DE2102617A1 - Sieve insert and process for its manufacture - Google Patents

Description

PATENT Attorneys ^V ^ ² " I" 7348

DIPL.-ING. R. SPLANEMANN _8ooo Munich ₂ 20 "JanUOT 1971

DIP L.- ING. J. RICHTER Theatmerstrasse 33/34 O 1 Π 0 C 1 "7

MÖNCHEN HAMBURG Telephone (0811) 22 62 07 £ \ UZO I /

Telegrams: Inventius Munich

EBA Gxoup Limited

Yorkshire »England

Pat eating tanme lon ng

Sieve insert
and process for its preparation

The LrfrLndimg concerns Siebeinsätis © -. which serve to separate and subdivide leilohen of different sizes, these selloheia stones, chemicals _p mineral krae odo d ^ l _o include, which in the following simply referred to as "raw materials"

Such a strainer (often referred to as "screen-mat ¹¹ is beaeißhnet and will also be hereinafter referred to as) m is provided with an array of openings having fixed dimensions, the check eratreckenr over the entire thickness © the screen mat so that the 'feilohen the raw material" the largest dimensions of which are smaller than those of the openings free through the screen mat; others can "while the larger 3 particles of the raw material are retained on its upper side. To facilitate the passage of the raw material particles through the openings", the screen mat is usually on attached to a metal frame, which is continuously or intermittently in

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a Ubane is set in vibration, which can run horizontally or at an angle to the horizontal _o On this., It is IaOgIiCh ₉ to sort a raw material batch into particles of different sizes,

A previously proposed method for sorting raw material used sieve mats a wire mesh made of chair or another metal result of the vibration fatigued .A further drawback metal3.isch.er screen mats is that the seven ,, often takes place under Peuchtigkeitseinfluß or under the influence of acids with the _t IoIge that a metallic screen mat rust or corrosion is exposed; although stainless metal screen mats have been suggested * these have a useful life which is short compared to their cost. which has a high elasticity _o Was a metallic screen mat therefore proposed? which was protected from Feuehtigkeitseinflüsse and corrosion by acids or alkaline agents, while the rubber surface represented a padding for the screen by migrating particles simultaneously _0. However, it has been found that the abrasion resistance of the reinforced by rubber wire mesh screen mat was low and that * when the screen mat was set in vibrations, the wire mesh cut and rubbed the rubber, which led to premature damage to the screen mat «,

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Ea, sieve mats made entirely of rubber were also proposed, "in which the openings were embedded or pushed into a flat rubber sheet, but this was not possible . to a 3ehr large proportion of waste of rubber and correspondingly expensive "In rubber sheets pushed-openings dasu tend _P convex-shaped walls to besxtsejß because it is difficult einaußtoßen openings in such a web, while ensuring * that the cross section of the opening through the entire thickness of the Path remains constant _o Raw material particles which are sieved through such a sieve mat made of rubber "whose openings are designed in this way" are often clamped between the convex walls in the area of an opening with a reduced diameter, which leads to the highly undesirable ¹¹ In addition to being expensive to manufacture, rubber screen mats have various other disadvantages during operation. For example, it has been found that the mechanical strength of a rubber screen mat is usually insufficient to support a heavy load of raw material

It is an object of the present invention to provide a sieve

matte to create that on reducing the problems and leads to disadvantages in connection with previously proposed screen mats, as described above.

According to the invention, a screen mat is proposed which Made from liquid polyurethane in a casting process isto

Furthermore, according to the present invention, a method for producing a screen mat is proposed.

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ORIGINAL

is cast in the liquid polyurethane to a field patrizenartiger projections, the openings to be formed in size _s shape and arrangement in the screen mat are complementary ,, cured whereupon the molded polyurethane and the cured cast screen mat is removed from the patrizenartigen protrusions.

