US2816402A - Coated abrasive segment and wheel containing the same - Google Patents

Description

J. J. BALLATO Dec. 17, 1957 COATED ABRASIVE SEGMENT AND WHEEL CONTAINING THE SAME 2 Sheets-Sheet 1 Filed Sept. 21. 1956 INVENTOR JOSEPH J. BALLATO ATTORNEY Dec. 17, 1957 J. J. BALLATO 2,816,402

COATED ABRASIVE SEGMENT AND WHEEL CONTAINING THE SAME Filed Sept. 21, 1956 2 Sheets-Sheet 2 INVENTOR JOSEPH J. BALLATO ATTORNEY United States Patent 2,816,402 Patented Dec. 17, 1957 FEM;

COATED ABRASIVE SEGMENT AND WHEEL CONTAINING THE SAME Joseph J. Ballato, Albany, N. Y., assignor t Norton Company, Troy, N. Y., a corporation of Massachusetts Application September 21, 1956, Serial No. 611,294

9 Claims. (Cl. 51-193) The present invention relates to an improved abrasive wheel and more particularly to a segmented wheel utilizing coated abrasive material, to the segments which make up such wheel, and to the methods of making such segments and assembling such wheel.

Previous constructions of devices for polishing work pieces, particularly pieces having contoured shapes, have been subject to certain disadvantages. These devices include solid wheels formed entirely of abrasive material or wheels having abrasive peripheries. Most of the devices have utilized abrasive surfaces having straight line or fiat area contact with the work piece. In operation, an operator manually turns the contoured piece at various angles in an attempt to bring all the surface areas thereof into contact with the moving abrasive polishing surface. As a result, the polished piece either has some inaccessible and unabraded areas or numerous areas abraded in different directions effecting an unsightly appearance.

To overcome some of the foregoing disadvantages, use has been made of traveling flexible belts having an abrasive face. Limited contouring of the belt face has been possible by engaging contact wheels with certain portions of the belt to effect a desired cross-sectional shape. Some additional deformation of the flexible belt has been possible by forcing either the belt against the work piece or the work piece against the belt. As a result, portions of the belt are overstressed thereby materially shortening its Working life. In addition, the variable and excessive pressures exerted against diflerent portions of the belt surfaces quickly result in glazing caused by a filling or loading of the spaces between adjacent particles of abrasive material. These glazed surfaces damage the work piece either by streaking or burning the surfaces thereof and may, if the wall of the work piece is sufiiciently thin, result in deformation through the inadequate dissipation of the heat so generated.

in the operation of abrasive devices where excessive pressures are applied, lubricants such as water, oil, grease or the like are used to wash away material being removed by abrasion and to absorb and conduct heat from the work surface.

One step forward in eliminating the foregoing objections and disadvantages was made by the introduction of the pleated coated abrasive wheel elements described in detail and claimed in the copending applications of Fritz E. Hendrickson, Serial Nos. 388,308 and 540,853, filed on October 26, 1953, and October 17, 1955, respectively which matured as Patent No. 2,769,285, November 6, 1956, and Patent No. 2,770,927, November 20, 1956, respectively.

However, even though the pleated construction markedly improved the operation, particularly in the finishes produced, of coated abrasive Wheels, difficulty was experienced in obtaining a satisfactory degree of out due to the tendency of the pleated wheel utilizing the usual wrap around pin construction to gap or present a nonuniform peripheral surface. Additionally, the construction of such a wheel was quite ditficult, the folding of the pleated sheets about the pins of the cage being time consuming and hard to control. A further disadvantage was the amount of unusable coated abrasive material in the wheelthe material around the pin being discarded without having performed any cutting or abrading function.

Accordingly, it is an object of the present invention to provide an improved wheel which will overcome the foregoing objections and disadvantages.

An additional object of the invention is to provide a coated abrasive wheel which presents a uniform peripheral surface. 7

A further object of the invention is to provide a wheel composed of a plurality of easily constructed and easily replaceable segments.

Another object of the invention is to provide a segment for a coated abrasive wheel which is capable of assembly with a varying number of other segments to form coated abrasive Wheels of varying diameter.

A still further object is to provide a method for manufacturing coated abrasive wheels and segments therefor which is adaptable to mass production.

