What is a rotary joint?
Core definition and technical analysis
1. Definition of rotary joint
A rotary joint, also known as a rotary union or swivel joint, is a mechanical device. It connects stationary and rotating parts of machines. This device helps transfer media such as liquids, gases, electricity, or data. It is an important component used to connect pipes, mechanical equipment, and industrial equipment.
The choice depends on the use and the type of fluid being moved. It fits well with the customer’s equipment.It has a compact design structure and adopts a flange connection. Even if the connected parts move around each other, it makes sure that the fluid flows smoothly and continuously.
Manufacturers usually make it from steel, stainless steel, or brass. The choice depends on the use and the type of fluid being moved. It fits well with the customer’s equipment. It can rotate the pipe without harming it.
2. Structure of rotary joint
A rotary joint mainly consists of three parts: outer shell, axis, sealing parts, and bearing.
Shell
Function: fixed part of the rotary joint connected to the fluid supply.
Manufacturers often make the material from steel, stainless steel, or brass. This choice depends on the application and the type of fluid they move.
Axis
Function: The rotating part of a rotary joint connects to a rotating device. This device can be a drum, roller, or spindle.
Material: Usually made of steel or stainless steel to ensure durability and wear resistance.
Sealing parts
Function: Prevent fluid leakage between the fixed housing and the rotating shaft. Seals must withstand pressure, temperature, and friction while maintaining a tight seal.
Type:
Lip seals: Simple and effective, often used in low-pressure applications.
Mechanical end seals: Provide a more robust seal for high-pressure and high-speed applications.
Packing seals: made of woven or molded material, adjustable for tighter seal.
O-ring: Used with other seals to provide additional sealing.
Material: Typically made of elastomers like NBR (nitrile), FKM (fluoro rubber), or PTFE (Teflon). The choice depends on the fluid and operating conditions.
Bearing
Function: Support the rotating shaft and ensure smooth, low-friction movement. They help keep axes aligned and reduce fatigue.
Type:
Ball bearings: suitable for light to mass loads and high speeds.
Roller bearings Bearings: can withstand heavier loads and are more durable.
Plain bearings: simple and cost-effective, often used in low-speed applications.
Material: Usually made of steel or bronze, some special applications use ceramic or plastic bearings.
3. Working principle
The rotary joint operates based on the working principle of the bearing. It installs a bearing between the inner ring and the outer ring.
The sensor connects to the inner ring as the output end, and the drive device connects to the outer ring as the input end. The input end of the rotary joint changes rotary drive motion into axial thrust. It creates friction between the inner and outer rings through the bearing. This joint also sends the right rotary motion to the output end. It transmits torque and rotary motion between the inner and outer rings.
Types of Rotary Joints
There are many opinions on the types of rotary joints in the market and there is no unified standard. Experts usually classify the common types based on key factors. These factors include fluid medium, sealing type, medium temperature, working pressure, rotation speed, and number of channels.
1. By fluid media
The types are:
– Compressed air rotary joints
2. By connection channels
It can be divided into: single-channel rotary joint, dual-channel rotary joint, and multi-channel rotary joint. Multi-channel rotary joints are generally rotary joints with more than three channels.
3. By sealing forms
It can be divided into: ring seal rotary joint, mechanical seal rotary joint, and gap seal rotary joint. Many factors affect how the seal type rotates. These include the medium temperature, pressure, and the rotary joint’s rotation speed.
4. By pressures
It can be divided into: negative pressure, low pressure, medium pressure and high pressure rotary joints. Under normal circumstances, such as vacuuming, rotary joints need to be able to withstand negative pressure; our common heating and cooling industrial equipment usually only needs to withstand low pressure, and the fluid circulates due to the inlet and outlet; and hydraulic equipment needs to withstand certain medium and high pressures because of the large torque so that the hydraulic equipment can operate normally.
5. By different temperatures of the fluid medium
It can be divided into: normal temperature rotary joints, high temperature rotary joints and low temperature rotary joints. The fluid will go through different media based on its needs. This can include heating, cooling, or cleaning. In addition, some high-pressure rotary joints will heat up when the seal reaches a certain speed, and the design requires the rotary joints to withstand a certain high temperature.
6. By different speeds of the equipment
It is usually divided into: low speed, medium and high speed rotary joints. According to the speed requirements of the rotating equipment, we must fully consider the rotation speed working requirements that the rotary joint cannot adapt to.
