WO2008093974A1

WO2008093974A1 - Free-cutting copper alloy

Info

Publication number: WO2008093974A1
Application number: PCT/KR2008/000514
Authority: WO
Inventors: Seung Zeon Han; Chang Joo Kim; Su Hyeon Kim
Original assignee: Poongsan Corp
Current assignee: Poongsan Corp
Priority date: 2007-01-30
Filing date: 2008-01-28
Publication date: 2008-08-07
Anticipated expiration: 2009-07-30
Also published as: KR100864909B1; KR20080071276A

Abstract

The present invention relates to a free-cutting copper alloy containing calcium. The free-cutting copper alloy of the present invention consists of copper Cu, zinc Zn, and calcium Ca, with Cu at 59 ~ 79wt%, Ca at 0.1 ~ 1.5wt%, and zinc in remainder. The free-cutting copper alloy has inter-metallic compound of calcium and copper in a matrix, thereby improving industrial machinability.

Description

[DESCRIPTION] [TITLE OF INVENTION]

FREE-CUTTING COPPER ALLOY [TECHNICAL FIELD] The present invention relates to copper alloys, and more particularly, to a free- cutting copper alloy which contains calcium to improve machinability. [BACKGROUND ART]

The copper, one of non-ferrous metal, has various additives added thereto depending on purposes for using in various fields. That is, phosphor bronze, prepared by adding less than 1% of phosphor to copper for enhancing hardness and strength of an alloy containing copper, is used as a shaped material to be processed, such as plate and wire, for utilizing a high elasticity of the phosphor bronze, and as a material for casting pump components, gears, components for ships, components for chemical machines.

Aluminum phosphor bronze, having a small amount of aluminum added to copper, has not been spread much up to recently due to problems of melting and casting technique, self annealing, and so on. However, owing to recent metallographic demands and development of the melting and casting technique, application of the aluminum phosphor bronze becomes wider gradually.

High strength yellow brass called as manganese bronze has 1 ~ 3% of manganese added to brass. Other than those, by adding elements, such as aluminum Al, iron Fe, nickel Ni, tin Sn, and so on to copper, requirements of strength, corrosion resistance, and seawater resistance can be optimized.

Keeping pace with recent extension of application of copper, there are active studies for enhancing machinability of the copper alloys. That is, the copper has a poor machinability due to a high elongation to stick to a tool at the time of machining making the machining difficult. In order to solve such a problem, there has been various studies.

For an example, at an early stage when there are active studies for enhancing the machinability of the copper alloys, lead Pb of 2.5 ~ 3.7wt% is added to copper to prepare lead brass. However, as it is found out that lead Pb is harmful to human body, to restrict use of lead strongly, there were studies for additives that can substitute the lead.

As a result of this, free-cutting leadless brass has been developed, to which bismuth Bi is added instead of the lead.

[DISCLOSURE OF INVENTION] [TECHNICAL PROBLEM]

However, because it is not obvious whether the bismuth is harmful or not, it is the present situation in which people hesitate to use the bismuth.

As the lead Pb or the bismuth Bi does not make solid solution in a matrix of copper alloy, but spread as grains in the matrix, the machinability is improved.

Moreover, conclusively, recovery of the lead Pb or the bismuth Bi from the copper alloy by means of general process metallurgy or refining is impossible, and if it is intended to recover by physical means, there has been a problem in that a high energy is required, to increase a cost required to invest for recycling the lead Pb or the bismuth Bi. Furthermore, since, following a recovery ratio of the lead Pb or the bismuth Bi becomes lower, the recovery ratio of the copper becomes lower too, it is not desirable in view of recycling of the copper as we wholly depends on import for an entire amount of copper we use. [TECHNICAL SOLUTION] To solve the problems, an object of the present invention is to provide a free- cutting copper alloy in which a predetermined amount of calcium Ca is added to copper to make appearance of an inter-metallic compound having the copper Cu and the calcium Ca bonded together for improving machinability. Another object of the present invention is to provide a free-cutting copper alloy in which a predetermined amount of calcium Ca is added to copper, for enhancing a recovery ratio of the copper Cu, thereby permitting recycling of the copper.

