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In the case of grease lubrication, the steep flank of the RWDR is often placed in the direction of grease egress. As a result, some grease passes under the seal lip for lubrication of the sealing edge. The preload force of seal lips – in relation to their contact length – is normally 80 N/m to 150 N/m.

Sealing washers with one or more radial seal lips are also suitable for the sealing of rolling bearings with axial relative motion between the inner ring and outer ring (e. g. in spherical roller bearings or toroidal roller bearings).

Where contaminants that have an abrasive action are present in the bearing, the rolling contact surface partners undergo wear and there is a progressive increase in the bearing clearance. With an increasing operating duration, the running accuracy of the bearing in particular is reduced until it fails.

The roller bearing is a robust, resilient and largely maintenance-free wheel bearing that can be installed in a small space. Roller bearings (also called roller basket or needle bearings) have a small radial bearing clearance and are mainly used for transport equipment casters. The roller bearing consists of steel rollers in a synthetic or steel cage. These rollers roll between the axle and the wheel hub. The rotation around the axle causes rolling friction rather than dynamic friction. This keeps the rolling resistance of the wheel relatively low, even under heavy loads. Roller bearings are lubricated with a long-life grease and maintenance-free under normal application conditions. Stainless steel versions of roller bearings are also available (-XR in the product code).

Non contactseal bearing

In order to prevent the ingress of liquids while stationary, additional sealing measures are necessary, such as the supply of barrier media. Where higher requirements for sealing integrity are present, a relatively large design envelope is required for labyrinth designs.

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A considerably greater sealing action than with gap seals is achieved by labyrinths incorporating gaps filled with grease. A distinction is made between protective labyrinths and collector labyrinths.

The wheel bearing with grooved ball bearing (also called a precision ball bearing) meets high standards in terms of load capacity, rolling characteristics (even at high speeds) and resistance to environmental factors. Grooved ball bearings have the lowest level of bearing clearance, and are mainly used in technically-demanding transport unit casters and heavy-duty casters. A cover cap provides protection against dust (non-rubbing seal, also known as a Z bearing). Ball bearings can be installed with one or two sealing caps (slipping sealing, also known as an RS or 2RS bearing) for special requirements. Wheel bearings with ball bearings sealed on both sides (2RS) must not be lubricated to avoid damage to the ball bearing. Grooved ball bearings are lubricated using long-life grease and are maintenance-free under normal application conditions. Two ball bearings are installed in the hub as standard. A spacer sleeve is used to maintain the distance between the inner race of the ball bearing. This means that the wheel can be clamped axially into a rig (exception: roller for pallet trucks). In addition to the standard version, ball bearings are also available in a corrosion-resistant version (-XK in the product code), a version lubricated with heat-resistant special grease (-HK or -HXK (corrosion resistant) in the product code) or as a heat-resistant ball bearing (oven bearing, -IK in the product code). Heat-resistant ball bearings are suitable for use in temperatures between -30 °C and +300 °C with reduced load capacity.

The wheel bearing with two central ball bearings provides a high level of precision and smooth running performance. It also provides an effective seal while meeting demanding load capacity requirements. Positive locking is used to encapsulate the ball bearings with the wheel center. The central ball bearings are provided with two sealing caps (slipping sealing, so-called 2RS bearings) as standard. The ball bearings are lubricated using long-life grease and are maintenance-free under normal application conditions. The additional synthetic ball bearing cover provides protection for both the wheel hub and the thread. When the wheel is fitted in swivel and rigid rigs, no flanged bushes are required, unlike for conventional wheel bearings with ball bearings that are pressed in.

A felt ring is sufficient if the level of contamination is not too high. If the environmental conditions are less favourable, several felt rings can be arranged adjacent to each other.

At circumferential velocities over 12 m/s, experience shows that the V-ring must be radially located so that it does not become detached due to centrifugal force. Precise circumferential velocities for specific applications must always be agreed in consultation with the sealing ring manufacturer.

Various elastomers can be selected in accordance with the chemical and thermal requirements. In general, nitrile butadiene rubbers NBR are used. For applications with higher temperatures or speeds, sealing washers with lips made from fluoroelastomers FKM are frequently used.

Where oil lubrication is used and the shaft is horizontal, the through bore in some housings has a helical groove ➤ Figure. Depending on the spiral direction relative to the rotational direction of the shaft, oil creeping along the shaft is returned to the housing or contaminants are transported from the gap to the outside. A similar sealing action is achieved if the helical groove is located on the shaft.

