GB2123325A - Pipe bending machine - Google Patents

Abstract

In a fluid-operated pipe-bending machine having a fluid-driven motor (12) for feeding pipe to the bending head (10), a control device (14) is operated by pressure at the bending head and at the feed motor to control the pressure operating on the motor so that it is related in a predetermined manner to the pressure operating on the bending head. <IMAGE>

Description

SPECIFICATION Pipe bending machine This invention relates to machines for bending pipes or tubes.

In a known pipe bending machine, pipe is fed on a feed carriage driven by an electric feed motor to the bending-head between bending operations. During the bending operation, the feed-motor is not driven and the bending-head draws the pipe and feed carriage (to which the pipe is clamped) towards itself.

A disadvantage in this method of feeding pipe to the bending-head during bending is the risk of damage to the pipe and/or the pipe pulling away from the feed carriage. The risk arises because the pipe is relied upon both to accelerate and decelerate the heavy feed carriage. During acceleration, the tension in the pipe due to the inertia of the feed carriage can either stretch the pipe, crush is against the bending-head or pull it away from the feed carriage. During deceleration, where the problem is greater, the momentum of the feed carriage can buckle the pipe. The problem becomes more significant with lighter pipe as it is mechanically weaker, and therefore less able to withstand the stresses put upon it by the feed carriage.

The risk of damage to the pipe limits the operating speed of conventional machines because feed carriage momentum must be kept down and rapid changes of momentum avoided. Machine capacity will be wasted if the operating speed is limited, especialy when bending light pipes, where the bending-head could operate very quickly.

A way of overcoming the problems associated with the free-rolling feed carriage is to drive it during the bending operation. This has not been possible using electric feed motors to drive the feed carriage, as it is difficult to arrange a suitable current supply control to feed pipe to the bending-head at the correct rate. The difficulty arises because the behaviour of pipes during bending is difficult to predict.

The invention provides a machine for bending pipes or tubes comprising a fluid operable bendinghead for being the pipe or tube and a fluid drivable feed motor for feeding pipe or tube to the bendinghead, the machine being adapted so that the feed motor is supplied with fluid to drive it while the bending-head is bending a pipe or tube.

An advantage of such a machine is that, if the feed carriage is driven by the feed motor, the feed carriage is both accelerated and decelerated by the feed motor rather than the bending-head and pipe thus reducing the risk of damage to the pipe. This new arrangement will allow the operating speed of the machine to be increased, especially when bending light pipes, as the momentum of the feed carriage will no longer stress the pipe to the same extent.

A further advantage of a machine with positive pipe feed becomes apparent when bending heavy pipes. It is known to use a driven pressure die to provide a booster thrust to aid the bending-head to bend heavy pipe. A particular virtue of the booster thrust is that it reduces thinning of the pipe wall on the outer radius of the bend. Conventionally, the booster thrust has been provided using a ram activated after the bending-head has traversed a predetermined angle, and de-activated when the bending-head is at a predetermined angle from the end of the bend.

A preferred pipe bending machine according to the present invention has a source of fluid at a first pressure, a flow rate control for controlling the flow rate of the fluid and a control device for controlling the feed motor during a bending operation, which control device senses the pressure of the fluid at an inlet to the bending-head where pressurised fluid is supplied to cause the bending-head to bend the pipe, and which control device is connected to be able to supply fluid at a second pressure to the feed motor in a sense to feed pipe or tube to the bending-head during the bending operation, the second pressure varying in a predetermined manner in relation to the pressure sensed at the said inlet to the bending-head.

When such a construction is adopted, the feed motor may be connected to drive a feed carriage to which the pipe or tube is attached. Alternatively, the feed motor may be a fluid drivable ram acting on a pressure die which pressure die is in contact with a pipe or tube during a bending operation, the arrangement being such that during a bending operation drive transmitted from the ram through the pressure die forces the pipe or tube into the bending-head.

According to a further feature of the present invention, the pressure of the fluid supplied by the control device to the feed motor is small compared to the pressure sensed at the said inlet to the bending-head and at least during pressure surges and dips varies with the pressure sensed at the said inlet.

Furthermore, all pressurised fluid may be pressurised by a single pump, and pressurised fluid supplied to the control device may not pass through the flow rate control for controlling the supply of fluid to the bending-head.

Embodiments of the present invention will now be described with reference to the accompanying drawings in which: Figure 1 is a schematic diagram of a pipe bending machine according to the present invention; Figure 2 shows a pipe bending machine with a driven feed carriage; Figure 3 shows a pipe bending machine with a ram for supplying a booster thrust.