How to Choose the Right Rotary Joint
1. Core Parameter Comparison Table
Industrial Grade: Speed <5000RPM, Pressure <20MPa, Temperature -40~200℃
Precision Grade: Speed <10000rpm, Pressure <5MPa, Temperature -196~800℃
Extreme Environment: Speed >20000rpm, Pressure >100MPa, Temperature >1000℃
2. Selection Decision Tree
Consider these factors:
Media Type: Oil, water, gas, or electricity?
Pressure/Temperature: Check ratings (e.g., 300°C, 3,000 psi).
Speed: RPM requirements (e.g., 500 RPM vs. 10,000 RPM).
Applications of Rotary Joints
Swivel joints are widely used in chemical, shipbuilding, petroleum, natural gas, papermaking, and other fields.
1. Machine Tools
Coolant Delivery:
Lathes: Coolant is supplied through rotary joints to cool the cutting tool and workpiece during machining.
Milling Machines: Facilitates coolant flow to the cutting area, reducing heat buildup and improving tool life.
Grinding Machines: Ensures continuous coolant supply to the grinding wheel and workpiece interface.
Hydraulic Systems:
Transfers hydraulic fluids to power tools and actuators within machine tools.
2. Printing Presses
Ink Transfer:
Provides ink to the printing cylinders while allowing them to rotate freely.
Water Management:
Delivers water to dampening systems to control moisture levels on the printing plates, ensuring high-quality prints.
3. Plastic Injection Molding
Coolant Circulation:
Supplies coolant to molds for temperature control, ensuring consistent product quality and faster cycle times.
Maintains optimal mold temperature to prevent defects such as warping or shrinkage.
4. Textile Machinery
Dyeing Machines:
Facilitates the transfer of dye solutions to the rotating drums or cylinders used for fabric dyeing.
Finishing Equipment:
Ensures precise water flow control for washing, rinsing, and finishing processes in textile manufacturing.
5. Packaging Equipment
Labeling and Sealing:
Provides adhesive or sealing material to labeling heads and sealing stations.
Ensures efficient fluid transfer for hot melt adhesives and other materials.
6. Paper Manufacturing
Press Section:
Delivers steam or hot water to the press section for drying purposes.
Calender Rolls:
Provides heated oil or steam to calender rolls for maintaining the desired paper smoothness and thickness.
Coating Machines:
Transfers coating fluids to the coating applicator rolls, ensuring uniform application.
7. Robotics and Automation
Fluid Supply:
Integrated into robotic arms to supply air, hydraulic fluid, or coolant to end-effectors.
Enables complex movements while maintaining fluid connectivity.
8. Hydraulic Machinery
Hydraulic Fluid Transfer:
Facilitates the transfer of hydraulic oil between stationary and rotating parts of hydraulic machinery.
Commonly used in construction equipment, agricultural machinery, and industrial robots.
9. Food Processing
Washing and Rinsing:
Supplies clean water for washing and rinsing machines for fruits, vegetables, and other food products.
Sanitization:
Ensures proper distribution of sanitizing fluids to maintain hygiene standards.
Pasteurization:
Provides steam or hot water for pasteurization processes, ensuring food safety.
10. Medical Devices
Sterile Fluid Transfer:
Used in medical devices requiring sterile fluid transfer, such as dialysis machines and diagnostic equipment.
Temperature Control:
Maintains controlled temperatures in medical instruments and devices.
11. Agricultural Equipment
Irrigation Systems:
Supplies water to rotating sprinkler heads or irrigation arms.
Spraying Equipment:
Facilitates the transfer of pesticides and fertilizers to spraying nozzles on agricultural machinery.
12. Wind Energy
Pitch Control Systems:
Transfers hydraulic fluid or electrical signals to pitch control mechanisms in wind turbines.
Yaw Control Systems:
Ensures reliable fluid transfer for yaw control systems that orient the turbine blades towards the wind direction.
13. Steel and Metal Industry
Rolling Mills:
Provides coolant to rolling mill rolls to reduce friction and heat during metal forming processes.
Heat Treatment Furnaces:
Supplies cooling fluids to heat treatment furnaces for controlled cooling of metals.
14. Automotive Manufacturing
Painting Booths:
Supplies paint and solvent to rotating painting heads or robotic arms.
Assembly Lines:
Ensures efficient fluid transfer for various assembly line operations, including lubrication and cleaning.
15. Oil and Gas Industry
Drilling Equipment:
Transfers drilling mud and other fluids to the drill bit during drilling operations.
Refining Processes:
Facilitates the transfer of chemicals and fluids in refining processes, ensuring safe and efficient operation.
