Example 1 for Gearbox Selection

April 3, 2018 | Author: Nakkolop | Category: Transmission (Mechanics), Gear, Engines, Bearing (Mechanical), Belt (Mechanical)


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Example 1 for Gearbox Selection Gearbox selection for an elevator Available data about the application: Driven machinetype: Elevator Drive type: Electric motor Motor speed: 1460 rpm Driven machine speed nd: 23 rpm Torque required for driven machine Td: 900 kp.m Daily operation time: 24 hours No of start-ups per hour: Continuous Operation time within an hour: 60 minutes (FD = 100%) The gearbox is connected by hydraulic coupling to the motor and by elastic coupling to the driven machine. Gearbox is to operate in a closed area (Ambient temperature 20-25oC) Gearbox input speed equals motor speed: n1 = nm = 1460 rpm Gearbox output speed equals driven machine speed n2 = nd = 23 rpm. Gearbox types, which are suitable for this application, are DA3 and DK3 models. Calculations: Power Nd required for driven machine is calculated with below formula. Nd = Td(kp.m) nd(rpm) = 900 . 23 = 22.2 kw 974 974 Gearbox transmission ratio: i = n1/n2 = 1460/23 = 63/1 Load factor calculation Load factor is calculated by F = fm . fd . fs . ft Drive coefficient fm is taken as fm = 1 for a machine driven with electric motor. Driven machine coefficient fd is taken as fd = 1.5 for a medium shock loading machine elevator. Start-up coefficient fs is taken as fs = 1 for a machine operating continuously without start-up. Daily operation time coefficient ft is taken as ft = 1.25 for a machine operating 24 hours daily. Thus F = 1 . 1.5 . 1 . 1.25 = 1.875 Load factor can also be taken from the table. In the table, it is given that load factor for an elevator that is driven by an electric motor, operating 24 hours daily and with medium shock loading is 1.9. Power gearbox should transmit: Nre = F . Nd = 1.9 . 22.2 = 42.2 kw Nominal power Nn for selected gearbox should be greater than Nre. Nn > Nre In power table of DA3 model gearbox; it is found that for ninput = 1460, noutput = 23 rpm. Nominal power DA3-560 model gearbox can transmit is 45 kw. DA3-560 model gearbox is suitable for this application. Checking the thermal power: Thermal power of DA3-560 model gearbox is from thermal power table Nt = 240 kw. Nt > Nre therefore DA3560 model gearbox can transmit power Nre without cooling. Nn > Nre. nd (rpm) = 180 . n2 = nd = 60 rpm Gearbox will be operated in open air (ambient temperature 25o-30oC). DG2-250 model gearbox is suitable for this plant.m) .5 for a conveyor which is a machine driven with electric motor. 11 = 16. Example 3 for Gearbox Selection Gearbox selection for a drying plant.5/1 Gearbox input speed: n1 = 1450/1. . Available data about the application: Driven machine type: Conveyor belt Drive type: Electric motor Motor speed: 1450 rpm Driven machine speed nd: 60 rpm Torque required for driven machine: Td = 180 kp. operating 10 hours daily.6 kw Nominal power Nn for selected gearbox should be greater than power Nre. Nominal power DG2-250 model gearbox can transmit is 19 kw.5 = 960 rpm Gearbox is mounted on conveyor shaft.In tables it is given that nominal power of DK3-450 model gearbox is 45 kw under same operating conditions. 60 = 11 kw 974 974 Gearbox transmission ratio: i = n1/n2 = 960/60 = 16/1 Load factor is taken from the table. Gearbox output speed = Driven machine speed. Pulley ratio: 1. Power gearbox should transmit: Nre = F . Example 2 for Gearbox Selection Gearbox selection for driving a conveyor belt. In power table of DG2 model gearbox it is seen that for ninput = 140.5 . Check thermal power: Thermal power of DG2-250 model gearbox is Nt = 36 kw (from thermal power table. Nd = 1. Load factor is given as 1. DG2 model shaft mounted gearbox is suitable for this application Calculations: Power required for driven machine Nd is calculated by below formula: Nd = Td (kp. noutput = 60 rpm.) Since Nt > Nre DG2-250 model gearbox can transmit power Nre without cooling.m Daily operation time: 10 hours Start-ups in an hour: at most 5 Operation time in an hour: 50 minutes (FD = 80%) There is a V-belt pulley system between gearbox and motor. with medium shock loading. Nn > Nre therefore DK3-450 can also be used for this application. Gearbox input speed = motor speed = 1460 rpm. With profile shifting on the gears.5 = 22.5 = 60 rpm Gearbox operates in open air (ambient temperature 25o-30oC). thread cutting.95 Motorgear is selected with the safety factor greater than sufficient. Chain sprocket ratio = 2. 1.25 kw Since a motor with 15 kw power is connected to gearbox. 11.5 . the bearing surfaces of the gear shafts. The power gearbox should transmit: Nre = F .5 = 1. Shafts .5 kw 974 974 Load factor is taken from table.5 in the table for a drying mill which is a machine driven by electric motor.Available data about the application: Driven machine type: Drying mills Motor power to be connected to gearbox: 15 kw Motor speed: 1460 rpm Driven machine speed nd: 24 rpm Torque required for driven machine Td = 465 (kp. heat treatment operation is performed in order to attain the required cementation depth and a 58-60 HRC surface hardness. is suitable for this application Calculations: Power required for driven machine Nd is calculated with below formula: Nd = Td (kp.5 = 17. the undercutting on the pinion gears are prevented.5.5 that is nominal power Nn of gearbox is Nn = 15 . Gearbox is connected to drying mill with chain sprocket. operating 10 hours daily and with medium shock loading. 