GROUNDING TERMINAL

Abstract: It is described a grounding terminal for temporary fastening a grounding conductor to a construction to be welded. The grounding terminal uses permanent magnets, example given of neodymium (Nd-Fe-B-35) to fasten the terminal to the construction. A welder that uses the grounding terminal can by one grip easily scrape the contact surface of the construction free of paint, rust and oxide scale and thereafter fasten the grounding terminal to and unfasten it from the construction. Fastening and unfastening is based on relocation of the permanent magnets in such a way that an open and a closed magnetic loop respectively, are created.

Description: GROUNDING TERMINAL Technical field of the invention The invention concerns a grounding terminal for temporary connecting a grounding conductor to an object to be welded. Background of the invention By all welding a positive and a negative cable are used where the negative cable is the ground cable which is fastened to the construction to be welded. The welding is performed by the positive cable to which an electrode holder or a feeding piston is mounted. To fasten the ground cable to the construction a grounding terminal is used. Known grounding terminals comprise among other things earthing clamps, that grips over the construction, example given a pipe, by using a mechanical s force providing electrical contact with the construction. However, earthing clamps can not be fastened to all geometrical surfaces as they are dependent upon being able to grip around the object. The electrical connection is dependent upon that the jaws of the earthing clamps grip well around the construction to give sufficient contact. The mechanical force is often provided by screws or mechanical springs, o that after a while can get loose and thereby give poorer contact with the construction. If an earthing clamp shall be fastened on bigger constructions, an ear must first be welded to the construction to which the earthing clamp then can be fastened. Other known grounding terminals are based on magnetism, and comprise 5 terminals with permanent magnets and terminals based on the use of electromagnets. Such grounding terminals can be used when the construction to be welded is made of a ferromagnetic material. Example given, it is described in the patents US 2 287 112 and US 2 437 633 magnetic grounding terminals based on an electromagnet. When the current is switched on, the terminals are magnetised o and the contact surface is drawn towards the workpiece. Electromagnetic grounding terminals must however have their own power supply and their own conductor from the power supply to the coil in the electromagnet of the terminal. Grounding terminals with permanent magnets are example given disclosed in US 2 429 526 and US 4 676 562. The grounding terminal in US 4 676 562 is designed to be held and fastened by one hand. The terminal will however be hard to unfasten from the workpiece. James Morten™ has also put on the market a magnetic grounding terminal based on permanent magnets. Known grounding terminals with permanent magnets have generally the disadvantage that the magnetic force can not be "tur- ned off" in that way the current in an electromagnet can be turned off, or in another way be moved away from the contact surface with the construction. These magnetic grounding terminals will in a typical industrial environment also attract metal shavings that fasten on the contact surface. This is highly unwanted as it will give poorer contact between the workpiece and the grounding terminal. o To obtain a good ground connection between the grounding terminal and the workpiece to be welded, the contact surface on the construction must also be free of paint, rust and oxide scale. This is now done by using a separate scraper in some form. The welder must therefor be equipped with several tools during welding. 5 Objects of the invention It is an object of the present invention to provide a grounding terminal which can be fastened on all magnetic constructions/workpieces to be welded independent of the geometry of the construction. o Another object of the invention is to provide a grounding terminal with only one conductor, the grounding conductor, and which also can activate and deactivate the magnetic force in the contact surface with the workpiece. A third object of the invention is to provide a grounding terminal which can easily be fastened to and unfastened from the construction to be welded. 