| 摘要 |
The problem of loss of strength in carboard along a line of fold due to stretching and breaking of fibres on the outside of the fold is overcome by providing a machine having a support surface against which the sheet of cardboard which is to be folded is held by an element which has a knife edge. The support surface is provided by a taut flexible sheet material which extends around a rotatable and movable roller. On operation of the machine, the roller is moved around the knife edge, its longitudinal axis being kept parallel to the knife edge, thereby making a fold in the sheet and the cardboard. The flexible sheet which contacts the cardboard has a high coefficient of friction with respect to cardboard. The restrains the cardboard fibres on the outerside of the cardboard as the fold is made preventing their stretching and breaking and thereby providing an unweakened fold. |
