GB2093377A - Production of free-machining metal rod - Google Patents

Abstract

This invention relates to a method of producing free-machining brass rod or section of solid or hollow form. Known methods employ billet extrusion and thus require complex and expensive equipment. According to this invention such a method comprises the steps of passing a length of continuously cast rod or section 11, which is oversize with respect to desired final external dimensions by more than 0.5 millimetre, through a shaving device 15 having at least one shaving die so as to reduce said external dimensions by at least 0.5 millimetre, and cold working 17 the rod or section so as to reduce its external dimensions and improve its mechanical properties. <IMAGE>

Description

SPECIFICATION Production of free-machining metal rod This invention relates to the production of freemachining metal rod or bar and in particular to semi-finished free-machining brass bar or rod for the formation and fabrication of fittings and parts for use in the plumbing, electrical and building trades, components for the automotive and engineering industries and decorative parts for the jewellery and haberdashery trades.

Conventionally free machining brass bar or rod is produced by billet extrusion whereby there is first cast from molten metal a relatively large diameter brass billet. This is subsequently reheated and extruded under very high pressure.

The latter step in particular involves the use of large expensive machinery and for this reason the process is only suitable for relatively large scale production. Thus small and medium size nonferrous metal fabricators and engineering companies are dependent on large scale producer for their supplies of free machining brass rod which has to be transported from the latter's stocks to the former against specific orders therefor.

In addition any scrap metal and swarf produced by the fabricators cannot be readily used by the fabricators and has to be returned to the producer for reprocessing or sold to scrap merchants for disposal.

It is an object of the present invention to overcome or minimize one or more of theabove disadvantages.

The present invention provides a method of producing free-machining brass rod or section of solid or hollow form said method comprising the steps of passing a length of continuously cast rod or section, which is oversize with respect to desired final external dimensions by more than 0.5 millimetre, through a shaving device having at least one shaving die so as to reduce said external dimensions by at least 0.5 millimetre, and cold working the rod or section so as to reduce its external dimensions and improve its mechanical properties.

The amount of shaving required in any given case will depend on factors such as the quality of the cast rod or section surface obtained with the casting process used and the required surface smoothness of the rod or section product. In general though the cast rod or section is preferably oversize by more than 1 millimetre and shaving is effected to reduce the external dimensions by at least 1 millimetre.

Various conventional cold-working methods suitable for use with brass may be employed to reduce the dimensions of the shaved rod or section. Amongst those that may be mentioned are passing through a rolling mill; drawing one or more times through a drawing die(s) or roller die(s); in the case of round sections, rotary swaging or hammering; and, in the case of nonround sections such as for example, hexagonal rod, stationary swaging wherein each face of the rod or bar is separately hammered, either in parallel or in sequence by alternate or simultaneous blows. In general the cold-working step is carried out so as to produce a crosssectional area reduction of the order of from 2 to 20% with consequential elongation of the rod or section and improvement of the mechanical properties thereof.

The cold-working step may be carried out either prior to or following the shaving step. The compressive cold-working technique of rotary swaging has been shown to achieve particularly thorough working of the rod or section throughout its sectional area. An advantage of introducing such a compressive cold-working process prior to shaving is that the more closed nature of the surface of the rod or section then requires less metal to be removed in shaving to achieve a fine finish, thus reducing internally generated waste.

Where finished rods and sections are required in profiles other than rounds, these may either be continuously cast oversize in the profile of the finished material, or alternatively, may be continuously cast as round sections and then shaved to the finished profile required. This iatter course has advantages in simplifying the continuous casting die design enabling various finished sections to be produced from the same cast rod section and also in enabling the rod or section to be rotary swaged in the round state before being shaved to the profile required such as for example a hexagon.

By means of the present invention it is possible on the one hand to make the production of freemachining brass rod or section much more widely available by substantially reducing the capital costs involved in the introduction of the process, and on the other hand the invention provides a significantly more economical process than has been available heretofore in that it involves a reduced heating requirement as compared with previously known billet extrusion processes.

