Stationary vs. Crawler-Mounted Feeder-Breakers

Geordie Edmiston
By: Geordie Edmiston July 19, 2019
Both Stationary Feeder-Breakers and Crawler-Mounted Feeder-Breakers are used for the size reduction of ROM coal. While the design is generally the same, Stationary and Crawler-Mounted Feeder-Breakers have a few key differences.

Feeder-Breakers are designed for stationary, portable or semi-mobile crushing operations. They have enabled mining operators to increase production and improve material handling both above and below the surface. 

They can be located under hoppers to accept feed from haul trucks, have an integral hopper to accept feeds from loaders or have a dozer trap design employing an open intake for charging by a dozer, shuttle car or other methods. 

Generally, Feeder-Breakers accept ROM feed material and reduce it to a conveyable product for ease of handling and further downstream sizing. 

Design

Design elements of the feeder portion and breaker assembly, whether we are talking about a stationary or a crawler-mounted design, are essentially the same.

By design, Feeder-Breakers employ a drag chain/flight bar-style conveyor connected at either end by steel shaft assemblies equipped with sprockets and bearings. The breaker mechanism is a horizontal rotor that crushes material against the flights and conveyor deck and is located toward the discharge end of the unit. 

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The crawler-mounted design employs only a single drag configuration; however, depending upon capacities, stationary feeder-breakers may be a single or dual drag design. They are ideal for performing the primary crushing of ROM feed and reducing it to a conveyable product. This equipment is an essential piece for moving material out of a hopper, silo or from stockpiles, as well as for metering material into a crusher, truck or onto a conveyor belt. 

Chain and flight

The chain and flight concept has been around for many years and is a proven mechanism for moving bulk materials at varying rates. The smooth, steady travel of the conveyor is preferred over vibratory feeders when dust generation is a concern, and the chain and flight design can withstand the impact of crushing when used in conjunction with a breaker. 

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McLanahan employs an engineering-class roller chain of selected duty classes along the outer edges of the conveyor width. At prescribed pitch intervals, corresponding with the opposite side, an extended pin link provides the attachment of the flight bar. Flight bars are manufactured from solid steel and provide spacing between chains, as well as the means to drag the material. The end of each flight is machined and drilled to accept the pin attachment. In some applications where there is often heavy loading on the deck, an additional link attachment is utilized on periodic flights to prevent chain spreading and excessive side bar wear.

Head and tail shaft

The drive end of a feeder-breaker is the discharge end. The driven shaft, or head shaft, is constructed from heat-treated, alloy steel. A hardened steel sprocket is keyed to each side of the shaft in line with each chain. The head shaft is mounted to the side frames of the machine with flanged or pillow block bearing housings containing spherical roller bearings. At the intake end, the heat treated alloy steel tail shaft utilizes one keyed and one floating sprocket; however, the spherical roller bearings are of take-up design to allow for tensioning of the conveyor chains. Tensioning is accomplished by a grease cylinder system with the setting held in place by mechanical shims. Both head and tail shaft assemblies are designed to be easily removable without extensive dismantling of the machine.

Drive

There are two methods to drive the head shaft of a feeder-breaker – hydraulically or electro/mechanically. The hydraulic option utilizes a shaft-mounted, variable speed hydraulic motor with flow provided by an onboard or stand-alone hydraulic power unit. The electro/mechanical option utilizes a shaft-mounted reducer in combination with an electric motor and high speed coupling. A variable frequency drive (VFD) electrical package can be supplied to add variable speed to the mechanical option. The choice of high speed couplings between the motor and reducer include fluid, friction or shear tube. The direct drives and drive coupling feature set McLanahan apart from the competition by eliminating noisy chain drives and the nuisance of shear pins.

Decking

McLanahan fabricates all of its feeder-breakers with up to 1” (2.54 cm) thick steel plate that is reinforced by steel plate ribs and gussets. Solid steel deck plate is covered with renewable, abrasion-resistant steel liners to provide a surface with long wear life that is required to withstand constant material impact and the dragging action of the flights and abrasive materials. For added life, chromium carbide overlay can be supplied as an alternative deck material.