5 A fourth object of the present invention is to eliminate the need for extra equipment in form of scrapes for scraping away rust, paint and oxide scale from the contact surface on the workpiece. Summary of the invention o According to the invention the objects above are achieved by a magnetic grounding terminal for temporary connecting a grounding conductor to an object to be welded, the grounding terminal comprising permanent magnets, the permanent magnets having a first state for fastening the grounding terminal to the object and a second state for unfastening the grounding terminal from the object, the ground- ing terminal being arranged to be fastened and unfastened by one hand, the grounding terminal is fastened by pressing it towards the object to be welded and unfastened by pulling it out from the object to be welded. The permanent magnets may be moveable between a first and a second position, representing the first and second state of the permanent magnets respectively. Further, the grounding terminal may comprise a house, two upper parallel extended metal plates and two lower parallel extended metal plates in the house, the permanent magnets are arranged between the metal plates and in the first position constitute an open magnetic loop together with the metal plates for fastening the grounding terminal to the object, and in the second position constitute a closed magnetic loop together with the metal plates for unfastening the grounding terminal from the object. A magnet holder may be arranged between the metal plates, the magnet s holder having an upper and a lower compartment for mounting of the permanent magnets, that are being constituted by an upper permanent magnet and a lower permanent magnet respectively. In the first position the lower permanent magnet is arranged between the two lower metal plates and the upper permanent magnet is arranged between the two upper metal plates, and in the second position the o two permanent magnets are arranged between the two upper metal plates. The house may be equipped with a handle, to which the upper part of the magnet holder is fixed, and movement of the handle then causes the alteration of position of the magnet holder and thereby the permanent magnets. The lower metal plates may provide contact surfaces for contact with the object to be welded. 5 The metal plates may have a certain thickness providing defined end faces. The contact surfaces may then be constituted by the lower end faces of the two lower metal plates, and by a groove formed by the insides of the lower ends of the two lower metal plates, the groove facilitating the fastening of the grounding terminal on pipes and pipe constructions. In a preferred embodiment the insides of the o lower ends of the lower metal plates have the form of opposite slanting faces, the faces slanting upwards in a direction towards each other. The groove may be milled out on the innermost part of the lower end faces of the metal plates. It is preferred to use permanent magnets made of Neodymium, Nd-Fe-B-35. The grounding terminal may also comprise scraping tools for scraping off rust, paint or oxide scale on the object, obtaining a better contact surface with the object. The scraping tool then having scraping knives being arranged protruding perpendicular outwards from the contact surfaces, but in such a way that the scraping tool does not affect the contact surfaces' contact with the object. Then, the grounding terminal has a shape so that scraping off rust, paint and oxide scale on the object to be welded, and fastening of the grounding terminal to the object and unfastening the grounding terminal from the object, may be performed in successive operations by using one hand only and without changing the grip on the grounding terminal. In a preferred embodiment the magnetic grounding terminal is also equipped with a quick release coupling for the grounding conductor so that this easily can be disconnected from the grounding terminal. Measurements have been performed showing that the grounding terminal s satisfies the requirements of sufficient grounding by ordinary welding without power loss in the transition resistor between cargo and earthing magnet causes overheating in the grounding terminal, and it may thereby replace a conventional grounding terminal. The grounding terminal does naturally only work on magnetic materials, and provides a safe grounding during welding on plane surfaces. By o welding on large constructions and pipe dimensions it has quite unique advantages compared to conventional grounding tools, like grounding clamps, since welding, cutting and grinding of an attachment on the surface of the workpiece for the grounding clamp is avoided. The shape of the contact surfaces of the terminal do that it fits well on most dimensions, but of course it is dependent upon a fairly 5 clean surface to obtain a proper ground connection. The exchangeable scraping knives function well on painted or rusty surfaces, meaning that burns and overheating of the grounding are eliminated. The built-in scraping knives do also solve the problem by having to use extra tools for cleaning the surface to obtain proper contact. As the grounding terminal also sticks well to the surface, the problem of a o loose ground connection is eliminated. It is independent of external power supply, and therefore does not fall off by power failure, at the same time as an extra wire and switch are avoided. Brief description of the drawings In the following embodiments of the invention will be further described with reference to the accompanying drawings, where Figure 1 shows an embodiment of the grounding terminal according to the invention, where a part of the house is removed, and the terminal is in a first state for fastening to a construction, Figure 2 shows a