Patent Application
20220331861
The present invention relates to a process for obtaining a brass billet and to a brass billet thus obtained. In particular, the present invention relates to a lead-free or low lead content brass billet.
In particular, brass is conventionally defined “lead-free” if the lead content is lower than 0.1% by weight; it is defined “low lead content” if the lead content is comprised between 0.1% and 0.2% by weight.
As known, brass, alloy of copper (Cu) and zinc (Zn), is a material widely used in the manufacturing industry, above all by virtue of its excellent castability, which allows to obtain semi-finished castings by means of casing processes, and the excellent machinability, which allows to finish the semi-finished product appropriately by means of chipping machining.
The machinability of brass strongly depends on the amount of lead (Pb) it contains.
However, the need to make some artifacts, e.g. faucets or other components in contact with water, particularly drinking water, with lead-free alloys has arisen in recent years. Mainly, such requirement springs from the need to prevent the lead from dissolving in water, with consequences deemed negative for health.
The research and development efforts of very many manufacturers thus address the definition of lead-free brass, which has mechanical and machinability features similar to those of traditional brass.
In this direction, one of the most promising addresses is the replacement of lead with graphite. With this regard, the Applicant is the owner of Italian patent application for invention No. 10 2013 9021 8136 5.
The present invention is part of this context, and in particular relates to an innovative process for manufacturing lead-free or low lead content brass billets and to the billet thus obtained.
The features and the advantages of the process according to the present invention will be apparent from the description shown below.
According to a process, the billet is obtained by extrusion, either direct or inverted, of a powder comprising brass powder and graphite powder.
The extrusion is performed in temperature conditions such to achieve a sintering of the powders and at a predetermined advancement speed of the punch, e.g. 120 millimeters/second.
For example, before performing the extrusion, the mixed powder is preheated to a preheating temperature, preferably lower than the melting temperature, for a predetermined interval of time. For example, the mixed powder is preheated to 720° C. for 1 hour.
The brass powder is substantially a lead-free or has low lead content; furthermore, the graphite powder is preferably joined in measure between 0.5%-2% by weight with respect to the brass powder, preferably about 1%.
According to a variant embodiment, the brass powder is obtained by means of splat cooling, melt-spinning, atomization process, by means of chemical reactions, such as precipitation, or by means of mechanical processes, such as grinding.
In particular, the atomization process can be performed as gas atomization, vacuum or inert atmosphere gas atomization, water atomization, centrifuge atomization, revolving disc atomization, by ultra-rapid solidification, ultrasonic atomization.
Preferably, the brass powder has a wide grain size range, e.g. between 500 μm and 50 μm; such a wide range, and possibly the irregular shape of the grain size, promotes the compacting of the powders.
Furthermore, according to a variant embodiment, the graphite powder is obtained by grinding.
The brass powder and the graphite powder are mixed, e.g. in a mixer/batcher, for a predetermined interval of time.
According to a variant embodiment, the mixed powder is collected in cylindrical containers, named cans, e.g. made of copper, which after having been filled and inert gas having been blown inside them, are hermetically closed, e.g. by welding.
For example, the inert gas used is Argon (Ar).
The containers are loaded into the extrusion machine and after preheating or during a heating, the extrusion, either direct or inverted, is performed, thus obtaining a composite billet, which contains the material of the container, e.g. on the surface.
Successively, a peeling operation for eliminating the material of the container of the composite billet is performed, thus obtaining the desired billet.
According to a further variant embodiment, the extrusion press is directly loaded with the mixed powder, directly obtaining the desired billet; this avoids the peeling process.
According to a yet further variant embodiment, the mixed powder, before sintering, is pressed, e.g. either in the container or directly in the extrusion press.
Experimental Tests
For example, in an experimental test:
Preheating to 720° C. for 1 hour was performed on both cans C1, C2; the two cans C1, C2 were then subjected to direct extrusion, with extrusion ratio 8:1, punch speed 12 millimeters/second and final diameter of the billet of 30 millimeters.
Two bars were obtained: bar B1 from can C1 and bar B2 from can C2.
For both bars, the final density was about 8 grams/cm3 and a hardness HV5Kg of about 85.
Traction tests have indicated for both bars a Rp0.2% of about 170 MPa, a Rm of about 370 MPa and an A % of 23%.
Such tests indicate that the bars thus obtained have mechanical and micro-structural features which are mutually similar and practically identical to those of bars obtained by means of traditional cycle.
According to the invention, the billet is obtained by extrusion, either direct or inverted, of a mixture of lead-free or low lead content brass chips and graphite powder.
The mixture is preheated or, in a variant embodiment, is heated during the extrusion.
The word “chip” identifies a more or less thin strip of material, generally snarled. For example, the chip has the forms shown in table G.1 of International Standard ISO3685 (
The brass chips derive from the mechanical machining by chip removal performed on the semi-finished products made of lead-free or low lead content brass.
According to a variant embodiment, the brass chips are fragmented by grinding, so that the billet is obtained by means of extrusion, either direct or inverted, of a mixture of fragmented, lead-free or low lead content brass chips and graphite powder.
The chips are fragmented by grinding, e.g. in mills, with separation of the fraction having grain size smaller than a predetermined grain size, e.g. <0.5 mm (brass fragments), and recirculation of the remaining fraction.
Successively, the brass fragments are mixed with graphite powder (e.g. average grain size of 20 μm), e.g. 1% w/w, e.g. in revolving mixers, to obtain a uniform mixture.
Innovatively, the process according to the present invention is extremely advantageous from the industrial point of view because it envisages the relatively simple management of powders and chips and the use of the existing extrusion presses.
In particular, the use of chips advantageously allows to perform the mechanical manufacturing by chipping in a remote plant and the separation of the fragments and the extrusion in a main plant. The chip is transported from the remote plant to the main plant without incurring in the problems of powders transporting.
| Number | Date | Country | Kind |
|---|---|---|---|
| 102016000051168 | May 2016 | IT | national |
This application is a Continuation of U.S. patent application Ser. No. 16/302,494, filed 16 Nov. 2018, which is a National Stage Application of PCT/IB2017/052806, filed 12 May 2017, which claims the benefit of Serial No. 102016000051168, filed 18 May 2016 in Italy, and which applications are incorporated herein by reference. To the extent appropriate, a claim of priority is made to each of the above-disclosed applications.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 16302494 | Nov 2018 | US |
| Child | 17738674 | US |
