US2375276A - Method for treating sheet materials - Google Patents

Description

2,375,276 N, G. B. snow 0R TREATING SHEE METHOD v l lNvENToR .Agfa '/lf. I l ff/T @a L TORNEY Patented May 8, 1945 Y George B. Brown, ManvilleN. J., asslg'nor to .lohns-Manville Corporation, New York, N. Y., a corporation of New York Application October 27, 1942, Serial No. 463,545 z claims. (C1. 25.4154) The present invention relates to the manufacture of bro-cementitious sheets, and is more parl ticularly concerned with an improved method for smoothing the surfaces of libro-cementitious sheets and other shapes.

A primary object of the invention is to provide an effective method for imparting smooth surfaces to bro-cementitious sheets and other shapes.

Fibro-cementitious sheet materials of the type now manufactured for use as interior wall linings and for similar purposes have surfaces which are frequently so rough as to require smoothing as by sanding or other treatment, preparatory to -application of nishing or decorative coatings of paint' and the like. I'he libres employed in the manufacture of such sheet materials may be vegetable fibres such as wood bre, or mineral libre such as asbestos; and the cementitious bondingl agents may comprise inorganic binders such as Portland cement, hydrated lime, or gypsum, or organic binders such as phenol-formaldehyde resin or other synthetic or natural resin. Frequently the sheet material also embodies inert iiller substances such as finely-divided silica. vOne method frequently used for manufacturing fibre-cementtious sheet material is to deposit a mixture of bres and cement from an aqueous slurry on a pervious screen, and after forming a sheet of suitable thickness, to compress, densify andpartially dewater the sheet by means of a, pressure filter mold. The final manufacturing operation is that of subjecting the sheet to heat-curing or other suitable treatment whereby to set and kharden the cement'itious bond. f p

Both continuous and discontinuous methods have been employed in the manufacture of brocementitious sheets; and the sheets produced by such methods generally have rough and irregular surfaces. Such irregularities or -imperfections in the sheet-surface frequently include the `impressions of wire mesh screensor other pervious` elements employed in. the sheet forming operation.

Conventional methods which have been used in an eifort to remove such irregularities and to impart a smooth surface to the sheet have been found in practice to be generally costly and im practical or unsatisfactory. For example, the use of wire brushes or sand o r other abrasives applied to a completely hardened sheet has proven, -to'be a costly and time-consuming operation, and

one which frequently imparts to the surface under vtreatment disguring marks or scratches which are as objectionable as the irregularities which it is sought to remove. The use of calender rolls or 55 smoothing methods.

conventional troweling devices for smoothing incompletely hardened sheets has also proven to be ineffective, costly and time-consuming, and t'o frequently involve undesirable stretching of the l sheet under treatment. y A A more specific object of the present invention is therefore to provide an improved method whereby the surfaces of substantially rigid but incompletely hardened fibro-cementitious sheets may be smoothed without stretching or otherwise changing the dimensions of the sheet, by a single,

rapid and efficient operation which may becon- A tinuous.

With the above and other'objects and features inlview, the invention consists in the improved method and means for smoothing the surfaces of fibro-cementitious sheets, as hereinafter described and more particularly defined in the accompanying claims.

In the attached drawing, which illustrates an embodiment of the invention, and wherein like lreference characters designate like parts:

Fig. I isa diagrammatic perspective view of apparatus adapted for carrying out the'process of the invention; and

Fig. II is a perspective view of afmodiiied type of smoothing roll which may be substituted for the cylindrical roll in the. apparatus illustrated in Fig. I.

The surface smoothing method which forms the subject of this invention is particularly adapted ytothepsurface treatment of cementitious sheet materials containing reinforcing bre. Examples of such sheet materials are bro-cementitious building shapes and sheets containing 20 %50% asbestos or vegetable fibre, together with a cementitious lime or Portland cement binder and an lnert filler such as'nely-divided silica.

The present method is particularly adapted for treating the surfaces of -bro-cementiti'ous sheets having a high nbre content. As they proportion of fibre-is decreased, thefadvantages of the present method of smoothing'the surfaces of the sheet material are proportionately reduced, although if the material has any substantial amountof libre present in the areas adjacent the surface to be smoothed, the invention will give better results than conventionallyknowngmethods for smooth. ing such surfaces. Generally, the length of the fibre as used` inthe sheet material affects the operation of the invention in the same manner 'as does the amount of fibre used; that is, the longer the individual bres present` in the material, the more effective is the invention over` conventionaly In the following description, the method will be described as applied, for example, `to a fllbrocementitious sheet which has been formed by 4pouring a slurry suspension of fibres and cement into a mold having a perforated bottom covered 5 with a wire mesh screen of suicient neness to prevent the fibre-cement mixture from passing therethrough while permitting drainage of water from the mold under applied molding pressure.

After the sheet has been thus formed, it is per- 1o mitted to set to a stage at which it is incompletely hardened, but sui'ciently rigid to retain its shape and form without support. While in this incompletely hardened stage the sheet is advanced at a predetermined uniform rate over a supporting surface and the improved smoothing treatment of the present invention is applied to the exposed upper surface of the sheet by subjecting such surface to the rapidly repeated impact rulbbin'g and troweling action of a high-speed 20 rotary cylindrical roll segment troweling element. When the dimensions and curvature of the troweling element and the relative spacing and directions and rates of movement of the troweling element and sheet are properlyadjusted, such rotary troweling action is effective for smoothing the surface of the sheet and for eliminating any imperfections therein, including imperfections caused by contact `with a Wire screen during the sheet-forming operation.

