US2351922A

US2351922A - Treatment of silicon-iron alloys

Info

Publication number: US2351922A
Application number: US385759A
Authority: US
Inventors: Stephen L Burgwin
Original assignee: Westinghouse Electric and Manufacturing Co
Current assignee: CBS Corp
Priority date: 1941-03-28
Filing date: 1941-03-28
Publication date: 1944-06-20
Anticipated expiration: 1961-06-20

Description

June 20, 1944. s LBURGWW 2,351,922

TREATMENT OF SILICON-IRON ALLOYS Filed March 28, 1941 2 Sheets-Sheet l WITNESSES: INVENTOR Patented June 20, 1944 TREATMENT OF SILICON-IRON ALLOYS Stephen L. Burgwin, Wilkinsburg, Pa" assignor to Westinghouse Electric & Manufacturing Company, of Pennsylvania East Pittsburgh, Pa., a corporation Application March 28, 1941, Serial No. 385,759 8 Claims. (Cl. 148-215) This invention relates generally to magnetic material and to the heat treatment of siliconiron alloys to reduce magnetostriction.

Silicon-iron alloys containing up to 6% of silicon have been utilized for a number of years .as the magnetic material in diflerent electrical apparatus, and particularly as the core member of transformers. Many processes and methods have been employed for heat treating the silicon-iron alloys and fabricating them into sheet or strip form suitable for use as the magnetic cores of electrical apparatus. The known processes and methods have for their objective the development of the magnetic characteristics of the alloys by reducing the impurities in the alloys, relieving working strains, and/or imparting a preferred orientation to the grain structure of the alloy. The silicon-iron alloys now commercially produced in sheet or strip form have excellent magnetic characteristics.

In a number of commercial installations of electrical apparatus, such as large power transformers, which utilize the now commercially produced silicon-iron alloys in strip form as the magnetic core member, it has been found that undesirable and objectionable noise is developed when the transformer is energized. The noise developed in a transformer can be traced directly to the magnetostriction of the siliconiron alloy sheets or strips utilized as the core member of the transformer. The magnetostriction of magnetic material is recognized as being the expansion and contraction of the magnetic material when subjected to a magnetizing force.

For the purpose of this invention, thekind of magnetostriction of particular interest and the quantity to be measured is AL/L or the change in length per unit length in the direction of magnetization under the magnetizing force applied.

An object of this invention is to provide for reducing the magnetostriction of silicon-iron a1- loys which have been fabricated into strip form and treated to develop the magnetic characteristics of the alloy.

A more specific object of this invention is to subject silicon-iron alloys which have been fabricated into strip form and treated to develop the magnetic characteristics of the alloys to an annealing treatment under tension to effectively reduce the magnetostriction of the alloy strip.

Other objects of this invention will become apparent from-the following description when taken in conjunction with the; accompanying drawings, in which: I

Figure 1 is a schematic representation of the apparatus employed in practicing the method of this invention,

Fig. 2 is a schematic plan of test apparatus utilized in measuring the magnetostriction of alloy strips produced in accordance with this invention,

Fig. 3 is a view in elevation, with a part removed, of a portion of the apparatus of Fig. 2,

Fig. 4 is a graph, the curves of which illustrate the magnetostriction values obtained on alloy strips by utilizing the test apparatus of Fig. 2,

Fig-5 is a schematic plan of a further test apparatus utilized for measuring the magnetostriction of assembled core members such as are employed in transformers,

Fig. 6 is a graph, the curves of which illustrate the losses encountered in alloy strips treated in accordance with this invention as compared with the losses found in similar alloy strips which have been subjected to only a part of the treatment of this invention, and

Fig. 7 is a graph illustrating the magnetostriction as measured by the apparatus of Fig. 5 for core members of transformers which have been given difierent treatments.

