Abstract:
A method of producing synchronous belts having two or more tracks of teeth extending obliquely from the belt. The method includes forming an internal drum mold from a series of concentric rings, building a belt sleeve around the drum mold, vulcanizing the belt assembly, cutting the belt sleeve into widths and removing drum rings from the belt sections.

Description:
TECHNICAL FIELD 
     This invention relates to synchronous drive belts and timing belts and more specifically to a method and apparatus for manufacturing a synchronous drive belt having two or more tracks of teeth which extend from the belt surface at oppositely balanced oblique angles. 
     BACKGROUND ART 
     U.S. Pat. No. 5,209,705 to Gregg ostensibly discloses a synchronous drive belt with oblique and offset teeth. 
     U.S. Pat. No. 3,078,206 to Skura ostensibly discloses a method of forming belt teeth and reinforced positive drive belts. 
     U.S. Pat. No. 2,600,775 ostensibly discloses a method and apparatus for making and curing power transmission belts. 
     Finally, Japanese Patent No. 59-133,034 is also directed to a method of manufacturing a synchronous drive belt. 
     Synchronous drive belts generally comprise a resilient elastomer reinforced with a longitudinal tensile member made up of a plurality of cords of a high elastic modulus. The cords may be made from glass fiber, carbon fiber, steel, polyester, high tenacity rayon or preferably, polyamide. 
     The tooth surface of the belt may be reinforced with an abrasion resistant fabric, one example of which is nylon. 
     The elastomers may be any one of those known to be suitable for use in such belts, including polychloroprene, polyurethane, NBR, IIR, IR, SBR, CSM, EPDM, other thermosets, thermoplastic elastomers and other polymer alloys. 
     Typically, synchronous drive belts are manufactured by winding layers of fabric, unvulcanized elastomer and cord on a drum. The drum functions as an internal mold and may have a periphery consisting of axially oriented evenly pitched grooves. During vulcanization, the belt slab is molded by pressure exerted by an external diaphragm or autoclave which forces the slab radially inwardly against the drum periphery. After vulcanization, the belt sleeve is slid axially off the drum or mold. The sleeve is then slit transversely into individual belts in a separate operation. 
     The synchronous belts so formed normally have a single track of teeth extending from the belt at right angles to the belt circumference, the teeth having dimensions compatible with the grooves on the drum periphery. A simple grooved drum is utilized in the manufacture of such belts. 
     It is known in the art to provide synchronous belts having at least two transversely adjacent rows of teeth which are at oppositely balanced oblique angles to the direction of the belt. One such belt structure is disclosed in U.S. Pat. No. 5,209,705 the disclosure of which is incorporated herein by reference. The belt structure disclosed therein provides certain advantages, especially relating to noise, which offer improvements over belts having a single track of teeth which extend at right angles to the belt circumference. 
     A problem encountered in the art, however, is the ability to manufacture the improved belts by a method that allows the building and vulcanization of a band having more than one belt section on an internal drum mold. The presence of the two or more tracks of teeth extending at oppositely balanced oblique angles on each belt section bars the cured belt sleeve from being slid axially off the drum mold, as is done in the prior art manufacturing method described above. Heretofore there has not been a viable method of manufacture of the improved belts. 
     The inventive process described herein provides a method whereby a synchronous belt having two or more tracks of teeth extending at oppositely balanced oblique angles may be advantageously manufactured in a way that is simple and effective. 
     DISCLOSURE OF INVENTION 
     In accordance with the practice of the present invention, there is provided a method of manufacturing a synchronous drive belt having teeth extending from a belt surface which comprises the steps of: 
     assembling an internal drum mold having a first set of concentric molding rings comprising adjacent right hand and left hand rings, the right and left hand rings having teeth-forming grooves therein, the grooves on each of the right and left hand rings being separated by a pre-determined pitch; 
     building a multi-plied belt band around the drum mold; 
     curing the belt band; 
     segmenting the cured belt band into belt widths; and, 
     removing the belt widths from the mold after segmenting the belt band into widths. 
     In accordance with another aspect of the invention, the grooves of the right hand ring are obliquely angled relative to a longitudinal direction and the grooves of the left hand ring are oppositely angled to the grooves of the right hand ring. In the inventive method, the step of assembling the internal drum mold comprises: 
     positioning the right hand ring in a predetermined position relative to the left hand ring such that the grooves on the right hand ring are offset from the grooves on the left hand ring by a predetermined distance; and, 
     employing holding means for holding the right hand ring in the predetermined position relative to the left hand ring. 
     In accordance with another aspect of the invention, the step of building a multi-plied belt band around the drum mold comprises: 
     laying a first fabric ply against the internal drum mold; 
     positioning a longitudinal tensile member over the fabric ply; 
     layering an elastomeric material over the tensile member; and, 
     layering a transverse reinforcement member over the elastomeric material. 
