WO1999007506A1

WO1999007506A1 - Hole cutting and threading apparatus

Info

Publication number: WO1999007506A1
Application number: PCT/GB1998/001314
Authority: WO
Inventors: Michael Carter
Original assignee: Pouvoir Limited
Priority date: 1997-08-09
Filing date: 1998-05-06
Publication date: 1999-02-18
Also published as: AU7343498A

Abstract

The invention which is the subject of the current application relates to apparatus for forming, and preferably threading, apertures in sheet material in environments which can be potentially hazardous such as, for example, in fuel storage tanks. The apparatus includes a cutter head which can include a locating or pilot drill which is arranged so as to allow location of the cutter head but not prior penetration of the sheet material. The cutter head is located in use within a housing in which is created a non volatile environment by the introduction of non volatile fluid therein such as foam, nitrogen and/or the creation of a vacuum therein.

Description

Hole Cutting and Threading Apparatus

The invention which is the subject of this application relates to drilling apparatus and particularly, but not exclusively, apparatus for use in drilling and/or threading apertures in volatile environments such as, for example, tanks which may store hazardous materials such as petrol or other chemical materials.

Conventionally, if it is necessary to drill a hole into a tank which contains a hazardous material, such as, for example, to allow the fitment of a measuring device or the like, the hole is normally drilled into a part of the tank which is removable and which is first removed so that the hole can be drilled at a safer location remote from the tank. The reason for this is that drilling and tapping holes creates a risk of sparking, explosion and/or contamination of the material in the tank which can be dangerous and cause, in some circumstances, injury and/or extensive damage. Furthermore, it is required to degas or flush the tank prior to the removal of the part to be drilled and it is also necessary to provide and fit a substitute part to be fitted while the original part is removed for drilling and this is inconvenient and can in itself be dangerous. The need to drill holes in tanks of this type and particularly in relation to petrol storage tanks at service stations is increasing as the desire to gauge the level of the material held within the tank increases and so the requirement to fit gauges through apertures into the tanks increases.

One known attempt to solve this problem is to drill holes and thread the same with the drill and tapping tools held within a housing placed on the material to be drilled and into which an inert gas is pumped to create an inert operating environment in which drilling can occur. A variation of this form of apparatus is disclosed in prior patent application No WO 9421409 which discloses apparatus which can allow the drilling of a tank in situ. This apparatus includes a conventional annular drilling head which is introduced onto the tank in an inert atmosphere and which is followed by a router to form the hole to the required dimension and in turn followed by a thread tapping tool to form a thread in the hole which is formed. However, the form and use of this apparatus is such that it is required to be held in position in relation to the tank by a rig which is heavy to transport, inconvenient to handle and it has therefore led to the use of this type of apparatus being relatively restricted due to the inconvenience and expense of transporting this type of apparatus to the numerous locations of petrol tanks.

A further problem with the apparatus of this prior art patent is that a centreless hole cutter is required to be used, i.e. an annular cutter without a pilot drill, as it is claimed that the use of a pilot drill is not possible as it is potentially hazardous. To allow the centreless hole cutter to be used and be sufficiently well located with respect to the tank, a specially designed fitting arrangement is provided between the drill head and the tapping tool and a router is provided intermediate the two. The fitting arrangement allows relative resilient axial movement between the tools along the same shaft and it is claimed that this allows a threaded hole of the required accuracy to be formed. However the fitting arrangement between the tools is relatively complicated and therefore expensive.

An aim of the present invention is to provide drilling apparatus which allows holes to be drilled in situ in hazardous situations and does^' not require the removal of any part of the tank to a remote location and, furthermore, to provide the apparatus in a form which allows the same to be easily transportable, safe and, in some instances, hand held. In a first aspect of the invention there is provided apparatus for drilling a hole, said apparatus comprising a cutter head, a housing within which said cutter head is located, a sealing means to allow said housing to be sealed to the plate material in which the hole is to be cut and a means for creating a non volatile environment in the housing and wherein said cutter head is associated with a pilot drill which locates on the surface of the material to be drilled prior to the cutter head to form a locating recess or aperture after which the cutter head contacts and cuts through the material accurately in relation to the centring recess or aperture to form the hole.

In a particular embodiment the cutter head forms a sleeve, along the central axis of which is located the pilot drill. Surrounding the pilot drill and located within the rotary hole cutter there may be a disc which can in one embodiment be a disc magnet and in one embodiment the disc is provided with a pilot drill protrusion depending downwardly therefrom so that the same form an integral unit and the pilot drill therefore only projects by a relatively small extent from the disc such that the depth of the recess to be formed by the pilot drill is determined by the extent of the projection. The pilot drill preferably projects by a small amount from the cutting end of the cutter head and to an extent sufficient to at least commence to form a recess in the sheet material which is to be cut by the cutter head prior to contact with the cutter head and sheet material. For example, the pilot drill may project beyond the cutting edge of the cutter head by an amount in the order of 3 mm so as to form a 3 mm countersink in the sheet material to centre and locate the assembly as the rotary hole cutter performs the cutting operation.

