CA1084712A - Apparatus for working sheet materials with ferromagnetic powder - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
The apparatus is provided with two rolls made of a magnetically conductive material, spaced to define a pas-sage for a sheet being worked. Either at the first ends, or at both ends of the rolls there are provided means for inducing a magnetic field, so arranged that the magnetic lines extend axially of the rolls and cross the gap there-between, whereby the rolls act as the opposite pole pieces of a single magnetic systems and are designed to retain the ferromagnetic powder which, with the rolls rotating, is pulled through the gap therebetween in a layer used to work the sheet material. The apparatus incorporates a device for levelling out the distribution of the grains of the ferro-magnetic powder throughout the length of the gap. The de-vice can be made in the form of a blade positioned to cut off a part of the magnetic powder body at the extremities of the rolls, which enhances the uniform distribution of the grains. The invention also provides for the rolls having tapering portions at their extremities, whereby the magnetic flux density at these extremities is reduced and made sub-stantially equal to the density centrally of the rolls.

Description

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APPARA~US FOR l,lJORKING SL~'E'~ MA'~RIA~S 'iVI~I
; ~:13RROMAGNE'.~IC POliVDER ~ .
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'~he present invention relate~ to -the machi~ing by .`
abrasion, and, more particularly, it relates to apparatus ~or working sheet ma-terials wi-th eerromagnetic powder and can be used to u-tmost adva~ltage for machi~i~g se~ ini~h~
ed prin-ted boards o~ various rad.ioelec-tronic devices. How- ~;
ever, the present invention can be used as advantageously in o-ther art~ and industries, wherever it is desirous to obtain sheet materials or s-tock with a high quality Oe sur- ;
face machining over the en-tire sureace o~ a workpiece.
'~here i9 already known an apparatus ~ O.L' working sheet materials, ~or which an application titled "Device ~or -the treatment o~ ~heet mateIials't was ~iled by I.A. Deresh et al~ with the United States Patent O~ice, SerO ~o 629,631;
1975, ~or which US Paten-~ No ~,0401209 has been issued.
he apparatus comprises a magne-tic system ~or retain-in~ or holdinbr the.abrasive powder in -the maahinin~ zone defined by two cylindrical rolls made O:e a magn~tically conductive material and spaced to deeine therebetween a gap ~or tho pa~a~e o~ a ~heet bein~ worked, the roll~ bein~
mounted ~or rotation in opposi-te direc-tions at subs-tantial- :
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~ . ly equal angular speeds~ :-1 :

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2--r~he apparatus is provlded with a mechanism ~or feed-ing the sheets to be workecl in-to -the machininK zone and means ~'or :inducing a magnetic :eield, includin~ a magnetic circuit arIanged at least at the side o~ the :eirst ends .
of t~e rolls, ~or the ma~netic li~es Oe -the magnetic ~lux to extend axially o~ the rolls and to cross the gap there-between. In -this s-tructure one o~ the rolls acts as one o~ the pole pieces o~ the m~gnetic system, while the other roll acts as the other pole piece o~ the same syste~, where-by particles O:e the abrasive powder are retained in the gap between -the rolls in the process o~ the machining.
-/ The abovespeci;eied apparatus has already proved its operational merits. It provides two-side working O:e semi-.~inished printed boards, i.e. O:e printed board blanks, by wtlich working ei-ther the metal oxide layer or the protec--tive coa-ting film are removed ~rom -the sheet surface, and the sur~ace attains the required degree Oe roughness ensur-n~ dependable adhesion o~ the photoresist layer to the blank sureaoe durin~ the subse~uent processing.
I 'rhe ~erromagnetic powder used as the working medium ; is both i~xpensive and no-t hard to get.
A particula.r adva~ta~e Oe the abov~specl:eied appara-tus is its ability to process e~-tra-thin printed board blanks (as t~in a~ 0603 mm) in a substantially continuous .
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proces~, i.e. on the conveyer technique basis.
However~ experience has prove~ that in the proce~s o~
the machining per~ormed by the abovespeci~ied appara-tus, the work passing betwee~ ~he rolls i9 machiLled more inten~e-ly a-t i-ts edges than at the central portion, 50 that mQre material is removed o~E the work at the edge area~ than at the centre. ~his means that the machining over the entire surface is not adequately uniform, which aYfect9 the quality o~ the machined work, e~g. o~ printed boards~
It is an ob~ect o~ -the present invention to provide an apparatus ~or working with ferromagnetic powder`~ which should provide ~or uni~orm mac~ining Oe a sheet workpiece over its entire sur~ace area.
It is another object o~ the pre~ont invention to im-prove the quali-ty o~ -the machining.
These and o-ther objects are attained in an apparatus ~or working sheet materials wi-th ~erromagnetic powder, com-prising a magnetic system ~or retaininK the powder, de~ined by roll~ made oE a ma~ne-tically cond~ctive material, spaced to de~ine thsrebetw~en a E~aP l'or the passage o~ th~ material being worked, and an inducer o~ th~ magnetic elu~, arranged at least at the ~ir~t ~ace ends oE the rolls, ~or the mag-netic lines to exbend a~iall~ o~ the rolls and to cross the . . .

