Solid material comminution or disintegration – Processes – With heating or cooling of material
Patent
1996-01-24
1997-09-23
Rosenbaum, Mark
Solid material comminution or disintegration
Processes
With heating or cooling of material
241 2428, 241 80, 241 29, B02C 1912
Patent
active
056695594
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a process for pulverising polyurethane, polyurea and/or polyurethane/polyurea materials in a roller mill whose at least two rollers rotate at different circumferential speeds, wherein the material to be milled is fed to the roll slit formed by the rollers and after its passage is separated into a coarse fraction and a fine fraction, the coarse fraction being returned to the roll slit and the fine fraction being passed on for further processing.
In recent years, the recycling of plastics has obtained a very high status. Possibilities have even been sought for the material recycling of cross-linked polyurethanes, such as are used, for example, for highly stressed motor vehicle bumpers. For recycling, it is generally necessary to comminute, and in particular to mill, these scrap materials in order to be able to re-use them in powder form, in particular as fillers. Particularly fine pulverisation is required if they are to be added as fillers to formulations for polyurethane reactive systems. The use of roller mills is known (DE 42 07 972-Al). Milling leads to a mixture of a large quantity of very coarse and a small quantity of already fine particles. The coarse particles are screened out and returned to the gap between the rollers. This screening process is very uneconomical because the screen is loaded with a large quantity of very large particles and thus comparatively small quantitites of fine material are obtained.
The object of the present invention is to improve the previously known process in order to make it more economical.
This object is achieved by collecting and returning the coarse particles which fall freely downstream of the roll slit, while the fine fraction which remains as a sheet adhering to the roller with the larger circumferential speed is discharged separately from the coarse fraction.
According to the known process, both rollers were cleaned with a scraper so that all the milled material was fed to the screen. In contrast, according to the invention, the sheet consisting of the fine fraction, which forms on the roller which rotates more rapidly during the pulverisation of the materials mentioned above, can be utilised so that this sheet is no longer passed to the freely falling coarse fractions, but is discharged separately.
Obviously the sheet also contains some coarse fractions, but the particle size spectrum is very favourably shifted to the finer end.
For many possibilities for recycling, the fine fraction can therefore be directly re-used. However, if a particularly fine powder is required, then the sheet consisting of the fine fraction is preferably classified again into coarse and fine particles. Known screening methods can be used for this purpose. When screening in this process step, the fine fraction is much larger and may even be larger than the coarse fraction. If there is a possibility of direct re-use for the now relatively small coarse particles then these are discharged, but on the other hand they may be returned to the roll slit for re-milling.
It is understood that the sheet may also be stripped off and fed to another roll slit.
One particularly advantageous variant comprises feeding the sheet adhering to the roller, by means of this roller, directly to the roll slit formed between this roller and a third roller.
However, since this third roller has to be arranged in such a way that it rotates upwards, the coarse fraction here cannot--as in the first roll slit--be separated by free falling. Thus, if the coarse particles are required to be isolated once again after passage through the second roll slit, screening must be carried out.
Preferably, the coarse fraction to be recirculated is cooled.
There is considerable friction during the comminuting process and heat is therefore produced. Since some of the particles in the coarse fraction pass through the roll slit several times, the milled material would become hot, and thus damaged, if no cooling were provided.
The starting materials for performing the process are preferably a polyurethane flexi
REFERENCES:
patent: 2686011 (1954-08-01), Oishi
patent: 3372878 (1968-03-01), Verdier
patent: 4684070 (1987-08-01), Dicky
patent: 4687144 (1987-08-01), Irwin et al.
Peltzer Karl
Wagner Joachim
Wirth Jurgen
Bayer Aktiengesellschaft
Cheung Noland J.
Gil Joseph C.
Maschinenfabrik & Hennecke GmbH
Rosenbaum Mark
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