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3225 Timing Belt Selection Using Visual Basic Edward M. Vavrek Purdue University North Central Abstract Timing belts are used in many different machine applications. The sizing and selection of an appropriate timing belt and its components is usually done with a belt manufactures catalog. The catalog gives the necessary equations, figures, charts, and tables in order to select a complete timing belt system. This program replaces the manufactures catalog and allows the user to properly size a belt drive system and select all the relevant components using the computer. The program is written in visual basic. Visual basic was selected because of the windows environment in which most users would feel comfortable using. Also, figures and pictures can be inserted to enhance the capabilities of the program and allow the user to visualize and understand the process and procedure of selecting a belt system. The user will go through the program inputting values into text boxes, initiating

events by clicking on command buttons and using list boxes to select different components. The user is prompted to input horsepower, speed requirements, shaft diameters, and center distance between pulleys. Since the program supports figures and tables, the user can look up values required directly on the screen. The belt pitch is selected based on design horsepower and pulley speed. The user can simply select the required belt pitch based on the graph shown The program will calculate and display the belt and pulley combinations based on input values of the center distance and pulley ratio. The belt width is determined based on input values of horsepower, pulley size, and pulley speed. The program guides the user through the selection procedure outputting a complete belt drive system. Page 5.6681 The complete belt drive system consists of the following output. Two pulleys required to match the speed ratio. The corresponding bushing that goes with the pulleys to hold them to the

shaft, the key size required with for bushing and shaft size. The selected belt pitch and belt width required for the design horsepower and speed is also displayed. The final output is the belt length required to maintain the center distance between the two pulleys. The program simplifies the process of selecting and sizing a complete belt drive system. The user can make changes to different input values quickly and easily to modify the output to the desired results. Introduction The belt program is a windows based interactive program that allows the user to size a belt drive system. The program is written in visual basic because of the coding necessary to do basic calculations and also the windows environment in which most users are familiar and would not need special instructions in order to use the program. Also, the windows environment allows more than just text input and output. Tables, figures, pictures, and graphs1 can be imported in the program enhancing the program

versatility and allowing the user to visually see information required to size a belt drive system. This improves the program by allowing the user to select information and data off of charts and tables. The program can be used in both an industrial and academic environment. The belt selection procedure established in the classroom environment is the method used to size belts using standards set by industry. Students gain invaluable experience designing belt drive systems for different industrial applications. The belt selection program is used in a 200 level machine elements course. Some of the topics discussed in this course are gears, bearings, shaft design, and power transmission topics. A section of the course covers belt drive systems. This part of the course covers the different types of belts and typical arrangements of belt drives. After a general introduction is given on belts2 drives, a more thorough lecture is given in the area of timing and synchronous belt drives.

Synchronous pulleys and belts have teeth, which give a positive slip proof engagement. The basic formulas, design principles and analytical techniques are covered for synchronous belt sizing3. Speed ratios, angular pulley speeds, belt speeds, belt center distances, and belt pitches are introduced in the lecture material. Students are given a manufactures synchronous belt catalogue as a reference. They use the catalogue to reference the different types of pulleys, bushings, and belts available. The manufactures catalogue outlines the steps in sizing a belt drive system. The students are given different belt drive applications and are asked to size and select all the components required to drive the system. Page 5.6682 The software is introduced to assist the student in mastering basic skills required to size a belt drive system and gain a solid understanding of belt components. The program replaces the belt manufactures catalog and allows the user to easily step through the process of

selecting a belt drive system. The program assists the student in allowing them to size different belt drive applications quickly and easily. It also reinforces the basic design principals and analytical techniques of properly sizing a belt. The software is not a text based input-output program, where data is input and where output values are displayed and the user does not understand the in between process. The program takes the user through a step-by-step procedure, asking for basic design information and using this data to allow the user to select belt drive components based on this design criteria. The user inputs data or selects data from charts, tables, and graphs in the program. This is one of the benefits using visual basic It is a visual interactive program that allows the user to look at more than just a specific questions prompting for some input value. For users with little or no experience in selecting belt drive components, it is a cumbersome process to become familiar