The action of the rotary cylindrical roll segment troweling element consists essentially in repeatedly striking the surface of the sheet at closely spaced intervals of space and time in such a manner that the incompletely hardened and still mounted transversely to the direction of sheet travel.

one suitable apparatus construction-is inustrated in Fig. I,\in which is shown a smoothing roll 2 of approximately 2 inch diameter mounted on bearings above the surface of a sheet l to be smoothed. Roll 2 extends transversely across the direction of travel of sheet l and parallel there-I to, with the axis of its shaft 3 off center approximately 1/64 inch with respect tothe axis of the roll 2. the sheet I 'from the axis of rotation of roll 2 may be adjusted so that when rotated on shaft 3,

the eccentric portion of the surface of the roll Will impact and penetrate into the surface of the sheet to a depth approximately equal to or slightly o less than the maximum depth of recesses or imperfections 4 in the surface of the sheet. The i roll is then rotated by suitable driving means 8 at a rate of approximately 2000 revolutions per minute; and the sheet is simultaneously advanced over a supporting element 9, as by the action of a pusher l0, in a direction opposite to the direction of rotation of the roll at their zone of contact, at a speed of approximately 20 lineal: feet per minute. When the roll rotates in a direction opposite to the direction of travel of the sheet at their zone of contact a very effective smoothing action is effected. yWhen both the roll and'y the sheetare moving in the same direction at their The distance separating the surface of m5 tendency to accelerate the speed of they sheet and this has an adverse effect on its smoothing action. While the diameter of the smoothing roll 2 may be varied to some extent, it is important that that portion of the roll surface which functions as a troweling element have a sufficiently small arc length and small radius of curvature so that the interval of contact with the sheet is comparatively short, andso that the energy which is transmitted to the sheet is primarily that of rapidly repeated impact troweling tending to burnish the surface. On the other hand, the radius of curvature of the troweling surface portion of the smoothing roll should be sufficiently large to effect a definite troweling action and to force the somewhat plastic material at the surface of the sheet into surface depressions so as to smooth the surface without developing transverse ridges or other irregularities.

The modied form of smoothing roll which is shown in Fig. II comprises a roll 5 having on its outer surface a plurality of uniformly spaced, rounded or arcuate ridges or projections Shaving their major axes of curvature extending longitudinally 'of the roll surface and parallel but eccentric with respect to the roll axis. This type of roll has the advantage lover the roll of Fig. I

that it may -be driven at a lower speed and may have a greater diameter, since it is provided with a greater number of troweling or striking surfaces. The rate of rotation of a smoothing roll of this type may be varied in inverse proportion with the diameter and with the number of troweling or striking surfaces. The curvature of the troweling surfaces or projections should be large enough to effectively trowel the surface of the sheet without fbeing so large as to dislodge or displace the ment of substantially less than 90 subtended angle mounted for rotation about a supporting axis suitably spaced from the sheet surface so as to insure impact contact between the troweling surface and the 'sheet for a short period during each revolution about the axis, and troweling to a suitable depth of approximately 1/64 inch maximum.

v The troweling action of the eccentric troweling roll which 4is shown in Fig. I is effected by a comparatively small segment of the roll surface having an arc length which may not substantially exceed 1/2 inch, and which is spaced from the axis of rotation a distance greater than any other part of the roll surface. Each of the uniformly spaced longitudinally extending ridges 5 on the surface of the troweling roll 5 illustrated in Fig. II forms a cylinder segment located at the line of greatest radial distance from the axis of rotation, which cylinder segment functions as a troweling surface. It will be recognized that these cylinder segment troweling surfaces need not be carried on the peripheries of -rolls such as shown in Figs. I and II, but will perform their troweling function just as well when individually mounted on the ends-of cranks, or with any other equivalent mounting which enables the troweling zone of contact, the rapidly rotatingroll has a surface to impact the surface of the sheet for only @essere a short portion of each revolution of the supporting shaft, so that the period of contact of the t'.'owellng surface with the sheet surface is iollowed by a longer interval in which the sheet is permitted to advance Without contact by a troweling element, prior to the delivery of another troweling stroke either by the same troweling element or by .a second troweling member. Thus, the terms cylinder segment or arcuate roll segment are herein employed to define a cylinder or roll segment having an arc length equivaient to a subtended angle which may be very much smaller than 90, and having'e. substantially cylindrical outer surface curvature.

Itis desirable that the speed of rotation of the cylinder segment troweling element be so ad' justed relative to the speed of advance of the sheet that the sheet advances not substantially more than 1A; inch betweensuccessive revolution impacts of the troweling element. This adjustsheets in which there is a comparatively high proportion of cementitious bonding medium, the

method herein described has also been found to 1. `A process for smoothing a rough surface of a. substantially rigid ybut incompletely hardened flbro-cementitious sheet which comprises, ad vancing the sheet continuously at a predetermined uniform rate past a. troweling station, ap-

i plying to the surface of said sheet, at said sta.-

tion, a rapid succession of short, arcuate trofweling impacts, the direction of application of said impacts being counter to the direction of sheet travel, and the arcuate path of travel of said tire area of sheeliI surface passing said station is beeective when applied to a fibrous sheet comnothing effected may result primarily from leveled and burnished without displacing or pulling the ibers away from the bonding material and without stretching or otherwise changing the original dimensions of the sheet.

2. A process for smoothing bro-cementitious sheet surfaces as dened in claim l, in which the rate of advance of said sheet and the frequency of application of said troweling impacts, are controlled to deliver impacts to the sheet surface each time the sheet advances a distance no substantially greater than 1A; inch.

GEORGE B. BROWN.

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