TRACTION ROLLING STOCK OPERATION PDF

___________________________________________________________________________ 7. TRAIN PARTING 7.1 TYPES OF COUPLER FORCES: 1. Draft Force :- It is the force on coupler required for pulling other attached coupler / wagon. Pulling of attached wagon starts onl...

___________________________________________________________________________ 7. TRAIN PARTING 7.1 TYPES OF COUPLER FORCES: 1. Draft Force :- It is the force on coupler required for pulling other attached coupler / wagon. Pulling of attached wagon starts only after complete extension of the couplers attached together. DRAFT-FORCE & KNUCKLE-SLACK ON COUPLER (DRAW-GEAR) IN RUN-OUT 2. Buff Force :- It is the force on coupler required for pushing other attached coupler / wagon. Pushing of other wagon starts only after complete compression of couplers attached together. BUFF-FORCE ON COUPLER DURING RUN-IN Traction Rolling Stock : OPERATION. 157 ___________________________________________________________________________ Spring-slack shown during Run-Out and Run-In respectively in Draft Gear 7.2 DEFINITION OF SOME TERMS : 1. Draw Gear : The actual coupling between loco & wagon or between wagons. 2. Draft Gear:- The impact absorbing apparatus, whereby the draw-gear is attached to a its loco or wagon. 3. Slack :- It is the free play provided in draw-gear and in some draft-gear. It is required for movement around curves & grades 4. Free Slack or loose slack :- It is the clearance within the draw-gear, which can run-in or run-out, without compressing / stretching the draft-gear. Its value is upto 1 inch for a wagon. 5. Spring Slack : It is the additional longitudinal movement that can occur after “free slack” movement is finished, and when draft-gear is compressed or rebounds directing all slack in opposite direction. Its value is upto 5 inches, when draft-gear is fully pressed. Total slack for 40 vehicles is about 20 feet. 6. Run-In: It is the rapid change of the train’s coupler-slack to buff (compressed). It may happen when rear section of a train travelling at faster speed bumps against the front portion of the train travelling at slower speed, due to sudden braking. 7. Run-Out: It is the rapid change of a train’s coupler-slack to draft (stretched). It may happen when rear section of a train travelling at slower speed stretches against the front portion of the train travelling at faster speed, due to sudden acceleration. 8. Slack Action : It is the movement of one part of a coupled train at a speed different from another part of the train, causing run-in or run-out. Impact Force due to bump on couplers varies as square of the difference of these speeds. Such repeated impacts cause wear and fatigue and finally coupler-breakage. Traction Rolling Stock : OPERATION. 158 ___________________________________________________________________________ 7.3 RUN-IN / RUN-OUT MECHANISM CAUSING COUPLER FORCES :- Run-In Mechanism at Km.167 due to undulating graded section is described on next page, with respect to the sketch of tension / compression forces shown above. As the locomotive start to climb the grade(B) the group of wagons near the bottom of the grade slow down after being in tension and begin to compress as the rear portion on the downhill grade runs into them. When the couplers in this region finally become compressed (C), the rear of the train runs in rapidly (D, E) until the wave reaches the rear of the train at which point the entire train begins to oscillate at its natural frequency. Traction Rolling Stock : OPERATION. 159 ___________________________________________________________________________ 7.4 CAUSES OF TRAIN PARTING: 7.4.1 DRIVING STRATEGIES : One of the key factors in limiting longitudinal coupler forces is the ability to control the slack action within the train. Relatively low forces will result if the coupler slack is taken-up one wagon at a time; however it is not possible with longer trains on undulating grades. It is important to prevent the relative movement of large groups of wagons that behave as single mass. High impact forces result when two blocks of bunched (or stretched) wagons separated by a number of stretched (or bunched) wagons move together (or apart) due to differences in speed along the train. When all slack between the two separate blocks of wagons is used up, the resultant run-in (or run- out) can easily cause longitudinal coupler forces in excess of the permissible limit. Maximum chances of train parting arise while negotiating undulating graded section. Following precautions may help in avoiding excessive coupler-forces & parting : 1. Try to maintain constant speed by MP manipulation and coasting by utilizing gradient rather than brakes. 