Table of contents
Rolling bearings, rolling bearing parts and Arcanol rolling bearing greases are high quality goods and must therefore be handled with care.
Storage of rolling bearings
Even slight deviations in functional areas will impair the performance capability of the bearings
The performance capability of modern rolling bearings lies at the boundaries of what is technically achievable. The materials, dimensional and running tolerances, surface quality and lubrication have been optimised for maximum levels of function, which means that even slight deviations in functional areas, such as those caused by corrosion, can impair the performance capacity. In order to realise the full performance capability of rolling bearings, it is essential to match the corrosion protection, packaging, storage and handling to each other.
Corrosion protection and packaging constitute part of the bearing
Corrosion protection and packaging constitute part of the bearing and are optimised such that they preserve all characteristics of the product at the same time as far as possible. In addition to protecting the surface against corrosion, this includes emergency running lubrication, friction, lubricant compatibility, noise behaviour, resistance to ageing and compatibility with rolling bearing components (cage and seal material).
Storage conditions for rolling bearings
As a basic prerequisite, parts must be stored in a closed storage area which cannot be affected by any aggressive media, such as exhaust gases from vehicles or gases, mist or aerosols of acids, lyes or salts. Direct sunlight should be avoided since, apart from the harmful effects of UV radiation, it can lead to wide temperature fluctuations in the packaging. The temperature should be constant and air humidity should be as low as possible. Extreme shifts in temperature and increased humidity lead to condensation.
Conditions for storing rolling bearings
The following conditions must be fulfilled:
- frost-free storage, i. e. a temperature of ＞ +5 °C (this prevents formation of white frost, a maximum of +2 °C is permissible for up to 12 hours per day)
- maximum temperature +40 °C (to prevent excessive drainage of anti-corrosion oils)
- relative humidity ≦ 65% (with temperature changes, up to 70% permissible for up to 12 hours per day)
The temperature and humidity must be continuously monitored. This can be carried out using a datalogger. The measurements must be taken at intervals of no more than 2 hours. At least 2 measurement points must be selected: the highest point and the lowest point in the vicinity of an external wall at which the goods can be stored.
Storage periods for rolling bearings
Maximum storage period of 3 years
Rolling bearings should not be stored for longer than 3 years. This applies both to open and to greased bearings with sealing shields or washers. In particular, specifically greased bearings should not be stored for too long, since the chemical-physical behaviour of greases may change during storage. Even if the minimum performance capacity remains, the safety reserves of the grease may have diminished.
Check the bearings at the end of the storage period
In general, rolling bearings can be used even after their permissible storage period has been exceeded, if the storage conditions during storage and transport were observed. If the conditions are not fulfilled, shorter storage periods must be anticipated. If the periods are exceeded, it is recommended that the bearing be checked for corrosion, as well as for the condition of the anti-corrosion oil and the condition of the grease, before it is used. The aforementioned storage periods are empirical values based purely on practice and do not constitute an extension to the legal or, where applicable, contractually agreed warranty period.
Storage of Arcanol rolling bearing greases
The information on storage of rolling bearings applies as appropriate to Arcanol rolling bearing greases. The precondition is that the grease is stored in closed, completely filled original containers.
Storage periods for Arcanol rolling bearing greases
Rolling bearing greases do not have unlimited stability
Rolling bearing greases are mixtures of oil, thickener and additives. Such mixtures of liquid and solid substances do not have unlimited stability. During storage, their chemical-physical characteristics may change and they should therefore be used up as soon as possible.
The storage period for Arcanol greases is 3 years
If the storage conditions are observed, Arcanol greases can be stored without loss of performance for 3 years. As in the case of rolling bearings, however, the permissible storage period should not be seen as a rigid limit. If storage is carried out as prescribed, most greases can also be used after 3 years, if allowances are made for small changes. If there is any doubt when using older greases, random sample checking of chemical-physical characteristics is recommended in order to determine any changes in the grease. It is therefore not possible to state storage periods for containers that have been opened. If containers are to be stored after opening, the grease surface should always be brushed flat, the container should be sealed airtight and it should be stored such that the empty space is upwards. High temperatures should be avoided in all cases. The aforementioned storage periods are empirical values based purely on practice and do not constitute an extension to the legal or, where applicable, contractually agreed warranty period.