Moreover, the shaving step along produces a surface finish which is substantially smoother and has a finer surface tolerance than that customarily associated with continuous cast rods and sections.

A further advantage of the present invention is that whereas during the reheating of the billet in conventional extrusion processes, there can occur a precipitation of an iron-rich silicon phase, leading to a reduction in machining tool life. This does not occur in the above process of this invention.

In a further aspect there is provided a process of the invention which includes the preliminary step of continuously casting brass rod or section which is oversize with respect to desired final external dimensions by at least 0.5 millimetre, and preferably coiling and/or cutting into convenient lengths, the cast rod or section.

In still further aspects the present invention provides free machining brass rod or section having a solid or hollow cross-section, when produced by a method of the invention; and a production line comprising continuous casting apparatus, a shaving device downstream of the casting apparatus, and at least one cold working apparatus upstream or downstream of the shaving device. It will, of course, be appreciated that in view of the different rates and modes of advance, especially between the casting and subsequent steps, there will normally be a degree of interruption between these steps in that the cast rod is not fed directly from the casting apparatus to the subsequent steps though it will usually be convenient to minimize the extent of any such interruption.

Further preferred features and advantages of the invention will appear from the following description given by way of example of one embodiment of the invention illustrated with reference to the accompanying drawings in which: Figure 1 is a schematic sectional side view of a production line for use in a method of the invention.

Figure 1 shows an apparatus comprising a conventional continuous casting apparatus 1 comprising a crucible 2 provided with a heating means 3 (preferably electrical e.g. induction or resistance type), an inlet 4 and an outlet 5. Scrap metal, swarf and/or raw metal 6 is fed in via the inlet 4 and molten metal 7 flows out of the outlet 5 under the influence of gravity through a submerged casting die 8 provided with a cooling jacket 9 through which a suitable coolant such as water is circulated with the aid of a coolant circuit 10* Solid or hollow, rod or section, 11 is drawn out of the casting die 8 by a drawing means, conveniently in the form of rollers 12 or hydraulic vices provided with a drive and control means 13 arranged for subjecting the bar to an intermittent pulling force so that the bar is pulled through a short distance, say 5 mm, pulling discontinued for say one second, and the cycle then repeated.

Various other aspects of suitable continuous casting processes, for example the use of an inert gas atmosphere, are well known from the literature, including for example British Patent Nos. 936 717, 894 783, 934484, 896 387 and many others, and will therefore not be described further herein.

The continuously cast rod or section 11, which at this stage is oversize relative to the final desired cross sectional area and may or may not be of similar section (e.g. round or hexagonal) as the final desired one, is then cut to length by cutting means 20 and passed through a guide means in the form of a guide die 14, from which it passes through a shaving die 1 5. The shaving die 1 5 is dimensioned and arranged so as to take a surface cut of from about 0.25 mm to about 1.50 mm. If desired there could be used instead a plurality of shaving dies arranged in series, each taking a smaller cut -- possibly of the order of 0.1 mm though in this case it is necessary to use a single die holder arranged so as to ensure concentricity of the rod or section with respect to the individual shaving dies.Also the continuously cast rod or section could be cut to convenient lengths, e.g.

3 m, and end-pointed or tagged if necessary, prior to the shaving thereof.

Most desirably there is used a shaving die with a negative cutting angle in order to produce compressive cutting as this results in a superior surface finish. As the shaved rod emerges from the die and the compressive force thereon is removed, the shaved rod expands to a slightly larger external dimension than the die cross-section. If desired an even smoother surface finish can then be obtained by passing the shaved rod or section through the same shaving die a second time or through another die with the same cross-sectional dimensions, this time shaving only a fine skin off the rod or section surface.