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A narrow gap between the shaft and housing is a simple and, in many cases, adequate means of sealing against the egress of grease and slight contamination impact from outside ➤ Figure. The sealing gap can be held to a relatively narrow size.

During mounting, this sandwich construction allows concentric alignment of the rubber seal lip with the inner ring. The outer washer protects the seal lips effectively against damage caused by coarse contaminants.

BearingRubberSeal

Non-contact seals are particularly suitable for applications with high speeds and high requirements for freedom from friction and low heat generation. They are free from friction, except for a small amount of lubricant friction in the sealing gap. In general, non-contact seals are free from wear and have an almost unlimited operating life.

Depending on the contamination load, labyrinths are configured with one crosspiece or several crosspieces ➤ Figure. Labyrinths with several radially aligned crosspieces are only considered, for reasons of mounting, for split housings ➤ Figure. Their advantage is that the grease propelled outwards is held in U-shaped housing slots, which thus improves the sealing action.

In the case of sealing washers for axial sealing, an additional outer seal lip is often provided ➤ Figure. The outer seal lip (protective lip) is of a non-contact design and, together with the undercut on the inner ring, forms an additional protective labyrinth against the ingress of contamination.

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Seal Bearingbike

Low-friction sealing of bearing positions with a small radial design envelope, such as bearing positions with needle roller bearings, can be effectively achieved using sealing rings G, GR and SD; see product chapter. These sealing rings can be used individually or in a double arrangement ➤ Figure. In the double arrangement, one seal lip faces inwards to seal the lubrication medium, while the second seal lip faces outwards to give protection against contamination. In order to improve the protective function, the space between the seals can be filled with grease. With an extended inner ring, a sealing ring with the same outside diameter as the outer ring can be used, where the seal lip runs on the extended inner ring. Sealing rings give good protection against contamination and spray water as well as against the egress of oil and grease under slight pressure differentials. In order to reduce friction and protect the seal lip against damage, the sealing edge must be lubricated.

Where the design envelope is small, rolling bearings (e. g. ball bearings, roller bearings, spherical roller bearings, toroidal roller bearings) with integrated sealing washers are frequently used; see product chapter. These sealing washers comprise a sheet metal washer for reinforcement and have a vulcanised elastomer seal lip.

A central ball bearing provides extremely precise and smooth operation, and a good seal. These bearings are primarily used for synthetic wheels supporting small loads and for guide rollers. The ball bearing is encapsulated with the wheel center. The central ball bearing is provided with two sealing caps (slipping sealing, so-called 2RS bearings) as standard. Ball bearings are lubricated with long-life grease and are maintenance-free under normal application conditions. The additional synthetic ball bearing cover provides protection for both the wheel hub and the thread. When the wheel is fitted in swivel and rigid rigs, no flanged bushes are required, unlike for conventional wheel bearings with ball bearings that are pressed in.

If contaminant particles enter the bearing, overrolling of the particles at the rolling contact forms indentations that cause running noise and may constitute initial points for rapidly propagating material fatigue.

Additional sealing can be provided for ball bearings used in highly-corrosive wet areas. Combining sealing caps (slipping sealing, so-called 2RS bearing), clearance sealing and an additional slipping sealing provides ball bearings with optimal protection against water spray and dirt. Wheels with an additional ball bearing seal are suitable for machine washing. The slipping seal increases the rolling resistance slightly. Ball bearings are lubricated with long-life grease and are maintenance-free under normal application conditions. The additional synthetic ball bearing cover provides protection for both the wheel hub and the thread. When the wheel is fitted in swivel and rigid rigs, no flanged bushes are required, unlike for conventional wheel bearings with ball bearings that are pressed in. Versions with the ball bearing cover (-HKA, -XKA or -XKF in the product code) do not have the additional rubber sealing ring provided in the version with a ball bearing seal. The -XKA version is also suitable for machine washing due to the corrosion-resistant ball bearing.

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Lip seals of a three-part construction with single or multiple lips (comprising an NBR sealing element  between two sheet steel washers) are used, for example, in radial insert ball bearings ➤ Figure.

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Collector labyrinths are labyrinths of highly complex design with collector grooves and drain holes in the housing that are also suitable for the sealing of sealing positions subjected to very high impact by liquids.

