CA1121125A - Manufacture of abrasion-resistant screening apparatus - Google Patents

Abstract

MANUFACTURE OF ABRASION-RESISTANT
SCREENING APPARATUS

ABSTRACT OF THE DISCLOSURE
Manufacture of a perforate screening member having a structurally strong substrate supporting a layer or coat-ing of abrasion-resistant elastomer, the elastomer having perforations coincidental with perforations in the substrate, the perforations in the elastomer in some cases being smaller in cross sectional area than the perforations in the substrate and in some cases having sidewalls which taper downwardly and outwardly, by forming a layer coating of flowable, harden-able elastomer on the upper surface of the substrate while the substrate has its perforations blocked by forms which project through the layer of elastomer, the upper section of the form in some cases being of smaller diameter throughout the thickness of the layer of elastomer than the diameter of the substrate perforation and in some cases tapering upwardly and inwardly. An elastomer treatable by heat an pressure, such as crude rubber, can form the abrasion-resis-tant layer or coating on the substrate and can be treated, as by vulcanization, in the same mold. Where the substrate is formed of a castable material, the same mold can be used to cast the substrate as is used to form the elastomer coating on the substrate after the latter has hardened.

Description

'rhe present: :i.nvent:iorl rcl~tes to a r/le~hod of coa-tincJ a perforated substra-te to produce a screeniny member of increased abrasion resistance.
The type of apParatus produced by the me-thod of the present invention separates mix-tures into resul-tant portions consisting of ~articles of more uniform size than those of the original mixture or in some situations is used to separate materials of different specific gravities. This type of apparatus is used in the fields of mining/ construction and agriculture :Eor respectively screeniny ore, sand, gravel and grain.
The ahrasive nature of the material which is screened coupled wi-th t~pical almos-t constant use oE the apparatus progressively deteriorates unpro-tec-ted apparatus, requiring fre~uent replacemen-t.
According to the present inven-tion there is provided a method of coating a perfora-ted substra-te to produce a screening member of increased abrasion resistance, the subs-trate having upper ancl lower major surfaces and having perEorations clefined by sidewalls extendincJ between the major surfaces.
plurality oE forms i5 provided, each form having sidewalls, the cross sectional area of which in planes parallel to the upper major surface of the substrate does not increase throughout the height of the form. One of the forms is placed in each per-~ foration, and a layer of hardenable elastomer in a plastic ; state is formed on the upper surface of the subs-trate to a depth not greater than the height of the form. The elastomer is hardened to form a coating of abrasion-resistant elastomer adhered to the upper surface of the substrate and surrounding the form. The form is removed after the layer of abrasion-resistant elastomer is formed.
In a specific embodiment of the inv~ntion a tm/ -1-lower section oE e`c~Cil ~OJ^m COrr~-~Sr)OrlCIS :in .~ ,e an(l shape to ~he si.dewa:Lls of the suhstrate per~orclt:ioll. 'rhe ~hape o~ the sidewalls of the lower section ma,y be, for example, cylindrical.
According to ano-ther aspect oE the present invention, the sidewalls oE each form may slope upwardly and inwardly. For example, the form may have frusto-conical sidewalls, and the sidewalls may have a rate o~ slope between about 0.0001" and abou-t 0.01" Eor each ~" -thickness o~
coatiny.
10According to a specific embodiment of the invention there is provided a method of formi.ny a perforated substrate having an abrasi.on-.res.is-tant coating layer-thereon comprising providing a mo:Ld having a bottom and sidewalls, the heigh-t of the sidewalls being greater than the thickness o~
the substrate and desired coating layer combined, the bot-tom supporting a plurality of upstanding forms, each form having a pair of sections one superposed on the other, the sidewalls ,, of the lower section of each form corresponding in heiyht and shape to the sidewalls of perforations in a substrate to be placed in -the mold, -the sidewalls o~ the upper section of each form being concentric-tm~ ' ~2-,~ ~

