Choosing a linear bearing is not an easy task, as the requirements to be taken into account depend on what applications it is going to be used for. It is not the same to choose a bearing for a conveyor system as for a precision device: in the first case, you would be looking for precision and speed, while in the second case the focus is on precision and firmness.
In this article, you will discover the most important problems that could appear when using a linear bearing, the most important advantages and a guide with useful tips for choosing an element with the appropriate features.
What are Linear Bearings?
Linear bearings are rolling elements for translation movements. As in the case of rotary bearings, we need to keep in mind that there’s a difference as to whether the forces produced are transmitted by rotating elements or by friction elements.
They consist of a plastic cage that is combined with hardened steel bearing segments for better guiding ball assemblies. There are various types of bearings on the market, each on providing different benefits.
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Types of Linear Bearings and their Advantages
Next, you will find the different types of linear bearings that exist:
Linear ball bearings:
These bearings offer the lowest friction of all types. There are two kinds of products that should be highlighted: traditional linear ball bearings and linear guides.
Traditional linear recirculating ball bearings:
They are used with hardened and ground axles. The balls have a very small point contact area that allows very low rolling friction. However, having a small contact area means that they exert a large force on the axle. Therefore, it is essential that they are only used on hardened axles.
These bearings can be open or closed:
- Open linear bearings: These have a small opening and are used in applications where several axles supports, or a complete axle support is needed to prevent the axle from bending.
- Closed linear bearings: These refer to those bearings that are totally closed.
Applying these types of linear bearings in projects provides various advantages, such as:
- Reduction of friction and noise.
- Its closed design also makes an unlimited range possible.
- High load capacities and long lifespan.
- Simple structure and high reliability.
- High performance and replacement capacity.
- Easy lubrication (both oil and grease can be applied)
These are also linear ball bearings, but they run on a profiled rail. The ball groove in these rails is generally shaped like a gothic arch to maximize the load carrying capacity. The rail must be strong enough to prevent the balls from deforming the rail. These guides offer precise linear movement.
Applying this type of linear bearings in projects brings different benefits such as the following:
- They are up to 40 % more economical than linear recirculating ball bearings
- 100% lubrication and maintenance free
- Hygienic and corrosion resistant
- Insensitive to dirt, dust and moisture
- Extremely quiet operation
- Long lifespan
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Roller bearings have a higher basic load rating than ball bearings of equivalent size. However, they are less tolerant of lateral forces. Roller bearings are mainly used as a roller chain, but they can also be used in crossed roller guides.
These are bearings that roll on their outside diameter along a track. They normally contain rollers as rolling elements but may sometimes contain balls (generally when radial load capacity is required). Chain bearings are very versatile and come in many styles. The simplest is a full-service roller bearing, while others have profiled outer rings (V-shaped or concave). They can be connected by means of nipples, threaded studs or weldable hubs. Other designs incorporate a secondary axial roller to accommodate lateral loads (for instance, combined roller bearings).
These are similar to the ball guides but offer a higher load capacity compared to the ball version of equivalent size. Since they are very compact and precise, they are often used in medical applications.
Cross Roller Linear Slide
They offer a very high precision and a great load capacity. However, the nature of their design makes them vulnerable to contamination and therefore they are predominantly used for cleanroom applications.
These types of bearings have undergone rapid evolution over the last 20 years with the development of low-friction plastics. These bearings are made from plastic or ceramic and, although they offer reduced friction, the coefficient of friction is generally significantly higher than rolling element bearings.
Plastic Linear Bearings
These are cheap and offer reduced friction compared to other materials. Because they are free of rolling elements, there is less concern about product contamination, dirt, dust and debris. Nowadays, there is a wide range of plastics that offer different advantages.
Ceramic Linear Bearings
They offer similar attributes to plastic linear bearings. They are quiet and smooth and are generally available in the same sizes as traditional linear recirculating bearings and may not require lubrication. In addition, some allow rotary motion to be combined with linear motion.
Certainly, these bearings provide many benefits, but they also present certain problems if they are not properly maintained or used.
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Most Common Problems When Using Linear Bearings
Linear bearings have a long lifespan. However, they can be the source of a few setbacks from time to time. On the one hand, linear guides present various problems such as scaling on the rail tracks, which can be caused by misalignment of the mounting.
In addition, insufficient lubrication can lead to wear on the tracks and corrosion on the balls. Dents in the raceway and electrical corrosion or sparking can also occur due to an electrical current between the rail and the slide.
In the case of linear ball bearings, problems might arise due to lack of lubrication and the use of unsuitable lubricants. In addition, contamination of the bearings by swarf and improper handling can cause problems.
Corrosion, incorrect mounting and fatigue can be another cause of significant alterations in the operation of this type of bearing.
What do you need to consider when choosing a linear bearing?
The characteristics of the linear bearing you choose to buy condition its operation, so it is very important to choose the most suitable one for your project.
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If you are interested in acquiring a linear bearing for your business, you need to consider the following factors:
- Load capacity. This factor conditions the weight supported and its duration.
- Lifespan. It is key to predict whether it will be short, medium or long term.
- Operating speeds. Its speed is conditioned by the operating temperature of the bearing.
- Acceleration. This factor is important when choosing between one bearing or another.
- Dimensions. The size of the bearing is important to ensure that it fits correctly into the drive mechanism.
- Price. This is always a crucial and determining factor in choosing between one product or another, and this is also true for the purchase of bearings.
- Operating temperature. It is important to know this information, because if it changes, the conditions of the bearing may vary. In this sense, it must be said that when working at high temperatures the hardness of the material varies and the load that the bearing can support will be lower.
Linear bearings have applications in all sectors of industry, whether in general mechanics, packaging machines or handling units.
In particular, they are often used in precision projects such as welding or assembly robots, 3d printers and automation projects in packing, packaging or palletizing machines.
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They can also be used in the automotive world in projects such as test equipment; in the film industry on tripods to move the cameras; in some equipment for gyms; in silent elevator projects for single-family homes; in machinery and test bench projects; and in projects in the medical world, mostly test benches.
Choosing the right linear bearing is key to the performance of your project’s mechanisms. Contact our engineering team, we will surely be able to design that high-performance gear motor you need.