Hand mold

Cast and Hand-Molded Refractories. Large shapes such as burner blocks and flux blocks, and intricate shapes such as glass feeder parts saggers are produced by casting sHps, hydraulic cement bonded mixtures, or hand-molding clay or chemically bonded materials. Because these techniques are labor intensive, they are reserved for articles that caimot be satisfactorily formed in any other way, owing to complexity or small production quantities. 

Forming. Most refractory shapes are formed by mechanical equipment, but some very large or intricate shapes require hand molding in wooden, steel-lined molds with loose liners to permit easy removal of plaster of Paris molds. 

Other common refractory forms include setter tile and kiln furniture, fusion-cast shapes, cast and hand-molded refractories, insulating refractories. castables and gunning mixes, plastic refractories and ramming mixes, mortars, composite refractories, and refractory coatings,... 

Refractory shapes are generally produced on a mechanical toggle press, screw press, or hydraulic press. Some special shapes are produced by air-ramming which is similar to hand molding, except that reinforced steel molds are required. Special shapes can also be formed by slip easting and hot pressing. 

Suitable pharmaceutical for- Tablet molding profile tool. Hand molding,... 

The general process of hand molding can be subdivided into specific molding methods such as those that follow. The terms of some of these methods as well as others reviewed here overlap the same technology the different terms are derived from different sections of the RP and other industries. 

Of the other techniques used to fabricate brick, dry pressing provides accurate dimensional control, while hand molding is generally used to fabricate small quantities of specialty shapes and can result in a more porous piece. 

Brick made from a mixture of crushed coke and clay or from coke bonded by means of tar have been made many years ago. These materials are usually hand molded, dried and fired in muflBles with as complete exclusion of air as possible. The carbonization of the tar cements together the coke particles to a compact mass. The coke may also be replaced by graphite. Refractories of this type combine good heat-resisting power with excellent thermal conductivity. 

Compression molds can be divided into hand molds, semiautomatic molds, and automatic molds. The design of any of these molds must allow venting to provide for escape of steam, gas, or air produced during the operation. After the initial application of pressure the usual practice is to open the mold slightly to release the gases. This procedure is known as breathing. 

Hand molds are used primarily for experimental runs, for small production items, or for molding articles which, because of complexity of shape, require dismantling of mold sections to release them. Semiautomatic molds consist of units mounted firmly on the top and bottom platens of the press. The operation of the press closes and opens the mold and actuates the ejector system for removal of the molded article. However, an operator must load the molding material, actuate press controls for the molding sequence, and remove the ejected piece from the mold. This method is widely used. 

Compared to both compression and transfer CM, injection molding requires shorter vulcanization and cycle times as well as better automation. On the other hand, mold costs are so high that only large-series production is economical. 

Hand mold n. A mold that is removed from the press after each shot for extraction of the molded article generally used only for short runs and experimental moldings. 

Production molds are generally multicavity and have integral heating provisions and ejection systems. And when they follow single-cavity hand molds, cavity dimensions may be fine timed, and vents and gates can be repositioned, based on experience with the single-cavity molds. 

Ejector locations. Ejection devices for plastic parts can range from screwdrivers used to pry parts out of a hand mold to mechanized stripper plates and elaborate mechanisms which also retract collapsible cores. All of them share one common characteristic they exert pressure on a newly formed part. That pressure can distort the part to the point of disturbing its function or appearance if it occurs while the part is still too soft to withstand it. Therefore, the processor must delay ejection until the moldment can endure it. The more ejectors there are, the more ejection surface there is to distribute that pressure and the sooner the part can be removed from the mold, thereby shortening the molding cycle. However, ejectors cost money and leave marks on the surface of the moldment. Therefore, there is a mold cost associated with a faster molding cycle. (Differences between bidders on a project are often based on variations in cooling and ejection systems.) Additional ejectors leave more marks on the surface and their number and location may be limited by functional and appearance concerns. 

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