To achieve these objects and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, a free-cutting copper alloy consists of copper, zinc, and calcium.

The calcium is added to a composite matrix of brass which is an alloy of the copper and the zinc, the matrix having α-phases only or a mixture of α-and β-phases. The addition of the calcium causes to form CaCu₅ grains.

The copper is at 59 ~ 79wt%, the calcium is at 0.1 ~ 1.5wt%, and the zinc is remainder.

The free-cutting copper alloy takes a form by extrusion, rolling, or drawing. The copper alloy of the present invention having above composition shows improvement of mechanical properties, and has CaCus phases that is a calcium and copper compound, improving machinability. In general, though there is no numerical definition on the machinability of a copper alloy, the machinability is defined according to a shape and a length of machined chips.

A copper alloy having machinability thereof improved as lead and bismuth added thereto shows no solid solution, but distributed in grains, to make machined chips thereof to have forms of broken pieces, thereby improving the machinability. The alloy suggested in the present invention has calcium, not lead and bismuth, added thereto, to make CaCu₅ to appear in a metallic matrix, for improving the machinability. Noticing this point, though the present invention is different from one which has lead, bismuth, and other elements added to make a spread phase appeared in a matrix in view of function and form, the present invention is the same with the one in view of improvement of the machinability.

[ADVANTAGEOUS EFFECTS]

As has been described in detail, the free-cutting copper alloy of the present invention has a predetermined amount of calcium added to a copper alloy. According to this, the copper alloy shows higher hardness, and reduction of ductility and elongation, with improvement of machinability.

Since the copper alloy of the present invention enables recycling of copper and calcium from chips of a cutting tool, a production cost can be reduced.

Moreover, the calcium added to the copper alloy of the present invention is not harmful to a human body, a working safety of a worker can be improved. [BRIEF DESCRIPTION OF THE DRAWINGS]

The accompanying drawings, which are included to provide further understanding of the disclosure and are incorporated in and constitute a part of this application, illustrate embodiments of the disclosure and together with the description serve to explain the principle of the disclosure. In the drawings:

FIG. 1 illustrates a photograph of actual shapes of chips of copper alloys varied with machinabilities of the copper alloys;

FIG. 2 illustrates a photograph of drill chips from a widely used lead copper alloy; FIG. 3 illustrates a photograph of a cast block of Cu-Zn-Ca prepared for a machinability test in accordance with a preferred embodiment of the present invention;

FIG. 4 illustrates a photograph of drills used to form chips from the cast block of FIG. 3; FIG. 5 illustrates a table of weight percents (wt%) of copper, zinc, and calcium in a free-cutting copper alloy in accordance with a preferred embodiment of the present invention;

FIG. 6 illustrates a photograph of a scanning electron microscope showing distribution of Cu₅Ca phases on an outside surface of a cast block of a free-cutting copper alloy having α and β -phases at the same time in accordance with a first preferred embodiment of the present invention;

FIG. 7 illustrates a photograph of a scanning electron microscope showing distribution of Cu₅Ca phases on an outside surface of a cast block of a free-cutting copper alloy having α and β-phases at the same time in accordance with a second preferred embodiment of the present invention;

FIG. 8 illustrates a photograph of a scanning electron microscope showing distribution of Cu₅Ca phases on an outside surface of a cast block of a free-cutting copper alloy having α and β-phases at the same time in accordance with a third preferred embodiment of the present invention; FIG. 9 illustrates binary equilibrium diagrams of Cu-Zn and Cu-Ca, respectively;

FIG. 10 illustrates an enlarged view of a photograph of drill chips from a cast block in FIG. 6;

FIG. 11 illustrates an enlarged view of a photograph of drill chips from a cast block in FIG. 7; FIG. 12 illustrates an enlarged view of a photograph of drill chips from a cast block in FIG. 8;

FIG. 13 illustrates comparative graphs of drilling torques among a pure copper block and cast blocks each prepared in accordance with the first to third preferred embodiments of the present invention;

FIG. 14 illustrates a table of compositions in wt% of free-cutting copper alloys in accordance with fourth to seventh preferred embodiments of the present invention, wherein the wt% of the copper is fixed while wt% of zinc and calcium are varied;

FIGS. 15 to 18 illustrate photographs of a scanning electron microscope of surfaces of free-cutting copper alloys prepared in accordance with the fourth to seventh preferred embodiments of the present invention in FIG. 14 showing each matrix has α- phases; and

FIG. 19 illustrates comparative graphs of drilling torques among a pure copper block and cast blocks each prepared in accordance with the fourth to sixth preferred embodiments of the present invention.