Additional objects, if not specifically set forth herein, will be readily apparent to one skilled in the art from the following detailed description of the invention.

In the drawings:

Figure 1 is a front elevation view of a segmented coated abrasive wheel constructed in accordance with the present invention.

Figure 2 is a perspective view of one type of pin and associated element of the segmented coated abrasive wheel of Figure 1.

Figure 3 is a side elevation view in partial section of a squirrel cage type mounting showing one manner in which a plurality of the wheels of the present invention may be combined to make a wide faced wheel or abrasive drum.

Figure 4 illustrates one method of forming the segments of the wheel of the present invention.

Figure 5 is an enlarged end view in elevation of a pleated coated abrasive sheet as seen along that portion of the periphery of the wheel indicated by 5-5 of Figure 1. 7

Generally, the. present invention contemplates the formation of a coated abrasive wheel wherein the individual sheets of pleated coated abrasive material are usable over substantially their entire areas, and wherein a plurality of such sheets are pre-formed into a segment adapted to fit into wheels of varying diameters.

More specifically, the individual segments are made up of a plurality of sheets of coated abrasive material, pleated in the manner hereinafter described, each of which has some portion thereof embedded in a shaped plastic mass. The plastic mass or base of the segment is preferably so designed and shaped as to function in the finished wheel as a portion of the inner periphery thereof.

Referring now to the drawings, and specifically to Figures 1 and 2 thereof, it will be seen that a vertical crosssection of the preferred form of the base 11 of the segment It) is essentially an isosceles trapezoid having the longer (A) of the two parallel sides (A--A') at the top of the rigid resinous base member. While the included angle of the non-parallel sides (B-B) to the parallel sides may be varied as desired, it is preferred that it be within the range of from 60 to measured from the top or longer parallel side A. This configuration permits the use of from 6 to 16 segments as the total components of a wheel without the necessity of changing the shape of the base member 11. As most clearly shown in Figure 2, a plurality of pleated coated abrasive sheets 12 extend radially outward from the upper surface of the base member 11. A relatively short portion 13 of one the resinous base.

cage .or-similar ty emounting device. P

{9 end ofeach of these sheets is embedded within the upper surface of base member '11. In actual practice, only about A to /2 of one inch'thereof need be embedded in A mounting tube 14 isimoldedinto 'ba'se rnemberfll, extending substantially centrally lengthwise-of said member. This tube preferably is of a light metal although fiber or other materials may be used if desired. 'Due to the strength of the resinous material used to form the base member, the mountingtube may consist only of the walls of resinous material if desired.

However, for ease of forming it is preferred to have a tube of metal or-the like fixedly molded into the base member. Tube 14 is adapted to receive in snug but slidable engagement a mounting pin 15 of a fsquirrel Slots 16 are cut, moldedv or milledintothe base member 11 to receive retaining flanges as illustrated in Figure 2 and more fully .described below.

ke'ferringrnowto Figure l,-.it will be seen that the segments ltlaremounted on a squirrel cage type hub by insertion of the mountingpins '15 of such hub intothe mounting tubes .14 of the individual segments 10. The

shorter parallel'sides Aof each base member 11' of'each segment form a series of chords which in turn represent the-innerperiphery ofthe wheel 20. As seen in :Figure l,

noneof the coated abrasive material of the pleated sheets 12 extendsbelow theretaining flange 24, the lower edge of the coated abrasive material being as shown by the -dotted:line.13 which represents the extent of embedment of .the ends of-the coated abrasive sheets 12 in the base member 11 of each segment 10.

In the construction of Figure l, the retaining flange 24 is positioned internallyof the Wheel 20, extending up through slots 16 in base members 11 of each segment 10. The pins-15- extend through slots in the retaining flangeld which are-in registry with the tube 14 openings in the slots 16 of each base member 11. By virtue of .this construction,:any number of wheels 20 may be mounted side by side without any gapping occurring due to the spacing which would beefiected if the retaining flanges were positioned'onthe exterior sides of the wheel.

