US2225877A - Method and apparatus for manufacturing granular coated webs - Google Patents

Description

24, 19 0 R... MELTQN M. 2,225,877

METHOD AND APPARATUS FOR MANUFACTURING GRANULAR COATED WEBS Filed Sept.- 22, 1939 2 Sheets-Sheet l INVENTORS. ROMIE L MELTON RAYMOND c. BENNER By HENRY P. KHQCHNER ATTORNEY.

Dec. 24, 1940. R. L. MELTON ETAL METHOD AND APPARATUS FOR MANUFAQTURING GRANULAR COATED WEBS 2 Sheets-Sheet 2 Filed Sept. 22, 1939 INVENTORS, Rob HE L. MELTON B RAYMOND C. BENNER H EN RY LRCHN ER ATTORNEY.

Patented Dec. 24, 1940 METHOD AND APPARATUS FOR MANUFAC- TURING GRANULAR COATED WEBS Itomie L. Melton, Raymond C. Benner, and Henry P. Kirchner, Niagara Falls, N. Y., assignors to The Carborundum Company, Niagara Falls,

N. Y., a corporation of Delaware Application September 22, 1939, Serial No. 296,132 11 Claims. (01. 91-33) This invention relates to the manufacture of granular coated webs of such material as paper, cloth and the like. More particularly, this invention relates to the application of the siz ing coat of adhesive to abrasive coated webs and the removal of such adhesive from the projecting points of the abrasive granules.

In the usual process, by which coated abrasive materials have been made for many years, it has been customary to coat the backing sheet of paper or cloth with a layer of glue or other suitable adhesive and then apply a layer of abrasive grains to the adhesively coated sheet. After this first layer of adhesive had set, a sec- 0nd or sizing layer of adhesive was applied over the layer of abrasive grains in order to more firmly attach the grains to the web backing. This sizing layer of adhesive was applied by means of a rubber covered roll partially immersed and revolving in a pan of liquid adhesive and contacting with the abrasive coated surface. When this sizing layer dried or set, the adhesive shrunk around the bases of the grains and held them firmly in position.

The quantity of adhesive applied by the glue roll was regulated by varying the pressure of the glue roll against the abrasive coated surface and pressure roll and thereby squeezing the layer of adhesive to a desired thickness.

Thus the layer of sizing adhesive was applied as a sheet or blanket along on top of the layer of abrasive granules. Due to the fluidity of the adhesive and the pressure from the rolls, the adhesive flowed down the sides of the grains and partially filled the space between adjacent grains to more firmly anchor them to the base coating of adhesive. While this process was effective in anchoring the abrasive granules securely in place it was disadvantageous in that the entire surface of the abrasive grains remained covered with a film of adhesive and the sharp projecting points of the grains did not abrade at their maximum efliciency. Furthermore the adhesive coated surface of the granules, which softened by heat, retained particles of abraded material and quickly filled or clogged the spaces between the abrasive granules. This reduced the cutting efliciency of the abrasive and materially reduced its effective life. so The above difficulties were even more pronounced with the recently developed abrasive paper and cloth commonly known as oriented abrasive paper and cloth in which elongated granules of the abrasive grain have been orient- 55 ed with respect to the surface of the backing material, so as to be upstanding therefrom and therefore in a position to afford a maximum cutting or abrading action.

a We have found that the above difficulties of roll sizing can be overcome and the sizing adhesive completely removed from the projecting tips of the abrasive grains by means of a jet or series of jets arranged traversely across the web and adapted to direct a stream or series of streams of high velocity gas against the abrasive coated surface. This gas is suitably heated and/or treated with a solvent of the adhesive so that it will not set or chill the adhesive when directed against the grain tips but will drive the adhesive from the uppermost points of the grains down and around the bases of said grains. Thus the cutting points are freed of the deleterious effect of the adhesive film, a stronger bond is produced at the base of the grains and a greater space is provided between the grains for cutting clearance and the formation of chips during subsequent 'abrading action.

A better understanding of the invention may be obtained by reference to the accompanying drawings, in which:

Figure 1 is an enlarged section through a fragment of the abrasive coated web at one stage of its manufacture;

Figure 2 is a similar section showing a fragment of an abrasive coated web in'which the sizing adhesive has been applied in the usual W y;

Figure 3 is a similar section showing a fragment of an abrasive coated web embodying our invention;

Figure 4 is a similar section showing a fragment of an abrasive coated web embodying an alternative form of our invention;

Figure 5 is a diagrammatic elevation of apparatus for manufacturing abrasive coated materials in accordance with our invention;

Figure 6 is a detailed side elevation of the adhesive applying mechanism shown diagrammatically in Figure 5; and

Figure '7 is a front view of the apparatus shown in Figure 6.