A seal geometry that is designed in particular for applications with a rotating outer ring and high requirements for retention of the grease is the sealing washer with a seal lip in axial contact in accordance with ➤ Figure. This seal has increased sealing action against the egress of grease. An additional non-contact lip that repels the grease provides a grease chamber in front of the main seal lip for axial outward sealing.

Sealing washers RSD have a seal lip with radial sealing action and are characterised by low seal friction ➤ Figure. The seal lip is initially in very light contact with the shaft (little or no contact pressure). After running-in, a minimal sealing gap is created.

Contact seals are in contact at their sliding surface under a certain contact pressure. In many cases, they represent the most favourable solution in terms of design envelope and costs. The general disadvantage, however, is the loss of energy due to friction at the sealing contact.

Schaeffler sealing rings are highly suitable for a small radial design envelope and in combination with needle roller bearings

Bearing sealmaterial

For oil sealing of rotating shafts, rotary shaft seals (RWDR) in accordance with DIN 3760 and DIN 3761 and with spring preload are suitable. Frequently used designs are shown in ➤ Figure. The sealing rings are designed for applications with slight pressure differentials.

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Additional sealing can be provided for ball bearings used in highly-corrosive wet areas. Combining sealing caps (slipping sealing, so-called 2RS bearing), clearance sealing and an additional slipping sealing provides ball bearings with optimal protection against water spray and dirt. Wheels with an additional ball bearing seal are suitable for machine washing. The slipping seal increases the rolling resistance slightly. Ball bearings are lubricated with long-life grease and are maintenance-free under normal application conditions. The additional synthetic ball bearing cover provides protection for both the wheel hub and the thread. When the wheel is fitted in swivel and rigid rigs, no flanged bushes are required, unlike for conventional wheel bearings with ball bearings that are pressed in. Versions with the ball bearing cover (-HKA, -XKA or -XKF in the product code) do not have the additional rubber sealing ring provided in the version with a ball bearing seal. The -XKA version is also suitable for machine washing due to the corrosion-resistant ball bearing.

In the case of grease-lubricated bearings, the egress of grease can be prevented in many cases on the stationary bearing ring by the use of simple baffle plates. Depending on the mounting and operating situ­ation, the plates are braced on either their outer or inner edge ➤ Figure. The grease collar that forms at the sealing gap gives protection against slight contamination impact from outside.

In practice, labyrinths filled with grease are frequently used in order to achieve better sealing against contamination. In a highly contaminated environment, fresh grease is occasionally pressed into the sealing gap, which has the effect of pressing contaminated grease out of the sealing position.

At the sealing contact, the sprung sealing washer beds into the bearing ring during the running-in process and the preload decreases. A groove is formed in the bearing ring that, together with the seal edge, forms a small "microlabyrinth" under light contact. Due to this principle, these seals are suitable for bearing positions that require no static or pressure-resistant sealing of the bearing.

Felt rings are simple sealing elements that have proved effective primarily with grease lubrication ➤ Figure. After a short running-in time, the felt forms a sealing surface in preload-free contact with excellent sealing action against dust. Before mounting, the rings are soaked with oil.

Bearing sealtypes SKF

Lip seals are seals with one or more seal lips that give axial or radial sealing. These seals are predominantly elastomer seals. Typical designs are shown in ➤ Figure to ➤ Figure.

For designs in which there is no space adjacent to the bearing for a seal, there are rolling bearings with sealing shields integrated on both sides ➤ Figure; see product chapter. These bearings are supplied with a grease charge. Bearings with only one sealing shield on one side are also commercially available.

Spherical roller bearings have two rows of rollers to increase the contact surface of the rolling elements and achieve extremely high load capacities while keeping dimensions relatively small. Spherical roller bearings allow for angular adjustment and are therefore resistant to the axle being bent. The extremely high load capacity provides outstanding operational performance. Spherical roller bearings are therefore used in heavy duty wheels, with a focus on plant engineering (three shift operation). Two spherical roller bearings are installed in the hub as standard. A spacer sleeve is used to maintain the distance between the inner races of the spherical roller bearing. This means that the wheel can be clamped into a rig. Spherical roller bearings are not normally sealed. A special seal is available for spherical roller bearings upon request

If significant angular deviations of the shaft are expected in the case of spherical roller bearings, for example, there is a risk that grazing of the crosspieces will occur in labyrinths in accordance with ➤ Figure. In this case, labyrinths with bevelled crosspieces are used. The bevel is matched to the motion about the centre point of the bearing ➤ Figure.

