By PYC Bearings
©2004-2008
All machines with rotating elements depend on their bearings for smooth performance, and long and trouble free lifetimes. In heavy duty industries, bearings are subjected to all the conditions most likely to cause their deterioration: vibration, ingress of dirt and contamination, extreme heat and cold to name a few.
Therefore, the quality of the bearings must be matched by the quality of the seals, lubricants and housings to maximise the performance of the system.
As a result SKF has invested heavily in developing bearing systems capable of withstanding the rigours of tough duty cycles. This is particularly true of the bearing housings which are commonly exposed to the harshest environments.
However, no matter how good the bearing is, its performance is dramatically affected if it is fitted poorly or installed in a poor quality housing. SKF's ranges of bearing units and housings have been proven in the broadest cross section of rugged industries.
Some of SKF's most widely used bearing units and housings include:
Y-bearing units
Simple, economic bearing arrangements can be made by using Y-bearing units, which are particularly suitable for applications such as materials handling equipment. The unit consists of a Y-bearing, which is a single row deep groove ball bearing sealed at both sides with a sphered outside curved surface, combined with a housing, typically made from either cast iron, pressed steel or a composite material with a sphered bore.
Y-bearing units are based on proven deep groove ball bearings, with bore tolerances allowing easy mounting on shafts. The units can compensate for initial errors of alignment between shaft and housing of up to ˇŔ5 deg during mounting, and are capable of working at shaft speeds of up to 100 rev/min. An extended inner ring, with holes to accept set screws, enables simple shaft attachment, for metric shafts ranging in siz e from 12 to 100 mm diameter.
All Y-bearing units are equipped exclusively with highly efficient rubbing seals, with slightly different designs depending on the series, for full protection even under extreme operating conditions. Units are filled with a lithium base grease which has good corrosion inhibiting properties and are suitable for operating temperatures between -30 and + 110ˇăC.
Depending on the series, the seals usually consist of a pressed steel washer, on the inside of which a synthetic rubber sealing lip is vulcanised. The pressed steel washer forms a narrow gap with the cylindrical surface of the inner ring shoulder and provides efficient protection for the land-riding sealing lip against coarse contaminants.
For more difficult conditions, the units can be fitted with flingers outside the seals, which considerably enhance the sealing effect without adding to the friction. Flocked flingers of pressed steel, coated with a polyamide fibre flock, can also be supplied to provide further protection against moisture, mud, sand, soil and similar contaminants.
SKF ConCentra bearing units
These bearing units overcome the possibility of incorrect fitting and makes dismantling for service simplicity itself.
Indeed, all that is needed to effect a speedy change of bearing is a spanner and an Allen key - rather than a sledgehammer and a plethora of fitting and removal tools! The ConCentra, bearing unit is simply pushed along the shaft to the required position, the axial set screws are adjusted and the attachment bolts tightened. There is no need for a special tightening tool and there is no risk of tilting the inner ring, which is possible if brute force is applied in conventional bearing mountings.
In effect, the design combines the principal benefits of sealed bearing units, namely easy assembly and mounting and environmental friendliness, with those of standard plummer block housings - such as less fretting and easier mounting and dismounting.
There is a patented multi-tapered sleeve arrangement through which the ConCentra bearing unit achieves almost a 3600 interference fit with the shaft, permitting the use of less expensive commercial grade shafts and eliminating gouging of the shafts from set screws. At the same time the interference fit minimises fretting corrosion between the bore and the shaft.
The multi-tapered, or stepped, design is the fundamental design breakthrough. The bearing inner ring has machined steps in the bore, which correspond with those machined on the sleeve. The bearing is pushed onto the shaft and the set screws are located, by number and size, to give the correct clearance in the bearing. The internal sleeve releases its interference fit on the shaft by means of set screws positioned opposite those at the mounting side. Once released, the unit can be slid off the shaft.
SNL plummer block housings
SNL housings make installation easy by allowing pre-assembled shafts to be mounted. Since the housing bases are attached to the base plate and only the positioning of the housing caps and tightening attachment bolts need to be done.
The housings also allow easy access for inspection, maintenance and service. The housings are mainly intended for self-aligning ball bearings, spherical roller bearings or CARB bearing and can be fitted with a variety of seal designs. Users should therefore be able to match exact requirements, without the expense of a tailored solution.
For added protection from over zealous tightening of the foot attachment bolts, the design incorporates increased stiffness on previous versions. The SNL's casting design enables improved heat flow from the bearing outer ring to the base plate, with the bearings running 5% to 10% cooler than with other housing alternatives.
In addition to the standard range of housing sizes for ISO Dimension Series 02, 03, 22, 23 and 32 larger ranges to match ISO 39, 40 and 41 which cover shaft sizes up to and including 450mm, are also available. Commonly referred to as SNL Large and Extra Large, the housings are a replacement for the previous SD housing design and use the same size designations.