a:Lly clisposed .~ela-t.ive to the sidewal.Ls oE th~ l~wer sect:ion and correspondincJ in shape to the ~esirecl siclew~lls o~ peror-ations ln the abras.ion-resistant coating layer, the c,ross sec-tional area of the upper section of each form in planes normal .to the height dimension o the form being of clecreasing cro~s sectional area upwardly throuyhout the height dimension of the form corresponding to the thickness of the desired coating layer/ placing a substrate in the mold with'the lower section of a form filling each~perforation in the substrate and with the top surface of the substrate exposed, placing a la~er of . material which in final form is abrasion-resistant within the mold in contact with the exposed surface of the.substrate con-fined by the sidewalls of the mold and contiguous to the side-walls of the upper sections of the forms, hardening the layer of material to make the material abrasion-resistant, and aclher-ing the material to the substrate to form a layer o abrasion-resistant coating on the substra-te, the last two s-teps takincJ
place .i.n any oxcler or simultaneously.
Brief Description o'f the Several Views_of the Drawing Figure l.is a vertical sectional view of prior - art screening apparatus which is deficient from an abrasion-res.istant standpoint;
Figure 2 is a schematic illustration of, a conven-tional method,of forming the structure of Figure li .
- - Fiyure 3 is a fragmentary perspective view of screening apparatus within the scope of the present invention;

: : ' 3 ~'~ ~ ". ,, ... . ~

~ ZS

E'i~ure ~ .~s a v:iew in ver-t.~cal seGtion of cl,porki~on of a screeniny me,m~er incorporat~ncJ the present inven-tion;
Figure 5 is a schematic illustration of steps in a preferred ~etl~od f,or manufacturiny the apparatus oE Figure 3;.
S Figures 6 and 7 are vertical sectional views illustra-ting apparatus for carrylny out and cértain steps ,.
in a Figure 5 method;
Figure 8 is a view in ver-tical sectlon illustrat-ing apparatus for producing a modifled form of screening . 10 member by a.variant of the met~od of,the lnvention;
Fi,gure 9 is a vle~ tn vertical section of a further modified form of apparatus for carrying out another variant of the present invention;' Figure 10 is a view i.n plan of the apparatus of .. 15 Figure 9; and Figures 11 and 12 are perspective views of exarnple~
of diferent shaped.Eorms.
Detailed Description of the Preferred . . .
Embodiments of the Present Invention A prior art screeniny member depicted in Figure 1 consists of a perforate metal plate 10 having its upper 1 working surface covered with a protective coating of rubber ¦ or rubber-like substance'as sho~n at 12 to impart abrasion ¦ . resistance... While t~s apparatus~ is superior in abrasion-resistance compared to a b.are ~etal plate, ik eYentu~
deteriorates due to a~ras.ion at per~oration s,.-~de~a~.l$ of t~e metal plate. .
. l y . . 1~
'' - ' `. , This prior art screen:!.ncf ~ember carl ~e producc~d b~ adh~rlng a rubber sheet to the top sur~ace o a rnetal plate and then per~orating th,e covered plate. ~pparatus per-forating the covered plate is sho~n in Fiyure 2. It consis-ts of an upper punch carrying member 14 and a lower die suppor-t member 16 which have cooperatlng punches 18 and dies 20, re-spectively. The rubber covered plate is positioned on die support member 16. Punch carrying member 14 is then moved toward die support member 16 to carry out the perforating.
1~ The material which is punched out, includlng coating portions 22 and metal portions 23, is disposed to waste.
It h'as been proposed to form a ruhber-covered screening member by molding rubber around a metal substr,ate - which is already perforated or of wire screen form, as in ! 15 U. S. Patent 1,718,385 and Australian Patent 108,053. A
screen produced in this manner lncorporates an excess of rubber disposed throughout the screen where :it serves no useful purpose. The elastomer coating maker:Lal designed -for' resistance to abrasion is expensive and its waste cannot be ~, 20 economically tolerated.