The shaved bar 1 6 is then passed through a suitable cold working apparatus 1 7 with the aid of a drawing means 1 8 to reduce the external crosssectional dimensions of the rod or section and to improve the mechanical properties of the product 19. In one version of this invention, the coldworking apparatus is so positioned that the continuously cast rod or section is first coldworked and subsequently shaved to the required final dimensions. In another version, the continuously cast rod or section is first shaved to an intermediate dimension and subsequently reduced to the final desired dimensions by coldworking. Various cold working processes may be used as already referred to above, depending upon the particular cross-sectional form of the bar and any particular desired mechanical properties (e.g.

tensile strength, elongation) of the bar. In the present embodiment the cold working apparatus 17 is a rotary swaging die. Naturally the cold working step can be carried out in more than one stage and/or using more than one type of cold working process according to individual requirements. If desired the shaving can also include more complex operations with the aid of specialist tooling for forming special sections, for example, for cutting a keyway which may extend for the whole length of the rod or section. If necessary a final straightening may be carried out by suitable means e.g. reeling or, in the case of non-round profiles by multi-roll straightening, by stretching or by hand-straightening.

It will be appreciated from the above description that the present invention avoids the need for any reheating of the rod or section (thereby saving an expensive energy consumption), eiiminates the risk of iron-rich silicon phase precipitation with its consequential adverse effects on machine tool life, and avoids the need for complex and expensive high pressure extrusion apparatus, whilst providing good quality 'semi-finished' free-machining brass bar or rod having mechanical properties which are in line with generally accepted standards for freemachining brass bar or rod. By utilising relatively simple components which can be readily constructed and efficiently used on a relatively small scale, the present invention is readily accessible to even relatively small scale users of free-machining brass rod, enabling such companies to re-cycle their own internal arisings of brass scrap and swarf and affording to them a degree of independence in the supply of their requirements of this important raw material.

Claims (13)

1. A method of producing free-machining brass rod or section of solid or hollow form, said method comprising the steps of passing a length of continuously cast rod or section, which is oversize with respect to desired final external dimensions by more than 0.5 millimetre, through a shaving device having at least one shaving die so as to reduce said external dimensions by at least 0.5 millimetre, and cold working the rod or section so as to reduce its external dimensions and improve its mechanical properties.

2. A method as claimed in Claim 1 wherein cold working is effected after passage through the shaving device.

3. A method as claimed in Claim 1 wherein cold working is effected before passage through the shaving device.

4. A method as claimed in any one of Claims 1 to 3 wherein the cold working comprises one or more of passing through a rolling mill, drawing one or more times through a drawing die(s) or roller die(s), rotary swaging, hammering, and stationary swaging.

5. A method as claimed in any one of Claims 1 to 4 wherein cold working is carried out so as to produce a cross-sectional area reduction of from 2 to 20%.

6. A method as claimed in any one of the preceding claims which includes the preliminary step of continuously casting brass rod or sections which is oversize with respect to desired final external dimensions by at least 0.5 millimetre.

7. A method as claimed in Claim 6 which includes the step of cooling the continuously cast rod or section prior to the shaving and cold working thereof.

8. A method as claimed in Claim 6 or Claim 7 which includes the step of cutting and/or coiling the continuously cast rod or section prior to the shaving and cold working thereof.

9. A method as claimed in any one of Claims 1 to 8 wherein the cast rod or section is oversize by more than 1 millimetre and shaving is carried out so as to reduce the external dimensions by at least 1 millimetre.

10. A method as claimed in any one of Claims 1 to 9 wherein is used a shaving die with a negative cutting angle.

11. A method as claimed in Claim 10 wherein the rod or section is subjected to two passes through said shaving die or through respective ones of two shaving dies having the same crosssectional dimensions.

12. A free machining brass rod or section of solid or hollow cross-section when produced by a method as claimed in any one of the preceding claims.

13. A production line suitable for use in carrying out a method according to any one of Claims 1 to 11 which production line comprises continuous casting apparatus, a shaving device downstream of the casting apparatus, and at least one cold working apparatus upstream or downstream of the shaving device.