2DMA model. Helical spur gears and helical bevel gears are produced from case hardened steel.m) . The power table of 2DMA model motor gearbox is calculated so that load factor is at least 1. gear bores and teeth profiles are grinded. heavy industry motorgear. Nd = 1.5/1 Gearbox output speed = 24 .nd (rpm) = 465 . 2DMA 6 model gearbox transmits 15 kw power at 60 rpm with a load factor of 1. safety factor in motor selection is as Nm/Nd = 15/11. 24 = 11.5 = 1.5/11.5 Actual load factor based on power required for driven machine Nd is Nn/Nd = 22. After the heat treatment process.3 In the power table of 2DMA model motor gearbox for 15 kw power and 60 rpm gearbox output speed. burring and keyway cutting). After the machining operations of the gears (lathing.m) Daily operation time: 10 hours Start-ups in an hour: at most 5 Operation time in an hour: 60 minutes (FD = 100%) Motor is directly connected to gearbox. 2. Load factor is given as 1. it is concluded that 2DMA 6 model gearbox should be selected. Teeth profile grinding process ensures quiet operation of the gearbox. forced air-cooled lubrication system is utilized. lifting rings are placed to ease handling. Shaft Connections The gearbox output shafts can be connected to the driven machine with elastic or rigid couplings. Oil filling and draining plugs and oil level indicators are present on the housing. Housing can be produced with GGG-42 quality sphero cast iron upon request. In case of connecting with couplings. spur gears or sprocket systems. The keys of the input and output shafts are supplied with the gearbox. The keys and keyways on the input and output shafts are machined according to DIN 6885/1. In case of connecting with belts. the shafts should be parallel to secure an operation without vibration and a long lifetime for the connecting elements. Vertical operating gearboxes are lubricated with oil bath method as well. For heavy gearboxes. In this case. In case of connecting with gears. If the transmission power is close to the thermal power limits or above it. the motor and gearbox shaft bearings. Bearings Tapered roller or cylindrical roller bearings are used in shafts and gear beds. The oil filling plugs of the gearbox also function as ventilation holes. Threaded centering and dismantling holes are bored into the shaft ends according to DIN 332. bearings and couplings. however. The input and output shafts are grinded with k6 tolerance until Ø50 mm diameter and with m6 tolerance for diameters greater than Ø50 mm. Lubrication Oil bath splash lubrication is applied for gearboxes working in horizontal position. Housing Housing is GG 20 quality grey cast iron. In cases where necessary.The input shafts of the gearboxes are usually pinion gear shafts.000 hours. . Some models have inspection lids to see the gears inside. If the pinion gear on the input shaft is shaft mounted. the shafts should be parallel and the gears should contact each other along the teeth surface. input gear shaft material is case hardened steel. The output shafts of the gearboxes are produced from C45 material as well. since splash method is not possible. Sealing The sealing between the housing and covers are attained with liquid gaskets and the sealing of the input and output shafts is attained with rubber oil seals. hydraulic or electromagnetic lamelled couplings. forced lubrication system is applied. It is convenient to connect the input shafts to the motor with belts. elastic. In case of connecting with couplings. fine adjustment of the shaft axis and the minimization of the angular and linear misalignment between the shaft axis are necessary to ensure an operation without vibration and to prolong the lifetime of the shafts. Special design gearbox housings are produced with welded construction steel. the oil level should be almost or completely full. the shafts should be coaxial. The bearing selection is made to ensure a lifetime of at least 50. the input shaft material is C45 quality steel. the most economical option is selected. The most appropriate gearbox is selected taking into consideration the technical information and operating conditions stated below. • The gearbox operates without noise and vibration.5% occurs at each reduction stage of a gearbox unit with helical spur gears. This prevents problems regarding heating or spilling over of the oil. For a gearbox unit with helical bevel gears. gearbox selection is very important to ensure a flawless operation and a long lifetime. an alternative method of lubrication is forced lubrication. efficiency factor for helical spur gear units can be taken as follows: Single reduction (1 gear pair) gearbox: 98. Dyeing The inner surfaces are dyed with ground coats. eliminating the need to load the gearbox fully with oil. For worm geared units. Gearbox selection First of all. Gearbox selection is based on the following criteria: • Mechanical data of the gearbox • Type and specifications of the driving motor • Type and specifications of the driven machine • Operating conditions • Environmental conditions • Cooling possibilities . The selection can be