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~8~7:~L2 gap wherei~, with the roll~ rotating, -the ~erromagnetic powder is pulled in a la~er, which appa.ra-tus, in accordance with the pre~ent inven-tion, ~urther comprise~ a device ~or levellinrJ out the distributio~ of the grains o~ the powder in the said layer throuKhout the length o~ -the gap between the magne-tic rolls.
'~he herein disclosed invention i~ based on the i~act we have established, residing in non-uni~orm distribution o~ the ~erromagnetic powder longitudinally of the rolls, on accoun-t O:e the magne-tic rolls e~hibiting de~inite, how-ever small, re~istance -to the passage of the magnetic :~lux -therethroUKh~ whereby non-uni.~ormity takes place in the distribution of the magnetic flu~ in the gap therebetween longitudinally o~ the machinin~; zone. In th~ ~reas of the machining zone, adjoining the coils inducing the magnetic f lux 5 the inten~i-ty of the magnetic flux is somewhat higher than in -the central area o~ the ~achini~g zone.
'rhe abovedescribed phenomenon resul-ts bo-th in -the quan-tity of the ~erromagnetic powder retained by the mag~netic i'lux and the densit~ thereoi' bein~ non-uniform longi-tudinal-ly oi' the maKnet:ic rolls, and, oon~e~1uently 7 over the ma-ohining ~o~e. ':L`here~ore, a sheet workpiece pa~sing between :~
the magnetic rolls is more inten~ely machined at the edge ', .
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areas o~ the machining zone than in the central area there-o~ e. it is machined non-unieormly over the sureace area tnereo~, the edge areas being machined mor~ in-~ensely, and -the central area less intensely.
~ he introduction by us of -the device for levelling out the di~tribution o~ grains of the magnetic powder 7 aris-ing ~rom the otherwise non-uni~orm magnetic flu~, as it ha9 been already mentioned, provides for ~ubstantially ~ni~orm intensi-ty Oe the machining o~er the entire work area, and, consequently, the enhanced quality oP -the machining Oe shee-k materialc The devices and mean~ ~or ensuring the unl~ormity o~
-the distribution Oe the grains o~ the eerromagnetic powder may be varLous, , In one embodiment of the present invention the leve~l-ing out Oe the distribution of t~e ~Eerromagnetic powder is provided ~or by tapering portions at the e~tremities O~e the magnetically conductive or permeable rolls, i.e. in the zone o~ the most inten~e magnetic elux at the ends o~ the rollsO
This embodiment is the ~imples-t ~rom the structural realiza-tion point O:e view. It provides l'or a deorea~e o~ the ma6ne-tic induction or elu~ densit~ at -the e~tremities Oe the rolls, because the magnetîc lines have to cross the air gap in their '` .

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~6.--travel ~rom one roll to the o-ther one, and -this gap o~er~
con~J.d~.rablc resl9tance to th~7 pasC;age oY the magnetic ~lux, :th~ magnetic permeabi.lity o~ air being as i-t is thousands to dozens o.L' t~ousands times smaller -than that o~ iron and ~pecial-purpose electrical engineerin~r ~teel~, the exact proportion being dependent on the magnetic saturation cha-racteristics o~ the iron and steels. So, it is obvious that but a s~all increase oI' the operational air g~p by the pro-vi~ion ~ the tapering portions o~ the magne-tic rolls in the area o~ the relativ~ly higher densi-ty o~ the ma~netic flu~ i5 capable o~ levelling out the magnetic induc-tion throughou-t the working ~ap, and, hence, the di~trlbu-tion o~ the powder in -the layer.
This uni~ormity o~ the dis-tribution of the ~errite powder longi-tudi~ally o~ the working gap is signi~ican-tly enhanced by the tapering being do~e along a smooth curve, so -tha-t the rolls acquire a barrel-like shape. :
This can be e~plained by the fact that variat~on of `~
the magnetic permeability o~ iron and other electrical engineering materials is not directly proportlonal to the varying value o~ the ~agnetic induction longitudinally o~ :
~he magnetic roll, but is govexned by law~ ~pec:LI'Lc ~or each individual magnetically conductive or permeable mate-rial.

