CA1199306A

CA1199306A - Abrasion resistant, reinforced screen panel member

Info

Publication number: CA1199306A
Application number: CA000411375A
Authority: CA
Inventors: Raymond A. Koehler; Gregory A. Gryskiewicz
Original assignee: UOP LLC
Current assignee: Honeywell UOP LLC
Priority date: 1981-09-14
Filing date: 1982-09-14
Publication date: 1986-01-14
Also published as: AU556366B2; US4374169A; AU8836282A

Abstract

"ABRASION RESISTANT, REINFORCED
SCREEN PANEL MEMBER"

ABSTRACT

Screen member for use in fixed or rotating screen support devices and in either a vibrating or non-vibrating mod for grading or dewatering comprises a first plurality of elongated, parallel surface wire members which are formed by extruding a resilient, abrasion resistant layer of elastomeric material completely around a core portion which is more rigid than the elastomeric layer, A
second plurality of elongated, paralled support rod members arranged transverse to the first plurality are also formed by extruding a layer of elastomeric material completely around a more rigid core portion. The first and second plurality of wire members are bonded to each other at every intersection by a partial melting together of the contacting elastomeric layers under pressure. The melting is preferably insufficient to permit the core portions of the respective first and second wire members to bond to each other and produces a resilient joint at each intersection which enhances the ability of the screen to remain relatively free of lodged particles. The core portions of each of the first and second sets of wire members have a flexural modulus of at least 100,00 p.s.i. Binding of the screen is minimized by having the open space between adjacent support rods at least 10 times greater than the slot width between adjacent sur-face wires.

Description

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"ABRASION RESISTANT, REINFORCED
SCREEN PANEL MEMBER"

BACKGROUND OF THE INVENTION

The invention relates to elastomeric screen panels and particularly to polyurethane screen panels. It is known that poly-urethane offers excellent abrasion resistance and a number of poly-urethane screen panels are commercially ~vailable for use in severely abrasive mining applications for grading or dewatering. Patents relating to such screens wherein elastomeric ma~erial is molded in-clude Nos. 3,~28,184, 3~483~976, 3,557,276, 39900~628, 3,980,55~, 4,0629769 and 4,1009248. Patent No. 4,120,785 discloses a screen formed from melt bonded transverse layers of elongated polyurethane rope members which have a tensile core. The tensile core portions of the rope members in one layer have a high elongation at break and are preferably formed of twisted strands of fiber or metal, while the tensile core portions of the rope members which define the ad-jacent layer have a low elongation at break. Apparently, the rope members in each l~yer are substantially equally spaced. Also, being of filamentary construction, they would seem to have a very low flex-ural modulus. Patent No. 4,247,007 shows a tensioned strand screen~

SUMMARY OF THE INVENTION

It is among the objects of the present invention to pro-vide an abrasion resistant, reinforced screen panel member which will provide long life when contacted by abrasive material in either a vibrating or non-vibrating mode of operation. It is another object to provide such a screen panel which is sufficiently rigid that the ~3~ 3~

support rods can be spaced from each other by at least about 10 times the spacing of the surface profile wires, thereby increasing the screen's open area and greatly reducing the tendency of the screen to become blinded.
In a preferred construction, the support rods comprise a rigid steel core portion about which a thick annular layer oF polyure-thane is extruded. Since the core is covered~ low carbon steel is satisfactory. The surface wires preferably have an extruded polyure-thane surface layer and a co-extruded core which may be formed of a more rigid polyurethane, or of polyvinyl chloride or ABS, for example.
The shape of the surface and of the core is preferably trapezoidal to reduce blinding and to facilitate cooling of the extruded material.
Where it is desirable to space the support rods quite far apar~, such as 3 inches, it is usually pre~erable to extrude the polyurethane sur-face layer of the wires about a steel wire core. Such a core, which should also be of a trapezoidal shape, has a much higher flexural modulus than a plastic core, thus providing a sufficient rigid~ty to the wires over their relatively long unsupported portions so as to maintain a uniform slot width. A deep trapezoidal shape also provides significant beam strength. The cores of the wires and rods are much stiffer than the outer layer of polyurethane and h~ve a ~lexural mod-ulus of at least 100,000 p.s i. The outer layer of polyurethane or other elastomer on the wires and rods preferably has a durometer suf-ficient to provide good abrasion resistance and a value of about 80 Shore A has proved satisfactory. Where the core of the wires is also polyurethane or other plastic, it is preferably one which has a duro-m~ter sufficient to provide substantial rlgidity to the wlres. A
value of about 70 Shore D has been found to be satisfactory.

