Needle roller linear guideways are offered in two designs, type N/O and type M/V. These types of linear guides are for use in high load applications with limited stroke. They support and guide high loads and moments with a high degree of precision and within a compact design. The non-recirculating bearing design results in ultra-smooth linear motion.
In general frictionless linear guideways, also called precision rail guides or linear bearings, for limited stroke length are equipped with cages which retain the rolling elements. At both rail ends it is possible to mount end pieces to prevent the cage from running out.
Linear guides are fitted with either ball cages (precision ball linear guides), cylindrical rollers in a crossed arrangement, also called crossed-roller cages (crossed-roller linear guides), or needle rollers cages, also called needle roller linear guides. The stroke length is defined as the twice the difference in length between the guideways and cage.
The different types of linear bearings have different load-carrying characteristics and rigidity. But just as crossed-roller linear guides offer a “next level” in performance of ball linear guides, especially in terms of load capacity and rigidity – needle roller linear guideways offer the “next level” in performance of cross-roller linear precision guides.
With the stiffness of a linear guide we mean the amount of deformation of a linear guideway under load. As the length of needle rollers is at least 2.4 times its diameter, they offer a larger contact area compared to cylindrical rollers with a diameter-to-length ratio less than 1. As the diameter of needle rollers is smaller compared to cylindrical rollers, the number of needle rollers which fits in a cage is much more.
Since needles need less space, there are more needle rollers used in a cage to distribute the load. Another main difference between cylindrical rollers and needle rollers is the smaller diameter of needle rollers the number of rows in a cage can be doubled resulting in a larger contact area.
A smaller diameter of rolling element increase also the stiffness of a linear bearing. Less load per needle roller also means less deformation and therefore, higher rigidity which could be about 50% higher compared to cross-roller guides RSDE by an equal cage length.
Compared to other linear guides for limited stroke length, the needle roller linear guide provide the following main advantages:
Compact size - High load carry capacity; since the rolling elements are compact in size they need less space. Due to the long contact length of the needle rollers with the guideway and the higher number of needle rollers in a cage they are able to carry higher loads as ball and cross-roller guides with similar dimensions.
High Stiffness - High rigidity; due to the smaller diameter of the needle rollers, the higher number of needle rollers and the longer contact length between needle roller and guideway they offer higher stiffness and rigidity compared to ball and cross roller cage linear bearings.
Smooth and accurate movement - all used elements are high-precision finished at micron level and in the highest quality grade. The needle roller cage helps to reduce the friction resistance which is a bit higher compared to ball and crossed-roller linear bearings.
Interchangeable; some of the needle roller linear guideways are interchangeable in size with the ball and cross-roller linear guides type RSD and RSDE. This makes them a good alternative in existing applications where higher load ratings or higher stiffness are required without changing the available space requirements.
Linear bearings for limited stroke lengths are equipped with cages that retain the rolling elements.
The main purposes of a cage are:
Needle roller cages are available in two types: aluminum cages type HW and plastic cages type FF-ZW type.
Cage type HW is made from aluminum, whereas steel and brass are optional. These type of cage is designed for use in extreme conditions and are well equipped for high accelerations and speed. We offer cage type HW with a flat double row cage bent in a 90 degrees angle. The permissible operating temperature is -30 to +120 degrees Celsius.
Plastic cage type FF-ZW is a single element cage with a double row of needle rollers suitable for easy to normal operating conditions. The material of the cage is durable plastic. Greater lengths can easily be created to connect individual elements together using a "snap in" technique with dovetail grooves on both ends of the cage. The permissible operating temperature of the cage is -30 to +80 degrees Celcius.
One set of needle roller linear guides includes 2 pairs of guides. One set consists of four guideways, two cages and eight end pieces. In this video, all parts are mentioned and it is visual explained how they operate.
PM delivers the linear guides with a corrosion protective oil film that has to be removed prior to installation. After installation and during service intervals, the linear guides need to be lubricated. This is necessary to create and maintain an oil film between the needle rollers and guideways to reduce friction, protection against corrosion and to extend the operational life. The lubrication can be applied between the pair of guideways and a very small amount of oil or grease is sufficient.
It is important to realise that due to the smaller diameter of the needle rollers compared to balls or cylindrical rollers, there is less space available for the lubricant. PM recommend a regular inspection of the lubrication condition to prevent dry running operation.
At a glance to the needle roller guideways type N/O and M/V they look similar. However, if you look more closely, you see a number of differences. This is because of the origin of the guides. Size N/O-62015 and N/O-92025 are interchangeable with the cross-roller guide sizes 6 and 9 mm.
Type M/V guides are not interchangeable since their dimensions are not identical. Type N/O has countersunk holes with thread for mounting while type M/V offers countersunk holes without thread. Optional type M/V guides are offered with an adjusting gib (guideway type ML) to apply an evenly preload force on the guides instead of using laterally placed set screws.
As needle roller linear bearings offer higher stiffness and higher load carry capacity than crossed roller linear bearings they are commonly used in machine tools such as grinding machines, EDM machines but also in measurement machines and in medical applications as in patient beds and.