POWER TRANSMISSION BELT AND METHOD

Abstract: A power transmission belt (10) with discontinuous fiber (32) protruding and bent (40) from oppositely facing friction driving surfaces (36, 38) to expose lateral side portions (42) of fiber. A method of forming friction driving surfaces by grinding so as to have protruding and bent portions of fiber.

Description: Background of the Invention The invention relates to endless power transmission belts, but more particularly, the invention relates to what some in industry term as "raw edge" belts where oppositely facing friction driving surfaces are formed of an elastomeric body and in which are dispersed transversely oriented fibrous members. There are several belt configurations which have "raw edge" friction driving surfaces defined as part of a layer where discontinuous fibers are dispersed and transversely oriented in an elastomeric matrix. An example of a joined belt utilizing fibers dispersed in an elastomeric matrix is shown in U.S. Patent No. 1,777,864. An example of a "raw edge" V-Belt employing discontinuous fibers dispersed in an elastomeric matrix is shown in U.S. Patent No. 3,416,383. The fibers are transversely oriented at angles varying from 90°. Ribbed-belts also may have a "raw edge" construction and employ a layered construction with discontinuous fibers transversely oriented in an elastomeric matrix. U.S. Patent No. 4,330,287 discloses such a construction. All of the foregoing patents disclose a construction where generally the end portions of the dispersed fibers terminate or are severed at their oppositely facing friction driving surfaces; however, the ′383 Patent further shows that portions of the "raw edge" may wear at a faster rate than embedded fabric layers but not faster than the surfaces where there are embedded fibers. The friction characteristics of the driving surfaces for all of the described belts may be modified by construction where there are discrete protrusions of fiber extending beyond an elastomeric portion of the driving surfaces. The file history of the U.S. Patent No. 3,871,240 includes photomicrographs showing that end portions of fiber are exposed at oppositely facing frictional driving surfaces of the belt. As further explained in the ′240 Patent, cord or fabric at concentrations of 20 percent by volume are preferred although concentration as low as 5 percent may be used. This Patent also teaches, that fiber, when loaded in an elastomer at the preferred concentrations, do not give the best results. The preferred construction of U.S. Patent No. 3,871,240 may not be a suitable solution for all belt types because of the relative height of the friction driving surfaces. For example, the use of cord or fabric is not a desirable solution for a multi-ribbed belt because of the relative small height of the ribs. Another use of fibers at friction driving surfaces is shown in U.S. Patent No. 3,190,137. Flocked fibers are embedded an vulcanized into peripheral sides of oppositely facing driving surfaces leaving very little, if any protruding fiber. According to a first aspect of the present invention there is provided a power transmission belt of the raw edge type comprising an elastomeric body portion with oppositely facing friction driving surfaces and having discontinuous fibres dispersed in, oriented transversely of and protruding from the elastomeric body portion at the driving surfaces characterised in that the portions of fibre protruding from the body portion are bent against the body in such a manner as to expose lateral side portions of fibre which define part of the friction driving surface. According to a second aspect of the present invention there is provided a method of making an elastomeric type power transmission belt of the raw edge type with an embedded load carrying section and an elastomeric layer having dispersed discontinuous fibres oriented transversely of the belt by grinding the elastomeric layer and forming oppositely facing friction driving surfaces, characterised by the steps of: dispersing discontinuous fibres in the elastomeric layer to a fibre loading from about 1 to about 6 percent by volume, the fibres having a greige tensile modulus sufficient to inhibit the fibres from being severed during grinding; forming the oppositely facing friction driving surfaces while grinding elastomer away and leaving portions of fibre protruding from the oppositely facing driving surfaces; bending a majority of protruding fibre portions and exposing lateral side portions of fibre; and establishing part of the friction driving surfaces with the lateral side portions of fibre. A belt construction is thus provided which is suitable for various belt forms with oppositely facing friction driving surfaces such as V-belts, joined V-belts, and multi-ribbed belts. An advantage of the invention is that the lateral side portions of fiber