Search Results for Cold shuts

A lever (machined from a casting made of AISI type 410 stainless steel, then surface hardened by nitriding) that was a component of the main fuel-control linkage of an aircraft engine fractured in flight after a service life of less than 50 h. Investigation (radiographic inspection) supported the conclusions that the lever broke at a cold shut extending through approximately 95% of the cross section. The normally applied load constituted an overload of the remainder of the lever. Recommendations included adding magnetic-particle inspection to the inspection procedures for this cast lever.

A paper drier head manufactured from gray cast iron was removed from service as a result of NDE detection of crack-like surface discontinuities. This component was subjected to internal steam pressure to provide heat energy for drying. Investigation (visual inspection, chemical analysis, mechanical testing, as-polished 54x magnification, etched with nital 33x/54x/215x/230x magnification) supported the conclusions that the NDE indications were the consequence of a cold-shut condition in the casting. The cold shut served as a stress-concentration site and was therefore a potential source of crack initiation. The combination of low material strength and a casting defect was a potential source of unexpected fracture during service, because the component was under pressure from steam. Recommendations included removing other dryer heads exhibiting similar discontinuities and/or material quality from service.

Compound bow handle risers that had failed in service and during assembly along with an unassembled riser were submitted for analysis. The risers were die cast from magnesium-base alloy AM60A. Inspection of the failed risers and metallurgical investigations conducted on the stock riser revealed the presence of cold shuts at the same site in all specimens. It was recommended that all risers be thoroughly inspected and that the bow company work with their die casting shop to design a mold with acceptable filling characteristics.

A forging of 7075-T6 aluminum alloy, which formed a support for the cylinder of a cargo door, cracked at an attachment hole. Fluorescent penetrant inspection showed the crack ran above and below the hole out onto the machined flat surface of the flange. A 6500x electron fractograph proved the crack to be a forging defect called a cold shut. Because defects of this type are usually detected when the raw forging is inspected, this occurrence was considered to be an isolated instance.

Two sand-cast low-alloy steel equalizer beams (ASTM A 148, grade 105-85) designed to distribute the load to the axles of a highway truck broke after an unreported length of service. Normal service life would have been about 805,000 km (500,000 mi) of truck operation. Investigation (visual inspection, chemical analysis, tensile testing, unetched 65x and 1% nital etched 65x magnification) supported the conclusions that the steel was too soft for the application – probably due to improper heat treatment. Fracture of the equalizer beams resulted from growth of mechanical cracks that were formed before the castings were heat treated. Recommendations included the following changes in processing: better gating and risering in the foundry to achieve sounder castings; better shakeout practice to avoid mechanical damage; better inspection to detect imperfections; and normalizing and tempering to achieve better mechanical properties.

Several of the aluminum alloy 6061-T6 drawn seamless tubes (ASTM B 234, 2.5 cm (1.0 in.) OD with wall thickness of 1.7 mm (0.065 in.)) connecting an array of headers to a system of water-cooling pipes failed. The tubes were supplied in the O temper. They were bent to the desired curvature, preheated, then solution treated, water quenched, and then aged for 8 to 10 h. Analysis (visual inspection, slow-bend testing, 65x macrographic analysis, macroetching, spectrographic analysis, hardness tests, microhardness tests, tension tests, and microscopic examination) supported the conclusions that bending of the connector tubes in the annealed condition induced critical strain near the neutral axis of the tube, which resulted in excessive growth of individual grains during the subsequent solution treatment. Recommendations included bending the connector tubes in the T4 temper as early as possible after being quenched from the solution temperature. The tubes should be stored in dry ice after the quench until bending can be done. The tubes should be aged immediately after being formed. Flattening and slow-bend tests should be specified to ensure that the connector tubes had satisfactory ductility.

Three sprinkler system dry pipe valve castings (class 30 gray iron), two that had failed in service and one that had been rejected during machining because of porosity, were submitted for examination. The two failures consisted of cracks in a seating face. All three were from the same heat. Visual examination showed that the casting had cracked through a thin area in the casting sidewall. Evidence of a sharply machined corner at the fracture site was also discovered. Tensile testing and metallographic analysis revealed no metallurgical cause for the failure. It was recommended that the manufacturer work with the foundry to evaluate the criticality of core placement and to eliminate the undesired thin section.

This article focuses on the general root causes of failure attributed to the casting process, casting material, and design with examples. The casting processes discussed include gravity die casting, pressure die casting, semisolid casting, squeeze casting, and centrifugal casting. Cast iron, gray cast iron, malleable irons, ductile iron, low-alloy steel castings, austenitic steels, corrosion-resistant castings, and cast aluminum alloys are the materials discussed. The article describes the general types of discontinuities or imperfections for traditional casting with sand molds. It presents the international classification of common casting defects in a tabular form.

Both halves of a gray cast iron transmission housing from a 50-ton dump truck were found to contain numerous cracks. The housing material was possibly G3000 grade designation for automotive gray cast iron. No service duration or material specifications were provided. Investigation (visual inspection, tensile testing, 2% nital etched 59x cross sections, and metallographic analysis) supported the conclusion that failure was due to applied stresses sufficient to fracture the castings which exhibited brittle overload cracks at highly stressed locations. No recommendations were made.

This paper describes the analysis of the failure of a Zr-2.5Nb pressure tube in a CANDU reactor. The failure sequence was established as: (1) the existence of an undetected manufacturing flaw in the form of a lamination, (2) in-service development of the flaw by oxidation of the lamination, (3) delayed hydride cracking, which extended the flaw through the wall of the tube, resulting in leakage, and (4) rupture of the tube by cold pressurization while the reactor was shut down. The comprehensive failure analysis led to a remedial action plan that permitted the reactor to be returned to full-power operation and ensured a low probability of a similar occurrence for all CANDU reactors.

Lakes in zinc die castings are areas encompassed by irregular lines or waves on flat or slightly contoured surfaces which are intended to look uniform. The laked areas have to be removed by polishing before the castings can be plated. This adds considerably to the overall cost of production. Castings examined were of an automobile name-plate holder with two flat sides of approximately 113 sq cm. All castings produced during a trial showed laking defects, the number and position varying from casting to casting. It was found that formation of metal waves and lakes depended primarily on the design of the gate and runner system and operating conditions. High flow efficiencies, with adequate feeding to all sections of the die, and short cavity fill times are desirable.