Textiles: fiber preparation – Assembling – Web forming
Reexamination Certificate
2001-02-05
2004-01-13
Welch, Gary L. (Department: 3765)
Textiles: fiber preparation
Assembling
Web forming
C019S304000
Reexamination Certificate
active
06675445
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to an apparatus for producing a mineral wool nonwoven fabric including a shroud comprising fiberizing means and a conveyor means for transporting the mineral wool nonwoven fabric, as well as to a method for producing mineral wool nonwoven fabric. The invention relates furthermore to a mineral fiber product having a defined density distribution across the thickness.
2. Prior Art
The intention in producing mineral wool nonwoven fabric is obtain a product of best possible quality for the least amount of energy required. In mineral wool nonwoven fabric production the raw materials are fed molten to a fiberizing means which generates the mineral wool fibers. The mineral wool fibers are discharged into a shroud and deposited on the conveyor means. The bottom conveyor means is usually an air-permeable circulating transport belt. Located under the transport belt is a suction device for generating a specific vacuum.
Since the fiberizing means typically employed in this field convey the vitreous fibers emerging centrifugally from a body in high-speed rotation by a strong downflow of air, a considerable proportion of the air flow is blown into the shroud. This air flow impinges the conveyor means arranged at the bottom of the shroud and is deflected upwards thereby in a zone of high turbulence, resulting in return flow within the shroud. It is this return flow that tends to return upwards the mineral wool fibers already deposited on the conveyor means. To counteract this effect a high-power suction blower needs to be provided so that the mineral wool fibers deposited on the conveyor means are held in place by an adequate vacuum. This vacuum needs to be sufficient so that also in the case of thick mineral wool layers on the conveyor means the topmost layers still remain in place.
When it is desired to produce a relatively thick mineral wool nonwoven fabric several fiberizing means are arranged in a shroud in the conveying direction of the conveyor means. This, however, increases the energy consumption of the suction device since the thicker the layers of the mineral wool nonwoven fabric the higher is the relatively difference in pressure between suction device and the nonwoven surface. This can be counteracted by increasing the suction capacity, but this has the disadvantage that, on the one hand, the energy consumption is increased and, on the other, the lower portions of the mineral wool nonwoven fabric are compressed to such an extent that the mineral wool nonwoven fabric leaves the shroud already precompacted. Such a density gradient within the thickness of the insulant is undesirable since this reduces the insulance and other quality data such as e.g. pliancy and compressive stress of the product.
To obtain a bulk density distribution across the thickness of the product which is as even as possible the thickness of the raw nonwoven upstream of the curing oven needs to correspond to at least twice the product thickness.
It is known from experience that the thickness of the raw nonwoven upstream of the curing oven considerably effects the density distribution and thus the pliancy of compressed products.
Prior art attempts of reducing the density gradient across the thickness of the insulant involved directing an air flow firstly from the bottom upwards in the drying oven configured as a circulating air oven so as to loosen up the higher density lower layers.
Proposed in German patent 39 21 399 is an apparatus in which the collection conveyor is configured so that the carrying surface area of the collection conveyor increases in each case in the conveying direction. This is achieved by inclining the collection conveyor from the horizontal so that the suction surface area is increased and a lower vacuum is needed in this zone.
EP 0 406 107 too, describes one such method for depositing fibers generated by a plurality of fiberizing means. In this arrangement each fiberizing means has its own interceptor zone and the intercepted fibers are discharged from the interceptor zone by conveyor belts. The web of the conveyor belts is convex and the surface areas of the interceptor zones become larger with increasing surface area weights on these conveyor belts. The disadvantage of such an apparatus is that the rotary walls surrounding the shroud in this system are not configured down to the conveyor belts, thus resulting in leakages which increase the blower capacity needed. This is why a fixed wall section adjoins the rotary walls downwards. These fixed sidewalls result in the product being more exposed to dirt which tends to collect in these areas to then periodically drop onto the conveyor belt located underneath. This has the further disadvantage that these random dirt droppings negatively effect the consistent quality of the resulting product.
In addition there is an optimum to the spacing between the fiberizing means and the collection conveyor. If the spacing is too small, strong horizontal air flows materialize on the collection conveyor which tend to roll up the deposited fibers into bundles. If the spacing is too large largish bundles of fibers (also termed hanks) tend to already form in the collection shroud which likewise render the product inhomogenous.
To minimize both effects a precise spacing as calculated or obtained from trial and error needs to be maintained between fiberizers and collection conveyor.
U.S. Pat. No. 4,463,048 describes a method and an apparatus for producing mineral wool nonwovens comprising several fiberizing units which deposit the fibers as a primary nonwoven on a collection conveyor which conveys horizontally in the region of the fibers being deposited. The conveyor belts of the collection conveyor are then guided over guide pulleys so that a secondary nonwoven materializes from two primary nonwovens. Since two primary nonwovens having half conveyor contact are generated the resistance coefficient in the throughflow of the primary nonwovens is roughly half that for a secondary nonwoven twice as thick, enabling the vacuum needing to be applied by the blower to be reduced roughly by 50%. However, the various fiberizing means need to be set very precisely to minimize the differences in density due to the transverse distributions. Setting the fiberizing means with high accuracy is also important to minimize the property differences, especially as regards their symmetrical distribution across the thickness of the secondary nonwoven.
Described in U.S. Pat. No. 4,917,750 is an apparatus and a method in which the mineral wool nonwoven fabric is sliced along a generally horizontal plane prior to entering a curing oven. The upper section is compressed and subsequently redeposited on the lower section so that the resulting mineral wool product has density distribution across the thickness, whereby the upper portion has a higher thickness than the lower portion located thereunder. The slice through the mineral wool nonwoven fabric is made in a substantially horizontal plane, parallel to the transport belt.
Known from U.S. Pat. No. 3,824,086 is producing a very thick mineral wool nonwoven fabric in making use of various fiberizing means. In this arrangement each of the individual fiberizing means deposits on an individual conveyor belt assigned to it. The individual mineral wool sections thus produced are subsequently deposited on each other.
SUMMARY OF THE INVENTION
The invention is based on the object of improving an apparatus and a method for producing a mineral wool nonwoven fabric so that a product having enhanced properties can be produced with low energy consumption.
The substantial feature of the mineral wool blanket or mineral wool mat is that two layers in each case feature identical properties as regards fiber quality and/or binder content. As already explained above, each single fiberizing means produces two layers in the secondary nonwoven which are in addition symmetrical as regards the plane of symmetry running parallel to the top and bottom side of the mineral wool product, thus p
Naber Wilfried
Schorr Ludwig
Pfleiderer Dammstofftechnik International GmbH & Co.
Welch Gary L.
Young & Thompson
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