GB2158473A - Shearing table - Google Patents

Abstract

A shearing table for machines for shearing goods having non-slip or easy slip bottom surfaces, has a recess 20 extending in its longitudinal direction and in which there is a freely rotatable and radially movable cylindrical member 3. A duct 12 to which compressed air is supplied communicates with the recess 20 via bores 14 in a block 9 to cushion the member 3. <IMAGE>

Description

SPECIFICATION Shearing table The invention relates to a shearing table for shearing machines for machining material having non-slip and easy-slip properties.

Known shearing tables operate as follows: In the case of the beaded table, the goods are drawn over a flattened portion which requires that the goods to be machined must have good sliding properties since friction over the flattened portion is at its maximum due to the angle which the material forms. In this respect, please refer to DAS 1 054951.

In the case of the rolling shearing table, the material is guided over a rolling supporting surface in order to reduce the friction, particularly where the material to be machined has a nonslip bottom layer.

The rolling shearing tables known at present consist of a carrier tube or cast body on which are mounted bearing blocks to accommodate the shaft. The shafts are maintained in the bearings by journals or they rest on ball bearings which are arranged as a support and which are such as those described in DAS 1 067 402 and DAS 1 1 24 463.

The disadvantages of these shearing tables are: Only material which slides easily can be handled on the beaded table.

Any materials can be machined on the rolling shearing table. However, such a shearing table is very expensive to manufacture and considerable wear and tear occurs by virtue of the supporting bearings which cannot be lubricated because the material would be dirtied by the lubricant.

Furthermore, rapid dirtying cannot be avoided. In the case of the rolling shearing tables, where the shaft is supported by the bearings, feed-in marks are made on the shaft which lead to errors on the shearing table, particularly if the shearing table is made from profile material, and vibrations are increased as a result.

To sum up, it can be stated that the beaded table can only machine materials having ready sliding properties and which are characteristic for use on beaded tables while the rolling shearing table is very expensive to produce, is subject to high wear and tear and requires regular maintenance.

The object of the invention is to provide a low-maintenance and self-cleaning shearing table.

The invention is based on the problem of providing a shearing table for shearing machines for machining materials having both non-slip and also easy-slip bottom layers, and which is intended to replace the rolling shearing table and the beaded table.

According to the invention, this problem is resolved in that, like the beaded table and the rolling shearing table, the system can be controlled by cutting off or supplying compressed air and in that a shearing table is provided with the profile for the mounting of a cylinder and a channel or groove for guiding the compressed air. The cylinder is mounted on air. A duct corresponding to the length of the shearing table is provided with transverse slots for dissipating the pressure of the compressed air in order to guarantee a regular spacing from the shearing cylinder. The radius of the cylinder is greater than the radius of the profile at the shearing table so that the greatest possible area is projected which is decisive to the bearing capacity.

The material must be guided over a small radius in order to guarantee the pile opening up for shearing purposes. The small supporting surface required for this can with considerable width be achieved only with considerable expense if the table is a rolling shearing table.

The system of rolling shearing table and beaded table operates with low pressure, is selfcleaning and requires minimal maintenance.

The invention will be explained in greater detail hereinafter with reference to an example of embodiment.

The drawings show in: Figure 1 the shearing table in its installed position; Figure 2 shows a cross-section through the shearing table on the line A-A in Fig. 1; Figure 3 shows a longitudinal section through the shearing table on the line B-B in Fig. 2, and Figure 4 shows the pressure drop in the form of a diagram.

Fig. 1 shows the shearing table in use. It consists of the actual shearing table 1 and the shearing cylinder 2 and the cylinder 3 together with the disposition of the left-hand plate 4, right-hand plate 5 with the seal 6 in front and the part of the feed line for air, consisting of the angle 7 and the compressor hose 8.

With considerable width, preferably the air supply line is provided on both sides in order to guarantee an adequate supply of air.

The air pressure required is determined by the force exerted by the material on the supporting surface, by the projected area of the cylinder. It is ascertained from the formula Force F Pressure = p Area A care being taken to ensure that air constantly escapes at the upper profile edges 21 in the system and must be replaced, see Fig. 2.

For this reason, the shearing table must be connected to the in-house air line, the working pressure being adjusted via a pressure limiting valve.

The escaping air guarantees that the shearing table is not made dirty and/or does not require cleaning. The air serves as the only carrier medium for the cylinder 3, so that friction and wear and tear are out of the question.

Fig. 2 shows the shearing table 1 in section A-A with the cylinder 3, the strip 9 and the duct 12.

It can be seen that the cylinder 3 is the narrowest point on the upper profile edge 21 which forms a line over the entire table. The clearance 1 9 makes it possible to build up a layer of carrier air. In order to form this clearance 19, the radius of the shearing table 1 with the profile 20 is smaller than that of the cylinder 3, the difference amounting to only a few hundredths of a millimetre.

