GB2061135A - Coating hollow articles - Google Patents

Abstract

Manufacture of holloware (14) such as cups, mugs, jugs, bowls and plates by lowering the holloware vertically into a bath of liquid coating such as glaze in an inverted position, withdrawing air from the interior of the item through a first upstanding pipe (21). The coating is then pumped upwardly into the interior of the item through a second upstanding pipe (70) to coat the internal surface of the holloware. Only the rim may be coated or the exterior may be coated to any desired extent depending on the degree of immersion. <IMAGE>

Description

SPECIFICATION Manufacture of Holloware This invention relates to the manufacture of holloware such as cups, mugs, jugs, bowls, plates etc.

by a method which includes application of a coating to the interior of the hollow portion of the ware.

The invention has been particularly, but not exclusively, developed for the application of glaze to pottery holloware. Hitherto this has been carried out by dipping the holloware in liquid glaze, or by spraying the hollowarewith glaze. Bytheterm "pottery" we include china, porcelain, earthenware or stoneware and by the term "coating" we include glaze, slip, and colour.

An object of the invention is to provide a new and improved method of applying a coating to holloware.

According to one aspect of the invention we provide a method of applying a coating to the internal surface of an item of holloware and to a desired extent of the external surface thereof, comprising introducing, the item in a base uppermost orientation into contact with the surface of a bath of liquid coating contained within a first container, and immersing the external surface of the holloware to a desired extent in said bath, withdrawing air from within the item through a first upstanding pipe and pumping coating upwardly through a second upstanding pipe into the interior of the holloware to coat the internal surface thereof, and thereafter removing the item from the bath.

Thus the complete glazing of the interior of an item of holloware can be achieved.

If it is desired only to glaze the rim of an item, the rim only will be brought into contact with the bath and there is no immersion whatsoever of the external surface of the item. In this case the desired extent of immersion is zero.

Alternatively, if it is desired to glaze the whole of the external surface of the item, the entire item will be immersed in the bath of liquid. In this case, the desired extent of immersion is total.

Of course if it is desired to glaze only part of the external surface of the item, the item may be immersed to a desired extent accordingly.

Preferably, the lower end of said first upstanding pipe for withdrawing air, is open to atmosphere, and said second upstanding pipe may be positioned within said first upstanding pipe.

The liquid level in the bath may be maintained constant by a liquid level pipe which extends to a second container, withdrawal of liquid coating from the first container being effected by way of said liquid level pipe which is upstanding within the first container, the upperend of the liquid level pipe acting as a weir for the flow of the liquid coating from the first container to the second container. Preferably, liquid coating is pumped upwardly from said second container through said second upstanding pipe to the interior of the holloware.

By circulating coating between the second container and the first container in this manner, the necessity of mechanically agitating the coating in the first container by a separate agitator or the like is avoided.

As the item is withdrawn from the bath, preferably it is maintained in said base uppermost orientation, and may be introduced into and removed from the bath by movement in a vertical path.

A holder may be provided to transfer the article from a loading station to said bath and, after coating, from the bath to an unloading station.

The item of holloware, at least during the coating operation, may be held by a vacuum applied to the item to bring the base of a foot rim of the item into engagement with a holder. The base of the foot rim may be engaged by the holder and no coating applied to the base of the foot rim.

At the loading station, coating may be applied to the base of an item priorto engagement with the holder, preferably by means of an applicator pad which is immersed in the coating during the coating operation.

Alternatively, coating need not be applied to the foot rim of the item.

According to a second aspect of the invention we provide an apparatus for applying a coating to the internal surface of an item of holloware and to a desired extent of the external surface thereof comprising a first container for containing a bath of liquid coating, first and second upstanding pipes in said first container, means for introducing a holloware item in a base uppermost orientation into contact with the surface of said bath and to immerse said item in the bath to a desired extent, the first and second upstanding pipes being located within the item, means to withdraw air trapped in the interior of the item through the first upstanding pipe, and pump means to convey coating upwardly through said second upstanding pipe to the interior of the item to coat the internal surface thereof.

The lower end of the first upstanding pipe may be open to atmosphere.

Preferably, the apparatus includes a liquid level pipe to maintain the liquid level in the first container constant, the pipe extending upwardly through the first container, the upper end of the pipe acting as a weir for the flow of liquid coating from the first container.

The lower end of the liquid level pipe may extend to a second container which contains liquid coating, and said pump means and said second upstanding pipe may convey coating from the second container to the interior of the item. The second upstanding pipe may be located within the first upstanding pipe.

