bridge | memory alpha | fandom

bridge | memory alpha | fandom

On Starfleet ships, it was generally located near the top and front of a vessel. From here, the commanding officers supervised all ship's operations, ranging from vessel course control to tactical systems.

On Starfleet vessels, the bridge was usually located on Deck 1, on top of the vessel's primary hull. The bridge was the nerve center of every starship, and it was manned by the top officers of each department except for engineering and medical. There was typically an engineering station that the chief engineer could use when on the bridge, as well as science stations that the science officer or chief medical officer could use.

The commanding officer could supervise all the ship's operations while seated in the command chair, typically located in the center of the room, while having visual access to all major personnel stations and viewscreens, facilitating the decision-making process. By the mid-24th century, the standard was that a first officer was assigned to assist a ship's captain in this process.

The forward bulkhead of the bridge was typically dominated by the main viewscreen. Directly in front of this was usually the helm console, from where navigation and vessel course control were carried out.

Many of the support stations that were present on 23rd century bridges were combined into one post by the 24th century, mainly that of the operations officer. Some bridges featured an operations console alongside the helm station, from where the officer on duty had access to internal systems control, communications, sensors, resource scheduling, and hardware and system usage.

Each bridge typically featured several supportive consoles for engineering, gravity control, damage control, environmental engineering, sciences, and library computer, most of which did not necessarily need to be manned under normal circumstances. Internal security along with weapons control could be found at the security station.

The bridge command stations provided seating and information displays for the commanding officer and one or two other officers, typically including the first officer. The command chairs were located in the center of the bridge, to maximize interaction with all key bridge personnel, while permitting an unobstructed view of the main viewscreen.

Typically, the armrests of the captain's chair featured miniaturized status displays. Using a keyboard or vocal commands, the captain could use these controls to override the basic operation of the starship. (TOS: "Court Martial"; TNG: "Peak Performance", et al.)

The 24th century flight control position, also referred to as the conn, evolved from the 23rd century helm and navigation positions. The officer manning the flight control console was responsible for the actual piloting and navigation of the starship. Despite many of these functions being heavily automated, their critical nature demanded a humanoid officer to oversee these operations at all times.

Many shipboard operations involved scheduling resources or hardware that affected a number of departments. In many such cases, it was common for various operations to present conflicting requirements. It was the responsibility of the operations officer to coordinate such activities so that mission goals were not jeopardized.

The operations position, also known simply as ops, evolved from older 23rd century positions. The bulk of the duties held by the helm and navigation positions were combined into the conn position. Other functions of the helm panel, such as internal systems control, became the purview of ops, as well as some communications and sensor system usages.

The bridge station dedicated to defensive systems control and starship internal security was tactical. Parts of the default control layout presented the security officer with information readouts dealing with the internal protection of the starship and its crew. A wide variety of starship defensive systems were available to the chief tactical officer (sometimes doubling as chief of security), ranging from the defensive shields to phaser and torpedo systems, as well as intrusion detection systems.

Every Starfleet bridge also included several supportive consoles and backup stations. These could include consoles for planetary sciences, engineering, mission operations, and environmental control. Most of these were meant to relieve the senior bridge officers of secondary duties during alert and crisis situations.

Mission ops provided additional support to the operations officer, and was specifically responsible for monitoring activity relating to secondary missions. Mission ops was responsible for assignment of resources and priorities according to guidelines specified by the operations officer and by operating protocols. This station was also responsible for monitoring away teams. (Star Trek: The Next Generation Technical Manual, pp. 41-42)

The environmental control console provided similar relief to the operations officer, monitoring the starship's life support systems. Due to the highly automated nature of these systems, this console was unattended under normal circumstances, but became of crucial importance during alert situations to maximize crew survivability.

The bridge's engineering station duplicated in simplified form the chief engineer's primary status displays from main engineering. The purpose of this station was to permit the chief engineer to maintain supervision over the engineering system while on the bridge.

When the crew of Enterprise NX-01 had to take shelter at the ship's catwalk in September 2152, Commander Tucker and Travis Mayweather built a "command area" within one of the compartments to replace the main bridge. Conn and the communications station included, the small area also included a provisional captain's chair, a cargo container with a netting, and place for Archer and T'Pol to sleep. (ENT: "The Catwalk")

Most of the bridges during the later half of the 23rd century shared a similar layout to that of the upgraded Constitution-class vessels, which evidently set the standard for bridge design and layout.

The Crossfield-class bridge was placed in a spherical section within the inner negative space of the saucer section. It possessed a wide window as the viewscreen, similar to Kelvin-type and Walker-class ships.

In the early half of the 24th century, before the introduction of the Galaxy-class starship, bridge design was based on the successful layout of the Constitution-class starship, featuring a single captain's chair in the center of the room with two consoles directly in front of it and additional consoles surrounding this central command area.

The Intrepid-class bridge was ovoid in shape. At the bridge's rear was a large bank of consoles and data-readout screens. Center of that area was the master systems display. Control consoles flanked it on either side, mission ops I to starboard and mission ops II to port.

Starboard of that information center, past the starboard side turbolift, was the chief tactical officer's console. This area was maintained mostly for internal security and combat situations. An identical station could be found on the other side of the bridge, where the operations console was found.

Two turbolifts provided access throughout the ship, and there was an emergency ladder which connected the bridge with lower decks. Forward of the upper ship operations areas were doorways to the briefing room at one side, and the captain's ready room at the other.

Directly forward of the central command area (where the captain and first officer were seated) and sunken down by two steps was the Conn. From here, the flight control officer served as helmsman and navigator for the vessel. To the Conn's right sat the chief engineer. The console allowed complete control over all engineering systems. Directly opposite sat the chief science officer in a similar console. (VOY: "Caretaker")

Behind the captain's chair, there was a small secondary tactical console located on the handrail. On the USS Voyager, this station was typically unmanned, however Seven of Nine used this station on several occasions, particularly on encounters with the Borg. Other crew members, such as The Doctor and B'Elanna Torres, used this station on occasion.

In between the captain's and first officer's chairs there was a small console which could be folded down when not in use, or opened and accessed by either officer. Like the larger consoles on the bridge a phaser could be stored within this unit.

After six years as production designer on The Next Generation, Richard James was no stranger to the legacy of Star Trek and the production requirements of episodic television. When given the assignment to create a new starship from the inside out, he had to start up from scratch.

Nothing had yet been established, and thus for his first meeting with Star Trek: Voyager's creators and producers, James decided to push the boundaries of everything that had gone before. Early concept sketches show bridge designs without the large viewscreen in the front of the bridge and command functions decentralized, obviously breaking the traditional bridge mold.

