GB2032312A - Jammed press release apparatus - Google Patents

Abstract

In a press, the driving force is transmitted from a connecting rod (17) to a slide via a body (26) of low-melting point alloy. This body is disposed in a chamber (20) which communicates with a space into which material of the fused body can flow to release a jammed press. One boundary of the space is defined by a slidable piston (30) which can be used to force the molten alloy back into the chamber when the jam has been cleared. The piston may be driven by a screw or pneumatically. <IMAGE>

Description

SPECIFICATION Improvements relating to presses and the like This invention relates to a machine, for example a press, comprising first and second members which are relatively movable towards and away from each other and a driving mechanism for applying a driving force to said members to cause relative movement of the members.

It is known to provide in a press a piston and cylinder assembly containing a pressurised fluid through which the driving force is transmitted.

During normal operation of the press there is no movement of the piston relative to the cylinder. In the event of the press becoming jammed, fluid is released from the cylinder to permit relative movement of the piston and cylinder so that the press can be freed.

The present invention provides an alternative means for enabling a jammed press to be freed.

According to the invention there is provided a machine comprising first and second members which are relatively movable towards and away from each other and a driving mechanism for applying a driving force to said members to cause relative movement of the members, wherein the driving mechanism includes a body through which the driving force is transmitted, at temperatures below 30"C said body is capable of transmitting without substantial flow of the body the driving forces which arise in normal use of the machine, there is provided heating means for heating said body to a temperature at which the body would flow if subjected to the driving forces which arise in normal operation, the machine further comprises a piston arranged in slidable fluid-tight engagement with boundaries of a space which communicates with a chamber containing said body and there is provided means for moving the piston in a direction to reduce the volume of said space and thereby expelling material of said body from said space to said chamber.

The heating means is preferably capable of heating said body to a temperature at which the body is capable of flow under the action of gravity acting on the body alone.

Examples of presses embodying the invention will now be described with reference to the accompanying drawings wherein: Figure 1 shows diagrammatically a press; Figure 2 shows a cross-section of a part of the press of Figure 1; and Figure 3 is a cross-section similar to Figure 2 but illustrating an alternative press.

The press shown in Figure 1 comprises a frame 20 on a lower part of which there is supported a bed 11.

At a position above the bed, there is a slide 12 which is guided on the frame for rectilinear movement towards and way from the bed 11. For moving the slide towards and away from the bed, there is provided a driving mechanism which includes a crankshaft 13 supported by the frame 10 in a position above the slide 12 for rotation about a horizontal axis 14. A flywheel 15 is mounted on the crankshaft and an electric motor 16 is provided for driving the flywheel. The driving mechanism further comprises a connecting rod 17 which connects an eccentric of the crankshaft 13 with the slide 12 so that the slide is reciprocated towards and away from the bed 11 when the crankshaft rotates.

The slide 12 comprises a hollow member 18, to the underside of which there is secured a platen 19. A chamber 20 is defined in the member 18 by walls at all boundaries of the chamber, that is above and below the chamber and around the chamber in all horizontal directions. A lower boundary of the chamber is defined by a block 21 which rests on upwardly facing abutment surfaces 22 provided inside the hollow member 18. The peripheral boundary of the chamber 20 is defined by a cylindrical lining 23 provided in the hollow member 18 and resting on the block 21. The lining is secured in the hollow member 18 by a ring 24 which is screwed into the interior of the member 18 adjacent to the upper end thereof to urge the lining downwardly onto the block 21.An upper boundary of the chamber 20 is defined by a piston 25 which is a sliding fit within the lining 23 and is also retained within the hollow member 18 by the ring 24. A lower end portion of the connecting rod 17 is secured to the piston 25 in an articulated manner.

The chamber 20 contains a body 26 which is in contact with all boundaries of the chamber. When the press is in use, a driving force is transmitted from the crankshaft 13 through the connecting rod 17, the piston 25, the body 26, the block 21 and the hollow member 18 to the platen 19. The body 26 is subjected to compression between the piston 25 and the block 21.

Means is provided for heating the body 26. In the particular example illustrated, the heating means comprises an electrical heating element 27 which is disposed within the chamber 20 and is spaced from the walls thereof so that it is embedded in the body 26. The body 26 completely fills the chamber 20, except for that part of the chamber which is occupied by the heating means.

In the lower boundary of the chamber 20, there is provided an orifice 28 leading to a cylindricai space 29 provided in the block 21. Except for the orifice 28, the space 29 is totally enclosed but one boundary of the space is provided by a movable wall portion in the form of a piston 30. This piston can move longitudinally of the space 29 to vary the volume thereof.

The body 26 is formed of an alloy of bismuth, lead and tin which, at temperatures below 30"C, is capable of transmitting without substantial flow the driving forces which arise in operation of the press.

By means of the heating element 27, the body can be heated to a temperature at which it would flow if subjected to the driving forces. Preferably, the alloy is a eutectic mixture which can be melted completely by energisation of the heating element and is then capable of flowing under the action of gravity acting on the alloy alone. The alloy also occupies the orifice 28 and the space 29.

When tools are mounted in the press, they are aligned with the body 26 in the direction of move ment of the slide 12.

It will be noted that the chamber 20 is spaced from the platen 19 and that there is an air gap 31 between the platen and the walls of the chamber. Thus, even if the temperature of the platen rises above the ambient temperature, the temperature of the body 26 is not likely to rise above the ambient temperature unless the heating element 27 is energised.