The silicon-iron alloys containing up to 6% of silicon are well known and the processes for developing the magnetic characteristics of such alloys have been commercially practiced in the past. For example, silicon-iron alloys containing up to about 4 A of silicon are commercially produced in sheet or strip form by subjecting them to different heat treatments, including the step of cold rolling them to the final stages and then subjecting the resulting strip to an anneal at a temperature of 900 C. or higher to develop the magnetic characteristics of the alloys. Silicon-iron alloys containing higher contents of silicon up to about 6% are not being commercially produced by cold rolling processes, since the higher silicon content renders them somewhat brittle and it has therefore become customary to hot work such alloys to the final stages after which a final anneal is employed for relieving working strains. Other methods are well known and practiced for developing the magnetic characteristics of the silicon-iron alloys containing up to 6% of silicon.

' In order to reduce the magnetostriction of the commercially produced silicon-iron alloys containing up to 6% of silicon, in accordance with this invention the commercially produced alloy sheets or strips are subjected to a further heat treatment whereby the alloyed components of, the strip are in such a condition that the magapplied for short periods of netostriction of the commercially produced alloys is effectively reduced. For the purposes of this invention the terms sheet and strip are synonymous in their meaning as employed in this application.

Referring to Fig. 1 of the drawings, there is schematicall illustrated a representative apparatus for practicing the method of this invention. The apparatus consists of an annealing furnace l having open ends through which the strip [2 of silicon-iron alloy which has already been treated and fabricated to develop its magnetic characteristics is. passed from a supply reel H to a winding reel l6. A brake I8 is associated with a supply reel H for applying a suitable dra thereto to impart a predetermined tension to the sheet or strip l2 as it is drawn through the annealing furnace Hi, the purpose of which will to the strip l2 as it is subjected to the annealing temperature is below the elastic limit of the alloy strip and preferably between 500 and 2000 pounds per square inch. The elastic limit as employed in describing this invention and in the claims is a point on the stress-strain curve which represents a stress equal to half of the maximum stress which the strip will hear at the heating temperature without breaking. Where tension below the elastic limit defined hereinbefore is time such as one to two minutes, it is found that no permanent elongation, except that which is concomitant by the tensioning within the elastic limit, results. In practice the strip i2 is drawn through the furnace l0 at a speed which will p'ermitthe heating of the strip to the desired annealing temperature while the winding reel I6 is positioned far enough away from the furnace 10 to permit the strip l2 to cool to a temperature of about 100 C. before it is wound on the reel Hi.

It is not known exactly what change takes place in the components or structure of the alloy when subjected to the hereinbefore described annealing treatment under tension. The results obtained, however, illustrate quite definitely that the tension applied during the anneal in air at a temperature between the Curie point of the alloys and 825 C. cooperates to effectively reduce the magnetostriction of the commercially produced silicon-iron alloy strip.

In order to illustrate the beneficial efiects of the treatment of this invention, reference may 'be had to Fig. 4 of the drawings, the curves of which illustratethe magnetostriction of siliconiron alloy sheets or strips after different treatments. Curve 20 represents a measure of magnetostriction for a silicon-iron alloy strip which contains about El /2% silicon asmeasured at different flux densities in a strip having surfaces which are free from films. Curve 22 represents the measure of magnetostriction for a stripof the same material when subjected to only the heat treatment utilized inthe method of this invention. Curve 24 represents the magnetostriction of another strip of the same materialv which has been subjected to the annealing treatment of this invention under tension.

In particular, curve 22 represents the measure of magnetostriction obtained by subjecting the commercially produced silicon-iron alloy sheet or strip to a temperature of 700 C. in air while curve 24 represents the measure of the magnetostriction obtained for the same commercially produced silicon-iron alloy strip when subjected to an annealing. temperature of 700 C. while maintained under a tension of 2000 pounds per square inch. From the curves it is quite evident that the treatment of this invention effectively reduces the magnetostriction of the commercially produced silicon-iron alloy strip.

Since the methods of measuring magnetostriction are not well known, and since it has been found necessary to utilize more than on method for measuring the magnetostriction, it is believed to be desirable to briefly-explain the apparatus and method employed in measuring the magnetostriction as represented by the

curves

20, 22 and 24 of Fig. 4 of the drawings.

