Search Results for lead screens

Radiography is the process or technique of producing images of a solid material on a paper/photographic film or on a fluorescent screen by means of radiation particles or electromagnetic waves of short wavelength. This article reviews the general characteristics and safety principles associated with radiography. There are two main aspects of safety: monitoring radiation dosage and protecting personnel. The article summarizes the major factors involved in both and discusses the operating characteristics of X-ray tubes. It describes the various methods of controlling scattered radiation: use of lead screens; protection against backscatter and scatter from external objects; and use of masks, diaphragms, collimators, and filtration. The article concludes with a discussion on image conversion media, including recording media, lead screens, lead oxide screens, and fluorescent intensifying screens.

Film radiography requires the development of the exposed film so that the latent image becomes visible for viewing. It describes the general characteristics of film, including speed, gradient, and graininess, and the factors affecting film selection and exposure time. The article discusses the three major inspection techniques for tubular sections, namely, the double-wall, double-image technique; the double-wall, single-image technique; and the single-wall, single-image technique. It illustrates the arrangements of penetrameters and identification markers for the radiography of plates, cylinders, and flanges. The article discusses various control methods, including the use of lead screens; protection against backscatter and scatter from external objects; and the use of masks, diaphragms, collimators, and filtration. The radiographic appearance of specific types of flaws is also discussed. The article concludes with a discussion on two methods of radiographic film processing: manual and automatic processing.

This article describes the various factors that affect the extent of corrosion resulting from galvanic coupling. The factors include galvanic series, polarization behavior, and geometric relationship of metals and alloys. The article briefly discusses the various modes of attack that lead to galvanic corrosion of anodic members. It also explains the three electrochemical techniques of screening tests for predicting galvanic corrosion. The electrochemical techniques comprise of potential measurements, current measurements, and polarization measurements. The article provides a detailed discussion on the performance of alloy groupings. It concludes with information on various control methods that reduce or eliminate galvanic-corrosion effects.

Melting with induction crucible furnaces (ICFs) is a well-established and reliable technology, and their maintenance must be performed at regularly scheduled intervals to ensure safe operation. This article discusses monitoring of the refractory lining, and presents an overview of the various wear-indication methods, namely, manual checks, ground leakage indication, evaluation of electrical values of the furnace, and temperature measurement. It also presents the working principle, physical restrictions, limitations, and remarks on these methods.

Radiography is a nondestructive-inspection method that is based on the differential absorption of penetrating radiation by the part or test piece (object) being inspected. This article discusses the fundamentals and general applications of radiography, and describes the sources of radiation in radiographic inspection, including X-rays and gamma rays. It deals with the characteristics that differentiate neutron radiography from X-ray or gamma-ray radiography. The geometric principles of shadow formation, image conversion, variation of attenuation with test-piece thickness, and many other factors that govern the exposure and processing of a neutron radiograph are similar to those for radiography using X-rays or gamma rays.

Digital radiography is a technique that uses digital detector arrays (linear or area) to capture an X-ray photonic signal and convert it to an electronic signal for display on a computer. This article begins with an overview of real-time radiography and provides a schematic illustration of a typical radioscopic system using an X-ray image intensifier. It discusses the advantages and limitations of real-time radiography. Computed radiography (CR) is one of the radiography techniques that utilizes a reusable detector comprised of photostimuable luminescence (PSL) storage phosphor. The article provides a schematic illustration of a typical storage phosphor imaging plate. It concludes with a discussion on the benefits of digital radiography.

Soldering represents the primary method of attaching electronic components, such as resistors, capacitors, or packaged integrated circuits, to either printed wiring board whose defects is minimized by consideration of proper PWB design, device packages, and board assembly. This article discusses the categories that are most important to successful electronic soldering, namely, solders and fluxes selection, nature of base materials and finishes, solder joint design, and solderability testing.

This article focuses on the recycling of metals including iron and steel, stainless steel, superalloys, nickel, aluminum, copper, precious metals, lead, magnesium, tin, titanium, and zinc. It provides information on the identification and sorting of scrap metals and discusses the equipment and procedures used for small-scale and large-scale scrapping operations.

