To reduce reactions in a freight train
In January of this year, on the South-Western Road (Ukraine), a coupling was broken in the middle part of a cargo train weighing 5.2 thousand tons and 56 wagons long, which was operated by an electric locomotive VL80T. The defect was committed in a cliff—prone area with a critical track profile (ascent — small platform - descent) at the moment of brake release, when, after discharging the brake line (TM) by 0.7 kgf/cm2, the speed decreased from 58 to 40 km/h.
In the train, as it was later found out, the brakes did not work in six wagons, five of which were in its head, and the tail contained eight loaded tanks. On a rolling profile, the brakes in the head of the train were released much earlier than in the tail, so the head cars, already on the descent, rolled forward. At the same time, the tail section was still in a braked state on the site.
Additionally, at the time of the forward jerk of the head of the train, the weight of the tanks contributed to its rupture, the brakes of which, moreover, had not yet been released (the break occurred on the 25th second after the start of setting the crane handle of the driver in the release position with the actual release of the tail cars in 44 seconds). Traces of old cracks with an area of up to 9% of the total cross-section were visible on the shank of the broken coupling. When releasing the car brakes with the auxiliary brake crane No. 254, the driver should keep the electric locomotive in a braked state until the release process in the train is complete.
Could the train driver have known when the brakes on the train would be released, so that only then would the auxiliary brake of the locomotive be released by steps? Of course, there was enough time and braking before that (the last one before the cliff was the fifth one from the beginning of the movement). After all, the driver, checking the effectiveness of the car brakes on the way (along the traveled path and a 10 km/ h drop in speed), must also evaluate how they will behave during the vacation period. If, having carried it out with the driver's crane, the speed of the train stopped decreasing (stabilized) or began to rise (on the descent), then it can be roughly assumed that the car brakes have already been released. This time is usually 40-100 seconds.
Now let's look at the requirements for releasing brakes in freight trains according to instructions No. CT-CV-CL-VNIIZHT/277 in the Russian Railways system and No. CT-CV-CL/0015 — roads of Ukraine. The braking time of the 1.5 — 2.0 kgf/cm2 step by crane No. 254 during the release of the car brakes on the train, the first instruction sets 30 — 40 s, the second 40 — 60 s, and then the locomotive brake must be released in steps. Moreover, instruction No. CT-CV-CL/0015 specifies the condition that the handle of crane No. 254 should be permanently installed in the release position only after the brakes are fully released in the train, including in its tail section.
However, as a rule, the winter vacation for all freight trains exceeds the time set by the instructions. The same applies to any time of the year when following trains that contain tanks and hopper dispensers of all modifications, and also have an increased length. The release of brakes in trains takes much longer than the time set by the instructions of 30 — 40 (40 — 60) s. If after this time you release the brake of the locomotive, the previously compressed train will begin to "shoot". When a freight train is traveling downhill, when the brakes of the wagons in its tail section have not yet been released, a break in the coupling in the second or third part is guaranteed.
What should a train driver do? Of course, the regulated 30 — 40 (40 — 60) from holding the locomotive brakes must be increased until the brakes in the train are fully released. According to the same instructions, the brake release time of the tail cars in a train with a length of more than 200 axles can be 80 seconds, and at subzero temperatures — 120 seconds. Of course, the driver can be guided by the time specified in the VU-45 certificate, in accordance with the procedure established for Russian roads (unfortunately, such regulations have not been introduced on Ukrainian roads). But this time may be fictitious. Therefore, the driver additionally evaluates the duration of the release of the brakes when he checks their effectiveness. He should be guided by this time, driving the train in the future.
Thus, when checking the effect of the brakes, the time of their release is approximately determined from the moment when the driver's crane handle is placed in the release position until the train speed reduction (stabilization) is clearly stopped. If the vacation time was 60 — 120 seconds (which corresponds to the instructions), then questions arise: how will the locomotive's wheelsets behave, will they overheat, and will the bandages shift when braking with crane No. 254 at the same time? Here, of course, the ambient temperature matters. In winter, of course, the probability of overheating of the bandages decreases and, accordingly, it is possible to increase the continuous braking time with the auxiliary brake tap.
