Document 6bEKjna2g0rQM9GJBo8kbQwyE

penenced workmen Crucibles should be supported on foundations or pedestals of fire brick, graphite, or other infusible material The removal of heavy crucibles from fur naces calls not only for special skill but also for physical strength If the men are over strained, serious accidents are likely to result Where possible, therefore, a mechanical de vice should be employed for removing heavy crucibles --those exceeding 100 lb in com bined weight of crucible, tongs, and metal (Fig 28-9) Crucible furnaces The operation of crucible furnaces is a rela tively hazard-free operation if suitable ex haust hoods are installed on all furnaces used for melting metals which give off harmful fumes Upright furnaces having crown plates more than 12 in above the surrounding floor should be equipped with metal platforms having standard rails Such platforms should extend along the front and sides of the furnace flush with the crown plates and clear of all obstruc tions Crucibles containing molten metal should be lowered from these platforms me chanically Many crucible furnaces are oil fired, and unless the motors driving the oil pump and the air supply for the furnaces are connected to the same source of power, a considerable quantity of oil may flow onto the floor if the power goes off the air line One remedy is to put a gate valve in the oil supply line so that in case of an air failure, oil can be shut off from the entire battery of crucible furnaces m one operation If the pilot and burner are electrically controlled, this valve can be so arranged that it will be similar to an interlock A mechanical shutoff can be made by the installation in the oil line of a gate leveroperated valve which is closed by the release of a weight Since the weight is held up normally by an air cylinder, the oil supply is stopped at once when the air goes off A small hole may be drilled in the cylinder so that air in it may be released promptly when the oil pressure goes off Ovens The pnncipal hazards in the construction and operation of core ovens and mold drying ovens are excess smoke, gases, and fumes given off into the foundry atmosphere Other unsafe conditions are unprotected firing pits, unguarded vertical sliding doors or their counterweights (which may drop on workers), and flashbacks from fire boxes Finng pits into which men may fall should be guarded with substantial railings or with grating covers having trap doors to give access to the steps leading down into the pits Safe types of vertical sliding doors should be installed Cables and chains having a high factor of safety, substantial cable and chain fastenings, large sheaves to prevent undue wear of cables, and guarded counter weights are also necessary All sliding doors should be thoroughly inspected at frequent intervals Safety dogs may be used to hold the doors in raised position Many vertical core ovens are 60 to 70 ft high and have a driving mechanism located at the top Some foundries have installed steel stairways with standard treads wherever possible Where metal ladders must be used, not less than 6 in of clearance should be maintained from the center of each ladder rung to the side of the oven A caution sign should be placed on the wall near core ovens, giving necessary pre cautions and manufacturer's instructions to be observed when ovens are being lighted Gas-fired ovens Gas-fired ovens should, whenever possible, be located in a room separate from the mold ing floors and also from the coremaking room by a partition This measure will help pre vent equipment failures caused by sand in the controls Blast tip pipe burners should be equipped with baffles to keep sand out of the tip and also to spread the flame Tips should also be horizontal to protect them from sand Safety pilot valves will prevent the flow of unbumed gas into the oven combustion chamber should the burner pilot light go out, or should a cock or burner be accidentally opened A valve of this nature should be installed on every gas-buming furnace or oven A bleeder valve in the line between two control valves close to the burner is an addi tional safety device The operator can then 817