Figure 1 shows a fluid operable bending-head 10 connected to be supplied with pressurised fluid from a pump 11. The supply of fluid is controlled by a flow-rate control 13 which can control the flow rate of the fluid. Incorporated in the flow rate control 13 is a reversing device (not shown) which can change the direction of flow of the fluid. Stop valve 15 can isolate the bending-head 10 from the pump 11.

These components are interconnected by pipes which are shown but not referenced.

The pump 11 is also connected to be able to supply fluid to a fluid drivable feed motor 12 which feeds pipe in the direction towards the bending-head 10. This fluid supply path bypasses the fluid flowrate control 13, and is controlled by a feed motor control device 14. The feed motor control device 14 is also connected to be able to sense the pressure in the fluid supplied to operate the bending-head 10.

The feed motor 12 can be isolated from the feed motor control device 14 and the pump by stop valve 16.

The flow-rate control 13 operates to maintain a constant flow rate of fluid, within certain bounds, independent of the pressure at its inlet and outlet.

The flow rate through the flow-rate control can be varied within bounds.

Referring now to Figure 2, a pipe-bending machine is shown in which the feed motor 12 (Figure 1) is a fluid drivable feed carriage motor 17. The feed carriage motor is connected to drive a feed carriage 18 to which the pipe 19 is attached by collet 20. The feed carriage motor is connected to be supplied with fluid from the fluid flow rate control 13 as well as the feed motor control 14. Stop valve 21 can isolate the feed carriage motor 17 from the fluid flow-rate control 13. The feed carriage motor 17 can be isolated from the feed motor control by stop valve 16.

The fluid operable bending-head 10 comprises a former 22, a bend-arm 23 incorporating a pipe grip 24, and a pressure die 25. The pump 11 can be connected to supply other fluid operable devices (not shown) of the machine, as is indicated by the pipes extending to the right of the stop valve 21.

Such devices would normally include a motor for rotating the pipe relative to the bending-head.

To feed pipe through the bending-head 10 between bends, pressurised fluid is supplied to the feed carriage motor 17 via the flow-rate control 13 by opening the valve 21. The rate at which the pipe is fed is determined by the fluid flow-rate, and therefore by the flow-rate control 13.

When a bending operation is to be carried out, the stop valve 21 is closed and the stop valves 15 and 16 are opened. The flow-rate to the bending-head 10 is then progressively increased to its operating value, which it maintains until the end of the bending operation is approached, when the flow rate is progressively decreased. The flow rate is progressively increased and decreased to avoid undue stresses on the pipe or the machine, and possible damage to either.

When the flow-rate is initially increased, the pressure in the inlet to the bending-head, to which fluid is supplied to bend the pipe, rises to a maximum, then drops to an intermediate value which it maintains throughout most of the bending operation. When, towards the end of the bending operation, the flow rate to the bending-head is decreased, the pressure in the inlet to the bendinghead drops again. This further dip is due to the momentum of the bending-head and the reduction in viscous friction.

The feed motor control device 14 senses the pressure in the inlet to the bending-head and in relation to to this pressure, supplies pressurised fluid to the feed motor 12 (Figure 1) which in Figure 2 is the feed carriage motor 17, to feed pipe to the bending-head 10 during the bending operation. The control device is switchably connected to the feed motor via valve 16. It was realised that the pressure cycle required to drive the feed motor has the same general features as the pressure cycle at the inlet to the bending-head.

In particular, a surge in the pressure supplied to the feed motor is required to overcome the inertia of the feed carriage 18, and a dip in the pressure is required to slow the moving carriage towards the end of the bending operation at the same time as the surge and dip at the bending-head. The supply of fluid to the feed motor is controlled by the feed motor control device 14.

This control device 14 is connected to sense the pressure at the inlet to the bending-head where pressurised fluid is supplied to operate the bendinghead, and the control device 14 is connected to be able to supply pressurised fluid to the feed motor 12 (Figure 1) to feed pipe towards the bending-head 10 during the bending operation. The pressure in the pressurised fluid supplied to the feed motor 12 (Figure 1) is controlled bythecontrol device 14 and varies in a predetermined manner in relation to the pressure sensed at the inlet to the bending-head.

The control device 14 incorporates a pilot operated pressure control element. A suitable element is that supplied by G.L. Rexroth Ltd listed by them as ZDC 10P-10. Pressure limiting valves could also be incorporated in the control device 14 to limit the pressure supplied to the feed motor. Similarly a pressure sensitive valve could be incorporated to brake the feed motor when the pressure dip at the bendinghead occurs.