The polyurethane blend used in accordance with the present invention can be any combination of one or more polyisocyanates with one or more active hydrogen-containing compounds? which are connected to one another as liquids (if necessary with heating) and after hardening provide an elastomeric product ,, The polyisocyanate can be a simple polyisocyanate leg ,, like ZoBo a 2 _? 4 - "! Polylene diisocyanate _s , m- = phenylene diisocyanate, 1,5-naphthalene diisocyanate or triphenyl methane triocyanate or a prepolymer containing free isocyanate groups

The prepolymers can be formed by an active Vvasstsrstoff Verbinöungeimit containing a molar excess of a simple polyisocyanate, as defined above, reacts as ζ · _Β ο a PoIytetramethylen glycol equipped with a 2s, 4-toluene diisocyanate in molecular Ratio of 1: 2 reacted «The term active hydrogen refers to Vrasestoffatoms that develop an activity according to the Zerewitinoff test, as described by Kohler in the Journal of the American Chemical Sooiety 49» 3181 (1927). These hydrogen atoms then react with isoyanate groups to make a chain extension or cross-connection points »Representative examples

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of active hydrogen-containing compounds include polyethers with terminal hydroxyl groups * such as Z ₀ B ₀ polypropylene glycol * polytetramethylene glycol, polyester with terminal hydroxyl G groups »such as ζ _β Β _β polyethylene adipate _s Polypropyle.n -Sebacate, or simple molecules like 55 »Bo Ts4 butanediols 4-4 'methylene-bi © - (orthoehlor anilin) odor friiasthylol-propane, It was found? <ea £ dx © polyurethane -Gießmaterialiön "the Adiprene and as Adiprene L 100 Ii 167 (both from DuPont Company), are j ^ len To-diisocyanate Polytötrainethylen- Jj glycol compounds are _f if by DuPont MOCA (4-4'-Methylen-bie-COrthochlos? Aniline)) are cured, are particularly suitable materials for a © sieve mat according to the present invention.

It _"9 pigments Plastifizlerungezusätze, Flammenheiamer and / or stabilizing agents can be added _s among experts in the field of deformation of polyurethane elastomers are well known, the liquid castable polyurethane in different ratios additives such J3.B" filler ·

Polyurethane is an elastomer with high rigidity and as such is capable of carrying a considerable raw material load without causing an unacceptable sag or damage to any of this Material formed sieve mat is to be feared,

Polyurethane also has a good resistance to abrasion and a high sonic strength, what a screen mat with excellent wear properties results o Since polyurethane is in a liquid, pourable form is available, it is a considerable advantage of the

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Eri \ inä'aixg _t . that a relatively simple pouring technique can be used to manufacture the sieve mat. By using such a simple pouring technique, a large variety of opening profiles can be achieved? where the opening profile is understood to mean the cross-section for a cut through the diameter of the hat, _c where such a range of variation has normally not been achievable when using the above-mentioned methods for pounding the holes

In order to produce a screen mat according to the invention, it is first necessary to "produce" a mold into which the polyurethane can be poured. The mold preferably comprises a substantially horizontal _t flat trough which is hereinafter referred to as the molding box, and the inner dimensions are those of the desired screen mat "The openings within the Siebßiatte are made by _s that patrise-like projections are arranged in a preferably ordered field spaced from each other" which stand upwards relative to the essentially horizontal base of the molding box "The patrix-like projections are naturally profiled so that they match the dimensions ; the shapes and the distribution of the openings desired in the finished screen mat are complementary.

The male-like projections in the molding box can be viewed as negative moldings for the screen mat and A positive cast (i.e. the screen mat) is made by pouring liquid polyurethane onto the negative Molded parts is poured on. The molding box comes with

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Polyurethane filled and the molding is then cured either by _s that he remains standing at ambient temperature (self-curing) or _f duroh heat. The cast screen mat is then made from the molding box

all, burrs are removed and at this point are / made of polyurethane,

which Iäng3 the edges of the mat may have formed through a .Reinigungs- and Zurichtbearbeitung away To the easy removal of the wire mat "to facilitate from the mold box and the male may be required _for the male and the interior of the mold (| kästens with a release agent »such as a silicone coating»

If a positive cast, that _o the screen-mat has been obtained * may advantageously this positive cast in e: LNEN another flask _F are introduced without patrizenartige projections to give a positive form, can be molded after the more negative moldings This "reduces the cost of subsequent casting operations considerably because only one master pattern or _o a U-shape box is required. It Xb t should be noted that when using a mold box A

or a negative mold made of polyurethane, the surface of the molding box, which will come into contact with the liquid polyurethane to be cast, must be coated with a suitable release agent to prevent the cast screen mat from connecting with the male-like projections made of polyurethane

As an alternative to using a pre-cast polyurethane screen mat as a positive form, after the further

