Tolerance Rings Information
Figure 1: Tolerance rings are crucial in joining cylindrical components. Source: Pixabay
To relax tolerances, compensate for misalignment, and simplify assembly, tolerance rings are crucial in joining cylindrical components. These highly engineered frictional fasteners are used to mate cylindrical parts by compensating for tolerances between the parts. Waves or corrugations on the tolerance rings are designed to compress between the parts being joined which exerts a holding force to keep the parts in place. These rings help prevent misalignment and fluctuations in fitment due to temperature or loading and greatly simplify assembly.
Theory of Operation
A tolerance ring is a type of fastening device, typically made of metal, that provides a reliable, friction-based fastening solution. It's particularly useful where there's a need to accommodate wide tolerances, compensate for thermal expansion and contraction, or provide electrical insulation or shock resistance. These rings are often used in applications involving bearings, bushings, and other round or cylindrical components.
The basic operation of a tolerance ring works on the principle of radial spring force. A tolerance ring is essentially a corrugated or wave-formed metal strip that creates a series of high points or "waves." These waves allow the ring to act as a spring, applying a radial force between two mating components when installed.
Hooke’s Law of Elasticity
The main driving force behind a tolerance ring is spring theory, or Hooke’s Law of Elasticity. The theory can be summarized by saying the force needed to extend or compress a spring is directly proportional to the distance displaced.
Figure 2: Ballpoint pen coil spring. Source: Santeri Viinamäki/CC BY-SA 4.0
The spring constant can be thought of as the material’s stiffness. This stiffness can be increased or decreased by tweaking the parameters of the tolerance ring to the needs of the application. The shape of the waves, material thickness, and the material’s young modulus all factor into the tolerance ring’s spring constant.
Tolerance rings can absorb variations in roundness, compensate for thermal expansion, and even provide some level of vibration or shock damping. Their use can often simplify design, assembly, and service procedures, and reduce overall manufacturing costs.
Specifications
The specifications for tolerance rings can vary greatly depending on the specific application, the types of components being joined, the operating conditions, and other factors. General specifications for tolerance rings include:
Material
Tolerance rings are typically made of spring steel, stainless steel, or other metals or alloys with suitable spring characteristics. The choice of material can be influenced by factors such as corrosion resistance, temperature resistance, strength, and cost. Material choice has a great impact on the tolerance ring’s spring constant.
Size
The size of the tolerance ring is typically specified by the inner diameter, outer diameter, and width (or thickness). These dimensions should be suitable for the components being joined.
Form or Wave Pattern
The form or wave pattern of the tolerance ring (i.e., the shape and number of the waves or corrugations on the ring) can affect the spring force and the load or torque that can be transmitted. Different forms may be used for different applications. Tighter spacing between the waves stiffens the tolerance ring. The pattern and wave shape can also affect the shape of the force curve as the waves are compressed.
Radial Load or Spring Force
This is the force exerted by the tolerance ring when it is compressed between the components. This force can affect the frictional grip and the load or torque that can be transmitted. Heavier loads or loads with a great deal of radial force require stronger tolerance rings.
Torque Capacity
The torque capacity is the amount of torque that can be transmitted through the tolerance ring without slippage. This is an important specification for applications involving rotational motion.
Operating Temperature Range
This is the range of temperatures at which the tolerance ring can operate without loss of function or damage. This parameter can be very important as the material properties of a tolerance ring can change with elevated temperatures.
Hardness
The hardness of the material can be an important factor in the durability and wear resistance of the tolerance ring.
Corrosion Resistance
Depending on the application and environment, the tolerance ring may need to be resistant to corrosion.
When choosing a tolerance ring for a specific application, it's important to consider all of these specifications and choose a ring that meets the requirements of the application.
Types
Tolerance rings can be categorized based on their shape, size, material, and other properties. However, there are two main types based on their corrugation or wave profile:
Type AN Tolerance Rings
These rings have corrugations or waves that point radially inward. This makes them suitable for applications where the ring is installed into a housing, often to hold a bearing race. The inward-pointing waves grip the inner component, while the outer edges of the ring grip the inner surface of the outer component. These tolerance rings can also be referred to as housing variable (HV) tolerance rings.
Light duty versions of AN rings are referred to as ANL type tolerance rings. ANL type tolerance rings are made from very thin material and do not maintain their shape in a free state. These tolerance rings are only suitable for light-duty applications.
Type BN Tolerance Rings
These rings have corrugations or waves that point radially outward. This makes them suitable for applications where the ring is installed onto something like a motor shaft. The outward-pointing waves grip the inner surface of the shaft and secure the shaft to a bearing or other component. The tolerance rings are also called shaft variable (SV) tolerance rings.
Both types of tolerance rings are available in a variety of sizes and materials to accommodate a wide range of applications. The choice between Type AN and Type BN, and the choice of size and material, depend on the specific requirements of the application, including the sizes and materials of the components to be joined, the loads or torques to be transmitted, and the operating conditions.