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, The optimum shape o~ -the ~eneratrix o~ -the curvilinear working ~rface o~ the magne-t.ic rolls can bo calculated with the use o~ -~he known ~ormulae of ma~netio ~luxes.
'~hese formulae, however, are complicated and ofeer -the re sultant accuracy well short o~ 10 per cen-t; there~ore, we deem it not nece~sary to describe it in detail here. Let ;
us say that the final shape of ~e 6eneratri~ of the barrel-shaped magnetic roll is best eound by experience ~or each individual design of the appara-tu9 ~or working sheet ma-terials) Alterna-tively, the device ~or levelling out the dis-~ribution O:e the ~erromagnetic powder may include a kniee with a blade spaced erom the rolls by a dis~ance deterrnin-ing the height o~ the layer o~ the ~erromagnetic powder Wi th respec-t of the roll sur:eace. '~he blade o~ the kni~e is preferably longitudinally curvilinear, its concave side ~-facing the roll 7 whereby the edge of the blade is more re-mote ~rom the mag~etic rolls in the zone with the smaller mag~etic ~lux densi~y than i~ the zone where ~his density is greater, ~ he incorporatiorl o~ the device ~or levelling out the distribution o~ the ~erroma~netic powde:r, includin~ the kni~e mechanically removing the ~urplus part o~ the layer o~ the ferromagnetic powder retained on the rolls by the . .
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magne-tic l~ield, provides for passing tLIe ferromagnetic powd-er t~lrou~h the working gap in a predeterr~ined qua~ti~y, as well as for adjustin~ easily the quantity o~ the ferromagne-tic powder fed into the machinin~ zone by var~ing the spac-ing of tha knife from the ma~netic roll. As it has been al-ready s-ta-ted, the blade o~: the knife is preferably longitudi-nally curvelinear to be more remote ~rom the m~gnetic roll in the aIaas wi-th the smaller ~lagnetic ~lu~ c3ensity, where the layer of the ~erroma~netic powder is s.imilarly less dense, than in the areas with the grea~er magne-tic flux density, and, hence, the greater den~i-ty of the ~erromagnetic powder. ::
The structure with the levelling-out device including the blade removing the surplus ferroma~netio po~der in the area~ of the latter' 5 increa9ed den~ity 3 by the edge of the blade in these area~ not permit-ting the passage o~ a thick layer of the powder into the machining zone, enable~ to ad- ;
just the feed of -the ferromagnetic powder in-to the machin-ing zone so that its quantity is substantially uniform thro~
ughout the workinK gap be-tween the rolls.
;With the distribution of the ferromagnetic po~vder in the working gap thus levelled out, lt ls possible to have -the magnetic roll9 with a rectilinear genera-trix, to adiust, whe~ever necessary, the height of the layer of the ferro-.~
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ma~netic powder on the roll3 and to obtain ~hee-t material~
mac~lined in the presantly described appa:ratus with adequate uniformity ol' the ~ach.ining over the entire sur~ace o~' a sheet workpiece, T~e blade o~ the kni~e may e~tend alon~ the magne-tic rolls. However, t'ne ferromagnetic powder has b~n ~ound to redis~tribute i-tsel~ more u~i~ormly throughout the work-ing gap when the apparatus includes the kni~e wi-th the curvi-linear blade havin~ two portions extending at an angle to the generatri~ 50 that -they par-tly enclo~e the sur~ace o~
-the adjace~t magnetic roll and toe-in :~rom the extremities of -the roll toward the centre thereof ? thus ad~itionally ur~-in~ the ~erromagne-tic powder toward the oentre o~ the roll.
'rhis has been ~ound to preclude the phenomena of the fer-roma~netic powder accumula~ing in a rotating blob in the areas o~ i bS maximum removal by the blade. The inclined por-tions o~ the blade have been ~ound to efficiently guide the ferromagnetic powder -to the centre of the magnetic roll, to be taken up by the ma~netic flux~
. It i~ also possible to provicle the device llor levell-; ing out the distribution Oe the map~netic powder hy the spe-¢i:eic structure O:e the magnetic rolls, ensurin~ the vary-ing ma~netic permeability longitudinally of the rolls, with ;
the central portion being o~ a higher permeability than the end portion~.

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z In one embodiment O:r ~he present invention this vary-in~ magn~tic p~rrneability is attained by the corresponding chemical~ or else thermal/chemical -treatment of the roll material.
In an embodiment of a more simple structure -the roll~ -are assembled as laminations or 5 tacks o~ washers made o~
electrical engineering steel grades o~ di~erent magnetic permeabili~y values, received around a magnetically permeable rod or core. r~'he washers making up the extreme portions of the magne~ic ro~l,s, adjoining the electric coils o~ the magne~
~ic system, are made in -this case of sheet steel with a small- :
er rnagnetic permeability than that of the wa~hers mal~ing up -the central portion of the magnetic rolls. ~he rod or core in this ca~a should be made of steel wi~h high magnetic per- ~ ;
meability, so that it should pass the magnetic flux in a quan-tity providing that the ~nagnetic induction or flux den-sity in the washers o~ the cen-tral portion should be substan-tially equal to that in the washeLs of -the extreme por-tions of -the magne-tic rolls.
~he present invention will be fur-th~r described in oonnection wi~h ibs embodiments in ~ apparatu~ inuorporat ?
iny~ a powder layer levellin~-ou-t device, with re~'erence be-ing had to the accompanying drawings 9 wherein:

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Fig. 1 schem~tically illustrates -th~ em~odiment of th~ apparatus f or working sheet In~terial~, wllerein the de-vice ~or levelling out the layer o~ the ferroma~netic powder in the working gap is in the form o~ -tapering portions a-t the e~tremi-ties o~ -the magnetic rolls, in -the area o~ the re~
latively high density o~ the magn~tic ~lux~ -Fig~ 2 schema~ically illustrates a version o~ the above embodiment, with the tapering portions being s~ch that -the rolls acquire a barrel-like 9hape;
Fig. ~ illustrates the apparatus for working sheet materials, wherein -the device includes a kni~e with a blade extending along the magne-tic rolli P~ig. 4 illustrates an appara-tus basicallg similar to -the one ilLu~-trabed in ~ig. 3, but with the kni~e made up o~ individual sections adiustable relative to the roll;
~ 'lg. 5 is a perspective view of -the apparatus with ~he knife of which the blade e~tends along the magnetic rollsj Fig. 6 illustrabes ano-ther embodiment of ~he appara-tus for working sheet materials, wherein the blade~ are ar-ranged at an angle relative to the generatri~ of the magne-tic rolls;
~ ig. 7 is a perspecblve view of the appara~us o~
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Fig. 8 i9 an embodiment of the apparatu~, wherein the magnetic rolls are aæsembled o~ washers recei~ed arou~d a magnetically permeable core.
Le-t us now consider Fig. 1 o~ -the appended drawings, wherein numeral 1 is ~od -to indica-te in general an appara-tus for working sheet materials wi-th ~erromag~etic powder, de~cribed in detail i~ the Application ~iled with the US
Patent Of~ice in 1975, Ser. No. 629~631, now Patent ~o 4, 040,20g to which reeerence is hereb~ made. Consequently, there is no need here -to de~cribe -this apparatus in great de-tail, and i-t i9 seemed su~icient to re~er to its major parts whenever essentiaJ IJor the clari ~ o~ the present disclosure~.
'~he apparatus i8 provided with electric coils 2 de-sig~ed to induce a magnetic ~lux in the system, ma~netic circuits 3 and a drive 4 ~or rotating magnetic rolls 5 on ?
which the magnetic ~lux is capable o~ retaining ~erromagne-tic powder 6~ As it has been already stated, and as describ-ed in detail in the abo~e-cited previous application, -the rolls are spaced to pass therebetween bhe sheet material to be machlned and act as thc pole pieces O:e a ~ln~le ma~nr3-tic system. rL'h~ roll~ 5 are adapted to be rotabed in opera-~ ~' ,' -~

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-tion in oppositc directiollc) at subs.tantially ~ual an~ular 3peeds, so tha-t the powder retained thereby e~:eects the ma-chining o-, the passing sheet material, with -the ferromagnetic powder ~orming a l~yer in the gap be-tween the rolls~
~ he rolls 5 have -tapering portions 7 at their e~-tremi-tieS t i~e. in the areas Oe the relatively higher den-sit~ o~ the magnetic flux. rL'hese kapering portions 7 in -the presen-tly described embodiment consti-tute the device ~or levelling out the distribution o~ -the ~erromagnetic powder 6 in the layer extending longitudinally Oe the mag-netic rolls 5, in the gap therebetween. ~his levelling-out is e~plained by the air gap 8 between the ~aid rolls 5 having the magnetic resistance or reluctance ear greater than that Oe the motal elements Oe the magnetic rolls 5, whereby but a slight variation o~ the air gap 8 invariably leads to a redistribu-tion o~ the dens.ity o~ the magnetic flux therein. 'rherefore, the appropriate selection o~ the diameters o~ the magnetic rolls 5 and o~ the taper angles o.~ their e~tremities enabLes to level out the magnetic ~lu~ density throu~hout the entire gap between the magne-tic rolls 5, and, consequently, the quantity O:e the ~e.rro-magnetic powder in the contral and e~treme portions o~` the magnetic rolls, so that the powder is more uniformly dis-~ , ; ~ ;. . . ............................. -:
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By calculations which are too voluminou~ -to be ~uo-ted here and by the outcome o~ a vas-t number o~ experiments we have conducted with various roll dimen3ion~, it has been founcl, ~or instance, that with the roll diameter o~ 120 mm . ~:
and its length of 300 mm the di~erence between the diameter of the cen-tral portion and the minimum diameter o~ the taper-ing portions i9 not in e~cess o~ 1 mm.
It should be poin-ted out that in the embodiment des~ ~ !
cribed -the electric coils 2 providing -the magnebic ~lu~
are arrangsd at both ends oI' the ma~netic roll~ 5 O:e the appara-tu~, and the tapering por-tions, consequentl~, are pro-vided at both ends of the rolls 5. It is clear, however, ~.
that in struotures where the coils are arranged solely at ~ ~:
the ~irst ~nds o~ -the rolls, the -tapering portlons should :~
be provided exclusiv01y in the e~treme portions o~ the rolls, adjoining the coils ln Fig. 2 there is schematically illustrated another embodim0nt of the ap~ara-tu~ ~or worki~ ~heet mater~al~
in aooordance with the invention.
In this ~igure and ln ~ s componsn~s o~ ths ., 1 '`~'' ' ; ' ~