made either by the technical staff of the company which will be using the gearbox or by our technical staff upon the submission of the necessary information. To make the right selection. If there is more than one gearbox model adequate for the job or project. Efficiency A power loss of 1. • The oil level is sufficient.5% Quadruple reduction (4 gear pairs) gearbox: 94%. Accordingly. input speed and the quality of the material and machining of the worm gear pair. The gears and bearings at the highest level of the gearbox are lubricated directly by spraying oil.5% Double reduction (2 gear pairs) gearbox: 97% Triple reduction (3 gear pairs) gearbox: 95. Quality control Upon assembly. the outer surfaces are dyed with ground coat and two finishing coats. After quality inspection. required technical information and operating conditions for the gearbox should be provided during the order process. • There is no oil leakage from oil seals and covers. power loss ranges between 5% . the gearbox is operated without load and following inspections are done to ensure. thread angle.For the vertical operating gearboxes.50% depending on the thread number. the gearbox is delivered ready to operate together with maintenance instructions.5-3% at each stage. the power loss is between 2. delivery time. motor gears are preferred for economical and easy mounting reasons. the input and output shafts of DA2 model parallel shaft gearbox can be arranged in four different positions.B6 . with the operation safety factor F. is calculated by multiplying the power required for the driven machine. Project engineers should select the type of gearbox in the project phase. Gearboxes without motor are produced for specific operating positions. ease of assembly. . The mounting positions of the shafts are shown in dimension pages for each gearbox type. If the gearbox is connected to the motor via a belt system. Nre = F . If the gearbox is connected to the motor with a coupling.Power Nre (kW) transmitted by the gearbox The power of the gearbox Nre. with right input – right output. Gearbox input speed is higher than output speed: n1>n2 The shaft of the gearbox connected to the motor is input shaft and the shaft connected to the driven machine is output shaft. the input speed of the gearbox changes according to the ratio of the pulleys. For example. Higher speed of the motor is reduced to lower speed required for the driven machine. Special operating positions should be stated during the order. with left input – right output. The operating positions are specified in dimension pages. Mounting positions of shafts The input and output shafts of gearboxes can be arranged in different positions. Gearbox type The gearbox type suitable for the project can be chosen from our product range shown on pages 21 . At low power ranges. Nd (kW) Operation safety factor calculation is explained in a separate section and the factor can be taken from the table on page 19. Gearbox input speed n1 (rpm) Gearbox output speed n2 (rpm) Gearboxes are generally used for speed reduction. The operating positions of foot mounted gearboxes with motor are B3 .V5 and V6.V1 and V3.B8 . Reduction ratio i = n1 : n2 The ratio of the input speed to the output speed is the reduction ratio. space available for the gearbox and operating conditions play an important role for the selection process. The operating positions of flange mounted gearboxes with motor are B5 . and with left input – left output. There can be more than one type of gearbox suitable for the same job. Nd (kW). the input speed is equal to the motor speed.26. Gearbox mounting positions (Operation positions): The operating positions of motor gears are labeled according to DIN 42950 and are shown on page 20.B7 . The price. These are respectively. with right input – left output. position and direction of the forces should be stated. hydraulic motors.8. If it is necessary to use a 3000 rpm motor. All special requirements should be stated during order.The requested mounting positions for the shafts of gearbox without motor should be stated during order according to the descriptions on dimension pages. The electric motor for the motor gear can be supplied either by us or by the customer. Machines with heavy shock loads and high moment of inertia 4. This safety factor and the safety factor for gearbox selection do not have to be the same.25 and 1. it is recommended to decrease the gearbox input speed to 1500 or 1000 rpm by placing a V-belt pulley between the motor and the gearbox. The power Nm (kW) and speed of the motor that will drive the gearbox nm (rpm) The power of the motor to be connected to the gearbox should be selected as greater than the power Nd required for the driven machine. As in gearbox selection. Using rigid couplings at gearbox input should be avoided. the motor safety factor can be taken between 1. It is not economical to choose the motor power greater than necessary since operating costs might increase due to excessive use of electricity. According to type of plant and daily working hours. Machines with very heavy shock loads and very high moment of inertia. Type of Motor All types of electric motors. There are four main groups: 1. the motor power is calculated by multiplying the required power for the driven machine by a certain safety