Search Results for gating systems

In the EMD-2 Joint Directed Attack Munition (JDAM), the A357 aluminum alloy housing had been redesigned and cast via permanent mold casting, but did not meet the design strength requirements of the previous design. Mechanical tests on thick and thin sections of the forward housing assembly revealed tensile properties well below the allowable design values. Radiology and CT evaluations revealed no casting defects. Optical microscopy revealed porosity uniformly distributed throughout the casting on the order of 0.1 mm pore diam. Scanning electron microscopy revealed elongated pores, which indicated turbulent filling of the mold. Spherical pores would have indicated the melt had been improperly degassed. Based on these findings, it was recommended that the manufacturer analyze and redesign the gating system to eliminate the turbulent flow problem during the permanent mold casting process.

Two investment-cast A356 aluminum alloy actuators used for handles on passenger doors of commercial aircraft fractured during torquing at less than the design load. Visual examination showed that cracking had occurred through a machined side hole. Fractography revealed that the cracks originated in hot tear locations in the castings. Microprobe analysis of fracture surfaces in the hot tear region indicated a much higher silicon-to-aluminum ratio compared with the overload fracture area. No microstructural anomalies related to the failure were found during metallographic examination. It was concluded that the strength of the castings had been compromised by the presence of the casting defects. Modification of the gating system for casting was recommended to eliminate the hot tear zone. It was also suggested that the balance of the castings from the same manufacturing lot be radiographically inspected.

Of the many different nondestructive evaluation (NDE) techniques, ultrasonic inspection continues to be the leading nondestructive method for inspecting composite materials, because measurements can be quantitative and the typical defect geometries and orientations lend themselves to detection and characterization. This article focuses on the three common methods for ultrasonic nondestructive inspection of plastics, namely pitch-catch, through-transmission, and pulse-echo, as well as the three basic types of ultrasonic NDE scans: the A-scan, B-scan, and C-scan. The discussion includes the linear and phased array systems that are sometimes used for large-scale inspection tasks to reduce scan times, the various gating and image processing techniques, and how ultrasonic data are interpreted and presented. A brief section on future trends in ultrasonic inspection is presented at the end of the article.

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.

A gray cast iron (ASTM 247 type A) gate valve in an oleum and sulfuric acid piping loop at a chemical process plant fractured catastrophically after approximately 10 years of service. The valve was a 150 mm (6 in.) bolted flange type rated to conform to ANSI B16.1 for service at 1034 kPa (150 psi) and 120 deg C (250 deg F) maximum in 93 to 99% sulfuric acid. The fracture originated at stress-corrosion cracks that occurred in a high-stress transition region at the valve body-to-flange juncture. The mechanical properties of the failed valve were below those of the manufacturer's cited specification, and the wall thickness through which the fracture occurred exceeded the minimum 9.5 mm (38 in.) thickness cited by the manufacturer The valve flange had been unbolted and rebolted to a maintenanced piping coil immediately prior to failure. It was recommended that the flange-to-valve body juncture be redesigned to reduce stress levels. A method of maintenance and inspection in concert with a criterion for life prediction for this and other valves and components in the system was also recommended.

After six years of service, three water shut-off valves on a copper water line in a residential building were found to be inoperative. Macroscopic examination of the valves after disassembly revealed that all three failed at the key that holds the spindle in the gate. In addition, the color near the key changed from yellow to red-brown. The gate was made from leaded red brass (85-5-5-5) while the spindle was made from silicon brass. It was concluded that the valves failed by dezincification resulting from bimetallic galvanic corrosion. It is common in the valve industry to use components made of different alloys in the same valve, but this is not the best approach for all applications.

The information provided in this article is intended for those individuals who want to determine why a casting component failed to perform its intended purpose. It is also intended to provide insights for potential casting applications so that the likelihood of failure to perform the intended function is decreased. The article addresses factors that may cause failures in castings for each metal type, starting with gray iron and progressing to ductile iron, steel, aluminum, and copper-base alloys. It describes the general root causes of failure attributed to the casting material, production method, and/or design. The article also addresses conditions related to the casting process but not specific to any metal group, including misruns, pour shorts, broken cores, and foundry expertise. The discussion in each casting metal group includes factors concerning defects that can occur specific to the metal group and progress from melting to solidification, casting processing, and finally how the removal of the mold material can affect performance.

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.

Manufacturing process selection is a critical step in plastic product design. The article provides an overview of the functional requirements that a part must fulfil before process selection is attempted. A brief discussion on the effects of individual thermoplastic and thermosetting processes on plastic parts and the material properties is presented. The article presents process effects on molecular orientation. It also illustrates the thinking that goes into the selection of processes for size, shape, and design factors. Finally, the article describes how various processes handle reinforcement.

