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Think beyond conventional linear ball guides
06 October 2014
In crude form roller linear bearings have facilitated linear motion almost since the dawn of time – early man used rows of logs to transport heavy loads, removing the last log and transporting it to the front as the load moved along the ground. Although modern linear ball guide designs are somewhat more advanced, it doesn’t mean they are without constraints, as this article from Hepco Motion explores
For instance, ball guide assemblies require the routine addition of lubricants, because without the presence of grease inside their recirculating ball channels (and along the length of the rail) they simply do not work. In addition, lubrication will eventually find its way out from behind the sealing system and contaminate the working environment.
Today, a considered alternative to the ball guide bearing is vee bearing/rail technology, which is designed for reliability in environments where other product types fail. Typically, a system comprises a rail, four vee bearings and a hard anodised carriage plate for mounting the customer’s components.
Made from hardened and ground, high carbon bearing steel, the rail is accurate, durable, friction-free and quiet in operation, while the precision vee bearings are designed specifically for use in linear motion systems and based on a deep grooved ball bearing configuration. These eccentric bearings can be adjusted in situ to increase or decrease the running stiffness between the rail and the carriage as required.
Importantly, once the rail starts to show signs of wear it can be adjusted quickly to remove any play and restore the running quality back to its original condition, thus costing nothing in replacement parts. What’s more, if one of the vee bearings fails then it can be replaced individually and not as a whole assembly.
In use, vee guide systems are incredibly tolerant of debris, as opposed to roller bearings which can fail catastrophically following the ingress of dirt, dust or debris. This is because vee guide systems have a self-cleaning action, which means that any contamination is wiped away by the vee bearings as they run along the rail.
In industries where fine abrasive dust and high levels of contamination are commonplace, like the glass industry, a vee guide system offers clear advantages.
Vee guide systems work both with and without lubrication, largely because the bearings are greased internally during manufacture and then nitrile sealed for life. This makes them suitable for use in food, medical or cleanroom applications where the presence of oil or lubrication is not tolerated.
Similarly, those designing machines or mechanisms used in high temperature or vacuum environments will know the difficulties in sourcing the right components to cope in these extreme conditions. Nearly all off-the-shelf linear motion guide systems are made from unsuitable materials. However, vacuum and extreme temperature vee bearings now exist that have been manufactured using only stainless steels for all components – no plastic is used in the assembly.Another inherent disadvantage of linear ball guides is the required precision of the mounting surface. Many manufacturers can testify to the hours spent milling and potentially even grinding mounting surfaces to make them flat and accurate, just so the rails can be fitted properly.
Conversely, a vee guide system is incredibly compliant, which means it still works effectively when the mounting surface is not machined flat, or two parallel rails are not aligned perfectly. This is because the bearing contact along the slide is at single points, and not continuous like in a recirculating system. Consequently, a small amount of distortion in the mounting surface will not adversely affect the running quality.
There is even the option to fit two-piece, 'twin' type bearings that yield fractionally to allow for small deviations in mounting surface flatness or parallelism when setting a system, saving hours in time and cost during installation.
Last but not least, non-caged version ballways, which are the general standard, generate significant noise in operation. This is caused by the balls coming in and out of contact with one another. In contrast, vee bearings incorporate caged balls as standard, resulting in virtually silent operation.
- Designed for reliability, an alternative to the ball guide bearing is vee bearing/rail technology
- Nearly all off-the-shelf linear motion guide systems are made from materials unsuitable for high temperature or vacuum environments
- Food, medical and cleanroom industries cannot tolerate the presence of oil or lubrication – vee guide systems work both with and without lubrication