EP1154026A1 - Process for preparing composite tin-tungsten shot of small dimension - Google Patents

Abstract

A method for the fabrication of composite tin-tungsten elements having a thickness between 1 and 6 mm from a mixture of tin and tungsten powders consists of directly extruding the mixture of powders in the solid state to form a wire with a thickness of 1 to 6 mm, with a drawing speed of less than or equal to 80 mm/s. The wire produced is then cut into sections that are then stamped to obtain the desired shape. An Independent claim is included for the production of a composite tin-tungsten wire from a mixture of tin and tungsten powders.

Description

The present invention is essentially located in hunting and fishing and more specifically for a new manufacturing process low-tin-tungsten composite elements thickness, especially the manufacture of shot spherical for hunting cartridges or for lead shot peach.

It is known, in the state of the art, to use such a non-toxic shot in replacement of lead shot.

U.S. Patent 5,877,437, for example, describes spherical tin-tungsten composite shot for hunting cartridges, in the form of a malleable tin matrix containing, so evenly distributed, like tungsten powder charge.

According to a first method, the shot can be obtained by dispersing the tungsten powder in molten tin, then formation of drops through calibrated openings at the top of a tower. We provoke then the drop of these drops in air or water, this which allows, by cooling, the shot spherical.

According to a second method, the shot can be obtained by molding the dispersion of the powder tungsten in molten tin, but such a process is very expensive to obtain shot and is more suitable for obtaining projectiles or larger objects bulky.

Furthermore, these fusion processes are delicate. of implementation because it is very difficult to obtain a homogeneous distribution of the powdered tungsten in the tin matrix, especially because tungsten is not "wet" by the molten tin.

They also have the disadvantage of training a decrease in the malleability of the tin matrix and the appearance of soldering of the tungsten powder, this which leads to an undesirable increase in hardness of the material.

According to a third process, one compacts at high pressing in a mold a mixture of tin powders and tungsten at a temperature below the point of tin fusion.

It is thus possible to produce projectiles a few grams (bullets) suitable for weapons shoulder or fist striped, but the process is too expensive to obtain thin elements such as shot.

US Patent 5,399,187 further describes obtaining composite balls which can be consisting of a tin matrix loaded with powdered tungsten.

For ductile metal matrices such as tin, balls can be obtained by mixing powders metal, followed by compacting in bars or billets which are then extruded into wires. The balls are then obtained by forging wires using punches.

It turns out, however, that if one seeks, according to a usual technique of stretching tin wires, drawing a strand of diameter 10-20 mm in composite tin-tungsten to reduce the diameter and obtain a wire with a diameter between 1 and 6 mm, there are many tears at the interface tin / tungsten and wire breakage.

Those skilled in the art are therefore looking for a simple and inexpensive process for manufacturing components thin tin-tungsten composites (1 to 6 mm approximately) such as spherical shot for cartridges for hunting or for fishing sinkers.

The present invention relates to such a method.

It was unexpectedly discovered that could, by simple extrusion of a mixture, in the state solid, tin and tungsten powders, get directly, without an intermediate drawing step and / or for obtaining bars or billets, a thread of which the thickness is between 1 mm and 6 mm having satisfactory mechanical strength, without tearing at level of the tin / tungsten interface, provided that the spinning speed is less than or equal to 80 mm / s.

To obtain the desired composite elements, the wire obtained can be cut into sections which are then stamped to the desired shape, using machines well known to those skilled in the art for exercising such a function.

Such a process is particularly simple and not very expensive.

It also allows, in particular due to the absence a step of melting the tin, to preserve the malleability of the tin matrix and obtain a homogeneous distribution of tungsten powder in the matrix.

According to the invention, the mixture of tin powder and tungsten powder is directly extruded, to solid state, in a wire whose thickness is included between 1 mm and 6 mm, preferably between 2 mm and 4 mm, limits included, especially when the section of the wire is circular, which is also preferred.

The section of the wire can however be arbitrary, especially elliptical, square, triangular, rectangular, polygonal.

By "directly", it should be understood that the passage of the mixture of powders to the wire is done without step intermediate, in particular without intermediate obtaining of large diameter billets or strands, greater by example at 8 mm, and without intermediate operation of wire drawing.

By "extruded", we must classically understand that the powder mixture is pushed through a Faculty. The term "spinning" is synonymous of "extrusion".

By "solid state" it should be understood that the mixture of tin and tungsten powders is extruded to a temperature below the melting point of tin.

Preferably, the mixture is extruded at a temperature between 170 ° C and 225 ° C, better yet between 190 ° C and 220 ° C, limits included.

According to the process which is the subject of the present invention, first of all, in the proportions necessary to achieve the desired density, using a suitable mixer, tungsten powder and tin powder, the particle size of the powders preferably being in the range 1 μm -200 μm , better still in the range 10 μm -50 μm .

The tin / tungsten weight ratio is preferably between 0.5 and 2.0, better still between 0.7 and 1.5. We thus obtain composite elements, especially shot, having a density approximately between 9 and 12.5.