This article describes the methodology for performing a failure modes and effects analysis (FMEA). It explains the methodology with the help of a hot water heater and provides a discussion on the role of FMEA in the design process. The article presents the analysis procedures and shows how proper planning, along with functional, interface, and detailed fault analyses, makes FMEA a process that facilitates the design throughout the product development cycle. It also discusses the use of fault equivalence to reduce the amount of labor required by the analysis. The article shows how fault trees are used to unify the analysis of failure modes caused by design errors, manufacturing and maintenance processes, materials, and so on, and to assess the probability of failure mode occurrence. It concludes with information on some of the approaches to automating the FMEA.

This article provides background information needed by design engineers to create part designs optimized for plastics and plastic manufacturing processes. It describes the four essential elements of plastic part development, namely, material, process, tooling, and design, and provides general design rules for the plastic forming processes covered. It also discusses the steps involved in design validation and verification.

A femoral knee implant was returned to the casting vendor for analysis after exhibiting poor bond strength between the cast substrate and a sintered porous coating. Both the coating and the substrate were manufactured from a cobalt-chromium-molybdenum alloy. Metallographic analysis indicated that a decarburized layer existed on all surfaces of the casting, which prevented bonding during the sintering thermal cycle. Bead-to-bead bonding within the coating appeared sufficient, and no decarburized layer was present on the bead surfaces. It was concluded that the decarburization did not occur during the sintering thermal cycle. It was recommended that the prosthetic manufacturer investigate atmosphere controls for all thermal cycles prior to coating.

This article discusses technologies focused on processing plastic materials or producing direct tools used in plastics processing. The article focuses on extrusion and injection molding, covering applications, materials and their properties, equipment, processing details, part design guidelines, and special processes. It also covers the functions of the extruder, webline handling, mixing and compounding operations, and process troubleshooting. Thermoforming and mold design are covered. Various other technologies for polymer processing covered in this article are blow molding, rotational molding, compression molding, transfer molding, hand lay-up process, casting, and additive manufacturing.

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.

A system of carbon steel headers, handling superheated water of 188 deg C (370 deg F) at 2 MPa (300 psi) for automobile-tire curing presses, developed a number of leaks within about four months after two to three years of leak-free service. All the leaks were in shielded metal arc butt welds joining 200 mm (8 in.) diam 90 deg elbows and pipe to 200 mm (8 in.) diam welding-neck flanges. A flange-elbow-flange assembly and a flange-pipe assembly that had leaked were removed for examination. Investigation (visual inspection, hardness testing, chemical analysis, magnetic-particle testing, radiographic inspection, and 2% nital etched 1.7x views) showed varying IDs on the assemblies and supported the conclusions that the failures of the butt welds were the result of fatigue cracks caused by cyclic thermal stresses that initiated at stress-concentrating notches at the toes of the interior fillet welds on the surfaces of the flanges. Recommendations included using ultrasonic testing to identify the appropriate joints and then replacing them. Special attention to accuracy of fit-up in the replacement joints was also recommended to achieve smooth, notch-free contours on the interior surfaces.

This article describes the historical background, uncertainties in structural parameters, classifications, and application areas of probabilistic analysis. It provides a discussion on the basic definition of random variables, some common distribution functions used in engineering, selection of a probability distribution, the failure model definition, and a definition of the probability of failure. The article also explains the solution techniques for special cases and general solution techniques, such as first-second-order reliability methods, the advanced mean value method, the response surface method, and Monte Carlo sampling. A brief introduction to importance sampling, time-variant reliability, system reliability, and risk analysis and target reliabilities is also provided. The article examines the various application problems for which probabilistic analysis is an essential element. Examples of the use of probabilistic analysis are presented. The article concludes with an overview of some of the commercially available software programs for performing probabilistic analysis.

Severe pitting was found on the internal surfaces of SA-210 Grade C waterwall tubing of a coal-fired boiler at a cogeneration facility. Metallographic examination showed the pits to be elliptical, having an undercut morphology with supersurface extensions,. a type of pitting characteristic of acidic attack. Energy-dispersive X-ray spectroscope revealed the presence of chlorine in the pit deposits, indicating that the pitting was promoted by underdeposit chloride attack. The presence of copper in deposits on the internal surface of the tubing may have acted as a secondary factor. Acidic conditions may have formed during a low-pH excursion that reportedly occurred several years prior. To prevent future failures, severely damaged tubing must be replaced. Internal deposit buildup must be removed by chemical cleaning to prevent further pitting. Water quality needs continued monitoring and maintenance to ensure that another low-pH excursion does not occur.

This article provides an overview of the structural design process and discusses the life-limiting factors, including material defects, fabrication practices, and stress. It details the role of a failure investigator in performing nondestructive inspection. The article provides information on fatigue life assessment, elevated-temperature life assessment, and fitness-for-service life assessment.