What’s New in Milling: Barmac Crusher

Not new to the overseas aggregates industry, but a relative newcomer to Canada, is the Barmac crusher, distributed by Wajax Industries of Markham, Ont. Developed and manufactured in New Zealand, this tertiary crusher applies the principle of crushing rock on rock to keep wear to a minimum.

Feed, ranging up to a maximum of four inches, but more frequently of about 2 1/4 inches, is flung from a high-speed rotor against a bed of impacted, crushed rock. The rock is further subjected to impact crushing when it drops through the stream of rock leaving the rotor. A high reduction ratio is achieved by this impact-attrition process, and closed-circuit operation will make a final product in the passing 5-to-20-mesh range. Practically all of the wear and tear is absorbed by the rock surfaces themselves.

The interior of the crusher, the crushing chamber, is designed to create a bed of crushed rock concealing practically all of the metal components. Those parts that are exposed are the rotor itself, which will require regular hardfacing, and plating on the path of the rock flow. It is claimed that the latter can be replaced by one man in less than an hour. Otherwise, the parts are of mild steel and take very little wear.

The Barmac crusher comes in a number of sizes and two different forms. The Duopactor is the more common model and its crushing action is described above, i.e. by dual impact. The original model is the Rotorpactor, in which the feed is impacted once in the crushing chamber, and falls by gravity to discharge.

The Duopactor is offered in three sizes, ranging from 30 to 600 tonnes per hour and, in horsepower, from 25 to 600. Clearly, power and capacity will be determined by the characteristics of the rock and the size reduction effected. Similarly, if the crusher is to take advantage of the differential hardness of the rock, then field testing may show one model more suitable than the other.

The crushers made their first appearance in aggregate production for the construction industry and for road-building, where feed ranged from siliceous gravels to basalts. The field was later expanded to include metallurgical slags and, in Canada, syenitic rocks and quartzites. Until recently, the Indusmin Division of Falconbridge operated a number of pits in Ontario and Quebec producing nepheline syenite, feldspar and crushed silica sand. At these plants, five Barmac crushers variously crushed run-of-quarry quartzite to 30-mesh sand, syenite to 40-mesh and common sandstone to natural grain-size sand. Of particular interest is the fact that the quartzite is broken across the grain rather than along grain boundaries, and comparable observations are noted from time to time in the vendor’s literature. (The Indusmin Division has since been sold and is now known as Unimin Ltd. The company declined to release information on the plants it now operates and the above data were retrieved from a number of private sources.)

Cal Graphite uses a Barmac crusher to produce a minus-16-mesh feed that goes directly to a series of column flotation cells. This is the new graphite producer situated near Huntsville, Ont.

It should be emphasized that the size reduction possible with the Barmac avoids the need for rod milling, where this precedes the ball mill. In other circumstances, it will produce a much finer ball mill feed than is usually the case. All in all, the Barmac crusher represents a major advance in the closing of the gap between conventional crushers and impactors and could herald significant reductions in down-time and in maintenance costs.

Circle Reply Card No. 119

DISC FILTRATION SYSTEM

Outokumpu Equipment Canada of Mississauga, Ont. is introducing a filtration system to the Canadian market that has been successfully adopted at more than a dozen operations so far. The majority of these installations are in Scandinavia; the first was in Finland in 1985.

The unit is a disc filter that produces a much drier cake than is usually the case and consumes only a fraction of the energy of conventional filtration. The key elements of the filter are microporous, ceramic filter plates. The plates are composed of fused alumina that have an active pore diameter of 0.5 to 1.5 microns. Because of the mechanical strength and chemical inertness of the alumina, the plates may have a working life in excess of a year and will function in a variety of chemically reactive solutions.

The initial stage of filtration mimics the initial stage of the conventional filter — the filter plate dips through the pulp and a cake starts to form — but it is the plate that is the filtration medium rather than the filter cake itself. Once the plates are coated, there is sufficient surface and interfacial tension between the walls of the pores and the filtrate to prevent the passage of either solids or air and a nearly complete vacuum can be maintained. The filtrate passes through the pores by virtue of the vacuum and capillary action.