Unpacking of rolling bearings
Observe guidelines on unpacking
Perspiration leads to corrosion. Hands should be kept clean and dry and protective gloves worn if necessary. Bearings should only be removed from their original packaging immediately before assembly. If bearings are removed from multi-item packaging with dry preservation, the package must be closed again immediately, since the protective vapour phase is only effective in closed packaging. Bearings should be oiled or greased immediately after unpacking.
Observe guidelines on compatibility and miscibility
The anti-corrosion agents in bearings with an oil-based preservative are compatible and miscible with oils and greases having a mineral oil base. Compatibility should be checked if synthetic lubricants or thickeners other than lithium or lithium complex soaps are used. If there is an incompatibility, the anti-corrosion oil should be washed out before greasing, especially in the case of lubricants with a PTFE/alkoxyfluoroether base and thickeners based on polycarbamide. Bearings should be washed out if the lubricant is changed or the bearings are contaminated.
Cleaning of rolling bearings
Suitable agents for degreasing and washing
The following are suitable for degreasing and washing of rolling bearings:
- aqueous neutral, acidic or alkaline cleaning agents. Check the compatibility of alkaline agents with aluminium components before cleaning
- organic cleaning agents such as paraffin oil free from water and acid, petroleum ether (not petrol), spirit, dewatering fluids, freon 12 substitutes, cleaning agents containing chlorinated hydrocarbons
Cleaning should be carried out using brushes, paint brushes or lint-free cloths. In the case of resinous oil or grease residues, precleaning by mechanical means followed by treatment with an aqueous, strongly alkaline cleaning agent is recommended. Legal regulations relating to handling, environmental protection and health and safety at work must be observed. The specifications of cleaning agent manufacturers must be observed. Paraffin oil, petroleum ether, spirit and dewatering fluids are flammable, while alkaline agents are corrosive. The use of chlorinated hydrocarbons is associated with the risk of fire, explosion and decomposition as well as with health hazards. These hazards and appropriate protective measures are described comprehensively in Datasheet ZH1/425 of the Hauptverband der gewerblichen Berufsgenossenschaften (German Federation of Institutions for Statutory Accident Insurance and Prevention). Rolling bearings must be dried and preservative applied immediately after cleaning.
Comprehensive information on mounting and dismounting is given in the publications Mounting Handbook MH 1 and IS 1, Mounting and Maintenance of Rolling Bearings.
The following guidelines must always be taken into account:
- The assembly area must be kept clean and free from dust.
- Protect bearings from dust, contaminants and moisture. Contaminants have a detrimental influence on the running and operating life of rolling bearings
- Before mounting work is started, familiarise yourself with the design by means of the final assembly drawing
- Before mounting, check whether the bearing presented for mounting corresponds to the data in the drawing
- Check the housing bore and shaft seat for dimensional, geometrical and positional accuracy and for cleanliness.
- Check that the shaft and housing bore have a lead chamfer of 10° to 15°
- Wipe away any anti-corrosion agent from the seating and contact surfaces, wash anti-corrosion agent out of tapered bores
- Lightly oil the bearing ring seating surfaces or rub with solid lubricant
- Do not cool the bearings excessively. Moisture due to condensation can lead to corrosion in the bearings and bearing seats
- After mounting, provide the rolling bearings with lubricant
- Check the correct functioning of the bearing arrangement
Avoid applying direct blows to the bearing rings with a hammer.
Mounting of non-separable bearings
In the mounting of non-separable bearings, the mounting forces must always be applied to the ring with a tight fit ➤ Figure. This ring is also mounted first. Forces acting on the ring with a loose fit are transmitted by the rolling elements. This can damage the raceways and rolling elements.
Tight fit of the inner ring, mount this ring first
Mounting of separable bearings
Mounting is easier in the case of separable bearings; the two rings can be mounted individually ➤ Figure. Rotating the ring while fitting to give a screwdriver effect will help to avoid scraping marks.
Tight fit of the inner ring, individual fitting of rings
Mechanical, hydraulic and thermal accessories
The mounting method is dependent on the bearing type and size
Due to the different bearing types and sizes, rolling bearings cannot all be mounted and dismounted using the same method.
Mechanical or hydraulic mounting
Cold fitting/driving on of bearings
Where smaller bearings with cylindrical seats must have a tight fit on their mating parts and the interference values are not too large, they can be pressed onto the shaft or into the housing. Mechanical or hydraulic presses can be used for this purpose ➤ Figure.