As an alternative to the pilot drill projecting from the cutter head, it could be arranged so as to move forward after the cutter head is positioned in relation to the plate to be cut whereby the pilot hole or recess is formed before cutting of the coupon to form the aperture takes place.

In a further embodiment of the invention, there is provided apparatus for drilling a hole into sheet material, said apparatus comprising a cutter head for drilling an aperture, and a pilot or second drill and wherein the cutter head has a cylindrical annular teeth arrangement and within the annular teeth arrangement there is provided the second drill and at least once the cutter head forms the hole the second drill is positioned so that the tip of the same is rebated from the end of the cutting teeth of the cutter head so that the second drill does not break through the sheet material prior to the teeth of the first drill. The second drill acts as a pilot drill and can in one embodiment be of a twist drill form with a composition such that it has a number of flanges on the cutting flutes which in addition to forming the recess can serve to exert a gripping action on the coupon cut to form the hole, thus ensuring that the coupon is securely held by the drill and can only be released by reverse rotation of the object from the flutes when the drills have been removed from the drilling position. This prevents the disc from dropping into, for example, a tank.

.In whichever embodiment the pilot or second drill is prevented from protruding through or piercing the sheet material prior to the cutter head. This can, in one embodiment, be achieved by providing the pilot drill so that it is capable of forming a recess of a depth of less than that of the sheet material such as, for example causing the same to protrude from a plane which abuts against the sheet material such as a disc or disc magnet when the pilot drill is advanced, by the required distance equalling the required depth of the recess to be formed. In one embodiment the extent of protrusion can be adjusted to suit different sheet material thickness or alternatively different pilot drill arrangements can be fitted. Preferably the apparatus includes a control means such that the atmosphere within the housing is maintained in a non volatile condition within set limits during use and controls the same to maintain the set limits and, if the atmosphere is detected to be outwith the said limits the operation of the cutter head and thread former is prevented.

In one embodiment of the invention there is provided apparatus for drilling a hole in sheet material, said apparatus comprising an annular drill head, said drill head positioned within a housing which contacts with the sheet material in which the hole is to be drilled to form a substantially fluid tight seal between the housing and the sheet material, and wherein there is provided a connection to the interior of the housing which, in operation, creates a negative pressure within the housing to expel other potentially hazardous materials from the housing. Thus a vacuum is created in the housing by connecting the housing to a vacuum pump.

In one embodiment there is provided a non volatile fluid supply to the housing which is set to be introduced at a pressure lower than that of other gases in the housing such that at any time, if the vacuum fails, the non volatile fluid is fed into the housing to again expel other potentially hazardous gases, such as oxygen, from the housing.

hen drilling is completed and the hole is formed, the vacuum in the housing is lost and a non-volatile fluid is introduced into the housing to fill the housing and any space or ullage on the other side of the hole formed has nitrogen or an inert gas flowing therein throughout the drilling and tapping process. It should be noted that the non volatile fluid can be nitrogen or any suitable inert gas or alternatively may be a foam. Indeed in a further embodiment of the invention, rather than create a vacuum, the housing can be filled with nitrogen or a foam material to allow the non volatile conditions required to be created in the housing.

In a preferred embodiment of the method, the supply of the non volatile fluid is maintained to the housing during the drilling process such that if for whatever reason the vacuum is lost or there is escape of non volatile fluid already supplied to the housing, the non volatile fluid is automatically introduced into the housing.

Typically, there is provided a coolant supply which is fed into the housing via a suction feed and a vacuum return line which are positioned in the housing closer to the drill head than the vacuum line which is used to create the negative pressure within the housing.

The apparatus in one preferred embodiment comprises only a cutter head and a thread tapping tool and there is no need for a hole reamer or other component to be provided intermediate the same. This is achieved by increased control of the location of the cutting and threading tools using the pilot drill and the selection and utilisation of specifically designed components. This simplifies the process and also reduces the time taken to form and thread the hole in contrast with the conventional in situ apparatus which requires a reaming operation to be performed after the hole is cut to form the hole^' to the required dimension for thread forming.

