Abstract:
A method and apparatus for making a can, such as a paint can, includes the steps of: i. providing a cylindrical body; ii. arranging a piston in a first opening of the cylindrical body for defining the diameter of the opening; and iii. curling a free end of the first opening radially outwardly and axially along the cylindrical body thereby forming a curl.

Description:
BACKGROUND OF THE INVENTION 
     1) Field of the Invention 
     The present invention relates to a method for making a can such as a paint can, to an apparatus for making a can and to such can and can body. 
     2) Prior Art 
     Cans such as paint can, are generally provided with ring which is adhered to the can body such as by seaming, welding or gluing. This ring has an opening with a diameter which is selected such that a lid for such can will be accommodated in the ring opening with a well defined clamping force. This clamping force is selected such that under normal handling conditions the lid will stay on the can and the can content not spoiled. At the same time the clamping force is such that the user is able to remove the lid from the can without application of excessive force and without damaging the can, particularly when a tool such as a screw driver, is used for removing the lid. These characteristics for the lid generally require that the ring is made in a separate process and apparatus such that the delicate form and shape can be maintained and controlled independently from the process and apparatus for making the can body. Ultimately, the separate ring is adhered to the can body thereby forming the can. 
     Obviously, the separate production of such rings from a sheet of metal results in a relatively large amount of spoiled material formed when cutting out the central area thereby forming the ring opening. In addition, an additional operational step is required for adhering the ring to the can body. 
     When under circumstances the clamping of the lid on the can body by the ring cannot be guaranteed then an separate clamping band or strip is to applied to the upper area of the can in order to generate additional clamping force. The use of such clamping band or strip is costs increasing and after its removal the clamping force is no longer optimal. 
     The present invention has for its object to provide a can which substantially overcomes the above mentioned drawbacks and still a lid can be applied to the can body and maintained with adequate clamping force without the need of a separate adhered ring and/or clamping band or strip. At the same time the lid can be removed by the user in the usual manner without exerting excessive force. 
     SUMMARY OF THE INVENTION 
     In order to solve this problem the invention provided according to a first aspect of the invention a method for making can, such as a paint can, comprising the steps of:
         i. providing a cylindrical body;   ii. arranging piston means in a first opening of the cylindrical body for defining the diameter of the opening;   iii. curling a free end of the first opening radially outwardly and axially along the cylindrical body thereby forming a curl, such that the defined diameter of the first opening is substantially circumferentially, dimensionally stable.       

     These method of the present invention is able to avoid the use of a separate clamping ring because the opening of the can body into which the lid is to be accommodated with the required clamping force has a sufficient radial strength and circumferential dimensional stability because of the formed curl and the presence in the opening of piston means dictating and maintaining the defined diameter during the formation of the can body. The curl is radially outwardly curled so that the form stability is maintained and substantial variation in contour and wall thickness is avoided. 
     An advantage of the can body provided with such integral outwardly curled clamping curl is that the inner surface is smooth and continuous so that content of the can is able to be released without any material remaining in inner grooves or slots at the connection between the can body and the ring. 
     According to a preferred embodiment, is the free end of the first opening of the can body is provided with a precurl prior to the formation of the curl in step iii). Accordingly, the edge of the cylindrical body which is often a sharp cutting edge is protected and hardly exposed thereby avoiding possible corrosion problems. 
     As stated above, it is required that the curl is formed radially outwardly and axially along the cylindrical body. This implies that the outer diameter of the curl is larger than the outer diameter of the cylindrical body and the ultimate can body. 
     When it is preferred that the curl is not to extend to a major extent beyond the can body or preferably lies within the confinement of the can body and thus have an outer diameter which is equal or less than the outer diameter of the can body then the curl is to be formed in a portion of the can body having a smaller diameter. Such can body portion with a reduced diameter cannot be formed by necking that portion of the can body because when necking the circumferential dimensional stability and wall thickness cannot sufficiently controlled. Still this objective can be met when according to a preferred embodiment of the invention the cylindrical body is partly radially stretched up to the first free end, such that the curl is formed in an unstretched necked portion of the otherwise stretched cylindrical body, and preferably the curl lies within the outer imaginary envelope of the radially stretched cylindrical body part. Thus, the necked portion of the cylindrical body is formed by increasing the diameter of the other part of the cylindrical body and thus not manipulating the free end of the opening which has due the presence of the piston means the desired defined diameter and remains free end untouched. 
