This article takes an in depth look at gears and their applications.
This article will discuss topics such as:
A rotary circular machine with a tooth in its structure and is used to transfer torque and speed from one shaft to another is called a gear.
Gears are also known as cogs and have cut teeth in the cogwheel or gear wheel. These teeth mesh together, and are used to transfer torque and speed. Gears are mechanical devices that work on the level principle. The direction, speed and torque of the power device can be changed by the presence of gears. Gears are simple machines that can be different sizes and produce a different amount of torque, giving a mechanical advantage. The speed depends on the rotational speed and diameter of two meshed structures attached to it. The shape of teeth in all the gears are the same and evenly spaced. The teeth provide torque and prevent slipping gears. If two or more meshing gears are working in a sequence, it is called transmission or gear train. A linear toothed pack is called a rack and if the mesh works in a linear direction, it produces translation.
Gears can be classified by shape and also by the shaft positions. The shapes of gear can be involute, cycloid, and also tricoidal. Whether the shaft position could be parallel shaft gears, or intersecting gear and also as non-parallel shaft gears or non -intersecting shaft gears. The gears are usually mounted on the objects or attached to it with the help of shafts or base. Typically the toothed component is attached to the shaft of the object and when the driving force is applied to it, the shaft rotates. The driven gear also translates and has rotary motion. The gears are defined by the radius and the number of teeth that are present in it.
The radius of the gear differs based on the type of gear. The two important gear measurements are the root radius and the addendum or pitch radius. The root radius is defined as the distance between the center of the gear to the tooth base. The pitch radius is the distance from the center of the gear to the outside of the teeth that are in a complete circle.
The teeth of a gear help one gear connect to another. For proper functioning of both gears equal pitch is important. The equal pitch helps in preventing gear slippage and boosts the efficiency of the gears to 98°.
A change in the rotation and torque of the machine part is possible if the gear pairs are not equal to each other or are constructed in some other way. The change of movement and rotation is within the driving shaft and the driven shaft.
Gears can have a complex design. However, most gears have the following parts:
A toothed crown is where the movements are transferred from one gear to the other.
The bearing is the part of the gear where the shafts are connected.
A partition is the space between these two which sometimes appear as arms.
The tooth of the gear has the following parts:
Gears are mechanical devices that are usually circular in shape and have teeth like structures on the edges or top. The gears are used in many machines to provide rotational force and torque for its working. The gears work in pairs, which helps in preventing slipping, one gear’s teeth engaged in the other. Gears are machines that have teeth and are placed on the rotating shafts. If the gear pair is circular then the rotary speed and the torque produced is constant. But if it is non circular then the speed and torque ratio may vary.
For a constant speed and non varying torque it is important to carefully shape the profile of the gear. The smaller pair of gears, also called pinion, is on the driving gear. The pair will move and reduce the speed and increase the torque of the gear. But if the pinion is on the driven shaft then the speed will increase and torque will decrease. The shaft that the gear pair is on must be placed close but with space between. The rotating shaft can be parallel, non parallel, intersecting, or non intersecting. The gears connect each other with a rotating shaft. This shaft works as a lever. The main function of gears is to transfer energy or rotation from one part to another. Many gears can be connected at one time. Three things can occur in gears such as:
If two wheels are connected to each other and one has 40 teeth and the other has 20 teeth, then the smaller one with 20 teeth will move twice the speed as the first one to keep up the pace of both wheels. The speed will increase but the force will be reduced for the smaller wheel to move.
If the smaller wheel has more teeth rather than the bigger one then its speed will slow down and force will increase. It means more force will be required by the smaller wheel to move.
If the two gears that are connected to each other move, then one gear will move clockwise and the other will move anti clockwise. If we want to turn the angles of its movement then we have to use a special type of gears that are specific for this function.
