EP0761310B1 - Method and installation for milling and sifting of material - Google Patents

Abstract

The grinding and sifting process involves passing the material through a coolant and grinding it in a mill (8). The ground material is then taken to a sieve (14) designed to keep out the ambient air, and in particular the moisture in it. This is done in a closed process. The sieve is supplied with the same gas coolant as the mill so that losses from the sieve gas circuit can easily be made good. The upper portion left on the sieve is fed back to the mill. There is a line on the output side of the mill which leads back to the input side.

Description

The invention relates to a method for grinding and classifying regrind according to the preamble of claim 1 and one for implementation device suitable for the method.

According to the state of the art, what is to be comminuted during cold grinding Regrind, especially plastic, by cooling with a coolant embrittled and fed to a mill for comminution. The crushed Grist leaves the mill in a cold state, is collected and temporarily stored, with an adjustment of the temperature of the ground material to the ambient temperature. During this storage electrostatics formed on the regrind can degrade. To the itself subsequent sighting of the regrind is improved in many A release agent is added to cases. This is mixed into the regrind. When sifting, the commodity is separated from the fines and can be fed to the grinding process again. While the temperature the ground material during the intermediate storage of the ambient temperature adapts, water from the ambient air condenses on the particles of the regrind. This makes the ground material very visible limited. Interim drying and adding of separating agents can therefore be used for the screening in previous cold grinding not be waived. The work steps involved are Time and cost consuming.

So the production of fine goods for the duration of the intermediate storage be interrupted and there are costs for the use of Release agent and the work involved.

DE-PS 38 33 830 C2 shows a device of the applicant for the Production of extremely fine dusts with particle sizes down to less than 10 Micrometer in which a classifier is integrated. EP 0 044 507 A1 describes a process in which labels are applied to plastic parts Views are separated. In EP 0 317 935 B1 there is a device shown in which the cold gas emerging from a mill by a Cyclone is freed from particles. In DE-OS 23 18 549 that is Cold grinding ground material is classified by a sieving device. The writings mentioned in the prior art relate either others rely on the production of extremely fine dusts Based on tasks. For example, EP 0 044 507 A1 does not refer to particle size but separated according to material properties.

EP 0 610 162 A2 describes a device for cryogenic decomposition and screening of solid waste, in which the waste by Brittle contact with a cryogenic coolant, crushed in a mill and then into individual components using a view is classified. The classifiers are in a closed pneumatic Cycle arranged and with a dry carrier medium operated. This prevents water from getting on the cooled Regrind condensed.

The invention is therefore based on the object, a method and a To create device with which the production of fine goods cost-saving and can be carried out with less time.

Starting from that considered in the preamble of claim 1 State of the art, the object is achieved with the im characterizing part of claim 1 specified features.

It is now with the method and the device according to the invention possible, fine material in a closed process and without intermediate storage to produce. Gaseous gas accumulating in the mill Coolant can also be used for the classifier circuit.

Advantageous developments of the invention are specified in the subclaims.
The drawings illustrate a device for carrying out the method according to the invention in schematic form.

Figur 1:

Eine Vorrichtung bei der ein Sichter an eine Mühle an geschlossen ist,

Figur 2:

eine Abwandlung der Vorrichtung in Figur 1.

Show it:

Figure 1:

A device in which a classifier is connected to a mill,

Figure 2:

a modification of the device in Figure 1.