Preferably, the apparatus also includes a means for introducing coolant to the immediate environment surrounding the cutter head so as to introduce the coolant during the operation of the cutter head and the thread former. Preferably, the apparatus also includes suction means for removing coolant. This is especially important if the plate material is part of a tank so that the removal of the coolant from the housing prevents the coolant from entering, and possibly contaminating, the material held in the tank of which the plate material can form a wall or lid closure. In one particularly inventive feature of the apparatus the thread former, cutter head and/or shaft on which the same are mounted for rotation includes a reservoir of coolant and feed means which allows a controlled feed rate of coolant from the reservoir to the immediate environment surrounding the cutter head and thread former during operation thereby ensuring supply of the coolant at the required rate. In one form the reservoir is fed with coolant from a remote location and a series of bleed holes are provided to allow the controlled flow of coolant from the reservoir to the immediate environment around the cutter head.

In an alternative embodiment the coolant supply to the area of cutting and forming is propelled by nitrogen which has the added effect of excluding oxygen from the cutting area and therefor encouraging an inert atmosphere within the housing. The coolant is held in a pressurised reservoir to ensure positive supply of the coolant. In order to improve the efficiency of the apparatus and system a collection system is provided for used coolant which serves to remove said used coolant under vacuum from the cutting area into a return tank..

In a further embodiment of the invention the apparatus is provided with; depending downwardly from the drilling head and thread former, retaining means which allow the retention of the coupon formed by the cutting of the hole in the plate material, thereby preventing the disc from falling into the storage tank. In one form the retaining means can be a magnet and particularly a rare earth magnet as this type maintains the attraction force with variation in gap between the magnet and the disc. In one preferred embodiment the magnet is spring mounted with relation to the cutting tool.

Alternatively, other retaining means may be used such as suction means or the like.

In a further embodiment of the invention there is provided a system for cutting and forming a hole, said system comprising introducing a cutting tool to the material to be cut to cut a hole in the material, introducing a tapping tool mounted on the same arbour as the cutting tool to form a taper thread in the hole previously formed, enclosing said cutting and tapping tools in a housing during operation which is sealed with the material being cut, to form a controlled non-volatile environment.

The tapping tool used is preferably provided to cut a taper thread rather than a parallel thread as it provides improved sealing when a component is ultimately screwed into the hole. Alternatively a reaming tool could be used. Typically the cutting tool is formed from tool steel with a number of teeth around an annular wall which has flutes depending therefrom to aid the removal of debris away from the hole.

Additional non volatile fluid such as nitrogen can also supplied from a separate source to the ullage of the tank in which the hole is formed which maintains a positive pressure to further exclude the introduction of air containing oxygen into the cutting area within the housing.

In use, for a certain period of time before, and during the cutting and threading operation, a non volatile fluid such as nitrogen is supplied into the ullage of the tank which will be calculated prior to the use of the apparatus and sufficient nitrogen is supplied to reduce the oxygen content within this area to less than 5%. During initial set up a monitor can be placed at the vent pipe system for the tank and oxygen levels emanating from the tank tested.

The apparatus is also provided with a monitoring system that can detect lack of positive nitrogen pressure to the housing and sound an audible alarm should the pressure fall below a preset value. The monitoring system control unit contains no electrical components and is therefore safe to use close to the point of use of the apparatus, thereby allowing observation of the same by the operators of the apparatus.

It is preferred that the system is modular thereby improving ease of use and storage between sites. The cutting apparatus is provided to be assembled from sections, each preferably weighing less than 20 kg thereby allowing the sections to be carried and assembled by two persons on site. Furthermore the apparatus can be transported in a vehicle such as a car or small van and the modular system enables cutting into tank lids which can be between the range of 3 and 10 feet below the forecourt surface..

In one particular embodiment of the invention the cutter head has a hollow centre cavity defined by an annular wall, said wall at one end having cutting teeth spaced therearound and, leading away from said teeth, flutes formed in the outer surface of said wall.

In one embodiment a tapping tool is attached to the cutting tool to follow the same into the hole as the cutting tool passes therethrough thereby providing a continuous cutting and tapping operation without the need for removal of either of the tools before use of the other. In a further aspect of the invention the apparatus housing includes clamping means which allow the apparatus to be clamped in position prior to operation and in a manner so as to minimise the force required to be exerted on the apparatus to allow the forming of the hole. In one preferred feature, the apparatus is provided with first clamping means immediately adjacent the area in which the hole is to be drilled thereby allowing the apparatus to be clamped securely to the plate material and for the sealing means to act effectively and second clamping means are provided to allow the apparatus to be clamped to articles or surfaces to the side of the housing of the apparatus.