According to a third aspect of the invention we provide an item of holloware having coating applied thereto by the method according to the first aspect of the invention or utilising the apparatus according to the second aspect of the invention.

The invention will now be described by way of example with reference to the accompanying drawings in which: FIGURE 1 is a diagrammatic fragmentary side elevation partly in section with parts omitted for clarity of a glazing apparatus not embodying the invention; FIGURE 2 is an end elevation partly in section of the apparatus of Figure 1; FIGURE 3 is a fragmentary cross-sectional view of a modified form embodying the invention, of the apparatus shown in Figures 1 and 2.

Referring to Figures 1 and 2 there is illustrated apparatus for applying glaze to pottery holloware such as mugs. The apparatus comprises a storage tank 10 in which is received liquid glaze. If desired the apparatus and method of the present invention may be utilised to apply other coating than glaze to an article, for example, slip or paint. The invention can also be utilised with articles of holloware made of material other than pottery.

The storage tank 10 may be made of any suitable material such as a suitable synthetic plastics material and is provided with flanged wheels 11 engaged with angle section rails 12 to permit the storage tank 10 to be withdrawn outwardly of the apparatus for cleaning.

At a level above the storage tank 10 is disposed a dipping tank 13 in which application of glaze to mugs 14 is carried out by dipping of the mugs 14 into liquid glaze contained within the tank 13. A duct 15 extends from the tank 10 to the dipping tank 13, a pump 16 being provided in the duct for pumping the liquid glaze from the tank 10 to the tank 13. An overflow pipe 17 may be provided if desired, and is provided in the present example, extending from an upper part of the tank 13 for carrying liquid glaze back to the tank 10 should the level of liquid glaze in the tank 13 become too high. The overflow pipe 17 feeds any such overflow into the tank 10 via a fine sieve 18 movably mounted, to permit cleaning, atthe lower end of a cylindrical neck 19 depending downwardly from a top cover 20 of the tank 10.

Two upstanding cylindrical pipes 21 are mounted in a base part 22 of the tank 13. As shown in Figure 2 one pipe is directly behind the other and so only one pipe can be seen in Figure 1.

Each pipe 21 is mounted in a boss 23 provided with sealing O-rings 24 and the construction of the mounting assembly is such that the extent of projection of the pipes 21 above the base part 22 can be adjusted to suit the articles of holloware to be coated.

At its upper end each pipe 21 terminates at a position near the top of the tank 13 which is spaced slightly below the normal glaze level 25 in the tank.

The precise position atwhichthe upper end of the pipes 21 terminate is adjusted in accordance with the article to be coated so that the upper end edges 26 are spaced closely adjacent to, for example 1/32" away from the downwardly facing surface 27 of a base part 28 of articles of holloware 14 placed over the pipes.

At their lower ends 29 the pipes 21 are arranged to return liquid glaze descending the pipes as hereinafterto be described to the storage tank 10 through the filter 18.

The pump 16 in the present example operates continuously, and if desired may be arranged to operate only whilst an article is being dipped into the tank 13.

In any event when the pump 13 is operating the upper end 26 of each pipe 21 acts as a weir for the overflow of liquid glaze from the dipping tank 13, the glaze returning to the storage tank 10 as mentioned above through the filter 18. The flow of glaze from within the tank 13 through the pipes 21 is such, as a result of the rate of delivery of the pump 16 and the diameter of the pipes 21 that the liquid glaze follows the wall of the pipes 21 and creates a generally cylindrical space within each pipe 21 which is not filled by liquid and is thus available for withdrawal of air from within the mug 14. In addition, the flow of glaze over each edge 26 has the effect of forcing the liquid glaze into contact with the surface 27 thus ensuring the application of glaze thereto and hence to the whole of the interior of each mug 14.

Means are provided in association with the dipping tank 13 for holding the mugs 14 and for moving the mugs into and out of the tank 13. In the example illustrated each mug 14 has a cylindrical sidewall 30 a generally flat base 28 and a foot rim 31 around the periphery of the bottom. The foot rim 31 has a base 32 upon which the mug will stand when in use.

A holder is provided for each mug and are indicated generally at 33. Each holder comprises a disc 34 having on the lower surface a layer 35 of resilient material, for example, soft rubber. The disc 34 has formed integrally therewith an upstanding boss 36 to which is screwed a pipe 37 having a central bore 39 connected to a vacuum line, not shown.

