GB2308089A

GB2308089A - Injection moulding shuttlecock cork

Info

Publication number: GB2308089A
Application number: GB9525615A
Authority: GB
Inventors: Jaswinder Singh
Original assignee: VIC TREE
Current assignee: VIC TREE
Priority date: 1995-12-15
Filing date: 1995-12-15
Publication date: 1997-06-18
Also published as: GB9525615D0

Description

IMPROVEMENTS IN OR RELATING TO SHUTTLECOCKS This invention relates to improvements in or relating to shuttlecocks for the game of badminton and is more particularly concerned with method and apparatus for making the shuttlecock "cork" as well as with the shuttlecock "cork", itself.

The shuttlecock "cork" is the domed end of the shuttlecock which traditionally has been made of cork but which is often made of other materials such as P.V.C.

(polyvinyl chloride). Cork tends to be expensive, supplies are limited and manufacture tends to be inexpedient so other, synthetic materials have been investigated which may yield similar bounce and resilience characteristics. The problems involved with making shuttlecock corks from P.V.C.

are well known and, although the P.V.C. material itself may be relatively inexpensive, the moulding process itself necessarily tends to involve a high scrap rate of product of perhaps 60 or 70% of the shuttlecock corks. Generally, the process for moulding shuttlecock corks from P.V.C.

involves filling a compression mould with a thick P.V.C.

paste and tends to be a slow inefficient process which may take in the order of thirty minutes to an hour to produce a batch of sixty or so shuttlecock corks per mould, by a compression moulding process in which the majority of those corks have to be scrapped. Furthermore, the scrap material is useless and has to be discarded. In addition to the moulding process for P.V.C. shuttlecock corks tending to involve a large amount of waste material, the material (P.V.C.) itself and manufacturing process are not considered to be environmentally friendly and thus there is a general need to formulate shuttlecock corks from materials other than P.V.C.

Although the need has been recognised to try to formulate shuttlecock corks from foamed plastics other than P.V.C., as far as the Applicant is aware, all efforts to date have been unsuccessful. Processes have been experimented with for several years involving foam plastics materials such as E.V.A. (co-polymers of ethylene and vinyl acetate) but, owing to the complex problems involved, results have been generally poor yielding unsatisfactory and distorted products.

It is an object of the present invention to at least alleviate the aforementioned, or other problems associated with shuttlecock corks, or at least to provide an improved method or apparatus for making shuttlecock corks, which shuttlecock corks may be improved in at least some respect.

According to the present invention there is provided a method of making shuttlecock corks by an injection moulding technique, said method comprising: (a) injecting plastics material into a mould and blowing the plastics material and causing cross-linking of the plastics material by activation of a cross linking agent in such manner that the finished shuttlecock cork is rotationally symmetric about its axis and without discontinuities throughout its cross section, said shuttlecock cork thus comprising a blown cross linked foamed plastics structure and/or (b) feeding plastics material into a mould in a direction which is axial of the finished shuttlecock cork in order to provide a structure to the cork which is uniform.

Preferably, the plastics material will be injected to a location which will be on the inside of the finished product so that there will be no aberration or pip left on the exterior surface of the shuttlecock cork that will need removing, said aberration or pip instead being on the inside of the product and thus substantially hidden from view, and preferably being disposed axially of the cork.

Preferably, the plastics material is vented during the process to alleviate any "gassing" that could give rise to discontinuities in the material structure.

In one embodiment of the method, both the plastics material and the mould are heated in order to provide activation of a blowing agent and of a cross linking agent so that on removal from the mould the shuttlecock cork expands substantially instantaneously into its required size. Advantageously, use of a cross-linking agent allows a skin to be formed on the shuttlecock cork easing extraction from the mould and also allows a lower product density to be obtained. Preferably, a plurality of shuttlecocks such as two, four or twenty are moulded substantially simultaneously by the same moulding tool.

Preferably, the plastics material is heated to a temperature of about 110it prior to injection into the mould which may be heated to about 200it and preferably the cycle time for each moulding is about 2 to 3 minutes.

Where the plastics material is vented as aforesaid, preferably, venting is provided from the mould at at least two diametrically opposed positions which are axially spaced from the injection location of plastics material into the mould.

Also preferably, the method includes moulding an internal flange means or recess means on the shuttlecock cork so that the shuttlecock cork remains on a male die portion of a moulding tool, during extraction of the shuttlecock cork from a moulding cavity of a female die portion of said tool. The flange means may comprise an annular rib or e.g. a series of pips which can be utilised to lock the cork to a shuttlecock flight.

