THE WORLD OF TIMING BELTS - MAELabs UCSD

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Steel Tensile Strength 360,000 lbs/in2 Elongation at break 2.5% Modulus (approx.) 15,000,000 lbs/in2 Additional characteristics of tension members and their effect on the drive design are shown in tabulated form in Table 1. Belt Requirements Table 1 Comparison of Different Tension Member Materials* E = Excellent G = Good F = Fair P = Poor Operate over Small Pulley High Pulley Speed High Intermittent Shock Loading Vibration Absorption High Torque Low Speed Low Belt Stretch Dimensional Stability High Temperature 200° F Low Temperature Good Belt Tracking Rapid Start/Stop Operation Close Center-Distance Tolerance Elasticity Required in Belt * Courtesy of Chemiflex, Inc. 6.2 Cord Twist And Its Effect On The Drive There is a specific reason for not applying the yarn directly in the form of untwisted filaments around the mold. If the filament would be applied continuously, the top and bottom of the belt body would be prevented from being properly joined, and separation could result. See Figure 15. Two strands each composed of several filaments are twisted around each other, thus forming a cord which is subsequently wound in a helical spiral around the mold creating a space between subsequent layers, which corresponds to the step of the helix. The two strands, however, can be twisted two ways in order to create an "S" or a "Z" twist construction. See Figure 16. Nylon E E F E P P P P F E F P E Polyester Cont.Fil. Yarn G E G G P P P P G G G P G Polyester Spun Yarn E E G E P P P P G E E P E Kevlar-Polyester Mix F F E G F P F P G G G P G Step of Helix Kevlar Cont.Fil. Yarn P P E F G G G E G F P G P Kevlar Spun Yarn F F E F F F G E E G G F P Spirally Applied Filament Fig. 15 Belt Cross Section Fig. 16 Cord Twist Glass P P P P E E E E E F P E P Continuously Applied Filament Stainless Steel P P G P E E E E E P E E P Polyester Film Reinforcement G G F F F G G F G E G G P T-12
The "S" twist is obtained if we visualize the two strands being held stationary with our left hand on one end, while a clockwise rotation is imparted by our right hand to the two strands, thus creating a twisted cord. The "Z" twist is obtained similarly, if a counterclockwise rotation is imparted to the two strands. Different types of cord twist will cause side thrust in opposite directions. The "S" twist will cause a lateral force direction which will obey the "Right Hand" rule as shown in Figure 17. Belt Travels Toward Motor Belt Travels Away From Motor (a) Clockwise Rotation (b) Counterclockwise Rotation Fig. 17 Right Hand Rule Applicable to "S" Twist A "Z" type cord twist will produce a direction of lateral force opposite to that of "S" cord. Therefore, in order to produce a belt with minimum lateral force, standard belts are usually made with "S" and "Z" twist construction, in which alternate cords composed of strands twisted in opposite directions are wound in the belt. This is illustrated in Figure 18. The lay of the cord is standard, as shown in Figure 18, and it is wound from left to right with the cord being fed under the mold. The smaller the mold diameter and the fewer the strands of cord per inch, the greater will be the helix angle, and the greater the tendency of the lay of the cord to make the belt move to one side. In general, a standard belt of "S" and "Z" construction, as shown in Figure 18, will have a slight tendency to behave as a predominantly "S" twist belt, and will obey Fig. 18 "S" and "Z" Cord Lay of the Mold the "Right Hand" rule accordingly. 6.3 Factors Contributing To Side Travel The pulleys in a flat belt drive are crowned to keep the belt running true. Since crowned pulleys are not suitable for a timing belt, the belt will always track to one side. Factors contributing to this condition include: I. In the Drive 1. Misalignment – A belt (any belt – any construction) will normally climb to the high end (or tight) side. 2. Tensioning – In general, lateral travel can be altered or modified by changing tension. 3. Location of plane – Vertical drives have a greater tendency to move laterally due to gravity. T-13
Page 1 and 2: SECTION 1 INTRODUCTION THE WORLD OF
Page 3 and 4: The main stress line in a trapezoid
Page 5 and 6: Figure 5 shows an illustrative grap
Page 7 and 8: 4.3 Noise The smoother meshing acti
Page 9: The tension members are embedded in
Page 13 and 14: SECTION 7 BELT TOOTH PROFILES There
Page 15 and 16: In order to provide fast reference,
Page 17 and 18: No. of Pitch Diameter Outside Diame
Page 19 and 20: No. of Pitch Diameter Outside Diame
Page 21 and 22: T-23 7.003 7.066 7.130 7.194 7.257
Page 23 and 24: T-25 13.130 13.250 13.369 13.488 13
Page 25 and 26: T-27 6.015 6.053 6.090 6.128 6.166
Page 27 and 28: T-29 5 mm Pitch HTD ® Pitch Pulley
Page 29 and 30: T-31 8 mm Pitch HTD ® Pulley Dimen
Page 31 and 32: T-33 2 mm Pitch GT ® Pulley Dimens
Page 33 and 34: T-35 Table 13 (Cont.) 3 mm Pitch GT
Page 35 and 36: T-37 5 mm Pitch GT ® Pulley Dimens
Page 37 and 38: SECTION 9 DESIGN AND INSTALLATION S
Page 39 and 40: slip), and because they require min
Page 41 and 42: elts than pure water. Urethane timi
Page 43 and 44: angular shaft alignment, resulting
Page 45 and 46: • Design with large pulleys with
Page 47 and 48: inch (0.4 mm per 25 mm) of span len
Page 49 and 50: overloaded which may cause an edge
Page 51 and 52: 4. Pulleys for fixed center systems
Page 53 and 54: When identifying a shaft center loc
Page 55 and 56: procedures can be used for finding
Page 57 and 58: In measuring the length of a synchr
Page 59 and 60: Tolerancing/Inspection Procedure: A
Page 61 and 62:
Table 31 ISO Pulley O.D. Tolerances
Page 63 and 64:
Belt Type MXL XL 2 mm GT 3 mm GT &
Page 65 and 66:
Drive selection procedures for driv
Page 67 and 68:
Fig. 39 Belt Nomenclature The use o
Page 69 and 70:
T-71 1.000 1.042 1.053 1.056 1.059
Page 71 and 72:
T-73 2.000 2.083 2.100 2.105 2.118
Page 73 and 74:
SECTION 22 CENTER DISTANCE FORMULAS
Page 75 and 76:
22.6 Determination Of Belt Size For
Page 77 and 78:
pm of Faster Shaft 14,000 12,000 10
Page 79 and 80:
20,000 10,000 8,000 6,000 5,000 4,0
Page 81 and 82:
The number of teeth in mesh on the
Page 83 and 84:
Table 40 (Cont.) Rated Torque (N⋅
Page 85 and 86:
Page 87 and 88:
Page 89 and 90:
Table 43 (Cont.) Rated Kilowatts fo
Page 91 and 92:
Page 93 and 94:
Table 45 Rated Torque (N⋅m) for S
Page 95:
Table 47 Rated Torque (lb⋅in) for
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THE WORLD OF TIMING BELTS - MAELabs UCSD

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