Controls

Functional control of the breaker and conveyor is accomplished through a programmable logic controller (PLC) that can interface with downstream conveyors and belt scales and be tied in with central controls. The control logic provides timed sequence starting of the conveyor and breaker, as well as timed shutdown of each when idle. This saves wear and tear on the machine and promotes safety. 

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The crawler-mounted feeder-breaker is a machine specifically designed for underground mining in room and pillar mines. Many times, the crawler-mounted feeder-breaker is an afterthought when it comes to purchasing the necessities for a mine; however, it should be recognized as an extremely important, multi-functional piece of equipment that operates overall as a workhorse in many ways. Not only is this piece a mobile unit that advances with the mine face, but it allows producers to crush and convey material all in one machine.

Initially known as a feeder or feeder car, the crawler-mounted feeder-breaker has undergone many changes over the years. This unit not only conveys, or feeds, material onto a conveyor belt at a metered rate, but it also de-lumps, or breaks, oversized feed and tows the section tailpiece/belt during face advancement. 

Now equipped with many add-on features, crawler-mounted feeder-breakers can include touchscreen PLC controls with diagnostics, electric distribution panels and power takeoffs that power auxiliary equipment, dust and fire suppression systems, area lighting, improved panic switches and emergency stopping devices, high-powered track assemblies, remote tram controls, warning horns and strobe lights, and various starting devices such as manual pendants, photo cells, and infrared transmitters and receivers. Some operators have also added a rock duster and elaborate filtration systems to filter the water that flows through the onboard dust suppression system and onto the miner for dust suppression at the cutter head.

With an emphasis toward production and panel development in high-capacity longwall mining, today’s crawler-mounted feeder-breaker is expected to accept a payload of 20 tons or more from haulage equipment in continuous discharge so that the haulage operator is not delayed returning for the next load. Decreased cycle times of the haulage runs typically relate to increased productivity and face advancement. Since shuttle cars can routinely discharge 20 tons in approximately 40 seconds, the crawler-mounted feeder-breaker must be designed with a well-built chain and flight assembly, powerful conveyor drive and ample storage capacity to accept the load as fast as the driver can discharge. It must then meter the crushed product onto the belt at a specified rate to match the capacity of the particular section of the conveyor.

In addition to handling the large volume of material, the machine is expected to handle almost anything it is fed. Though primarily designed as a coal breaker, it is common practice by mine operators to dump slabs of rock from roof falls, overcasts or broken bottoms into the crawler-mounted feeder-breaker. It is also highly possible that occasional pieces of wood from cribbing and mine timbers, roof bolts, water hoses and other mine debris will find their way into the machine. Speed sensors are employed to circumvent major damage to components if the machine encounters a truly unbreakable object, while torque control couplings and hydraulic relief have replaced the archaic shear pin method of drive protection.

When it becomes time to add belt to keep up with the advancing mine face and to keep the haulage runs at a manageable distance, the crawler mounted feeder-breaker is the preferred machine to tow the tailpiece. Some units are designed and equipped with an integral belt tail pulley system that acts as the tailpiece. When pulling belt, the weight of the machine, power of the crawler drives and design of the tracks determine the amount of pulling power available to effectively advance belt lines that can run up to 18,000’ (5,486.4 m) for some large longwall panels. While some older designs could barely pull themselves, today’s crawler-mounted feeder-breaker designs must not only have great tractive effort, but must also be able to tram over rough, uneven bottom conditions that can be encountered underground. 

Whether it is a Stationary or Crawler-Mounted Feeder-Breaker design, they both employ a drag chain and flight bar-type conveyor, and a breaker mechanism made of a horizontal rotor to crush material against the flights and the conveying deck toward the discharge end. The conveyor system can be driven either hydraulically or mechanically, while the breaker assembly is generally driven mechanically. Depending on capacities, feeder-breakers may be of single or dual drag design. In general, feeder-breakers are ideal for the primary crushing of ROM feed and reducing it to a conveyable product, while crawler-mounted feeder-breakers take one step further in being mobile — perfect for room and pillar mining in production sections and in preparation of longwall panels.

Tags: Mining, Crushing, Coal