Assembly, maintenance and storage of bearings
General guidelines on assembly
Roller bearings for machine tool axes are precision machine elements.
These high-precision roller bearings only achieve their maximum duration of use and functionality if they are correctly assembled and maintained.
Because it is not possible to present all variations of the adjacent construction or deviating fits, these assembly and maintenance instructions refer to the most frequent installation case of the rotating inner ring and an adjacent construction in accordance with the recommendations of the myonic catalogue.
In case of deviating assembly or application cases, the bearings are to be installed appropriately. We are happy to assist in case of queries.
You can find the details for recommended installation in the product section.
Storage room
Closed rooms which are free of aggressive media (acids / lyes / exhaust gases /etc.) are suitable as storage rooms. The temperature and the air humidity should be permanently monitored.
Temperature range: +5 to 40°C – as constant as possible; relative humidity: max. 65%
Direct sun, especially on the packaging, should be avoided.
Temperature fluctuations and high humidity lead to condensation.
The temperature and the air humidity must be permanently monitored. This can be done using data loggers. The measurements must not be more than 2 hours apart.
Storage periods
Roller bearings should never be stored longer than 3 years. Usually, bearings, if stored correctly, can still be used without problems even after this time period.
Pre-greased bearings should be installed as early as possible, at the latest within a year, as grease properties reduce due to aging.
As a result the grease operating period may be reduced.
General cleanliness
Roller bearings for machine tools must be treated with great care. Handle the bearing carefully and impact-free, and do not remove it from the packaging until directly prior to assembly.
The workplace and all connecting parts must be clean and dust-free. Only use lint-free cloths for cleaning purposes.
Tools and measuring equipment
Only use calibrated tools and measuring equipment.
Design of the assembly station
It is essential that you keep the assembly station of the bearing clean and dust-free.
During on-site repairs, cover the machine in order to avoid contamination from the surroundings.
Any contamination will influence the bearing function.
Condition on delivery
All bearings are preserved, and dispatched packaged in VCI foil.
Do not unpack the bearings until immediately prior to assembly. In case of contamination of the bearing prior to assembly, return it to myonic for inspection and, if applicable, for cleaning and regreasing.
Initial greasing
As standard grease, a special grease acc. to DIN 51825-KPH-C1N-30 is used. The quantity of lubrication used depends on the intended purpose.
Bearings with the suffix L120 are delivered ungreased; only corrosion protection oil is added to the bearings.
The corrosion protection oil used is compatible and miscible with most mineral oil-based greases and oils.
Check for compatibility when using synthetic lubricants and consistency enhancers other than lithium (complex) soaps.
In case of incompatibility, please consult the myonic application engineering team as to further procedures.
Cleaning the bearings
When cleaning the bearing, only use lint-free cloths! Only the outer areas of the bearing may be cleaned! When doing so, the following agents can be used:
organic cleaning agents, e.g. benzine or thin, clean oil for warm cleaning.
Transportation of the bearings
Only store and transport large bearings in prone position. Do not store bearings vertically!
Only transport heavy bearings with lifting gear on eyebolts or with textile straps. Never use chains to transport bearings!
Handling of bearings with measuring system
All myonic measuring systems function inductively which is why they are not sensitive to magnetism.
The measuring rings mounted on the bearing are to be protected against mechanical damage.
Preparing connecting parts
The connecting parts for the bearing rings must be clean and burr-free. For this proceed as follows:
Treat the surfaces and burrs with an oil stone. Apply cleaning agent with a brush or suitable cloth onto contact and bearing-seat surfaces. Clean surfaces and dry them.
Selecting assembly screws
Only fasten the bearing using the specified screws. The information in the product tables is decisive for this purpose.
Checking tolerances of the adjacent construction
All tolerances must lie within the stated values for the adjacent construction in the product parts.
Deviating tolerances lead to functional problems on the assembled bearing. As a result severely increased friction values may occur, or problems with the preload.
Check the bearing tolerances
The information figures on the bearing diameter are mean values. The accuracy requirements for the bearing can only be measured on an installed, screwed and fully supported bearing!
Documentation of the values during assembly
Over the course of assembly, the friction values should be continuously documented. Severely increased friction values during assembly indicate an adjacent construction of poor quality.
We recommend that you archive the actual dimensions of the adjacent construction in addition to the friction values, and the myonic measuring log with the serial number enclosed with the bearing.
Interrupted assembly
If the assembly is interrupted, the bearing must be covered to avoid it becoming dirty.
Plastic sheeting or lint-free cloths can be used for this. In case of prolonged interruptions, use cover material with rust protection inhibitors (e.g. VCI paper).
