MILLING: WHAT”S NEW AN ATTRACTIVE LINER

Thanks to a new grinding concept in the form of rubber magnetic mill linings, considerable savings in energy and grinding media consumption can now be achieved. “In some cases, it (the magnetic liner) can cut liner wear costs down to nothing,” says manufacturer Trelleborg Inc. of Sweden. The technology consists of powerful ceramic magnets which are attached, without any bolting, to the mill shell. Sufficient magnetic material from the ore is attracted to the inner surface of the magnets, thereby forming a protective layer — the ore bed. The ore grinds against this ore bed, which protects the magnets. This eliminates the need to replace the liners. “In other words,” says Trelleborg, “we have now created a potentially non-wearing lining.” The ore bed layer consists of a hard stationary layer of fine particles at the bottom and an outer layer of constantly replaced coarser material. The total thickness of the liner is between 2 1/2 and 3 inches. The magnets used are hard ceramic materials composed chiefly of iron oxide and barium or strontium carbonate. (In ore which has no magnetic minerals, the protective layer in the mill is formed by minute particles of steel which are worn off the grinding balls or rods.)

In March, at a Toronto conference on new Swedish technology, the president of Trelleborg’s Ohio subsidiary compared the magnetic lining with other, more common linings. “A traditional lining, steel or rubber, wears by time,” explained Roland Andersson. “By this wearing, the profile will change, thus creating different grinding conditions. The outer layer of the ore bed (by comparison), where the magnetic forces are weaker, will continuously be removed and replaced. This means that the lining keeps its profile constant, resulting in a constant grinding process.

“One can control the mill throughput easily and keep it at a maximum. As the total lining thickness, including the protective layer is much thinner than traditional linings, it will also increase the effective mill diameter and, consequently, the mill capacity.”

The largest costs in grinding ore are energy and grinding media (balls and rods). The success of the magnetic mill lining is its ability to eliminate lifter bars and reduce the thickness of mill liners. And since the magnets need never be replaced, there are no bolting, fixing or catchment devices involved.

Since the liner itself can help reduce energy and grinding media costs, it can actually pay for itself, Andersson said. “So far, all magnetic mill lining installations have shown a considerable savings in energy costs. The figure varies from application to application, but a savings of 10%-20% is possible * * * The liner profile, in turn, is the reason for the considerable reduction of grinding media costs. Here we have noticed anywhere from a 5% to 50% cost reduction.”

The only limiting factor of the magnetic mill lining concept is that the iron oxide ceramic is a brittle material. If it is exposed to too much impact, it can be crushed. However, Trelleborg is busy researching the problem in order to develop a protective layer on the lining. Poly-Met

In direct competition with Trelleborg is Skega AB, also of Sweden, which has developed a new rubber lining for tertiary and secondary grinding mills. By combining the strength quality of steel with the resiliency of rubber, the company has increased the life of lift bars in grinding mills.

The main advantage of the Skega Poly-Met lining is shorter downtime, which means the added production pays for the higher cost of the linings.

The lining was developed in co- operation with the Canadian mining industry and Skega’s Canadian subsidiary. “Skega has made quite a lot of progress in Canada,” says Skega AB’s technical director, Gustav Nilsson. “And this is partly the result of the open-mindedness of Canadian mine operators.” Scalpers

A full line of vibrating scalpers is available from Simplicity Engineering, a Lukens Inc. company based in Durand, Mo. Designed to handle run- of-quarry or run-of-mine material, the scalpers are available in 2-bearing and 4-bearing models.

When installed ahead of a crusher, the scalper performs coarse sizing and provides a controlled, high-capacity flow of material, Simplicity says. It eliminates crusher overload due to material surges, as well as reducing crusher wear and minimizing production of fines by bypassing material already at or below the desired size.

The scalpers are available in three deck styles: rail-type grizzly deck with tapered longitudinal openings, fabricated sub-deck covered by perforated plate, or a one-piece welded crown deck with screen cloth. Plate and screen decks can be supplied with or without wear bars. Rail-type decks can be furnished with replaceable wear caps. Units may be single- or double- deck.

Two-bearing scalpers are built for high performance and minimum maintenance. Decks are secured to the side plates with fasteners, providing a permanent structure that does not require retightening. Four-bearing scalpers provide smooth, positive action under all loading conditions, Simplicity says. The company adds that rugged H-beams are tied with strong channels to form a rigid main frame, assuring accurate component alignment.

A wide range of sizes may be engineered for the specific application, up to 8×24 ft, to handle capacities in excess of 4,000 tons per hour. Dry/Liquid Feed System

The new PolyBlend cents Feed System offers considerable versatility in feeding polymers, says Stranco of Bradley, Ill. The system includes all the operations required in polymer preparation (dosing, dilution, aging and activation). And since the system is programmable, every polymer gets the exact treatment it requires. The result is that users can see a dramatic improvement in flocculation and sludge dewatering. Also, since the system can handle any polymer, equipment needn’t become obsolete if the type of polymer used at some future date changes.

A compact, plug-in system, Polyblend is easy to install and operate. Unlike many batch systems, where the performance varies depending on who is running it, the Polyblend system is fully automatic and runs unattended.

In the new dry/liquid polymer feed system, the operator can change from dry to solution to emulsion polymer with flip-of-the-switch convenience. Another unique feature is that a single system can feed differently blended concentrations of polymer to different application points. Thus, one unit can do the work of several. New Mixer

Kentucky-based Littleford Bros.’s fkm Series batch mixer with its unique plow-shaped mixing elements is used to mix coke, carbon or graphite with a pitch binder to form a uniform granulate suitable for molding. The unique mixing action is the key to its ability to perform difficult mixing requirements. The elements create a fluidized mixing action which results in a homogeneous mix in a fraction of the time required in conventional mixers. In the process, the carbon can be mixed with liquid pitch or ground solid pitch. The mixer offers significant reduction in mixing cycles over current industry practice, the company says.

The resulting molding composition (ready mix), when using liquid pitch in the mixer, will have a bulk density of about 60 lb per cu ft and a grain size of 2-10 mm. Total mixing time is about 25 minutes.

When using solid pitch, the finished product (molding composition) is a well-mixed granulate of 3-20 mm grain size witha bulk density of about 60 lb per cu ft.

The mixer is equipped with special abrasion-resistant mixing plows, and is available in standard sizes ranging from the 300-L/11-cu-ft total capacity model to an 8,000-L/283-cu-ft unit. — 30 —