EP1339497B1 - Device and method for producing fine material from chemically active milled stock - Google Patents

Abstract

According to known milling and sighting methods, the stock is comminuted in an inert atmosphere in order to prevent moisture from entering the material and to avoid coagulation resulting therefrom. These methods can however not prevent an impairment of the flowablity and thus the sieving properties after milling by chemical reactions taking place in the milled stock. The inventive method is characterized in that the milled stock is cooled after milling and before classification in order to reduce the speed at which the chemical reactions take place and to maintain the flowability of the milled stock until classification. The device and the method according to the invention are especially useful for comminuting partially vulcanized elastomers.

Description

The invention relates to a device and a method for producing fines from chemically active millbase.

According to the state of the art, during grinding, grinding material to be comminuted, in particular plastic, is embrittled by cooling with a coolant and fed to a mill for comminution. The comminuted material leaves the mill in a cold state, is collected and stored, with an adjustment of the temperature of the ground material to the ambient temperature. During this storage, electrostatics formed on the regrind may degrade. In order to improve the subsequent screening of the ground material, a release agent is added in many cases. This is mixed in with the millbase. When sifting the oversize is separated from the fines and can be fed to the grinding process again. While the temperature of the ground material adapts to the ambient temperature during intermediate storage, water from the ambient air condenses on the particles of the ground material. As a result, the visibility and screening ability of the ground material is very limited. On interim drying and adding release agents can therefore not be waived for screening and screening in the previous cold milling. The associated work steps are time-consuming and costly.

Thus, the production of fines must be interrupted for the duration of the intermediate storage and there are costs for the use of release agent and the associated work.

The DE-PS 38 33 830 C2 describes a device for the production of extremely fine dusts with particle sizes up to less than 10 micrometers, in which a classifier is integrated. The EP 0 044 507 A1 teaches a method in which labels of plastic parts are separated by sifting. In the EP 0 317 935 B1 a device is shown in which the exiting a mill cold gas is released by a cyclone of particles. In the DE-OS 23 18 549 the comminuted by comminuted grinding material is classified by a sieve.

In the DE 195 33 078 describes a method for grinding and sifting regrind, in which the material to be ground is held and fed to the sifter during and after comminution in a mill in an inert atmosphere, with removal of ambient air and the associated moisture. Milling and sifting thus takes place in a closed process that prevents the entry of atmospheric oxygen. A disadvantage of this previously known method, however, is that it is not or only insufficiently suitable for chemically active millbase, since its sieving capacity is reduced during transport from the mill to the classifier even under inert gas conditions. For example, partially vulcanized elastomers stick together very rapidly after the cold grinding, as a result of which the flowability and thus the ability to screen are very severely impaired. The addition of a release agent provides only a slight improvement.

The object of the present invention is therefore to specify a device or a method which improves the production of fines in the case of chemically active starting materials, in particular in partially vulcanized elastomers.

This object is achieved by a device according to claim 1.

In the device according to the invention, the ground material to be ground is kept at a low temperature by means of the device for cooling, whereby the reactivity is reduced. The flowability of the ground material thus remains at least substantially preserved until reaching the classification arrangement and classification is readily possible.

The classifying device comprises a sieve, which - in contrast to the classifiers often used for classifying - can also be used at low temperatures, and at the same time achieves a high selectivity. A particularly reliable and convenient sieve is a tumble screen.

The ground product cooler includes a coolant supply line fluidly connected to a source of liquid or gaseous refrigerant. Such a coolant, such as liquefied petroleum gas, can easily be added to the millbase and separated after completion of the grinding and classification process. The source may be a tank, a compressed gas cylinder or a supply network. The choice of a suitable coolant depends on the respective regrind. Thus, the reactivity of partially vulcanized elastomers is reduced at temperatures below-100 ° C. to -120 ° C. in such a way that the flowability after grinding is substantially maintained. For such a grinding and classification process, liquid or cold gaseous nitrogen is suitable, which is fed to the material to be ground after passing through the mill. Of course, when choosing the coolant, care must also be taken to ensure that no chemical reaction between the millbase and the coolant is triggered unless it is intended.

When using a sieve in the classification arrangement, it is advantageous to fluidly connect the coolant supply line to at least one spray nozzle, by means of which liquid or gaseous coolant can be dispensed onto a sieve surface intended to receive the ground millbase from the mill. As a result, the ground material is cooled immediately before or during the classification process.

Appropriately, in addition to the aforementioned cooling of the screen surface, a flow connection between the coolant supply and a mill bunker of the mill, in which the material to be ground is taken after the grinding process. In this arrangement, the heat that has taken up the ground material during the grinding process, absorbed by the coolant very quickly.

In an advantageous development, the cooling device for cooling the grinding material to be supplied to the mill with the same source of liquid or gaseous coolant flow connected, as the cooling device for cooling the already ground Guts. This makes it possible to supply coolant from one source during the entire production of fines.

In a preferred embodiment of the invention, the mill and the classification arrangement is integrated in a pressure-tight Zei-kleinerungseinheit. The production of fines can thus take place in an inert atmosphere separated from the outside atmosphere and under overpressure, whereby the entry of outside air is reliably prevented.