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negative forms are prepared _(e n h "forms with patrizenartigen projections) can be made an independent master model are that coincides with the wire mat to be cast. Similar to the use of a pre-cast polyurethane screen mat as a positive mold, the master model can be inserted into a molding box and a negative mold can be created through this, e.g. by pouring polyurethane over the master mold in order to produce the male-like projections of a female mold , positive master model may be made of material (for example polypropylene), or a metal sheet or a wood board that is processed in a suitable manner _s to agree to practice the shape of the screen-mat?, are in each case covered in such a case the positive master form with a suitable release agent _r has the removal of the negative mold parts from the molded thereon screening mat ermöglichenο ZVL

It should be noted that the _p patrizenartigen projections may be formed on a negative original model. The negative master model can be produced in such a way "that it has male-like projections of any desired shape, or alternatively it can be produced by suitable processing of a plastic plate (for example made of polypropylene) g a metal plate or a wooden board" if the openings formed in the cast screen mat are in the mat plane have a reohteok-like shape «,

They openings in the top of the screening mat can have any desired shape, for B _o 'the an oval, an ellipse, or a regular polygon "generally

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However, pre-weighed that it is Although this nioht handeltρ a circular or rectangular shape in the plane of the screen mat besit2en ₀ to significantly © features it advantageous if the shape and size of all the apertures in siner given screen mat same. and some or all of these openings can have a constant cross-section over the entire thickness of the mat. blinding of the openings) · it has been found ,, that it is advisable to the blocking of the openings to overcome this problem _f the cross-sectional area of the openings to vary over the thickness of the screen mat * it is therefore vorges3ogen _s that the cross section of an opening there ₈ where in AEIE bottom of the screen mat open out, iat larger than the mouth at the top of the screen mat "Taking into account these considerations, some or all of the openings in the screen mat is erweltern uniformly over the thickness of the mat from its top to its bottom conical _o However, it is preferred that some or all of the openings || have a Part of their longitudinal extension through the thickness of the mat, which extends from the top of the mat, have a constant cross-section, the remaining part of the length of these openings then tapering outwards over the remaining part of the mat dioke towards the underside of the mat extended »in one embodiment, each aperture in the mat, in a cross-section through the Dloke the screen mat is seen _s wherein the opening is of smaller kegeistumpfförmiger shape Durohmesser at the top"

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Alternatively, and in a preferred embodiment $ eäe opening beeitat a partially cylindrical portion of the _r müüdet at one end in the top of the mat and merges into a frustoconical portion at the other _end? wherein the kegslstumpfförmige portion of the opening; iet that Absohnitt ₉ which opens into the underside of the mat. Ea vmrde found _t that then "if partly cylindrical"? and partially frustoconical openings are formed in the screen mat, the risk of the openings becoming blind is lower _e

When a sieve mat under heavy raw material loads If the mat is to be used or subjected to other harsh conditions, it may be necessary to replace the mat with a reinforcement structure »such as metal bars, a wire grate or a plastic grille to reinforce. Such reinforcement structures are preferably incorporated into the polyurethane during the casting process embedded in the corridor of the screen mat (e.g. by arranging the reinforcement structure so that that they are between the adjacent male-like projections runs in the molding box before the polyurethane is poured). When arranging a reinforcement structure consisting of metal rods or such comprises, two or more such rods can advantageously run the length of the edge of the polyurethane of the screen mat and be used to hold the mat to attach a vibrating frame, for example by the fact that the had with the bars of the frame is screwed or riveted. This technique has the Advantage that the vibratory forces and the weight of the raw material to be screened are uniform along the entire length

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Edge of the screen mat can be distributed <>

Based on the following description of the in the drawing illustrated embodiments of the invention this © is described in more detail. It saigent

Figo 1 is a perspective view of a

screen mat according to the invention, in which, for the sake of simplicity, not all openings the screen mat are shown,

FIG _o 2 is a cross section through the in Fig. 1

screen mat shown along the line II - II in Fig. 1,

Figure 3 is a perspective view of an _o

Hegativforra are with a field patrizenartiger projections which are arranged laid down in the screen-mat according to Figo 1 and complementary apertures formed _f wherein all not shown for simplicity these projections »J

4 shows a section through a molding box,

in which the negative mold shown in FIG. 3 for the casting of one in FIG screen mat shown is located,

Figs. 5-8 each show a cross section

through the thickness of the screen mat according to the invention to the different shapes of the openings to show the in the

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Mat can be provided, with a plan view of the opening from the lower part of the mat is also shown _£ and

Pigο 9-11 sections of one according to the invention

_{The screen mat 9} produced is shown in particular in the manner in which the openings are arranged on the upper side of the mat

