GB2081611A - Method of making a transformer or like core from amorphous strip metal - Google Patents

Abstract

The invention relates to a method of making a magnetic core from amorphous strip material for use in a transformer or similar electrical induction apparatus. In accordance with this method, a continuous strip of non-annealed amorphous metal is wound around a mandrel to form an initially round core which thereafter is clamped in a predetermined way and cut entirely through one transverse section thereof while a rust inhibiting liquid coolant is applied thereto. The resulting unconnected strips are then separated into a number of groups which are assembled together in a predetermined manner to form a substantially oval core. This core, in its final shape, is annealed and simultaneously subjected to a magnetic field of predetermined strength. <IMAGE>

Description

SPECIFICATION Method of making a transformer or like core from amorphous strip metal The present invention relates generally to magnetic cores for use in transformers or like electrical induction apparatus, and more pa rticularly to a specific method of making a magnetic core from amorphous strip metal.

One common way to make a magnetic core for use in an electrical apparatus, such as a transformer, is to use magnetic strip material having a preferred direction of orientation parallel to the longitudinal direction of the material, i.e. non-amorphous metal material. This material is relatively flexible and easy to form into the ultimate shape of the core, either before or after it is stress relief annealed. Therefore, after the core is formed, it can be readily provided with an unconnected joint, for example by cutting entirely through one circumferential section, and, because of its flexibility, an associated electrical coil can be easily assembled around one section merely by opening the joint and inserting the coil therethrough.While this technique is entirely satisfactory when the core is made from non-amorphous metal strip material, it has not been proved to be satisfactory when forming a core from amorphous strip material. This is because the latter, for example METGLASX (a registered trademark) strip material manufactured by Allied Chemical Corp., a very thin, very brittle and very hard. Most attempts to make a core from this material conventionally have been unsuccessful, mainly because amorphous strip metal is difficult to shear without backcracking along the shear line. Moreover, even if this thin and brittle material could be sheared without cracking, the time required to make joint cores using the heretofore conventional approach would be increased significantly due to the thinness of the material.Nevertheless, it is desirable to use amorphous metal to form the core because of the reduced core losses achieved thereby.

In view of the foregoing, it is a main object of the present invention to provide a relatively uncomplicated and economical method of making a magnetic core from amorphous strip metal for use in a transformer or like electrical induction apparatus, and particularly a method which is reliable in use. As will be described in more detail hereinafter, the method disclosed starts with a continuous strip of nonannealed amorphous metal which is initially wound about a cylindrical mandrel to form an initially round core, and thereafter is clamped in a predetermined way and cut entirely through a predetermined transverse section. This cutting procedure, which requires the application of a rust inhibiting liquid coolant at the cutting section of the core, results in a plurality of unconnected elongated metal strips.The unconnected strips are separated into the number of individual groups which are assembled, one group at a time, into a substantially oval shaped core, and then formed into the desired final shape, if not already in the desired final shape. Thereafter, the core is annealed and simultaneously subjected to a magnetic field of predetermined strength.

The method just recited will be described in more detail hereinafter in conjunction with the drawing wherein: Figure lisa side elevational view of an assembled magnetic core made in accordance with the invention; and Figures 2a-2e diagrammatically illustrate a number of steps in the disclosed method of making the magnetic core illustrated in Figure 1.

Turning now to the drawing, wherein like compo- nents are designated by like reference numerals throughout the various figures, attention is first directed to Figure 1 which, as stated above, illustrates a magnetic core assembled in accordance with the present invention. This core, which is especially suitable for use in a transformer or like electrical induction apparatus, is formed from a continuous strip of amorphous metal, for example the METG LASX strip material referred to previously. The core can be round, rectangular, quasi-rectangular, as illustrated in Figure 1, or can have any other suitable and desired shape.In the quasi-rectangular shape shown, the core includes opposite legs 12 and 14, an upperyoke 16 and a loweryoke 18. One of these four sections, for example the upper yoke 16, includes a joint 20 which serves as an access into and around the core for positioning an associated electrical coil or coils. One such coil is shown in Figure 1 at 22.

Joint 20 may comprise a planar or straight butt joint, it may be a stepped joint, may be V-notched, or may take any other suitable form. In addition, the opposite end sections forming this joint may include protective coatings as described in co-pending Lin et al United States Patent Application Serial No.

133,344, March 1980, entitled AMORPHOUS METAL CORE AND METHOD OF ASSEMBLING AN ELECTRICAL CORE AROUND THE CORE (Attorney Docket N35088/SCS), and assigned to the assignee of the present application. Reference is made to this application which also discloses a way of assembling its associated coil (corresponding to coil 22).

