REPAIR & MAINTENANCE

Topics to Cover Repair of Cracks Threads Gear tooth, drives Bush bearing Assembly and dismantling of antifriction bearing; Maintenance of bearing, clutches, brakes, belt and chain drives, centrifugal pump, pipe and pipe fittings, electrical wiring, isolators and main switches, small induction motors; worn shafts, keyways, coupling, alignment of shafts,

REPAIR OF CRACK Process 1 Drilling fixture is attached at right angles to the crack. A hole pattern is drilled and this is repeated at intervals from 3 4 to 1 1 4 inches apart. Metal between each drilled hole is removed by ripping it away with pneumatic tools to form a slot. The stock thus removed is narrower than the drilled hole, thus forming a serrated opening. Preformed locks of high tensile alloy are inserted into the slot. These locks are peened into the slots, one on top of the other, to a depth limited by the casting thickness and determined by the strength required. After the locks are installed, holes are drilled, tapped and threaded fasteners are applied. These are spotted along the entire length of the crack, overlapping one another. Their purpose, in part, is to fill the fracture with new metal and provide a pressure seal. Entire repair area is peened flush and finish ground as you see here.

REPAIR OF CRACK Process 2 Process 3 Hot bolts are tightened when cools and closes the crack. Process 3 The cracks on oil tank machine bed are most commonly observed and repaired by this process. Riveting headless copper screws at the end of the crack, so that the crack doesn’t propagate further. Two plates are placed on either side of the crack and bolted onto the bed. Then they are wekded. When welding cools it shrinks and closes the crack.

REPAIR OF THREAD By thread repairing tool

REPAIR OF THREAD Contd.. By thread repairing tool

REPAIR OF GEAR Wear : On Open Transmission Gear, it is 0.5m (module) or about 32% of original tooth thickness and for closed transmission it is 0.3m (module) or 20% of original thickness. Uniform Tooth Face Wear on One Side: If gears are running in one single direction only. There will be a uniform wear on one face of all the teeth. Such gears are turned over by 180o. Uniform Tooth Face Wear on Both Side : The usability of tooth can be enhanced by : Replacing the smaller gear with thicker teeth. Replacing larger gear with negative correction and smaller with positive correction.

REPAIR OF GEAR Contd.. Broken Teeth : If there is impact load, broken tooth for module m > 4 is easily repaired. Copper template is used to avoid any sticking with iron thus smooth shape of tooth is produced. Damaged or Cracked Rim or Bore of the Gear Wheel: The defective bore portion in machined away and fitted with a new machined one. This is locked by sets of screws or welding.

REPAIR OF GEAR Contd.. Proper meshing of the spur and helical gears : It is done by applying blue paste on the teeth of the driving gear, giving it several rotations and seeing the blue marks on the teeth faces of the meshing driven gears. Identification of correct and incorrect meshing is done by following : Correct faces of the meshing 70-80% of tooth surface. Axes not parallel. Axes not parallel and center distance is too small. Axes not parallel and center distance between the axis in more. Axes parallel but distance between the axes in excessive. Axes parallel but center distance between is two small.

REPAIR OF GEAR Contd.. The correct meshing of the worm and worm wheel is decided by applying blue paste on the worm threads, giving it several rotations and seeing to the blue marks on the teeth faces of the worm wheel. Identification of correct and incorrect meshing is done by following : Normal mashing covering 64% of the tooth length. Incorrect meshing wheel shifted to right. Incorrect meshing wheel shifted to left.

ASSEMBLY AND DISMANTLING OF ANTIFRICTION BEARING Bearing Handling : It is generally a good idea to use gloves as well as carrying and lifting tools, which have been specially designed for mounting and dismounting bearings. This will save not only time and money but the work will also be less tiring and less risky. Use of heat and oil resistant gloves is recommended when handling hot or oily bearings. These gloves should have a durable outside and a soft non-allergenic inside. Satisfactory arrangements for carrying and lifting these bearings can be made on site in a workshop by using the bearing handling tool. If large, heavy bearings are to be moved or held in position using lifting tackle they should not be suspended at a single point but a steel band or fabric belt should be used. A spring between the hook of the lifting tackle and the belt facilitates positioning the bearing when it is to be pushed onto a shaft. When mounting a large housing over a bearing that is already in position on a shaft, it is advisable to provide three-point suspension for the housing, and for the length of one sling to be adjustable. This enables the housing bore to be exactly aligned with the bearing.

ASSEMBLY AND DISMANTLING OF ANTIFRICTION BEARING Assembly method (Cold mounting) : Bearings may be driven into position by applying light hammer blows to a sleeve placed against the bearing ring face mounting a bearing without heating. The blows should be evenly distributed around the ring to prevent the bearing from tilting or skewing. Most basic and direct mounting method. Applicable for small bearing. Applicable for interference fit, not so tight.

ASSEMBLY AND DISMANTLING OF ANTIFRICTION BEARING Contd.. Assembly method (Temperature/ Hot mounting) : To mount larger bearings this method is adopted as cold mounting force required to mount a bearing increases considerably with increasing bearing size. The necessary temperature differential can be obtained in one of three ways: Heating one part (most common) Cooling one part Simultaneously heating one part and cooling the other. Normally a bearing temperature increase of 150° F above the shaft temperature provides sufficient expansion for mounting. As the bearing cools, it contracts and tightly grips the shaft.

ASSEMBLY AND DISMANTLING OF ANTIFRICTION BEARING Contd.. Precaution to be taken : Heat the bearing uniformly and to regulate heat accurately. Bearings should not be heated above 250°F, as excess heat can destroy a bearing’s metallurgical properties, softening the bearing and potentially changing its dimensions permanently. Standard ball bearings fitted with shields or seals should not be heated above 210°F because of their grease fill or seal material. Localized overheating must be avoided. To heat bearings evenly induction heaters are recommended. If hotplates are used, the bearing must be turned over a number of times. Hotplates should not be used for heating sealed bearings.