GB2181744A

GB2181744A - Surface treating hollow objects

Info

Publication number: GB2181744A
Application number: GB08522516A
Authority: GB
Inventors: Barry George Morton Helme; Patrick Gregory Byrne
Original assignee: LARCUM KENDALL Ltd
Current assignee: LARCUM KENDALL Ltd
Priority date: 1985-09-11
Filing date: 1985-09-11
Publication date: 1987-04-29
Also published as: GB8522516D0

Abstract

Apparatus for electroplating or deplating the interior of hollow objects comprises an electrode 4 for insertion into the object 1, a spacer 5 to space and insulate the electrode from the object, and a non-conductive inlet 2 and outlet 3 for sealed connection to the object for the passage of fluid. A method of plating or deplating the interior of a hollow object which is closed at one end comprises inserting a pipe 13 into the interior of an object 7 to be plated, charging the interior of the object with a fluid through the pipe and emptying the object of the fluid on completion of the plating step. The tube 13 may be wrapped spirally around electrode 12 in order to space the electrode from the surface of the tube. One or more of the plating steps may be effected by electroless plating. Tube 7 may be non-conductive. The spacer 5 or pipe 13 may be oscillated. The invention allows objects having an inside diameter of upwards of e.g. 2mm and a length of more than one metre to be uniformly plated. <IMAGE>

Description

SPECIFICATION Apparatus and method for surface treatment of objects This invention relates to apparatus and a method for the surface treatment of objects and has particular reference to the plating of the interior of hollow objects, especially those having a large length to cross-sectional area ratio.

The concept ofthe present invention is applicable to both plating and reverse plating and throughout this specification the term "plating" is to be construed as including reverse plating.

Furthermore, the invention is applicable to both electroplating and electroless plating, or a combination thereof.

There are a number of known methods of plating the interior of hollow objects but these do not function satisfactorilywhen the object is relatively long and has a relatively small cross-sectional area. Particular difficulty is experienced when one end of the hollow object is closed. However, whether the object is open-ended or closed at one end, it is difficult, if not impossible, to "throw" the material to be plated uniformly into the interior of hollow objects using known electroplating methods. This problem is aggravated if the interior of the object has recesses, for example if it is convoluted.

One known method is that of barrel plating in which objects to be plated are placed in a nonconductive barrel which is filled with a plating solution and rotated with an electriccurrentpassing through the plating solution and the objects. However, with relatively long objects of relatively small cross-sectional area compared with the length, these are difficultto contain in a barrel and in any event, the electric field strength decays within the member and thusthe plating "decays" giving unsatisfactory results.

Another known method used to plate difficult objects, including relatively long objects, which are electrically conductive, involves using the objects themselves as electrodes but this does not overcome the problem of plating satisfactorilythe interior of long hollow objects of small crosssectional area.

In a further known process specifically for reverse plating or etching, the etchant is passed through the hollow object but the etchant becomes diluted and contaminated as it flows through so that a satisfactory finish is not achieved.

The object of the present invention is to provide a method of electroplating the interior of hollow objects uniformly with special reference to the plating of small bore objects which are either open-ended or closed at one end.

According to one aspect of the present invention there is provided a method of electroplating the interior of hollow objects comprising the steps of inserting first electrode means within the object to a depth to which plating is required, spacing the first electrode means from the interior of the object, introducing a plating fluid into the object, applying a potential difference between the first electrode means and second electrode means associated with the object, and extracting the plating fluid from the object.

If the object to be plated is electrically conductive, then the object itself can be made the second electrode means. However, if the object is nonconductive, then the second electrode means is provided in the form of an electrode secured around the mouth of the interior of the object, whereby plating progresses into the interiorfrom the electrode, the plating effectively extending the electrode as it is laid down.

The step of spacing the first electrode means from the interior of the object may be accomplished by wrapping the electrode means with an insulator, for example in spiral. Ideally,the spacer means needs to be a relatively loose fit within the interiorofthe object so as not to maskthe plating at the areas of contact. However, in the case of objects having very small cross-sectional areas or bores, possibly ofthe order of a few millimetres, then a loose fit is not possible, whereby the method may include the further step of oscillating the spacing means so that is does not permanently cover one or more areas of the interior of the object and hence mask plating.

In the case of an open-ended object, the first electrode means preferably extends therethrough, and non-conductive inlet and outlet means forthe plating fluid are provided at respective ends, the first electrode means passing through, and being sealed with respect to the inlet and outlet.