In the event of the press becoming jammed, the heating element is energised to melt the alloy occupying the chamber 20, orifice 28 and space 29.

The piston 30 is then permitted to move away from the orifice 28, thereby permitting alloy to flow from the chamber 20 into the space 29. This permits the block 21, hollow member 18 and the platen 19 to move upwardly relative to the piston 25 so unjamming the press. The crankshaft 13 is then turned until the connecting rod 17 is at the upper extremity of its stroke. As the connecting rod and piston 25 rise, or after they have risen, the hollow member 18 and block 19 are permitted or caused to move downwardly relative to the piston 25 until the ring 24 rests once more on the piston. During this relative movement of the piston 25 and block 21, the molten alloy will flow once more through the orifice 28 from the space 29 into the chamber 20. The heating element is then de-energised and the alloy is permitted to solidify once more within the chamber.

To assist flow of the alloy from the space 29 into the chamber 20 and downward movement of the block 21 relative to the piston 25, the piston 30 may be urged towards the orifice 28 to reduce the volume of the space 29. In the press shown in Figure 2, this can be achieved by admitting air under pressure through the inlet 32 to the interior of the block 21 at the rear of the piston 30.

The press illustrated in Figure 3 differs from that illustrated in Figures 1 and 2 only in that an alternative means is provided for controlling movement of the piston in the block and in that the boundaries of the chamber are defined by materials selected to reduce the flow of heat from the chamber. In Figure 3, parts corresponding to those already described with reference to Figure 2 are illustrated by like reference numerals with the prefix 1 and the preceding description is deemed to apply, except for the differences hereinafter mentioned.

Movement of the piston 130 to vary the volume of the space 129 is controlled by a screw 135. The screw is threadedly engaged in an aperture in a plate 136 secured to an external surface of the hollow member 118. The screw extends from the plate 136 through an aperture in the hollow member 118 and along a cavity formed in the block 121 to engage the piston 130 at the side thereof remote from the space 129. A lock nut 137 is provided to secure the screw releasably against rotation relative to the plate 136.

If the press becomes jammed, the electrical heating element 127 is energised to melt the body 126 and the alloy occupying the orifice 128 and space 129. The screw 135 is then screwed away from the piston 130 to allow the volume of the space 129 to increase. Alloy flows from the chamber 120 to allow the block 121 and hollow member 118 to rise relative to the piston 125 and so release the jam.

When the connecting rod has been raised, the hollow member 118 is caused or permitted to descend relative to the piston 125, alloy flowing into the chamber 120 through the orifice 128 and the piston 130 moving towards the orifice to reduce the volume of the space 129 accordingly.

The piston 130 may be forced towards the orifice 128 by means of the screw 135. The heating element 127 is then de-energised so that the alloy cools to reform the body 126 of solid metal.

During normal operation of the press, the temperature of the body 126 is below300C. At such temperatures, the body is capable of transmitting without substantial flow the driving forces which arise in normal operation. It will be seen that movement of the piston 130 in a direction to increase the volume of the space 129 is positively prevented by the screw 135. Accordingly, the solid alloy within the space 129 is constrained against movement and flow of alloy from the chamber 120 through the orifice 128 is entirely prevented. During normal operation, the pressure exerted on the body 126 by the piston 125 may be sufficiently low to ensure that no flow of alloy from the chamber 120 through the orifice 128 would occur, even if the piston 130 was free to move away from the orifice 128.

On the upper surface of the block 121 and the under surface of the piston 125, there are provided linings of material which is not as good a conductor of heat as is steel. The lining 23 is also formed of the same material. A material comprising resin-bonded asbestos fibres and which is commonly used in bearings is suitable. If required, the space 129 also may be lined with thermally insulating material.

Furthermore, a lining of thermally insulating material as described with reference to Figure 3 may also be provided in the press illustrated in Figures 1 and 2.

Claims (6)

1. A machine comprising first and second members which are relatively movable towards and away from each other and a driving mechanism for applying a driving force to said members to cause relative movement of the members, wherein the driving mechanism includes a body through which the driving force is transmitted, at temperatures below 30"C said body is capable of transmitting without substantial flow of the body the driving forces which arise in normal use of the machine, there is provided heating means for heating said body to a temperature at which the body would flow if subjected to the driving forces which arise in normal operation, the machine further comprises a piston arranged in slidable fluid-tight engagement with boundaries of a space which communicates with a chamber containing said body and there is provided means for moving the piston in a direction to reduce the volume of said space and thereby expelling material of said body from said space to said chamber.

2. A machine according to Claim 1 so arranged that, when tools are mounted on the first and second members the tools are aligned in the direction of relative movement of the members with said body and the walls of the chamber containing the body are spaced from both of said members.

3. A machine according to Claim 1 or Claim 2 wherein the chamber containing said body has boundary surfaces which are in contact with said body in all directions, and there is formed in one of said boundary surfaces an orifice through which the chamber communicates with said space.

4. A machine according to Claim 3 wherein said boundary surfaces of the chamber are presented by thermally insulating material arranged as a lining on metal members of the machine, the thermally insulating material having a lower thermal conductivits than do the metal members.

5. A machine substantially as herein described with reference to and as shown in Figures 1 and 2 of the accompanying drawings.

6. A machine according to Claim 5 modified substantially as herein described with reference to and as shown in Figure 3 of the accompanying drawings.