US2229490A - Method of spraying adhesives - Google Patents

Description

Jan. 1941- R. c. BENNER ETAL 2,

' us'mon 0F srnmm ADHESIVES Filed Ma 2a, 1936 INVENTOR.

RAYMOND C. BENNER ROMIE L. MELTON BY HENRY P. KIRGHNER ATTORNEY.

Patented Jan. 21, 1941 2,229,490 METHOD OF SPRAYING ADHESIVES Raymond C. Benner, Romie L.

P. Kirchner, Niagara Falls, mesne assignments, to The pany, Niagara Falls, Delaware Melton, and Henry N. Y., assignors, by Carborund'im Com- N. Y., a corporation of Application May 26, 1936, Serial No. 81,910

3 Claims.

This invention relates to a method of treating granular coated material and particularly to a process for applying a sizing coat of adhesive such as animal or hide glue to sheet material which has been coated with abrasive granules.

Sheet abrasive material such as paper or cloth is usually formed by depositing abrasive granules or particles on an adhesively coated surface of such material. The web of sheet material is first coated with an adhesive such as glue by any well known means such as applying a layer of glue to the web material by means of a roll. Earlier methods of spreading the abrasive grain over the adhesive surface usually consisted of moving the web along below a hopper filled with abrasive grain from which the abrasive particles were permitted to fall onto the adhesive surface of the web. The falling abrasive grain in such a method is caused to be spread evenly over the surface of the web by moving the same at a uniform rate and substantially in the direction of the surface thereof below the hopper. The abrasive particles spread along the adhesive coated surface of the web while evenly distributed by such a method were nevertheless haphazardly arranged with respect to each other. That is to say the abrasive grains were not oriented with respect to each other or the web material. Abrasive granules are often of an elongated shape and the elongated grain, by permitting the same to fall onto the adhesive, generally come to rest therein with the major axis thereof in a plane along that of the flat surface of the web material. Abrasive paper or cloth formed in such a manner presented no real problem in applying a sizing coat to the granular surface. That is to say the haphazardly arranged particles were easily bonded to the sheet material by a simple method of applying the sizing adhesive thereto. The additional or sizing coat of adhesive being usually applied to the abrasive surface by means of a roll partially immersed in a glue container from which the glue is carried to the abrasive coated'web.

More recently, however, methods have been devised whereby the abrasive particles are arranged in an oriented fashion with respect to each other and with respect to the sheet backing material. Elongated abrasive grains by such methods are usually projected upwardly in an oriented manner into engagement with a layer of adhesive and carried by the under side of a moving sheet or web. The abrasive grains, by reason of their orientation, engage the adhesive layer in such a manner that only the end portions thereof are embedded in the adhesive layer.

The sheet or web material is generally maintained in the upside down position until the adhesive coat obtains a preliminary set and the abrasive particles are thus temporarily prevented from moving or losing the oriented arrangement thereof along the web surface.

It will be appreciated that such an arrangement of abrasive granules requires an unusually well applied sizing coat of an adhesive since only the end portions of the abrasive particles'are embedded in the first layer of adhesive and therefore a relatively insecure anchorage of the abrasive particles is provided. It will also be apparent that the customary method of applying the sizing coat by means of a roll can not be advantageously employed since the oriented abrasive particles temporarily aflixed to the sheet material would be caused to move by the engaging roll and the oriented arrangement thereof would be destroyed. 20

An object of the present invention is, therefore, to provide a method of applying a sizing coat to sheet material carrying abrasive granules which will not disturb the previous arrangement of the abrasive particles.-

Another object of the invention is to devise a process of applying a sizin coat to abrasive surfaces whereby only the base portion of the abrasive particles will be coated to securely afiix the same to a sheet backing material, leaving the uppermost end portions substantially free of the sizing material. V

Methods of applying a sizing coat of adhesive such as glue wherein the same is-applied without rolling the granular surface have been devised in the past. Such methods usually include a nozzle arrangement adjacent the granular surface into which adhesive is forced under constant pressure and sprayed along the abrasive surface. The spraying method has been successfully employed when used in connection with an adhesive having a relatively constant viscosity. The spraying method provides the desired results of coating the base portion of the abrasive granules and furnishes the adhesive to the abrasive granules in such a manner as to improve the anchorage thereof without coating the upper portion or cutting edge. This sprayingprocess is described in considerable detail in Patent No. 2,201,194, issued May 21, 1940, to Romie L. Melton, Raymond C. Benner and Henry P. Kirchner.

