GB1571808A - Method and apparatus for forming a survace layer on containers - Google Patents

Description

(54) METHOD AND APPARATUS FOR FORMING A SURFACE LAYER ON CONTAINERS (71) We, CLEAMAX LIMITED, a British Company of 35 The Causeway, Potters Bar, Hertfordshire, England, 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 forming a surface layer on the walls of an open-mouthed container, and is a modification of the invention claimed in British Patent No. 1,498,795.

It is common practice to provide a protective coating of varnish, lacquer or resin to containers, and containers made of certain materials have to be provided with a surface layer adapted to promote adhesion of varnish or lacquer. Many aluminium containers, for instance, are made from an alloy containing a proportion of magnesium to provide toughness and other qualities for drawing, but the magnesium content inhibits bonding of varnish or lacquer to the surfaces of the containers.

Such aluminium containers are normally given a chromate treatment after washing to promote adhesion of lacquers. Tin plate or steel containers may be subjected to phosphate treatment.

Aluminium containers may be treated with hot water or water vapour which reacts with the aluminium to form a hydrate having the general formula A12O, nH2O with the liberation of hydrogen. The presence of such a hydrate promotes adhesion of lacquer. The process is best carried out at a temperature greater than 1000C and a pressure greater than that of the atmosphere. This is impossible to achieve in normal washing systems which are open to the atmosphere.

According to the present invention there is provided a method of forming a surface layer on the walls of an open-mouthed container, comprising mounting the container in a cavity in a structure, the cavity having a shape corresponding substantially to that of the container and a size such that the walls of the cavity co-operate with the inside surfaces of the container to form a first chamber and co-operate with the outside surfaces of the container to form a second chamber, and passing through said chambers a fluid which forms a surface layer on the container, the walls of the cavity being spaced so close to the inside and outside surfaces of the container that said fluid flows along the surfaces of the container. The fluid may react chemically with the material from which the container is made, or the fluid may comprise a varnish or other liquid which adheres to the surfaces of the container and then dries or hardens to form a coating thereon.

The method of the invention can conveniently be carried out in a modified construction of the apparatus described and illustrated in British Patent Spedficatioa 1,498,795.

Thus according to the invention there is also provided apparatus for forming a surface layer on the walls of containers of a given size, comprising a pot assembly having a core, a shell surrounding the core, and a lid cooperating with the core and shell to form a cavity for reception of a container, the lid being movable into an open position to permit introduction of a container into the cavity, and the cavity being of a size such that the shell co-operates with the outside surfaces of a container in the cavity to form one chamber and the core co-operates with the inside surfaces of the container to form a second chamber, means for centering a container in the cavity, a reservoir of fluid adapted to form a surface layer on a container in contact with the fluid, and conduit means for passing fluid from said reservoir through said chambers and returning the fluid to the reservoir, the walls of the cavity being spaced so close to the inside and outside surfaces of a container mounted in the cavity by the centering means that fluid passing through the chambers flows along the surfaces of the container.

A modified form of the apparatus described in Specification 1,498,795 which is particularly suitable for treating aluminium containers with a chromate solution in accordance with the method of the invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 is a vertical section through the rotational axis of the machine showing one half of the machine only, and Figure 2 shows in diagrammatical form support equipment required for handling the chromate solution.

The machine described and illustrated in British Patent Specification 1,498,795 is for use in cleaning open-mouthed containers and comprises a plurality of pot assemblies each having a body and a lid defining a cavity for reception of a container, the lid being movable into an open position to permit intro duction of a container into the cavity, means for centering the container in the cavity, the cavity having a shape corresponding approximately to that of the container and a size such that the container subdivides the cavity into two chambers in which the walls of the cavity are spaced close to the inside and outside surfaces of the container, and conduit means for passing cleaning fluid through said chambers so that the cleaning fluid fills the chambers and flows along the inside and outside surfaces of the container. The pot assemblies are supported on a turret rotatably mounted on a frame, the apparatus including drive means operable to rotate the turret so that each pot assembly passes in succession past a container unloading station and container loading station, lid control means operable to move the lid of each pot assembly into an open position immediately prior to passage of the pot assembly past the unloading station and to move the lid into the closed position immediately after passage of the pot assembly past the loading station and valve means for regulating flow of fluids through said conduit means and chambers only during passage of each pot assembly between the loading station and the unloading station.

