Chapter 3
Plumber Blocks
The materials employed are flats, rounds, tubes and plates. This plummer block is made from flat bar and round tube. The fillet weld between the tube and the bar by its notch formation presents a severe problem of cracking at the weld root. This weld is to be avoided wherever possible, but there are occasions, like this, where it must be employed.
Fig. 20 is an enlargement of the details of the problem, and shows the danger. The large mass of metal labelled 'Chill Zone' being at room temperature when welding begins rapidly chills and solidifies the weld metal at the root of the weld. The top of the weld deposit is of greater cross section and contains more molten metal than the root, so it remains liquid longer.
When cooling, and thus contracting, it tends to compress the root metal which has already set. Consequently a crack forms in the lop of the root run. Subsequent welds when contracting during cooling are restricted by the already solidified root run and the problem again rises. The cure is to make the initial and subsequent runs as heavy as possible consistent with the size of materials in use, to use as large a gauge of electrode as these circumstances permit and to deposit as much metal in each run as is practicable.
These measures ensure a high heat input to the base metal, thus reducing its chilling action and therefore slowing up considerably the speed with which the molten weld metal solidifies. The use of low hydrogen electrodes which are proof against cracking will greatly lessen the danger of such trouble arising in this particular notch formation. The nomenclature of low hydrogen electrodes is by no means settled and they are often referred to as basic and lime fcrritic electrodes.
Plummer Blocks or Axle Bearings
Tube spaced away from flat bar.
This is a dual-purpose fabrication. It can be used as a plummer block, or reversed as an axle bearing for a trolley or similar vehicle. The construction is clear from the sketch (Fig. 21); additional strength can be gained by adding four fillet welds inside the enclosure formed by the tube and flat bar. For exceptional strength the space between the bar and the tube, approximately a truncated triangle in outline, can be occupied by a plate fillet welded into position.
Split Plummer Block (Fig. 21 (a)
Materials used are flat bar and or square bar plus bolts. The two bars to form the bearing housing are first cut off. marked out, the top one clearance drilled and the lower drilled and tapped. These two bars, bolted together, arc then fillet welded to the base plate and allowed to cool. After cooling is complete the bearing is drilled, reamered and the bush fitted. Subsequently an oil hole is drilled through the steel bar housing and bush.