have a greater surface area than the generally end portions of protruding fibers as disclosed and taught in the prior art. Consequently lower loading of fibers in percent by volume may be used to alter the frictional characteristics of the oppositely facing driving surfaces. Another advantage is realized when in a multi-ribbed belt of the invention is exposed to low angular frequencies of about 20 Hz and high angular acceleration (e.g., angular accelerations up to 3,000 rad/sec²). The invention has the beneficial result of substantially inhibiting pilling of the lateral surfaces at the low frequencies. Consequently, belt life is improved in such applications. In accordance with the method of the invention, high tenacity and wear resistant fibers are dispersed in an elastomeric matrix of which a body is formed. The matrix with dispersed fibers, is optionally ground in the presence of a moisturing liquid and oppositely-facing friction driving surfaces are formed. The fibers have sufficient tensile modulus so as to inhibit them from being cut or ground off at an elastomer interface during the grinding operation. The fibers are bent along the driving surfaces and lateral side part portions. An object of the invention is to provide a belt construction where discontinuous fibers may be effectively used to control the frictional properties of a driving surface; a resulting advantage of the invention is that discontinuous fibers may be used at a volumetric loading of approximately half of that preferred as taught in the prior art where end portions of fiber are exposed. Other advantages or objects of the invention will be apparent after reviewing the drawings and description of preferred embodiments. Although the invention is adaptable to power transmission belts in general, a multi-ribbed belt is shown in detail for illustration purposes wherein; Figure 1 is a schematic view showing a multi-ribbed belt of the invention trained around grooved pulleys and tensioned with a backside idler; Figure 2 is an enlarged fragmentary cross sectional view taken along the line 2-2 of Figure 1 showing the belt in free span; Figure 3 is an enlarged view taken generally along the line 3-3 of Figure 2 but showing a portion of the belt in partial isometric view to further illustrate a friction driving surface; Figure 4 is an enlarged view taken along the line 4-4 of Figure 3 and showing protruding fibers bent to expose lateral side portions of fiber at a frictional driving surface; cross hatching is not used for clarity; Figure 5 is a view similar to Figure 2 but showing a V-belt of the invention; and Figure 6 is a view similar to Figure 2 but showing a joined V-belt of the invention. Description of Preferred Embodiments Referring to the Figures, a power transmission belt 10 of the invention with a multi-ribbed configuration is trained around multi-grooved pulleys 12, 14 and tensioned by a backside idler 16. The belt is fabricated using known techniques and has a tensile member 18 or load carrying section that is sandwiched between a first layer 20 forming the top portion 22 of the belt and a second layer 24 in which is formed a plurality of circumferential ribs 26. Any desired material may be used as the tensile member 18 such as cord of cotton, rayon, nylon, polyester, aramid, steel or even discontinuous fibers oriented for load carrying capability. Any of the suitable elastomeric materials may be used in constructing the first and second layers. For example, elastomers such as synthetic rubbers, natural rubbers, blends thereof, or castable elastomers such as polyurethane may be used. One or more layers 28, 30, of a textile material may be embedded in the top of the first layer to form a wear resistance surface such as to accomodate backside idlers or pulleys in a drive system. Discontinuous fibers 32 are dispersed in at least a major portion of that part of the second layer 24 which forms a body portion 34 having oppositely facing friction driving surfaces 36, 38. The fibers preferably have a length in a range from about.04 in. (1 mm) to about.47 in. (12 mm); but more preferably, the fibers have a length from about.16 in. (4 mm) to about.28 in. (7 mm); and most preferably from about.16 in. (4 mm) to about.24 in. (6 mm). It is important that the fibers have a greige tensile modulus sufficient to inhibit the fibers from being severed at the elastomer-fiber interface during a grinding operation when forming the oppositely facing sides (which is hereinafter explained in conjunction with the method of the invention). The fibers should have good wear resistant qualities so that it is not substantially worn away during belt use. Examples of fiber having suitable tension modulus and wear resistant qualities are aramid fibers, such as those sold under the trademark KEVLAR by du Pont de Nemours & Company; the trademark TECHNORA as sold by Teijin of