In this form, the apparatus is thereby prevented from moving in line with the direction of cut and laterally to the direction of cut thereby minimising the external forces required to be applied to the apparatus for the drilling/ cutting and thread forming operations. In practice, during the drilling part of the operation, a downward force is required to be exerted and during the threading action a lateral retaining force is required to be provided and it is found that the dual clamping means provide the required clamping forces to such an extent that no rig or other external support mechanism is required and also that it is possible for the apparatus as a whole to be hand held for certain operations.

In a further feature of the invention the cutter head and thread former are mounted on a shaft for rotation with the shaft, in turn connected to a drive means which can be mounted on the end of the housing opposing that at which the cutter head lies. In one embodiment the drive means is a hydraulic motor which is connected to a hydraulic compressor which can in one embodiment be provided in the transport means for the apparatus. Specific embodiments of the invention will now be described with reference to the accompanying drawings wherein;

Figure 1 illustrates the components of the apparatus at the drilling and forming end of the same, in one embodiment;

Figure 2 illustrates the apparatus of the invention in situ in one embodiment;

Figures 3A and 3B illustrate a further embodiment of the invention;

Figure 4 illustrates a connection diagram for the apparatus of the invention;

Figure 5 illustrates the cutting and tapping apparatus of the system;

Figure 6 illustrates apparatus according to one embodiment of the invention; and

Figures 7 - 10 illustrate a further embodiment of the apparatus according to the application.

Referring firstly to Figure 1 there is illustrated one embodiment of the device and apparatus of the invention. The device is shown in location for drilling and threading a hole in plate material, in this case a flange cover 2 which can be part of a tank 3. The device includes a housing 4 , shown partially cut away and at the end of the housing 4 are provided sealing means 6 which are provided as part of clamping means 8. The clamping means depend downwardly from the housing and are provided to be clamped to the plate material around the area where the hole 10 (shown in broken lines for illustration) is to be cut. The clamping means also ensure that the sealing means 6 are held in close contact with the plate material 2 thereby minimising or preventing leakage from the housing to the external atmosphere in use. Mounted within the housing and passing along the length thereof there is provided a shaft 12 which is connected to a drive means 14, shown in Figure 2 and a hand wheel 13 for feeding the cutter head and thread former onto the plate material. Mounted at the end of the shaft is a cutter head 16 in the form of a round cutter for cutting a disc from the plate material and a thread former 18 which follows the cutter head 16. Also provided is a retaining means 20 which is operable to contact and retain the disc of plate material when the hole 10 is formed. The retaining means is typically a magnet of rare earth and is movable between a retracted position and retaining position by biasing spring 22.

The thread former tool 18 can also include a reservoir 24 of coolant which is supplied from an external line 26. A series of bleed holes ( not shown) allow a controlled quantity of coolant to leave the reservoir 24 and flow to the area in which the hole is formed to aid the forming process. A coolant extraction means 28 is also provided to remove coolant from the housing so as to prevent contamination of the material in the tank and allow optimum conditions to be maintained during forming.

In addition to the above features a supply of nitrogen 29 is provided to be introduced into the exterior of the housing during operation of the apparatus. The supply of nitrogen allows the housing to be held in an inert atmosphere and the operation of the cutter head and thread former to be significantly less dangerous in operation. A nitrogen supply is also provided into the fill pipe 31 of the tank 3 to maintain the ullage in the same in a non volatile condition during operation of the apparatus.

The operation of each of these features is controlled by monitoring and control means at a remote location and connected by pipes and cables 33 to ensure that the optimum operating conditions, such as the nitrogen and coolant supplies and clamping means are maintained. The control means also ensure that if preset safety levels of operation are exceeded the apparatus is automatically stopped.

Figure 2 illustrates the apparatus in use in one embodiment wherein the device is shown with the drive means 14 mounted on the housing 2 and connected via supply lines 31 to nitrogen, coolant and hydraulic power supplies 35 located the transport vehicle 32.

In use the apparatus of the invention allows a hole to be formed by the cutter head and then tapped by the thread former in one operation. To further enhance the safety of the device it is envisaged that suitable materials such as beryllium can be used for the cutter head which has reduced or no sparking properties. It is also envisaged that in a preferred embodiment a pilot drill will be mounted on the shaft so that the same passes partially into the plate material prior to the cutter head and acts as a centring device to ensure that the cutter head is accurately positioned on the plate material during operation.

