GB2166059A - Dart flight - Google Patents

Abstract

At least part of at least some wings of a dart flight are embossed. The embossments may comprise rectilinear or sinuous corrugations or a rectangular pattern of dimples (8) and protuberances (9). This is effected by passing the flight between two dies, (Fig. 3 - not shown), each having cylindrical male protuberances, the protuberances on one die being offset from those on the other. Alternatively, the dies may have protuberances and complementary recesses, respectively. The flight is introduced between the dies With pairs of flights (3, 4 and 5, 6) in juxtaposed relationship. Improved rigidity and aerodynamic properties are obtained. <IMAGE>

Description

SPECIFICATION Improvements in dart flights This invention relates to an improved dart flight and is especially directed to dart flights formed from a thin sheet of plastics material which is folded, with adjacent sides thereafter being brought together and adhered so as to form a flight having a cruciform cross section.

Various-methods are known by which such flights may be manufactured and two techniques can be adopted, in one, a sheet of material is passed through a cruciform section die using a punch to form same into a fourflight assembly wherein adjacent sides are joined either by a contact adhesive or else by means of heat sealing. Another method makes use of a continuous strip of material which is passed through a die longitudinally and caused to conform progressively to produce the cruciform shape.

Such flights are generally of thin construction and it is one object of this invention to provide a flight which not only has a greater strength imparted thereto but which also has improved aerodynamic properties.

According to this invention there is provided a dart flight formed from a thin plastics material wherein a surface of the flight is embossed, the embossing comprising a plurality of discrete small areas, preferably arranged in a regular pattern over all or only over a part of the flight surface.

The discrete areas may be circular or polygonal in planform or they may comprise corrugations extending across the flight wing surface rectilinearly or with a sinous course, thus forming an embossed line comprising humps on one side and channels on the other.

The embossing may take a fan-shape convoluted course or be waffle-like in shape, and may be applied to all wings of the flight either to one or both surfaces of a wing, or possibly only to certain wings forming the flight, preferably in such a case to opposed wings in a cruciform flight.

Each discrete area may typically have a width, or diameter in the case of circular areas, of about 0.1 mm to 5.0 mm, preferably between 1 and 2 mm. The spacing between discrete areas may be between 0.1 and 2 mm, preferably between 0.2 mm and 1.5 mm and typically 0.5 mm. The height may be between 0.1 mm and 0.5 mm typically.

In one preferred method of forming the embossing, the flight after forming to shape and adhering or bonding is placed between two cc-operating dies, the one having a plurality of cylindrical protuberances and the other having a complementary set of cylindrical recesses.

In a further preferred embodiment the two dies are of similar form and each with cylindrical protuberances, the protuberances on respective dies being relatively offset so that the protuberances of one die enter between the interstices of the other. The flight when of cruciform cross-section is compressed with pairs of adjacent flights in juxtaposed relationship and lying in the same plane as the opposed pair of flights whereby embossing is imparted to the pair of flights together and transmitted through the juxtaposed relationship of the flights.

Step-wise embossing constitutes one method of production but a rotary embossing process is equally suitable.

It has been found that by providing the embossing as a regular pattern of discrete circular areas improved aerodynamic performance is obtained and in addition the flight is thereby made more rigid and less easily bent or flexed. When the embossing is applied to translucent or transparent printed flights it has been found that enhanced colour saturation is obtained resulting in improved visual appeal.

In one embodiment each discrete embossed area has a diameter of about 1.5 mm and the spacing between adjacent areas is about 0.5 mm with the lines of embossing extending diagonally to the longitudinal axis of the flight.

Tests have shown that the flights embossed according to the invention as compared with an unembossed flight of similar dimensions have improved flight characteristics and in particular the angle of board impact is better.

This is surprising and is expected to be due to increased drag or lift produced by the dimples on the surface related to the angle of attack of the airflow.

One embodiment according to this invention is shown by way of example in the accompanying drawings wherein: Figure 1 shows a dart flight in plan view, Figure 2 shows the flight of Figure 1 in section on the line l-l, Figure 3 shows a flight in the process of being embossed according to this invention, and Figure 4 shows a section through a flight along a line of dimples.

