Precision casting

Precision casting Precursors of dyes Predelignification Predictive maintenance Predmcarb ate Prednisolone Prednisolone [50-24-8]... 

The superheated steam generated in the superheater section is coHected in a header pipe that leads to the plant s high pressure steam turbine. The steam turbine s rotor consists of consecutive sets of large, curved, steel aHoy disks, each of which anchors a row of precision-cast turbine blades, also caHed buckets, which protmde tangentiaHy from the shaft and impart rotation to the shaft when impacted by jets of high pressure steam. Rows of stationary blades are anchored to the steam turbine s outer sheH and are located between the rows of moving rotor blades. 

Type IV, extra hard (partial denture) alloys, are indicated where high strength, hardness, and stiffness are requked. They are harder, stronger, and less ductile than the type III alloys. These partial-denture alloys are used for cast removable partial dentures, precision-cast fixed bridges, certain three-quarter crowns, saddles, bars, arches, and clasps. 

These super-alloys are remarkable materials. They resist creep so well that they can be used at 850°C - and since they melt at 1280°C, this is 0.72 of their (absolute) melting point. They are so hard that they cannot be machined easily by normal methods, and must be precision-cast to their final shape. This is done by investment casting a precise wax model of the blade is embedded in an alumina paste which is then fired the wax bums out leaving an accurate mould from which one blade can be made by pouring liquid super-alloy into it (Fig. 20.4). Because the blades have to be made by this one-off method, they are expensive. One blade costs about UK 250 or US 375, of which only UK 20 (US 30) is materials the total cost of a rotor of 102 blades is UK 25,000 or US 38,000. 

Axial compressor blades are usually forged and milled. Precision casting has been used on occasion. The most common material used is a 12 chrome steel, in the AISI 400 series, and is also known as 400 series stainless steel. While the stator blades are occasionally shrouded, the rotor blades are free-standing. Lashing wires have been used on rotor blades, but are generally used to solve a blade vibrational stress problem. 

A crystalline form of free silica, extremely hard and inert chemically very resistant to heat. Quartz in refractory bricks and amorphous silica in diatomaceous earth are altered to cristobalite when exposed to high temperatures (calcined). Cristobalite is extensively used in precision casting by the hot wax process, dental laboratory work, and certain speciality ceramics. 

The oxidised waxes (containing various ratios of fatty acids, esters and alcohols) are used in the manufacture of various polishes, anti-corrosion coatings, tile glazing carriers, precision casting waxes, mould release agents, metal coatings etc. 

C(Process). See "C Process (Croning Process of Precision Casting)... 

IR-7734, Present Status of the Shell-Mold or "C Process of Precision Casting of Metals ,... 

In lost wax casting, the most widely used precision casting method, a model is made of the desired product. 

Use Intermediate for siloxane compounds for precision casting of high-melting alloys pigment binder for paints surface hardener for sandstones. 

Preliminary experiments on the ultrasonic treatment of solidifying precise castings (into ceramic molds) have shown that significant warming of a melt in a mold occurs with development of cavitation and introduction of acoustic power above 100 W. As the volume of a casting is not large and the melt mass is hardly above 0.2 kg, the data obtained allow one to follow the improved filling of thick channels under ultrasonic action. 

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