Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Patent
1991-01-11
1993-09-28
Simmons, David A.
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
156193, 156229, 156426, 82 47, 82102, 83180, 83403, 834041, 29 21, 29 218, 29 22, 29 223, 264 461, 264 462, 264 463, 264 459, B32B 3100
Patent
active
052483665
DESCRIPTION:
BRIEF SUMMARY
Helical cutting of a flexible tubular sheet or film of polymeric material is disclosed in GB 816,607. The object in that patent was to manufacture bands having a strong molecular, oblique, orientation. The bands are mainly used for manufacture of high strength cross laminates of uniaxially oriented plies. In order to achieve the desired properties, the tubular film is strongly oriented in its original longitudinal direction prior to the helical cutting, which is generally conducted over a mandrel. The tube is forwarded either with a screw movement before cutting with a fixed knife, or with a linear movement before cutting with a rotating knife, in which event the winder for taking up the helically cut film must rotate with the knife in a planetary type of movement.
Helical cutting of flexible tubular film is also used in GB 1,526,722. The tube that is to be cut generally has a uniaxial polymer grain, this being produced during the extrusion. However the extrusion need not, prior to the helical cutting, provide any significant orientation of the film below its melting point. The object again is the manufacture of high strength cross laminates but in this case the plies are biaxially oriented by stretching after or during the lamination, the transverse and longitudinal stretching processes being mutually independent steps and each step generally being uniaxial.
These patents do not disclose means for synchronising the different movements that control the helical cutting, i.e., the advancement of the film, the rotation of the film or the cutter, and the withdrawing of the cut film. However some degree of such synchronisation can be developed using conventional engineering techniques.
Nevertheless certain problems do remain.
One problem is that the take-off of the cut strip is at an angle to the original direction of advance of the film and therefore tends to produce torque forces in the tubular sheet. This tends to result in distortion of the tube at the time of cutting, and thus distorts the cut and the resultant cut strip. It is very difficult to balance the forces so as to avoid this distortion.
Another problem is that it can be difficult to achieve a regular and accurate supply of film towards the cutting station, particularly when the film is provided in flat form wound on a very heavy reel.
As is well known, there are many instances when it is desirable to provide films of sheet material which is oriented under an angle to the longitudinal direction and, as indicated above, the known processes of helical cutting can be used to this end. However it is desirable to provide a more technically feasible and reliable process, that is also suitable for heavy or wide reels and for high production speeds.
Objects of the invention are to overcome these various problems and to provide methods and apparatus for improved helical cutting of films, and to provide improved films.
According to a first aspect of the invention, a flexible tubular sheet or film of polymeric material is supplied to a first position in a flat form and is helically cut to form a cut strip that is drawn away from the tubular sheet, and the method is characterised in that the sheet is drawn from the first position, opened to a tubular form, drawn over a mandrel and helically cut while passing over the mandrel, and in this process the tubular sheet is inflated by air that is continuously supplied through the mandrel towards the first position to form a stiff tube that makes a sliding fit with the mandrel and that resists deformation during the cutting.
Thus, in the invention air is forced from the mandrel into the tubular film as it travels from its flat state to the mandrel and thereby inflates the film to a tube. The mandrel must have a diameter only very slightly smaller than the tube, in order to allow an adequate pressure to exist within the tube to render it sufficiently stiff. However some air inevitably escapes between the tube and the mandrel and this escaping air can provide lubrication between the tube and the mandrel.
As a result of
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Daniel William J.
Dixon Merrick
Simmons David A.
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