. Electric railway journal . ased by the useof this switch as itpermits the handlingof a greater amountof material, sincethere is no necessityof losing time by ap-proaching the limitof travel slowly andcautiously. The safe-ty limit guards theequipment irrespec-tive of the kind ofcontrol or the posi-tion of the controllerhandle or brakes. Under normaloperating conditionsthe limit switch isheld in the operatingposition by the coun-terweight, as shown,which overpowersthe torsion operating springs. In case of overtravel,the counterweight is raised by the hoisting hook orother moving part, which pe
. Electric railway journal . ased by the useof this switch as itpermits the handlingof a greater amountof material, sincethere is no necessityof losing time by ap-proaching the limitof travel slowly andcautiously. The safe-ty limit guards theequipment irrespec-tive of the kind ofcontrol or the posi-tion of the controllerhandle or brakes. Under normaloperating conditionsthe limit switch isheld in the operatingposition by the coun-terweight, as shown,which overpowersthe torsion operating springs. In case of overtravel,the counterweight is raised by the hoisting hook orother moving part, which permits a strong torsionspring to operate the switch. This disconnects themotor from the line and establishes a closed dynamicbraking circuit. The operation of the switch alsoreleases the series magnetic brake which holds the loaduntil the controller handle is moved to the loweringposition. As soon as the hook has been lowered beyondthe limit, the switch is again ready to function as be-fore, as it resets itself Limit Switch Held in OperatingPosition By Means op Counter-weight November 19, 1921 Electric Railway Journal 909 New Light on Quenching Cracks OUENCHING cracks are very prolific sources oftrouble to tool hardeners, especially if the tools aremade from high carbon steel. Usually these crackshave been thought to be due to high quenching tempera-ture and non-uniform distribution of the temperaturein the part. An investigation at the Imperial Univer-sity of Japan by Honda brings out some other causeswhich tend to form quenching cracks. In all quenched steels a certain amount of austeniteis generally present mingled with some martensite, theamount increasing as the quenching temperature in-creases, and in small pieces of steel the periphery isharder than the central portion only when the quenchingis very slow. In a moderate quenching the hardnessis everywhere about equal and in hard quenching theperiphery is always softer than the interior. Thisphenomenon is ex
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