US2919862A - Process and apparatus for comminuting solid viscous substances, with a liquefied gas as a precooling agent - Google Patents

Description

Jan. 5, 1960 H. BEIKE E'rAL 2,919,852

PROCESS AND APPARATUS FOR COMMINUTING soLID VISCOUS SUBS TANCES, WITH A LIQUEFIED GAS AS A PRECOOLING AGENT Filed Aug. 24, 1954 /6 BY Mig/,n

/6 ATTORNEYS United States Patent() M PROCESS AND APPARATUS FOR COMMINUTING SOLID VISCOUS SUBSTANCES, WITH A LIQUE- FIED GAS AS A PRECOOLING AGENT Hans Beike and Gnther Erberich, Frankfurt am Main,

Germany, assignors to Knapsack-Griesheim Aktiengesellschaft, Knapsack Bezirk Koln, Germany, a company of Germany Application August 24, 1954, serial No. 451,735 Claims priority, application Germany August 31, 1953 4 Claims. (Cl. 241-23) The present invention relates to a process and apparatus for comminuting substances that are solid and viscous at normal or room temperatures.

The term comminuting means herein subdividing to any degree of fineness, especially to the state of powder, whilst the term comminuting device means herein any grinding device, pulverizing device or mill.

The process and apparatus of the invention are suitable for comminuting, for example, thermoplastics, such as polyethylene, polyisobutylene, polyvinylchloride and other polymers; poly-addition products, such as polyurethanes; rubber, caoutchouc, synthetic caoutchouc, bitumen or asphalt. The invention is also applicable to materials comprising substances that are, as such, solid and more or less brittle at normal or room temperatures, for example polyvinyl chloride, but which have been rendered plastic and viscous by the addition of a plasticizer, e.g. tricresylphosphate.

The process of the invention consists in first treating the solid viscous substance or material with a cooling agent until it has become brittle and then comminuting it whilst it is brittle.

Preferably, the embrittlement is effected by maintaining the substance or material for a controlled period of time in intimate contact with the cooling agent.

As cooling agent, there maybe used any liquid or liquefied gas of low boiling point at a'temperature-between about 80 C. and about -200 C. Liquid nitrogen and liquid -air are very suitable. l

The process may be carried out as follows: The material to be comminuted is introduced directly into a bath of a low-boiling liquefied gas having a temperature of between 80 C. and 200 C. The material is kept in the bath long enough to be cooled to the temperature of the bath and thereby converted into a brittle state. The brittle material is conveyed to and operated upon by a comminuting device.

In order to cool the viscous material to low temperatures and to keep it cool until it has entered the comminuting device, it is desirable to prevent, as far as possible, any introduction of vair-which would warm the materialto the material on its way from the liquefied gas bath to the comminuting device as well as in the comminuting device itself. For this purpose, a liquefied gas seal may be provided by suitably arranging and locating the liquefied gas bath and the conveyor casing which is advantageously associated with the bath and which contains'a screw conveyor, or the like, leading to the comminuting device. v

The seal effectively prevents the relatively warm air from penetrating into the comminuting device. In a very simple arrangement, the liquefied gas entirely fills part of the conveyor casing which, for the purpose in question, is upwardly inclined. Y The supply of the liquefied gas may be regulated in dependence upon the level of the liquefied gas bath and thus of the liquefied gas seal.

Patented Jan. 5, 196,0

For this purpose, a valve is advantageously installed in the supply line for the liquefied gas from a tank in whic it is stored.

For pre-cooling as far as possible the material tov be comminuted and for keeping all essential parts of the apparatus cool, it is convenient to use the liquefied gas vapours which are inevitably evolved in the apparatus. For example, part of the vapours which are formed over the liquefied gas bath due to the introduction of the material to be comminuted which has a relatively higher temperature is passed, if desired, by sucking off by means of a fan or the like, through the incoming material to be comminuted aud through the supply vessel containing the said material. Another part of the vapours flows towards the comminuting device. Likewise, the liquefied gas vapors which are evolved in the conveyor casing arranged between the liquefied gas bath and the comminuting device are sucked ofi into the latter thus serving to cool it.

The speed of the conveyor may be regulated so as to ensure a complete cooling of the material in its passage through the bath of liquefied gas and to the comminuting device. lf only partial cooling is required, the desired low temperature can be attained by suitably regulating the time during which the material is in the liquefied gas bath and/or in the area between the liquefied gas bath and the comminuting device. This may be effected by appropriately forming the screw and adjusting its speed. In this manner the material to be comminuted may be cooled uniformly to any desired temperature lying above that of the cooling liquid.