However, by exhaustively reexamining the dramatic requirements and technological underpinnings of the Star Trek bridge without preconceptions, James rediscovered the strengths of the basic template laid out by Matt Jefferies almost thirty years earlier. But with the broad strokes of the bridge's layout firmly embedded in Star Trek's past, James and his team went on to bring a fresh new interpretation to the heart of every Star Trek adventure, investing it with a sleek, efficient, and welcoming appearance that made Voyager something of its own the Star Trek for the nineties and beyond.

The central area of the main bridge provided seating and information displays for the captain and two other officers. The captain's chair was raised from the rest of the bridge officers, to that of the surrounding level which included Tactical and Operations. The two officer seats were equipped with fully programmable consoles for a variety of uses.

Directly fore of the command area was the conn officer, who faced the main viewer. To the port side of the conn officer, also facing the main viewer, was the operations officer's console, which was identical in size and design to the helm station. At the very front of the bridge chamber was a large viewscreen. In 2373, when the screen was not active, a standard bulkhead was present.

Aft and to the left of the command area was an elevated platform on which tactical and security consoles were located. To the captain's right, behind the tactical console, was the mission operations section of the bridge. Against the port side walls of the main bridge were the consoles for sciences along with others that were programmable for a multitude of functions.

Located against the aft wall of the bridge was a large master systems display monitor, similar to the one in main engineering. All relevant ship information (such as damage, power distribution, etc.) was displayed on the cutaway image of the vessel. This monitor could be used to direct ship operations and could be configured for limited flight control if necessary. Also located against the aft wall of the main bridge was the large engineering console. This had a smaller cutaway diagram of the vessel, which displayed all engineering-relevant data and showed warp fields and engine output.

There were two turbolifts on the bridge that could handle normal transit around the Sovereign-class starship. In addition, there was an emergency ladder that connected the bridge to lower decks. There was also one door, on the aft platform of the bridge, that led to the observation lounge, directly aft of the main bridge, with another door leading to the captain's ready room. (Star Trek: First Contact)

The bridge layout of the Defiant-class was compact, but nonetheless accommodated the familiar engineering, tactical, science, conn, and ops stations. The bridge module was sunken into a much larger deck 1 than on most Federation starships to provide added protection during combat situations. Access to the bridge was provided by two doorways at the back, located on both port and starboard sides. Just forward of the starboard entryway was the location of the ship's dedication plaque, as well as an auxiliary computer access panel.

The port side of the bridge housed the engineering and tactical I stations, while the starboard side featured the science and tactical II consoles. Because of its nearly exclusive role as a combat vessel, stations aboard Defiant-class vessels were designed with speed in mind.

The center of the bridge featured the lone captain's chair, which was on a raised platform and had a clear view of all bridge stations, as well as of the main viewscreen. On both sides of the command chair were separate control panels, allowing the occupant access to virtually every system aboard the ship. Between the command chair and the viewscreen was an integrated flight control and operations panel, capable of performing the joint duties of those stations' larger counterparts on other Starfleet vessels. Like all of the bridge stations on Defiant, the conn had been designed for maximum speed and efficiency of commands input by the operator, allowing the craft to be handled almost like a fighter when under the hands of a skilled pilot.

Flanking both sides of the viewscreen were two tactical stations, which had primary access to the ship's powerful pulse phaser cannons, torpedo launchers and various other special ordinance packages. Working closely with conn, the officers stationed at these consoles were responsible for firing the various weapons aboard the Defiant-class starship during combat operations. The purpose of the tactical II station was to lighten the load on its sister station, particularly in battle.

The Borg possessed the only known vessels not to have a discrete bridge, but whose controls were instead highly decentralized, being run collectively by the Borg drones. (TNG: "Q Who") However, Borg ships did have a command center known as the central plexus.

Jem'Hadar attack ships had a bridge that was very peculiar in that it had no chairs, and only two head-mounted Virtual sensory displays instead of a viewscreen. Only the Jem'Hadar First and leading Vorta were allowed to view the outside of the ship. (DS9: "A Time to Stand")

The bridge of the Terran Empire's NX-class ISS Enterprise was quite similar in appearance to that of its counterpart from the prime universe, only that it featured Terran Empire emblems painted on the walls. (ENT: "In a Mirror, Darkly") The bridge of Admiral Black's flagship, the ISS Avenger, was similar in appearance to that of the Enterprise. (ENT: "In a Mirror, Darkly, Part II")

Similarly, the only differences between the bridge of the 23rd century ISS Enterprise from the mirror universe and its counterpart from ours was the appearance of Terran Empire emblems appearing on walls and doors, and a high-backed throne-like command chair. Also, guards were stationed on the bridge under all circumstances. (TOS: "Mirror, Mirror")

The bridge of the Terran Rebellion's ISS Defiant was similar to that of the Defiant-class bridge from the prime universe, the vessel's schematics being based on specifications stolen from Starfleet at Deep Space 9. (DS9: "Shattered Mirror")

The alternate reality's Constitution-class bridge retained the largeness of the Kelvin-type bridges, as well as the use of the viewscreen as a window. It was larger than the prime or mirror universe's bridge, featuring more consoles in addition to the command chair, science station, communications station, helm, and navigation consoles, which were roughly in the same place. It was aesthetically much brighter and smoother, with white paint, blue monitor screens, more lights (that would bathe the room red when red alert was signaled), and even transparent touchscreen boards. A turbolift was located on the port side, while airlock doors were on the starboard side. (Star Trek)

internal structure of crusher

internal structure of crusher

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gyratory crushers

gyratory crushers

The belowimage shows a sectional view of a typical gyratory crusher. This type of machine is, by virtue of chronological priority, known as the standard gyratory crusher. Although it incorporates many refinements in design, it is fundamentally the same crusher that first bore the name of gyratory; its crushing chamber is very much the same shape; the motion is identically the same, and the method of transmitting power from belt to crushing head is similar. It is an interesting fact that the same similarity in essential features of design exists in the case of the standard, or Blake type, jaw crusher, which is something in the way of a tribute to the inspiration and mechanical ability of the men who originated these machines.

Essentially, the gyratory crusher consists of a heavy cast-iron, or steel, frame which includes in its lower part an actuating mechanism (eccentric and driving gears), and in its upper part a cone-shaped crushing chamber, lined with wear-resisting plates (concaves). Spanning the crushing chamber across its top is a steady-rest (spider), containing a machined journal which fixes the position of the upper end of the main shaft. The active crushing member consists of the main shaft and its crushing head, or head center and mantle. This assembly is suspended in the spider journal by means of a heavy nut which, in all but the very large machines, is arranged for a certain amount of vertical adjustment of the shaft and head. At its lower end the main shaft passes through the babbitted eccentric journal, which offsets the lower end of the shaft with respect to the centerline of the crusher. Thus, when the eccentric is rotated by its gear train, the lower end of the main shaft is caused to gyrate (oscillate in a small circular path), and the crushing head, likewise, gyrates within the crushing chamber, progressively approaching, and receding from, each element of the cone-shaped inner surface.

