Universal Joint Coupling

Universal joint uses characteristics of its mechanism to make two shafts not on the same axis, and two axes can be continuously rotated under condition of angle of axis, and torque and movement can be reliably transmitted. The biggest feature of universal coupling is that its structure has large angular compensation capability, compact structure and high transmission efficiency. The angles of the two axes of different structural types of universal joints are different, generally between 5° and 45°.

Structure type

Universal couplings are available in a variety of configurations, such as: cross shaft, ball cage, ball fork, bump, ball pin, ball joint, ball plunger, three pin, three fork , three ball pin type, hinge type, etc.; the most commonly used is the cross shaft type, followed by the ball cage type. In practical applications, according to the magnitude of the transmitted torque, it is divided into heavy, medium, light and small.

Application

A mechanical part used to couple two shafts (active shaft and driven shaft) in different mechanisms to rotate together to transmit torque. In high-speed and heavy-duty power transmissions, some couplings also have the function of damping, damping and improving the dynamic performance of the shafting. The coupling consists of two halves, which are respectively coupled to the drive shaft and the driven shaft. Most of the general power machines are connected to the working machine by means of a coupling.

National standard

The cross-shaft universal coupling is a universal coupling with a large amount of use, and the bearing is a consumable part of the cross-shaft universal coupling. The main difference between several large cross-shaft universal couplings is the variation of the bearing housing and the crosshead, forming different structural forms. In order to ensure the synchronism of the main and driven shafts, the double-link form is adopted in practical applications. The double-joint connection method is nothing more than welding or flange bolting, and the length of the middle can be changed in various forms. The cross-shaft universal coupling crosshead part has the following form:

SWC type integral fork cross shaft type universal coupling (JB/T 5513-2006), SWP type partial bearing seat cross shaft type universal coupling (JB/T 3241-2005), SWZ type integral bearing seat Cross shaft type universal coupling (JB/T 3242-1993), WS type small double cross shaft type universal coupling (JB/T 5901-1991), WSD type small single cross shaft type universal coupling (JB/T 5901-1991), Cross bag for SWP type cross shaft type universal coupling (JB/T 7341.1-2005), cross package for WGC type cross shaft type universal coupling (JB/T 7341.2-2006) .

The above heavy-duty and small cross-shaft universal couplings are universal. Different models in the automotive industry have their own special cross-shaft universal couplings or other types of universal couplings. For example, the car uses a ball cage universal coupling. In addition, agricultural machinery, industrial machinery and other sports machinery products also have dedicated universal couplings, most of which use cross-shaft universal couplings.

Classification

There are many types of couplings, which can be divided into: 1 fixed coupling according to the relative position and position of the two shafts being connected. It is mainly used in places where the two axes are strictly centered and there is no relative displacement during the work. The structure is generally simple, easy to manufacture, and the instantaneous speed of the two axes is the same. There are mainly flange couplings, sleeve couplings and clamps. Shell couplings, etc. 2 movable coupling. It is mainly used for the deflection of the two axes or the relative displacement in the work. According to the method of compensating the displacement, it can be divided into a rigid movable coupling and an elastic movable coupling. The rigid movable coupling is compensated by the movable joint formed between the working parts of the coupling with a certain direction or several directions of motion, such as a dental coupling (allowing axial displacement), a cross groove coupling (for connecting two shafts with parallel displacement or angular displacement), universal joint (for large deflection angles of two shafts or large angular displacement during operation), gear coupling (Allow integrated displacement), chain coupling (allowing radial displacement), etc. Elastic movable coupling (referred to as elastic coupling) utilizes the elastic deformation of the elastic element to compensate for the deflection and displacement of the two axes. The elastic element also has cushioning and damping properties, such as serpentine spring coupling, radial multi-layer leaf spring coupling, elastic ring bolt coupling, nylon bolt coupling, rubber sleeve coupling, etc. . Some of the couplings have been standardized. When selecting, first select the appropriate type according to the work requirements, then calculate the torque and speed according to the diameter of the shaft, then find the applicable model from the relevant manual, and finally make the necessary check for some key parts.

Funiction

It is used to connect the two shafts together. When the machine is running, the two shafts cannot be separated. Only when the machine stops and the joint is disassembled, the two shafts can be separated.

Type

The two shafts to which the coupling is coupled may cause changes in the relative positions of the two shafts due to manufacturing and installation errors, deformation after load, and temperature changes, and strict alignment is often not guaranteed. According to the coupling with or without elastic elements, whether there is any ability to compensate for various relative displacements, that is, whether the coupling function can be maintained under relative displacement conditions and the use of the coupling, the coupling can be divided into rigid couplings. Flexible coupling and safety coupling.

Rigid couplings only transmit motion and torque, and do not have other functions including flange couplings, sleeve couplings, cage couplings, etc.

Flexible coupling Flexible coupling without elastic components, not only can transmit motion and torque, but also has different degrees of axial, radial and angular compensation performance including gear coupling and universal joint , chain coupling, slider coupling, diaphragm coupling, etc.

