METHOD OF REMOVING LIQUID FROM A RECESS OF AN ARTICLE

Abstract: A method of removing a first liquid such as paint from the recess of an article such as a multiparallel sided recess in a head of a fastener, comprises the steps of immersing the article in a second liquid which has a higher density than the first liquid.

Description: Title: Method of removing liquid from a recess of an article. Description of Invention This invention relates to a method of removing liquid from a recess of an article. Metal finishing processes are known which involve the dipping of an article in a bath of coating such as paint. To ensure an even coating of paint, it is common practice subsequently to spin the article to remove excess paint. However, where the article contains a recess, unless the article is carefully aligned during spinning with the recess facing outwardly, excess coating can remain in the recess. For economic reasons it is usual to coat and spin a plurality of articles together and it is uneconomic to align carefully each of the " articles for spinning. __ Where the article comprises for example a fastener having a threaded shank and a head, the head having a multi parallel-sided recess, it will be appreciated that any excess liquid in the recess which cures and hardens, can inhibit correct registration between an assembly tool and the fastener which can cause great problems in an automated assembly process. According to one aspect of the invention we provide a method of removing first liquid from a recess of an article comprising the step of immersing the article in a second liquid which has a higher density than the first liquid. It has been found that by simply immersing the article in the second more dense liquid, first liquid can be displaced from the recess by the second liquid. The second liquid may simply have a density significantly larger than the first liquid and/or the article may be immersed in the second liquid to a sufficient depth for the second liquid to exert a sufficient force to displace first liquid. By "significantly higher" density we mean at least three times denser, preferably at least five times denser, and more preferably at least ten times denser. Where the first liquid is paint or another liquid coating which may have a density of around 1 gram per cubic centimetre one suitable significantly higher density liquid is mercury which has a density in the order of 13.5 grams per cubic centimetre. Because the mercury performs no chemical operation but only the mechanical operation of displacing first liquid, the mercury is not consumed in the method. The method may include immersing the article in the mercury or other significantly higher density second liquid to a depth of at least 50 cm, preferably at least 80 cm and more preferably at least 90 cm. Where the second liquid is denser but not significantly denser than the first liquid, cleaning the article simply by dipping may require the article to be immersed to an unacceptable depth to achieve displacement of the first liquid from the recess. Hence in a preferred arrangement, to avoid this problem, the second liquid is pressurised with the article immersed therein. In each case, when the article is removed from the second liquid, to ensure that second liquid is not trapped in the recess or elsewhere in or on the article, the article may be washed, for example with a water or other liquid spray. However, preferably the second liquid is selected so that natural or forced drying substantially removes the second liquid but any residue does not affect registration of an assembly tool for example in the recess. To assist the displacement of first liquid by the second liquid when the article is immersed, the article may be carefully aligned to ensure that the recess opens generally upwardly. However, where careful alignment can prove an economic disadvantage to the method, the method may include changing the orientation of the article whilst immersed in the second liquid. For example, the article may, whilst immersed, be contained with a plurality of other articles in a cage, which cage may be at least partially rotated, or otherwise agitated, or at least re-orientated. If desired, where the material from which the article is made is less dense than the second liquid, to remove the article from the second liquid, the article may be released when immersed, such that the article simply floats to the surface of the second liquid. The method is particularly but not exclusively applicable to a surface finishing process such as painting or otherwise coating, in which case the first liquid may comprise paint, or another coating. According to a second aspect of the invention we provide a method of coating an article which has a recess, the method comprising the steps of applying coating to the article, and removing excess coating from the recess of the article by the method according to the first aspect of the invention. The method of the second aspect of the invention may include the intermediate step of spinning or otherwise agitating the coated article to remove excess coating from the article overall, prior to immersing the article in the second liquid. The paint or other coating may be applied to the article by dipping, spraying, or any other process. The method of the second aspect of the invention may be applied to the surface finishing of a metal article such as for example a fastener, in which case, the method may include the initial