[BEST MODE]

Reference will now be made in detail to the specific embodiments of the present invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference, numbers will be used throughout the drawings to refer to the same or like parts.

FIG. 1 illustrates a photograph of actual shapes of chips of copper alloys varied with machinabilities of the copper alloys, an excerption from the Copper handbook (Jeseph, Gunter, Kundig, J.A. Konrad ASM International). Referring to the photograph in FIG. 1, the type III shows drill chips from high purity copper. Such rolled chips without breakage imply that the cutting object has a high ductility, leading to have poor machinability due to sticking of the cutting object to the drill. The type II shows rolled chips with short breakages substantially, implying that the cutting object is a copper alloy of high hardness and strength, having a room for improving machinability if cutting conditions are adjusted.

The type I shows a most ideal form of chips in machinability of a copper alloy. That is, the copper alloy of the type I chip has lead Pb, bismuth Bi, sulfur S, and tellurium Te added thereto, leading to form fine and uniform chips, implying that the copper alloy is not sticky when drilled, to discharge chips easily.

However, since the cutting object that forms the type I chips is an expensive copper alloy which is not used generally, the inventor performed tests while varying conditions to obtain chips similar to the copper alloys (lead containing copper alloys) having generally accepted machinabilities.

That is, in the present invention, hexahedral blocks of copper alloys with varied amounts of calcium added thereto are cast and drilled to obtain chips similar to ones shown in FIG. 2 (a copper alloy containing lead).

FIG. 3 illustrates a photograph of a cast block of Cu-Zn-Ca prepared for a machinability test in accordance with a preferred embodiment of the present invention, and FIG. 4 illustrates a photograph of drills used to form chips from the cast block of FIG. 3.

The drills in FIG. 4 are formed of HSS (High Speed Steel) each with 8mm diameter. The free-cutting alloys in accordance with preferred embodiments of the present invention will be described with reference to FIGS. 5 to 13.

FIG. 5 illustrates a table of weight percents (wt%) of copper, zinc, and calcium in a free-cutting copper alloy in accordance with a preferred embodiment of the present invention, and FIGS. 6 to 8 illustrate photographs of a scanning electron microscope showing distribution of Cu₅Ca phases on an outside surface of cast blocks of free-cutting copper alloys each having α and β-phases at the same time in accordance with first to third preferred embodiments of the present invention, respectively.

FIGS. 10 to 12 illustrate enlarged views of photographs of drill chips from cast blocks in FIGS. 6 to 8 respectively, and FIG. 13 illustrates comparative graphs of drilling torques among a pure copper block and cast blocks each prepared in accordance with the first to third preferred embodiments of the present invention.

As shown, in the copper alloys in accordance with the first to third embodiments of the present invention, zinc is fixed at 40wt%, copper is varied from 59 to 59.7wt%, and calcium is varied from (Ll to 1.0wt%.

Referring to FIGS. 6 to 8, scanning electron microscopic photographs of surfaces of cast blocks prepared with above compositions show CaCu₅ distributed as inter-metallic compounds uniformly in a brass matrix of α- and β-phases, wherein it can be noted that the greater a content of the calcium Ca, the greater an amount of the CaCu₅. FIG. 9 illustrates binary equilibrium diagrams of Cu-Zn and Cu-Ca, respectively. There have been no report on Cu-Ca binary equilibrium diagrams and no results of studies for formation of the inter-metallic compound of Zn-Ca. As shown in the Cu-Ca binary equilibrium diagram, it can be known that CaCu₅ phases are formed even if a copper content varies. Referring to FIGS. 10 to 12, it can be known that, as a calcium content becomes the greater, a shape of drill chips becomes the closer to the type I in FIG. 1, implying that a copper alloy containing calcium has an improved machinability.

