Plaster to plated bar

Plaster board to plastic

Plaster board. (Arch.) A building board made of plaster and faced with paper on both sides.

Plaster cast. A plaster of Paris model ,. which has been reproduced by use of a mold. Plastering. The act of applying plaster.

Plastering trowel. A thin rectangu­lar piece of steel 4 to 5 in. wide and 10 to 12 in. long, with handle attached, offset but parallel to the blade.

Plaster lath. (Arch.) The thin strips of wood nailed to studding, joists, or rafters to receive plaster.

Plaster of Paris. (Chern. and Bldg.) Calcined gypsum, marketed in the form of a white powder. When mixed with water, it sets quickly, and is useful in making casts and models.

Plastic. (Cerarn.) Capable of being molded or modeled. Moldable material.

Plastic art. Ceramics or sculpture in which things are modeled.

Plastic flow. (Plast.) Row which is proportional to the pressure in ex­cess of a certain minimum pres­sure (yield value) necessary to start the flow.

Plasticity. (phys.) That property of a body which permits a change of shape without fracture. (Plast.) Susceptibility to and retention of deformation. Capacity of taking and retaining the form of a mold.

Plasticize. (Plast.) To soften a ma­terial and make it plastic or mold­able.

Plasticizers. (Plast.) Chemical agent added to plastic compositions, especially those to be used as coatings, to make them softer and more flexible.

Plastics. In the broad sense there are many plastic substances, from pitch to Portland cement, and on, through the synthetics. All flow at some stage of use. The com­mon.acceptance of the term, how­ever, refers. to the synthetics. These are a large group of vari­ously based types of high mo­lecular weight, which solidify in the finished state, and though they resemble the natural resins in some respects, they are chemi­cally and physically different.There are many combinations of plastic source materials; therefore, there is a large and growing num­ber of members in the plastics family. The major divisions are : I. The theflriosets, which set per­manently under heat, catalysts, ul­traviolet light, etc. The members of this group are the Aminos (ureas and melamines), most polyesters, alkyds, epoxies, and phenolics. (SEE POLYMERS, etc.) 2. The thermoplastics, which can be repeatedly softened and shaped, and hardened by cooling are: styrene polymers and copo­lymers, acrylics, cellulosics, polyethlenes, vinyls, nylons, and various fluorocarbons. (SEE POLY­ MERS, etc.) Each memebr of the plastic family has properties suit­able to certain particular demands;

Plastic tooling to plated bar

some are hard surfaced, some abrasion resistant, some flexible, some tough, and some are high in dielectric strength. Of the two plastics most common in schools, acrylics (plexiglas and lucite), and polyesters; the former is supplied as sheet and is sawed, filed, and worked much like wood; while the polyesters, under various trade names such as Casto lite, Castoglas, Vibrin, Hetron, etc., are chemically treated and hardened from liquid in the classroom, and they are used to produce castings and laminations by simple class­room methods. Polyesters are the familar boat lamina::~iI1g resins.

Plastic tooling. Dies, jigs, and fix­tures for metal forming, boring, assembly, and checking, made at d saving time and labor, of lami­nated and cast components, and cemented into higly stable indus­trial tools, chiefly with epoxy and some with polyester resins. Expoxies are strong adhesive res­ins, particularly useful because of their low shrinkage factor. Poly­esters have a cost advantage and are easy to handle. (SEE ExPOxy RESIN.)

Plastic wood. (Woodwk.) A wood compound which quickly hard­ens on exposure to air, for filling in cracks and defects. It can be painted over almost immediately after applying:

Plastisol. (Plast.) Vinyl dispersions in mixture with plasticizers, which can be molded or converted into film. Often used for flexible moldi

Plate. '(Arch.) The top horizontal tim­ber of a wall on which re~t, and are fastened, attic joists, roof rafters, etc. (Print.) A stereotype or electrotype of material to be printed. (Radio) A solid metallic element of a vacuum tube which attracts the electrpns from the cathode and acts as an output elec­trode for the external circuit.

Plate circuit. (Radio) The complete circuit the plate current would make from the plate, through the reproducer or coupling devices, power supply, ground, and back to the cathode of the same tube.

Plate clutch. (Auto. Mech.) A clutch which transmits power through two or more plates which are held in contact by the pressure of springs.

Plate condenser. A condenser, in which the alternating sheets of metal are joined to give two ter­minals. The separators may be of mica, parafined paper, air, etc.

Pate current. (Radio) The pulsating direct current which flows in the plate circuit of any stage Ip (Plate currellt. )

Plate cylinder. (Print.) The revolv­ing . section of a rotatry press to which curved printing plates are attached.

Plated bar. (Metal.) This is blister steel in tbe form of bars which have been rolled or hammered while hot. This treatment Oattens down the blisters and tends to toughen the metal.