US2323564A - Perforated plasterboard - Google Patents

Description

July 6, 1943. J. PAGE PERFORATED PLASTER BOARD Filed Bed. 19', 1938 N\ M w $1.

Patented July 6, 1943 PERFORATED PLASTERBOARD John Page, Evanston, Ill., assignor to United States Gypsum Com ration of Illinois l any, Chicago, 111., a. corpo- Application December 19, 1938, Serial No. 246,625

' In Canada October 6, 1938 6 Claims.

This application is a continuation in part of my original application Serial No. 168,343, filed October 11, 1937, for Process and apparatus for perforating sheet materials, now Patent No. 2,220,270, issued November 5, 1940.

The present invention relates to perforated sheet materials, more particularly to an improved perforated plasterboard, and the invention has for an object the provision of an improved product of this character.

Although my invention in its broadest aspects is not limited thereto, it is particularly applicable to and will hereinafter be described in connection with perforated plasterboard of the general type described and claimed in Patent No. 1,938,354, issued December 5, 1933, to Carlisle K. Roos. In this Roos patent the finished plasterboard, which is formed and dried in a conventional manner, is perforated after drying by subjecting a stack of plasterboards to a simultaneous drilling operation.

While such apparatus and the product formed thereby is to a large extent satisfactory, repeated sharpening of the drills with the consequent expenditure of considerable time and labor has been found to constitute a considerable item of expense. Furthermore, the flexibility of such apparatus is rather limited, the apparatus being designed to receive a predetermined number of boards of predetermined thickness for each drilling or perforating operation. Furthermore, some objection is found to the product thus formed due to the fact that considerable dustis forced into and accumulates in the pores of the plaster core around the hole. When the plasterboard is later erected on ceilings or walls by nailing, a portion of this dust is dislodged and falls into the workmans eyes, which is of course objectionable. In some instances the dust contained in the pores of the plaster core around the perforations may act as a coating and prevent a proper bond between the perforated board and the plaster forced into the perforation during the plastering operation to form keys.

Something is yet to be desired, therefore, in perforated plasterboard of this character, and it is accordingly a further object of my invention to provide an improved product formed in accordance with my improved process of manufacture, by perforating the plasterboard while in its partially moist condition before the plasterboard passes to the drying apparatus.

It is a still further object of my invention to provide a product of this character comprising a plasterboard having a gypsum core containing adhesive materials capable of migrating to the surfaces of the core upon drying and which is perforated in a particularly advantageous manner while in a partially set or moist condition so as to compact and compress the surrounding portions of the plasterboard core.

By perforating the plasterboard before it enters the drying kiln, I am able to speed up the drying operation and therefore reduce the production costs. Quicker drying of the product is made practical by reason of the fact that perforating the board before drying removes a substantial percentage of the weight of material to be dried and by reason of the fact that the perforations increase the turbulence of the drying gas passing over the board. Thus while an unperforated board presents a smooth surface over which the drying gases flow whereby a relatively thick film of cold air or gas is formed next to the board, the stream of gases passing over a perforated board and through the perforations thereof provide a turbulent motion which reduces the thickness of this cold gas film.

Furthermore, in normal' operation of a board kiln or dryer the boards are usually separated slightly as they pass through the kiln.- With unperforated boards the drying gases pass through the spaces between the boards and contribute to the burning or overdrying of the ends and edges. In drying previously perforated board the currents of gases are not localized at the ends of the board but also pass through the perforations so as to provide a uniform drying of the board without overdrying the ends and edges.

An advantage of primary importance obtained in practicing my invention is found in connection with perforated plasterboards having gypsum cores. In Patent No. 2,044,401, issued June 16. 1936, to CarlisleK. Roos, there is described and claimed a gypsum core composition containing suitable soluble gums and starches which have V the property of migrating to the surfaces of the core, especially during the drying operation. Although various migrating materials may be employed in the gypsum core of perforated plasterboard embodying my invention", the particular materials described in this Roos patent as gelable, starchy, partially dextrinized adhesives have been found particularly advantageous. These migrating materials upon drying provide hard glazed surfaces, and by perforating the board before drying the core I obtain a perforated board in which the walls of the perforations are formed of hard glazed material substantially identical with the end surfaces of the board so as sub-' stantially to prevent small pieces of the core from dropping out of the perforations during nailing of the boards to studding or similar supports.

