EP3659723A1

EP3659723A1 - Method and device for manufacturing a metal can

Info

Publication number: EP3659723A1
Application number: EP18209281.7A
Authority: EP
Inventors: Frederik Jonker; Franciscus Petrus Johannus WEEL
Original assignee: Tata Steel Ijmuiden BV
Current assignee: Tata Steel Ijmuiden BV
Priority date: 2018-11-29
Filing date: 2018-11-29
Publication date: 2020-06-03

Abstract

The invention relates to a method of manufacturing a metal can comprising the steps of:
- providing a metal sheet,
- cutting a blank from the metal sheet,
- drawing the blank into a cup,
- redrawing the cup
- and wall ironing the cup into a can,
wherein the can is cooled by spraying a cooling medium against the exterior of the can after the step of redrawing.

Description

Field of the invention

The invention relates to a method for the manufacturing of a metal can, more in particular a method of forming a steel can from a steel sheet, as well as to a device used in the manufacturing of the metal can.

Background of the invention

In can making sheet metal is formed into finished cans in which the important steps for two-piece cans are cutting a blank from the steel sheet, deep drawing of the blank into a cup and redraw and wall ironing of the cup into a can with a predefined wall thickness. After the wall ironing step further steps may include the trimming, bottom forming, flanging, beading of the can and finally putting a closure on the can.
There are many important factors in the can making process, which include the type of material that is used, the thickness of the material, the work hardening exponent, the blank size, the draw ratio, the draw radius, the draw speed, the reduction of the wall thickness, the lubricant, the temperature, to name the more important factors.
Most of the process of forming a can is typically done with two separate devices, respectively the "cupper" and the "bodymaker". With the cupper a blank is cut from the metal sheet the shape of which is dependent on what the final shape of the can should be. Most cans are of a circular cross-section for which a round disc is cut from the metal sheet. Subsequently, the blank is subjected in the cupper to a deep drawing step wherein a cup is formed with a diameter of the bottom part larger than that of the final can to be formed as well as with a height of the wall far less than that of the final can.
In the bodymaker further forming steps are carried out starting with a redraw step wherein the cup is subjected to a second deep drawing step, the re-draw step, wherein the diameter of the bottom part is reduced and the height of the wall increased. Immediately after the re-draw step the cup is subjected to one or more wall ironing steps in which the thickness of the wall is reduced therewith increasing the height of the wall. Typically a number of successive wall ironing steps are carried out to realise a wall height slightly larger than the height of the final can. The total number of wall ironing steps depend on the type of can that is made which for example could be a can from uncoated steel such as tin plated steel, electrolytic chromium coated steel (ECCS), or a can from a steel provided with a polymer coating.
In the process of drawing, redrawing and wall ironing a lot of heat is generated and to prevent damage to the metal can cooling media are used, which includes a cooling medium to cool the bodymaker or parts thereof or a cooling medium to cool both the bodymaker or parts thereof and the metal cans. Where the cooling medium is also used to cool the metal cans the cooling medium is an emulsion of a lubricant and a cooling medium such as an oil in water emulsion.
With polymer coated metal cans also a so called "dry" method is used wherein a lubricant (approved for human consumption) is applied to the metal can, for instance a wax, without using an emulsion as cooling medium for the metal can itself. In this case only a cooling medium is used to cool the bodymaker or parts thereof wherein the cooling medium is guided through the bodymaker or parts thereof without getting in touch with the metal cans. This is the method of choice for food-cans which have to comply with strict requirements. The use of oil in water emulsions should preferably be avoided for food-cans because of the otherwise necessary extensive cleaning process to remove the emulsion from the can.
All these methods have their drawback. Cooling the bodymaker and the cans with an oil in water emulsion as cooling medium means that the cans have to be cleaned and that a considerable amount of the used emulsion has to be processed into its constituent parts to allow discharge thereof.
The dry method does not have the drawback of having to process large amounts of used emulsions, but because of the limited cooling of the can the number of cans that can be manufactured per unit of time is below that of the other methods wherein the can is directly cooled in a bath of an oil in water emulsion. With increased speed the polymer coating gets damaged (scuffed) or may even partially peel off which inevitably means rejection of the cans.