Preferably, the method involves a plastics material of an E.V.A. formulation or similar or any suitable ethylene polymer or copolymer. E.V.A. material provides a good degree of cross-linking and a good uniformity of cross-linking.

In an alternative embodiment, the shuttlecock cork or corks is/are extracted from the mould in "dummy" or "blank" form in which the temperature of the injection moulding has been kept below the temperature required for activation of blowing and cross linking agents contained in the plastics material. In such an embodiment, the moulding cycle time may be only 30 seconds and the mould itself may be heated. A plurality of shuttlecock cork dummies may be placed into a compression mould or similar and heated (e.g.

for example to about 165 for about five minutes) to activate said blowing and cross-linking agents so that finished shuttlecock corks can be extracted from the compression mould. It is an advantage of this alternative method that the scrap rate for shuttlecock corks may be as low as 2 to 7% or 2 to 4%. The specific gravity of the dummies may be about four times that of the finished cork, i.e. the specific gravity of the dummy may be about 1 and the specific gravity of the finished product may be about .25. The aforementioned alternative method has the advantage that the weight of the dummies and thus of the finished product can be carefully controlled.

It is also possible that the method may involve forming the shuttlecock cork with a syntactic structure in which microspheres of one material are embedded in a matrix of a core plastics material, in order to produce a shuttlecock cork with specified bounce characteristics.

In another alternative method of manufacture of the shuttlecock cork, the cork (or dummy) may be moulded in a solid form, the internal shape of the cork (or dummy) being determined (e.g. by drilling) in a post moulding operation.

Further according to the present invention there is provided injection moulding apparatus for moulding shuttlecock corks, said apparatus comprising means to inject plastics material along an axis corresponding to the shuttlecock cork axis or at least having means to provide a substantially uniform flow of material in the mould about said axis, said mould having vents to alleviate gassing of the plastics material during moulding.

In one embodiment of the present invention, the moulding tool is a multi-impression tool so that a plurality, for example 2, 4 or 20 shuttlecock corks can be produced at the same time by the same tool.

Preferably, the mould design is such that it allows substantially instantaneous release of the product from the mould.

In one embodiment of the moulding apparatus, a female die is provided having one or more cavities with a part spherical bottom portion, the or each cavity being provided to mould the or each shuttlecock cork. For the or each cavity there may be provided a male die having a projecting portion which projects into the associated cavity during the moulding process. Preferably, the or each projecting male portion is arranged on the axis of its associated cavity in the female die, so that in use, plastics material can be injected along the axis of the male die projecting portion into the bottom of the cavity from the inside, so that on ejection from the mould, no aberration or pip will be left on the outside of the shuttlecock cork.In one embodiment of the apparatus, a female die is made up from a number of plate sections and female die inserts whilst the male die may also be made up of a number of plate sections with male die inserts. It is envisaged that the male and female dies will be substantially circular in shape and each may be surrounded by a heater band. Guide means may be provided, preferably in the form of guide pins cooperating with guide holes for interfacing the male and female dies, preferably, under the action of a ram piston.

Advantageously, means may be provided to hold a shuttiecock cork onto its associated male die insert on extraction from the moulding cavity of the female die.

This means may conveniently be provided by a recess (usually an annular recess) on the male projecting portion so that an internal flange is moulded onto the internal surface of the shuttlecock cork which in turn engages in the recess on the male projecting portion as the shuttlecock cork is removed from the mould. Additionally, this flange may have the advantageous secondary function of lockingly retaining the shuttlecock flight to the shuttlecock cork.

The apparatus may be used to form finished, expanded shuttlecock corks by heating the mould to an appropriate temperature at which blowing agents and cross linking agents in the plastics material undergo decomposition.

Alternatively, the apparatus may be used to produce shuttlecock cork dummies or blanks which can be subsequently transferred to a compression moulding tool.

Further according to the present invention there is provided a method of making shuttlecock corks, said method being a two stage process, the first stage of the process involving injection moulding a dummy shuttlecock cork and extracting same from the mould before activation of a blowing agent in the dummy, the second stage of the process comprising heating a plurality of dummy corks made from the first process, in a compression mould, to activate the blowing agent in order to provide expanded foam plastics shuttlecock corks.