In the drawings of the present application components corresponding to similar components in specification 1,498,795 are identified by reference numbers consisting of the reference number of the corresponding com- ponent in 1,498,795 with the addition of 200. For example, the base plate is identified by 10 in the drawings of 1,498,795 and 210 in the drawings accompanying the present specification. Reference should therefore be made to specification 1,498,795 for a fuller description of the construction and operation of components in the accompanying drawings.

Referring now to the accompanying drawings, the turret machine comprises a circular base plate 210, an upright spindle 212 secured to the center of the base plate, and a turret 214 rotatably mounted by bearings 215; 216 on the spindle. Figure 1 shows only half of the machine on one side of the vertical axis X-X. The turret comprises a hub 217 on which the bearings are mounted, and a circular top plate 219. A cylinder 225 co-axial with the spindle 212 is secured to the underside of the top plate 219, the lower end portion of the cylinder 225 being formed with teeth 226 which mesh with a pinion 227 rotatable by drive mechanism (not shown) for turning the turret The top plate 219 is fitted with twenty-four pot assemblies 228 (only one of which is shown in the drawings) for reception of the containers to be cleaned, and a manifold ring 229 connected by flexible pipes to the pot assemblies for conveying treating and drying fluids to and from the pot assemblies, as described hereinafter. A plate 232 on the top of the spindle 212 supports a distributor ring 233 for feeding fluid into and away from the manifold ring.

Each pot assembly comprises an upright cylindrical shell 238 closed at the bottom but open at the top thereof, a cylindrical core 242 within the shell and a lid 258 which co-operates with the shell and core to form a cavity 246 for the reception of a container to be treated. The lid is connected through a slipping clutch 287 to a vertical shaft 281 fitted with cam rollers 296, 297 adapted to run in circular cam tracks on the base plate, the cam rollers being operable to raise the shaft and lid of each pot assembly and pivot the shaft to swing the lid to one side of the shell 238 to permit a treated container to be ejected from the pot assembly during passage of the pot assembly past an unloading station during rotation of the turret, and to permit insertion of a container to be treated into the pot assembly during passage of the pot assembly past a loading station. The lid 258 is connected to a sleeve 280 on the shaft 281, the sleeve having teeth 287 adapted in recesses in a further sleeve 282 fixed on the turret only when the lid is aligned with the shell of the pot assembly and in the closed position.

The lid is urged downwards relative to the shaft 280 by a spring 290 against a stop formed by abutment of the co-operating elements of the slipping clutch 287.

The components of the turret machine described above are similar to corresponding components in the machine described and illustrated in Specification No. 1,498,795 and reference may be made to this specification for a fuller explantion of the construction of the pot assemblies and operation of the lids thereof by the cam rollers. The construction and function of the components of the turret machine which differ from those of 1,498,795 will now be described.

The distributor ring 232 is formed in two parts, namely an inner distributor ring 10 and an outer distributor ring 11. The outer ring 11 has a flange 12 which overlaps the outer edge of ring 10, and the two rings are held stationary by three pegs 14 (only one of which is shown) which extend through apertures in the flange 12 and into recesses in the ring 10, the pegs 14 being secured to the stationary plate 232. The two distributor rings 10, 11 are urged into sliding contact with the manifold ring 229 by springs 15, 16 compressed between the rings and the plate 232. The manifold ring 229 rests on resilient spacers 17 on the top plate 219 of the turret and is connected to the top plate 219 for rotation therewith by three locating pegs 18 (only one of which is shown). The resilient spacers 17 avoid distortion of the manifold and distributor rings and minimize heat loss therefrom.

