Rack and pinion type lift is compact and easy for erecting and dismantling, does not require contentious support and neither heavy foundation nor lift motor room. This article gives an insight into to the benefits and advantages of using rack and pinion type lifts over the wire rope type of elevators.Cement plants have many tall structures like pre-heaters, central control room (CCR), silo, etc, which encompasses heaters, kiln and the pressure regulating systems. The height of the pre-heater varies from 110 meters to 150 meters. Thus, climbing up and down with steps on this structure during construction, regular maintenance and operation with or without material is a tedious task. This is waste of time and energy of technician and is unsafe way.
The conventional traction (wire rope type of elevators) do not suit this application due to exposure of its sensitive components to dust and heat. Conventional elevators also require supporting guide structure (RCC wall or steel cage) which are costlier than lift. Self supported rack and pinion elevators overcome these limitations and are more suitable for such applications. Almost all the new cement plants now consider these elevators in their project planning stage itself. The Table shows the pros and cons of rack and pinion elevators against the conventional stack elevators.
The rack and pinion elevators work on the rack and pinion principle, whose simplicity is beyond question. It provides 100 per cent mechanical efficiency with precise and positive control in operations for transportation to unlimited heights. The elevators comprise of two main units
(a) Car cage with drive unit
(b) Mast structure
The drive unit is attached to the main frame of the car on vibration damping brackets. The drive unit gives a positive drive to the pinion through a vibration absorbing direct coupling and a worm and screw reduction gear box. The car operates on the mast and is guided by individually adjustable ball bearing guide rollers. The pinion meshes with rack on the mast thereby providing positive drive to the system. When electrically powered, the motor drives the pinion which in turn drives the cage up or down. Control of the elevator is through semi automatic control system (push buttons). Operation of the elevator is possible from both, the car as well as the landings. The mast structure on which the car runs comprises of 1.5 meters long mast sections bolted together consisting of lattice work of steel tubes and angle profiles welded together. These sections are provided with a precision cut rack with which the drive pinion meshes. The mast structure is bolted to the wall by bolts.
The elevator is provided with top and bottom limit cams with actuate limit swithces attached to the lift car preventing over travel and causes the car to stop automatically at the top and bottom landings. Individual cams are provided on the mast for stopping the car at the intermediate landings.
Variable frequency drive (VFD) gives jerk free operation during start and stoppage of lift. Lift is provided with electromagnetic and fail safe break to avoid free fall. Cabin of lift is closed from all side to avoid entry of dust.Safety features
(a) Ascent/decent limit switch (b) Limit switch on cage entrance and landing door (c) Safety device to prevent free fall (d) Manual brake release device for emergency decent (e) Phase failure relay (f) Flap arrangement for safer exit (g) Barricade arrangement to protect lift (h) Lock out master switch Suitability for old plants:
Rack and pinion type lift does not require contentious support and neither requires heavy foundation nor lift motor room. It is more compact and easy to errect and dismantle. It can be stopped at any height of total installation. Many old mini cement plants do not have lifting arrangement at high rise structure. These plants can install rack and pinion type lift without much expenditure on civil construction work. This lift finds definitely economical over a period of its operation.
Lift is used in following location :
- Pre-heater buildings
- Central control room
- Packing plant
- Power plant
- Central control room