Forming fabric

Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Including interlaminar mechanical fastener

Patent

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Details

162348, 428225, 428257, 428258, 428259, D03D 300, D21F 110

Patent

active

053606604

DESCRIPTION:

BRIEF SUMMARY
The present invention relates to a woven fabric fourdrinier forming belt, preferably for paper pulp or cellulose driers according to the preamble of claim 1.
Forming belts, as in fourdrinier machines, consist of an endless, continuously moving belt, and are intended to receive a fibrous slurry in a uniformly thick layer, where the major amount of water runs off through the belt, leaving the fiber layer on top of the fabric. The flat, upper part of the forming belt passes a plurality of suction boxes for improving dewatering, and possibly one or more press nips to obtain further dewatering. The lower part of the belt passes over a plurality of tensioning and guide rolls on its way back to the first roll. The belt is given a desired tension, which is typically 6-10 kN/m in today's machines, with the aid of the tensioning rolls. During operation, the belt is subjected to heavy wear, particularly during contact with the suction boxes, but also in passing rolls and press nips, as well as generally, due to pulsating tension. Wear also increases as a result of increased machine speed.
From originally being made as woven metal wire webs, forming belts were later made from synthetic material, particularly polyester, inter alia because of its good dimensional stability. However, polyester has poor wear resistance, inter alia due to fibrillation which led to belts made from this material having a relatively short life. In order to solve this problem to a certain extent, polyamide threads, being transversal to the moving direction of the fabric in the machine, have sometimes been woven into the fabric, thus somewhat improving resistance to wear of the belt.
Many modern cellulose driers are constructed such as to have good stretching potencial for the belt, which has meant that these machines can operate without problems where change in belt length is great in the comparison between a loose, dry belt and the same belt when tensioned and wet. This has resulted in the utilisation of belts made entirely from polyamide PA6, which is preferable from general technical and economic aspects, although the change in length for the conditions just mentioned is about 6-9%. Belts from this material are very durable, but compared with belts having polyester threads in the direction of belt travel they have instead much poorer dimensional stability.
In contradiction to modern cellulose driers, the forming belts of older ones of this kind have been afforded very small potential for stretching, and such belts made from polyamide 6, with their obvious advantages, have not been able to be used in these machines without expensive alterations.
It is therefore an object of the present invention to achieve a woven fabric forming belt, made to a major extent from some polyamide material that utilises the good properties residing in this group of material, while the finished product has an elongation of at most about 5% from loose dry belt to tensioned belt in the wet state.
This object is attained by a woven fabric forming belt that has been given the distinguishing features disclosed in the characterising portion of claim 1. Accordingly, even older machines may be equipped wich forming belts made from a material that is very durable, permits considerably longer operation times between belt replacements, permits higher machine speeds and leads on the whole to more effective production with the machines. Since the thread material is selected from polyamides where the ratio between methylene groups and amide groups has a quotient of at least 7, good fabric stability and low moisture absorption ability are obtained. In addition, if the fabric is round-woven, i.e. its longitudinal threads in the belt are weftwise in the weaving machine, such that there is a weaving pattern where the longitudinal threads extend in separate layers of two or more, and the belt fabric is rendered stable by heating, pressing and stretching so that the relationship between knuckle height measured on the inside of the thread and total fabric thickness givs a quotient of

REFERENCES:
patent: 3885602 (1975-05-01), Slaughter
patent: 3885603 (1975-05-01), Slaughter

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