Gear drives, sometimes referred to as gear trains and gearboxes, are mechanisms consisting of an assembly of gears, shafts, and other machine elements for mounting the rotating parts...
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This article takes an in depth look at gear reducers and their use.
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A gear reducer is a mechanical system of gears in an arrangement such that input speed can be lowered to a slower output speed but have the same or more output torque. The operation of a gear reducer involves a set of rotating gears that are connected to a shaft with a high incoming speed, which is sent to a set of rotating gears where the speed or torque is changed. How many gears are in a gear reducer assembly is dependent on the speed requirements of the application.
The use of a gear reducer occurs when the drive gear is smaller and has fewer teeth than the driven gear. This is unlike the condition where the drive gear is larger with more teeth than the driven gear, which is referred to as overdrive.
Gear reducers are an essential component in cars and trucks where the high rotational speed of the engine is converted such that the slower motion of the tires can interpret and use the power safely.
Gear reducers, or reduction gears, are necessary for high efficiency machinery operating at elevated speeds. For the speed produced by the machinery to be practical, it has to be reduced to a lower speed to meet the needs of the powered application. The basic construction of a gear reducer consists of a large gear that is positioned with a smaller gear with both gears turning together.
In the case of a single gear reducer where a large gear is connected to a single smaller gear, the smaller gear makes two turns for every one turn of the larger gear. With the multiple turns of the smaller gear, there is greater speed but a loss of torque.
The gear reduction process takes place at preset ratios that meet the characteristics of the input and output gears. A gear reducer achieves the change in energy by changing the ratio of the moving gears.
The gear ratio is a way of measuring how different sizes of gears interact to transfer energy. The essential aspect of this calculation is the measurement of a circle, which is a major part of gears. The determination of the gear ratio can be understood by examining the circumference of a circle. A gear that makes two rotations to turn a larger gear once has a ratio of 2:1, which means that the output speed has been cut in half.
This example simplifies more complex gear reducers with several gear pairs in a series for converting revolutions per minute (RPMs) to torque. The example below presents a slightly more complex gear reducer with an idler gear between the small gear and the larger.
In determining the gear ratio, the only gears that influence the gear ratio are the drive gear and driven gear. Any gears inserted in between the two are not calculated in the gear ratio. An easy way to calculate the gear ratio is to count the number of teeth in the drive and driven gear. In the example, the drive gear has seven teeth while the driven gear has 30. The drive gear has to turn 4.3 times before the driven gear will turn.
Torque is a rotational force that is received by the gear reducer and changed into a different force and speed with the amount of power remaining the same. Gear reducers are a gear or series of gears designed to reduce the torque of a motor, which increases in direct proportion to the reduction of rotations per unit of time or revolutions per minute. This is accomplished by base mounted or shaft mounted gear reducers.
Gears are used to multiply or divide torque, which is determined by the size of the gears. The ratio of the gear sizes increases or decreases torque, which is the foundational aspect of the operation of a gear box.
Drive gears or gear drives are designed to change the speed, torque, or direction of a rotating shaft. In their simplest form they are a small gear that drives a larger gear connected to the output shaft. They are essential for providing variable output speed from a constant power source.
In the image below, the silver worm shaft with a worm gear is the drive gear for this two gear gear reducer. The driven gear is the brass colored worm wheel of the worm gear set.
The driven gear is connected to the output shaft and transfers the reduced power to the application. They are the larger of the gear set regardless of how many gears there are in the series and come in a variety of shapes. In the compound gear train example below, there are two driven gears connected to different shafts, B and C. The gear ratio for the driver gear for shaft B and the one for shaft C is the same.
Speed reducer is another term used to describe gear reducers. They are a gear train placed between machinery and its motor to adjust the speed of the shaft of the motor when it is delivered to an application. The gears of a speed reducer have more teeth than those that are present in the input gear, which enables the output gear to rotate slower and increase torque.
Located between a motor and a piece of machinery, a speed reducer lowers the speed delivered by the motor such that an application can make use of the motor’s energy. In a speed reducer, a set of large and small gears work together to lower the input speed while increasing the torque. Changing the speed output of a machine allows for better and more precise control of a process to produce better results.
Speed reducers take the same form as gear reducers and have four basic forms, which are worm, planetary, spur, and bevel with transmission single and multiple stages. Included in the types of speed reducers are the shapes of the gears that are cylindrical, bevel, and cone cylindrical.
A worm speed reducer uses a worm wheel that allows for a reduction ratio of 10:1 up to 60:1. They have perpendicular input and output shafts and are irreversible, which provides for a high level of system security.
There are several advantages to planetary speed reducers that include compactness of design, low ground clearance, high efficiency, exceptionally long service life, and high rated output torque with a coaxial assembly. Although planetary speed reducers are compact, they deliver outstanding transmission efficiency with losses of 3% per stage, which means that a high proportion of the input energy is changed into torque.
