Search International and National Patent Collections
Some content of this application is unavailable at the moment.
If this situation persists, please contact us atFeedback&Contact
Note: Text based on automatic Optical Character Recognition processes. Please use the PDF version for legal matters


Background of the invention

The present invention refers to a device for stretching and fixing a cloth such as a screen-, strainer-, bol ting-, filter cloth or similar on a frame of the kind comprising a frame-shaped stand, a pressure plate being movable in the border of the stand and extending over an essential part of said border and at least one member acting upon the pressure plate for dis placing the pressure plate towards the cloth.

When mounting cloths of the above mentioned kind it is important that the cloth is stretched regularly over the whole surface area. For small frames the stretching and fixing have been made manually and inevitable irregularities following such a manual operation had to be tolerated. For large frames including several square metres pneumatic frame stretching devices have been used, which by means of a great number of pneumatic stretching means stretches the cloth until the sufficient stretching force is obtained. With these machines a good result is obtained, but the fixing of a great number of stretching means is difficult and very time-requiring. Moreover such machi nes are very expensive and requires a large space.
An example of such a device is described in the Swiss patent specification 402.790.

In the German Auslegeschrift 2 . 020 . 958 is described a device of the kind mentioned in the introduction, which however has certain drawbacks. Thus the pressure plate can be displaced only perpendicular to the guides in the frame. By reason of that the pressure plate
cannot compensate possible irregularities of the stretching of the cloth against the frame.

In the US patent specification 1.778.385 a device
for stretching a skin against a stencil is described, at which pneumatic pads are used. The purpose is to
make the stencil lie tightly against the skin, thus
avoiding that the dye or other colouring material
used is running underneath the stencil. This device
is accordingly intended for a quite different pur
pose and for a different technical field than the
device according to the invention.

Description of the invention

The purpose of the present invention is to provide
a device, which facilitates the procedure of stretching and fixing the cloth and which by simple means and
at a reasonable price gives a perfect result. It is
ah important condition that the pressure plate can
be adapted also to irregularly mounted cloths.

This has according to the invention been achieved
by the fact that the frame-shaped stand is provided
with a bottom, that said member comprises at least
one pad inflatable with a fluid and arranged between the bottom of the stand and the pressure plate, which is so much smaller than the border of the stand that the pressure plate is adjustable in different angles in relation to the bottom and that on the upper edge of the border of the stand a clamping device is attachable for clamping the cloth on all sides against the border, said clamping device comprising a frame, which by means of tightening means can be pressed against the stand.

Description of the drawings

The invention will now be further described with reference to an embodiment shown in the accompanying drawing.

Figure 1 is a plane view of the device according to the invention, and
Figure 2 is a section according to the line II - II in figure 1.

Description of an embodiment

The stretching and fixing device according to the
invention comprises a box-shaped stand 11 comprising a rectangular border 12, a perforated bottom plate
13 and an underframe 14. A clamping device 16 can
by means of tightening means 15 be pressed against
the upper edge of the border 12, which is made by
square tubes.

The clamping device 16 comprises a frame of substan-tially the same size as the border 12, said frame
also being made by square tubes. At the pressure surfaces of the clamping device 14 and the border 12 facing
and cooperating with each other a friction lining
17 and an elastic pressure lining resp. or vice versa are attached.

On the perforated bottom 13 of the stand 11 an expandable member 19 is placed, which according to the embodiment shown comprises a pneumatic pad of a plastic or rubber material. The inflation and the discharge of air can be made by way of a flexible tube 20 connected with a pressure gauge 21 and a stop valve 22. A pressure plate 23 rests against the pad 19, said pressure plate extending over a substantial part of the free space between the side edges of the border 12.

The cloth is stretched and fixed in the following
way. A frame 24. over which a cloth 25 is to be stretched is placed substantially in the middle of the pressure plate 23 and the cloth 25 is uncoiled from a supply roller 26 and is widened over the frame 24 and over the edge of the border 12. At this initial working
moment the clamping device 16 is removed and the air is evacuated from the pad 19. After having placed
the cloth over the frame 24 and the border 12 of the stand the clamping device is placed on the cloth 25 just opposite the upper edge of the border and the
tightening means 15 are tightened, so that the clamping device 16 is pressed against the border and an effective fixing of the cloth 25 is achieved. Then the
pad 19 is inflated to an appropriate pressure, which can be read on the pressure gauge 21. When the pad
19 is expanded the pressure plate 23 with the frame
24 will be pressed against the fixed cloth 25 and
if this is irregularly fixed the pad will compensate such irregularities, so that an absolute regular stret ching is achieved.

At very large stretching and fixing devices several pneumatic pads could be used, or the pad could be
divided into a number of sections communicating with each other.

The invention is not limited to the embodiment described above and shown in the drawing, but a number of variations are possible within the scope of the claims. Thus
the tightening means 15 of the clamping device 16
can be of another type, e.g. pneumatically or hydrau lically operated.