The object of the invention is also achieved by a method having the features of patent claim 6.

In the method according to the invention, therefore, the millbase is cooled after grinding and before classifying to reduce the chemical reactivity of the millbase and thus reliably prevent "clumping" of the millbase after the grinding process.

Advantageously, the cooling takes place before and after the comminution of the ground material in the mill by the addition of a liquid or gaseous coolant.

The coolant used can be used in an advantageous development of the method according to the invention to generate an inert atmosphere within the mill and / or within the classification arrangement. Such a configuration, which is also in the DE 196 35 778 A1 , which is incorporated herein by reference, serves, in particular, to inhibit the entry of moisture from the ambient air. As a coolant, for example, liquid nitrogen is used, which evaporates during the cooling process and produces an inert atmosphere in this way.

Advantageously, the inert atmosphere in the mill and / or the classification arrangement is kept under a certain overpressure in order to reliably prevent the entry of ambient air even in the presence of any leaks.

In order to make the process according to the invention particularly economical, the oversize removed during the classification becomes immediately after the classification fed again to the mill. The usually still cold oversize contributes to the cooling of the grinding stock to be ground and thus reduces the consumption of refrigerant.

As in many cases, particularly advantageous and inexpensive coolant is nitrogen, which is supplied to the millbase in liquid or cold gaseous state. However, other refrigerants can be used with comparable properties.

The method according to the invention and the device according to the invention are suitable for the comminution of substances which have a temperature-dependent chemical reactivity or whose chemical or physical parameters which are decisive for a comminution process are temperature-dependent. A preferred use of the device according to the invention or of the method according to the invention is the comminution of partially vulcanized elastomers.

Reference to the drawing, an embodiment of the invention will be explained in more detail below.

The drawing shows a schematic view of an inventive device for producing fines.

In the apparatus 1 shown in the drawing, the feed material is fed via a hopper on a screw conveyor 2, the output side of a metal separator 3, a rotary valve 4 and a cooling screw 5, which is charged by an injection 6 with liquid coolant, connects. The outlet of the cooling screw 5 is fluidly connected to an impact mill 8, which in turn is fluidly connected to a hopper 10. In the funnel 10 also opens a supply 7 for coolant. The hopper 10 is followed by a rotary valve 11, from which a connection 12 leads to a tumbler 14. Ideally, the tumble screen 14 is located directly in front of the outlet opening of the rotary valve 11. In the tumble screen, a supply line 13 for coolant, with a plurality of spray nozzles, not shown here, opens on a serving for receiving the ground grinding material Sieve surface of the tumbler 14 are directed. The supply line 13, as well as the supply 7 and the injection 6, with a source not shown here for coolant, such as a tank or a supply network, fluidly connected.

From the tumble screen 14 branches off a line 15 with a rotary valve 16, which serves for the return of oversize. Another line 17 serves to discharge the fine material and opens into a filter 18, which is equipped on the output side with a rotary valve 19. At the funnel 10, a line 21 is connected to a filter 22. The line 21 leads gaseous coolant to the input side 25 of the mill 8 back. From the line 21 branches off an exhaust pipe 23, which is equipped with a valve 24.

During operation of the device 1, the feed material is fed via the hopper 1 to the screw conveyor 2, which introduces the feed material via the metal separator 3 in the rotary valve 4, which feeds the feed material of the cooling screw 5. The liquid coolant, in this case liquid nitrogen, is introduced into the cooling screw 5 via the injection 6. As a result, the feedstock is cooled and embrittled. The feed material pretreated in this way is fed to the mill 8, which comminutes the feed material. The millbase comminuted in this way in the gas stream of the evaporated liquid nitrogen is fed to the hopper 10 and the rotary valve 11. By means of the feed 7, the comminuted material to be ground in the funnel 10 is subjected to a flow of cold liquid or gaseous coolant, for example nitrogen. The cooled ground material is conveyed via the connection 12 to the tumble screen 14, where it is again acted upon by the flow from the supply line 13 with the spray nozzles with coolant. In this way, the material to be ground is kept at a low temperature throughout the comminution process. In the comminution of partially vulcanized elastomers, liquid nitrogen is used as the coolant, by means of which the temperature of the millbase in the mill 8 and in the tumble screen 14 is maintained at a value of minus 10 ° C to minus 80 ° C.

The device is pressure-sealed along the path from the mill 8, the funnel 10, the rotary valve 11 and the connection 12 with respect to the environment. An overpressure, which is produced either by adding an inert gas or - when using a liquefied gas, such as liquid nitrogen, as a coolant - by evaporation of the coolant, thereby preventing the entry of ambient air and the associated moisture in the mill 8 or the tumble screen 14th ,

The material to be ground falls out of the mill 8 via the hopper 10 and the rotary valve 11 in the tumble screen 14 when the sieve is structurally located below the mill. However, it is also conceivable to use instead of such a gas stream as a blowing agent for the promotion of the comminuted material to be ground and other device elements such as another screw conveyor. The comminuted millbase gets in the cold gas stream of the coolant via the line 13 in the tumble screen 14, in which the oversize is separated from the fines. The oversize passes back via the line 15 and the rotary valve 16 in the screw conveyor 2. The fine material is conveyed via the line 17 into a filter 18, in which it is separated from the cold gas stream and discharged via the rotary valve 19. By the filter 22 in the line 21 accumulating particles are separated. The gas stream exiting the filter, which has a low temperature, can be recirculated via the continuation of the line 21 to the inlet side 25 of the mill 8 in order to reduce the total consumption of liquid nitrogen as a coolant.