step of applying an organic or inorganic, preferably corrosion resistant, surface coating to the article prior to applying paint or other coating to the article. For example, the article may be dipped in zinc phosphate or otherwise have zinc phosphate applied to prepare the metallic surface to receive paint. It has been found that immersing the article in the second liquid removes excess paint from the recess of the article but does not significantly remove paint or other coating bonded to the metal/surface coating from the article overall. The invention will now be described with reference to the accompanying drawings in which: FIGURE 1 is a perspective view of a fastener having a recess from which liquid can be removed by the method of the first aspect of the invention, FIGURE 2 is an illustrative view of an apparatus for use in performing the method of the invention, FIGURE 3 is a flow diagram of method steps included in performing the invention. Referring to figures 1 and 3 of the drawings, a typical recessed drive metal fastener 10 comprises a threaded shank 11 and a head 12. The head 12 comprises a recess 13 having six curved sides 14 which each extend generally parallel to each other and the longitudinal axis A of the fastener 10. The fastener 10 is surface finished by phosphate surface coating and painting as follows. As a first step, the fastener 10 is thoroughly cleaned and then dipped or otherwise coated in zinc phosphate which provides corrosion resistance and prepares the surface of the fastener 10 to receive paint. The fastener 10 is one of a plurality of such fasteners which may be contained in a cage and thus dipping in the zinc phosphate is accomplished by lowering the cage containing all of the fasteners 12 into the zinc phosphate. When the phosphate coating is dry, the cage containing all of the fasteners 10 is then dipped in paint. Examples of typical paints which may be used are Xylan or Polyseal although any other waterbased or organic based paint may be applied. Upon removal, the cage is spun to remove excess paint from the cage and the fasteners and to ensure that the fasteners 12 are evenly painted. However, spinning or otherwise agitating tends not to remove all excess paint from the recess 13 of the fastener 10, particularly when the fastener 10 is not ideally orientated i.e. with the axis A of the fastener 10 pointing generally towards the centre of rotation such that the recess 13 faces outwardly. If desired, the zinc phosphate surface coating step need not be carried out if not required, or any other suitable surface coating for preparing the surface of the article may alternatively be applied. The paint may be applied by spraying instead of dipping if this is more convenient and if desired, a plurality of fasteners need not be contained together in a cage during phosphate coating or painting, but the fasteners can otherwise be contained or individually treated as desired. Two examples of how excess paint from recess 13 is removed will now be described, both methods being in accordance with the invention. Example 1 The cage containing the plurality of fasteners 10 is immersed in a bath of mercury, preferably to a depth of between 90 and 100 cm so that the pressure of the mercury can act in the recess 13 to displace excess paint therefrom. The excess paint thus displaced being considerably less dense than the mercury, will float to the surface of the mercury from where the paint may conveniently be removed when a sufficient quantity has gathered. It will be appreciated that the metal of the fastener 10 will also in general, be less dense than mercury and accordingly the cage containing the plurality of fasteners needs to prevent the fasteners escaping from the cage by floating to the top of the mercury. It has been found that the mercury tends not to remove paint from the fastener 10 generally, even when the paint is not yet cured, but only displaces excess paint which is not bonded to the metal/phosphate coating. In the event that some of the fasteners 10 in the cage are not ideally aligned when immersed in the mercury bath to facilitate displacement of excess paint from the recesses 13 thereof, the cage may be agitated or re-orientated when immersed to cause the fasteners 10 each to be re-orientated so that all of the fasteners will, for at least some of the time for which they are immersed, be generally ideally orientated with their recesses 13 facing generally upwardly. Such re-orientation of the fasteners 10 may naturally occur during immersion in the mercury bath if the cage in which they are contained permits the fasteners to re¬ orientate themselves through floation. It will be appreciated that a fastener 10 such as that shown in figure 1 of the drawings, will tend naturally to float head upwardly i.e. with the recess 13 opening upwardly. The cage, and hence the fasteners 10, is then removed from the mercury bath and gently agitated to remove excess mercury. Alternatively or preferably in addition, the fasteners 10 may be subjected to washing, for example by water sprays to ensure that all traces of the mercury are removed. The mercury removed in this way can be subsequently recovered from the water to conserve the mercury. It has been found that such washing need not significantly remove paint which is well bonded to the metal surface/phosphate. Finally, the paint can be cured by e.g. heating. Because during the method described parts of each of the plurality of