Linear Motion system

A roller screw is a mechanical actuator similar to a ball screw that uses rollers as the load transfer elements between nut and screw instead of balls. The rollers are typically threaded but may also be grooved depending on roller screw type. Providing more bearing points than ball screws within a given volume, roller screws can be more compact for a given load capacity while providing similar efficiency (75%-90%) at low to moderate speeds, and maintain relatively high efficiency at high speeds. Roller screws can surpass ball screws in regard to positioning precision, load rating, rigidity, speed, acceleration, and lifetime. Standard roller screw actuators can achieve dynamic load ratings above 130 tons of force (exceeded in single-unit actuator capacity only by hydraulic cylinders).

The three main elements of a typical planetary roller screw are the screw shaft, nut and planetary roller. The screw, a shaft with a multi-start V-shaped thread, provides a helical raceway for multiple rollers radially arrayed around the screw and encapsulated by a threaded nut. The thread of the screw is typically identical to the internal thread of the nut. The rollers spin in contact with, and serve as low-friction transmission elements between screw and nut. The rollers typically have a single-start thread with convex flanks that limit friction at the rollers' contacts with screw and nut. The rollers typically orbit the screw as they spin (in the manner of planet gears to sun gear), and are thus known as planetary, or satellite, rollers. As with a lead screw or ball screw, rotation of the nut results in screw travel, and rotation of the screw results in nut travel.

For a given screw diameter and quantity of thread starts more rollers corresponds to higher static load capacity, but not necessarily to a higher dynamic load capacity. Preloaded split nuts and double nuts are available to eliminate backlash.

With a wide range of designs to choose from, SKF tapered roller bearings are also customizable to match your specific speed, load, contamination, temperature or vibration conditions.

SKF Tapered roller bearings feature a cup and cone assembly. The cup is comprised of the outer ring and the cone assembly consists of inner ring, rollers, and cage. This bearing construction accommodates combined loads and provides low friction during operation. By adjusting one single row tapered roller bearing against a second tapered roller bearing and applying a preload, a rigid bearing application can be achieved.

SKF tapered roller bearings are also made to Explorer class. SKF Explorer combines our expertise in bearing design, tribology, metallurgy, lubrication and manufacturing. SKF Explorer tapered roller bearings are typically used in bearing solutions where there is a need to increase performance, reduce friction or increase power density in applications.

In the quest for higher productivity, greater accuracy, and longer product life, machine tool and robotic arm OEM’s are constantly pushing the limits of spindle technology fitted to their equipment.

Conventional bearing systems, usually ball bearings, cannot always deliver the very high speeds demanded by these industries while still maintaining high rotational precision, thermal stability, and long service life. This is primarily due to the mechanical contact between the balls and the races, which can result in rapid wear and excessive heat generation at high D/N ratios, leading to a loss in accuracy and even premature failure of the bearing.

In addition, many advanced industries require oil free bearing systems to avoid workpiece contamination, particularly in a clean room application.

One of the most consistent sources of bearing failure in industrial applications is improper lubrication. What this means is that bearings aren’t properly being lubricated which is causing stress to build up from constant force and friction. This force and friction leads to a bearing failure that can be, at minimum, a pain the neck and at maximum a productivity killer for your business. This has led to an industry wide panic which means that workers are now frantically lubing up every bearing, whether they need to or no. This naturally brought us to an innovative piece of technology and a problem solver: the self-lubricating bronze bearing.

Now, self-lubricated bronze bearings don’t look any different than regular, non-self-lubricated bronze bearings. The difference comes at a more technical level when comparing the two. The self-lubricating bronze bearing is made up of metallic components that have a porosity rate of nearly 25%. A high porosity rate means that liquid can be transferred easier. This is where the self-lubrication comes into play. These bearings are imbued with a special kind of oil upon being manufactured. This lubing is naturally secreted from the bearing while it is in usage. Manual lubing is not necessary for these types of bearings and, in fact, could end up deteriorating the quality of the metal.

Thrust bearings come in several varieties.

• Thrust ball bearings, composed of bearing balls supported in a ring, can be used in low thrust applications where there is little axial load.
• Cylindrical thrust roller bearings consist of small cylindrical rollers arranged flat with their axes pointing to the axis of the bearing. They give very good carrying capacity and are cheap, but tend to wear due to the differences in radial speed and friction which is higher than with ball bearings.
• Tapered roller thrust bearings consist of small tapered rollers arranged so that their axes all converge at a point on the axis of the bearing. The length of the roller and the diameter of the wide and the narrow ends and the angle of rollers need to be carefully calculated to provide the correct taper so that each end of the roller rolls smoothly on the bearing face without skidding. These are the type most commonly used in automotive applications (to support the wheels of a motor car for example), where they are used in pairs to accommodate axial thrust in either direction, as well as radial loads. They can support greater thrust loads than the ball type due to the larger contact area, but are more expensive to manufacture.

Customized type (CRBX): The crossed roller bearing can be designed and modified in accordance with the customer requirements. Different surface treatments could also be selected based on the customer’s environmental requirements.

Data Sheets Cross Roller Bearings

Rod ends consist of an eye-shaped head with integral shank that forms a housing for a spherical plain bearing. As a rule, rod ends are available with left- or right-hand female (internal) or male (external) threads.

SKF supplies rod ends with a threaded shank with a right-hand thread as standard. With the exception of rod ends with the designation suffix VZ019, all rod ends are also available with a left-hand thread. They are identified by the designation prefix L.

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