Robust solution for man and material handling
The lastest preference of cement plants are a new set of elevators that work on the Rack & Pinion principle. The Rack and Pinion principle is simplicity beyond question with 100 percent mechanical efficiency providing precise and positive control in operations for transportation to unlimited heights.
Cement plants have many tall structures like preheaters, CCR (Central Control Room), and Cement Silo which encompasses heaters, kiln arrangement and the pressure regulating systems. The height of the preheater varies from 110 meters to 150 meters. Climbing up and down with steps on this structure during construction, regular maintenance and operation with or without material is tedious task. This wastes the time and energy, and is unsafe.
The conventional Traction (wire rope type of elevators) does not suit this application as its sensitive components are exposed to dust and heat. Conventional elevators also require supporting guide structure (RCC wall or steel cage) which are costlier than lifts. Self supported Rack and pinion elevators overcome these limitations and are more suitable for this application and becoming more popular among cement plants. Almost all the new cement plants now consider these Elevators in project planning stage itself.
Rack and Pinion Elevator: The elevators comprise two main units: Car (Cage) with drive unit and the mast structure. The drive unit is attached to the main frame of the car on vibration damping brackets, and 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. Through electrical power, the motor drives the pinion, which in turn drives the cage upwards or downwards. Control of the elevator is through push buttons i.e. Semi Automatic Control System. Operation of the Elevator is possible from both the car as well as the landings. The mast structure on which the car runs comprises 1.5 m long mast sections bolted together. Each mast section consists 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 which actuate limit switches attached to the lift car preventing over travel and causes the car to stop automatically at the top/ 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.
- Ascent Limit Switch: Ascent limit switch defines the upper travel limit of the lift. Two-ascent limit switches are provided as a safety measure to prevent the lift from over traveling, the first prevents over travel and the second acts if the first fails and stops the lift. Even then if the lift travels up, the topmost mast is provided with a half rack to prevent over travel.
- Descent Limit Switch: Similarly two descent limit switches are provided; they define the lower travel limit of the lift.
- Limit Switch on Cage Entrance and Landing Door: Electro Mechanical locks are provided on both doors as a safety measure. The lift will not operate until the doors are properly closed. The doors cannot be opened during operation / travel of the cage, thus the operator has control on the door
- Safety Device To Prevent Free Fall: Centrifugal brakes are provided to prevent free-fall, in case of a free fall the centrifugal brake are operated and they do not allow the speed of the lift to exceed 40-44mtrs/ min.
- Manual Brake Release Device For Emergency Decent: In case of a power failure or such emergencies the lift will stop instantly, manual brake release devices are provided if it has to be brought to the nearest landing. The operator has to release these brakes which are placed with the motor and can be brought down to the nearest landing.
- Emergency Light & Hooter Arrangement: These basic arrangements are provided in case of an emergency.
- Phase Failure Relay: In case of failure of any phase (three phase) the lift does not start.
- Flap Arrangement for Safer Exit: Landing arrangement provided for people to move out of the cage.
- Barricade Arrangement in Total to Protect Lift: The Lift is provided by a barricade arrangement to avoid any external medium getting in the vicinity of the lift.
- Lock Out Master Switch: A key on the control panel is provided with a master lock, the lift can be operated only when the authorized person in charge of the lift unlocks the lock of the panel.
- Self Braking Electric Motors: The motors provided for the lift are electromagnetic brake motors, which act as means of safety device in case of power failure. In such a case the lift could be brought down to the nearest landing by inching method.
- Half Rack: The top most rack is a half rack provided to guard the lift in case the lift over travels, the provision of half-mast will not allow the lift to run over it.
Suitability for old cement plant
Rack and pinion type lift does not require contentious support, or heavy foundation, or lift motor room. It is more compact and easy for erection and dismantling. It can be stopped at any height of total installation. Few of the old plant has installed wire rope (traction) type lift, however installation of these lifts are laborious and requires R.C.C. duct for continuous support to its guide rail. It also requires enclosed head room at top of duct to place the motor and control panel. It requires heavy foundation for rails and buffers. Overall rope type lifts are more costly than rack and pinion type lift. Many of the old mini cement plants dont have lifting arrangement at high rise structure. These plants can be installed with rack and pinion type lift without more expenditure on civil construction work. This lift is found to be definitely economical over the period of its operation.
Lift is used in following location:
- Preheater buildings
- Central Control Room
- Packing Plant
- Power Plant
- Central Control Room
- For Erection of the Plant & Machinery: During erection of preheater building, lifts facilitate to carry men and material.
- Quality inspection during construction: Consultants, engineers and supervisors can visit the place of work frequently to check the accuracy and quality of work. Lift is installed in stages hence one can keep track of quality from initial work.
- For maintenance during operation: PM Lift becomes an instant utility device which helps in immediate action in case of break down at any level. Technical staff and required tools can be conveniently moved for maintenance. In case of an accident or a mishap the constraint of reaching high heights becomes a problem thus causing damage to life or property.
Marginal capital investment on installation of PM Lift is found to be profitable over long term use, saving on time and energy.
A. D. Bhosale is a graduate in Civil Engineering, from College of Engg., Pune with more than 10 years of experience in Project Planning, Execution. Presently working with Universal Construction Machinery as a SBU Head .