There are many different types of gears in industrial applications. Each is designed differently from each other according to its application. The main characteristics that differ include:
Most of the time the gears are circular in shape, though are also found in elliptical, triangular, or square shape. A circular gear will give a better gear ratio. This means that the ratio of the input given will give the same ratio of output. This is applied for rotary speed and the torque of the gear. However, if the gear is non-circular it will give a variable gear ratio. That means the speed and the torque will continue to change, alternatively increasing and decreasing.
The tooth design and configuration is an important characteristic of a gear. Each type of gear differs in their tooth design. Gear tooth design is determined by factors such as:
Gear tooth structure depends on the type of the gear and its application. The teeth are either embedded directly into the cut or can be placed separately in the cut. Sometimes the teeth wear off during gear usage. If the teeth are embedded in the cut then the whole gear must be removed. However, if the teeth are placed separately and become embedded, they are easier to remove. This minimizes the cost of gear replacement and can be customized according to the application.
Gear teeth can be inserted into the cut either placed externally or internally. External teeth means that they face outward of the gear center, whereas internal gear teeth placement mean they face towards the gear center. In a mated pair the teeth placement plays a key role in determining the rotation of the gear. If the mated pair has a tooth placement that is external then the rotary motion will be in the opposite direction. If there is an application that requires the same direction of motion then an idler gear is placed in between these two pairs which changes the direction of rotation. If the mated pair has both the placements (external and internal) then the rotation will be in the same direction. This will eliminate the need for an idler gear and is well fitted for many applications.
The other characteristic of a gear tooth is the tooth profile. The tooth profile is the cross sectional area of the tooth that is important for speed and friction production in a gear. There are many types of tooth profiles but the most common are the involute, trochoid, and cycloid. Involute tooth gear has a curve that forms a locus shape. This curve is important as it produces constant pressure in the gear performance. The most commonly used profile is involute as it can be used in many applications. Trochoidal gears are used in pumps and cycloid gears are used in pressure blowers and clocks.
Gear axis configuration means the axis on which the gear’s shaft rotates and its orientation or lay out. There are three main configurations for a gear. These are:
In this configuration the gears are connected to the rotating shaft on the same plane in a parallel axis. The driven gear moves opposite to the other driven gear. This also enhances its efficiency. The motion transmission or the rotation of gears joined in parallel fashion is very high. Gears in the parallel axis configuration include spur gears, helical gears and some internal gears.
In this type of configuration the gear shafts intersect with each other on the same plane. This configuration also has high transmission efficiency. Intersecting gears work best for changing the motion direction within high transmission of energy systems.
The gear pairs with non parallel and non-intersecting configuration have their rotating shafts on the cross axis. These are neither parallel nor on the same plane. Contrary to the other configurations, non parallel and non intersecting has a low rotary motion and low transmission power efficiency. Some examples are screw gears and worm gears.
All these characteristics are important to consider when choosing a type of gear for a specific application. Things to consider when purchasing gears include material types used for construction of a gear, surface treatments, tooth number, angle, and the type of lubricant.
Metallic and non-metallic materials are the two types of material used in gears. There are certain characteristics of both materials that should be considered before using any type of material.
Metallic material is tensile, able to be compressed, bendable, and flexible. The properties of corrosion ability, hardness, temperature fluctuation, conductivity, heat resistance, magnetism, and specific gravity should be considered for metallic material.
Non metallic material consists of wood, plastic, or resin. Any engineered product that is used in manufacturing gears is non-metallic. Non metallic materials also have chemical and heat resistivity, change in size, humidity, temperature, and self lubricity.
The materials that are generally used for the production of gears are:
Carbon is the element responsible for the tensile strength of the material. Stainless steel grades, SS330 and SS490, have low carbon content, meaning they cannot be hardened.
Cold rolled steel plate is an iron based alloy that is made from one or many different kinds of chemical compositions. Generally, the cold rolled steel plates are not available with high carbon content, because they cannot be molded easily at room temperature. Low carbon content to medium carbon content are more suitable depending on the weight. Cold rolled steel plates with low to medium carbon content are used for making gears.
