GB1604035A

GB1604035A - Method and apparatus for electrolytically treating a container body

Info

Publication number: GB1604035A
Application number: GB49016/77A
Authority: GB
Original assignee: Metal Box PLC
Current assignee: Crown Packaging UK Ltd
Priority date: 1978-05-31
Filing date: 1978-05-31
Publication date: 1981-12-02
Also published as: IT1100579B; ZA786246B; IT7830168A0

Description

(54) METHOD AND APPARATUS FOR ELECTROLYTICALLY TREATING A CONTAINER BODY (71) We, METAL BOX LIMITED, of Queens House, Forbury Road, Reading RG1 3JH, Berkshire, a British Company, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a method and apparatus for electrolytically treating a container body formed from sheet metal.

Container bodies are known which are drawn from sheet metal to have a cylindrical side wall closed at one end by an end wall. During the drawing process the surfaces of the sheet metal are subjected to frictional engagement with the drawing tools and the surface may become scratched or generally disturbed. This disturbance is more apparent on containers which have been wall ironed than on containers which have been redrawn with a positive clearance between punch and die.

The tinplates, used for the manufacture of drawn containers, comprise a layer of tin on the mild steel substrate. The surface of the tin is usually passivated by a known chemical treatment. When the passivated tinplate is drawn, in a press tool, the tin layer is subjected to frictional engagement with the tool surface and so the passivated layer is liable to be destroyed. If the degree of drawing or redrawing is severe, as could be the case in a wall ironing operation, the tin layer may be broken to leave the steel beneath, exposed and vulnerable to attack when the container is packed with certain food products, as is well known in the art. One known remedy is to use tinplate having a thicker layer of tin but this is a costly remedy.

The aluminium sheet used for manufacturing containers, is often anodised, etched or treated with chromates because such surface treatments help subsequent organic coatings to adhere to the sheet. As already explained, with reference to tinplate, these surface finishes for aluminium sheet may also be spoiled in the press tool and so with both drawn aluminium containers and drawn tinplate containers there is a need for a method and apparatus for repairing the surfaces of the containers after the metal working operations; such operations may include drawing; redrawing with a positive clearance;. redrawing with a negative clearance herein called wall ironing; flanging or beading.

Tinplate container bodies having a side seam are commonly soldered. However, certain products require that the side seam be protected after forming, the usual remedy being the application of a stripe of organic lacquer. Tinplate container bodies having a welded side seam also suffer damage to the metal surface adjacent the weld and again there is a need for a method of repairing the interrupted surfaces of the metal of the side seam.

The application of organic coating materials to containers is often impeded by the presence of lubricants. The problem is more serious with wall ironed cans and so the cans are usually washed and dried before coating. British Patent Number 1498 795 describes a method and apparatus for cleaning can bodies by means of a solvent or detergent which removes the greasy lubricants. The method described therein comprises mounting the container in a cavity in a body; the cavity having a shape corresponding approximately to that of the container, with the walls of the cavity spaced close to the surfaces of the container; and the container sub-dividing the cavity into two chambers; and passing the cleaning fluid through the chambers so that the cleaning fluid fills the chambers and flows along the surfaces of the container.The flow is preferably turbulent to obtain a good cleaning action, in contrast to the galvanic actions which are the subject of this specification.

That is to say that movement of fluids into and out of a treatment cell prevents the use of such an arrangement in an electro coating apparatus. In our British Patent Number 1,117,831 apparatus is described in which a tubular side seamed can body is moved to surround an electrode and define with the electrode an electrocoating cell. Electrocoating material is passed into the space between the interior of the can body and the internal electrode and application of a potential difference between the can body and the electrode causes a current to pass through the coating material so that the internal surface of the can body becomes coated. The weight of coating applied to the body is proportional to the current passed. After coating the can the electrolyte is removed from the cell and the body is removed from the apparatus.However this apparatus is not capable of applying an external coating to the can body.

