Bearing Features

Areas of Application

AXRY-NGS (NGS-SBI) bearings are designed for applications requiring high load-capacity, ultra-precise and play-free high-speed bearings. Typical applications include:

• Machining centers with rotary tables for milling/turning
• Vertical lathes
• Gear cutting machines

To fully leverage the advantages of the NGS series, the design of the adjacent construction is also important. The entire system of the axis must be considered, including lubrication, cooling, heat flow, and the components themselves, to achieve optimal results.

Accuracy Requirements

For higher accuracy requirements, NGS and NGS-SBI series are available with tighter axial and radial runout tolerances.

The inner ring and axial washer have identical axial runout characteristics.

PL = Axial runout, RL = Radial runout

Measuring Systems

AXRY-NGS bearings can accommodate inductive angle measurement systems. These systems are available in incremental or absolute versions, as single or multi-head systems, with varying accuracy grades.

myonic supplies only the "mechanical part" - the bearing, including mounted measuring ring and threads on the outer ring for axial or radial scanning head mounting. For high-speed applications, only absolute measurement systems are suitable. Incremental measurement systems are not suitable for high-speed operation.

By mounting the measuring ring directly on the bearing ring, concentricity errors relative to the axis (worktable) are minimized, achieving highest accuracies of a few angular seconds.

Lubrication Variants

Grease Lubrication, Relubrication

For high-speed bearings, scheduled relubrication at appropriate intervals should be arranged.

A good option is a controlled relubrication system that relubricates with small quantities of lubricant at specified intervals during operation.

For calculation of relubrication quantities and intervals, please contact us with load spectrum details (speed, duty cycle, load) and environmental conditions.

Circulating Oil Lubrication

Primarily used for larger bearings. Due to larger cooling oil volumes, cooling and lubrication occur simultaneously.

Due to the large amount of lubricant available, these systems can also use lower viscosity oils.

Oil-Air Lubrication

Similar to spindle bearings, oil-air mixture is injected directly into or beside the raceway; lubrication uses minimum oil quantity. Lubrication is supplied axially through 6 holes in the outer ring.

myonic bearings can be supplied with all necessary holes, connection threads, and seals for oil-air lubrication.

The customer must define parameters such as lubrication cycles, lubricant quantities, and air pressure according to the application. The myonic application engineering team can support you.

Over-Lubrication

Lubrication Bores / Lubrication Grooves

Inner Ring Rotation

NGS bearings for inner ring rotation can be lubricated through a radial circumferential groove on the outer ring or axially. For correct positioning of bearing lubrication holes with machine housing lubrication holes, the bearing has locating pin holes. (See Positioning chapter)

For relubrication through outer ring/inner ring lubrication grooves, we recommend completely filling the lubrication groove with grease before assembling the bearing. This allows grease to reach the bearing faster during relubrication. The housing lubrication channel should be positioned close to the bearing's radial lubrication hole.

Please ensure that axial lubrication holes are closed with plug screws upon delivery. For axial lubrication, remove axial plug screws and close radially.

Outer Ring Rotation

NGS-SBI bearings for outer ring rotation can be lubricated through a radial circumferential groove on the inner ring.

For relubrication through lubrication grooves, it is recommended to completely fill the groove with grease. The lubrication hole in the bearing should be positioned close to the housing lubrication channel.

Inner Ring Rotation (Oil-Air Lubrication)

NGS bearings for inner ring rotation are available as special designs for oil-air lubrication. This series has 6 evenly distributed lubrication holes in the outer ring.

Lubricant can enter axially from both sides. When lubricant enters the bearing, 3 times toward the inner ring direction and 3 times toward the axial washer direction.

The exit side in the bearing is indicated by arrow markings on the outer ring.

All lubrication holes are closed with plug screws upon delivery. For lubrication, remove the relevant plug screws.

For all bearing sizes, lubrication holes are uniformly designed with M4 threads.

Sealing

When using oil-air lubrication, it is recommended to equip the bearing with non-contact gap seals. This keeps oil-air lubrication within the bearing working space, ensuring optimal lubrication. Due to the minimal gap between seal and outer ring, oil-air lubrication also acts as seal air. This effectively protects the bearing from contamination.