Preferred screening apparatus within the scope of this invention, shown in Figures 3 and 4, has a narrow--thick-ness rectangular parallel piped configuration. It has an upper surface 24, a lower surface 25 and side su~Eaces ~6 Perforations 27 e~tend upwardl~ ~om lower su~face 25' throug~

, ' upper surface 24. Each, per~oration 27 is def~ned ~y~ a slde~
wall 28. The perforations 27 are'o~ c.~rcular cross~section ancl are spaced apa:Lt :in ad~acent rows Z9. Eac~l xow Z~
extends along the lengtl-L o~ the apparatus. Perforations in adjacent rows are longitudinal].y ofse-t from one another, The apparatus co~pri~es a subs-trate 30 and a coating 31. Substrate 30 has an upper major surface 32, and lower major su~face:which is coeY.tensiVe with lower surface 25 of the scxeening apparatus. rrhe substrate perforati.ons 27 have cylindrical interior sidewall surfaces 33 which are perpendicular to the upper and lower major surfaces of the substrate. Surfaces 32 and 25 are substantially planar.
Coating 31 lS supported on.and adhered to the surface 32 of the substrate. Openings 34 in the coating are coincident with perfoxations'27 but are smaller in dia,meter than open--- ings 27 so that ther~ is a ledge 36 fo.rmed by coatiny 31 overllanging each cylindrical sidewall surface 33 of perfora-tions 27. This overhang or ledge 36 is great enough so that objects passiny through the openiny 34 in the coating will not contact and abrade the cylindrical sidewalls 33 of the substrate. Each opening 34 in coating 31 has a sidewal'l .surface 38 in the form of a truncated cone, greatly exagger-ated in the drawing. ~ere again due to -the tapering effect of sidewalls 38 an object passing through an opening 34 will not engage sidewalls 38 of.coating 31 so as to become lodg'ed in the coating.
. The underI~.~ng subst~até. 30. can b~ of, an~m,atex~al useful for structural ~urposes. Iron and steel are pre:Eexred structural materials~ Other suitable materials-Eor construc 't:iOIl inc]uc'le other ~onctr~lcl:lon In~aLs such ac, ~Lurnl.nu~, certaill plasti,cs and wood. ~lthough tlle per~oratiorls and openings are shown and described as being circular in this application, other cross-sectional shapes, such ~s elonyated slots are within the scope oE -the present invention.
Ordinarily eac~ of the perforations 27 ~as a , diameter ranging from one-sixty fourth of an inch to five or more inches,' preferably ranging from about one-eighth of an inch to about two inches.
,10 The substrate ordinarily has a thickness ranging from one-'sixteenth of an inch to four or more inches, prefer-- ably from about one-eighth to about three-fourths of an inch.
- The coating 31 is oE an elastomeric material which can be applied in pourable form and then hardened to solid ' form. Such materials are well kno~m. Suitable materials in-clude polyurethane and epoxy resins. A suitahle polyurethaneelastomer is sold under the tra'~e name Fle~arle h~ Devcon Corporation of Cambridge, Massachusetts.
Preferably, the coating thickness at the substrate upper surface and at the perforation sidewall can range in .
various embodiments from about one-sixteenth inch to about 'one-half inch.
The application of protective coating to underly-ing substrate to produce the above descrxbed scxeenin~
-25 apparatus is illustxated in Figures 5~7.

The met~od of the present in~ent~on utiliz~s plugs or forms indicated generall~ a-t ~0 in Pigures 6 and 7. Each , , ~&- , .

plug cornpr:ises a base port.ion 42 and a pair o seation~ ~ and 46, with a shoulde:r ~5 therebetwecn, which are supe~rposed on base port.ion ~2. Lower section 4~ has a cylirld.rica:L sidewall surface which is dimensioned and shaped to be received snugly within opening 27, the heigh-t of this section being the same as the thickness of the substrate 30. Upper sec-tion 4~ has a sidewall in the form oE a truncated cone, the amount of taper in this wall being greatly exaggerated in these figures.
In one form of the invention, the rate of slope of the sidewalls is between about 0.0001" and about 0.01" for each ~" -thickness of coating. The heigh-t of upper section ~6 can be appreciably greater than the desired thickness of the coati.ng 31 but at - least must be as great as the thickness of the coating.
Where desired the base por-tion 42 of each plug can sit in a recess of a mold or jig indicated generally at 47 having sidewalls 49 and a bottom 48 which holds all the plugs with some lateral tolerance in their proper position before insertion into perforations 27. Sidewalls 49 of mol.d 47 act ; as a dam for coating material 31. IE desired, base portions 42 and gangi.ng device 4g can be integral where lateral toler-ance is not needed.
With reference to Fiyure 5, a preferred coating process comprises the steps of applying primer to a perforated steel substrate plate, coating plugs with releasing agent, inserting the plugs into the perforations in the substrate to define molding cavities, then leveling the plate, formulat-ing a hardenable elastomeric coating material, pouring orplastering the elastomeric material onto the top surface of tm~
s ~

