EP0857516A2 - Apparatus and method for coating articles - Google Patents

Abstract

Apparatus (10) for coating articles (28), comprising a support structure(11), a container (23) to contain the articles (28), container support means (21),and means (16a) to rotate the container, wherein resilient means (17) areprovided to connect the container support means (21) to the support structure(11). The resilient means (17) preferably comprise metal coil springs, such thatany wobble or other undesired vibrations caused by rotation of the container(23), conveniently a metal basket are absorbed by the coil springs (17), suchthat the basket, whilst rotating at high speed, exhibits a high degree of stability,in a manner similar to that of a gyroscope.

Description

This invention relates to apparatus for coating articles, primarily but notexclusively, to apparatus for coating metal articles, and to a method of coatingarticles. Although the term "metal" will be used henceforth, it should beunderstood that the term is intended to encompass other materials.

Several techniques presently exist by which metal articles may becoated, with paint, varnish, corrosion resistant formulations and the like, suchtechniques including dipping, spraying, powder coating, and electroplating.

Such techniques generally impart an acceptable coating to the articles,but a preferred technique has been found to be centrifugal coating, whereby thearticles to be coated are placed in a rotatable container such as a perforated basket,a coating material such as paint is applied to the articles, by dipping the basket andarticles into a paint reservoir, and the basket is then removed from the paintreservoir and rotated at high speed about a generally vertical axis to remove excesspaint from the articles and to ensure that a generally uniform thickness of paint isapplied thereto.

The articles are often relatively heavy, and it is often the case that whenloaded the distribution of articles therein will be uneven. When the basket isrotated about a vertical axis at high speed, which may exceed 2500 rpm, significant"wobble" may exist, putting considerable strain on a mounting to which an upperpart of the basket is secured.

In order to ensure that the rotating basket does not become detachedfrom the mounting during rotation of the basket, it has hitherto been necessary tohold the mounting in a very rigid manner, requiring the use of strong and heavymaterial about the mounting.

However, significant stress may still be imparted to parts of theapparatus, presenting a risk of failure, which if occurring during high speed rotationof the basket, may have serious implications.

It is one of the various objects of the present invention to provideimproved apparatus for coating articles which overcomes or reduces the problemsabove.

According to one aspect of the invention, there is provided apparatusfor coating articles, comprising a support structure, a container to contain thearticles, container support means and means to rotate the container whereinresilient means are provided to connect the container support means to the supportstructure.

Preferably, the container support means is connected to or forms partof drive means associated with the means to rotate the container.

Preferably, the container support means comprises a plate like memberon which the means to rotate the container and its drive means are mounted.

The resilient means preferably comprises a coil spring, one end ofwhich is attached to the container support means, the other end of which is attachedto the support structure, which may be in the form of a frame assembly, supportbeam, or the other suitable construction.

Preferably, more than one resilient means is provided, andconveniently, four coil springs may be provided in a generally cruciformarrangement, and lying in a generally horizontal plane, by which the containersupport means is mounted to the support. The springs are preferably metallic butmay equally be formed from other suitable materials, such as plastics materials, ifdesired.

The means to rotate the container preferably comprises a motor, andconveniently, comprises an air motor, driven by compressed air. The air motorpreferably connected to a compressed air source by a flexible hose. The motor ispreferably generally vertically oriented, such that a drive shaft rotated by themotor extends generally vertically, and downwardly, from the motor towards thecontainer.

There may also be provided guide members, integral with or secured tothe container support means through which the drive shaft from the motor passes.

Preferably, the guide members comprise a first part, which in use isfirmly secured to the drive shaft and a second part, relative to which the first partmay rotate, such that in use, the weight of the container attached to a lower part ofthe drive shaft is at least partly supported by the guide members, rather than by themotor alone.

Conveniently, the guide members comprise plummer blocks.

The container is preferably in the form of a basket, by which it is meantthat the container comprises a plurality of apertures in at least the side thereof, andconveniently also in the base, the motor being connected to the container by meansof the rotatable drive shaft.

The shaft may comprise a hook at the lower end thereof, which hook inuse engages with a receiving formation located on an upper part of the containersuch as an inverted U-shaped arm or carrying handle.

According to a further aspect of the invention, there is provided a hook,comprising a channel adapted to receive part of an article to be held by the hook,the channel comprising a first part having a first width, and a second part, having asecond width, wherein the second width is greater than the first width.