In carrying out my invention in one form a continuous plasterboard sheet having inner and outer covering sheets with a core therebetween of gypsum plaster or similar hydrated composition material containing migrating constituents is formed in the conventional manner and passed over suitable conveyors to my improved perforating apparatus. The continuous imperforate sheet or board is fed to the perforating apparatus in partially set or moist condition and corresponding portions of the opposite surfaces of the imperforate sheet or board are cut so as to form incompletely severed segments therein, which segments are thereafter forcibly ejected from the plane of the board to form perforations therein. Subsequent to the perforating operation the continuous sheet is cut into desired lengths and subjected to a suitable drying or hardening treatment.

In order efficiently to carry outthis process, I provide a perforating machine which preferably comprises spaced roller means adapted to progress sheet material therebetween having means carried by the roller means for cutting corresponding portions of the upper and lower surfaces of the sheet material as it passes between the roller means to form a plurality of incompletely severed segments therein, and means are provided for ejecting the incompletely severed segments from the sheet material to form perforations.

A preferred type of perforating machine is disclosed in my above referred to Patent No. 2,220,270, and comprises a pair of spaced rollers adapted'to pass plasterboard therebetween, each of the rollers having a plurality of circumferentially spaced tubular cutting members extendin outwardly from the periphery thereof, the cutting members on each of the rollers being similarly shaped and similarly spaced so that as said rollers are rotated in opposite directions corresponding portions of the upper and lower surfaces of the plasterboard passing between the rollers will be cut by the tubular cutting members to form incompletely severed segments in the plasterboard. Preferably the cutting members on one roller are slightly larger than the corresponding cutting members on the other roller so that a shoulder is formed in each perforation when the incompletely severed segments are ejected. Disposed in the smaller set of tubular cutting members on one of the rollers and slidable therein between a withdrawn and an extended position are a plurality of ejecting plungers, and operating means are provided for momentarily operating the ejecting plungers to their extended positions at the instant that the corresponding cutting members on the rollers are in aligned pletely severed segments are forced out of the plane of the board and into the cutting members on the opposite roller to complete the perforating operation.

For a more'complete understanding of my invention, reference should now be had to the drawing in which:

Figure 1 is a somewhat schematic representation of an apparatus and process for manufacturlng plasterboard embodying my invention;

Fig. 2 is a plan view of a perforated plasterboard formed in accordance with my invention;

Fig. 3 is an enlarged fragmentary View of a position whereby the incomportion of the board shown in Fig. 2, illustrating in detail the character of the perforations formed therein.

In Fig. 1 I have shown, for purposes of illustration, means for manufacturing in a continuous manner my imprqved plasterboard having a core of gypsum or other hydrated composition, and top and bottom covering sheets or liners of suitable fibrous material such. for example, as paper. As shown, the apparatus includes a table or support I50 over which a lower cover sheet or liner I5I is passed, a pair of feed rolls I52 being arranged to draw the sheet I5I from a suitable supply roll I53. As the bottom cover sheet I5I passes over the support I50, a plastic ,body or mass of gypsum or other hydrated composition in its plastic or manageable state, containing migrating materials of the character hereinbefore referred to, is deposited on the sheet I5I, for example, from a suitable supply spout I54. Although my invention is not limited thereto. the plastic mass is preferably of the character disclosed in the above Roos Patent No. 2,044,401.

