Wednesday, 7 November 2018

New Tracks

"Report #014
Bureau 540
May 21st, 1940

On trials of cast Hadfield steel tracks on the A-34 tank
...

2. Trials
  1. A set of tracks composed of track links cast from Hadfield steel was installed on the A-34 tank #311-18-3, which travelled over 417 km between May 12th and May 17th, 1940, of which 195 was on dirt roads, 80 was on sand roads, and 142 was on a cobblestone highway. The average speed of driving on the dirt road was 22.9 kph, the average speed of driving on the cobblestone highway was 37 kph.
  2. The following took place during the travel: rivets bursting and loss of 50% or rivets, cases of pins wobbling out of the eyes (2 cases at the start of the trials, the first at 61 km, the second at 120 km). The wobbling is explained by the fact that the pins have not yet broken in thanks to the large gap between the eye and the pin (18 +/- 1 mm, while the pin is 18 +/- 0.12 mm thick). In addition, the tracks were tightened three times.
  3. Tracks composed of cast track links were subjected to special trials on cobblestones, consisting of the following:
    1. Driving on the cobblestone highway in 4th gear at 1700-1800 RPM.
    2. 3 trials of braking while moving in 4th gear at 1700-1800 RPM.
    3. Driving over stones (cobblestones).
While driving on a cobblestone highway at 1700-1800 RPM at a speed of 36-37 kph, the tank had travelled for 111 km. No defects were discovered along the way, aside from lost track pin splints.

Braking: 
  1. Braking was performed while travelling at 1600 RPM with a headstart of 300-350 meters. The braking distance was 7 meters. No defects were discovered.
  2. Braking was performed while travelling at 1800 RPM with a headstart of 360-400 meters. The braking distance was 12 meters over 4 seconds. No defects were discovered.
  3. Braking was performed while travelling at 1800 RPM with a headstart of 250-300 meters. The braking distance was 12 meters over 5 seconds. No defects were discovered.
In addition to this, the tank drove over stones that were additionally piled onto the cobblestone highway. The tank drove over the stones, and no defects were discovered.

After the trials ended, the tracks were taken off and the right track was inspected carefully. 50% of track pin splints were lost. The track was taken apart and each link was examined with a magnifying glass.

Results of the inspection:
  1. The flat tracks have no cracks from impacts and driving on the cobblestone highway, or any other mechanical damage.
  2. The tracks with teeth, of the 37 inspected, have the following:
    1. 6 have no cracks or damage.
    2. 29 have tracks along the wheel contact surface near the base of the tooth from the side of contact of the tooth and the drive wheel, 10 mm to 40 mm in length.
    3. 2 have cracks down to the middle.
      The cracks at the base of the tooth are all of the same type. This means that the track link with a tooth has a weak point in the base of the tooth that must be reinforced. This is a design defect.
    4. To compare, stamped track links that have been through 3131 km of trials were inspected. Out of 40 inspected track links, only one crack was found, 15-20 mm long, on the first track link near the tooth.
Measurements were made of the pins and eyes of the cast tracks, the results were as follows:

Item
Distance travelled in km
Average wear in mm
Maximum wear in mm
Cast link pin
417
0.25
0.48
Cast link eye
417
0.34
0.62
Stamped link pin
3131
1.2
1.34
Stamped link eye
3131
1.22
1.34
The table of average wear of track link pins and eyes shows that the pins of the cast track links are worn down less than the eyes, but on stamped links the pins and eyes wear down at the same rate. Larger wear on the cast tracks is a disadvantage of the Hadfield steel track links, as it is desirable to replace the pins rather than the links when refurbishing tracks.

Note: the data on the wear of the pins and eyes of either the cast Hadfield tracks or the stamped Chromansil tracks cannot be considered definitive, as the stamped tracks were tested in winter conditions and the cast tracks were tested in the summer.

Conclusions

Trials showed that a tank equipped with track links cast from Hadfield steel did not stop due to track breakage during the run of 417 km. The tracks composed of cast links worked well without jamming, slipping, or other defects, and in general were analogous to the stamped track performance.

The results of assembly and trials revealed that the following is necessary:
  1. Correction of casting defects (cracks, pits)
  2. Creation of cleaner casts that would allow the eyes to line up and the pins to fit without individual filing down of the track links, as had to be done for the test tracks.
  3. Ensuring a clean eye so the pins break in better.
  4. Reinforcement of the track tooth base to prevent cracks from forming in the indicated spot.
We consider that the above trials confirmed the possibility of using track links cast from Hadfield steel on the A-34 tank instead of stamped links. With the aforementioned changes, the cast links will be useable on the A-34 tank.

Track links that are cast and do not need mechanical finishing and expensive stamping equipment are easier and cheaper to make.

As for the lifespan of the cast track links, it is necessary to produce a track made of links with the aforementioned corrections and put it through warranty trials in summer conditions. At the same time, we consider it necessary for the first tracks to continue testing past the 417 km until their total destruction to determine the effect of the discovered defects on the lifespan of the tracks."


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