The first part may be generally straight, such that the first partcomprises generally parallel extending inner side walls, whereas the second partmay be generally circular in cross section, such that the diameter of the crosssection is greater than the shortest distance between the inner side walls of the firstpart.

By providing a second part of greater width than the first part, the hookis effectively provided with shoulder formations, which restrict upward movementof the article, relative to the hook.

The hook preferably comprises a recess in the first part, andconveniently, the hook comprises a recess in each side wall of the first part.

Preferably, the hook is cut from steel plate, conveniently ofapproximately 1-1.5 cm thickness.

The apparatus preferably also comprises a reservoir adapted to containa liquid with which the articles are to be coated.

The reservoir is preferably located generally beneath the container, andthere is preferably provided means to induce generally vertical relative movementbetween the reservoir and the container.

The means may comprise a moveable platform, hoist, table or the like,whereby the reservoir, containing the required liquid, may be raised up to a point atwhich the liquid contained therein comes into contact with the articles in thecontainer, thus applying the liquid to the articles. The platform or hoist may beraised/lowered by any convenient means, although preferably, hydraulic means isutilised.

Alternatively, the apparatus may comprise means to lower the containertowards the reservoir below, and to subsequently raise the container prior tocommencement rotation thereof. Again, such means is preferably hydraulic.

According to a still further aspect of the invention, there is provided amethod of coating articles comprising placing the articles in a container, applyingliquid to the articles, rotating the container to remove excess liquid from thearticles, and placing the articles in a heated environment, wherein the articlesremain in the container when placed in the heated environment.

The heated environment is preferably provided by an oven,conveniently an airless oven.

The liquid may comprise paint, a corrosion resistant formulation, orother metal protective composition, such as are used during centrifugal coating ofarticles.

If desired, the coating and heating operations may be repeated.

According to yet still further aspect of the invention, there is providedapparatus for coating articles, comprising coating means, whereby liquid is appliedto articles in a container, heating means, whereby heat is imparted to the articles inthe container, and conveying means whereby the container is conveyed from thecoating means to the heating means.

The coating means preferably comprises centrifugal coating apparatus,conveniently such as that described in relation to the first aspect of the invention.

The conveying means may comprise a conveyor belt arrangement, butpreferably, comprises a chain conveyor having attached thereto a plurality ofengaging formations such as hooks, to which upper parts of the containers may beattached.

Preferably, the conveying means extends into the heating means.

Thus, the chain conveyor may be in the form of a loop, wherebycontainers containing articles may be attached to the chain at a position adjacentthe coating means, transported via the chain to an into the heating means, andsubsequently returned from the heating means to the coating means.

Thus, if desired, the coating and heating operation may be repeated.

Of course, the containers and articles may be removed from the chainshortly after the heating operation if no further coating is required.

The invention will now be described with reference to theaccompanying drawings, wherein:

FIGURE 1 is a perspective view of a preferred embodiment of oneaspect of the invention,

FIGURE 2 is a side view of part of the assembly shown in Figure 1,with a modified hook, and

FIGURE 3 is a schematic view of a preferred embodiment of a furtheraspect of the invention.

Referring first to Figure 1, a centrifugal coating assembly generallyindicated at 10 is shown comprising a support structure in the form of anoverheadframe assembly 11 consisting ofbeams 12, 13, 14 and 15, located generallycentrally of which is anair motor 16, attached to acontainer support plate 21,which is suspended between the beams by fourmetal coil springs 17. Theairmotor 16 is connected to a source of compressed air 16a by aflexible hose 16b.

Theplate 21 is connected to the springs through nylon bushes (notshown).

Connected to a lower portion of theair motor 16 is adrive shaft 18,which passes throughplummer blocks 19 and 20 which are connected to thesupport plate 21, the plummer blocks serving to restrict sideways movement of theshaft 18 during rotation thereof, and to take a large portion of the weight of thecontainer attached to theshaft 18.

The lower end of theshaft 18 is provided with anupturned hook 22 towhich, in use, is connected abasket 23 having ahandle 24 under which the hookpasses.

There is provided beneath the basket apaint bath 25 containingpaint26, the bath being provided on amoveable platform 27, which may be raised orlowered in a conventional manner by use of hydraulic or pneumatic arrangement.

