GB2175231A - Tool for setting screw-threaded fasteners in position - Google Patents

Abstract

A power tool has a reversible air motor (11) which is arranged to drive a mandrel (25). A drive connection (26) allows the mandrel to move axially freely relative to the motor. On the end of the mandrel is a screw-threaded bit (27) which extends beyond an abutment collar (31) for engaging a fastener. A piston (43) is movable in a cylinder (42) and is arranged to pull the bit rearwardly relative to the abutment collar in order to set a fastener. When an operator pulls the trigger (12), a fastener is run on to the bit, the fastener is then set, and the motor then reverses so that the bit is withdrawn from the fastener. This all happens automatically. The operator then just has to release the trigger, and the tool automatically resets itself for installing the next fastener. <IMAGE>

Description

SPECIFICATION A power tool This invention relates to a power tool for setting in position a screw-threaded fastener. The sort of screw-threaded fastener involved here is the wellknown sort which has a screw-threaded bore and which is anchored or "set" in position by means of an axial loading.

Some proposals have been put forward for a tool in which the axial loading is applied to the fastener by axial movement of a screw-threaded mandrel relative to an abutment collar. However, these tools tend to need both hands to operate, and require of the operator two or more distinct movements for each fastener that is installed, and this is not only demanding on the operator but also inefficient in terms of the time taken.

According to the present invention there is provided a power tool for setting a screw-threaded fastener in position, comprising a screw-threaded mandrel for engaging a fastener, motor means operable to drive the mandrel in forward and reverse directions, an abutment for engagement by the fastener on the mandrel, and setting means operable to cause relative axial movement between the mandrel and the abutment whereby to set the fastener, the tool requiring only a single actuating movement by an operator in order for the tool to act sequentially and automatically to run a fastener onto the mandrel by rotation of the motor in the forward direction, then to set the fastener by operation of the setting means, and then to withdraw the mandrel from the fastener by rotation of the motor in the reverse direction, there being means automatically to start operation of the setting means after forward rotation of the motor has brought the fastener into engagement with the abutment, and means automatically to initiate rotation of the motor in the reverse direction once the fastener has been set in position.

The tool may include any of the features claimed in Claims 2 to 14.

By way of example, an embodiment of the invention will now be described with reference to the accompanying drawings, in which: Figures 1A and 1B show a power tool according to the present invention, and Figure 2 shows diagrammatically the control circuit of the tool of Figures 1A and 1B.

A power tool is shown in Figures 1A and 1B which is for installing the well known type of screw-threaded fastener which has a threaded bore and which is anchored or "set" in position in, for example, sheet metal by means of an axial loading. In this tool, a hydraulic/pneumatic piston and cylinder arrangement is provided for "setting" the fastener, whilst an air motor is provided for engaging and disengaging the fastener, and the sequence of steps required for the installation of a fastener occurs automatically once the operator has actuated the tool.

The tool is actuated by means of a trigger 12, which has a stem 13 which is slidably mounted in a bore 14 in the housing 10. A conduit 15 connects the bore 14 directly with a source of pressurised, "live" air via a conventional air line connection 16.

The trigger stem 13 has a small hole 17 running down its centre which communicates the live air conduit 15 with a second bore 18 in the housing 10, when the trigger is in its "off" position, as shown in Figure 1A. In the second bore 18 there is slidably mounted a spool valve 19: this is the motor control valve. It will be seen that the motor control valve 19 is always returned to the position shown in Figure 1A when the trigger is in its "off" position because of the live air pressure communication through the hole 17 in the trigger stem 13.

This is the forward drive position of the motor control valve 19.

When the trigger is in its "on" position, i.e., moved fully to the right in Figure 1A, the live air pressure communication to the second bore 18 is closed off, and the live air remaining in the second bore is able to leak away to atmosphere via the gap around the trigger stem.

When the trigger is pulled into its "on" position, live air is able to pass into bore 14 via the reduced diameter portion 20 of the trigger stem 13 and through to the motor control valve 19. Initially, as has been explained, the motor control valve 19 will be in its forward drive position, as shown in Figure 1A, and in this position it will deliver live air via its reduced diameter portion 21 through passages 22, 23 and 24 to the motor 11 to drive the motor in the forward direction. A restrictor 50 is preferably included in this connection, as indicated in Figure 2.

The motor 11 is arranged to drive a mandrel 25 via a conventionally known ball and axial groove arrangement 26. This drive arrangement 26 means that the motor 11 is always drivingly coupled to the mandrel 25, but the mandrel is free to move axially relative to the motor. Other drive arrangements could equally well be used, for example, the motor and mandrel may both move axially relative to the housing but be immovable relative to each other. It will also be appreciated that the drive from the motor to the mandrel could be arranged to be delivered via a gear box.

