The pulao handle of the
Yongle Bell was cast with the lost- wax method before the body of
the bell was cast. Then it was placed at the joint of the inner and
outer moulds for connecting casting. The root of the handle was
threaded through the cavity between the inner mould and the outer
mould at the top of the bell. Steel cores were inserted into the
pulao handle to increase the strength of this part of the
bell. The ends of the handle were connected with the lower part of
the cavity at the top of the bell mould like four big round
weights. The diameter is longer than that of the upper part of the
bottom of the bell handle. In the process of casting, the handle
was connected with the top of the bell itself, so it grasped the
bell. If you examine the bell, you can hardly find any trace of
"hot crack" from the joint of the handle and the body of the bell.
Bronze is liable to "hot crack," but it is not so liable to "cold
crack." It was quite possible that the handle was preheated before
the body of the bell was cast. When a modem bell is cast at a
certain factory, they weld the cast handle and the body of the
bell. The top of the body of the bell is liable to "hot crack" if
no remedial measures are taken. The "connecting casting" technology
of the Yongle Bell provided much for us to learn from.