| 摘要 |
1,073,830. Films; extrusion sheeting machines. E. I. DU PONT DE NEMOURS & CO. Sept. 6, 1965 [Oct. 19, 1964], No. 38019/65. Headings B5A and B5B. [Also in Division D1L] In apparatus for forming a layer of viscous material, consisting of a smooth, continuous casting surface carried by a wheel journalled in a stationary frame, and an extrusion hopper supported by the frame adjacent the casting surface, there is provided a sensing device, upstream of the hopper, so that variations in the casting surface are detected and signalled to means for adjusting the position of the hopper relative to the casting surface, thus ensuring uniform film thickness. In Fig. 1, frame 1 carries casting. wheel 2, feed hopper 9 and floating sensing device 13, which is constrained by the frame except for movement in a direction normal to the casting surface. The sensing device is supported in this direction by a stream of gas which flows into the housing of the sensing device via tube 23 and flows out between the bottom of the housing and the casting surface. Eccentricities in the rotation (e.g. wobble) of the casting surface causes the sensing device 13 to tilt or to move towards or away from the casting surface. Any such change from the preset position of the sensing device is detected by differential transformer detectors 14A, 14B, which generate signals which are trasnmitted to electronic analogue-to-digital converters 16A, 16B. These signals are then delayed (to compensate for the distance between the sensing device and the hopper 9) by temporary storage on magnetic memory drum 17. Signals from feedback detectors 15A, 15B, which monitor the position of hopper 9 with respect to wheel 2, are transmitted, together with the delayed signals from drum 17 (reconverted to analogue form at 18A, 18B) to differential amplifiers 19A, 19B. The signals are here differentiated to give resultant error correction signals for transmission to variable-power amplifiers 20A, 20B connected to independently operating magnetostrictive actuators 7A, 7B. The error correction signals cause the actuators to lengthen or shorten, thus moving hopper 9 upwards or downwards, to adjust the thickness of the layer or film. The casting surface may be integral with the wheel, which may be provided with spaced bead-forming grooves, or may be an endless metal belt supported by the wheel. The apparatus may be used for casting films from molten polymers, or for the formation of uniform coatings on webs of film, foil or textile material. |