Figure 2 illustrates the device being held in position by a person without the need for support rigs or the like and with the cutter head and thread former end of the housing below ground level in the access hole 38 in which the plate material 2 to be cut is located. This is achieved by the provision of clamping means 8 as shown in Figure 1 and as previously described which comprise chains 35 attached to anchoring means on the plate material and a second set of clamping means which allows the housing to be clamped to vertical surfaces 37 of the access hole along the side of the housing and which define the access hole below floor level 39 in which the housing is typically located. To this end the housing can be provided with a series of grooves which lie at spaced intervals around the housing and run the length of the same. Articulated arms attach to the slots to allow the secure location of the housing in relation to the tank. Thus any combination of the first and second clamping means can be used depending on the available surfaces for clamping and so the secure location of the housing can be achieved without the need for external support rigs.

An embodiment of the invention will now be described, by way of example, with reference to Figures 3A which is a diagrammatic sectional elevation through a cutter head and thread forming tool according to the invention and Figure 3B which is a plan view of the cutter and threading tool and usable in accordance with the method of the invention.

In the drawing, a steel plate 110 of, for example, a petrol tank is to be drilled and the hole threaded by a unit 111 comprising a cutter head in the form of a cylindrical rotary hole cutter 112 having an annular cutting edge 114 at the lower end thereof and a thread forming tool 118. Inside the rotary hole cutter 112 is a pilot drill 116 having a conical tip 119. The tip 119 as illustrated at 120 projects beyond the face 121 of a disc 123, which in this case includes a magnet, by a small amount, in this case 3 mm and when first advanced to the sheet material the pilot drill extends beyond the cutting edge 114 of the rotary hole cutter.

During the cutting process the disc 123 and pilot drill tip 119 are enclosed inside the rotary hole cutter 112 as the same advances through the sheet material. In the embodiment shown the pilot drill 116 and disc form an integral component.

For the cutting of the plate 110, initially the pilot drill tip 119 is advanced in the position shown so as to first engage and penetrate the plate 110 as shown to advance to form a countersunk hole 122 which forms a centralising and locating means for the rotary hole cutter. Continued advancing of the pilot drill and cutter head and thread former causes the pilot drill to advance to a point at which the face 121 of the disc 123 contacts the sheet material to prevent further advancement of the pilot drill into the sheet material and a drive pin for the pilot drill to be released to prevent further rotation of the same. Meanwhile continued advancement causes the cutter head to pass through the sheet material to form the hole and be followed by the thread forming tool to thread the same. The coupon formed when forming the hole is held by the magnet in the disc 123 when the hole is formed and the cutter head is eventually retracted.

The pilot drill 116 may be driven independently of the rotary cutter 112 and may be movable axially independently of the rotary cutter 112 or, as shown, may be prevented, in this case by the disc 123 from penetrating further in to the sheet material and acts against spring 125.

The pilot drill is however not allowed to penetrate through the sheet material 110 but only penetrates sufficiently to make the countersink location hole/recess 122. In this connection the disc 123 is utilised to stop movement of the pilot drill 116 to prevent it from penetrating too deeply into the plate. An alternative control may be provided for limiting the penetration of the pilot drill.

The invention provides that it is the cutter head 112 which penetrates through the plate 110 and not the pilot drill which is the preferred arrangement in all circumstances.

Instead of, or in addition to, the magnet retaining the cut coupon, this may be retained by providing special flutes or other holding means on the pilot drill for retaining the cut coupon. Figures 4 and 5 illustrate a further embodiment of the invention wherein the cutting and tapping apparatus 202 with the cutting and tapping tools mounted within the housing 204 are shown in more detail in Figure 5. The housing is connected by pipes to a coolant supply reservoir 206 and used coolant reservoir 208 to allow the supply and removal of coolant from the area of cutting, and to a nitrogen supply 210 via pipe 212 and control unit 214. The control unit is also connected via lines 216, 218 and 220 to monitor the pressure in the housing, the coolant supply and coolant return respectively. The nitrogen supply 210 is also connected to a filling means 222 which, prior to the use of the cutting and tapping apparatus 202, is positioned over the lid of the tank to introduce nitrogen into the tank to fill the ullage in the tank and reduce the oxygen level in the ullage to less than 5%. Although not show the system is also connected to a drive means such as a diesel hydraulic drive and power means to allow operation of the apparatus of the system. However this drive means should be positioned away from the area of operation.

Figure 5 illustrates the cutting and tapping apparatus of the invention in more detail. The apparatus comprises the housing 204, shown in section, which includes a series of outlets and inlets 230 to allow connection of the nitrogen supply 212, nitrogen monitoring 216, coolant supply 232 and coolant return pipes 234. The housing is also provided, at the open end 236 with a sealing means to allow a seal to be created between the housing and the tank sheet material 238 when in use. Within the housing there is provided the cutting tool 240 which has a hollow cavity 241 in which there is provided a magnet 243, said cutting tool connected for rotation by shaft 242 and, mounted on the same shaft behind the cutting tool is the tapping tool 244. The position of the housing relative to the support and clamping means is determined by the position of the housing bracket 246 on the rack 248 and the linear movement of the shaft and hence cutting and tapping tools 240, 244 is determined by movement of the manual winding wheel 250 which can be operated manually to control the position and movement of the shaft along the rack 248 during operation.