When an object to be plated has a closed end, i.e. a blind recess or bore, the first electrode means may extend to the required depth and then be returned encased within a sheath of an insulating material.Thesheath may form partofthe path ofthe plating fluid, for example by providing an inletforthe plating fluid to the interior of the object, the fluid flowing out of the object viva an outlet.

The sheath may be of solid material, such as PTFE, when the object is electrically conductive, or may be of porous material to aid the plating of nonconductive objects, especially when the plating current is of a pulsed nature. If the crosssectional area of the interior of the object is so small such that the first electrode means and the spacer means are a relatively tight fit therein, then again the sheath is porous in order to prevent it masking the plating of areas of the interior surface which it contacts.

The method according to the invention may com prisethe furtherstep of replacing a first charge of plating fluid by a second charge ofsimilarfluid in order to increase the thickness ofthe plated layer, or by a second charge of a different plating fluid to build up a composite plated layer although in this instance, an intermediate charge of a washing fluid is introduced between successive plating charges.

According to another aspect of the present invention there is provided apparatus for electroplating the interior of hollow objects comprising first electrode means adapted for insertion into the object spacer means operable to space and insulate the first electrode means from the interior of the object, and non-conductive inlet means and outlet means adapted for sealed connection to the objectforthe passage of plating fluid.

In the case of an open-ended object, the inlet and outlet means are provided at respective ends with the first electrode means extending through the object, but only being exposedfora length determined by the extent of plating required within the interior ofthe object, and passing through the inlet and outlet means and being sealed with respect thereto.

In the case of an object closed at one end, the first electrode extends to the required plating depth and is returned within a non-conductive sheath which may itself provide the inlet means for the plating fluid. The sheath may be of solid material ifthe objectto be plated is electrically conductive, or of porous material if the object to be plated is non-conductive or the first electrode means and the spacer means are a relatively tightfit in the interior of the object.

In all the above aspects ofthe present invention,the interior surface of the object to be plated preferably is first reverse electroplated using either a pulsed orcontinuous current in orderto clean the surface, and then plated with one or more layers of metal as required. It should be noted that one or more ofthe plating steps may be effected by electroless plating rather than by electroplating.

According to yet another aspect of the present invention there is provided a method of plating the interior of a hollow object which is closed at one end comprising the steps of inserting pipe means into the interiorofan objectto be plated, charging the interior ofthe object with a plating fluid through the pipe means and emptying the object ofthe plating fluid on completion ofthe plating step.

This aspect of the present invention lends itself well to the total use of electroless plating which in some instances can be more conveneientto use although there is a limitation on the plating thickness and sometimes on the uniformity and adherence characteristics thereof. The pipe means not only provide an inletforthe plating fluid but also provides a strengthening or stabilising function in the case of long objects of relatively small cross-sectional area. It will be appreciated that if, for example, a first layer has been plated electrolessly and this layer requires thickening, or a layer of a different metal is required, then any additional layer can be provided byelectroplat- ing by employing an electrode within the pipe means, wherebythe method of plating accords with the other recited asepcts ofthe invention.

Apparatus and methods for electroplating hollow objects will now be described in greater detail, byway of example, with reference to the accompanying drawings, in which Figure lisa diagrammatic representation of appar atus for electroplating an open-ended hollow object, and Figure2is a diagrammatic representation of appar anus for electroplating a hollow object having a closed end.

Referring first to Figure 1, the object to be plated is a metallictube 1 formed throughout its length with a spiral convolution, the tube being shown in cross-section. The tube may have a length in excess of one metre and an inside diameter ofupwardsof2mm.An inlet2for plating fluid is sealed to one end ofthe tube 1, and an outlet3 for the plating fluid sealed to the opposite end of the tube, these components being in the form of end caps. The inlet and outlet 2,3 are of a non-conductive material such as PTFE,forexample.

Afirst electrode4 extends through the bore of the tube 1, passing through the walls of the inlet2 and outlet 3 and being sealed with respect thereto. The electrode 4 is spaced from the interior surface ofthe tube bore by spacer means in the form of a length of insulating material 5 which is wrapped spirally around the electrode 4, the spacer being a generally loose fit within the bore of the tube so as notto mask any area or areas from being plated. The tube 1 has an electrical connection 6 madeto itsexteriortoprovidesecond electrode means.