Hydraulic press for mounting
Direct pressing-in forces through the inner ring
Mounting of small bearings
Small bearings can be driven onto the shaft using a mounting sleeve made from aluminium with a flat end face ➤ Figure. The mounting sleeve must be matched to the bearing ring to be mounted. During mounting, it must be ensured that no other bearing components, such as seals, are damaged.
Sleeve for driving up small bearings
Sliding on of warm bearings
Larger bearings, or bearings that must have a large interference fit, are generally mounted by means of thermal methods.
For the interference values normally used with rolling bearing seats, it is sufficient to heat the bearings to approx. +80 °C, with a maximum of +100 °C ➤ Figure.
Induction heating technology and electric ovens
Heating can be carried out using induction heating technology ➤ Figure. A distinction is made here between the low frequency technique (50 Hz to 60 Hz) and medium frequency technique (10 kHz to 25 kHz).
Induction heating devices
The induction heating devices described in ➤ section can be used to heat rolling bearings quickly, safely and, above all, cleanly to the correct temperature for mounting ➤ Figure to ➤ Figure. The temperature is measured directly on the inner ring. Since the inner ring heats up more quickly than the outer ring, the bearing can be positioned on the shaft and in the housing at the same time with only slight heating of the outer ring.
Electric ovens, oil bath, heating plate
Furthermore, an electric oven, a clean oil bath or a thermostatically controlled heating plate, ➤ Figure, can be used. In the case of electric ovens and induction heating devices, the temperature is controlled by means of a temperature sensor or thermostat and is therefore held to very high accuracy. This is important since the hardness of the rings must not decrease due to the tempering effect.
When bearings are heated on a heating plate, all parts of the bearing must be protected against overheating (e. g. plastic parts, seals, lubricant) ➤ Figure.
Bearings with plastic cage: heating on a heating plate
Mounting on tapered bearing seats
In order to give a tight fit, the inner ring is pressed on axially
In the case of tapered seats, the tight fit required is achieved by pressing the inner ring on axially. Whether a sufficiently tight fit is achieved can be determined from the expansion of the inner ring and therefore the reduction in the radial internal clearance, or from the axial drive-up distance on the taper; see corresponding product chapters.
Reduction in radial internal clearance
Checking of the clearance is necessary during mounting
The reduction in radial internal clearance is the difference between the radial internal clearance before mounting and the bearing clearance after mounting of the bearing. The radial internal clearance must be measured first. During pressing on, the radial clearance (bearing clearance) must be checked until the necessary reduction in the radial internal clearance and thus the required tight fit is achieved.
Measuring the radial internal clearance of spherical roller bearings using a feeler gauge
The radial clearance of larger bearings is measured using a feeler gauge. In the case of spherical roller bearings, it must be ensured that both rows of rollers are measured at the same time ➤ Figure.
It can only be ensured that the inner ring is not laterally offset relative to the outer ring when the internal clearance values are identical for both rows of rollers.
Radial internal clearance in spherical roller bearings
sr = radial internal clearance
Measuring the axial drive-up distance
Measuring axial drive-up distance as an alternative to measuring radial internal clearance
Instead of reducing the radial internal clearance, the axial drive-up distance on the taper can be measured; see corresponding product chapters. For a shaft seat with a normal taper 1:12, the axial drive-up distance is approx. 15 times the reduction in radial internal clearance.
The mounting of small bearings with a tapered bore requires particular care. Since the radial internal clearance is often smaller than the thinnest measuring sheet, measurement using a feeler gauge is no longer possible. The bearing is therefore slid on, where possible, outside the housing. It may only be pressed on so far that the outer ring can still be rotated easily and, in the case of self-aligning bearings, can be swivelled out by hand under slight resistance. The shaft with the mounted bearing is inserted in the housing.
Mounting of withdrawal sleeves
With large ring cross-sections, high forces are necessary for pressing-in
Withdrawal sleeves are pressed on and secured between the inner ring and shaft by means of a nut seated on the shaft. For bearings with large ring cross-sections, considerable forces are necessary for pressing-in. In such cases, mounting is made easier by means of the nut with pressure screws shown in ➤ Figure.
Pressure screws must always be tightened in a crosswise sequence
In order that the withdrawal sleeve is not pressed in skewed, the nut is first tightened so far that the pressure ring is fully in contact with the withdrawal sleeve. The pressure screws distributed uniformly around the circumference are then tightened uniformly in a crosswise sequence until the required reduction in radial internal clearance is achieved. Since the taper of the withdrawal sleeve is self-locking, the nut can then be removed; the position of the withdrawal sleeve is secured by the shaft nut.