The action of the gyratory crusher, and of the other member of the reciprocating pressure family, the jaw crusher, is fundamentally a simple one, but as will be seen a great deal of thought and some very progressive engineering has been expended upon the design of crushing chambers to increase capacities and to permit the use of closer discharge settings for secondary and fine-reduction crushing (various crusher types).

Referring to the table, always available from the manufacturer, it will be noted that standard gyratory crushers are manufactured in commercial sizes ranging from 8 to 60 receiving openings. Capacities are listed, for minimum and maximum open-side discharge settings, in short tons per hour, and the horsepower requirements for soft and hard materials are listed for each size. The capacities, and the minimum settings, are based upon the use of standard (straight-face) concaves.

Primary gyratory crushers are designated by two numbers. These are the size of the feed opening (in inches) and the diameter of the mantle at its base (in inches). A 60~x~89 crusher would have an opening dimension of 60 inches (152 cm) and a diameter across the base of the mantle of 89 inches (226 cm).

To stand up under the extremely rugged work of reducing hard and tough rock and ore, and in doing so to maintain reasonably true alignment of its running component, the crushermust necessarily be of massive and rigid proportions, rigidity being of equal importance to ultimate strength. Regardless of the tensile strength of the metal used in the main frame, top shell, and spider, these parts must be made with walls and ribs thick enough to provide this rigidity. Therefore it is practicable to use close-grained cast iron, and special high-test mixtures of cast iron, for these parts, if the machine is intended for crushing soft or medium materials. When very hard and tough materials are to be crushed, the machine is usually strengthened by substituting cast steel in one or more of its parts.

Wearing parts in the gyratory crusher may be either chilled cast iron or manganese steel, depending on the character of the material to be crushed and the particular class of service for which the machine is intended. Standard crushers, in the small and medium sizes, are customarily fitted with chilled-iron head and concaves for crushing soft and medium limestone and materials of similar hardness and abrasiveness, because its relatively low first cost and excellent wearing qualities make it the most economical material to use when the service is not too severe. Manganese steel, which combines extreme toughness with unsurpassed wear-resistance, is the universal choice for crushing hard, tough rock regardless of the class of service or type of crusher. Even though the rock be quite soft and non-abrasive, it is general practice to use manganese steel concaves in the larger sizes of primary crushers because of the shocks attendant upon handling large and heavy pieces of rock.

The primary rockbreaker most commonly used in large plants is the gyratory crusher, of which a typical section is shown in Fig. 5.It consists essentially of a gyrating crushing head (521) working inside a crushing bowl (522) which is fixed to the frame (501).

Thecrushing head is carried on a short solid main shaft (515) suspended from the spider (502) by a nut (513) ; the nut fits into the seating of a sleeve (514) which fixes its position in relation to the spider and, therefore, to the frame (501). The lower part of the main shaft fits into a sleeve (530) set in an eccentric (527), to which is keyed the bevel driving gear (528) ; the bevel pinion (533) is similarly fastened to the countershaft (535) and engages with the bevel gear. The whole of this driving assembly is protected from grit and dust by means of a dust seal (524), (525), and (526).

The countershaft carries the driving pulley, and as it revolves it causes the eccentric to rotate ; as it rotates the main shaft gyrates and with it the crushing head ; the top of the shaft at the point of suspension has practically no movement. Although the motion of the head is gyratory, the main shaft is free to rotate in the eccentric and it actually revolves slowly in relation to the bowl, thus equalizing the wear on the mantle (519) which lines the head and on the concave liners (522 and 523) which comprise the bowl. Both mantle and bowl liners are usually made of manganese steel. The suspension nut (513) is adjustable and enables the crushing head and main shaft to be raised in relation to the bowl to compensate for wear. The size of the product is determined by the distance between the bottom edges of the crushing head and the bowl, in the position when they are farthest apart.

The crushing action is much the same in principle as that of a jaw crusher, the lumps of ore being pinched and broken between the crushing head and the bowl instead of between two jaws. The main point ofdifference between the two types is that the gyratory crusher does effective work during the whole of the travel of the head, whereas the other only crushes during the forward stroke. The gyratory crusher is thereforethe more efficient machine, provided that the bowl can be kept full, a condition which is, as a rule, easy to maintain because it is quite safe to bury the head in a pile of ore.

Tables 7 and 8 give particulars of different sizes of gyratory crushers. As in the previous paragraph, the capacity figures are based on material weighing 100 lb. per cubic foot and should be increased in direct proportion for heavier ores.

Primary and secondary gyratory crushers, including the cone crusher, can be directly connected to slow speed motors if desired, but the standard method of drive is still by belt and pulley. Jaw crushers must be belt-driven.

An efficient substitute for the flat belt in all cases is the Texrope drive, which consists of a number of V-shaped endless rubber belts running on special grooved pulleys. The grip of these belts is so great that the distance between the pulley centres can be reduced to about 30% of that required for a flat belt. This results not only in a saving of space but also in greater safety, since the drive is easier to protect and there is no danger of an accident such as might occur if a long belt were to pull through its fasteners. Moreover, the short drive makes it possible for any stretch to be taken up by moving the motor back on its rails without the necessity of cutting and rejoining the belts. The flexibility and ease of maintenance of the Tex-rope drive makes it very suitable for crushing machines.

LOW OPERATING COSTS Vertical adjustment compensates for wear on crushing surfaces (also maintains product uniformity). Oiling system provides proper lubrication throughout, including spider. Effective dust seal prevents dust infiltration to moving parts. Long life bearings, easy to replace.

Strength, of course, makes an all-important contribution to the rugged heavy duty service and day-in, day-out dependability demanded of a crusher. However, strength does not necessarily mean excessive weight. The metals and alloys used in construction and the distribution of weight are actually the determining factors in the strength of a gyratory crusher.

MAINSHAFT ASSEMBLY mainshaft forged steel; annealed quenched and tempered. Tapered to gauge for head center fit. Head center of cast steel. Head mantle of manganese steel. Mainshaft sleeve shrunk on mainshaft to provide renewable wearing surface on spider bearing.

Gyratory crusher advanced design includes the placing of circumferential ribs around the top and bottom shells. These integrally cast reinforcing rings prevent distortion provide the rigidity necessary to maintain true alignment of running parts.

Hollow box construction of the cast steel spider affords maximum strength with the least amount of feed interference. Arms are cast integrally with the heavy outer rim. Crushing stresses are transmitted to the rim, which is taper-fitted to the top shell. Because spider and top shell are interlocked, they reinforce each other to provide maximum stability and rigidity.