The use of animal glue and particularly hide lue as a sizing coat for abrasive surfaces has been recognized as particularly desirable in providing a good anchorage for the abrasive particles 55 and the constant pressure method of moving such adhesive to a nozzle and spraying as a sizing substance has not been satisfactory. The difliculty in spraying such sizing material arises from the peculiar variations in the viscosity of the glue. The imperfect fluid nature of such a glue is highly susceptible to changes resulting from a wide variety of causes and conditions. It has been found that the best working fluid condition of glue is obtained by maintaining the same at a temperature of approximately 146 F. In one instance the glue maintained at such a temperature appears to have a certain viscosity and when tested within a relatively short period of time has been found to present a wide difference in the tendency thereof to resist movement. It appears therefore that time alone will cause the fluid condition of animal or hide glue to change and this probably results from such causes as hydrolysis or possibly as a result of bacterial decomposition. The addition of new glue of substantially the same constituency to a partially consumed container of hide glue has been found to materially alter the viscosity of the entire batch. Small variations in the manner in which the fluid glue is mechanicallyv agitated is known-to cause the fluid nature of the otherwise unchanged glue to be altered. For example, the precarious nature of hide glue to become less fluid during the normal course of manipulation renders the use of compressed air or gas at a constant pressure impractical as a means for feeding a nozzle in spraying a sizing coat of such glue onto an abrasive surface since the conventional spraying apparatus often becomes clogged by the coagulating glue. The passages of the spraying apparatus often become restricted by the congealing of less viscous glue and an irregular application of the sizing coat results from the use of a constant pressure as a means of projecting the glue onto the abrasive coated material.

On the other hand, the glue may become more fluid as a result of one or more of the above indicated causes. A constant pressure feed for such less viscous adhesive will therefore move an excessive amount of glue to the spray nozzles and onto the surface to be coated.

It is therefore a further object of the present invention to provide means for projecting a stream of an adhesive such as hide glue onto an abrasive surface by a method which will furnish a uniform sizing coat irrespective of variations in the viscosity of the adhesive.

In the accompanying drawing,

Figure 1 is a diagrammatic view of apparatus for carrying out a method of spraying granular surfaces with hide glue.

Figure 2 is an enlarged sectional view of a portion of an abrasive coated web before the adhesive sizing coat has been applied.

Figure 3 is an enlarged section through a fragment of an abrasive coated web after the sizing application.

Referring to the drawing, there is shown generally at H) a number of festoons of abrasive coated web material arranged in a position to permit a proper drying or setting of the adhesive which is used to provide a preliminary anchorage for the abrasive granules previously attached to and carried by a web H. The abrasive granules l2 shown in Figure 2 are attached to the flexible sheet or web by means of a layer of adhesive M. The abrasive granules are shown to be oriented to more clearly illustrate the hereinafter described method of applying the sizing coat.

However, it will be appreciated that the present invention provides various advantages in applying the sizing coat of adhesive to any type of abrasive coated sheet material. The abrasive granules |-2 may be applied to the adhesive layer M by any suitable method and the adhesive layer M may be allowed to obtain a set by storing the abrasive coated web on drying racks in a festooned fashion as indicated generally at H].

After the adhesive layer M has been properly cured or set to temporarily amx the abrasive granules l2 to the backing material II, the web may be moved from the racks and supported in a horizontal manner by means of a plurality of suction rolls l6 and H. The rolls l6 and I! should be rotated at a constant rate of speed to move the abrasive surfaces of the web H beneath the nozzles l8 and |9 in such a manner as to permit a uniform sizing coat of adhesive to be sprayed.

thereon.

Adhesives, such as hide glue, which must be applied in a heated condition may be maintained in a desirable fluid state in a receptacle 2| by providing a heating jacket around the outer wall 22 into which hot water or steam may be injected through a supply line 23 to maintain the temperature of the glue contained in the receptacle 2| at approximately 146 F. An agitating device 24 is also provided and arranged to be rotated within the glue receptacle 2| so that the glue may be maintained at an even temperature and constituency throughout the entire bulk thereof.

The liquid adhesive is fed from the receptacle 2| to a constant volume pump 26 by means of pipes 21 and 28. The pump 26 is of the type which when operated at a particular speed will deliver a constant or uniform volume of liquid at the discharge end thereof. The discharge port of the pump 26 is connected. to the nozzle i8 by means of a. pipe or flexible tube 29. It is important that a pump of the constant volume character be included in the adhesive supplying line so that the fluid adhesive will be furnished to the nozzle l8 at a constant rate irrespective of the changes in the viscosity of the fluid adhesive. For instance, if the nozzle or the piping arrangement offers more resistance to the flow of more imperfect fluid adhesive, the pressure from the discharge port of the pump will build up by reason of the recurring equal volume pulsations and the more viscous adhesive will nevertheless be forced from the nozzle it) at a uniform rate.

