Complete Casting. Handbook. Metal Casting Processes,. Metallurgy, Techniques and Design. John Campbell. OBE FREng DEng PhD MMet MA. Emeritus. Steel is the most versatile engineering material available today. Steel can be easily welded and processed and plays a vital role in maintaining the high. With particular emphasis on the ability of castings to meet customer requirements , this guide tells you what you need to know about physical properties and other.
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NOTE: Proper selection of an alloy for a specific high temperature service involves consideration of some or all of the following factors: 1) required life of the part. Steel Castings Handbook - Download as PDF File .pdf), Text File .txt) or read online. Steel Casting Handbook - Download as PDF File .pdf), Text File .txt) or read online. steel casting handbook.
In these cases it is necessary that a limit of minimum section thickness per length be adopted in order for the molten steel to completely fill the mold cavity. Molten steel cools rapidly as it enters a mold. In a thin section close to the gate, which delivers the hot metal, the mold will fill readily. At a distance from the gate, the metal may be too cold to fill the same thin section.
A minimum thickness of 0. Wall thicknesses of 0. Draft Draft is the amount of taper or the angle, which must be allowed on all vertical faces of a pattern to permit its removal from the sand mold without tearing the mold walls. Draft should be added to the design dimensions but metal thickness must be maintained. Regardless of the type of pattern equipment used, draft must be considered in all casting designs. Draft can be eliminated by the use of cores; however, this adds significant costs.
In cases where the amount of draft may affect the subsequent use of the casting, the drawing should specify whether this draft is to be added to or subtracted from the casting dimensions as given. Ordering Steel Castings 2 The necessary amount of draft depends upon the size of the casting, the method of production, and whether molding is by hand or machine.
Machine molding will require a minimum amount of draft.
Interior surfaces in green sand molding usually require more draft than exterior surfaces. Parting Line Parting parallel to one plane facilitates the production of the pattern as well as the production of the mold. Patterns with straight parting lines, parting lines parallel to a single plane, can be produced more easily and at lower cost than patterns with irregular parting lines.
Complete Casting Handbook
Casting shapes that are symmetrical about one centerline or plane readily suggest the parting line. Such casting design simplifies molding and coring, and should be used wherever possible. They should always be made as split patterns which require a minimum of handwork in the mold, improve casting finish, and reduce costs.
Cores A core is a separate unit from the mold and is used to create openings and cavities that cannot be made by the pattern alone. Every attempt should be made by the designer to eliminate or reduce the number of cores needed for a particular design to reduce the final cost of the casting.
The minimum diameter of a core that can be successfully used in steel castings is dependent upon three factors; the thickness of the metal section surrounding the core, the length of the core, and the special precautions and procedures used by the foundry.
The adverse thermal conditions to which the core is subjected increase in severity as the metal thickness surrounding the core increases and the core diameter decreases. These increasing amounts of heat from the heavy section must be dissipated through the core. As the severity of the thermal condition increases, the cleaning of the castings and core removal becomes much more difficult and expensive.
The thickness of the metal section surrounding the core and the length of the core affect the bending stresses induced in the core by buoyancy forces and therefore the ability of the foundry to obtain the tolerances required.
If the size of the core is large enough, rods can often be used to strengthen the core. Naturally, as the metal thickness and the core length increase, the amount of reinforcement required to resist the bending stresses also increases. Therefore, the minimum diameter core must also increase to accommodate the extra reinforcing required.
The cost of removing cores from casting cavities may become prohibitive when the areas to be cleaned are inaccessible. The casting design should provide for openings sufficiently large enough to permit ready access for the removal of the core. The volumetric contraction which occurs within a cross section of a solidifying cast member must be compensated by liquid feed metal from an adjoining heavier section, or from a riser which serves as a feed metal reservoir and which is placed adjacent to, or on top of, the heavier section.
The lack of sufficient feed metal to compensate for volumetric contraction at the time of solidification is the cause of shrinkage cavities. They are found in sections which, owing to design, must be fed through thinner sections.
The thinner sections solidify too quickly to permit liquid feed metal to pass from the riser to the thicker sections. Right Click and Open in a New Window.
