THE DEPENDENCIES OF THE DEFECTNESS OF PYROCERAMICS GOODS ON THE CONDITIONS OF THE DIAMOND GRINDING PROCESS

ALEXANDR MIKHAYLOV, LUDMILA KALAFATOVA

Pyroceramics goods, diamond grinding processes, cutting forces, defectness

The efficiency of the processes of mechanical treatment of glass ceramic articles is defined by the maximum productivity when the treated surface quality requirements are met. This material based articles operation characteristics are directly connected with the defects of the units surface layer formed under the treatment. The treated surface defects parameters such as size, form, density, the defects penetration depth were stated to be defined in high degree by the level and force direction to the cut material under the mentioned material grinding. In their turn, the grinding process force characteristics depend on the treatment conditions.
The influence of grinding conditions on the cutting process energy parameters and the articles surface layer defects was investigated and modeled in laboratories and at the plants. To investigate the depth and structure of the material layer broken by treatment the fluorescent dye penetrant testing in combination with the samples layer by layer etching was applied [1].
The cutting force components under the grinding process are known to be dependent on the grinding condition parameters. The intensification of cutting conditions and, first of all, those of depth and feeding were stated to be accompanied by the cutting force increase, especially of its normal component directed into the treated material and defining the defects growth. All this checks the treatment productivity raise at the expense of the grinding conditions intensification.
When the glass material is grinded the level of forces which appear in the zone of contact between the tool and unit is increased when the wheel dulls. It is connected with the change of the areas of contact of grains with the treated surface and redistribution of nominal pressure at these areas. The wheels wear depends on the grinding condition, the tool technology characteristics, and the chosen dressing method. For all treatment methods under discussion which are notable for their graininess and the applied diamonds brand there is a tendency of defects decrease when dressed but not grow dull wheel is used. It is seen most vividly when the wheels with finer graininess and the diamonds with smaller density are used. Thus, the application of wheels with fine graininess (100/80 against 250/200) under the glass ceramic treatment was stated to provide the decrease of size of introduced defects not depending on the tool wear degree practically on all levels of treatment defects occurrence (up to 600 mkm). At the depth of 300 mkm this decrease is 8 times as much. The application of fine grains wheels will decrease two times as much the surface layer volume removed under the article forming. The data which demonstrate that the application of the diamond and abrasive tool with stronger diamond grains (AC20 if compared to AC6) leads to significant increase of the treated surface defects were obtained. At the etching depth equal to 420-500mkm the size increases 12 times as much. The application of progressive wheels dressing methods allows increasing the tool durability to a considerable extent and decreasing the defects level just after the dressing up to 3 times and by the end of the tool durability period -up to 5-7 times as much.
The mentioned data allow to drive to the conclusion that the tool with stronger diamond grains and hard graininess should be preferably applied at the stage of preliminary rough grinding when the treatment labour intensity decrease being a very important factor can be provided at the expense of the operations intensification. Under the operations of fair grinding which finish the article surface layer forming the diamond fine grained wheels in combination with the tool periodic dressing should be applied because of paramount importance of depth and structure of the formed defect layer.
The technology media (TM) with purposeful properties is one of the effective methods of influence on the cutting processes under the glass based material treatment. In this case the TM make considerable dispersion influence besides such functions as cooling, lubrication and washing, which are traditional. This allows to make the cutting processes more intensive and, therefore, to raise the treatment productivity and the tool serviceability at the expense of the material surface layers strength loss achieved because of the media influence. The energy expenses decrease falling at the volume unit of the removed allowance tells favourably on the depth and structure of the layer broken by the treatment.
The TM to treat the glass material is to be related to the treated material as to the physical and chemical structure. That means that it is to be polar, have surface-active properties, easily penetrate into the cutting zone, have lubrication properties, and facilitate both the tool operation and the grinding process. The rational composition of the TM as the water solution of surface-active substances based on the formed requirements was found [2]. The operations of rough and semifair grinding of glass and glass ceramic material is the area of the TM rational application. The developed medium provides developed cracking in the surface volume of the broken layer in combination with the fine defective structure of deeper layers at the expense of increased disperse ability. It also allows to reduce considerably the treatment time at the succeeding technology transitions. The recommended medium application allows the 1.4-3.5 reduction of the size of isolated defects, the reduction of the defective layer depth being 30% as average. It makes it possible to achieve the 30-50% increase of feeding under the grinding process without bringing any harm to the treatment quality and the articles strength.
The obtained results application allowed to develop and implement the technology processes of mechanical treatment of articles made of glass and glass ceramics which are notable by their rational grinding operations, applied TM components and tools with pre-arranged characteristics. The enumerated actions made it possible to achieve the 20-30% raise of treatment productivity when the requirements as to the formed surface quality are met.

Received February 28h, 2000		Donetsk State Technical University, Ukraine
					Mechanical Department