About technical ceramics
The strongest material against abrasion and wear available is ceramics. Good electricity insulator even at high temperatures. Ceramics has become a common name for a variety of materials used in industry, these are inorganic and non-metallic materials.
Ceramics have undergone enormous development in recent years, but despite this, they still account for very few percent of the materials used in today’s industry. In recent years, the use of ceramic components has increased more and more as the outstanding properties of ceramics positively affect the service life and thus the value of the end product.
Use of technical ceramics
The ceramics are specially developed materials used for applications up to 2100°C and more, resistant to extreme wear and chemical influences, very good electrical insulator even at high temperatures.
After many years of experience in the manufacture of ceramics and cooperation with our customers, we have developed several programs for the use of technical ceramics. It is almost impossible to list all the places in the industries where technical ceramics have found their use today.
Materials have unique properties and can be used in many high-performance applications, such as: in the pulp industry, food industry, automotive, in furnace production, energy and electronics, ignition electrode, brick industry, chemical industry, in metal industry, welding industry, laboratories, pump industry, temperature measuring equipment, in metal industry in all places where components are subjected to extreme wear, high temperature and chemical influences, etc.
The heart of any ceramic production lies in the powder preparation. The starting powder must be prepared to a special distribution, fineness and shape
The heart of any ceramic production lies in the powder preparation. The starting powder must be prepared to a special distribution, fineness and shape. During preparation, special auxiliaries and additives are added to obtain processing and sintering powder. These additives and aids are then burned out completely at the time of sintering. To ensure quality, it is important to characterize the output state very carefully, as defects at this stage significantly affect the final product.
design, manufacture of tools
The prepared powders (granules) must now be pressed under high pressure into compact parts. The most common design methods for ceramic products are dry pressing (automatic pressing), isostatic pressing, extrusion and injection molding. The choice of method depends on the size, geometry and required number of parts. Methods such as sludge casting and hot pressing are not as suitable for ceramic technical components.
Here, in particular, double-sided pressing (tablet pressing) is used. Overstamp and understamp press granules in a matrix into a "greenbody" (=detail before sintering). Undercutting, as with injection molding, is not pressible. However, it is possible to produce holes (round as well as oval, square, etc.) and ledges in the axial direction. The crimping tools consist of carbide, are relatively expensive and only pay off in larger numbers. As press dispensers have limited compressive forces, the maximum detail press areas are approximately 80 mm², as well as detail heights up to 50 mm. Geometrical the details become very constant. As a rule, the part is sintered (=burned) without further processing.
This means a comprehensive compaction of the powders in an elastic form (most often rubber) with high hydraulic pressure of up to 4000 bar. The outer, of the rubber sheath shaped, the contour is not very precise and must be post-processed before sintering. The press molds are relatively inexpensive. The press cycle takes a long time, it consists of the three parts pressure build-up, pressure retention and pressure relief. This method is intended for smaller numbers or larger dimensions. The machining work is considerably more cumbersome compared to dry pressing.
A plastically malleable ceramic mass is prepared here and with a piston or screw press, the mass is pressed through a nozzle to lengths of up to 2 m. Using a piston or worm press, the mass is pushed through a nozzle to lengths up to 2 m. For mechanical components, rods with a maximum diameter of 12 mm are mainly made, which are then given their geometric shape and obtained the required tolerances by means of cutting and grinding machining.
The procedure largely corresponds to the familiar injection molding of plastics. However, after injection molding, the mixed plastic part must be removed chemically or thermally. The remaining material is sintered into a dense ceramic detail.
The ceramic powder is suspended in water and poured into a corresponding gypsum mold. The gypsum absorbs the water's suspension and the leftover powder is densified like "filter coffee boiling" and a detail corresponding to the inner contour of the gypsum mold is built up.
The dry and isostat-pressed parts have a chalk-like consistency and must now, where necessary, be green-worked by grinding, sawing, drilling, milling and turning (milling and turning are not possible after sintering). These processing methods, borrowed from the metalworking, allow manufacturing of complicated details. At this stage, only rough tolerances can be achieved.
Sintering refers to the process of densification of ceramic green bodies after molding. Under the influence of high temperature, the elimination of pores and volume shrinkage will occur, providing a solid sintered body with the expected geometry. The sintering process has a decisive impact on the performance of the material. It is very important to choose a suitable sintering method in the manufacture of different types of technical ceramics and for different property requirements. Sintering is the densification of a powder-pressed part into a compact body by a thermal treatment below the melting point of the powder. At high pure, poly crystalline, ceramic materials there are no bonding phases. To avoid costly post-processing of defective parts, a crack check is made on all parts after sintering.
For those applications where the tolerances obtained so far do not meet the requirements for dimensional accuracy and surface quality, the required precision is achieved by post-processing the sintered parts. It is done with the help of diamond tools, emulsions and pastes. However, surface and tolerance requirements should only be indicated on the detailed drawing where they are strictly necessary for the function. Through post-processing, it is now possible to manufacture according to ISO tolerances in series production. More accurate tolerances can be achieved at higher cost and additional work. Today you can fit shafts into holes with less than 5μm play. With special methods and measures, very fine tolerances can also be achieved in ceramics. However, it must be pointed out here that any reduction in the tolerance field increases production, test and measurement times and thus also significantly increases production costs. Therefore: tight tolerances only where absolutely necessary for the function! On flat and cylindrical surfaces, surface quality can be significantly improved with the help of lapping and honing, as well as subsequent polishing at reasonable costs