Our recent page on Casting-Repair introduces an overview including also other cast metals. It is limited in scope to general issues. While stressing important aspects it cannot delve into details. The present List of Links may provide useful references to those looking for specific answers to their particular questions.
It has been calculated that the huge economic impact of Casting Repair saves to industry important assets that should otherwise be scrapped. The Griffin foundries nearly meet this stringent condition, having been producing steel rail road wheels with a single pour from the melting furnace, followed by uphill filling out of the ladle and into the mold. However, of course, counter gravity becomes less practical for very large cast products, and for purely practical engineering reasons may be limited to weights in the region of —10 kg.
It is a powerful solution. Most cast steels are transformed by this approach. It is so simple, it costs practically nothing to implement. The technique may benefit from laser triangulation and feedback to the overhead crane to achieve good positioning. The seal is easily formed from compressible ceramic fiber blanket: its compressibility gives sufficient latitude for sufficiently accurate lowering by the crane.
Although the pot running system will work with tolerable effectiveness, the exchange of the pots for accurately molded sand cores represents a further benefit to quality and reduction in costs. The adoption of this simple technique has been demonstrated to be of huge benefit in the casting of steel products in the region of 50—50 kg.
In summary, for the casting of shaped steel and Ni alloy castings, the ultimate solution of counter gravity is strongly recommended.
This fundamentally perfect process can give perfect cast products. Alternatively, if counter gravity cannot be used, the adoption of contact pouring together with a design of filling system based on the author's naturally pressurized filling system 2 has been repeatedly demonstrated to work well. This technique is based on a design of filling channels which guide the liquid metal into the mold, ensuring that air is excluded at all points, and the final filling speed into the mold cavity is less than the critical 0.
This value ensures that surface tension forces dominate over inertial forces in the liquid, so that breaking waves, jetting, and splashing cannot occur so that bifilm damage cannot be generated. The processes can be preceded by vacuum induction melting VIM to make up an appropriate charge and cast this into an electrode to be consumed by the remelting process.
The casting of the electrode, whether in air or in vacuum, is almost inevitably carried out by directly pouring the liquid metal into the open top of an ingot mold.
This very regrettable and unnecessarily turbulent casting process creates bifilm defects, visible as folds in the cast surface of the electrode, which can be clearly seen with the unaided eye from a distance of 10 m or more. Electrodes top poured in vacuum appear to contain similar faults, but the thinner oxide films ensure that they are not so visible.
Top poured electrodes contain such large defects that the remelting process cannot be expected to guarantee integrity in the finished product. The author vividly recalls seeing a defect in an ESR ingot the size of his hand; clearly, part of the electrode had detached prior to melting because of a massive defect, and had fallen in to the ingot. Unfortunately, such events are relatively common. As an aside, this use of VIM, generating damaged steels by directly top pouring into molds in a vacuum chamber is, of course, widely used in universities and laboratories everywhere in the world.
Thus, nearly all our current metallurgical research is unfortunately undermined by this technique. However, the VAR material had to be peeled its surface machined away on a lathe to a considerable depth, representing a large loss to the metallic yield of the process, before it could be forged without cracking. This behavior reflects the way in which the metal builds up to form the ingot. Although the center of the ingot beneath the arc is liquid, the outer regions of the ingot in contact with the water cooled mold are solid and will gradually oxidize in the relatively poor vacuum.
The spreading liquid will roll out its thin oxide film over the thicker oxide film on the pancake below. Waves can sometimes travel in both directions, complicating the final pattern.
The outer surface is faced by remelted and solidified crown material. There are, therefore, a number of sources of defects which are a cause for concern, because it is probable that not all defects will always be detected.
This seems to be the consequence of the remelting of the generally lower melting point constituents of the crown. Thus, the presence of surface cracks tends to be concealed beneath a surface layer of different composition.
