CS199000B1 - Method of graphite core mixture preparation - Google Patents

Description

The present invention relates to a process for preparing a mixture for solid cores, wherein the harder and softer components of the mixture are simultaneously milled, homogenized, kneaded and plasticized.

The prior art methods are known to homogenize and simultaneously grind the graphite mixture in the presence of water as a technologically necessary medium. An example of a classic technological solution is grinding on Czech mills, where grinding is carried out on two millstones, where powdered graphite and other admixtures were processed together with washed clay and content of about 70% water. After grinding, the water from the mixture must be removed on filter presses. Further, technological operations such as maturation, kneading, screening and extrusion into the desired profile follow, the frequency, length and order in which the individual technological operations are performed depends on the type and quality of the final product.

There are also known methods of grinding graphite mixtures on carborundum mills, which are principally identical to the Czech Mills. The difference is higher operating speed of mills and higher density of the mixture, content only about 60% of the water in floated clay. Other subsequent preparation operations are identical.

Further, methods of homogenizing and grinding the mixture carried out in ball or bead mills are known.

199 000

189 000

A disadvantage of these known methods is the need to use a considerable amount of grinding water, which is needed as a transport liquid. The water content of the mixture greatly exceeds the technologically necessary water content for further processing operations. Excess water has to be removed relatively costly for example by sedimentation, grinding and the like. Another disadvantage is the high time required for grinding graphite mixtures, which must be carried out several times.

These drawbacks are overcome by a process for preparing a mixture for solid cores, the principle of which is to dry first homogenize and grind harder and softer components of the mixture to a particle size of less than 10 / t *. whereupon the necessary amount of water is added to the mixture before kneading.

The process of preparing the composition according to the invention achieves a high quality of the entire composition while at the same time perfect homogenization, which makes it possible to produce graphite of very small diameters and it is possible to considerably simplify subsequent technological operations before extruding the composition into desired profiles. The perfect bonding of the microparticles of the processed raw materials is ensured in the dry grinding by preferential bonding of very fine graphite particles in the form of a microlayer, film, to clay particles.

Simultaneous homogenization and grinding of the mixture is made possible by different kinetic energy of different specific weight. The heavier particles, which at the same time have greater hardness in the compositions to be treated, act as a crushing medium in this dynamic process. The mutual contact of the harder particles causes their fragmentation, which results in further enlargement of the active surface. At the contact surfaces of the hard particles, the softer particles are smeared and a physically sorbed film composed of very fine particles of the mixture components is formed on the surface.

The specific properties of the milled graphite-clay mixture make it possible to perform grinding on a variety of devices, both in continuous and discontinuous design.

The forces applied between the layers of the various submicron particles of the homogenised mixture are of such a nature that further processing of the mixture does not destroy them. This preparation of the composition according to the invention for graphite cores creates the prerequisites for better sintering of graphite and clay particles in the final heat treatment, resulting in the higher strength required for graphite cores of small diameters.

The following Examples illustrate the invention.

Example 1

Mixture of 500 parts by weight of graphite, 490 parts by weight. parts of clay, 10 wt. parts of the carbon black are introduced into a turbo mixer and homogenized at 5000 rpm for about 120 s. This results in perfect homogenization and particle size reduction of the individual components in the dry mix.

The homogenized mixture is transferred to a browning plant where it is saturated with the technologically necessary water content for subsequent operations.

199 000

After a period of time necessary for perfect plasticization of the clay, the mixture is rolled on a three-roll friction stand about 10 times.

The final technological operation is to extrude the mixture according to any known method into solid cores which are further dried, fired and prepared.

The composition and method of homogenizing the composition of this example make it possible to prepare solid cores with a diameter of 0.5 mm at the middle gradation stage.

Example 2

Mixture of 350 wt. parts of graphite, 640 wt. parts of clay, 10 wt. parts of the carbon black are mixed in a drum mixer and then continuously milled in a mill at a rotor speed of about 3000 rpm. The fineness of grinding is controlled by the amount of mill functional units used and the feed rate of the feed mixture entering the mill. At this apparatus, very fine grinding of even larger feed particles of the mixture occurs.

The following manufacturing operations are identical to those of Example 1 in b, c, d.

In this example, cores can be prepared at the level of hard gradation grades.

Example 3

Mixture of 600 wt. parts of graphite having a particle size of less than 3 / h; 390 wt. parts of clay, 10 wt. parts of the carbon black is homogenized on a machine in which the grinding intensity is significantly suppressed, and (agitation favored).

Further processing according to b, c, d of Example 1.

In the case of equipment with lower grinding capacity, graphite of defined properties must be used for the preparation of 0,5 mm diameter leads.

The composition of the mixture makes it possible to prepare graphite cores of soft gradation stages.

Claims (1)

SUBJECT OF THE INVENTION Process for preparing a mixture for graphite cores, wherein the harder and softer components of the mixture are simultaneously ground, homogenized, kneaded and plasticized, characterized in that the dry homogenization and grinding of the harder and softer components of the mixture to a particle size of less than 10 µm is carried out first. the necessary amount of water is added to the mixture before kneading.