The main causes of edge cracking of ceramic embryo include the following.
(1) Boring, too fast.
(2) The mouth edge of the vessel is too thin to bear external force.
(3) If a ceramic vessel has just been made and cracks begin to appear before going through any important boring stage, it may be that the mud is used too many times. It is also possible that the additional filling (clinker or sand) in the mud guess is excessive. O sometimes, the mud prepared through recovery and reuse or from scratch will become difficult to use because it has been used too many times, such as the mud repeatedly drawn on the drawing machine.
(4) When glazing the ceramic body, it is easy to cause the thinner parts (generally the mouth edge of the instrument book) to be too wet when encountering the bonding parts with too large thickness distance. These parts will bear the intrusion of external forces in the later boring process.
(5) When the dry green body is placed in a wet environment, it will absorb water again. This phenomenon is quite special. I have seen a semi dry green body absorb water again. When the green body softens to a certain extent, it is crushed by its own weight, for example. When a dry blank is placed in a wet environment, the blank will expand while absorbing water again, which will form a tensile force in the thin and thick parts with large distance in the later boring process. For those ceramic blanks with relatively small clay content, such as some low-temperature white clay and porcelain clay, because their green strength is too low to bear the tensile force generated in the process of re water absorption, many small cracks appear, and these small cracks can be seen only after plain burning.
(6) A common reason is improper trimming. The trimming tool needs to be very sharp. It can’t be cut or scraped until the green body is half dry. When the body is too dry, it is easy to crack. As mentioned earlier, small cracks on the outer surface of the billet will double the pressure. Generally speaking, after trimming, the external surface of the billet is wiped smooth with the help of a wet sponge, which can effectively prevent cracking.
(7) In the field of ceramic industrialization, the cracking mode on the edge of the plate is called “bird’s mouth”, which is caused by improper trimming. Place the dried or nearly dried plate blank on the electric rotary table, and trim the plate edge from an appropriate point of view with the help of an “L” shaped blank trimming knife. If the point of view of the contact part between the trimming knife and the blank body is not appropriate, the knife edge will jump quickly and bump, or strain the outer surface of the vessel, and the resulting ear sleeve will appear after firing.