US2350861A - Abrasive belt joint - Google Patents

Description

Patented June 6, 1944 ABEASIVE'BELT JOINT Richard T. Argy and Carl W. Foss, Niagara Falls, N. Y., assignors to The Carborundum Company,

Niagara Falla, N.

Y., a corporation of Delaware Appueetion september 24, 194e, serial No. 459,523 s claims. (ci. .i1- 188) This invention relates to endless abrasive belts formed from strips of flexible, abrasive coated web material. More particularly, it is concerned with the belt splice or Joint formed by adhesively uniting the ends of the abrasive strip, and with the adhesive for uniting said ends. The invention is further pertinent to similar abrasive coated articles in which a continuous abrasive surface is obtained by adhesively joining contiguous ends of abrasive sheet material to form articles having endless abrading surfaces, such as cones, cylindrical drum covers and the like.

This application is a continuation-impart of our copending application Serial No. 369,198, filed December 9, 1940.

Endless abrasive belts and the like are commonly formed by adhesiveiy splicing or joining the ends of a flexible, abrasive coated web material together. The joint may be one of a number of different types, as for example, that formed by beveling a narrow area along each of the two ends, applying adhesive yto the beveled areas and superimposing the upper and lower adhesivecoated beveled portions one on the other, and subjecting the assembly to pressure untilthe adhesive sets. Another form of belt Joint or splice is obtained by skiving the end areas of the abrasive strip material free of` abrasive, applying adhesive to the one abrasive-cleared area and to the underside of the abrasive-cleared area at the opposite end of the strip, overlapping the two ends, pressing together and allowing the adhesive to set. Regardless of the 'particular type of Joint* or splice employed, it is desirable to provide an adhesive therefor which will be quick-acting and also will result in a strong and exible joint.

Hitherto, most abrasive belt failures'have been the result of a defective or weak joint or splice. During the constant andrepeated flexing of the belt joint in abrasive operations by the passage of the belt joint around the pulleys and under the work being ground, the belt joint has failed by a separation or delamination of the adhesively Joined ends. Considerable effort has been directed to providing a belt Joint which would be not only inexpensive and easily made, but which would have the requisite strength and flexibility to stand up under constant and repeated ilexing action for the normal abrading life of the belt. To accomplish the ends in mind, eiorts heretofore have been directed to the use of more complicated Joint structures. The bonding means employed have included such adhesives as animal are not of suilicient strength or flexibility and as a result a high percentage of them fail before the abrading life of the belt expires. While some improvenient in strength has been obtained by the use of phenol formaldehyde resins and the like, and latex adhesives have resulted in somewhat higher exiblity, no belt joint has heretofore been found completely satisfactory in possessing the desired combination of behavior and proper'- ties. Moreover. certain diiliculties of application, such as extended periods of cure, render the use of some adhesives undesirable or uneconomical.

It is therefore an object of the present invention to provide an improved belt splice which can be inexpensively and easily made and will also obviate to a large degree the former diillculties and disadvantages encountered in -belt splices.

because of their inherent brittleness and lack of flexibility, and such use is not herein claimed. However, it has been found that when the same urea aldehyde condensation products are properly modified by thevinclusion of suitable toughening agents, the exact nature of which will be described later in further detail, a belt Joint is 0btained which has an improved strength and nexibility and does not delaminate in use. Further'- more, the adhesive within the belt joint has a fast cure so that the belt joints can be quickly and inexpensively made.

In order that the invention may be more clearly understood it will be described as it pertains to one particular type of belt splice which can be and vegetable glues, latex, phenol formaldehyde resins and the like. The earlier glue adhesives abrasivesheet or web material is ilrst slit into satisfactorily made in accordance with the invention. although it is not desired to limit the practice of the invention to the specific belt splice set forth and described in the drawing. in which Figure 1 is a longitudinal, enlarged cross-section of the mating beveled ends of a belt, with adhesive coating, but prior to final splicing;

Figure 2 is a longitudinal, enlarged cross-section of a. completed splice; and

Figure 3 is a top plan view of the completed splice shown in Figure 2.

