Timing BeltsPage 1 of 7 Disclaimer: The information on this page has not been checked by an independent person. Use this information at your own risk. ROYMECH Timing Belts Manufacture Import Timing belts from 20 years' Timing Belt maker, Earn more Profit www.aa-top.com Seeking Fashion Belts Various Belts in One Shop China Stylish Design & Affordable Price www.OneShopChina.com Flat Wire Conveyor Belts Rugged, open mesh, large inventory We manufacture these belts. www.keystonemfg.com Home Drive Belts Timing Belts Important Note:..The notes below are intended to be concise informative guidance notes. Manufacturers literature and the relevant standards provide the necessary detailed information required for detail design. I have included links to sites providing good quality information on this topic. Introduction Synchronous / Timing belts are basically endless flat belts which pass over pulleys- the belts having grooves which mate with teeth on the pulleys. These belt drives, unlike flat and vee belt drives are positive. Any slip of the belt relative to the pulleys is minor in degree and is due to belt stretch, or erosion of the grooves. These belts are used for power transfer and for synchronised drives to ensure that the driven pulley is always rotating at a fixed speed ratio to the driving pulley. The first synchronous belts had a trapezoidal tooth profile, and is identified as timing belts. The belt tooth profile is a trapezoidal shape with sides being straight lines The profile of the pulley teeth which mates with the belt is involute. These belts are based on imperial (inch) pitch sizes and can provide power transmission up to 150 kW. The development of the classical timing belt with has a rounded tooth (curvilinear tooth profile) and is identified as as the high torque drive, or HTD. Advantages of this belt design include.. Proportionally deeper tooth; hence tooth jumping or loss of relative position is less likely Lighter construction, with consequent reduced centrifugal loss. Smaller unit pressure on the tooth since area of contact is larger. Greater shear strength due to larger tooth cross section. Lower cost as a narrower belts will handle larger load. Installation tension is reduced resulting in lower bearing loads. l l l l l HTD sprockets have metric pitches (3 5 8 14 & 20) and can transmit up to 1000 kW. The most advanced synchronous belts, has a modified rounded tooth profile with a higher tooth angle and shallower tooth. These belts e.g Gates Powergrip GT have available pitch sizes of 2mm, 3mm & 5mm and can powers up to transmit up to 600 kW . The belts have the advantages that they provide a smoother drive at higher accuracy, A correctly designed and installed synchronous belt drive should operate successfully for between 8000 and 12000 hrs and have an operating efficiency of about 98%. Synchronous belts have a number of advantages such that they are often used for applications not requiring shaft synchronization. Their section and flexibility enable timing belts to operate very well on miniature drives and in applications involving high speeds or small pulleys. They are extremely efficient when correctly installed. They can also be specified to continuous high loads. For these reasons, synchronous belts have proved to be cost effective in non-synchronous applications as drives for power saws, motorcycles, and domestic appliances. The disadvantages of synchronous belt drives are that they are generally more costly compared to other belt drive options and the require accurate alignment of the pulleys for efficient reliable operation http://www.roymech.co.uk/Useful_Tables/Drive/Timing_belts.html 4/3/2009 2 101. or lawn and garden equipment.7 19. nylon are low-cost options when power requirements are low as in office machines or home appliances such as vacuum cleaners.6 127101. H. Synchronous belts are often provided with nylon facings to provide the necessary wear resistance and can include conductive coatings.1 50.co. Relevant Standards The British Standard for timing belt drives was BS 4548:1987 :Specification for synchronous belt drives for industrial applications .032 5.6 127 HTD.000 mpm).Curvilinear Belt Section Designation Pitch mm Widths Available mm http://www.html 4/3/2009 .g natural rubber.826 6. keyways or by using proprietory shaft locking bushes such taperlock bushes. polychioroprene.08 