Flexible coupling with elastic elements, which can transmit motion and torque; have different degrees of axial, radial and angular compensation; also have different degrees of vibration damping and buffering to improve the performance of the transmission system. Various non-metallic elastic element flexible couplings and metal elastic element flexible couplings, various elastic couplings have different structures and large differences, and their roles in the transmission system are also different.

The safety coupling transmits motion and torque, overload safety protection. Flexible safety couplings also have different levels of compensation including pin-type, friction, magnetic powder, centrifugal, hydraulic and other safety couplings.

Selection

The choice of the coupling mainly considers the height of the required transmission shaft, the size of the load, the installation accuracy of the two components to be connected, the smoothness of the rotation, the price, etc., Refer to the characteristics of each type of coupling and choose a suitable coupling type.

The following points can be considered when making specific choices:

Most couplings are standardized or standardized. The designer's task is to choose, not design. The basic steps for choosing a coupling are as follows:

Select the type of coupling

According to the size of the transmitted load, the speed of the shaft, the mounting accuracy of the two parts to be connected, etc., refer to the characteristics of various types of couplings, and choose a type of coupling that is suitable.

1) The magnitude and nature of the torque to be transmitted and the requirements for the damping function. For example, for heavy-duty heavy-duty transmissions, gear couplings are available; for severe impact loads or transmissions that require shafting torsional vibration, high-elastic couplings such as tire couplings are available.

2) The working speed of the coupling and the magnitude of the centrifugal force caused. For high-speed transmission shafts, couplings with high balance accuracy, such as diaphragm couplings, should be used, and it is not suitable to use eccentric slider couplings.

3) The magnitude and direction of the relative displacement of the two axes. When the installation is adjusted, it is difficult to keep the two axes strictly aligned accurately, or when the two axes will produce a large additional relative displacement during the work, the flexible coupling should be selected. For example, when the radial displacement is large, the optional slider coupling can be used with a large angular displacement or a joint of two shafts.

4) Reliability and working environment of the coupling. Couplings that are usually made of metal components that do not require lubrication are relatively reliable; couplings that require lubrication are susceptible to the degree of lubrication and may contaminate the environment. Couplings containing non-metallic components such as rubber are sensitive to temperature, corrosive media, and strong light, and are prone to aging.

5) Due to manufacturing, installation, load deformation and temperature changes, it is difficult to maintain strict alignment of the two axes after installation and adjustment. There is a certain degree of displacement in the x, Y direction and the skew angle CI. When the radial displacement is large, the optional slider coupling can be used with a large angular displacement or a joint of two shafts. A flexible coupling should be used when the two axes produce a large additional relative displacement during operation.

Selection calculation

Calculated torque of the universal coupling:

Tc=TKnKhK Ka≤Tn(N·m)

When alternating load: Tc≤Tf (N·m)

The nominal torque of the Tn--universal coupling, N·m, (it is the theoretical calculation value under given conditions, ie the coupling speed, n≈10r/min. Bearing life Ln=5000h, The angle of the axis is 3°, and the value when the load is stable);

Tf-- universal joint fatigue torque, N·m

Theoretical torque of T-- universal coupling, N·m; where T=9550Pw/ N (N·m)

Pw--drive power, kw

N-- universal coupling speed, r/min

Kn--Universal Coupling Speed Correction Factor, Kh--Universal Coupling Bearing Life Correction System

K-Two-axis angle correction factor of universal coupling

Ka--load correction factor. Uniform load, when working smoothly, Ka=1.0; uneven load, moderate impact, Ka=1.1~1.3; large impact load and frequent positive and negative reversal, Ka=1.3~1.5, extra large impact load and frequent positive reversal When Ka>1.5.

L-For universal joints with high speed, large folding angle or beyond the specified length, in addition to the above calculation, the rotational flexibility must also be checked. The rotational flexibility is represented by n. In general, n > 18000.

M-Where - the axis of the universal joint is folded, (°); n--the speed of the universal joint, r / min.

Deviation knowledge

Universal couplings are widely used in various general-purpose mechanical applications due to their large deviation angle and high transmission torque. Common types of universal couplings are: universal, high-speed, miniature, retractable, high-torque Many types of couplings such as couplings. WS.WSD small cross shaft universal coupling is suitable for connecting the transmission shaft system with the angle of the two shaft axes β ≤ 45 °; the single cross shaft transmission with the nominal torque of 11.2~1120N·m Couplings and double cross shaft universal couplings.

The universal joint is suitable for the transmission occasion where the angle between the two axes of the joint plane is β≤45o, and the nominal torque of 11.2-1120N.m.WSD is a single cross universal joint, and the WS type is double cross. The universal coupling has a maximum angle between each section of the joint 45o. The finished hole H7 can be opened according to the requirements, the keyway, the hexagonal hole and the square hole. The angle between the two axes is allowed to change within a limited range according to the work requirements.

Material

45 steel, 45 forged steel, 40 chrome, cast iron.

