DE1241045B - Process for preparing a granulate made from coal tar pitch or petroleum bitumen which can be used as an additive in refractory masses - Google Patents

Description

Process for preparing an additive, in refractory masses Usable granules of coal tar pitch or petroleum bitumen The invention relates a process for processing granules from coal tar pitch or petroleum bitumen by grinding, the granules as an additive in refractory masses, in particular Molding materials and molding sands for foundries.

Peat pitch, wood pitch, coal tar pitch or petroleum bitumen the refractory masses, in particular molding materials and molding sands for foundries, added to improve the properties of the refractory materials. Molding sands with an addition of coal tar pitch or petroleum bitumen produce a better Surface of the castings poured into the molding sands, reduce the occurrence of grooves, rat tails or the like molding sand-related casting defects and reduce thus the risk of rejects. Coal tar pitch and oil bitumen also contribute Increase in strength of the molding sand.

Coal tar pitch or petroleum bitumen, which are finely granulated or grain size of the refractory materials, especially foundry molding sands, added tend during their grinding, the subsequent transport and also during the Storage to form lumps, this tendency depending on the grain size, the temperature and pressure of a bearing column that acts on the individual grains. Eventually, the pitch will be electrically charged if this one Is exposed to friction. This can happen during grinding, but also during transport in foundries, provided this is done with the aid of compressed air in pipelines.

For the production of bitumen-containing core binders for foundry purposes by transferring mixtures of bituminous substances and powdery fillers in fine distribution has already been proposed that molten bitumen and Fillers are mixed with one another in the usual mixing ratios, whereupon the mass in mills, air separators, sieve separators and similar devices is brought into fine distribution. It is also used to produce a molding compound known that a natural or artificial molding material such. B. Ouarzsand, metal powder or metal shavings, in a grain size, texture and size suitable for molding purposes Goodness with a melting binder, with the advantage of hard coal, tar pitch as well With bitumen, synthetic and natural resins o. The like., Is processed by heat, so that in a hot pulp of sand the grains of sand with a thin skin of the melted Binder are coated. The hot pulp is left in this condition to cool off. This then forms a hard, cemented mass, which on suitable Devices, e.g. B. by rubbing or pressing, on the original sand mold again is crushed and sieved.

The previous properties of a pure coal tar pitch or Petroleum bitumen, with a pure coal tar pitch or petroleum bitumen also the usual impurities present are understood with, lead to the fact that Coal tar pitches or petroleum bitumen in the refractory industry, in particular as an additive to molding sands, do not find the application which, according to them, their good Properties after addition to molding materials, in particular molding sands, is due. The present invention describes measures for the preparation of a granulate from coal tar pitch or petroleum bitumen to improve grinding, transportation and also to simplify storage, while also taking into account the properties of the Pitch in the molding sand or similar refractory building material can be improved.

According to the invention in a method for processing a as an additive in refractory materials, especially molding sands and molding materials for foundries, usable granulate from coal tar pitch or petroleum bitumen proposed by the invention by milling that the pitch before or during milling a liquid or an inorganic substance dissolved in a liquid, in particular a clay dissolved in water, is added and the grinding is carried out in a stream of air.

The pitch, which is present in lumps, thus becomes an inorganic one before grinding liquid substance or liquid solute added, with the grinding and thus crushing the pitch with the surface of the obtained granules inorganic Fabric is surrounded. By dissolving the inorganic substance in an excess of liquid, especially water, it is achieved that in connection with the constant, air flow present during grinding and the heating occurring during grinding, or Heating the liquid, especially water, evaporates. As a result, they are stored the inorganic substances on the surfaces of the granules in solid form, and the Evaporation of the water results in cooling during the grinding process, so that excessive Heating, which could lead to caking of the pitch, is avoided. Caking of the granules consisting of pitch is further prevented by the protective cover made of inorganic substances surrounding the individual granules or a uniform inorganic substance.

