The reason for the cracking of the ceramic embryo
The main reasons for edge cracking include the following.
(1) The drying speed is too fast.
(2) The rim of the vessel is too thin to withstand external forces.
(3) If a ceramic utensil has just been made and cracks begin to appear before it has gone through any important drying stage, it may be that the mud has been used too many times. It is also possible that the additional filler (clinker or sand) in the mud is too much. Sometimes, the recycled or reconstituted mud will become unusable because it is used too many times, such as Mud that has been drawn repeatedly on a billeting machine.
(4) When glazing the ceramic body, when encountering a joint part with a large thickness gap, it is easy to cause the thinner part (usually the mouth of the book) to be too wet, and these parts will dry later.
During the drying process, it can withstand the intrusion of external force.
(5) When the dried green body is placed in a humid environment, the green body will absorb water again. This phenomenon is quite special. I have personally seen an example of a semi-dry green body that absorbs water again, and when the green body softens to a certain extent, it is crushed by its own weight. When a dry blank is placed in a humid environment, the blank will expand while absorbing moisture again, which will cause tension in the parts where the thickness gap is large during the later drying process. Those ceramic blanks with relatively low clay content, such as some low-temperature white clay and porcelain clay, have too low green strength to withstand the tensile force generated during the re-absorption process, and many small cracks appear, and these small cracks are only in the It can only be seen after the bisque is burnt.
(6) One of the most common reasons is improper trimming. The trimming tool must be very sharp and cannot be cut or scraped until the blank is semi-dry. When the green body is too dry, its strength is very weak. In this case, the green body is easily broken by the tool for repairing the green body. As mentioned earlier, small cracks on the outer surface of the green body can multiply the pressure. Generally speaking, wiping the outer surface of the blank with a wet sponge after the trimming is completed can effectively prevent cracking.
(7) In the field of industrialized production of ceramics, the cracking method on the edge of the plate is called “bird’s beak”, which is caused by improper trimming. Put the dry or nearly dry plate blank on the electric turntable, and use an “L” shaped blank trimmer to trim the edge of the plate at an appropriate angle. If the angle of the contact part between the trimming knife and the green body is not suitable, the knife edge will jump quickly and collide with or strain the outer surface of the vessel, and the resulting cracked ear sleeve will appear after firing.