Paper making and fiber liberation – Processes and products – Including solid non-waterlaid preform
Patent
1982-07-30
1985-04-30
Chin, Peter
Paper making and fiber liberation
Processes and products
Including solid non-waterlaid preform
162108, 162123, 162129, 162150, D21H 382
Patent
active
045142580
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to the reinforcement of wood particle boards by means of reinforcing filaments of threads suitably fixed therein, and a method of reinforcing wood particle boards, e.g. for use as roofing boards directly against roofing trusses. The characterizing features of these reinforced wood particle boards and the method used to produce them will be seen from the following description and claims.
Different methods of reinforcing wood particle boards are already known, e.g. from the Swedish published specifications Nos. 7600758-2 and 7612014-6. According to these known methods, a reinforcing layer of net or unbleached paper having high tensile strength is used. These layers are glued onto the top or bottom faces of the boards in a separate process after manufacturing the boards. Special production lines are used for this process, in which the manufactured and finished boards are reinforced in order to obtain properties increasing their strength.
These known methods all have the drawback that the movement or creep of the reinforcing material, due to the effects of moisture and heat, deviates from that of the board material itself. As a result of the reinforcing material being applied to one side of the board, a so-called "bimetal" effect occurs, manifesting itself by the board becoming warped. The thinner the board is, the greater is this deformation, partly for reasons of geometry, and partly because thinner boards have, per se, less resistance to bending. This effect is apparent when the boards are painted, for example, a thin coat of paint being sufficient to cause deformation.
It has now been found that a very high rupture strength can be obtained for the wood particle board if, in accordance with the present invention, it is provided with interior reinforcement comprising glass fibre filaments or threads in conjunction with the manufacturing process for it. These threads, preferably gathered into clusters or bundles, are laid parallel, with constant or varying mutual spacing and are advanced continuously from bobbins onto a continuously advancing bottom web of the fibre of the fibre stock from which the board is formed, synchronous with the formation of the wet fibrous web, but before applying the top web of fibrous stock forming the whole of the still unfinished board. During subsequent dewatering and pressing steps, the threads are thus embedded and fixed between the top and bottom webs of material forming the board. Reinforcement over a larger surface area than would otherwise be obtained may be provided by laying the threads in a wavy and sinusoidal pattern.
The spacing of the threads to suit requirements relating to rupture strength as well as to the manufacturing process and cost of material has also been found to have great importance. While too large a distance between the threads or bunches thereof does not provide the desired reinforcing effect on the one hand, very small spacing gives raise to such practical drawbacks as excessive weight and material cost on the other hand. Furthermore, it has been found that if thread spacing is reduced to 10 mm or less, dewatering problems which cannot be ignored occur in the pressing step of the manufacturing process. Too closely laid reinforcing threads will thus delay the departure of water, and in some cases there may even be certain bursting effects in the board when pressure is released.
Although the kind of board dealt with here can take up quite large stresses in the direction of its surface, it is susceptible to loads perpendicular thereto, particularly concentrated loads. Thus, in many uses of the boards, such as for roofing or false sealings, there is always the risk of a punch-through, i.e. local rupture or collapse of the board due to a concentrated load, e.g. such as is caused by the weight of a person, or dropping a heavy tool.
It has thus been found that suitable spacing of the threads (measured between the centre lines of adjacent threads or clusters of filaments) should not fall below 10 mm. On the other hand, to avoid
REFERENCES:
patent: 2653090 (1953-09-01), Crandall
patent: 2881072 (1959-04-01), Clark
patent: 3303089 (1967-02-01), Roubicek
patent: 3867252 (1975-02-01), Skrabak et al.
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