9. core with reinforcement to provide increased tensile strength. Pulleys are mounted to shafts using pins.Pulleys ISO 5296-1:1989:1989: Synchronous belt drives -. Pulleys can have one or two flanges to ensure the belts are retained in place. L.g.652 12. In modern drives the most common reinforcement is glass fiber.Belts -.2 50. Basic Timing Belt Parameters Classical Timing belts Belt Section MXL XL L H XH XXH Meaning Extra Light Extra Light Light Heavy Extra heavy Double extra heavy 2.7 22. Plastic pulleys e.uk/Useful_Tables/Drive/Timing_belts.roymech.neoprene. Steel(and Stainless Steel )is preferred to iron when the drive will exceed the safe operating limits for cast iron (2000 mpm) or ductile iron (2500 to 3.8 76.2 101.225 31.6 50.35 6.Timing Belts Page 2 of 7 Construction Belts Synchronous belts are made with elastomer e.8 76.Part 1: Pitch codes MXL.75 Pitch mm Widths Available mm 3. Pulleys Synchronous drive pulleys are often made of ductile or cast iron.8 76. On pulleys with vertical shaft axes the lower face of each pulley should include a flange and one pulley should include two flanges. as in some power tools. polyurethane. For drives with horizontal pulley axes it is normal to have two flanges to retain the belt (two flanges on one pulley or one flange on each pulley on opposite sides). This standard is still in use but is declared as obsolescent the current standard in europe for timing belt drives is ISO 5294:1989: Synchronous belt drives -.05 4. XL.4 38.525 12.2 50.8 76. Plastic gears may also be acceptable when it is acceptable that the belt service life is short. These applications can include high speed drives with low inertia.Metric and inch dimensions This is not equivalent and belts and pulleys to the British Standard are not interchangeable with the ISO standard. These belts were originally reinforced with steel to provide the necessary strength. but aramid is used if maximum capacity is required.4 19.05 25.35 9. Aluminum is a often selected for drives that require low weight.05 25. XH and XXH -. 9.. Tr = P2(5.10-3 Belt width =6.048 mm. 4) A belt section is initially selected (assuming MXL) using a graph as typically shown below 5) A drive geometry is derived selecting suitable pulleys. and belt Centre Distance .P22).586. driven equipment and operating period a service factor is obtained .see below 3) A design torque is obtained based on the product of the torque required and the service factor ..213.co.P22).Timing Belts Page 3 of 7 3M 5M 8M 14M 20M 3mm High Torque Drive 3 5mm High Torque Drive 5 8mm High Torque Drive 8 14mm High Torque Drive 20mm High Torque Drive 14 20 6 9 15 9 15 25 20 30 50 85 40 55 85 115 170 115 170 230 290 340 GT ..10 -3 To design an MXL belt system using the torque method.see below 7) A suitable belt width is selected -Using a table as provided below. driven equipment and operating period a service factor is obtained .7 .2. shock loads.. etc) are calculated 2) From information on the driver. The method used for the HTD and other modern belt options will be provided at some future date.. The outline method for the MXL drive is provided below.Some iteration may be required Torque Method The classical MXL belt and the Curvilinear more advanced belt options are designed based on torque levels.Tr = P 2(11.. friction.. For the more advanced drive belt design refer to manufactures literature.10 -5.. 1) The driven speed and the maximum driven torque required (including inertia load...html 4/3/2009 .P22).uk/Useful_Tables/Drive/Timing_belts.5147.Some Pulley sizes are provided below 6) A Basic Power for the belt is calculated and a mesh factor is calculated . Torque ratings of belts T r (Nm) at P2 PCDs (mm) Belt width =3.. friction.10-5.roymech.36 . Tr = P2(8.see below 3) A design power is obtained based on the product of the Driven Power required and the service factor ..826mm. shock loads. I will include notes on these belt drives at a later date. etc) are used to calculate the required driven power 2) From information on the driver.10-6.35 mm. and belt Centre Distance . 