Nut with pressure ring for pressing in large withdrawal sleeves, bearing with tapered bore
In the mounting of bearings with a tapered bore, it must be ensured that the seats of the sleeve connections are rubbed with a very thin layer of oil. Mounting pastes must not be used. While a thicker layer of lubricant would reduce the friction and thus allow easier mounting, the sleeves could however become loose when the nut with the pressure screws is removed after mounting. In operation, the lubricant would be gradually squeezed out of the fit joint and the tight fit of the bearing would be progressively lost.
Measures to be taken if the bearing is to be mounted again after dismounting
If the rolling bearing has been dismounted and is to be used again, it is not sufficient to move the retaining nut to its earlier position. After longer periods of operation, the fit loosens again since the thread undergoes settling and the surfaces become smoothed. In this case also, the reduction in radial internal clearance or the axial drive-up distance, or the expansion of the raceways in the case of cylindrical roller bearings, must be measured again.
Mounting of large bearings using hydraulic nuts
Hydraulic nuts are available for all common sleeves and shaft threads
For the mounting of large bearings, it is advisable to use a hydraulic nut in order to slide the bearing into place or press in the sleeve ➤ Figure. Hydraulic nuts are available for all common sleeves and shaft threads. The hydraulic method described not only gives easier mounting, but in particular easier dismounting.
Hydraulic nut for mounting of bearings with tapered bore
The preset internal clearance gives the required bearing clearance after mounting
In some bearing arrangements, a certain radial and axial clearance necessitated by the design and temperature conditions is set during mounting which may also, if required, be zero clearance or light preload. In large volume situations, bearing units are increasingly fitted whose internal clearance has been preset such that the required bearing clearance is achieved when mounted; see product chapter and MH 1.
Dismounting of bearings with a tight fit is more difficult
The removal of a rolling bearing mounted with a tight fit is not always easy, especially if fretting corrosion has formed. Defective rolling bearings can be dismounted by cutting or splitting of the rings.
If the bearings are to be reused, the force used in pressing the bearing off must always be applied to the bearing ring with a tight fit ➤ Figure.
Incorrect dismounting: the rolling elements must support withdrawal forces
Dismounting of non-separable bearings: the tool must be applied to the ring with a tight fit
In the case of non-separable bearings, the ring fitted with a sliding seat must first be removed from its seat ➤ Figure. The ring with a tight fit is then pressed off. The tools must be applied to the bearing ring with a tight fit ➤ Figure and ➤ Figure. In order to apply the withdrawal device to the inner ring, extraction slots are provided in the shaft shoulder ➤ Figure.
Simpler dismounting with fixed press
Dismounting of rolling bearings is a simpler operation if a fixed press is used for pressing off ➤ Figure.
Dismounting of non-separable bearings
Withdrawal device with tie rods
Withdrawal device with adjustable arms
Pressing off a ball bearing using a fixed (stationary) press
Ball bearing extractor with clamping tool
In cases where the inner ring is in contact with the shaft shoulder and no extraction slots are present there, it is possible to remove ball bearings, tapered roller bearings and cylindrical roller bearings with the aid of an extractor with a clamping tool. In the case of the ball bearing extractor, the finger-shaped extensions of the clamping tool inserted in the extractor engage between the balls on the raceway edge of the inner ring ➤ Figure.
The clamping tool is part of a collet that is clamped against the inner ring by means of a conical clamping ring. It is extracted by means of a tensioning spindle. The extractor can also be used to remove bearings, that are still mounted in the housing, from the shaft.
Ball bearing extractor with clamping tool
Further precautions for the adjacent construction when using dismounting tools
The examples show that consideration must be given in the design of the adjacent parts to the placement of extraction tools. If the inner ring has a tight fit, its end face must be accessible. This can be achieved, for example, by restricting the shaft shoulder diameter or providing slots in the shaft shoulder ➤ Figure and ➤ Figure. Spacer rings or labyrinth rings must be designed such that they do not disrupt extraction.
Recesses or threaded holes must be provided for extraction screws
The same applies to the design of the housing. Pot type housings with a rigid end wall are preferred for strength reasons, but cause difficulties in dismounting of the bearing outer ring. If rigid shoulders are present, recesses or threaded holes for extraction screws should be provided ➤ Figure and ➤ Figure.