Referring to Fig. 2 of the drawings, there is illustrated the apparatus for measuring the magnetostriction of silicon-iron strips employing a direct current excitation means. In this apparatus the magnetic circuit consists of four strips 26 of the silicon-iron alloy arranged with double lap joints in a 25 cm. test frame. The magnetostriction of only one of the strips 26 is measured, the other three strips serving to complete the magnetic circuit. The test strip 26 whose magnetostriction is to be measured is clamped as by means of the screws 28 in a non-magnetic holder 'formed of the two

bars

30 and 32, the holder being disposed to slide over the strip 26. The

- bar 32 carries bronze bearing balls 34, as shown in Fig. 3, upon which the test strip 26 rests.

In order to measure the elongation of the test strip 26, a roller member 36 having a mirror 38 at one end thereof is disposed between the test strip 26 and the bar 30 of the holder for rotating when the test strip 26 is elongated. As illustrated, the mirror 38 is so positioned as to deflect a beam of light from a lamp 49 which is focused upon a split photox unit 42 which is disposed to be connected to a galvanometer 44 by means of the switch 46, so that the deflection of the galvanometer is proportional to the deflection of the light beam upon the photox unit.

In order to energize the magnetic circuit formed by the strips 26, a source of direct current, such as the battery 48, is disposed to be connected through the double-throw switch 50 to the winding 52 disposed about the strips forming the core member. Variable resistors 5| and 53 are connected in series with each other and the battery, a switch 55 being provided for shunting resistor 53. The double-throw switch 50 is employed for controlling the direction of the energization of the assembled test specimen.

Since it is desired to measure both the elongation of the test strip 26 and the flux densities under which such elongation is obtained, a winding 54 is disposed about the assembled test strips 26 and is adapted to be connected to the galvanometer 40 by means of the double-throw switch 46. Thus with the rotation of the mirror deflecting the light beam on the photox unit 42, a measure of the elongation of the strip 26 can be obtained on the galvanometer 44 as well as a measure of the flux-density causing the measured elongation.

Another winding 56 is disposed about the test assneaa 4 netostriction for inductions up to 20,000 Gausses.

In operation with the apparatus and test sheet or strip 28 set up as shown in Figs. 2 and 3, the

double-throw switch 48 is thrown to the right to connect winding 54 to the galvanoi'neter 44. The

double-throw switch 58 is then moved to the right to connect the battery 48 to winding 52 to energize it. Resistor Si is then adjusted until the induction as measured by the galvanometer upon reversal of switch 58 is equal to the desired value at which the test is to be conducted.

Resistor 53 is then adjusted to a value where the simultaneous reversal of the double-throw switch 58 and the opening of switch 55 so affects deenergization of winding 52 that the gal-' vanometer 44 indicates zero induction. With this adjustment of the resistors 5i and 53, when the switch 48'is thrown to the left to connect the photox unit 42 in circuit with the galvanometer 44, the deflection of the galvanometer which occurs upon the simultaneous reversal of switch 58 and the opening of switch 55, is a-measure of the magnetostriction of the strip 26 under test. That this deflection is a measure of the magnetostriction is quite apparent in that the roller 36 and mirror 38 move as the test strip contracts as the induction is changed from the maximum desired value to zero induction by operating the switches 58 and 55. This measure of magnetostrictionis for a unit length of the test strip extending from the center line of the overlapping joint at the secured end of the test strip to the point of contact of the roller 36.

coil, due to its inertia, will tend to remain substantially fixed,

with the pick-ups 84 disposed at the opposite ends of a leg of the core member 88 as shown in Fig. 4, andconnected in series opposition, the vibrations for given inductions are recorded through the amplifier and the wave analyzer. The pick-ups are disposed at a number of different locations at the end of the leg of the core member in order to get an average recording of the vibration of the core member. In recording the vibrations, the amplitude of the l-cycle fundamental'frequencyt alone is measured since for the purpose of this invention it is very closely proportional to the maximum amplitude of vibration. The values recorded by the wave analyzer are thus equal to the total vibration of the core leg and when analyzed with respect to the length of the core member, give magnetostriction values-which are quite close to the values obtained on individual test strips when the apparatus of Fig. 2 is employed for measuring the magnetostriction. In measuring the vibrations, the amplifier and wave analyzer are first calibrated by measuring a known vibration so that the correct value of the vibration of the core member at any given induction can be obtained.