4) A belt section is initially selected using a graph as typically shown below 5) A drive geometry is derived selecting suitable pulleys.Some Pulley sizes are provided below 6) The design torque is divided by the teeth mesh factor (see below) to arrive at an adjusted torque http://www.Curvilinear Belt Section 2MR (Gates) 3MR (Gates) 5MM (Gates) Name 2mm High Torque Belt 3mm High Torque Belt 5mm High Torque Belt 2 3 5 Pitch mm Widths Available mm 369 6 9 15 9 15 25 Note : The various notes below relate to the classical timing belt drives.1. The MXL belts operate generally at relatively low belt speeds so the torque levels are similar for the normal range of pulley rotational speed. Torque ratings can be calculated of each of the MXL belt widths as follows: I have converted an imperial formula to a metric formula and minor differences with the original formulae results..10 -3 Belt width =4. Designing a Synchronous Belt System Belt design procedures can be based on torque calculations or they can be based on power calculations. Power method 1) The driven speed and the maximum driven torque required (including inertia load.03 . A similar method is used for designating metric belt designations Initial selection of Timing Belt When the design power has been determined (Power x Service Factor) a synchronous belt can be selected generally using a graph similar to the one below.75 inches in width would be specified as a 300L075 Synchronous Belt.033 0.477 12MXL 7.071 0.html 4/3/2009 .This is provided for guidance only and is copied from published graphs generally available.040 0.. l r = Rpm of faster shaft /1000 P2 = Pitch diameter of smallest Pulley (mm) http://www.83mm width = 6.066 0. driven load types and operating periods. The first digits specify the belt length to one-tenth inch followed by the belt section (pitch) designation.roymech.co.097 0.087 0.090 14MXL 9.1102 0.166 24MXL 15.4056 0.097 0.Timing Belts Page 4 of 7 7) The table below is used to select the belt width which has a torque value equal to or larger than the corrected torque No Teeth -> PCD(mm) -> width = 4. Or even better let the suppliers do the design for you.054 0.078 0.106 Torque Rating for MXL Belt (Nm) 16MXL 10.5194 0.35mm 10MXL 6.211 30MXL 19.076 0.064 0. Horsepower Rating of Timing Belt This method is based on the method shown in Machinery's handbook.052 0.6332 0.000 inches pitch length and 0.uk/Useful_Tables/Drive/Timing_belts..108 0. It is preferable to use the calculation tool provided by the belt manufacturers to size the belts for detail design.227 width =3.092 0.0678 0.7724 0.151 22MXL 14. Typical service factor values are included on the linked page Service Factors Designating Classical Synchronous belts Synchronous Belt sizes are identified by a standard number.045 0.151 0.076 Service Factors When designing belt drives it is normal to apply a service factor to the drive operating load to compensate for allow for different driver type.130 0.05mm 0. an L section belt 30. The Power ratings of belts for the basic belt widths (in brackets) are as identified below.121 18MXL 11.059 0.182 28MXL 18.3378 0..163 0.224 0.119 0.136 20MXL 12. The digits following the belt section designation represent the nominal belt width times 100.9286 0.. For example. 73. Rounded down to nearest whole number.Z.07.Z2 ) For Belt (width) = XXH (127).2). 4) Use the table below and select a width with a width factor higher than the calculated width factor required http://www...Z.. P r = 0.746..4 For Belt (width) = XL (9.P2 ] /2 3) The belt contact angle α = arcsin(d /C) . Pr = 0..html 4/3/2009 .Z2 ) For Belt (width) = H (76.Z.r /25.7.C= Centre distance 4) The belt fall length = fl = d / tan α 5) The contact length Small Pulley= CL2= P2.(7.4 0.10-5.Z..Timing Belts l Page 5 of 7 Z = P 2.roymech.8 0....(0.21 . and smaller pulley size. For drives with small angles of lap on the smallest pulleys the mesh factor is required. smaller pulley speed.6 0.7.Z2 ) Determining the timing belt length 1) The Pitch dia of a pulley P = No Teeth on Pulley . Pr =0.6).746.81.01.CL1 + 2... Mesh Factor The horsepower ratings obtained above are based on the smallest pulleys having six or more teeth in mesh.. Pitch /π 2) The Drop distance d = [ P1 .uk/Useful_Tables/Drive/Timing_belts. Pr = 0.2 Determination of the Belt Width required 1) First establish the design power to be transferred(kW) = Service Factor x Power.. [90 + α]/180 degrees 7) The Belt Length L = (2.14 .4. π..10-3.change one or more of belt size .Z2 ) For Belt (width) = XH (101. 