The extrusion of the powder mixture can then be driving either continuously by feeding regularly an extruder adapted to this type which is preferred, so discontinuous.

According to this preferred discontinuous variant, we introduces the powder mixture into the container of extrusion (press pot) of an extruder adapted to this type of operation and also including and so usual one or more calibrated outlet nozzles (die), a piston whose geometry is adapted to that of the container allowing to exert a push of the mixing of powders through the spinning die, as well as a container heating system extrusion.

The size of the nozzle or nozzles corresponds to the desired section for the wire.

According to a particularly preferred variant of the invention, the mixture of tin powders and tungsten is subjected to a partial vacuum before being extruded. For this, a reduced pressure is imposed in the extrusion container containing the mixture, preferably less than 100 mm Hg, using pumping suitable and well known to those skilled in the art.

We get better quality yarns, very little porous, in particular showing no inclusion of air.

As mentioned earlier, the spinning speed, measured at the nozzle, or nozzles, outlet the die, must be ≤ 80 mm / s.

Otherwise, there is a poor condition surface of the product wire, tears at the tin / tungsten interface, and even the break of the wire and / or the appearance of molten particles.

Preferably, the spinning speed is between 1 mm / s and 80 mm / s, better still between 5 mm / s and 60 mm / s.

This limitation of the spinning speed corresponds a limitation of the energy supply during spinning. Preferably, the spinning power developed by the press piston is less than 150 W, by example between 10 W and 100 W, better still between 10 W and 70 W, by extrusion nozzle.

According to another preferred variant of the invention, the spinning pressure is between 100 MPa and 300 MPa.

We also prefer to operate with a ratio between the piston section and the total section of the nozzles, called the spinning ratio, between 80 and 250.

The speed of the press piston is generally less than 0.6 mm / s, preferably between 0.05 mm / s and 0.5 mm / s.

According to another preferred variant of the invention, the sector does not have a convergent (flat sector) and its range (thickness corresponding to the length of the nozzle hole) is preferably between 5 mm and 15 mm.

To obtain the desired composite elements, especially spherical shot, the wire is cut obtained in sections, more particularly in cylinders preferably having a length equal to the diameter of the wire, or close to it, then these elements are then stamped, preferably at temperature ambient, to obtain the desired shape.

Preferably, and in particular according to the variant preferred for which the wire sections are cylinders whose length is close to or equal to wire diameter, this stamping allows to obtain spheres, or pseudo-spheres which are then rectified to the state of spheres, whose diameter is very close to or identical to that of the wire.

Such spherical elements are particularly suitable for making hunting cartridges or Lead sinker sinkers for fixed, deep-sea fishing fly or whip, especially split pellets.

According to another preferred variant, it is also possible obtain, by stamping, from sections cylindrical for example, elements having a shape ovoid and a thickness close to the thickness or wire diameter.

Such ovoid elements are particularly suitable for use as ballasting olives for trolling or casting, especially split olives.

All these cutting and stamping operations can be carried out continuously, using machines well known to those skilled in the art and in particular used for the production of balls for ball bearings.

The thickness of the elements obtained is generally identical or very close to that of the wire.

Depending on the thickness of the wire produced, we can therefore obtain composite elements having a thickness can vary from approximately 1 mm to approximately 6 mm.

The present invention also relates to the aforementioned process for obtaining the wire, namely a process for obtaining a tin-tungsten composite wire from a mixture of tin and tungsten powders characterized in that the powder mixture is directly extruded, in the solid state, into a wire of which the thickness is between 1 mm and 6 mm and in that the spinning speed is less than or equal to 80 mm / s.

Low-tin-tungsten composite elements aforementioned thickness can be used for other purposes that the production of hunting cartridges or pellets fishing, in particular and for example to carry out balancing weights or shielding objects ionizing radiation.

Such screens and weights can also be obtained from the wire itself, without it being previously cut.

The following nonlimiting examples illustrate the invention and the advantages it provides.

Examples 1 to 6 : production of spherical tin-tungsten composite shot according to the invention, of various densities and particle sizes

The tungsten powder and the tin powder used have a median diameter of approximately 30 μm .

Tin and tungsten powders are mixed in the proportions mentioned later for each example using an appropriate type mixer Forberg, at room temperature (around 20 ° C), for about 10 min, so as to obtain a mixture homogeneous.

The homogeneous mixture of the 2 powders is then poured in the container of an extrusion press. The container, cylindrical in shape, has a piston internal diameter equal to the internal diameter of the container, to the nearest tolerance, so that ability to push the mixture towards the die.

For these examples, 2 diameters were used different piston-container (30 mm and 40 mm). This diameter is specified later for each example.

The piston displacement stroke (useful length container) is 70 mm.

The speed of movement of the spinning piston, moved by an appropriate device well known to those skilled in the art trade, is specified for each example.

