GB2211920A - Metal shot for sporting pellets - Google Patents

Abstract

Sporting shot-gun pellets of diameter 1.9 - 5.5mm and density 6.5-7.3, having no voids communicating with the outer surface, are formed from zinc or a zinc-based alloy. Preferred alloys are based on zinc/aluminium (3.5 - 6% Al) or zinc/tin (0.5 - 2% sn) with possible additions of copper, magnesium, silicon, an alkali metal or an alkaline earth metal. The pellets are made by vibrating drops of molten alloy through orifices into a bath of cooling fluid in which they encounter downwardly- inclined planes.

Description

Irlprovem.ents in or relating to metal shot and the production thereof This invention relates to metal shot, as used for game shooting and sporting purposes, e.g. in shot-gun cartridges.

There is increasing concern about the effects of lead and lead-based chemicals upon the environnent and particularly about the effects of lead and lead compounds on wildlife.

Recently legislation was introduced to phase out the use of lead in fishing weights and now attention has turned to the effects of lead pellets e.g. from shot-gun cartridges upon birds which feed on the ground and around fresh-water and sea-water areas.. It has been shown that birds can ingest lead pellets by ground feeding and that these pellets can lead in the long-term to lead poisoning in the species concerned. Particularly vulnerable are certain species of swans, geese and ducks. For exarple, it is estimated that, each year in Great Britain 8000 mallards die after ingesting lead gunshot (G.P.Fjudge 1983).

This invention seeks to ameloriate the problem of lead poisoning in wildlife by providing a safer alternative to traditional lead-shot and a cheaper alternative to the known mechanically-formed steel shot.

According to this invention we provide zinc or a zinc-based alloy which is formed into a substantially-spherical pellet having a diameter between 1.9 and 5.5 mm, and a density between 6.5 and 7.3 and without voids which communicate with the outer surface of the pellet.

Preferably the zinc based alloy is a zinc-aluminium or zinc-tin alloy with, optional additions of copper, magnesium, silicon, alkali metals, or alkaline earth metals.

There may be a small central cavity or micro-porosity within the spherical pellets due to the casting method of production, but the pellets should be substantially free from any voids which communicate with the outer surface of the pellet, and therefore will not affect ballistic properties. Typical porosity levels will be only of the order of 0.58 to 1.0E by volume.

The alloy fro which the pellets are produced should show a relatively low melting point and for this reason alloys based on Zn/3.5% aluminium to Zn/6% aluminium are preferred.

Alternatively, Zn/Sn alloys with a tin content of between 0.5 to 2.08 Sn may be used.

The zinc/aluminiunl alloys have the added advantage of low rates of corrosion attack on steel, when steel is used in the apparatus for producing the pellets.

It is desirable that the alloy used has a low specific heat, a low melting point and a low rate of attack on steel.

The pellets according to the invention are substantially spherical, free fror porosity and compare geometrically to current commercially- available lead shot.

Various methods of producing zinc based shot are technically possible, such as - die casting - ballheading/pressing fro wire/sheet - centrifugal casting of molten zinc or zinc based alloy However, these methods are believed to be somewhat expensive compared to methods which enable shot to be cast from molten zinc (or zinc based alloys) through a heated casting head such as an orificed plate or container into a bath of cooling fluid.

Shot sizes can be varied by altering the size of orifice in the casting head. the casting head can be fixed or can be vibrated to aid the formation of shot. The casting head can be between 1 and 50mr above the quenching medium but best results are obtained between 1.5me, and lOmm.

The quenching medium may be water based or oil based or a water/oil based combination can be used. Other additives such as surfactants, pH buffers and anti-corrosion chemicals can be used. It is advisable to minimize turbulence on the surface of the quenching medium to avoid shape variations.

Molten zinc and its alloys have a high heat content and thus require extended cooling periods which can be achieved by the use of deep quenching baths or inclined planes submerged below the coolant surface and careful control of coolant temperature. Casting temperature is dictated by factors such as size of shot, alloy used (which affects surface tension and viscosity) and the desire to minimise heat content.