The bottom shell is the foundation of the crusher. It must be strong enough not only to support the weight of the crusher, but to withstand extreme crushing stresses (most stresses terminate here) strong enough to protect vital mechanism the eccentric, gears and countershaft assembly housed in the bottom shell. In the Gyratory crusher, bottom discharge design makes possible a compact, squat structure of simplified design and comparatively high strength. Supplementing the strength of the bottom shell are the previously described circumferential ribs. Crushing stresses are transmitted directly to these reinforcing members through three radial arms.

Because the mainshaft does the actual crushing, it must literally possess crushing strength. In the Gyratory crusher, the eccentric is located directly below the crushing head. This design permits the use of a short, rigid mainshaft a mainshaft that will withstand the strain of severe service.

Flexibility is the keynote of the Gyratory crusher efficiency and economy. While your particular installation is designed to best meet your specific and immediate requirements, built-in flexibility permits adaptation to changing operating conditions anytime in the future.

A Gyratory crusher not only affords a maximum capacity-to-size ratio, but provides the variable factors which facilitate increasing or decreasing capacity as the need arises. Flexibility in a Gyratory crusher also permits compensation for wear and assures product uniformity.

In the Gyratory crusher, the use of spiral bevel gears instead of spur gears makes possible the broad range of speeds conducive to meeting varying capacity demands. Because the Gyratory crusher is equipped with an external oiling system, speed may be reduced as much as desired or required. Adequate lubrication is supplied at even the lowest speeds, because the flow of oil is not relative to the crushers operating speed as is the case with an internal system.

With a primary gyratory crusher running at a given countershaft speed, capacity is increased as eccentricity is increased. At a given eccentricity, greater capacity results from higher countershaft speeds. Conversely, reducing either the speed or eccentricity reduces capacity.

Another high capacity characteristic of the Gyratory crusher is a large diameter crushing head. Because the area of discharge opening is directly proportionate to head diameter, high capacities result.

VARIABLE INITIAL SETTINGS The contour of the crushing chamber at the bottom is designed to afford various initial settings without changing the angle of the nip. This is accomplished by installing lower tier concaves of the shape and thickness for the desired setting and capacity.

HOW SIZES ARE DESIGNATED The numerical size designation of Gyratory crushers represents the feed opening and the maximum diameter of the crushing head. For example, a 60-109 Gyratory crusher has a 60-inch receiving opening and an 109-inch maximum diameter crushing head.

ELIMINATES DIAPHRAGM In a gyratory crusher with aside discharge, sticky materials may pack on the diaphragm and eventually cause considerable damage. Thestraight down discharge of the Gyratory crusher is a design simplification that eliminates the diaphragm and itsmaintenance problems.

CONTRIBUTES TO BALANCED CIRCUIT The adaptabilityof a primary crusher to a large extent dictates the plantflowsheet the initial and overall operating costs of subsequent equipment. With a Gyratory primary crusher,these costs are kept at a minimum because the entirecrushing circuit remains in balance. The concrete foundation may be modified for use as a surge bin. This storagecapacity permits controlling the flow of material throughthe plant. Secondary and tertiary crushers, vibrating screens, etc. may be installed in size ranges and types tomeet the requirements of a constant tonnage. For thosefew installations where a side discharge is essential, a discharge spout can be furnished. Another factor in maintaining a balanced circuit is the vertical adjustment(pages 12 and 13) which permits retaining the initial discharge setting by compensating for wear on mantle andconcaves. Related equipment need not be readjusted because of variations of feed size from the primary crusher.

In the Gyratory crusher, the original discharge setting may be maintained for the life of a single set of alloy crushing surfaces with only one resetting of concaves. Raising the mainshaft compensates for wear onconcaves and mantle. This simplified vertical adjustment cuts resetting time facilitates holding product size.

The threaded mainshaft is held in and supported from the spider hub. (See illustration at lower left.) A vertical adjustment range of from 6 inches to approximately 11 inches is possible, depending upon the size of the machine. The original discharge setting can be maintained until the combined wear of mantle and concaves is about one-third of the vertical adjustment.

A cast steel, split adjusting nut with a collar issupported on a two-piece thrust bearing in the spider hub. The nut is threaded for the mainshaft. The outside of the nut is tapered, with the large diameter at the top. The weight of the head and shaft draws the nut down in its tapered seat in the collar to form a self-clamping nut. Desired setting is achieved by positioning split nut in the proper location on the threaded portion of the mainshaft.

The Gyratory crusher is also available with a Hydroset mechanism a hydraulic method of vertical adjustment. With the Hydroset mechanism, compensation for wear and product size control is a one- man, one-minute operation. The Hydroset mechanism consists of a motor-driven gear pump operated by push button.

The accompanying drawings show the simplicity of Hydroset design. The mainshaft assembly is supported on a hydraulic jack. When oil is pumped into the jack, the mainshaft is raised compensating for mantle and concave wear or providing a closer setting. When oil is removed from jack, the mainshaft is lowered and a coarser setting results.

Since the mainshaft assembly is supported on a hydraulic jack, its position with respect to the concaves, and therefore the crusher setting, is controlledby the amount of oil in the hydraulic cylinder.

Oil pressure is maintained in the hydraulic cylinder below the mainshaft by a highly effective chevron packing. The oil supply of the Hydroset mechanism functions independently of the crushers lubrication system.

If a Gyratory crusher equipped with Hydroset mechanism stops under load, the mainshaft may be lowered to facilitate clearing of the crushing chamber by merely pumping oil out of the cylinder. Only under extreme conditions is it necessary to dig out. When the cause of the stoppage is remedied, the oil is pumped back into the cylinder quickly, returning the mainshaft assembly to its initial position.

STEP BEARING consists of bronze mainshaft step, bronze piston wearing plate, and an alloy steel washer between the two. Washer is drilled for oil cooling lubrication. Bearing surfaces are grooved to permit oil distribution.

Utilizing pool lubrication, a gun-type fitting in the spider arm makes it easy to oil the spider bearing. A garter-type oil seal in the bottom of the bearing retains oil. Being flexible, the seal compensates for movement of crusher mainshaft.

The countershaft assembly is an anti-friction, pool-lubricated unit. Both ends of the bearing housing are sealed by garter-type spring oil seals which: (1) keep dust from anti-friction bearings; (2) separate pinion- shaft bearing lubricant from oil lubricating the eccentric and gears.

Getting the most out of a crusher in performance and capacity depends largely upon positive lubrication. And positive lubrication means more than just adequate oil lubrication. It also entails conditioning oil for maximum lubricating efficiency.

The Gyratory crusher is equipped with an externally located, fully automatic lubricating system. Positive and constant lubrication is maintained at all speeds even at the slowest speed. If desired, oil may be circulated through bearings of Gyratory crusher during shutdown periods.

