Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Particulate matter
Reexamination Certificate
2002-04-26
2004-11-09
Le, H Thi (Department: 1773)
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Particulate matter
C420S430000, C420S557000
Reexamination Certificate
active
06815066
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to composite materials, particularly to composite materials that can be used as lead replacements.
BACKGROUND OF THE INVENTION
Lead has been used in a variety of industrial applications for many thousands of years. In the last hundred years, the toxic effects of lead have become apparent. In an effort to reduce reliance on lead, there has recently been extensive research into materials that could be used to replace lead.
In this regard, much effort has been focussed on producing metal composites that mimic the properties of lead. Since the density of lead is the most obvious characteristic to mimic, most efforts have concentrated on finding composites that have the same or similar density as lead. However, other important properties of lead have been largely ignored and, as a result, no completely satisfactory lead replacement has yet been found.
In addition to being non-toxic and to having a similar density to lead, a successful composite should have reasonable softness coupled with structural rigidity. Ideally the composite is substantially homogeneous and relatively cheap to manufacture in large quantities.
One of the uses of lead has been in the manufacture of ammunition such as bullets and shot for shotguns. However, due to the increasing problem of lead contamination in the environment, arms manufacturers have begun looking for lead alternatives.
In a recent article, it has been reported that tungsten/tin and tungsten
ylon composites hold promise as lead replacements in ammunition (“Tungsten Outflanks Lead”
The International Journal of Powder Metallurgy
(2001) 37 (1):20)
Canadian patent 2,095,232 discloses an environmentally improved shot in which a lead or metal composite core is coated with an inert polymer like Teflon™.
Canadian patent application 2,202,632 discloses a ferromagnetic bullet that comprises a composite of a dense metal such as tungsten (W) or ferrotungsten with a lighter metal such as tin (Sn) or with a polymer such as phenyl formaldehyde or polymethylmethacrylate. A combination of tungsten, tin and polymer is not disclosed.
Canadian patent application 2,248,282 discloses a bullet core comprising a composite of a thermoplastic polymer and a metal filler such tungsten, bismuth or tin.
U.S. Pat. Nos. 5,279,787 and 5,877,437 disclose metal composites made from a mixture of a high density metal powder such as tungsten and a low density metal powder such as tin. Projectiles or shot are formed by moulding or drop forming.
U.S. Pat. Nos. 5,399,187 and 5,814,759 disclose lead-free bullets comprising a composite of a heavy constituent such as ferrotungsten or tungsten and a lighter constituent such as tin or a polymer such as phenyl formaldehyde or polymethylmethacrylate. A combination of tungsten, tin and polymer is not disclosed. This reference particularly exemplifies the use of ferrotungsten in combination with either a polymer or a low density metal, but not with both a polymer and a low density metal.
U.S. Pat. No. 5,719,352 discloses a low toxicity shot pellet comprising a composite of a mixture of finely divided molybdenum and tungsten particles in a polymer matrix such as polystyrene.
U.S. Pat. Nos. 5,760,331, 6,149,705 and 6,174,494 disclose lead-free bullets comprising a composite of a heavy constituent such as tungsten and a lighter constituent such as tin, aluminum, copper or zinc.
U.S. Pat. No. 5,894,644 discloses a lead-free bullet comprising a composite of a heavy metal such as tungsten and a lighter metal such as tin which is made by the infiltration of the lighter metal into a pre-form of the heavy metal.
U.S. Pat. Nos. 5,913,256 discloses a non-lead projectile comprising a composite of a heavy metal such as tungsten and a lighter metal such as tin together with a wetting agent such as aluminum or zinc.
U.S. Pat. No. 5,963,776 discloses a projectile comprising a composite of a heavy metal such as tungsten and a lighter metal such as tin, the composite being made by a process in which the lighter metal is coated on the heavy metal and the two are cold pressed.
U.S. Pat. No. 6,048,379 discloses a high density material comprising tungsten, a binder such as nylon and a fibrous material such as stainless steel fibres. The material is used for lead replacement.
SUMMARY OF THE INVENTION
There is provided a composite comprising tungsten, tin and an organic additive.
The composite of the present invention is generally in solid form. Throughout this specification, “solid object” has reference to a composite of the present invention in solid form.
In another aspect, there is also provided a process for preparing a solid object comprising:
mixing tungsten, tin and an organic additive to form a mixture; and
forming a solid object of tungsten, tin and an organic additive from the mixture.
In another aspect, this process may further comprise the steps of:
coating the solid object with a low surface energy organic polymer; and
heating the coated solid object to a temperature greater than the melting point of the tin.
The composites of this invention can be used to completely or partially replace lead in a variety of articles such as projectiles or ammunition (for example, bullets, bullet cores and shot), weights (for example, wheel weights), radiation shielding, vibration damping supports or sports products (for example, golf club heads or dart bars).
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Tungsten is preferably used in the composite in an amount of about 40-74%, more preferably about 55-69%, by weight of the composite. In a process for preparing the composite, tungsten is generally used in the form of tungsten particles, particularly in powder form. The relatively lower fraction of tungsten in the composite allows a greater processing window to achieve the target density, resulting in, at least in principle, an increased number of options in terms of particle size, shape and purity as compared to the use of deagglomerated, high purity tungsten with an average particle size of 4 &mgr;m, which is typically used in prior art tungsten/polymer composites.
Tin is preferably used in the composite in an amount of about 25-59%, more preferably about 30-44%, by weight of the composite. Generally, tin can be used in particulate form in a process to prepare the composite. Some alloying (generally <10%) may be done to adjust the processing characteristics in terms of wetting, and melting, as well as mechanical properties of the final product.
The ratio of tungsten to tin is generally adjusted to provide a composite with a density of about 9.5 to 14.0 g/cc. Ideally the density of the composite is about 11.3 g/cc, which is the density of lead. However, variations from the ideal density will still result in a useful composite.
The organic additive can be any organic substance that imparts a desired characteristic to the composite. The organic additive may be used, for example, as a binder, to increase lubricity (e.g., to reduce damage to a gun barrel when the composite is used in ammunition), to modify mechanical properties, to modify the wettability of tin and/or tungsten, to control viscosity or to inhibit the settling of tungsten in the composite. The organic additive may, for example, be a metal (e.g., zinc, lithium, nickel or copper) stearate or ethylene-bis-stearamide.
The organic additive may also be an organic polymer. If such is the case, ideally, desired characteristics can be imparted by a single organic polymer, but, separate polymers may be used to impart one or more of the desired characteristics to the composite. Polymer blends or copolymers may also be used as the organic polymer.
The organic polymer is preferably a thermoplastic polymer. Specific organic polymers include, but are not limited to, polyfluorinated hydrocarbons such as polytetrafluoroethylene (PTFE, e.g. Teflon™, DryFilm™), and ethylenechlorotrifluoroethylene (ECTFE), basic polymers such as polyamines and polyvinylpyrrolidone, and polypropylene. Polyfluorinated hydrocarbons are preferred, in particular, PTFE and ECTFE.
The organic additive is
Anissimoff & Associates
Le H Thi
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