Synthetic solution
November 1, 2005 By: Bill Elverman Pit & QuarryA California producer finds a way to reduce blinding and wear on screen decks
Regarding crushing and screening, Gary McCall, area manager for Hanson Aggregates' San Diego-area operations, says, "Things have not really changed in the last 150 years. You take large rocks and put them in a machine to make little rocks, and then you run that material across something with little holes in it and you sell what comes out."
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McCall acknowledges this is an overgeneralization, but the crux of his argument is accurate. Machines have added more steel and horsepower, but the basic technique has stayed the same. It reflects the fact that changes in this industry can be slow to take hold.
Synthetic screening media, for instance, has been available for decades. Yet many in the industry don't know its benefits and have been reluctant to try it over familiar wire cloth. Hanson Aggregates' facilities in Southern California, however, had been experiencing problems with blinding and excessive wear on its wire screens. A switch to Polydeck synthetic screens proved to be the right solution and also increased production, reduced noise pollution and made the workplace safer, the producer says.
Alluvial deposits
McCall oversees nine of Hanson's operations in the San Diego area and has partial responsibilities at a Hanson plant in Mexico. His sites produce up to 5 million tons of concrete and asphalt aggregate each year. While sites vary from alluvial deposits to "drill and shoot" quarry operations, a common problem was seen in the company's screening process — especially on lower decks and in its manufactured sand production.
"Particularly with the alluvial deposits," McCall says, "and even here [at the El Cajon quarry], with all the dust control that we use, our screens would blind over. There was, on average, about an hour of production per day spent cleaning screens."
Figure 1 shows the extent of the blinding that occurred with steel wire cloth at Hanson's Santee plant. The wasted time cleaning screens combined with decreased output caused by blinding forced McCall to take action.
 Figure 1: Wire cloth screen is blinded over at Hanson's Santee plant. |
Three years ago, Alan Tindall, regional sales manager for Polydeck Screen Corp., approached McCall with a potential solution to the blinding problem: synthetic modular screens to replace steel wire cloth. Tindall introduced his company's Rubberdex Flexi modular rubber screens with the claim that a flexible, rubber screen would prevent build-up often experienced on rigid, steel wire screens.
As seen in Figure 2, this claim proved accurate, and the blinding problem was solved. The 40 durometer rubber screens provided the perfect combination of flexibility to reduce blinding and strength to improve wear characteristics. In fact, McCall hasn't had to replace a single modular synthetic deck in three years. The product has helped improve aggregate production, increase employee safety and reduce noise — all while driving costs down.
 Figure 2: The deck is free of blinding after installation of synthetic screening media. |
"We've seen — depending on the site — at least a 10 percent improvement on a daily basis just in plant availability," McCall says, "which equates to additional product on the ground for the same cost."
McCall allows that synthetic modular screening media has a higher up-front cost than wire but is quick to point out that, in the past, he would have to change each wire deck once every two to three weeks. Match that with the added labor required to constantly check for blinding on the decks, the associated plant downtime and the energy spike when firing the plant back up and, McCall says, the synthetic modular screens quickly pay for themselves.
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