The container is provided on the one hand with a device (heating jacket) for heating of the powder mixture it contains, and on the other hand a vacuum connection associated with a frit allowing establish reduced pressure in the filled container of the powder mixture before extrusion.

The extrusion press also has a cylindrical flat die (without convergent) having a reach (thickness) of 10 mm and fitted with a single hole cylindrical centrally located with a diameter 2.6 mm or 3.2 mm is specified for each example.

The drilling of the die is initially blocked by an aluminum seal so that you can make a partial vacuum in the container.

The container is then heated and evacuated partial up to reduced pressure less than 80 mm Hg.

After heating to a temperature mentioned later for each test, and maintaining the vacuum partial, for about 45 minutes, we proceed to the extrusion of the powder mixture. The cover sealing the piercing of the die bursts due to the pressure exerted.

The following table specifies and summarizes the operating conditions specific to each example.

For all these examples, we obtain a wire having the following physical and mechanical properties:

Density measured by weighing and measuring dimensions

Example 1 9.43 Example 2 9.69 Example 3 9.84 Examples 4 to 6 not measured.

The densities measured are close to the density theoretical. Densification is ≥ 95%.

Metallographic analyzes

They show, for all the examples, a orientation of the elements in the direction of the length of the wire. There is a good homogeneity of distribution tungsten and tin, and little or no gas inclusions.

The surface condition of the wire, for all the examples, is very satisfactory. It is however less good for Example 6, while remaining satisfactory.

Wire ductility

It is encrypted by the bending angle of the wire (angle swept by the 2 parts of the wire at the time of breakage) Example 1 80 ° Example 2 60 ° Example 3 60 ° Examples 4 to 6 not measured.

This ductility is satisfactory.

Vickers hardness

It is practiced either on a section of the wire (hardness through), or on a cut of the wire in the direction of the length (hardness long direction) Example 1 13.52 (long) and 13.03 (cross) Example 2 15.07 (long) and 14.27 (cross) Example 3 14.87 (long) and 15.23 (cross) Examples 4 to 6 not measured.

This hardness is satisfactory.

The wires obtained for these 6 examples then have been cut into cylinders whose length is equal to wire diameter using a well known machine of the skilled person to exercise this operation.

The cylinders were then stamped, at the room temperature (around 20 ° C), in spheres with a diameter approximately identical to that of cylinders and wire, also using a machine well known to those skilled in the art to exercise this operation, particularly in the field of rolling bearings marbles.

This gives, for examples 1, 4, 5 and 6 of spherical shot with a diameter of approximately 3.2 mm, and for examples 2 and 3 of the spherical shot of diameter about 2.6 mm.

Comparative examples A and B

These comparative examples are not part of the invention. They were made for the sole purpose of show that the selection of a certain velocity domain spinning according to the invention is not arbitrary, but necessary to provide the desired technical effect, know how to obtain a surface finish wire satisfactory.

Examples 4 to 6 according to the invention were reproduced, all other things being identical, in modifying the speed of the spinning piston and therefore consequence, the expected spinning speed.

For comparative example A, we imposed a speed of the spinning piston of 1 mm / s. The pressure of measured wiring is 144 MPa.

The spinning power is 181 W.

The expected spinning speed is 156 mm / s, but we found that the wire comes out in pieces, which is undesirable.

For comparative example B, we imposed a spinning piston speed of 10 mm / s. The pressure of measured wiring is 255 MPa. The spinning power is 3200 W.

The expected spinning speed is 1560 mm / s, but only molten particles appear.

Claims (10)

Process for the production of tin-tungsten composite elements having a thickness of between 1 mm and 6 mm from a mixture of tin and tungsten powders, characterized in that : the powder mixture is directly extruded, in the solid state, into a wire whose thickness is between 1 mm and 6 mm, the spinning speed is less than or equal to 80 mm / s, the wire obtained is cut into sections which are then stamped to obtain the desired shape. Method according to claim 1, characterized in that the wire has a circular section and in that its diameter is between 2 mm and 4 mm. Method according to claim 1, characterized in that the mixture of tin and tungsten powders is extruded at a temperature between 170 ° C and 225 ° C. Process according to Claim 1, characterized in that the mixture of tin and tungsten powders is subjected to a partial vacuum before being extruded. Method according to claim 1, characterized in that the spinning pressure is between 100 MPa and 300 MPa. Method according to claim 1, characterized in that the spinning ratio is between 80 and 250. Method according to claim 1, characterized in that the spinning power is between 10 W and 100 W. Method according to claim 1, characterized in that the composite elements have a density between 9 and 12.5. Method according to either of Claims 1 and 2, characterized in that the composite elements constitute spherical shot for hunting cartridges or for fishing sinkers. Process for obtaining a tin-tungsten composite wire from a mixture of tin and tungsten powders, characterized in that : the powder mixture is directly extruded, in the solid state, into a wire whose thickness is between 1 mm and 6 mm, the spinning speed is less than or equal to 80 mm / s.