Thus, in use,articles 28 to be coated are placed within the basket, thebasket is then attached to thehook 22 of therod 18, and themoveable platform 27is raised so that the articles become submersed in thepaint 26. The moveableplatform is then lowered, excess paint being allowed to drip back into thebath 25through apertures in the base of thebasket 23.

The bath is lowered to a height at which the basket is no longer incontact with thepaint 26, but at which the side walls of the bath extend above thelevel of thearticles 28 contained within the basket.

The basket is then rotated at high speed, for example, 2500 rpm, toremove excess paint from the articles, which allows a generally uniform coating ofpaint on the articles to be obtained, in conventional manner.

Since the basket may be unevenly loaded with articles, the basket issubjected to uneven downwardly extending forces, which when the basket isrotated, can cause significant wobble to occur to the basket, and thus to the shaftand air motor, which has hitherto been overcome by rigidly mounting the motorassembly to theframe assembly 11.

However, it has been found by the applicants that by resilientlymounting the container support assembly to the frame, conveniently using asupport plate such as that shown at 21, any wobble or other undesired vibrationsare absorbed by the coil springs, and the basket, while rotating at high speed,exhibits a high degree of lateral stability, in a manner similar to that of a gyroscope.

Referring now to Figure 2, part of the assembly shown in Figure 1 isshown in side view. Theair motor 16 is mounted to thesupport plate 21 by agenerally L-shaped foot 60, the lower part of which is attached to the plate byscrews 61 and 62.

As shown in Figure 2, thedrive shaft 18 may be connected to the airmotor via auniversal joint 63, which conveniently is a rubber, or other flexibleuniversal joint.

Thehook 22 is generally of U-shaped construction, comprising a top 64andU arms 65 and 66. Achannel 67 extending into the hook, has aninlet 68 and aseat 69 which in use is occupied by an arm of the container which is supported bythe hook. The generally vertically orientated part of thechannel 67 comprisesinner side walls 70 and 71, which extend generally parallel to each other. Theseat69 is part circular in cross section, the diameter thereof being greater than thedistance between the parallel extendingside walls 70 and 71. Furthermore, there isprovided arecess 73 in theside wall 70.

It has been found by the applicants that the provision of a seat having a circular cross section whose dimension exceeds the distance between the parallelextending side walls of the channel reduces the tendency of a container or otherconstruction, attached to the hook by an arm passing through the channel of thehook, to become detached, when the hook is rotated at relatively high speed about agenerally vertical axis. The reason for this is thought to be that when the hookbegins to rotate, the arm of the container held by the hook, which passes throughthe bottom of thechannel 69, and which arm has a diameter less than the diameterof the second part of the channel, twists out of alignment with the channel.

Since the arm of the container is thus not in the line of sight of thechannel, upward movement of the arm relative to the hook is restricted , and theapplicants have found that over a prolonged period of use, the arm beds into thebase of thechannel 69. Furthermore, when an unevenly loaded basket is attachedto the hook, the arm of the basket passing through thechannel 69 will tend to lie toone side of the axis A. When the hook is rotated about the axis A, the centrifugalforce applied to the container biases the container firmly towards the side of theaxis. Thus, there is effectively provided ashoulder 74 or 75, depending on theweighting of the container, which restricts upward movement of the arm relative tothe hook.

Should however the arm slip past theshoulder 74 or 75, therecess 73catches the arm and restricts further upward movement.

It will be appreciated that whilst therecess 73 in the drawing is shownon the left hand side of the hook, there may in practice also be provided acorresponding recess on the other side of the hook.

Referring now to Figure 3, acoating assembly 50 is shown, whichincludes a centrifugal coating arrangement such as, for example, that described inrelation to Figures 1 and 2. Once the centrifugal process has been completed, thebaskets 23 are transferred to achain conveyor arrangement 51, which carries thebaskets towards and into anairless oven 52 through anentrance 53, in which oventhe paint is at least partially dried. The baskets exit the oven through anexit 54,and are then transferred back towards the coatingassembly 50, where the processmay be repeated if required.

By drying the articles in the baskets, rather than by removing the articles from the basket prior to the drying operation, and thus removing thenecessity of transfering the articles to a conventional working tray, which issubsequently put into the oven, it has been found that significantly less scratchmarks are imparted to the articles, thus providing a superior finish to the articlesover previously known techniques. Of course, some 'bare' areas may exist on thearticles, corresponding to areas of contact between the articles when the paint isfirst applied. However, by agitation of the articlesafter the drying process andsubsequently repeating the process, which effectively removes the possibility of thearticles touching one another at the same areas, articles having a very high qualityappearance may be obtained.