The pipe 37 is mounted in a transport head 40, as hereinafter to be described. The head 40 is reciprocable vertically upwardly and downwardly between the full and dotted line positions shown in Figure 1 by means of a conventional pneumatic piston and cylinder arrangement. The head 40 is also reciprocable between a position indicated at A in Figure 1 in which it is located above the tank 13 for dipping of the mugs 14 thereinto, a position B where mugs are engaged with the holder and a position C where mugs are released from the holder after dipping. The head 40 is movable between these positions by any desired means. For example, the head 40 may be mounted on a pair of supports 41 each provided with a linear bearing, not shown, which slidably mount the supports 41 on a pair of cylindrical rods 42.The head 40 may be moved along the rods 42 by any desired means but in the present example by con--; necting the support members 41 to a chain which is engaged around sprocket wheels, not shown, one of the sprocket wheels being connected to a further sprocket wheel of smaller diameter which has a further chain entrained therearound and the further chain being connected to a double acting ram. In this case the arrangement is such that when the head 40 is in the position indicated at A one piston of the double acting ram is in an extended position whilst the other is in a retracted position. To move the head 40 to the position B the other piston of the ram is likewise moved to its extended position whilst to move the head 40 to the position C both rams are in their retracted position.

If desired any other means for moving the head 40 may be provided including, for example, electric motors and indeed any other holding means for the mugs may be provided if desired.

Atthe position B is provided a loading table 43 mounted on a spindle 44 which is mounted for rota tion about a vertical axis in bearings, not shown. The spindle 44 is caused to rotate reciprocally about the vertical axis through 180 by any suitable means but preferably by means of a pneumatic ram the piston rod of which is connected to a chain entrained around a sprocket carried on the spindle 44. The table 43 is provided with two pairs of locating means 45 for mugs 14. Each locating means comprising an O-ring 46 held between a pair of plates 47, each provided with a rebate 48 to provide a groove for the O-ring 46, the plates 47 being clamped to the upper surface of the table 43.

At the position C is provided a receiving table 49 provided with a wire mesh upper surface 50 and carried on the upper end of a spindle 51 which is likewise mounted for rotation about a vertical axis but in this case is movable in a single direction only in steps of 90" by means of a pneumatically operated ratchet mechanism, not shown.

Beneath the table 49 is provided a receiving tray 52 from which a duct 53 leads to feed glaze received in the tray 52 back to the holding tank 10 through the sieve 18.

Also provided on the support head 40 are a pair of glaze applicators 54 each comprising a disc 55 formed integrally with a boss 56 which is fixed to a rod 57 mounted in the head 40.

The rods 57 are adjustable vertically relative to the head by virtue of being received in sleeves 58 which are slidable in apertures 59 in the head 40 and are clampable in a desired position longitudinally of the apertures 59 by means of screws 60 having knurled heads 61.

The pipes 37 of the holders are likewise adjustable, the pipes 37 being slidably received in apertures 59 in the head 40 and being clampable in a desired position longitudinally of the apertures 59 by means of screws 60 having a head 61.

The rods 57 have an abutment 62 at their upper ends and a coil compression spring 63 is engaged around each rod 57 and abuts, at one end, the boss 56 and at the other end the lower end of the sleeve 58. A suitably contoured piece of sponge rubber 64 is fixed to the downwardly facing surface of the disc 55. The contour of the pad 64 being such as to conform to the shape of the undersurface of the mug 14.

In operation, mugs 14 emerge from a drying oven on a wire mesh conveyor in an upside down condition and are deposited on the feed table 43 and are located in position as a result of engagement of the O-rings 46 with the interior of the mugs 14 at the location a as shown in Figure 1.

Assuming that the apparatus has been operating forsometime mugs previously located ata will have been moved to location b as a result of rotation of the table 43 through 1800 and thus after placing two new mugs 14 at location a there will be mugs at both the locationsa andb. The head 40 is then lowered to engage the holding means 33 with the base of the mug 14 at the location b whilst the pad 64 is moved into engagement with the base of the mug 14 at the location a. Twill be noted that the dimensions of the pad 64 are such that it does not contact the foot rim 32. Since the pad 64 will have been previously immersed in the glaze in the dipping tank 13, as hereinafter to be described, glaze is thus applied to the undersurface of the mug except for the foot rim.