Referring to Figure 3 which illustrates a fragment of an abrasive coated web made in accordance with our invention the reference numeral 2 indicates the web or backing which may be of any of the usual flexible materials such as paper, cloth, vulcanized fiber or a combination of these or other suitable materials. Applied to one face of the web is a base coating 3 of adhesive, such as glue, varnish, silicate or synthetic resin. The particles of abrasive grain 4 are shown in oriented or upstanding position with respect to the backing and are so deposited onto the adhesive base coating I by suitable means not shown in the present application. The sizing layer of adhesive 8 is deposited principally around the base of the upstanding grains 4 1111- ing the bottoms of the valleys and crevices between the adjacent grains. It will be noted that the tops of the grains are free of the sizing adhesive and that the sharp projecting points are in condition for most eflicient abrading. Furthermore the sizing adhesive applied to and built up around the bases of the elongated granules fills any depressions or irregularities in the surface of the individual grains and thereby increases the bonding or supporting action of the adhesive to hold the grains in position during subsequent use of the abrasive material.

Figure 1 shows a granular coated material prior to application of the sizing or reinforcing layer of adhesive. Only the bottoms of the granules 4 are in contact with the base layer of adhesive 3. This gives a very limited and insufficient support to the abrasive granules to maintain them against lateral pressure and grindin stresses when the coated web is used as an abradant. It is necessary therefore to apply additional adhesivearound the bases of the abrasive granules 4 so as to more firmly anchor them to the base coating and web backing material 2.

Figure 2 shows a granular coated web produced by the usual process, in which a blanket of adhesive 5a was applied over the granular coated surface and permitted to flow down between the graips of its own accord. The tips of the granular particles 4 are covered with a film of adhesive indicated by the reference 9. This film of adhesive is very detrimental when the coated material is used for abrasive purposes, since the tips of the grains are capped with the adhesive. In addition to covering the sharp points of the abrasive material, many adhesives soften during actual grinding, causing retention of abraded material and clogging of the spaces between the grains. This renders the abrasive material unfit for further use.

The preferred procedure in manufacturing granular coated webs in accordance with our invention will now be described. The previously coated abrasive material, such as that illustrated by Figure 1, is moved from suitable drying racks (not shown) by means of the suction drum H, passed around the rubber-covered idler rolls l2, l3 and I4, and between the adhesive roll l5 and cooperating pressure roll IS. The rubbercovered adhesive roll I5 is partially immersed and revolves in the liquid adhesive contained in the pan l'l so that a layer of sizing adhesive is applied to the abrasive side of the coated web. The pressure roll i 6 is adiustably supported above the adhesive roll and provided with adjusting means (see Figure 6) whereby the spacing between the rolls may be varied and thereby regulate the quantity or thickness of the layer of adhesive applied to the abrasive side of the coated web.

After passing between the adhesive applying rolls l5 and I6, the coated web is moved past a jet of high velocity gas issuing from the adjustable orifice 3l of the air knife generally indicated by the reference numeral 30. This jet of high velocity gas serves to drive the freshly applied layer of adhesive from the tips of the abrasive grains and cause it to flow down and around the bases of the grains.

The coated web then passes over the suction drum 40 and idler roll 4| to a suitable drying rack, where it is formed in loops by the festooning device 42 and hung on the supporting bars 43 m a drying or curing chamber to fully set the adhesive. After drying or curing, the coated web is taken down from the rack and cut into pieces of various sizes and sold.

Referring now to Figures 6 and 7, the operation of the gas jet will be described in more detail. The adhesive pan I1 is supported by a suitable frame 20, which also supports the adhesive roll IS in such a manner that said roll revolves in a liquid adhesive and applies afiim or layer of said adhesive to the coated web I. The pressure roll [6 is also journaled on the frame 20 and adapted to be adjusted vertically by means of the handwheel 2| and screw-threaded shaft 22. Such vertical adjustment of the pressure roll l6 varies the spacing between the coated web I and the adhesive roll l5 and thereby regulates the thickness of the layer of adhesive applied to the moving web. With a wide spacing between the rolls, a thick layer of adhesive will be applied, and with a close spacing, a relatively thin film of adhesive willbe applied.

