Mild Steel Hard Grove Grindability Index Tester

SCOPE : This International Standard specifies the method for determining the grindability index of hard coal using the Hardgrove machine. It also specifies the procedure for calibrating the test machine and for pre-paring the standard reference coal samples.

DEFINITION : For the purposes of this International Standard, the following definition applies. Hard Coal : Coal having a gross calorific value of more than 24 MJ/kg on a moist, ash-free basis.

 PRINCIPLE : This instrument can be used to test the coal grindability by Hardgrove method. Hardgrove Grindability Index Tester is a special tester for testing the grindability of soft coal and blind coal. Takes grinding law as the theoretical basis (The energy consumed in coal grinding in proportional to the new surface area of coal dust) Treatment of a prepared sample of coal of limited size range under defined conditions in a laboratory apparatus of standardized designed (calibrated Hardgrove machine). Derivation of the grindability index from sieve analysis of the ground product and by reference to a calibration chart prepared from standard reference material.

SIEVES : Test sieves, complying with the requirements of 16 mm, 4.75 mm, 2.36 mm, 1.18 mm, and 600 µm, 75 µm required as per ASTM D409 respectively.

MECHANICALSIEVING MACHINE : Capable of accepting an assembly of vertically nested sieves. The machine shall be able to simulate the motions of hand sieving. This may be achieved by imparting a horizontal oscillatory motion of amplitude 25 mm to 30 mm at a frequency of approximately 300 min -1, whilst striking the top of the oscillating assembly with a mass of 1.9 kg, moving through a vertical distance of about 25 mm under the influence of gravity, at a frequency of approximately 150 blows per minute. Alternatively, the nest of sieves, cover and receiver may be vibrated by an electromagnetic device, pro-vided the sieving performance is equivalent to the mechanically vibrated machine described.

HARDGROVE GRINDABILITY MACHINE : Hardened iron or steel, with a horizontal track in which run eight steel balls, each of diameter 25, 4 mm. The balls shall be driven by an upper grinding ring rotated at 20 r/min ± 1 r/min. The upper grinding ring, which shall be of similar material to the bowl, shall be connected to a spindle and shall be driven by an electric motor through reduction gears. Aload shall be added to the spindle so that the total vertical force on the balls due to the top ring, gear, load and spindle is 284 N ± 2 N, i.e. closely equivalent to a total mass of 29 kg ± 0,2 Kg. The machine shall be fitted with a revolution counter and an automatic for stopping the machine after 60 ± 0,25 revolutions.

PROCEDURE : Weigh a test portion of 50 g ± 0,01 g of the dedusted material, distribute it evenly in the grinding bowl and smooth the surface. Assemble the top grinding ring to the bowl and fasten the bowl in position to the driving spindle, making sure that the load is evenly applied. Present the counter and adjust the automatic stopping device so that the machine will operate for 60 ± 0,25 revolutions.

          The Machine is Suitable for Laboratory Use for Coal Testing. It is complact with a sturdy base, plate support is provided with a bowl, centring shaft, Gear & Weight 29kg. +- 200gm. (cone & 8 Nos. Balls are common) with gear box and gear assembly. 8 Nos. Steel Balls 25 mm and preset counter are provided. The Machine is fitted with 1/4 hp Motor. Single Phase. The Main Shaft revoultion are 20 RPM +- 1 RPM.Optional:- Digital CounterOperation on:- 1/4 hp Motor 220/230V 50 Hz Single Phase main AC.   Spindle Speed RPM                                    20 ± 1 r