     The formation of the radially stretched cylindrical body can be accomplished by any suitable technique such as rolling, stretching, (deep) drawing and ironing. Preferred is formation by radially outward stretching because this results in a stretched can body which is having a substantially constant wall thickness and allows stretching up to 20 to 25% providing additional material savings. Such stretching operation is for instance disclosed in WO2009/130034. In order to have this stretching operation be carried out in a controlled and elegant manner, it is preferred that a second opening of the cylindrical body is provided with a tromped mouth and the radially stretching is carried out with the stretching means via the tromped mouth up to, but not inclusive, the free end of the second opening. In doing so, the stretching means may be provided piston means required for defining and maintaining the defined diameter of the opening, and extending into this free end. 
     When the dimensions of the tromped mouth are such that the tromping angle with the cylindrical body lies within the range of 5° and 40°, such as between 10° and 30° then the tromped mouth and the precurl can be formed in one and the same operation and thus in the same apparatus unit or station. For reasons, that the axial force for forming the curl at one end of the cylindrical body is less than the axial force required for forming the tromped mouth at the other free end. However, dependent on the type of metal of the cylindrical body, its wall thickness, and the form of the tromping tool it is also possible to first form the tromped mouth and subsequently, the precurl. Under circumstances both the tromped mouth and the precurl may be formed substantially at the same time. 
     In order to radially stretch the cylindrical body in a controlled and reliable manner it is preferred that the cylindrical body is firmly held by clamping means. Thereto the cylindrical body is to be provided with a clamping flange. Thus, according to a preferred embodiment of the invention, prior to the radially stretching of the cylindrical body, the free end of the second opening is provided with a clamping flange for clamping with clamping means the cylindrical body during radially stretching. 
     This stretching while being clamped will not result in the formation of wavy structures in the cylindrical body, which are the result of axial resistance to the stretching, when the first opening of the cylindrical body which is remote of the tromped mouth is not supported. This can be accomplished by maintaining the distance between an apparatus support on which the cylindrical body rests and the support of the clamping means because the radial stretching will result in a reduction in length of the cylindrical body. The cylindrical body will be lifted, when suspended and clamped by the clamping means. 
     If it is preferred that the filled and closed can is easily handled and carried, particularly for cans with larger volumes then according to the invention handle means may be encaged in the curl during the curl formation. Such handle means may have the form of flexible strips or bands made from plastic or metal. They are elegantly incorporated in the curl during the curl formation. An additional advantage is that these handle means do not substantially extend beyond the confinement of the can and are thus easy to handle and stacked and stored at small surface areas. 
     The circumferential dimensional stability of the curled opening of the can which is obtained by the use of the diameter determining piston means lodged in the opening during the can making, is substantially equal for all diameters of the can. As an example the dimensional stability for can diameters of 32 mm to 300 mm, such as 48 mm to 286 mm, in particular 57 mm to 165 mm has a margin of error of ±0.10 mm or less. Preferably the margin of error for the dimensional stability is ±0.05 mm, and more preferably ±0.03 mm. This dimensional stability with such margin of error is such that for can with these diameters the clamping force is sufficient for a reliable fixation of the lid on the can without the need of a clamping ring and/or clamping band or strip. 
     Another aspect of the invention relates to apparatus for making the can according to the invention. This apparatus comprising piston means to be arranged in a first opening of a cylindrical body for maintaining the defined diameter of the opening substantially dimensionally stable, and curling means for forming a curl by radially outwardly and axially along the cylindrical body curling the free end of the first opening. In a practical embodiment comprises the apparatus a unit for arranging piston means in the opening and curling means for forming the curl. 
     For increasing the strength of the free end of the first opening and for avoiding exposure of the often sharp free end, it is preferred that the apparatus comprises means for precurling the free end of the first opening prior to the formation of the curl. 
     In order to arrange the curled free end in a necked portion of the can it is preferred according to the invention that another part of the can is radially stretched. Thereto it is preferred that the apparatus comprises stretching means for radially stretching the cylindrical body up to a first free end of the first opening, and preferably piston means are incorporated in the stretching means. 
     The radial stretching is elegantly controlled if preferably the apparatus comprises means for tromping a second opening of the cylindrical body. 
     The radial force for forming the tromping the second opening may be larger, smaller or equal to the radial force for forming the precurl so that one is made after the other or substantially at the same time. According to the invention the tromping means and the means for forming the precurl may be arranged in the same unit of the apparatus, thereby reducing the number of units and the time for making the can. 
     In order to properly control the radial stretching of the cylindrical body at the preferably tromped mouth it is recommended the provide the free end with a clamping flange. Thereto, the apparatus of the invention preferably comprises means for forming a clamping flange on the free end of the second opening, and means for clamping the cylindrical body during radially stretching. Such radial stretching can then be carried out with the remote opening of the cylindrical body not support, so that a counter axial force is substantially avoided. This results in an improved uniformity of the body wall thickness. It is preferred according to the invention that the means for forming the clamping flange and the means for forming the curl are incorporated in the same apparatus unit. 