The invention provides a method of treating a can body formed from sheet metal, said method including the steps of placing the can body in a cell such that the interior and exterior surfaces of the can body are in close spaced relationship respectively with a mandrel forming part of the cell and with a side wall of the cell, introducing an electrolyte into the cell, directing the electrolyte within the cell selectively between the interior surface of the can body and the mandrel, between the exterior surface of the can body and the side wall of the cell, or both between the interior surface of the can body and the mandrel and between the exterior surface of the can body and the side wall of the cell, and applying a potential difference between the cell and the can body for treating, respectively the interior surface of the can body, the exterior surface of the can body, or both the interior and the exterior surfaces of the can body.

According to another aspect of the invention, apparatus for simultaneously treating the interior and exterior of a metal container comprises a hollow apparatus for treating a can body formed from sheet metal, said apparatus comprising a cell which has a side wall and a mandrel arranged to receive therebetween in close spaced relationship a can body, passage means for introducing an electrolyte into and conducting the electrolyte from the cell, said passage means being adaptable for directing the electrolyte within the cell in use selectively between the interior surface of the can body and the mandrel, between the exterior surface of the can body and the side wall of the cell, or both between the interior surface of the can body and the mandrel and between the exterior surface of the can body and the side wall of the cell, and means for applying a potential difference between the cell and the can whereby to treat, respectively, the interior surface of the can body, the exterior surface of the can body, or both the interior and the exterior surfaces of the can body.

Additionally, the invention provides a can made by a method according to the invention or by means of an apparatus according to the invention.

An embodiment of the invention will now be described by way of example and with reference to the accompanying examples and drawings in which: Figure 1 is an open ended can body; Figure 2 is a sectional view of apparatus for treating both the interior and the exterior of the can body of Figure 1; Figure 3 is a diagrammatic sectional view of apparatus having a plurality of cells; Figure 4 is a plan view of the apparatus of Figure 5; Figure 5 is a diagram of the apparatus of Figure 5 and including a transfer turret to permit a sequence of galvanic or other treatments The can body 1 of Figure 1 has an end wall 2 and a side wall 3 extending from the periphery of the end wall to terminate in a flange 4, which defines the open end of the can ody.

The can body 1 has been drawn from a single piece of sheet metal, such as tinplate or aluminium, and thereafter been wall ironed so that the side wall 3 is thinner than the end wall 2. The side wall is therefore in need of repair treatment to restore its surfaces, while the surfaces of the end wall are substantially unaltered from the sheet condition.

In Figure 2, apparatus is shown which has passages as arrowed to conduct the treating fluid first across the exterior surface of the can body and then across the interior surface of the can body.

The apparatus of Figure 2 comprises a cell 21 and a cover 22. The cell has a bottom wall 23 and a side wall 24. A mandrel 25 extends centrally upwards from the bottom wall 23 within the side wall 24 to define therewith an annular cavity and to further define, with the cover 22, a space above the mandrel 25. An insulating locator ring 26 having triangular ribs 27 surrounds the mandrel 25 and rests on the bottom wall 23. The can body 1 is located centrally by the ribs 27 to be substantially equidistant from the side wall 24 and the mandrel 25.

An electrode 28 extends through an insulating grommet 29 to press on the end wall 2 of the can body so as to make good electrical contact and press the mouth of the can body into sealing engagement with the ring 26.

In Figure 2, the treating fluid enters through the bottom wall 23 via a passage 30 and passes as arrowed, between the exterior surface of the can body 1 and the cell side wall 24, to leave through a passage 31 which leads the treating fluid back towards the bottom wall 23 for entry into a central passage 32 in the mandrel 25. Upon emerging from the passage 32, the fluid impinges on the interior surface of the end wall 2 and passes on between the interior surface of the side wall of the can and the mandrel 25 to leave through the bottom wall 23 via a passage 33.

The cell is given a negative polarity, so that a direct current may be passed through a fluid in the cell. Therefore, when an electrocoating material is introduced as arrowed into the cell and a current is passed through the electrocoating material, the can body becomes coated with a surface coating. After coating the can body, the spent electrocoating material is drained from the cell and the coated can body is removed from the cell.

