GB2169622A

GB2169622A - Metallic products

Info

Publication number: GB2169622A
Application number: GB08600479A
Authority: GB
Inventors: William Ormond Thomas
Original assignee: Goricon Metallurgical Services Ltd
Current assignee: Goricon Metallurgical Services Ltd
Priority date: 1985-01-10
Filing date: 1986-01-09
Publication date: 1986-07-16
Also published as: GB8500578D0; GB8600479D0

Abstract

A metallic product which comprises magnesium or aluminium in a smooth-surfaced particulate form, at least a major proportion of the particles being of elongate configuration, having over the major part of their length a substantially continuously curved cross section and having their surfaces oxidised to provide a protective layer of oxidised metal may be produced by pulverising a supply of pieces of the metal to reduce it to said particulate form within a mechanical apparatus and maintaining an atmosphere of inert gas containing from 0.3 to 3.5% by volume of oxygen around the metal during the pulverising.

Description

SPECIFICATION Metallic products The present invention relates to metallic products and has as an object the provision of magnesium or aluminium in a novel particulate form. Another object is the provision of a method of producing magnesium in that form.

In accordance with the present invention, there is provided a metallic product which comprises magnesium or aluminium in a smooth-surfaced particle ulate form, at least a major proportion of the particles being of elongate configuration, having over the major part of their length a substantially continuously curved cross section and having their surfaces oxidised to provide a protective layer of oxidised metal. The said cross section may be generally circular or elliptic, geometrically pure shapes being unusual.

The particulate magnesium of the invention is suitable for high-temperature applications, especially the desulphurisation of molten steel. At the normal temperatures of transport and storage, and handling in a steel works, its protective layer and particle shape render it a desirable product from the safety viewpoint.

The particulate aluminium may be used as a chemical reactant or as an exothermic metal in thermite-type reactions. Its protective layer and particle shape render it a desirable product from the safety viewpoint.

Further in accordance with the present invention, there is provided a method of producing magnesium in the form aforesaid which comprises pulverising a supply of pieces of magnesium, eg.

magnesium swarf, to reduce it mechanically to said particulate form, within a mechanical apparatus and maintaining an atmosphere of Inert gas, preferably nitrogen helium or argon, containing from 0.3 to 3.5 O by volume of oxygen around the magnesium in said apparatus during the pulverising. The same atmosphere is advantageously employed during screening and collecting the product.

For best results the inert gas is supplied to the appratus in a cold state. In this way the oxidation of the newly produced surfaces of the metal takes place sufficiently slowly to produce the layer of oxidised metal in a close-packed, firmly adherent state.

Supplying the inert gas to the apparatus in a cold state is found to reduce wear of the apparatus by reducing the temperature produced by mechanical work.

Conveniently the inert gas is supplied to the apparatus separately from the oxygen, the apparatus Is sufficiently open to the atmosphere to admit the oxygen therefrom and the rate of suppiy of the inert gas Is controlled to maintain the required oxygen content. Alternatively air or oxygen can be fed nto the apparatus, the oxygen concentration being controlled by an oxygen meter which varies the amount of inert gas or alternatively the amount of air or oxygen which IS fed Into the apparatus.

In a preferred form of the method, the inert gas is nitrogen which is supplied to the apparatus in the liquid state. Its evaporation in situ to form the required atmosphere gives a desirable cooling effect and its lower-than-ambient temperature gives the atmosphere such a density that it is adequately retained in an open-top apparatus. The rate of feeding the liquid nitrogen is readily regulated to allow air to enter the apparatus at the rate required to maintain the oxygen content within the desired range.

In another preferred form of the method cold nitrogen is provided by liquid nitrogen in an evaporator equipment provided as part of the nitrogen storage and supply system.

Having the incidence of particles with severely angular edges of relatively long total length minimised, substantially reduces the occurrence of relatively thin regions in the oxide coating and also reduces abrasion when a bulk of the particles undergoes agitation during pouring or other handling such as transportation under conditions of vibration.

Injection into liquid iron for desulphurisation thereof is an important application of the product.

Flowability of the product is of great importance.

Lenticular particles with extensive sharp, or relatively sharp edges, give poor flowability and can, indeed, accumulate to block the injection equipment. Spherical particles would be ideal but are not readily provided, whereas the product of the present invention is however found to have an adequate flowability in practice.

The present product is naturally subject to some degree of abrasion during handling. Its low rate of ixidation at the low oxygen content during the milling operation tends to produce a durable oxidised coating and having a substantial degree of freedom from sharp edges minimises the occurrence of surface regions which are especially subject to damage. Such minimisation is shown by the maintenance of the electrical resistivity at a high level.

The following descripiton in which reference is made to the accompanying drawings is given in order to illustrate the invention.

The drawing shows an apparatus for producing the product in diagrammatic cross-section.

A hopper 1 receives the swarf via an open top 2 and feeds it, under gravity, to a horizontal cylindrical shell 3 housing a beater 4 having a rotary shaft 5 driven by a motor not shown). Beater heads 6 impact the swarf against the inner face of shell 3 to form shaped particles which, when reduced to the required size fell through a screen 7 into a receiving container 8 which is exchanged for another when filled.

Air for oxidation of the particles and low temperature nitrogen are passed into the shell via entrances 9 and 10 respectively.

A transducer 11 In thermal contact with shell 3 passes a signal representing temperature to a control device, represented at 12, which regulates the nitrogen supply.

Dust, inevitably produced by the action of beater 4, is pumped from near the top region of container 8 via a conduit 13.

The thickness and continuity of the oxide layer are shown by the electrical properties of the product. In the case of magnesium particles, a centimetre cube of mutually contacting particles has an electrical resistance of at least 100,000 ohms at 1000 volts per centimetre.

The metal can be supplied to the apparatus from a stock of previously formed swarf or can be supplied directly from an auger adjacent to the open top 2.

It will be appreciated that the apparatus is shown for purposes of illustration only and that various departures may be made therefrom within the ambit of the invention.

Claims

1. A metallic product which comprises magnesium or aluminium in a smooth-surfaced particulate form, at least a major proportion of the particles being of elongated configuration, having over the major part of their length a substantially continuously curved cross section and having their surfaces oxidised to provide a protective layer of oxidised metal.

2. A product according to claim 1 in which the said cross section is generally circular or elliptic.

3. A method of producing a product as claimed in either of claims 1 or 2 pulverising a supply of pieces of the metal to reduce it to said particulate form within a mechanical apparatus and maintaining an atmosphere of inert gas containing from 0.3 to 3.5 h by volume of oxygen around the metal during the pulverising.

4. A method according to claim 3 in which the inert gas is nitrogen, helium or argon.

5. A method according to either of claims 3 or 4 in which the inert gas is supplied in a cold state.

6. A method according to claim 5 in which the inert gas is nitrogen and is supplied to the apparatus in the liquid state.

7. A method according to claim 6 in which the rate of feeding the liquid nitrogen Is regulated to allow air to enter the apparatus at the rate required to maintain the oxygen content within the desired range.

8. A method according to claim 5 in which the inert gas is nitrogen and its rate of feeding is regulated to allow air to enter the apparatus at the rate required to maintain the oxygen content within the desired range.

9. A metallic product when produced by a method in accordance with any one of claims 3 to 8.

10. Apparatus for producing a metallic product according to any one of claims 1, 2 or 9 substantially as hereinbefore described and illustrated by reference to the accompanying drawing.