longitudinal section through the grounding terminal in figure 1 , Figure 3 shows the grounding terminal in figure 1 in a second state for un- fastening the terminal from the construction, Figure 4 shows a longitudinal section through the grounding terminal in figure 3, Figure 5 is an exploded view of the grounding terminal in figures 1-4, Figure 6 shows an embodiment of the grounding terminal according to the invention seen partly from the front and from the underside, Figure 7 shows the intact grounding terminal in figure 1 in a first state for fastening the terminal to a construction, and Figure 8 shows the intact grounding terminal in figure 1 in a second state for unfastening the terminal from a construction. Detailed description of the preferred embodiment of the invention Construction It is referred to figures 1-8 where the same reference numerals indicate the same elements on the different drawings. Figure 5 shows and exploded view of a grounding terminal according to the invention. Cover A 7, cover B 8, holder 9 and rubber grip 10 enclosing the holder 9, constitute the house of the grounding terminal. Cover A and B is made of heat resistant plastic, and can be integrated in one part, and holder 9 with rubber grip 10 can in the same way be integrated in one part. The inside of the grounding terminal consists in a magnet holder 6 of heat resistant plastic, two upper and two lower metal plates 1 and 2 made of steel, noncorrosive spacing plate 3, and permanent magnets 11a and 11 b of neodymium, Nd-Fe-B-35. The metal plates 1 , 2 are of a certain thickness and thereby have both defined lateral surfaces and end faces. The grounding terminal also has a quick release coupling for connection of a negative conductor 14 to the terminal, the quick release coupling consisting in a noncorrosive bolt 4, quick release coupling element 5 in brass connected to the bolt 4, and a rubber cap 13 enclosing the quick release coupling. The spacing plate 3 consists in two opposite parallel wall parts 3a, 3b spaced from each other, connected at their lower end by a bottom part 3c, shown in figure 5. The two upper and the two lower steel plates, 1 and 2 respectively, are of the same thickness, but the upper steel plate is longer than the lower steel plate. The two lower steel plates are accommodated on opposite sides of the spacing plate 3, and on the same opposite sides the upper steel plates are accommodated above the lower steel plates, but in such a way that the opposite end faces to a lower and an upper steel plate are parallel and in a distance from each other. Metal plates 1 , 2 are arranged on such opposite sides of the spacing plate 3, that the metal plates 1 , 2 and the spacing plate 3 constitute a space with an upper open- ing, the space being defined by the opposite metal plates 1 and 2, the wall parts 3a, 3b and the bottom part 3c of the spacing plate 3. The lower end faces of the lower steel plates constitute the contact surfaces of the grounding terminal with the object to be welded. The magnet holder 6 mainly consists of two parts. A lower rectangular part with an upper rectangular compartment and a lower rectangular compartment where the magnets 11a and 11b can be accommodated, constituting respectively an upper permanent magnet 11a and a lower permanent magnet 11b. The second part of the magnet holder is an upper fixing part for fixing the magnet holder to the handle of the grounding terminal. The fixing part has on top form of two arrow- shaped fixing devices which can be pushed into complementary fixing openings in the handle 9, as it appears from figures 1-4. The magnet holder 6 is made of heat resistant plastic and preferably molded in one piece. It is in the space defined by the steel plates 1 , 2 and the spacing plate 3, as it clearly appears from the figures 1-4. The magnet holder, and thereby the permanent magnets, can be moved in the longitudinal direction, that is parallel with the longitudinal direction of the steel plates, in this space by movement of the handle 9, 10. This will later be given a further explanation. As it appears from the figures 2, 4 and 5 the noncorrosive bolt 4 is in direct contact with one of the side walls 3b of the spacing plate 3. The spacing plate 3 is further in direct contact with the two upper and two lower steel plates 1 and 2. The electrical connection with the workpiece and the negative conductor (ground) is provided by the lower steel plates 2, which are in physical contact with the work- piece. When the grounding terminal is in the state for fastening to an object, as will be explained later, the terminal is very well fastened to the construction, and giving a good electrical contact between the grounding terminal and the construction, with little heating of the grounding terminal and minimal voltage drop over the ter- minal. When the grounding terminal is in the state for fastening and is fastened to a 10 mm steel plate, it is needed under optimal conditions a load equivalent to 100 kg to disengage the grounding terminal from the steel plate. Figure 6 shows the shape of the lower ends of the steel plates 2, which forms the contact surfaces with the