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and A. G. LuzinThe inserts for composite plates are produced from increased purity fused periclase. The method of preparation of the periclase inserts includes such energy consuming processes as grinding, pressing, and high temperature firing, the influence of which on quality and the production of scrap was investigated by us.The inserts must have a maximum open porosity of 14% and a minimum compressive strength of 80 MPa with a mininum 96.5 wt.% MgO. The apparent density of the pressed unfired part must be a minimum of 3.15 g/cm 3. The method of pressing on an NBF-1738 press with a force of 6.15 MN and repeated application of the load is the most favorable for removal of air, relaxation of stresses, and obtaining a high-density unfired part without overpressing cracks. Overpressing cracks are absent in an unfired part of a charge with a comparatively low content of vibroground periclase (15-20%).With an increase in the quantity of vibroground periclase in the charge to 30-35%, overpressing cracks are formed in the unfired part. The charge does not contain the coarser than 2 mm fractions in view of the negative influence of them on the quality of the ground working surface of the plates. With a comparatively small quantity of finely ground periclase constituent in the inserts it must be sufficiently fine to provide sintering of the parts in firing. A method was developed for grinding of periclase in a Palla vibromill, which consists of two cylinders connected in series and loaded with cylindrical pebbles as the grinding elements. The weight of the grinding elements is 786 kg in each cylinder. In the vibromill it is possible to obtain finely ground periclase with a 45% finer than 5-~m fraction with a capacity of 450 kg/h. With addition to the charge for the inserts of 15-20% vibroground periclase the open porosity of densely sintered parts is 10-14%.In a ball mill it is impossible to obtain periclase of the necessary fineness even with a grinding time of an order of magnitude more than in a vibromill. After 5 h of grinding in a ball mill the periclase contains 96% of the finer than 63-~m fraction with aspecific surface of 4000 cm2/g (Fig. i). The inserts to whose charge was added fine periclase ground in a ball mill have an open porosity of ~ 15% after firing at 1850~ that is, they do not satisfy the specification requirements. Figure 2 shows the change in height and apparent density of an unfired part in relation to the number of pressings. The strongest upsetting of the mixture and compaction of the unfired part occur in the first three pressings and after five pressings the apparent density and the height of the raw part stabilize. Therefore, increasing the number of pressings beyond five is undesirable.In the first comparatively weak pressing the loose mixture poured into the mold with a bulk density of 1.7 g/cm 3 compacts significantly to PaDD = 2.8 g/cm 3, primarily as the result of movement of the grains and partial further pulveriz~hion of the 2-1 and l-0.5-mm fractions to the 0.5-0.063 mm and finer than ...

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