The manifold ring 229 is provided with three ducts 20, 21, 22 for each pot assembly 228, the three ducts 20, 21, 22 being connected by flexible pipes 23, 24, 25 respectively to the associated pot assembly as hereinafter described. The ducts 20, 21, 22 open through the top surface of the ring 229, the ends of the ducts 20, 21, 22 lying respectively in three common circles concentric with the turret axis. The underside of the inner distributor ring 10 is formed with a first pair of arcuate grooves 30, 31 for circulating chromate solution through the pot assemblies a second pair of arcuate grooves 32, 33 for circulating purging air through the pot assemblies, and a third pair of arcuate grooves 34, 35 for extracting air and water vapour from the pot assemblies to create a vacuum therein. The grooves 30, 32, 34 are all arranged in a common circle and adapted to register in succession with each of the ducts 20 upon rotation of the manifold ring 229 with the turret, and the grooves 31, 33, 35 are all arranged in a common circle and adapted to register in succession with each of the ducts 21 upon rotation of the manifold ring with the turret. The underside of the outer distributor ring 11 is formed with three arcuate grooves 37, 38, 39 arranged in a common circle and adapted to register in succession with each of the ducts 22 upon rotation ob the manifold ring with the turret, the groove 37 being connected with a supply of compressed air at a pressure slightly in excess of the treating liquid and purging air pressures, the groove 38 being connected to a supply of compressed air, and the groove 39 being connected to a vacuum. All the arcuate grooves are connected through openings in the top of the distributor rings to pipes for supplying and exhausting the fluids.

The flexible pipes 23, 25 for each pot assembly are connected to ports 45, 46 respectively in the cylinder of a piston valve 47.

The piston 48 of the valve is connected to a stirrup 49 which is mounted on the sleeve 280 of the associated pot assembly so as to permit angular movement of the sleeve relative to the stirrup but prevent relative axial move ment therebetween. The piston 48 is thus raised and lowered whenever the lid is opened and closed respectively. The piston 48 is provided with a duct 50 arranged to connect port 45 and pipe 23 to a duct 51 in the base of the pot assembly whenever the lid 258 is in the closed position, the piston being arranged to block port 45 and uncover port 46 to connect pipe 25 and duct 22 to the duct 51 whenever the lid is in the open position. The duct 51 extends upwards through the core 242 and opens in the cavity 246 in the pot assembly.

Each pot assembly 228 is mounted on a platen 55 which rests on insulating washers 56 on the plate 219 of the turret, the platen being secured to the turret by screws 57.

The platen 55 is provided with electrical heating elements fed with current through wires 58, 59 and slip rings 60, 61 secured concentrically to the turn table by pillars 62 and insulated therefrom by bushes 63. A current is supplied to the rotating slip rings by brush gear 64 secured to the top of the stationary plate 232.

Referring to Figure 2, the turret machine is provided with a tank 70 for holding a supply of a chromate solution, a pump 71 operable to pump liquid from the tank through a pipe 72 to the groove 30 in the inner distributor ring 10, a vacuum pump 73 for extracting air and water vapour through pipes 74 connected to the grooves 34, 35, and a compressor 75 for compressing air from the pump 73 and tank 70 and supplying the air under pressure through pipe 76 to the groove 32 in the inner distributor ring 10. A valve 77, pressure gauge 78 and a filter 79 are fitted in pipe 72.

The tank 70 has an inlet pipe 80 for supply of chromate solution, an overflow pipe 81 for discharge of contaminated liquid, a flowsmoothing chamber 82 and a vapour separator 83 in the head space of the tank, and a cooling coil 85. The flow-smoothing chamber 82 is connected by pipes 86, 87 to the grooves 31, 33 respectively in the inner distributor ring 10 for receiving chromate solution therefrom, the chamber 82 including a plurality of baffles for smoothing the flow of fluid therethrough.

The vapour separator 83 is connected by a pipe 88 to the inlet of compressor 75 and also comprises a plurality of baffles.

The outlet of the vacuum pump 73 is connected by a pipe 95 to the inlet of the compressor 75, and the pump and compressor are driven in synchronism by a common pulley 96 so that air exhausted from the vacuum pump is drawn into the compressor at each stroke for recompression. The outlet pipe 88 of the vapour separator 83, which is also connected to the inlet of the compressor, is provided with a valve 97 for regulating the amount of supplementary air admitted to the compressor, thus regulating the pressure of air delivered through pipe 76. Pipes 74 and 76 are fitted with pressure gauges 98.