Related parameters

Cross bearing parameters for SWC type-universal coupling

Selection problem

Prerequisites and conditions must be clarified before the universal coupling is selected:

1. There is no transmission between the prime mover and the universal joint. If there is a gear ratio, there are several shaft outputs through the intermediate transmission, that is, whether there is power split. Consider the type of prime mover, power and speed.

2. It is necessary to consider the type of prime mover and the load category of the optional cross-shaft universal coupling to transmit load: one-way constant load, pulsating load or two-way alternating load. What is the installation status of the universal coupling? Install horizontally, vertically, or tilted. To make the axis angle less than 3 degrees as much as possible, if you have to tilt the installation, determine the horizontal and vertical angles.

3. Considering the working environment of the prime mover, whether there are high temperature, dust, water drench, chemical corrosion and other harsh environmental conditions, choose the corresponding type of universal joint according to the use environment.

4. It is necessary to know the required connection form and specific installation dimensions at both ends of the universal joint, and to understand the special requirements such as the installation bracket.

5. What is the rotational speed of the cross-shaft universal coupling itself. Whether it needs to be balanced. Requires dynamic balance or balance, which level of balance quality is required.

6. Is there a limit to the installation location? What is the specific installation length and whether it needs to be stretched. When it is required to expand and contract, what is the outward extension of the universal joint in the shortest state? For universal joints that do not require expansion and contraction, the compensation of the axial dimension error must be considered and the position to be compensated in the system should be determined.

After understanding the above prerequisites, gradually determine the specifications of the cardan shaft, and finally determine which structure to choose. The universal coupling has the structure of cross shaft, ball cage, ball fork, bump, ball pin, ball joint, ball plunger, three pin, three fork, three ball pin Type, hinge type, etc., the most commonly used is the cross shaft type, followed by the ball cage dragon, in practical applications, according to the magnitude of the transmitted torque is divided into heavy, medium, light and small. To choose a coupling suitable for the prime mover from so many universal couplings requires a deep understanding of the prerequisites and external influences described above.

Correction process

The search for the universal coupling is one of the important tasks of the machine installation. The purpose of the alignment is to make the center line of the two axes of the drive shaft and the driven shaft on the same line while the machine is working. The accuracy of the alignment is related to the machine. Whether it can operate normally is especially important for high-speed machines. The absolutely accurate alignment of the two axes of the cross universal coupling is difficult to achieve, and it is more difficult to maintain accurate alignment of the continuously running machine.

The uneven thermal expansion of the components of the cross universal coupling, the deflection of the shaft, the uneven wear of the bearing, the displacement generated by the machine and the uneven sinking of the foundation all cause the shaft to be difficult to maintain. Therefore, When designing the machine, it is stipulated that there is an allowable deviation value in the center of the two axes, which is also required when installing the coupling.

From the perspective of assembly, the cross universal coupling can provide the torque of the coupling safely and reliably. The larger the deviation allowed by the two shaft centers, the easier it is to achieve the installation. However, from the perspective of installation quality, the smaller the deviation of the centerline of the two axes, the more accurate the alignment, the better the operation of the machine and the longer the service life. Therefore, the allowable deviation of the two-axis alignment when the universal joint is installed cannot be regarded as the margin left by the installer's hasty construction.

Measurement sequence

The different axes of the universal coupling may be radial displacement, tilting or both. The measurement coaxiality should be performed at four positions evenly distributed on the end face and the circumference of the universal joint. The machine connected to the cross-shaft universal coupling is inevitably adjusted for coaxiality during the installation process, so that the opposite wheel is concentric and parallel, otherwise it will affect the efficiency of the pump or cause equipment operation accidents. Some large high-temperature equipment should also consider the factors that increase the height of the equipment base when the coupling is aligned.

Measurements can be made in the following order:

(1) Temporarily connect the half-million-way uranium A and B to each other and set up special tools.

(2) Rotate the coupling halves A and B at the same time to make the special tools or alignment lines rotate sequentially. The radial values (or gaps) and axial values of the two halves of the uranium are measured at each of the four locations.

If the installation BJ finds that the universal joint uranium is in different axes or non-parallel state, it must be adjusted. When adjusting, first adjust the level of the pump, then use the universal coupling of the pump as the reference to measure and adjust the counter wheel of the motor to ensure the coaxiality of the motor and the pump. When adjusting the concentricity of the shaft, Adjust the clearance and adjust the clearance. When adjusting the motor, the base of the gasket pad motor with different thickness can be used according to the d and the mouth value. The axial clearance is adjusted to make the two wheels parallel, and then the radial clearance is adjusted to make the two wheels concentric. There is no specific requirement for the bitter equipment manufacturer. The shaft speed is 2980rmin. The axial clearance (concentricity) and the clearance (parallelism) of the universal universal uranium are not more than 0.03mm; the shaft speed is 1500rmin, and the shaft clearance of the universal coupling And the gap error is not more than 0.05mm. When the coupling is aligned, the similar triangle principle can be utilized to take into account the influence of the adjustment of the axial clearance on the surface clearance, and the calculation can be corrected. The alignment speed of the universal joint can be greatly improved.