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apparatus are indicated Wi th like numerals. '1'he sam~ is true o~ -the rest o~ the appended drawing~.
~ he apparatus illustrated ln ~ig. 2 di~fers ~rom the one illustrated in ~ig. 1 in the shape o~ the taperi~g por-~ionsO In the cmbodiment illus-tra-ted in Fig. 2 these taper-ing portions ~ollow a smooth curve 9~ so that -the rolls ac~uire t~e shape o~ barrels with the smoothly curvin~ ex-treme portions. ~he manu~acture of the magnetic rolls of this shape is somewhat more complicated than tha-t O:e the magnetic rolls with rec-tilinearly tapering portions; how-ever, the barrel-shaped rolls have been ~ound -to provide ~or more uni~orm distribution ol' the grains o~ the pow~er through-out the leng-th of the workin~ gap, whereby the machining qua-lity O:e shee~ materials is enhanced still ~urther.
~ et u~ briefly di9cuss the operat.ion o~ the apparatus o~ the abovedescribed embodiments, presuming that i~s major aspects are su~ficientl~ explained in the abovecited previ~
ous applica-tion.
~ hc coil 2 are ~upplied with electric current, whereby magnetic flux is established in the magnetic ~ystem, pass-ing through the magnet circuits ~ and the magnetio rolls 5 ~nd closing up ln the working gap 8 bebween these rolls. ~he magnetic flux re~ains the ~erromag~e-tic powder 6 on the rolls . j, .

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5, which, wi-th the roll~ 5 bein~, rotated so th~t their peri-pheries have the linear-speed e~ceeding that of th0 motion o~ the sheet workpiece, e~ects the abrasive working of the ~ur~ace o~ the workpiece.
With the dimensions o~ -the tapering portions proper-ly selected, the ferromagne-tic powder is uniformly distribut-ed throughout ths entire working gap 8 longitudinally o~ the magnetic rolls 5, notwiths-tanding the ~act that the material o~ -the rolls 5 o~ers some resistance to the passage of the magnetic ~lux.
I~ we remember tha-t the reluctance O:e the air gap ~illed with the ~erromagnetic powder i~ signific~ltly great-er than the reluctance o~ a magnetically conductive or per-meable material, e.g. stsel, it is quite unders-ta~dable that the non-uni~ormity o~ the magnstic ~lux longitudinally 7' o~ the magnetic rolls is easily compensated ~or by a vari-ation o~ the height o~ the air gap ~etween -the mag~etic rolls, By either increasing or reducin~ ths siz~ o~ the gap 8 between -the ma~netic roll9 5 by varying the ~;eometry o~ ~
the taperin~ portions ~.r the ro;Lls, the ma~n~tic ~lux pass- ;
ing through thi9 gap in the rsspective a.reas is, correspond-ingly, either reducsd or increased.
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By taking into conside.ration the entire pa~tern of the resis-tarlce Oe reluotance to the magnetic flux passing throu~h -the magrne-tic rolls and the air gap therebetween, it is possible 9 by var~ing the value o~ -this gap, which i5 grea-ted in the areas o~ the tapering portions, to attain the uni~ormity of the passage o~ the magnetic ~lu~ through-out -the ~orking gap so tha-t the powder layer becomes uni-~ormly dis-tributed'in the gap between the rolls~
~ et us now consider ~'ig. 3 schematically lllustrat-ing a di~ferent embodiment of -the apparatus ~or working s.heet materials, ineorporating a device ~or levealing ou-t the distribution o~ the ~erromagnetic powder, inoluding a kni~e.
'Unlike the embodimen-ts described hereinabove, -the ap-paratu~ illustrated in Fig. 3 has the device ~or levelli~
out the la~er o~ the ~erromagne-tic powder, which is a mecha-nical appur-tenance including an arcua-te kni~e 10 having its concave edge facing the cylindrical magnetic roll 11 ~o 'that the blade 12 o~ -the kni~e 10 is more remote ~rom the magne--tic roll~ at the ce~tral portion o.~ the rolls, i.e. at the portion with a lower den~i.t~ o~ the magn~tic ~lux~ than at ' ' the e~tremitie~ o~ -the rol'ls, l.e. in areas with the greater density O:e the magnetic ,',':
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Fig. ~ i~ a plan view of -the appara-tus with the knives 10 arran~ed to both sides of the ma~netic roll 11~ '~his structure is pre~e.rable when ,sheet workpieces are machined by a method including reversing the ro,tatio~ of -the magnetic rolls, the assence o~ thi~ method being the subjec-t-ma-tter Of another invention disclosed in our co-pending applica-tion. ~ ~
However, when relatively thick workpiece~ ~e.K. thiok- ~'' er than 0.2 mm are worked), and the rolls are rotated in per~anent directions and are not reversed, it is suf~icient ~' to provide but the single kni~e 10 at one side o~ the magne-tic roll, i.e. on the side o~ -the ~eed ol' the ~erromagnetic powder into -the zone o~ machining by the magnetic roll.
Fig. ~ schematicall~ illustrates yet another embodi-ment o~ the invention, wi-th a further modi~ioation o~ the device for levelling out the distribution o~ the layer o~
the ~erromagnetic powder in the gap between the magne-tic ,.
roll~. The device includes a holder 13 and blades 14 mount- ;
ed on the end portions o~ the holder 1~, to di~ferent ~ides of the centre o~ the roll, the blades 14 e~tending along . ' the generatri~ o~ the adjacent roll which ha~ a cylindrical '`:
shap~, but at an angle to tho sur~ace o~ this cylindrical.
roll. '~he blades are mounted so that their spacing ~rom '' ' ` ' . 1 ., .