Japan; and the trademark Twaron as sold by Enka of Holland [all having a greige tensile modulus of at least about 9 × 10⁶ psi (6333 Kg/mm²)]. The elastomeric body portion is loaded with fibers preferably from about.5 to about 20 percent by volume, and more preferably from about 1 to about 6 percent by volume. Most preferably, the fiber loading is about 3 percent by volume of the body portion (i.e., that portion of the body having the oppositely facing driving surfaces). The oppositely facing friction driving surfaces 36, 38 are formed in such a manner as to leave portions of fiber protruding from the elastomer at the oppositely facing driving surfaces. Most of the fibers protrudes from about.004 in. (.1 mm) to about.012 in. (.3 mm) from the elastomeric body. In contrast, prior art belts using cotton fibers have protruding portions from about.0026 in. (.65 mm) to about.005 in. (.13 mm). Thus, belts of the invention have fiber protruding approximately twice as far as that of known prior art belts. The protruding fiber portions are bent 40 against the body in such a manner as to expose lateral side portions 42 which define part of the friction driving surface. As particularly shown in Figure 4, most of the fiber portions are bent substantially in the same general direction leaving them oriented generally longitudinally 44 with the belt driving surfaces. It is estimated that the lateral side portions of fiber cover from about 15 percent to about 52 percent of the driving surface area at fiber loadings from about 1.7 percent to about 6 percent by volume respectively. Method As previously mentioned, the elastomeric body with dispersed fibers is ground to form oppositely facing friction driving surfaces. It is already known to form oppositely facing driving surfaces by grinding elastomeric layer in which are dispersed discontinuous fibers. An example of such a grinding process is disclosed in U.S. Patent Number 3,839,116. However, such known processes sever or terminate the fibers at the elastomeric body so that substantially only end portions of fiber are exposed. As previously mentioned, it is important to have fibers with a sufficiently high greige tensile modulus to inhibit severing the fibers at the elastomer-fiber interface during the grinding operation. In accordance with the invention discontinuous fibers, such as aramid fibers, are dispersed in a elastomeric layer in known fashion and oriented transversely of the belt. The body is ground in the presence of a moisturing liquid such as water soluable oil or water. It is believed that the moisturizing liquid acts to lubricate the fibers and inhibit them from being severed at the elastomer-fiber interface. The grinding operation also operates to orient the fibers generally longitudinally along the driving surface by bending the fibers and exposing lateral side portions. The grinding operation may be used in defining opposite facing frictional driving surfaces 44 of a V-belt 46 as illustrated in Figure 5 or the opposite facing frictional driving surfaces 48 of a joined belt 50 such as illustrated in Figure 6. Use In use, a multi-ribbed belt of the invention is used as in a serpentine front end-drive of a firing diesel engine. During operation of the engine, in such an application, low oscillatory angular frequencies of about 25 Hz. are encountered along with angular acceleration as high as about 3,000 rad/sec². A belt of the invention operated for 50 hours with no appreciable pilling as measured by a weight loss of only about 1 percent, and the protruding fiber remained substantially intact. Comparatively, a prior art belt with discontinuous cotton fiber (flock) was operated on the same engine for 50 hours where there was significant pilling as measured by a belt weight loss of about 9.7 percent; the portions of protruding cotton fiber was worn away to the elastomeric body. A peculiar problem associated with multi-ribbed belts is that of "pilling buildup" between adjacent ribs where pills accumulate and are retained. Because of this, "weight loss" is not always a totally accurate measurement. Nevertheless, belts of the invention exhibited substantially no "pilling buildup" whereas the prior art belt exhibited "pilling buildup" accompanied with substantial weight loss. The improved performance of the belt of the invention is attributed to the exposed lateral side portions of fiber which define part of the friction driving surface. As a fiber loading of about 5.2 percent by volume, the lateral side portions of fiber cover about 45 percent of the friction driving surfaces which is about 3 times greater than a prior art belt having substantially the same loading of cotton fibers. It is of course understood that the preferred embodiments have been described purely by way of example only, and modifications of detail can be made within the scope of the invention as claimed.

