Gears and Racks
A gear is a rotating machine part with a cut or inserted tooth that engages with another toothed part to transmit torque. A gear rack (a rack and pinion) is a linear actuator consisting of a pair of gears that converts rotary motion into linear motion. These products are used in machine tools, forklifts, electric shovels and other heavy machinery. WLY, a professional China gears and racks supplier, is able to provide gear solutions to meet the requirements of customers’ unique application.
A gear is a mechanical part with teeth that can mesh with each other. It is used in a wide range of applications in mechanical transmission and throughout the mechanical field.
Different Types of Gears
There are many different types of gears, and the most common method of classification is based on the gear shaft nature. They are generally divided into three types: parallel axis, intersecting axis and staggered axis. Parallel axis gears include spur gears, helical gears, internal gears, rack and pinion gears, etc. Intersecting axis gears include straight bevel gears, spiral bevel gears, zero degree bevel gears, etc. Interleaved axis gears include screw gears, worm gears, hypoid gears, etc.
Parallel Axis Gears
|Intersecting Axis Gears||Interleaved Axis Gears|
Helical gears are cylindrical gears with helical tooth lines. It is widely used because it has higher strength than spur gears and runs smoothly. Axial thrust is generated during transmission.
Bevel gears are used to transmit motion and power between two intersecting shafts, and in general machinery, the bevel gears are at a certain angle between the two shafts. Similar to cylindrical gears, bevel gears have straight bevel gears, spiral bevel gears, zero degree bevel gears, etc.
Miter gears are gears where the axes of the two shafts intersect and the tooth-bearing faces of the gears themselves are conically shaped. Miter gears are most often mounted on shafts that are 90 degrees apart and with a gear ratio of 1:1.
Internal gears have teeth cut on the inside of cylinders or cones and are paired with external gears. The main use of internal gears are for planetary gear drives and gear type shaft couplings.
Gears and Gear Racks Materials
- 45 steel (carbon steel for mechanical structures)
45 steel is a representative of medium carbon steel, with a carbon content of 0.45%. Because it is very easy to get, spur gears, helical gears, rack and pinion gears, bevel gears, worm gears and other kinds of gears are mostly made of this material.
- 42CrMo (chromium and molybdenum alloy steel)
Medium-carbon alloy steel containing 0.40% carbon and chromium and molybdenum in its composition. It has higher strength than 45 steel and can be hardened by tempering or high-frequency quenching, and is used to make various gears.
- 20CrMnTi (chromium and molybdenum alloy steel)
A representative material for low-carbon alloy steels. In general, it is used after carburizing and quenching. The strength of the material after heat treatment is higher than that of 45 steel and 42Cr Mo. The surface hardness is about 55~60HRC.
- Su303 stainless steel
Mainly used in food machinery and other machinery that needs to avoid rusting.
- Cast copper alloy
It is the main material for manufacturing turbine. There are generally cast phosphor bronze, aluminum bronze, etc. Most of the worm gear materials used for engagement are 45 steel, 42Cr Mo, 20Cr MnTi and other steels. Different materials are used for worm and turbine in order to prevent tooth surface gluing and transitional wear caused by sliding when the worm and turbine gnaw together.
Heated Treatment of Gears
Surface treatment of gears is a treatment process performed to improve the surface condition of the material. The main purpose is to
- Improve corrosion resistance and rust prevention.
- Improve wear resistance
- Improve surface roughness (smoother surface)
- Surface is more polished and beautiful
- Improve fatigue strength
Gears are made of ferrous metals, non-ferrous metals and engineering plastics, depending on their respective applications. The strength of gears varies depending on the type of material and the heat treatment method.
During the manufacturing process, heat treatments play an important role in the performance and durability of gears and gear racks. In addition to improving the properties of metallurgical components, heat treatments are also important for cost control and overall manufacturing processes. These processes can also increase the surface hardness of gears and gear racks.
Induction Hardening is one of the most common heat treatment processes. During this process, steel is heated to 30-50 degrees above the upper critical point ACCM. After the process, the steel is cooled in still air. This process is used for plain carbon steels, cast irons, and certain stainless grades.
Flame Hardening is another heat treatment process. This process is used for large gears, plain carbon steels, and cast irons. It can be performed by spinning, spinning in a flame, or by progressive heating.
Number of Teeth and Shape of Gears
The involute tooth profile varies with the number of gear teeth. The more the number of gear teeth, the more the tooth profile tends to be straight. As the number of gear teeth increases, the tooth shape of the root becomes thicker and the strength of the gear teeth increases.
As can be seen in the above figure, the root of the tooth of a gear with a tooth number of 10 is partially gouged at the root of the tooth, and root cutting occurs. However, if a positive displacement is applied to the gear with tooth number z=10, the gear strength can be obtained to the same extent as that of the gear with tooth number 200 by increasing the diameter of the tooth apex circle and the tooth thickness.
The Role of Gear Shifting
It can prevent root cutting caused by the small number of teeth during machining.
The desired center distance can be obtained by shifting.
In the case of a pair of gears with a large ratio of teeth, a positive displacement is applied to the smaller gear, which is prone to wear, to thicken the tooth thickness. Conversely, negative shifting of the larger gear results in a thinner tooth thickness so that the life of the two gears is close.
How to Lubricate Gears？
Whether the gears are well lubricated or not will affect the durability and noise of the gears. Gear lubrication methods can be broadly divided into the following three categories.
- – Grease lubrication method.
- – Splash lubrication method (oil bath method)
- – Forced lubrication method (circulating oil spray method)
The selection of lubrication method is mainly based on the circumferential speed (m/s) and rotational speed (rpm) of the gear, etc. as a benchmark. The three types of lubrication methods are classified according to the circumferential speed and are generally grease lubrication at low speeds, splash lubrication at medium speeds, and forced lubrication at high speeds. However, this is only a general benchmark, and there are cases where grease lubrication is used at high circumferential speeds for maintenance and other reasons.
Gears VS Sprockets
- The gear is involute tooth shape, while the sprocket is “three arcs and a straight line” tooth shape.
- Gears are driven by meshing the teeth of two gears, while two sprockets are driven by chains.
- Gear can realize the transmission between parallel axes and any staggered axes, while sprocket can only realize the transmission between parallel axes.
- The torque transmitted by gears is larger than that of sprockets.
- The processing accuracy and installation cost of gears are higher than that of sprockets.
- Gear transmission is compact, while sprocket can realize long-distance transmission.
- Chain drive is suitable for transmission with large center distance, and has the characteristics of light weight and low cost.
- The processing accuracy and installation accuracy of chain and sprocket as well as the accuracy of center distance in chain drive are less than that of gears, and it is easier to change the parameters of existing chain drive (transmission ratio, center distance, etc.) for easy installation and maintenance.
- Usually, the chain drive has higher sprocket wheel teeth and chain simultaneously participate in the meshing and the sprocket teeth groove arc, the gear stress concentration is small, therefore, the chain drive has a large load-bearing capacity, and the gear tooth surface wear is relatively light.
- Because the chain has good elasticity and each hinge part of the chain can store lubricating oil, it has better buffering capacity and vibration absorption capacity compared with the rigid contact gear teeth.
- When the transmission capacity is limited by space, the center distance is small, the instantaneous transmission ratio is constant, or the transmission ratio is too large, the speed is very high, and the noise requirement is small, the performance of chain transmission is not as good as that of gear transmission.