This is the material that is widely used for gears after hardening it. From S15-S25 the carbon content is low therefore it can be used for gears that do not need to be hardened a lot. Carbon steel that is S30 or below has a high carbon content. This category is used to make hardened gears.
Before using this material heat treatment is needed. This material is called chromium molybdenum. It is the hardest material due to the presence of molybdenum it is not affected by the high temperature.
Copper alloy is an excellent material for gear production because of its high corrosion and wear resistance. It is used for general gears but can also be used in worm gears where sliding friction is a possibility.
Stainless steel has the best corrosion resistance and is used for making gears. Cast iron is another material that has very high carbon content in it. Cast iron is the strongest material of all, and can be used instead of stainless steel. US 303 has higher sulphur content and high machine ability.
Resins, nylon, plastic, and wood are the engineered materials that are used in making gears. Nylon is a self lubricating material and resins are rust proof. These materials should be designed carefully so that they don’t break when used in machines.
There are several types of gears that differ with each other on the basis of their characteristics or configurations as discussed above. The most commonly used gears types are:
In this chapter we will discuss these types one by one.
Bevel gears are conical in shape and the teeth of this gear are placed around its conical surface. These gears are used in applications where there is a need for change around its axis of rotation. These gears transmit energy and power to the intersecting shafts by changing its rotation. The configuration angles that are required for bevel gears is usually 90 degrees though not always. Bevel gears are made with cast steel, plain carbon steel, and alloy steels. All have different characteristics and can be used according to their applications.
Depending on the tooth designs there are some sub-types of bevel gears which are:
Crown bevel gears are also commonly known as face gears. These are cylindrical in shape and have teeth that are inserted perpendicular to the gear face. Crown gears can be paired with any other type of bevel gear though this depends on the teeth number and shape.
Hypoid bevel gears have curved and angled teeth that make it difficult to manufacture. Hypoid bevel gears are used for non parallel and non intersecting configurations. The design of this gear is such that it allows the components to be placed lower and thus creates more space above.
Bevel gears are used widely in cement, beverage, food, mining, energy, and bulk handling industries. Main applications of these gears include medium to large conveyors, crushing, water treatment, and in mixers.
Miter is also a type of bevel gear which when paired with another bevel gear gives a ratio of 1:1. This perfect ratio comes when two miter gears having the same number of teeth are paired together. Miter gears are used in applications where they must change in rotation while the speed remains constant.
Spiral bevel gears have a curved angle of teeth placement. It is more angled and also provides gradual teeth to teeth contact than that of straight bevel gears. This gradual engagement of teeth greatly reduces the vibration and the noise that is produced even at high velocities. Spiral bevel gears are also available in left and right hand angled teeth. Spiral bevel gears are difficult to manufacture and have a structure. However they have greater tooth strength, smooth operations, and low noise during operations.
Straight bevel gears are the most commonly used gears in many industries, because the tooth design is so simple and can be manufactured easily. The teeth of straight bevel gears are designed so that when a perfectly matched straight bevel gear comes in contact, it fits with each other at once and not gradually. This adjustment of teeth produces lots of noise while working and also increases the stress that is produced on the gear’s teeth. All these reduce the lifespan and durability of the gear and machine.
Zerol gears are the combination of both spiral and straight gears. These gears have all the characteristics of both kinds of gears. Zerol gears have curved teeth that are placed straight on the conical surface. This means that zerol gears are used in the same applications as that of straight gears, however, zerol gears are much quieter and have less friction compared to straight gears. Additionally zerol gears are not placed at any angle therefore, these can rotate in any direction and are also available in both left hand and right hand design.
Internal gears are the ones which have teeth that are placed on the inside of the diameter of the cylinder. Internal gears are the best to use for high transmission of energy in small areas, low noise production, less vibration, low speed reduction, and low cost. Internal gears are also called ring gears and are ideally used for areas where there are space issues. The mating of external gears results in rotation in opposite direction and if there is mating of external and internal mesh then the rotation will be in the same direction.
