forming method of piezoelectric ceramic embryo

There are many methods for forming ceramic embryo , such as pressure forming, plastic forming and slurry forming. Each type of forming method can be divided into several specific forming methods of Pzt ceramic disc. It can be selected according to the shape, specification and size of the product, but each has its own advantages and disadvantages. Only the widely used dry press molding method will be described here. Dry pressing is a process in which a granulated porcelain material is placed in a steel mold of a certain shape, and is pressed into a green body under a certain external force by means of a plug.

(1) Principle of dry pressing

Under the action of external force, the piezoelectric discs pietzoelectric ceramics particles are close to each other in the mold, and the particles are firmly connected by the internal force to become a blank body which maintains a certain shape. The structure of the dry compact body: it can be regarded as a three-phase combined system composed of a liquid phase (adhesive) layer, air, and porcelain particles. Internal force and its physical mechanism: 1 the meshing force caused by the contact of the particles; 2 the no-tubular pressure of the binder in the micro-pores between the particles; 3 the molecular attraction between the particles, the binder and the particles; 4 the contact electrostatic attraction caused by charge transfer.

General principles for selection of molding conditions 1) Pressurization method, dry compression molding of piezoceramic cylinder tube is generally divided into two modes: one-way pressurization and two-way pressurization. The thinner product can adopt the one-way pressing method; the thick product should adopt the two-way pressing, so that the density inside the blank is relatively uniform.

2) Pressure is determined by experiment for different porcelain materials and products of different shapes. Generally, it is in the range of 1-3T/cm3 to ensure that the density of the green body is uniformly 5.4-5.7 g/cm3. Pressurization speed and holding time is a large volume of the blank, the pressure must be slow, after reaching the maximum pressure, it needs to be kept for a certain time, in order to facilitate the removal of air in the blank to prevent delamination and cracks. For thin green bodies, the pressure can be faster, and the pressure can be kept for a few seconds.

(3) The use of adhesives, the role of adhesives in forming:

The porcelain material of soft PZT piezoceramic crystal is plasticized and easy to shape, and the green body has a high and uniform density; 2 increasing the adhesion of the ceramic material, so that the molded body has a certain mechanical strength;Reducing the friction between the porcelain material and the mold wall, facilitating the demoulding and reducing the delamination crack phenomenon. Requirements for adhesives for piezoelectric ceramics have adequate adhesion; Wide range of volatilization temperature can be slowly decomposed and volatilized, avoiding rapid concentration and volatilization is causing cracking of the body; Volatilization temperature should not be too low, so as to avoid simultaneously volatilize with water, causing deformation or cracking of the green body, but it should not be too high, causing lead and other volatilization; After heating and volatilization, there is no residual impurities, so as not to affect the performance of the small piezo tubes transducer. Preparation of adhesives are many types of adhesives. Piezoelectric ceramics are used in dry compression molding using polyvinyl alcohol (PVA), which is non-toxic and can basically meet the above requirements. The typical formulations, features and recipes are described below. 85% concentration of PVA aqueous solution, simple formula, low cost, but short storage period (within 10 days). 9 PVA: Glycerol: Alcohol: distilled water = 15:7:3:75 (wt%). The viscosity is large, the storage period is long, and it is not easy to deteriorate, but it is too thick at lower temperature and should not be used.Preparation: mixing, stirring at 90°C temperature, filtration, sealed and stored for use.