Objectives of the invention

It is an objective of the present invention to provide a method of manufacturing a metal can wherein sufficient cooling is realised for polymer coated and other metal cans.
It is an objective of the present invention to provide a method of manufacturing a metal can wherein less cooling medium is used.
It is an objective of the present invention to provide a method of manufacturing a metal can wherein the polymer coated cans do not get damaged.
It is an objective of the present invention to provide a method of manufacturing a metal can wherein the number of polymer coated cans manufactured per unit of time can be increased.
It is an objective of the present invention to provide a device for carrying out the method of manufacturing a metal can using less cooling medium.

Description of the invention

The invention relates to a method of forming a metal can as defined in claims 1 - 10 and a device for carrying out the method as defined in claims 11 - 16.
One or more of the objectives of the invention are realised by providing a method of manufacturing a metal can comprising the steps of:

providing a metal sheet,
cutting a blank from the metal sheet,
drawing the blank into a cup,
redrawing the cup
and wall ironing the cup into a can,

The limitation of the dry method of can making is the number of polymer coated cans per unit of time that can be made. Although applying waxes as a lubricant helps to realise a certain number of cans per minute, this however is limited as compared to the number of cans that can be realised with the normally used cooling with water based emulsions as cooling medium. In order to increase the number of polymer coated cans per minute further cooling of the can is necessary.
Applying the method according the invention with polymer coated cans in a first experimental set-up allowed to increase the number of cans per minute with 20% without that any damage like scuffing occurred. With the polymer coated cans water is used as cooling medium which is an effective cooling medium and does not have the drawbacks of using a water based emulsion.
Alternatively the method can also be applied in other can making processes where water based emulsions are used as cooling medium and lubricant. This is not limited to the wet method used for polymer coated cans but can also be used for all other can making processes wherein normally large volumes of water based emulsions are used, typically oil in water emulsions. Instead of using large volumes of water based emulsions, the water based emulsion is sprayed against the outside of the can. This means a large reduction of the volume of water based emulsion necessary for the cooling and lubrication process and therewith considerably less of the emulsion that has to be processed afterwards.
Spraying the cooling medium against a can is done after the step of redrawing which either means that it is done directly after the redrawing step before the first wall ironing step and/or further downstream in the bodymaker. Where the tools of the redrawing step and the first wall ironing step are closely spaced it might not be well possible to effectively spray the cooling medium against the can. If so, spraying of the cooling medium against the can has to be done after the first wall ironing step and for subsequent wall ironing steps. Accordingly it is provided that wherein wall ironing of the cup is carried out in two or more steps the can is cooled at least in between two successive wall ironing steps.
In the description the term "can" is used for all stages in the process even where the can is still a "cup".
According to a further aspect of the invention the cooling medium is applied as a mist of cooling medium against the can. It was found that spraying a cooling medium as a mist against the outside of a can provides a very effective cooling.