When the filter cake of an ordinary filter reaches the air, the cake will start to crack as it dries, and the vacuum will break down. Because of the microporous plates and the high surface tension, no air can pass and a high vacuum is maintained continuously. This dictates a much smaller vacuum pump and much lower power consumption than is required for conventional equipment. The filter assembly is completed with an ultrasonic plate cleaner, which can be augmented by a chemical back-wash if required. The filter is intended for the same service as the pressure filter, i.e., the production of a dry cake.

Circle Reply Card No. 120

ACCURATE FLOWMETER

A laboratory quality electronic flowmeter, the Series 300, produced by the McMillan Co. of Copperas Cove, Tex. has been designed to measure gas flow rates from 10 ml per minute to 200 litres per minute in 11 ranges with an accuracy of 3%. The visual display is a led bar graph which lights up one red led bar at a time. This light bar simulates the ball in a conventional rotameter flowmeter and is visible for a distance of up to 20 ft. (six metres) so technicians can observe the flow rate even in dimly lit laboratories.

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WET GRINDING SYSTEM

Mineral Processing Systems of York, Pa., which has been designing vertical stirred mills since 1979, is now manufacturing a system for wet grinding. The “VertiMill,” as it is called, was developed as an energy-saving alternative to the tumbling mill in fine grinding applications; the finer the product, the greater the power savings. The mill’s efficiency is due to the precision with which an accurate cut can be made of the overflow product, which, conversely, reduces the amount of extreme fines. If an ultra-fine product is required, the circuit can be reconstituted to generate the maximum amount of fine material.

The mill can grind any material less than 1/4 inches top size and is particularly suited to producing products 200 mesh and finer. Earlier models of the VertiMill principle are in present use by Canadian companies (among others) in capacities of up to approximately 50 tons per hour.

Circle Reply Card No. 122

POSI-TURNER

Park Industries of St. Cloud, Minn. has recently introduced its new “Posi-Turner” for suspending and rotating large, bulky, hard-to-handle objects in a safe and efficient manner. The device has a powerful roller system, combined with heavy-duty springs, that rotates any object smoothly, backwards and forwards 360deg or more. Mines might find the device useful in the headframe or the mill. The piece of equipment or machinery to be moved may be up to 40 ft. (12 metres) in length and up to 50,000 lbs. (22,500 kg) in weight.

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PULVERIZER

A pulverizing system has been developed by Economy Metals (tcd) of Baden, Pa. It promises a very short residence time in the crusher — less than one second for mine feed up to 12 inches pulverized to 325 mesh in a 100-ton-per-hour. machine. Power consumption, at 13 to 15 kwh per ton of feed, is low. A smaller floor space is needed, compared with a conventional ball or roller m
ill of the same feed rate. And air classification has been added to ensure proper product sizing. The machine has been tried on several hardrock ores, ferrosilicon, calcined alumina, limestones and coals.

Circle Reply Card No. 124

HAMMER IMPACT MILLS

Built in six sizes with capacities ranging from fewer than 500 lbs. to more than 40,000 lbs. per hour, the new Series 3 Imp mill system of ABB Raymond is capable of taking feed of nominal one-inch size and reducing it to five microns on suitable materials. The Imp mills are air-swept, swing-hammer impact mills and can be equipped with one of several air classifiers. They may also be fitted with flash drying systems and with electronic controls. A microprocessor-based system, “Raytrol,” monitors the mill’s power consumption and adjusts the feed rate to compensate for changes in feed, grindability or bulk density. The system can be hooked up with a computer, according to the Lisle, Ill.-based company.

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SYMONS CRUSHER

For years now, the Symons crusher has been the standard in most rock-breaking plants because of its high productivity and mechanical simplicity. The crusher has only three moving parts — head, eccentric and countershafts — which makes for relatively low maintenance costs. Nevertheless, clearing a choked crusher can often take several hours because the crushing chamber must first be emptied and the tramp iron either burned or washed out. Time is consumed in releasing the hold-down springs and then raising the adjustment ring. Nordberg Inc. has been investigating the problem for a number of years and developed a hydraulic lift in the mid-1970s. This system, using high-pressure hydraulics to open the crusher against the force of the hold-down springs, provided only a limited lift of about 1.5 inches. Despite the small lift, the system was a step in the right direction, and a number of crushers have since been modified to incorporate a new arrangement in which the springs are dispensed with entirely and hydraulic pressure alone used to maintain the desired crushing gap. A lift of up to five inches is obtainable using a low-pressure hydraulic system and a stalled crusher cavity can be cleared in little more than 15 minutes. All the operator has to do is move a lever.

