LEAD-FREE BRASS ALLOY AND MACHINE ELEMENT PRODUCED THEREFROM

Description

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation, under 35 U.S.C. § 120, of copending International Patent Application PCT/EP2023/074002, filed Sep. 1, 2023, which designated the United States; this application also claims the priority, under 35 U.S.C. § 119, of German Patent Application DE 10 2022 122 831.2, filed Sep. 8, 2022; the prior applications are herewith incorporated by reference in their entirety.

FIELD AND BACKGROUND OF THE INVENTION

The invention relates to a lead-free brass alloy.

In the past, the machining of brass alloys was improved by the addition of Pb to an extent of up to 4 wt %. For the future, however, there are severe limitations on the addition of Pb, due to foreseeable statutory stipulations.

There is therefore a demand for a lead-free brass alloy. Alloys of that kind are known per se; reference is made, for example, to the following publications: European Patent Application EP 2 009 122 A1, corresponding to U.S. Publication No. 2009/0022620 A1; European Patent Application EP 3 272 888 A1; International Publication WO 2016/045770 A1, corresponding to U.S. Publication No. 2017/0204501 A1; and European Patent Application EP 3 269 835 A1, corresponding to U.S. Pat. No. 10,316,398 B2. The absence of lead, however, is detrimental to the machineability of such brass alloys.

SUMMARY OF THE INVENTION

It is accordingly an object of the invention to provide a lead-free brass alloy and a machine element produced therefrom, which overcome the hereinafore-mentioned disadvantages of the heretofore-known alloys and machine elements of this general type and in which the lead-free brass alloy which has good machineability.

With the foregoing and other objects in view there is provided, in accordance with the invention, a lead-free brass containing: 55 to 59 wt % of Cu, 2.0 to 2.5 wt % of Mn, 0.65 to 1.5 wt % of Si, less than 0.1 wt % of Pb, and a balance of Zn and also unavoidable impurities.

The brass alloy of the invention possesses less than 0.1 wt % of Pb and is therefore deemed to be lead-free. It has emerged that in spite of the low lead content of less than 0.1 wt %, the brass alloy of the invention exhibits satisfactory machineability. In particular, machining is not accompanied by the formation of any unwanted long spiral chips. Furthermore, the frictional properties of the lead-free brass alloy of the invention are comparable with those of a lead-containing brass alloy.

In one advantageous configuration of the invention, the ratio of the weight percentages of Mn to Si corresponds to the inequation 2.0≤Mn/Si≤2.9. It has been found that this ratio between manganese and silicon leads to an optimal chemical composition and to the formation of manganese silicides.

In the lead-free brass alloy of the invention, the copper equivalent is 53 to 66%.

In the lead-free brass alloy of the invention there is preferably less than 0.2 wt % of Fe.

In the lead-free brass alloy of the invention there is preferably less than 0.5 wt % of Sn.

In the lead-free brass alloy of the invention there is preferably 1.5 to 2.6 wt % of Ni.

The following composition of the lead-free brass alloy of the invention is particularly preferred: 57 wt % of Cu, 2.3 wt % of Mn, 1.0 wt % of Si, 0.1 wt % of Fe, 0.1 wt % of Sn, 2.0 wt % of Ni, less than 0.1 wt % of Pb, and a balance Zn and also unavoidable impurities.

In one preferred configuration of the invention, the lead-free brass alloy contains less than 0.1 wt % of Al.

In the lead-free brass alloy, it may also be the case that there is less than 0.25 wt % of Cr and/or less than 0.25 wt of Ti and/or less than 0.25 wt % of Co.

With the objects of the invention in view, there is concomitantly provided a machine element produced from the lead-free brass alloy of the invention. Due to its good frictional properties, the lead-free brass alloy is ideally suited to the production of machine elements which are used with a lubricant.

Other features which are considered as characteristic for the invention are set forth in the appended claims.

Although the invention is illustrated and described herein as embodied in a lead-free brass alloy and a machine element produced therefrom, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.

