US2958037A

US2958037A - Magnetic shield for coils

Info

Publication number: US2958037A
Application number: US638968A
Authority: US
Inventors: John R Riede; Robert C Cahill
Original assignee: University of Minnesota
Current assignee: University of Minnesota
Priority date: 1957-02-08
Filing date: 1957-02-08
Publication date: 1960-10-25
Anticipated expiration: 1977-10-25

Description

Oct. 25, 1960 J. R. RIEDE ETAL MAGNETIC SHIELD FOR Cons 2 Sheets-Sheet 1 Filed Feb. 8, 1957 INVENTORS JbH/V R. R/EDE y RoBERTC' (AH/LL Wm W YJW Oct. 25, 1960 J. R. RlEDE EI'AL 2,958,037

MAGNETIC SHIELD FOR COILS Filed Feb. 8, 1957 2 Sheets-Sheet 2 l7 /0 IN V EN TORJ F 3 Jon/v R. R/EDE l6 y ROBERTC' (AH/u.

ATTORNErJ' United States Patent MAGNETIC SHIELD FOR cons John R. Riede, White Bear Lake, and Robert C. Cahill, Minneapolis, Minn, assignors to The Regents of the University of Minnesota, Minneapolis, Minn., a corporation of Minnesota Filed Feb. 8, 1957, Ser. No. 638,968

8 Claims. (Cl. 324-41) This invention relates to magnetic shields. More particuarly this invention relates to magnetic shield and support construction for an instrumentation system comprising primary and secondary coils used in providing an output signal functionally related to the content of term-magnetic substances in ores of the same character passed in the vicinity of said coils.

In a co-pending application, Serial No. 510,391, filed by Edward W. Davis on May 23, 1955 for an Instrumentation System, there is disclosed and claimed a method and apparatus for generating signals of continuous character which are functions of the percentage of magnetic iron ore contained in Wet or dry stream flows of finely divided iron ore.

One form of that invention comprises a conveyance element, on or through which a stream of ore having a term-magnetic component is carried, surrounded at a given point by one or more primary coils and a secondary coil. In the interests of accuracy of the determinations made by the instrumentation system, the conveyance element and the primary and secondary coils are shielded by means of a continuous surrounding outer protective shield formed from a magnetic material such as iron or steel. By this means the magnetic lines of force are confined and protected from disturbing outside magnetic influences. The coils are supported by an inner shield surrounding the conveyor and enclosed within the outer magnetic shield. The inner shield is formed of a conductive but non-magnetic material such as aluminum.

The principal object of this invention is to provide a magnetic shield and support construction for an instrumentation system comprising primary and secondary coils used in conjunction with a conveyance element for ferro-magnetic ore in the vicinity of the coils.

Other objects of the invention will become apparent as the description proceeds.

To the accomplishment of the foregoing and related ends, this invention then comprises the features hereinafter fully described and particularly pointed out in the claims, the following description setting forth in detail certain ill-u-stnat-ive embodiments of the invention, these being indicative, however, of but a few of the various Ways in which the principles of the invention may be employed.

The invention is illustrated by the drawings in which the same numerals refer to corresponding parts and in which:

Figure 1 is a side elevation of a conveyance element surrounded at one point by coils comprising part of the instrumentation system, the coils being supported and enclosed by one form of the shield construction of this invention;

Figure 2 is an enlarged vertical section taken along the line 2-2 of Figure 1 and in the direction of the arrows;

Figure 3 is a top plan view, partly in section, taken generally along the line 33 of Figure 2 and in the direction of the arrows;

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Figure 4 is a vertical section through a modified form of shield construction adapted for use with a conduit conveyance element;

Figure 5 is a horizontal section through the shield of Figure 4 taken on the line 5-5 and in the direction of the arrows;

Figure 6 is a vertical section through another form of shield construction adapted for laboratory analysis; and

Figure 7 is a further form of shield adapted for analytical use.

Refer-ring now to the drawings, and particularly Figures l to 3, there is shown an typical form of shield constructed according to this invention as used with an ore-carrying conveyor belt. Conveyor belt 10 is supported at its ends by rolls, 11 and 12, at least one of which is a driven roll. The upper and lower conveyor flights are supported respectitvely by

idlers

13 and 14. Belt 14} is preferably formed of a non-magnetic material, such as rubber. It may, however, contain structural reiniorcing elements of magnetic material, such as wires or cable, so long as the magnetic elements are substantially uniformly distributed throughout the belt. In this manner compensation may be made for that portion of the output signal which is related to the ferro-magnetic substances in the belt to avoid errors in calculating the iron content of the ore carried by the upper flight of the conveyor.