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SUPER MAGNET

A permanent magnet developed by Eriez Magnetics and available from Eriez of Canada is claimed to be up to 25 times more powerful than conventional magnets, with no increase in size. The material from which the magnets are made is Erium 3000. These super magnets can be used on wet or dry flows and the Erium 3000 is sufficiently powerful not only to attract weakly magnetic species but also to hold them so tightly that wipe-off by the flow of product is markedly reduced. The magnets are available in a number of configurations to fit wet or dry applications. They may be in one of several forms of grate, plate separators and drum and roll arrangements. In addition, there are several trap assemblies available for pipelines up to 18 inches in diameter where it is necessary to remove magnetic contaminants from a liquid or pulp flow.

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BIOLIFT REACTOR

After many years of laboratory study and extensive pilot testing, the bioleaching of refractory gold ores has at last seen commercial application, first in South Africa (1986) and more recently in Brazil, both under South African auspices. Eimco Process Equipment of Mississauga, Ont. has also been deeply involved at the pilot plant level and has recently unveiled its new “Biolift Reactor.” The reactors are available in sizes ranging from 18,000 to 300,000 gallons and incorporate the latest waste-water treatment technology with particular modification for the demanding requirements of biochemical leaching — that is, allowance for the high level of suspended solids (up to 40%), the necessity for maintaining close control of temperature, and the need for a high level of aeration.

Aeration is accomplished by diffusers mounted on the rake arms that rotate near the bottom of the tank. Process air at about one atmosphere, is supplied through a rotary valve above the reactor drive and distributed to the diffusers. These are self-cleaning flexible membranes producing bubbles ranging from 0.5 to 3 mm in diameter at the ideal depth of 6.5 metres in the slurry. As well as providing the oxygen and carbon dioxide needed by the process, the bubble stream induces an upward circulating force in the pulp and this, in turn, is opposed by a downward current imparted by the axial flow impeller situated higher up the tank. A complete turnover of the pulp occurs and a near-perfect blending of the constituents is ensured.

Any coarse particles that sink to the bottom of the tank are raked to the central shaft and returned to circulation via a low pressure air-lift. In practice, two, three or more reactors would be arranged in series followed by filtration, re-pulping, ph adjustment and cyanidation in the case of a gold ore. Should the ore be arsenical, the filtrate will carry more or less arsenic as well as iron and require suitable precipitants and stabilizers before it is in an acceptable condition for disposal.

Circle Reply Card No. 128

URETHANE SHOES

Sand classifier shoes made from urethane are said to last longer than ni-hard, white iron, steel or rubber shoes. These are now being produced by Durex Products of Luck, Wisc. These quality wear parts withstand heat and cold, resist oil, grease and solvents, and their high-tensile strength resists tears.

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HIGH-RATE THICKENERS

Another innovation by Outokumpu is its new series of high-rate thickeners. The Supaflo thickeners range in size from one to 30 meters in diameter and are characterized by the introduction of the feed pulp at the base of the tank rather than from the top.

Settlement of solids, accelerated by a controlled dosage of polymer flocculant, forms a loose, cohesive mat that effectively filters the incoming pulp. Overflow is unusually free from suspended solids and the underflow density can be maximized by increasing the polymer dosage rate. The Supaflo is claimed to thicken pulps three to 10 times faster than conventional settling units and, consequently, will be only one-third to one-half the diameter of the conventional unit. Other advantages are low capital costs, better process control and short retention time.

Circle Reply Card No. 130

FILTRATION BAGS

York Fluid Controls of Brampton, Ont. markets the 3M series 500 filter bag. The 500’s layer design incorporates more than 32 sq. ft. of filter area using by-pass transport and final filter layers.

Circle Reply Card No. 131