The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a diagrammatic, plan view showing a chip pattern generated by machining a reference alloy; and

FIG. 2 is a plan view showing a chip pattern generated by machining a lead-free brass alloy of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the diagrammatic figures of the drawings in detail, it is seen that one exemplary embodiment of the lead-free brass alloy has the following composition: 57 wt % of Cu; 2.3 wt % of Mn; 1.0 wt % of Si; 0.1 wt % of Fe; 0.1 wt % of Sn; 2.0 wt % of Ni; less than 0.1 wt % of Pb; and a balance Zn and also unavoidable impurities.

The copper equivalent (Cu Eq) of the lead-free brass alloy is between 53% and 66% and may be calculated as follows on the basis of the alloy constituents:

If : Si free = Si · 3.26 - ( Fe + Mn ) < 0 ⁢ and ⁢ Si free ⁢ 2 = Si · 3.26 - ( Fe + M ⁢ n + Ni ) < 0 , then Cu ⁢ Eq = Cu [ 100 ⁢ - Fe - Mn - S ⁢ i - Ni + ( ❘ "\[LeftBracketingBar]" Si free ❘ "\[RightBracketingBar]" × 0.7 ) + [ Ni × ( - 1 . 9 ) ] 1 ⁢ 0 ⁢ 0 ] If ⁢ Si free = Si · 3.26 - ( Fe + Mn ) > 0 ⁢ and ⁢ Si free ⁢ 2 = Si · 3.26 - ( Fe + M ⁢ n + Ni ) < 0 Cu ⁢ Eq = Cu [ 100 ⁢ - Fe - Mn - S ⁢ i - Ni + [ ❘ "\[LeftBracketingBar]" Si free ⁢ 2 ❘ "\[RightBracketingBar]" × ( - 1 . 9 ) ] 1 ⁢ 0 ⁢ 0 ] If ⁢ Si free = Si · 3.26 - ( Fe + Mn ) > 0 ⁢ and ⁢ Si free ⁢ 2 = Si · 3.26 - ( Fe + M ⁢ n + Ni ) > 0 Cu ⁢ Eq = Cu [ 100 ⁢ - Fe - Mn - S ⁢ i - Ni + [ ❘ "\[LeftBracketingBar]" Si free ⁢ 2 ❘ "\[RightBracketingBar]" 3.26 × 10 ] 1 ⁢ 0 ⁢ 0 ]

The meanings of the abbreviations are as follows:

• • Cu: wt % of copper
  • Fe: wt % of iron
  • Mn: wt % of manganese
  • Si: wt % of silicon
  • Ni: wt % of nickel

The lead-free brass alloy can be processed into intermediates such as plates, tubes or rods, from which machine elements used with a lubricant can be produced. One example of these are axial piston pump components that are subject to friction. The lead-free brass alloy includes manganese silicides, which are responsible for the good frictional properties.

The machineability of the lead-free brass alloy is compared with a reference alloy. In the table below, the compositions of the lead-free brass alloy and of the reference alloy are set out:

The machining trial was carried out by using an indexable cutting insert of type CNMG120404FP HC5010, with a rotary speed of 3000 rpm, an advancement per rotation of 0.25 mm and a cutting depth of 1.25 mm. FIG. 1 shows the chip pattern of the lead-containing reference alloy; FIG. 2 shows, in comparison to this, the chip pattern of the lead-free brass alloy. It is apparent that the two alloys generate chips of approximately the same size and kind. The chip quality of the lead-free brass alloy is therefore satisfactory.

For the two alloys, the frictional coefficient was ascertained in identical trials. It was discovered that both the lead-free brass alloy and the lead-containing reference alloy possess virtually identical friction coefficients. The friction coefficient is about 0.012.

These experiments showed that the lead-free brass alloy can be used without limitations as a replacement of the lead-containing reference alloy.

The lead-free brass alloy can be used for producing various machine elements, especially machine elements which are subject to friction and are used with a lubricant. An example of these are axial piston pump components or sliding blocks.