fasteners will be in contact with the cage or each other, parts of some at least of the fasteners 10 may not be adequately coated with zinc phosphate and/or paint. The entire method can thus be repeated so that substantially the entire surface of each of the fasteners 10 is surface finished to an adequately high standard. Various modifications may be made to the method of example 1 without departing from the scope of the invention. For example, The paint may be at least partially cured or permitted to cure, prior to immersing the fasteners in mercury or may be permitted to cure without heating subsequent to immersing in the mercury bath. It will be appreciated that where the paint is permitted at least partially to cure prior to immersion in the mercury bath, excess paint present in the recess will not in general be fully cured and thus can still be displaced during the mercury immersion step. Instead of removing a cage or other container containing a plurality of fasteners from the mercury bath in order to remove the fasteners, the fasteners may simply be released in the mercury bath and permitted to float to the surface of the mercury from where they may be removed. Instead of the second liquid in which the fasteners are immersed comprising mercury, any other suitably dense liquid which is substantially denser than the paint or other first liquid applied to the fasteners, may be provided. For example, the second liquid may comprise a metal or metal alloy heated to above its melting temperature. Examples of such alloys are D'Arcets alloy which has a melting point of about 93° C. and a composition of about 50% bismuth, 25% lead, and 25% tin, or alternatively Woods alloy which has a melting point of about 71° C. and a composition of about 50% bismuth, 24% lead, 14% tin, and 12% cadmium, or Lipowitzs alloy which has a melting point of about 68° C. and a composition of about 50% bismuth, 27% lead, 13% tin, and 10% cadmium. An example of a suitable metal is Gallium which has a melting point of about 28-30° C and a density of about 6g/cm 3 - Other suitable second significantly denser second liquids usable in the method according to example 1, are Cerrolow - 136, which has a melting point of about 58° C. and a composition of about 49% bismuth, 18% lead, 12% tin, and 21% indium or Cerrolow - 137 which has a melting point of about 64° C. and a composition of about 65% bismuth, 17% lead, 11% tin, and 6% indium, or Cerrolow - 117, which has a melting point of about 47° C. and a composition of about 44% bismuth, 23% lead, 8% tin and 15% indium. Although it has been found preferable to immerse the fastener in a bath of mercury or other significantly denser second liquid to a depth of between 90 and 100 cm, it will be appreciated that the desired displacement of first liquid may be accomplished at lesser or greater depths of immersion. Preferably though, the fastener is immersed in the bath of second liquid at least to a depth of 50 cm, and preferably to a depth of 80 cm, or more. Example 2 Referring now to Figures 2 and 3 of the drawings, a cage 15 containing a plurality of fasteners 10 is immersed in a bath of liquid 21 in a pressure vessel 20. The liquid 21 in the pressure vessel 20 comprises in this example, a high density flurocarbon liquid such as is sold under the trade name FC 5312 or PF 5060 by 3M Corporation. Such a liquid 21 has a density of about 1.8 grams per cubic cm and is thus denser, but not significantly denser as hereinbefore defined, than the excess paint (or other suitable coating) which may be contained within the recesses 13 of the fasteners 10. The pressure vessel 20 is then closed by a lid 22, and compressed air is fed into the pressure vessel 20 via an inlet 16 above the level of the liquid 21 to pressurise the liquid 21 contained therein. It has been found that the liquid 21 in the pressure vessel 20 acts in the recesses 13 of the fasteners 10 to displace excess paint therefrom. The excess paint thus displaced, and being less dense than the liquid 21 will tend to float to the surface of the liquid 21 from where the paint may conveniently be removed. By selecting an appropriate type of liquid 21 for the pressure vessel 20, any tendency for the liquid 21 to remove paint from the fastener 10 generally, even when paint is not yet cured, can be negated. The liquid 21 tends only to displace excess paint which is not bonded to the metal/phosphate coating of the fasteners 10. Preferably, the cage 15 is gently agitated whilst it is immersed in the pressurised liquid 21. This may be achieved by the cage 15 being retained in the bath of liquid 21 by a retaining means 24 which can be vibrated or moved so as to agitate the fasteners 10 in the cage 15. The cage 15 may otherwise be agitated or reorientated when immersed to cause the fasteners 10 each to be reorientated such that all of the fasteners 10 will, for at least some of the time for which they are immersed, be generally ideally oriented with their recesseses 13 facing upwardly. Preferably the liquid 21 is pressurised to a pressure of at least two atmospheres. After a sufficient time, the vessel 20 is de-pressurised and opened and the cage 15 and fasteners 10 are removed from the bath of liquid 21 and agitated to remove any liquid 21 which may be present in the recesses 13 and on the fasteners 10 generally. By selecting an appropriate liquid 21, the need for any subsequent washing to remove all traces of the second liquid 21 can be avoided. For