Also shown is the filling means 222 which is in connection with the interior of the tank via inlet 250 to allow nitrogen to be introduced into the same as described.

In operation of the system to cut a hole in a petroleum tank, the first step is to remove the man chamber cover for the tank and remove the tank lid for inspection and determination of the size and location of the threaded hole to be formed. The appropriate clamping means is chosen as set out in the co-pending application. The distances between the centre point of the hole to be formed and the clamping line, and the tank lid to forecourt level, are measured to determine any spacers, extensions and the appropriate tool housing required.

With the appropriate housing fitted to the suitable rack and clamped in position, the cutting and tapping tools are checked for damage and tightened in position.

The appropriate connecting pipes are positioned to the appropriate outlets and inlets on the housing and, to ease use, the same are colour coded. The housing is then positioned on the tank with the end of the housing lying around the area in which the hole is to be formed and the housing is clamped securely in position with the end sealed to the tank. If necessary, extensions can be connected to the shaft on which the cutting and tapping tools are mounted and the motor 254 and winding mechanism 250 is connected so as to complete the cutting and tapping apparatus 202.

The coolant supply and return reservoirs, nitrogen supply and control unit are then connected as required and the filling means 222 is connected to the nitrogen supply and the interior of the tank to introduce nitrogen into the tank. With this completed the coolant supply and return levels and nitrogen supply level to the housing 204 are set by the control unit and the power is connected. The coolant and nitrogen levels are again checked and the cutting tool is slowly introduced linearly onto the tank while rotating to cut the hole. With further additional winding the cutting tool is applied under gentle pressure to cut through the lid. When the hole is formed the tools are further wound down until the start of the tapping tool contacts the edges of the hole. At this point the winding mechanism is released as continued rotation of the shaft causes the tapping tool to wind down at a rate which is appropriate to the required thread pitch as it rotates.. Once the mechanism starts to self wind, one revolution is counted whereupon the rotation is stopped and reversed, at which stage the tapping tool itself winds in an upward direction for one revolution whereupon the tools are then manually wound up so as to avoid damage to the hole formed. When the tapping tool is withdrawn the coolant and power is switched off along with the nitrogen supply. The housing can then be released and a threaded plug inserted in to the hole formed before the required instrument is inserted in due course. The cutting and tapping tools can then be cleaned, the cut disc removed from the magnet, and the system disassembled to be transported to the next site. A yet further embodiment of the invention is shown in Figures 6- 10 and, referring firstly to Figure 6, there is illustrated in schematic form apparatus of the embodiment according to the invention. The apparatus comprises a housing 302 which is provided with end faces 304 to locate on sheet material 306 in which the hole is to be cut. In this case the sheet material is part of a tank lid for a petrol storage tank for filling stations and therefore is a hazardous environment. Passing through the opposing end of the housing is a shaft 310 upon which is mounted a tapping means 312 and, forward of the same, a drill head 316 with annular cutting teeth 318. The shaft, tap and drill head are movable downwardly onto the sheet material when rotated to form an aperture in the sheet material and thread the aperture respectively. In order to allow the disc which is cut when the aperture is formed to be retained, a centre or second drill 320 can be provided as indicated in broken line to lie within the annular drill head 316. The tip of the second cutter drill 320 is rebated from the end of the cutting teeth 318 so as to ensure that in all cases the cutting teeth 318 enter the sheet material first. Typically the drill 320 is provided with retaining means formed on the flutes so that the coupon formed when the aperture is cut is maintained in position on the drill until the same is counter rotated. This allows the apparatus to be used on sheet material whether or not the same be magnetic and allows the coupon to be retained in all circumstances.

As the environment in which the aperture is to be cut is hazardous, it is important that safety measures are provided and there is shown in Figure 6 a vacuum line 322 which is positioned to introduce and create a negative pressure or vacuum within the housing during operation of the drill and thus prevent potentially hazardous oxygen from gathering in the housing. Furthermore, if, for any reason the vacuum is lost during the drilling process, there is provided a nitrogen supply line 326 into the housing which will automatically introduce nitrogen into the housing and again act to prevent or evacuate oxygen from the housing. When the aperture is formed, the vacuum is lost and at this stage, nitrogen is pumped from line 326 into the housing to again evacuate oxygen from the housing and, at the same time, nitrogen is pumped into the tank and this occurs during the drilling and tapping process. There is also provided a coolant supply 328 and extraction system 320 to allow coolant to be introduced into the housing adjacent the drill head teeth 318.