the plate, all.o~LncJ l:he elac;tomer,ic ~nater:;al to harden to foxm a coatiny and removiny the plugs.
The primer is applied -to cause later applied elastomer to adhere to the plate. The particular primer utilized depends on the particular elastomer utilizec1. The primers suitable,for a particular elastomer are well known~
A suitable primer for the "~lexane" pol~urethane elastomer previously mentioned is sold under the trade name "Primer ~or Flexane" by ~evcon,Corporation.
The plugs are inserted into the perforations of the substrate. Figure 6 shows a plug of preferred configuration in inserted position in a perforation. Section 42 has a , diameter larger than the diameter of the perforation in plate 30 in order to prevent the plug from being inserted through the perfor,ation.

,, ~ Section 46 extends axially to a point sufE:iclently spaced past surEace 32 so that it wl:ll exkend beyoncl the applied coatiny. Pre~erably the plucJ extends past surace 32 a distance equal to at least twice the thickness of the coating to be applied to surface 32. In other words r when surface 32 is to be coated wi-th one-fourth inch of polyure-thane, section 46 of plug 35 should pro-trude at least one-half lnch above surface 32. Such protrusion facilitates -~

removal of the plu~ aEter co~tin~ has ~,een co~pleted~
In some case the plu~s are ~ade of a plast~c mate-rial for reasons of econom~ and ~uali,t~ control and bec~use it is not essential to uti,llze a release acfent ,w,i,th pluys of ' . _~ , ~. , , . ' , , ,.,,~ ,,, ~ 5 this material. In suc~ cases the plugs axe pre~erably of a thermoplastic material and very preferably of polyethylene.
Ho~ever there are situations in which -the plugs are made of a metal, such as iron or aIuminum or less desirably of wood ' or of wax.
, The plugs 40 are preferably insertea pnuematically.
Insertion by hand is also practical. , Treatment of plugs with releasing agent is not , re~uired if plastic plugs are utilized but can be re~uired with non-plastic plugs to prevent elastomer from adhering to a plug. The use of a releasing agent is desirable no matter what material the plug is made of to facilltate its insertion -(described previously) and its removal (described la-ter).
Suitable release agents include vaseline, wax, and mineral and petroleum oils.
Leveliny oE the plate permits the appl:Lcat.ion oE a uniform thickness coating to surace 32 where the appli~d elastomer is in liquid form and this is an a~vantag@ of free ', flowing material.
The elastomeric coating agent which is applied is preferably of pourable consistency. Ordinarily elastomeric agents are obtainable commerciall~ in this form. In some ' cases, ho~ever, the elastomeric agent may be com~ercially ; obtained in solid ~orm and melted to furni,sh a pourable or plasterable consistency~ ~or appli;cation or the,agent,may be of putty~like or plas~ic~like cons~stency and be spread o~
plastered on the substrate.' rn t~is spec~f~cation and ,: /0 LZS

