Electrohydraulic-impulse pressing of refractory powders

Abstract

Pressing is one of the most important operations in the production of refractories and on it depends their quality and working properties. In recent years, both in the Soviet Union and abroad, researchers have been rapidly developing methods of pressing refractory powders using different energy carriers, transmission media, and methods of applying the loads, which have extended the potential of powder technology. Impulse methods of pressing have been gaining ground among the new methods. One of the most promising, albeit the least studied of the impulse methods, is electrohydraulic-impulse pressing (EGIP) for powders [i, 21 . This article gives the results of a systematic study of this method for refractory powders of different grain-size composition. Studies were made of the technical possibilities of EGIP and we identified the most rational applications, the power and other technological parameters of the process; an experimental technology was developed for electrohydraulic-impulse pressing of refractory articles.Bodies made of fused quartz, magnesite powder, corundum, and alumina were used. The binder consisted of a water solution of sulfite lye. The technical potential of the method was studied on specimens in the form of continuous cylindrical briquettes of diameter and height 40-50 mm, and sleeves of height 30-100, external diameter 30-50, and wall thickness 5-15 mm~The test specimens and articles were pressed on the regular electrohydraulic impulse equipment "Udar 12M" with an energy capacity of up to 20 kJ and a working voltage of up to i0 kV.We studied the effect of the main technical factors of the EGIP equipment (loading method, reserve energy of the equipment and the number of discharges, the shape and dimensions of the specimens, the predensification pressure on the body and its vacuum treatment) on the basic properties of the pressings (density, porosity, strength, thermal-shock resistance) and the structure after firing. The specimens were fired with the standard factory technology in oxidative--reduction media at 1550~The EGIP scheme for powder is shown in Fig. i. The battery of condensors C was charged from the alternating-current mains through the increasing transformer Tr and the rectifier B. Following a signal from the discharge equipment P there is a high-voltage discharge between the electrodes 1 of the working chamber 2 filled with water 3. The duration of the discharge is 200-300 ~sec. With an electrical discharge energy of 60 kJ, impulse electrical capacities of 0.i GW are developed. In this case, the liquid forms an impulse pressure with a reverse front and an amplitude up to 150 MPa, which is spread in the form of a compression wave, and is densified through the elastic membrane 4 of the powder 5 filled in the matrix 6.The impulse nature of the load application determines a number of features and advantages of the EGIP. The rapid photographing of EGIP with the aid of the SFR photoregister showed that the displacement of the powder in the process of compaction occurred at a rate of 4...