WO2002043868A1

WO2002043868A1 - Device and method for producing fine material from chemically active milled stock

Info

Publication number: WO2002043868A1
Application number: PCT/EP2001/013799
Authority: WO
Inventors: Reinhard Krieg; Oliver Dietrich
Original assignee: Messer Griesheim Gmbh
Priority date: 2000-11-30
Filing date: 2001-11-27
Publication date: 2002-06-06
Also published as: EP1339497B1; DE10059442A1; ATE428503T1; EP1339497A1; DE50114844D1

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

Device and method for producing fine material from chemically active regrind

The invention relates to a device and a method for producing fine material from chemically active regrind.

According to the prior art, in the case of cold grinding, regrind, in particular plastic, is embrittled by cooling with a coolant and fed to a mill for comminution. The crushed ground material leaves the mill in a cold state, is collected and temporarily stored, whereby the temperature of the ground material is adapted to the ambient temperature. Electrostatics formed on the regrind can degrade during this storage. In order to improve the subsequent screening of the ground material, a release agent is added in many cases. This is mixed into the regrind. When sifting, the oversize is separated from the fine material and can be fed back into the grinding process. While the temperature of the ground material adapts to the ambient temperature during the intermediate storage, water from the ambient air condenses on the particles of the ground material. As a result, the visibility and sieving capacity of the ground material is very limited. In the meantime, drying and the addition of separating agents cannot be avoided for screening and sieving in the previous cold grinding. The associated work steps are time-consuming and costly.

For example, the production of fine goods has to be interrupted for the duration of the intermediate storage and there are costs for the use of release agents and the associated workload.

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. EP 0 044 507 A1 teaches a method in which labels are separated from plastic parts by sifting. EP 0 317 935 B1 shows a device in which the cold gas emerging from a mill is freed of particles by a cyclone. In DE-OS 23 18 549, the ground material crushed by cold grinding is classified by a sieving device. DE 195 33 078 describes a method for grinding and classifying ground material, in which the ground material is kept in an inert atmosphere while and after comminution in a mill, with the ambient air and the associated moisture being kept away, and fed to the classifier , Milling and sifting therefore take 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 regrind, 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 quickly after cold grinding, which greatly impairs the flowability and thus the sieving capacity. The addition of a release agent creates only a slight improvement here.

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

This object is achieved in a device according to the preamble of patent claim 1 in that the mill is followed by a cooling device for the ground regrind.

In the device according to the invention, the ground material is kept at a low temperature by means of the device for cooling, as a result of which the reactivity is reduced. The flowability of the ground material is thus at least essentially retained until the classification arrangement is reached, and classification is readily possible.

The classifying device preferably comprises a sieve which, in contrast to the classifiers frequently used for classifying, can also be used at low temperatures and which at the same time achieves a high degree of selectivity. A particularly reliable and functional sieve is a wobble sieve. Advantageously, the cooling device for the ground material comprises a coolant feed line, which is connected in terms of flow to a source for a liquid or gaseous coolant. Such a coolant, such as liquid gas, can be mixed into the regrind without any problems and can be separated from it after the grinding and classification process has been completed. A tank, a compressed gas bottle or a supply network can serve as the source. The choice of a suitable coolant depends on the respective regrind. The reactivity of partially vulcanized elastomers is reduced at temperatures from below minus 100 ° C to minus 120 ° C in such a way that the free-flowing properties are essentially retained after grinding. For such a grinding and classification process, liquid or cold gaseous nitrogen is suitable, which is added to the regrind after passing through the mill. When choosing the coolant, it is of course also important to ensure that no chemical reaction between the ground material and the coolant is triggered, unless it is intended.

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

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

In an advantageous further development, the cooling device for cooling the ground material to be fed to the mill is connected to the flow with the same source of liquid or gaseous coolant as the cooling device for cooling the already ground material. This enables the coolant to be supplied from one source throughout the entire fine material production process. In a preferred development of the invention, the mill and the classification arrangement are integrated in a pressure-tight shredding unit. The fines can thus be produced in an inert atmosphere separated from the outside atmosphere and under excess pressure, which reliably prevents the entry of outside air.

The object of the invention is also achieved by a method having the features of patent claim 8.

In the method according to the invention, the regrind is thus cooled after grinding and before classification in order to reduce the chemical reactivity of the regrind and thus reliably prevent the regrind from “clumping” after the grinding process.