It will be understood that the entry into and exit from the cell of the treating fluid through the bottom wall 23 permit convenient arrangement of feed pipes. Also, should it be desired to modify the cell of Figure 2 to treat only an interior or an exterior surface of the can body at one time, this may be achieved by movement of a plug 34 to block a connection passage 35 jointing the passages 31 and 32 and removal of base plugs 36 and 36A from the passages 31 and 32. Removal of the plug 36A also permits the use of a valved supply of compressed air to eject the can body from the cell 21.

It will be understood, that to fill the cavities completely and avoid residual remnants, the entry and exit openings are preferably annular and arranged to distribute the treating fluid around the can body.

It will be understood that the polarity of the can bodies and cells in Figure 2 may be reversed but that it is preferable to have the cells at an earthed polarity for safety.

The apparatus of Figure 2 is particularly suitable for incorporation in a rotary machine 37 having a plurality of such cells, as shown in Figures 3 and 4. Each cell 45 is fed with fluids from supply means in a base of the machine 37.

In Figure 3, the machine 37 can be seen to have a base plate 38 from which extends a centre post 39 supporting a drum cam 40. A turret 41 is arranged to rotate on the base plate 38, about the centre post 39. The turret comprises a top plate 42, a spacer 43 and a cell block 44. The equispaced arrangement of the cells 45 around the turret 41 is best seen in Figure 4.

Each cell 45 is closable by a cover 46 supported on a rod 47 which is urged to reciprocate by a follower 48, at the upper end, which engages with the drum cam 40, the rod being insulated from the cover, turret and cam.

An entry star wheel 49, acting with an entry guide 50, brings each can body 1 in sequence to be fitted in a cell and, after treatment, an exit star wheel 51, acting with an exit guide 52, removes each can from the apparatus.

A positive polarity is imparted to the cans 1 in the cells and a negative polarity is put upon the cell block 44.

Each cell is used to perform a like treatment on each can body. The can body 1 is therefore placed in the cell 45A (beneath it as shown in Figure 3) and, as the turret 41 rotates about the central post 39, the cooperation of the follower 48A with the cam 40 causes the rod 47A to lower the cover 46A to close the cell 45A. The cell is then filled in a manner described with reference to Figure 2. As the turret continues to rotate, the rod 47A contacts the contact bar 53 which puts a positive potential onto the rod 47A. The rod 47A conducts this polarity to the can body 1 in the cell so that for approximatley 1800 of rotation the galvanic treatment may be continued. If a cell, such as that shown in Figure 2 is in use both in internal and external surfaces of the can body may be treated.

Various arrangements of the treatment cells are possible. A calculation of process parameters, based upon the foregoing design and involving a passivation surface treatment, similar to the known "311 treatment" given to tinplate, suggests that the processing of small cans (202 x 212) is quite feasible.

For example a 40 heat unit with a throughput of 1,000 cans/minute could be constructed to fulfil the following requirements: Time of component on unit 2.4 secs.

Time of surface treatment (235 of cycle) 1.56 secs.

Type of surface treatment "311" 30 coulombs/sq. ft.

Can Size 202 x 212 300 x 408 3/4 Extent of treatment int only int. + ext int only int. + ext Current requirement/ can. (amps) 2.9 5.9 10.5 21.0 Total current requirement (amps) 75 153 273 546 (40 x 235 ) = 26 cans However, Figure 5 shows diagrammatically how a machine 60 having eight cells may be fitted with two sets of four different treatment cells 61, 62, 64. A transfer turret 72 is used to recycle each can from exit star wheel 71 back into the entry star wheel 73 for delivery to the next cell until the four stage treatment is completed. A finished coated can may be detected by an electrical conductivity test to prevent continuous cycling through the apparatus.

Examples of treatments which may be carried out, according to the method of the invention, are tabulated below together with the duration of time in seconds expressed as an order of magnitude: for example 3 seconds in the table means a range of from 1 to 9 seconds.