Turning to Figures 2a to 2e, attention is directed to a preferred method of making core 10 made from one or more continuous strips of amorphous metal, for example the METGLASs material referred to previously. In Figure 2a, two continuous strips 24 are illustrated. These strips are initially stored on their own reels 26. The first step in the present method calls for winding the continuous strip or strips about a cylindrical mandrel 28 to form an initially round core generally indicated at 30. In the preferred method, it is important that core 30 be wound round so that the strip or strips 24 is/are not subjected to a jerking or similar irregular motion that could cause breakage. Moreover, by winding the strips around mandrel 28 without excessive acceleration, the speed of winding 10 can actually be increased.

After forming an intially round core 30, the latter is clamped in the predetermined way such as illustrated in Figure 2b. The clamping arrangement generally designated by the reference numeral 32 is shown diagrammatically in this figure to include a steel or otherwise rigid base plate 34 and two removable steel or otherwise rigid clamping plates 36. While not shown, suitable means are provided to maintain the clamping plates 36 above base plate 34 such that the initially round core 30 is maintained therebetween in a somewhat compressed, substan tially oval state as indicated generally at 38. In this regard, the confronting ends of the clamping plates 36 are spaced from one another in order to expose a transverse section of the core.

With the oval core 38 clamped into the position illustrated in Figure 2b, a cutting tool, preferably a power saw including an abrasive circular saw blade 40 constructed of, aluminum oxide or silicon carbide with resin or rubber bond, for example, is used to cut entirely th rough the previously mentioned exposed transverse section from one edge of the oval core to its opposite edge. In this regard, the power saw itself may be a table or radial arm saw and an appropriate steel or otherwise rigid block 42 is preferably disposed inside the core, as shown in Figure 2b, to receive the inwardly projecting edge of saw blade 40 for guiding the latter across the core as the blade cuts through the exposed transverse section thereof.

At the same time, block 42 serves as a support between the base plate 34 and clamping plates 36 for allowing greater compression of the core laminations on either side of the transverse section being cut. This reduces the possibility of backcracking, burring and/or swelling along the cut. In any event, once the cut is made, a plurality of unconnected elongated strips of the material result.

An amorphous metal is a non-crystalline material.

When the amorphous metal is overheated, the material degrades its superior magnetic characteristics (i.e. loses is non-crystalline characteristics). Therefore, a supply of rust inhibiting coolant is needed to prevent overheating while cutting. Contact pressure between the material and the cutting wheel is critical. Heat will generate easily under high contact pressure. The contact pressure is controlled by the wheel running speed and the advance speed of the workpiece. The proper wheel running speed was 100 to 120 ft/sec (30.5to 36.6 m/sec) and the advance speed of the workpiece was 2 square inches per hour (12.9 cm2/hour) for cutting in an actual embodiment.

This of course may vary depending upon the cutting wheel and material being cut. The rust inhibiting coolant is continuously supplied in the form of a spray by suitable means including, for example, two nozzles generally indicated at44 in Figure 2b. In a preferred embodiment, the coolant is a water based coolant specifically water containing Nu-oil from Pittsburgh Chemical Mfg. Co. as a rust inhibitor.

Nevertheless, in order to further prevent rusting, the various unconnected elongated strips which resulted from the cutting operation discussed above, are soaked in an alcohol base compound, specifically methyl alcohol to remove most ofthe water coolant. The unconnected strips are then heated in an oven, preferably at 125"C, for a period of time sufficient for them to dry. While the present invention is not limited to a water base coolant, although it is preferred, and while the present invention is not limited to the particular parameters used in the dry ing of the strips, when a water based coolant is used, the drying step just mentioned is a very necessary step in the overal process to prevent excessive rust ing and swelling.The little oxide that is left on the unconnected strips as a result of the water is so thin that it does not appreciably affect the space factor between turns of the ultimately formed core, but does beneficially increase surface resistance. After this true atment,the unconnected strips will more readily slide past one another and not stick together so that they can be separated into groups and provided with the appropriate end shapes to be discussed.

As just stated, once the oval core 38 is cut and the resulting unconnected strips are dried (assuming a water based coolant is used), the individual unconnected strips are assembled into a number of groups having specifically shaped ends, depending upon the particulartype of joint 20 desired in the end product One group of unconnected strips is shown in Figure 2c and generally indicated at 46. This group is shown as having tapered ends 46a and 46b necessary to provide the ultimately shaped joint shown in Figure 1. This particular configuration may be provided by intially taking the full stack of unconnected strips and lining them up square on one end by tapping the ends with a flat block. If more slope is required, the stacks can be shifted by alternately clamping one end of the stack and then the other end, synchronized with flexing of the stack.For some types of joints, such as an alternate butt lap joint, this shifting is unnecessary. With the exception of a square butt joint or a sloping butt joint, the stack is divided into the previously mentioned individual groups 46. In any case, if the ends of each group are to have the coatings described in the above-recited Lin et al U.S. patent application, such coatings would be provided at this time.

