What Are Superalloys?

For purposes of this chapter superalloys are those nickel-, iron–nickel-, and cobalt-base corrosion-resistant alloys generally used above a nominal temperature of 540 C (1000 F).
The iron–nickel-base superalloys are an extension of stainless steel technology and generally are melted and cast to electrode / ingot shapes for subsequent fabrication to components. The iron–nickel-base superalloys usually are wrought, i.e., formed to shape or mostly to shape by hot rolling, forging, etc. On the other hand, after primary production by melting and ingot casting, the cobalt-base and nickel-base superalloys may be used either in wrought or cast form depending on the application or the alloy composition involved. The stainless steels, nickel–chromium alloys, and cobalt dental alloys which evolved into the superalloys
used chromium to provide elevated-temperature corrosion resistance. A Cr2O3 layer on the surface proved very effective in protection against oxidation. Eventually, cast superalloys for the highest temperatures were protected against oxidation by chromium and aluminum. In our opinion, superalloys must contain chromium, probably at the level of 5% (some would argue 8%) or higher for reasonable corrosion resistance.







Mechanical Engineers’ Handbook: Materials and Mechanical Design, Volume 1, Third Edition.
Edited by Myer Kutz
Copyright  2006 by John Wiley & Sons, Inc.


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  • Axonometric projection

    Axonometric projection is shown in Figure 2.3. This is the same as perspective projection except that the projectors are parallel. This
    means that there are no vanishing points. In axonometric projection, the object can be placed at any orientation with respect to the viewer. For convenience, axonometric projection can be divided into three classes depending on the orientation of the object. These are trimetric, dimetric and isometric projections (see Figure 2.4).


    Trimetric projection is by far the most common in that the object is placed at any position with respect to the viewer such that the angles c~ and [3 are unequal and the foreshortening in each of the three axes is unequal. The three sides of the cube are of different lengths.
    This is shown in the left-hand drawing in Figure 2.4. The 'tri' in trimetric means three. In dimetric projection, the angles 0t and 13 are the same as shown in the middle drawing in Figure 2.4. This results in equal foreshortening of the two horizontal axes. The third vertical axis is foreshortened to a different amount. The 'di' in dimetric means there are two 'sets' of axes. The particular class of axonometric projection in which all the three axes are foreshortened to an equal amount is called isometric projection. In this case the foreshortening is the same as seen in the right-hand drawing in Figure 2.4. In this case, the angles a and 13 are the same
    and equal to 30 ~ The foreshortening of each of the three a~:es is identical. The term 'iso' in isometric projection means similar.

    Isometric projection is the most convenient of the three types of axonometric projection because of the convenience of using 30 ~ angles and equal foreshortening. Isometric projection will be considered in detail in the following section.













    Engineering Drawing for Manufacture
    by Brian Griffiths

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  • Manual Material-Handling Systems

    Associations between physically demanding manual handling of materials and work-related musculoskeletal injury have been well documented by ergonomists and epidemiologists.
    Mechanized assistive devices are widely used to  control such problems. Material-handling systems can be generally categorized as positioners (e.g., lift tables, conveyors), used to place or orient objects, and manipulators (articulated arms, hoists), used to move and/or support objects. The latter were the focus of a detailed ergonomic/biomechanical analysis,
    with a goal of understanding the impact of using manipulators on task performance and the
    user’s physical demands.

    Only minimal investigation has been conducted on manipulators, mainly focusing on biomechanical modeling of the static gravitational component. While use of manipulators reduces the static component (i.e., object weight), substantial kinetic loads may result from body segment dynamics and the inertial dynamics of the manipulator and object handled. In addition, use of a manipulator frequently requires complex body postures and motions. 

    In the first study,two mechanical manipulators (an articulated arm and an overhead hoist; Fig. 2) were used to move objects with moderate masses (10–40 kg) for several shortdistance transfers. Differences between the two devices and manual (unassisted) movements were obtained for motion times, applied hand forces, and torso kinematics. Use of either manipulator increased motions times by 36–63% for symmetric motions (in the y–z plane) and by 62–115% for asymmetric motions (in the x–z plane). Hand forces were substantially lower when using either manipulator (by 40–50%), while torso motions were generally similar regardless of how the transfers were conducted. For self-paced job tasks (see below for effects of pacing), it was concluded that moderate-mass objects require significant increases in motion times, but with substantially reduced levels of upper extremity exertion.

    A second study examined physical loads in more detail using the same manipulators and motions. A 3D inverse dynamics biomechanical model was developed to allow for estimation of the strength demands (required moments versus joint strength) at the shoulders and low back as well as compressive and shear forces in the lower spine (the latter as estimates of the relative risk of low-back injury). Strength demands decreased substantially when using either manipulator in comparison to transfers done manually. Strength demands were also much less affected by increases in object mass. Spine compression and shear were
    reduced by roughly 40% when using either manipulator, primarily because of the decreased hand forces noted above and the resulting spinal moments. Estimates of trunk muscle activity (using EMG) suggested that the use of a hoist imposes higher demands on coordination and stability, particularly at extreme heights or with asymmetric motions. In contrast, the articulated arm imposed higher demands on strength and resulted in increased spinal compression, likely because of the higher system inertia. From both studies, it was concluded that use of either type of manipulator can reduce physical demands compared with manual methods, though performance (motion times) will be compromised. In addition, either a hoist or articulated arm may be preferable depending on the task requirements (e.g., height and asymmetry).

    Two companion studies were conducted to address additional aspects of manipulators as used in practice. Effects of short-term practice (40 repetitions) were addressed in the first study,13 using the two manipulators to lift and lower a 40-kg object. Nonlinear decreases in several measures were found (e.g., low-back moments and spine compression). These decreases, however, were fairly slow and comparable to rates of learning for manual lifting. Familiarization with material-handling manipulators is thus recommended, and the learning process may be somewhat lengthy. Effects of pacing (speed of object transfer) were determined
    in the second experiment14 by having participants perform transfers 20% more rapidly than those presented above. This requirement led to roughly 10% higher hand forces, 5– 10% higher torso moments, similar torso postures and motions, and 10% higher spine loads (compression and shear). When manipulators are used in paced operations (e.g., assembly lines) and the noted increases in required motion times are not accounted for, these results suggest that the risk of musculoskeletal injury may be increased.



    Maury A. Nussbaum
    Industrial and Systems Engineering
    Virginia Polytechnic Institute and State University
    Blacksburg, Virginia
    Jaap H. van Diee¨n
    Faculty of Human Movement Sciences
    Vrije Universiteit
    Amsterdam, The Netherlands

    Mechanical Engineers’ Handbook: Materials and Mechanical Design, Volume 1, Third Edition.
    Edited by Myer Kutz
    Copyright  2006 by John Wiley & Sons, Inc.


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  • Shaper Machines

    Is a simple machine where Ram Horizontal movement (movement back and forth). Ingestion of this machine only move in one direction only, whereas the reverse direction to move waste. So the time behind the movement of time is shorter than the time advance (movement Ingestion). The processes that can be done with a shaper machines, among others: 1. facing Top 2. facing Ride 3. slotting 4. Dovetail-Female 5. Dovetail-Male 6. Steps Shaper Machine parts 1. ram 2. tool Head 3. Clepper Box 4. table 5. Saddle 6. Column Read more........

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