Patent GB-977296-A (GB)
Title: Apparatus for stretching synthetic organic thermoplastic film in the longitudinal direction
IPC: B29C55/06
Filed: 1963-05-09
Abstract: 977,296. Film stretching apparatus. LINDAUER DORNIER G.m.b.H. May 9, 1963 [May 25, 1962], No. 18350/63. Heading B5B.  An apparatus for the longitudinal stretching of films comprises a lower row of spaced apart parallel rollers 21 to 29 and an upper row of spaced apart parallel rollers 11 to 18 positioned in staggered relationship to the rollers in the lower row (Fig. 1). The upper rollers are adapted to be lowered into the operative positions 11<SP>1</SP> to 18<SP>1</SP> indicated in dotted lines. When the apparatus has been threaded up with a web of film and is operating, the web of film is caused to travel in a sinuous path over and under the rollers from the inlet end E to the outlet end A of the apparatus and is thereby longitudinally stretched because the rollers are either all driven at speeds increasing from the inlet to the outlet end of the apparatus, or, alternatively, only the first roller 21 and the last roller 29 are driven (the draw roller 29 being driven at a higher speed than the roller 21) while the intervening rollers are idler rollers and therefore each of these automatically rotates at an intermediate speed according to its position in the row. When it is desired to thread up the apparatus with a fresh web of film, the rollers 11 to 18 are raised to the positions indicated by full lines, and two flexible steel bands or ribbons 1, 1<SP>1</SP> are withdrawn from the drums 3 and 3<SP>1</SP> in which they are normally wound up (Figs. 1 and 2) and are caused to travel on their edges towards the inlet end E of the apparatus. The widths of both steel bands lie in parallel vertical planes located at the ends of the rollers and outside the edges of the web of film when the latter is in the operative position. The front ends of the bands 1, 1<SP>1</SP> are joined together by a member 2, e.g. a lightweight tube, provided with a device for gripping the front edge of the web of film to be introduced into the apparatus. The rollers 21 to 29 are provided near their ends with grooves 35 to guide the bands 1, 1<SP>1</SP> (Figs. 3 and 4) and the rollers 11 to 18 may be correspondingly grooved. The bands 1 and 1<SP>1</SP> are moved longitudinally by means of rollers 4, 4<SP>1</SP> driven by a common shaft 32 through worm gears 33, 34. The rollers 4, 4<SP>1</SP> co-operate with idler pressure rollers 5, 5<SP>1</SP> rotatably mounted on arm 6, 6<SP>1</SP> which are mounted on pivots 7, 7<SP>1</SP> and connected through links 8 and 8<SP>1</SP> with a magnetic switch 9 by means of which the pressure rollers 5 and 5<SP>1</SP> can be made to engage the bands 1, 1<SP>1</SP> and thus cause them to travel towards the inlet end of the apparatus or can be disengaged from the bands when the front end of the web of film is gripped by the member 2. The steel bands are then retracted into the drums 3, 3<SP>1</SP> by springs 37 and the web of film is thereby pulled through the apparatus at the same rate as it is fed into the inlet end thereof. The upper rollers 11 to 18 are then lowered into their operative positions and the stretching operation can be started. The steel bands are slightly curved across their width as in the case of a ribbon rule to give it the rigidity necessary for travelling from one roller to the next and the peripheries of the rollers 4, 4<SP>1</SP> and 5, 5<SP>1</SP> are correspondingly curved.