The Blake Jaw Crusher, Principle, Construction and Working

Crusher definition: Crushers are slow-speed machines employed for the coarse reduction of large quantities of solids. Jaw crushers, Gyratory crushers, and Smooth-roll crushers are the main types of crushers. 

They operate or are used by compression and can break large lumps of hard materials. They find applications in the rockery and mining industries.

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Types of Jaw Crushers 

Jaw crushers compress the feed between a stationary and a movable jaw. There are 3 types of Jaw Crushers.

1. Blake Jaw crusher.

2. Dodge jaw crusher.

3. Overhead eccentric crusher.

In the Blake Jaw crusher, the movable jaw is pivoted at the top, thus giving the greatest movement at the bottom. In the Dodge jaw crusher, the movable jaw is pivoted at the bottom, thus giving the greatest/maximum movement at the top. The Dodge crusher is less widely used because of its tendency to choke due to the minimum movement of the jaw at the bottom.

Advantages and Disadvantages 

(i) movable jaw is pivoted at the top, 

(ii) maximum movement is at the bottom, 

(iii) no tendency to choke/clog, 

(iv) suitable for high production rates, 

(v) A large reduction ratio is not possible, 

(vi) low maintenance, 

(vii) comparatively made in large sizes, 

(viii) does not give uniform products, 

(ix) commonly/widely used. 

Dodge Jaw Crusher Advantages and Disadvantages

(i) movable jaw is pivoted at the bottom,

(ii) maximum movement is at the top,

(iii) tendency to choke (no  freedom from chocking),

(iv) suitable for low productivity rates,

(v) A large reduction ratio is possible,

(vi) high maintenance,

(vii) comparatively made in smaller sizes,

(viii) gives uniform products,

(ix) seldom/less widely used.

Blake Jaw Crusher Principle

The Blake Jaw crusher is it works on the Principle of compression.

Construction of Jaw Crusher 

A schematic diagram of the Blake jaw Crusher is shown in Fig. It has a fixed jaw and a movable jaw, which is pivoted at the top. The jaws are not set to form a V open at the top. The swinging jaw which reciprocates in a horizontal plane usually makes an angle of 20 to 30° with the fixed jaw.

Jaw crusher diagram

The jaws are usually made of manganese steel or some other material that will withstand abrasion. The faces of the crushing jaws are usually corrugated to concentrate the pressure on relatively small areas. In addition to the jaws, the crusher consists of a Pitman, toggles, flywheel, eccentric shafts, drawback rod, and spring and frame. In this vertical movement is communicated horizontally to the movable jaw by the toggles. 

The speed of operation should not be high or otherwise, a large quantity of fines is produced as the material cannot escape quickly and gets repeatedly crushed. As the crushing action is intermittent, the loading on the machine is uneven. Hence, the crusher incorporates a heavy flywheel.

Protection of Jaw Crusher 

The machine is usually protected so that it is not damaged if accidental pieces of iron such as hammerheads, stray bolts, etc. enter the crusher, making one of the toggles in the driving mechanism relatively weak. That is, one particular toggle is made into two pieces which are held together with bolts that are purposely made the weakest part in the crusher. 

If at all the material that causes the destructive strains, enters the crusher, these bolts shear through and allow the movable jaw to drop back far enough to discharge the obstacle. Thus, the failure is made at a point that can be easily and quickly repaired, instead of breaking some vital part of the machine.

Since the maximum movement of the jaw is at the bottom (discharge) there will be little tendency for a crusher of this kind to choke.

 Also Read: Kirchhoff's Law Engineering 

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Jaw Crusher Working Principle 

The material to be crushed is admitted between two jaws from the top. The material caught between the upper part of the jaws is crushed to a smaller size during forward motion by compression. The crushed material then drops/falls into the narrower space below during the backward motion and is recrushed as the jaws close next time. 

After sufficient reduction, the material drops out the bottom of the machine. The jaws open and close 250 to 400 times per minute. 

Take these Notes is, Orginal Sources: Unit Operations-II, KA Gavhane