BOGIES AND SUSPENSION - South Central Railway

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CHAPTER 6 – BOGIES AND SUSPENSION WAGON MAINTENANCE MANUAL Page 58 of 121 b. All spring will first be given a scrag test and also their camber will be checked. Facilities for these two checks should be provided in the lifting shop so that the springs, which pass both these tests, need not be transported to the smithy/ spring shop. The springs fail to these test should be taken to smithy/spring shop where it should be dismantled and scrag plate visually examined for presence of any surface defects such as cracks, corrossion, pits, dent marks etc. Those which are free from these defects should be re-heat treated (hardnened and tampered) under controlled conditions. The defective plates, if found, should be replaced by new once, properly heat treated. The assembled spring should be given scrag camber tests. c. Re-tempering of spring i. For restoring lost tamper, it is necessary to first re-harden the plate. ii. Water Hardening: The plates should be at a temperature of 810°C to 840°C at the time of quenching. If in resetting the plates to the required camber, the temperature drops below this limit, the plates should be reheated. For quenching the plate should be dipped edgewise taking care that the plate is kept horizontal. The plate or the quenching medium should be kept vigorously agitated. The plate should be withdrawn when it has cooled down. iii. Oil hardening: The plate should be at a temperature of 840°C to 870°C. the dipping of the plate should be done in the same manner as for water. The quenching medium would be quenching oil of an approved brand. The oil temperature should be prevented from rising abnormally be a water jacket in which water should be freely circulated. Aeration for the quenching oil would help in keeping down the temperature and also in keeping the oil in a state of agitation. iv. Tempering.: For tampering the correct temperature is even more important than hardening. A salt/lead bath maintained between 380°C to 420°C for water hardening quality, and between 450°C to 500°C for oil hardening quality spring steel should ensure plates being tempered uniformly. v. Temperature control: Hardening and tempering furnace should be provided with automatic pyrometric control to ensure correct hardening and tempering temperature. vi. Rolled eye: It should be ensure that there is a minimum gap of 2mm between the rolled end and the upper surface of the top plate. This is necessary to prevent the end bearing hard against the top plate when the spring is deflected. vii. Indentation: The malpractice of cold hammering of spring plate, as a result of which indentations are left should be seriously avoided as the indentations are potential stress raisers.
CHAPTER 6 – BOGIES AND SUSPENSION d) SCRAG TEST WAGON MAINTENANCE MANUAL Page 59 of 121 a) Measure camber. b) Press the spring home, six times. c) Re-measure camber. The loss of camber must not exceed half the thickness of the top plate. e) Load deflection Test At least 5% of C&W springs must be subjected to load deflection test. 605 D. CAUSES FOR FAILURE OF SPRINGS The spring may fail in service for reasons described below. Action/ precautions to be taken in each case are being indicated item wise: i. Incorrect composition of material: Different grades of steel plates some times get mixed up. It should be avoided. ii. Abnormal surface de-carburisation: This results in initiation of progressive cracks and hence reduction of spring life. This should be avoided during manufacture/repair. iii. Incorrect hardness of the plates: Brinell hardness of the plate should be within the specified limit. For heat treated laminated spring plates to IS 3885, range is 380-420. In case the hardness is beyond specified limit of material used, the spring plate should be re-heat treated. iv. Sharp edges of nib/groove: These act as stress raisers during service, causing cracks to originate from them. Sharp edges, if any, should be removed by grinding or other means. Nibbing tool should be properly chamfered to avoid sharp edges. v. Biting marks at the rolled eye portion: Biting marks act as stress raisers leading to fracture along the dent marks. A minimum gap of 2 mm should be ensured. vi. Punch marks on plates: These marks, particularly on tension side of plates, act as stress raisers during service and lead to early failure of springs. No punching should be done on spring plates. vii. Accidental injury to plate: Sharp dents or notches caused during manufacture or in service act as stress raisers and reduce the life of spring. It should be avoided during manufacture/ repair. If necessary, plate should be replaced. If such defects come to notice in service spring should be replaced. viii. Quenching cracks:-These are usually caused by (a) inadvertent use of wrong grade of steel for a given heat treatment procedure, (b) too drastic a quenching medium, (c) high hardening temperature, (d) insufficient soaking period, (e) surface defects such as seems laps, cluster of non-metallic inclusions occuring at or near the surface, (f) sharp grooves or dents on surface. In service, they act as stress raisers resulting in premature failure. Due care should be exercised during manufacture.
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BOGIES AND SUSPENSION - South Central Railway

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