It is further provided that the cooling medium is applied as a mist from at least two points around the circumference of the can. The right number of nozzles positioned around the path of the can depends on the diameter of the can and the distance of the nozzles to the can and should be chosen such that the cooling medium is applied against a can along most or all of the circumference of the can. This can easily be established by a number of routine trials.
In order to limit the amount of cooling medium as much as possible, which especially goes when the method is used to replace the cooling with a water based emulsion used for other can making methods than the dry method for polymer coated cans, it is provided that the cooling medium is sprayed no longer than a can is within the range of the cooling medium. This means within the range of the nozzles located between redraw and first wall ironing step and/or between at least two successive wall ironing steps. The nozzles could be arranged such that cooling medium over the whole area between redraw and first wall ironing step and/or between at least two successive wall ironing steps can be applied against the can. With successive groups of nozzles along the path of the can through the bodymaker this could be effected by switching on and switching off successive groups of nozzles depending on the position of the can with respect of each group of nozzles.
According to a further aspect further cooling is provided by cooling redraw tool and/or at least one ironing tool. This is an important part of cooling a can in the bodymaker process since within these tools a considerable amount of heat is generated in a can.
By spraying the cooling medium as a mist against the can the volume of cooling medium used is limited, part of which will evaporate on the can, as a result of which only little cooling medium will be adhered to the can after passing the last wall ironing step. In order to remove the remainder of the cooling medium on the can it is provided that the cans are passed along an air dryer and/or air knife to dry and/or remove the last of the cooling medium from the can. This is a large advantage with respect of cooling methods with large volumes of cooling medium wherein the cans have to be dried in an oven.
According to a further aspect of the invention a device is provided with a redraw tool and at least one wall ironing tool, wherein a cooling tool is provided after the redraw tool and/or after the at least one wall ironing tool wherein the cooling tool is provided with nozzles and connected to a cooling medium pressure system to spray the cooling medium on the metal can. Typically the pressure system and the nozzles are designed to spray the cooling medium as a mist on a metal can processed in the device.
In most cases the device is provided with two or more wall ironing tools in which case a cooling tool is provided at least in between two successive wall ironing tools. Since a can has to completely pass a wall ironing tool before entering the next wall ironing tool there is effectively enough space to provide a cooling tool between the wall ironing tools. Moreover, enough space to apply a sufficient amount of cooling medium to effectively cool a can between the wall ironing tools.
According to a further aspect the cooling tool comprises a channel connected to the cooling medium pressure system and provided with a plurality of nozzles wherein the channel is positioned around the path of a can through the device and wherein the nozzles are directed at a can passing through the device.
It is further provided that the channel is annular shaped. The channel is positioned coaxial with the redraw and wall ironing tools in order to have the same distance between each nozzle and a can processed in the device. Instead of a single channel, multiple channels can be provided for a better cooling of the can along the whole path between the wall ironing tools and/or redraw and wall ironing tool.
The redraw tool and at least one wall ironing tool are connected to a cooling system to supply a cooling medium for the internal cooling of these tools.
According to a further aspect an air dryer and/or air knife is provided following the exit of the device to dry and/or remove cooling medium from the can.