In the device shown in Figure 1, the feed is via a Hopper 1 placed on a screw conveyor 2, which is the feed feeds to a rotary valve 4 via a metal separator 3, the one cooling screw 5, which is injected 6 with liquid Coolant is filled with the feed. The exit the cooling screw 5 is connected to a mill 8 via the line 7, whose outlet 9 is connected to a funnel 10, which leads into a rotary valve 11. From the cellular wheel sluice 11 leads a connection 12 to the line 13, which in an external Sifter 14 opens. A line 15 branches from the classifier 14 with a rotary valve 16, which opens into the funnel 1 and serves to return Überkom. Another line 17 is used for Removal of the fine material and opens into a cyclone 18, the output side is equipped with a rotary valve 19. Line 20, which has a valve 21 and a blower 22 leads back into the line 13. From the line 20 branches off a line 23, which with is equipped with a valve 24 and in the fine material chamber 25 of the Classifier 14 opens. Furthermore, a line branches from line 20 26, which via a valve 27 and a filter 28 into a rotary valve 29 as well as the surroundings. Located on line 20 there is a feed 30 for liquid cooling medium. On the funnel 10 is a line 31 connected to a filter 32 which is gaseous Coolant returns to line 7. Branch off from line 31 the lines 33 and 34, which are equipped with the valves 35 and 36 are. Line 34 is connected to line 20, line 33 leads to the surroundings.

In Figure 2, the same device features are the same reference numerals assigned. It shows a device in which the line 20 is located only continues in lines 23 and 26 and the confluence of Line 20 in the line section 13 is omitted. The feed 30 opens into the Line 23.

During operation, the feed material is now transferred to the screw conveyor via the hopper 1 2 abandoned, which the feed material over the metal separator 3 introduces into the rotary valve 4, which is the feed of Cooling screw 5 feeds. The liquid coolant, in this case liquid nitrogen, entered into the cooling screw 5. As a result, the feed material is cooled and embrittled. That on this way pretreated feed is through line 7 fed to the mill 8, which crushes the feed material. That on this Way crushed in the vaporized liquid nitrogen gas stream Regrind is via the outlet 9, the hopper 10 and the rotary valve 11 fed from which the shredded via the connection 12 Grist in the cold gas stream is conveyed into the classifier 14. The Device is along the route from mill 8 via the exit 9, the funnel 10, the rotary valve 11 and the connection 12 sealed gas-tight to the environment. This is a Entry of ambient air and the associated moisture are excluded. In the examples shown in the drawing is the Conveying the ground material in the classifier 14 through the gas flow of the evaporating coolant guaranteed by line 12. However, it is also conceivable as instead of such a gas stream Blowing agents for the conveyance of the crushed ground material also others Device elements such as another screw conveyor use. The shredded regrind gets into the cold gas stream of the Coolant via line 13 in the classifier 14, in which the oversize is separated from the fines. The overcomer arrives via line 15 and the rotary valve 16 back into the hopper 1. The fine goods will conveyed via line 17 into a cyclone 18 in which it is from the cold gas stream separated and discharged via the rotary valve 19. The remaining cold gas passes through line 20 via the blower 22 in the form of a circuit again in line 13, which it again fed to the sifter. In line 20 can via the 30th continue to supply liquid nitrogen, which evaporates in line 20 to avoid any loss of cold gas within the classifier circuit to compensate. It is also possible to use a partial flow of the cold gas from line 20 via line 23 with the valve 24 of the Admit fine material chamber 25 of classifier 14. Possibly in the classifier circuit Any excess pressure can be via line 26 to the valve 27 are dissipated. For this purpose, the gas stream is passed through a filter 28 which is the cold gas of particles emerging from the filter polluting the environment could be liberated. The separated particles can can be separated and collected via a rotary valve 29. The funnel 10 also branches off in a gastight fashion Line 31, which leads through the filter 32, which in turn occurs Separates particles. The gas stream emerging from the filter, which is a has low temperature, can continue in the cycle line 31 can be returned to line 7 for total consumption to reduce liquid nitrogen as a coolant.

Alternatively, excess cold gas can be supplied via line 33 to the Valve 35 is equipped to be released to the environment. It is also possible, the classifier circuit through line 34, which with the Valve 36 is equipped with additional cold gas from the grinding process supply by feeding the cold gas into line 20 possible cycle gas losses in the closed classifier circuit to compensate.

