Overview of Lafarge's Caledon wash plant which produces quality asphalt and concrete aggregates for the company's operations in the Greater Toronto Area.

Spray on urethan combats wash plant wear at Lafarge pit

By Andy Bateman, Engineering Editor

A new approach to wash plant screen wear is being tested at one of the country's major sand and gravel operations.

A spray on urethane surface treatement has been applied to selected areas on both wash plant screens to improve plant availability and component life.

    Lafarge North America's Caledon, Ont. pit ranked 16th in last year's in Aggregates & Roadbuilding's Top 20 sand and gravel operations, reporting total production of 989 000 tonnes for 2001. That figure continues to grow, with plant manager Dean Sanderson reporting more than 1 million tonnes of total production for 2002. The operation's wash plant plays a significant role in this continuing growth, producing quality asphalt and concrete aggregates for the company's plants in the Greater Toronto Area.
      Using technology more often seen in underground mining applications, the Caledon team is experimenting with a spray on urethane surface treatment that promises effective protection of exposed steel surfaces in wet or abrasive conditions. The treatment has been applied to selected areas on both of the wash plant's screens and is part of the team's overall goal to improve plant availability and component life. Treated areas include longitudinal strips down the inside of each screen frame, next to the top and middle screen decks, together with the eccentric housing mounted over each screen. During operation, these areas are continuously wetted by wash water spray, with the screen frames also subject to the scouring action of material passing down the screen. Protection of the eccentric housing is essential as corrosion here can, in extreme cases, result in perforation through the housing wall and leakage from the eccentric's oil bath.

The wash plant receives 22 mm minus feed at a rate of 500 tonnes/h.

      Under normal operating conditions, the two Cedarapids 5x16 triple-deck screens receive 22 mm minus feed from a surge pile at an average rate of 500 tonnes/h. The feed material is sized by Major Wire square mesh screen cloths with openings of 13.2 mm and 6.3 mm on the top and middle decks, together with Major Wire's 4 mm triple chute slotted screen on the bottom deck. Clear sizes, 6.3 mm and larger, are stockpiled while minus 6.3 mm material goes to an 11-station Eagle Iron Works (EIW) Autospec classifier. The fine aggregate fractions from the classifier, together with a metered amount of 6.3 mm clear, are dewatered by an EIW twin 1372 mm fine material dewatering screw and stockpiled. Fine sand from the classifier reports to an EIW 1118 mm single fine material dewatering screw and stockpiled for cable bedding and fill applications.

Fine aggregates are dewatered at the wash plant by an EIW 1372 mm twin-screw unit.

      According to the urethane coating supplier, the surface treatment can usually be completed on site if required. In this case, field service company B & R Rubber applied the protective coating while the screens were being rebuilt at Grant Aggregate & Industrial Supply Inc.'s shop last winter. The treatment process includes the sandblasting of the selected areas and the application of a primer coat. Polyrea-urethane is then applied at 180Å F at 3000 psi to the chosen build up thickness of 3.2 mm, 4.8 mm or more if required. The spray on method is said to allow access to hard to reach locations and, once treated, equipment can be immediately put back into service.
      Observes Sanderson: "It will be interesting to see how this protective coating performs Æ if it delivers on the required durability, we will certainly consider it for other applications."

May/June 2003 issue

Aggregates and Roadbuilding Magazine
4999 St Catherine Street West. Suite 315
Westmount, Quebec H3Z 1T3
Tel: (514) 487-9868 Fax: (514) 487-9276
EMail: rocktoroad@sympatico.ca

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