The bearings best suited to the conditions described in 2.1 are heavy-duty spherical roller bearings of special design, as a rule FAG vibrating screen bearings of dimensional series 223.
The latest design of FAG vibrating screen bearings are spherical roller bearings of series 223E with outer-ring riding, surface-hardened pressed-steel window-type cages and great dimensional stability. This design, which is characterized by an extremely high load carrying capacity is used for bore diameters of up to 150 mm.
Of the larger bearings of series 223 the A-design is used which essentially is identical with the earlier vibrating screen design HLA. The inner ring features three fixed lips, with the centre lip guiding the rollers. The bearing design with two outer-ring riding machined brass cage halves has proved to be extremely suitable in practical application.
Where extremely high load ratings are required, PAG offers special spherical roller bearings of series 233A(S).MA.T41A with bearing bores ranging from 100 to 200 mm. The inner ring features three fixed lips. The split machined brass cage is of the outer-ring riding type.
In view of the aggravated operating conditions, all FAG spherical roller bearings for vibrating screens are made to specification T4IA. It prescribes a restriction of the bore tolerance to the upper half of the normal tolerance field. The outside diameter must be in the centre half of the normal tolerance field. Moreover, T41A specifies the standard clearance group C4 so that the bearing clearance does not have to be included in the bearing designation. The cage designs for FAG spherical roller bearings for vibrating screens are shown in figs. 15 and 16.
Sealing and lubrication of the bearings
Vibrating screens are usually operated either in the open or in roofed halls. Generally, they succed crushers . Temperature variations, exposure to huge amounts of dust, and variations in atmospheric moisture present particularly high requirements on the sealing of the bearing locations. Vibrating screen bearings can be lubricated either with grease or with oil.
Grease-lubricated rolling bearings are sealed on the inside towards the guard tube by means of a baffle plate. On the outside, the sealing consists of a relubricatable labyrinth whose sealing effect can be further increased by providing a V-Ring in the innermost labyrinth gap.
The newly supplied grease must get directly to the bearing’s rolling and sliding contact areas so that an even lubrication of both roller rows is ensured. We recommend lubrication through the circumferential groove and the lubricating holes in the bearing’s outer ring.
Oil sump lubrication
With an oil sump lubrication system, a relubricatable Labyrinth prevents dirt from penetrating into the bearing from outside. A flinger ring with an oil collecting groove is used to prevent oil from escaping. On the bearing side the sealing area is shielded by a flinger ring.
To prevent the Labyrinth grease from penetrating into the oil cavities, a V-ring is fitted between Labyrinth annd flinger ring. The oil level on both sides of the bearing is equalized by means of the connecting bore provided in the bottom of the housing. The oil level should be so high that the bottom most roller of the bearing is about half immersed in the oil with the bearing at rest.
This is achieved by providing an overflow hole at this level which is plugged up after filling the housing with the required amount of oil. The oil outlet screw contains a small permanent magnet which collects wear particles from the oil. The oil sump should contain the largest possible amount of oil to achieve the longest possible replenishment intervals. Generally, the guard tube around the shaft serves as an additional oil reservoir.
Oil splash lubrication
In two bearing screens with oil splash lubrication the oil is churned in the exciter space by the synchronized gearwheels mounted onto the imbalance shafts. Bearing lubrication is effected by the oil flung off by the gearwheels and by a flinger ring.
Baffle plates provided at the bottom halves of the housing ensure a sufficient oil level in the bearings. The passage for the drive shaft is fitted with a flinger ring seal preceded by a Labyrinth as an extra protection against the ingress of dirt. In addition, a V-ring can be provided between labyrinth and flinger ring. Lateral oil level indicators allow the oil level to be inspected.