     It is also preferred that the apparatus according to the invention comprises means for encaging handle means in the curl. 
     Finally, a third aspect of the invention relates to a can and a can body therefore. The can may be a paint can or food can, and is obtainable by the method of the invention as described above. This can having a clamped lid, is characterized by a free end provided with a curl which is integral with a can body, and which defines a can opening having accommodated the lid, and which opening is substantially dimensionally stable, preferably having a dimensional stability with a margin of error of ±0.10 mm, preferably ±0.05 mm, more preferably ±0.03 mm. The can body for the can of the invention is characterized by a first opening having a necked free end provided with a curl defining a substantially dimensionally stable opening, and preferably a second opening having a clamping flange. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Mentioned and other features of the method and apparatus for making a can and can body of the present invention and of the can and can body as such will be further illustrated by several embodiments which are given for information purposes only and are not intended to limit the invention to any extent. In relation to these embodiments reference will be made to the annexed figures of which: 
         FIG. 1A  is a plan view of a metal sheet for making a cylindrical body; 
         FIG. 1B  is a perspective view of a cylindrical body formed from the metal sheet of  FIG. 1A ; 
         FIGS. 2A to 2F  show schematically the various stages for forming the tromped mouth and the precurl; 
         FIGS. 3A to 3E  show schematically the various stages for forming part of the curl and of the clamping flange; 
         FIGS. 4A to 4C  show schematically the clamping and radial stretching of the cylindrical body; 
         FIGS. 5A to 5C  show schematically formation of the curl in the necked portion of the cylindrical body; 
         FIGS. 6A and 6B  show schematically the application of a bottom to the cylindrical body; 
         FIGS. 7A to 7C  show schematically the mounting and removal of the lid; 
         FIGS. 8A and 8B  show schematically the stacking of the can of the invention closed with a lid; 
         FIGS. 9A to 9F  show another embodiment of the can of the invention having an integral bottom; and 
         FIGS. 10A to 10C  show still another embodiment of a can according to the invention provided with flexible handles. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1A  shows a sheet  1  of metal, such as steel, tin plate, aluminium and the like. The sheet has a wall thickness of about 0.12 to 2 mm dependent on the metal and the operation of forming a can of the invention. The sheet  1  is formed into a cylindrical body  2  and provided with a weld seam  3 . 
       FIG. 2A-2F  show a first unit  4  of the apparatus of the invention for forming the tromped mouth  5  at the second free end  6  on the cylindrical body  2 , and for forming a precurl  7  on the first free end  8  on the cylindrical body  2 . Thereto the unit  4  comprises a tromping tool  16  having an entry section  9 , a first diverging section  10  with a moderate diverging angle in the range of about 5° to about 15°, and a second diverging section  11  having a larger diverging angle in the range of about 15° to about 35°. 
     The cylindrical body  2  is mounted at the free end  6  on the entry section  9  of the tromping tool  16 . Subsequently, a pusher tool  12  pushes along the arrow  13  the cylindrical body over the diverging sections  10  and  11 , thereby forming the tromped mouth  5  (see  FIG. 2B ). 
     Thereafter, the pusher tool  12  is retracted and a piston means  14  is arranged in the first free end  8  thereby defining and controlling the defined diameter of the first free end  8  during structuring thereof (see  FIG. 2C ). The piston means  14  are mounted on a forming tool  15 . This forming tool  15  comprises a forming cavity  17  designed such that by the downward movement according to arrow  19  the precurl  7  is formed in the body wall  18  with the piston means  14  in the defined opening  20  (see  FIGS. 2D and 2E ). The axial downward force for forming the precurl  7  is less than the force required for forming the tromped mouth  5 . Thus the cylindrical body  2  mounted on the tromping tool  16  is substantially maintained in its original position. Accordingly, ultimately is formed in the unit  4  a cylindrical body  21  having at the first free end  8  the first opening  20  defined by the piston means  14  and the precurl  7 , and further at the second free end  6  the tromped mouth  5  (see  FIG. 2F ). As indicated before dependent on for instance the material of the cylindrical body, its wall thickness, and the form of the tromping tool  16  the forming of the tromped mouth and the precurl may be in different order or at substantially the same time. 