appellCte'Cl cLaim5 khe term "plastic gkate" i.s used to de~cribe an elastomer in pourable, pl~sterab:le or putt~-like condition, i.e. not hardene~ into Einal abrasion-resistant form.
~ust prior to application, the elastomexic sub-S stance to be applied is admixed with a curing agent toformulate a hardenable coat:ing material. Such CurincJ agents are ~ell }cnown in the art. A suitahle curing agent for the "Flexane" polyurethane previously mentioned is sold under the trade name "Plexane Curing Agent". ~lternatively where crude rubber or other vulcanized material is used, metal plates can be used to heat the vulcanizable material from the top and through the substrate. In such case the plu~s would of course not protrude above the surface of the vul-canizable material. -The hardenable coating material can simply be poured out o~ a ladle onto surface 32. It can be kepk fromoverflowing the sidewalls of plate 30 by an~ 3uitable mekhod, ~or exarnple, by utiliæing dams. The amount of the m~texial to be poured is readily calculated and is a function of the surface area 32 and the coatiny thickness desirecl.
Hardening occurs to a degree suitable for demold-ing in a time ranging from about two hours to about 24 hours.In othex words the plug inseXts can be removed within this time period. Hardenin~ to full stren~th occurs in a period ranging from about one da~ to about seyen da~s. T~e appli~

cation o~ heat can aocelerate the h~rdenin~. Thé tec~olo~

relatlng to curing times and the accelerat~on of these ti~es by the applicatlon of heat is well known in the art.

, s F~c3ure 7 sho~s the coatlrlcJ :in place cl~ter the llardeninc3 step and before the plug5 have been removed.
Pluy xemoval is suitably carried ou-t pnuematically or'by hand. If the plugs are of a material meltable at low temperature such as wax, they may be removed by the applica-tion of heat causing melting o:E the plug materia]..
' . The plate.to be coated can have any predetermined pattern of perforations. ~oreover, the perforations can be of cross sectional conflguration other than circular, for example, square or rectangular; suitable adjustment is made in the shape and dimensions of the plug members. . ' ~ oreover, the thickness of the coating'on surface 32 (Figures 4 and 7~ can be varied from portion to portion of the surface where des.ired by inclininy plate 30 during the pouring step instead of maintaining it level.

Flgure 8 cli.scloses a modiEication of the present invention. In th.is embodiment the plugs o:r forms, indicated . .
generally at 50, have a base portion 52, a lower section 54 ' and an upper section 56. Lower section 54 and upper section .
56 can merge together without being dis-tinguishable from one another by Eollowing a frusto-conical shape all the wa~ from base member 52., The lowermost por-t.ion of section 54 can have the same shape and diameter as perforation 27 whereby the plug will be properl~,positioned in the perfoxa.tion ~hen driYen h.ome with't~e base'poxtion 52 up Rgainst lower surface 25 o~'the substrate 3Q. ~s~ng.khis fox~ of plug, some of the flo~able coating lines: t~.e sidewall.s 33 o~ perforc~tion ',. .., , ~ ' .

/;~, ,~ 5 27 whiLe the downward:ly ancl ou-twar~l,y lapered open:irlg :is st:iLL
presenl~ed to'ma-terial being treated by the screeniny member~
~s in the previously described embodimen-t, the sidewalls 33 of the substrate are protectecl by t,he downward and outward -tape~
o~ the coating opening sidewalls 58. A mold or gany jig 'indi-cated generally at 60 having a bottom 62 and s:idewalls 64 can be used as in the precediny embodiment.
, Turning now to Fi~ures 9 and 10, apparatus is shown for carrying'ou-t the present invention where the elastomer material is'oE a nature, such as rubber, which can be vulcanized or hardened by heat and pressure. In this variant of the invention, a mold indicated generally at 70 is used haviny sidewalls 71 and a bottom wall 72.

This,mold can be rectangular as shown or have any conEigura-tion which will accommodate a screen member of -the desired shape. In the illustrated form, the substxat~ oE metal or any material o~ re~uisite strenyth :is shown a-t 7~ received in the bo-ttorn of mold 70. Pluys indicated generally at 76 can have their lowermost portions 77 frictionally held in depressions 78 formed in the bottom 72 of mold 70 or whexe desired depressions 78 can be dimensioned with some toler-ance to permit sllght lateral movement of the plugs to ac'commodate a solid substrate. These plugs correspond in this variant of the invention to base por-tion 42 and sections 44 and 46 of'the plugs in the ~irst described variant. In the variant of the method illu~tra-ted in ~igures 9 and 11, the lower and upper sections o~ the plugs above lowermost, /c;~ ' .

t , ., ;,.