Example No. Treatment/use Time in Seconds order of magnitude 1 Electrolytic passivation of 3 Tinplate or Blackplate 2 Chromating treatment of Aluminium 10 3 Anodising treatment of Aluminium 3 4 Electrolytic tin stripping of 3 Tinplate 5 Partial tin stripping: A.C. Current 4 of Tinplate 6 Anionic electrocoating Tinplate or 3 Aluminium but not preferred for Blackplate 7 Cationic electrocoating Tinplate 3 or Aluminium It is possible to fill or empty each cell, of the treatment fluid (such as would be used for a can 3" diameter by 3" deep) in about 1/4 second. Therefore the turret of Figures 3 and 4 would rotate at about 10 revolutions per minute when working on a single repair treatment.

The dissolution treatments such as tin stripping or cleaning may be accelerated if desired by applying ultrasonic vibration to the can body. The transducer for such vibration may be situated in the mandrel or in the wall of each cell.

The apparatus of Figures 2 to 5 may also be used to carryout a sequence of repair and metal finishing treatments ds already described and examples of such sequences follow: Example 1 In the production of plain or lacquered drawn and redrawn cans from tinplate, the following steps are used:- ELECTRO < SURFACE ELECTRO CLEANING TREATMENT < COAT Electrocleaning as a separate first stage improves the efficiency and uniformity of treatment of the subsequent stages. The surface treatment chosen could be either the equivalent of the known "311" electrochemical process of passivation or the known "300" chemical immersion process of passivation, the choice depending upon the specific application and the need for electrocoating.

Example 2 In the production of a drawn and wall ironed beverage container, the following steps may be used: ELECTRO ~ ELECTRO ~ SURFACE CLEANING DETINNING TREATMENT (1) ELECTRO + SURFACE COATING TREATMENT (2) In this case, after electrocleaning the tin is stripped from the can by anodic dissolution.

Thereafter the additional surface treatment (1) would be used to replace the tin coating by a film approximately equivalent to that on known steels bearing chromium/chromium oxide layers. The second surface treatment (2) could, if desired be a passivation treatment. The final stage would be electrocoating, with an organic lacquer or the like.

The coating composition used for electrocoating may be a water-dispersed coating composition, such as a partially neutralized acrylic interpolymer and an amine-aldehyde condensation product or polyepoxide or both. Examples of such interpolymers are found listed in the patent issued to Donald P. Hart, U.S. Patent No.3,403,088, and assigned to P.P.G. Industries, Inc.

It will be understood that these protective coatings have high di-electric strength, coat metallic articles completely, have efficient electro-depositing qualities, and result in cured films which are clear, glossy and have attractive appearance and good durability.

The apparatus of the invention may alternatively be used as a means to examine the quality of the electro-chemical treatment or as a separate apparatus for testing coatings applied by conventional means.

Whilst the invention has been described in terms of cans formed from tin plate and aluminium it is not limited thereto, for example the cans may be built up from components made of blackplate or other mild steel sheets. Furthermore the cans may be drawn from an uncoated steel so that the method and apparatus described provide all or part of the can finishing treatment.

WHAT WE CLAIM IS: 1. A method of treating a can body formed from sheet metal, said method including the steps of placing the can body in a cell such that the interior and exterior surfaces of the can body are in close spaced relationship respectively with a mandrel forming part of the cell and with a side wall of the cell, introducing an electrolyte into the cell, directing the electrolyte within the cell selectively between the interior surface of the can body and the mandrel, between the exterior surface of the can body and the side wall of the cell, or both between the interior surface of the can body and the mandrel and between the exterior surface of the can body and the side wall of the cell, and applying a potential difference between the cell and the can body for treating, respectively, the interior surface of the can body, the exterior surface of the can body, or both the interior and the exterior surfaces of the can body.

2. A method as claimed in claim 1 further including the steps of draining the electrolyte from the cell, and thereafter introducing a second electrolyte into the cell and applying a second potential difference between the cell and the can body.

3. A method as claimed in claim 2 wherein the interior and exterior surfaces of the can body are treated sequentially using the two electrolytes.