Still further according to the present invention there is provided a shuttlecock cork of a cross linked expanded foam plastics material, said shuttlecock cork having one or more of the following properties: (a) rotational symmetry about its axis, (b) structural uniformity or lack of discontinuity about its axis, (c) a weight lying in the range 1.5 to 1.9 grammes and/or specific gravity of about 0.25 or less, (d) no external pip or aberration moulded thereon, (e) an undistorted shape, (f) dimensional stability, (g) internal locking means, preferably in the form of an internal flange, which in use locks the weight of the flight of the shuttlecock to the shuttlecock cork, preferably by snap location of part of the weight behind said locking means, (h) being moulded from an E.V.A. formulation or similar (e.g.E.M.A.) or ethylene polymer or copolymer including a cross-linking agent, preferably a peroxide, a blowing agent, a lubricant and a filler, (i) being aerodynamically formed without any post moulding operations.

The present invention may also comprise providing internal locking means on a shuttlecock cork for locking the shuttlecock flight thereto.

Although attempts have been made previously to injection mould shuttlecock corks out of materials other than P.V.C., for example E.V.A., such attempts have been highly unsuccessful for many reasons. The Applicant has realised that in order to produce a successful product there has to be a balance between the material formulation selected, the operational parameters such as temperature, time of curing and so forth, the particular design of tooling and the manner in which the material is injected into the mould. Moulding of relatively small items with high expansion rates without distortion is a relatively onerous task.A previous attempt at injection moulding a shuttlecock cork out of E.V.A. material which resulted in a highly unsatisfactory and distorted product involved injecting the E.V.A. plastics material into the mould at the side of the shuttlecock cork and this resulted in a non-uniform product with discontinuities due to flow patterns of the material into the mould as well as due to gassing and the selected formulation of E.V.A. material.

Additionally, injecting the plastics material into the mould in this manner resulted in an external pip or aberration on the shuttlecock cork which would have to be removed. In order to obtain best results the formulation of the material needs to be considered in detail and matched to the mould to obtain the right degree of blowing, and cross-linking in combination with tool design. The Applicant's injection moulding technique speeds up production of the shuttlecock corks (perhaps by a factor 6 over previous processes using P.V.C. material) and provides seemingly minimum requirements for post moulding operations, as well as simultaneous multi-part moulding.

Accordingly, further according to the present invention there is provided a method of making shuttlecock corks, said method comprising injecting plastics material into a mould, said plastics material comprising at least 90% of a resin based on ethylene polymer or copolymer, optionally blended with rubber and/or a filler material, together with up to 10 of additives including a blowing agent, a cross-linking agent, a co-agent, an activator and a lubricant.

A preferred general formulation of such plastics material is: (1) Resin: Polythene at least 50 parts by weight up to 100 parts by weight; balance substantially E.V.A.

(2) Additives (proportions to 100 parts of resin): Peroxide at least 4 Zinc Stearate about 1 OB Genitron from 2 to 2.5 ADCK from 2 to 2.5 the above blended with a binder such as DOP about 0.7.

More generally according to the present invention there is provided a shuttlecock cork of an expanded foam plastics material having a self-skinned, closed cell, structure said plastics material comprising at least 90% by weight of cross-linked ethylene polymer or copolymer optionally blended with a rubber and/or filler material, and up to 10% by weight of the residues of moulding additives including gaseous material trapped in the closed cell structure.

In a preferred embodiment, the cross-linked polymeric material includes E.V.A.

The E.V.A. material may have a melt flow index of 0.5 to 7 and vinyl acetate content of 4 to 28%. The melt flow index is preferably 1 to 3 and the vinyl acetate content is preferably 4 to 18%.

A particularly effective formulation is provided by plastics material of about 60 to 80% LLDP (linear low density polyethylene) and about 20 to 40% E.V.A.

An embodiment of apparatus and method for making shuttlecock corks, in accordance with the present invention, will now be described by way of example only with reference to the following much simplified accompanying drawings, in which: FIGURE 1 shows schematically in diametrical cross sectional elevation a four impression moulding tool comprising male and female die portions; FIGURE 2 shows an enlarged sectional view of a female die insert shown juxtaposed to a similar view of a male die insert, and FIGURE 3 shows a cross-sectional view of a shuttlecock cork in accordance with the present invention.