Referring further to the drawing, the coated of the beveled surfaces quickly and kallne.

` the strip material and equal in appropriate widths and then cut to' length. The end or cross cut l is usually made at an angle to the lengthwise direction of the strip as shown in Figure 3, but this is not a limiting condition as the cut could be made normal to the lengthwise direction. In the actual preparation of the splice narrow areas at the ends 2 of the abrasive coated strip are beveled in the manner shown in Figures 1 and 2. The beveled surface 5 at one end of the abrasive strip is on the under side of area to the abrasive-cleared'and beveled top surface area 6 at the opposite end of the abrasive strip. After the two endshave been skived and beveled, one or both 5 and 6 are given a. thin coating 1 of modiiled urea aldehyde condensation product. 'I'he beveled areas are then super-imposed as shown in Figure 2 and subjected to pressure and heat to form the joint 8 in which the intervening adhesive layer 1 serves to securely unite and hold the two ends in position.

Modified urea aldehyde adhesives which have been found to be highly satisfactory for belt joints have been obtained by modifying urea aldehyde condensation products by the inclusion therewith of an alkyd resin of the polyhydric alcohol-polybasic acid type, as exemplified by sorbitol phthalate, or other equivalent toughening agent. The resulting reaction products produce belt joint adhesives which arefast curing and which provide joints of high strength and ilexibility capable of withstanding the constant nexing action encountered in the use of abrasive belts and the like products wherein splices are essential.

The initial reaction products of a, urea with a methylene-containing body are obtainable in the form of aqueous solutions or suspensions, which products when spread into a rllm and heated pass directly to the iinal, cured state and require temperatures and/or periods of cure substantially lower than those required to heatharden the phenolic resins. They are obtainable in a considerable number of varieties. depending upon the specic urea compound employed, the relative proportion of the urea body and the methylene-containing body which are initially reacted, and the type of catalyst employed in bringing about the reaction. While our invention is not limited to any particular type of such resin, we have found that it is generally desirable to employ an initial reaction product which is not heat-hardening unless mixed with a separate liquid which acts as a catalyst and hardening agent for 'the reaction product and which ma.. tures quickly and directly to the final cured state when spread into a film, and to include a toughening agent to increase the strength and reduce the friability of the urea resin.

The usual urea condensation products are obtainable by reacting a urea such as thiourea or ordinary urea or mixtures thereof with a methylene-containing body such as formaldehyde, the formaldehyde probably being present in excess over that required to form dimethylol urea. Upon heating such mixture in the presence of either an acid or basic catalyst, it is generally believed that the latter product is obtained in colloidal form suspended in water. The reaction may be stopped by bringing the liquid to approximately the neutral point where it is neither acid nor al- Such a product may then be made reactive by mixing with a suitable proportion of a hardening agent or catalyst which is preferably purpose.

becomes acidic. For example, the hardening agent may be prepared by dissolving urea or thiourea in water containing substantial proportions of ammonia. Alternatively, ammonium thiocyanate may be substituted for at least part of the urea or thiourea. In general, sulphurcontaining compounds, such as an ammoniacal solution' of ammonium sulphate in water, or, in fact, an ammoniacal solution of any ammonium salt which will give an acid reaction in water, may be employed to bring about the reaction of the initial product to the nal infusible condition. Various alkyl derivatives of ammonia may be used instead of ammonia in preparing the hardening agent. Such compounds have the advantage that the fumes evolved therefrom when the articles are heated are less objectionable than ammonia.

It has been further found that the ammoniacal solution of ammonium sulphate in water and the alkyl derivatives of ammonia which are used as catalysts or hardening agents for the urea condensation products can be replaced by certain organic materials such as organic phosphates and the like which are very satisfactory for the Bakelite )IK-15256 is a commercial organic phosphate available on the market and suitable for use as a hardener in practicing the present invention.