The advantages inherent in the. improvements described above all combine tozfullfill the objects of the present in- Wention. As aresultof the increased number of pieces of coated abrasive material per pin, the density'of .the .wheelgis substantially increased and the ability 'of the wheel to cut raggressivelyis likewise increased. Although increasing by a :substantial amount the number of 'in vdividual pleated'coated abrasive sheets inthe-wheel, the new -construc tion doesnot materially increase the cost of the wheel. Neglecting'savings resulting from increased easeuof assembly, the actual area of coated abrasive materialin theznew Wheel is substantially the .same as when theicoated abrasive elements are folded about the mountpresent invention. Substantially all of the abrasive coated surface may beused in this construction with the exception of the small-amount of each sheet embedded in the shaped-plastic base member 11. Also, in the construction of wrap around pin type Wheels, it was found necessary to use double-faced coated abrasive-material :in order to achieve satisfactoryresults, whereas in the improved construction single-faced coated abrasive material has been-found completely satisfactory.

As an illustration ofthe foregoing, a comparison of two types of wheels having a 4" facewidth, i. 'e. a wrap around pin construction and that of Figure l,for coated abrasive material of grit (or abrasive grain) size 220 -is given. mounting pins '15"are'-long enonghto hold two 4" face portion 31'. end-flanges ZW-aboutshaft29 to maintain the flanges in shows that in the wrap around pin type construction, five sheets of thirteen inches by thirteen and three-eighths inches coated abrasive material, having an abrasive coat ing on both sides thereof, were the maximum which could be used per pin. Since there were 16 pins in the Wheel, this amounted to a total of sheets of this size in the complete wheel. Sincein'this construction the sheets are doubled about the pins, in etiect there were radially extending coated abrasive pleated pieces. In the construction of Figure 1, using the same 16 pin cage, 20 pieces of single-faced, i. e. coated on one side only with abrasive, coated abrasive sheets were used per pin for a total of 320 radially extending pleated coatedabrasive sheets. Obviouslythis wheel was twice the density of the first-described wheel. The size of the sheets used in the second wheel was four inches by thirteen and three-eighths inches.

l n-the illustration given above, one additional important -factor:should 'be-noted. Both wheels initially having a diameter; of 17" wererusable down to a diameter of 11 /2".

This -meant that while'4'2 /z-% of each icoatedabrasivc sheet in the wrap around;pin..type-construction .wasused 't'oreifective :abrading purposes-49% of eachsheet in the constructiorrof Figure l was usable. This increased usable .abrasive area is 5111016 strikingly brought out'by c'omparingtthe total abrasive area of the sheets in each wheel against jthe total usable abrasive area for each wheel. Whereasthe wheel built according to Wrap around ,pin construction had ,-'a total abrasive area of 27,800

square inchesandthat of Figure 1 had a total abrasive area of 17,,l20zsquare inchesor 10,680 square inches less area thanthat'of'theiformer wheel, the usable abrasive area vof the'Figure '1 wheel 'Wasidentically'the same, -i. ,e. 11 ,810 squareinches, .as that of the .said former wheel.

Reference has :previously been made .above to the fact dividual segments 10'. Referring now tothis drawing. a clearer illustration ofthe squirrel cage 'type mounting In the -'particular wheel illustrated, bars or width-wheels. Obviously the pins may be shortened or "lengthenedwas desired :to accommodate either plural groups of narrow face Width segments or toaccommodate a'single group of segments of 'any desired facewidth. -Wheels havingsegments ranging from a 'face width of formtmntingon'aclriveshaftas. The drive-shaft has a reduced end portion -29 terminating at one end in an abutmentshoulder 30"-and attheother end in a'threaded A sleeve 32' a may be inserted between the thedesired spaced relationship -A nut 33 is threaded on the shaft and serves to clamp the assembly together.

"It will be seen that since 'end flanges or retaining-flanges 24' are so recessed as to be flush with the ends of the segmentbases 1'0 ',--there is no gapbetween the adjacent pleated sheets of coated-abrasive at thepoint where the two segments 10' meet. This, permits a'srnooth uniform abrading action across-the entire face of the wheel.

