Patent Application
20050025935
The present invention is directed towards a fabric with attached guides, particularly one wherein the attachment mechanism is the encapsulation of the fabric by the guide.
In the papermaking industry, there is an apparatus which is used to thicken pulp and paper stock. Early on such devices were commonly referred to as deckers. These early devices involved the use of cylinder molds which included a porous cylinder mold rotating in a vat of liquid with a controlled input of slurry. Water would be drained off through the cylinder mold thus thickening the remaining slurry which would be drained off. An example of this type of device can be found in U.S. Pat. No. 4,106,980.
An improvement on the then conventional thickeners can be found in U.S. Pat. No. 4,722,793. This patent describes a device which avoids the use of a cylinder mold. It employs a single pair of smooth-surfaced rolls and a single fabric trained around those rolls so that it wraps substantially 180° of the surface of each roll. The pulp stock to be thickened is initially delivered to the inside of a fabric run approaching the top of one roll so that the pulp is trapped in a zone between the fabric and the roll and is made to travel around the roll with the fabric. Centrifugal force causes liquid to be expressed through the fabric from the pulp trapped between the fabric and the roll.
The resulting partially dewatered pulp then travels on a lower fabric run to the other roll, where it is similarly subjected to centrifugal force causing further expression of liquid through the fabric. After travelling around the surfaces of both rolls, the pulp is removed from the surface of the second roll.
In order to guide the fabric in a path perpendicular to the axes of the two rolls, the fabric was provided along one or both of its edges on its bottom surfaces with a strip of material or guide in the shape of a V-belt. This guide was intended to fit into a peripheral groove in each of the rolls.
This belt is made separate from the fabric and mechanically attached thereto. Due, however, to the high-speed operation of the device, difficulty was encountered in maintaining the guide on the fabric.
In an effort to improve on this arrangement, U.S. Pat. No. 5,039,412 teaches providing for stitching the V-belt guide to the fabric and providing a band of adhesive on the fabric in the area of the stitching. The application of the adhesive extends a short distance inward from the side of the fabric. Also, guides are provided on the outer edge of the fabric so that they are positioned on the outside of the rolls rather than in a groove or grooves in the rolls.
In other industrial belting applications, certain machines have been constructed without any controlled mechanical active guiding system. These types of machines require belt fabrics with very secure v-guides on the wear side for frictional guiding against the outer edges of rolls, or in specific grooves in the rolls machined at either edge or in the center thereof. In addition, the fabric must maintain a low coefficient of friction on its wear side to facilitate machine thread-up.
The current industry standard for these types of machines include permeable fabrics with v-guides secured by one or a combination of the following four methods: 1) sewing the v-guide onto the fabric using various types of monofilament or multifilament threads; 2) gluing the v-guide onto the fabric by choosing appropriate combinations of glue and v-guide materials to create a chemical bond; 3) filling the fabric structure with the same material used to manufacture the v-guide, to create a bond through fusion upon heating and mating both surfaces under pressure; and 4) priming the fabric with a material chemically compatible to that used in the v-guide, so to create a combination of chemical and thermal surface fusion upon mating both structures under heat and pressure.
U.S. Pat. No. 5,039,412 (discussed above), U.S. Pat. Nos. 5,558,926 and 5,840,378 (discussed later) all teach applications of the first, second and third methods. In addition, the fourth method has been and continues to be used in the production of impermeable/solid belting.
Unfortunately, all the above methods have certain drawbacks. For example, the sewing method is susceptible to fatigue failure due to both flexing of the threads, and to the abrasion on the exposed opposite side of the fabric to which the v-guide is attached. On the other hand, the second, third and fourth methods depend on a surface bond between two interfaces, which is a function of both the available surface area as well as the chemical affinity between the two materials. Although methods two through four avoid the abrasion problem of method one, the less than ideal bonding and flex fatigue at the interface may nevertheless impair durability. A related disadvantage is that the bond strength between the fabric and v-guide is always less than the tear strength of either the fabric or v-guide materials alone. This allows for the possibility of v-guide delamination.
In other belt applications, single or multi-ply polyurethane, polyvinyl chloride, or synthetic rubber structures supplied as flat stock are threaded and joined endless on the machine, via either a non-marking pin seam, or via splicing using a time consuming skiving and chemical bonding type process. The high degree of available surface area for bonding on the wear side of these structures makes it possible to attach v-guides using a simple melt fusion process, with or without surface priming (depending on the compatibility between polymer types in the belt and v-guides). However, the disadvantage with this method is, again, that the bond strength is always less than the tear strength of either the belting or v-guide materials alone.
In view of the foregoing, it is desirable to employ a non-marking, pin-seamable fabric in these applications, so to avoid the excessive time and inconvenience of the skiving and bonding process which requires expensive outside contractors to perform this specialized time-consuming process. In this connection, it has been suggested that a coated, spiral fabric might provide an easy-to-pin, non-marking seamable structure. On the other hand, currently available coated spiral structures are difficult to produce with v-guides for two reasons. First, unfilled constructions with less than 0.20 mm plane difference on the v-guide bonding surface exhibit insufficient surface area for fusion bonding. Second, fully filled structures with uniformly smooth bonding surfaces offer little durability advantages over the current standards—again, due to the bond strength being less than the tear strength of either of the two laminates.
Other prior art includes the following:
While some or all of the foregoing references have certain attendant advantages, further improvements and/or alternative forms, are always desirable.
It is therefore a principal object of the invention to provide a fabric with guides securely attached thereto.
It is a further object of the invention to provide for a fabric with attached guides that is resistant to flex fatigue, abrasion and delamination.
A further object of the invention is to provide a fabric with guides secured in a manner that overcomes the drawbacks inherent in the sewing, gluing and fusing methods.
These and other objects and advantages are provided by the present invention. In this regard, the present invention is directed towards a fabric with attached v-guides wherein the primary attachment mechanism is encapsulation of the fabric by the guide material, and not the chemical compatibility of the two materials.
Thus by the present invention, its objects and advantages will be realized the description of which should be taken in conjunction with the drawings wherein:
Turning now more particularly to the drawings,
Advantageously, the attachment mechanism is primarily the encapsulation of the fabric 10 by the v-guide 14, and not the chemical affinity of the fabric and guide materials. This results in an improved bond strength between the fabric 10 and the v-guide 14 being equal to the tear strength of the either the fabric or guide material alone. Consequently, the inventive fabric 10 with encapsulated v-guides 14 performs satisfactorily for greater than twice the life of fabrics with conventionally attached guides, as shown in comparison tests.
A further advantage of the attachment mechanism being primarily the encapsulation and not the chemical compatibility of the fabric 10 and guide 14 is that the fabric 10 can be of almost any construction and composition. Thus, while the exemplary fabric 10 shown in
In the preferred embodiment shown in
In a preferred embodiment of the invention, a rectangular stuffed spiral 10 is employed to control the depth of coating penetration. Alternatively, an open and/or otherwise stuffed spiral can be similarly used. Note that the coating thickness 18 above the surface plane of the spiral 12 can vary from 0 to 4 mm. It is further noted that the coating 16 may comprise polyurethanes, polyvinyl chloride, silicone rubber, synthetic rubbers such as nitrile or styrene butadiene rubber, or other material suitable for the purpose.
Thus by the present invention its objects and advantages are realized, and although preferred embodiments have been disclosed and described in detail herein, its scope and objects should not be limited thereby; rather its scope should be determined by that of the appended claims.
