ADC JAW CRUSHER INFORMATION

Introduction to Jaw Crushers

This section of the Aggregate Designs Corporation web site is intended to inform the reader about different aspects of jaw crushers.  There isn't a tremendous variation in jaw crushers, the primary differences is in their size.  Some units have hydraulic relief systems that can allow non-crushable material to go through the jaw crusher without snapping the toggle plate.  These aren't terribly popular though, as pit operators seem to prefer simplicity over the rare chance of breaking a toggle plate.

Part 1 — Components of a Jaw Crusher

Jaw Crusher Pitman

The pitman is the main moving part in a jaw crusher.  It forms the moving side of the jaw, while the stationary or fixed jaw forms the other.  It achieves its movement through the eccentric machining of the flywheel shaft.  Total back and forth movement of the top of the pitman is only about 1 1/2".  This gives tremendous force to each stroke.

As an interesting aside the term "pitman" means "connecting rod", but in a jaw crusher it really doesn't perform this function, that is it doesn't connect two things.  Other mechanisms called pitmans such as linkages in car/truck steering systems actually do connect things.  Thus it appears this is just the name that was applied to this part.

Manganese Dies in the Jaw Crusher

The jaw crusher pitman is covered on the inward facing side with dies made of manganese, an extremely hard metal.  These dies often have scalloped faces.  The dies are usually symmetrical top to bottom and can be flipped over that way.  This is handy as most wear occurs at the bottom (closed side) of the jaw and flipping them over provides another equal period of use before they must be replaced.

Jaw Crusher: Fixed Jaw Face

The fixed jaw face is opposite the pitman face and is statically mounted.  It is also covered with a manganese jaw die.  It is shown in the illustrations.

Eccentric Jaw Crusher Input Shaft

The pitman is put in motion by the oscillation of an eccentric lobe on a shaft that goes through the pitman's entire length.  This movement might total only 1 1/2" but produces substantial force to crush material.  This force is also put on the shaft itself so they are constructed with large dimensions and of hardened steel.

Jaw Crusher Input Sheave/Flywheel

Rotational energy is fed into the jaw crusher eccentric shaft by means of a sheave pulley which usually has multiple V-belt grooves.  In addition to turning the pitman eccentric shaft it usually has substantial mass to help maintain rotational inertia as the jaw crushes material.

Protecting the Jaw Crusher: the Toggle Plate

The bottom of the pitman is supported by a reflex-curved piece of metal called the toggle plate.  It serves the purpose of allowing the bottom of the pitman to move up and down with the motion of the eccentric shaft as well as serve as a safety mechanism for the entire jaw.  Should a piece of non-crushable material such as a steel loader tooth (sometimes called "tramp iron") enter the jaw and be larger than the closed side setting it can't be crushed nor pass through the jaw.  In this case, the toggle plate will crush and prevent further damage.

Retaining the Toggle Plate: the Tension Rod

Without the tension rod & spring the bottom of the pitman would just flop around as it isn't connected to the toggle plate, rather just resting against it in the toggle seat.  The tension rod system tensions the pitman to the toggle plate as shown in the illustrations.

Jaw Crusher Sides: Cheek Plates

The sides of the jaw crusher are logically called cheeks and they are also covered with high-strength manganese steel plates for durability.

Jaw Crusher Eccentric Shaft Bearings

There are typically four bearings on the eccentric shaft: two on each side of the jaw frame supporting the shaft and two at each end of the pitman.  These bearings are typically roller in style and usually have labyrinth seals and some are lubricated with an oil bath system.

Jaw Crusher Adjustment: Closed Side Opening Shims

Depending on the disposition of the material being crushed by the jaw different maximum-sized pieces of material may be required.  This is achieved by adjusting the opening at the bottom of the jaw, commonly referred to as the "closed side setting".  Shims (sometimes implemented and a more adjustable or hydraulic fashion) allow for this adjustment.

Part 2 — Important Considerations for Jaw Crushers

Jaw Crusher Opening Size

Jaw crushers are referred to by two sets of numbers, the first being the opening size of the jaw; the second being the width.  So, a "1036" jaw would accept a 10" boulder at the top and be 3' wide.  If the pit where the jaw is being used has river rock which does not exceed 10" in size then this size crusher would be acceptable.  Larger crushers are better choices when the average size is larger, such as where rock is blasted using explosives.  The width of the jaw directly impacts its throughput rate.

Jaw Crusher Nip Angle

The nip angle describes the angle the stationary jaw plate and the pitman make with each other.  The exact value of this angle isn't quoted or even determinable due to curvature in the jaws themselves but what is important is how wide vs. narrow it is.  Wide nip angles can tend to expel material as the jaw closes as a large ball might squirt out from under a car tire.  If the nip angle is narrow, not much vertical upward force is generated and more consistent crushing takes place.

Part 3 — Jaw Crusher Terminology

Jaw Crusher Terms

"aggregate" Any combination of crushed rock, gravel, sand or granular material suitable for the manufacture of hot mix asphalt, batch mix concrete or any other construction purpose

Part 4 — Jaw Crusher Illustrations *

	Cutaway view of a Jaw crusher.  Click on the picture to open a seperate window with a larger view
	Cutaway view of two of the eccentric shaft bearings.  This shows how the lobe portion of the shaft is enclosed in the pitman.  Click on the picture to open a seperate window with a larger view
	Animated view of a jaw crusher operating.  A grizzly feeder would normally divert material smaller than the closed-side opening around the jaw

 * Trademarks and photos are property of their respective companies