Referring to Fig. 71 of the drawings, there 'is illustrated the diflerence in the magnetostriction obtained with two core members of the same size constructed from the same commercially produced silicon-iron strips which have been subjected todifferent treatments. Curve I00 represents the magnetostriction measured on a core member of the commercially produced strips which have been subjected to only the further anneal at a temperature oi 100 C., while curve I02 represents the magnetostriction measured at diflerent flux densities fora core member of identical size formed of identical silicon-iron strip material but which has beensubjected to In order to illustrate that the method of this 4 Referring to Fig. 5 of the drawings, there is 4 shown the apparatus utilized for measuring the magnetostriction of a core member 88. In this apparatus the core member 88 is built up on a support 98 of non-magnetic steel and is clamped in position by means of a top clamping frame (not shown) secured to the support 88. A winding '82 is provided about'the core member 88 and disposed to be connected to a 60 -cycle source of power. Matched vibration pick-ups 94 are positioned at each end of one of the legs of the core member 88 and are electrically connected in series to an amplifier 88 which, in turn, is elec trically connected to a wave analyzer-88. The core member is then energized at different flux densities at 60-cycle excitation and the vibrations of the leg of the core member measured to obtain the magnetostriction effect of the core memher.

The vibration pick-ups 84 are well known and need not be described or shown in'detail, the pick-ups consisting generally of a small coil floating in a magnetic field produced by a permanent magnet firmly attached to the case of the casing of the pick-up will vibrate while the an annealing treatment in air at a temperature of 780 C. while under 'a tension of 1200 pounds per square inch, and thereafter cooled under tension to approximately C. The curve I88 and I82 clearly illustrate that the method of 7 this invention when applied to commercially produced silicon-iron alloys which have been fabricated into strip form and treated to develop their magnetic characteristics is effective for reducing the magnetostriction of core members formed from the treated alloy strip.

The method of this invention is also effective in reducing the losses in core members constructed from the commercially produced alloy sheets or strips as illustrated by Fig- 6 of the drawings. In this figure, curve I84 represents the true watts loss obtained 'at difierent flux densities for the core member upon which the magnetostriction curve I88 of Fig. '7 is obtained while curve I88 represents the true wattsloss at diflerent flux densities for the core member treated inaccordance with this invention and upon which curve I02 01' Fig. 7 is based.

While it is not known exactly what happens in the alloy when it is treated in accordance with the method of this invention, it is quite apparent that the combination of annealing in air at a sets the components of the alloy as to efiectively reduce the magnetostriction and insure the maintenance of the reduction of the magnetocharacteristiol.

magnetic Although'this invention has been described with reference to a particular embodiment thereof, it is, of course,"not to be limited thereto except by the scope of the appended claims.

1 I claim asmyinvention:

actress strlction at thg operating temperatures of the MAL treated alloy strip through an chamber, subjecting the alloy strip to a temperature between 700 C. and 825 C. in the annealing 1. In the method of reducing magnetostriction in a silicon-iron alloy containing up to 6% of silicon and which has been fabricated into strip form and treated to develop magnetic characteristics, the steps of, subjecting the treated.

alloy strip to an annealing treatment at a temperature between the Curie point of the alloy and 825 C. while applying tension to the strip, the tension applied to the strip during the anneal being below theelastic limit of the alloy strip.

the tension being the only treatment applied to the alloystrip in addition to said annealing treatment for effectively, reducing the magnetostriction of the alloy strip.

