Apparatus for applying liquid to fabric
United States Patent 2191827

This invention relates to methods and apparatus for applying sizing material to a layer of abrasive granules on a fabric backing. Heretofore in the production of abrasive coated fabric, it has been the practice to apply a surface coating of suitable adhesive to the fabric or web and then apply...

Benner, Raymond C.
Melton, Romie L.
Application Number:
Publication Date:
Filing Date:
Primary Class:
Other Classes:
51/295, 101/DIG.37, 118/309, 118/630, 118/634, 118/638, 159/4.07, 159/DIG.1, 427/222
International Classes:
View Patent Images:


This invention relates to methods and apparatus for applying sizing material to a layer of abrasive granules on a fabric backing.

Heretofore in the production of abrasive coated fabric, it has been the practice to apply a surface coating of suitable adhesive to the fabric or web and then apply a layer of abrasive granules on the adhesive coating by suitable means.

By this method the individual grains are retained on the surface of the web by the adhesive coating and after the adhesive has set, a second; or sizing, coating of adhesive is customarily applied over the granular layer in order to more firmly secure the granules to the web. This sizing coat18 ing of adhesive has been applied heretofore by passing the web carrying the layer of granules between two rolls, one carrying liquid adhesive material; the web being positioned to contact the abrasive coating with the roll carrying the adhesive material.

This method of sizing is detrimental to the production of'a good abrasive surface. The pressure of the roll necessary to apply the sizing to the abrasive granules tends to flatten out any upSstanding grains and generally turns grains which present sharp edges or points so that they present flat surfaces. This is particularly true and especially detrimental in the production of oriented abrasive fabric wherein a substantial proportion s of the abrasive granules are upstanding and present points. Furthermore the use of the roller tends to apply the sizing on the tops of the abrasive granules and not into the spaces between the granules.

SThe present invention contemplates forming a mist of charged droplets of liquid sizing material and electrostatically projecting the droplets onto the abrasive surface of abrasive coated fabric by the action of an oppositely charged body. This may be done by establishing a high potential electrostatic field, passing a stream of charged droplets of liquid sizing material into the field whereby they are impelled in the direction of the fleld, and moving a sheet of abrasive coated fab4 ric into the path of the thus electrostatically impelled droplets whereby they impinge on the abrasive coating of the fabric. The fabric may be positioned with respect to the electrodes which produce the field whereby it is between the stream 60 of charged droplets and the oppositely charged electrode, with the side bearing the abrasive coating toward the stream, or mist, of droplets. Alternatively, the fabric may be charged electrostatically and a stream of droplets bearing U charges opposite in polarity to the fabric may be passed around or across one or both sides of the fabric as is desired, to project the charged droplets onto the fabric.

The charge may be produced on the droplets by impressing a high potential of appropriate polarity on the atomizing or other forming means.

The droplets may then be subjected to the influence of an oppositely charged body of substantially the same potential and thereby projecting onto the abrasive surface. The charge may also be produced by passing droplets, which may bear positive charges, near a negatively charged body of such condition and potential, that the air surrounding it is ionized. The ionized air will neutralize the positive charge, if any, on the droplets and produce negative charges on them. This will cause them to be repelled by the negatively charged body and they may be acted upon by a positively charged body to project them on an abrasive surface. In applying a sizing coating to an abrasive coated web according to the invention, the web may be translated horizontally over a suitable electrode, for example a horizontally disposed plate which serves as one electrode of a highpotential electrostatic field. A mist or stream of droplets of liquid adhesive material each bearing a charge opposite in polarity to the said electrode may be passed over the web whereby they enter the electrostatic field and are impelled toward the web. The other electrode of the field is arranged so that the resulting electrostatic field is substantially vertical at the web with the lines of force passing substantially vertically through the horizontal web. Due to the direction and high potential of the field the droplets travel in it with increasing velocity in the direction of the web and impinge on the web substantially at right angles to the same and with great force. Due to the direction and velocity of impact of the droplets and the continuing pull of the electrostatic field, the droplets travel down the sides of the abrasive granules and come to rest in the spaces between the said granules. In this position they are most helpful in anchoring the granules on the web and least injurious to the abrasive character of the finished abrasive coated fabric.

