Plasticization stages

The majority of the cyanuric acid produced commercially is made via pyrolysis of urea [57-13-6] (mp 135°C) primarily employing either directiy or indirectly fired stainless steel rotary kilns. Small amounts of CA are produced by pyrolysis of urea in stirred batch or continuous reactors, over molten tin, or in sulfolane. The feed to the kilns can be either urea soHd, melt, or aqueous solution. Since conversion of urea to CA is endothermic and goes through a plastic stage, heat and mass transport are important process considerations. The kiln operates under slight vacuum. Air is drawn into the kiln to avoid explosive concentrations of ammonia (15—27 mol %). 

Recent work in this Division has shown that various substances other than vitrinites, such as pitches from coal tars and petroleum tars, polyvinyl chloride, and polynuclear hydrocarbons, develop similar mosaic structures on heating. In fact this effect occurs with most high carbon materials which pass through a plastic stage during carbonization. 

An additional property of coal that is worthy of mention at this time is the softening point, which is generally defined as the temperature at which the particles of coal begin to melt and become rounded. The softening point indicates the onset of the plasticity stage and is (as should be anticipated) a function of the volatile matter content of coal. For example, coal that produces 15% w/w... 

British Carbonization Research Assoc iatioriTBCRA), "An Infrared Spectroscopic Study of the Influence of Oxygen in Coal on the Plastic Stage of the Coking Process", Carbonization Research Report 64, 1979, 22 pp. 

During the plastication stage, the polymer melt is typically plasticized from solid granules or pellets through the combined effect of heat conduction from the heated barrel and the internal shear heating caused by molecular deformation with the rotation of an internal screw. Screws in injection molding have many... 

When the blends are subjected to tensile testing, a certain fraction of the overall strain is accommodated by conservative deformation of the material. In the PP matrix, deformation results from the combination of amorphous phase hyperelasticity and crystal plasticity, as discussed earlier (50). The PA6 phase is also capable of deforming plastically, but its flow stress in the plastic stage is much higher than that of PP. Consequently, in the PP/PA6 blends the isolated PA6 particles exhibit less... 

It is during the plastic (fluid) stages of carbonization that the most important features of coke structure are formed, particularly porosity (6) and pore wall structure. During the plastic stage, the optically isotropic parent material undergoes a phase transition to an optically anisotropic melt which finally... 

When coal is heated, it passes through a plastic stage, which is an indication of the initial softening, chemical reaction, gas liberation, and resolidiflcation process within the coke oven and is an important requirement in the coke blend required for end product coke strength. In addition, the fluidity of the plastic stage is a major factor in determining what proportion of coal is used in a blend. 

Although it is possible to formulate the general stages that occur up to and during the plastic stage of coal, the exact mechanism of coal fusion is not completely understood. There seems to be little doubt that the process is concerned with the production and/or liberation of liquid tars within the coal. 

Thus, as coal is heated to the plastic stage, it is probable that some thermal conversion to lower-molecular-weight species can occur with the release of liquids and gases. These changes (including the liberation of water, carbon dioxide, and traces of hydrocarbons) can occur at temperatures below 300°C (570°F) and are accelerated markedly when a temperature of 350°C (660°F) is reached. 

In general, concrete cracking may be distinguished into two cracking that developed when the concrete is fresh (plastic stage) and cracking that developed when the concrete is hardened. 

The usual techniques used are to brush, burlap drag or tine the concrete at its plastic stage. They all texture the surface in the transverse direction. 

A metal failure as a result of being stretched to the point where the yield stress has been exceeded over a large area. The metal reaches the plastic stage and failure when ductile fracture occurs. 

Much effort has been spent on studying extrusion, as the plastication stage is applicable to other processes. Plastication models were given in Ref. 3. However, the plastication process is still actively researched today, particularly with regard to mixing and screw efficiency. ... 

At some stage of packing, the gates have completely frozen. Eventually the cavity pressure is reduced to zero or a low value. The part continues to cool down and to solidify. Meanwhile, the screw starts rotating and moving backward, and the next plasticizing stage takes place. 

---