Coupled to the free end of the mandrel 25 there is a screw-threaded bit 27, which may simply be an Allen screw. A hexagonal piece 28 delivers drive from the mandrel 25 to the bit 27, and a suitable retaining cage 29 keeps the bit fixed axially and rotationally fast with respect to the mandrel. The threaded bit connection with the mandrel is housed within a nose portion 30, which is removably mounted on the housing 10 to enable the threaded bit 27 to be replaced or changed. An abutment collar 31 is adjustably connected to the end of the nose portion 30. This allows adjustment to be made to suit particular lengths of fastener.

When the motor 11 is driving the mandrel 25 in the forward direction, a fastener can be threadedly engaged on the threaded bit 27 until the fastener comes up against the abutment collar 31. This is the first step in the sequence once the operator has pulled the trigger to actuate the tool. At this point, with the fastener contacting the abutment collar 31, the motor 11 stalls, and there will be a consequential build up of air pressure on the forward drive side of the motor. A port 32 is connected between the forward drive side of the motor 11 and a pressure sensitive valve 33: this is the setting piston control valve.To ensure that a suitable pressure reduction is obtained in the air supply to the motor 11, special porting may be incorporated into the motor, or alternatively, a restrictor 50 (see Figure 2) may be included in the supply line 22, 23, 24. The pressure reduction has to be sufficient to allow the motor to run, but not enough to trip the pressure sensitive valve 33.

Upon sensing a predetermined build up of pressure, the setting piston control valve 33 opens, against the biasing action of a return spring, and puts a chamber 34 (Figure 1B and 2) into communication with the live air conduit 15 via passages 35 and 36. Inside the chamber 34 there is slidably mounted a piston 37, whose piston rod 38 is extendable into another chamber 39. A return spring 40 is provided to ensure that the piston 37 returns to the position shown in Figure 1 B when not subjected to pressurised air in chamber 34.

Chamber 39 is filled with hydraulic fluid, preferably oil, and because the piston 37 has a much larger area than the piston rod 38, it will be seen that the piston and cylinder arrangement has the effect of acting like an intensifier. Hydraulic fluid in chamber 39 which is pressurised by movement of piston rod 38 is transmitted via a passageway 41 a to further chamber 42. The mandrel 25 extends into this further chamber 42, and a piston 43 is mounted on the mandrel in this further chamber. A return spring 44 biases the piston 43 and mandrel 25 to a forward most position in which the threaded bit 27 is in its most outwardly extending position, as shown in Figure 1A. When pressurised fluid enters into chamber 42 via passageway 41, the piston 43 and mandrel 25 are forced rearwardly against the biasing action of return spring 44.In use, when a fastener has already been engaged on the threaded bit 27, this rearward axial movement of the mandrel pulls the threaded bit 27 rearwardly relative to the abutment collar 31, thereby "setting" the fastener.

At the rear of chamber 42 there is arranged a poppet valve 45: this is the limit sensing valve. The limit sensing valve 45 is movable in a bore 53 of a valve body 54 which is adjustably mounted on the housing 10. The stroke of the mandrel 25 and piston 43 is set to suit a particular fastener by adjustment of the valve body 54 relative to the housing 10. A spring 46 holds the limit sensing valve 45 normally closed. When the piston 43 and mandrel 25 have reached the end of their stroke, and the fastener has been "set", the end of the mandrel opens the limit sensing valve 45. This opens a line of communication from the live air conduit 15 via passage 47, through the bore 53 of the valve body 54 and to the second bore 18 via passages 48 and 49.The live air pressure thus acting on this end of the motor control valve 19 will cause it to move to the left in its bore 18 (looking at Figure 1A). In this position, which is its reverse drive position, a second reduced diameter portion 50 of the motor control valve 19 is now in communication with the live air conduit 15, via bore 14 and the reduced diameter portion 20 of trigger stem 13 with the trigger still in its "on" position. The second reduced diameter portion 50 opens into a port 51 which leads to the motor to drive the motor in the reverse direction. The threaded bit 27 is therefore driven backwards, which enables it to be withdrawn from the installed fastener.

The air pressure in port 32 at this stage is no longer sufficient to hold open the setting piston control valve 33, which therefore closes under the biasing action of its return spring. This means that the live air connection to the intensifier system is cut off. To avoid trapping the air in passage 36 when the setting piston control valve 33 closes, a small bleed hole 51 is provided in this passage.