The material used for manufacturing internal gears depends on its application. Usually, forged steel, cast and ground steel, aluminum, and plastic material are used.
Internal gears are used as planetary gears in robotic arms, hybrid vehicle power transmissions, and in turbine generators.
A helical gear is a type of gear that has parallel configuration. This type of gear is also used for non parallel and non intersecting configuration. The teeth of helical gears are twisted around the cylindrical body and angled towards the gear face. Helical gears are designed with left and right hand angled teeth. Each gear pair is composed of a right and left hand gear of the same helix angle. This angled tooth design gives helical gear an advantage because it can mate with other gears differently than those of straight cut teeth. If the mated pair is perfectly matched to each other then the contact level between the corresponding teeth is at a maximum and at intervals, rather than the whole tooth engagement at once. This engagement will help in reducing the noise created from machines and also lower the impact on the teeth.
Some disadvantages of helical gears are that it may work with great efficiency but its capacity is quite less than that of spur gears. Along with that the tooth design of these gears is quite difficult to manufacture and also costs a lot. Single helical gears also create axial thrusts thus; there is a need for thrust bearing in the applications that use single helical gears. This necessity also increases the cost related issues of these gears. Helical gears are made of aluminum, bronze, steel, and nylon. Other subtypes of helical gears are:
Double helical gears have double or mirrored rows of angled teeth. Advantages for double helical gears are that they are more durable, strong, and have a lower axial load.
Herringbone gears are a type of double helical gear in which the two teeth track touches each other rather than being separated by a channel. This forms a V shaped structure.
Screw gears are also a sub type of helical gears and they are used for non parallel and non intersecting configurations. Herringbone gears are employed as right hand and left hand pairs but screw gears are employed for the same hand pair. These types of gears are usually low capacity and low efficiency and cannot be used for high power applications.
Helical gears are widely used in industries like cement, beverage, food, mining, marine, energy, forest, and bulk material handling. Its applications are for medium to large conveyors, mixers, large pumps, water treatments, and crushers. Double helical gears and herringbone gears are used in mining, marine, and heavy industries. It is also used in milling, steam turbines, and ship propulsions.
Single helical gears have a single row of angled teeth cut or embedded around the perimeter of the gear body.
Different types of plastic gears are now widely used in the engineering industry for manufacturing gears. Plastic gears are becoming the first choice of many industries due to their wide range of applications and its availability to work in all types of configuration. Plastic gears are used in a parallel axis configuration such as helical cylindrical gears, double helical gears, and spur cylindrical gears. It is also available for non parallel configuration such as bevel gears, screw gears, and worm gears. Plastic is also used in gears that are used for special applications such as internal gears and rack and pinion gears.
A variety of plastic gears can be made according to the application and can be differentiated on the basis of shape and shaft position. Plastic material is melted and can be molded into any required shape. The material could be PVC, Teflon, or nylon.
Plastic gears are the best option in industries because these are noise dampening, less vibratory, manage the impact load, low cost, low weight, reduced coefficient of friction, absorbs shocks, low maintenance and protects the teeth from wear and tear by distributing the load. Along with all these advantages there are some disadvantages of using plastic gears. These gears have low capacity of load carrying, can be negatively affected by certain chemicals, high cost of initial molds and greater dimensional instability.
Plastic gears are widely used in cameras, toys, electronic equipment, wall clocks, projectors, speedometers and many other home appliances that use plastic gears in their working.
Rack and pinion is a gear pair and it consists of a gear rack and a gear that is cylindrical in shape known as pinion. The gear rack is a flat bar that has infinite radius and it also has straight teeth that are inserted on the surface of the bar. The configuration of these gears is dependent on the type of pinion gear with which these are mated. If it is mated with a spur gear then it is parallel and if it is mated with a helical gear then it is angled. Both these designs can be used in a rack. The rotational movement can be changed into linear one and linear can be changed into rotational one. One rack and pinion gear advantage is the design of this gear. It is also the simplest to manufacture and is also low in cost. But there are some limitations to this design in that the transmission of energy cannot continue in one direction for infinite time. The motion can be limited by the length of the rack, and a great space present between the mated pair which will create a lot of friction and stress on the teeth of the gear.