On the other hand, the machinability of the copper alloys can be determined from drilling torques transmitted to a drill.

That is, if the torque transmitted to the drill at the time the copper alloy is drilled is high, it implies that the machinability of the copper alloy is poor, and if low, it implies that the machinability of the copper alloy is good.

In more detail, referring to FIG. 13, the torque to the drill from the pure copper block when the pure copper block drilled with the drill is approx. 0.25 N.m. On the other hand, it can be known that the torques to the drill from the copper alloy blocks in accordance with the first to third preferred embodiments of the present invention are below 0.19 N.m, and become the lower gradually as the calcium content becomes the lower. Copper alloys in accordance with other embodiments of the present invention will be described with reference to FIGS. 14 and 19.

FIG. 14 illustrates a table of compositions in wt% of free-cutting copper alloys in accordance with fourth to seventh preferred embodiments of the present invention, wherein the wt% of the copper is fixed while wt% of zinc and calcium are varied, FIGS. 15 to 18 illustrate photographs of a scanning electron microscope of surfaces of free- cutting copper alloys prepared in accordance with the fourth to seventh preferred embodiments of the present invention in FIG. 14, and FIG. 19 illustrates comparative graphs of drilling torques among a pure copper block and cast blocks each prepared in accordance with the fourth to sixth preferred embodiments of the present invention. As shown, in the copper alloys in accordance with the fourth to seventh embodiments of the present invention, a copper content is fixed at 79wt%, while a calcium content is varied from 0.1 to 1.5wt%, and a zinc content makes a balance.

Referring to FIGS. 15 to 18, it can be known that scanning electron microscopic photographs of surfaces of cast blocks prepared with above compositions show CaCu₅ increased sharply following an increased calcium content, and as shown in

Vickers hardness in FIG. 14, and have hardness higher than Vickers hardness 90 of the copper alloy containing lead.

Alike the first to third embodiments, it is evident that such a CaCu₅ increase improves the machinability of the copper alloys-.

Moreover, alike the first to third embodiments, as a result of measurement of the torques to the drill from the copper alloys in accordance with the fourth to seventh embodiments, it can be known that, if calcium is added to the copper alloys (brass) each having the α- and β-phases in a matrix at the same time and the copper alloy having the α-phases in a matrix only, the torques become significantly lower than the torque of the pure copper.

Eventually, it is proved that addition of calcium to a copper alloy improves machinability better than pure copper or general copper alloys, and by varying a content ratio of copper to zinc in the copper alloy, preparation of copper alloys having a variety of mechanical properties is possible.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents. For an example, though the embodiments show a zinc or copper content fixed while contents of other elements are varied, by fixing a calcium content within a range of content of the calcium and varying the contents of copper and zinc, a free-cutting copper alloy meeting the purpose of use can be prepared. Moreover, in the embodiments of the present invention, though the free-cutting copper alloy takes a form by casting, the free- cutting copper alloy may take a form by a variety of processing, such as extrusion, rolling, drawing, or so on. [INDUSTRIAL APPLICABILITY]

The present invention relates to a free-cutting copper alloy containing calcium. The free-cutting copper alloy of the present invention consists of copper Cu, zinc Zn, and calcium Ca, with Cu at 59 ~ 79wt%, Ca at 0.1 ~ 1.5wt%, and zinc in remainder. The free- cutting copper alloy has inter-metallic compound of calcium and copper in a matrix, thereby improving industrial machinability.

Claims

[CLAIMS]

1. A free-cutting copper alloy consisting of copper, zinc, and calcium.

2. The free-cutting copper alloy as claimed in claim 1, wherein the calcium is added to a composite matrix of brass which is an alloy of the copper and the zinc, the matrix having α-phases only or a mixture of α-and β-phases.

3. The free-cutting copper alloy as claimed in claim 2, wherein the addition of the calcium causes to form CaCu₅ grains.

4. The free-cutting copper alloy as claimed in claim 3, wherein the copper is at 59 ~ 79wt%, the calcium is at 0.1 ~ 1.5wt%, and the zinc is remainder.

5. The free-cutting copper alloy as claimed in one of claims 1 ~ 4, wherein the free- cutting copper alloy takes a form by extrusion, rolling, or drawing.