CONQUIP   SUPPLYING EQUIPMENT SINCE 1974



JAW CRUSHER INFORMATION
JAW CRUSHER GOOD PRACTICE

•    Jaw crushers should be fed a consistent rate of feed that will result in the crushing chamber being kept full at all times.
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•    Deep-chambered jaw crushers will have more rock-on-rock crushing while the feed is passing through, and a better nip-angle.

•    Deep-chambered jaw crushers will typically produce more cubical product and have a longer wear life from the manganese per ton processed.

•    A jaw crusher should not be sized to the maximum size rock that might pass through it. It will result in buying a jaw crusher that will be under-utilized, difficult to keep choke-fed, cost more than necessary, and have a much higher operating cost.

•    A jaw crusher should be sized to handle 95-98% of the raw feed material, with the larger sizes being removed prior by using a grizzly.

•    Do not feed a jaw crusher with rock larger than its capacity, nor with rock that is smaller than the closed-side setting. This will prevent damage to the jaw, plugging, increase the total plant production, and extend the wear life of the manganese.
 
OVERHEAD ECCENTRIC JAW CRUSHER

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DOUBLE-TOGGLE JAW CRUSHER
A: Swing jaw
B: Stationary jaw
C: Pivot point
D: Double set of toggles
E: Offset eccentric shaft



                                                      
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INTRODUCTION TO JAW CRUSHERS
 

Jaw crushers are typically used as primary crushers, or the first step in the process of reducing rock. They typically crush using compression. The rock is dropped between two rigid pieces of metal, one of which then move inwards towards the rock, and the rock is crushed because it has a lower breaking point than the opposing metal piece.

There are two basic types of jaw crushers, the overhead eccentric style and the double-toggle style. Which will work best for a given operation depends upon several factors.

Jaw crusher movement is obtained by using a pivot point located at one end of the “swing jaw”, and an eccentric motion located at the opposite end.
 
OVERHEAD ECCENTRIC JAW CRUSHER

        On an overhead eccentric jaw the “pivot point” is actually the point where the toggle plate and seat mate, which is at the bottom of the swing jaw. The eccentric motion is created at the top of the swing jaw by a shaft that has a eccentric shape on its circumference. The shaft is supported on both sides by typically four heavy-duty bearings. To create inertia to overcome the resistance of the rock there is a large flywheel located at each end of the main shaft. This style typically requires substantially more horsepower to operate than an equally sized   double-toggle style.

    The motion created by the eccentric on the swing jaw is elliptical. The movement is greatest at the top of the jaw plate and is both inwards towards the rock and downwards towards the discharge end. This results in both compressive and attrition types of crushing. The tonnage throughputs will typically be greater with this style of jaw crusher, but the wear on the manganese will be greater too, especially when crushing abrasive rock.
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DOUBLE-TOGGLE STYLE JAW CRUSHER

    In a double-toggle style of crusher the moving jaw plate’s pivot point is at the top. The moving jaw plate is typically referred to as the swing-jaw for that reason. The eccentric shaft is mounted separately from the swing-jaw and is located towards the bottom of the crusher. The eccentric motion is transferred to the lower part of the swing-jaw by the use of a shorter toggle plate. There are several major advantages to this arrangement:
•    The horsepower requirement is substantially reduced and only one small diameter flywheel is used
•    The eccentric, toggle plates, and shaft bearings run in an oil bath and are protected from dust and other contaminants
•    The tramp-iron release mechanism is mounted on the much smaller flywheel and is easily reset
•    The swing motion is in a straight line rather than elliptical and the manganese wear plates last longer

    Over the years many mines have used the double-toggle style of crusher because of its ability to crush materials, including mineral bearing ores that were both tough and abrasive. While many aggregate producers have used the overhead eccentric style. There are many factors that should be considered when deciding which style would be best for your application.