~he welding process can be hot platen welding, vibration welding, electromagnetic welding, solvent welding, hot gas welding~
or any other appropriate process used to join thermoplastic materials.
~ Welds can be made individually or ~he entire panel can be assembled in a fixture and welded at one time. A machine sui~able for assembling and welding polyurethane covered wires and rods into a pane1 is dis-clo~ed in U.S. Patent 4,295,918, issued October 20, 1981.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is an isometric view, partially broken away, showing the improved screen panelg ~ig. 2 is a sectional view taken on line 2-2 of Fig. l; and Fig. 3 is a sectional view taken on line 3-3 of Fig. 1 DETAILE~ DESCRIPTION OF THE PREFERRED EMBO~TMENT

Fig. 1 illustrates a screen panel assembly 10 consisting of a first set of closely spaced parallel, surface pro~ile wi-res 72 and a second set of widely spaced, parallel, support rods 14. Typioally, the pitch or spacing distance between the centers of adjacent support rods 14 is about 1.5 inches. Thus~ for an outside rod dia~eter of 0.25"~ the open space between adiacent rods is typically about 1.25 inches. The screen ~ires 12 have a maximum width at their upper sur-face oF about 0.120", and are spaced apart sufficiently to provide slot openings 16 of a dimension appropriate to the size of the material being screened. Typically~ the dimension 16 is about 0.0~0-.080".
Thus, for the dimensions noted, the open space between adjacent rods along the length of the slot 16 is from about 15-30 times the slot 4~3~

width. The magnitude of this relationship means that very little of the open area of the slots will be lost should portions of ~he slots 16 become clogged or "blinded" due to the presence of the underlying support rods 14. The possibility of "blinding" and its consequent reduction in the open area of the screen duriny use is lessened even further when the pitch between the support rods is increased further~
such as to 3.0 inches. To achieve such a wide pitch between support rods, however, the screen wires 12 must be quite stiff. In such a situation, it is sometimes necessary to use a core member 18 compris-ing a solid steel wire inside the wire 12 in order ~o achieve a suf-Ficiently high flexural modulus. A steel core member 18 would have the outer layer of abrasion resistan~ elastomeric material 20~ pre~-erably polyurethane, ex~ruded around it. For more typical installa-tions, where the rods 14 can be at a closer pitch~ such as 1.5 inches, the core members 18 inside the wires 12 can have a Flexural modulus as low as about 100,000 psi. Suitable core materials for the wires 12 include rigid polyvinyl chloride, ABS, and polyurethane~ with the latter being preferable since it will bond to the outer layer of poly urethane if melted~ while polyvinyl chloride will not. Either materi-al is, however~ preferred over steel for the core since two plastic materials can be co-extruded, a much simpler process than trying to extrude a uniform plastic coating around a trapezoidal shaped metal core. The typically larger and stronger rods 14 are almost always pro-vided with a core 24 of solid steel wire to provide stiffness and rigidity to ~he overall panel 10. The rods 14 do not need a precisely dimensioned surface or a trape~oidal shape and can be made quite easily by ex'cruding a polyurethane outer layer 26 around the round steel wire core 24.
Figs. 2 and 3 are drawn to about 8 times normal size for clarity, while Fig. 1 is drawn to full size. As can be seen in these t`igures, the cores 18 in the wires 12 preferably remain separated from the cores 24 in the rods 14 when the polyurethane coatings 20 of the wires are melted into the polyurethane coatings 26 of the rods 14 5~ to form the screen panel 10. The preferred amount of overlap of the wires 12 and rods 14 after they are mel~ed together is 0.040" and should not exceed about 0.060". In the preferred embodiment, the wires 12 are trapezoidal in shape with an 8 side taper. They are about 0.140l' high and 0.120" wide with the polyurethane coating 20 having a thickness on the upper wear surface of about 0.030" and a thickness on the three other sides of about 0.020". The rods 14 have an outer diameter of about 0.250" while the diameter of the steel core 24 is abou-t 0.128".
In a pr ferred assembly method, a heater bar (not shown) is brought into pressure contact with the entire length of a selected support bar 14 to be attached and to those areas of all of the wires 12 which are to be bonded to the selected support bar when the heater bar is removed. The heater bar softens the polyurethane coatinys 26 and 20 about 0.030" and 0.018" respectively, and causes the top of the circular rod member 14 to be flattened as shown at 14'. The heater bar also deforms the bottom of the wire members 12. Thus, when the heater bar is removed and the heated and flattened portions of the wires and the rods are forced toge~her7 the softened coatings 26, 20 will fuse together. A slight amount of additional compression will also take place and will enhance the bond. For the dimensions shown, it is apparent in Fig. 2 that a slight additional amount of penetra-tion of the top surface 14' of the rod into the bottom coating 20 of the wire will eliminate the small thickness of coating material 20'.

