Search Results for dimensional stability

In cast iron, residual stresses normally arise due to hindered thermal contraction, meaning that they are associated with the presence of constraints that prevent the natural, free volumetric variation of the material upon solid-state cooling. This article explains their mechanism of formation by introducing the scalar relation, known as the additive strain decomposition. The main factors influencing casting deformation are volume changes during solidification and cooling, phase transformations, alloy composition, thermal gradients, casting geometry, and mold stability. The article reviews the dimensional stability in cast iron and discusses macroscopic and microscopic stresses in cast iron.

Tool steels are any steel used to make tools for cutting, forming, or shaping manufactured parts. Most tool steels are wrought products alloyed with relatively large amounts of tungsten, molybdenum, vanadium, manganese, and/or chromium. The article describes a wide variety of tool steels, including high-speed steels, hot and cold-work steels, shock-resisting steels, and special-purpose steels. Hot-work steels are designed to withstand excessive amounts of heat, pressure, and abrasion, suiting them for punching, shearing, and high-temperature forming applications. Cold-work tool steels have exceptional dimensional stability and wear resistance, but lack the alloy content necessary to resist softening at temperatures above 205 to 260 deg C. The article examines standard designations for all tool steel types and provides corresponding composition and property ranges. It also discusses surface treatments, fabrication issues, and in-service measures of performance.

Low-expansion alloys are characterized by their dimensional stability, suiting them for applications such as geodetic tape, bimetal strip, glass-to-metal seals, and electronic components. This article describes the composition of such alloys along with related properties and behaviors. It explains how humidity and other factors, such as heat treating and cold drawing, influence thermal expansion rates. It also provides machining information on some of the more common low-expansion alloys, and reviews special alloy types including iron-cobalt-chromium alloys, hardenable alloys, and high-strength controlled-expansion alloys.

This article begins with an overview of classes and applications of gray iron. It discusses the castability of gray iron in terms of section sensitivity and fluidity. The article provides information on the dimensions of prevailing sections recommended for gray irons and reviews the properties and specifications of test bar. Properties of gray iron, such as fatigue limit, pressure tightness, impact resistance, machinability, and dimensional stability, at both room and elevated temperature, are reviewed. Wear behavior of gray iron castings during sliding contact under conditions of normal lubrication is also discussed. The article evaluates the use of alloys and heat treatment to modify as-cast properties. It concludes with information on the physical properties of gray iron castings.

Steels may be annealed to facilitate cold working or machining, to improve mechanical or electrical properties, or to promote dimensional stability. This article, using iron-carbon phase diagram, describes the types of annealing processes, namely, subcritical annealing, intercritical annealing, supercritical or full annealing, and process annealing. Spheroidizing is performed for improving the cold formability of steels. The article provides guidelines for annealing and tabulates the critical temperature values for selected carbon and low-alloy steels and recommended temperatures and time cycles for annealing of alloy steels and carbon steel forgings. Different combinations of annealed microstructure and hardness are significant in terms of machinability. Furnaces for annealing are of two basic types, batch furnaces and continuous furnaces. The article concludes with a description of the annealing processes for steel sheets and strips, forgings, bars, rods, wires, and plates.

Tempering of steel is a process in which hardened or normalized steel is heated to a temperature below the lower critical temperature and cooled at a suitable rate, primarily to increase ductility, toughness, and grain size of the matrix. This article provides an overview of the variables that affect the microstructure and mechanical properties of tempered steel, namely, the tempering temperature, tempering time, carbon content, alloy content, and residual elements. Tempering after hardening is performed to relieve quenching stresses and ensure dimensional stability of steel. The article discusses the embrittlement problems associated with tempering. Four types of equipment are used for tempering, namely, convection furnaces, salt bath furnaces, oil bath equipment and molten metal baths. Special procedures for tempering are briefly reviewed.

