GB2237935A

GB2237935A - Method of making articles from magnetically hard ferrites and a device for comminuting magnetically hard ferrites

Info

Publication number: GB2237935A
Application number: GB8924715A
Authority: GB
Inventors: Vladimir Alexandrovi Abrosimov; Jury Nikolaevich Kuznetsov; Viktor Fedorovich Luzev; Vladimir Mikhailovich Sigida; Valery Sergeevich Tikhonov
Original assignee: JUMATOVA ANNA IVANOVNA
Current assignee: JUMATOVA ANNA IVANOVNA
Priority date: 1989-11-02
Filing date: 1989-11-02
Publication date: 1991-05-15
Also published as: GB8924715D0; FR2654373A1; DE3937506A1

Abstract

In a method of making articles from magnetically hard ferrites the initial calcined ferrite is magnetized prior to comminution. Calcined ferrite granules are fed from a hopper 16 through a magnetising field produced by a winding 13 and conveyed by the alternating field of a winding 12 to a container 1 supplied with water from a vessel 5 via a pump 6. The magnetic field produced by a winding 10 causes the granules to collide and comminute thereby forming a suspension which is fed to the vessel 5. An outlet pipe 9 supplies the suspension to a mould and the moulded workpieces are then fired. <IMAGE>

Description

- 1 METHOD OF 1,1A.-KING ARTI'CLES PRO_ LIAGI.-TICALILY HARD FERKITES AN.L

A DEVIOE FUR COIZIIIITIIG IAGITETICALLY H.A RD FE RT-LI TE S This invention relates to powder meta]-lurgy, and more particularly to a method of making articles from magnetically hard ferrites and a device for comminuting magnetically hard ferrites.

The invention can be used'for fabricating m agnets from magnetically hard ferrites to be used in the electronic and chemical industries.

There is known a method of making articles from magnetically hard ferrites in which the initial calcined ferrite is comminuted, a %orkpiece is moulded from the thus obtained powder or from its aqueous suspension,the workpiece is fired and mechanically treated, and the article's parameters are checked.

However, this method of making ferrite articles is characterized by a high rate of rejects due to cracks and spalling caused by firing and mechanical machining to result in low magnetic properties of ferrite articles. Also, the process of comminuting the initial ferrite is time and labour consuming. High percentage of rejects is caused by contamination of the initial ferrite and foreign inclusions during comminution. These foreign inclusions are mostly particles of metal grinding bodies which act to provide concentration stress centers in the course of firing, whereby cracking of the articles J is promoted and magnetic parameters thereof are affected.

Retreatment of rejects according to thic l=own method complicated due to their high hard-ness and -Door COMMi nutability.

There is Imown a device for commirrating, magneti call,.

hard ferrites comprising a casing, an electric v.,-.nding connected to a source of electric current, embracing the casing, and providing therein an alternating magnetic field, as ivell as inlet and outlet pipes.

Under the action of an alternating magnetic field produced by the electric winding lumps (or grarralez) of the initial magnetically hard ferrite are caused to move, collide and be comminuted.

A disadvantage of this device is low quality of comminution when the magnetically hard ferrites are comminuted in a continous cycle and high povier expend itures. Another disadvantage is a rather low efficiency of the device.

Comminuting magnetically hard ferrites by this de- vice fails to ensure the desired dispersion, whereby the comminuted ferrite contains rough particles affecting the quality of the finished product.

It is an object of this invention to ensure that fabrication of articles from magnetically hard ferrites is more economical.

Another object is to improve the magnetic parameters of articles made from magnetically hard ferrites.

The present invention aims at provinding a method of making articles from magnetically hard ferrites and a de- 11 3 vic- for comminuting magnetically hard ferrites whereby _it would be possible to ensure a higher commixatabilityand higher yield of fine fraction throu,,:.h additional processing of the initial calcined ferr-te.

The aims of the invention have been attained in a me'ly hard ferrites thod of making articles fror. magnetica.

in which the initial calcined ferrite is rp..-,:.,ietized, com- C5 minuted, moulded in the form of a work.

kpiece, the workpiece is fired, and parameters of the thus obtained ferrite article are checked.