portion 77 are desi~nated by -the re:E~rerlce numera:Ls 7~ ancl 80, respecti~ely, with a shoulder 81 between them. The upper section 80 can be cylindrical or any other shape where desired, instead of tapered as shown, so long as the cross sectional area in planes normal to the height dimension OL
the plug does not prevent withdrawal of the plug from the final abrasion-resistant coating.
The elastomeric coating substance in the form of . a layer of raw material which in final form is abrasion-.10 resistant is shown:at 82. As will be evident from the pr~-ceding déscription, the raw material 82 is poured, plasteredor placed in any convenient manner on top of subs-trate 74 in such depth or thickness as will achieve a final form of abrasion-resistant elastomeric coating on the subs-trate which is o~ the same height as plugs 76 after vu:Lcani~cltion or h~iat and pressure treatm~nt. When the raw or untreated material has been placed in posit:ion, a lower heat treating plate 84 and an upper heat treating and pressure applying pla~e 86 are bxought in-to contact with the bottom of the mold and the top of the raw material, respectively. Heat is supplied to plates 84 and 86 and where necessary pressure is applied to plate 86 so that material 82 is vulcanized or heat . cured in the desired thickness, which preferably corresponds ,. . . . .
to the height of.upper sect~on 8Q of pluc~s 76. ~t wi;ll be noted that where compressing act.~Qn is ne.cessar~, ~lugs 76 ~ill act as a stop for upper heat treat2nc~ plate 86 and with the proper amount of material 82 oric~inally on t~e surface of ..

11~11~5 substrate 74,, the heiyht of plugs 76 will act to stop the com~ , pressing action at the desired depth, of -thermoplastlc material.

When the vulcani~ation, curing or desi~ed heat treatmen-t of material 82 is completed, plates 84 and 86 are removed and the coated screening member can be removed from mold 70 ~n fini~hed condition. As mentioned earlier in connection with the first descrl~ed variant of the method, plugs 7Ç where desired can have pr,eviously been coated with a materi:al Wh~ch ~ ac~litate their withdrawal. In case the plugs adhere to the substrate and/or.the thermoplastic material and hlnder extraction of the completed scxeen member from the mold, the plugs can be loosened by tapping their bottoms through openings 88 in the bottom 72 of mold 70. Of . course, with the completed screening member removed Erom molcl 70,'any plugs retained in the coated sc.reen can be removed by tappiny them ~xom the top or coated ~ide of the ~creen.
A special advantaye of this varlan-t of the inven-tion is that substrate 74 can also be formed in si-tu in mold 70 where the material of the substrate is of a castable .
.20 nature, such as aluminum, fiberglass or,any plastic material structurally strong enough to support abrasion-resistant elastomer coating 82 to form a satisfactory screen member.
In such case, this variant of the me-thod need not neces~arily involve a heat treata~.le. c~at~ng 82 b,ut c~n use th.e ,s,c~e type o~ coating p~eyi~ously~ d~scr,i.b..e.d ,~n respect to th.e varlant illustrated ~n Fi~yures 5 to ~ n the Var.i~ant of the ~nven~
tion in ~h~ch'th.e subs.trate i~s formed in siku in ~old 70, ~S

'Z5 plugs 76 (F:LcJures 9~ are sccurcly posi-tioned in de~r~s~l.on 78 and the castable substrate material is poured .~nto the mold to a depth flush with shoulders 81 on plugs 76. When the substrate material has hardened, the method pxoceeds as described above. It is concei~able that the substrate can be made from hard rubber or some such material tha~ would be brought to its final shape, hardness and strength by heat , treatment and it ~ill be obvious in such case that the ? plates 84 and 86 can be used for this purpose at the same time as the coatiny is heat treated or a specially shaped ~' plate-can be substituted for plate 86- to heat treat and apply pressure to substrate 74 separatel~ and prior to the .
heat treatment o~ thermoplastic material 82.
Figures 11 and 12 show two additional examples .
of plugs or forms. In these figures the same reference numerals are applied -to si~ilar parts but Wi-th lOO beincJ
added in ~igure 11 and 200 in ~'igure 12. It will be noted that upper section 280 of Figuxe 12 has walls which do not slope, this feature being desirable under some conditions in respect to all variants of the invention.