The cooling advantageously takes place before and / or after the grinding of the ground material in the mill by adding a liquid or gaseous coolant.

In an advantageous development of the method according to the invention, the coolant used can be used to generate an inert atmosphere within the mill and / or within the classification arrangement. Such an embodiment, which can also be found in DE 196 35 778 A1, to which express reference is made here, serves in particular to prevent the entry of moisture from the ambient air. Liquid nitrogen, for example, is used as the coolant, which evaporates during the cooling process and in this way creates an inert atmosphere.

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

In order to make the method according to the invention particularly economical, the oversize separated during the classification is used immediately after the classification fed to the mill again. The oversize, which is usually still cold, contributes to the cooling of the ground material to be ground and thus reduces the refrigerant consumption.

Nitrogen, which is supplied to the regrind in liquid or cold gaseous state, is a particularly advantageous and inexpensive coolant in many cases. However, other coolants with comparable properties can also be used.

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

An exemplary embodiment of the invention will be explained in more detail below with the aid of the drawing.

The drawing shows a schematic view of a device according to the invention for producing fine goods.

In the device 1 shown in the drawing, the feed material is fed via a funnel to a screw conveyor 2, which is followed on the output side by a metal separator 3, a cellular wheel sluice 4 and a cooling screw 5, which is fed with liquid coolant through an injection 6. The outlet of the cooling screw 5 is fluidly connected to an impact mill 8, which in turn is fluidly connected to a funnel 10. A feed 7 for coolant also opens into the funnel 10. A cellular wheel sluice 11 connects to the funnel 10, from which a connection 12 leads to a wobble screen 14. Ideally, the wobble screen 14 is located directly in front of the outlet opening of the cellular wheel sluice 11. A feed line 13 for coolant opens into the wobble screen, with a plurality of spray nozzles, not shown here, which act on a nozzle for receiving the ground material. Nende sieving surface of the wobble screen 14 are directed. The feed line 13, like the feed 7 and the injection 6, is flow-connected to a source for coolant, not shown here, such as a tank or a supply network.

A line 15 branches off from the tumbler screen 14 with a cellular wheel sluice 16, which is used to return oversize particles. Another line 17 is used to discharge the fine material and opens into a filter 18, which is equipped on the output side with a rotary valve 19. A line 21 with a filter 22 is connected to the funnel 10. The line 21 leads gaseous coolant back to the inlet side 25 of the mill 8. A waste line 23 branches off from line 21 and is equipped with a valve 24.

During operation of the device 1, the feed material is fed via the hopper 1 onto the screw conveyor 2, which feeds the feed material via the metal separator 3 into the cellular wheel sluice 4, which feeds the feed material to 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 feed material is cooled and embrittled. The feed material pretreated in this way is fed to the mill 8, which comminutes the feed material. The ground material that has been comminuted in the gas stream of the vaporized liquid nitrogen is fed to the hopper 10 and the rotary valve 11. A supply of cold liquid or gaseous coolant, such as nitrogen, is applied to the comminuted ground material in the hopper 10 by means of the feed 7. The cooled regrind is conveyed via the connection 12 to the swash screen 14, where it is again acted upon with coolant from the spray nozzles which are connected to the supply line 13. In this way, the regrind is kept at a low temperature throughout the shredding process. In the comminution of partially vulcanized elastomers, liquid nitrogen is used as a coolant, by means of which the temperature of the millbase in the mill 8 and in the tumbler screen 14 is kept at a value of minus 10 ° C. to minus 80 ° C. The device is sealed pressure-tight to the environment along the path from the mill 8, the funnel 10, the rotary valve 11 and the connection 12. An overpressure, which is produced either by adding an inert gas or - when using a liquid gas, such as liquid nitrogen, as a coolant - by evaporating the coolant, prevents the entry of ambient air and the associated moisture into the mill 8 or that Tumbler screen 14.

The regrind falls out of the mill 8 via the funnel 10 and the rotary valve 11 into the tumbler sieve 14 when the sieve is structurally arranged under the mill. However, it is also conceivable to use other device elements such as, for example, a further screw conveyor instead of such a gas stream as a blowing agent for conveying the ground material. The comminuted ground material arrives in the cold gas stream of the coolant via line 13 into the tumbler sieve 14, in which the oversize particles are separated from the fine material. The oversize particles return to the screw conveyor 2 via the line 15 and the rotary valve 16. The fine material is conveyed via line 17 into a filter 18, in which it is separated from the cold gas flow and discharged via the rotary valve 19. Particles are separated by the filter 22 in the line 21. The gas stream emerging from the filter, which has a low temperature, can be recirculated in the circuit 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 released to the environment via the exhaust line 23. For this purpose, the exhaust pipe is provided with the valve 24, which can also be a pressure relief valve.

