Bone China forming 15

Temperature difference ( Gradient) Kinetic energy causes water molecules, and the surface tension of the water in the capillary void in air pressure, caused by high temperature to low temperature in water molecules move ( Heat transfer) , the degree of difference ( Intensity) The water molecules from high humidity to low humidity in mobile ( Wet conduction) 。 That is to say, and the temperature gradient in the direction of heat conduction, The heat flow direction) Agree, face wet conduction direction same as the moisture gradient. So there are two forms of diffusion, caused by bone porcelain body internal moisture gradient of water wet moisture diffusion and caused by the temperature gradient in the thermal diffusion. Request as far as possible, make two gradient directions close to consistent ( By inside and outside) 。 Bone China uniform phase, the inner diffusion velocity is equal to the outer diffusion velocity. As a result, the drying rate depends on a proliferation of bone porcelain surface evaporation speed. But as a result of bone China body contraction, grains, internal diffusion resistance increases led to the decrease of the internal diffusion speed, results in diffusion speed control the drying rate, drying process in slow down stage, the drying rate slow down gradually. In phase equilibrium, the bone porcelain blank free water in the body has ruled out entirely, internal diffusion speed drop to zero, the surface water medium to reach a dynamic balance with the outside world. Bone China the main factors influencing the internal diffusion is as follows. ( 1) Of bone porcelain body material properties of coarse particle, desert material content more bone porcelain body for its existence within the capillary diameter thick, diffusion resistance small and conducive to the diffusion velocity increase. Bone China ( 2) Bone China body temperature varies with temperature, water surface force is reduced, but the more significant reduction in viscosity, easy to move, and diffusion speed. Bone China ( 3) Bone China body surface and internal humidity poor wet diffusion rate is proportional to the moisture gradient relationship. To sum up, in the process of drying moisture diffusion and performance of the diffusion process in the material transfer, the mass transfer process, because of the mass transfer process was conducted under the action of heat, so the essence of the drying process is a process of energy exchange and material transfer. Bone porcelain body in the process of drying shrinkage cracking and deformation without dry bone porcelain in the billet temperature solid particles separated by water film separation. In drying process, as the free water, membrane deformation, water particles gradually close, bone China body to contract, about equal to the line of free water volume shrinkage. When the water film thickness thinning to critical point - - - - - - - Bone China body among the particles reach the level of contact with each other, internal diffusion resistance increases, the drying speed and shrinkage rate change sharply, contraction, basic end into falling rate drying). Continue to dry, began to rule out the possibility of contact each other the intergranular pore water, small shrinkage, until dry with the surrounding medium contained moisture balance. Bone porcelain bone porcelain body of clay with the size of the reduction performance, bone porcelain blank composition, moisture content and the processing technology and other factors. Clay particle size is fine, the adsorption of water film is thicker, the greater the shrinkage rate. Plastic clay, kaolin, colloid particles of montmorillonite in the dry line contraction of 3% ~ 8%, 6% ~ 10% and 10% ~ 25%. On the premise of meet the formability and to increase desert sexual material or part adopts presintering dehydration of clay, can reduce dry shrinkage. Bone China with Na + as thinner, when the clay particles in parallel, can contain clay minerals content of Na + shrinkage rate is greater than the clay minerals content of Ca2 +. Bone China has for sludge particle orientation, space ( Or water) Also has corresponding orientation lead to drying shrinkage anisotropy, as shown in figure 5 - 6. Bone porcelain body body each part of the outer layer or shrinkage internal stress, the difference between the bone porcelain body when the internal stress is more than a plastic state yield value, bone China body deformation. Internal stress too much more than the destruction of the plastic state bone porcelain body points or more than the state of elastic strength, leading to bone porcelain body cracking destruction. Bone China & ndash; Tangshan bone porcelain tableware suit to be continued. 。 。 。 。 。