Where desired in this variant of the méthod and in the earlier described variants, the plugs can be formed of metal economically manu~actured in large nu~bers by an ordinary metal injection m~lding machine. ~he elastomeric material may be placed on the upper sux~ace of khe substrate in laminated form or in whcitevex ~or~ is most co~venient con~
sidering its consistency. The heat kxeatable form of coatin~

. ~ , .
~ . ' ' . .

can be crllcle rubbe~ ln putt~ c C~n'~ llC~y or arl~ q~ th~
many substances of si.~lilar charclc-l.eric.t:;cs now avai.:labl~
~here heat treatment alone is :involved the material 82 may be NYLON, DERLIN, polyethylerle or similr.substances.
S The above descri,bed Variants of the invention are to be considered.in all respects as il:lustrative and not restr.ictlve since the inventi.on ma~ be carr~ed out dif~erently without departing from its spirit or essential characteris-tics. Therefore, the scope of the invention i.s .indicated b~r the claims rather than b~ the ~oregoing description, and all changes which come w.ithi.n the meaninc3 and range of the equivalents oE the claims are intended to be embraced therein.

.-.

Claims (25)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method of coating a perforated substrate to produce a screening member of increased abrasion resistance, the sub-strate having upper and lower major surfaces and having per-forations defined by sidewalls extending between said major surfaces, said method comprising the steps of providing a plurality of forms, each form having side-walls, the cross sectional area of which in planes parallel to the upper major surface of the substrate not increasing through-out the height of the form, positioning a form in each perforation;
forming a layer of hardenable elastomer in a plastic state on the upper surface of the substrate to a depth not greater than the height of the form, hardening the elastomer to form a coating of abrasion-resistant elastomer adhered to the upper surface of the sub-strate and surrounding the form, and removing the form after the layer of abrasion-resistant elastomer is formed.

2. The method of claim 1 in which the sidewalls of a lower section of each from corres-pond in size and shape to the sidewalls of a substrate per-foration.

3. The method of claim 2 in which the shape of the sidewalls of the lower section of each form is cylindrical.

4. The method of claim 1 in which the sidewalls of each form slope upwardly and in-wardly.

5. The method of claim 4 in which each form has frusto-conical sidewalls.

6. The method of claim 5 in which the rate of slope of the sidewalls is between about 0.0001" and about 0.01" for each ?" thickness of coating.

7. A method of forming a perforated substrate having an abrasion-resistant coating layer thereon comprising providing a mold having a bottom, the bottom supporting a plurality of upstanding forms, each form having sidewalls corresponding in shape to the desired sidewalls of perforations in the abrasion-resistant coating layer, each form having a pair of sections one superposed on the other, the cross sectional area of the upper section of each form in planes normal to the height dimension of the form being no greater than the lower section and being of decreasing cross sectional area upwardly in the height dimension of the form corresponding to the thickness of the desired coating layer, placing a substrate in the mold with the lower section of form filling each perforation in the substrate and with the top surface of the substrate exposed, placing a layer of material which in final form is abrasion-resistant within the mold in contact with the exposed surface of the substrate, confined by sidewalls of the mold contiguous to the sidewalls of the upper sections of the forms, hardening the layer of material to make the material abrasion-resistant; and adhering the material to the substrate to form a layer of abrasion-resistant coating on the substrate, the last two steps taking place in any order or simultaneously.

8. The method of claim 7 in which the material is an elastomer initially in a plastic state, the hardening step involves curing the material to final abrasion-resistant form, and the adhering step involves creating an adhesive action at the interface between the exposed top surface of substrate and the abrasion-resistant coating.

9. The method of claim 7 in which the upper section of each form has frusto-conical sidewalls.

10. The method of claim 9 in which said cross sectional area of each form decreases upwardly at a rate between about 0.0001" and about 0.01" for each ?"
of thickness of the coating.

11. The method of claim 10 in which the substrate is placed in the mold in liquid form and hardened to form the perforated substrate.

