Proper refractory installation ensures longer crucible life.Proper Refractactory Installation Ensures Longer Crucible Life Today, many investment casters are melting high quality metal in coreless induction furnaces with oxide crucibles. In this application, oxide crucibles provide excellent nonwetting characteristics, thermal shock Thermal shock in mechanical models Thermal shock is the name given to cracking as a result of rapid temperature change. Glass and ceramic objects are particularly vulnerable to this form of failure, due to their low toughness, low thermal conductivity, and high resistance and turnaround flexibility, while maintaining conditions conducive to superior metal cleanliness. This article offers guidelines for the installation and startup of coreless induction alumina, magnesia Magnesia, ancient cities, Lydia Magnesia (măgnē`zhə), two ancient cities of Lydia, W Asia Minor (now W Turkey). They were colonies of the Magnetes, a tribe of E Thessaly. , zircon zircon Silicate mineral, zirconium silicate, ZrSiO4, the principal source of zirconium. Zircon is widespread as an accessory mineral in acid igneous rocks; it also occurs in metamorphic rocks and, fairly often, in detrital deposits. and zirconia crucibles used for ferrous melting. Grout Grout A binding or structural agent used in construction and engineering applications. Grout is typically a mixture of hydraulic cement and water, with or without fine aggregate; however, chemical grouts are also produced. Installation A furnace coil must first be lined with a high-temperature refractory grout. The grout should be of a consistency that minimizes slumping when applied. The grout should be installed between each turn of the coild (if applicable). This stabilizes the coil structure and prevents arching between turns. Enough grout should be applied evenly to a 1/4 in. thickness on the face of the coil to form a near-perfect cylinder. After each campaign, the grout should be inspected for cracks or holes. Repairs should be made prior to relining the furnace, and thoroughly dried prior. Leak detector ground wires should be set in place according to according to prep. 1. As stated or indicated by; on the authority of: according to historians. 2. In keeping with: according to instructions. 3. the furnace manufacturer's specifications. It is recommended that a slip plane be installed to allow vertical expansion of the working lining. This consists of a nonasbestos fiber paper lining hung from the top of the furnace to the bottom. Enough paper should be hung to cover all exposed areas of the coil grout and contoured to form a near-perfect cylinder. Refractory Installation After the installation of the slip plane, the backup refractory material can be installed into the bottom of the furnace. This dry, loose material is installed in 3-4 in. layers. Each layer must be leveled, de-aired and firmly tamped. These procedures are completed using a tamping tamp tr.v. tamped, tamp·ing, tamps 1. To pack down tightly by a succession of blows or taps. 2. To pack clay, sand, or dirt into (a drill hole) above an explosive. foot and forking tool. De-airing and tamping are considered complete after three to four passes of each step and the refractory appears to be dense. Prior to introducing the next layer, the surface of the previously tamped layer must be thoroughly scratched to avoid laminations and grain segregation. Continue this practice until the bottom height is one inch greater than required. The additional one inch is removed with the use of a straight edge and the bottom leveled. This provides optimum density and bottom support for the crucible. Consult your furnace manufacturer for optimum positioning of the crucible relative to the power coil. The crucible is then lowered into the furnace and centered. Recheck to be sure the crucible is level. A heavy weight may be lowered into the crucible to help maintain its position. After inserting the crucible, the exposed area of the backup material should be thoroughly scratched prior to introducing additional material. The backup sidewall side·wall n. 1. A wall that forms the side of something. 2. A side surface of an automobile tire, between the edge of the tread and the wheel rim. Noun 1. refractory is installed using the same standard de-airing tamping and scratching procedures employed in the installation of the bottom. Continue adding sidewall refractory in 3-4 in. loose layers to a height of one inch greater than desired. Scrape back one inch of material to reveal a dense surface. The backup refractory is designed as a dense support system for the crucible. The exact dimensions and crucible size are determined by OEM (Original Equipment Manufacturer) The rebranding of equipment and selling it. The term initially referred to the company that made the products (the "original" manufacturer), but eventually became widely used to refer to the organization that buys the products and specifications. Top Cap Air-set top cap material is emplaced to provide a seal for the dense backup refractory and an abrasion resistant surface for charging. This same material also may be used in the spout area. If a wet top cap is used, vent holes must be made in the material to allow for moisture dehydration. A heat lamp heat lamp n. A lamp that emits infrared light and produces heat, used to apply topical heat to the skin for therapeutic purposes. heat lamp Infrared lamp, see there may be used to facilitate water removal. Once the top cap is properly installed and the crucible is free of moisture, sintering sintering, process of forming objects from a metal powder by heating the powder at a temperature below its melting point. In the production of small metal objects it is often not practical to cast them. can be initiated. The crucible can be charged with metal to assure a uniform sinter sinter Mineral deposit with a porous or vesicular texture (having small cavities). Siliceous sinter is a deposit of opaline or amorphous silica that occurs as an incrustation around hot springs and geysers and sometimes forms conical mounds (geyser cones) or terraces. cycle. The sinter cycle can be initiated under induction power at a rate of 500 degrees F/hr for the first hour. Heat to the maximum use temperature, back-filling as the initial charge melts. The exact heat-up rate is dependent upon crucible composition and size. If the same crucible is reused under cold startup conditions, care must be taken to radiate ra·di·ate v. 1. To spread out in all directions from a center. 2. To emit or be emitted as radiation. ra heat from the charge prior to going molten to prevent thermal shock to the crucible. This is completed under induction power. It is essential that the crucible be emptied at the end of each day's use and before cooling to ambient temperatures. A solidified metal heel left in the bottom of the crucible could cause cracking or spalling during cold startup. Contact your refractory supplier for detailed information and sinter instructions for your specific application. |
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