The piston 37 is then duly able to return to its normal position, as shown in Figure 1 B, under the biasing action of spring 40, while air vents through bleed hole 51, when the setting piston control valve 33 closes. Similarly, piston 43 and mandrel 25 return to their normal position, as shown in Figure 1A, under the biasing action of spring 44.

When the threaded bit 27 has become completely withdrawn from the fastener, which has now been "set" the operator can release the trigger. This concludes the installation cycle. The live air connection from the conduit 15 to the motor control valve 19 is cut off when the trigger is released and so the motor 11 ceases to rotate. To avoid trapping air in the passages between the motor control valve 19 and the limit sensing valve 45 when it closes, a small bleed hole 52 is provided in these passages. The live air connection through the hole 17 in the trigger stem 13 to the second bore 18 is restored, which causes the motor control valve 19 to move back to its forward drive position, as shown in Figure 1A. Thus, the various valves and pistons in the tool have all returned to their starting positions, as shown in Figure 1A and 1 B, and the tool is ready for the operator to begin another automatic installation sequence.

Claims (15)

1. A power tool for setting a screw-threaded fastener in position, comprising a screw-threaded mandrel for engaging a fastener, motor means operable to drive the mandrel in forward and reverse directions, an abutment for engagement by the fastener on the mandrel, and setting means operable to cause relative axial movement between the mandrel and the abutment whereby to set the fastener, the tool requiring only a single actuating movement by an operator in order for the tool to act sequentially and automatically to run a fastener onto the mandrel by rotation of the motor in the forward direction, then to set the fastener by operation of the setting means, and then to withdraw the mandrel from the fastener by rotation of the motor in the reverse direction, there being means automatically to start operation of the setting means after forward rotation of the motor has brought the fastener into engagement with the abutment, and means automatically to initiate rotation of the motor in the reverse direction once the fastener has been set in position.

2. A power tool as claimed in Claim 1 wherein the said means automatically to start operation of the setting means is actuated as a result of the motor stalling when its forward rotation is halted by the fastener being brought into engagement with the abutment.

3. A power tool as claimed in Claim 2 wherein the motor is an air motor, and the said means au tomaticaily to start operation of the setting means is actuated by a build-up of air pressure which occurs on the forward drive side of the motor when it stalls.

4. A power tool as claimed in Claim 1, Claim 2 or Claim 3 wherein the said means automatically to initiate rotation of the motor in the reverse direction is actuated as a result of the setting means reaching the end of its stroke.

5. A power tool as claimed in Claim 4 wherein the setting means comprises a piston and cylinder arrangement where the piston is connected to the mandrel so that axial movement of the piston within the cylinder causes axial movement of the mandrel relative to the abutment.

6. A power tool as claimed in Claim 5 wherein to set a fastener the piston is driven in the cylinder by hydraulic fluid and the tool includes air/hydraulic intensifier system for providing hydraulic fluid under pressure for the piston and cylinder.

7. A power tool as claimed in Claim 6 wherein the said means automatically to start operation of the setting means comprises a first air valve which is actuated upon sensing a predetermined build-up of pressure and which, when actuated, causes air to be delivered to the intensifier system.

8. A power tool as claimed in Claim 5, Claim 6 or Claim 7 wherein the said means automatically to initiate rotation of the motor in the reverse direction comprises a second air valve which is actuated by the piston, or a member movable therewith, at the end of the stroke of the piston.

9. A power tool as claimed in Claim 8 comprising a third air valve for delivering air selectively to the motor to drive the motor in either forward or reverse direction, where actuation of the second air valve causes the third air valve to shift and cause the motor to rotate in the reverse direction.

10. A power tool as claimed in Claim 8 or Claim 9 wherein the second air valve is incorporated in a limit stop which defines the end of the stroke of the piston, and there is means for adjustably mounting the limit stop on the housing.

11. A power tool as claimed in any preceding claim wherein the single movement required for actuating the tool is for the operator to pull a trigger and keep it pulled until the fastener is installed.

12. A power tool as claimed in Claim 11 wherein the trigger operates a fourth air valve, and when the trigger is released, the fourth air valve provides an air bleed to the third air valve which returns the third air valve to its position for forward rotation of the motor, so that the tool is automatically set for installing the next fastener.

13. A power tool as claimed in any preceding claim wherein the motor means comprises a reversible motor.

14. A power tool as claimed in Claim 13 wherein the motor means further includes a gear box through which drive from the motor to the mandrel is delivered.

15. A power tool substantially as hereinbefore described with reference to and as shown in the accompanying drawings.