A gear pump circulates oil from storage tank, through crusher and back. Each time oil is pumped to the crusher, it passes through the filter and cooler. The cleaned, cool oil lubricates the step bearing (in Hydroset mechanism only), the eccentric wearing plate and the inner eccentric bearing. At the top of the bearing, most of the oil flows through ports in the eccentric to the outer eccentric bearing. Theoil then flows down the outer eccentric bearing and lubricates the gear and pinion before it is returned to storage. The overflow oil which may have become contaminated is returned immediately to the oil conditioning tank. It does not contact any other wearing parts within the crusher.

The oil conditioning system may be modified to meet your particular applications. In cold climates immersion heaters are installed in the storage tank to preheat oil. This arrangement permits circulating warm oil through the crusher during shutdown periods. A thermostatic control turns heater on and off. Only in a crusher specifically designed for external oiling is it possible to circulate warm oil when the crusher is stopped.

An added measure of safety is providedby the oil conditioning system. Foreignmaterial is removed by pumping warm oilthrough a mechanical filter. After oil isfiltered, it flows through a condenser-type cooler before it is returned to the crusher.

An oil flow switch provides automatic protection against possible damage caused by oil system failure. This switch stops the crusher immediately if oil flow is insufficient for proper lubrication. Interlocks between pump motor and crusher prevent starting crusher before oil circulation begins.

In addition to its other advantages, the externally located oil conditioning system is easy to service. The unit consists of (A) an oil storage tank, (B) a motor-driven gear pump, (C) a pressure- type filter, and (D) a condenser-type cooler.

In the gyratory crusher, expensive castings are protected by replaceable parts. Rim and arm liners protect the spider from wear. Bottom shell liners and shields provide protection below the crushing chamber. An alloy steel shaft sleeve protects the mainshaft in the spider bearing. The eccentric sleeve and bushing are easily replaced when worn.

Because all parts are readily accessible and removable, down time is kept to a minimum. For example, the countershaft assembly is removed as a unit and can be taken to your machine shop for convenient servicing. Eccentric bearings are bronze bushings. Because bronze is used, the need for babbitt mandrels and melting facilities is eliminated.

Sealing out dirt and dust and their equipment-destroying abrasive action results in obvious maintenance economies. The type of dust seal used in the gyratory crusher is the most reliable and effective device ever developed for preventing excessive wear caused by dirt and dust.

In the gyratory crusher, a synthetic, self-lubricating, light-weight ring is used as a dust seal. The ring is enclosed between a dust collar bolted to the bottom shell and a recess in the bottom of the head center. Regardless of the eccentric throw and vertical positioning, the ring maintains its contact with the outer periphery of the dust collar. Because of its light weight and self-lubricating characteristics, wear on this ring is negligible.

Provisions have been made on the gyratory crusher for the introduction of low pressure air to the dust seal chamber. This internal pressure, which can be obtained through the use of a small low pressure blower, creates an outward flow of air through the dust seal. This prevents an inward flow of abrasive dirt and dust. The combination of a highly effective sealing ring and the utilization of internal air pressure protects the eccentric and gears from destructive infiltration even under the most severe conditions. When required, this additional protection is supplied at a nominal additional cost.

All of the operating advantages all of the engineering and construction features described in this bulletin are found in both the primary and secondary gyratory crushers. Of course, certain modifications have been made to efficiently accomplish the tough, rugged job of secondary crushing. For instance, the secondary gyratory crusher has been engineered to accommodate the greater horsepower requirement of secondary crushing. Increased strength and durability have been built into all components.

In the past, primary crushers had to be set extremely close in order to provide an acceptable feed for secondary crushers. As a result, primary crushers were penalized by reduced capacity and excessive maintenance. The secondary gyratory crusher was engineered to solve this problem.

Anticipating product size variations, Allis-Chalmers has designed the secondary crusher with a large feed opening one large enough to accept oversized materials. This design feature is particularly advantageous when the secondary gyratory crusher follows a primary crusher that has no vertical adjustment for wear.

A large diameter crushing head along with tailored-to-your-operation design results in big capacity. An acute angle in the crushing chamber and a long parallel zone facilitate precision setting assure a cubical, well graded product distributes even the normal wear throughout the crushing chamber.

1. Spider cap 2. Spider 3. Hour glass bushing 4. Spider bearing oil seal 5. Spider bearing oil seal retainer 6. Spider bearing oil seal retainer screws 7. Spider joint bolts 8. Spider joint bolt nuts 9. Spider joint bolt lock nuts 10. Spider arm shield 11. Spider arm shield bolts 12. Spider arm shield bolt nuts 13. Center spider rim liners (not shown) 14. End spider rim liners 15. Rim liner bolts 16. Rim liner bolt nuts 17. Spider bearing spherical support ring 18. Spider bearing spherical support ring seat 19. Spider lubricating hose bushing 20. Spider lubricating hose 21. Spider lubricating hose bracket 22. Spider lubricating hose grease fitting 23. Spider lubricating hose bracket bolts 24. Spider joint studs (not shown) 26. Mainshaft thrust ring 27. Mainshaft thrust ring bolts 31. Top shell 32. Concave support ring 33. Upper concaves 34. Upper middle concaves 36. Lower middle concaves 37. Lower concaves 43. Bottom shell 44. Bottom shell joint bolts 45. Bottom shell joint bolt nuts 46. Bottom shell joint bolt lock nuts 47. Bottom shell bushing 48. Bottom shell bushing key 49. Bottom shell bushing clamp plate 50. Bottom shell bushing clamp plate bolts 51. Bottom shell front arm liners 52. Bottom shell rear arm liners 53. Bottom shell side liners 54. Bottom shell hub liners 55. Dust collar 56. Dust collar cap screws 57. Dust collar gasket 63. Bottom plate 64. Bottom plate studs 65. Bottom plate stud nuts 66. Bottom plate stud lock nuts 67. Bottom plate dowel pin 68. Bottom plate drain plug 69. Bottom plate gasket 95. Eccentric 96. Eccentric sleeve 97. Eccentric sleeve key 98. Bevel gear 99. Bevel gear key 100. Bevel gear key cap screws 101. Eccentric wearing plate 107. Mainshaft 108. Head center 109. Mantle lower section 110. Mantle upper section 111. Head nut 112. Dowel pin (for keying head nut to mantle) 113. Mainshaft sleeve 114. Adjusting nut 115. Adjusting nut collar 116. Enclosed ring type dust seal sealing ring 117. Enclosed ring type dust seal retaining ring 118. Enclosed ring type dust seal bolts 119. Adjusting nut tie bar 120. Adjusting nut tie bar bolts 121. Adjusting nut key 124. Pinion bearing housing 125. Pinion bearing housing gasket 126. Pinion bearing housing studs 127. Pinion bearing housing stud nuts 128. Pinion bearing housing stud lock nuts 129. Pinion bearing housing dowel pin 130. Pinion bearing housing oil drain plug 131. Pinion bearing housing oil level plug (not shown) 132. Pinion bearing housing oil filler plug 133. Pinionshaft 134. Drive sheave and bushing 135. Drive sheave key 136. Pinion shaft lock nut spacer 137. Pinion shaft lock nut spacer lockwasher 138. Pinion shaft lock nut spacer lockwasher gasket 139. Pinion bearing seal plate 140. Pinion bearing oil seal 141. Pinion bearing seal plate gaskets 142. Pinion bearing seal plate bolts 143. Pinionshaft outer bearing 144. Pinionshaft inner bearing 145. Pinionshaft bearing spacing collar 146. Pinionshaft bearing spacing collar gasket 147. Pinion 148. Pinion key 149. Pinion retainer plate 150. Pinion retainer plate bolts