Once the individual groups 46 are provided, the outermost group, e.g. the group of longest unconnected strips, is fixedly maintained in an oval (preferably elliptical) shape with its ends brought together and taped to remain in place, as illustrated in Figure 2d. As seen there, outermost group 46 is held in the position just described by suitable means, for example a pair of confronting clamping plates 48. Once the outer group 46 is so positioned, the remaining groups are successively placed, one at a time, inside the outermost group, starting with the next longest group of ucnonnected strips and ending with the shortest group. This is accomplished by flexing each individual group into itself so that the latter may be located concentricallv within the last assembled group. The group being so assembled is then allowed to snap back into position such that its opposite ends engage one another in the manner shown in Figure 2d. Whilernot shown, a wire, band or other suitable means may be provided to prevent disassembly of the ultimately formed oval tor elliptical) core formed between the clamping plates 48 when the latter are moved. The oval (or elliptical) core is generally indicated at 49.

Once the core 49 has been formed, if its oval or elliptical shape is not the final shape desired, the latter shape is provided. This is best accomplished by using a series of clamps which may be readily provided. For example, Figure 2e illustrates a series of inner and outer clamping plates 50 which com prise part of an overall clamping apparatus readily provided by those with ordinary skill in the art. While not shown, the overall apparatus will include means for adjusting the space between the various confronting plates and the location of the plates relative to one anotherto provide the desired shape for the core. In Figure 2e, the oval or elliptical core 48 of Figure 2d is shown converted to the somewhat rectangular shape of Figure 1.This quasirectangularly shaped core which is generally designated by the reference numeral 53 is provided with a current coil, indicated generally at 54, which is wound around one section of the core 53 and is connected to a source 56 of either direct current or alternating current which, in passing through the coil, turn, subjects the coil to a magnetic field. In a preferred embodiment, this field is between 5 and 20 oersteds, specifically 10 oersteds in a most preferred embodiment. At the same time, the entire core is annealed, preferably in a protective atmosphere, for example, a vacuum, an inert gas such as argon, or a reducing gas such as a mixture of nitrogen and hydrogen.In a preferred embodiment, the core is annealed for between 1 and 3 hours, most preferably for two hours, at a temperature between about 340"C and 370"C (the range of these temperatures is suitable for Allied Chemical Corp.'s METGLASs materials 2605S and 2605SC). The core is colled down preferably gradually specifically at a rate of 1.67"C per minute until the core is 1500C. By annealing the core and subjecting it to a magnetic field as described, its core losses are reduced, as is known. Once the core 52 has been annealed and subjected to the magnetic field, the coil 54 can be removed and the final electrical coil or coils 22 can be placed around one section thereof in a suitable manner including preferablythe way disclosed in the previously recited Lin et al U.S.

patent application.

Claims (6)

1. A method of making a transformer core from amorphous strip metal, characterized by the steps of: (a) winding at least one continuous strip of amorphous metal about a cylindrical mandrel to form an initially round core; (b) thereafter, clamping together transverse sections of said initiallyrnund core on opposite sides of a predetermined transverse section such that the latter is sufficiently exposed for cutting by a specific cutting tool; (c) cutting entirely through said exposed transverse section with said cutting tool while simultaneously applying a rust inhibiting liquid coolant onto said core and cutting tool at said exposed section, thembytoform a plurality of unconnected elongated strips of said metal;; (d) freeing said cut core and separating said unconnected strips into a number of groups shaped at their opposite ends in a predetermined way; (e) assemblying said groups into a substantially oval shaped core by first forming and maintaining the outermost one of said groups into said oval shape and thereafter successively placing the remaining groups, one at a time, into the outermost group such that the opposite ends of each.group define one segment of a specifically shaped joint across a transverse section of said oval shaped core; (f) forming said oval shaped core into its final shape if it is not already in its final shape; and (g) thereafter, annealing said core while simultaneously subjecting it to a magnetic field of predetermined strength.

2. A method according to claim 1, characterized in that said coolant includes water, and said unconnected strips are soaked in an alcohol solution and then heat-dried before being assembled into said groups.

3. A method according to claim 1 or 2, characterized in that the cutting step is performed with an abrasive wheel constructed of aluminum oxide or silicon carbide with resin or rubber bond.

4. A method according to claim 1, 2 or 3, characterized in that said final shaped core is annealed in a special non-ambient atmosphere for about two hours at a temperature of between about 340"C and 370"C while subjecting it to a magnetic field strength of at least about 5 oerstedsto 20 oersteds.

5. A method according to claim 4, characterized in that said annealed core is initially cooled from its maximum temperature to about 150"C at a rate of about 1.67"C/minutes (or 105 /hour).

6. A method according to any of the preceding claims, characterized in that said cutting step is controlled, and said coolant is provided, in such manner that the temperature of said strip material I resulting from said cutting step remains sufficiently low for said strip material to retain its amorphous noncrystalline characteristic.