In orderto plate the bore of the tube 1, including the recesses formed by the convoluted nature thereof, it is preferable first to reverse plate the bore by passing a charge of an appropriate fluid or etchantintothetubethroughthe inlet 2. Acurrent (which may be pulsed) is passed through the electrode 4for a predetermined time and at a prede terminedvoltageso asto establish a potential difference between the electrode and the body ofthe tube 1.Thusthetube bore is cleaned and the etchant is then removed and repiaced by an inert washing fluid. Next, a charge of plating fluid is passed into the tube and again, a current passed through the electrode 4 for a predetermined time and at a predetermined voltage.Thus metal is laid down on the borethroughoutits length and in all the recesses in a layer of substantially uniform thickness. If the thickness of the plated layer isto be increased, the initial charge of plating solution is extracted through the outlet 3 and replaced by a fresh charge. This can be repeated as many times as required.

Alternatively, if a composite plated layer is required, i.e. a layer made up of different metals, the procedure is to pass a first charge of plating solution into the tube 1 and plate as already described, extractthe spent charge either independently or by pushing it out with a following charge of an inert washing fluid which does not oxidise the pre viously plated layer, replacing the washing fluid by the next charge of plating solution to plate the next metal in the composite layer, and soon until the required composite layer has been built up. As before, the thickness of a given part ofthe composite layer can be increased by repeating the charge of the appropriate solution as many times as is necessary.

Turning nowto Figure 2,the objectto becoated in a tube7 having a closed end, i.e. a blind bore, the tube being formed from a non-conductive material and again having a length in excess of one metre and an internal diameter of upwards of 2mm.

The open end of the tube 7 fitted with an inlet/outlet arrangementfor plating fluid intheform of a non-conductive end cap 8 having an outlet 9 and an inlet opening 11. Afirst electrode 12 extends through, and is sealed with respect to, the end cap 8 and into the bore of thetube 7, essential- lyto the closed end ofthe tube from where it is returned back along thetube in a sheath 13 ofa non-conductive material such as PTFE. The sheath 13 is wrapped spirally around the exposed portion ofthe electrode 12 and serves a second purpose of spacing the electrode 12 from the interior surface ofthe tube bore. The sheath 13 passes through the inlet opening 11 in the end cap8 and serves a third purpose in providing the actual inletforthe plating fluid.The electrode 12 is taken outofthe sheath 13 through thewall thereof via a seal 14.

Second electrode means 15 are attached to the end face ofthe open end of the tube 7 and an electrical lead 16 thereto is taken through the end cap 8 via a seal 17. Thus the second electrode 15 is of annularform.

The plating procedure is identical to that described with reference to Figure 1, a first charge of plating solution being fed to the bore of the tube 7 via the inlet sheath 13 and then extracted and replaced if necessary, with an intermediate wash if the successive charges are of different plating solutions. The build-up of the plated layer is, howev er, different from that ofthe embodiment of Figure 1. This is because the tube 7 is non-conductive which means that the electric field is initially set up directly between the electrodes 12 and 15 when a potential difference is applied therebetween.Hence plating takes place only around the mouth ofthetube bore in the immediate vicinity of the electrode 15 but this plating effectively extends the electrode 15, whereby the next portion ofthetube bore is plated and soon until the entire bore, including the blind end, is plated.

The current applied to the electrode 12 may be pulsed.

lfthetube 7 were composed of an electricallyconductive material, then the tube itself would form the second electrode as in the embodiment of Figure 1.Shouldthediameterofthetubebore be such asto make the electrode 12 and sheath 13 a tight fit therein,the sheath is preferably made porous so that plating can take place therethrough so that no discontinuity in the plated layer is occasioned by the presence of the sheath 13. It should be noted that one or more ofthe plating steps may be effected by electroless plating as opposed to electroplating although the latter is preferred as it provides a more uniform plated layer with better adherence characteristics.

If in eitherofthe embodiments of Figures 1 and 2 the spacer 5 or sheath 13 is a close, as opposed to a tight, fit in the tube bore, it may be oscillated generally axially ofthe tube in order not permanently to mask certain areas ofthe surface of the bore and hence prevent the plating thereof.

As already mentioned, one or more ofthe plating steps may be effected by employing electroless plating and in the case of an object with a closed end, it can be convenientto use the electroless plating technique. For example, in the embodiment of Figure 2, the electrode 12 can be dispensed with and the sheath used as pipe means to charge the object with the plating fluid as indeed happens when the electrode is employed. If a plated layer put down electrolesslyrequires augmenting or a different layer plated thereon, this can be accomplished by re-introducing the electrode 12 and proceeding as already described with reference to Figure 2.