Although it is known that on a shunting locomotive, where often a decrease in the speed of movement of the train occurs only through the use of crane No. 254, the time of 30 — 40 (40 — 100) s is significantly exceeded, but no bandages are observed. Therefore, it is necessary to conduct additional research (theoretical and practical) in order to definitively say what the duration of continuous braking by crane No. 254 can be and with what permissible pressure in the shopping center so that the braking conditions are acceptable for the condition of the wheelset bandages.
Here, of course, in addition to the ambient temperature, the diameter of the wheel, the thickness of the bandage, and the speed of movement should also be taken into account, i.e., the conditions for the distribution (dissipation) of thermal energy. It is clear that if the locomotive has an electrodynamic brake, these problems are eliminated. Braking, release and traction conditions are facilitated if the train and the locomotive have a pressure monitoring device for the TM of the tail car.
On the other hand, regulatory documents allow holding the brakes of a freight train at one braking stage for up to 2.5 minutes (and for two or more stages — even longer). Therefore, the locomotive's brake may also be in such a braked state. After all, it is not written anywhere that during the period of operation of the car brakes on the train, crane No. 254 should be put on the buffer," i.e. release the locomotive brake (except when checking the operation of the car brakes). It is also not specified anywhere how long the auxiliary brake can be applied (simultaneously with the braking of the train) and then, accordingly, continue to keep it in a braked state already during the release of the brakes in the train.
Probably, if the auxiliary brake of the locomotive was not used during the braking period by the train, then the duration of its use may exceed the established 30 — 40 (40 — 60) s. Therefore, in the Instruction Manual for brakes of roads of Ukraine N° CT-CV-CL/0015, the holding time of the locomotive in a braked state with pressure in The brake cylinder of 1.5 — 2.0 kgf/cm2 was increased from 30 — 40 to 40 — 60 s when releasing the brakes of a freight train with a length of up to 350 axles. But after that, the locomotive's brake is released in steps so that its full release by crane No. 254 does not exceed the time of full release of the brakes of the train. An exception can be made only in cases when the train is traveling on a platform or ascent.
The use of position II of the driver's crane handle for releasing the car brakes makes it possible to slow down this process somewhat and thereby keep the train in a compressed state (without moving its head forward), using the permissible pressure in the shopping center for such cases up to 2.0 kgf/cm2. After the brakes are gradually released, the longitudinal-dynamic reactions will also not change quickly. And in the future, the position of the first crane of the driver will ensure reliable release of the tail section of the train. That is, when following the descent of a high-mass train, it is better to release the brakes in the above way, and of normal or increased length, as well as containing tanks and hopper-metering type wagons (with delayed release), to accelerate the release, use the position IV of the driver's crane.
Of course, it is difficult to keep a high-mass train that follows the descent in a compressed state during the release of the brakes using only crane No. 254. It is necessary to increase the pressure in the shopping center to 2.5 — 4.0 kgf/cm2 or keep the faucet in a stalled state for a long time. Therefore, in the newly issued instruction No. CT/0150 on the roads of Ukraine on preventing the breakage of automatic couplings, the driver is allowed to release the brakes on descents by setting the crane handle to position II for 20-30 seconds. Then, in position I, according to the requirements of the brake instructions, the pressure in the TM is set to 0.5 — 0.7 kgf/cm2 above the charging pressure. During the release process, crane No. 254 remains in the braking position with pressure support in the shopping center from 1.5 to 2.5 kgf/cm2. Or use an electric brake (if available).
Knowing approximately the release time of the car brakes, the driver can control the train, with less risk of breaking the automatic coupling. Let's consider several options for the operation of car brakes.
The first argument is that the brake release time is overestimated. This feature is already determined when checking the brakes — the speed of the train, even after setting the crane handle of the driver in the release position, continues to fall (see figure). Such differences can range from the starting speed of the brake check of 40 — 60 km/h to its reduction within 10 — 30 km/ h, i.e. the speed decreases by 20 — 40 km/h. This phenomenon is especially often observed in trains with hopper-dispenser type wagons and tank cars.
27.11.2022, 15:36
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