Plastic and nonmetallic article shaping or treating: processes – Forming articles by uniting randomly associated particles – Plural – intermittent pressure applying
Reexamination Certificate
1999-05-13
2001-02-20
Theisen, Mary Lynn (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Forming articles by uniting randomly associated particles
Plural, intermittent pressure applying
C264S109000, C425S149000, C425S371000
Reexamination Certificate
active
06190588
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a method of continuously pressing a material particle mat in the production of wooden material panels or the like such as particle boards (chipboards) and MDF (medium density fiber) panels, as well as a twin-belt press suitable for this purpose.
BACKGROUND
In the production of chipboard and fiber panels there is a requirement for precompression of the blanks by continuously working prepresses. Twin-belt presses in which the particle mat (“cake”) of chips mixed with bonding glue deposited on a support is pulled off from the support before it enters the two forming belts of the press are known per se in the continuous production of wooden chipboard with precompression (DE 4441017 A1).
In other systems, on the other hand, known as “FLEXOPLAN” systems, the particle mat is formed by scattering the “glued chips” onto a flexible metal support screen on which they remain during precompression. At the head end of the support screen, a catch strip member is attached, 25 mm high, for example, which is engaged by chains that draw the support screen to the press. In these systems, it has not been possible to date to use a continuously working prepress because, in the passage of the catch strip member through the roller pairs and pressing segments of the known twin-belt presses, an inadmissibly high pressing pressure results and damages the forming belts and/or other parts of the press.
Systems in use to date do not allow continuous precompression of the panel material before hot pressing. Therefore, it has been necessary to provide a relatively large press plate spacing of about 25 cm, into which the chipboard cake was fed and then pressed relatively slowly, so that air can escape from the material. Precompressed panels are much thinner, so that a press plate spacing of 15 cm is sufficient and, for a press of the same height, it is possible to arrange 15 units one above the other instead of only ten with a larger plate spacing. Continuous precompression of the panel material is consequently very desirable. Not only because of the greater capacity of the hot press, but also because of the shorter pressing time since the precompressed material can also be pressed faster as a result of the smaller air content. In this way, productivity can be increased by about 50%.
OBJECT OF THE INVENTION
Accordingly, an object of the invention is to provide a method and press that enables continuous pressing, preferably precompression, without the risk of damage to the press through the presence of foreign bodies, especially the above mentioned catch of a support screen, that do not belong in the particle mat or chip cake or the like.
Other objects and advantages of the invention will become apparent to those skilled in the art and from the drawings, the detailed description and the appended claims.
SUMMARY OF THE INVENTION
In accordance with aspects of the invention, pressure rollers can be pushed away or apart by a passing catch of a support screen or other foreign bodies because of their sprung or resilient mounting and the entire pressure roller with its rotary axis is shifted or tilted and, subsequently, spring back automatically to their operating position to enable a continuous pressing operation without degradation by the foreign bodies.
At least one but preferably at least between two and four sprung pressure rollers are possible, although a much greater number may be appropriate for the purpose, e.g., up to about 20 sprung pressure rollers. As each of them is separately sprung and, therefore, individually shifted or tilted by the foreign body, the remaining other pressure rollers can during the same time stay in their normal position as necessary for the desired compression forming operation. The spring pressure of the pressure rollers can be generated hydraulically, pneumatically or also mechanically, e.g., by steel springs, and should preferably be adjustable, and/or controllable in a closed control loop as a function of setpoint values to maintain stability. In the case of a plurality of sprung pressure rollers, their spring pressure, depending on system requirements, can be the same or be set differently from one pressure roller to the next.
The spring pressure, for matching to the usually adjustable operating line pressure of the pressure rollers, can be adjustable between a minimum figure and a figure that amounts to at least about two times but, preferably, more than about five times this minimum figure. For example, the line pressure (the “punctiform” pressure applied by a roller across its width upon a surface) can be selected for normal operation depending on the required level of precompression between about 30 and about 200 kg/cm and, as the pressure rollers should not be pressed away until this nominal pressure is exceeded, the spring pressure can be set to figures corresponding to a line pressure of about 30 to about 200 kg/cm.
In the case of continuous prepresses with pressure rollers opposite one another, the upper pressure roller will preferably be sprung, while the other, i.e., the lower pressure roller, may serve as a rigid counter-pressure roller.
REFERENCES:
patent: 5762980 (1998-06-01), Bielfeldt
patent: 5788892 (1998-08-01), Graf
patent: 44 41 017 A1 (1996-05-01), None
Schlingmann GmbH & Co.
Schnader Harrison Segal & Lewis LLP
Theisen Mary Lynn
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