Referring now to Figures 7 - 10, there is illustrated a process for removing an internal fill pipe from a tank to facilitate retrofitting of overfill prevention devices into the tank.

Firstly, a double bung is located into the internal fill pipe and secured using a bar which is connected through the hollow centre of the cutting device of the tool. This prevents the internal fuel pipe from dropping into the tank once the cutting process is complete. With the fuel pipe secured, the apparatus 400 is inserted by threading the same onto the fill pipe 401 assembly with the leading cutting edge of the drill head located in the neck of the internal fill pipe as shown in Figure 7. A housing 402 is then installed over the drill head and secured to the thread on the external fill pipe 404. The drive unit is then fitted to drive the drill head in the conventional manner. The drill head is then rotated to remove the fill pipe in a first stage as shown in Figure 8. The drill is then continued to rotate to cut a larger opening through the weld of the fill "pipe to provide additional clearance so that the sheared off section can be withdrawn from the tank and subsequent components fitted as required.

Thus the apparatus of the present invention allows safe and securely positioned cutting of holes in situ in environments which are dangerous and susceptible to explosion without the need for extensive and additional supporting apparatus and indeed allows the apparatus to be hand held in use which is a significant advantage over the prior art apparatus.

Claims

1 Apparatus for drilling a hole, said apparatus comprising a cutter head, a housing within which said cutter head is located, a sealing means to allow said housing to be sealed to the plate material in which the hole is to be cut and a means for creating a non volatile environment in the housing and wherein said cutter head is associated with a pilot drill which locates on the surface of the material to be drilled prior to the cutter head to form a locating recess or aperture after which the cutter head contacts and cuts through the material accurately in relation to the centring recess or aperture to form the hole.

2 Apparatus according to claim 1 wherein the cutter head forms a sleeve, along the central axis of which is located the pilot drill and which has a tip protruding from a surface, the extent of protrusion defining the depth of locating recess to be formed.

3. Apparatus according to claim 1 wherein the pilot drill has located therearound and at a spaced distance from the tip thereof a magnet for retaining the coupon of sheet material cut to form the hole.

4. Apparatus according to claim 3 wherein the magnet is mounted in a disc and the pilot drill tip projects from the disc to an extent sufficient to form a recess in the sheet material which is to be cut by the cutter head.

5 Apparatus according to claim 1 wherein the tip of the pilot drill protrudes beyond the cutter head such that as the cutter head and pilot drill are advanced to the sheet material the pilot drill first contacts the sheet material to form a centring and locating recess.

6. Apparatus according to claim 1 wherein the pilot drill is arranged to move forward with respect to the cutter head after the cutter head is positioned in relation to the sheet material to be cut whereby the locating recess is formed before cutting of the coupon to form the hole is completed.

7. Apparatus for forming an aperture in sheet material, said apparatus comprising a cutter head for drilling a hole, and a pilot or second drill and wherein the cutter head has a cylindrical annular teeth arrangement and within the annular teeth arrangement there is provided the second drill, and at least once the cutter head has formed the hole, the second drill is positioned so that the tip of the same is rebated from the end of the cutting teeth of the cutter head so that the second drill does not break through the sheet material prior to the teeth of the first drill.

8 Apparatus according to claim 7 wherein the second drill is a twist drill with a composition such that it has a number of flanges on the cutting flutes which serve to exert a gripping action on a coupon which is cut to form the aperture, thus ensuring that the coupon is securely held by the drill for subsequent release when the cutter head has been removed from the drilling position.

9 Apparatus according to claims 1-6 wherein there is provided a control means such that the atmosphere within a housing in which the cutter head is positioned is maintained in a non volatile condition within set limits and controls the same to maintain the set limits and, if the atmosphere is detected to be outwith the said limits the operation of the cutter head and thread former is prevented.

10 Apparatus for forming an aperture in sheet material, said apparatus comprising an annular cutter head, said cutter head positioned within a housing which contacts with the sheet material in which the hole is to be formed to form a substantially fluid tight seal between the housing and the sheet material, and wherein there is provided a connection to the interior of the housing which, in operation, creates a negative pressure within the housing to expel other potentially hazardous materials from the housing.

11. Apparatus according to claim 10 wherein a vacuum is created in the housing.

12. Apparatus according to claim 10 wherein there is provided a non volatile fluid supply to the housing which is controlled to be introduced at a pressure lower than that of other gases in the housing such that at any time, if the negative pressure fails, the non volatile fluid is fed into the housing to expel other potentially hazardous gases from the housing.