2) Select a suitable belt and calculate the basic power using the belt size...Z2 ) For Belt (width) = L (25.. pulley size or speed.652).co.746..746.CL1 8) Total number of teeth on belt = L / Pitch 9) Number of teeth in mesh (small pulley) = CL2 /Pitch.10 -3.0916 . 3) Divide the Basic power/ Design power to obtain a belt width factor.1. π... 3) If the basic belt power is less than the design power. [90 .α]/180 degrees 6) The contact length Large Pulley = CL1=P1.436 ..(0.3.Z. No Teeth in mesh 6 or more 5 4 3 2 Mesh Factor 1 0.10-4..41..fl) + 2.. Pr =0..(3.4).68.10-3..746.(11. 62 340.94 30 31.43 0.43 39.25 8.60 21 19.35 0.58 13.63 1.19 300.06 OD 5.64 11.53 144. DANotes Vee Belt Drives.72 303.02 96.50 262.00 - Page 6 of 7 0. 8.29 0.70 0.68 64.11 103.79 167.57 46.6 127 MXL XL L H XH XXH 0.39 33 121.81 75.35 9.73 1.31 24 40.87 202.15 XXH Teeth PCD OD 181.47 421.35 848.57 50.uk/Useful_Tables/Drive/Timing_belts. I recommend this product Timing belt selection and Troubleshooting .07 22 38.37 17 27.18 153.A definitive theoretical and practical review with various useful tables Helixtech.25 26 60.09 232.72 18 15.62 1.com .13 15 12.78 1.93 72 L Teeth PCD OD 30..53 10.93 25 42. .19 48 339.04 25 78.72 1.42 40 76. 7. 2.85 79.40 132.45 219.37 32 72.43 115.30 220.45 41.36 506.93 129.45 136.25 591.07 26 84.12 20 48.01 133.11 7.83 78.81 38.81 38.27 161.Timing Belts Table of Belt Width Factors Belt Width Belt Section 3.58 90 594.57 48 H Teeth PCD OD 40.96 6.60 150.826 6.19 485.70 20.15 70.html 4/3/2009 .76 259.16 22 52.02 20 18.40 18.72 1.35 50 87.56 0.66 239.41 38.70 65.17 15.14 145.70 160.80 75.57 35.10 141.01 30 51.96 90.uk http://www.65 13 42.23 13.19 111.87 25.Timing Belt Supplier .99 83.67 10 17.90 12 21.49 138.Catalogue download available HPC Gears . .00 Typical Pulley Sizes Below are listed a collection of pulley Dimensions (PCD and OD) for pulleys in the classical timing belt range.54 72 92.29 28 64.23 209.37 26 27.74 51.costly Wyko.35 9.00 0.72 67.77 71.94 181.64 152.28 44.91 178.00 - 0.88 19 63.10 482..8 76.32 86.36 128.57 906..67 28 28.98 91.51 34 127.83 40 163.07 17 14. 6.30 30 212.47 7.54 26 45. In practice there are a vast number of pulleys available from suppliers on the belt sections shown and on other higher specification sections.43 39.62 77..00 23 75.40 132. 5.19 24 23.99 18 29.46 21 35.52 15.46 27.14 14 24. 4.98 280.46 48 80.60 40 282.08 195.87 176.46 636.Some Formulae -Power ratings for HTD belts included Fennerprecision .13 199.29 22.21 57.51 48.34 124.64 59.77 38 151.59 11 36.66 648.21 0.56 10 33.Vee belt supplier (Fenner) -limited information available online Mitcalc.96 33.45 0. Additional data is available using the links below and preferable by contacting the suppliers.44 177..78 17 57.co.76 96 113.28 120.84 18 60.68 14 48.11 28.35 32.68 20 155.04 41.32 29.A software package for belt /chain drives .90 22 20. MXL Teeth PCD 10 11 12 14 16 18 20 21 22 24 28 30 32 36 40 42 44 48 60 72 6.7 19.29 11 19.63 84 101.60 55.08 18 44.41 42 71.05 25.94 21 72.78 16 13.Supplier -Technical library includes comprehensive design downloads for timing belts Gates-Europe .41 909.34 31.32 727.53 32 38.50 60 84.15 44 218.82 54 97.91 67.04 192.Some Calculators Ads by Google Timing Belts Ribbed Belts PU Belts Synchronous Belt Special Belt This Page is being developed Home Drive Belts Send Comments to [email protected] 84.11 17.roymech.71 36 64.91 20 66.71 90 105.91 181.67 72 509.76 9.52 60 116.26 23. 3.05 30.78 28 48.79 168.2 101.28 119.78 25 25.19 30 97.01 25 183.45 0.78 60 424.33 30 68.94 11...57 336.67 62.05 4.00 0.47 43.65 44 77.Excel based software providing coded belt calculations( very reasonably priced.62 12 39.51 44.15 108.26 32 109.84 11.61 7.24 32 58.64 59.84 20 33.55 10 11 12 13 14 XL Teeth PCD OD 16.15 26 198.64 36 145.17 26..69 XH Teeth PCD OD 127..54 47.38 223.Very useful notes Stock Drive Produces/Sterling Instruments .00 679.20 24 56.85 80.96 42 181.Timing Belt Supplier .05 137..34 126.72 162.07 606.co.1 50.45 0.72 15 51.84 120 121.30 36 46.52 13 22.49 140.45 34 226.25 401.38 603.652 12.79 17.51 47.87 25.40 18.49 26.00 - 0.12 48 80.75 16 54.18 40 67..15 343.05 40 42 44 48 50 54 60 72 Links to Belt Design 1.53 144.58 35 133.02 20.76 16 25.38 35.52 194.54 18 141.13 28 90.15 676. 9.62 152.02 90.61 56.56 404.77 72.Leading timing belt drive supplier.30 252.55 51.83 23 169.06 99.35 169.61 19 32.68 63..4 38.64 22. .93 846. Timing Belts Last Updated 31/07/2008 Page 7 of 7 http://www.co.html 4/3/2009 .uk/Useful_Tables/Drive/Timing_belts.roymech.