     In accordance with another aspect of the invention, the step of assembling the internal drum mold further comprises: 
     placing a spacer ring between first and second sets of molding rings. 
     In accordance with another aspect of the invention, the step of segmenting the cured belt band into belt widths comprises: 
     mounting the drum mold assembly onto a lathe; and, 
     cutting the cured belt band on either side of the first molding ring set. 
     According to another aspect of the invention, the step of removing the belt widths from the mold after the step of segmenting the belt band into widths comprises: 
     sliding the right hand ring away from the belt width in a first direction; and, 
     sliding the left hand ring away from the belt width in a second direction. 
     One advantage of the present invention is the ability to effectively manufacture synchronous belts having two or more adjacent rows of obliquely angled teeth. 
     Another advantage of the present invention is the ability to vary the number of synchronous belts made in one curing operation. 
     Another advantage of the present invention is the precision with which the angled teeth of a finished belt can be produced. 
     A Another advantage of the present invention is the replaceability of drum sections which may be damaged or become out of desired tolerance during operation. 
     Another advantage of the present invention is the ability to incorporate portions of conventional belt building methods to form an improved belt structure. 
     Still other benefits and advantages of the invention will become apparent to those skilled in the art to which it pertains upon a reading and understanding of the following detailed specification. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     The invention may take physical form in certain parts and arrangement of parts, a preferred embodiment of which will be described in detail in this specification and illustrated in the accompanying drawings which form a part hereof and herein: 
     FIG. 1 is a bottom plan view of a portion of a synchronous drive belt produced by the method of the present invention. 
     FIG. 2 is a side view partly in section taken along line  2 — 2  of FIG.  1 . 
     FIG. 3 is a drum mold assembly used in accordance with the method of the present invention. 
     FIG. 4 is a cross-sectional view of the drum mold assembly taken along the line  4 — 4  of FIG.  3 . 
     FIG. 5 is a side view of a molding ring used in accordance with the method of the present invention. 
     FIG. 6 is a front view partly in section taken along the line  6 — 6  of FIG.  5 . 
     FIG. 7 is a blow up of a section of a right hand molding ring used in accordance with the method of the present invention. 
     FIG. 8 is an enlarged view of a section of a left hand molding ring used in accordance with the method of the present invention. 
     FIG. 9 is a sectional view of an uncured belt band built in accordance with the method of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawings wherein the showings are for purposes of illustrating a preferred embodiment of the invention only and not for purposes of limiting the same, FIGS. 1 and 2 show a belt  10  such as the type manufactured in accordance with the inventive method. The belt  10  has at least two transversely adjacent rows of teeth  13 , having centerlines  13   a  and  13   b.  The teeth are uniformly spaced apart in the longitudinal direction by their pitch P and extend obliquely to the longitudinal direction such that the teeth  13  in the transversely adjacent rows are at oppositely balanced angles  17  and the centerlines  13   a  and  13   b  are offset from each other by a distance  21  of from 10% to 90% of the pitch P. Optimally, the offset distance is 50% of the pitch P. The oblique angle  17  can range from 15° to 45°. 
     According to the inventive method, a drum mold  24  is assembled in order to form the belt  10 . With reference to FIGS. 3-6, the drum mold  24  comprises at least one ring set  28 . Each ring set  28  will form one synchronous belt  10 . Each ring set  28  comprises a right hand ring  30  and a left hand ring  32 . Right hand and left hand refer to the direction of the helical grooves  34 A,  34 B formed on the peripheral surfaces of the rings  30 ,  32 . The helical grooves  34 A on the right hand ring  30  will form one track of obliquely extending teeth  13  of the finished belt  10  whereas the helical grooves  34 B on the left hand ring  32  will form the adjacent track of obliquely extending teeth  13  of the finished belt  10 . Because the grooves  34 A and  34 B are oppositely angled, the teeth  13  formed thereby exhibit the oppositely balanced teeth of the improved belt structure. 
     The drum mold  24  may comprise more than one ring set  28 . Successive ring sets  28  may be separated by center blank rings  36  which act as spacers. Adjacent the outermost edges of the ring sets  28  may be positioned end ring blanks  38 . Finally, bottom and top end rings  40  and  42 , respectively, may be placed at the ends of the drum mold  24 . The bottom and top end rings  40 ,  42  may provide flanges  44  for the drum mold  24  to assist in the belt building process. 
     In a preferred embodiment, each drum mold  24  comprises four ring sets  28 , spaced from each other by three center blank rings  36 . The grooves  34 A,  34 B on successive ring sets  28  form a series of chevron shaped grooves around the drum mold  24 . In the preferred embodiment, the right hand, left hand, center blank, and end blank rings  30 ,  32 ,  36 ,  38  comprise aluminum alloy, although other material may be employed. 
