Notes on Annealing Lehrs

JSGT 1937 V21 T177-T186

Although the muffle lehr possesses certain obvious advantages it has not entirely replaced the open-fired lehr because, in certain cases, the latter typo provides a greater margin of safety in the strength and durability of the ware. The results of strength and durability tests upon bottles and jars annealed in the two types of lehrs are given, and it is shown that whilst bottles annealed in open-fired lehrs gave somewhat higher values, the results for ware from muffle lehrs reached a standard well above that required in commercial usage. The reason for the difference in performance of the two types of lehr is discussed briefly, and it is shown that this difference lies in the contact of the circulating acid fumes present in open-fired lehrs. These hot fumes appear to have a beneficial healing effect upon the surface of the ware with which they come into contact, a benefit not provided by the hot air contact of muffle lehrs.

C. J. Peddle