4. A method as claimed in claim 1 further including the steps of draining the electrolyte from the cell after treatment of the can body, and expelling the can body from the cell by

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. Example 1 In the production of plain or lacquered drawn and redrawn cans from tinplate, the following steps are used:- ELECTRO < SURFACE ELECTRO CLEANING TREATMENT < COAT Electrocleaning as a separate first stage improves the efficiency and uniformity of treatment of the subsequent stages. The surface treatment chosen could be either the equivalent of the known "311" electrochemical process of passivation or the known "300" chemical immersion process of passivation, the choice depending upon the specific application and the need for electrocoating. Example 2 In the production of a drawn and wall ironed beverage container, the following steps may be used: ELECTRO ~ ELECTRO ~ SURFACE CLEANING DETINNING TREATMENT (1) ELECTRO + SURFACE COATING TREATMENT (2) In this case, after electrocleaning the tin is stripped from the can by anodic dissolution. Thereafter the additional surface treatment (1) would be used to replace the tin coating by a film approximately equivalent to that on known steels bearing chromium/chromium oxide layers. The second surface treatment (2) could, if desired be a passivation treatment. The final stage would be electrocoating, with an organic lacquer or the like. The coating composition used for electrocoating may be a water-dispersed coating composition, such as a partially neutralized acrylic interpolymer and an amine-aldehyde condensation product or polyepoxide or both. Examples of such interpolymers are found listed in the patent issued to Donald P. Hart, U.S. Patent No.3,403,088, and assigned to P.P.G. Industries, Inc. It will be understood that these protective coatings have high di-electric strength, coat metallic articles completely, have efficient electro-depositing qualities, and result in cured films which are clear, glossy and have attractive appearance and good durability. The apparatus of the invention may alternatively be used as a means to examine the quality of the electro-chemical treatment or as a separate apparatus for testing coatings applied by conventional means. Whilst the invention has been described in terms of cans formed from tin plate and aluminium it is not limited thereto, for example the cans may be built up from components made of blackplate or other mild steel sheets. Furthermore the cans may be drawn from an uncoated steel so that the method and apparatus described provide all or part of the can finishing treatment. WHAT WE CLAIM IS:

1. A method of treating a can body formed from sheet metal, said method including the steps of placing the can body in a cell such that the interior and exterior surfaces of the can body are in close spaced relationship respectively with a mandrel forming part of the cell and with a side wall of the cell, introducing an electrolyte into the cell, directing the electrolyte within the cell selectively between the interior surface of the can body and the mandrel, between the exterior surface of the can body and the side wall of the cell, or both between the interior surface of the can body and the mandrel and between the exterior surface of the can body and the side wall of the cell, and applying a potential difference between the cell and the can body for treating, respectively, the interior surface of the can body, the exterior surface of the can body, or both the interior and the exterior surfaces of the can body.

compressed air.

5. A method as claimed in claim 4 wherein introduction of the electrolyte into the cell and supply of compressed air to the cell for expelling the can body is effected through the same opening.

6. A method as claimed in any preceding claim wherein the treatment or treatments include anionic treatment of the can body.

7. A method as claimed in any of claims 1 to 5 wherein the treatment or treatments include cationic treatment of the can body.

8. A method as claimed in any of claims 1 to 7 of treating a can body drawn from tinplate, said method including the steps of electrocleaning and repassivation.

9. A method as claimed in claim 8 including the further step of electrocoating the repassivation can body.

10. A method as claimed in any of claims 1 to 7 of treating a can body drawn from tinplate and wall ironed to have a worked side wall, said method including the steps of electrocleaning and electrodetinning.

11. A method as claimed in claim 10 wherein the detinned can body is electroplated with a coating containing chromium.

12. A method as claimed in claim 11 wherein the chromium containing coating is electrocoated with an organic lacquer.

13. A method as claimed in claim 1, including the step of sealing the interior of the body from the cavity defined between the exterior surface of the body and the side wall of the cell, then introducing an electrolyte into the cavity and thereafter applying a potential difference between the cell and the can body to treat the exterior surface of the can body.

14. A method as claimed in claim 13 including the further steps of draining the electrolyte from the cell and thereafter removing the can body from the cell.

15. A method as claimed in claim 14 including the further steps of introducing a second electrolyte into the cell after removal of the first electrolyte and applying a second potential difference between the cell and the can body to give the exterior surface of the can body a second treatment.