FIGURE 1 shows schematically moulding apparatus for injection moulding shuttlecock corks C (FIGURE 5 shows a cross-sectional view of a shuttlecock cork). The apparatus is a generally circular, four impression tool so that four shuttlecock corks can be made at any one time, although it could easily be adapted as, for example, a twenty impression tool. The apparatus comprises a female die 1 (made up of various plate sections 4a,4b,4c,4d bolted together) having four die inserts 2 (only two shown in FIGURE 1); a female die insert is shown on its own in FIGURE 3. The female die inserts 2 are equiangularly spaced about axis XX of the female die 1. As should be evident from FIGURE 1, each die insert 2 has a cavity 2a (formed by a .75 inch - 1.9 cm - ball-nosed cutter) with a part-spherical bottom portion 2b which, in use, will shape the domed end of the shuttlecock cork C.The die inserts 2 are securely mounted into the female die 1 in a manner which should be self-evident. The male die 3 (shown only in part in FIGURE 1) is made up of various die plate sections 3a,3b bolted -together and comprises four die inserts 5 (see FIGURE 2) which are incorporated into the male die 3 such that each male die insert 5 is axially aligned with an associated cavity 2a of each female die insert 2. Once the male projecting end Sa of each male insert 5 has been introduced into its associated cavity 2a of each female insert (by relative linear displacement of the male and female dies 1,3) plastics material can be injected under pressure through tapered sprues 7 in the direction of arrows A in a generally standard manner.

Importantly, each cavity 2a is provided with two diametrically opposed vents 2c axially spaced, during moulding, from the open end or sprue gate Sc on the projecting male end 5a of each male die insert 5. The vents may be in the order of 0.003 inches (.0076 cm) in diameter and the FIGURES of the drawings are generally to scale. It is believed the particular dimensions of the male and female dies 1,3 are advantageous. As the male and female dies 1,3 interface preferably by action of a ram piston (not shown) with one another four cylindrical guide pins 8 (only two shown) of the male die 3 engage into receiving holes 9 in female die 1 in a manner which should be self-evident. The female and male dies 1,3 are provided with circular heater bands 10,11 surrounding the respective die inserts 2,5 as should be evident from FIGURE 1.Heater band 10 is approximately 2,000 watts whilst the heater band 11 is 1,600 watts.

It is important that the plastics material is injected axially of each cavity 2a, from within the cavity, so that on removal of the finished shuttlecock cork C from the cavity there will be no aberration or pip on the exterior surface of the shuttlecock cork where the sprue gate was located; rather any aberration or pip P (see FIGURE 3) will be hidden from view on the inside surface of the shuttlecock cork C. Furthermore, spacing the vents 2c axially as far as possible, during moulding, from the gate Sc allows the plastics material injected to spread out from the axis XX uniformly from the domed part of the shuttlecock cork towards the rear, displacing any air in this direction, in order to avoid gassing and in order to avoid any discontinuities within the internal structure of the shuttlecock cork.Injecting plastics material into the side of the cavity from the outside would necessarily introduce anomalies into the integral structure of the shuttlecock cork resulting in a non-uniform flow and gassing.

Thus it is believed that the moulding die is a unique tool design which allows dimensional stability to be achieved for complicated shapes by a semi-automatic process. Furthermore, the tool design (female cavity dimensions and male projection dimensions) allows the cork to expand and "pop" out of the female cavity practically instantaneously. Additionally, the tool design allows easy cleaning of the male and female parts.

Each projecting end Sa of each male die 5 has an exterior surface shaped to provide the internal shape of the shuttlecock cork and to give the required wall thickness of shuttlecock in cooperation with its associated cavity 2a and is additionally designed to overcome release problems of the shuttlecock cork from the mould and in particular from the moulding cavity 2a. It has been found, in practice, that there may be tendency for the exterior shape of the shuttlecock cork to distort on extraction from the cavity 2a on occasion and this is due to the rapid expansion of the shuttlecock cork as it "pops" from the cavity. Sometimes the domed portion of the shuttlecock cork remains momentarily in the cavity whilst expansion of the remainder takes place giving rise to some distortion when the shuttlecock cork is finally ejected from the cavity. Therefore, advantageously, in order to alleviate such a problem each male die insert 5 is provided with an annular indentation 5d which allows an internal flange F (see FIGURE 3) to be moulded on the shuttlecock cork C, so that as the male projecting end 5a of each male die is withdrawn from its associated cavity 2a the shuttlecock cork will remain on the male die and be pulled clearly from the cavity 2a, thus avoiding any problems of distortion.

The Applicant believes that this latter described feature is very important in the moulding process in addition to which the internal flange F on the shuttlecock cork provides a locking means for locking the weight (not shown) of a shuttlecock flight (not shown) firmly into the shuttlecock cork by a snap-locking action rather than by the present friction fit employed.