Tempering of induction-hardened steel is a form of subcritical heat treatment, primarily carried out to increase ductility, toughness, and dimensional stability, to relieve residual stresses, and to obtain specific values of mechanical properties. This article describes tempering with emphasis on different time-temperature exposure requirements for furnace and induction tempering. It discusses two parametric methods for correlating equivalent time-temperature condition: Hollomon-Jaffe tempering correlation and Grange-Baughman tempering correlation. The article describes different methods of induction tempering, namely, single-shot, progressive or continuous, scanning, and static heating methods. The effects of induction heating variables and hardenability on tempering response are examined. The article also provides examples of how tempering affects the mechanical properties of induction-hardened steels.

The choice of heat treatment depends on the service requirements of a given bearing and how the bearing will be made. This article describes the design parameters, material characteristics required to sustain performance characteristics, metallurgical properties, and dimensional stability. It also provides a description of various extensively-used heat treatment processes, namely, carburizing, carbonitriding, induction surface hardening, and nitriding associated with various bearings. In addition, the article explores the factors to be considered in selecting a process and explains why it is optimum for a specific application.

The design of a tool-steel part directly affects the susceptibility to shape distortion on heating and cooling. This article provides information on the selection of chemical composition and the effect of composition on size distortion. It explains the various factors considered to control distortion in tools steels, namely, design, initial condition, machining procedure, and heat treatment. Distortion can occur both during and after heat treatment. The article discusses the chief ways to precisely control the extent of distortion by heat treating and auxiliary mechanical methods. Stabilizing treatments, namely, stabilizing by tempering and stabilizing by cold treatment are used to minimize dimensional changes that occur following heat treatment.

This article outlines the fundamentals of polymer science and emphasizes the aspects that are necessary and useful to applications of engineering plastics. The basic structure of polymers influences the properties of both polymers and the plastics made from them. An understanding of this basic structure permits the engineers to understand which polymers may be acceptable for a certain application, and which may not. There are various possible classification schemes for polymers. Typical classification categories include polymerization process, chemical elements that make up the monomer, or crystalline versus noncrystalline structure. The article describes the various aspects of chemical structure that are important to an understanding of polymer properties and, thus, affect eventual end uses. It discusses different types of names assigned to polymers. The article details the aspects of polymer structure and examines the properties of polymers and the way they are altered by structure.

The 391-type hypereutectic aluminum-silicon alloys are hypereutectic alloys designed for applications where excellent wear resistance is needed. They are similar to the 390 family of alloys, except for a low copper content to improve castability and corrosion resistance. This datasheet provides information on key alloy metallurgy and processing effects on mechanical properties of separately cast test bars of these alloys.

This datasheet provides information on key alloy metallurgy, fabrication characteristics, processing effects on physical and mechanical properties, and applications of Al-Mg high-strength casting alloy 535.0.

This introductory article describes the various aspects of chemical structure that are important to an understanding of polymer properties and thus their eventual effect on the end-use performance of engineering plastics. The polymers covered include hydrocarbon polymers, carbon-chain polymers, heterochain polymers, and polymers containing aromatic rings. The article also includes some general information on the classification and naming of polymers and plastics. The most important properties of polymers, namely, thermal, mechanical, chemical, electrical, and optical properties, and the most significant influences of structure on those properties are then discussed. A variety of engineering thermoplastics, including some that are regarded as high-performance thermoplastics, are covered in this article. In addition, a few examples of commodity thermoplastics and biodegradable thermoplastics are presented for comparison. Finally, the properties and applications of six common thermosets are briefly considered.

Resin transfer molding (RTM) and structural reaction injection molding (SRIM) are two similar processes that are well suited to the manufacture of large, complex, and high-performance structures. This article discusses the similarities and differences of RTM and SRIM processes and the unique design considerations with respect to the physical properties, geometry, surface quality, process economics, equipment, and tooling of a component that should be considered in choosing RTM or SRIM over other competing processes for fabricating reinforced components.

Alloys 771.0 and 772.0 are high-strength, shock-resistant, aluminum sand-casting alloys that develop a high combination of physical and mechanical properties in the as-cast and room-temperature-aged conditions. This datasheet provides information on key alloy metallurgy, processing effects on physical and mechanical properties, and fabrication characteristics of these 7xxx series alloys.