- Bevel Helical (BCV)
- Bevel Planetary (BBP)
- Bevel Helical Planetary (BVP)
- Bevel and two planetary (BPP)

Vertical mills are used for grinding of limestone, clinker, slag, lime, gypsum, and coal in Cement industry, and for coal preparation in cement and thermal power plant.

Vulcan has developed the above gear units for vertical mill drives. These gear units are made for special service conditions. They have to transmit the power, reduce the speed of the high speed motor to the required mill speed, and also support the grinding table. The high axial forces developed have to be transmitted to the foundation via a special bearing and the rigid gear housing.

For these of application two gear unit designs are available.

BCV type bevel-helical gear units, power range lies between 30 and 1425 kW BBP and BVP type power range from 75 upto 6200kW.

Description

- Bevel gear stage, case hardened with lapped or HPG or ground gear teeth depending on load factor.
- Sun gear and planet gears are case hardened and ground planet gears are supported with self aligned roller bearings.
- Internal ring gear out of high-alloy quenched and tempered steel, and the internal spur gear produced by hobbing or shaping.
- Load distribution is by a self-aligning sun gear, which is connected with the bevel gear shaft through gear coupling.
- Planet carrier out of nodular graphite cast iron.
- Thrust load from the mill absorbed by tilting pad thrust bearing.
- Housing out of fabricated steel heavily ribbed, circular form; thus, passing on the thrust load equally and directly into the housing wall.
- Bearings; calculated service life at least 85 000 hrs.
- Dust and oil proof seals on the input and output shaft along with labyrinth seals.
- On type BVP type gearboxes, a helical gear stage (case hardened and ground) is added between bevel and planetary gear set thereby reducing the size of bevel set.

Tilting pad thrust bearing

The high thrust loads caused by the grinding process in the mill are absorbed by a tilting pad thrust bearing. The bearing may be designed for hydrodynamic or hydrostatic lubrication. All pads have a white-metal Coating.. Low surface pressure, a thick oil film and thus, good damping are ad-vantages of this proved design. For lubrication and cooling, oil is pressed between the pads. The emerging oil is thus mixed with fresh oil again before entering the next segment. The temperature is monitored by means of a fitted temperature sensor.

Hydrodynamic lubrication

By the rotational motion, oil is drawn into the bearing. The bearing tilts a little bit forward and thus a wedge-shaped hydrodynamic oil film forms. Due to the in-built design of the segments, only a small amount of oil is displaced sideways, and a stable and thick oil film remains at the outlet.

Hydrostatic lubrication

The oil is pressed into the bearing under high pressure. Each segment has a separate connection and is always supplied with an equal quantity of oil, independent of the load. In addition, owing to the hydrodynamic effect oil is drawn in. The oil film is nearly as twice as thick if compared with Hydrodynamic lubrication. For the oil supply, multi-cylinder high-pressure pumps or a high pressure pump with oil distribution valves are provided which guarantee equal distribution of the oil.