Certain of the toughening agents which we have discovered as capable of increasing the strength and reducing the friability of the urea resins are special esters which are soluble in aqueousv alkalies such as aqueous solutions of ammonia. They are therefore compatible with the urea resin emulsions which are also provided in an aqueous vehicle. Upon heat treatment the toughening agents are converted to a tough condition in which they are sufficiently compatible with the urea condensation product that the films obtained by heat treatment of a mixture of the liquid urea resin with the toughening agent have a material which is normally basic but ultimately V,the necessary strength and toughness required in the bonds for uniting the ends of the abrasive strip material to form a strong joint. This is iii\. -f-

contrast to the ordinary urea resins which do not include specialtoughening agents and which are so brittle and friable as to be unsatisfactory for this use. An example of a toughening agent employed in this embodiment of our invention is sorbitol phthalate. Sorbitol is a hexahydric alcohol, in contrast .to glycerol, a trihydric alcohol, which is commonly employed to make resinous polyesters. Like glycerol it forms esters with polybasic acids, such as phthalic acid. These esters are somewhat similar to the ordinary alkyd resins butl are especially adapted for toughening the urea resins. Other similar products have recently been developed which likewise have this property of toughening and strengthening the urea resins as by reacting sorbitol or other hexahydric alcohol such as mannitol with other polybasic acids such as succinic, glutamic, adipic, suberic, tartaric, maleic, or citric acids or their anhydrides. Mixed esters formed by reacting mixtures of acids 4with the alcohols or mixtures of them have also been found to be suitable for-this purpose, as have esters formed by other polyhydric alcohols such as glycerol, particularly where the proportions of alcohol and acids are such as to leave unreacted hydroxyl groups to promote water solubility or unreacted acid groups winch can form water-soluble salts of the estcrelris -in aqueous alkalies such as aqueous ammo a.

2,so,sei l 3 Many initial condensation products formed by reacting a polyhydrlc alcohol with a polybasic acid or anhydride, such as a condensation product of the glycerin-phthalic anhydride type, are readily soluble in dilute aqueous .ammonia by reason of the formation o f the water-soluble ammonium salt of the ester. Other alkaline solutions can be used in place of ammonium hydroxide, such as equivalent alkaline solutions such as sodium hyd-oxide or`potassium hydroxide, although the ammoniacal solution is preferred because of its ready removalby volatilization during the latter treatment of the material. 'I'hese initial condensation products oi' the glycerin-phthalic anhydride type can be further modified, if desired, by the inclusion of ingredients like glycols, succinic acid, and adipic acid, to impart further exibilizing action to the material.

For example, a suitable toughening agent may be made of the following ingredients: 32 parts of a somewhat soft, plastic, vdeformable but not substantially tlowable A stage glycerin-phthalic anhydride type resin which on curing remains flexible dueto the presence of constituents such as glycols, succinic acid and adipic acid; 4 parts of concentrated ammonia solution of a speciic gravity of .90; and 36 parts of water. The resulting ammonium salt of the modiiled glycerinphthalic anhydride ester is water-soluble and compatible withthe water-soluble urea aldehyde initial condensation products and serves satisfactorily as a toughening agent therefor.

The following specic examples are offered by way of illustration only, and give in detail the manner in which the invention is practiced and the nature of the adhesive used to form the belt joint.

Example I Any suitable iiexible, abrasive coated web material is rst cut to the appropriate length and width and the ends of the resulting abrasive strip beveled and one end skived of abrasive in the manner previously set forth. The beveled areas are then coated with an adhesive consisting of:

Parts by weight Liquid heat-hardenable urea-aldehyde condensation product, such as the urea-formaldehyde resin sold under the trade name Bakelite XRU13108-- 100 The urea resin is an aqueous suspension of a urea-aldehyde condensation product containing 65% solids.