Referr'ingnow to Figure 4 of the drawings, one method of'forming 'the segmentso'f -the presentinvention is-illus- 'trated. A mold '40 of suitable configuration '(here' shown with a cross-section having the shape of an isosceles trapezoid) is prepared and the interior surfaces thereof coated with a release coating 41 to permit freeing of the plastic block after it has been cast. In order to position a tubular mounting member through the center of the cast block, recesses 42 are provided in the ends of mold 40 to slidingly receive the ends of a tubular member 43. Tube 43 is preferably positioned as near the top of the mold 40 as possible, consistent with the requirement that approximately one-half inch be available between the top surface of the cast block and the top of the tube for the reception of the ends of the coated abrasive sheets to be mounted therein. Once the tube is in place, the particular resin selected for the resinous component of the segment is poured into the mold as at 44. A curing catalyst 45 is added if necessary during or prior to pouring and then when the level of the resinous mass has reached the desired height in the mold, the ends 46 of a pack of pleated coated abrasive sheets 47 are placed in the mass and the same cured by heat, air drying or the like, depending on the requirements of the particular resin-catalyst mix used. After curing, the segment is removed from the mold and is ready for insertion into a wheel after appropriate slots for receiving the retaining flanges of the wheel have been cut therein if desired. Obviously many variations in shape in the mold are possible, as for example, provision may be made to mold into the block the flange receiving slots rather than milling or cutting them in after the block is formed.

In forming the plastic base of the segments of the pres ent invention, any of various resins or types of resins may be used. While some of the higher melting thermoplastic resins and such materials as molded rubber can be used, it is preferred to use resins of the thermosetting type. Of this latter class, resins which are capable of cure at room temperatures in a relatively short time are preferred for ease of handling in the preparation of the segments. Resins of the so-called epoxy type are in this category and a specific illustration of such a resin, the method of preparing the same and of using in the formation of the resinous segment bases of the present invention is given below:

Example I The epoxy resin used was Shell Chemical Corp. Epon 828. Its properties as listed in Shell Chemical Corp. Technical Bulletin SC:55-26 were as follows:

Melting point C 8-12 Viscosity (Gardner-Holdt) poises 50-150 Epoxide equivalent 175-210 1 Grams of resin containing one gram equivalent of epoxide. A resin of this type can be prepared as described for polyether A on page 4 of U. S. Patent 2,643,239 issued to E. C. Shokal and T. F. Bradley and assigned to Shell Development Company. This polyether A has the following properties:

Melting point C 9 Epoxide equivalent 200 Molecular Weight 370 The castings were prepared by mixing 8% (based on the weight of the Epon 828) of diethylene triamine with the Epon 828 and stirring well at room temperature for about 5 minutes. When well mixed, the mixture was poured into a mold which had been coated with silicone grease as a mold release agent and the folded coated abrasive embedded to about /2 inch. Some of the resin wicked up the abrasive and the mold was refilled to level. The casting started curing as soon as the two components were mixed and the casting became quite warm due to the exothermic reaction which occurred. Within 2 hours, the reaction was complete and after cooling to room temperature the casting was removed from the mold.

Other resins, some of which may require cure at elevated temperatures and for extended periods of time 6 may be used. Examples of such resins and their use in forming the elements of the present invention are given below:

Example II This polyester resin was prepared from the following materials:

Grams Moles Maleic Anhydrlde 171.5 1. 75 Phthalic Anhydride 55.5 .375 Adipic Acid 54. 75 375 Ethylene Glyco 85. 25 1.875 Diethylene Glycol. 146. 0 1. 375

Pr0cedure.-Charge the glycols into a resin flash assembly fitted with thermometer, stirrer, N inlet tube, and Dean and Stark water takeoff. Start stirring and introduce a slow stream of nitrogen. Heat to about C. and add maleic anhydride followed by the phthalic anhydride and the adipic acid. Raise the temperature to C. in 1 hour and then about 10 C./hour until the temperature has reached 210 C. Keep at 210 C. until the acid number is less than 60. Apply vacuum (100-120 residual) and let the temperature drop to 180 C. When the acid number is below 40, end the vacuum treatment. Cool and add inhibitor if material is to be stored.

For the present example, the above procedure was varied only in that after reaching 210 F., it was necessary to cool down and store over nitrogen overnight.

A polyester varnish was made by dissolving 100 parts polyester in 42.8 parts of styrene monomer. To 200 grams of this varnish were added 1.0 gram of 6% cobalt naphthenate solution which was stirred in well without beating the airthen 3.0 grams (1.5% on varnish) of Lupersol DDM (60% methyl ethyl ketone in dimethyl phthalate). This was quickly poured into a mold and the pleated coated abrasive pack embedded to about /2 inch. The reaction was completed in about 2 hours. When cool, the casting was removed.

