For any mechanical engineer, bearing technology has been the first concern. It was not until rolling element bearings were introduced and were used in automobile wheels and electric motors. Soon after, the same bearings were tested for their technical limits with increased use in high-resolution scanning, high-speed machinery, and semiconductor manufacturing. It seems like air bearings are the next best bearing design with plenty of applications.
Air bearings have been used in coordinate measuring machines for more than 20 years. Ask any machine designer, and they will tell you about the enormous technical benefits of air bearings, such as high speed and high precision capabilities, no oil lubrication, zero friction and wear, and more. Although the benefits are many, the commercial manufacturing of air bearings started only recently. Many companies are now manufacturing easy-to-use, simple, and inexpensive air bearings.
What is Air Bearing?
Coming to an important part – what actually are air bearings?
Air bearings utilize a thin film of pressurized air in them. The pressurized air works as a thin film between load-bearing surfaces, which will otherwise end up in contact with one another. With the help of the pressurized thin film, air bearings work far greater than the traditional bearings that come with the problems of lubricant handling, friction, and wear. Furthermore, air bearings promise high-speed applications and precision positioning.
The pressurized thin film in the air bearings is made by supplying airflow into the bearing gap. The air enters the bearing from the bearing face. Usually, a porous media or an orifice is used to supply the air into the air bearings.
The air constantly escapes from the air bearing gap. One thing that is looked after in a machine is to maintain the flow of pressurized air in the bearing with the one flowing out of the bearing gap. Because of this restriction, the working load and the pressure under the bearing are maintained.
If there were no restrictions, it would result in low stiffness, high flying height, and high air consumption. It’s known as an air bearing compensation. This process helps optimize the benefits of air bearings such as stiffness, lifting, and loading for multiple applications.
What is the Use of Air Bearing?
What is the Use of Air Bearing?Due to their plenty of benefits, air bearings are used in multiple applications, including semiconductor wafer processing machines, precision machine tools, high-speed and precision positioning, Coordinate Measuring Machines, and others. From the different benefits of air bearings, the most common ones are here.
It Offers Zero Friction
Air bearings promise high repeatability due to zero static friction and infinite resolution.
It Offers Zero Wear
Air bearings ensure low particle generation and consistent machine performance due to non-contact between surfaces resulting in virtually zero wear.
It Allows Straighter Motion
Air bearings are not influenced by guide irregularities and surface finish, reducing average errors.
It Offers Silent and Smooth Operation
Unlike recirculating rollers or balls, air bearings do not make noise or change direction when loaded or unloaded elements. It ensures a smooth operation throughout the process.
It Offers Higher Damping
Air bearings promise a squeeze film damping effect, which leads to more controllability and improved dynamic stiffness.
It Eliminates Oil
Since the air bearings make no use of oil; therefore, there are fewer problems in the entire system. The use of lubricants leads affects the environment in the system, which technically affects the outcome. The pressure in the bearing helps reduce the pressure and eliminate all kinds of dust particles.
It Ensures High Speeds
Since rollers or balls are not involved, the acceleration and speed eventually increase.
Types of Air Bearing Technology
Are you wondering about different kinds of air bearing technologies? Here’s a list of them.
Aerodynamic Bearings
Coming to aerodynamic bearings – they are dependent on the relative motion between spiral grooves and bearing surfaces. Spiral grooves are used in the system to draw the air in between the bearing lands. You might have witnessed this process yourself when you drive your automobile at full speed on a puddle of water. The case might be a little different when you drive through the puddle at low speed.
In aerodynamic bearings, the relative motion plays a huge role and is responsible for the entire functioning of such bearings. Because of this motion, the surfaces do not come in contact with one another. Remove the relative motion, and the elements will come in contact with one another. The motion also needs to be at an accurate speed to generate the air film.
The other names of aerodynamic bearings are self-acting bearings and foil bearings. Some examples are thrust bearings for electrical generator turbines, crankshaft journals, read-write heads flying over a spinning disk, and camshaft journals.
Aerostatic Bearings
After aerodynamic bearings come the aerostatic bearings. For them, an external pressurized air source is required. The air pressure enters into the bearing surfaces through steps, porous compensation techniques, precision holes, or grooves. Unlike aerodynamic bearings, aerostatic bearings do not require a constant relative motion to maintain the air gap. Since they work with external air pressure, it’s easy for them to maintain an air gap without a relative motion.
Different Applications of Air Bearing
Air bearings offer multiple applications. Here are a few of them.
Ultra-Precision Machine Tools (Optical Grinding)
Air bearings ensure repeatability and high positioning accuracy as well. It’s one reason that air bearings are continuously used in ultra-precision machine tools such as optical grinding.
They are frictionless and promises zero mechanical contact. Hence, it shows that air bearings are free from hysteresis or stick-slip effects. Air bearings are the perfect choice to achieve nanometer-level precision with zero errors.