The Applicant has been successful in producing shuttlecock corks which are undistorted using various formulations of E.V.A. copolymer material. The Applicant takes the raw resin E.V.A. material and adds to it various agents such as a blowing agent, lubricant, filler, accelerator, cross-linking agent and so on to produce the desired plastics material in pelletized compound form which is fed by hopper into the injection mould.

The Applicant believes the E.V.A. formulation to be highly important in the finished product in order to achieve the correct weight and density distribution and hysteresis or bounce characteristics. The degree of crosslinking of the final foam plastics product and blowing is critical to providing a satisfactory product.

It will be noted how much smaller the cavity 2a is than the external dimensions of the shuttlecock cork and this will give an idea of how much the product expands on ejection from the mould. The expansion from the mould is practically instantaneous.

During the process, the plastics material is heated prior to injection to a temperature of about llOC and parts of the male and female dies 1 and 3 are heated (as indicated in FIGURE 1 by heater bands 10,11 to a temperature of about 200 C). The moulding process takes only two to three minutes.

An advantage of the aforesdescribed Applicant process is that a scrap rate of about 5 to 7% can be achieved as opposed to scrap rates of 60 to 70* with present processes involving P.V.C.

In an alternative process, the mould itself is unheated and the temperature is kept below that required for activation of blowing and the cross-linking agents contained within the plastics material. With a cycle time of approximately thirty seconds the result is the production of shuttlecock cork dummies or blanks which can be extracted from the mould in a non-expanded form. The dummies or blanks can then be transported to a compression mould and heated to activate cross-linking and blowing agents (by thermal decomposition) in order to provide the finished shuttlecock cork. The advantage of adopting such a process lies in the number of shuttlecock corks that can be manufactured at once, since the compression tool can easily be arranged to make sixty or so shuttlecock corks in one batch with a scrap rate of only about 2 to 4%.

The plastics material formulation may comprise one or more of the following: (a) a cross-linking agent for example a peroxide chosen from one of the following: Dicumyl peroxide Bis (tert-butyl peroxyisopropyl) benzene 4,4-Bis (t-butyl peroxy) butylvalerate 2,5-Bis (t-butyl peroxy) -2,5- dimethylhexane -3 2,5 Bis (t-butyl peroxy) -2,5- dimethylhexyne -3 (b) a blowing agent selected from one of the following:1. azodicarbonamide, pp'oxybisbenzene sulphonydrazide, p-Toluene sulphonhydrazide and their activated versions thereof.

2. Activators include metal salts of Zinc, Barium, calcium, cadminum and lead; particularly Zinc oxide, Zinc stearate and zinc dibenzene sulphinate.

3. Amines and glycols as organic activators, particularly urea, ethanolamine.

4. Activators may also include combinations of metal salts and organic activators such as zinc oxide and urea in combination with Azodicarbonamide.

5. Compositions may include mixture of blowing agents particularly Azodicarbonamide and p'p oxybls benzene sulphonhydrazides and their combinations with standard activators outlined in the sectors 2, 3 and 4 above.

(c) a lubricant selected from one of the following: Organic fatty acids (stearic acid) Organic metal fatty acids (metal sterates) Waxes (crodamide) paraffinic waxes Organic sterates.

(d) an additive: Fillers e.g. calcium carbonate, silica, carbon blacks, silcates etc Pigments Wetting agents Co-agents (eg Perkalink 300-50 D).

Commercial products available for blowing agents are: Genitron SCE Porofor ADCK Cenitron EPC Celogen 754 or 765 Genitron EPE Supercell C Genitron OB Supercell X Commercial products available for peroxides are: Perkadox BC40 Perkadox 14/40 Retilox F - 40 CO Agents or Accelerators for the Peroxides are commercially available under the name Perkalink 300 - 50D (Triallyl Cyanurate).

Polymers may be TR and LDPE, VLDPE which are all polyethylene products as well as E.V.A., E.M.A., EAA, EBA which are all ethylene thermoplastics copolymers and blends of these could also be provided. Additionally EPDM, SBR (styrene butadiene rubber) and NR could be blended with all the above as resin compositions.

During the moulding process decomposition of the blowing agent may occur between 130-180 C, preferably 145 165"C. The compounding temperature for compound production may be 85-135 C and is preferably 115-130"C. The barrel temperature of the moulding apparatus may be 95-145"C, preferably 110-130"C. The mould temperature (set) may be 160-200 C with a true temperature of 155-185"C.