The complexity of planetary speed reducers requires specialized maintenance and constant care.
Spur speed reducers have a simple design but provide more torque. They have a straight configuration of gears, which makes them exceptionally efficient and perfect for high speed applications. Of the different forms of speed reducers, spur speed reducers are the most common and are generally preferred by the majority of industries.
Bevel speed reducers are used for applications that require a right angle speed reducer with a low ratio. They have an angled bell crank, which allows users to change a machine’s rotation system from lateral to longitudinal. Bevel speed reducers are designed to handle high power and high torque. The gear meshing ratio can be increased on a bevel speed reducer by using helical gears.
A gear reducer is a speed reducer that changes the rotational speed using gears, shaft positioning, and the arrangement of gears. They are widely used with reduction transmission equipment where the transmission structure integrates the drive motor and the gearbox or gear reducer.
Devices that use gear reducers can use planetary, cylindrical, parallel shaft, worm, or screw gear boxes with each type of gear reducer having a different use and function to fit the needs of an application. The majority of gear reducers have multiple series of gears with different gear ratios between each gear. These designs provide significant gear reduction.
Bevel gear reducers have an angular bell crank that allows users to change the rotation of the system from transverse to longitudinal. They are compact and can handle a great deal of power from three phase asynchronous motors, synchronous motors, or asynchronous servo motors.
As with helical and hypoid gear reducers, bevel gear reducers operate quietly at a very high performance level with exceptional energy efficiency.
With a cycloidal gear reducer, the input shaft drives a bearing assembly that drives a cycloidal disc that is connected to an output shaft. The cycloidal has teeth that engage with a cam follower that has pin or needle bearings. The cam rotation produces a rotation of an output shaft at a much lower speed and higher torque than the input shaft.
The major benefit of cycloidal gear reducers is the elimination of backlash, which leads to higher precision and accuracy that is needed in robotic applications and machine tools. Additionally, cycloidal gear reducers have rolling contact that leads to less wear.
A gear train gear reducer includes a series of gears that transfer power from an input shaft to an output shaft. They are used for applications that require a great deal of power and operate on parallel axes. There are several versions of gear train gear reducers with two gear trains being the simplest with a drive gear and driven gear. In multiple versions of gear trains, there is a drive gear with driven gear with idler gears in between.
Helical gear reducers are another form of space saving gear reducer with durability and high overload capacity. They are used for forward speeds where the gear train is operating at medium to high speeds. The tooth traces of helical gears are slanted creating a higher meshing ratio to produce less noise and make them stronger. Their synchromesh design never disengages and provides more surface area.
The angular cut of the helical cut of helical gears allows for the teeth to be longer but have the same number of teeth as a spur gear.
Hypoid gears are cone shaped that send power between non-intersecting shafts. The small hypoid pinion side is offset from the hypoid gear side, which makes them able to pass without interference. The large contact ratio of hypoid gears allows for heavier load transmission with smooth meshing. As with helical gear reducers, the smooth meshing of hypoid gears produces less noise. Hypoid gear reducers are capable of very high speed reduction.
It is common to find hypoid gears being used when the angle is square and the distance between axes is small. Hypoid gears are used as an intermediate between bevel and worm gears.
Magnetic gear reducers are a very unique form of gear reducer that uses magnetic attraction instead of physical contact. They do not have gear teeth but use opposing magnets that repel each other, which makes them capable of applying pressure regardless of the angle. Magnetic gears create motion just like traditional gears without touching, making them unaffected by wear.
Additionally, magnetic gears do not require lubrication or sealed barriers. They are manufactured using permanent magnets or electromagnets.
A planetary gear reducer has a sun gear, planet gears, and large ring gear. The planet gears depend on the support of the output shaft, inner gear ring, and the sun gear. The power drives the sun gear in the middle of the gear configuration, which drives the planetary gears to rotate following the inner gear ring. The rotation of the planet gears drives the output shaft connected to the output power.
A planetary reducer has a long service life, small size, high carrying capacity, low noise, high output torque, and high efficiency. It has power splitting and multiple tooth meshing to produce a reducer with wide versatility.
Spur gear reducers have straight teeth that are parallel to the axis. They are the most common and frequently used type of gear reducer and can include multiple gears with multiple gear ratios. Spur gear gearboxes have exceptionally high efficiency with very low backlash and are very rugged and stable.
A worm gear reducer has a worm pinion input and an output worm gear with a right angle orientation. They are used to take a motor’s speed and produce a lower speed output with a higher torque. Worm gear reducers are ideal for saving space due to their sleek design and the small diameter of their output gear as well as the excellent speed reduction using a small package.
A coaxial axis gear reducer uses planetary gear types where the set of gears rotates around the sun gear. Input and output gears are installed concentrically to gain higher torque and efficiency. In a coaxial axis gear reducer, three to five planetary gears mesh with the internal gear to send power to multiple branches. The goal of the design is equal distribution of power.