The gas jet 30 is mounted on the bearing 23 by a suitable bracket 24 and moves up or down with any vertical adjustment of the pressure roll I8. Thus theadjustment of the jet with respect to the surface of the coated web remains constant regardless of any vertical adjustment of the roll l6. However, the jet is adjustable with respect to the roll l6 and web I and means are provided for both angular and horizontal movement of the jet 30. Cradle supports 25 are suitably mounted in gibs 26 secured to the bracket 24 and adapted to be moved horizontally by means of the small handwheel 21 and screw-threaded shaft 28 which are journaled on the bracket 24 and engage a threaded portion of the base of the said cradle 25.- By loosening the clamping bolt 29, the jet 30 may be tilted by means of the handle 33 to any desired angle so that the impingement of the gas stream against the coated web can be at an angl of thereto or at any desired oblique angle. x

The thickness of the gas stream 3| issuing from the jet 30 may be adjusted by means of the bolts 32 which regulate the orifice opening of the jet 30. This orifice opening is readily adjustable from .002" to approximately .025" and may extend the full width of the web I, or, if desired, a number of such jets may be employed to cover the entire width of the web. It has been found that too thick a stream of gas causes splattering of the adhesive and does not cause the adhesive to fiow down and around the bases of the grains as desired. Moreover, the impact of too thick a jet of high velocity gas will tend to blow over or entirely dislodge the upstanding granular particles on the coated web. We have found that a jet of approximately .005 inch in thickness is satisfactory for most purposes, though with drastic changes in size of granular particles, it may sometimes be necessary to increase or decrease the orifice opening. We have also found that the leading edge of the gas orifice should preferably be spaced from about A; inch to I; of an ably designed jetat' relatively low gas pressures ranging from about 2 to 15 pounds per square inch gage and when an orifice opening of approximately .005 of an inch is employed. The gas velocity, and hence gage pressure, required will, of course, depend upon the character, condition andthickness of the particular adhesive being used. With thick viscous adhesives, a high gas pressure will be required, and with thin or less viscous adhesives, a relatively lower pressure will be required to clear such adhesive from the tips of the granular particles and produce a supporting mound of adhesive around the base of the granules.

We have found the character and composition of the gas stream to be of particular importance in carrying out the method of the present invention. With adhesives that harden by evaporation of a solvent, we find it advisabl to introduce a solvent of said adhesive into the gas to prevent setting of the adhesive before it is cleared away from the tips of the granules or built up around the bases thereof. When using thermoplastic adhesives, we may heat the gas sufliciently to prevent premature chilling and hardening of the adhesive, and with certain adhesives w may add both a solvent and heat to the gas. Hide or animal glue, which falls in the latter classification,

is the adhesive most generally used in the coated abrasive industry and, for this reason, will be discussed in more detail. Such hide glue is applied to the coated web at a temperature of approximately 150 F. and jells very quickly when the temperature drops much below 140 F., or if there is any substantial evaporation of moisture. If the adhesive is permitted to become set or j-elled, it cannot be properly removed from the tips or cutting points of the grains. For this reason it is necessary that the gas stream directed against the coated web be humidified with water vapor, which is a solvent for the glue, and heated to a temperature of 150 F. or above. In actual practice we have found it convenient to use a mixture of heated compressed air and steam. The compressed air is heated to approximately 150 F. by means not shown, and sufficient steam I mixed therewith to saturate the air with water vapor.. It is necessary that the compressed air 'and steam be thoroughly mixed and, for this reason, a separate mixing chamber (not shown in the drawings) is provided. We have found in certain instances that dry steam may be used alone as the gaseous medium, but for most purposes, it is desirable to use a mixture of compressed air and steam.

Certain adhesives, such as varnishes and synthetic resins of the alkyd, urea and phenol formaldehyde types, become softer and more liquid during the initial heating period. With these adhesives we prefer to use hot compressed air as the gaseous medium and to heat the air to a temperature of 100 F. to 300 F., depending upon the particular solvent employed in the adhesive used.

We have also found that the character of the coated abrasive material produced by the hereindescribed process can be altered by varying the angle of impingement and velocity of the jet.

