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310Machined surfaces of very high quality are required in honing the most important and most precise machine parts (for example, cylinder linings in internal-combustion engines for cars, trucks, and tractors), whose operational reliability is a primary concern in competitive markets.We know that the formation of even one deep scratch on the cylinder surface requires additional finishing (honing by bars with micropowder or lapping), with considerable loss of production time.Such scratches are due to the considerable size variation of the cutting grains that is permitted by the standard regarding the manufacture of diamond and abrasive honing bars. As a rule, the time required for the elimination of such scratches is up to 30% of the total machining time. Therefore, there is a pressing need to reduce the likelihood that large cutting grains will form part of the abrasive tool.The standard size distribution of diamond and abrasive grains in the tool does not permit the elimination of such defects in machining important parts (such as the linings of hydraulic cylinders in heavy-duty mechanisms within excavators, bulldozers, cranes, and other transport systems).One promising approach is to use a new single-component abrasive tool based on white corundum [1]. In the manufacture of this tool, boron-carbide powder must be added to white-electrocorundum abrasive powder (10-20 wt % boron carbide). Then a compressive shock wave is passed through the powder mixture, with subsequent high-temperature sintering in an electrovacuum furnace.When the shock wave passes through the powder mixture, the particles of each component are crushed.The size distribution of the white-electrocorundum and boron-carbide grains will be different.However, under the action of the impact force, the electrocorundum grains briefly move at enormous speed toward the boron-carbide grains (whose hardness is 37-43 GPa, as against 20-24 GPa for the electrocorundum) and are further crushed, which considerably changes their size distribution, since additional pores are formed in the high-temperature sintering of boron-carbide powder.After honing the 40 ï steel parts (the cylinder linings of A-type motors and hydraulic cylinders) by the new abrasive tool, the following results are obtained: the number of surface scratches is reduced to 0.1% (in other words, practically to zero); and the stable mean surface roughness of the machined part is Ra = 0.14-0.2 µ m, which is 2.4-3.2 times less than the value after machining with a diamond tool. CONCLUSIONSThe action of a compressive shock wave on whiteelectrocorundum grains or on boron-carbide grains is insufficient to permit the use of these powders individually for abrasive tools in finishing. However, the application of a fast compressive shock wave to a mixture of white-electrocorundum and boron-carbide grains changes the size distribution of the grains at the working surface so that the machined surfaces obtained exhibit high performance. REFERENCES 1. Russian Patent 2293013.

A new technology for fabricating ceramic articles (bricks, tiles, and others) is described. This technology shortens the production cycle by intensifying the processes occurring during pressing and firing, which makes it possible to obtain ceramic articles with enhanced mechanical strength (45 -60 MPa) and improved appearance and quality. The processing regimes chosen are validated.Modern technologies for manufacturing ceramic articles used in home construction and paving roads are very labor-intensive and time-consuming. The common technologies include the following: preparation of a clay body, which involves coarse milling of the initial material, drying, fine milling, sieving of large inclusions, mixing with additives and wetting; compaction of loose powder bodies with moisture content 8 -12% under pressure 15 -40 MPa in hydraulic presses; drying of the green part in conveyer and tunnel dryers for 8 -24 h and firing. Articles are fired at temperatures 920 -1200°C in tunnel furnaces for 40 -80 h [1]. Such a technology is very time-consuming, requires considerable equipment and many operators, and it is difficult to obtained ceramic articles of high quality.During pressing air bubbles are present between and inside large inclusions of the initial raw material. During firing these bubbles expand and, escaping to the outside, often result in the formation not only of microcracks but also quite large cracks, reducing their mechanical strength and degrading the appearance and, correspondingly, the quality of the ceramic articles.The technology proposed in [2] for manufacturing ceramic articles makes it possible to significantly shorten the production cycle by the elimination of a number of operations, which became possible owing to the intensification of the processes occurring during pressing and firing. This makes it possible to obtain ceramic articles with high mechanical strength, improved appearance and, correspondingly, higher quality.The new technology for manufacturing ceramic articles includes drying of clay, preparation of the body and pressing articles followed by firing. In addition, the drying is performed for 2 -4 h at 30 -40°C. The product obtained is comminuted to particle size 0.3 -0.5 mm, pressed by a shock wave in an electrohydrodynamic press under pressure 800 MPa, and then heated to the firing temperature at a rate 1 -4 K/min.Drying at 30 -40°C for 2 -4 h is necessary in order to impart minimal plastic properties to the initial material, making possible the subsequent comminution of large particles without sticking on the working parts of the crushers.The crushing of the product to particle size 0.3 -0.5 mm is necessary in order to create a uniform, finely disperse body uniformly distributed over the entire volume of the article and ensuring the minimal initial porosity when filling the die.It is well-known [3,4] that in order to obtain a strong bond between materials in the solid state a certain degree of activation of the atoms of the surfaces being joined is required. This is attained by intr...

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