Process for manufacturing magnetic pole assembly

Abstract

 A process for manufacturing a magnetic pole assembly (10) for a switchable magnet base (12), which magnetic pole assembly has non-magnetic member means (20) and a pair of magnetic pole members (18) coupled to each other, with non-magnetic member means interposed therebetween. Holes (24) are provided in the pair of magnetic pole members in the opposing surfaces thereof, and the non-magnetic member means is formed between the pair of opposing magnetic pole members by using the magnetic pole members as part of the mold, whereby the non-magnetic member means is formed, and at the same time, the non-magnetic member means and the pair of magnetic pole members are coupled into a unitary body by the non-magnetic materials cast in the aforesaid holes.

Description

[0001] This invention relates to a process for manufacturing a magnetic pole assembly having a non-magnetic member and a pair of magnetic pole members coupled together with the non-magnetic member interposed therebetween, and more particularly to a process for manufacturing a magnetic pole assembly suited for a magnetic circuit block for a switchable permanent magnet device.

[0002] A well known prior art process for producing a magnetic circuit block for a switchable permanent magnet device has been such that non-magnetic member is formed in a desired shape beforehand; then a pair of magnetic pole members are disposed with non-magnetic members of a desired configuration interposed therebetween,--and the pair of magnetic pole members and the non-magnetic member are integrally coupled each other by the tightening means, such as screws or rivets, or joining means, such as projection welding or brazing.

[0003] The prior art process requires the steps of forming a non-magnetic member in a desired configuration, and coupling a pair of magnetic pole members each other, with the non-magnetic members of a desired configuration interposed therebetween. The prior art process has suffered from misalignment of one member from the other particularly in the coupling step, thus requiring a cutting or grinding step for making the surfaces of these components in alignment.

[0004] It is accordingly an object of the present invention to provide a process for manufacturing a magnetic pole assembly, which is reduced in number of manufacturing steps, for the simplicity sake.

[0005] A process for manufacturing a magnetic pole assembly having a non-magnetic member and a pair of magnetic pole members coupled together, with the non-magnetic member interposed therebetween, according to the present invention, comprises the steps of; providing holes with one open end in the opposing surfaces of the pair of magnetic pole members, respectively; forming non-magnetic member means between the pair of magnetic pole members by a molding process by using the pair of opposing magnetic pole members as part of the mold, whereby the non-magnetic member means is formed, and at the same time, the non-magnetic member means and the pair of magnetic pole members are coupled into a unitary body by non-magnetic materials cast into the holes in the pair of magnetic pole members.

[0006] The further features of the present invention will be apparent from the ensuing part of the specification taken in conjunction with the accompanying drawings which indicate an example of a magnetic pole assembly obtained according to the process of the present invention.

Fig. 1 is an exploded perspective view of a magnet base including a magnetic circuit block, according to the present invention;

Fig. 2 is a longitudinal cross sectional view taken along the line II-II of Fig. 1; and

Figs. 3(a), 3(b), 4 and 5 are fragmentary longitudinal cross sectional views of magnetic pole members for illustration of holes of different types provided in the magnetic pole members, respectively.

[0007] In Fig. 1, there is shown in an exploded state a magnet base 12 including a magnetic pole assembly 10 which has been made by the process of the present invention.

[0008] The magnet base, namely switchable permanent magnet device 12, comprises a magnetic pole assembly 10, a columnar permanent magnet 14 rotatably received in a bore 12' in the magnetic pole assembly and magnetized in a diametrical direction, a knob 16 for rotating the permanent magnet, and an end plate 17 for holding the knob thereon rotatably. By turning the knob 16, the bottom surfaces 10a of the magnetic pole assembly 10 becomes magnetized or demagnetized, as is well known. The magnet base 12, in general, is used for supporting various instruments, such as measuring instruments, through the medium of a support pole or leg which is attached to the top surface of the magnetic pole assembly 10, which in turn is attached at the lower surfaces 10a thereof to a magnetic plate by magnetic attraction.

[0009] The magnetic pole assembly 10, which is a magnetic circuit block for receiving the permanent magnet 14 rotatably, includes a pair of opposing magnetic pole members 18 made of a magnetic material, such as soft iron, and non-magnetic members 20 interposed therebetween. The pair of magnetic pole members 18 are respectively formed in a given configuration, for example, by a cold drawing process. Provided in the opposing surfaces 18a of the pair of magnetic pole members 18 are recesses 22 having a semi-circular cross section, so that these recesses cooperate to define the central bore 12' for receiving therein the permanent magnet 14, as best seen in Fig. 2.