Sensor Bore / Bearing Monitoring

AXRY-NGS bearings have a sensor bore in the outer ring as standard; NGS-SBI bearings also have a sensor bore in the inner ring. These sensor bores extend beneath the raceway.

When equipped with temperature sensors, the current temperature in the bearing system can be used to continuously monitor and control cooling, or to detect system overheating.

Height Tolerances H1 and H2

Both height dimensions H1 and H2 can be significantly restricted.

Height dimension H1 is restricted as standard up to and including size 460. Sizes 580 and 650 can optionally be restricted.

H1 indicates the worktable position. Restricted height variation provides the following advantages:

• Labyrinth seal gaps can be optimally adjusted to prevent coolant penetration from the machining area
• Clamping gaps can be optimally adjusted

Height dimension H2 is not restricted as standard, but all sizes can be supplied in restricted versions.

H2 indicates the adjacent construction below the bearing, for example for adjusting worm gear clearance.

Exact tolerances are in the product tables.

Customer-Specific Bearing Adjustment AC

AXRY-NGS (NGS-SBI) bearings can be mounted as exposed bearings or with whole-surface support. If the L-section ring is fully supported by a support ring, the tilting rigidity of the bearing increases by 15 to 20%.

To prevent bearing friction torque from increasing, the bearing alignment can be adjusted (suffix AC). If a normally aligned bearing with supported L-section ring is used, bearing friction torque increases significantly.

The support ring height should be at least twice the axial washer height.

Support Ring Dimensions

Customer-Specific Design Jxxxx

myonic offers customer-specific designs identified by J followed by a four-digit number.

Bearings with J designations can include the following additional features:

• Application-specific preload values
• Special marking or packaging directives
• Customer-specific design modifications

Limiting Speed n_G

The limiting speeds given in the product tables are guide values determined on our test benches under the following conditions:

• Grease distribution run-in according to specified procedures (see run-in cycle)
• Maximum bearing temperature rise of 40K in the raceway area (sensor bore)
• Active bearing cooling
• 2-hour duty cycle operation at limiting speed n_G
• Bearing fully bolted, no external loads, only preload and mounting weight

To achieve these limiting speeds, the guidelines for adjacent construction must be strictly followed. Please also note the Friction/Temperature Development section.

Friction / Temperature Development

The axial-radial bearings of the AXRY-NGS (NGS-SBI) series feature cages in both radial and axial sections. This ensures bearings rotate with very low friction at full preload. At higher speeds, friction torque increases only slightly, so bearings of the AXRY-NGS (NGS-SBI) series can operate at high speeds over extended duty cycles.

During extended high-speed operation, factors that increase bearing friction and temperature must be avoided or compensated. For this, the entire axis including all drives must be considered.

Main Factors Influencing Axis Friction Torque:

• Bearing Friction Torque: Bearings are radially and axially play-free and preloaded after assembly and complete bolting. Preload is a factor in achieving specified rigidity but also produces friction torque.
• Lubricant Used: In high-speed applications, bearing lubricant must be carefully selected. Only few greases with appropriate viscosity are suitable for higher speeds. Viscosity depends on selected lubricant and operating temperature. Low viscosity lubricants can cause mixed friction, especially during slow or intermittent operation under high loads. On the other hand, excessively high viscosity causes high friction and is barely suitable for fast rotation applications.

Points to Note When Designing the Axis and Assembly:

• Geometric errors in adjacent construction cause bearing deformation and thus higher friction torque. Please observe our recommendations in the Adjacent Construction Design section.
• Asymmetric housings can deform during heating, increasing bearing preload.
• Assembly errors can increase friction torque. We recommend rotating the bearing and measuring friction torque during assembly. This reveals serious errors regarding adjacent construction geometry, screw connections, or additional parts.
• Contact seals increase friction torque and introduce additional heat into the system. For high-speed axes, contact seals should be avoided where possible.
• High acceleration and strong braking processes can introduce additional friction into the system through moments of inertia.
• Machining forces, eccentric clamping, and high loads increase friction torque.
• Heat input from drives should be minimized.

Only by considering the entire system can sufficient knowledge be gained to design appropriate cooling or heating/cooling systems.

Our test bench results show the basic performance capability of bearings and lubricants, but only limited conclusions can be drawn about actual operating temperatures of machine tool axes.