TllANSFiUJMHR CASES AND TANKS 149 



-i)'<>ii Cases. For the majority ui' transformer cases, gal- 

 vanised sheet-iron or sheet steel is generally preferable, owing 

 to the small thicknesses which suffice with such constructions. 

 Another advantage of employing sheet-iron or sheet-steel for 

 transformer cases, relates to the lightness of such designs 



mpured with cast-iron cases, and the ease with which they 

 may be ribbed, thus not only providing a greater surface for 

 brat emission, but increasing the mechanical strength of the case. 

 Tin- sheet-iron is, however, generally used only for the sides of the 

 case. The bottoms and covers of the cases are usually formed 

 either of cast-iron or wrought-iron, these being subsequently 

 jinted to the sides by some one of several suitable method-, 

 by means of which the joints may be- made oil-tight. Where 

 the sides are constructed of sections, these sections may be 

 welded together, but this, although sound practice, is expensive. 

 \Yrtical joints are necessary with cases of corrugated sheet 

 iron, owing to the fact that the iron rollers cannot corrugate 

 inn of more than a certain width. In Fig. 86 is illustrated a 

 factory method of jointing the sides to the bottom of the 

 case. This method consists in providing two pieces of boiler- 

 iron riveted together to form the bottom, in addition to the 

 ordinary cast-iron base. These pieces of metal are so un- 

 equally dimensioned that when flanged to a certain bright a 

 channel is formed into which the sheet-steel sides are placed. 

 Snider is then poured into the channel, in order to render the 

 joint oil-tight. An alternative method of accomplishing the 

 ' object consists in forming the channel of two rib- oast 

 into the base itself. These methods are both rather expensive. 



ially when the corrugations in the sides are very d< 

 since this requires a large amou nt of solder to till in the channel. 



joint thus obtained is, however, quite oil-tight , j-.iul the 



method constitutes a reliable means of providing a joint that 



will continue to resfol the hot oil after tin- transformer has 

 been placed in service. A cheap and fre.pi, ntly-emplo\ed 

 method -'i jointio ic to the sides consist the 