As shown in Figure 1, the underside of the inner distributor ring 10 is provided with concentric grooves 100, 101 adjacent the radially inner and radially outer edges respectively of the ring 10. The grooves 100, 101 are connected by pipes (not shown) to the pipe 74 leading to the inlet of the vacuum pump 73, so that any liquid which may leak across the mating surfaces of the distributor and manifold rings from the grooves 3033 will be drawn back into the system and thereby avoid wastage and atmospheric contamination. The grooves 100, 101 have been omitted from Figure 2 in order to show the grooves 30--35 more clearly.

In operation, the tank 70 is filled with a chromate solution, and the solution is pumped from the tank 70 by the pump 71 through the pipe 72 and filter 79 to the groove 30 in the inner distributor ring 10. The pressure of liquid in pipe 72, as shown on gauge 78, is controlled by the valve 77. When a duct 20 in the manifold ring 229 moves into register with the groove 30 upon rotation of the turret, the liquid in the groove 30 flows through duct 20 and pipe 23 to the piston valve 47 of the associated pot assembly. When the lid 258 of the pot assembly is in the dosed position, with the piston 48 in its lowermost position as shown in Figure 1, chromate solution from pipe 23 flows through the duct 50 in piston 48 and through the duct 51 into the cavity 246 in the pot assembly. A container in the pot assembly subdivides the cavity 246 into an inner chamber and an outer chamber, the inner chamber being formed between the inside surface of the container and the core 242 and the outer chamber being formed between the outside surface of the container and the shell 238 together with the lid. The two chambers are of the- minimum practical width, for example 0.005 inches, and should preferably not exceed 0.15 inches, so that the chromate solution completely fills the chambers, displacing any air therein, and flows through the inner chamber and along the inside surface of the container, around the mouth of the container, through the outer chamber and along the outside surface of the container, before passing out of the cavity through pipe 24 to the grove 31 in the inner distributor ring 10. The chromate in the solution reacts with the aluminium of the container to form a surface layer on the walls of the container. The pipe 86 carries the solution from groove 31 to the flow-smoothing chamber 82 from which it is discharged back into the holding tank 70.

Continued rotation of the turret causes the pipes 23, 24 of the pot assembly to be disconnected from grooves 30, 31 and connected with grooves 32 and 33 respectively. This is the station in which the cavity in the pot assembly is purged free of chromate solution by the introduction of air supplied by the compressor 75 which delivers air to the groove 32 via pipe 76. The chromate solution which is expelled from the cavity in the pot assembly is collected in groove 33 and carried by pipe 87 to the flow-smoothing chamber 82 from which it is discharged into the tank 70.

Continued rotation of the turret then causes the pipes 23, 24 to be disconnected from groves 32, 33 and connected with grooves 34, 35 respectively which are at a high vacuum.

The cavity in the pot assembly and all valves, channels and pipe work connected to grooves 34, 35 are then also subjected to vacuum.

Due to the low pressure, residual liquid boils off almost instantaneously from all parts of the system to effect quick drying, and the machine may thus be operated at higher speeds with minimum loss of liquid due to the expellation of residue when the containers are ejected from the chambers.

Upon further rotation of the turret to bring the pot assembly to position B shown in Figure 2 the lid of the pot assembly is lifted and swung clear by the cam rollers 296 and 297. Lifting movement of the lid also raises the piston 48 of the valve 47, as hereinbefore described, and thereby connects the duct 51 to pipe 25. When the duct 22, which is connected to pipe 25, registers with groove 38 compressed air from groove 38 flows into the cavity of the pot assembly and ejects the container therein.

When the pot assembly reaches position A shown in Figure 2 containers to be treated are presented to the pot assembly by a mechanism not shown. The duct 22 is then in register with groove 39 and the vacuum therein causes air to be sucked into the cavity and along the pipe 24. This flow of air causes the container to be sucked down into the cavity prior to closure of the lid. In addition air in the chambers between the container and the walls of the cavity is extracted so as to create a vacuum therein immediately prior to closure of the lid. When the lid closes, the piston valve 47 is again in the down position blocking off pipe 25 and connecting pipe 23 to duct 51 for the start of the next cycle.