Conveniently the pellets of the invention can be produced by means of a piece of proprietary equipment already known for making lead shot and known under the name BLEINEISTER (Manufactured by H. COLLIE GmbH of W.Germany). In this machine drops of molten alloy are vibrated through orifices into a bath of cooling fluid in which they encounter downwardly-inclined planes and roll down these planes. From the bottom end of the planes they fall more or less vertically through the fluid and reach the bottom of the fluid container solidified and substantially spherical in shape. Again, parameters such as diameter of orifice, slope of plane, and temperature of cooling fluid will have an effect on the size, and shape, of the product pellets, as will the composition of alloys being dispersed.

Suitable alloys for the production of shot according to this invention include zinc/aluminium (3.5-6.0%) and zinc/tin (0.5 to 2%) alloys; with or without the addition of the following additional alloying elements: (a) Copper 0.5 to 3.5% (b) Magnesium 0.01 to 2.5% (c) Lithium 0.001 to 0.5% (d) Silicon 0.001 to 1.0% (all percentage values being by weight) Examples of suitable alloys for shot forming are as follows:: EXAMPLE 1 3.8% - 4.5% Al 0.04% - 0.06% Mg + Zn + impurities EXAMPLE 2 3.8% - 4.5% Al 0.5% - 1.25% Cu 0.04% - 0.06% Mg + Zn + impurities EXAMPLE 3 3.8% - 4.5% Al 2.5% - 3.5% Cu 0.04% - 0.06 Mg + Zn + impurities EXAMPLE 4 3.8% - 4.5% Al 2.5% - 3.5% Cu 0.85% - 1.7% Mc + Zn + impurities EXAILE 5 3.8% - 4.5% Al 2.5% - 3.5% Cu 0.04% - 0.06% Mg 0.005% - 0.05% Li + Zn + impurities EXAMPLE 6 1.0 - 1.4 Sn 0.001 - 0.003 Li remainder Zn + impurities The reasons for deliberately adding various alloying elements to the Zn/Al - and Zn/Sn- based alloys for shot formation are as follows: I. For Zn/Al based alloys (a) Aluminium can be used to reduce melting point and thermal content of shot as well as to reduce attack on steel process machinery.

(b) Copper can be used to increase fluidity of molten metal which helps processing (particularly for smaller sizes). It also reduces porosity to minimal/negligable level.

(c) Magnesium can be used to decrease dendrite size and content in microstructure, thereby enhancing sphericity and also lowering (slightly) melting point.

(d) Lithium can be used to suppress dendritic growth and refines microstructure which enhances sphericity and surface finish.

(e) Silicon may be added to increase fluidity of molten metal thereby improving production of smaller shot by making the metal flow more freely through orifices in the production apparatus..

(f) Tin may be added in small quantities to improve size/weight distribution i.e. a larger proportion of shot is close to the mean size.

II. For Zn/Sn based alloys (a) Tin can be used to achieve product with minimal/negligable porosity and close size/weight distribution.

(b) Lithium can be used to enhance sphericity and good surface finish.

Claims (10)

CLAIMS:

1. A sporting pellet composed of zinc or a zinc-based alloy formed into substantially spherical form and having a diameter between 1.9 and 5.5 millimetres, a density between 6.5 and 7.3 and being without voids which communicate with the outer surface of the pellet.

2. A pellet as claimed in claim 1 which is based on a zinc/aluminium alloy or a zinc/tin alloy.

3. A pellet as claimed in claims 1 or 2 based on zinc/aluminium or zinc/tin which further contains an element selected fro aluminium, tin, copper, magnesium, silicon, an alkali metal or an alkaline earth metal.

4. A pellet as claimed in claim 3 wherein the alkali metal is lithium.

5. A pellet as claimed in any one of claims 1 to 4 which is cast from a zinc/aluminium alloy having a melting point no higher than 3900C.

6. A pellet as claimed in claims 1 to 4 of zinc/tin alloy having a melting point no higher than 430"C.

7. Sporting pellets as claimed in any one of claim 1 to 6 and substantially as hereinbefore described.

8. A method of producing a sporting pellet as claimed in claims 1 to 7, substantially as hereinbefore described.

9. A shot-gun cartridge containing a plurality of pellets as claimed in any one of claims 1 to 7.

10. A zinc-based alloy containing 0.5 to 2.0 of tin and 0.001 to 0.5E of lithium, with optionally small additions of copper magnesium or silicon.