The apparatus for carrying out the process of thel invention may comprise a vchamber or container which contains a cooling agent for cooling the viscous substances, means for introducing the latter into the chamber or container and a conveyor for transporting them therefrom, after they have been converted into `a brittle state by the action of the cooling agent, into a comminuting device.

For example, the apparatus comprises a supply vessel for the viscous material, a supply vessel for the cooling agent and a chamber or container into which the viscous material and the cooling agent .are introduced from their respective supply vessels. The chamber or container is provided in its interior with a conveyor to transport the substances in the manner described aboveinto the comminuting device. It is of advantage to construct the apparatus so that the chamber for the liquefied gas `and the material to be comminuted is mounted before the conveyor casing containing the conveyor screw. Said chamber, being in connection with .the supply vessel for the material to be comminuted, is arranged substantially vertically and at an angle with the conveyor casing. The liquefied gas thus entirely fills part of the conveyor casing whereby a complete liquefied gas seal is obtained. In this manner, the conveyor casing with the conveyor screw and the comminuting device itself are effectively and completely protected from any access of relatively warm air. A quick and thorough cooling and, consequently, a sufi'icient embrittling of the material to be comminuted are thus assured.

An apparatus suitable for use in carrying out the process of this invention is illustrated diagrammatically by way of example in the single figure of the accompanying drawing which is in section.

A supply vessel l1 contains the plastic material' toibe comminuted. The cooling agent, for instance liquid nitrogen, is stored as indicated at 2 in a suitably insulated tank. This insulation and the insulation of other parts of the apparatus is marked 23. The plastic material drops on to a conveyor 3 which takes it into the liquefied'g'as bath 4 in a chamber 5 in to which the cooling' agent is conducted by means` of a tube 6. 1 Chamber ,51 is vv.sucjf ceeded by a conveyor casing 7 containing a screw conveyor 8. Chamber 5 and conveyor casing 7 are at such an angle that the bath of cooling agent forms a liquid seal which completely separates conveyor casing 7 from chamber 5 and effectively protects it from outside access of air which might penetrate into the apparatus from supply vessel 1 through casing 7. 1n order to keep the bath of liquid cooling agent at a constant level, it is of advantage to adjust its supply, dependent on the level of the liquid, by a valve 9 which may be operated by hand.

When the material to be comminuted, which has a relatively higher temperature, enters the liquefied gas bath, lively evaporation sets in. The relatively cold gases evolved thereby are wholly or partially sucked off by a fan 10 installed above the supply vessel 1 and thus serve to precool the material. A further part of the gases may be conducted through a conduit 11 and also a shaft 12 into a comminuting device 13 in order also to keep the latter as cool as possible. The quantity of the gas volume can be adjusted at will in each particular case by shutters 14 and 15.

The suction effect which the comminuting device 13 necessarily has upon the spaces opening into the mill, i.e. conveyor casing 7 and conduit 11, can be adjusted at will by an adjustable valve 19 installed in a conduit 20 behind the comminuting device. In this manner, by throttling the blowing conduit 20, the sucking effect of the comminuting device can be regulated in such a manner that only cool liquefied gas is sucked in; the amount of the latter can be limited without difficulty so that the amount of cool liquefied gas sucked in is substantially equal to the amount of vapours evolved within the apparatus.

The comminuting mill 13 is similar to the type shown in U.S. Patent 2,609,150 to Bludeau which patent is directed to the mechanical pulverization of refrigerated plastics. As seen in Fig. 5 of this patent the paddle wheel mill 52 operates on the principle of a ventilator. Briefly, vaporized refrigerant is drawn from the heat exchanger 56 by and into the mill 52 through passage 59 and is discharged by the mill through line 54 leading from the mill. The operation is apparent from Fig. 5 of the drawing of the above cited patent and the accompanying description.

