Restoration of ancient bronze bells: Part I: powder metallurgy
de la Vega,José
There is a big number of church bells from the Colonial Period in the highlands of Northern Chile, which are damaged by use during centuries and by falls due to earthquakes that periodically affect the region. The aim of this work was to create a non-invasive method to restore these valuable pieces, leaving minimum trace of repair. A fissured church bell from the late nineteenth century was restored. Powder metallurgy was used to repair only in the thin line of the crack, and to prevent coarse material removal action on both sides of the crack, with subsequent filling with conventional weld at high temperatures. Fissures were filled with copper and tin powder, which were then welded with tin at a low temperature. The advantage of this method is that it does not cause local heating that can brittle the vicinity of the welded area, resulting in a smooth joint and a good adhesion surface for good sound transmission that can withstand stresses. Results: In order to verify the efficiency of the method, joint material strength was measured, and the sound was compared to the dominant note required by the DIN4178 Standard. A finite element model incorporating a filler ring in the repair area was as well verified. The rationale for these repair works lies in that the old bells in question need to be preserved, since they are culturally valuable artifacts that hold rich metallurgical knowledge and are part of the national heritage.