The most basic mounting options for placing gear reducers are base and shaft.
Gear reducers with orthogonal axes are bevel gear reducers with input and output shafts that are perpendicular. Orthogonal gear reducers are less precise than parallel axes gear reducers due to bad teeth contact. They are used as power branching devices.
Parallel axes gear reducers have the output and input shafts parallel. They have very high precision and transmission efficiency. Parallel axes gear reducers can use large sized standard spur gears or helical gears. They are used in machines with high rotations on the load side, such as cranes, elevators, and conveyors.
When the input and output axes of a gear reducer are offset but orthogonal to each other, the gear reducer is referred to as skew axes. The skew axes form of gear reducer are non-intersecting and non-parallel axes with the gear centerline offset, which allows for more tooth surface contact and a higher contact ratio. The result is increased torque capacity and smooth transmission.
There are certain factors that have to be evaluated before deciding to purchase a gear reducer. The main purpose of a gear reducer is to adapt the characteristics of torque and speed of the input and output axis of a mechanism. It is for this reason that it is necessary to understand the torque and rotational speed of the application.
A gear reducer increases the torque of a motor and creates a new torque for the receiving application. As an assist to customers, manufacturers express maximum and minimum torque in newton meters (Nm) for their products with the torque density varying between different gear reducers.
The second purpose of a gear reducer is to reduce motor speed, which is expressed in terms of the reduction ratio. The rotational speed of a motor is changed by the rotational ratio to produce the output rotational speed, which is described in revolutions per minute.
At this stage of the selection process, an expert, engineer, or designer that is knowledgeable in gear reducers is necessary since there are so many types of gear reducers designed to meet the requirements of a wide assortment of functions and parameters. The configuration of the input and output shafts are the first criteria related to choosing the type of gear reducer.
To decide on the dimensions of a gear reducer, it is important to choose the right shaft, which can be orthogonal, coaxial, and parallel. Each of these shaft types have a different orientation in regard to the gear reducer, which are perpendicular, aligned and parallel.
In some applications, motors experience shock or cyclic loads. When choosing a gear reducer, it is important to factor in these conditions in order to allow the gear reducer to be able to deal with the increased torque.
Choosing a gear reducer that operates efficiently is necessary regarding its cost. The correct one for an application can be beneficial in regard to long term costs.
Planetary gear reducers are used with applications that demand fast acceleration, low speed, and high torque. They are used in machine centers, machine tools, and agricultural operations.
Worm gear gear reducers are used in applications with a high transmission ratio. They are less costly than other gear reducers and operate very quietly. Worm gear gear reducers are used on conveyors, winches, and material handling due to their non-reversibility.
Gear train gear reducers are designed for high powered applications and save money on maintenance due to their exceptional performance and low reduction ratio.
Bevel gear reducers permit operators to change their rotation scheme. They are small, strong, and can endure a great deal of force. The drawbacks to bevel gear reducers is their poor performance, high cost, and constant need for maintenance. Bevel gear reducers are found in farm equipment and heavy duty conveyors.
Gear reducers are critical factors in a wide assortment of machines and are important components for the smooth operation of the machines. The correct selection of a gear reducer ensures the effectiveness and efficiency of a mechanism. A qualified manufacturer with the proper knowledge and tools can guide the perfect solution for any application.
Once the proper choice has been made, the next step in the successful operation of a gear reducer is to maintain a regular maintenance schedule to ensure its effectiveness and efficiency. Upkeep of gear reducers is a necessity and highly recommended. With routine assessment, failures, errors, and poor performance can be minimized or avoided.
Every gear reducer manufacturer sells or recommends the correct lubrication material for their products. The lubricant has to have the right properties to enhance performance. Initially, during the break in period, it may be necessary to filter the lubricant to remove contaminants. The quality of the lubricant should be checked regularly as well as its level.
The only thing that is permitted in a gear reducer is the lubricant. Dust and water that can enter through faulty seals can cause extensive damage to the gears.
Gear reducers are stored in clean, dry, and climate controlled conditions with all of its covers, vents, and drains closed and sealed. Though the gear reducer is not in operation, its lubrication cycle must be maintained. During the process, it should be rotated to ensure the even distribution of the lubricant.
The initial indications of problems with a gear reducer are noise. Assessment can be made by operating it without a load. Essentially, noise and vibration are an indication of the need for gear reducer overhaul or replacement.
Overheating is an indication that the gear reducer is not receiving sufficient lubrication. The harm of overheating can be prevented by regular checks of the surface temperature of the gear reducer. Overheating can be due to friction between the gears caused by a lack of lubricant.
Properly maintaining a gear reducer guarantees its continuous operation for many years.
Gear drives, sometimes referred to as gear trains and gearboxes, are mechanisms consisting of an assembly of gears, shafts, and other machine elements for mounting the rotating parts...
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