Component temperature
Only screw together components with the same temperature.
Give cold or heated components time to adapt to the ambient temperature.
Screw connection
All screw connections are to be executed with screws in strength class
10.9 (former designation 10K) acc. to DIN 267-3 or DIN
EN ISO898-1.
All countersunk holes are designed for cylinder screws
with internal hexagons acc. to ISO 4762 (DIN 912).
Strength class 10.9
Tensile strength Rm = 1,000 MPa
0.2% yield limit Rp 0.2 = 900 MPa
Screw connections with other strength classes lead to changed preload values on the AXRY axial/radial bearings, and can lead to unwanted clearance or increased friction.
All calculations are executed with cylinder screws with internal hexagons acc. to ISO 4762 (DIN 912) 10.9. In particular the static rigidities and the area pressures in the bearing, which are the basis for the life time, change with the different strength classes.
Tightening torques for fixing screws 10.9:
All bearings must be screwed on crosswise; the tightening sequence is partly marked on the bearings.
The bearing preload and therefore the friction torque are determined through the tightening torque of the screws.
Higher and lower preload values can be adjusted via the screw tightening torque.
In case of lower tightening torques of screws in strength class 10.9 or the use of screws in strength class 12.9 with specified tightening torque, the screws must be secured accordingly acc. to Table 10.9.
Fastening the bearing inner ring
Lightly oil the seating surfaces for the bearing inner ring on the adjacent construction.
Before pushing on the bearing, align the bearing hole pattern with the hole pattern of the adjacent construction.
Threaded rods cut to size are highly suitable for this purpose.
Push the bearing onto the shaft without tilting the bearing.
To facilitate assembly, the bearings can be heated up slightly, 20 °K over room temperature is generally sufficient; prior to screwing on, allow the bearing to cool down.
The extraction thread can be used to align the bearing. To do this, insert the appropriate screws and screw in up to the bearing construction height. Insert longer fixing screws into 4-6 holes and screw them tight.
Loosen the screws in the extraction threads bit by bit and retighten the fixing screws. Repeat the process until the bearing sits tightly on the shaft.
Insert all fixing screws into the holes and tighten them slightly by hand.
Tighten the fixing screws with a torque wrench crosswise in three stages to the specified tightening torque MA:
Stage 40 % of MA
Stage 70 % of MA
Stage 100 % MA
For tightening torques for the fixing screws, see Table of tightening torques.
Fastening the bearing outer ring
Oil the seat area slightly for the bearing outer ring in the housing.
Adjust and assemble the outer ring of the bearing in the housing hole.
Align bearings of type NGS via the positioning hole.
Insert all fixing screws into the holes and tighten them slightly by hand.
Tighten the fixing screws with a torque wrench crosswise to the specified tightening torque MA.
Tightening torques for the fixing screws, see Table of tightening torques.
Functional inspection
After correct screwing on, the bearing must rotate evenly and jerk-free. The friction torque is not set until after the bearing has been completely screwed on. Measuring AXRY-EX series bearings in unscrewed condition is not permitted.
The friction torque is influenced by:
■ additional loads
■ the screw tightening torque
■ the form errors of the mating, contact and screw connection surfaces
■ the lubricant (quantity / viscosity / general suitability)
■ the fits
■ the difference between the bearing ring temperature inner ring and outer ring
■ the operating temperature
A slight increase of the friction torque after assembly is normal. In case of unusually high values, loosen the bearing screw connection, check for the abovementioned influence factors, correct if necessary and screw on again.
Fits can be optimised with the actual dimensions of the bearing bore or the bearing outer diameter.
Inspection of accuracy requirements
An inspection of the accuracy requirements is only permitted in installed condition. Every myonic precision bearing is checked prior to delivery for roundness and axial runout. The absolute values are supplied with the inspection report. Further information, for example regarding repeatability, is available via the bearing serial number directly at myonic.
Causes of incorrect accuracy requirements after assembly:
■ Adjacent construction inaccuracies
■ Clearance fit of rotating ring to adjacent construction, eccentricity of the raceway to the axis centre
■ Fixing screws incorrectly tightened
■ Fixing screws incorrectly aligned
■ Fastening screws loosened prior to assembly
Safety inspection
The fixing screws must be regularly inspected. High, alternating loads may trigger settling symptoms. After initial commissioning, check the tightening torques. Check during the service intervals.
Use fixing screws only once, use new screws during assembly of a replacement bearing. If necessary, tighten the fixing screws crosswise to the specified values.
Packaging material disposal
Packaging material must be disposed of in accordance with the regional official waste disposal guidelines.