Features
Tolerance rings have several distinct features that make them useful in a variety of applications:
Tolerance Compensation
Tolerance rings can accommodate a wide range of component tolerances. They can absorb variations in size, roundness, or alignment between two mating components. This can simplify manufacturing and assembly processes and reduce costs. Tolerance rings also help to extend service life by minimizing required tolerances and reducing tolerance stack up.
Thermal Expansion Compensation
Tolerance rings can compensate for thermal expansion and contraction of components, maintaining a secure frictional grip even under changing temperature conditions.
Vibration Damping
The spring characteristics of tolerance rings can provide a degree of vibration damping or shock resistance, protecting components from damage.
Electrical Insulation
When made from non-conductive materials, tolerance rings can provide electrical insulation between components, preventing electrical currents from passing between them.
Ease of Assembly and Disassembly
Tolerance rings make it easy to assemble and disassemble components. The components can be separated by simply overcoming the frictional force of the ring, making these rings ideal for applications where components may need to be serviced or replaced. Without tolerance rings assembly methods like press fits might be needed making disassembly quite difficult.
Torque Transmission
Tolerance rings can transmit significant amounts of torque between components, making them suitable for use in applications involving rotational motion.
These features make tolerance rings a versatile and cost-effective solution for a wide range of fastening, mounting, and assembly applications.
Figure 3: Sebastian Stabinger Paethon/CC BY-SA 3.0
Manufacture
The manufacturing of tolerance rings generally involves several steps, which may vary depending on the specifics of the design and the material used. However, the typical steps are as follows:
- Material selection
- Tape preparation
- Stamping or forming
- Curling
- Shearing
- Heat treatment
The first step is to select the appropriate material for the tolerance ring. Commonly used materials include spring steel, stainless steel, and other metals or alloys with good spring characteristics. The choice of material depends on the requirements of the application, such as the need for corrosion resistance, strength, or temperature resistance.
The selected material is prepared in sheet or strip form and often rolled into a tape of desired thickness. The sheet is typically cleaned and may undergo other preparation processes to ensure it is suitable for manufacturing.
The basic shape of the tolerance ring waves is created by stamping or forming the material. This process involves using a die to stamp the desired pattern into the tape. The specific form of the tolerance ring, including the size, the number of waves or corrugations, and other features, is determined by the design of the die.
After stamping or forming, the tolerance ring passes through a curler and spindle that curves the tape into the proper ring diameter. Once curled, the tape is sheared and the tolerance ring is fully formed.
Depending on the tolerance ring material, the ring may undergo a heat treatment process to improve its spring characteristics and other properties. This process typically involves heating the material to a specific temperature and then cooling it in a controlled manner.
Figure 4: Tolerance rings are used in a variety of applications across different industries. Source: Pixabay
Applications
Tolerance rings are used in a variety of applications across different industries due to their unique properties of compensating for tolerances, reducing noise and vibration, and providing a simple assembly and disassembly mechanism. Here are a few examples of where tolerance rings are used:
Automotive Industry
Tolerance rings are widely used in automotive applications, such as mounting bearings in transmissions, differentials, and wheel hubs. They're also used in electric motors for electric vehicles, helping to secure the rotor to the shaft and handle the thermal expansion between different materials.
Electrical Motors and Generators
Tolerance rings can be used to mount components like bearings or to secure the rotor in place. They help to handle variations in component sizes and to reduce noise and vibration.
Appliances
In household appliances, such as washing machines or air conditioners, tolerance rings can be used in the assembly of motors or fans, providing a secure grip and reducing noise and vibration.
Figure 5: In household appliances, such as washing machines or air conditioners, tolerance rings can be used in the assembly of motors or fans. Source: LG??
Computer Hard Drives
Tolerance rings are used to mount bearings in the spindle motor assembly, helping to reduce noise and vibration, which is critical for the operation of the hard drive.
Aerospace
Tolerance rings can be used in various aerospace applications, where they help to cope with the thermal expansion and contraction caused by the extreme temperature changes.
Pumps and Compressors
Tolerance rings can be used to mount bearings or other components in pumps and compressors, providing a secure grip and reducing noise and vibration.
Medical Devices
In medical equipment, such as MRI machines, tolerance rings are used to reduce noise and vibration and to secure components in place.
These are just a few examples. The versatility of tolerance rings allows them to be used in a wide range of applications across many different industries.
Standards
The specifications and performance characteristics of a tolerance ring are primarily determined by the manufacturer based on the intended application, and the requirements of that application. These may include factors such as the size, form, material, spring force, torque capacity, operating temperature range, and corrosion resistance of the ring.
Material standards and manufacturing standards are important to ensure the quality and consistency of the tolerance ring. Some commonly seen standards include:
- IATF 16949:2016
- ISO 9001