Any number of nozzles may be arranged along the surface of the web H to properly spray the sizing coat onto the abrasive surface. It will be necessary in each case to provide a constant volume pump to supply the liquid adhesive to each additional spraying nozzle. Such'a pump 3| is therefore employed to move the liquid adhesive from the receptacle 2| through the pipe or flexible tube 32 and into the nozzle IS.

The pumps 26 and 3| may be driven by any suitable means such as by a variable speedmotor 33 appropriately belted to the two pumps. The speed of the driving device should be controllable in order that the volume of adhesive supplied to the spraying equipment may be regulated. That is to say the quantity of adhesive delivered by the pump will be constant for a given speed by reason of the structure of the pump but it may be desirable to adjust and fix the speed of the pump by means of the variable speed motor to control the rate of the constant delivery and therefore control the amount of adhesive delivered to the spraying nozzle and accordingly the extent of the sizing coat. It will be appreciated that the thickness or extent of the sizing coat may also be controlled by adjusting the speed of the moving web ll. After the speed of the pump or pumps have been adjusted to provide the proper volume of adhesive to be supplied to the nozzle or nozzles, the speed of the motor 33 should be fixed and the speed of the rotating rolls I6 and .l'! should be adjusted and fixed at a uniform rate in order that the sizing coat may be evenly and uniformly depositedalong the abrasive surface of the web,

In order that the liquid adhesive may be properly dispersed or atomized during the spraying thereof, a gaseous medium under pressure is supplied to the nozzle or nozzles by means of pipe 35. With the particular spray nozzles used, it has been found that steam at a pressure of approximately 130 lbs/sq. in. is particularly adaptable for the purpose of atomizing hide glue. Compressed air has a tendency to cause hide or animal glue to set or become chilled before it reaches the surface being coated and not be deposited in a suitably fluid condition. The use of moist steam eliminates this difiiculty since the moisture in the steam prevents evaporation of the water from the liquid glue and steam heat prevents cooling and jelling of the glue during the spraying thereof. Furthermore, the steam serves as an atomizing agent for breaking the liquid into droplets and carrying same into engagement with the base portion of the abrasive granules.

The abrasive coated web ll, after passing the spraying equipment, is coated with a sizing layer of adhesive as indicated in Figure 3, It is to be noted that the spraying of adhesive onto the abrasive surface drives the liquid adhesive to the base portion of the abrasive granules leaving the tips or cutting portion thereof free of the adhesive coating. The spraying method in addition to rendering the cutting portion v of abrasive granules uncoated also forces the adhesive to a position at the base of the particles to firmly bond the same to the web backing material. The adhesive is projected from the nozzles at a. rather high velocity so that the sizing coat of adhesive 36 is forced between the abrasive granules l2 in such a manner that the layer is considerably thinner at a midpoint between the grains and the force of the sprayed droplets causes the glue to extend upwardly along the granules to further provide an im proved anchorage thereof. i

While the present method of employing a constant volume pump has been described as being particularly advantageous in spraying glue onto a granular coated surface, it will nevertheless be apparent that other liquid adhesives which are subject to changes in viscosity such as heat hardenableor phenolic resins are equally adaptable to the present method.

We claim:

1. The method of applying a layer of glue to an abrasive coated web comprising the steps of preparing a heated solution of animal glue, said glue being of such character that the viscosity changes appreciably under normal conditions, continually pumping a constant volume of said glue to a spray nozzle irrespective of any changes "in viscosity thereof, atomizing and projecting a uniform layer of a predetermined quantity of said glue onto the abrasive coated web.

2. The method of applying a. layer of sizing adhesive to an abrasive coated web comprising the steps of preparing a liquid adhesive, said adhesive being of a type which does not re main constant as to viscosity, continually pumping a constant volume of said adhesive to a spray nozzle irrespective of any changes in' viscosity and spraying a uniform layer of said adhesive onto the abrasive coated surface.

3. The method of manufacturing coated materials which comprises bringing an adhesive to a fluid state, said adhesive being of such character that the viscosity changes appreciably under normal conditions, continually moving a constant volume of the fluid adhesive to a nozzle irrespective of any changes in viscosity and applying a uniform layer of said adhesive to the surface being coated.

- RAYMOND C. BENNER.

ROMJE L. MELTON.

HENRY P. KIRCHNER.

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