This jet of high velocity gas serves to drive the film of freshly applied adhesive from the tips of the abrasive grains and cause it to flow down and around the bases of the grains. The force of the Jet produces a depression, indicated by the reference numeral 8 in Figure 3 of the drawings, in the adhesive film 5 between adjacent grains and forces the film of adhesive up along the sides of the grains, as indicated by reference I, thereby surrounding the base of each individual granule in a mound of adhesive. When the angle of impingement of the jet is approximately 90 with respect to the surface of the coated web, the depression 6 of the adhesive film is approximately midway between adjacent grains, as shown in Figure 3. In an abrasive article of this character, the granules are supported against lateral displacement in an equal manner regardless of which direction the coated web is moved during subsequent grinding action.

By varying the angle of impingement of the gas stream so that it strikes the coated abrasive surface at an oblique angle, we are able to build up the mound of adhesive to a greater height on one side of the individual grains than on the other. This feature is clearly illustrated in Figure 4 of the drawings, in which the layer of sizing adhesive, generally indicated by 5, is shown as extending well up the back of the grains 4,

as indicated by the reference In. The depressed portion 6a of the adhesive film is well over near the front of the next succeeding grain. Thus greater reinforcing or supporting action is obtained by a given amount of sizing adhesive when the abrasive material is moved in the direction indicated by the arrow 10. This feature is of particular importance in connection with abrasive belts used in grinding wood, metals and other materials, and increases the rate of cut and effective life of the article to a marked degree. Grindposition or degree of orientation of the grains with respect to the web backing. For this reason, we provide means for readily adjusting and maintaining the angle at which the jet of gas is directed .at the surface of the adhesive sizing coating 5 on the web I. The jet may be adjusted through a wide arc, as indicated by the arrow in Figures 5 and 6, by loosening the clamping bolt 29 and rotating the jet in the journals of the bracket 25. Such movement is facilitated by the handle 33, and when the angle is properly adjusted, the jet is securely locked in position by tightening the bolts 29. In producing coated abrasive material, such as that shown in Figure 4, we have found that satisfactory results are obtained when the angle of impingement of the gas stream is between 20 degrees and '75 degrees with respect to the surface of the coated web. More particularly, it has been found that the best results are obtained when the angle between the jet and the web is approximately 50 degrees.

Since the stream of gas strikes the coated web with appreciable force, we have found it desirable to set or cure, at,least partially, the base coating of adhesive 3 before subjecting the abra-.

sive coated web to the further treatment of a sizing coating of adhesive, as described in the present application. Such curing or setting of the base coating is effected in a suitable curing zone through which the web is moved prior to passing over the drum II. This initial set or cure of the base coating prevents the upstanding abrasive granules 4 from being laid flat or entirely dislodged by the forceof the gas stream. However, any loosely adhering or improperly attached granules are removed from the coated web.

' Other advantages in the herein-described process for applying the sizing layer of adhesive, to

abrasive coated articles will be apparent from a comparison of the sections of the coated webs illustrated by Figures 2, 3 and 4. The granular particles 4 are very irregular in shape and surface contour, particularly so with abrasive particles,

so that a layer of sizing adhesive applied in the ordinary manner entraps air around the bases of a large portion of the grains. In Figure 2, which shows a section of granular material made by the usual process, reference numerals 8a, 8b, 8c and 8d indicate voids around the bases of the grains 4 which are not filled with adhesive. These voids are caused by the fact that a sheet or blanket of liquid adhesive is applied to the granular coated web in the usual process and the fluidity of the adhesive and pressure of the rolls are the only forces acting to cause the adhesive to fill the interstices between adjacent grains. Since the adhesive is fluid at the time of application, it does tend to fiow down the sides of the granules to the bases thereof. Any crevices, however, are not properly filled because of the surface tension of the blanket of adhesive and the air entrapped in the said crevices. Obviously, these voids, such as 811, materially weaken the anchorage of the granules and when the coated material is used as an abrasive, the grains are broken away from the backing before their useful life is spent.

In the granular coated material produced by the present process and illustrated by Figures 3 and 4, the above difficulties have been entirely eliminated. In addition to driving the film of adhesive from the tips of the granules, the force of the solvent treated gas stream is sufficient to fiow the adhesive into any crevices at the base of said grains and to displace any air which may have been entrapped therein.

While we have specifically illustrated and described the preferred embodiment of our invention, it is to be understood that the invention may be otherwise embodied and practised within the scope of the following claims.