This difference in dimension makes it possible to use the shearing table as a beaded table in that the compressed air is switched off. In this case, the cylinder 3 is carried by the top profile edges 21 and cannot perform any movement.

The compressed air passes through the passage 21 to the cylinder 3, right and left of the shearing table 1, where the strip 9 is provided, the air flowing through the bore 14 which, as required, can be blocked by the threaded pin 11. The recess 1 3 serves as a technological aid to the making of a screwthread.

Fig. 3 shows the section B-B extending along the shearing table. Above the shearing table 1 is the cylinder 3 and under it the duct 1 2 in which the strip 9 is held by the notched pins 1 8.

The task of the transverse grooves 10 is to dissipate the air pressure from the left-hand limiting point 22 to the righthand limiting point 23 as can be seen from the diagram in Fig. 4.

The strip 9 is characterised by the transverse grooves 10, the bore 14 and the threaded pins 11, with which it is possible to regulate the air pressure between cylinder 3 and strip 9. This is important in so far as the material to be machined does not lie over the entire shearing table 1 and a pressure gradient must be established in order to obviate the possibility of a lever action on the part of the cylinder and in order to prevent errors in the run of the outside edges.

The cylinder 3 or the cylinders if they do not consist of a single piece are laterally braced by a ball 1 5 while the threaded pins 1 8 with lock nuts 1 7 are braced by the left-hand connecting part 4 and right-hand connecting part 5.

The cylinder is however not clamped between left-hand connecting part 4 and right-hand connecting part 5 by means of threaded pin 16; instead, they serve only as an abutment so that the cylinder 3 cannot shift.

Fig. 4 shows the diagram with possible pressure drop curves which arise with differing working pressure due to the strip 9 and transverse grooves 10.

Without the strip 9 with the transverse grooves 10, the cylinder ends 3 would be lifted since the material would not occupy the nominal width of the shearing table 1 and so there would be a short age of pressure on the cylinder 3.

The pressure drop per transverse groove is: P1 = P0 - (PWid. PNarr. + tPstraight) in which p, is the pressure after the transverse groove and p0 is the reference pressure. We understand Paid. as the differential pressure upon widening and PNa" as the differential pressure upon narrowing, and out of the groove a narrowing of pressure results. The pressure loss in the straight line from transverse groove to transverse groove can be disregarded by reason of the very small distances between the transverse grooves.

Consequently: P1 = Po - (Apw1 + aPNarr.) If we understand c to be the speed and 0 to be the density while A, is the area between cylinder 3 and strip 9 in the vertical section and A2 is the area of the transverse groove 10 at a right-angle thereto, then the pressure loss for the widening of cross-section and narrowing of cross-section will be as follows A, Q Pwidening = (1 - - 2 ' -. c1 A2 2 A2 Q bPnarrowing =(= 1)2 . -. c22 A1 2 The velocity of the compressed air occasioned by the pressure differential in the system amounts to 2. p0 c = Q Or with the resistance coefficient t which takes in the total losses, the result for a transverse groove and for the pressure loss is as follows: 0 p = D . --C2 2 P=t- PO P1 = p0 - Ap The number of transverse grooves 10 required will establish the minimum length of the strip 9.

The pressure drop via the strip 9 can be regulated by means of the bores 14.

Claims (11)

1. Shearing table for shearing machines for machining goods having non-slip and easy slip bottom layers, characterised in that the shearing table (1) has a hollow profile (20) extending in its longitudinal direction and in which there is a freely rotatable and radially movable cylinder (3) and a duct (1 2) for guiding the compressed air and communicating with the hollow profile (20).

2. Shearing table according to Claim 1, characterised in that the radius of the cylinder (3) is greater than the radius of the hollow profile (20) and the cylinder (3) can be supported on the upper profile edges (21) of the hollow profile (20).

3. Shearing table according to Claim 1, characterised in that the radius of the cylinder (3) and the radius of the hollow profile (20) are of equal magnitude.

4. Shearing table according to Claim 1, characterised in that the hollow profile (20) is provided with transverse grooves (10).

5. Shearing table according to Claim 1, characterised in that the hollow profile (20) communicates with the duct (12) through bores (14).

6. Shearing table according to Claim 1 and 4, characterised in that the flow cross-section of the bores (14) is variable.

7. Shearing table according to Claim 5, characterised in that movable threaded pins (11) are preferably provided transversely of the axis of the bores (14).

8. Shearing table according to Claim 1, characterised in that the air pressure in the duct (12) is variable.

9. Shearing table according to Claim 1, characterised in that the axial mobility of the cylinder (3) is limited.

10. Shearing table according to Claim 1, characterised in that if the compressed air is switched off, the shearing table (1) can be used as a beaded shearing table.

11. Shearing table according to Claim 1, characterised in that by switching on the compressed air the shearing table (1) can be used as a rolling shearing table.

1 2. Shearing table as claimed in Claim 1 and substantially as described herein with reference to and as illustrated by the example shown in the accompanying drawings.