The adhesive-coated ends are then airor force-dried, assembled and pressed in a Warm clamp having" a temperature of about 120 F. for

' 20 seconds, following which the joined parts are removed and clamped in a hot clamp having a temperature of aboutl 300 F. for 20 seconds.

' Example II An abrasive belt joint was made as described in Example I except that in preparing the adhesive therefor the Bakelite XKU-12435 hardening constituent was replaced by Bakelite Parts by weight XK-14616,hardener. which consists of an' ammoniacal solution of ammonium sulphate, con'- l taining 22% free ammonia and 10% yammonium sulphate. 5 It is not desired to be limited to the type of belt joint or splice shown, as th'e invention can be practiced with any type of splice where two abrasive coated strips or sheets are adhesively united to providea continuous, flexible abrasive surl0 face. For example, joints or splices can be made by skiving the abrasive from two `end portions of an abrasive strip and overlapping the two cleared ends with a layer of intervening adhesive. Likewise V-shaped splices, or joints having various other configurations, can be made in which the modied urea condensation products as above set forth can be employed as the combining means to produce an improved splice. Likewise, the invention is not to be considered as limited to the sriiecic adhesive compositions of the examples g ven.

In the claims we have used the word urea to include both ordinary urea and derivative or substitution products of urea such as thiour'ea and the like.

Similarly, other forms of apparatus for applying heat and pressure other than the heated clamps set forth in the examples may be used, such as hot presses, mandrels or rolls.

While'we have described our invention with particular reference to certain specic examples,`

it will be understood that other equivalent materials may be employed, together with other modifications, and embodiments common to the art. The invention is therefore not to be restricted to the specific steps and materials herein described, but rather is to be considered as of the scope defined in the appended claims.

We claim: l 1. An endless abrasive belt of flexible abrasive coated web material having a joint formed by l two adhesively joined end portions, the' adhesive of said joint comprising the reaction product of a mixture comprising a major proportion of a 45. water-soluble urea aldehyde condensation product and a minor proportion of an alkyd modier. 2. An endless abrasive belt of flexible abrasive coated web material having a joint formed by two adhesively joined end portions, the adhesive of said joint'comprising a major proportion ofa urea aldehyde condensation product and a minor proportion of an ester of a hexahydric alcohol and a poly-basic acid.

3. An endless abrasive belt of exible abrasive coated web material havingfa joint formed by two adhesively joined end portions, the adhesive of said joint comprising a major proportion of a urea aldehyde condensation product and a minor proportion of a toughening agent such as sorbitol phthalate.

4. An endless abrasive belt of flexible abrasive coated web material having a joint formed by two adhesively joined end portions, the adhesive Iof said joint -comprising the reaction product of a mixture comprising a major proportion of a water-soluble urea aldehyde condensation prod-V tion product and a minor proportion of an ester of a polyhydric alcohol and a polybasic acid.

6. An endless abrasive belt of flexible abrasive coated web material having a joint formed by two adhesively joined end portions, the adhesive of said Joint comprising the reaction product of a mixture comprising a major` proportion of a water-soluble urea aldehyde condensation product and a minor proportion of a water-soluble toughening agent therefor.

7L In the process of forming endless abrasive articles the stepwhich comprises adhesively uniting the end portions of an abrasive sheet material by means of an intervening layer of an adhesive comprising a major proportion of a urea aidehyde condensation product and a minor proportion of a toughening agent therefor.

8. The method of forming endless abrasive articles which comprises removing the abrasive from an end of a exibie abrasive sheet, applying a liquid adhesive comprising a major proportion of a water-soluble vurea aldehyde condensation product and a minor proportion of a toughening agent therefor to a terminal portion of the abrasive sheet, drying the liquid' adhesive, overlapping the terminal portions with the adhesive therebetween. and applying heat and pressure to set the adhesive.

RICHARD T. naar. CARL w. ross.

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