Adjacent the forward end of the support I50 is a pair of forming rolls I55, and as the cover sheet I5I and the plastic mass thereon pass from th -support I50, these forming rolls I55 operate on the plastic mass to provide a plastic mass of predetermined thickness, an upper cover sheet I56 being drawn from a suitable supply roll I51 and applied to the upper surface of the formed plastic mass or core by the upper one of the master rolls I55. The apparatus thus far described is entirely conventional and is of the type commonly employed in the art for forming gypsum core plasterboard of this character, the formed board 3'! passing from the master or forming rolls I55 to a suitable conveyor I58. Although I have shown an apparatus for forming open or raw-edge plasterboard, it will of course be understood that my invention is not limited thereto and may be applied with equal facility to apparatus for forming closed-edge plasterboard in which the liners or cover sheets completely enclose the edges of the core. In such apparatus suitable means are provided in advance of the master rolls for properly scoring and folding the bottom cover sheet I 5I was completely to enclose the core after the upper cover sheet I56 is applied.

The conveyor I58 is of sufficient length so that the plaster core of the board 31 attains a partially set condition before passing to the perforating apparatus, here shown diagrammati cally as comprising a pair of perforating rolls I6 and 22, the construction and operation of which is fully described in my Patent No. 2,220,270. From the perforating apparatus the perforated board 31 is fed to suitable cutting means shown diagrammatically as a pair of reciprocating knives I59 which are controlled in any suitable manner so as to sever selected lengths of the perforated board from the continuous sheet, the severed board then being fed by suitable conveyors I60 and I6I through a drying chamber or kiln I62 wherein the core of the board is completely dried. The resulting product comprises a perforated board, such as the board 31 shown in Fig.- 2, having a plurality of apertures I28 (Fig. 3) the character of which will be more fully described hereinafter.

For a complete description of the preferred form of perforating apparatus employed in manufacturing my improved plasterboard, the method of operation thereof. and the character of the aaaaeea' knife-edged cutting tools employed. reference may be had to my above referred to Patent No. 2,220,270 and to Southwick Patent No. 2,141,492 granted December 2'7, 1938, for Cutting tool. For the purposes of the present application it is sufllcient to point out that when the sheet of the upper and lower perforating wheels 22 and i6 reach aligned positions suitable plungers or ejectors are momentarily operated'to their extended positions so as forcibly to eject the incompletely severed segmentsfrom the plane of the plasterboard.

terior of the perforation so as to eliminate the danger of catching and tearing.

As stated in'iny Patent No. 2,220,270, the cut-- ting tools associated with the lowerperforating wheels have a slightly larger diameter than the cutting tools of the upper wheels, and accordingly a continuously straightwalled hole is not provided as is the case in drilled board of the type disclosed in the Roos Patent No. 1,938,354

referred to above. Instead, each of the perforations I28 includes a shoulder I280, as shown best in Fig. 3, which shoulder is highly advantageous in the application of plaster to the board, partic- As the plasterboard passes between the peri forating wheels, a plurality of perforations I28 are formed therein, the character of the perforations being shown in Fig. 3. Since the core of the plasterboard is in a partially set condition at the time of the perforating operation it is susceptible to compression, and as the edges of the cutting tools are forced through the liner sheets HI and I56 and into the partially set core the liner sheets are slightly depressed, as shown, and the core material adjacent the perforations is compacted or compressed to form an annular area of'greater'density than the remainder of the core. sheets by reason of the above described compacting operation extend into the perforations so as partially to cover the walls thereof, and the toothed cutting edges of the cutting tools sever the liner sheets along jagged lines so as to pro: vide inwardly extending ragged fringes of exposed fibers within the perforations.

The particular character of the perforations just described adds greatly to the utility of the resulting product. The compacted areas of core material surrounding each perforation add to the strength of the core, and, in conjunction with the glazed surfaces produced by the migrating core materials as hereinbefore described, provide a product which is capable of withstanding the abrasive action of a body of plaster when applied to the board and pressed through the perforations, thereby permitting the formation of a more dense plaster plug and a better bond without crumbling or disintegration of the walls of the perforations.

