Universal Shaft Joints

Universal joint is a mechanical device that can transmit torque and rotational motion between two shafts, and its biggest feature is that it allows for significant angular deviation between the connected shafts. Compared with ordinary couplings, universal shafts can compensate for shaft angle deviation, axial displacement, and radial displacement, making them an indispensable key component in mechanical transmission systems.

The standard universal joint mainly consists of the following parts:

• Cross shaft: located at the center of the coupling, with four shaft necks forming a 90 ° angle with each other
  

• Fork shaped components: two, connecting the input shaft and output shaft respectively
  

• Bearing components: usually needle roller bearings, installed between the cross shaft and fork shaped components
  

• Lubrication system: including oil nozzles, oil passages, etc., used to reduce friction and wear

The universal shaft joint transmits torque through the rotation of the cross shaft. When there is an angular deviation between the input shaft and the output shaft:

• The rotation of the input shaft is transmitted to the cross shaft through the first fork shaped component
  

• The cross axis transfers this rotational motion to the second fork shaped component
  

• The second fork transfers motion to the output shaft
  

• Throughout the entire process, the cross shaft swings freely within the bearing, compensating for the angular deviation between the shafts

It is worth noting that a single universal joint can cause uneven output shaft speed, resulting in the so-called "speed fluctuation" phenomenon. To solve this problem, double universal couplings are often used in engineering to eliminate speed fluctuations through phase adjustment.

Cross universal joint coupling

• The most common type is suitable for situations where the angle deviation is not greater than 15-20 °. According to the specific structure, it can be further divided into:
  

• Lightweight series: suitable for small machinery and instrument equipment
  

• Medium Series: Widely used in automotive transmission systems
  

• Heavy duty series: used for heavy-duty applications such as construction machinery and metallurgical equipment

Main material selection

• Cross shaft: usually made of alloy steel (such as 20CrMnTi, 20CrMo, etc.), treated with carburizing and quenching, with a surface hardness of HRC58-62
  

• Fork shaped components: forged parts made of medium carbon steel or alloy steel, with some lightweight couplings made of aluminum alloy
  

• Bearings: high-precision needle roller bearings or ball bearings, self-lubricating bearings are used in special occasions
  

• Sealing element: Nitrile rubber or fluororubber, oil and high temperature resistant

Key manufacturing processes

• Forging: Fork shaped parts and cross shaft blanks are usually precision forged
  

• Heat treatment: carburizing quenching, high-frequency quenching and other processes to improve wear resistance
  

• Mechanical processing: high-precision turning and grinding to ensure matching accuracy
  

• Dynamic balance: High speed couplings require strict dynamic balance testing
  

• Surface treatment: phosphating, chrome plating, etc. to improve anti-corrosion performance

Main performance parameters

• Rated torque: The maximum torque that the coupling can stably transmit over a long period of time
  

• Maximum speed: related to balance accuracy and bearing performance
  

• Allowable angle deviation: Single universal joint is usually 15 ° -20 °, and ball cage type can reach 45 °
  

• Service life: usually calculated in hours or cycles
  

• Efficiency: High quality universal joint transmission efficiency can reach over 98%

Key factors for selection

• Torque requirement: Calculate the required torque based on the power source and load characteristics
  

• Speed range: Consider the maximum operating speed and critical speed
  

• Axial deviation: Evaluate possible axial, radial, and angular deviations
  

• Environmental conditions: temperature, humidity, corrosive media, etc
  

• Space limitations: Dimensional constraints on installation space
  

• Maintenance requirements: lubrication cycle, convenience of replacing vulnerable parts

Application fields of universal joint

• automotive industry
  Transmission shaft in the transmission system
  Half axle of front wheel drive vehicles
  Steering column connection in steering system

• construction machinery
  The transmission system of excavators and loaders
  Crane slewing mechanism
  Arm system of concrete pump truck

• metallurgical equipment
  Main drive of rolling mill
  Drive system of continuous casting machine
  Power transmission of straightening machine

• Other industrial sectors
  Ship propulsion system
  Wind turbine
  Oil drilling equipment
  Printing machinery

Correct installation steps

• Clean all mating surfaces
  

• Check the alignment of the axis and use a laser alignment device if necessary
  

• Align the phases of each component according to the markings
  

• Assemble using appropriate methods to avoid hitting the bearings
  

• Add specified lubricating grease
  

• Conduct no-load trial operation inspection

Key points of daily maintenance

• Lubrication management: Regularly replenish or replace lubricating grease, pay attention to cleanliness
  

• Vibration monitoring: Regularly check the vibration level and detect abnormalities early
  

• Temperature inspection: The temperature of the bearing area should not exceed 70 ℃
  

• Sealing inspection: prevent contaminants from entering the bearing
  

• Regular alignment inspection: prevent the increase of alignment deviation due to foundation settlement and other reasons

As a key component in the field of mechanical transmission, universal joint technology continues to advance with industrial development. From simple cross axis structures to precise cage designs, from simple mechanical parts to intelligent transmission components, universal couplings play an irreplaceable role in improving transmission efficiency and adapting to complex working conditions. In the future, with the application of new materials and processes and the development of intelligent technology, universal couplings will move towards higher performance, longer lifespan, and greater intelligence, providing more reliable transmission solutions for various industrial fields.

Correctly selecting, installing, and maintaining universal couplings can not only ensure the normal operation of equipment, but also significantly extend its service life and reduce maintenance costs. Engineers should fully consider the characteristics and application requirements of universal couplings when designing transmission systems to achieve optimal transmission effects.