The invention will now be further described with reference to the accompanying drawing. It bu is obvious and is to be understood however that the drawing is illustrative only and is not to be construed as limiting the invention.

In the drawingFigure 1 is a longitudinal vertical section along 65 line I-I of an apparatus embodying the invention; and Figure 2 is a transverse vertical section along lines II-II of Figure 1.

Referring to the drawing, a strip of fabric I, with a layer 2, of abrasive granules is passed from left to right over an electrode 3 which may be in the form of a metallic plate, preferably of substantially the same width as the fabric 1, as shown in Figure 2. Atomizing means 4, provided with a pipe 5 to conduct liquid and atomizing medium to the atomizing means 4, is placed at one side of the electrode 3 and functions to provide a mist or stream of droplets of liquid to be applied to the said fabric. Walls 6 are provided to enclose the space containing the electrode 3 and the atomizing means 4 and provide a substantially completely enclosed chamber 7 for the treatment of the fabric I. Longitudinal slits 8 and 9 are provided in each end of the chamber 1 to permit the entrance and exit of the fabric I.

The electrode 3 is embedded or surrounded on all sides by poorly conducting material 10 of wood or resin. The thus sheathed electrode 3 is spaced from the walls 6 of chamber 7 on all sides and the space between the electrodes and the wall 6 is filled with hard rubber 11. The electrode 3 and its poorly conducting sheath 10 and the hard rubber II and the walls 6 completely enclose the chamber 1 set forth except for openings 8 and 9 which permit the fabric I to enter and leave the chamber 1. The walls 6 are preferably of metal and a metallic plate 12 is located in the upper portion of the chamber 7 adjacent the walls 6 35 along the sides of the chamber 7 and spaced from the walls at the ends so as to provide means for circulating the droplets produced by atomizing means 4 from left to right (Fig. 1) around the plate 12 and back to the place of atomization. 40 Rolls 15 and 16, are provided to properly position the fabric I for passage through chamber 7. The walls 6, of the chamber 7 are arranged to provide'a space for the atomizing means 4 whereby the latter is not directly above a portion of the 45 fabric I while the latter is in the chamber 7.

Portion 17 of the w.lls 6 is inclined from right to left (Fig. 1) so that any liquid which drips down from the atomizing means 4 will not reach the fabric 1. Closable means 18 are provided to draw 50 off any liquid which may thus collect at the left hand end of portion 17. Slit 9 has connected to it an elongated rectangular case 13 which extends about the strip I for a suitable distance from the end of chamber 7. Means 14 are pro55 vided connected with case 13 for applying suction to case 13. A heavily insulated electric cable 19 is provided extending through the poorly conducting sheath 10 to provide electrical connection with the electrode 3. Means not shown are 60 provided for establishing a high-potential electrostatic field between the electrode 3 on the one hand and atomizing means 4, walls 6 and plate 12 on the other hand. In order tb simplify requirements for insulation the electrode 3 is pro65 vided with the negative charge by connecting it to the negative side of the source of potential.

The positive side of the source of potential is ordinarily grounded. An electrostatic field may therefore be provided here by merely grounding 70 the atomizing means 4, the walls 6 and the plate 12.