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i . ". ' ', ' ,: ' ' .' '. '' ' ,' ' ' . ' ' ' :' '~ " . . " ' '' ' ' ' . . . ', ,' , " :'~' ' ' '' . :,' ' '' ' '.' ' ,. ' ' ', ' ' ' ' ' ~, 7~2 the roll i.q adjustable, whc~eb~ in ope~ation it i~ pos~ible to adjust the blacles 1~ to a position whereat -the ~exromagne-tic powder layer i9 uni~ormly diq-tributed throughout the le~rth o~ -the rolls.
Fig, 5 is a perspective view o~ the device ~or levell-ing ou-t the dis-tribution of -the ~erromagnetic powder in the magnetic gap between -the rolls. This view is r~ean-t to make the arrangement o~ the blades and of the kni~e along the generatrices o~ the magnetic rolll more clear.
Fig. 6 shows yet another embodiment of the device ~or levelling out the powder layer in the apparatus ~or work-ing sheet materials wi.th .~erromagnetic powder, this clevice likewise including a kni~e of which, however~ the design and arran~ement are di~erent from those described herein-above in connection with ~igs ~ and 4. In the presently des-cribed embodiment the'kni~e has blades 15 and 16 arranged to opposite sides o~ the ce~tre of the generatrix o~ the roll, the blades partly enclosing the surface oI~ the adjacent roll 11 by being posit:ioned at an angle to the gene.ratrix o.~ this roll and toeing in toward the ga,~ 8. ~he an61e bet-ween the generatrix and the blades should be seleot~d to provide ~or intense guiding o~ the ~'erromagne-tic powder ~rom the peripheral e~treme por-tions of -the roll toward the centre thereo~. Fig, 7 illu~-trates the device o~ Fig. 6 in a perspective view and clearly shows, as indicated wi-th arrows 17, how the powder is urged ~rom the extremi-ties o~
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the rolls toward the centre thereo~, arrows 1~ inclicating ~-the direction o~ the rotation Oe the rolls.
I-t is clear that in every modi:eication o~ the apparat-us for working sheet materials wi-th ferromagne-tic powder, incorporating the device for levellin~ cut th~ powder lay-er, including the knife, the rolls themsleves can be either of a cylindrical shape or of a barrel-like shape.
~ he operation of the apparatus incorporating the levell-ing knives is substantially ~imilar to -the apparatus of the prior art and the apparatus described hereinabove in connec~
tion with Figs 1 and 2. '.rhe di~ference resides solely in .
that the knives mechanically remove or cut of~ some portion o~ the ferromagnetic powder 6 in areas with the Kreater den-sity o~ the magnetic ~lux, instead of varying this d~nsity of~ .
the ~lux in these areas, as it has been t~e case with t.he ap-. . .
paratus illustrated in Figs 1 and 2. :
: Let us discuss certain peculiarities assooiated with .
the incorporabion of the knives. The height of the layer '. o~ the ferromagnetic powder 6 which is l~ft on the magnetic rolls is adju9table by displaoing th~ blade o~ the knife to-; ward and away ~rom the working surface of the magnetic roll 11. '~he use o~ a curvilinear blade O:e the k~i~e enables to leave the layer o~ the ferromagnetic powder 6 on the rolls ~, , .; . , ~:
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' ' " ' ' , ' ' , . ' ' ~" ' ' . :, ' '' ': ' . , . : : , 7 ~ 2 117 0~ which the hei~ht is rlon-unif'orm longitudinally o~
the rolls, this height bcing smaller at the e~trernit.ies than at the centre. However~ with -the density of the layer o~ the ferromagnetic powder retai~ed by the magnetic ~lux being greater a~ the extremi-ties OL -the magnetic rolls 11 than at their centre, the resulting quantity o~ the :~rromagnetic powder 6 carried into the ~achining zone is equalized or levelled out throughout the length o~ the gap between the magnetic rolls 11. ~herefore, there is ef~,eoted the removal o~ the uniform ~ur~ace layer o~ the material being machined by the grains of the ferromagnetic powder 6, whioh grains cut in-to the sur~ace o~ the sheet material adVanQed through the rnachining zone.
To provide for varying machining condi-tions, it is expedient that -the knives should be mounted so that the spacing Q~ their blades ~rom -the surface of -the rolls 11 -~
is adjustable.
The mo~t structurally simple arrangement o~ the knives is the one where they e~tend longi-tudinally of the magnetio roll 11.
However~ we have ~ound by e~perienoe~ that at bhe areas where the greate~t amount o~ the powder is being rem- `
oved in the structures with the blade extending longitudi- -'. ' ' ~.`