The supply of fluid to the feed motor through the control device 14 need not pass through the flowrate control 13. This fluid could be supplied from an independent source if necessary.

When the machine shown in Figure 2 is operating, a pipe 19 is clamped by collet 20 to feed carriage 18 which is driven by the feed carriage motor 17. The pipe is then fed into the bending-head by the feed carriage motor until the position where the bend is required is reached. The pipe is then clamped into the bending-head by grip 24. The pipe could be rotated relative to the bending-head 10 by a further hydraulic motor (not shown) before being clamped to the bending-head 10. The bending-head 10 is then operated to bend the pipe and during the being operation, the feed motor control device 14 monitors the pressure in the fluid supplied to the bendinghead 10, and controls the pressure in the fluid supplied to drive the feed carriage motor so as to feed pipe to the bending-head 10 according to the monitored pressure.

If light pipe is being bent, the pressure required at the bend head fluid inlet is small and in consequent the pressure supplied to the feed carriage motor from the control device 14 will be small, sufficient only to help overcome the inertial and frictional forces associated with the feed carriage. However if a heavy pipe is being bent, the pressure required at the bend head inlet will be much greater and may be substantially the same as the supply pressure available from the pump 11. This could result in the pressure supplied to the feed motor 17 by the control device 14 being higher than than provided when bending a light pipe, such that the resultant thrust from the feed carriage motor 17 would exceed the frictional and inertial forces associated with the feed carriage and thus provide a positive thrust to the tube being bent to aid the bend head.

An alternative embodiment of the present invention is shown in Figure 3 in which the same reference numerals represent elements common to both embodiments. In this embodiment, the feed motor 12 (Figure 1) is a fluid driveable ram 26 connected to be able to drive pressure die 25. The ram 26 is connected to be supplied with fluid from the feedmotor control 14, and stop-valve 16 can interrupt this flow. In this embodiment the feed carriage motor 17 is not connected to the feed motor control 14. The feed carriage motor is still connected to be able to receive fluid from the fluid flow rate control 13.

In operation, pipe to be bent in this pipe bending machine is fed through the bending-head between bending operations by the feed carriage motor 17. In this embodiment, however, the feed carriage motor 17 is declutched by valve 27 during any bending operation.

During bending, the feed motor control 14 monitors the pressure in the fluid supplied to the bending-head and supplies pressurised fluid to the ram which then provides a booster thrust to force pipe into the bending-head and aids bending. The pressure in the fluid supplied to the ram varies in a predetermined manner in relation to the pressure at the bending-head.

A machine could be built in which the control device supplies fluid to both a feed carriage motor and a ram connected to the pressure die during a bending operation.

Claims (8)

1. A machine for bending pipes or tubes comprising a fluid operable bending-head for bending the pipe or tube and a fluid drivable feed motor for feeding pipe or tube to the bending-head, the machine being adapted so that the feed motor is supplied with fluid to drive it while the bending-head is bending a pipe or tube.

2. A machine as claimed in claim 1 having a source of fluid at a first pressure, a flow-rate control for controlling the flow rate of the fluid and a control device for controlling the feed motor during a bending operation, which control device senses the pressure of the fluid at an inlet to the bending-head where pressurised fluid is supplied to cause the bending-head to bend the pipe, and which control device is connected to be able to supply fluid at a second pressure to the feed motor in a sense to feed pipe or tube to the bending-head during the bending operation, the second pressure varying in a predetermined manner in relation to the pressure sensed at the said inlet to the bending-head.

3. A machine as claimed in claim 2 in which the feed motor is connected to drive a feed-carriage to which the pipe or tube is attached.

4. A machine as claimed in claim 2 in which the feed motor is a fluid drivable ram acting on a pressure die which pressure die is in contact with a pipe or tube during a bending operation, the arrangement being such that during a bending operation drive transmitted from the ram through the pressure die forces the pipe or tube into the bending-head.

5. A machine as claimed in any of claims 1 to 4 wherein the pressure of the fluid supplied by the control device to the feed motor is small compared to the pressure sensed at the said inlet to the bending-head and at least during pressure surges and dips varies with the pressure sensed at the said inlet.

6. A machine as claimed in any of the preceding claims wherein all pressurised fluid is pressurised by a single pump.

7. A machine as claimed in any of the preceding claims wherein pressurised fluid supplied to the control device for subsequent supply to the feed motor does not pass through the flow-rate control for controlling the supply of fluid to the bendinghead.

8. A pipe bending machine substantially as hereinbefore described with reference to and as illustrated in Figures 1 and 2 or Figures 1 and 3 or Figures 1,2 and 3 of the accompanying drawings.