The screen mat shown in FIGS. 1 and 2 has an essentially rectangular shape and is made from a liquid, castable polyurethane, for example by the company E. I ₀ DuPont de Nemours & Co. under the trade name "Adiprene L 100" is sold, with a hardening agent M.0.CA ₀ in the ratio of 100 ζ 12.5 parts by weight is added. This type of polyurethane was found to be particularly suitable, when cured, to form screen mats that have high abrasion resistance combined with good load-bearing capacity. 22 m wide and the required thickness to accommodate a field of openings, which are generally designated with 2. The openings 2 extend through the thickness of the screen mat and open at one end into the top 3 and at their other end into the bottom 4 of the hat. The openings 2 are arranged in the mat at the required distance from one another and are provided in straight and parallel rows, the cross section in FIG

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The screen mat shown in Figures and 2 has cylindrical openings "so that they have a constant circular cross-section over the entire bead of the screen mat * and in a special" embodiment these openings have a diameter of 2 *> mm and are evenly spaced from one another in such a way that there is a free area of about 50 % in the screen mat

is formed, which are generally denoted by 5 (Fig. 5) and which are duroh in the longitudinal and transverse directions extend the polyurethane of the screen mat and are embedded in this.

Although the openings are shown in FIGS Sieve mat have a cylindrical shape (as can be seen from the enlarged cross section according to FIG. 5), can differently shaped openings may be provided in the screen mat, as shown in FIGS. 6 to 8 the opening 2 is formed with a circular cross-section in the plane of the mat, it has a longitudinal section 6 through part of the thickness of the mat 1, J which longitudinal section extends from the upper side 3 and has a constant cross section, ie cylindrical, while the remaining longitudinal section 7 the opening through the remaining part of the mat thickness is truncated cone:? Or mige shape and sloh outwards widened conically from the length abeohnltt 6 to the Bottom 4 of the mat opening out. In a special embodiment, the truncated cone shape extends Longitudinal section 7 of the opening approximately over half the bead the slebaatte and closes an angle of approximately

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10 ° to the opening in Pig. 7 has a square cross-section in the plane of the mat and has a constant cross-section over the entire bead of the mat. The opening in FIG. 8 has a square cross-section in the plane of the mat, but has a longitudinal section over one! ö rieh extends from the top 3 and has a constant cross-section, while the remaining longitudinal section 9 of the opening widens from the longitudinal section 8 in a conical map-shape to open into the bottom 4 of the hat. The opening according to Figo 8 is designed in a special embodiment so that the frustoconical Ifingsabschnitt 9 extends approximately over half the thickness of Siebeatte 1, while the opposite side walls of the longitudinal section 9 are inclined at an angle cL of approximately 10 °.

As mentioned above, the openings 2 in the Sieve mat 1 advantageously arranged at a distance from one another in straight and parallel rows, like them at A, B and C in Figures 9-11. The rows A, B and Q extend across the width of the Screen mat, the openings in each of these rows can be distributed so that they are straight and parallel Rows of openings in the extension of the sieve mat result, as shown in Fig. 10. When the openings are arranged in longitudinal and transverse rows as shown in Fig. 10, however, it is possible that the raw material to be sieved and moving along the top 3 of the sieve mat in the direction of arrow X. of the continuous webs formed between adjacent openings migrates and thereby not with regard to

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the particle size can be sorted.Bs is therefore preferred if the openings in two adjacent rows (A and B and / or B and C) are offset in relation to each other in the direction of the width, so that a system of openings is formed which is oriented in the direction of the As seen from arrow X, a dense and essentially without gaps (or closed) field of openings forms (Fig. 9 and 11) ο When the raw material is then over the top. 3 of the screen mats to Figo 9 and 11 in the direction of the X moving PJTeiles _t should the material departures g clearly the particle size by at least one opening 2 are sieved ,, TJnter this in mind, and in a preferred embodiment of the distribution of the openings 2, as is shown in Figo 9 and Figo 11 «the openings of the two adjacent rows A and B (and B and C) are arranged so that the centers of the surfaces of two adjacent openings in the upper side 3 in row A (or row C) and the center of an opening in the upper side in row B lie at the corner points of imaginary equilateral triangles on the upper side, which are shown in FIGS. 9 and 11 by broken lines. ,

When producing a screen mat _f as described above with reference to FIGS. 1 »2 and 5 to 11, a negative form 11 (FIGS. 3 and 4) of the screen mat is first produced, which has a field of particle-like projections 12» the size , Shape and arrangement correspond to the openings that are to be formed in the sieve mat »Such a negative mold is used in a horizontally arranged molding box in the form of a rectangular low trough 13, the one