In a preferred arrangement, there may be provided in thecoatingassembly 50, more than one centrifugal assemblies of the type generally shown at10 in Figure 1, and conveniently, there may be provided three such centrifugalassemblies, thus enabling a greater number of articles to be coated in a given time.

The centrifugal assemblies may be connected to a common source ofcomprises air, but preferably, each is independently controlled such that thecontainers associated therewith mat be caused to rotate at different speeds, whichmay be desirable in vie of differing articles contained therein, or differingcompositions to be applied to the articles.

Further more, the complete centrifugal coating process is preferablyautomated such that by operation of a single switch which is spaced from thecoating assembly 50, themoveable platform 27, on which rests thepaint bath 25 isfirst raised so as to submerse the container and articles in thepaint 26, maintainedat the raised height for a sufficient time for paint to be imparted to the articles(approximately 2 seconds has been found to be sufficient), and subsequentlylowered to a position at which the basket no longer contacts the paint but at whichthe side walls of the paint bath extend above the level of the articles containedwithin the basket.

The automated procedure is then such that rotation of the basketscommences, continues for a present length of time, and then ceases.

The procedure may also involve the raising and lowering of a safetyscreen located towards the front of the centrifugal assembly, such that during rotation of the baskets, an operator is shielded from any articles which mayconceivably be ejected from the baskets, or, in the event of failure of the basket ordrive shaft, from any other parts which may be ejected from the assembly at highspeeds.

The features disclosed in the foregoing description, or the following claims,or the accompanying drawings, expressed in their specific forms or in attaining thedisclosed result, as appropriate, may, separately or in any combination of suchfeatures, be utilised for realising the invention in diverse forms thereof.

Claims (13)

1. Apparatus (10) for coating articles (28), comprising a support structure(11), a container (23) to contain the articles (28), container support means (21)and means (16a) to rotate the container;
      characterised in that resilient means (17) are provided to connect thecontainer support means (21) to the support structure (11).
2. Apparatus according to Claim 1 wherein the resilient means (17)comprises a coil spring (17).
3. Apparatus according to Claim 2 wherein four coil springs (17) areprovided in a generally cruciform arrangement.
4. Apparatus according to any one of the preceding Claims wherein themeans to rotate the container comprises an air motor (16).
5. Apparatus according to Claim 5 wherein the air motor (16) is generallyvertically orientated.
6. Apparatus according to Claim 4 or Claim 5 comprising guide members(19,20), integral with or secured to the container support means (21), andthrough which a drive shaft (18) extending from the motor (16) may pass.
7. Apparatus according to Claim 6 wherein the guide members (19, 20)comprise a first part, which in use is firmly secured to the drive shaft (18), anda second part which is integral with or secured to the container support means(21), and relative to which the first part may rotate.
8. Apparatus according to Claim 6 or Claim 7 wherein the guide members(19, 20) comprise plummer blocks.
9. A hook (22) comprising a channel (67) adapted to receive part of anarticle to be held by the hook, the channel (67) comprising a first part (70, 71)having a first width, and a second part (69), having a second width, wherein thesecond width is greater than the first width.
10. A hook (22) according to Claim 9 wherein the first part comprisesgenerally parallel extending inner side walls (70, 71), and wherein the secondpart (69) is generally circular in cross-section, the diameter of the second part(69) being greater than the distance between the side walls (70, 71) of the firstpart.
11. A hook (22) according to Claim 9 or Claim 10 comprising a recess (73)in the first part.
12. A method of coating articles (28) comprising placing the articles in acontainer (23), applying liquid (26) to the articles (28), rotating the container(23) to remove excess liquid from the articles (28), and placing the articles in aheated environment (52), wherein the articles (28) remain in the container (23)when placed in the heated environment (52).
13. Apparatus for coating articles (28), comprising coating means (10)whereby liquid (26) is applied to articles in a container (23), heating means(52) whereby heat is imparted to the articles (28) in the container (23), andconveying means (51) whereby the container (23) is conveyed from the coatingmeans (10) to the heating means (52).

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