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

The inventive method is not limited to the use of impact mills, rather other mills such as. B. Cutting mills can be used. The feed material can be comminuted with the method and the device essentially to a particle size of less than 150 micrometers in the main proportions.

With the method 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. This improves the product quality and has a significant positive impact on the subsequent separation stages; the addition of a release agent is not necessary. If liquid nitrogen is used as the coolant, both processes, grinding and classifying, are carried out simultaneously under inert gas. This reduces the risk of explosion, particularly in the case of regrind that is sensitive to oxygen. The previously required steps of mixing, adding release agent and intermediate storage can be dispensed with; associated with this is a significant reduction in personnel, operating and investment costs. The oversize particles returned to the grinding system have already cooled down during the process, which means that the consumption of coolant can be reduced. The method can be carried out with particular advantage in online operation.

LIST OF REFERENCES

1. Device

2. Screw conveyor

3. Metal separator

4. Cell wheel lock

5. Cooling screw

6. Injection

7. Feeding

8. Mill

9.-

10. Funnel

11. Cell wheel lock

12. Connection

13. Feed line

14. Swashplate

15. Management

16. Cell wheel lock

17. Management

18. Filter

19. Cell wheel lock

20.-

21. Management

22. Filters

23. Exhaust pipe

24.Valve

25. Entry page

Claims

claims

1. Device for the production of fines from chemically active regrind, in particular for the production of fines from partially vulcanized elastomers, with a mill (8) for comminuting the regrind, a cooling device (5) for

Cooling the ground material to be fed to the mill (8) and a classification arrangement (14) for classifying the ground ground material, characterized in that the mill (8) is followed by a cooling device for the ground ground material.

2. Device according to claim 1, characterized in that the classification arrangement comprises a sieve, in particular a wobble sieve (14).

3. Device according to claim 1 or 2, characterized in that the cooling device for the ground regrind comprises a coolant supply (7, 13) which is connected to a source of a liquid or gaseous coolant flow.

4. Apparatus according to claim 2 and 3, characterized in that the coolant supply (13) is fluidly connected to a spray nozzle, by means of the liquid or gaseous coolant on a sieve surface of the sieve (14) intended for receiving the ground material from the mill (8). is spreadable.

5. Device according to one of claims 3 or 4, characterized in that the coolant supply (7) is flow-connected to a mill bunker (10) of the mill (8) receiving the millbase after the milling process.

6. Device according to one of claims 3 to 5, characterized in that the cooling device (5) for cooling the material to be fed to the mill (8) to be ground is flow-connected to the source for a liquid or gaseous coolant.

7. Device according to one of the preceding claims, characterized in that the mill (8) and the classification arrangement (14) are integrated in a crushing unit sealed in a pressure-tight manner.

8. A process for the production of fines from chemically active regrind, in particular for the production of fines from partially vulcanized elastomers, in which the regrind is embrittled by a coolant, comminuted in a mill (8) and then classified in a classification arrangement (14), characterized in that that the ground material is cooled in the mill (8) after comminution, but before the classification in the classification arrangement (14).

9. The method according to claim 8, characterized in that the cooling takes place before and / or after the grinding of the ground material in the mill (8) by adding a liquid or gaseous coolant to the ground material.

10. The method according to claim 9, characterized in that the added coolant is used to generate an inert atmosphere within the mill (8) and / or within the classification arrangement (14).

11. The method according to claim 10, characterized in that the inert atmosphere in the mill (8) and / or in the classification arrangement (14) is kept at an overpressure relative to an outside atmosphere during the grinding process.

12. The method according to any one of claims 8 to 11, characterized in that the oversize particles separated in the classification arrangement (14) are fed back into the mill (8), preferably in the cold state.

13. The method according to any one of claims 9 to 12, characterized in that liquid or cold gaseous nitrogen is used as the coolant.

4. Use of a device according to one of claims 1 to 7 or a method according to one of claims 8 to 13 for comminuting substances with temperature-dependent reactivity, for example partially vulcanized elastomers.