In Figure 2, the classifier gas cycle is narrower and only includes the fine chamber of the classifier, the line 17 with the cyclone 18, the Line 20 with the blower 22 and the line return 23 with the valve 24.

It is now with the method and the device according to the invention possible, in a closed process, on-line, with remote control of ambient air and the associated humidity without further intermediate steps such as tempering, drying and adding Release agents to produce and sift fines. It can therefore be in considerable time and cost can be reduced. Ideally is the process with liquid nitrogen, which in the Process evaporated, operated. However, it is also possible for others Use coolants that have similar properties. The procedure is not limited to the use of impact mills, rather can also other mills such. B. micro vortex mills and Air jet mills are used. The coarse feed can with the method and the device essentially down to 50 micrometers Particle size can be crushed in the main proportions. With the method and the device according to the invention is the entrance prevented from humidity. This improves the product quality and has a significant positive influence on the subsequent separation stages, it is not necessary to add a release agent. Problems through Electrostatics can be prevented. That for sighting required cycle gas is taken from the upstream cold grinding process, so that the coolant can be used twice. For an economical mode of operation is a classifier 14 with a classifying gas circuit required. However, at The method according to the invention is also present in a special case a sighting without a sight gas cycle.

In case of using liquid nitrogen as a coolant both processes at the same time, grinding and sifting made under the inert gas. This makes it especially sensitive to oxygen Regrind limits the risk of explosion. On the previously required steps of mixing, release agent addition and intermediate storage can be dispensed with; associated with this is a clear one Reduction of personnel, operating and investment costs. That in the Oversize material returned from the grinding plant is already through the process cooled, which can reduce the consumption of coolant. The method can be carried out with particular advantage in online operation become.

Claims (10)

1. Method for milling and gas-classifying material which is to be milled, in which the material which is to be milled is made brittle by a coolant and is comminuted in a mill (8), the comminuted material being fed, in the absence of ambient air, to a gas classifier (14), in which the comminuted material is classified, characterized in that the gas classifier (14) is integrated in a classifier gas circuit, which is separate from the mill (8), the classifier gas circuit being operated with the coolant which was used to make the material brittle, and the comminuted material being fed into the gas classifier (14) in an atmosphere of gaseous coolant.
2. Method according to Claim 1, characterized in that oversize material which is separated out in the gas classifier (14) is fed back to the mill (8).
3. Method according to one of Claims 1 or 2, characterized in that some of the coolant used in the mill (8) is fed in the gaseous state to the classifier gas circuit, in order to compensate for gas losses and refrigeration losses in the classifier gas circuit.
4. Method according to one of Claims 1 to 3, characterized in that some of the coolant used in the mill (8) is fed back to the mill (8) in the gaseous state.
5. Method according to one of Claims 1 to 4, characterized in that the oversize material which has been separated out in the gas classifier (14) is fed back to the milling process in the cold state.
6. Apparatus having a mill (8) for comminuting material which is to be milled, the mill (8) being assigned a gas classifier (14) which is in communication with the mill via means which allow the comminuted material to be passed into the gas classifier (14) without contact with ambient air, characterized in that the gas classifier is integrated in a classifier gas circuit which is separate from the mill (8) and at a line (20, 23) is in communication with the outlet side of the mill (8) through a line (34) which introduces gaseous coolant into the gas classifier circuit.
7. Apparatus according to Claim 6, characterized in that the gas classifier (14) is in communication with the mill (8) via means which feed the oversize material to the mill (8).
8. Apparatus according to one of Claims 6 or 7, characterized in that at the outlet side of the mill (8) there is a line (31) which is in communication with the inlet side of the mill (8).
9. Apparatus according to one of Claims 6 to 8, characterized in that a filter (32) is integrated in the line (31) which branches off from the mill (8) on the outlet side.
10. Apparatus according to one of Claims 6 to 9, characterized in that the line (20) of the classifier gas circuit is assigned a gas outlet which comprises a filter (28) with particle outlet.

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