Soldering is defined as a joining process by which two substrates are bonded together using a filler metal with a liquidus temperature. This article provides an overview of fundamentals of soldering and presents guidelines for flux selection. Types of fluxes, including rosin-base fluxes, organic fluxes, inorganic fluxes, and synthetically activated fluxes, are reviewed. The article describes the joint design and precleaning and surface preparation for soldering. It addresses some general considerations in the soldering of electronic devices. Soldering process parameters, affecting wetting and spreading phenomena, such as temperature, time, vapor pressure, metallurgical and chemical nature of the surfaces, and surface geometry, are discussed. The article also describes the applications of furnace soldering, resistance soldering, infrared soldering, and ultrasonic soldering. It contains a table that lists tests commonly used to evaluate the solderability properties of selected soldered components.

Field ion microscopy (FIM) can be used to study the three-dimensional structure of materials, such as metals and semiconductors, because successive atom layers can be ionized and removed from the surface by field evaporation. The ions removed from the surface by field evaporation can be analyzed chemically by coupling to the microscope a time-of-flight mass spectrometer of single-particle sensitivity, known as the atom probe (AP). This article describes the principles, sample preparation, and quantitative analysis of FIM. It also provides information on the principles, instrument design and operation, mass spectra and their interpretation, and applications of AP microanalysis.

Microvalve jetting, with its advantages of low cost, ease of operation, high printing speed, and ability to process living cells with high viability, has been primarily used for fabricating high-throughput drug-screening models, in vitro cellular structures for fundamental cell biology research, and cell-laden structures for regenerating tissues or organs in the human body after disease or trauma. This article provides an overview of microvalve jetting of biomaterials, including operational parameters. The jetting technologies covered are inkjet printing, microvalve jetting, and laser-assisted jetting. The parameters covered include nozzle size (nozzle inner diameter), pneumatic pressure, valve-opening time, and printing speed of microvalve jetting. Subsequently, the article discusses biomaterials for microvalve jetting in terms of biomaterial definition, required properties for a suitable biomaterial, currently used biomaterials, and cells and cellular structures. Additionally, applications of microvalve jetting in biomedical engineering are presented, which include cellular and RNA analysis, high-throughput drug screening, and tissue engineering.

Ceramic and glass manufacturers take environmental regulations into consideration during all stages of the product cycle, from research and development to purchasing, processing, end use, and disposal. Ceramic and glass products are finding application in the construction industry and as raw materials for other processes. This article describes the recycling of in-process scrap and industrial wastes (fly ash, red mud, metallurgical waste, and other waste products), and applications of these recycled products. It focuses on environmental regulations such as Resource Conservation and Recovery Act and Clean Air Act. The Clean Air Act requires all states to meet minimum emissions standards for nitrogen-oxygen compounds, volatile organic compounds, and carbon monoxide.

Affordability is the key issue facing design engineers and manufacturers of composite components for current and next-generation aircraft, spacecraft, propulsion systems, and other advanced applications. This article describes the software tools available for modeling and analyzing costs associated with design and manufacturing options for advanced composites programs. It presents an example of a composite exhaust nozzle shroud where the design and manufacture options were analyzed and adjusted, based on the use of cost analysis tools. The article also lists some of the attributes found in various cost modeling software and the potential cost benefits.

Ultrasonic inspection is a nondestructive method in which beams of high-frequency acoustic energy are introduced into a material to detect surface and subsurface flaws, to measure the thickness of the material, and to measure the distance to a flaw. This article provides a detailed account of ultrasonic flaw detectors, including ultrasonic transducers and types of search units and couplants. The article describes pulse-echo and transmission inspection methods and data interpretation. The general characteristics of ultrasonic waves and the factors influencing ultrasonic inspection are also addressed. The article concludes with a review of the advantages and disadvantages of ultrasonic inspection compared with other methods applications of the technique.

This article introduces the concepts of electron and light microscopy with some general features of imaging systems and the ideas of magnification, resolution, depth of field, depth of focus, and lens aberrations as they apply to simple and familiar light-optical systems. In addition, it describes the differences between electron and light in the context of their respective microscopy techniques.

Induction heating system control is straightforward after the design and application of the coil and power supply required for the job. This article provides an overview of the basic components of an induction heating system, including a machine controller (computer or programmable logic controller), interface wiring, an operator interface, and safety controls. It also provides information on programming devices and temperature controllers, such as manual, auto, and auto-manual temperature controllers.

Vapor-phase soldering is a process of condensation heating in which the product prepared for soldering is passed through or into a layer of saturated vapor. This article provides an overview of the soldering process with emphasis on its applications and the equipment used.