12. The method of claim 7 in which each form has frusto-conical sidewalls.

13. The method of claim 12 in which said cross sectional area of each form decreased upwardly at a rate between about 0.0001" and about 0.01" for each ?" of thickness of the coating.

14. The method of claim 13 in which the substrate is placed in the mold in liquid form and hardened to form the perforated substrate.

15. The method of claim 7 in which the substrate is placed in the mold in liquid form and hardened to form the perforated substrate.

16. The method of claim 8 in which the substrate is placed in the mold in liquid form and hardened to form the perforated substrate.

17. The method of claim 7 in which the material of the layer of material is a soft, rubbery substance, and the hardening step is a vulcanizing step under heat and pressure.

18. The method of claim 17 in which each form has sidewalls sloping inwardly.

19. The method of claim 18 in which each form has frusto-conical sidewalls.

20. The method of claim 19 in which the rate of slope of the sidewalls is between about 0.0001" and about 0.01" for each ?" thickness of coating.

21. The method of claim 20 in which each form has sidewalls sloping upwardly and inwardly, and the rate of slope of the sidewalls is between about 0.0001" and about 0.01" for each ?" thickness of coating.

22. The method of claim 17 including providing a plate means having a lower planar surface corresponding in area to the desired upper surface of the final form of the layer of abrasion-resistant coating, at least some of the forms including stop means, the height dimension of the stop means corresponding to the thickness of the final layer of abrasion-resistant coating, placing the plate means in heat and pressure supplying relation to the layer of raw material, supplying heat and pressure to the plate means until the plate means engage the form stop means and the layer of material is in abrasion-resistant form.

23. The method of claim 7 in the mold also has sidewalls, the height of the sidewalls being greater than the thickness of the substrate and desired coating layer combined.

24. A method of coating a perforated substrate to produce a screening member of increased abrasion-resistance, the substrate having upper and lower major surfaces and having perforations defined by sidewalls extending between said major surfaces, said method comprising the steps of ] providing a plurality of forms, each form having a base portion and a pair of consecutively superposed sections carried by the base section, the lower section contiguous to the base having sidewalls not greater in size and shape than the sidewalls of a perforation, the upper section having side-walls inwardly spaced from the sidewalls of the first upper section, the cross sectional area of the upper section in planes parallel to the upper major surface of the substrate not increasing being designed to limit movement of the form relative to the lower major surface of the substrate, positioning a form in each perforation with the base portion contiguous to the lower major surface of the substrate, with at least the lowermost portion of the lower section embraced by the sidewalls of the perforation and with the upper section protruding above the upper major surface of the substrate, forming a layer of hardenable elastomer in a plastic state on the upper surface of the substrate to a depth not greater than the height of the upper portion of the form, hardening the elastomer to form a coating of abra-sion-resistant elastomer adhered to the upper surface of the substrate and surrounding the upper portion of the form, and removing the form after the layer of abrasion-resistant elastomer is formed.

25. A method of forming a perforated substrate having an (Claim 25 cont'd...) abrasion resistant coating layer thereon comprising providing a mold having a bottom and sidewalls, the height of the sidewalls being greater than the thickness of the substrate and desired coating layer combined, the bottom supporting a plurality of upstanding forms, each form having a pair of sections one superposed on the other, the sidewalls of the lower section of each form corresponding in height and shape to the sidewalls of perforations in a substrate to be placed in the mold, the sidewalls of the upper section of each form corresponding in shape to the desired sidewalls of perforations in the abrasion-resistant coating layer, the cross-sectional area of the upper section of each form in planes normal to the height of dimension of the form being of decreasing cross sectional area upwardly in the height dimension of the form corresponding to the thickness of the desired coating layer, placing a substrate in the mold with the lower section of a form filling each perforation in the substrate and with the top surface of the substrate exposed, placing a layer of material which in final form is abrasion-resistant within the mold in contact with the exposed surface of the substrate, confined by sidewalls of the mold and contiguous to the sidewalls of the upper sections of the forms, hardening the layer of material to make the material abrasion resistant, and adhering the material to the substrate to form a layer of abrasion-resistant coating on the substrate, the last two steps taking place in any order or simultaneously.