Groove 37 is in register with duct 22 throughout the treating of a container and purging of the cavity, and this groove supplies compressed air to pipe 25 at a pressure slightly in excess of the treating liquid and purging air pressures so as to prevent back leakage of treating liquid through piston valve 47 and into the pipe 25. If such leakage did occur treating liquid would be lost to atmosphere when the container was ejected.

It will be appreciated that the purging air is heated adiabatically by the compressor 75 and it is not necessary to provide additional heat to the purging air.

On the vacuum side there is, of course, heat lost by the system on account of vaporisation within the pot assembly. This heat is however replaced by heat supplied by the electric heating coils in the platen 55.

It is an important feature of the turret machine that, in the event of a container being misfed into a pot assembly, the supply of treating liquid to the pot assembly is cut off during the remainder of the cycle, and also the misfed container is ejected before the pot assembly reaches the unloading station B. This ensures firstly that treating liquid is not discharged into the atmosphere through a jammed pot assembly, and secondly that any container which is not treated is separated out from treated containers.

In the event of a container being misfed into a pot assembly, the lid 258 will not be able to swing back to the position above the shell 238 under the influence of cam roller 297. The shaft 281 will turn the slipping clutch 287 and when the shaft is drawn downwards by the cam roller the teeth 287 will not engage with the slots and spring 290 will be compressed. The valve 47 will thus remain in its upper position in which pipe 23 is closed and pipe 25 is open. There will then be no flow of treating liquid through pipe 23 and a check valve 102 in the lid prevents back flow of liquid from grooves 30, 32 and pipe 24.

As soon as duct 22 moves into register with groove 37, compressed air from this groove will flow through pipe 25 and then through the cavity in the pot assembly, thereby ejecting the faultily-fed container before the pot assembly reaches the unloading station B.

During operation of the machine, a metered flow of chromate solution is continuously delivered to the tank 70 through pipe 80. This displaces an equal quantity of liquid through pipe 81. The whole system continually gains heat from the electric heaters in the platen 55, and the temperature of the liquid in tank 70 is maintained at a few degrees below boiling point by the thermostatically-controlled cooling coil 85.

In the operation of the turret machine, the chromate solution in the tank may be maintained at boiling point and the steam generated in the tank used instead of air to purge chromate solution from the pot assemblies.

In the turret machine illustrated in the drawings, the pot assemblies can be used as autoclaves permitting a chemical reaction between a fluid and the material of a container to be carried out at a high pressure and temperature. The machine is thus particularly suitable for use in treating aluminium containers with hot water or water vapour to form a layer of aluminium hydrate on the surfaces of the containers, which process is best carried out at a temperature greater than 100"C and a pressure greater than that of the atmosphere.

It has been proposed in a British Patent 1,323,782 (Aluminium Swiss S.A.) to form a surface layer of aluminium hydrate in which said surface is exposed to a gaseous mixture obtained by heating water, an organic solvent the boiling point of which is greater than 100"C at atmospheric pressure and which can form an azeotropic mixture with water, and ammonia on a volatile amine; the proportion by weight of water in said gaseous mixture being less than the proportion by weight of water in an azeotropic mixture of said solvent and water.

This is said to require an exposure time of 15 to 30 seconds at atmospheric pressure when carried out according to 1,323,782. If, however, the turret machine as described above is used for this process, temperatures and pressures can be increased and exposure time reduced to speed up the production rate of the machine. Moreover, the turret machine of the present invention can be used to form a surface layer of aluminium hydrate on aluminium containers by a process similar to that of Patent 1,323,782 but using an organic solvent having a boiling point less than 100"C at atmospheric pressure.

The turret machine illustrated in the drawings could also be used to apply to the surfaces of a container a liquid which adheres to the surfaces and then dries or hardens to form a coating. For example, a base coat of vinyl or other resin may be applied to the surfaces of containers in the machine by pumping a dilute resin emulsion or solution through rhe machine, purging the cavities with air or steam and ejecting the containers for subsequent drying. A varnish or lacquer may similarly be applied to the surfaces of a container. If the liquid is noc toxic, or if the liquid was applied at a temperature and pressure well below that at which there was any serious risk to health due to vaporisation, the purging and evacuating sequences could be omitted and the containers ejected in a wet condition.