Sealing washers are available with seal lips for radial or axial contact ➤ Figure. They are suitable for sealing against loss of grease and ingress of contamination at low pressure differentials.

Operating temperatures up to +100 °C are possible. At higher temperatures, sealing rings made from wound yarns are required that comprise PTFE, graphite or aramide and glass fibres, and are impregnated with PTFE or graphite.

The V-ring is a lip seal with axial sealing action ➤ Figure. The ring is made from elastic rubber NBR. During mounting, it is stretched and slid onto the shaft so that the seal lip is in contact with the housing wall.

Bearing sealtypes

Where there is heavy liquid impact and sealing positions are inundated by surge flows, so-called collector labyrinths are used. These seals effectively repel liquids if the sealing position is not subjected to prolonged inundation while stationary.

Protective labyrinths are centrifugal force seals. They protect sealing positions subjected to little external load due to liquids against the egress of grease and the ingress of contamination.

Rubbersealvs metalseal bearing

In addition to simple sprung sealing washers, there are also washers in double arrangements. The intermediate space is additionally filled with grease at the mounting stage. Due to their small section width, these seals can normally be fitted retrospectively and without design modifications to the adjacent construction.

When using grease lubrication, effective sealing can also be achieved by axially sprung metallic sealing washers ➤ Figure. These thin sheet metal seals are braced in the end face of the inner ring or outer ring and are in spring contact with the other bearing ring. In order to prevent fretting of the seal tongues during running-in, these washers are greased before mounting.

If heavy contamination impact or direct impact by liquids is expected at the sealing position, the sealing gap can be protected on the outside by means of a flinger shield ➤ Figure. The same purpose is fulfilled by a simple rubber shield that – without additional means of location – is seated under tension on the shaft or shaft bush ➤ Figure. At higher speeds, however, there is a risk that the rubber shield will become detached from the shaft under the influence of centrifugal force. For this reason, vulcanised flinger shields with sheet metal reinforcement are available that are used very effectively in, for example, passenger car wheel bearing units of the 1st Generation or shaft support bearings ➤ Figure.

Sealing washers with seal lips in axial running contact are used primarily in bearings with lower axial operating clearance (e. g. in deep groove ball bearings).

➤ Figure shows a double lip seal made from NBR for use in standard plummer block housings. The radially split seal can be easily inserted in the annular slot in the housing. Ingress of contamination is prevented by the outer seal lip, while the inner seal lip prevents the egress of lubricant. The grease between the two seal lips supports the sealing action.

Ballbearing sealtypes

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In the case of splash rings and flinger shields, sealing action is achieved by means of rotation and centrifugal force displacement ➤ Figure and ➤ Figure. Splash rings can give effective sealing, for example, where oil lubrication is used and the shaft is horizontal ➤ Figure. The oil creeping along the bush is propelled away by the splash rings and flows back into the housing via a drain hole.

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If grease lubrication is used, the sealing action of the gap can be increased by several grooves in the through bore of the housing ➤ Figure. The grooves act as storage chambers and hinder the ingress of contaminants as well as the egress of lubricant.

The plain bore is a simple, cost-effective and resilient wheel bearing. It is also corrosion-resistant and maintenance-free under normal conditions. Plain bores are mainly used for light duty and transport equipment casters, which are only moved infrequently and at slow speeds. Nylon plain bore sockets are used for wheels with tubular steel hubs. Plain bores may run hot at high speeds and under high loads. Cast iron wheels with plain bores must be lubricated on a regular basis.

Depending on the seal material and the surface structure of the shaft, the geometry of the seal lips generates a pumping action in the sealing gap towards the steep flank of the seal lip. The sealing ring is therefore mounted with the steep flank facing in the direction of the medium against which sealing is required.

Seals RSR with radial contact are equipped with a seal lip geometry that is similar to a rotary shaft seal ➤ Figure. The angles of the seal edge are selected such that the pumping action at the sealing contact repels liquids outwards and a small amount of grease is conveyed under the seal edge in order to lubricate the seal lip.

In order to make optimum use of the potential life of a rolling bearing, the egress of lubricant (grease, oil) must be reliably prevented and the bearing must be securely protected against the ingress of solid and liquid contaminants (e. g. dust, sludge, water, cleaning liquid) ➤ Figure.

If liquid or vaporous media enter the bearing, the lubrication conditions at the rolling contacts are disrupted. If corrosive media are present, oxidative damage of the surfaces will also occur. Both of these situations lead to a considerable reduction in the operating life of bearings.