The electrostatic field thus set up will be one of non-uniform intensity, depending upon the distance between the electrode 3 and the various 75 oppositely charged elemerits, In the apparatus illustrated the field will be most intense between the electrode 3 and that part of plate 12 which is directly above electrode 3, with the result that the field will extend through the fabric I, substantially vertically at the parts which are adjacent electrode 3. There will also be a field between the atomizing means 4 and electrode 3, and the wall 6 and electrode 3, but as they are not as close to electrode 3 as plate 12, the fields will not be as intense. When the droplets of liquid are formed by atomizing means 4 they will be charged positively with respect to electrode 3 and will be subject to three forces. Depending upon the type of atomizing means used the atomizing force will tend to drive the droplets more or less horizontally toward the strong field between electrode 3 and plate 12. The force of gravity,will tend to pull the droplets down and the lines of force between atomizing means 4 and electrode 3 will influence the droplets to follow their direction. The first of these forces however, will be stronger at first than the latter two so that the droplets will travel toward the strong field between electrode 3 and plate 13 in a slightly downward course. Upon entering the strong electrostatic field they will be affected by it and drawn toward electrode 3 so that their course of travel will turn in the direction of the fabric I and they will approach fabric I with increasing velocity. The path of travel of the droplets from the atomizing means 4 to the fabric I will therefore be curved but they will impinge on the fabric I substantially vertically due to the greater attractive force of the electrostatic field between electrode 3 and plate 12. 3s.

As the upper surface of the fabric I is provided with a layer of abrasive granules, the vertical impact of the droplets and the continuing pull of electrode 3 will cause them to travel down the sides of the granules and come to rest at the base of the granules on the fabric I with the result that substantially all the liquid applied will be around the base of the granules rather than on top of them. Due to the fact that the droplets, the plate 12, the atomizing device 4, walls 6 and the fabric I, are of the same polarity, the droplets will repell each other and thus will not tend to agglomerate in midair and will be repelled from all parts of the apparatus except that portion of fabric I which is immediately above electrode 3 or those portions of the fabric which are just beyond the end of electrode 3, but still within the field between electrode 3 and the other parts of the apparatus. Those droplets which are carried by the flow of the gaseous medium from the atomizing means 4, past the electrode 3, will be carried around plate 12, as indicated by the arrows, and back to the point of atomization where they will join the stream of droplets produced there and passing over electrode 3. The pressure set up by the introduction of atomizing medium into chamber 7 will cause gaseous medium to tend to pass out through slits 8 and 9. The velocity of the stream produced by the atomizing means 4 will tend to neutralize the pressure at slit 8 with the result that substantially all the excess gaseous medium will be withdrawn through slit 9. When air is used as the atomizing medium and glue is used as the sizing material, the excess pressure may be relieved directly into the open air. However when other materials such as resin solutions are used as the sizing material, it may be expedient to recover the solvent used for the resin, and evaporated in chamber 7. In such case the elon- 76 gated case II is provided, connected to opening 9, and exhaust means 14 are provided to draw off all the gaseous medium passing out of chamber 7 through opening 9, to suitable solvent re6 covery apparatus. The suction on means 14 may be so adjusted with relation to the pressure in chamber 1 to maintain the pressure at the outer end of case 13 at atmospheric pressure.

The potential of the electfostatic field used may be any suitable value but It will be found that 30,000-75,000 volts are necessary to produce the best results. The source of potential may produce a continuous unidirectional current, an intermittent unidirectional current, or a rectified alternating current.

The polarity of the charges produced on the droplet may be negative or positive according to the location of the electrodes of the electrostatic field. The droplets should be opposite in polarity to the electrode lying on the opposite side of the fabric to be coated. In the drawing the droplets are illustrated as being charged positively, with electrode 3 carrying a negative charge. This is the simplest arrangement since the negative electrode is the one which should be heavily insulated. The atomizing means 4, the wall 6 and the plate 12 must be charged at the same polarity in order to provide uniform distribution of the droplets and prevent their being deposited on the wall. The area of the electrode 3 is considerably smaller in this arrangement than the opposite electrode, and is therefore, much easier to suitably insulate. This arrangement is only illustrative however and the polarity of the electrodes may be reversed with equal efficiency of operation of the apparatus.

The sheath about the high potential electrode 3 should be poorly conducting so that not enough current can flow along or through it to cause arcing between the electrodes but should be sufficiently conducting to allow a small leakage current to supply charges to the droplets so that they may be impelled toward the negative electrode and the fabric.