Tables 1,2 and 3 show some specific examples.

TABLE 1 Example A B C D E RESIN POLYTHENE 59 50 60 40 50 EVA (209) 41 50 40 - 50 EVA (218) - - - 60 ADDITIVES Peroxide 40% 5 5 2.5 2.5 5 Zinc Stearate 1 1 1 1 1 OB Genitron 2.3 2.3 0.7 0.7 1.9 ADCK 2.3 2.3 0.7 0.7 1.9 BINDER DOP 0.7 0.7 0.7 0.7 0.7 TABLE 2 Example F G H I RESIN POLYTHENE 100 100 100 100 ADDITIVES Peroxide 40% 5 5 5 5 Zinc Stearate 1 1 1 1 OB Genitron 2.3 2 1.8 1.3 ADCK 2.3 2 1.8 1.3 BINDER DOP 0.7 0.7 0.7 0.7 TABLE 3 Example J K RESIN EVA (209) 100 100 ADDITIVES Peroxide 40% 4 5 Zinc Stearate 1 1 OB Genitron 2.3 2.3 ADCK 2.3 2.3 BINDER DOP 0.7 0.7 The following are four further workable plastics material formulations for injection into the mould: 1. The Resin (parts by weight): LPDE 50 E.V.A. 50 The Additives (per 100 parts of Resin): Genitron EPC 4 Perkadox BC40 2 Zinc stearate 0.5 Wax 0.5 2. The Resin: E.V.A. 100 The Additives: SCE 1.5 OB 1 14/140 2 ZNST 1 Pigment 2 3. The Resin: E.V.A. 50 E.M.A. 50 The Additives: Perofor ADCK 3.5 Perkadox BC40 2 Stearic acid 0.6 Perkalink 300 0.1 4. The Resin: E.V.A. 100 The Additives: EPC 3 ZNO 1 Wax 1 14/40 1.3 Perkalink 300-50 0.05 The numbers as used above for the additives represent the relevant parts per 100 parts of resin as applied in the formulation.

It is to be understood that the scope of the present invention is not to be unduly limited by the particular choice of terminology and that a specific term may be replaced by an equivalent or general term where sensible.

Further it is to be understood that individual features, method or functions relating to the moulding apparatus, the method, shuttlecock cork or formulation thereof might be individually patentably inventive. The singular may include the plural and vice versa.

Additionally, any range mentioned herein for any variable or parameter shall be taken to include a disclosure of any derivable sub-range within that range or of any particular value of the variable or parameter arranged within, or at an end of, the range or sub-range.

Therefore, still further according to the present invention there is provided a shuttlecock comprising a shuttlecock cork lockingly retained to a shuttlecock flight by a snap locking action.

In an alternative method of manufacture of the shuttlecock cork, if preferred, it is possible that no male die projecting portion 5a be provided at all so that a solid shuttlecock cork (or dummy) is formed filling the cavity 2a of female die insert 2. Of course, such method would involve a post moulding operation to remove (by drilling or by laser cutting or by any other means) the inside of the cork or dummy to the required internal specifications (i.e. wall thickness etc) for the shuttlecock cork.

Also, the method of manufacture of the shuttlecock cork (solid or otherwise) may include ejector means (not shown in the drawings) which positively ejects the cork from the moulding cavity (e.g. cavity 2a).

The ejector means may comprise a slidable (preferably spring loaded) ejection member resting at the inner end of, and effectively forming the bottom part of, the moulding cavity and conforming to the general shape thereof. The apparatus may be arranged to provide automatic actuation of the ejector means in synchronised manner after moulding, with the ejection member being moved axially relative to the remainder of the cavity (in a direction towards the opening of the cavity) to eject the shuttlecock cork. The ejection member may then be returned to its original position prior to another moulding operation in said cavity.

Claims

1. A method of making shuttlecock corks by an injection moulding technique, said method comprising: (a) injecting plastics material into a mould and blowing the plastics material and causing cross-linking of the plastics material by activation of a cross linking agent in such manner that the finished shuttlecock cork is rotationally symmetric about its is axis and without discontinuities throughout its cross section, said shuttlecock thus comprising a blown cross linked foamed plastics structure, and/or (b) feeding plastics material into a mould in a direction which is axial of the finished shuttlecock cork in order to provide a structure to the cork which is uniform.

2. A method as claimed in Claim 1 in which the plastics material is injected to a location on the inside of the finished product.

3. A method as claimed in Claim 2 in which the finished product has an aberration or pip on the inside of the product and thus substantially hidden from view and preferably disposed axially of the cork.