The material that is used in rack and pinion gears are aluminum and steel. This gives maximum strength to these gears.
Rack and pinion gears are commonly used in the automotive industry in steering systems and also in weighing scales.
Spur gears are one of the most commonly used gears. These gears have a circular or cylindrical body with teeth that are cut straight and are aligned parallel to the gear shafts. If the mated pairs are present then the spur gears are placed on parallel axis configuration for transmission of motion and power. Mating of spur gears depends on its application and can be mated with some other spur gear, internal gear or even with a planetary gear. Spur gears are widely used in many industries because the tooth design is simple and this allows a high degree of precision and is easier to manufacture. Spur gears also lack axial load, high speed, and handling of high loads. However, these gears have a high efficiency rate. These gears can also give off too much noise when in use for high speed applications.
Spur gears can be made from brass, steel, and plastic such as nylon and polycarbonate. There are two primary sub types of spur gears. These are:
External spur gears have teeth outside on the surface of the cylinder. If two external gears are mated they will move in opposite directions.
Internal spur gears have teeth cut that are placed on the inside of the cylinder surface. The external gears are placed inside the internal gears and are moved together.
The spur gears are widely used in many industries such as food, forest, unit handling, beverage, automotive, and energy. It has a variety of applications such as uses in clocks, washing machines, watering systems, small conveyors, package handling equipment, automotives, planetary gear sets, and many more.
Worm gears are also called cylindrical gears or screw shaped gears. It consists of a worm wheel and a worm or screw shaped gear. These gears are manufactured to work with non parallel and non intersecting configurations. The design and angle of these gears is such that the worm can make the wheels rotate but the wheels cannot change the rotation of the screw or worm. This mechanism works in machines that require self locking ability. These gears have a high gear ratio and capacity making them suitable for work in a quieter environment and producing less noise. Some disadvantages include low transmission power and a lot of friction that is produced during functioning. This friction requires lots of lubrication for these gears to run smoothly.
The material that is used for manufacturing worm gears is steel for the worm or the screw that is placed in between and bronze or cast iron for the gears. This combination gives a high speed of rotation to these gears.
Worm gears are used in food, beverage, automotive, forest, energy, and unit handling industries. It's application is in small conveyors, package handling equipment, lifts, elevators, and farm machinery.
Gears are used in almost everything used in daily life. Gears come in many styles and can be used in specific applications according to its structure and design. In this chapter we will discuss the uses of gears in different industries.
A bevel gear is a toothed rotating machine element used to transfer mechanical energy or shaft power between shafts that are intersecting, either perpendicular or at an angle. This results in a change in the axis of rotation of the shaft power...
A gear is a particular kind of simple machine that controls the strength or direction of a force. A gear train is made up of multiple gears that are combined and connected by their teeth. These gear trains allow energy to move from...
A planetary gear is an epicyclic gear that consists of a central gear, referred to as the sun gear and serves as the input gear, which has three or more gears that rotate around it that are referred to as planets...
A plastic gear is a toothed wheel made up of engineering plastic materials that work with others to alter the relation between the speed of an engine and the speed of the driven parts. The engineering plastic materials used in manufacturing plastic gears can be...
A spur gear is a cylindrical toothed gear with teeth that are parallel to the shaft and is used to transfer mechanical motion and control speed, power, and torque between shafts. They are the most popular types of cylindrical gears and...
A worm gear is a staggered shaft gear that creates motion between shafts using threads that are cut into a cylindrical bar to provide speed reduction. The combination of a worm wheel and worm are the components of a worm gear...
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