The ore body carried by the conveyor 10 is indicated at 15. At some intermediate point between the end rolls the upper flight of the conveyor is surrounded by one or more primary coils and a secondary coil. For illustrative purposes, only one of these coils, a primary coil 16, is shown here. Coil 16 may be any continuous coil of wire of appropriate gauge and number of turns for the purpose, as described in the co-pending Davis application. The particular form of coil construction shown is one described and claimed in our co-pending United States application Serial No. 534,295 filed September 14, 1955, now abandoned, this coil construction permitting ready formation of coils having a relatively large num :ber of turns by means of a relatively few turns of multistrand cable the ends of which are connected through a multiple pin and socket connector in such a manner to form a continuous coil. Such coil construction avoids much tedious winding. The shield of this invention is not dependent upon any particular coil construction.

Coil 16 is supported upon an inner duct or tube 17 of a conductive but non-magnetic material, such as aluminum, which surrounds the ore-bearing upper flight of the conveyor. The coil 16 and its supporting duct 17 are in turn encased in a duct or tube 18 of the same general shape and configuration as duct 17 but spaced apart slightly from it to provide room for the coils. Duct 18 is formed of a magnetic substance, such as iron or steel. The entire shield and support construction is of a shape to conform generally to the conveyance element which passes through it and of a length sufficient to accommodate the number of coils which are to be used. The entire structure is mounted on brackets 19 supported from the floor or from the conveyor frame.

The inner non-magnetic shield, in the form illustrated in Figures 1 to 3, is comprised of a top plate 20 and an inner bottom and side piece 21. The two pieces are joined together in such a manner as to be out of direct metalto-metal contact with one another. This is accomplished by means of an aluminum angle 22 bolted to each of the pieces along their length with a strip of insulating material 23, such as Formica, interposed between one of the sides of angle 22 and the non-magnetic shield (Formica is the trademark of the Formica Co. for a line of thermosetting ureaand phenol-aldehyde resins).

The outer shield of magnetic material is formed of a top plate 24, bottom plate 25 shaped to conform generally to the bottom of inner shield 17 and belt 10, and opposite flanged

side members

26 and 27. These elements are bolted or otherwise fastened together so as to be in direct metal-to-metal contact to permit the flow of magnetic flux. The inner and outer shielding ducts or tubes 17 and 18 are held spaced apart by magnetically conducting blocks 28 to which they are bolted or otherwise secured. The entire assembly is desirably constructed for easy assembly and disassembly to permit alteration, addition, repair, replacement, etc. of the coils and/ or conveyor belts.

, In Figures 4 and there is shown a similar shield and coil support construction, adapted in this instance for use with a tubular conduit or pipe 30 through which the iron ore 31 passes. As in the case of the conveyor belt 10, pipe 30 is preferably formed of rubber or some similar non-magnetic substance. However, the presence of reinforcing elements or the like made of magnetic material is not objectionable provided they are substantially uniformly distributed throughout the pipe. The ore-carrying pipe 30 is surrounded by a closely adjacent tubular shield 32 of non-magnetic conductive material comprised of two semi-cylindrical shells 33 of aluminum held slightly spaced apart at their facing edges by insulating strips 34 of Formica or similar insulating material.

Surrounding this inner shield of non-magnetic material is an outer tubular shield 35 of magnetic material. The appropriate number of coils are positioned around the pipe 30 in the annular space between the two shields. In the form of construction shown, the opposite ends of tubular shield 35 are provided with lugs or flanges 36 and by this means annular rings 37 are secured by tie bolts 38. The inner shield 32 of non-magnetic material is slightly shorter than the outer shield 35 and is held in position between annular rings 37 in grooved annular rings 39 formed of a conducting material.

In Figures 6 and 7 there are shown two further forms of shield construction adapted for analytical use. The construction of Figure 6 is intended for use on small samples of ore, here indicated at 40, contained in a glass test tube 41. The inner tubular shield 42 of non-magnetic material is short in length so as to accommodate a small ore sample. This shield 42 is comprised of two spaced apart aluminum semi-cylindrical shells held in position in rings 43 of conducting material. Outer shield 44 is of a size large enough to accommodate the required coils but is necked down to a narrow throat 45 to receive the short aluminum shield 42.

In Figure 7 there is shown a similar shield for use when somewhat larger ore samples are available for analysis. The finely divided ore 50 is contained in test tube 51. The inner shield 52 is again made up of at least two pieces of aluminum spaced apart so as to provide an insulating gap between the adjacent edges. The inner shield is held positioned within the outer magnetic shield 53 by means of grooved rings 54 of conducting material. The coils are supported in the space between the shields.

