Fluid sprinkling – spraying – and diffusing – Container for non-fluid material – and scattering means – With means generating or supplying gaseous mixing current
Patent
1990-11-27
1992-02-25
Kashnikow, Andres
Fluid sprinkling, spraying, and diffusing
Container for non-fluid material, and scattering means
With means generating or supplying gaseous mixing current
239 71, B67D 508
Patent
active
050906267
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a dusting apparatus.
Dusting apparatus of this type, such as are described for example in DE-A-26 37 875, are used in printing machines, in order to provide freshly printed sheets or endless webs with a thin covering of dust, which prevents the sheets from sticking together. If the dusting apparatus dispenses too little powder, then this object is not reliably achieved, if too much powder is applied to the printed products, then this results in an unpleasant feel of the product for the user and increases the costs for dusting. Sometimes, an excessive layer of powder is also a drawback at the time of subsequent mechanical treatment of the printed products, since reproducible friction ratios do not exist. In a dusting apparatus according to DE-A-26 37 875, the powder requirement is ascertained relatively roughly by a sensor, which produces a signal proportional to the operating speed of the printing machine.
Hitherto the actual monitoring of the thickness of the powder covering applied by the dusting apparatus to the printed products took place due to the fact that a black control sheet was allowed to travel through the dusting apparatus and the whitening on the sheet was monitored optically. However, this type of control is obviously not possible during routine operation, so that in this case careful supervision by the operator was necessary in order to ascertain both a shortage as well as an excess of powder, which resulted from variations in the powder properties (for example increase in the moisture content) and the adjustment of the dusting apparatus in long term use.
My dusting apparatus described hereafter should therefore be developed by the present invention so that a uniform quality of the powder coating applied to the printed products is guaranteed even during production. This object is achieved according to the invention by a dusting apparatus according to claim 1. In the dusting apparatus according to the invention, the density of a powder stream falling freely from the dosing device into the atomization device is measured. This density is as a whole still relatively high, so that when using less sensitive measuring devices, a great variation of the measurement signal is obtained. If one were to measure variations of density directly in the mist produced, which is obtained by atomization of the powder in a carrier gas, one would have to use very sensitive measuring devices, which in addition still react very sensitively to interference effects.
Since, in the dusting apparatus according to the invention, a relative movement between the free-falling powder stream and the measurement gate is carried out at regular intervals, one can use the output signal of the measurement gate at those times when the powder stream does not pass therethrough, for the purpose of compensating for interference effects caused by impurities or ageing. Thus, in particular, it is not necessary to incorporate a cleaning device in the dusting apparatus, which cleaning device keeps the measuring section free of impurities continuously or intermittently. Also, temperature influences are obviated in this way.
Apparatus are known per se for determining the suspended particle concentration in gases, in which the optical parts of the measurement gate are placed at regular intervals in a reference path, which is free from suspended particles. Examples of this are EP-A-00 47 049 and CH-A-567 721.
In these known measuring apparatus for determining the suspended particle content, either a closed light path or a tube through which a pure gas passes, is placed by an electric motor at regular intervals in the measuring gate or the measuring gate is shifted accordingly. In this case, precise evaluation electronics are required on account of the generally only low fluctuations of the optical density. On the other hand, according to the invention, the density of the powder stream falling freely into the atomization device from the dosing device is measured.
Advantageous developments of the invention are described i
REFERENCES:
patent: 2301136 (1942-11-01), Moreland et al.
patent: 3091368 (1963-05-01), Harley et al.
patent: 3731743 (1973-05-01), Marshall
patent: 4503806 (1985-03-01), Prusak et al.
patent: 4702931 (1987-10-01), Falcoff
patent: 4815414 (1989-03-01), Duffy et al.
Industrieelektronik Dr-Ing Walter Klaschika GmbH & Co.
Kashnikow Andres
Morris Lesley D.
Philpitt Fred
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