We claim:

1. The method of manufacturing granular coated webs which comprises the steps of applying a layer of liquid adhesive to the granular surface of a web previously coated with granular particles and then directing a high velocity stream of gas against the said adhesive layer whereby the peaks of saidgranular particles are cleared of said adhesive.

2. The method of manufacturing granular coated webs which comprises the steps of applying a layer of liquid adhesive to the granular surface of a web previously coated with granular particles and immediately thereafter directing a high velocity jet of gas against the said adhesive layer whereby said adhesive is driven from the peaks of said granular particles and deposited around the bases thereof.

3. The method of manufacturing granular the bases thereof.

4. The method of manufacturing granular coated webs which comprises thesteps of applying a layer of liquid adhesive to the granular surface of a web previously coated with granular particles and directing against the said adhesive layer a high velocity jet of gas emerging from an orifice extending across the full width of said web whereby said adhesive is driven from the peaks of said granular particles.

5. The method of manufacturing granular coated webs which comprises the steps of applying a layer of liquid adhesive to the granular surface of a web previously coated with granular particles and directing against the said adhesive layer a high velocity stream of gas of .002 to .025 inch in thickness and extending across the full width of said web whereby said adhesive is driven from the peaks of said granular particles.

6. The method of manufacturing granular coated webs which comprises the steps of applying a layer of liquid adhesive to the granular surface of a web previously coated with granular particles and directing against the said adhesive layer a high velocity stream of gas emerging from an orifice under gage pressure of 2 to 15 pounds per square inch, said orifice having an opening of .002 to .025 inch and extending across the full width of said web, whereby said adhesive'is driven from the peaks of said granular particles.

7. The method of manufacturing granular coated webs which comprises the steps of applying a layer of liquid adhesive to the granular surface of a web previously coated with granular particles and then directing at an oblique angle to said adhesive layer a high velocity stream of gas whereby said adhesive is driven from the peaks of said granular particles and deposited around the bases thereof forming a suppo'rting mound of adhesive located principally on one side of said granular particles.

8. The method of manufacturing granular coated webs which comprises the steps of applying a layer of adhesive of predetermined thickness to the granular surface of a web previously coated with granular particles and then directing against said adhesive layer a high velocity stream of gas whereby said adhesive is driven from the peaks of said granular particles and deposited around the bases thereof.

9. The method of manufacturing granular coated webs which comprises the steps of applying a layer of adhesive of predetermined thickness to a web previously coated with granular particles, the thickness of said adhesive layer being that required for the particular size of the said granular particles, and then directing against said adhesive layer a high velocity stream of gas whereby all of said adhesive is retained on the web but is driven from the peaks of said granular particles and deposited around the bases thereof.

10. Apparatus for the manufacture of granular coated webs comprising, a frame member, means for moving and supporting a granular coated web, an adhesive roll Journaled on said frame and adapted to apply a layer of adhesive to iii) said granular coated web, adjustable supporting members mounted on said frame, a pressure roll mounted in closely spaced relationship to said adhesive roll and :Iournaled on said adjustable supporting members, means for moving said roll supporting members to regulate the spacing between the coacting pressure and adhesive rolls,

whereby the thickness of the adhesive layer applied to the web may be controlled, and a gas jet also mounted on said pressure roll supporting members to direct a high velocity stream of gas against said adhesive layer, said apparatus being adapted to maintain a definite spaced relationship between said gas jet and the surface of said adhesive coated web regardless of adjustments in spacing between said adhesive and pressure rolls.

11. Apparatus for the manufacture of granular coated webs comprising, a frame member, means for moving and supporting a granular coated web, an adhesive roll ioumaled on said frame and adapted to apply a layer 01' adhesive to said granular coated web, adjustable supporting members mounted on said frame, a pressure roll mounted in closely spaced relationship to said adhesive roll and journaled on said adjustable supporting members, means for moving said roll supporting members to regulate the spacing between the coacting pressure and adhesive rolls, whereby the thickness of the adhesive layer applied to the web may be controlled, a gas jet also mounted on said pressure roll supporting members to direct a high velocity stream of gas against said adhesive layer, and means for varying the spacing between said air jet and said pressure rcll, said apparatus being adapted to maintain a definite spaced relationship between said gas jet and the surface of said adhesive coated web regardless of adjustments in spacing between said adhesive and pressure rolls.

ROMIE L. MELTON. RAYMOND C. BENNER. HENRY P. KIRCHNER.

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