Open molding

Open-arc furnaces Open-celled foam Open-circuit potential Open-mold processes Open-pit mining Operating line... 

Catalyst Selection. The low resin viscosity and ambient temperature cure systems developed from peroxides have faciUtated the expansion of polyester resins on a commercial scale, using relatively simple fabrication techniques in open molds at ambient temperatures. The dominant catalyst systems used for ambient fabrication processes are based on metal (redox) promoters used in combination with hydroperoxides and peroxides commonly found in commercial MEKP and related perketones (13). Promoters such as styrene-soluble cobalt octoate undergo controlled reduction—oxidation (redox) reactions with MEKP that generate peroxy free radicals to initiate a controlled cross-linking reaction. 

Open-Mold Processes. Polyester resins are fabricated easily in open molds at room temperature. Such processes account for over 80% of production volume, the remaining being fabricated using matched metal dies in high temperature semiautomated processes. 

Although more and more zinc sheet and strip are produced in continuous mills, some is stiU produced by rolling slabs cast in open or closed book-type molds made of cast iron (124—127). The casting temperatures are between 440 and 510°C, mold temperatures between 80 and 120°C. The contact surfaces of the mold must be smooth and clean to allow unrestricted shrinkage of the cast slab. Mold lubricant is not necessary, but if used should be held to a minimum. Slabs cast in open molds must be skimmed immediately to remove surface oxide. Rolling slabs are cast 1.87—10 cm thick. 

Zinc rolling slabs have been cast successfully by semicontinuous direct-chill casting methods. This is the preferred method for superplastic zinc alloys which, because of their large freezing range, display unacceptable surface shrinkage when cast in open molds. 

Process used provides different control capabilities. As an example closed molding (injection, compression, etc.) provides fine detail on all surfaces. Open molding (blow molding, thermoforming, spray-up, etc.) provides detail only on the one side in contact with the mold, leaving the second side free-formed. Continuous production (extrusion and pultrusion) yields products of continuous length. Hollow (rotational or blow) produces hollow products. These processes can be used creatively to make different types of products. For example, two molded or thermo-formed components can be bonded together to form a hollow product, or they can be blow molded. 

Contact molding Also called open molding or contact pressure molding. It is a process for molding RPs in which the reinforcement and plastic are placed in a mold cavity. Cure is either at room temperature using a catalyst-promoter system or by heating... 

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... 

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. 

The extrusion blow molding cycle is illustrated in Fig. 14.2. The extrusion component of the cycle is normally continuous. As soon as one length of parison has been captured by the mold, another length starts to form. To allow room for a new length of parison to emerge from the die, the mold moves aside as soon it has captured a parison and the knife has severed it. The mold is rapidly translated to a remote blowing station where inflation takes place. After the product is ejected, the open mold moves back under the die where it surrounds and captures another length of parison. 

Open manometers, 20 646—647 Open-mold process, for unsaturated polyesters, 20 116-117 Open-mold processing, 19 558 Open-pit zinc mining, 26 557 Open reading frames (ORFs), 26 480, 481 with yeasts, 26 491—492 Open system... 

MACT COMPLIANCE TOOL FOR OPEN-MOLD BOATBUILDERS... 

Although most boats are produced via the open mold spray-up process, environmental pressures are mounting due to the high styrene monomer emissions that are inherent in open molding techniques. Closed molded techniques are beginning to be commercially practiced, and it is anticipated that these processes will replace the open mold process. 

Molds can be of three basic types. Open molds are used to define one surface of a product. They can be of the female (indenting) or male (projecting) type. Two matched female half-molds can be used to make hollow items, and a matched female and male pair is used to form a cavity that is to be completely filled. Shaping of the polymer inside the mold is usually achieved by applying pressure to cause the fluid to conform to one or both mold surfaces. The variation in types of molding is primarily due to the type of mold used and the method of melt delivery to the mold. 

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