Referring to Figures 1 and 2 of the drawings the dart flight shown is of cruciform cross section (not essential to the invention) and this example is manufactured from a continuous strip of heat sealable plastics material which is conformed to a cruciform pattern through dies with the adjacent surfaces of the sheet parts forming each flight being thereafter heat sealed in an appropriate machine forming part of the forming apparatus. After the heat sealing operation the flight is passed between two dies 1 and 2 shown in Figure 3, both the dies having cylindrical shaped male protuberances over the surfaces thereof of a height of about 2 mm, the protuberances on each die being relatively offset.As can be seen the flight is introduced between the dies with pairs of flights 3 and 4, and 5 and 6 in juxtaposed relationship whereafter the dies are brought together and sufficient force applied to deform the flights so as to produce in the surface a regular series of dimples and protuberances. Only a few of the discrete areas are shown in the drawings.

The protuberances 7 on the die 1 cause deformation of the flights 3 and 5 and this is transmitted through to the surfaces of the flights 4 and 6 which are thereby indented with the same pattern. The protuberances 7 on die 2 cause deformation of flights 4 and 6 which are thereby indented with the same pattern. The protuberances 7 on die 2 cause deformation of flights 4 and 6 which is transmitted through to flights 3 and 5. With this method, a series of dimples 8 are formed over the whole or optionally a part only of the one surface of each flight and complementary protuberances 9 are formed on the opposite side surface.

The preferred shape for embossing is circular but many other shapes can be adopted without departing from the spirit of this invention. Following the embossing process the flights may then be cropped into the final profile illustrated in Figure 1 as example. The height of the protuberances formed in the flight is small, generally in the order of 0.1 mm. A typical range would be 0.05 mm to 1.0 mm for useful effect.

Part only of the flights may be embossed by providing the die with plain areas and embossing patterns over the surface area may be varied in size and spacing by using an appropriate arrangement over the die surfaces. The nose of the flight may be left plain to facilitate engagement with the shaft.

In a further embodiment, not illustrated, the one die 1 has a set of cylindrical protuberances 7 whereas the other die 2 has a complementary set of recesses to receive the protuberances thereby to effect the embossing.

Claims (17)

1. A dart flight formed from a thin plastics material wherein a surface of the flight is embossed, the embossing comprising a plurality of discrete small areas.

2. A dart flight in accordance with Claim 1, wherein the discrete areas comprise dimples and/or protuberances.

3. A dart flight in accordance with Claim 1 or 2, wherein the discrete areas are circular or polygonal in planform.

4. A dart flight according to Claim 1, wherein the discrete areas comprise corrugations or are rectilinear.

5. A dart flight in accordance with any preceding claim, wherein the discrete areas are arranged in a regular pattern over substantially the whole of a flight surface.

6. A dart flight in accordance with any preceding Claim 1 to 4, wherein the discrete areas are arranged in a regular pattern over a part only of the flight surface.

7. A dart flight in accordance with any preceding claim wherein the embossing is applied to the surfaces of opposed wings forming the flight.

8. A dart flight in accordance with any preceding Claim 1 to 6 wherein the embossing is applied to the surfaces of all wings forming the flight.

9. A dart flight in accordance with any preceding claim, wherein the width of each discrete area is between 0.1 mm and 5.0 mm.

10. A dart flight in accordance with any preceding claim, wherein the width of each discrete area is between 1 mm and 2 mm.

11. A dart flight in accordance with Claim 10, wherein the spacing between discrete areas is between 0.1 mm and 2 mm preferably 0.2 mm and 1.5 mm.

12. A dart flight in accordance with any preceding claim, wherein the embossing is formed by placing the wings of the flight, after forming to shape and adhering or bonding between two co-opeating dies, the one having a plurality of cylindrical protuberances and the other having a complementary set of cylindrical recesses.

13. A dart flight in accordance with any preceding Claim 1 to 11, wherein the embossing is formed by placing the wings of the flight between two co-operating dies each of similar form and each with cylindrical protuberances, the protuberances on respective dies being relatively offset so that the protuberances of one die enter between the interstices of the other.

14. A dart flight in accordance with Claim 12 or 13, wherein the flight has a cruciform cross-section and is compressed with pairs of adjacent flights in juxtaposed relationship and lying in the same plane as the opposed pair of flights whereby embossing is imparted to the pair of flights together and transmitted through the juxtaposed relationship of the flights.

15. A dart flight in accordance with any preceding claim, wherein each discrete embossed area has a diameter of about 1.5 mm and the spacing between adjacent areas is about 0.5 mm with the lines of embossing extending diagonally to the longitudinal axis of the flight.

16. A dart flight as described herein and illustrated in the drawings.

17. A method of forming a dart flight in accordance with any preceding claims and as described herein and illustrated in the drawings.