object to be welded. The lower end faces of the steel plates 2 are plane, and the inside of the lower ends of the steel plates 2 have opposite slanting faces forming a groove. The slanting faces are preferably plane and slant upwards in a direction towards each other, and are milled out on the inside of the lower end faces of the lower steel plates 2. The special design of the slanting contact surfaces and the dimension of the grounding terminal, makes the grounding terminal especially suited for fastening on pipes and pipe constructions. The grounding terminal in itself is well suited for fastening on surfaces as the fastening is provided by magnetism, and the contact surfaces are then constituted by the end faces of the steel plates 2. The terminal can be fastened to ferromagnetic materials as example given iron and steel. The scraping tool consists in two scraping knives 12 of hardened steel, which are provided perpendicular protruding compared with and close to the contact surfaces of the grounding terminal, but so that the scraping tool does not influence the contact surfaces' contact with the workpiece. The scraping knives 12 are fixed to the inside of the lower parts of cover A and cover B respectively. From figures 7 and 8 the placing of the scraping knives on the grounding terminal clearly appears. Function In figures 1 and 2 the permanent magnets of the grounding terminal are in a first state for fastening to a construction to be welded, while figures 3 and 4 show the permanent magnets of the grounding terminal in a second state for unfasten- ing the terminal from the construction. It can be seen from figures 1 and 2 that when the permanent magnets are in the first state the lower permanent magnet 11 b is accommodated between the two lower metal plates 2 and the upper permanent magnet 11a is accommodated between the two upper metal plates 1. When the permanent magnets are in the second state, the two permanent magnets 11a, 11 b are accommodated between the two upper metal plates 1. In the second state the permanent magnets will, that are placed with the south pole on the upper magnet facing the north pole of the lower magnet, create magnetic field lines mainly in the upper steel plates; a so-called closed magnetic loop. Magnetic field lines will essentially not be created in the lower steel plates, and thereby there are no mag- netic field lines emanating from the lower end faces of the lower steel plates. Therefore, magnetic forces will not be established between the contact surfaces and a workpiece. Possible metal shavings or other magnetic objects will neither be able to fasten on the grounding terminal when the permanent magnets are in the second state. When the permanent magnets are in the first state, the permanent magnets will create magnetic field lines extending through the upper and lower metal plates, where the field lines will emanate from the lower end faces. This is denoted an open magnetic loop. A magnetic field is created in the contact surfaces of the grounding terminal, and thereby magnetic forces for secure fastening of the grounding terminal to a construction to be welded. By movement of the magnet holder and thereby the permanent magnets between the two positions as explained above, the grounding terminal will easily be fastened to and unfastened from a construction. As the upper part of the magnet holder 6 is fixed to the handle 9, movement of the handle 9 causes alteration of positions of the magnet holder 6 and thereby the position of the permanent magnets 11a, 11b. By fastening the terminal to a construction to be welded, the grounding terminal is held by one hand and pressed against the construction. This causes the magnet holder and thereby the permanent magnets, that initially are in the second position, to be moved to the first position, and a powerful magnetic field is established in the contact surface with the construction as explained above. The grounding terminal is thereby fastened to the construction. After welding, when the grounding terminal shall be unfastened from the construction, the handle, which is still held by the same one-hand-grip as by fastening, is pulled out from the surface of the construction. Thereby the mag- net holder is moved, and thereby the permanent magnets, to the second position with the result that the magnetic field in the contact surface disappears, and the terminal disengages from the construction. As the scraping knives 12 are fixed close to the contact surfaces of the grounding terminal, rust, paint and oxide scale can be scraped off the construction before welding, so that a good electrical connection is obtained between the grounding terminal and the construction. During scraping the grounding terminal is also held by the same one-hand-grip as by fastening to and unfastening from the construction. This design of the grounding terminal implies that scraping the fastening surface of the construction, fastening the grounding terminal to the construc- tion and unfastening the grounding terminal from the construction can be performed in successive operations and by using the same one-hand-grip on the terminal.