     The positioning of the grooves  34 A of the right hand ring  30  relative to the grooves  34 B of its mating left hand ring  32  is crucial in order to maintain the proper distance  21  of the finished belt  10 . Therefore, the rings  30 ,  32 ,  36 ,  38 ,  40 ,  42  which form the drum mold  24  may include holding means for holding the proper positioning therebetween. For instance, the rings  30 ,  32 ,  36 ,  38 ,  40 ,  42  may comprise interlocking grooves or registers on their upper and lower faces (not shown) such that the rings may be stacked and remain concentric and properly positioned. 
     With particular reference to FIG. 4, a cross sectional view of a preferred embodiment of the drum mold  24  is shown. The successive rings  30 ,  32 ,  36 ,  38 ,  40 ,  42  are mounted on a central shaft  46  to permit rotation of the drum mold  24  while a belt band is being built thereover. The presence of the central shaft  46  also allows the drum mold  24  to be rotated on equipment while the cured belt band is being segmented into belt widths. The preferred embodiment also comprises an internal annular channel  47  to allow steam heating of the drum mold  24 . 
     The successive rings  30 ,  32 ,  36 ,  38 ,  40 ,  42  are held in proper relation by the presence of one or more keyways  48 . 
     As more clearly shown in FIG. 5, there are three keyways  48  in a preferred embodiment of the drum mold  24 . The keyways  48  are equally spaced around the internal surface  50  of each ring. A dowel (not shown) may be inserted into keyway  48 . 
     In FIG. 6, a right hand ring  30  is shown partly in plan and partly in section. The helical grooves  34 A make an oblique angle  17 A which corresponds to the oblique angle  17  formed by the teeth  13  of the finished belt  10 . The helical grooves of a left hand ring (not shown) make an oppositely balanced oblique angle. 
     Referring now to FIGS. 7 and 8, the relationship of the keyway  48  with the grooves  34 A,  34 B of mating right hand ring  30  and a left hand ring  32  is shown. In a preferred embodiment, the centerline  52  of a keyway  48  is aligned with the centerline  54 A of a groove  34 A on a right hand ring  30 . The centerline  52  of the keyway  48  on the mating left hand ring  32  is offset from the centerline  54 B of groove  34 B by a distance D that will determine distance  21  of the belt  10  formed using the drum mold  24 . In a preferred embodiment, the distance D is 40% to 60% of the pitch P. It is understood that the presence of a keyway  48  is only one holding means for holding the right hand ring  30  in proper relationship to its mating left hand ring  32  and other holding means may be employed. It is, however, a crucial element of the invention, that the grooves  34 A and  34 B of mating right and left hand rings  30 ,  32  be offset a given distance D in order to provide the offset teeth  13  of the finished belt  10 . 
     With reference to FIG. 9, the inventive method includes building a belt band  60  around the internal drum mold  24 . The inventive method may include conventional construction methods which utilize a fabric teeth jacket  62  laid against the periphery of the drum mold  24 , followed by a longitudinal tensile member  64 , and an elastomeric material  66  to form the body of the belt  10 . In addition, one embodiment of the inventive method includes adding a transversely laid reinforcement member  68  on the outside of the band  60 . The inclusion of the transverse reinforcement member  68  allows the finished belt  10  to absorb internal side forces created within the two rows of teeth  13 . 
     After the band  60  is built, it is then cured by means that are typical in the art. One such curing means may be to place the built assembly in a can containing a diaphragm. Pressure is applied to the diaphragm and the belt band  60  is heated in order to mold and vulcanize the material. Alternately, a free diaphragm in an autoclave may be used. 
     After cure, the belt band  60  is not axially slid off the drum mold  24 , as is typical in prior art methods of producing synchronous belts. In the inventive method, the cured belt band  60  is maintained on the drum mold  24 . The drum mold  24  is placed on equipment similar to a lathe and the cured belt band  60  is cut into separate widths. The cuts are made into the cured belt band  60  over the center blank rings or spacers  36 . 
     Because the center blank rings  36  and the end ring blanks  38  are not helically grooved, they are easily slid away from the belt widths. The right hand ring  30  is moved away from the belt width in a first direction, and the left hand ring  32  is moved away from the belt width in a second, opposite direction. In that way, the right hand ring  30  is removed in a direction compatible with the belt teeth  13  formed therewith, and the left hand ring  32  is removed in a direction compatible with the belt teeth  13  formed therewith. 
     Following the removal of all the ring sections, the lateral edges of the individual belt widths can be trimmed to their finished width. 
     The preferred embodiments have been described, hereinabove. It will be apparent to those skilled in the art that the above methods may incorporate changes and modifications without departing from the general scope of this invention. It is intended to include all such modifications and alterations in so far as they come within the scope of the appended claims or the equivalents thereof.