THE ROYAL ARTILLERY INSTITUTION. 
417 
The triple coil is made of three bars all of the same section, viz.— 
41 " x 41 " x 4 ", hut differing of course in length, the first or innermost 
one being 78 feet, the second 118 feet, and the third 158 feet in length, 
the middle one being coiled in the reverse direction so as to break joints. 
In order to weld its folds, it is placed in a furnace for about ten hours, at 
the end of which time it is at a welding heat, whereupon it is rapidly- 
transferred to a powerful hammer, and receives a few smart blows on its 
upper end, which close the folds longitudinally. A mandril somewhat 
larger in diameter being then forced down it, it is turned on its side, and 
well hammered all round to make it dense. It is replaced in the furnace 
for about six hours, and the same process repeated at the breech end, but 
with a smaller mandril. 
When cold, the ends are faced and the outer coil is turned down at the 
muzzle end to form a shoulder 14" long for the reception of the trunnion 
ring. 
The C coil is made of bars of the same section as those used for the triple 
coil. The inner bar is 46 feet in length, and the outer one 69 feet. This 
double coil being welded, has a shoulder formed on the lower end about 
9 inches long and J- inch deep, so that it may overlap the trunnion in the 
welding. 
The trunnion ring is made like all wrought-iron trunnion rings—namely, 
of slabs of iron consecutively welded together on the flattened end of a 
porter bar, and gradually formed into a ring by means of, first, a small iron 
wedge, which is driven through the centre and punches an oval hole, and 
then by a series of taper mandrils increasing in size, which make the hole 
sufficiently large and round. The trunnion ring has to be heated for each 
punching, and the occasion is used to hammer the trunnions roughly into 
shape, one of which is in continuation of the porter bar. Eventually the ring 
is cut off from the bar by means of strong blunt hatchets of steel hammered 
through it. The trunnion ring is next roughly bored out. 
All three parts (breech coil, C coil, and trunnion ring), being thus pre¬ 
pared, the trunnion ring is heated to redness, lifted by a crane, and dropped 
on to the shoulder of the triple coil, which is placed upright on its breech 
end for the purpose. 
While the trunnion ring is still hot, the C coil is dropped down upon the 
front of the triple coil, through the upper portion of the trunnion ring which 
was left projecting. The trunnion ring thus forms a band over the joint, 
and in cooling contracts round the two coils, and grips them sufficiently 
tight to allow of the whole mass being placed bodily in a furnace, where it 
is raised to a welding heat in about thirteen hours (see diagram, breech coil, 
trunnion ring, and C coil ready for welding). 
The glowing mass is then quickly placed on its breech end under the 
most powerful hammer in the Department. Six or seven blows on the top 
suffice to amalgamate the three parts together; but to make the welding more 
perfect on the interior, as well as to obviate any bulging inside, a cast-iron 
mandril somewhat larger than the bore is forced down to within 20 inches 
of the breech end, a series of short iron plugs being used to drive it down. 
The mass is then reversed, and the mandril is driven out with the same 
plugs, -which have fallen out in the tilting over. 
