Continuous sheet press and method of operating same

Abstract

A press for making a continuous sheet from composite material has upper and lower press belts having respective lower and upper reaches that vertically spacedly confront one another across a press gap having an upstream inlet end and a downstream outlet end, and that have transversely spaced outer edges extending in the direction. The belts are advanced direction and thereby draw a mat of the composite material in the inlet end, compress it into the sheet, and expelling the sheet from the downstream end. Two transversely spaced elastic seal strips extend in the direction in the gap and are each engaged between a respective one of the outer edges of the upper belt and the respective outer edge of the lower belt. Each belt has at each of the edges a surface in engagement with the respective edge strip and having an average peak-to-valley height of less than 1 m.

Claims

1. A press for making a continuous sheet from composite material, the press comprising: upper and lower press belts each having respective lower and upper reaches that extend horizontally in a travel direction, that vertically spacedly confront one another across a press gap having an upstream inlet end and a downstream outlet end, and that have respective outer edges extending in the direction and spaced apart transversely to the direction with the outer edges of the upper belt being directly above the outer edges of the lower belt; means for advancing the belts in the travel direction and thereby drawing a mat of the composite material in the inlet end, compressing it into the sheet, and expelling the sheet from the downstream end; and two elastic seal strips extending in but spaced apart transversely to the direction in the gap and each engaged between a respective one of the outer edges of the upper belt and the respective confronting outer edge of the lower belt, each of the belts having at each of the respective outer edges a surface in engagement with the respective edge strip and having an average peak-to-valley height of less than 1 m, each belt further having a central region between the respective outer-edge surfaces with a peak-to-valley height greater than that of the respective outer-edge surfaces.

2. A press for making a continuous sheet from composite material, the press comprising: upper and lower press belts each having respective lower and upper reaches that extend horizontally in a travel direction, that vertically spacedly confront one another across a press gap having an upstream inlet end and a downstream outlet end, and that have respective outer edges extending in the direction and spaced apart transversely to the direction with the outer edges of the upper belt being directly above the outer edges of the lower belt; means for advancing the belts in the travel direction and thereby drawing a mat of the composite material in the inlet end, compressing it into the sheet, and expelling the sheet from the downstream end; and two elastic seal strips extending in but spaced apart transversely to the direction in the gap and each engaged between a respective one of the outer edges of the upper belt and the respective confronting outer edge of the lower belt, each of the belts having at each of the outer edges a surface in engagement with the respective edge strip and having an average peak-to-valley height of less than 1 m, a central region of each of the belts between the respective outer-edge surfaces having a peak-to-valley height greater than that of the outer edges of the respective belt.

3. The press defined in claim 2 wherein the peak-to-valley height is less than 0.1 m at the outer edges.

4. The press defined in claim 3, wherein the surfaces of each of the outer edges with a peak-to-valley height of less than 1 m have a width dimension measured perpendicular to the travel direction greater than a similarly measured width dimension of the respective strips.

5. The press defined in claim 2, wherein the elastic seal strips are elastomeric plastic and/or polymer.

6. The press defined in claim 5, wherein the elastic seal strips are of silicone.

7. The press defined in claim 2, wherein the seal strips are endless like the belts and each move synchronously with the belts in the gap.

8. The press defined in claim 2, further comprising: means for heating the composite material in the gap.

9. The press defined in claim 2, further comprising: means for maintaining the mat in a first upstream region of the gap immediately downstream of the inlet end and in a third downstream region of the gap immediately upstream of the outlet end at a low temperature below a melting point of a matrix material; and means for heating the mat in the gap in a second central region downstream of the upstream region and upstream of the downstream region to a temperature above a melting point of the matrix material such that the matrix material liquefies in the central region and leakage from the gap transverse to the direction is impeded by the seal strips.

10. The press defined in claim 9, wherein the first region is below 80 C., the second region is above 120 C., and the third region is below 100 C.

11. The press defined in claim 10, wherein the first region is below 50 C. and the second region is above 150 C.

12. The press defined in claim 9, where a length in the direction of the first region is 0.5 m to 2 m, a length in the direction of the second region 2 m to 6 m, and a length of the third region is 0.5 m to 2 m.

13. The press defined in claim 9, further comprising: means for compressing the strips in the gap between the belts with a pressure of less than 10 N/cm.sup.2.

14. The press defined in claim 9, further comprising: means for compressing the strips in the gap between the belts by at most 10%.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) The above and other objects, features, and advantages will become more readily apparent from the following description, reference being made to the accompanying drawing in which:

(2) FIG. 1 is a side schematic view of a press for making plate-type composite materials from a semifinished mat;

(3) FIG. 2 is a schematic end sectional view of the press;

(4) FIG. 2A is a large-scale view of the detail indicated at IIA in FIG. 2; and

(5) FIG. 3 is a schematic top view of the press illustrating the method of this invention.

