Apparatus for Testing Grinding Wheels for Strength
Abstract Generated abstract
This paper describes the development of a special test rig for strength and burst testing of high-speed grinding wheels intended for operation at peripheral speeds of 60 to 100 m/s. The apparatus uses a direct-current motor, belt transmission, high-speed spindle, reinforced protective chamber, and continuous speed regulation to test wheels up to 350 mm in diameter at rotational speeds up to 18,000 rpm, corresponding to peripheral speeds up to 200 m/s. A magnetic speed-sensing arrangement connected to a frequency meter provides rotational speed measurement, while generator-based motor control and auxiliary current regulation enable controlled acceleration and testing beyond the range of standard industrial machines.
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TEST RIG FOR STRENGTH TESTING OF GRINDING WHEELS
V. A. GOVORUKHIN, B. F. SHERKUNOV, N. V. YAREMENKO
(Presented by the scientific seminar of the Department of Machine Tools and Metal Cutting and the Department of Mechanical-Engineering Technology)
All grinding wheels must be tested for strength before operation at a speed exceeding the operating speed by at least 1.5 times for 5–10 min, depending on the diameter of the wheel being tested. Industrially produced machines for testing grinding wheels make it possible to test wheels operating at speeds of 35–50 m/s.
Fig. 1. General view of the rig for strength testing of grinding wheels.
The designs of high-speed grinding wheels for operation at speeds of 60–100 m/s, being developed in the laboratory of the Department of Machine Tools and Cutting Metals, required the creation of a special test rig (Fig. 1) for testing their strength and destruction at peripheral speeds of up to 200 m/s.
All parts and assemblies of the rig are mounted on a steel plate 1, which is rigidly fastened to the foundation by means of channels. The direct-current motor 2 transmits motion by a flat belt, through pulleys with a transmission ratio equal to 6, to the high-speed spindle 3, mounted in the bore of the grinding headstock 4. The spindle rotates in high-precision rolling bearings. A grinding wheel 5 with a maximum diameter of 350 mm is mounted on the spindle. For safe operation in the event of destruction of the wheel under the action of centrifugal forces, it is placed in a welded chamber reinforced with stiffening ribs. The chamber is made of steel sheet 15 mm thick around the peripheral part of the wheel and 10 mm thick on the end faces of the wheel.
The rotational speeds of the grinding wheel are varied continuously from 0 to 18,000 per minute. To measure the rotational speed of the grinding wheel being tested, a speed sensor was mounted on the second end of spindle 1 (Fig. 2).
Fig. 2. Device for measuring rotational speed
The fastening bolt of the small pulley 2 is replaced by a special bolt 3 with a permanent magnet 4 built into it. The winding 5 enclosing the magnet is connected to a frequency meter, which indicates the frequency of the induced emf, corresponding to a definite number of revolutions.
Power is supplied to the direct-current motor from a generator of 4.5 kW power, driven in rotation by a three-phase asynchronous electric motor. Regulation of the motor speed is effected by changing the emf of the generator, which depends on the value of the rheostat resistance. To reduce the armature current, an adjustable transformer with a rectifier bridge is connected into the shunt winding of the motor.