The particular fold or pleat used in the coated abrasive sheets of the present invention may be varied somewhat in order to produce varying distribution of density of abrasive across the face of the wheel if desired. However, it is generally preferred to utilize a pleat similar to that disclosed and claimed in the aforementioned copending application of Fritz E. Hendrickson. Referring now to Figure 5 of the drawings, such a pleated construction is shown. The coated abrasive sheets 50 are folded on themselves such that one pleat partially overlaps an adjacent pleat as shown to produce an undulated edge outline having a wavy form with successive curves 52-53 in alternate directions. Also shown in Figure 5 is an effect which occurs when the periphery of the pleated segments engages a work piece. Certain of the marginal edges of the pleats are bent at a substantial angle to the radial direction of the sheets per se, thereby providing a plurality of small abrasive areas 51 for engaging a surface to be polished. These areas are on opposite sides of each loop which generally bends as at 51 away from the direction or rotation of the wheel. The portions so bent are generally of the order of to inch and of a length dependent on the peripheral length of the sides of the particular loop or pleat. As the bent portions are relatively narrow for their length and are supported by the relatively flexible body of the coated abrasive sheet, they become self-adjustingto completely engage a contoured surface under a minimum of contact pressure. It will thus be seen that one important advantage of the pleated construction is the presentation of constantly renewing surfaces of abrasive material since as the wheel is used, the flags or bent portions of the sheet Wear down and new material from the body of the pleated sheet is presented to the work piece. A second and equally important advantage of the pleated construction is the increased rigidity or resistance to flexing given to each coated abra sive sheet and thus to the coated abrasive segment as a whole. This is easily demonstrated by taking a single sheet of ordinary letter or tablet paper. Placing the sheet in a vertical position so that it rests on one edge only, it is very easy to bend the sheet-in fact, it will bend under its own weight. But pleat this same sheet as described above and the sheet will stand alone-requiring substantially more pressure to cause bending than is required in the case of the unpleated sheet. Consequently, although variations in the widths and amount of overlap of the pleats may be made, it is essential that the pleat lines extend substantially radial to the wheel so that they are essentially normal to the work surface to which the wheel periphery is presented.

The particular abrasive sheet to be used in the wheel will depend upon the ultimate use to which the wheel is to be put. Generally, it is preferred to use a fabric, e. g. cloth backing, but paper or other flexible material may be used as the backing of the coated abrasive sheets if desired. The abrasive material may be any of the commonly used abrasive grains such as silicon carbide, aluminum oxide, garnet, flint or emery. The grains may be'bonded to the backing in any of the known manners and the bond may consist of the resin over resin, the resin over glue or the glue over glue type. going refers to the well-known practice of providing coated abrasive sheets having both an initial bonding coat known as the maker coat and a second bonding coat known as the sizer coat.. For example, resin over glue means that the sizer coat is composed of a resinous adhesive and the maker coat of a glue adhesive. The coated abrasive sheet may carry abrasive grains either on one or on both sides as may be desired. The number of coated abrasive sheets per segment may be varied to any desired density, although generally it is preferred to maintain a relatively close engagement between adjacent sheets in order to prevent gapping and undue flexibility in the face of the wheel.

In order to cut down on the quantity of resin used in forming the segment base and also to increase the bonding ability of the resin, it is possible to incorporate a filler such as aluminum powder, glass fiber or the like in the resin. Likewise, reinforcing media such as glass cloth or the like mty be incorporated in the segment base. How

ever, the resins described above have been found satisfactory for use in the absence of fillers or reinforcing media.

Although the construction of the wheel illustrated herein has utilized flanges or face plates cooperating with associated slots or grooves in the plastic base of the seg ments to hold the segments in place on the wheel, bviously any other type of fastening means such as solid steel pins, screws, bolts, etc. can be cast or molded into the segment base to adapt the same to fit into other types of supporting cage structures. Likewise, knobs or similar projections, adapted to engage matching holes in the side retaining plates may be formed of the same plastic as the resinous base to replace the steel pins, etc. if desired.

Further modifications include forming the segments with interlocking knobs and recesses made of the same plastic as the resinous base, thus locking each segment to the next to form a complete wheel which can be combined with end flanges for mounting, the end flanges engaging in appropriate recesses in the outer face of each segment.