factor. the motor safety factor taken or the actual power required (Nd) for the driven machine should be stated. The ideal motor speed to run the gearbox is 1500 and 1000 rpm. electromagnetic brake or electromagnetic coupling. turbines. diesel and gasoline motors can be used as drive machine. External forces on the input shaft of the gearbox from coupling or motor The type (radial or axial). the speed nd (rpm) of the machine . magnitude. Required power Nd (kW) to run the machine at full load or torque Td (N. Type of coupling connecting motor to gearbox Elastic couplings. It is not recommended to use high speed motors with the gearbox. In some gearbox types there’s also the possibility to put double input shafts and double output shafts. hydraulic couplings and other special coupling types and V-belt pulleys can be used as connecting elements. Special requirements The gearbox can be equipped with backstop. High speed increases the noise level of the gearbox as well as decreases the lifetime of the bearings and gears. At the time of order. The diameters and lengths of input and output shafts of gearbox can be in different dimensions than given values on dimension pages. Machines with moderate shock loads 3. Uniformly operating machines without shock loads 2.m). NECESSARY INFORMATION ABOUT THE DRIVEN MACHINE Type of driven machine It is very important to know the type of driven machine in gearbox selection. It should be stated whether a flywheel will be put to decrease the effect of variable loads and shock loading.The required power Nd and the speed for the machine is calculated by the technical staff. whether there is excessive dust. . gearbox selection will be done in two stages: 1) Selection of gearbox type 2) Determining the size of the selected gearbox type Selection of Gearbox Type The gearbox type suitable for the driven machine is determined during project phase. whether there is tap water. If a flywheel will be added. whether the gearbox will work in a covered place or open air. chain mechanisms. magnitude. Similar machines can also be taken as reference. For systems requiring less power. number of stop-starts within an hour. high) if the machine is subject to shock loading. COOLING POSSIBILITIES The important factors are: if a forced cooling system is needed. operation time (as percentage) under load in an hour. Motor gears are less expensive and are easily mounted. whether the driven machine is loaded uniformly or variably and the extent of shock loading (low. The technical staff designing the project decides on the type of gearbox according to his past experiences or examining applications done before. motor gears are the recommended solution. Shaft mounted gearboxes are also preferred due to same reasons. OPERATING CONDITIONS The important factors are: average daily operation hours. well water or other source of water and the temperature of the water to be used. the mass momentum of the flywheel and other technical specifications should be considered. GEARBOX SELECTION After above mentioned criteria are considered. ENVIRONMENTAL CONDITIONS The important factors are: lowest and highest average temperatures of the place where the gearbox will operate. position and direction of the forces should be stated. rigid couplings. medium. moisture. External forces on the output shaft of the gearbox from coupling system or driven machine Type (radial or axial). spur gears and bevel gears can be used as connecting element. Type of the coupling connecting the gearbox to the driven machine Elastic couplings. water or a heat source to effect the gearbox at the operation place. gear coupling and other special coupling types. Machines with very heavy shock loading and very high moment of inertia: The coefficient fd is taken as 2. fd 2) The coefficient for the driving motor. The power and torque values given in tables are nominal values. The output torque the gearbox can transmit is also given in a separate table. the coefficient fd is taken as 1. On these tables. the gearbox should transmit. Please find below the method to calculate the operation safety factor. The nominal power of the selected gearbox should be equal to or more than the Nre value. which operate without shock loading and without sudden moment increase. The power Nre. Determining the size of the selected gearbox Gearbox size can be determined with the help of the gearbox power tables. fm . gearbox transmission ratios. Uniformly operating machines without shock loading: For machines with constant power demand.5. is determined by multiplying the power Nd needed for the driven machine by the operation safety factor. fs Operation safety factor F is attained by multiplying the four coefficients: F = fd . . Driven machines can be classified in four main groups according to their level of shock loading and moment of inertia. powers and summary information on gear systems are given. the coefficient fd is taken as 1. The power and torque needed for the driven machine should be less than the nominal power and torque the gearbox can transmit so that the gearbox can operate at a certain safety. ft 4) The coefficient for the start-up number. Machines with medium shock loading: For machines which operate with medium shock loading and where load increases or decreases by at most 50%.The gearbox