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Has bottom 14 and side walls 14a (Pig * 4). The reinforcing metal rods or bars 5 can be arranged (if provided) so that they are length and width between the Male-like projections 12 extend »with these rods or rods advantageously arranged in this way be (for example, by storage on shoulders in the side walls 14a) »that they are about halfway Height of the male-like projections 12 are located at right angles relative to the bottom 14 of the molding box protrude from the top ο There is now liquid polyurethane around the Field of partrizen-like projections 12 (and - if present - poured around the reinforcement structure 5) to a level coincident with the top of the Partrizen-like projections collapse “The cast Polyurethane is now cured, either by self-curing or by accelerated curing under Influence of heat, whereupon the cast screen mat of the male-like protrusions are removed

The negative form 11 of the screen mat is made as a one-piece unit by casting from a positive master model that corresponds to the screen mat to be produced can be generated by pouring liquid polyurethane over the positive master model (which is coated with a release agent), whereupon the cast polyurethane is cured and the hardened polyurethane is removed from the master model to expose the male-like projections formed by the liquid polyurethane penetrated into the openings in the positive master model ₀

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In a preferred method for producing a negative mold similar to that shown in FIG 1.85 in length and 1.22 m in width and of the same thickness as the sieve mat to be cast, through-bores are drilled which have the same size and the same spacing as the opening parts 6 of the sieve mat to be cast (for example round bores with a diameter of 25 mm _s which maintain a uniform distance from one another, so that there is a free area in the polypropylene sheet of approximately 50 % ). These holes are then countersunk from the opposite side so that they match the opening sections 7 to a depth that corresponds to about half the thickness of the polypropylene plate and at an included angle (equal to the angle oc) of approximately 10 °. An approximately 3 mm thick polypropylene support plate is then fastened flat against the drilled plate, preferably by means of screws, so that the ends of the holes with the larger diameter are on the side of the polypropylene plate provided with the holes on the side facing away from the support plate bonded polypropylene sheets are then placed on a flat horizontal surface with the open ends of the bores facing up. Now a frame made of metal plates or metal sheets is assembled on the polypropylene plate provided with holes in such a way that a rectangular edge is created above the surface of the polypropylene plate provided with holes. Liquid

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Polyurethane of the above-described mixture of the materials "Adiprene L 100" and "HoOoO.A." will now poured into the rectangular frame from where it penetrates into the bores, wherein such liquid polyurethane is filled until it is inside the frame a depth of approximately 10 mm above the surface the drilled polypropylene plate has reached o The take has been treated with a silicone-based release agent »to ensure that it is close can be easily removed as the cast polyurethane cures.

The frame described may be adjustable to enclose a variable, but predetermined, area on the surface of the drilled polypropylene sheet. If necessary, special bores in the polypropylene plate within the area enclosed by the frame on the upper side of the plate provided with bores by adhesive strips or the like correspond to the areas covered; demnaoh we full Materialdioke the polyurethane also obtained at the locations in the finished molded screen mat »to these covered bores corresponding _o example, may be erwünsoht of the polyurethane in the screening mat to the edges of the mat adjacent sites the full material thickness to their attachment to a Vibration frame "u facilitate",

Haohdem the polyurethane in those enclosed by the frame Area has been poured, the assembly is heated to cure the polyurethane. Then the

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2 Ί Ο 2 6 1 7

Frame removed or dismantled , the stuta plate made of polypropylene removed from the drilled polypropylene plate and any burrs on the polyurethane cast removed Pie made of polyurethane is now removed from the drilled polypropylene plate and is ready to produce a polyurethane screen mat, as described below «

The hegative form 11 made of polyurethane is marked with " treated with a silicone-based release agent and placed on a flat horizontal table or flat base plate 14 placed »in such a way that the male-like projections 12 stand upwards from the table (Fig · 4) ο Metallic side plates 14a treated in the same way with a release agent are now on both longitudinal sides and clamped both broad sides of the negative mold to lie firmly on your hand and form the molding box 15 au. The side panels 14a of the flask are suitable that to carry metallic reinforcing rods or bars 5 so that they can be molded into the screen mat «. Such reinforcing rods or bars are sandblasted, degreased (e.g. with Triohlor) and with a J Binder treated (for example a material sold under the name "Thixon XAB - 1153" is).

