Plastic clay

A plasticizer is a substance the addition of which to another material makes that material softer and more flexible. This broad definition encompasses the use of water to plasticize clay for the production of pottery, and oils to plasticize pitch for caulking boats. A more precise definition of plasticizers is that they are materials which, when added to a polymer, cause an increase in the flexibiUty and workabiUty, brought about by a decrease in the glass-transition temperature, T, of the polymer. The most widely plasticized polymer is poly(vinyl chloride) (PVC) due to its excellent plasticizer compatibility characteristics, and the development of plasticizers closely follows the development of this commodity polymer. However, plasticizers have also been used and remain in use with other polymer types. 

Plastic Refractories and Ramming Mixes. Plastic refractories are mixtures of refractory grains and plastic clays or plasticizers with water. Ramming mixes may or may not contain clay and are generally used with forms or steel work. The amount of water used in these products varies but is held to a minimum to faciUtate drying. Plastics are generally suppHed in a ready-to-use state. 

Plastic clays composed largely of poorly crystallized kaolinite but having small amounts of iUite, and at times montmorillonite, are widely used ia bonding mol ding sands, especially ia the United States. 

Fireclays can be dividea into plastic clays and hard flint clays they may also be classified as to alumina content. Firebricks are usually made of a blended mixture of flint clays and plastic clays which is formed, after mixing with water, to the requirea shape. Some or all of the flint clay may be replaced by highly burned or calcined clay, called... 

Plastic clay is dried to a moisture content of less than 5% and stemming material is made from it by mixing four parts by weight of the clay with one part by weight of water. The mixture is stirred carefully until a uniform paste is obtained. 

A No. 8 instant fulminate-tetryl electric detonator is fixed to the cartridge next to the mouth of the mortar and the hole hermetically sealed with stemming of plastic clay. 

The thrower or workman engaged in the formation of the plastic clay scats himself upon the stool, a—Pig, 473—supporting himself with his feet against the board 5, so as to obtain a sufficiently stable position to... 

By using a similar mixture of plastic clay, in which a proportion of leurite, instead of the necessary amount of potassa, was present, a well-glazed porcelain was obtained, though somewhat spotted. When lime was employed in place of chalk, or the quartz-sand was replaced by flint, no alteration in the properties of the normal mass was observed. 

The relative values of plastic clay for the manufacture of fitw and common stoneware, with and without glaze may be hero given—... 

The composition fe more simple only one addition being made to the plastic clay, which, having no tendency to shrink in the furnace, prevents the- clay from any Very Serious contraction, the amount of which varies, as in the finer stonewares, from eight to ton per cent, ... 

As the- plastic clays generally possess this property of contraction in a high degree, objects formed from them without this addition and tolerably thick in the sides, infallibly crack in the firing. 

Fine Earthenware.—The English manufacture may be selected as the type of this ware it is composed essentially of a mixture of plastic clay and quartz, and is, therefore, more refractory, harder, and denser than the delft ware, the chief ingredients of which are potters clay and marl, and which is in consequence soft and calcareous. Fine earthenware again is always coated with a transparent glaze the commoner sorts with enamel, producing the favorite Majolica ware. Neither kinds, however, are fitted for oulinary use, as they either split when exposed to heat, or the glaze becomes cracked and crazed. 

Tho crude materials used in England in the manufacture of fine earthenware, are Cornish stone and China clay, a kind of kaolin brought from Cornwall, two varieties of plastic clay, both of which burn white, and chalk-flints. That class called ironstone china is made from ft mixture of plastic clay, kaolin, Comish stone in excess, and silica, Hie formula of which is subjoined —... 

Yellow or Nankin-colored earthenware, composed of grey plastic clay from Vallendar, near Coblentz, and clay from Eifol, which bums yellow, The glazo contains lead,... 

Porcelain Stoneware, containing plastic clay from the Palatinate and from Vallendar, with ground quartz and hono ashes. The glazo free from lead and composed of borax, alkali, and felspar. 

Amongst tho varieties of fine earthenware may bo classed the peculiar manufacture of day pipes. The clay used in the construction of these requires extreme plasticity, together with a certain amount of porosity upon firing. The plastic clay found in the foyers forming the basis of the clay deposit, is used without the addition of a flux, but to insure tho perfect uniformity and pliability of the mass, great care is taken with the kneading and slapping processes. 

In the composition of the mass, certain proportions of potter s and plastic clay, clay marl, and quartz or sand, will always bo found—these constituents varying in their nature according to tbo different localities in which they occur. Thus Paris earthonwaro consists of—... 

Bentonites may generally be divided into two classes a) Those capable of absorbing large amts of water and which swell tremendously in the process. They also have the property of remaining in suspensions in thin water disDersions and b) Those that absorb no more water than ordinary plastic clays or Fuller s earth and do not swell appreciably. They settle rapidly in thin water dispersions... 

In the extrusion process the plastic clay mass is forced through a die by a screw mechanism (figure 9.12). 

Vitrified clayware is sintered stoneware which is hardly porous and can withstand chemical and mechanical outside influences. For those reasons vitrified clayware is used for sewers, as a coating for vessels, reactor inlets, pipes, valves and pumps. Plastic clay with a relatively high content of aluminium and alkali metals and a low lime content is used as raw material... 

The die produces a column of clay with the desired form and a steel wire cuts it in individual parts. Products made by an extruder bricks (both perforated and not), hollow bricks, large building blocks, drainage pipes, sewer pipes, riven slabs, tiles and roof tiles. The extruder requires the use of a plastic clay. The baked product is characterized by its square shape and smooth surface. 

A stamping press is used in the manufacture of roof tiles. This is a machine which compresses a plastic clay mass between two moulds to obtain the desired shape. This compression technique is only rarely applied in coarse ceramics. 

---