     In the unit  23  of the apparatus of the invention the cylindrical body produced in the apparatus unit  4  is mounted on a support  24  (see  FIG. 3A ). Piston means  25  mounted on forming tool  26  are mounted in the defined first opening  20  provided with the precurl  7 . Movement following arrow  27  will result in the formation of a curl part  22  in a forming cavity  28  of the forming tool  26 . This curl part  22  carries the precurl  7  (see  FIGS. 3B and 3C ). Thereafter, the forming tool  29  is axially moved following arrow  30  towards a free edge  31  of the tromped mouth  7  residing in a forming cavity  32 . This forming cavity  32  is formed between the support  24  and the tool  34 . A forming edge  33  of the forming tool  29  contacts the free edge  31  and forms a clamping flange  35  at the tromped mouth  5  (see  FIGS. 3D and 3E ). In this manner is formed a cylindrical body  36  having a tromped mouth  5  provided with the clamping flange  35  and a first opening  20  of the defined diameter and provided with a curl part  22  and the precurl  7 . 
     This cylindrical body  36  is turned upside down (in comparison to  FIG. 3B ) and suspended in clamping arrangement by the clamping means  37 . These clamping means  37  comprise the clamping tools  38  and  39 . A stretching tool  40  is passed through the tromped mouth  5  and on passing through the clamping tool  40  following arrow  42  stretches radially outwardly the cylindrical body  36  over the outer surface of the stretching tool  40 . This results in a reduction of the length of the cylindrical body  36  (see  FIGS. 4A-4C ). A substantial part of the cylindrical body  36  is radially outwardly stretched. The remaining unstretched part of the cylindrical body now forms the necked portion  43  defined by the piston means  44  mounted on the stretching tool  40  (see  FIGS. 4A and 5A ). 
     As shown in  FIGS. 5A-5C , a forming tool  45  is moved upwardly following arrow  50 . This forming tool  45  comprises a forming cavity  46  which first forms an elongated curl  47  having the precurl  7  along the cylindrical body in the necked portion  43 . The elongated curl  47  is formed along the piston means  44  which defined the diameter of the first opening now provided with the elongated curl  47 . Ultimately, following the movement of arrow  50  the forming cavity which encloses part of the elongated curl  47  forms the step  48 . The result is the formation of an elongated and stepped curl  49 . The cylindrical body  51  having the elongated stepped curl  49  in the necked portion  43  is provided with a bottom  52  via a seam connection  53 . This results in a can body  54  according to the invention (see  FIGS. 6A and 6B ). 
     The can body  54  can be provided with a lid  55  of which an annular lid part  56  rests on the elongated curl  49  and a lid curl  57  extends radially over the step  48  in the elongated curl  49  (see  FIGS. 7A to 7C ). This forms an access  59  for a tool  58  by which the lid  55  can be removed from the cylindrical body  51  of the can  61  of the invention. The opening  60  defined by the elongated curl  49  corresponds to the diameter of the piston means  44  and has a dimension stability with a margin of error of 0.03 mm. The lid  55  is clamped with a clamping force in the opening  60  that the closed can of the invention can be used as for instance a paint can. The clamping force is generated by the form of the elongated and stepped curl  49 . 
       FIGS. 8A and 8B  show two stacked cans  61  of the invention. The bottom of the upper can  61  rests with the bottom on the annular lid part  56  of the lid  55  of the lower can  61 . The seam connection  53  extends beyond the curl  57  and over closes the curl  57 , such that the upper stacked can  61  is locked against a radial displacement. 
     The can body  54  consists of two pieces, namely the cylindrical body  51  with the integral elongated and stepped curl  49 , and the seamed bottom  52 . Inclusive the lid  55 , the can  61  of the present invention consists of three pieces. 
       FIGS. 9A to 9F  show the making of another can  62  of the invention consisting of two pieces, namely the can body  63  and the lid  64 . The can body  63  with an integral bottom is formed from a cylindrical body  65 . A free end  66  of the cylindrical body  65  is provided with an elongated curl that may be optionally stepped. Thereto the free end is provided with a precurl  67  as described in relation to  FIG. 2E  using a forming tool  15  having a precurl forming cavity  17 . A curl  68  is formed by using a forming tool  69 . This curl  68  is transformed into an elongated curl  70  using a forming tool  71 . Optionally, the elongated curl  70  is provided with a step  48  using a forming tool  72  and supporting tool  73 . The forming tools  71  and  72  are provided with piston means  74  which are arranged in the opening  75  of the cylindrical body  65  during the formation of the integral curl  70 . This means that the can  62  of the invention has a can body  63  with an integral bottom and curl  70  having a defined diameter closely corresponding to the outer diameter of the piston means  74 . 
       FIGS. 10A to 10C  show another embodiment of a can  76  according to the invention. The can  76  comprises a lid  77  are closing in a necked portion  78  an opening provided with an integral curl  79 . This defined opening is produced in the same manner as for the above described cans according to the invention. However, during the formation of the integral curl  79  handle means  80  are placed in the necked portion  78  where the integral and elongated curl  79  is to be formed. After formation of the curl  79  the handle means  80  are encaged and tightly fixed to the can  76 . These handle means may be used when carrying the can  76  of the invention.