2. In the method of reducing magnetostricof silicon and which has been fabricated into strip form and treated to develop its magnetic characteristics, the steps of subjecting the treated alloy strip to an annealing treatment at a temperature between 100" C. and 825 C. in air, while applying tension to the strip, the ten- .sion applied to the strip during the air anneal being below the elastic limit of thealloy strip,

'the tension being the only treatment applied to the .alloy stripin addition to said annealing treatmentfor effectively reducing the magnetostriction of the alloy strip.

H 3. In the method of reducing magnetostriction in a silicon-iron alloy containing up to-8% strip form and treated-to develop its magnetic characteristics, the steps of subjecting the treated alloystrip to an annealingtreatment at a temperature between I00 0. and 825 C. while applying a tensionof between 500 and 2000 pounds persquare inch to the strip, the tension being the only treatment applied to the all y strip in addition to the annealingtreatment, the tension applied cooperating with the anneal to eilbctively reduce the magnetostriction of the alloy strip.

4.'In the method of reducing magnetostriction in a silicon-iron alloy containing up to 0% of silicon and which has been fabricated into strip form and to develop its magnetic characteristics, the steps of. subjecting the treated alloy strip to anannealing treatment at a temperature between tension being the only treatment applied to the alloy strip in addition to the annealing treatment, the-tensionapplied cooper ting with the 700' C. and- 825C. inv air, while applying a tensionof between 500 and 2000 poundsper square inch to the strip, the

chamber while applying tension to the strip as it passes through the annealing chamber, the tension applied being below the elastic limit of the alloy strip, and cooling the heated alloy strip under tension'from the annealing temperature to a temperature of about 100' 0., the Y tension being the only treatment applied to the alloy strip during the heating and cooling of the strip, the. tension applied cooperating with the heating and cooling treatment to effectively reduce the magnetostriction of the alloy strip.

6. In the method of reducing magnetostriction in a silicon-iron alloy containing up to 6% of silicon and which has been fabricated into strip form and treated. to develop the magnetic tion in a silicon-iron alloy containing up to 6% characteristics, the steps of passing the heat treated alloy strip through an annealing chamber having, open' ends, subjecting the alloy strip to a temperature between 100 C. and 825 'C. in the annealing chamber in air while applying tension to the strip, the tension applied being below the elastic limit ofthe alloy strip, and cooling the heated alloy strip in air under tension from the annealing temperature to a temperature of about 100 0., the tension being the only treatment applied to the alloy strip during the heating and cooling of the strip, the tension applied cooperating with'the air' heating and cooling treatment to-eifectively reducethe m8!- netostriction of the alloy strip.

'I. In the method of reducing magnetostri tion in a' silicon-iron alloy containing up to 6% of silicon and which has been fabricated into of silicon and which has been fabricated into strip form and treated to develop the magnetic characteristics, theg steps of passing the' heat treated alloy strip through an annealing chamber, subjecting the alloy strip to a temperaturebetween 700 C. and 825 C. in the annealing chamber while'applying a tension of between ,500 and 2000 pounds per square inch to the strip.

and cooling the heated alloy strip under tension from the annealing temperature, the tension being the only treatment applied to the alloy anneal to effectively reduce the magnetostricticn 10! the alloystrip. a 0. In the methodof reducingmagnetostriction in a silicon-iron alloy containing up to 6%,

of silicon and which has been fabricated into strip form and todevelop the magnetic the-steps ofpassing the heat ing'with the-anneal'to-eflectively magnetostrlction of the alloy strip.

strip during the heating and cooling of the strip,

the tension applied cooperating with the heating and cooling treatment to effectively reduce the magnetostriction of the alloy strip.

8. In the method ofreducing magnetostrlc tween 100 C. and 825C. in the annealing chamber in air-while applying a tension of between 500 and 2000 pounds per square inch'to the strip for a period of time of from one totwo minutes, the tension being'the only treatment applied tothe alloy strip in" addition to the an-.

nealing treatment, thetension applied cooperatne t