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Journal Boxes and their inspection

By February 7, 2016February 10th, 2016Features

By Steve Smith, Wiscasset, Waterville & Farmington Railway Museum
Photos by the author; diagram by John McNamara.

Reproduced with permission from the WW&F newsletter.

There is a journal box at each of the four corners of any truck under a freight or passenger car at the WW&F Railway Museum. The picture below shows a typical journal box with the cover swung part way open.

P4Top Truck Photo SS

A journal box has three main functions:

  • To transfer a share of the car and cargo weight to the axle while allowing the axle and its wheels to rotate.
  • To lubricate the mating surfaces of the bearing and journal for minimum friction and wear.
  • To protect the components in the box from grit or water.

The photo and vertical section drawing below show the key parts.

P4Mid Bearing Diagram JPEG P4Mid Bearing Photo SS

The bearing is made of bronze with a thin, smooth layer of babbit metal on its curved under side. The bearing transfers a share of the weight of the car and cargo to a mirror smooth section of the axle called the journal. Lubrication of the bearing-journal interface comes from oil-saturated packing (for example, textile waste or braids of woolen yarn) in the bottom half of the box. As the axle rotates, the underside of the journal picks up oil from the packing.

The shim is a rectangular block of steel separating the bearing from the top of the box. The purpose of the shim, which is cast iron, is to allow removal of the bearing without disassembling the truck. Without a shim, the bearing would be much thicker, and the top of the box thicker, to get the axle center in the correct vertical placement within the box. There would be insufficient vertical clearance to jack the box enough for the bearing to clear the axle end cap. With the shim design, the box only needs be jacked about 1/2”; then the shim and bearing can be pulled out easily. Each end of the axle has an end cap that is larger than the journal, but smaller than the wheel press-fit diameter of the axle. For the WW&F axles, the diameters are: end cap 3-1/2”; journal 3” and wheel press-fit: 3-7/8”. The axle can move only a short distance either way in the direction of its axis before one end cap or the other contacts its corresponding bearing and prevents further movement.

Almost all the journal boxes at the Museum are as described, and the bearings in them are called friction (or plain) bearings because the journal and bearing surfaces glide relative to each other. Friction/plain bearings are a thing of the past on most railroads now, rendered obsolete by roller bearings. The latter are vastly more reliable and require much less maintenance than friction bearings, but the WW&F went out of business before roller bearings became standard. The only four journal boxes at the Museum with roller bearings are on the south truck of excursion car 103. So far, the only service those bearings have required is maintaining enough oil in the box so that the rollers dip slightly into the oil on each revolution.

The practice at the Museum is to inspect/service each journal box quarterly, to ensure that the packing is saturated with oil (the Museum uses SAE 30 motor oil) and in proper place as shown in the drawing. If the packing surface is found to be higher than shown in the drawing, it is tamped back down. This minimizes the risk of a “waste grab” and consequent pulling of packing strands all the way around the bearing. That situation could lead to localized oil starvation in part of the journal-bearing contact zone and cause damage. In case of a waste grab, the journal box in question is jacked up so that the misplaced packing can be removed. Prior to box jacking, the box on the other end of that axle must be firmly supported by blocking. Otherwise, jacking will raise the journal and the box together and prevent bearing removal. Also, if the wheel set in question has a brake shoe, the car must be secured from rolling and then the brakes released. If not, when jacking commences, the brake shoe lifts wheel, axle, and box together and makes it impossible to slide out the bearing.

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