Optical Inspection Equipment (Medical Device Manufacturing)
Air bearings allow flat and straight travel as well, which is why they have incredible applications in medical device manufacturing. Rotary air bearings usually show some problems, such as tilt and wobble errors, which does not happen with air bearings. It happens because air bearings support the load in all its length. In contrast, mechanical rolling element bearings only support them at the contact points of the rollers or balls.
Tensile and Friction Testing Equipment
Another top benefit of air bearings is force control with precision. It’s the first reason they have plenty of tensile and friction testing equipment applications. Air bearings help create precision stages when combined with voice coils or ironless linear motors. These precision stages help in operating transducers and force generators.
Wafer Scanning (Digital Printing)
One top benefit of using air bearings is that they offer constant and smooth velocity due to no involvement of rolling elements to disturb the motion. It’s highly beneficial for digital printing and wafer scanning.
Semiconductor Wafer Processing (Medical Device Manufacturing or Medical Research and Testing)
Air bearings promise low particle generation, which does not affect the motion of the elements in the system. For this reason, air bearings have plenty of use in medical device manufacturing, research, and testing. Air bearings are perfect for use in environments where only undetectable particle generation can occur.
Semiconductor Manufacturing (Equipment Located In Remote or Difficult-To-Access Locations)
Air bearings also don’t show any change in their performance over an extended period of time. Air bearings offer low to no friction, which is why the whole process is steady and stable over time.
Processes Requiring Continuous Operation or Extremely High Duty Cycles
One of the main benefits of air bearings is that they have an unlimited service life. The parameters involved in the process do not influence the air bearing life. Unlike other bearings, air bearing comes with a linear motor and voice coil, which can be replaced upon corrosion. Hence, the limiting factor reduces in the whole process.
What is the Effect of Environment on Air Bearings?
The environment plays a crucial role in affecting the overall performance of air bearings. Here’s a list of environmental factors and their influence on air bearings’ performance.
Dust
Without proper care, the dust can build up at the clearance areas, influencing the pressure in the air bearing. It’s recommended to opt for angled surfaces, so there’s no chance of dust buildup inside the air bearing.
Temperature
Air bearings are meant to be operated at room temperature. A slight difference of about +/-30F is acceptable, but not more than that. It’s important to study the thermal effects on the structures for better outcomes.
Oil
OilTo avoid the creation of a drag, it’s important to keep the oil away from the oil bearings. It will fill the air gap and will cause multiple issues. If there’s oil spotted in the air bearings, then it’s important to perform thorough cleaning according to the guidelines to remove it.
Water
Another thing that you must avoid is water dripping on the guide. Again, water will act similar to oil and will fill the air gap. It further results in the creation of a drag. If you want to restore the air bearings’ original performance, then it’s best to dry the air guideway. Water can also lead to corrosion and other reactions in the air bearing.
Air Bearing Design Guide
The choice of guide material varies for air bearings. They can work on different guide materials, including ceramics, granite, chromed steel, stainless steel, and hard-coated aluminum. Before you choose the guide material for the air bearing, you have to pay attention to a few considerations. For instance, local flatness, holes in the counter surface, and surface finish need to be checked before choosing an air bearing guide material.
Let’s pay close attention to them.
Surface Finish
For air bearing guide material surface finish, it’s recommended to opt for a 16rms finish or better than this one. You can use rough surfaces as well. If you’re working on small gaps, then the surface roughness can become a problem as it adds to the gap, so the design can be influenced. Bearing face is also susceptible to damage during a touchdown as it’s in motion.
Local Flatness
Local flatness is the flatness under the bearing. It must be less than 50%. However, it’s a rough estimation and is not the ideal number. Normally, it’s not that hard to maintain the air gap. In most conditions, it’s possible to keep it less than 10% and maintain it as well.
Seams in the Guide Way
It’s important to keep the seams out of the guide way. The air gap must be maintained by 5 microns a step in a seam. An air gap of even 10 microns is not ideal for the situation.
Holes in the Guide
In the case of holes, remember that orifice surfaces do not work well with holes in the guide way. It’s best to opt for porous bearings that work well flying over perforated surfaces.
Are You In Search of Air Bearing Products Online?
Whether you’re looking for air bearing kits, air lifting bags, or anything else – you can shop it all from Hovair. The company is located in Seattle, Washington, and is highly known for its high-quality products. The company holds more than 50 years of experience in air caster and air bearing manufacturing.
The company also holds licenses to work in the industry, so customers can blindly trust them. They possess a thorough knowledge of how heavy loads work and their movement. Their air bearings are designed with zero error to ensure efficiency and speed at all costs.
They have an experienced team of engineers working with them who holds enormous knowledge of moving loads and their characteristics. Their air bearings offer multiple applications in different industries.
If you want to purchase products that won’t disturb the outcome and are long-lasting as well, then there’s no one better than Hovair to get it from. They supply their products to some top companies in the industry, so they become the next one on the list.
You can also contact them for further queries.