The liquid polyurethane is now poured into the molding box, which is then heated to cure the polyurethane. The metal side plates of the molding box are now removed, the polyurethane screen mat 1 removed from the polyurethane Hegativforra 11 and the Polyurethane rate that may change during the

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Pouring on the sieve mat * will be carried out in a cleaning and dressing operation distant

As an alternative to heating the molding box and the cast polyurethane sieve mat, the polyurethane cast in the molding box can also be allowed to cure at ambient temperature ₉ whereupon the hardened sieve mat is removed from the molding box and hardened to the end in an oven by further heating.

Expectations"

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Claims (1)

Claims j 1α screen mat «characterized in that it duroh Semolina produced from liquid polyurethane is to 2ο sieve mat according to claim 1 _e, characterized in that at least some of the openings in the plane of the sieve mat and over its entire thickness have the same constant cross section. 5. Screen mat according to one of claims 1 or 2 _e, characterized in that the opening cross-sections of at least some of the openings (2) on the top of the screen mat are smaller than the opening cross-sections of these openings on the underside of the screen mat, where these openings after crossing the ' Opening out the sieve mat 4ο sieve mat according to claim 5 _S, characterized in that at least some of the openings widen evenly outwards in the shape of a truncated cone over the entire cross section of the mat from top to bottom 5o sieve mat according to claim 3, characterized in that that at least some of the openings (2) in two longitudinal sections (6, 8, 7, 9), the first section (6, 8), which extends from the top of the screen mat, being constant in the screen mat plane Cross-section possesses, while the second section (7, 9), which is duroh the remaining part of the screen mat thickness extends, extends outward in sighting on the underside of the screen mat. 6ο sieve mat according to one of the preceding claims, characterized in that the cast polyurethane has a reinforcement structure embedded therein (5) is provided. 109831/1532 - 22 - 7o sieve mat according to claim 6, characterized by » that the reinforcement construction (5) comprised a grid 3. A method of making a screen mat, characterized by pouring liquid polyurethane around a field patrix-like projections "which in their size" form and arrangement correspond to the openings that are to be formed in a screen mat that the cast Polyurethane is hardened and the hardened sieve » Matt is removed from the patrise-like protrusions. 9ο method according to claim 8, characterized by that liquid polyurethane is poured into a substantially horizontally arranged molding box, the the male-like projections carries, such that these projections relative to a substantially horizontal Stand the bottom of the molding box according to Olsen and form a negative shape of the sieve mat 10 "Procedure naoh one of claims 8 or 9" daduroh characterized in that the male projections are coated with a release agent before the polyurethane is potted in order to remove the cast screen mat from the male-like projections after hardening to facilitate. 11. The method naoh one of claims 8 to 10, characterized in that before the casting of the polyurethane a reinforcement structure for the male protrusions is arranged adjacent, such that the reinforcement structure is within the cast and hardened screen mat is embedded. - 23 - 09831/1532 12. Method according to one of claims 8 to 11, characterized in that the male-like projections are made from polyurethane by pouring polyurethane into a preformed positive original form which corresponds to the sieve mat to be cast, so that the polyurethane poured into the positive original form comes out «Cured and the cured polyurethane is removed from the patrlzen-like projections of the positive original form _{9 to} obtain a negative form of the screening mat. 13 »The method according to claim 12, characterized in that that a positive original form made of wood »metal or plastic is produced by machining« 14o method according to claim 13 »characterized in that that the positive original form is formed from a polypropylene plate 15o method according to any one of claims 12 to 14> characterized in that the preformed positive original shape on the surface that comes into contact with polyurethane, which is poured into the positive original form of the screen mat, is coated with a release agent in order to remove the J the cast hegative form made of polyurethane from the positive To facilitate the original form 16 «Method according to one of claims 8 to 11, characterized in that characterized in that on a wood, metal or plastic plate by machining the patrix-like Projections are generated when these projections Openings of rectangular cross-section in the plane of the mat one produced by polyurethane molding around the projections Screen mat correspond » - 24 - 109831/1532 Method according to claim 16, characterized in that the male-like projections are produced by machining a polypropylene plate _{or the like} 18ο Method according to one of Claims 16 or 17 _9, characterized in that the wood, metal or plastic plate is coated with a release agent on that surface which comes into contact with poly urethane which is cast around the male-like projections, to facilitate the removal of the cast sieve mat from the wood, metal or plastic plate « 10 9 8 3 1/15 3 2