US3096235A - Suction box cover for fourdrinier machines - Google Patents

Description

y 2, 1963 J. s. TAYLOR 3,096,235

SUCTION BOX COVER FOR FOURDRINIER MACHINES Filed March 21, 1961 i i ii I l i i i INVENTOR. john SIJyIOK BY ATTORNEY Unite This invention relates to a suction box cover for Fourdrinier machines and has for an object the provision of improvements in this art.

One of the particular objects of the invention is to provide a suction box cover which furnishes a very long life to the screen which moves thereover; which will itself have a long life; and which is much less expensive than the better types of coverings now available.

Patent No. 2,876,685 discloses the use of polytetrafluoroethylene (PTFE or Teflon) for suction box covens. This is a great improvement over wooden covers in that it furnishes a much longer wear life of the screen wire material. However, it is very expensive and relatively soft so that it wears away rapidly, thus increasing the cost. The loss of time and product in shutting down a Fourdrinier machine to replace either the screen or the suction box cover involves very considerable expense, say $10,000 or more, hence it is highly desirable to provide the best possible cover, especially if it can be attained for less expense than previous covers.

I have found that polypropylene gives a screen life almost as long as Teflon and is much cheaper in price. In addition it is much harder than Teflon and wears out far less rapidly.

Polypropylene is a hydrocarbon polymer thermoplastic material with a high softening temperature, maintaining its rigidity at temperatures Well above that of boiling water. It has a lower density than any other commercial plastic and has a high strength-to-weight ratio. It is a translucent milky white substance. One wellknown commercial supplier is Hercules Powder Company of Wilmington, Del., and their bulletin of 1959 entitled Pro-fax may be referred to for further information on the character, production and fabrication of this product.

Propylene has the chemical formula 1-1 and a lattice arrangement of CH CHCl-l Polypropylene consists of connected molecules of propylene and the method of polymerization has a great effect on the character of the product since each propylene monomer unit can take various arrangements in the chain formed during polymerization. This is the subject of stereochemistry which is important to the manufacturer of the product but which need not be elaborated here. It can be obtained in powder form suitable for molding, extruding or forming in other ways.

Polypropylene in its normal state does not bond readily with most adhesives but may be treated, as by chromic acid, to make it bondable. See pamphlet Bonding of Polyethylene (which acts similarly) PB 131099 of United States Department of Commerce, Office of Technical Services, March 1957, for further information on bonding. After treatment, the usual good bonding materials are effective.

As an aid to the understanding of the invention the accompanying illustration is provided, wherein:

3,095,235 Patented July 2, 1953 "ice The single FIGURE is a cross-section through a suction box cover embodying the invention.

In the drawing, a base member 10 and its upper layer 11 are provided with apertures -12. It will be understood that the cover is secured over a vacuum drain box and that the screen carrying the pulp slurry slides over the top of the layer 11.

The base may be of various materials but preferably is phenolic condensate impregnated fabric. One known on the market as Dilecto is suitable. The upper layer is polypropylene. The polypropylene is oxidized on its lower surface, as by concentrated chromic acid, to make it cementable and is bonded by suitable adhesive 13 to the base. One suitable cement is phenol condensate which is heat-cured, the polypropylene having a sufficiently high melting point to resist injury at the required temperature. Epoxy resins are satisfactory and easy to use. Rubber and vinyl base type curing agents are also satisfactory. A suitable method of bonding is to iron on (with an electric iron or some other suitable method) a layer of thin fabric 14 (e.g. cotton, glass, or synthetic fibers, etc.). A temperature of about 400 to 450 F. is required. Only the surface of the polypropylene sheet melts and bonds to the fabric. The sheet can now be bonded to the Dilecto base as described.

The results of recent laboratory and field evaluation tests show that polypropylene gives a longer screen life than Teflon. The screen wear for Teflon and polypropylene when tested under mild abrasive conditions is about the same. As the abrasive content of the slurry is increased, the polypropylene shows relatively less wear than the Teflon.

Because of its low coefficient of friction, Teflon has often been incorporated in fabrics and the resulting material used as a base for laminates and molding compositions. When compared to these Teflon composition laminates, the polypropylene produced a wire wear of 18 to 20 points (milligrams in a standard test procedure) as compared to 20 to 43 points (milligrams) for the Teflon laminate. In another standard test procedure using a more abrasive slurry, the figures were points (milli grams) for polypropylene, 250 points (milligrams) for the Teflon composition, and 2.12 points (milligrams) for pure Teflon. These figures indicate that polypropylene is superior to both Teflon and the Teflon compositions.

It is thus seen that the invention provides a hard wearresistant covering which provides a screen wear life very close to that of the best previously known materials and with great economy because of the relatively low cost of polypropylene.

While one embodiment of the invention has been described for purposes of illustration it is to be understood that there may be various embodiments and modi fications within the general scope of the invention.

What is claimed is:

A suction box cover for use in contact with the moving screen wire of Fourdrinier machines, said cover comprising a screen contacting element and a base element, the screen contacting element consisting essentially of polypropylene, the base element being formed of a phenolic condensate impregnated fabric laminate, and a fabric layer bonded to said screen contacting element by fusion of the polypropylene material and thereafter bonded to the base element, whereby a low cost suction box cover 3 4 is provided which increases the useful life of the moving OTHER REFERENCES Screen and Suction box cover System Polypropylene, Kresser, Rheinhold Publishing Corp.,

R f ences C't d :11 m f th's t t New Yorke er 1 e m e e O 1 pa en Wear of Fourdrinier Wire Bearing Materials, Pye,

UNITED STATES PATENTS 5 Pulp and Paper Magazine of Canada, pp. 124136. 2,668,134 Horton Feb. 2, 1954 Linear and Stereo Regular Addition Polymers, Gaylord 2,876,685 Holmes Mar, 10, 1959 and Mark Interscience Publishers Inc., New York, 1959, 2,927,047 Sohulde et a1 Mar. 1, 196 0 p. 323.

2,970,078 Nielsen Jan. 31, 1961

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