example, by using the liquids specified above, the fasteners 10 can simply be dried after removal from the liquid 21, naturally or by force drying, such that the second liquid 21 will be substantially removed. Any residue of the second liquid, will not affect registration of an assembly tool for example, within the recesses 13. The drying step may be carried out simultaneously with curing of the paint, or drying may be carried out at a lower temperature than subsequently the fasteners 10 are heated to for the purposes of curing the paint. If desired, the entire method described above can be repeated so that the fasteners 10 are surface finished to an adequately high standard. It will be appreciated that the examples of kind of liquid 21 present in the bath within the pressure vessel 20 are only examples of suitable liquids which can be used. Where the paint applied to the fasteners 10 is a water based paint, preferably the liquid 21 is an organic based product to avoid any tendency of the liquid 21 to remove the water based paint. Where the paint applied to the articles is an organic based paint, preferably the liquid 21 is an organic based product which does not tend to dissolve or otherwise remove the paint from the fasteners 10. Although in both examples described, the invention has been described with reference to a method of removing excess liquid from a recess of a fastener, it will be appreciated that the method of the invention may be applied to removing liquid from a recess of any other article which may be made of metal or of any other suitable material, where the article has a recess in which first liquid can be trapped after first liquid has been applied to the article. The features disclosed in the foregoing description or the accompanying drawing, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, or a class or group of substances or compositions as. appropriate, may, separately or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

Claims: CLAIMS 1. A method of removing first liquid from a recess of an article comprising the step of immersing the article in a second liquid which has a higher density than the first liquid. 2. A method according to claim 1 wherein the second liquid has a density significantly higher than the density of the first liquid, by which we mean at least three times denser, preferably five times denser, and more preferably, at least ten times denser. 3. A method according to claim 2 wherein the second liquid is mercury. 4. A method according to claim 3 wherein the article is immersed in the significantly higher density second liquid to a depth of at least 50 cm, preferably at least 80 cm and more preferably at least 90 cm. 5. A method according to claim 1 wherein the second liquid is pressurised with the article immersed therein. 6. A method according to claim 5 wherein the second liquid is pressurised to a pressure of about two atmospheres. 7. A method according to claim 5 or claim 6 wherein the article is immersed in a bath of second liquid contained within a pressure vessel. 8. A method according to claim 7 wherein the liquid in the pressure vessel is pressurised by introducing compressed air into the vessel above the liquid. 9. A method according to any one of the preceding claims wherein when the article is removed from the second liquid, the article is washed. 10. A method according to any one of the preceding claims wherein to assist the displacement of the first liquid by the second liquid when the article is immersed, the article is aligned with the recess opening generally upwardly. 11. A method according to any one of claims 1 to 9 wherein to assist the displacement of the first liquid by the second liquid when the article is immersed therein, the orientation of the article is changed. 12. A method according to claim 11 wherein the article whilst immersed, is contained with a plurality of other articles in a cage, and the cage is at least partially agitated or at least reorientated. 13. A method according to any one of the preceding claims wherein the first liquid comprises paint. 14. A method of removing first liquid from a recess of an article substantially as hereinbefore described with reference to the accompanying drawings. 15. A method of coating an article which has a recess, the method comprising the steps of applying coating to the article, and removing excess coating from the recess of the article by a method according to any one of the preceding claims. 16. A method according to claim 15 which includes the step of spinning or otherwise agitating the coated article to remove excess paint from the article overall prior to immersing the article in the second liquid. 17. A method according to claim 15 or claim 16 wherein the coating is applied to the article by dipping or spraying. 18. A method according to any one of claims 15 to 17 which includes the step of applying an organic or inorganic surface coating to the article prior to applying final coating to the article. 19. A method according to claim 18 wherein zinc phosphate is applied to the article to prepare the metallic surface to receive coating comprising paint. 20. A method of coating an article which has a recess substantially as hereinbefore described with reference to the accompanying drawings.

Inventors: STOKES MALCOLM WILFRED, STOKES, MALCOLM, WILFRED
Applicants: ANOCHROME LTD, ANOCHROME LIMITED
Application year: 1993
Main classification: B01D12
IPC codes: B01D12, B08B3, B08B7, C23G5