16. A method as claimed in any of claims 13 to 15 including the steps of entering an electrolyte between the interior surface of the can body and the mandrel and applying a potential difference between the interior surface of the can body and the mandrel to treat the interior surface of the can body independently of treating the exterior surface.

17. A method as claimed in claim 16 wherein the electrolyte used to treat the interior surface of the can body is also used to treat the exterior surface.

18. A method as claimed in claim 16, wherein the interior and exterior surfaces of the can body are treated simultaneously.

19. A method as claimed in claim 16 or 17 wherein the interior and exterior surfaces of the can body are treated sequentially.

20. Apparatus for treating a can body formed from sheet metal, said apparatus comprising a cell which has a side wall and a mandrel arranged to receive therebetween in close spaced relationship a can body, passage means for introducing an electrolyte into and conducting the electrolyte from the cell, said passage means being adaptable for directing the electrolyte within the cell in use selectively between the interior surface of the can body and the mandrel, between the exterior surface of the can body and the side wall of the cell, or both between the interior surface of the can body and the mandrel and between the exterior surface of the can body and the side wall of the cell, and means for applying a potential difference between the cell and the can whereby to treat respectively, the interior surface of the can body, the exterior surface of the can body, or both the interior and the exterior surfaces of the can body.

21. Apparatus as claimed in claim 20 wherein the passage means comprise first passage means in the mandrel and second passage means in the side wall of the cell, said first and second passage means being arranged selectively to be brought into communication with and to be separated from one another.

22. Apparatus as claimed in claim 21 wherein the first and second passage means are joined by a closable connection passage.

23. Apparatus as claimed in claim 21 or 22 wherein the first and second passage means each has an inlet and an outlet in a bottom wall of the cell.

24. Apparatus as claimed in claim 21 22 and 23 wherein means are provided for directing compresssed air through the first, passage means for expelling the can body from the cell after treatment.

25. Apparatus as claimed in claim 20, further comprising a can body disposed within the cell such that an exterior surface of the body is in close spaced relationship with the side wall of the cell, a sealing arrangement sealing the interior of the body from the cavity formed between the exterior surface and the side wall, means to introduce electrolyte into the space between the side wall of the cell and the exterior surface of the can body, and means to create a potential difference between the body and the side wall.

26. Apparatus as claimed in claim 25 wherein the mandrel is inserted into the can body in close spaced relationship with the interior surface of the can body, and is electrically conductive.

27. Apparatus as claimed in claim 26, wherein an electrode presses the open end of the can body into engagement with a spacer ring arranged to locate the can body m close spaced relationship with the mandrel and the side wall.

28. Apparatus as claimed in claim 26 or 27, having first passage means arranged to pass electrolyte between the exterior surface of the can body and the side wall and second passage means arranged to pass electrolyte between the interior surface of the can body and the mandrel such that the interior and exterior surfaces of the can body may be treated simultaneously or sequentially.

29. Apparatus as claimed in claim 28 wherein the first and second passage means are arranged selectively to be brought into communication with and to be separated from one another.

30. Apparatus according to claim 29 wherein the first and second passage means are joined by a closable connection passage.

31. Apparatus according to claim 29 and 30 wherein the first and second passage means each has an inlet and an outlet in a bottom wall of the cell.

32. Apparatus as claimed in any of claims 25 to 31 wherein the cell is mounted on a rotatable turntable.

33. A method substantially as hereinbefore described with reference to Figure 2 of the accompanying drawings.

34. A method substantially as hereinbefore described with reference to Figures 3 and 4 of the accompanying drawings.

35. A method substantially as hereinbefore described with reference to Figure 5 of the accompanying drawings.

36. Apparatus substantially as hereinbefore described with reference to Figure 2 of the accompanying drawings.

37. Apparatus substantially as hereinbefore described with reference to Figure 3 and 4 of the accompanying drawings.

38. Apparatus substantially as hereinbefore described with reference to Figure 5 of the accompanying drawings.

39. A can made substantially according to the method of any of claims 1 to 19 or claims 33 to 35.

40. A can made by apparatus substantially as claimed in any of claims 30 to 32 or claims 36 to 38.