with the catalogue. The manufactures catalogue forces the user to decipher a large amount of information and the catalogue is not user friendly in stepping the user through the process of sizing a belt. The program follows the catalogues design calculations and parameters, but simplifies the process used to size the belt. This is an advantage for new users of belts drive systems over using a manufactures catalogue. Another advantage of the program compared with the manufactures catalogue, is the ease of changing input values and rerunning the program. PROGRAM FUNCTION The timing belt drive selection procedure is the first form the user encounters (fig.1) The user enters rated horsepower, service factor, and the shaft speeds where the pulleys will be mounted. This is basic initial information a designer would be using if working with a belt drive. In order to enter a service factor, the user clicks on the Service Factor Command button shown below, which opens the service factor

form2. The form allows the user to select a service factor based on the driving machine, the driven machine, and the hours of operation. For an example, the driving machine can be piece of printing equipment operating eight hours per day, and driven be a 5 horsepower AC motor. A service factor of 16 would be entered into the service factor text box shown below. Fig. 1 Timing Belt Drive Selection Form Page 5.6683 The user then enters a rated horsepower of 5hp into the rated horsepower text box and clicks the calculate command button, the program uses the service factor and the rated horsepower to calculate a design horsepower to be used in all calculations. In the example problem this would be equal to a design horsepower of 8hp. The other input required is the speed of the two pulleys mounted on each shaft. Continuing with the example, inputs of 1000 rpm and 500 rpm are entered for the speeds of the faster shaft and slower shaft respectively. The user then clicks on the continue

command button to proceed to the next form (fig. 2) in the program This form is the belt pitch selection guide. A belt pitch is the distance between teeth of the belt or pulley. There are four different sizes 5mm, 8mm, 14mm, and 20mm The user selects the proper size belt pitch based on calculated design horsepower and the faster shaft speed or smallest pulley rpm. The calculated design horsepower of 8hp is displayed on the side of the Belt Pitch Selection Guide graph, while the faster shaft of 1000 rpm is displayed on the bottom of the graph shown below. The Belt Pitch Selection Guide Graph4 is used to allow the user to select the proper belt pitch based on these two inputs. In the example, an 8mm belt pitch would satisfy these criteria. Fig. 2 Belt Pitch Selection Guide Page 5.6684 Once the user has selected a belt pitch, this tells the program which belts and pulleys are used. There are different belt and pulley sizes for each of the different belt pitches. In this case the

user selected a 8mm belt pitch, the manufactures pulley sizes and belt sizes for that specific belt pitch is used throughout the program. The number of teeth of all pulleys2 available and the belt perimeter in mm of all belts available for the 8mm belt pitch are listed in table 1. Clicking on the continue command button takes the user to the next form. The next form (fig 3) allows the user to select a pulley and belt combination for a required belt center distances. The program uses the input shaft speeds to calculate the speed ratio. For the example given, the 1000 rpm shaft speed and the 500 rpm shaft speed give a 2:1 speed ratio. Using the speed ratio of 2:1 and the belt pitch of 8mm, all pulley combinations are calculated (reference in table 2). From this all center distances are calculated for each pulley combination and for each belt size. This is a lot of information and can be simplified. All this data is buried inside the program and is used Table 1 Pulley Number of Teeth

and Belt Perimeter for a 8mm Belt Pitch. Pulley Number of Teeth for a 8 mm Belt Pitch 22 24 26 28 30 32 34 36 38 40 44 48 56 64 72 80 90 112 144 192 Belt Perimeter for a 8mm Belt Pitch 480 560 600 640 720 800 880 960 1040 1120 1200 1280 1440 1600 1760 1800 2000 2400 2600 2800 3048 3280 3600 4400 to calculate the necessary drive information. The designer usually lays out the belt drive system with some CAD package and has the center distance required of the belt drive system. The program allows the user to specify this value along with an allowable center distance deviation. The deviation value is the allowable distance the belt center distance can deviate from the specified value. The program looks at the different pulley combinations calculated from the speed ratio required (table 2) and calculates the center distances based on each belt length available (table 1) from the manufacture. It compares these belt center values with the belt center distance required by the designer. Any