It is advisable that the magnetized calcined ferrite be comrdnuted in an aqueous medium through circulation of a suspension of ferrite under the action of an alternating magnetic field.

It is further advantageous that the strength of the alternating magnetic field be preset vithin a range

4.10 4 - 105 A/m.

It is preferable that powdered ferrite in an amount of 1 to 100 parts per one part of the initial calcined ferrite be added to the circulating suspension.

It is further preferable that the concentraticn of ferrite in the circulating suspension be maintained within 1 to 30 mass per cent.

In view of the aforedescribed, the preliminary magnetization of the initial calcined ferrite, as well as comminution of the ferrite in a circulating suspension having a ferrite concentration of 1 to 30 mass per cent under the action of an alternating magnetic field of a strength 4.10 4 - 105 A/m, affords a higher yield of the fine fraction of the ferrite powder whereby the time ne- cessary for comminution is reduced. Another acco=-,a,.--Y_Jns advantage is reduced percentage of rejects and improved U - f rite art- magnetic parameters o Iie fer- _Lcles.

Adding to the suspension of the powdered ferrLte in an amount 1 to 100 parts per one Dart of the initial calcined ferrite promotes a higher yield of the fine fraction of ferrite powder and results in higher magnetic characteriBtics of the finished ferrite articles. Thanks to the aforedescribed, the proposed method makes the fLb- rication process more economical.

The aims of the invention have been further attained in a device for comminuting hard ferrites comprising a casing having inlet and outlet pipes, an electric winding connected to an alternating current source, embrac- ing the casing and producing therein an alternating magnetic field the device being provided with an auxiliary vessel positioned over the casing, communicating therewith and arranged coaxially with the casing, and an intermediate vessel communicating witi-. the inlet pipe of the casing through a circulation pump and with the outlet pipe of the casing through a pipe for feeding a suspension to form a circulation circuit, and also having pipes for feeding viater and evacuating the com.- dnuted material, the device further having two additional elect- ric windings embracing the auxiliary vessel, one of the additional electric windings being connected to the alternating current source, whereas the additional winding is connected to a direct current source.

1 It is desirable that tne JLntermediate vessel be coneshaDed, the pipes for feedinil the Easpension and water being arran-ed tangentially to the intermediate vessel, U whereas tne pipe for evacuatin7 the comminuted material C> is arranged axially of the intermediate vessel.

f' the de-;ice for The aforedescribed arrangement o. comminuting magnetically hard ferrites makes it possible to reduce contamination of the ferrites with foreign inclusions to result in a lower percentalse of rejects and improved magnetic parameters of ferrite articles.

The invention will now be described in greater detail with reference to specific embodinients thereof taken in conjunction with the accompanying drawings, in which:

Fig. 1 is a general sectional view of a device for comminuting magnetically hard ferrites; and Fig. 2 is a section taken along the line II-II in Fig. 1.

The proposed method of making articles from magnetically hard ferrites resides in that the initial calcined ferrite is magnetized by the action of a pulsed magnetic field, after which the calcined ferrite is comminuted, moulded into a workpiece and fired in any knovin suitable production line, the viorkpiece is then mechanically machined, and parameters of the thus obtained ferrite article are checked.

Comminution of the initial calcined magnetized ferrite is done in an aqueous medium under the action of an alternating magnetic field accompanied by circulation of in an inc-rease in r_ suspension t.ius obtained the yield of the fine fraction and reduction in the aw,:)- " t -ing unt of power consumed. The of Uhe alternat magnetic field is preset a ranrye 4. 104 _ 1051,/M.

cl In order to increase the yield CiL fine fraction, a povidered ferrite is added to the circalating pLip in ean amount of 1 to 100 parts per one part of the initial calcined ferrite, whereas the concentration of ferrite in the circulating suspension is maintained at 1 to 30 mass Der cent.

The invention will be more fully understood from examples of carrying it out represented hereinbelow.