16. Marine and Shipbuilding
Propulsion Systems:
Transfers hydraulic fluid to steering gears and propulsion systems.
Cooling Systems:
Supplies seawater or coolant to engine cooling systems and other onboard machinery.
17. Pharmaceutical Manufacturing
Process Equipment:
Ensures sterile fluid transfer in pharmaceutical process equipment, including reactors and mixers.
Filtration Systems:
Provides necessary fluids for filtration and purification processes. In short, the rotary joint is a very important mechanical element that can realize the rotation and movement of pipelines and meet the needs of various industrial equipment. In the future, with the continuous development of industrial technology, the application field of rotary joints will be more extensive.
Benefits of Rotary Joints
As a key mechanical component, the rotary joint plays an important role in industrial equipment. Its advantages are reflected in many aspects, which are explained in detail below:
1. Excellent sealing performance
Prevent leakage: Use special materials and structures (such as silicon carbide seals, and labyrinth seal design) to ensure no leakage during the transportation of high-pressure, high-temperature, or corrosive media, and improve equipment safety.
Adapt to complex environments: The sealing ring consists of corrosion-resistant and high-temperature resistant materials that maintain stable sealing under harsh working conditions to prevent leakage of media or intrusion of external impurities.
2. Long life and low maintenance cost
Wear-resistant materials: Key components are made of high-strength stainless steel, nitrided steel, etc. to reduce friction loss and extend service life.
The design allows for easy maintenance: You can judge the wear of the seal by its visual appearance, which makes timely replacement convenient. Some structures support quick disassembly and assembly to reduce downtime.
3. Improve equipment operation efficiency
Efficient transmission: Precision bearing design (such as angular contact ball bearings) ensures flexible and smooth rotation and reduces energy loss.
Reduce the failure rate: Optimize the seal and structure to avoid equipment failure caused by medium leakage and improve overall operation stability.
4. Flexible equipment connection and motion conversion
Multi-channel design: supports single and dual-circuit structures. This meets the transmission needs of different media like water, steam, oil, and air.
Motion form conversion can change rotary motion into linear motion or the other way around. This helps meet the needs of complex mechanical systems.
5. Energy saving and environmental protection
Reduce resource waste: prevent medium leakage, and avoid energy (such as steam, cooling water) and material waste.
The design reduces noise and vibration.
It uses an elastic diaphragm for pre-stressing.
This improvement makes the work area more pleasant.
6. Wide applicability and customization
Multi-field application: covers multiple industries such as chemical, petroleum, metallurgy, papermaking, food, etc., to meet the connection needs of different equipment.
We can offer customized solutions. This includes special rotary joints for high temperature, high pressure, and high-speed needs. We create these solutions based on several factors. These include the characteristics of the medium, like temperature, pressure, and corrosiveness. We also consider the speed of the equipment.
7. Reduce long-term operating costs
Reduce downtime: A high-reliability design reduces failure frequency and shortens the maintenance cycle.
Save on replacement costs: You can replace seals one at a time when they wear out. This way, you don’t have to replace all the equipment, which lowers maintenance costs.
Maintenance and troubleshooting
Maintaining rotary joints is important. This includes regularly replacing seals, lubricating bearings, and cleaning out dirt. These steps help ensure they work well and last longer. Proper maintenance can not only improve the operating efficiency of mechanical equipment but also reduce the failure rate.
1. Regular replacement of seals
The wear of seals is the main cause of leakage, and regular replacement can ensure the tightness of the connection.
2. Lubrication of bearings
Lubrication of bearings is the key to keeping the rotary joint running smoothly. Regular addition of lubricants can reduce friction and wear.
3. Cleaning internal impurities
Impurities may accumulate inside the rotary joint, and regular cleaning can prevent blockage and performance degradation.
Common Challenges & Solutions
Leakage: Caused by worn seals.
Fix: Regular maintenance and high-quality materials like PTFE seals.
Heat Buildup: Common in high-speed applications.
Fix: Integrate cooling channels or heat-resistant alloys.
Material Compatibility: Avoid corrosion with stainless steel or ceramic components.
Conclusion
Rotary joints are the backbone of modern automation, enabling everything from wind energy to precision manufacturing. Whether you’re upgrading machinery or designing a new system, understanding rotary joints ensures optimal performance and longevity.
Do you need a Rotary Joint? Contact our experts for tailored solutions!
Any problems, kindly contact us via email: dannhydraulic@gmail.com
Kindly read this blog: https://dannhydraulic.com/what-is-rotary-joint/.