belt center distance inside the allowable range set by the user is listed in a list box in the program. Depending on the range size the user sets the number of belts meeting the criteria can change. The larger the acceptable deviation, the more belts center distances will be inside the range. The smaller the deviation, the fewer belts center distances will be acceptable. If the user required a belt center distance of 4550 in and a deviation of 1 in., the program would look for a belt and pulley combination that would have a center distance in the range of 45.00 to 4600 In this example, three belt lengths would meet the criteria these are shown in figure 3. The user then selects one of the three pulley and belt combination that is listed. At this point other criteria may come into play in altering which of the three combinations the user should select. For example, the 44:22 pulley ratio may be rejected on the basis of the size of the pulleys. A 22 tooth pulley is a small pulley with a

pitch diameter of 2.20 in and a maximum bore range of 1-3/16 in If the shaft where the pulley is mounted were larger than bore of the bushing, a different pulley combination would be selected. Page 5.6685 Fig. 3 Belt Center Distance Form Table 2 Pulley Combinations for a 2:1 Speed Ratio. Pulley Combinations For a Given Speed Ratio 72:144 56:112 40:80 36:72 32:64 28:56 24:48 22:44 Table 3 Belt and Pulley Combinations with the Required Belt Center Distance. Pulley ratio: 80:40 Pulley ratio: 48:24 Pulley ratio: 44:22 Belt: 2800mm Belt: 2600mm Belt: 2600mm Center Distance = 45.63 Center Distance = 45.50 Center Distance = 45.97 Page 5.6686 The last criteria required in selecting a belt system, is to size the correct belt width. There are different width belts depending on the belt pitch selected. For example, the 8mm pitch belt has widths of 20mm, 30mm, 50mm, and 85mm. Again, the program adjusts for the belt widths based on the 8 mm belt pitch selected earlier. Selection of the

belt width is based on three criteria, calculated design horsepower, fastest shaft speed (rpm), and smallest pulley selected. Using these three data, a horsepower rating table2 (fig.4) comes up for the narrowest belt available and allows the user to see if the rated horsepower is exceeds the design horsepower at the given shaft speed and using the selected pulley. If the horsepower rating is insufficient the user picks the option button with the next larger belt width and compares these ratings until a belt width horsepower rating is found to be sufficient. In the example given, a 30mm wide belt has a horsepower rating of 10.14hp that would exceed the calculated design horsepower of 8hp Therefore the user would select the 30mm wide belt. Fig 4 Belt Width Selection Form The last form of the program display the selection of all the components of the drive belt system. It shows the two pulleys, belt, and center distance, based on speed ratio and horsepower required. The output can

then be printed or the program can be rerun. For the example discussed above the printed output would be: Table 4 Display of Input Specification and Belt System Components Required INPUT SPECIFICATIONS: Faster Shaft rpm: 1000 rpm Slower Shaft rpm: 500 rpm Speed Ratio: 2:1 Design Horsepower: 8 BELT SYSTEM COMPONENTS Pulley 1: P80-8mm-30 Pulley 2: P40-8mm-30 Belt: P2800-8mm-30 Pulley Center Distance: 45.63 Conclusion Page 5.6687 The belt drive selection program is an interactive program used to size and select components for a synchronous belt drive system. The program is designed to follow the manufactures recommended sizing procedure as shown in the manufactures catalogue. It simplifies the procedure by taking the user through step by step. The program is used in a machine elements course to supplement the lecture material on belt drives. It gives the student an opportunity to size many different belt drive applications quickly and easily. It reinforces the belt design

principals and analytical techniques used in sizing a belt drive system. The program can also be used in an industrial environment where machine designers are sizing belt drive systems. Bibliography 1. Dayco, “Dayco Engineering Guide for Synchronous Belt Drives”, Dayco, Dayton, 1982 2. R Mott, “Machine Elements in Mechanical Design”, Prentice Hall, New Jersey, 1999 3. Gates, “PowerGrip HTD Systems for Industrial Drives”, Gates, Denver, 1989 4. Martin, “Sprocket and Gear”, Martin, Arlington, 1992 Edward M. Vavrek Edward M. Vavrek is an Assistant Professor of Mechanical Engineering Technology at Purdue University North Central. He has a BS in Mechanical Engineering from Purdue, a Masters degree in Mechanical and Aeronautical Engineering from Illinois Institute of Technology, and a Masters in Business Administration from Indiana University Northwest. He has worked as a design engineer for 11 years in the printing industry Page 5.6688