Slots in housing wall for placement of extraction tool
Pressure screws in housing wall for extraction of bearing ring
Separable bearings allow easier dismounting
The requirement for easy dismounting of bearings also influences bearing selection. Since they are easy to dismount, separable bearings such as magneto bearings, tapered roller bearings, cylindrical roller bearings and needle roller bearings are often used in preference to other bearing types.
Method for dismounting a withdrawal sleeve
The withdrawal sleeve is also an accessory to give easier dismounting. For dismounting of the sleeve, it is possible in difficult cases – principally in the case of large size bearings – to use a nut with quenched and tempered pressure screws or a hydraulic nut in place of the extraction nut that is otherwise normally used ➤ Figure.
Dismounting of a withdrawal sleeve
Hydraulic methods or induction heating are suitable for overcoming high adhesive friction
In practice, the high level of adhesive friction in the seating surfaces of tightly fitted bearings often causes problems in extraction. If fretting corrosion has formed in the fit joint, the fit surfaces often undergo fretting during extraction. This can be combatted by means of induction heating or – in the case of larger bearings – by means of hydraulic mounting methods.
Oil between the seating surfaces causes slight expansion of the bearing ring
In hydraulic mounting methods, oil is pressed between the seating surfaces of the tight bearing fit, which slightly expands the bearing ring ➤ Figure. The fluid film eliminates the contact between the fit parts to the point where these can be displaced with little application of force and without the risk of surface damage.
The hydraulic method is only suitable for dismounting in the case of cylindrical fit parts. Conical fit parts can, however, be mounted and removed using the hydraulic method ➤ Figure.
During dismounting, the inner ring becomes loose abruptly. It must therefore be axially secured.
Principle of hydraulic mounting
Oil grooves, feed ducts and threaded connectors are necessary
In order to press oil in, oil grooves and feed ducts as well as threaded connectors for the pressure generation devices must be provided ➤ Figure. There are designs of adapter and withdrawal sleeves that already have these ducts ➤ Figure.
Oil ducts and grooves in a tapered shaft
B = bearing width
Adapter and withdrawal sleeves with oil ducts
Oil injector for bearings with tapered bore and tapered shaft journal
In the mounting and dismounting of bearings with a tapered bore that are mounted on a tapered shaft journal, a simple oil injector is sufficient ➤ Figure. If cylindrical fit surfaces are present and adapter or withdrawal sleeves are used, more oil must be pressed in due to the oil loss that occurs at the edges of the fit surfaces. In this case, a twin-stage hand piston pump with an oil pressure of up to 1 600 bar can be used ➤ Figure.
Oil injector and valve nipples
Twin-stage hand piston pump
Oil pressure of up to 1 600 bar
Expansion of the rings by induction heating
In addition to the hydraulic method, the expansion of bearing rings by means of induction heating has gained considerable importance for the mounting of rolling bearings and is currently the state of the art. ➤ Figure shows a portable device (rigid coil) that is used for the mounting and dismounting of cylindrical roller bearing inner rings. ➤ Figure shows the flexible inductor for medium frequency technology. These inductors give safe and reliable heating of rolling bearings or other ring-shaped steel parts even at locations with poor accessibility. Due to the targeted application of heat and the high energy density, medium frequency technology allows short heating times and environmentally acceptable heating.
As a result of rapid local heating, very little heat enters the shaft
If fixed coils are used, a separate device is necessary for each size of ring. Heating takes place so quickly that very little heat enters the shaft during dismounting and the inner rings that previously had a tight fit can easily be loosened from the shaft.
The method is economical if cylindrical roller bearing inner rings are mounted in large quantities or if large size bearings – such as in the replacement of rolls in a rolling mill – must be dismounted and mounted again frequently.
Induction heating devices for sealed and greased bearings
Two further induction heating devices which can be used to heat complete rolling bearings of any type for mounting are shown in ➤ Figure. These devices can also be used to heat sealed and greased bearings.
The devices operate on the transformer principle, where the bearing acts as a short-circuited secondary winding. As long as the primary current is switched on, a short circuit current is induced in the bearing that heats the bearing to +80 °C or a preselectable temperature. Depending on size, the heating time is between a few seconds and a few minutes. Heating devices are available for the normal mains voltages. Shrink fit and labyrinth rings or other ring-shaped metallic parts can therefore also be heated by this method.
Induction heating device with medium frequency technology
Induction device with flexible inductor
Induction heating devices for the mounting of complete rolling bearings