[0010] The recesses 22 are open from the opposite ends of the magnetic pole members 18, respectively. Plural pairs of threaded holes 24 are provided in the opposing magnetic pole members 18 in the upper and lower portions thereof i.e. on the both sides of each recess 22. One threaded hole 24 runs parallel to another threaded hole in each magnetic pole member, with one end open to the surface 18a, and with the other inner end closed. It is possible that each threaded hole 24 be open at the opposite ends thereof. However, in the latter case, after a non-magnetic material has been cast into each threaded hole, which will be described later, a finishing step for closing the other end of each threaded hole is required, so as to provide a neat appearance for the magnetic pole assembly 10.

[0011] From the viewpoint of reduction of the number of manufacturing steps, it is desirable that the other (inner) end of each threaded hole is a blind end.

[0012] The non-magnetic members 20 between the opposing magnetic pole members 18 are formed by a molding process by using these magnetic pole members 18 as part of the mold. More in detail, the magnetic pole members 18 are incorporated in a molding device (not shown) in a manner that the recess 22 of one magnetic pole member 18 opposes the recess 22 of the other member at a given spacing therefrom. In order to ensure the bore 12', a columnar core (not shown), having an outer diameter slightly larger than the outer diameter of the permanent magnet 14, is placed in the central bore defined by the recesses 22 of the opposing magnetic pole members 18 incorporated in the molding device. After the core has been set in place, non-magnetic molten metal, such as aluminum or zinc, or non-magnetic molten resin, such as ABS synthetic resin, is filled into the gaps defined by the core and the opposing magnetic members 18, and the non-magnetic material thus charged is then cooled, whereby non-magnetic members 20 are formed in a predetermined configuration.

[0013] As the non-magnetic members 20 are molded by using the magnetic pole members 18 as part of the mold, as described, a lid 26 closing one end of the bore 12' and molten materials 28 are simultaneously cast into the threaded holes 24 (herinafter referred to as cast portions) and are integrally formed with the respective non-magnetic members 20 in the manner shown in Fig. 1. The cast portions 28 are firmly retained in corresponding threaded holes 24 due to shrinkage stress resulting from the cooling of these portions. As a result, simultaneous with formation of the non-magnetic members 20 for magnetically insulating one magnetic pole member from another, the opposing magnetic pole members 18 are integrally coupled together through the medium of the cast portions 28 of respective non-magnetic members 20.

[0014] In order to form the non-magnetic members 20, it is preferable to employ so-called die casting. In case of forming the non-magnetic members 20, it is recommended to provide in the non-magnetic members tapped threaded holes 32 for receiving therein screws 30 for fixing the end plate 17 to the magnetic pole assembly 10 and a female threaded hole 34 for receiving the aforesaid support pole or leg. In this connection, a strong tightening force acts on the female threaded hole 34 when the support pole or leg is threadedly fitted therein, and the strong tightening force is developed into a strong expansion force which would act on the peripheral portion of the threaded hole.,34, of the non-magnetic member 20. The pair of cast portions 28 located on the opposite sides of the threaded hole 34 in the coupling portion between the opposing magnetic pole members 18 contribute to preventing the upper non-magnetic member 20 being deformed due to the strong expansion force.

[0015] Although, in the embodiment shown, the lid 26 is formed integrally with the upper and lower non-magnetic members 20, the lid may be formed separately from the non-magnetic members 20. However, from the viewpoint of simplicity in manufacturing steps, it is recommended to form the lid 26 integrally with the non-magnetic members 20, as described above.

[0016] The threaded holes 24 provided in respective magnetic pole member 18 may be holes 36 having no threads, as shown in Fig. 3(a). Also, in the case of the non-threaded holes, the opposing magnetic pole members 18 and the non-magnetic members 20 are firmly coupled together by the cast portions 28 due to shrinkage stress resulting from the cooling of these portions, likewise in the threaded holes.