Alternatively, excess cold gas can be discharged via the exhaust pipe 23 to the environment. For this purpose, the exhaust pipe is provided with the valve 24, which may also be a pressure relief valve.

With the device 1, it is possible to easily and inexpensively produce and classify fines even with chemically active substances. The process also takes place in a closed process, on-line, while keeping out ambient air and the associated humidity, without further intermediate steps such as tempering, drying and addition of release agents. Ideally, the process is operated with liquid nitrogen that evaporates in the process, however is also the use of other coolants with similar properties conceivable.

The inventive method is not limited to the application of impact mills, but other mills such. B. granulators are used. The feed can be comminuted with the method and apparatus substantially to less than 150 microns particle size in major proportions.

With the method according to the invention and the device according to the invention, the chemical reactivity of the ground material is reduced during the entire process and, moreover, the ingress of atmospheric moisture is prevented. As a result, the product quality is improved and significantly influenced the subsequent separation stages, a release agent is not required. In the case of using liquid nitrogen as a coolant while both processes, the grinding and classifying are carried out under inert gas simultaneously. Thus, the risk of explosion is limited especially in oxygen-sensitive regrind. The previously required steps mixing, release agent addition and intermediate storage can be omitted; this is associated with a significant reduction in personnel, operating and investment costs. The oversize grain returned to the grinding plant has already cooled down during the process, which can reduce the consumption of coolant. The method can be carried out with particular advantage in on-line operation.

LIST OF REFERENCE NUMBERS

1.

contraption

Second

Auger

Third

Metal separators

4th

rotary

5th

cooling screw

6th

injection

7th

feed

8th.

Mill

9th

-

10th

funnel

11th

rotary

12th

connection

13th

feed

14th

tumble screen

15th

management

16th

rotary

17th

management

18th

filter

19th

rotary

20th

-

21st

management

22nd

filter

23rd

exhaust pipe

24th

Valve

25th

input side

Claims (12)

1. Device for producing fine material from chemically active milled stock, in particular for producing fine material from partially vulcanized elastomers, with a mill (8) for comminuting the milled stock, a cooling device (5) for cooling the milled stock to be fed to the mill (8) and a classifying arrangement (14) for classifying the milled stock that has been milled, wherein a cooling device for the milled stock that has been milled is arranged downstream of the mill (8) and the classifying arrangement comprises a screen, wherein the cooling device for the milled stock that has been milled comprises a coolant feed (7, 13), which is flow-connected to a source for a liquid or gaseous coolant, and the coolant feed (13) is flow-connected to a spray nozzle, by means of which liquid or gaseous coolant can be delivered onto a screening surface of the screen (14) intended for receiving from the mill (8) the milled stock that has been milled.
2. Device according to Claim 1, in which the screen is a tumble screen (14).
3. Device according to either of Claims 1 and 2, characterized in that the coolant feed (7) is flow-connected to a mill bunker (10) of the mill (8), receiving the milled stock after the milling operation.
4. Device according to one of Claims 1 to 3, characterized in that the cooling device (5) for cooling the milled stock to be fed to the mill (8) is flow-connected to the source for a liquid or gaseous coolant.
5. Device according to one of the preceding claims, characterized in that the mill (8) and the classifying arrangement (14) are integrated in a pressure-sealed comminuting unit.
6. Method for producing fine material from chemically active milled stock, in particular for producing fine material from partially vulcanized elastomers, in which milled stock is made brittle by a coolant, comminuted in a mill (8) and subsequently classified by means of a tumble screen (14), characterized in that, after comminution in the mill (8) but before classification in the tumble screen (14), the milled stock is cooled by coolant being applied to the tumble screen (14) through spray nozzles.
7. Method according to Claim 6, characterized in that the cooling before and after the comminution of the milled stock in the mill (8) takes place by adding a liquid or gaseous coolant to the milled stock.
8. Method according to Claim 7, characterized in that the added coolant is used to produce an inert atmosphere inside the mill (8) and/or inside the tumble screen (14).
9. Method according to Claim 8, characterized in that the inert atmosphere in the mill (8) and/or in the tumble screen (14) is maintained at an overpressure with respect to an outside atmosphere during the milling operation.
10. Method according to one of Claims 6 to 9, characterized in that the oversize segregated in the classifying arrangement (14) is re-fed to the mill (8), preferably in the cold state.
11. Method according to one of Claims 6 to 10, characterized in that liquid or cold gaseous nitrogen is used as the coolant.
12. Use of a device according to one of Claims 1 to 5 or of a method according to one of Claims 6 to 11 for comminuting substances with temperature-dependent reactivity, for example partially vulcanized elastomers.

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