13 Apparatus according to claim 12 wherein when the hole is formed, the negative pressure in the housing fails and a non-volatile fluid is introduced into the housing to fill the housing with the same and any space or ullage on the other side of the aperture formed has nitrogen or an inert gas flowing therein throughout the drilling and tapping process.

14 Apparatus according to any of the claims 11-13 wherein the non volatile fluid can be nitrogen or any suitable inert gas or a foam.

15. Apparatus according to any of claims 1-6 and 9- 14 wherein a non volatile environment in the housing is formed by introducing nitrogen or an inert gas or a foam material to allow the non volatile conditions required to be created in the housing.

16 Apparatus according to claim 15 wherein the supply of the non volatile fluid is maintained to the housing during the drilling process such that if there is escape of non volatile fluid already supplied to the housing, the non volatile fluid is automatically introduced into the housing.

17. Apparatus according to any of claims 1-6 and 9-16 wherein, there is provided a coolant supply which is fed into the housing via a suction feed and a suction return line.

18 Apparatus according to any of the preceding claims wherein there is provided, in addition to the cutter head, a thread tapping tool mounted coaxially and behind the cutter head so that continued advancement of the cutter head through the aperture when formed brings the tapping tool into contact with the aperture walls to thread the same.

19. Apparatus according to claim 18 wherein the thread tapping tool used is provided to cut a taper thread.

20 Apparatus according to any of the preceding claims wherein the cutter head and/or thread tapping tool, if provided, and/or shaft on which the same are mounted for rotation includes a reservoir of coolant and feed means which allows a controlled feed rate of coolant from the reservoir to the immediate environment surrounding the cutter head during operation.

21 Apparatus according to claim 20 wherein the reservoir is fed with coolant from a remote location and a series of bleed holes are provided to allow the controlled flow of coolant from the reservoir to the immediate environment around the cutter head.

22 Apparatus according to any of the claims 1-6 and 10-21 wherein there is provided a monitoring system to detect a lack of supply of non volatile fluid to the housing and sound or indicate an alarm should the pressure fall below a preset value.

23. Apparatus according to claim 22 wherein the monitoring system control unit contains no electrical components and is safe to use close to the point of use of the apparatus to allow observation of the same by the operator of the apparatus.

24. Apparatus according to any of the preceding claims wherein the cutter head comprises a hollow centre cavity defined by an annular wall, said wall at one end having cutting teeth spaced therearound and, leading away from said teeth, flutes formed in the outer surface of said wall.

25 Apparatus according to claim 24 wherein there is provided in fixed engagement with the cutter head a thread tapping tool to follow the cutter head into the hole thereby providing a continuous cutting and tapping operation.

26. Apparatus according to any of the claims 1-6 and 10-25 wherein the housing includes clamping means which allow the housing to be clamped in position prior to operation and so as to minimise the force required to be exerted on the apparatus to allow the forming of the hole.

27. Apparatus according to claim 26 wherein the apparatus is provided with first clamping means immediately adjacent the area in which the hole is to be drilled thereby allowing the apparatus to be clamped securely to the sheet material and second clamping means are provided to allow the apparatus to be clamped to articles or surfaces to the side of the housing of the apparatus.

28 Apparatus according to any of the claims 1-6 and 10-27 wherein the shaft upon which the cutter head and, if provided, pilot drill and thread tapping tool, are mounted for rotation is connected to a drive means which is mounted on the end of the housing opposing that at which the cutter head lies.

29 Apparatus according to claim 28 wherein the drive means is a hydraulic motor which is connected to a hydraulic compressor which is provided in the transport means for the apparatus.

30 A method for cutting and forming a hole, said method comprising introducing a cutting tool with a cutter head having an annular cutting edge to the material to be cut to cut an annular hole in the material, introducing a thread forming tool mounted on the same arbour as the cutter head to form a thread in the hole previously formed, enclosing said cutter head and thread forming tool in a housing during operation which is sealed with the material being cut, to form a controlled non-volatile environment.

31. A method according to claim 30 wherein the hole is cut in sheet material forming a wall of a tank and a non volatile fluid is supplied to the ullage of the tank in which the hole is to be formed to exclude the introduction of a gas containing oxygen into the cutting area within the housing.

32 A method according to claim 31 wherein for a period of time before, and during the cutting and threading operation, nitrogen or another non volatile gas is supplied into the ullage of the tank to a sufficient extent to reduce the oxygen content within this area to less than 5%.

33. A method according to claim 30 wherein there is provided a magnet mounted within the cutter head which acts to attract and retain the coupon cut from the sheet material to form the hole.

34 Apparatus as hereinbefore described with reference to the accompanying drawings.