Solid Mold Casting

This process evolved to be used for relatively large statuary where smaller parts were molded and then welded together. For much smaller parts like jewelry items a solid molding process was evolved. Essentially, the wax pattern was immersed in a fluid plaster-like material 

Molten metal was poured into the clay mold and allowed to solidify. 

FIGURE 12.35 Lost wax casting as it may have been practiced. 

The wax was covered with clay, dried and the wax melted out and the clay mold was fired. 

The clay mold was broken away leaving the metal casting. An exact duplicate of the original wax. 

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The process as it is practiced now actually produces a ceramic shell of modest thickness (about 0.2-0.5 in. thick) around the wax pattern. The relatively thin shell when compared to solid mold casting not only saves material but also allows for more uniform and rapid cooling of the metal parts. This is an important factor in maintaining fine grain size that results in stronger parts. 

Metal molds and cores are used in permanent mold casting. The process works best in continuous operation so that the mold temperature can be maintained within a fixed operating range. The operating temperature of the mold is one of the most important factors in successful permanent mold casting. Mold cavities are machined from solid blocks of graphite. Mold life is the major cost factor in permanent mold casting. 

In open-mold casting, the shape of the desired object is carved as a "negative" depression or hollow into a suitable bulk of material that withstands the temperature required for the process wood is often used for cold casting molds stone, sand, and dry mud, for hot casting. The fluid casting material is then poured into the carved depression, where it is left to set and from which, when solid, it is finally removed. 

For investment (sometimes called lost-wax) casting, the pattern is made from a wax or plastic that has a low melting temperature. Aroimd the pattern a fluid slurry is poured that sets up to form a solid mold or investment plaster of paris is usually used. The mold is then heated, such that the pattern melts and is biumed out, leaving behind a mold cavity having the desired shape. This technique is employed when high dimensional accuracy, reproduction of fine detail, and an excellent finish are required—for example, in jewelry and dental crowns and inlays. Also, blades for gas tinbines and jet engine impellers are investment cast. 

The seal must also resist the vibrations from the explosions of internal combustion in the engine, chassis and wheel vibrations, and even potholes in the road. This seal must resist strong chemicals (anti freeze, anti-rust agents, radiator stop-leak and sealant chemicals, gasoline and lubricant residuals), and also solid particles (rust, iron slag, minerals, asbestos fibers, and silica from the engine casting mold). In spite of all this, the mechanical seal on the water pump of your car can run 7, 10, even 15 years without problems. 

Absorption - Processes water can be removed from a material by the capillary action of porous bodies. An example is the cream of clay and water used for casting pottery, which is deprived of the greater part of its water by placing it in molds of plaster of Paris. The capillary character of this mold withdraws the water from the liquid clay mixture and deposits upon itself a layer of solid clay, the thickness of which is controlled by the time of standing. Certain types of candies, such as gumdrops, are dried mainly by contact with the starch molds in which they are cast. The drying effect of sponges, towels and materials of this kind is due to this same action. 

Some TPs and TSs begin as liquids that can be cast and polymerized into solids. In the process various ornamental or utilitarian objects can be embedded in the plastic. By definition, casting applies to the formation of an object by pouring a fluid plastic solution into an open mold where it completes its solidification. Casting can also lead to the... 

Arsenic and antimony are metalloids. They have been known in the pure state since ancient times because they are easily obtained from their ores (Fig. 15.3). In the elemental state, they are used primarily in the semiconductor industry and in the lead alloys used as electrodes in storage batteries. Gallium arsenide is used in lasers, including the lasers used in CD players. Metallic bismuth, with its large, weakly bonded atoms, has a low melting point and is used in alloys that serve as fire detectors in sprinkler systems the alloy melts when a fire breaks out nearby, and the sprinkler system is activated. Like ice, solid bismuth is less dense than the liquid. As a result, molten bismuth does not shrink when it solidifies in molds, and so it is used to make low-temperature castings. 

Slip casting is common in the ceramics industry. The material to be cast is milled to a mean particle size of a few microns. A slip is made by mixing the finely divided material with a liquid suspending medium. The slip is then poured into a suitable mold (e.g., of plaster of pans). The liquid in the slip is drawn into the mold by capillary forces and the solids are deposited in a coherent form. For TiBj, ZrBj and CrBj a suspending medium of 5-7 wt% cyclopentadiene in xylene is recommended. A 3 wt% aqueous solution of carboxymethylcellulose is the best dispersing medium... 

Along this line, sol-gel materials based on Si02find increasing use in solid-phase assisted synthesis. The sol-gel synthesis creates well ordered porous glasses which retain a rigid and exposed surface area (300-1000 m g ) [56]. Gelation occurs after a sol is cast into a mold so that the monolithic samples can be tailored to a desired size or shape [57]. 

Antimony is unique in that when it solidifies from a molten liquid state to a solid state, it expands, which is just the opposite of most metals. This is useful in making some typesetting castings in which the expansion assures an accurate reproduction of the letter mold. 

Bismuth has a characteristic similar to water. It expands when changing from the hquid phase to the solid phase. This factor makes it useful as an alloy in metals that are used to fill molds, given that it will expand to the casts dimensions. 

Bismuth is similar to antimony in that it expands from the molten hquid state to the solid state. This property makes it an excellent material to pour into molds and can produce fine details in whatever is being molded, such as metallic printing type and similar fine castings. 

The reaction was carried out at 100°C for about two hours until the theoretical isocyanate content, as determined by the di-n-butylamine titration method (27), was reached. The PU prepolymer with or without tertiary amine nitrogen groups was dissolved in dry MEK to obtain a prepolymer solution of 30-40% solids. It was then mixed with a mixture of 1,4-BD/TMP (4 1 by equiv. ratio) at an NCO/OH = 1.05/1.0 ratio in the presence of T-12 catalyst (0.05% based on total weight). The reaction mixture was cast in a metal mold treated with a release agent at ambient temperature. After standing 3-5 hours at room temperature, the mold was placed in an oven and post-cured at 100°C for 16 hours. The samples were then conditioned in a desiccator for one week before testing. 

Molding employs a mobile prepolymer that may be thermoset or using a thermoplastic polymer. The polymer can be injection-molded (often for solid objects), blow-molded (for hollow objects such as bottles), rotation-molded, compression-molded, transfer-molded, or thermoformed. Casting is closely related to molding, except that the pressure is typically not used. 

This reactor contains at least two solid phases, two Hquid phases, and a gas phase. The flows are largely driven by gravity caused by the density differences of the soHd and Hquid phases. Taconite and coke are admitted at the top of the reactor and O2 at the bottom. Liquid Fe and slag are withdrawn at the bottom of the reactor. The Hquid iron is either cast into ingots in molds or directly passed from the reactor through rolling mills to process it into sheets. 

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