SPECIFIC DESCRIPTION OF THE INVENTION

(6) The drawing shows a press for making a continuous composite sheet 1 from a (thermosetting) semifinished mat 2, in particular for pressing and consequently consolidating semifinished SMC mats. The press is fundamentally designed as a double-belt press of generally standard design.

(7) Such a double-belt press has a continuously rotating top steel belt 3 in the top part of the press in a design that is fundamentally known, and a continuously rotating bottom steel bent 4 in the bottom part of the press. Furthermore, a heatable top press platen 5 is provided in the top part of the press and a heatable bottom press platen 6 is provided in the bottom part of the press. The press belts 3 and 4 are braced respective upward and downward against the upper and lower press platens 5 and 6 via arrays of unillustrated roller rods 7 or bars. The press pressure is created by press actuators, for example hydraulic press cylinders 8 that are supported on a fixed press frame 9 and are effective on the top and/or the bottom press platen 5 or 6. Here the upper platen 5 is vertically movable by the cylinders 8 and the lower platen 6 is fixed in the stationary frame 9, although the opposite arrangement is within the scope of this invention. A motor illustrated schematically at 15 serves for advancing the lower stretch of the upper belt 3 and the upper stretch of the lower belt 6 in a horizontal travel direction D.

(8) The semifinished mat 2 to be pressed passes through a horizontally throughgoing press gap 14 formed between the steel belts 3 and 4 and extending in the workpiece travel direction D. The semifinished mat 2 is thereby pressed and subsequently consolidated by applying pressure and preferably also heat to form the composite workpiece sheet 1. To this end the press has a heater shown schematically at 16 in FIG. 1.

(9) The press gap is sealed laterally by elastic seal strips 10 provided between the steel belts 3 and 4 at parallel longitudinal outer edges 11 of the steel belts 3 and 4 and move with the mat 2 and with the steel belts 3 and 4. These elastic seal strips 10 can be manufactured from elastomeric silicone, for example and consequently may be embodied as silicone strips or silicone belts. This laterally seals the press gap 14, in particular taking into account the fact that the material to be pressed is soft and/or liquefied in the press and consequently at least at some paint in liquid form, so that escape of material past these lateral seal strips 10 can be prevented. According to the invention, the steel belts 3 and 4 have a structure-free and profile-free flat surface at these edges 11 where the strips 10 are mounted, the flat surface preferably having an average peak-to-valley height of less than 1 m, especially preferably less than 0.1 m. The edge strips 11 are consequently polished to a high gloss, so that they have a so-called optical quality (for example in the submicrometer range). This information also refers to the facing surfaces 12 of the steel belts 3 and 4 and consequently also to the confronting faces of the steel belts 3 and 4 between the edges 11.

(10) However, in the embodiment shown here, the steel belts 3 and 4 do not have this highly polished flat surface over the entire surface area but only at the edges 11 described here. In the central region 12 where the belts 3 and 4 press directly against the composite material mat passing through the press gap 14, the steel belts 3 and 4 are not as flat and therefore have a greater surface roughness than at the edges 11. The surface quality of the steel belts 3 and 4 is based primarily on the requirements for making the product, so that the surface qualities depend primarily on the surface quality of the product to be achieved. According to the invention, however, especially high quality surfaces are required at the edges 11 because the elastic seal strips 10, for example silicone belts, surprisingly adhere especially well to such extremely smooth surfaces, so that no special guides are needed for the seal strips 10 at the edges 11.

(11) Whereas the lateral sealing is effected by the seal strips 10 described here, sealing of the upstream input end and the downstream output end of the gap is done by the product itself. FIG. 3 shows how that the semifinished mat 2 first passes through a first upstream inlet section A at a low first temperature, so that the mat remains in the solid phase over a certain length in this inlet section A. This is then followed by the liquid phase in the second section B where the mat passes through a second section at a second temperature that is higher than the first temperature and in which the matrix material of the mat is liquefied. This is then followed by a third section C at a third temperature that is in turn lower than the second temperature, so that the material is converted back into the solid phase. Thus, at both the inlet and output ends the liquid phase is sealed by the product that is already consolidated.

(12) The length of the first section A in the embodiment amounts for example to 1.5 m. The length of the second section B amounts for example to 4 m, and the length of the third section C to 1.5 m. Here, the first section A is unheated, while in the second section B, the temperature is set for example at 170 C. In a third section C, the temperature is for example 80 C., these specifications being based on the temperatures of the material to be pressed that is heated by the heating platens 5 and 6.