Cleaning and liquid contact with solids – Processes – Longitudinally traveling work of bar – strip – strand – sheet...
Patent
1997-03-06
1999-06-29
Alexander, Lyle A.
Cleaning and liquid contact with solids
Processes
Longitudinally traveling work of bar, strip, strand, sheet...
134 21, 134 37, B08B 102
Patent
active
059163739
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a process for removing dust particles from a web surface without contact, as well as a dedusting device for accomplishing the process.
2. Related Art
The designs of dedusting systems for moving material webs, also referred to as web-cleaning systems, can be roughly divided into those that operate without contact and those that operate with brush support. In the latter dedusting systems, the dust particles were mechanically removed from the material web with rotating brushing rollers or rows of stationary brushes and then suctioned off. The composition of the brushes, as well as their strength, material, and bristle design were matched in this case to the properties of the material surface that was to be cleaned. Such non-generic dedusting systems are described in Bundesverband Druck e.V. Information Services!," II/1985, pp. 1 to 20, as well as in WO87/06527.
Dedusting systems that operated without contact had an injection unit, which directed a gas jet onto the web to be cleaned, as well as a suctioning unit, with which the gas that picked up the dust particles was suctioned off in turn. To discharge the dust particles that were found on the material web, discharge electrodes were arranged together with the injection unit or near it. Such dedusting systems are known from EP-A 0 245 526, EP-A 0 520 145, EP-A 0 524 415, EP-A 0 395 864 and CH-A 649 725.
Another approach was used in EP-A 0 084 633. Here, a turbulent flow of gas was directed toward a fabric web that was to be dedusted, and the latter was made to vibrate by the turbulent flow, causing the dust particles to be removed from the surface of the fabric. It was possible to use this type of dedusting only in the case of thin material webs, however, that could be made to vibrate by the gas jet.
A non-generic cleaning system for removing a liquid adhering to a moving belt, especially a rolling belt, is described in DE-A 4 215 602. The problems that arise in the case of a dedusting system with particles that adhere to the surface owing to electrostatic forces did not occur here.
To the extent that a fluidic configuration of the nozzle outlets of the injection units was implemented in the above-indicated dedusting systems, they were designed as channels that were inclined toward the material web with a constant channel cross-section in the area of the nozzle opening, as depicted in, e.g., EP-A 0 245 526, EP-A 0 520 145 and DE-A 4 214 602. Only in EP-A 0 084 633 and in an embodiment variant of DE-A 4 215 602 was an exhaust port cross-section of the nozzle with a variable cross-section described. In EP-A 0 084 633, the flow of gas was directed perpendicularly to the fabric web. In DE-A 4 215 602, a nozzle that was inaccurately referred to as a Laval nozzle was used with a cross-section which, after a narrowing, widens in a pear shape and then narrows again.
The invention achieves the object of ensuring the dedusting of a moving, stable material web that is not to be made to vibrate for dedusting, in which discharge electrodes are unnecessary.
BRIEF SUMMARY OF THE INVENTION
The invention is based on the first surprising finding that efficient dedusting is possible only through the selection of a gas jet, especially its pressure, on an area of a material web surface that is to be dedusted as well as through the selection of the spacing of this area from a grounded surface. It is now assumed that efficient dedusting is possible only if the gas pressure of the flow of gas that is produced in the area to be dedusted is so large that the critical voltage that corresponds to the product of the gas pressure and the above distance according to Paschen's Law is smaller than the electrostatic voltage (charge) of the dust particle, which mainly causes the latter to adhere to the material web surface. Thus, under these conditions, self-discharging of the dust particles is carried out. They are neutralized. They now adhere owing only to the considerably weaker van der Waals forces and other
REFERENCES:
patent: 4486238 (1984-12-01), Bando
patent: 5304254 (1994-04-01), Chino et al.
patent: 5421901 (1995-06-01), Whitney et al.
Alexander Lyle A.
Patent Consulting & Development GmbH
LandOfFree
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