GB2219218A

GB2219218A - Coating dart bodies

Info

Publication number: GB2219218A
Application number: GB8813172A
Authority: GB
Inventors: Cedric Charles Hanson
Original assignee: Diffusion Alloys Ltd
Current assignee: Diffusion Alloys Ltd
Priority date: 1988-06-03
Filing date: 1988-06-03
Publication date: 1989-12-06
Also published as: GB8813172D0

Abstract

A body, for a playing dart, of a powder metallurgical tungsten-based alloy is provided with a coating of titanium nitride. The dart body has a bright gold colour. The coating may also be applied to the point of the dart. The coating may be applied by physical vapour deposition. This is carried out at a temperature which does not have an adverse effect on the point of the dart so that this may be coated in position in the body.

Description

Improvements relating to a body for a playing dart and darts incorporating such body.

This invention relates to playing darts. More particularly it relates to bodies for such darts.

For many years darts as used for throwing in the game of darts, that is playing darts, have had the body made from brass.

This has sometimes been left in its natural colour and perhaps lacquered to preserve the finish or it has been nickel and/or chromium plated.

There have been evolved many designs on the barrel section of the body in attempts to improve the grip within the fingers and hence the accuracy of the dart when thrown.

A further and recent development has been to make the body of the dart from alloys based upon the metal tungsten. These alloys, being much heavier than brass, have considerably improved the accuracy of darts when thrown and are now the most widely used for darts of good quality and performance. Again there have been various designs developed which are machined or cut into the body to provide a more effective grip within the fingers without interfering with the aerodynamic characteristics of the dart made from the high density alloys.

The alloys are grey in colour and made by a powder metallurgical process, and although they can be machined by turning in a lathe so that a brighter surface is obtained they lack the attraction of the appearance of the brass bodies or the appearance of those bodies which are nickel and chromium plated. A further disadvantage is that the finish, as machined, deteriorates in use in contact with the fatty acids secreted by the skin.

Therefore there has been a demand for an attractive, durable finish which can be applied to the dart body.

It is possible to apply brass as an alloy by electroplating the tungsten alloy but experience has shown that it does not adhere satisfactorily to such tungsten alloy and has a marked tendency to wear away in use.

It is also possible to apply by various means clear and coloured lacquers which although initially attractive can deteriorate with use. Coatings of nickel silver have been applied but these are of yellow-white colour and somewhat soft.

We have now surprisingly found that an attractive, durable finish for a body for a playing dart is provided by titanium nitride.

The invention therefore provides a body, for a playing dart, of a powder metallurgical tungsten based alloy with a coating of titanium nitride.

Titanium nitride is gold in colour, has a hardness of about 3000 V.P.N. (Vickers Pyramid Numerals) and is therefore very durable and withstands the effects of the fatty acids referred to above.

There are two general methods of applying titanium nitride, one chemical vapour deposition (C.V.D.) and the other physical vapour deposition (P.V.D.) C.V.D. is carried out at a temperature of about 10000C while P.V.D. is carried out at temperatures between 300 and 5000C.

Of these methods the P.V.D. process is preferred. When using the P.V.D. process in particular it was found that gold coloured hard adherent layers of titanium nitride could be obtained on the tungsten alloy which had a degree of reflectivity corresponding with the initial surface finish of the base material. Also because the temperature of application could be below the tempering temperature of the carbon steel used for the point it was possible to coat the assembled body and point thus giving a very attractive product.

P.V.D. units take one of three general forms (a) multiple electric arc with hard vacuum, (b) multiple electric arc with soft vacuum, often termed sputter ion plating, and (c) electron beam melting in hard vacuum. In the following example type (c) was used, although any of the other techniques are equally applicable.

EXAMPLE A quantity of ultrasonically cleaned and assembled dart bodies, that is dart bodies with points but without flights, were placed in the work chamber of the P.V.D. apparatus. This can be achieved because the rear end of the body used has a counterbored hole into which are fixed the flights. The chamber was then evacuated to the required degree of vacuum (10-20 mtorr) and a quantity of pure argon admitted. With the application of the plasma excitation the parts heat up to about 3000C and the argon atoms bombard the surface of the parts and remove surface oxide contamination. An applied voltage of 500-1000 volts is used, nitrogen is bled into the chamber and after various adjustments of temperature the titanium is evaporated and combines with nitrogen to form titanium nitride on the exposed surfaces of the darts. Deposition rate is about 1 micron per hour and after two hours the process was stopped and the apparatus cooled down and restored to atmospheric pressure. The dart bodies on removal were of a bright gold colour and metallographic examination of prepared sections showed them to have an adherent coating of 2 microns of titanium nitride.

Although the invention has been described with particular reference to the application of the titanium nitride by a physical vapour deposition process any other suitable process for the application of this coating may be used.

The thickness of the titanium nitride layer which is applied is preferably within the range of 1 to 6 micron.

Claims

CLARETS:

1. A body, for a playing dart, of a powder metallurgical tungsten-based alloy with a coating of titanium nitride.

2. A body as claimed in claim 1 in combination with the point of the dart which is also provided with a coating of titanium nitride.

3. A playing dart comprising a flight, a body and a point in which the body and optionally the point are provided with a coating of titanium nitride.

4. A body for a playing dart, and a dart including such body, substantially as herein described with reference to the Example.

5. A process of forming a body as claimed in claim 1 which comprises applying a layer of titanium nitride on a dart body of a powder metallurgical tungsten-based alloy.

6. A process as claimed in claim 5 in which the coating of titanium nitride is applied by physical vapour deposition.

7. A process as claimed in claim 5 or claim 6 in which a coating of a thickness of approximately 2 micron is applied.

8. A process as claimed in any of the claims 5 to 7 in which the body to which the layer of titanium nitride is applied has the point of the dart positioned therein so that the point is also coated with the layer of titanium nitride.

9. A process as claimed in any of claims 5 to 8 substantially as herein described with reference to the Example.

10. A body for a playing dart, optionally additionally including the point of the dart, when made by a process as claimed in any of claims 5 to 9.

11. A playing dart comprising a flight, a body and a point, in which the body and optionally the point are as claimed in claim 10.