Brief description of the drawings

The invention will be further explained on basis of the example shown in the drawing, in which a cross section of a device with redraw and wall ironing tools is shown.

Detailed description of the drawings

The drawing shows a device 1 with a redraw tool 2, a first and second wall ironing tool 3,4 and a cooling tool 18. Redraw tool 2 comprises a redraw tool body 5 with a redraw ring 6, an inlet 7 for a cooling medium to cool the redraw ring 6 and the redraw tool body 5. The redraw tool body 5 has an internal channel for the cooling medium and an outlet for the cooling medium, both not shown in the drawing.
The first wall ironing tool 3 comprises a wall ironing body 9 with a wall ironing ring 10, a ring seat 11 for the wall ironing ring 10, a retaining element 8 to retain the ironing ring 10 in ring seat 11, an internal channel 12 for a cooling medium to cool the wall ironing ring 10 and wall ironing body 9. The retaining element 8 has also a function as spacer sleeve between the first wall ironing tool 3 and the redraw tool 2. The wall ironing tool 3 is further provided with an inlet and an outlet for the cooling medium, both not shown in the drawing.
The second wall ironing tool 4 is provided at the end of device 1 opposite of the end with redraw tool 2 and comprises a wall ironing body 13 with a wall ironing ring 14, a ring seat 15 for the wall ironing ring 14, a retaining element 17 to retain the wall ironing ring 14 in the ring seat 15, an internal channel 16 for a cooling medium to cool the wall ironing ring 14 and wall ironing body 13. The retaining element 17 has also a function of spacer sleeve between the second wall ironing tool 4 and the cooling tool 18. The wall ironing tool 4 is further provided with an inlet and an outlet for the cooling medium, both not shown in the drawing.
The cooling tool 18 is provided between the first and second wall ironing tool 3,4. Between the first and second wall ironing tool 3,4 sufficient space is available since the can 23 has to pass first wall ironing ring 10 before entering second wall ironing ring 14.
The cooling tool 18 has a cooling tool body 19 provided with a channel 20 for a cooling medium, a number of nozzles 21 provided on the inside of cooling tool body 19, connected to the channel 20 and directed at the path passed by a can being processed in device 1. The number of nozzles 21 is chosen to provide optimal cooling with as little use of cooling medium as possible. The cooling tool is further provided with an inlet 22 and an outlet 24 for the cooling medium.
The nozzles 21 are distributed along the inner circumference of cooling tool body 19 and are positioned close to the first wall ironing body 3 to cool the can 23 as soon as possible after passing redraw tool 2.
Inside the cooling tool 18 shown in the drawing there is enough space for another set of nozzles at a distance from the set of nozzles 21. Such a further set of nozzles could be useful to lower the temperature of the can even further before entering the second wall ironing tool 4. Another reason to use a further set of nozzles is dependent on whether or not a better ratio between the needed amount of cooling medium and the lowering of the temperature can be realised.
Although the space between redraw tool 2 and the first wall ironing tool 3 is limited it is possible to have another cooling tool between redraw tool 2 and the first wall ironing tool 3. Therewith the temperature of a can processed in device 1 could be controlled even better.
With the cooling of polymer coated cans the cooling medium is preferably water which is sprayed as a mist against the passing cans. A cooling medium which is sprayed as a mist provides very good cooling results.
Instead of water also other cooling media could be used. Cans that are normally cooled with a large volume of water based emulsion could also be cooled with device 1 wherein the cooling medium used is a water based emulsion that is sprayed as a mist against the cans.

Claims

Method of manufacturing a metal can comprising the steps of:
- providing a metal sheet,

- cutting a blank from the metal sheet,

- drawing the blank into a cup,

- redrawing the cup

- and wall ironing the cup into a can,
characterised in that the can is cooled by spraying a cooling medium against the exterior of the can after the step of redrawing.
Method according to claim 1, wherein the can is a polymer coated can.
Method according to claim 1 or 2, wherein wall ironing of the cup is carried out in two or more steps the can is cooled at least in between two successive wall ironing steps.
Method according to any of the previous claims, wherein the cooling medium is applied as a mist of cooling medium against the can.
Method according to any of the previous claims, wherein the cooling medium is applied as a mist from at least two points around the circumference of the can.
Method according to any of the previous claims, wherein the cooling medium is applied no longer than a can is within the range of the sprayed cooling medium.
Method according to any of the previous claims, wherein the cooling medium is water.
Method according to any of claims 1-6, wherein the cooling medium is an oil in water emulsion.
Method according to any of the previous claims, wherein further cooling is provided by cooling redraw tool and/or at least one ironing tool.
Method according to any of the previous claims, wherein the cans are passed along an air dryer and/or air knife to dry and/or remove cooling medium remained on the can.
Device for redrawing and wall ironing a metal can wherein the device is provided with a redraw tool and at least one wall ironing tool, characterised in that a cooling tool is provided after the redraw tool and/or after the at least one wall ironing tool wherein the cooling tool is provided with nozzles and connected to a cooling medium pressure system to spray the cooling medium as a mist on the metal can.
Device for redrawing and wall ironing according to claim 12 wherein the device is provided with two or more wall ironing tools and wherein a cooling tool is provided at least in between two successive wall ironing tools.
Device according to claim 11 or 12, wherein the cooling tool comprises a channel connected to the cooling medium pressure system and provided with a plurality of nozzles wherein the channel is positioned around the path of a can through the device and wherein the nozzles are directed at a can passing through the device.
Device according to claim 13, wherein the channel is annular shaped.
Device according to any of claims 11-14, wherein the redraw tool and at least one wall ironing tool are connected to a cooling system to supply a cooling medium for the internal cooling of these tools.
Device according to any of claims 11-15, wherein an air dryer and/or air knife is provided following the exit of the device to dry and/or remove cooling medium from the can.