Example 1

Rings sizing 85 X 35 x 10 =m are fabricated from barium ferrite. The initial calcined ferrite in the form of granules up to 12 nLn across is magnetized to satura tion in a pulsed magnetic field and co=inuted in a de vice for comminuting magnetically hard ferrites. The set tled comminuted ferrite mass is then conveyed for moulding.

The moulded ring workpieces are fired at a temperature of 1200 0 C, polished, and the magnetic characteristics of the rings are checked.

Example 2

Rings of the same type and size as in Exam.ple 1 are made from barium ferrite. The initial ferrite in the form of rejects crushed to 12 mm across is magnetized to saturation in a pulsed constant field to be continuously fed at a rate of 5 - 8 kg/h to an apparatus for cor=inuting magnetically hard ferrites. The strength of the ragnetic _r field in the casing of the dev-ce is va-ried by a veltage re.gulator. A pump circulates the sus--c.-isior.. T1he concentration of ferrite in the sLsDensi-on is maintuained Y.ithin a preset ranEe by controlling the a:.-. curt of viater adaed.

C Tae co=,-,inuted ferrite mass laavinr, a -specific surface 2 area of between 1.1 and 1.6 r,"Vg i-- ccnt_nuou_-lI,,,, evacuated from the circulating floy; of suspension. The settled comminuted ferrite mass is conveyed for moLlding. Idoulded ring viorkpieces are fired at a tempez-ature of 1200 0 0, Po- lished, and magnetic parameters of the thus obtained ferrite article are checked.

Example 3

Articles from barium ferrite are fabricated as heretofore described in Example 2, the difference being in that at the stage of comminution a povidered ferrite in an amount 1 to 100 parts per one part of the initial calcined ferrite is added to the suspension.

For comparison, similar articles were fabricated according to the known method by comminuting the initial calcined ferrite, moulding workpieces therefrom, firing the workpieces, polishing the ferrite articles, and checking their magnetic characteristics.

Results of co.-,.parative tests of ferrite articles fabricated as described in ExamDles 1, 2 3 by the pro-he known method are re- posed method and according to t presented in Table 1.

Table 2 represents comparative data in terms of the yield of fine fraction of the comminuted ferrite powd- 4 1 z Table 1

Parameters of the process and characteristics of ferrite articles Liet.'-.o of =alking ferrite articles Knovin Pro-osed Exarrple 1 Example 2 Example 3 Duration of comminu- tion, hrs 2 1.8 1.2 1.5 Speci.Cic surface area of the comminuted ferrite, m 2 /g 1.1 1.1 1.3 1.6 Coersive force, Oe 1900 Residual induction, G 3200 3300 3800 3500 Per cent of effec- tive items 81 86 90 91 2000 2300 2400 er and magnetic characteristics of the ferrite articles made according to the known and proposed methods (.,ixample 2) at different content of ferrite in the suspension and different strength of the alternating magnetic field.

Table 3 represents comparative data in terms of the 25 yield of fine fraction of the comminuted ferrite-powder ""' the ferrite articles acand magnetic characteristics o.L cording to the known and proposed method (Example 3) when 1 to 100 parts of powdered ferrite per one part of 1 Parameters of the:3rocess and characleristics of ferrite articles Table 2 lyle t lio d of ria-k.ing llroDosed -1, AIM 3 104 4. l C)4 4,104 Known c, % 1.0 0.5 1.0 1 2 3 4 5 6 1.Yield of fine fraction (1.1 -1.6 M2/g) of powder during comminution, kg/h 1 0.2 0.1 0.16 0.3 2.Coersive force,Oe 1900 3-Residual induction, 1800 1800 2050 G 3200 3200 3100 3300 4-Per cent of effec- tive articles 81 80 86 Table 2 (continued) 6.104 6.104 105 105 5.0 15.0 20.0 35.0 30.0 7 8 9 10 11 1. 0.9 1.2 0.3 0.2 0.2 2. 2200 2400 2100 1900 1850 3. 3500 3500 3200 3000 2950 4. 89 91 84 81 80 Note: H is the strength of the alternating magnetic field during comminution, A/m;

C is the concentration of ferrite in the suspension, 70.