A rotating shaft driven by either a diesel engine or an electric motor produces all jaw crushers’ motion. To keep the motion as consistent as possible the overhead eccentric unit uses two large flywheels, one located at each end of the shaft. The weight of these flywheels produces inertia that helps even out the surges inherent in crushing material that is inconsistent in size and volume.
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MAJOR COMPONENTS OF A JAW CRUSHER

•    The main frame, which may be fabricated or cast.
•    Manganese liners which protect the frame from wear, these include the main jaw plates covering the frame opposite the moving jaw, the moving jaw, and the cheek plates which line the sides of the main frame within the crushing chamber.
•    The main shaft that rotates and has a large flywheel mounted on each end. Its eccentric shape moves the moving jaw in and out.
•    Bearings that support the main shaft. Normally they are spherical tapered roller bearings on an overhead eccentric jaw crusher.
•    The toggle plate and seats. The toggle plate provides a safety mechanism in case material goes into the crushing chamber that cannot be crusher. It is designed to fail before the jaw frame or shaft is damaged. The seats are the fixed points where the toggle plate contacts the moving jaw and the main frame.
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IMPORTANT CONSIDERATIONS WHEN PURCHASING A JAW CRUSHER

•    The size of the opening into the crushing chamber. Two numbers, such as 24X36, commonly describe this. Where the opening between the top of the front and rear jaw plates is 24”, and the width between the side cheek plates would be 36”.  The width number is directly related to the production capacity, while both numbers will provide guidance for what the maximum size of rock that can be fed to the crusher. Typically you would not want to feed the crusher rock that is larger than 90% of the maximum opening.

•    Nip angle is a function of the depth of the crushing chamber and the curvature of the jaw plates. Typically the smaller the nip angle, the better. Where nip angle can be important is when crushing tough or hard materials, or rounded river rock. If the nip angle is too large then the stones can be pushed upwards. A long chambered jaw crusher usually has a smaller nip angle.

•    The discharge opening is the major factor for determining production capacity. The width will remain the same, but opening and closing the discharge setting will affect both the maximum discharge stone as well as the tonnage capacity. The larger the opening the greater the capacity. The discharge setting will be determined by the maximum size rock you want to discharge from the crusher. The maximum size you want discharged will be determined by what the discharged material will be used for. If you want to directly use the discharged material as a final product, then the discharge setting will need to be smaller than the maximum size of the final product. If the discharged material will go on to a secondary crusher, then the discharge setting will need to be set a little smaller than the maximum size rock that can be fed to the secondary crusher.

•    It is important to remove all materials that are already sized to the target final product prior to feeding the material to be crushed into the crusher.  This will increase the productive capacity of your crushing operation, and reduce the cost per ton for wear items.

•    The physical characteristics of the crushing chamber directly influences the crusher capacity, output gradation, and wear life. A longer chamber maximizes the amount of stone-on-stone crushing that occurs while the rock is within the chamber. The design of the manganese wear plates also influences the capacity, gradation, and forces exerted on each introduced rock. 
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GUIDELINES FOR PURCHASING A USED JAW CRUSHER

    There are several factors to consider and techniques to use when deciding to purchase a used jaw crusher. The following are examples:

•    What application was the jaw crusher used in? The type of rock can make a considerable difference. Limestone is easier to crush, and less hard on the crusher, than crushing granite.
•    Did the company have a good maintenance program and practice preventive maintenance and repairs during the off-season?
•    Does the main frame have cracks and welds indicating the crusher was subjected to tough crushing conditions?
•    Are there any cracks or welds on the flywheels? Unless the crack was welded professionally and then used for an extended period of time it is best to steer clear of any cracked flywheels.
•    Is the gap between the jaw plates and the sides equal on both sides? If it is not, that might be an indication of a failure or excessive wear inside the eccentric housing.
•    If the jaw crusher has been running for a while, is the eccentric housing hot to the touch? Does the grease nipple show signs of regular lubrication?
•    How worn are the manganese wear parts, both the jaw plates and the cheek plates?
•    Does the toggle plate fit tightly into the toggle seats or is there excessive wear? Does the toggle plate have any cracks in it? Has the toggle plate been replaced by a steel plate to save money?
•    How worn are the grooves on the flywheel?
•    Can the flywheels be turned by hand smoothly and without noise indicating a bearing failure or worn shaft?
•    Are there repair records or historical knowledge available?
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To see some of our available jaw crushers go to:
JAW CRUSHERS

For more information on crushing go to:
CRUSHING INFORMATION
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