Geology Talk

VSI helps sand quarry become self-reliant

Before adopting the Sandvik CV229 vertical shaft impact (VSI) crusher, Oahu-based company Hawaiian Cement had been forced to import sand from British Columbia, Canada, more than 3200km away.

The company is now able to supply high quality materials for the island’s infrastructure projects and reduce its own carbon footprint by being able to use naturally occurring resources.

The island of Oahu – the headquarters of the United States Pacific Command and home to the state capital, Honolulu – possesses more than 75 per cent of the Hawaiian population and produces most of the state’s economic output.

While the island had not been immune to the hardships of the recent recession, it had generally weathered the storm due to investment in infrastructure and residential property projects by the State of Hawaii, the US Government and the US Department of Defence.

The Hawaiian Cement-owned Halawa Quarry, which has been open since the 1940s, played a critical part in supplying materials for these projects, helping the island deal with the economic crisis.

Hawaiian Cement, part of the Knife River Corporation, and its predecessor companies possess a history of supporting the state’s construction needs going back to the 1940s.

Currently the company leases seven quarries on three of the main Hawaiian islands, employing 200 people in a variety of roles.

The business now operates in four divisions – cement, aggregate, ready-mix concrete and coloured concrete products – and has nine offices throughout the state. Within the aggregate division, Hawaiian Cement ranks among the three biggest aggregate suppliers in Hawaii, with the Halawa Quarry being one of the largest on the island of Oahu.

Modern production at the quarry began in the 1960s, and until recently some of the equipment installed at the site dated back to those times.

Fifty years on, the expectations of the customer base had dramatically veered towards obtaining high quality sand particle shape – demands that the outdated technology could not satisfy.

Particle shape has become increasingly important in the cement industry. It 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 less water needed. This allows for sturdier concrete, thus directly influencing the strength and durability of built roads and maximising the return on investment of a construction project.

The cubicity of the sand is also essential, with the desired shape producing strength; this contrasts with round or elongated particles, which can have a higher number of voids and, therefore, result in spongy and weaker concrete.

Although the shape of some of the natural sand available on the island suited Hawaiian Cement’s expected quality standard, this particular type of sand was very scarce.

Additionally, its use was limited by legislation due to environmental factors. As a result, it became necessary for Hawaiian Cement to source sand from British Columbia.

The need for a self-produced material that would not harm the island’s natural resources spurred the development of an on-site solution.

Hawaiian Cement decided to use the CV229 impact crusher after a demonstration of the machine in the field.

This demonstration was supported by analysis of crushed particles in Sandvik’s laboratories in Sweden and Wisconsin, and material flow studies through Sandvik’s Plant Designer software.

The machine was installed with an HP85 rotor, which had the lowest number of wear parts within a closed rotor of its size on the market.

Hawaiian Cement vice-president of operations Jason Macy said: “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 made the machine easier to run in terms of manpower and reduced the number of spare parts that needed to be stocked – both key factors in the smooth and continuous running of a complex operation.

The CV229 is one of the more recent developments in Sandvik’s line of autogenous crushers. Introduced in 2002, this line utilises a rock-lined rotor to accelerate material. This is then impacted in a highly energised rock-lined crushing chamber, with material falling through the biflow system.

The crushers incorporate the Sandvik Hurricane rotor, which became a major breakthrough in VSI autogenous rotor design 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 the safety of maintenance personnel, combined with electrical isolation. Also supplied and fitted as standard are a vibration detection switch and a pre-start alarm siren.

These and other features have enabled the CV229 to deliver a very impressive performance.

“Since its installation in December 2012, the machine has produced 200,000 tonnes at an average rate of 40,000 tonnes per month,” Kevin Bohanon, sales manager for Sandvik Construction in the US, said.

“Considering the rotor wear, there is at least another 200,000 tonnes that can be crushed before the parts need to be replaced.”

Steve Pegler, sales manager at Elrus – Sandvik Construction’s distributor of stationary crushers in Hawaii, northwest US, western Canada and Ontario – added these low cost, high production rates could also be achieved in 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,” he said.

Halawa Quarry general manager Don Matsumura said the ultimate goal would be to eliminate the need to import sand from British Columbia by producing No. 4 product (-40mm) using the CV229 on-site.

“This machine asks lots of questions of us, like the feed it needs and the moisture it can handle,” he said.

“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, from the savings the CV229 will give us comparatively in terms of production. The low parts wear further validates this investment. Changes of parts on the older models were made every month. With this one, no changes have been needed for five months.”

Source: Sandvik Construction

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