Search Results for Muffle furnaces

A brazing-furnace muffle 34 cm (13 in.) wide, 26 cm (10 in.) high, and 198 cm (78 in.) long, was fabricated from nickel-base high-temperature alloy sheet and installed in a gas-fired furnace used for copper brazing of various assemblies. The operating temperature of the muffle was reported to have been closely controlled at the normal temperature of 1175 deg C (2150 deg F); a hydrogen atmosphere was used during brazing. After about five months of continuous operation, four or five holes developed on the floor of the muffle, and the muffle was removed from service. Analysis (visual inspection, x-ray spectrometry, and metallographic examination) supported the conclusion that the muffle failed by localized overheating in some areas to temperatures exceeding 1260 deg C (2300 deg F). The copper found near the holes had dripped to the floor from assemblies during brazing. The copper diffused into the nickel-base alloy and formed a grain-boundary phase that was molten at the operating temperature. The presence of this phase caused localized liquefaction and weakened the alloy sufficiently to allow formation of the holes. No recommendations were made.

A locomotive type boiler was fitted with a copper firebox of orthodox construction. Flanged tube- and firehole-plates were attached to a wrapper plate by means of copper rivets. Shortly after it was put into service the fireside heads of a number of rivets broke off at different parts of the seams. By the time the investigation was begun a total of fifty heads had broken off. Repairs had been effected from time to time by fitting screwed rivets, none of which gave trouble in service. Microscopic examination confirmed the fracture path to be wholly intergranular. In the region of the fracture the grain boundaries were delineated as a near-continuous network of cavities and films of oxide. It was evident that the failure of the rivets in service was attributable to intergranular weakness in the material due to gassing.

This article focuses on manufacturing-related failures of injection-molded plastic parts, although the concepts apply to all plastic manufacturing processes It provides detailed examples of failures due to improper material handling, drying, mixing of additives, and molecular packing and orientation. It also presents examples of failures stemming from material degradation improper use of metal inserts, weak weld lines, insufficient curing of thermosets, and inadequate mixing and impregnation in the case of thermoset composites.

This article discusses the thermal properties of engineering plastics and elastomers with respect to chemical composition, chain configuration, and base polymer conformation as determined by thermal analysis. It describes the processing of base polymers with or without additives and their response to chemical, physical, and mechanical stresses whether as an unfilled, shaped article or as a component of a composite structure. It summarizes the basic thermal properties of thermoplastics and thermosets, including thermal conductivity, temperature resistance, thermal expansion, specific heat, and glass transition temperature. It also provides information on polyimide and bismaleimide resin systems. Representative examples of different types of engineering thermoplastics are discussed primarily in terms of structure and thermal properties.