In the dimension charts above, the first number in each size classification designates the size of the receiving opening in inches. The second number is the largest diameter of the mantle in inches. Primary crushers having the same mantle diameter use the same size bottom shell, gears, eccentrics and countershaft assemblies.

Secondary crushers use the same size bottom shells as certain size primary crushers, but different size top shells, mainshaft and spider assemblies. The 30-70 secondary gyratory crusher uses the bottom shell of the 42-65 primary crusher; the 24-60 secondary uses the 30-55 primary bottom shell.

Capacities given here are based on field data under average quarry conditions when crushing dry friable material equivalent to limestone. Because conditions of stone and methods of operation vary, capacities given are approximate only.

Where no capacity data is given the crusher is under development.Figures under Maximum Horsepower are correct only for throw and pinion Rpm given above. When speed is reduced, Maximum Horsepower must also be reduced proportionately.

This graph is based on customary practice and is principally a guide. Size of crusher may vary considerably with different materials, depending upon stratification, blockiness, quarry methods and size of quarry trucks. Pieces that cannot be handled by crusher without bridging should be broken in the quarry.

The screen analysis of the product from any crusher will vary widely, depending upon the character of the material, quarry conditions, and the amount of fines or product size in the initial feed at the time

the sample is taken. These factors should be taken into consideration when estimating the screen analysis of the crusher product. Product gradation curves based on many actual screen analyses have been prepared which can be used for estimating.

The crusher discharge opening on the open side will govern the product gradation from a crusher if corrected to take into consideration quarry or mine conditions, particularly as to the amount of fines in the crusher feed. The tabulation at the left is basedon an average of many screen analyses and gives the approximate percentage of product equal to the open side setting of the crusher. Its actual use when the feed conditions are definitely known should be corrected to take care of these conditions, particularly insofar as fines or product size in the feed are concerned. The curves on these pages have been prepared giving the approximate screen analysis of the crusher product and should be used in conjunction with Table I

Table I shows 90% of product should pass a 6-inch square opening flat testing sieve. Using the 90% vertical line on Table II, follow it up to the horizontal line of 6 inches. Follow the nearest curve to the intersection, and using this curve you will get the following approximate screen analysis.

Until recently, there has been no way of accurately determining the power required for agiven crushing operation. With little or no factualoperating data correlated into useful form, it wasdifficult even for the most experienced operators toarrive at a correct size crusher or a proper size crusher motor to do a given job.

The correlation of all this factual material, from extensive field operating data and laboratory data covering wide varieties of material, ranges of reduction sizes, and types of equipment, made it possible to establish a consistent common factor known asthe Work Index for accurately determining the power required for crushing.

In the Work Index method, frequently referred to as the Bond method, the Work Index is actually the total work input in kwhr per short ton required to reduce a given material from theoretically infinite particle size to 80% passing 100 microns or approximately 67% passing 200 mesh. Knowing the Work Index, you need only apply the given equation to determine power input required. The calculated power input enables you to select the proper crusher.

In order to simplify the selection of a crusher by the Work Index method, the following form has been developed. References below the form explain the various parts of the calculation, and, immediately below, a complete example is worked out.

REFERENCE I Average Impact. As noted, the Work Index is determined from the average impact value and the specific gravity of the material being crushed. The impact value and Work Index can be determined in the Processing Machinery Laboratory, or these values can be determined from a comparable operation in the field. Acomplete listing of Work Indexes of materials which have been tested in the laboratory.

REFERENCE II Feed Size. In the case of a primary crusher this may be somewhat difficult to obtain. Experience indicates, however, that in most cases 80% of the feed size will pass a square opening equal to from half to two-thirds of the crusher receiving opening.

A crushed stone producer desires a primary crusher to handle the product from a 3-yard shovel at an average rate of 350 tph. The rated capacity of the crusher must, of course, be greater than this because of inevitable quarrying and crushing delays. A crusher setting of 5 in. on the open side is desired because of following equipment and the requirements for stone.

MATERIAL: Limestone WORK INDEX 10.7 CRUSHER: 42-65 Primary gyratory Open Side Setting: 5; Eccentric Throw: 1 Recommended Operating Speed; 400 Rpm (Approximately 80% of Maximum Speed) Capacity at Recommended Speed: 438 Short Ton/Hour Maximum Horsepower Allowable at Selected Throw and Speed: 213 Horsepower. FEED SIZE: (F) 80% Passes 28 (66% of Feed Opening) F 711,000 Microns F = 842 PRODUCT SIZE: (P) 80% Passes 4, P = 108,000 Microns P = 328 F P = 514 HORSEPOWER/SHORT TON = 10.7 x 13.4 x 514/842 x 328 = .267 .267 Horsepower/Short Ton x438 Short Tons/Hour Capacity = 117Horsepower Required RECOMMENDED MOTOR SIZE: 150 Horsepower Motor.

Tabulated data presented has been compiled from tests made in the Allis-Chalmers Research Laboratory. This data is a cross section of impact and compressive strength tests made on hundreds of different rock samples for customers in the U.S. and abroad.

Ten or more representative pieces of broken stone, each of which passes a square opening three inches on a side and will not pass a two-inch square, are selected and broken individually between two 30-lb pendulum hammers. The hammers are raised by an equal amount and released simultaneously. This is repeated with successively greater angles of fall until the specimen breaks. Its impact strength is the average foot-pounds of energy represented by the breaking fall divided by the thickness in inches. The average impact strength is the average foot-pounds per inch required to break the ten or more pieces, and the maximum is the foot-pounds per inch required to break the hardest piece, the highest value obtained.

The compressive strengths of many materials have been measured in the Laboratory by cutting samples into one-inch cubes which are then broken under slow compression in a Southwark compression tester. This indicates the compressive strength in pounds per square inch.