2. Reduce power slightly just before approaching top of the hump, to avoid subsequent excess speed and use of severe braking. 3. Similarly increase power slightly just before approaching dip. 7.4.2 TRAIN BRAKE APPLICATION : The application and release of train brakes has been found to be a key factor in many of the recorded train partings and knuckle failures. A train brake application usually results in compressive coupler forces. However, much of the severity of the resultant run-in depends on the force and slack distribution within the train prior to the brake application. The wagons may or may not be uniformly loaded, so wagons may brake differently to each other accordingly. A good train handling practice for freight trains usually consists of keeping the consist stretched. This is achieved by keeping the consist in power while a brake application is made and by bleeding the air off the locomotives brakes before they apply. It is not possible to do this with the use of dynamic brake, which presents its own train handling challenges. The use of dynamic brake can result in a severe slack action, when applied; run-in is highly possible if brought-in at an inappropriate time (with respect to track geometry and train speed) and if released at an inappropriate time, can result in a run-out. Both can potentially snap train draw-gear, causing the train-parting. 7.4.3 Coupler Maintenance : It is observed from majority of C&M’s investigation reports of broken couplers that, the failure is often due to poor tensile strength (UTS) of coupler, caused by :- 1. Excessive & uneven wear on knuckle and plates. 2. Improper heat treatment of knuckle. Traction Rolling Stock : OPERATION. 160 ___________________________________________________________________________ 3. Casting Defects & Blow Holes. 4. Improper material composition. 5. Fatigue or old cracks. The CBC coupler is designed to withstand 295 T of UTS, whereas the maximum force found to be exerted on coupling due to worst driving of full load on a heavily graded section, as simulated on AC Loco Simulator at Bhusaval, is only 190 T, which can not cause parting, unless an old flaw in knuckle is existing. 7.5 Reasons of train-parting, due to uncoupling etc. : Lock not properly engaged Ineffective anti-creep device Uncoupling lever dropping on the run Unauthorized tampering with uncoupling lever Uncoupling due to vertical slipping out of knuckle 7.6 Precautions to reduce train parting:- 1. While starting from standstill, back the train a little. This will help in dropping of the locks where the lock has not fully dropped at the time of initial coupling. 2. Avoid sudden notching up. 3. Avoid sudden application of brakes from rear. 4. Allow time for brakes in rear wagons to get fully released before further notching up. 5. Try to keep the couplers in slack-stretched condition. 6. Ensure proper casting and maintenance of couplers. It is further explained as 6.1 Procurement of the coupler spares of proper quality needs to be placed on sound footing. 6.2 Purchase inspection by RDSO at coupler manufacture’s works is required to be stricter. 6.3 It is considered that some type of locking arrangement should be provided in the uncoupling gear to guard against unauthorized tampering with unlocking mechanism. 6.4 The wearing surfaces of the knuckle like the nose, lock face and hub may hardened by some suitable local hardening process like Plasma weld deposition process to reduce wear. 6.5 No coupler component should be lubricated at any stage. 6.6 Weld reclamation of pre and post heat treatment of the knuckle and lock to be carried out properly. It has been noticed during checks in certain Traction Rolling Stock : OPERATION. 161 ___________________________________________________________________________ workshops that the heat treatment procedure particularly is not being done properly. 6.7 All reclaimable components of the coupler, like shank , knuckle, lock and draft gear should be sent to workshop for reclamation/rejection. The operating mechanism and rotary lifting gear should be examined for any bent rod, broken bracket and defective/missing components. 6.8 Repairs/replacement to be carried out and where not possible, Wagon to be marked sick. 6.9 Some defects like excessive dropping of the coupler, crack in the coupler head, crack in the knuckle itself, loose and inadequate fastening of yoke pin support plate should checked properly. 6.10 Checking of anti-creep feature to be done on all wagons leaving sick line according to the method prescribed and any malfunctioning should be corrected. 7. Ensure proper working of DV. 8. Ensure correct handle position in wagon to empty / loaded. 9. Maintain proper height of couplers. 10. Arrest the air-leakages from BP pipe. ------------------------- Traction Rolling Stock : OPERATION. 162