The present invention enables hollow objects, especially long objects of small internal crosssectional area to be plated uniformly whereas this is virtually impossible with known plating techniques. Accordingly, the present invention represents an extremely significant advance in the art of electroplating. Mention has been made ofthe plating oftubes having diameters of upwards of 2mm but smaller diametertubes can be plated using the present invention provided the first electrode means and spacer means can be accommodated. Also, the length of objects which can be plated may be many metres. The invention finds particular, but not exclusive, application to the plating of microwave cable sheaths and fluid transmitting pipes, for example hydraulic pipes, where leakproof and sterile conditions are essential.

Claims

1. A method of electroplating the interior of hollow objects comprising the steps of inserting first electrode means within the object to a depth to which plating is required, spacing the first electrode means from the interior of the object, introducing a plating fluid into the object, applying a potential difference between the first electrode means and second electrode means associated with the object, and extracting the plating fluid from the object.

2. A method according to claim 1, wherein the hollow object is electrically conductive and is made the second electrode means.

3. A method according to claim 1, wherein the hollow object is electrically non-conductive and the second electrode means is in the form of an electrodesecured around the mouth of the interior of the hollow object.

4. A method according to any of the preceding claims, wherein the step of spacing the first electrode means from the interior of the object is accomplished by wrapping the electrode means with an insulator.

5. A method according to claim 4, wherein the insulator is wrapped in a spiral.

6. A method according to any ofthe preceding claims and includingthefurtherstepofoscillat- ing the spacing means.

7. A method according to any of the preceding claims, wherein the hollow object is open ended and the first electrode means extends therethrough and is sealed with respect to non conductiveinletandoutletmeansfortheplatingfluid which are provided at respective ends ofthe object.

8. A method according to any of the preceding claims, wherein the hollow object is closed at one end and the first electrode means extends to the required depth of plating and then returns encased within a sheath of insulating material.

9. A method according to claim 8,wherein the sheath forms part of the path of the plating fluid.

10. A method according to claim 8 or 9, wherein the sheath is of solid material.

11. A method according to claim 10,whereinthe sheath is of PTFE.

12. A method according to 8 or, wherein the sheath is of a porous material.

13. A method according to any of the preceding claims, and further including the step of replacing afirstcharge of platingfluid by a second charge of plating fluid.

14. A method according to claim 13, wherein the second charge of plating fluid is different from the first charge, and further including a step of introducing a washing fluid between the applications ofthe first and second charges.

15. A method according to any of the preceding claims, including the further step of first reverse plating the interior ofthe hollow object using either a pulsed current or a continuous currentto clean the surface priorto plating.

16. Apparatus for electroplating the interior of hollow objects comprising first electrode means adapted for insertion into the object, spacer means operable to space and insulate the first electrode means from the interior of the object, and non-conductive inlet means and outlet means adapted for sealed connection to the objectforthe passage of plating fluid.

17. Apparatus according to claim 16, wherein the hollow object is open ended and wherein inlet and outlet means are provided at respective ends of the object with thefirst electrode means extending through the object but only being exposed for a length determined by the extent of plating required within the interior of the object, the first electrode means passing through the inletand outlet means and being sealedwith respect thereto.

18. Apparatus according to claim 16, wherein the hollow object is closed at one end and the first electrode extends to the required plating depth and is returned within a non-conductive sheath.

19. Apparatus according to claim 18, wherein the sheath forms part of the inlet means.

20. Apparatus according to claim 18 or 19, where- in the sheath is of a solid material.

21. Apparatus according to claim 20, wherein the sheath is of PTFE.

22. Apparatus according to claim 18or19,where- in the sheath is of a porous material.

23. Apparatus according to any of claims 17 to 22, wherein means are provided for oscillating the spacer means within the hollow object.

24. A method of plating the interior of a hollow object which is closed at one end comprising the steps of inserting pipe means into the interior of an object to be plated, charging the interior of the object with a plating fluid through the pipe means and emptying the object of the plating fluid on completion ofthe plating step.

25. A method of plating the interior of a hollow object substantially as herein particularly described with reference to the accompanying drawings.

26. Apparatus for plating the interior of a hollow object substantially as herein particularly described with reference to the accompanying drawings.