The layer of soft rubber 35 forms a seal with the foot rim 32 ofthe mugs 14 of the locationb and the vacuum applied through the bore urges the foot rims into close engagement with the holders so that they are attached to the holders. The head 40 is then raised to liftthe mugs 14 atthe locationb out of engagement with the table 43 and is then moved from the position B to the position A whereupon the head 40 is lowered to dip the mugs 14 into the glaze as shown in dotted line in Figure 1 and at the same time to dip the applicator pad 55 into the glaze.During this operation the table 43 is moved through 1800 to move the mugs previously loaded at location a into locations and to permit further mugs to be loaded onto the table at location a.

When the mugs 14 are dipped at the position A each mug is coated with glaze over the entire outer surface except for the foot rim and the part thereof within the foot rim, which has been previously coated with glaze by the applicator 54 and in addition the entire internal surface of the mug is coated as described hereinbefore.

After dipping the head 40 is raised and transported to position C where the mugs are lowered onto the receiving table 49 and the vacuum disconnected so that the mugs 14 are deposited upon the mesh 50 of the table 49 and any excess glaze which may run from the mugs passes through the mesh 50 and is returned to the tank 10 through the duct 53.

The head 40 is then raised and returned to position B to be engaged with two further mugs at location b and the operation is repeated.

Turning now to Figure 3, a modified version of the apparatus of Figures 1 and 2 as described, which embodies the invention. The apparatus is essentially the same as that described hereinbefore in Figures 1 and 2 and hence only position A is illustrated and the same reference numerals have been used to apply to the corresponding parts.

This modified apparatus, embodying the invention, is utilised when it is desired to only partially externally glaze an article of holloware; in the example illustrated mugs 14.

In this modified arrangement two furthertubes 70 are positioned one within each tube 21 and are connected to a pump which can pump glaze up thorough the pipes 70. In addition a glaze level pipe 71 is provided mounted in the base 22 of the tank 13 by means of a mounting assembly 72 similarto the mounting assembly 23 for the pipe 21. The upper end 73 of the pipe 71 is arranged to maintain the level 74 of the glaze at a predetermined position in the bath which is related to the extent of downward movement of the head 40 and hence the extent of immersion of the exterior of each mug 14 into the glaze. In the example illustrated there is no immersion whatsoever of the external surface 14a of each mug 14 and in this example when glaze is pumped through each pipe 70 the glaze is applied only to the internal surface of the mug. As the mugs are lowered into contact with the surface of the bath and glaze pumped through the pipes 70 air trapped within the mugs 14 is permitted to escape through the pipes 21 the lower end of which is open to atmosphere.

Other possible modifications or additions to the apparatus shown in Figures 1 and 2 are as follows: An adjustably positioned float member, not shown, may be arranged to be lowered into the tank 13 at the same time as is the holloware items. The introduction of such a float member into the liquid glaze temporarily raises the level of the glaze within the dipping tank 13 and by an adjustment of the position of the float member the maximum level of glaze reached in the tank 13 can be arranged to ensure glazing of the foot rim of the holloware items. This enables glazing of items of different thickness to be controlled.

An end piece or nozzle, not shown, may be incorporated in the upper end of each pipe 21 to restrict the flow of liquid glaze through the pipe. A range of nozzles of different sizes may be provided or a single nozzle of adjustable flow rate may be provided for use with holloware items of different sizes and thicknesses to ensure the correct relationship for efficient glazing of each item.

A vacuum pump or other vacuum source may be connected to the pipes 21 orto a further pipe disposed within the pipes 21 for assisting extraction of air from the interior of each holloware item undergoing glazing. This may, for example, be desirable when a large item isto be glazed.

If the vacuum source is connected directly to the pipes 21 a trap for liquid glaze passing down the pipes 21 is provided to prevent glaze reaching the vacuum source.

A valve, not shown, may be inserted in the pipes 21 in order to restrict the flow of glaze through the pipes to maintain the required glaze level in the dipping tank 13 between successive glazing operations.

The valve may be operated pneumatically or electrically, for example, in co-ordination with the operation of the apparatus for lowering the items of holloware into the glaze.

When the apparatus of Figures 1 and 2 or a modified apparatus in accordance with the invention as shown in Figure 3 is operating rapidly, waves may be formed in the glaze bath and this can create irregularities in the glaze applied.

In order to overcome or to reduce this problem a sheet of buoyant material 90, see Figures 1 and 2, is provided, which floats on top of the glaze and is provided with apertures to permit the articles to be glazed and the glaze applicators to pass through the sheet and into the glaze.