The patchy nature of this layer may be the result of the migration of the arc, or microscopic buckling of the ingot and mold, leading to local changes in the heat transfer coefficient, changing the degree of inverse dendritic segregation against the surface. Furthermore, it is clear that the VAR ingot can never be certain to be free from residual cracks, because of the understandable effort to reduce the depth of the peel to reduce losses, so that not all bifilm cracks will be completely removed, as illustrated in Figure The depth of peel may be difficult to judge, because the wandering of the arc and slight variations in melt rate are likely to vary the thickness of the solidified rim, and thus the depth of bifilm cracks.
Checking by a dye penetrant test to ensure all cracks have been removed, unfortunately, cannot be expected to be reliable because of the extreme thinness of oxide bifilms when produced under vacuum conditions.
Furthermore, the natural compressive stresses in the surface which are exhibited by all cast products will assist to keep surface cracks firmly closed, adding to the difficulty of detection.
Returning to my early experience, in sharp contrast, Waspalloy when produced by ESR would forge like butter, without the removal of any of its outer skin. This contrast in behavior was not confined to Waspalloy. The fundamental difference in behavior results from the liquid oxide environment of the surface of the liquid metal in the ESR process.
It is reminiscent of the benefits of liquid oxide films on steels discussed above, being different merely in the depth of the surface liquid. In terms of fundamental issues associated with the consolidation of metals, 6 among all metals and alloys, ESR material has the unique benefit of a complete environment of liquid oxide which ensures its unique freedom from bifilm cracks. The claims can be relatively easily addressed. It will be forced to remain in solution where it will be expected to act as any other solute, perhaps contributing to some solid solution strengthening.
However, of course, this subversive new thought requires to be proven. The second aspect is that the hydrogen is relatively easily reduced during melting by the provision of a flow of dry gas over the molten slag surface although it has to be admitted that hydrogen penetrating the steel mold wall or from the water cooling will probably act to reduce to some extent the effectiveness of this attempt to limit hydrogen uptake.
The lower temperature gradient leading to channel defects freckles in large molds. The segregation effects resulting from channel defects are expected to be relatively harmless in the absence of bifilms, but, once again, this has to be proven. As the ingot surface is revealed as the collar moves higher, water cooling can be applied directly to the ingot surface.
This cooling action is more effective than that possible in VAR because the gap between the mold and ingot is eliminated, greatly increasing heat transfer. The relatively low rate of solidification leading to increased dendrite arm spacing DAS.
An increase of DAS will correspondingly lengthen heat treatment times for homogenization and solution treatments, and is therefore unwelcome. It is easily avoided once more by providing enhanced cooling using the short collar mold technique. The association of such inclusions with porosity and decohesions cannot be the result of the explanations of conventional metallurgy, 16 since such volume defect features do not appear to be explicable by homogeneous or heterogeneous nucleation, nor by stress, or gas, or vacancy deposition.
In contrast to all these mechanisms which can be shown to be energetically as unlikely as to be impossible, the bifilm mechanism is logical and exhibits no nucleation difficulty. The author is aware of the apparent stark boldness of these conclusions, but the reader is encouraged to check the detailed logic and mass of evidence 2 , 16 which is too extensive to present in a short paper. This new thinking will be a challenge.
The larger droplets float out rapidly as a result of their high buoyancy, leaving only the small droplets of entrained liquid oxide, whose rate of rise is too slow to permit escape, but whose presence in the steel is tolerated because of their small size and spherical shape. Even so, the clear fact is that the inclusions are present because of an entrainment process; they have been introduced from the outside into the bulk of the steel.
Such entrainment processes are sometimes avoidable, so that, in principle, the entrainment of inclusions can be eliminated. It is of interest to note that the aluminum casting industry now has foundry designs in which the liquid metal is never poured, and never permitted to flow downhill at any point.
The cast metal can achieve a perfection previously unattainable.Volunteer Profiles. Austenitic stainless steel castings Castings. The test results include tensile strength.
D A See original specification for full details on required mechanical tests. ASTM E severity level 2. The minimum diameter of a core that can be successfully used in steel castings is dependent upon three factors; the thickness of the metal section surrounding the core, the length of the core, and the special precautions and procedures used by the foundry.
An ultimate system is counter gravity casting.
Special Practices ASM Chapter Education.
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