In the operation of the instrumentation system of which these shield and support structures may form a part, the primary coils are energized with an appropriate alternating current voltage. A magnetic flux circuit is set up through the primary coil, the magnetically permeable material in the ore lying within the coils and the secondary coil. All of the magnetic values of the flux path remain substantially constant except for variations produced, by the magnetic content of the ore. The varying magnetic reluctance of the ore is sensed by the secondary coil and a signal is generated. As explained in the above mentioned Davis application, the iron content of the ore is calculated from variations in value of voltage induced in the secondary coil.

The flux path is axially through the coils through the body of ore lying there and normally the path of return would be through the air outside of the coils. By providing the outer shield of magnetic material an easier path of return is furnished. The magnetic conducting spaces between the inner and outer shields attract the magnetic lines of force to the outer return shield. The magnetic lines of force running lengthwise through the ore normally try to escape outwardly from the ore body. Eddy currents are induced in the inner aluminum shield setting up a counter magnetomotive force which tends to drive the lines of force back and route them towards the ends of the shield structure where they are attracted by the magnetic spacers to the outer iron return shield. The insulator blocks which separate the inner aluminum shield break up the paths of electromotive force induced in the shield so that voltage is induced but no current flows.

It is apparent that many modifications and variations of this invention as hereinbefore set forth may be made Without departing from the spirit and scope thereof. The specific embodiments described are given by way of example only and the invention is limited only by the terms of the appended claims.

In the claims:

1. A magnetic shield and coil support structure comprising an inner tubular shield and coil support formed from an electrically conductive non-magnetic solid sheet material and a surrounding outer tubular shield formed from a magnetic solid sheet material, said inner shield being positioned in spaced relation with respect to said outer shield, but in electrical contact therewith and having at least one longitudinal insulated space separating adjacent edges of the inner shield, said outer shield being magnetically conductive throughout.

2. A shield structure according to claim 1 further characterized in that said conductive non-magnetic material is aluminum.

3. A shield structure according to claim 1 further characterized in that said magnetic material is selected from the group consisting of iron and steel.

4. A shield structure according to claim 1 further characterized in that the inner and outer shields are held spaced. apart but in conductive contact by means of spacers of magnetic material adjacent the ends of the shield structure.

5. A shield structure according to claim 1 further characterized in that the longitudinal insulating space separating adjacent edges of the inner shield is maintained a strip of resinous insulating material affixed to the adjacent edges of the inner shield.

6. A magnetic shield and coil support structure comprising an inner tubular sheet aluminum shield and coil support and a surrounding outer tubular shield formed from a magnetic sheet material selected from the group consisting of iron and steel, said inner aluminum shield being positioned in spaced relation with respect to said outer shield but in conductive contact therewith by means of spacers of magnetic material adjacent the ends of the shield structure, said inner aluminum shield having at least one longitudinal insulated spaced extending the length of the shield and separating adjacent edges of the inner shield, said outer shield being magnetically conductive throughout.

7. A shield structure according to claim 6 further characterized in that the longitudinal insulating space separating adjacent edges of the inner aluminum shield is maintained by a strip of resinous insulating material aflixed to the adjacent edges of the inner shield.

8. A magnetic shield and coil support adapted to surround the upper tlight of a flexible conveyor belt comprising an inner tubular sheet aluminum shield and coil support having an arcuate bottom wall, a pair of vertical side walls and a horizontal top Wall and a surrounding outer tubular shield of substantially the same length havingan arcuate bottom wall, a pair of vertical side walls and a horizontal top Wall formed from magnetic sheet material selected from the group consisting of iron and said outer shield being magnetically conductive throughsteel, said inner aluminum shield being positioned in coout.

axial spaced relation within the outer shield but in conductive material therewith by means of spacers of mag- R f r n Cited n h file of this patent netic material between the inner and outer shields adja- 5 UNITED STATES PATENTS cent the ends of the shield structure, said inner aluminum shield having at least one longitudinal insulated space 5 {A extending the length of the shield and separating the 2388848 uysen 1945 adjacent edges of the inner shield, said insulating space owe 2598 252 Gossick May 27 1952 being maintained by a strip of resinous insulating ma- 0 terial affixed to the adjacent edges of the aluminum shield, 2714710 Bradley 1955 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 2358,03? October 25, 1960 John R. Riede et al.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 5, line 4,' for "material" read contact Signed and sealed this llth day of April 1961.

(SEAL) At'tcst:

ERNEsT W. SWIDER ARTHUR W. CROCKER Attesting Oflicer Acting Commissioner of Patents UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No 2358,03? October 25, 1960 John R. Riede at al.

It is hereby certified that error appears in the printed specification of theabove numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 5, line 4, for "material" read contact Signed and sealed this 11th day of April 1961 (SEAL) Attest:

- T W. SWIDER ARTHUR w. CROCKER 251 53 5 12 Ofiicer Acting Commissioner of Patents