Tremendous technological advances in stone crushing have taken place in the post-second world war period to build back the war-torn countries. Modern mechanized construction and the need for high strength concrete and asphalt mixes have brought in new quality standards for aggregates with severe conditions.
Since our historians as Stone Age, the human environment and their existence, aptly call the creation of mankind, centered on rocks and stones lying around in the nature. The man dug, broke and shaped the stone to build his home, townships and roads. With stone, he built weapons to hunt, walls to protect his family, dams to irrigate his Fields etc. The copious rock on earths crest is one of the greatest gifts nature has given to the mankind. Though modern technologies have come into use in quarrying and crushing, it is the same old rock used by our ancestors that still remains the main building material of the modem times.
The crushed rock produced by labour or by machines - popularly known as crusher plants - is termed as Aggregates in the civil engineering terminologies, which are the basic materials for construction works. A new era of rock processing was ushered in. We can rightly say we have entered Aggregate Age from Stone Age.
Quality Standards for Aggregates
Tremendous technological advances in stone crushing have taken place in the post-Second World War period to build back the war-torn countries. Modern mechanized construction and the need for high strength concrete and asphalt mixes have brought in new quality standards for aggregates with severe conditions, namely
·Distribution of the particle sizes called Gradation falling within a specified closed loop
·Cubic particle size called Cubicity meeting a particular flakiness and elongation indices (FI&EI) Whether it is a high-speed expressway or a massive dam project, together with quality the need for production of large quantities of aggregates pose the greatest challenge to the machine manufacturers. The manufacturers are still searching for a crusher that can produce it all.
In the present day India where a rapid infrastructure development is on, the challenges have been multifold to meet the growing demand for aggregates. The launching of an ambitious Rs 54.000 crore - 13,242 km long National Highway Development Project (NHDP) by GOI towards the end of last century, involving up-gradation and strengthening of Golden Quadrilateral and East-West and North-South Corridors have opened up big opportunities to the Indian machine builders to develop a new breed of aggregate crushing equipment and systems in India. World-class stone crushing technologies and a high standard specification for aggregates and road base materials for modern highway construction have been ushered in to Indian quarry and construction industries.
Hunt for New Equipment
Conforming to high standards meant new equipment and improved processing. The conventional stone crushers- jaw, gyratory and impact - tend to produce sliver and slabby material. Most 2-stage and 3-stage crushing plants with the conventional crushers that have been installed at NHOP works, failed to deliver the crushed stone of required cubicity. The highway contractors and quarry operators were in chaos by the rejections of all that crushed. The authorities, which enforced the high standards for the aggregates, faced with the delayed project schedules.
The solution was found in a Vertical Shaft Impact (VSI) crusher that should be deployed in tertiary or quaternary stage to meet the high aggregates standards set forth. VSIs produce cubical crushed stone ideal for the high strength concrete and asphalt mixes required in modern structures be it a super highway or a multipurpose darn or a skyscraper. The VSI product meets the stringent of the cubicity and gradation standards. The project authorities thereupon insisted on insertion of VSI crushers in all crusher plants for highway construction. Contractors thus faced with import of expensive VSIs from multinationals. Added to their debts the VSIs were not excused from high custom duties prevailing (only cone type crusher plants are entitled duty-free import for highway projects).
NAWA Engineers and consultants (P) Ltd have ventured into developing an indigenous VSC. The aim was to put in market world-class equipment readily available to the users at a competitive price without going through the hassles of importation. Nawapactor instantly gave the desired solution for the shape and gradation in the crushing tasks of many a contracting companies and quarry owners. In the last 5 years the company has set up more than 50 VSI installations, capacities ranging 50-350 tons per hour. Some of them are located in the difficult tracks of Mizoram, Jammu & Kashmir, Bhutan, Himachal Pradesh and Uttaranchal, giving the owners a consistent and satisfied performance in most rigorous conditions.
How Nawapactor VSI Works
The best way to get good cubic shaped aggregates is allowing the rock to break along its natural cleavages under free impact conditions. VSI uses basic physics and geometry to generate free impact conditions. The mechanism involved is very simple. The biggest stones are fed through the hopper and a feed tube onto the centre of closed rotor with ports. The rotor spinning at high speed throws the material with a great centrifugal force. When the accelerated bigger pieces hit the stationary rock shelf encircling the rotor, known as; Rock-on-Rock principle, the bigger pieces break due to impact along the natural fault lines. The result is broken smaller pieces in cubical-crystal- line shape. They then fall freely by gravity through the gap between the rotor and the rock-shelf on a conveyor belt below. A ring of anvils converting Nawapactor to a Rock-on-Steel VSI can replace the rock-shelf. The result is the same cubic product but of different gradation to meet users need. Changing the design parameters, like speed and throw distance, can alter the product gradations.
Nawapactor as Crushed Sand Producer
The greatest use of VSI crusher is its ability to produce manufactured sand. The rock-on-rock principle simulates nature way of impact and grinding that occurs in natural river sand. The gradation and the Fineness Modulus (FM) are the measure of quality and suitability of sand for construction purposes as set out in IS: 383. The crushed sand produced by Nawapactor VSI is consistently tested meeting these standards. The Nawapactor VSI is delivered as complete and stand-alone unit that facilitates quick installation on a simple foundation. The user is saved of procuring any add-ons before installation at site.
Using the in-depth knowledge and vast experience of its technical team in crushing and screening, the company has developed a totally indigenous range of equipment and systems for the needs of mining, quarry and construction industry, covering -
·Primary Single Toggle Jaw Crushers
·Vibrating Grizzly Feeders
·Hydraulic Cone Crushers
·Vertical Shaft Impact (VSI) Crushers
·Complete Aggregate Plants
·Concrete Conveying and Placement Systems
·Operation & Maintenance Services
|Posted : 8/12/2005|