The expression "poorly conducting material" is used to distinguish between such materials as metals, carbon and the like which are relatively good conductors of electricity on the one hand, and highly insulating materials such as glass, hard rubber, varnished cambric or the like which are such good insulators at the voltages used herein that the leakage current which flows through them is insufficient to charge the droplets sufficiently to cause them to be propelled toward the fabric.

As such "poorly conducting material" it has been found that ordinary dry knot-free wood is satisfactory. While dry wood is so poorly conducting that it will not carry enough current to permit arcing between the electrodes, it is conductive enough for the purposes of the invention.

Other materials may be employed which are ordinarily classified as insulators but are in fact poor conductors of high tension electric current. Such materials include fibrous material bonded with an insulating resin. Such fibrous material should not have insulating laminations but the fibers should furnish poor electrical conducting paths from the lead in wire to the negative electrode surfaces.

The present invention provides a method and apparatus for applying a sizing coating to an abrasive coated fabric which obviates the objections to previous methods set forth above. By means of the present invention, the liquid sizing material is applied to the abrasive coating with a minimum deposition of liquid elsewhere than on the abrasive coating. Furthermore substantially all the liquid applied will be at the base of the granules where it will be most effective in anchoring the granules to the fabric and least injurious to the abrasive qualities of the finished product. Substantially all of the liquid used is applied to the fabric, and it is uniformly applied, due to the fact that the droplets are of the same polarity and therefore repel each other with the same force. This will cause them to spread out above the surface to be coated and when drawn toward that surface they will be substantially evenly spaced from each other with resuiting even deposition of liquid on the fabric.

The invention also provides for producing the mist or stream of charged droplets at one side of the place of deposition and passing the stream into the zone of action adjacent the place of deposition. In this way it is possible to carry away the inevitable drippings from the atomizing apparatus and prevent them from reaching the fabric being coated. The present invention also provides that each droplet is travelling at a maximum speed at the point of Impact with the surface to be coated. This is of importance when sizing abrasive coated fabric because it assists in placing the liquid at the base of the granules of abrasive material. The increasing velocity of the droplets provided for herein is in contradistinction to the speed of droplets produced by ordinary spraying methods wherein the velocity is at a maximum at the point of atomization of the droplets and decreases to a minimum at the point of impact.

The present invention therefore provides more efficient and economical use of sizing material and greater strength and better abrasive action by the resulting product. The method and apparatus of the present invention has been described with reference to specific embodiments but it will be understood that the invention is capable of other embodiments and is broad enough in scope to include such other embodiments and is limited only by the following claims.

We claim: 1. Apparatus for applying a liquid sizing material to an abrasive coated web, comprising spaced-apart electrodes, one of said electrodes being covered with a poorly conducting material, which permits a leakage current to flow therethrough but is of sufficient resistance to prevent arcing or spark-over between said electrodes, means for, applying a high electrical potential difference between said electrodes to produce an electrostatic field therebetween, means for passing an abrasive coated web between said electrodes, means for introducing finely divided droplets of liquid sizing material into the space between the abrasive coated side of said web and one of said electrodes, said apparatus being adapted to electrostatically propel the liquid droplets into engagement with the abrasive coated surface of the web.

2. An apparatus for sizing an abrasive coating on a web backing, comprising means to translate horizontally a web backing material having the upper side thereof coated with abrasive partides, oppositely charged electrodes arranged at a point in the travel of the said web to produce a substantially vertical high potential electrostatic field extending through the said coated web, one of said electrodes being covered with a poorly conducting material which permits a leakage current to flow therethrough, but is of sufficient resistance to prevent arcing or sparkover between said electrodes, means for producing a stream of atomized droplets of liquid sizing material, and means for passing said stream into the said field above the said abrasive coated web, said apparatus being adapted to electrically charge said droplets and electrostatically propel them against the upwardly facing surface of the abrasive coated web.