A clay mineral is particularly advantageous as an inorganic substance used, a clay from the clay mineral groups kaolinite, micaceous clay minerals or illite or from montmorillonite can be selected. Within the tone group Montmorillonite, a bentonite is proposed, and preferably an activated one Bentonite, in which the calcium ions are replaced by sodium ions. To the deposit to lighten the clay mineral flakes on the surfaces of the small pitch grains, it is also proposed that the mineral bentonite, especially an activated one Bentonite, dissolved in a relaxed or alkaline water and then before or is added to the pitch during milling. This will result in a lower viscosity achieved as if only ordinary water mixed with the same amount of clay would. The relaxed or alkaline water also has the advantage that the clay, which is present in aggregates of individual leaflets, and to the envelope If the granules of pitch are to be broken down into individual leaves, this becomes easier splits into the individual leaflets. It should be noted that other tones, for example the clay mineral groups kaolinite or illite, the relaxed or alkaline water can be added.

The tone to be added to the pitch can be a natural tone, which is sufficient Amount of water is dissolved. However, it can also be a dried and ground clay added to the water and in sufficient time prior to addition to the pitch swell or muddy in the water.

According to a further feature of the invention, grinding is advantageously carried out in a mill with a vertical, rapidly rotating and radially protruding one Blades or rods provided with shaft, the material being the bottom part of the mill added and also by the air flow introduced into the bottom area of the mills conveyed up in the mill and then through an air classifier or cyclone is collected. In the direction of the work flow behind the cyclone there is then a dust filter arranged to extract and clean the conveying air.

The inventive addition of a liquid or dissolved in liquid inorganic material before or during the grinding of coal tar pitch and petroleum bitumen prevents an electrical from occurring by encasing the individual grains of pitch obtained Charging of the material to be ground, which would occur with dry grinding or friction. The thickness of the layer of inorganic material surrounding the pitch grains, especially a clay, can be adjusted by the amount of clay dissolved in water and adding this mixture or solution to the pitch. You can also use the setting the amount of water or the degree of dilution and by regulating the amount to be enforced Amount of air can be achieved that the envelope made of the inorganic substance, in particular Clay, after the grinding process is dry or a certain adjustable humidity having.

If the casing has a certain amount of moisture, the grist can Can be transported dust-free and also packed, for example in sacks. but even if the casing is dry, it prevents clumping later of the pitch granules in storage before consumption. It should be noted that Additives for molding sands are often stored in silos that are outdoors and are exposed to solar radiation. The inventive encasing of the However, small pitch grains can be stored regardless of external temperature influences.

A pitch granulate according to the invention is also advantageous in the Use in molding sands, because drying out of the sand is delayed as the Pitch grains are better wettable and other binders added to the molding sand, especially bentonite, easily adhere to the coating of the pitch grains, so that in addition the strength of the molding sand is increased.

Claims (4)

Claims: 1. A method for preparing an additive in refractory masses, in particular molding materials and molding sands for foundries, usable Granules from coal tar pitch or petroleum bitumen by grinding, d u r c h characterized in that the pitch before or during grinding a liquid or in dissolved inorganic substance is added to a liquid and the grinding in takes place in an air stream. 2. The method according to claim 1, characterized in that the pitch to be ground a clay, preferably of the clay group montmorillonite and in particular Bentonite, dissolved in a relaxed or basic water, is added. 3. Process according to claims 1 and 2, characterized in that the grinding in a mill with a vertical, rapidly rotating and radially protruding one Wings or rods provided wave takes place, whereby the pitch together with the liquid inorganic matter is added to the bottom part of the mill and through that in the bottom area the air flow introduced into the mill is conveyed upwards. 4. A method for preparing a molding sand for foundries, characterized in that a granulate prepared according to claims 1 to 3 is added to the molding sand, the individual granulates being surrounded by a shell made of an inorganic substance, in particular bentonite. Documents considered: German Patent No. 535 561; German interpretative document No. 1056 791; K umanin: "Core binder materials", 1953, pp. 122 to 141.