The turret machine illustrated in the drawings is also the subject of our co-pending application No. 52126/76 Serial No. 157,180.

WHAT WE CLAIM IS: 1. A method of forming a surface layer on the walls of an open-mouthed container, comprising mounting the container in a cavity in a structure, the cavity having a shape corresponding substantially to that of the container and a size such that the walls of the cavity co-operate with the inside surfaces of the container to form a first chamber and cooperate with the outside surfaces of the container to form a second chamber, and passing through said chambers a fluid which forms a surface layer on the container, the walls of the cavity being spaced so close to the inside and outside surfaces of the container that said fluid flows along the surfaces. of the container.

2. A method as claimed in claim 1 in which

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

Claims (11)

**WARNING** start of CLMS field may overlap end of DESC **. within the pot assembly. This heat is however replaced by heat supplied by the electric heating coils in the platen 55. It is an important feature of the turret machine that, in the event of a container being misfed into a pot assembly, the supply of treating liquid to the pot assembly is cut off during the remainder of the cycle, and also the misfed container is ejected before the pot assembly reaches the unloading station B. This ensures firstly that treating liquid is not discharged into the atmosphere through a jammed pot assembly, and secondly that any container which is not treated is separated out from treated containers. In the event of a container being misfed into a pot assembly, the lid 258 will not be able to swing back to the position above the shell 238 under the influence of cam roller 297. The shaft 281 will turn the slipping clutch 287 and when the shaft is drawn downwards by the cam roller the teeth 287 will not engage with the slots and spring 290 will be compressed. The valve 47 will thus remain in its upper position in which pipe 23 is closed and pipe 25 is open. There will then be no flow of treating liquid through pipe 23 and a check valve 102 in the lid prevents back flow of liquid from grooves 30, 32 and pipe 24. As soon as duct 22 moves into register with groove 37, compressed air from this groove will flow through pipe 25 and then through the cavity in the pot assembly, thereby ejecting the faultily-fed container before the pot assembly reaches the unloading station B. During operation of the machine, a metered flow of chromate solution is continuously delivered to the tank 70 through pipe 80. This displaces an equal quantity of liquid through pipe 81. The whole system continually gains heat from the electric heaters in the platen 55, and the temperature of the liquid in tank 70 is maintained at a few degrees below boiling point by the thermostatically-controlled cooling coil 85. In the operation of the turret machine, the chromate solution in the tank may be maintained at boiling point and the steam generated in the tank used instead of air to purge chromate solution from the pot assemblies. In the turret machine illustrated in the drawings, the pot assemblies can be used as autoclaves permitting a chemical reaction between a fluid and the material of a container to be carried out at a high pressure and temperature. The machine is thus particularly suitable for use in treating aluminium containers with hot water or water vapour to form a layer of aluminium hydrate on the surfaces of the containers, which process is best carried out at a temperature greater than 100"C and a pressure greater than that of the atmosphere. It has been proposed in a British Patent 1,323,782 (Aluminium Swiss S.A.) to form a surface layer of aluminium hydrate in which said surface is exposed to a gaseous mixture obtained by heating water, an organic solvent the boiling point of which is greater than 100"C at atmospheric pressure and which can form an azeotropic mixture with water, and ammonia on a volatile amine; the proportion by weight of water in said gaseous mixture being less than the proportion by weight of water in an azeotropic mixture of said solvent and water. This is said to require an exposure time of 15 to 30 seconds at atmospheric pressure when carried out according to 1,323,782. If, however, the turret machine as described above is used for this process, temperatures and pressures can be increased and exposure time reduced to speed up the production rate of the machine. Moreover, the turret machine of the present invention can be used to form a surface layer of aluminium hydrate on aluminium containers by a process similar to that of Patent 1,323,782 but using an organic solvent having a boiling point less than 100"C at atmospheric pressure. The turret machine illustrated in the drawings could also be used to apply to the surfaces of a container a liquid which adheres to the surfaces and then dries or hardens to form a coating. For example, a base coat of vinyl or other resin may be applied to the surfaces of containers in the machine by pumping a dilute resin emulsion or solution through rhe machine, purging the cavities with air or steam and ejecting the containers for subsequent drying. A varnish or lacquer may similarly be applied to the surfaces of a container. If the liquid is noc toxic, or if the liquid was applied at a temperature and pressure well below that at which there was any serious risk to health due to vaporisation, the purging and evacuating sequences could be omitted and the containers ejected in a wet condition. The turret machine illustrated in the drawings is also the subject of our co-pending application No. 52126/76 Serial No. 157,180. WHAT WE CLAIM IS:

