Hawaii benefits from manufactured sand
The island of O’Ahu in Hawaii, headquarters of the United States Pacific Command and the capital, Honolulu, houses over 75% of the population and produces most of the economic output in the Aloha state. The island was however not immune to the hardships of the recession a few years ago but the investment on infrastructure and residential property from the state of Hawaii, the Federal government and the Department of Defense allows the island to weather the challenging economic times much more comfortably.
Key contributor in the construction sector of O’Ahu, the Hawala quarry, in existence since the late 40’s, property of Hawaiian Cement and one of the biggest quarries on the island, is a critical part of the residential, commercial and public construction projects currently being undertaken throughout the island.
Hawaiian Cement, a company belonging to Knife River Corporation, and its predecessor companies, has a history of supporting the state’s construction needs going back to 1939. The company leases seven quarries on three of the main islands, employs two hundred employees within its four divisions: cement, aggregate, ready-mix concrete and colored concrete products, and has nine offices throughout the state of Hawaii. Within the Aggregate division, Hawaiian Cement ranks among the three biggest aggregate suppliers within the state and the Halawa quarry, one of the biggest ones within the island of O’Ahu.
Having started back in the 1960’s, some of the equipment installed in the Halawa quarry dated back to those years. Fifty years on, the expectations of the customer base has dramatically veered towards obtaining high quality sand particle shape, demands that outdated technology could not satisfy.
The case for particle shape
Particle shape is the key factor influencing sand quality and therefore concrete strength. The tighter the sand particles sit together, the fewer the number of voids and the lower the amount of water needed. This allows for sturdier concrete, thus directly influencing the strength and durability of built roads and maximizing the return on investment of a construction project. Cubicity is the desired shape to suit strength, as opposite to round or elongated shape which can have a higher number of voids between particles and therefore result in spongy and weaker concrete.
Although the shape of some natural sand available on the island suited Hawaiian Cement’s expected quality standard, that type of sand was very scarce. Hawaiian Cement had to therefore resort to sourcing it from outside the island, as it happened, from British Columbia, Canada. However, the need for self-sufficiency, highly praised in a spot nearly 2,000 miles away from the mainland, spurred the need for sourcing adequate on-site technology to produce the 4 minus 3/16 inch product in the concrete produced.
The Sandvik VSI crusher
The Sandvik CV229 impact crusher was the product chosen by Hawaiian Cement after demonstration of the machine in the field, supplemented by analysis of crushed particles in the Sandvik’s laboratories in Sweden and Appleton, Wisconsin, and material flow studies through the Sandvik’s trademarked Plant Designer software. The machine is installed with an HP85 rotor, which has the lowest number of wear parts within a closed rotor of its size in the market at the moment. As Jason Macy, Vice President of Operations, puts it “we liked the simplicity of the Sandvik crusher. Other VSIs in the market we looked into had many more parts than the Sandvik crusher”. This simplicity makes it easier to run in terms of manpower needed and lower parts stockage, key in the smooth and continuous running of a complex operation.
Introduced in 2002, Sandvik’s line of autogenous crushers use a rock lined rotor to accelerate material, which is then impacted in a highly energized rock lined crushing chamber and it impacts with material falling through the biflow system. The crushers incorporate the Sandvik Hurricane™ rotor, which became a major breakthrough in VSI autogenous rotor design at the time, due to its decreased vibration levels and wear part design, which results in increased crusher bearing life combined with reduced maintenance.
Standard Sandvik VSI crushers are fitted with a timed trapped two key system, which ensures maintenance personnel’s safety combined with electrical isolation. Also supplied and fitted as standard are a vibration detection switch and a pre-start alarm siren.
“Since its installation in December 2012, the machine has produced 200,000 tons, at an average rate of 40,000 tons per month. Considering the rotor wear, there is at least another 200,000 tons that can be crushed before the parts need to be replaced” says Kevin Bohanon, Sales Manager for Sandvik Construction in the USA.
Steve Pegler, Sales Manager at Elrus, Sandvik Construction’s distributor of stationary crushers in the state of Hawaii, as well as the north west of the USA and western Canada and Ontario, explains how the high production rates at lower costs can benefit non Sandvik crushers: “Sandvik offers a Rotor Retrofit Program, which makes it possible for customers with various makes of autogenous VSI crushers to achieve the benefits Hawaiian Cement is seeing on their CV229”.
Don Matsumura, General Manager at the Halawa quarry says: “Our goal is to get rid of importing the BC sand and produce our own number 4 product (1.85” minus) with the CV229. This machine asks lots of questions of us, like the feed it needs and the moisture it can handle. We need to figure out how the rest of the plant has to work to keep up with the production rate of this new crusher. The cost of the BC sand alone however, validates the capital expenditure on the savings the CV229 will give us comparatively in terms of production. The low parts wear further validate this investment. Changes of parts on the older models were made every month. With this one, no changes have been needed for five months”.
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