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and will bring the polyurethane surface 26' into contact with the material oF the wire core 18. This presents no problem when the core 18 is also a polyurethaneg since the two like materials will readily fuse to each other. However, when the core 18 is rigid poly-vinyl chloride, for example, no -Fusion can take place and thus there will be no bond on the common surface between the coating 26' and the core 18. However, when the small gap 20' is present, the coating 20 will retain its mechanical bond with the core 18 and will also be completely fused to the coating 26.
The provision of rigid cores within the wires and rods pro-vides many advantages besides those previously discussed. For ex-ample, the core 18 could be made oF a color different than that of the outer layer 20. Thus, when the upper thickness of the layer 20 wears away sufficiently to expose the contras~ingly colored core mate~
rlal, one would have a visible indication ~cha~ it was 'cime to replace the screen. For example~ iF a white core 18 of PVC were located in-side a black polyurethane outer layer 20, it could be extrudPd into an exact location corr~sponding to the point below the wire's top sur~
Face at which the screen slots 16 would have widened to an unaccept-able degree. Also, by altering the core material, or by changing its physical dimensions, the physical properties of 'che wire can be greatly modified while retaining the abrasion resistance benefits af-forded by the outer skin. One possibility would be the varying of the stiffness or natural frequency of the screen panel, thus permit-ting a screen to be matched to the input Force of a vibrating screen machine to produce a maximum excita'cion.
In addition, some studies have indicated that the ratio o-F
surface energy to hardness is important in predicting a material's behavior to friction and wear. Conceivably, a two-material construc-tion could effectiYely offer a very low surFace energ~y to hardness ratio by using a material with a low surface energy over a reasonably hard core, thus proving the co-extruded or coated wire to have better resistance to abrasion than a solid polyurethane wire shape.
It will be readily obvious that the disclosed screen incor-porating co-extruded or coated wires combines the many advantages oF
stainless s~eel screens such as maximum open area~ V-shaped slot, con-tinuous slot the length of the panelg high strenythg rigidity, with the advantages of existing polyurethane screens; superior abrasion resistance for long life, corrosion resistance, and light weight.

Claims

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

1. A reinforced, abrasion resistant screen member for use in either a vibrating or non-vibrating type screen apparatus comprising a first plurality of closely spaced elongated profiled surface wires arranged parallel to each other and in a plane so as to define elongated slots between the wires which have a width less than the width of the wires, each of said first plurality of wires including a rigid core portion having a flexural modulus of elasticity of at least 100,000 p.s.i. and a layer of a less rigid thermoplastic, abrasion resistant material extruded over it and in intimate bonded relationship to it; a second plurality of less closely spaced elongated support rods positioned in a plane and arranged parallel to each other and transverse to said first plurality of wires, each of said second plurality of support rods including a rigid core portion having a flexural modulus of elasticity of at least 100/000 p.s.i. and a layer of less rigid thermoplastic, abrasion resistant material extruded over it and in intimate bonded relationship to it, said first plurality of wires and said second plurality of rods having portions of their layers of thermoplastic abrasion resistant material fused together in overlapping relationship at every intersection, the cores of said wires and rods being unfused and spaced from each other at every intersection, and the dimension of the open spaces between adjacent screen rods being at least 10 times the width dimension of the slots define by the surface wires.

2. The screen member of claim 1, wherein the dimension of the open space between adjacent screen rods is at least 15 times the width dimension of the slots defined by the surface wires.

3. The screen member of claim 1, wherein said abrasion resistant material on said surface wires and on said support rods is polyurethane.

4, The screen member of claim 1, wherein said abrasion resistant material has a durometer of about 80 Shore A.

5. The screen member of claim 1, wherein said core portion of each of said surface wires has a cross-section which is of greater dimension in a vertical direction than in a horizontal direction when the wire is in a horizontal plane.

6. The screen member of claim 5, wherein said core portion of each of said surface wires has a cross-section which is trapezoidal and the outer cross-section of the wire is also trapezoidal, the vertical sides of said cross-sections being upwardly divergent.

7. The screen member of claim 3, wherein said support rods each have a core portion comprising a solid steel wire.

8. The screen member of claim 7, wherein said surface wires each have a core portion comprising a solid thermoplastic member.

9. The screen member of claim 8, wherein said thermoplastic member is polyvinyl chloride.

10. The screen member of claim 8, wherein said thermoplastic member is polyurethane.

11. The screen member of claim 7, wherein said surface wires each have a ore portion comprising a generally trapezoidal-shaped solid steel wire, the open space between adjacent screen rods being at least 30 times the width dimension of the slots defined by the surface wires.

12. The screen member of claim 1, wherein the core portions of the surface wires are of a different color than the color of the extruded abrasion resistant material which overlies them whereby a wearing away of the abrasion resistant material during use will expose the core material and visually signal the need to replace the screen.

13. The screen member of claim 1, wherein said profiled surface wires have a height greater than their width and a cross-sectional shape that is trapezoidal with algenerally flat top surface which is wider than its bottom surface and angled side surfaces which define tapered slots between the wires.