A fastener or fastening is a component that mechanically joins or fixes two or more objects together.
Fasteners are used in a wide number of domestic and industrial products from warehouse robotics to cars and from washing machines to toys, they fasten components such as bearings, gears, pulleys and fans. The material of the objects, their size, location and the environmental conditions they need to withstand all play a role in the type of fastener required.
As a rule, fasteners fall into two types: permanent fixings and non-permanent fixings. Permanent fasteners include adhesives, welding, thermal shrink fit, locking nuts and once joined they cannot be removed. A non-permanent fixing is one that allows the assembly or system to be dismantled without damaging the components. Non-permanent fasteners are predominately made of metal; nuts and bolts are common options.
For more complex systems an engineered fastener is required. Depending on the system, you can choose from off-the-shelf solutions however, when performance, torque or load requirements are more precise a custom-designed option might be more suitable.
The choice of fastener is often based on the application. Other considerations include: What are the type of objects that need to be joined? What physical location are they used in? And what materials are involved? All of these and more will be factored into the decision on the choice of fastener.
Here we’ll look at the fasteners needed for electric motors. With the increasing use of electric motors in numerous applications the demand for fasteners has also increased. The shape and variety of fastener along with their performance requirements are changing. For example, the stator fastener needs to tolerate thermal expansion and cooling which causes a change in component clearances. Where dissimilar materials are used between electric motor components, the fastener will be required to secure the components together at min and max clearances. Bearing mounts and rotor mounts (also fasteners) need to be compliant to overcome issues such as misalignment and shock loads whilst retaining the components position.
Off-the-shelf solutions in these situations are possible, but bespoke engineered fasteners provide reassurance of fit and performance.
Electric motors produce two types of force: linear or rotary (torque). The force is used to power a mechanism, such as a fan, a pump or household appliances. The efficiency of electric motors has made them a popular choice and their uses are increasing and expanding.
An electric motor normally requires a fastener that will rigidly fix it to the housing. There are situations where the electric motor mount may have to withstand high heat, high vibration and manufacturing tolerances, such as the throttle body motor mount. In these instances, using a tolerance ring to fix, or provide additional support, to the motor into the housing is a more suitable solution over screws or rubber O-rings.
The stator is the static component in a rotating mechanism, used in electric motors or generators for example, that generates the rotational output of the motor. One of these fields needs to be moving and the other static, which is why a stator is needed in these systems and because of the stator’s purpose it is typically made of steel, a dense material.
With the trend to reduce weight in systems, new materials for motor housings are being introduced such as aluminium. However, this introduces the problem of dissimilar materials being used between the motor housing and the stator. Using a tolerance ring as an engineered fastener for stators has the benefit of tolerating clearance changes due to temperature.
Alongside its ability to cope with changes in component clearance as a result of temperature variation, the tolerance ring overcomes assembly process issues, using a press-fit method rather than adhesives or shrink-fit options.
“No heating, acceptable forces and no messy glue; I am always impressed by the simplicity of the solution when I use a tolerance ring to assembly a stator” Andy Broadwell, Senior Application Engineer.
The RENCOL® Tolerance Ring fixes the stator into the housing and as a stator mount it is an effective choice.
If thermal transfer is important, the Thermoclad Tolerance Ring has the additional benefit of increasing thermal transfer between stator and housing because of the bi-metallic material construction.
The other vital component of an electric motor is the rotor. As the name suggests, the rotor is the rotating component that moves or generates force, produced by the interaction between the windings and the magnetic fields.
The rotor needs to be fixed onto the shaft, this fixing, often referred to as the rotor mount, needs to compensate misalignment while providing a constant, secure fixing. Vibrations can amplify and change as the motor speed increases and the fixing needs to withstand these variations and remain reliable.
The tolerance ring as a rotor mount is a flexible fixing due to the elasticity created by the waves which act as springs. Depending on the type of material, its thickness and the formation of the waves, the stiffness can be managed to deal with the force created by the rotor. A RENCOL® Tolerance Ring is custom designed to meet the demands of the motor and fit exactly between the rotor and the shaft, whilst also providing a simpler assembly process compared to press or heat shrink processes.
The tolerance ring as a fastener can be used in many other applications. The mounting of bearings, sensors and magnets are popular choices. The performance requirements of each is explored more below.
Before we completely move away from electric motors, it’s worth noting that fasteners are used to mount an electric motor bearing.
But bearings are not just limited to electric motors and wherever a bearing is used the inner and outer race needs to be securely attached to the housing, application or system the bearing is being used in.
A bearing needs to be carefully mounted to ensure optimum performance. Too tight and it will prevent movement, too loose and the bearing may dislodge or rattle. Because RENCOL® Tolerance Rings are custom-designed they are built to fit the bearing exactly and provide a secure fixing. As a bearing mount a tolerance ring can be used for large diameter bearings in applications such as electric motors and all the way to smaller Hard Disk Drive (HDD) bearings, and provide benefits such as secure retention across operating ranges, simplified assembly, and cost and weight reduction.
Fasteners are widely used in electric motors, but there are other sub-components that need to be fixed into place. Sensors, magnets and magnetic sensors are widely used in the automotive industry for detection or positioning and all need to be held in place throughout their lifetime to perform.
There has also been an increase in domestic and industrial equipment using sensors. Mechanical systems have sensors incorporated to improve detection of potential problems and they can aid users to understand and better handle their own systems.
Magnets and sensors can be brittle or delicate which means selecting the right fastener is important to prevent damage. Glue is an option but it doesn’t allow for movement so should it be hit the magnet or sensor may shatter or break. The tolerance ring can protect a sensor, magnet or magnetic sensor while holding it securely in place and allowing for movement. And, like a bearing mount, because the tolerance ring is a fastener with waves it secures the components and also allows dis-assembly for rework, saving precious and expensive magnets from being scrapped.
The RENCOL® Tolerance Ring has been used in a wide number of devices as a fastener. It was first commissioned for use in the self-fixing ball knob for machinery.
When used as a fastener the tolerance ring provides a number of benefits:
These static fixings are designed for each use case. During the design phase the engineers can help develop a fastener that also focuses on the other performance benefits that need to be achieved.
Interested in finding out more? Contact us to speak to an engineer about how you could use a RENCOL® Tolerance Ring.