(19)
(11) EP 0 447 251 A3

(12) EUROPEAN PATENT APPLICATION

(88) Date of publication A3:
04.12.1991 Bulletin 1991/49

(43) Date of publication A2:
18.09.1991 Bulletin 1991/38

(21) Application number: 91302205.9

(22) Date of filing: 14.03.1991
(51) International Patent Classification (IPC)5: B21D 39/03, B21C 37/15
(84) Designated Contracting States:
AT BE CH DE DK ES FR GB GR IT LI LU NL SE

(30) Priority: 14.03.1990 GB 9005703

(71) Applicant: HADLEY INDUSTRIES PLC
Warley, West Midlands B66 2PA (GB)

(72) Inventor:
  • Humpage Roy
    Halesowen West Midlands B62 8 RA (GB)

(74) Representative: Lewis, Samuel H. (GB) 
Burnbrae Nenthorn
GB-Kelso, Roxburghshire TD5 7RY
GB-Kelso, Roxburghshire TD5 7RY (GB)


(56) References cited: : 
   
       


    (54) Tube and method of forming same


    (57) A polygonal tube is produced from metal strip by forming rows of recesses (15) and projections (16) along opposite edges of the strip and then bending the strip until each projection is received in a corresponding recess to form the tube.
    The projections are then squeezed between opposed surfaces (26,28) one inside and other outside the tube. The surface inside the tube forms a groove (27) in the tube wall at the inside of the tube, spreads each projection to take up any clearance between edges of the projections and boundaries of the corresponding recesses. The surface outside the tube allows the tube to remain flat.






    Search report