GATE-CH-1993-10-a-mo-2mark

Match the following:

• I. Gyratory crusher

Answer 1C. Compression forceB. AttritionD. ImpactA. Shear force

• II. Hammer mill

Answer 2C. Compression forceB. AttritionD. ImpactA. Shear force

• III. Buhrstone mill

Answer 3C. Compression forceB. AttritionD. ImpactA. Shear force

• IV. Fluid energy mill

Answer 4C. Compression forceB. AttritionD. ImpactA. Shear force

GATE-CH-1989-3-i-a-mo-1mark

The angle formed by pouring a powder as a heap on a flat surface is known as:

• Contact angle

• Angle of nip

• Angle of repose

• Critical angle

GATE-CH-1990-3-i-mo-2mark

In a gyratory crusher the size reduction is effected primarily by:

• compression

• impact

• attrition

• cutting action

GATE-CH-1995-1-g-mo-1mark

A fluid energy mill is used for

• cutting

• grinding

• ultra grinding

• crushing

GATE-CH-1997-1-10-mo-1mark

For crushing of solids, the Rittinger’s law states that the work required for crushing is proportional to

• the new surface created

• the size reduction ratio

• the change in volume due to crushing

• none of these

GATE-CH-1998-1-12-mo-1mark

The work index in Bond’s law for crushing of solids has the following dimensions

• No units (dimensionless)

• kWh/ton

• kW/ton

• kW m\(^{1/2}\)/ton

GATE-CH-2002-1-17-mo-1mark

Arrange the following size reduction equipment in the decreasing order of the average particle size produced by each of them.

• Jaw crushers, Ball mills, Fluid energy mills

• Ball mills, Jaw crushers, Fluid energy mills

• Fluid energy mills, Jaw crushers, Ball mills

• Fluid energy mills, Ball mills, Jaw crushers

GATE-CH-2003-12-mo-1mark

Energy requirement (per unit mass of material crushed/ground) is highest for

• Jaw crusher

• Rod mill

• Ball mill

• Fluid energy mill

GATE-CH-2005-17-mo-1mark

The critical speed of the ball mill of radius \(R\), which contains balls of radius \(r\), is proportional to

• \((R - r)^{-0.5}\)

• \((R - r)^{-1}\)

• \((R - r)\)

• \((R - r)^{2}\)

GATE-CH-2007-12-mo-1mark

Size reduction of coarse hard solids using a crusher is accomplished by

• attrition

• compression

• cutting

• impact

GATE-CH-2008-14-mo-1mark

The power required for size reduction in crushing is

• proportional to \(\displaystyle \frac {1}{\text {Surface energy of the material}}\)

• proportional to \(\displaystyle \sqrt {\frac {1}{\text {Surface energy of the material}}}\)

• proportional to Surface energy of the material

• independent of the Surface energy of the material

GATE-CH-2010-1-mo-1mark

The critical speed (revolution per unit time) of a ball mill of radius \(R\), which uses balls of radius \(r\) is

• \(\displaystyle \frac {1}{2\pi }\sqrt {\frac {g}{Rr}}\)

• \(\displaystyle \frac {1}{2\pi }\sqrt {\frac {g}{R}}\)

• \(\displaystyle \frac {1}{2\pi }\sqrt {\frac {g}{r}}\)

• \(\displaystyle \frac {1}{2\pi }\sqrt {\frac {g}{R-r}}\)

GATE-CH-2014-17-mo-1mark

In order to produce fine solid particles between 5 and 10 \(\mu \)m, the appropriate size reducing equipment is

• fluid energy mill

• hammer mill

• jaw crusher

• smooth roll crusher

GATE-CH-1989-3-iii-a-mo-1mark

For proper functioning of a ball mill, it has to be operated at a speed ––––- (less / more) than its critical speed.

• Answer

GATE-CH-1989-13-ii-mo-4mark

A material is crushed in a jaw crusher and the average size of the particle reduced from 5 cm to 1 cm, with the consumption of energy of \(1.32\times 10^4\) J/kg. What will be the consumption of energy (in kJ/kg) to crush the same material of an average size of 7.5 cm to 2.5 cm, assuming:
(a) Rittinger’s law
{#1}

(b) Kick’s law
{#2}

GATE-CH-1991-14-i-mo-6mark

1. The power required to crush 100 ton/hr of a material is 179.8 kW, if 80% of the feed passes through a 51 mm screen and 80% of the product passes through a 3.2 mm screen. What is the work index (in kWh/ton) of the material?
   {#1}

2. What will be the power (in kW) required for the same feed at 100 ton/hr to be crushed to a product such that 80% is to pass through a 1.6 mm screen?
   {#2}

GATE-CH-2006-78-79-mo-4mark

A continuous grinder obeying the Bond crushing law grinds a solid at the rate of 1000 kg/h from the initial diameter of 10 mm to the final diameter of 1 mm.

(i) If the market now demands particles of size 0.5 mm, the output rate of the grinder (in kg/h) for the same power input would be reduced to

{#1}

(ii) In order to restore the output back to 1000 kg/h, an additional grinder was installed. The two grinders can be operated either in series (configuration-1) or parallel (configuration-2). Compare the two configurations in terms of the additional power consumption over the case above.

{#2}

GATE-CH-2001-2-8-mo-2mark

The energy required per unit mass to grind limestone particles of very large size to 100 \(\mu \)m is 12.7 kWh/ton. An estimate (using Bond’s Law) of the energy to grind the particles from a very large size to 50 \(\mu \)m is

• 6.35 kWh/ton

• 9.0 kWh/ton

• 18 kWh/ton

• 25.4 kWh/ton

GATE-CH-2002-2-20-mo-2mark

What is the critical rotational speed, in revolutions per second, for a ball mill of 1.2 m diameter charged with 70 mm diameter balls

• 0.5

• 1.0

• 2.76

• 0.66

GATE-CH-1987-13-i-mo-2mark

n a ball mill of diameter 2000 mm, 100 mm dia steel balls are being used for grinding. Presently, for the material being ground, the mill is run at 15 rpm. At what speed (in rpm) will the mill have to be run if the 100 mm balls are replaced by 50 mm balls, all the other conditions remaining the same?

• Answer

GATE-CH-1988-13-i-mo-4mark

A pair of rolls is to take a feed equivalent to spheres of 3 cm in diameter and crush them to spheres having 1 cm diameter. If the coefficient of friction is 0.29, what would be the diameter (in cm) of rolls?

• Answer

GATE-CH-1992-14-a-mo-6mark

Particles of average feed size \(25\times 10^{-4}\) m are crushed to an average product size of \(5\times 10^{-4}\) m at the rate of 15 tons per hour. At this rate the crusher consumes 32 kW of power of which 2 kW are required for running the mill empty. What would be the power consumption (in kW) if 10 tons per hour of this product is further crushed to \(1\times 10^{-4}\) m size in the same mill? Assume that Rittinger’s law is applicable.

• Answer

GATE-CH-1996-15-mo-5mark

The rate of grinding of uniform sized particles is assumed to follow first order breakage of particles. 50 grams of powder of average diameter 215 microns was ground in a laboratory batch mill. The amount of unground material (215 microns) was measured at various times of grinding and the results are given in table. Estimate the specific rate of grinding (in s\(^{-1}\)).

• Answer