types produced by our company are listed schematically on pages 21 . For each gearbox type a separate power table is laid out. fs The driven machine coefficient (fd) This coefficient depends on the type of driven machine. Machines with heavy shock loading and high moment of inertia: For machines with high inertia which operate with heavy shock loading and where load increases or decreases by at most 100%. the coefficient fd is taken as 2. ft .26. Operation safety factor (F): Coefficients determining the factor: 1) The coefficient for the driven machine. The table shows the maximum power (kW) a given gearbox size can transmit according to the input speed and transmission ratio.5-3 for this group. fm 3) The coefficient for the daily operation time. 1. This classification is a guidance based on past experiences. If the daily operation time is less than 3 hours. making at most five start-ups in an hour. the coefficient fs is taken between 1. the operation safety factor can be taken lower or higher than the value in the table. fd . If the system makes more than five start-ups in an hour. F can be taken as 1. 3. 1 . Connecting the gearbox to the motor with hydraulic or electro-mechanical coupling will reduce the effect of shocks during stop-starts.8 or 2.25 . the ft coefficient is taken as 1. the coefficient fs is taken as 1. Driving motor coefficient ( fm ) This coefficient is determined according to the type of motor driving the system. Operation safety factors (F) are given in the table on page 19. synchronous.30?C ambient temperature and for continuous operation (FD = 100%). ft . The fm for this group is taken as 1.Group: Internal combustion.10 hours. water turbines. 1. The fm for this group is taken as 1.5. hydraulic motors. 1 = 1. with moderate shocks: F = fm . 2.6 cylinder engines (gasoline or diesel). the ft coefficient is taken as 0.Group: Internal combustion. with heavy shock loading. and with very heavy shock loading and high moment of inertia. In this table. 4 .The types of machines within these four main groups are given in operation safety factor table. Start-up number coefficient ( fs ) If the system makes at most five start-ups in an hour.8. Thermal power values each gearbox size can transmit are given in gearbox power tables. steam turbines. Thermal Power (Nt) This is the power the gearbox can transmit without heating up.25 – 2.25. operation area (covered place or open air) and the operation time in an hour (FD).3 cylinder engines (gasoline or diesel.5 . ambient temperature. direct current motors).) The fm for this group is taken as 1.25. medium shock loading.875. . the ft coefficient is taken as 1. driven machines are classified into four groups. Thermal power values (Nt) given in tables are valid for gearboxes operating in a closed area. fs = 1 . Considering economical and safety factors together. special precautions might be needed.24 hours. An example for operation safety factor calculation The safety factor (F) for a system operating 24 hours daily with an electric motor. without shock loading. There are three main groups: 1. Thermal power of gearbox depends on the size of external surface of the gearbox housing. In this case. with 20 . If the daily operation time is between 10 .Group: Electric motors (Asynchronous. Daily operation time coefficient ( ft ) If the daily operation time is between 3 . The power gearbox should transmit (Nre) is obtained by multiplying power required for driven machine (Nd) and operation safety factor. a greater size should be selected. 60% of the value given in the table should be taken. Nt can be increased by 50%. Nre = F . gearbox should be forced cooled. 75% of the value given.m) . for 50?C ambient temperature. If the gearbox is cooled with air or the gearbox oil is cooled. For an operation of 15 minutes in an hour (FD = 25%). Hence. If Nre is close to or greater than thermal power. Nt can be increased by 25%. The power required to obtain the required torque for the driven machine at the selected speed is calculated in (kW) as: Td (N. ( Nre < Nt ). power required should be calculated considering the highest speed. If there is no cooling possibility. Operation safety factor F can be taken from the table taking into consideration type of driven machine. If the gearbox is operating 30 minutes in an hour (FD = 50%). Determination of gearbox size Torque required for the driven machine is determined either by calculation or by past experience.50% depending on the effect of the cooling. if the machine will operate at variable speed. . Speed suitable for driven machine is again found either by experience or by trial and error method. The gearbox size having a nominal power greater than or equal to the Nre should be selected from the table. The Nre value is the key for gearbox selection. thermal power can be increased by 10% . nd (rpm) ____________________ 9550 Nd = Provided that torque required for the driven machine stays constant.For 40?C ambient temperature. The Nre value calculated should be less than the thermal power (Nt). motor and daily operation time. Nd The power table for selected gearbox type shows the nominal power Nn (kW) a given gearbox size can transmit according to the input and output speed. gearbox selection is completed.
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