1 i the initial calcined ferrite are added to t.;,.= suspension.

Table 3 -Iet.iod of making Parameters of the process and characte ristics of Known ferrite ar ticles Yield of fine fraction (1.1- - 1.6 m 2 /g) of powder during comminution, kg/h 1 Coersive force, Oe By adding powdered ferrite to the suspension, parts 0.5 1.0 10 30 60 100 110 0.2 1.2 1.25 1.4 1.82.0 1.2 1.1 1900 2400 2450 2500 2600 2470 22001800 Residual induc tion,G 3200 3500 3550 3800 3980 3570 3300 3100 Note: The strength of alternating magnetic field during comminution is 6. 104 A/m; Concentration of ferrite in the pulp is C = 157o.

A device for comminuting rrnagnetically hard ferrites comprises a casing 1 (Fig. 1), inlet pipe 2 and outlet pipe 3. Provided over the casing 1 coaxially therewith is an auxiliary vessel 4 communicating with the casing 1 and 1 i k 11 arranged coaxially therewl-th.

The device is also provided with an intermediate vessel 5 communicating.%, ith the inlet nine 2 of the casing 1 throaSh a circulation pump 6 (of any known suitable design) and with tne outlet pine 3 of the casing 1 through - a pipe 7 for feeding a suspension to define a circulation circuit. The intermediate vessel 5 has a pipe 6 for feeding water and a pipe 9 for evacuating the comminuted material. The casing 1 is embraced by an electric wind- ing 10 connected to a source 11 of alternating current to generate an alternating magnetic field therein. The device has two additional electric windings 12 and 13 embracing the auxiliary vessel 4, one such winding 12 being connected to a source 14 of alternating current where- as the other additional winding 13 is connected to a source of direct current. Secured over the auxiliary vessel 4 is a hopper 16 to contain the initial calcined ferrite.

The intermediate vessel 5 is cone-shaped, the pipes 7 and 8 (Fig. 2) for feeding the suspension and water being arranged tangentially, whereas the pipe 9 for evacuating the comminuted material is arranged axially of the intermediate vessel 5.

The device for comminuting magnetically hard ferrites operates in the following manner. The initial calcined ferrite in the form of granules or rejects crushed to 12 mm in size is charged to the hopper 16 (Fig. 1) wherefrom it flows by gravity and under the action of a 1 constant magnetic field produced by tne additional winding 13 to the auxiliary vessel 4 whe-re it is magnetized and convejed by the alternating magnetic field produced by the winding 12 to the casing -1. Water is supplied thro5 ugh the pipe 8 of the intermediate vessel 5 and circulation pump 6 to the casing 1. Under the action of the alternating magnetic field produced by tne electric winding 10 embracing the casing 1 the magnetized lumps (or granules) of the initial calcined ferrite fed to the cas- ing 1 are caused to move, whereby they collide and comminute. The suspension of the thus comr.inuted f errite is discharged through the outlet pipe 3 to tile intermediate vessel 5. The circulation pump 6 ensures circulation of the suspension about the circulation circuit between the casing 1 and intermediate vessel 5 to result in an increase in the quantity of the fine fraction of the ferrite in the suspension as it successively passes ttirough the casing 1 to result in a wore dispersed product.

In order to Improve the quality of dispersed pro20 duct, the pipes 7 and 8 of the intermediate vessel 5 are tangential whereas the vessel 5 per se is cone-shaped. This in turn allows swirling of the flow suspension in the intermediate vessel 5, whereby particles of the ferrite which failed to be sufficiently comminuted are thrown to the walls of the intermediate vessel 5 to be recomminuted, whereas the suspension carrying the finely disperse.d particles is discharged through the pipe 9 arranged axiRlly of the intermediate vessel.5. The suspension is J k.

discharged ti.rough the pine 9 by gravity or by a pump (not shown).