1. A method of forming a surface layer on the walls of an open-mouthed container, comprising mounting the container in a cavity in a structure, the cavity having a shape corresponding substantially to that of the container and a size such that the walls of the cavity co-operate with the inside surfaces of the container to form a first chamber and cooperate with the outside surfaces of the container to form a second chamber, and passing through said chambers a fluid which forms a surface layer on the container, the walls of the cavity being spaced so close to the inside and outside surfaces of the container that said fluid flows along the surfaces. of the container.

2. A method as claimed in claim 1 in which

the fluid reacts chemically with the material of the container.

3. A method as claimed in claim 2 in which the container is made of an aluminium alloy containing magnesium, and the fluid comprises a chromate solution which reacts with the metal of the container to provide a coating en the container which promotes adhesion of lacquers thereto.

4. A method as claimed in claim 2 in which the container is made of tin plate or steel and the fluid comprises a phosphate solution.

5. A method as claimed in claim 2 in which the container is made of a metal which includes aluminium, and the fluid comprises hot water or water vapour which reacts with the aluminium to form a hydrate having the general formula A1203 nH2O.

6. A method as claimed in claim 5 wherein the hot water or water vapour is at a temperature greater than 100 C and a pressure greater than that of the atmosphere.

7. A method as claimed in claim 1 in which the fluid comprises a dilute resin emulsion or solution which applies a coat of vinyl or other resin to the surfaces of the container.

8. A method as claimed in claim 1 in which the fluid comprises a varnish or other liquid which adheres to the surfaces of the container and then dries or hardens to form a coating thereon.

9. A method as claimed in any of the preceding claims in which the fluid is circulated around a closed circuit.

10. Apparatus for forming a surface layer on the walls of containers of a given size, comprising a pot assembly having a core, a shell surrounding the core, and a lid cooperating with the core and shell to form a cavity for reception of a container, the lid being movable into an open position to permit introduction of a container into the cavity, and the cavity being of a size such that the shell co-operates with the outside surfaces of a container in the cavity to form one chamber and the core co-operates with the inside surfaces of the container to form a second chamber, means for centering a container in the cavity, a reservoir of fluid adapted to form! a surface layer on a container in contact with the fluid, and conduit means for passing fluid from said reservoir through said chambers and returning the fluid to the reservoir, the walls of the cavity being spaced so close to the inside and outside surfaces of a container mounted in the cavity by the centering means that fluid passing through the chambers flows along the surfaces of the container.

11. Apparatus for forming a surface layer on the walls of open-mouthed containers of a given size, said apparatus comprising a frame, a turret rotatably mounted on said frame, a plurality of pot assemblies supported on the turret, each pot assembly having a core, a shell, and a lid co-operating with said core and shell to define a cavity for reception of one d said containers, means for centering a container in the cavity, the cavity having a shape corresponding approximately to that of the containers and a size such that a container therein subdivides the cavity into two chambers in which the walls of the cavity are spaced close to the inside and outside surfaces of the container, a reservoir for storing a treating fluid adapted to form a surface layer on a container in contact with the fluid, conduit means for passing treating fluid from said reservoir through said chambers, so that the fluid fills the chambers and flows along the inside and outside surfaces of the container, drive means operable to rotate the turret so that each pot assembly passes in succession past a container unloading station and a container loading station, lid control means operable to move the lid of each pot assembly into an open position immediately prior to passage of the pot assembly past said unloading station to permit ejection of a treated container at said unloading station and introduction of a container to be treated into the cavity of the pot assembly at said loading station, said lid control means also being operable to move the lid of each pot assembly into a closed position immediately after passage of the pot assembly past said loading station, and valve means operable should a container fail to feed properly into the cavity of a pot assembly to cut off the flow oE treating fluid and apply compressed air to eject the faultily-fed container before it reaches the unloading station.