[0017] If a punch 38 as shown in Fig. 3(a) is forced onto the hole 36 from the open end thereof, then a diametrically reduced portion 36a is provided at the circumferential edge of the open end thereof, in the manner shown in Fig. 3(b). The diametrically reduced portions 36a of respective holes 36 ensure a stronger coupling between the magnetic pole members 18 and the non-magnetic members 20. Instead of the diametrically reduced portions 36a, a pair of holes 36 in each magnetic pole member 18 may run, with their axes running non-parallel, as shown in Fig. 4, or otherwise. The adjacent holes 36 may cross each other at the inner ends thereof, as shown in Fig. 5, with the result that a strong coupling between the opposing magnetic pole members and the non-magnetic members is ensured.

[0018] In the magnetic circuit block according to the present invention, simultaneously with formation of the non-magnetic members 20, the opposing magnetic nole members 18 are integrally coupled together through the medium of the non-magnetic members 20. The number of manufacturing steps is thus reduced.

[0019] According to the process for manufacturing the magnet block of the present invention, the bore 12' for receiving the permanent magnet 14 is provided with high accuracy by formation of the non-magnetic members 20, so that the non-magnetic members 20 have no likelihood of protruding into the bore 12'. Thus, a cutting or grinding step for the inner peripheral wall of the bore is no longer needed.

[0020] Since the lid 26 for closing one end of the bore 12' is formed integrally with the non-magnetic members 20, a step for closing the end of the bore by another material is eliminated.

[0021] In the foregoing, we have set forth an example in which the process of the present invention is applied to the manufacture of a magnetic pole assembly used as a magnetic circuit block serving as a magnet base. The process of the present invention is not limited to the manufacture of the magnet assembly, but applicable for manufacturing various magnetic pole assemblies having no bore.

[0022] In summing up, the non-magnetic member means is formed between the pair of opposing magnetic pole members having holes in the opposing surfaces thereof, by using the magnetic pole members as part of the mold, whereby the non-magnetic member means .is formed, and at the same time, the pair of opposing magnetic pole members and the non-magnetic member means are firmly coupled to each other with high accuracy through the medium of the cast portions in the aforesaid holes, whereby simplicity of the manufacturing process is attained and an inexpensive and highly accurate magnet assembly is obtained.

Claims

1. A process for manufacturing a magnetic pole assembly having non-magnetic member means and a pair of magnetic pole - members coupled together, with said non-magnetic member means interposed therebetween, comprising the steps of; providing, in said pair of magnetic pole members, holes each having one end open from the opposing surface of said magnetic pole members; and molding said non-magnetic member means by using as part of a mold said pair of magnetic pole members disposed in an opposed relation to and at a given spacing from each other, thereby coupling said pair of magnetic pole members to each other through the medium of said non-magnetic member means.

2. A process for manufacturing a magnetic pole assembly as defined in claim 1, wherein each said hole having one end open from the opposing surfaces of said pair of magnetic pole members is blind at the other end thereof.

3. A process for manufacturing a magnetic pole assembly as defined in claim 1 or 2, wherein each said hole is a threaded hole.

4. A process for manufacturing a magnetic pole assembly as defined in claim 1 or 2, wherein each said hole has a diametrically reduced portion.

5. A process for manufacturing a magnetic pole assembly as defined in one of claims 1 to 4, wherein at least two holes are provided in each magnetic pole member, with the axes thereof non-parallel.

6. A process for manufacturing a magnetic pole assembly as defined in one of claims 1 to 5, wherein at least a pair of holes are provided in each magnetic pole member, said holes in each magnetic pole member crossing each other.

7. A process for manufacturing a magnetic pole assembly as defined in one of claims 1 to 6, wherein said magnetic pole assembly is a magnetic circuit block for a switchable permanent magnetic device; the pair of magnetic pole members having in the opposed surfaces thereof recesses of semi-circular cross section, respectively, said recesses cooperating to define a bore for rotatably receiving therein a columnar permanent magnet magnetized in the diametrical direction thereof; said holes being provided on both sides of each such recess and said process further comprising forming the non-magnetic member means by placing a core in said bore.

8. A process for manufacturing a magnetic pole assembly as defined in claim 7, wherein said recesses are respectively open from the opposite ends of said respective magnetic pole members, and said process further comprises forming a lid for closing one end of said bore integrally with said non-magnetic member means when the latter is molded.

9. A process for manufacturing a magnetic pole assembly as defined in claim 7 or 8, wherein said non-magnetic member means consists essentially of non-magnetic metal.

10. A process for manufacturing a magnetic pole assembly as defined in claim 7 or 8, wherein said non-magnetic member means consists essentially of non-magnetic synthetic resin.

Drawing