MEANS FOR REDUCING OR ELIMINATING FIELDS OF REMANENT MAGNETISM

TECHNICAL FIELD :

The present invention relates to a means and a method for the reduction or elimination of a remanent magnetic field around for example a joint which is intended to be welded.

PRIOR ART :

When ferromagnetic materials are treated in some way for example by being formed to pipes or are used in electromagnetic fields some magnetism will arise in the material, which magnetism will be left as remanent magnetism. This is a known phenomenon and it does usually not bring about any larger problems. In some cases however, this remanent magnetism can be detrimental especially when the material shall be used in electrical applications or they shall be further treated by means of electric methods. Such a method is electrical welding. If one for example shall weld together two pipe ends and these pipe ends have a remanent magnetism that can create a magnetic field in or around the welding joint this magnetic field may disturb the welding. The same is of course the case even when for example plate edges are welded together.

The above problem has been observed earlier and one has proposed solutions for removing such problems. One method and a means for this purpose is described in the European patent application 0251423. According to this application

the problem is solved by applying a magnetic field of the same strength as the one of the remanent magnetic field but in an opposite direction and thereby neutralizing the magnetic field. To bring about this one has arranged an apparatus which works on the principle that one applies electric leads at each side of for instance the welding joint and send electric current in the desired direction and with desired strength through these leads. To know which current power and in what direction the current has to go one uses a Hall effect sensor for measuring the remanent magnetic field and let this Hall effect sensor determine the current size and the current direction in the conduits which have been put at the remanent field. The current that must go through the leads must be a direct current and a rectifier is therefore usually necessary to get this type of current from the alternating current net. The device in question can work well if one puts the electric leads accurately and control that they do not move or is influenced of the working operation. This is however a very complicated method and the means will also be complicated and expensive i.a. through the expensive electric equipment which is based on the Hall effect sensor and the equipment which through signals from this guides the amount of current and its direction.

THE SOLUTION:

It has therefore long been a desire to be able to create a device which in a very simple, cheap and handy way eliminates or reduces the remanent magnetic field at working operations such as for example welding. This desire has been fulfilled through the present invention which consists of a means for weakening or eliminating the remanent magnetic field around for example a joint which is intended to be welded and which is characterized in that it comprises a permanent magnet which is displaceably mounted

between two yokes of magnetically conducting material intended to be brought into contact with the materials having remanent magnetism.

It is according to the invention suitable that the magnet and the parts of the yokes which surround it are built in in a house.

Further according to the invention the magnet can be displaσeable between the yokes by means of a screw.

The invention includes also a method for weakening or eliminating a remanent magnetic field using the means according to the invention. It is characterized in that the strength and direction of the remanent magnetic field is measured, that the yokes are brought into contact with the materials having the remanent magnetism and that the position of the permanent magnets are adjusted so that the remanent magnetic field completely or partly is eliminated.

The invention will in the following be described more in detail in connection with the attached drawing that shows a means according to the invention when welding two pipe ends.

PREFERRED EMBODIMENT EXAMPLE:

The figure shows two pipe ends 1 and 2 which are arranged towards each other and intended to be welded together. Around the welding joint between these pipe ends 1 and 2 there is a magnetic field which depends on remanent magnetism in the pipe ends, which magnetism has been created by the production and treatment of the pipes. Against these pipe ends 1 and 2 the yokes 3 in the means according to the invention has been brought into contact with the pipes at a certain distance from the intended

welding joint. These yokes 3 shall be of magnetically conducting material such as soft iron and they should be shaped so that they abut well against the pipe ends. As appears from the figure the yoke has a semi-circular recess to flush with the pipes, but when welding for instance plates the yokes should have a straight end edge.

The yokes 3 are at their other ends fastened by screws or riveted in a house 4. Between these yoke ends a permanent magnet 5 has been displaceably mounted. It can then be pushed forward in between the yoke ends or be pulled out as is shown in the figure. When the permanent magnet 5 is inserted forward a strong magnetic field will be present between the yoke ends 3 and when the magnet is pulled out the field will be weak or completely disappear. On the figure a screw 6 is further shown which penetrates the end wall of the house 4. In this wall a screw groove has been made which corresponds to the screw groove on the screw 6 so that when this screw is rotated the magnet 5 will be pushed in between the yoke ends or pulled out from these.

The use of the apparatus according to the invention will be carried out by first measuring the strength and the direction of the remanent magnetic field by arranging a Gauss eter in the welding joint whereupon one screws the permanent magnet 5 out or in until one can see that the magnetic field is eliminated or reduced. If one unintentionally happens to put the arrangement against the end pipes so that an increase of the remanent magnetic field is created then it is only to turn the arrangement 180° so that the remanent magnetic field instead will be counteracted.

The means according to the invention is very practical. It can for example be put on a support so that one does not have to keep it in hand and it can be swung around the

pipes. Welding can also be carried out between the yokes without disturbing or hindering the welding process itself.

By the present invention one has accordingly brought about an extremely simple and practical device for eliminating the remanent magnetic field between two pipe ends or between two other materials that are to be united. The apparatus is easy to change so that pipes having other dimensions or plate edges can be welded together by simply changing the yokes 3 and replacing them with other yokes having suitable and adjusted end edges.

The invention is not limited to the embodiment example shown and it can be varied in different ways within the scope of the claims.