Search Results for Hard surfacing

A cast dragline bucket tooth failed by fracturing after a short time in service. The tooth was made of medium-carbon low-alloy steel heat treated to a hardness of 555 HRB. The fracture surface was covered with chevron marks. These converged at several sites on the surface of the tooth. A hardfacing deposit was located at each of these sites. Visual inspection of the hardfacing deposits revealed numerous transverse cracks, characteristic of many types of hardfacing. This failure was caused by cracks present in hardfacing deposits that had been applied to the ultrahigh-strength steel tooth. Given the small critical crack sizes characteristic of ultrahigh-strength materials, it is generally unwise to weld them. It is particularly inadvisable to hardface ultrahigh-strength steel parts with hard, brittle, crack-prone materials when high service stresses will be encountered. The operators of the dragline bucket were warned against further hardfacing of these teeth.

River water was pumped into a brine plant by a battery of vertical pumps, each operating at 3600 rpm and at a discharge pressure of 827 kPa (120 psi). The pumps were lubricated by means of controlled leakage. The 3.8 cm (1 in.) OD pump sleeves were made of an austenitic stainless steel and were hard faced with a fused nickel-base hardfacing alloy (approximately 58 HRC). Packing for the pumps consisted of a braided PTFE-asbestos material. After several weeks of operation, the pumps began to leak and to spray water over the platforms on which they were mounted at the edge of the river. Analysis supported the conclusions that the leaks were caused by excessive sleeve wear that resulted from the presence of fine, abrasive silt in the river water. The silt, which contained hard particles of silica, could not be filtered out of the inlet water effectively.

The crankshaft of a 37.5-hp, 3-cylinder oil engine was examined. The engine had been dismantled for the purpose of a general overhaul and in the course of this work the crankpins were chromium-plated before regrinding. The engine was returned to service and after running for 290 h the crankshaft broke at the junction of the No. 3 crankpin and the crankweb nearest to the flywheel. A typical fatigue crack had originated at a number of points in the root of the fillet to the web. In its early stages it ran slightly into the web but turned back to the pin when it encountered the oil hole. The shaft had been made from a heat-treated alloy steel. The thickness of the plating was approximately 0.025 in. and numerous cracks were visible in it, several of which had given rise to cracks in the steel below. The primary cause of the crankshaft failure was the plating of the crankpins. The presence of the grooves alone would result in considerable intensification of stress in zones which are normally highly stressed, while the crazy cracking introduced a multiplicity of stress-raisers of a type almost ideal from the point of view of initiating fatigue cracks.

Plastics or polymers are used in a variety of engineering and nonengineering applications where they are subjected to surface damage and wear. This article discusses the classification of polymer wear mechanisms based on the methodologies of defining the types of wear. The first classification is based on the two-term model that divides wear mechanisms into interfacial and bulk or cohesive. The second is based on the perceived wear mechanism. The third classification is specific to polymers and draws the distinction based on mechanical properties of polymers. In this classification, wear study is separated as elastomers, thermosets, glassy thermoplastics, and semicrystalline thermoplastics. The article describes the effects of environment and lubricant on the wear failures of polymers. It presents a case study on nylon as a tribological material. The article explains the wear failure of an antifriction bearing, a nylon driving gear, and a polyoxymethylene gear wheel.

This article briefly reviews the analysis methods for spalling of striking tools with emphasis on field tests conducted by A.H. Burn and on the laboratory tests of H.O. McIntire and G.K. Manning and of J.W. Lodge. It focuses on the metallography and fractography of spalling. The macrostructure and microstructure of spall cavities are described, along with some aspects of the numerous specifications for striking/struck tools. The article also describes the availability of spall-resistant metals and the safety aspects of striking/struck tools in railway applications.

This article presents the mechanisms of polymer wear and quantifies wear in terms of wear rate (rate of removal of the material). Interfacial and bulk wear are discussed as well as a discussion on the wear study of "elastomers," "thermosets," "glassy thermoplastics," and "semicrystalline thermoplastics." The article also discusses the effects of environment and lubricant on the wear failures of polymers. It presents a case study on considering nylon as a tribological material and failure examples, explaining wear resistance of polyurethane elastomeric coatings and failure of an acetal gear wheel.

The first part of this article focuses on two major forms of machining-related failures, namely machining workpiece (in-process) failures and machined part (in-service) failures. Discussion centers on machining conditions and metallurgical factors contributing to (in-process) workpiece failures, and undesired surface layers and metallurgical factors contributing to (in-service) machined part failures. The second part of the article discusses the effects of microstructure on machining failures and their preventive measures.

Deformation, surface cracking, and spalling on the raceway of the outer ring (made of 4140 steel) of a large bearing caused it to be replaced from a radar antenna. The raceway surfaces were to be flame hardened to 55 HRC minimum and 50 HRC 3.2 mm below the surface, according to specifications. Samples from both the inner and outer rings were examined. A much lower hardness (25.2 to 18.9 HRC) was indicated during a vertical traverse 4.1 cm from the outer surface of the outer ring while slightly lower hardness values (46.8 to 54.8 HRC) were seen on the hardness traverse on the inner ring raceway. The lower hardness values were attributed to improper flame hardening. It was confirmed by metallographic examination of a 3% nital etched sample that the inner ring (tempered martensite and ferrite) and the outer ring (ferrite, scattered patches of pearlite, and martensite) were not properly austenitized. Displacement of metal on the outer raceway was revealed by elongation of grain structure. It was concluded that the failure of the raceway surface was due to incomplete austenitization caused by the improper heat treatment during flame hardening process.