Claims: 1. A power transmission belt (10) of the raw edge type comprising an elastomeric body portion (34) with oppositely facing friction driving surfaces (36, 38) and having discontinuous fibres (32) dispersed in, oriented transversely of and protruding from the elastomeric body portion (34) at the driving surfaces (36, 38) characterised in that the portions of fibre (40) protruding from the body portion (34) are bent against the body portion in such a manner as to expose lateral side portions of fibre (42) which define part of the friction driving surface (36, 38). 2. The power transmission belt of claim 1 wherein the driving surfaces (36, 38) are ground. 3. The power transmission belt of claim 1 wherein the fibres (32) comprise from about 1 to 6 percent by volume of the elastomeric body portion (34). 4. The power transmission belt of claim 1 wherein majority fibres (32) have a length from 4 to 6 mm. 5. The power transmission belt of claim 1 wherein a majority of fibre portions (40) protruding from the body portion (34) have a length from 0.004 in.(0.1 mm) to 0.012 in.(0.3 mm). 6. The power transmission belt of claim 1 wherein a majority of the fibre lateral side portions (42) are oriented generally longitudinally (44) with the driving surfaces (36, 38). 7. The power transmission belt of claim 1 wherein a majority of the protruding fibre portions (40) are bent in the same general direction (44) at each driving surface (36, 38). 8. The power transmission belt of claim 1 wherein the fibres (32) are aramid. 9. The power transmission belt of claim 8 wherein the fibres (32) are of the type as sold under the trademarks consisting if KEVLAR, TECHNORA and TWARON. 10. The power transmission belt of claim 1 wherein the protruding fibre portions (40) define a means for inhibitting pilling of the elastomer at friction driving frequencies as low as about 20 Hz. and angular accelerations as high as 3,000 rad/sec². 11. A method of making an elastomeric type power transmission belt (10) of the raw edge type with an embedded load carrying section (18) and an elastomeric layer (24) having dispersed discontinuous fibres (32) oriented transversely of the belt by grinding the elastomeric layer (24) and forming oppositely facing friction driving surfaces (36, 38), charaterised by the steps of: dispersing discontinuous fibres (32) in the elastomeric layer (24) to a fibre loading from about 1 to about 6 percent by volume, the fibres having a greige tensile modulus sufficient to inhibit the fibres from being severed during grinding; forming the oppositely facing friction driving surfaces (36, 38) while grinding elastomer away and leaving portions of fibre (40) protruding from the oppositely facing driving surfaces; bending a majority of protruding fibre portions (40) and exposing lateral side portions of fibre (42); and establishing part of the friction driving surfaces with the lateral side portions of fibre (42). 12. The method of claim 11 comprising dispersing discontinuous aramid fibres (32) in the elastomer layer (24). 13. The method of claim 11 comprising dispersing discontinuous aramid fibres (32) in the elastomer, the fibres being of the type as sold under the trademarks KEVLAR, TECHNORA and TWARON. 14. The method of claim 11 comprising grinding oppositely facing friction surfaces (36, 38) while forming a multiribbed belt (10). 15. The method of claim 11 comprising grinding oppositely facing friction surface (44) while forming a V-belt (46). 16. The method of claim 11 comprising grinding oppositely facing friction surface (48) while forming a joined V-belt (50).

Inventors: SEDLACEK, DOUGLAS R.
Applicants: THE GATES RUBBER COMPANY
Application year: 1988
Main classification: F16G5
IPC codes: F16G5, B29D29, B32B7