.While the coated abrasive sheets illustrated herein have The forebeen inserted into the plastic base member in a pleated but unfolded manner, it is within the scope of the pres ent invention to first fold said pleated sheets about a medial fold line and embed the same in the plastic of the base member at said fold so that both ends of the pleated sheet extend outwardly from the base.

The term shaped plastic base as used herein and in the appended claims is intended to cover a base member formed from a material which initially is sufficiently plastic or liquid to permit insertion of coated abrasive mate rial within its surface and thereafter is cured, set-up or molded to a self-sustaining form adapted to firmly bond said coated abrasive sheets in place.

While preferably each segment is so disposed and arranged as to comprise only a portion of any completed wheel periphery, it is within the scope of the present invention to form the segment as a complete wheel so that the assembled wheel will have a circular periphery made up of but one segment.

Obviously many variations and modifications not specifically set forth herein may be made without departing from the spirit and scope of the invention disclosed above, and therefore only such limitations should be imposed as appear in the appended claims.

I claim:

1. A segment adapted to form at least a portion of the periphery of a coated abrasive wheel which comprises: a shaped plastic base member having an upper and lower surface, said memberhaving in cross-section sides connecting said upper and lower surfaces, at least one pair of said sides inclining inwardly from said upper towards said lower surface; a pair of slots extending upwardly from said lower surface and spaced inwardly from the ends of said base member and adapted to engage with holding means on an abrasive wheel mounting; and a plurality of pleated coated abarsive sheets, a portion of each sheet being firmly embedded in said upper surface of said base member,

2. A segment adapted to form at least a portion of the periphery of a coated abrasive wheel which comprises: a shaped plastic base member having a substantially fiat, rectangular upper surface and sides extending downwardly and inwardly therefrom; mounting means associated with said base member; and a plurality of pleated coated abrasive sheets firmly embedded at one end of each sheet in said upper surface of said member.

3. A segment adapted to form at least a portion of the periphery of a coated abrasive wheel which comprises: a shaped plastic base member having a substantially fiat, oblong upper surface and sides extending downwardly and inwardly therefrom; mounting means associated with said base member; and a plurality of pleated coated abrasive sheets firmly embedded at one end of each sheet in said upper surface of said member; the lines of contact between said sheets and the upper surface of said member being substantially parallel to the long sides of said oblong upper surface of. said base member.

4. A segment adapted to form at least a portion of the periphery of a coated abrasive wheel which comprises: a shaped plastic base member having a substantially fiat, rectangular upper surface and sides extending downwardly and inwardly therefrom; mounting means associated with said base member; and a plurality of pleated coated abrasive sheets firmly embedded at one end of each sheet in said upper surface of said member, said pleated sheets being closely adjacent one another with the outside sheets of said plurality of sheets in substantially the same radial plane as said inwardly-extending sides of said base member.

5. A segment as in claim 4 wherein the cross-section of said base member is in the shape of a trapezoid.

6. A segment as in claim 5 wherein said shaped plastic base member is formed from a thermosetting resin.

7. A segment as in claim 6 wherein said shaped plastic base member is formed from rubber.

8. A coated abrasive wheel which comprises: a hub member adapted for mounting on a drive shaft; mounting means associated with said hub member to receive and hold coated abrasive segments; and a plurality of segments having shaped plastic base members positioned on said mounting means, said segments each having a plurality of pleated coated abrasive sheets extending outwardly from said base member, said sheets being partially embedded in the outer surface of said base member.

9. A coated abrasive wheel which comprises: a hub member adapted for mounting on a drive shaft; mounting means associated with said hub member to receive and hold coated abrasive segments; and at least one coated abrasive segment mounted on said mounting means and disposed annularly about said hub member, said segment comprising a shaped plastic base member having an outer surface and an inner surface; a pair of slots 10 extending upwardly within said base member from said inner surface, said slots being spaced inwardly from the sides of said base member and adapted to engage with said mounting means; and a plurality of pleated coated abrasive sheets embedded at one end thereof in said outer surface of said base member, the coated abrasive sheets of said segment extending substantially radially outward from said hub member and the outer ends thereof forming a substantially uniform wheel periphery of undulating wave-like edges of coated abrasive material.

Churchill Feb. 7, 1939 McLaughlin et al. Nov. 6, 1956

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