4. A method as claimed in any one of the preceding claims in which the plastics material is vented during the process.

5. A method as claimed in any one of the preceding claims in which a plurality of shuttlecocks are moulded substantially simultaneously by the same moulding tool.

6. A method as claimed in any one of the preceding claims in which both the plastics material and the mould are heated in order to provide activation of a blowing agent and of a cross-linking agent so that on removal from the mould the shuttlecock cork expands substantially instantaneously into its required size.

7. A method as claimed in Claim 6 in which the plastics material is heated to a temperature of about llO"C prior to injection into the mould.

8. A method as claimed in Claim 7 in which the mould is heated to about 200"C.

9. A method as claimed in any one of Claims 6 to 8 in which the cycle time for each moulding is about 2 to 3 minutes.

10. A method as claimed in Claim 4 or any claim dependent therefrom in which venting is provided from the mould at at least two diametrically opposed positions which are axially spaced from the injection location of plastics material into the mould.

11. A method as claimed in any one of the preceding claims including moulding an internal flange means or recess means on the shuttlecock cork.

12. A method as claimed in Claim 11 in which the flange means comprises an annular rib.

13. A method as claimed in Claim 11 in which the flange means comprises a series of pips.

14. A method as claimed in one of the preceding claims involving a plastics material of an E.V.A. formulation or similar or any suitable ethylene polymer or copolymer.

15. A method as claimed in any one of Claims 1 to 5 in which the shuttlecock cork or corks is/are extracted from the mould in "dummy" or "blank" form in which the temperature of the injection moulding has been kept below the temperature required for activation of blowing and cross-linking agents contained in the plastics material.

16. A method as claimed in Claim 15 in which the moulding cycle time is only 30 seconds.

17. A method as claimed in Claim 15 or 16 in which the mould itself is unheated.

18. A method as claimed in any one of Claims 15 to 17 in which a plurality of shuttlecock cork dummies are placed into a compression mould or similar and heated to activate said blowing and cross-linking agents so that finished shuttlecock corks can be extracted from the compression mould.

19. A method as claimed in any one of the preceding claims involving forming the shuttlecock cork with a syntactic structure in which microspheres of one material are embedded in a matrix of a core plastics material.

20. A method as claimed in any one of the preceding claims in which the cork or dummy is moulded in a solid form, the internal shape of the cork or dummy being determined in a post moulding operation.

21. A method of making shuttlecock corks substantially as herein described.

22. Injection moulding apparatus for moulding shuttlecock corks, said apparatus comprising means to inject plastics material along an axis corresponding to the shuttlecock cork axis or at least having means to provide a substantially uniform flow of material in the mould about said axis, said mould having vents to alleviate gassing of the plastics material during moulding.

23. Apparatus as claimed in Claim 22 in which the moulding tool is a multi-impression tool.

24. Apparatus as claimed in Claim 22 or 23 in which the mould design allows substantially instantaneous release of the product from the mould.

25. Apparatus as claimed in any one of Claims 22 to 24 in which a female die is provided having one or more cavities with a part spherical bottom portion, the or each cavity being provided to mould the or each shuttlecock cork.

26. Apparatus as claimed in Claim 25 in which for the or each cavity there is provided a male die having a projecting portion which projects into the associated cavity during the moulding process.

27. Apparatus as claimed in Claim 26 in which the or each projecting male portion is arranged on the axis of its associated cavity in the female die.

28. Apparatus as claimed in any one of Claims 22 to 27 in which a, or the, female die is made up from a number of plate sections and female die inserts.

29. Apparatus as claimed in any one of Claims 22 to 28 in which a, or the, male die is made up of a number of plate sections with male die inserts.

30. Apparatus as claimed in any one of Claims 22 to 29 having male and female dies substantially circular in shape.

31. Apparatus as claimed in Claim 30 in which the male and female dies are surrounded by a heater band.

32. Apparatus as claimed in Claim 31 in which guide means are provided for interfacing the male and female dies.

33. Apparatus as claimed in Claim 32 in which the guide means are in the form of guide pins cooperating with guide holes.

34. Apparatus as claimed in Claim 32 or Claim 33 including a ram piston.

35. Apparatus as claimed in any one of Claims 22 to 34 having means provided to hold a shuttlecock cork onto an associated male die insert on extraction from the moulding cavity of a, or the, female die.