Claims: CLAIMS 1. A magnetic grounding terminal for temporary connecting a grounding conductor to an object to be welded, the grounding terminal comprising permanent magnets (11a, 11 b), the permanent magnets having a first state for fastening the grounding terminal to the object and a second state for unfastening the grounding terminal from the object, characterized in that the grounding terminal being arranged to be fastened and unfastened by one hand, the grounding terminal is fastened by pressing it against the object to be welded and unfastened by pulling it out from the object to be welded. 2. Magnetic grounding terminal according to claim 1 , characterized in that the permanent magnets (11a, 11b) are moveable between a first and a second position, representing the first and second state of the permanent magnets respectively. 3. Magnetic grounding terminal according to claim 1 , characterized in that it comprises a house (7, 8, 9, 10); two upper parallel extended metal plates (1) and two lower parallel extended metal plates (2) in the house (7, 8, 9, 10), the permanent magnets (11a, 11b) are arranged between the metal plates (1,2) and in the first position constitute an open magnetic loop together with the metal plates (1 , 2) for fastening the grounding ter- minal to the object, and in the second position constitute a closed magnetic loop together with the metal plates (1 , 2) for unfastening the grounding terminal from the object. 4. Magnetic grounding terminal according to claim 3, characterized by a magnet holder (6) arranged between the metal plates, the magnet holder (6) having an upper and a lower compartment for mounting of the permanent magnets (11a, 11 b), which are constituted by an upper permanent magnet (11a) and a lower permanent magnet (11 b) respectively. 5. Magnetic grounding terminal according to claim 4, characterized in that in the first position the lower permanent magnet (11b) is arranged between the two lower metal plates (2) and the upper permanent magnet (11a) is arranged between the two upper metal plates (1), and in the sec- ond position the two permanent magnets (11a, 11b) are arranged between the two upper metal plates (1). 6. Magnetic grounding terminal according to claim 5, characterized in that the house (7, 8, 9, 10) has a handle (9), the upper part of the magnet holder (6) being fixed to the handle (9), whereby movement of the handle (9) causes alteration of the position of the magnet holder (6) and thereby the permanent magnets (11a, 11b). 7. Magnetic grounding terminal according to claim 3, characterized in that the lower metal plates (2) provide contact surfaces for contact with the object to be welded. 8. Magnetic grounding terminal according to claim 7, where the metal plates have a certain thickness providing defined end faces, 0 characterized in that the contact surfaces are constituted by the lower end faces of the two lower metal plates (2), and by a groove formed by the insides of the lower ends of the two lower metal plates (2), the groove facilitating the fastening of the grounding terminal on pipes and pipe constructions. 5 9. Magnetic grounding terminal according to claim 8, characterized in that the insides of the lower ends of the lower metal plates (2) have the form of opposite slanting faces, the faces slanting upwards in a direction towards each other. o 10. Magnetic grounding terminal according to claim 1 , wherein the permanent magnets (11a, 11b) are made of neodymium, Nd-Fe-B-35. 11. Magnetic grounding terminal according to claim 1 , characterized in that it comprises scraping tools for scraping off rust, paint or oxide scale on the object, obtaining a better contact surface with the object. 12. Magnetic grounding terminal according to claim 11 , characterized in that the scraping tool has scraping knives (12) arranged protruding perpendicular outwards from the contact surfaces, but in such a way that the scraping tool does not influence the contact surfaces' contact with the object. 13. Magnetic grounding terminal according to claim 12, characterized in that the magnetic grounding terminal is designed so that scraping off rust, paint and oxide scale on the object to be welded, and fastening the grounding terminal to the object and unfastening the grounding terminal from the object, can be performed in successive operations by using one hand only and without changing the grip on the grounding terminal. 14. Magnetic grounding terminal according to claim 1 , characterized in that the magnetic grounding terminal is equipped with a quick release coupling (4, 5, 13) for the grounding conductor so that this easily can be disconnected from the grounding terminal.

Inventors: SOERNES ESPEN, SOERNES, ESPEN
Applicants: FACTOR TOOLS AS, SOERNES ESPEN, SOERNES, ESPEN
Application year: 2000
Main classification: H01R11
IPC codes: B23K37, H01R11