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nally o~ the magnetic roll, there are sometim~s accumulated relatively great blobs of the ferromagnetic powder, which gradually move alon~ the kni~e toward the centre of the roll 11, to be taken up by the latter.
The accumulation of the blobs o~ the powder on the knives has been ~ound to impair the performance of the ap~
paratus.
~ he cut-off or removed portion o~ the ~erromagnetic powder is signi~icantly more swi~tly redistributed ~rom -the zone with the greater magnetic flux inten~ity into the zone with the ~aller magnetic flux intensity, without oonsider-able blobs of the ferromagnetic powder being formed, in the apparatus wherein the blade of the knife extends at an angle to the generatri~ o~ -the adjacent roll, partlg enolosing the roll sur~ace, as i-t is illustrated in Figs 6 and 7.
The e~perimen-ts we have conducted show tha-t when the ~
kni~e position relative to one of the rolls is adjusted so .:.
: that -the ferromagnetic powder is uni~ormly distributed in ths gap bebween the rolls 7 the layer O:e the ferromagnetic powder on the other roll i9 automaticall~ maintained in si- :
milarity with the layer on the fir~t roll. ~hus, it is ob-~; viou~ -that the kni~e can be arrang~e~ adjacent to either one o~ the two rolls, be it the upper one or the lower one. How-' ,/
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~" .. .. ~ . , -2~-ever, i-t has b~en ~ound expedlent to provide the krli~e adja-cen~ ~o the bo-t-tom roll in ~ructures where -the addi-tio~al feed oL the ~errornagnetic powder i~ e~:eected from a tray underlying the magnetic rolls, or else adjacent to -the upper roll if the met0red-out additional feed of the ~erromag~etic powder is e~fected ~rom above~
It should be also born in mi~d tha-t it is po~sib~e . -to ha~e various combinations o~ the abovedescribed features, i,e. o~ the knives and barrel-shaped rolls, and that the selection of the overall design o~ the apparatus i9 deter-mined by the machinin~ qualit~ requirements and by the rela-tive complex~ty o~ the manu~actule o~ -the levelling-out de-vice.
~ et us now consider ~ . 8 showing ~chematlcally still another embodiment o~ bhe appa.ratus ~or workinK sheet mate-rials with ~erromagne-tic powder, in a longitudinal sectional view, wherein the device ~or levelling out the ferromagnetic powder layer is in the ~orm o~ a rnodi~ied structure o~ -the ;.:
magnetic rolls.
~ he apparatu~ dif~ers ~rom thase described hereinabove i~ that -the magnetic rolls are so constructed that the mag~e-ti¢ permeabilit,y o~ their central portion i~ hi~her than the permeabilit~ o~ -their extreme o:r end portions.

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A magneti~ roll ol this type can ba made of a material o~ wh:ich the chemical composltion varies lon6itudinally o~
the roll, or else by some specific thermal treatment, e~g.
by hardening the e~treme portion~, or else by carburizing the roll wi-th a varying carburization depth, and with léav~
ing the central por-tion of the roll unhardened, or uncarburiz-ed. However7 it is clear that the techniques o~ obtaining a roll with the di~ferent magnetic permeability values of ~he central and extreme portioQs are ¢omplicated.
Still, it is possible to have a roll with different mag~etic p~rmeability o~ the central and end areas, by assemb-ling -the roll of a stack of washers or discs of electrical englneering s-teel Krades with dif~erent magneti¢ permeabili-ty values, received about a magnetically permeable rod or core.
~ s it can be seen in ~ig. 8, the magnetic roll 19 has a central core 20 of a high magnetic permeability, hav-ing recaived thereabout and ~ixed a stack of was~ers 21 of electrical engineèring s~Qel, de~ining -the roll 19. ~he washers are made of ma-terials wi-th di~erent value9 of ma~-netic parmeability, the ma~netic permeability value~ of the material8 of th~ washers bein~ selected so that the portion~ o~ the made-up magnet~c rolls 19, ad~oininK the solenoid coils 2, are made o~ washers with the smallust mag-~ ~ .
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'7~'o2 netic perm~ab:;lity, so tllat th~ c.Loser the washers.become -to t~le cen-tre, the ~reater i5 their magne-tic permeabili-~.
Let us brie~ly discuss the operation olJ the appara-tus i 1 1 US trated i~ Fig~ 8~
The ma~netic f'lu~ created 'oy the solenoid coils 2 passes through the ma~netic cores 3 and the rod or core 20 of the hi~h ~agnetic permeability, in which way the ~lu~
i~ guided into the magnetic rolls 19.
Althou~h the rods 20 are made of' a material with the hig~h magnetic permeabili-ty, they nevertheless o:eI'er some resis~ance to -the passage o~ the magnetic .~lux. ~he ~lux also passes ~rom one magnetic roll 19 through the air gap 8 into the other magnetic roll 19. There:~ore, the magnetic induction or ~lux density in the co:res 20 is highar in the areas adjoining the solenoid coils 2 than at -the centres o~
these cores 20. By selecting the washers 21 so tha-t -the per-meability o~ -the washers adjoining the solenoid coils 2 is lower than the permeability o~ the washer~ in the cen-tral portion, the uni~'orm density o~ the magnetio ~lu~ through-out the length of the air gap 8 between the rolls 19 can be attained~ '~his ls explained by the ~act that altho~jh the magnetic ~lu~ guided in operatlon via the core 20 to -the internal diameter o~ the washers 21 has a greater den-ff~f4frf~ff~,~2 sity in the areas adjoining the solenoid coil9 2 than in; .
the cerltral portion o~ th~_ mfaff3netic roll 19, IfJhis ~lux pafs- ~.
ses with more di~`iculty to the external diameter o~' the roll 19 through the washers 21 r~ade o~ the ma-terial with the lower magnetic permeability, whereby the greaber portio , .
ef~ the flux passes through the washers 21 with the hi~her permeability 9 which are gathered in the central portion of the roll 193 which mean3 -that by selecting -th~ appropriate ~.
:~ pattern o~ arra~ging the washers 21 with the di~erent va-:
lues o.~ the magnetio permeability, it i9 possible to attain the uni~orm density of the magnetic ~llux longitudinally o~
-the working gap 8, thus levelling ou-t the layer o~ the I'erromagnetic powder 6 retained by the magnetic ~lux on the roll~ 19, whereby the sheet material is machirled uni-~ormly over the entire area thereo~.
I I~ -the su~fL¢ient amoun-t or a5sortment of washers ~ :
¦ with di~ferent values o~ the magne-tic permeability is un-available, -the gradual required variation o~ the magnetic permeability longitudirlally o~ the air ~ap can be attained by having a combination structure, USif.~g both wa~hers o~
di~ferent magnf_tic permeabilit~ values and -the powder-re-moving~rf bladfes~ or else them and th~f -tapf3frinff~r portion~f at t~l~ ends of the rcll~.