The screw conveyor 8 in casing 7 is rotated by a gear 16, the pitch and the speed of the screw conveyor being adjusted in such a manner that the material to be comminuted remains suiciently long in the liquefied gas, i.e. until it has assumed the desired low temperature. The now brittle material is dropped through shaft 12 into the comminuting device 13 where it can be comminuted without diiculty to yield a powder. The vapours evolved in conveyor casing 7 are, likewise sucked ofi' through the device 13, thus keeping the latter cool so that also by the comminuting process no heat is evolved in the apparatus that could not be compensated for. Moreover, all parts of the apparatus that, either directly or indirectly, come into contact with the liquefied gas and/or the cooled material to be comminuted are provided with a suiciently strong insulating layer as indicated at 23.

The resulting powdered plastic of normal grain size is fed through a funnel 17 into a collector 1S sealed against external air, whereas--throttle 19 being open-the very fine powder is blown together with the evolved gas through conduit 20 into a filter bag 21 and then collected in a container 22.

The apparatus may be modified in various ways and is not limited to the above example of execution. In particular, the comminuting device and the chambers before and behind it and the conveyors for the material to be comminuted may be arranged and constructed as desited, depending upon the purposes of each individual case, provided that care istaken that by appropriate measures the material is in intimate contact with the cooling agent for a sufficient time and, moreover, that any undesired access of relatively warm external air to the cooled material is prevented as far as possible. The process of the invention may naturally be applied not only to the cold comminuting of thermoplastics but can be used wtih equal success for comminuting other substances whenever the material to be comminuted should be rendered especially brittle by low-cooling, or the access of air to the material should be prevented.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

We claim:

l. Apparatus for comminuting a solid viscous substance comprising a chamber, a supply vessel for a solid viscous substance communicating with said chamber, means for supplying a liquefied gas as a cooling agent to said chamber, said means providing an excess of liquid cooling agent and thereby maintaining a liquid pool in said chamber, means for supplying the substance to a point below the pool level, means for withdrawing cooled substance in a state of embrittlement, said withdrawal means including a conduit connected at one end to said chamber at a point below the level of said pool and leading upwardly therefrom to a point at least above the liquid level of said pool, conveyor means within said conduit for withdrawing cooled substance from said chamber and conveying it upwardly through said conduit, a comminuting device associated with the other end of said conduit for receiving upwardly conveyed substance in a state of embrittlement and comminuting the same, a second conduit establishing vapor communication between said chamber at a level above the liquid pool level and said point above the liquid level of said pool at which the aforesaid conduit terminates adjacent the comminuting means whereby vapors of the cooling agent evolved in the chamber flow to said comminuting device, and means positioned beyond the comminuting means for regulating the ow of vapor from said chamber through the comminuting means.

2. Apparatus according to claim l wherein means are supported by the supply vessel for withdrawing vaporized cooling agent directly into said substance supply vessel from said chamber for precooling the solid viscous substance supply.

3. The process for comminuting a solid viscous substance comprising the steps of supplying liquefied gas as a cooling agent to a closed cooling zone while maintaining a liquid pool of said cooling agent in said zone, supplying below the pool level a solid viscous substance from a supply zone, cooling the supplied solid viscous substance to a temperature at least as low as that required for maintaining the substance in a state of ernbrittlement, withdrawing embrittled substance from said zone at a point below the level of said pool by conveying the same upwardly to a point at least above the liquid level of said pool while maintaining said withdrawn substance in said state of embrittlement, comminuting said upwardly-conveyed substance while at said temperature, withdrawing vaporized cooling substance from said cooling zone, and cooling said solid viscous substance during comminuting with said withdrawn vaporized cooling substance, and regulating from a point beyond and spaced apart from the comminuting point the amount of said vaporized cooling substance used to cool the solid viscous substance during the comminuting step.

4. The process of claim 3 wherein vaporized cooling agent is withdrawn directly from said cooling zone and passed directly therefrom into said supply zone for the viscous substance to precool said viscous substance.

(References on follog page) References Cited in the file of this patent UNITED STATES PATENTS Gerner Mar. 30, 1880 Algert Apr. 2, 1907 Novotny July 22, 1930 Atwell Jan. 23, 1934 Hurt Oct. 23, 1934 Runyon Aug. 27,1935 Miller July 2, 1940 Cuno Apr. 25, 1944 Arnold May 14, 1946 6 Hill Aug. 17, 1948 Bludeau May 8, 1951 Hendry et al. Jan. 29, 1952 Bludeau Sept. 2, 1952 FOREIGN PATENTS Germany Aug. 7, 1939 OTHER REFERENCES only one pass, by Gerard Miller.

Food Engineerm' s,

July 1951, pages 36 and 37.

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