The settled ferrite mass is conveyed for moulding to a known press, the moulded workpieces are then convey- ed f or firing and tnen for mechanical treatment, after which the magnetic parameters of the ferrite articles are checked.

As can be seen in tables 1 to 3, the calcined ferrite is magnetized priorto comminution and is comninuted as the suspension having 1 to 30% concentration of ferrite is circulated under the action of a variable magnetic field at a magnetic trerl6th of 4.10 4 _ 10.5 A/m to allow an increase in the yield of fine fraction of the ferrite powder and thereby reduce the time of the com- minution process. The accompanying advantage is an increase in the yield of standard quality articles with improved magnetic parameters.

Deviation from the preferred range of the magnetic field strength and concentration of ferrite in the sus- pension affects the magnetic parameters of the articles and reduces the yield of fine fraction of the ferrite during comminution.

By additionally introducing a powdered ferrite in an amount of 1 to 100 parts of such'ferrite per one part of the initial calcined magnetically hard ferrite-to the suspension makes it possible to increase the yield of fine fraction of the ferrite powder and improve the magnetic 14 - 1 parameters of the f errite articles. Deviation from tne preferred operation range results in a somewLiat reduced yield of the fine ferrite fract-Lon and affects the magnetic parameters of f errite artv.Jk.C'Les.

The proposed method allows a substantial saving in the manufacture of f errite articles through reducing the amount of rejects and time necessary for comminuting the initial f erzite. Another advantage of the method is easy utilization of rejects and improved magnetic proper10 ties of ferrite articles.

The proposed device for comminuting magnetically hard ferrites Is characterized by structural simplicity and high efficiency. The device allows to reduce contamination of ferrite with. foreign inclusions during com20 minution.

h i

Claims

CLAIMS:

1. A method of making articles from magnetically hard ferrites in which the initial calcined ferrite is magnetized, comminuted and moulded in the form of a workpiece, and the workpiece is fired and mechanically worked.

2. A method as claimed in claim 1, in which the magnetized calcined ferrite is comminuted in water by suspending the magnetized ferrite in water and circulating the suspension under the influence of an alternating magnetic field.

3. A method as claimed in claim 2 in which the strength of the alternating magnetic field is within a range 4 x 104 - 105 A/m.

4. A method as claimed in either claim 2 or claim 3, in which powdered ferrite in an amount of 1 to 100 parts per one part of the initial calcined ferrite is added to the circulating suspension.

5. A method as claimed in any one of claims 2 to 4. in which the concentration of ferrite in the circulating suspension is maintained within 1 to 30 weight percent.

6. A method of making articles from magnetically hard ferrites as claimed in claims 1 to 5 and substantially as described herein.

4.

1 - 16

7. An apparatus for comminuting magnetically hard ferrites comprising a container having inlet and outlet pipes and an electric winding connected to an alternating current source and surrounding the container to produce therein an alternating magnetic field, an auxiliary vessel positioned above the container and communicating therewith, and an intermediate vessel communicating with the inlet pipe of the container through a circulation pump and with the outlet pipe of the container through a pipe for feeding a suspension of ferrite in water to define a circulation circuit, and also having pipes for feeding water and evacuating the comminuted material, the apparatus further having two additional electric windings surrounding the auxiliary vessel, one of the additional electric windings being connected to an alternating current source, the other additional electric winding being connected to a direct current source.

8. An apparatus as claimed in claim 7, in which the intermediate vessel is substantially cone-shaped and the pipes for feeding the suspension and water are arranged tangentially to the intermediate vessel, the pipe for removing the comminuted material being arranged axially of the intermediate vessel.

9. An apparatus for comminuting magnetically hard ferrites substantially as described herein with reference to the accompanying drawings.

- 1 111 -1 1991 at The Patent Ofte. State Housp-66/71 High HoIbom. LDndonWCIR47?.FurLhcr copies may be obtained from Sales Bramb. Unit a. Nine Mile Point. CwmMinfitch. Cross Keys. NcwporL NPI 7HZ. Printed by Muluplex techniques Rd. St M2ry Cray. Kent.

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