU2207394C1 - Silver-based alloy - Google Patents

Abstract

FIELD: precious metal alloys. SUBSTANCE: silver-based alloy useful in art castings, electrical engineering, and instrumentation engineering contains, wt %: silver 92.5-93.0, copper 5.8-6.8, nickel 0.3-0.5, tin 0.5-0.9, titanium 0.015-0.025, and boron 0.025-0.035. EFFECT: expanded technological possibilities of alloy and reduced rejects.

Description

 The invention relates to silver-based alloys and is intended for use in the jewelry industry, but can also be used in electrical engineering and instrumentation, as well as for art casting.

Known silver alloy 925 ^o containing copper in the following ratio of components, wt. %: silver - 92.2-92.8; copper - 7.2-7.8 (GOST 6836-80), the disadvantage of which is the relatively low strength and plastic characteristics, which negatively affects the quality of both cast and stamped products and parts and complicates the technology of their manufacture.

 Closest to the proposed technical essence and the achieved result is an alloy based on silver containing copper and nickel in the following ratio of components wt.%: Silver - 92.5-93.0; copper - 5.3-6.2; nickel - 1.3-1.7 (RF patent 2049136, 11/27/95).

 A significant drawback of this alloy is its low casting properties, in particular fluidity, which limits the scope of its application to the production of mainly stamped and extruded products, as well as relatively simple castings, such as rings. Obtaining more complex castings, for example, cast rings with castes, is not possible due to the poor filling of the mold with the melt due to its low fluidity, which was noted above. In addition, the production of castings from this alloy is accompanied by a high percentage of rejects: up to 12% for non-spills and nullites, and up to 15% for gas shrinkage defects.

 The task to which the proposed technical solution is directed is to expand the technological capabilities of the alloy, in particular, by achieving a technical result consisting in the possibility of obtaining complex shaped products from it, for example, solid cast rings with tinctures, as well as reducing casting rejects.

The technical result is achieved by the fact that the proposed silver-based alloy containing copper and nickel additionally contains tin, titanium and boron in the following ratio of components, wt.%:
Silver - 92.5-93.0
Copper - 5.8-6.8
Nickel - 0.3-0.5
Tin - 0.5-0.9
Titanium - 0.015-0.025
Boron - 0.025-0.035
The introduction of additional tin, titanium and boron into the alloy, as well as the upper and lower limits of the content of elements in the alloy are due to the following considerations.

 1. When the content of nickel in the alloy exceeds 0.5%, the melting and pouring temperature rises, and if the content exceeds 1%, nickel becomes a harmful impurity, since it does not dissolve in silver and worsens machinability by cutting (see E. Brepol. Theory and the practice of jewelry, 4th ed., Leningrad, 1982, p. 27).

 2. Tin, even in small quantities, significantly reduces the melting point of the alloy, lowers its viscosity and increases fluidity. The content in the tin alloy of more than 1% makes the alloy dull, soft and ductile; the hardness and strength of the products decreases (ibid., pp. 26-28).

 3. Titanium and boron are modifiers of the 1st and 2nd kind, they grind grain and increase the physicomechanical characteristics of the alloy, in particular strength and ductility, and boron, in addition, is an effective deoxidizer.

 However, the introduction of titanium in an amount in excess of 0.025%, and boron in excess of 0.035%, increases the melting temperature of the casting of the alloy, increases segregation, reduces the fluidity of the alloy and increases the fragility of products (see A.V. Kurdyumov et al. Foundry of non-ferrous and rare metals , M., 1982, p. 78). The content in the alloy of the introduced elements below the lower limit reduces the effectiveness of their impact.

 The technology for preparing the inventive alloy was developed taking into account the fact that nickel, titanium and boron are insoluble in silver, so first you need to prepare the copper-tin-nickel-titanium-boron alloy and then use the alloy to prepare the silver alloy mentioned above .

The ligature was prepared as follows. The crucible of the induction vacuum melting furnace was heated to a temperature of 1090-1100 ^o C and the calculated amount of copper was loaded into it. After melting the copper, the required amount of tin was calculated into the crucible and the extract was allowed to stand for 2 minutes. Then the melt was thoroughly mixed and successively refractory components of the charge — nickel, titanium, and boron — were introduced into it. After 2 minutes, the melt was thoroughly mixed and its temperature was adjusted to 1030-1050 ^o C. After 3 minutes, the melt was mixed and poured into molds, in which ingots (ingots) of ligatures were obtained.

 Example. The inventive silver-based alloy was prepared as follows. In the crucible of the induction vacuum furnace, the calculated (92.7% of the total mass of the charge) amount of silver was melted. After the melting of silver, 7.3% of the total mass of the charge was loaded into the copper-nickel-tin-titanium-boron ligature.

 After the ligature was melted, the melt was thoroughly mixed and poured into ceramic molds made by investment casting, in which solid cast-ring products were obtained.

 Previously, these products were obtained in two stages: first, the ring blank was cast, then the cast blank, after which they were joined together by soldering or welding.

 This technology, as noted above, was due to the low fluidity of the alloy, taken as a prototype, and a high percentage of marriage castings.

The experimental work showed that it is easy to obtain cast products from the inventive alloy, including solid cast ring products, which were previously obtained from the standard alloy 925 ^o , as well as from the alloy taken as a prototype, it was practically impossible to obtain according to the specified above reasons.

 The use of the proposed alloy, along with the fundamental possibility of producing solid cast complex shaped castings, made it possible to sharply reduce the percentage of castings rejects: for gas-shrinkable defects from 15 to 2-3%, and for defects "non-spillage" and "non-slit" - from 12 to 1-2% .

This became possible due to the fact that the presence of tin in the alloy, as noted above, significantly improved the fillability of the casting molds with the melt, due to the increase in its fluidity, and the use of copper-nickel-tin-titanium-boron alloys for the preparation of alloys made it possible to lower the casting temperature molds from 1030 to 1000-1005 ^o С, flask temperature - from 680 to 630-620 ^o С, which significantly reduced the volumetric shrinkage of the alloy, reduced the time of casting the molds with metal and created conditions for directional crystallization of the alloy, which, in turn, allowed It is necessary to drastically reduce the number of defects in castings by gas-shrink porosity.

 It should be noted that the positive features of the alloy were achieved without compromising its strength and plastic characteristics, which is explained by the modifying effect of nickel, titanium and boron.

 From the given example of a specific implementation, it can be seen that the process of producing the alloy does not require fundamentally new equipment or go beyond the capabilities of the conventional technology for casting silver alloys.

 The process can easily be repeated many times in a production environment.

Claims (1)

A silver-based alloy containing copper and nickel, characterized in that it additionally contains tin, titanium and boron in the following ratio of components, wt.%:
Silver - 92.5-93.0
Copper - 5.8-6.8
Nickel - 0.3-0.5
Tin - 0.5-0.9
Titanium - 0.015-0.025
Boron - 0.025-0.035o