The sheet material may be of any suitable material which will float on the glaze such as nylon, PVC, polypropylene, plywood or the like.

Although in the above examples the unloading table has been described as rotating through 90 at the end of each cycle with the intention that each mug will remain thereon for 1-3 dipping cycles before being removed so as to give a reasonable amount of time for excess glaze to drain therefrom, if desired, the unloading table may be rotated through an appropriate more or less number of degrees and be of appropriate size to permitthis orthe apparatus may be unloaded the dipped articles directly onto a wire mesh conveyor at position C.

If desired one or more than one article or holloware may be dipped simultaneously by providing an appropriate number of holding means.

Claims (21)

1. A method of applying a coating to the internal surface of an item of holloware and to a desired extent of the external surface thereof, comprising introducing the item in a base uppermost orientation into contact with the surface of a bath of liquid coating contained within a first container, and immersing the external surface of the holloware to a desired extent in said bath, withdrawing air from within the item through a first upstanding pipe and pumping coating upwardly through a second upstanding pipe into the interior of the holloware to coat the internal surface thereof, and thereafter removing the item from the bath.

2. A method according to Claim 1 wherein the lower end of said first upstanding pipe for withdrawing air is open to atmosphere.

3. A method according to Claim 1 or Claim 2 wherein said second upstanding pipe is positioned within said first upstanding pipe.

4. A method according to any one of the preceding claims wherein the level of liquid in the bath is maintained constant by a liquid level pipe which extends to a second container, withdrawal of liquid coating from first container being effected by way of said pipe which is upstanding within the container, the upperend of the pipe acting as aweirfortheflow of liquid coating from the first container to the second container.

5. A method according to Claim 4wherein liquid coating is pumped from said second container through said second upstanding pipe to the interior ofthe holloware.

6. A method according to any one of the preceding claims wherein the item is retained in said base uppermost orientation during removal from the bath.

7. A method according to Claim 6 wherein the item is introduced into and removed from the bath by movement in a vertical path.

8. A method according to any one ofthe preceding claims wherein a holder is provided to transfer the, article from a loading station to said bath and, after coating, from the bath to an unloading station.

9. A method according to any one of the preced- ing claims wherein at least during the coating operation the item of holloware is held by a vacuum applied to the item to bring the base of a foot rim of the item into engagement with a holder.

10. A method according to Claim 9 wherein the base of the foot rim is engaged by the holder and no coating is applied to the base of the foot rim.

11. A method according to any one of Claims 8 to 10 wherein at the loading station, coating is applied to the base of an item prior to engagment with the holder.

12. A method according to Claim 11 wherein the coating is applied at the loading station by means of an applicator pad which is immersed in the coating during the coating operation.

13. Amethod accordingto Claim 11 or Claim 12 wherein coating is not applied to the foot rim of the item.

14. Apparatus for applying a coating to the internal surface of an item of holloware and to a desired extent of the external surface thereof comprising a first container for containing a bath of liquid coating, first and second upstanding pipes in said first container, means for introducing a holloware item in a base uppermost orientation into contact with the surface of said bath and to immerse said item in the bath to a desired extent, the first and second upstanding pipes being located within the interior of the item, means to withdrawn air trapped in the interior of the item through the first upstanding pipe, and pump means to convey coating upwardly through said second upstanding pipe to the interior of the item to coat the internal surface thereof.

15. Apparatus according to Claim 14 wherein the lower end of the first upstanding pipe is open to atmosphere.

16. Apparatus according to Claim 14 or Claim 15 wherein a liquid level pipe is provided to maintain the liquid level in the first container constant, the pipe extending upwardly through the first container, the upper end of said pipe acting as a weirforthe flow of liquid coating from the first container.

17. An apparatus according to Claim 16 wherein the lower end of said liquid level pipe extends to a second container which contains liquid coating, said pump means and the second upstanding pipe conveying coating from the second container to the interior of the item.

18. An apparatus according to any one of Claims 14to 17 wherein the second upstanding pipe is located within the first upstanding pipe.

19. A method of applying coating to an item of holloware substantially as hereinbefore described with reference to Figures 1,2 and 3 of the accompanying drawings.

20. Apparatus for applying coating to holloware items substantially as hereinbefore described with reference to and as shown in Figures 1,2 and 3 of the accompanying drawings.

21. An item of holloware having coating applied by the method claimed in any one of Claims 1 to 13 or 19, or utilising the apparatus of any one of Claims 14to 18 orClaim 20.