The correlation between the compressive strengthand the impact crushing strength is inconsistent, and experiencehas shown that theimpact strength is abetter criterion of theactual resistance tocrushing. The impactdevice more nearly approaches actual crusher operation, both invelocity of impact andin the fact that broken stone is used intesting.

The average impactcrushing strength isan indication of theenergy required forcrushing, while themaximum compression values indicate the danger of crusher breakage and the type of construction necessary. Crusher capacities do not vary greatly with the impact strength. There is a capacity increase of less than 10% from the hardest to the softest stone, where packing is not a factor.

crusher - an overview | sciencedirect topics

crusher - an overview | sciencedirect topics

Roll crushers are generally not used as primary crushers for hard ores. Even for softer ores, like chalcocite and chalcopyrite they have been used as secondary crushers. Choke feeding is not advisable as it tends to produce particles of irregular size. Both open and closed circuit crushing are employed. For close circuit the product is screened with a mesh size much less than the set.

Fig. 6.4 is a typical set up where ore crushed in primary and secondary crushers are further reduced in size by a rough roll crusher in open circuit followed by finer size reduction in a closed circuit by roll crusher. Such circuits are chosen as the feed size to standard roll crushers normally do not exceed 50mm.

Cone crushers were originally designed and developed by Symons around 1920 and therefore are often described as Symons cone crushers. As the mechanism of crushing in these crushers are similar to gyratory crushers their designs are similar, but in this case the spindle is supported at the bottom of the gyrating cone instead of being suspended as in larger gyratory crushers. Fig. 5.3 is a schematic diagram of a cone crusher. The breaking head gyrates inside an inverted truncated cone. These crushers are designed so that the head to depth ratio is larger than the standard gyratory crusher and the cone angles are much flatter and the slope of the mantle and the concaves are parallel to each other. The flatter cone angles helps to retain the particles longer between the crushing surfaces and therefore produce much finer particles. To prevent damage to the crushing surfaces, the concave or shell of the crushers are held in place by strong springs or hydraulics which yield to permit uncrushable tramp material to pass through.

The secondary crushers are designated as Standard cone crushers having stepped liners and tertiary Short Head cone crushers, which have smoother crushing faces and steeper cone angles of the breaking head. The approximate distance of the annular space at the discharge end designates the size of the cone crushers. A brief summary of the design characteristics is given in Table 5.4 for crusher operation in open circuit and closed circuit situations.

The Standard cone crushers are for normal use. The Short Head cone crushers are designed for tertiary or quaternary crushing where finer product is required. These crushers are invariably operated in closed circuit. The final product sizes are fine, medium or coarse depending on the closed set spacing, the configuration of the crushing chamber and classifier performance, which is always installed in parallel.

For finer product sizes, i.e. less than 6mm, special cone crushers known as Gyradisc crushers are available. The operation is similar to the standard cone crushers except that the size reduction is caused more by attrition than by impact, [5]. The reduction ratio is around 8:1 and as the product size is relatively small the feed size is limited to less than 50mm with a nip angle between 25 and 30. The Gyradisc crushers have head diameters from around 900-2100mm. These crushers are always operated in choke feed conditions. The feed size is less than 50mm and therefore the product size is usually less than 6-9mm.

Crushing is accomplished by compression of the ore against a rigid surface or by impact against a surface in a rigidly constrained motion path. Crushing is usually a dry process and carried out on ROM ore in succession of two or three stages, namely, by (1) primary, (2) secondary, and (3) tertiary crushers.

Primary crushers are heavy-duty rugged machines used to crush ROM ore of () 1.5m size. These large-sized ores are reduced at the primary crushing stage for an output product dimension of 1020cm. The common primary crushers are of jaw and gyratory types.

The jaw crusher reduces the size of large rocks by dropping them into a V-shaped mouth at the top of the crusher chamber. This is created between one fixed rigid jaw and a pivoting swing jaw set at acute angles to each other. Compression is created by forcing the rock against the stationary plate in the crushing chamber as shown in Fig.13.9. The opening at the bottom of the jaw plates is adjustable to the desired aperture for product size. The rocks remain in between the jaws until they are small enough to be set free through this opening for further size reduction by feeding to the secondary crusher.

The type of jaw crusher depends on input feed and output product size, rock/ore strength, volume of operation, cost, and other related parameters. Heavy-duty primary jaw crushers are installed underground for uniform size reduction before transferring the ore to the main centralized hoisting system. Medium-duty jaw crushers are useful in underground mines with low production (Fig.13.10) and in process plants. Small-sized jaw crushers (refer to Fig.7.32) are installed in laboratories for the preparation of representative samples for chemical analysis.

The gyratory crusher consists of a long, conical, hard steel crushing element suspended from the top. It rotates and sweeps out in a conical path within the round, hard, fixed crushing chamber (Fig.13.11). The maximum crushing action is created by closing the gap between the hard crushing surface attached to the spindle and the concave fixed liners mounted on the main frame of the crusher. The gap opens and closes by an eccentric drive on the bottom of the spindle that causes the central vertical spindle to gyrate.

The secondary crusher is mainly used to reclaim the primary crusher product. The crushed material, which is around 15cm in diameter obtained from the ore storage, is disposed as the final crusher product. The size is usually between 0.5 and 2cm in diameter so that it is suitable for grinding. Secondary crushers are comparatively lighter in weight and smaller in size. They generally operate with dry clean feed devoid of harmful elements like metal splinters, wood, clay, etc. separated during primary crushing. The common secondary crushers are cone, roll, and impact types.

The cone crusher (Fig.13.12) is very similar to the gyratory type, except that it has a much shorter spindle with a larger-diameter crushing surface relative to its vertical dimension. The spindle is not suspended as in the gyratory crusher. The eccentric motion of the inner crushing cone is similar to that of the gyratory crusher.

The roll crusher consists of a pair of horizontal cylindrical manganese steel spring rolls (Fig.13.14), which rotate in opposite directions. The falling feed material is squeezed and crushed between the rollers. The final product passes through the discharge point. This type of crusher is used in secondary or tertiary crushing applications. Advanced roll crushers are designed with one rotating cylinder that rotates toward a fix plate or rollers with differing diameters and speeds. It improves the liberation of minerals in the crushed product. Roll crushers are very often used in limestone, coal, phosphate, chalk, and other friable soft ores.

The impact crusher (Fig.13.15) employs high-speed impact or sharp blows to the free-falling feed rather than compression or abrasion. It utilizes hinged or fixed heavy metal hammers (hammer mill) or bars attached to the edges of horizontal rotating discs. The hammers, bars, and discs are made of manganese steel or cast iron containing chromium carbide. The hammers repeatedly strike the material to be crushed against a rugged solid surface of the crushing chamber breaking the particles to uniform size. The final fine products drop down through the discharge grate, while the oversized particles are swept around for another crushing cycle until they are fine enough to fall through the discharge gate. Impact crushers are widely used in stone quarrying industry for making chips as road and building material. These crushers are normally employed for secondary or tertiary crushing.

