A Permanent Magnet Device for Measuring the Coercive Force

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Lucy Underwood
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1 7th Wold Confeence on Nondestuctive Testing, 5-8 Oct 008, Shnghi, Chin A Penent Mgnet Device fo Mesuing the Coecive Foce Edud S. GORKUNOV, Ve P. TABACHNIK Institute of Engineeing Science, RAS (Ul Bnch) 4 Kosoolsk steet, GSP-07, 609, Ekteinbug, Russi Tel: +7(4) 74475, Fx: +7(4) 7450 E-il: ges@ich.un.u, web: Abstct An ttched gnetic device copising two penent gnets fo gnetizing nd degnetizing is consideed. The ngul displceent of one gnet, with the othe being set t peset ngle, is the test pete popotionl to the coecive foce of the ticles. Kewods: Coecive foce, Penent gnets, Testing, Metl stuctues The nondestuctive testing of the phsico-echnicl popeties of steel ticles b coecive foce is cuentl pplied to estite the in-sevice dge of opeting fbicted etls nd to pedict thei sevice life. Coecietes copising ttched electognets test the degnetizing cuent esued when the gnetic flux psses though zeo in soe potion of n electognet-ticle gnetic cicuit [,]. The need fo lowe powe consuption nd instuent weight when opeting unde field, high-ltitude nd flble conditions hs popted the developent of coeciete with two penent gnets to gnetize nd degnetize ticles. In this cse, the ottion ngle of one of the gnets is the test pete [, 4]. Fig.. The gnetic cicuit of the coeciete: gnets (, ) nd oke (). Figue shows the gnetic cicuit of coeciete copising oke with linted gnet plced in its clindicl petue, the gnet being de of the Nd-Fe-B llo nd divided into two pts. The gnetootive foce М of the gnet equied to gnetize the ticle nd then degnetize it long the hsteesis loop close to jo cn be defined b eqn () obtined ccoding to the nlticl cicuit (fig. ) s M U b + δ = ( + ) + + сφ d, ()

2 whee = + ; b ( + ) + ; U U Φ = Φ + ; Φ = Φ +. F = F F с = b δ + + ; d = Φ Φ ; Hee, Φ, U nd Φ, U e the flux nd potentil dop in the ticle nd the oke, espectivel; nd e the gnetic esistnces of the ticle nd the oke; is the totl esistnce of the gnet nd the oke potion gnetized b the gnet lekge flux; F nd F e esistnces to the lekge fluxes F nd F shunting, espectivel, the ticle nd the gnet; δ is gp eluctnce between the oke nd the ticle; Φ, Φ, Φ e the ticle, oke nd gnet fluxes, espectivel. Fig.. Anlticl cicuit: gnetiztion. Fig.. Anlticl cicuit: degnetiztion. Duing degnetiztion, the flux is chnged in the ticle b the ottion of the gnet fo its initil position coesponding to the gnetiztion ode nd ngle α=0. The ticle is degnetized long the descending bnch of the hsteesis loop, nd, when α=90, it psses the e of esidul gnetiztion. When the gnet is otted b 80, the ticle becoes gnetized oppositel [5]. The vlue of the gnetootive foce М dc coesponding to the coecive foce Н c of the ticle cn be found fo the expession R + F М dс = ( + ) Uс + Uс, R = () R F + F obtined fo the nlticl cicuit shown in fig. when Φ =0. The gnetic potentil dops on the ticle nd the oke (U с nd U с, espectivel) coespond to the gnetic fields equl to thei coecive foces. The gnetootive foce М d cn be ssued to v ccoding to the cosine lw М d = Мcosα s the gnet ottes. In this cse, when the flux Φ in the ticle psses though zeo, ngle α 0 is the test pete fo ticles inspected with espect to the coecive foce. Note tht it is not onl the f М d tht vies s the gnet ottes, but lso the esistnces nd F. An expeient ws pefoed with pltes iitting ticles.5 9 in the coss section. Figue 4 shows the induction in the centl section of the ticle s dependent on the gnet ottion ngle α 0 fo thee pltes with Н c : 0.5 A/c (cold-olled tnsfoe steel); 8.7 A/c (steel ShKh5, with C ~.5 % nd C ~ %, s deliveed); 4.6 A/c (steel