36. Apparatus as claimed in Claim 35 in which said holding means is provided by a recess on a, or the, male projecting portion so that an internal flange is moulded onto the internal surface of the shuttlecock cork which in turn engages in the recess on the male projecting portion as the shuttlecock cork is removed from the mould.

37. Apparatus as claimed in Claim 36 in which the recess is annular.

38. Injection moulding apparatus for moulding shuttlecock corks substantially as herein described with reference to the FIGURES of the accompanying drawings.

39. Use of apparatus as claimed in any one of Claims 22 to 38 to form finished, expanded shuttlecock corks by heating the mould to an appropriate temperature at which blowing agents and cross-linking agents in the plastics material undergo decomposition.

40. Use of apparatus as claimed in any one of Claims 22 to 38 to produce shuttlecock cork dummies or blanks which can be subsequently transferred to a compression moulding tool.

41. A method of making shuttlecock corks, said method being a two stage process, the first stage of the process involving injection moulding a dummy shuttlecock cork and extracting same from the mould before activation of a blowing agent in the dummy, the second stage of the process comprising heating a plurality of dummy corks made from the first process, in a compression mould, to activate the blowing agent in order to provide expanded foam plastics shuttlecock corks.

42. A shuttlecock cork of a cross linked expanded foam plastics material, said shuttlecock cork having one or more of the following properties: (a) rotational symmetry about its axis, (b) structural uniformity or lack of discontinuity about its axis, (c) a weight lying in the range 1.5 to 1.9 grammes and/or specific gravity of about 0.25 or less, (d) no external pip or aberration moulded thereon, (e) an undistorted shape, (f) dimensional stability, (g) internal locking means, preferably in the form of an internal flange, which in use locks the weight of the flight of the shuttlecock to the shuttlecock cork, preferably by snap location of part of the weight behind said locking means, (h) being moulded from an E.V.A. formulation or similar (e.g.E.M.A.) or ethylene polymer or copolymer including a cross-linking agent, preferably a peroxide, a blowing agent, a lubricant and a filler, (i) being aerodynamically formed without any post moulding operations.

43. A method of making a shuttlecock cork comprising providing internal locking means on said shuttlecock cork for locking a shuttlecock flight thereto.

44. A method of making shuttlecock corks, said method comprising injecting plastics material into a mould, said plastics material comprising at least 90% of a resin based on ethylene polymer or copolymer, optionally blended with rubber and/or a filler material, together with up to 10% additives including a blowing agent, a cross-linking agent, a co-agent, an activator and a lubricant.

45. A method as claimed in Claim 44 in which a general formulation of plastics material is: (1) Resin: Polythene at least 50 parts by weight up to 100 parts by weight; balance substantially E.V.A.

46. A shuttlecock cork of an expanded foam plastics material having a self-skinned, closed cell, structure said plastics material comprising at least 90% by weight of cross-linked ethylene polymer or copolymer optionally blended with a rubber and/or filler material, and up to 10% by weight of the residues of moulding additives including gaseous material trapped in the closed cell structure.

47. A shuttlecock cork as claimed in Claim 46 in which the cross-linked polymeric material includes E.V.A.

48. A shuttlecock cork as claimed in Claim 47 in which E.V.A. material has a melt flow index of 0.5 to 7 and vinyl acetate content of 4 to 28%.

49. A shuttlecock cork as claimed in Claim 48 in which the melt flow index is 1 to 3.

50. A shuttlecock cork as claimed in Claim 48 or 49 in which the vinyl acetate content is 4 to 18%.

51. A shuttlecock cork as claimed in any one of Claims 47 to 50 having a plastics formulation of about 60 to 80% LLDP (linear low density polyethylene) and about 20 to 40% E.V.A.

52. A shuttlecock comprising a shuttlecock cork lockingly retained to a shuttlecock flight by a snap locking action.

53. A method as claimed in any one of Claims 1 to 21, 41, 43, 44, 45 including positively ejecting the cork from the moulding cavity.

54. Apparatus as claimed in any one of Claims 22 to 38 including ejector means for positively ejecting the cork from the moulding cavity.

55. Apparatus as claimed in Claim 54 in which the ejector means comprises a slidable ejection member resting at the inner end of, and effectively forming the bottom part of, the moulding cavity and conforming to the general shape thereof.

56. Apparatus as claimed in Claim 55 in which the member is spring loaded.

57. Apparatus as claimed in Claim 55 or 56 arranged to provide automatic actuation of the ejector means in synchronised manner after moulding, with the ejection member being moved axially relative to the remainder of the cavity.