If size reduction is not completed after secondary crushing because of extra-hard ore or in special cases where it is important to minimize the production of fines, tertiary recrushing is recommended using secondary crushers in a close circuit. The screen overflow of the secondary crusher is collected in a bin (Fig.13.16) and transferred to the tertiary crusher through a conveyer belt in close circuit.

Primary jaw crushers typically operate in open circuit under dry conditions. Depending on the size reduction required, the primary jaw crushers are followed by secondary and tertiary crushing. The last crusher in the line of operation operates in closed circuit. That is, the crushed product is screened and the oversize returned to the crusher for further size reduction while the undersize is accepted as the product. Flow sheets showing two such set-ups are shown in Figs. 3.1 and 3.2.

Jaw crushers are installed underground in mines as well as on the surface. When used underground, jaw crushers are commonly used in open circuit. This is followed by further size reduction in crushers located on the surface.

When the run of mine product is conveyed directly from the mine to the crusher, the feed to the primary crusher passes under a magnet to remove tramp steel collected during the mining operation. A grizzly screen is placed between the magnet and the receiving hopper of the crusher to scalp (remove) boulders larger than the size of the gape. Some mines deliver product direct to storage bins or stockpiles, which then feed the crushers mechanically by apron feeders, Ross feeders or similar devices to regulate the feed rate to the crusher. Alternately haulage trucks, front-end loaders, bottom discharge railroad cars or tipping wagons are used. In such cases, the feed rate to the crusher is intermittent which is a situation generally avoided. In such cases of intermittent feed, storage areas are installed and the feed rate regulated by bulldozers, front loaders or bin or stockpile hoppers and feeders. It is necessary that the feed to jaw crushers be carefully designed to balance with the throughput rate of the crusher. When the feed rate is regulated to keep the receiving hopper of the crusher full at all times so that the volume rate of rock entering any point in the crusher is greater than the rate of rock leaving, it is referred to as choke feeding. During choke feeding the crushing action takes place between the jaw plates and particles as well as by inter-particle compression. Choke feeding necessarily produces more fines and requires careful feed control. For mineral liberation, choked feeding is desirable.

When installed above ground, the object of the crushing circuit is to crush the ore to achieve the required size for down stream use. In some industries, for example, iron ore or coal, where a specific product size is required (iron ore 30+6mm), careful choice of jaw settings and screen sizes are required to produce the minimum amount of fines (i.e. 6mm) and maximum the amount of lump ore within the specified size range. For hard mineral bearing rocks like gold or nickel ores where liberation of minerals from the host rock is the main objective, further stages of size reduction are required.

A gold ore was crushed in a secondary crusher and screened dry on an 1180micron square aperture screen. The screen was constructed with 0.12mm diameter uniform stainless steel wire. The size analysis of the feed, oversize and undersize streams are given in the following table. The gold content in the feed, undersize and oversize streams were; 5ppm, 1.5ppm and 7ppm respectively. Calculate:

The self tuning control algorithm has been developed and applied on crusher circuits and flotation circuits [22-24] where PID controllers seem to be less effective due to immeasurable change in parameters like the hardness of the ore and wear in crusher linings. STC is applicable to non-linear time varying systems. It however permits the inclusion of feed forward compensation when a disturbance can be measured at different times. The STC control system is therefore attractive. The basis of the system is:

The disadvantage of the set up is that it is not very stable and therefore in the control model a balance has to be selected between stability and performance. A control law is adopted. It includes a cost function CF, and penalty on control action. The control law has been defined as:

A block diagram showing the self tuning set-up is illustrated in Fig. 18.27. The disadvantage of STC controllers is that they are less stable and therefore in its application a balance has to be derived between stability and performance.

Bone recycling is a simple process where useful products can be extracted. Minerals such as calcium powder for animal; feed are extracted from the bone itself. The base material for cosmetics and some detergent manufacturing needs are extracted from the bone marrow.

The bone recycling process passes through seven stages starting from crushing and ending with packing. Figure 13.14 gives a schematic diagram showing the bone recycling process which goes through the following steps:

Following the standard procedures in the Beijing SHRIMP Center, zircons were separated using a jaw crusher, disc mill, panning, and a magnetic separator, followed by handpicking using a binocular microscope. The grains were mounted together with the standard zircon TEM (417Ma, Black etal., 2003) and then polished to expose the internal structure of the zircons. Cathodoluminescence (CL) imaging was conducted using a Hitachi SEM S-3000N equipped with a Gatan Chroma CL detector in the Beijing SHRIMP Center. The zircon analysis was performed using the SHRIMP II also in the Beijing SHRIMP Centre. The analytical procedures and conditions were similar to those described by Williams (1998). Analytical spots with 25m diameter were bombarded by a 3nA, 10kV O2 primary ion beam to sputter secondary ions. Five scans were performed on every analysis, and the mass resolution was 5000 (at 1%). M257 standard zircon (561.3Ma, U=840ppm) was used as the reference value for the U concentration, and TEM standard zircons were used for Pb/U ratio correction (Black etal., 2003). Common Pb was corrected using the measured 204Pb. Data processing was performed using the SQUID/Isoplot programs (Ludwig, 2001a,b). Errors for individual analyses are at 1, but the errors for weighted average ages are at 2.

A stockpile can be used to blend ore from different sources. This is useful for flotation circuits where fluctuations ingrade can change the mass balance and circulating loads around the plant. Blending can also be done on the ROMpad.

The lowest cost alternative is to have no surge at all, but rather to have a crushing plant on line. This is workable for small-scale plant with single-stage jaw crushers as the availability of these simple plant is very high provided control over ROM size is maintained.

The second alternative is to use a small live surge bin after the primary crusher with a secondary reclaim feeder. Crushed ore feeds this bin continuously and the bin overflows to a small conveyor feeding a dead stockpile. In the event of a primary crusher failure, the crusher loader is used to reclaim the stockpile via the surge bin, which doubles as an emergency hopper.

For coarse ore, the next alternative is a coarse ore stockpile. Stockpiles of this type are generally 1525% live and require a tunnel (concrete or Armco) and a number of reclaim feeders to feed the milling circuit.

Multi-stage crushing circuits usually require surge capacity as the availability of each unit process is cumulative. A fine-ore bin is usually required. Smaller bins are usually fabricated from steel as this is cheaper. Live capacity of bins is higher than stockpiles but they also require a reclaim tunnel and feeders.

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