3 ShKh5 hdened fo 850 ). Angle α 0 coesponding to zeo induction is seen to v between 98 nd 0, i. e., the nge of vitions in α 0 is α 0 =..0.5 B, T, T B,T,T α α Fig.4. Induction B s function of the ottion ngle α of cobined gnets и (see Fig. ). Fo thee pltes: Н c 0.5 A/c (), 8.7A/c (), 4.6 A/c (). Fig.5. Induction В s function of the ngle of ottion of the second gnet (α ) t fixed ngle α =60 of the fist gnet., nd e the se s in fig. 4. To incese the sensitivit of the test pocedue, the gnet ws divided into two pts. Afte the both gnets hd been zeoed, one of the (No.) ws otted b the ngle α < 90. The ticle is futhe degnetized b the othe gnet. In this cse, М d = М cosα М cosα. Figue 5 shows the descending bnches of the hsteesis loops fo the se pltes s in fig. 4. The nge of vitions α 0 is seen to exceed α 0 b fcto of.6. To incese the technologicl effectiveness of testing, ngles α 0 nd α 0 wee futhe esued t zeo voltge t the output of Hll device ounted in the nonfeognetic gp between the oke pole nd the ticle. Fo two pltes with Н c = 8.7 nd 4.6 A/c α 0 ws esued t α =const in the nge between 0 nd 90. The esueent esults, s well s the vlues of α 0 fo Н c = 8.7 nd 4.6 A/c, e shown in fig. 6. As is seen, α 0 exceeds α 0 b fcto of.6 when α = 60, nd this ws found when the flux Φ ws esued in the centl section of the ticle in the bsence of gp between the ticle nd the coeciete oke.

4 α α 0 + х α Fig.6. The dependences α 0 (α ) fo Н c = 8.7 A/c ( ); 4.6 A/c ( ). The vlues of α 0 fo Н c = 8.7 A/c ( ) nd 4.6 A/c (+). In conclusion, fig. 7 shows the dependence of α 0 t α = 60 fo ten pltes with the coecive foce nging between.4 nd 48 A/c; fo copison, the vlues of α 0 e given fo two pltes with Н c = 8.7 nd 4.6 A/c. Thus, fo the coecive foce nging between 5 nd 50 A/c, the sensitivit of the test ethod is bout A/c pe one degee of the α scle. α Н С, A/c Fig.7. The Н c -dependences of ottion ngles α 0 ( ) of the second gnet t α = 60 nd of ngles α 0 ( ) t siultneous ottion of two gnets. We hve deonstted the dvntge of using two independentl otted gnets nd testing b the ottion ngle of one of the, the othe being set t fixed ngle, less thn 90. Expessions hve been obtined tht enble the vlues of the gnetootive foces of the gnets equied fo gnetizing nd degnetizing n ticle, M nd M dс, espectivel, to be evluted. Sll nd light, the coeciete is intended fo popt testing when powe suppl is hindeed o liited b sfet equieents. 4

5 Refeences [] Mikheev M.N., Neizvestnov B.M., Moozov V.M., Suin G.V., Coecietes with ttched electognets, Defektoskopi, 965, Nube, p89-90 (in Russin). [] Muzhitsk V.F., Popov B.E., Bezludko G.Y., Mgnetic inspection of the stess-stin stte nd eining sevice life of steel stuctues in hoisting chines nd pessuized vessels, Defectoscopi, 00, Nube, p8-46 (in Russin). [] Gokunov E.S., Tbchnik V.P., Bshkov Yu.F., Dunitsk V.N., A coeciete with penent gnets, RF Ptent Nube 0786, published Mch 0, 00 (in Russin). [4] Gokunov E.S., Tbchnik V.P., Siventsev A.A., A coeciete with penent gnets, Khiicheskoe i Neftegzovoe. Mshinostoenie, 005, Nube, p4-4 (in Russin). [5] Gokunov E.S., Tbchnik V.P., A penent-gnet-bsed ttched instuent used to inspect ticles on the bsis of thei coecive foce, Defectoskopi, 007, Nube, p

U>, and is negative. Electric Potential Energy

U>, and is negative. Electric Potential Energy Electic Potentil Enegy Think of gvittionl potentil enegy. When the lock is moved veticlly up ginst gvity, the gvittionl foce does negtive wok (you do positive wok), nd the potentil enegy (U) inceses. When