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Claims (11)

WHAT IS CLAIMED IS :

1. In an apparatus for working sheet materials with ferromagnetic powder, comprising a magnetic system adapted to retain the ferromagnetic powder, including two rolls of a magnetically permeable material, mounted with a gap left therebetween for the passage of the material to be worked and rotatable in opposite direction, and means for induc-ing a magnetic flux with a magnetic circuit provided at least at the side of the first ends of the rolls, so that the magnetic lines of the magnetic flux pass axially of the rolls and across the gap therebetween, one of the two rolls acting as one of the pole pieces of the system, and the other roll acting as the other pole piece of the same system, whereby the ferromagnetic powder can be pulled in operation in the form of a layer through the gap between the rolls, an improvement residing in a device for levelling out the distribution of the grains of the ferromagnetic powder in the said layer formed in the gap between the rolls through-out the length of this gap.

2. An apparatus as set forth in Claim 1, wherein the device for levelling out the distribution of the grains of the ferromagnetic powder includes tapering portions made at the extremities of the magnetically permeable rolls, in the area of the relatively high density of the magnetic flux.

3. An apparatus as set forth in Claim 2, wherein the tapering portions are such that the rolls, as a whole, are barrel-shaped.

4. An apparatus as set forth in Claim 1, wherein the device for levelling out the distribution of the grains of the ferromagnetic powder in the layer includes a knife with a curvilinear blade having its concave edge facing the sur-face of the adjacent roll, so that the blade of the knife is more remote from the magnetic roll in the area where the density of the magnetic flux is lower and is closer to the roll in the area where the density of the magnetic flux is higher.

5. An apparatus as set forth in Claim 4, wherein the means for inducing the magnetic flux are provided at both extremities of the rolls, the knife being of an arcuate shape, the centre of the blade of the arcuate knife being situated at the central portion of the roll, where the den-sity of the magnetic flux is lower than at the extremities of the rolls.

6. An apparatus as set forth in Claim 4, wherein the blade of the knife extends longitudinally of the generatrix of the magnetic roll.

7. An apparatus as set forth in Claim 5, wherein the blade of the knife extends longitudinally of the generatrix of the magnetic roll.

8. An apparatus as set forth in Claim 4, wherein the blade of the knife includes two portions disposed to oppos-ite sides of the centre of the adjacent roll and extending at an angle to the generatrix thereof, toeing-in toward the gap between the rolls, for the interaction with the blade to guide the powder from the extremities of the roll toward the central portion thereof.

9. An apparatus as set forth in Claim 1, wherein the device for levelling out the ferromagnetic powder effected a knife arranged adjacent to the roll onto which additional matered-out feed of the ferromagnetic powder is effected in operation.

10. An apparatus as set forth in Claim 17 wherein the magnetic rolls have a structure providing for the extreme portions of the rolls having a lower magnetic permeability than the central portion of the roll.

11. An apparatus as set forth in Claim 10, wherein the magnetic rolls are assembled of washers made of a magnet-ically permeable material grades having different magnetic permeability values, received on a magnetically permeable core, the washers in the central portion of the roll having a greater magnetic permeability than the washers at the extremities of the rolls.