The character of the bond between the plaster plug and the plasterboard is further improved by the presence of the jagged edges of the fiber liner sheets within the perforations, and the depressed edges on both the front and back surfaces facilitate the formation during the plastering operation of a plaster plug having an enlarged head. Furthermore, where exceptionally wet plasters are used the ragged fringes of fibers within the perforations not only assist in providing a keying action but also are effectiv by capillary action to remove considerable water from the plaster immediately adjacent the perforations and so prevent sagging of the plaster.

The provision of a ragged edge about each perforation is disadvantageous in conventional dry perforated plasterboard, since in packing and handling this fringe may catch on an adjacent board and result in tearing off a considerable portion of the cover or liner sheet. In my improved product, however, th ragged fringe of fibers is contained within and directed to the in- As shown best in Fig. 3, the fibrous liner reached the gel stage.

ularly -in the construction of ceilings. If a smooth straight-walled perforation is provided as, for example, by drilling a previously dried sheet of plasterboard, plaster when applied to the board with a trowel enters the perforation with very little resistance and is not forced outwardly V against the sides of the perforation. Accordingly, a poor bond is obtained and when a thick coat of plaster is applied to a ceiling trouble may be encountered due to the plaster sagging. With perforations formed as shown in Fig. 3, the shoulder 128a, assisted by the ragged fringes of I the liner sheets, offers considerable resistance to the plaster so as to cause it to contact the walls of the perforation with suificient' pressure. to form a satisfactory bond. The shoulders l28a, therefore, cooperate with the heretofore described compacted areas and the inwardly extending fringes of the liner sheets to provide a bond superior to the plaster bonds heretofore obtained with conventional perforated or drilled plasterboard.

Furthermore, by providing somewhat larger cutting tools in the lower wheel I eliminate the possibility of the paper liner on the upper surface of the segments formed by the cutting tools catching on the teeth of the lower cutting tool when the segments are ejected from the plane of the board 31 into the lower cutting tool, and I likewise eliminate the possibility of the segment being caught on the inwardly extending ragged fringes of the lower liner sheet l5l. The number and spacing of the perforations of course depends upon the arrangement of the perforating wheels and the perforating tools carried thereby, and in Fig. 2 the plasterboard 31 is shown as having been provided with four rows of uniformly spaced perforations 28.

The apparatus described and claimed in my Patent No. 2,220,270 is capable of operation at high speeds and is adapted to large scale manufacture. This high speed operation is of paramount importance in manufacturing perforated plasterboard in accordance with my invention, utilizing gelable adhesive materials of the type disclosed in the Roos Patent No.- 2,044,401. As there disclosed, the particular materials used do not reach the gel stage before the core has set and are therefore free to migrate to the surfaces of the core, and in order to insure the formation of a satisfactory glazed surface on the walls of the perforations the perforating operation must be performed before the adhesive materials have Since the gypsum core sets in a comparatively short time a high rate of board travel on the board forming machine and a high speed perforating operation are important.

The preferred form of apparatus is particularly useful in perforating gypsum core plasterboards before drying, in accordance with my invention, because of .the character of the perforations formed. As heretofore pointed out, one purpose of perforating before drying is to effect migration of the adhesive,,glaze-forming materials to the walls of the perforations during the drying operation, and to obtain the full benefits of thus perforating before drying it is advantageous to form the perforations in substantially the manner shown so as to form compacted areas in the core and inwardly extending ragged fringes on the liner sheets, without unduly crushing or tearing the wet imperforate board adjacent the perforations.

While I have shown a particular embodiment of my invention, it will be understood, of course, that I do not wish to be limited thereto since many modifications may be made, and I, therefore, contemplate by the appended claims to cover any such modifications as fall within the true spirit and scope of my invention,

Having thus described my invention, what I claim and desire to secure byv Letters Patent is:

l. A perforated gypsum core board in which the perforations are defined by the inner edges of annular areas of gypsum core material having a greater density than the remaining portions of the core and the walls of said perforations presenting a substantially glazed surface, the-walls forming said glazed surface including a farinaceous adhesive composition.

2. A perforated plasterboard comprising a core and inner and outer fibrous cover sheets, the perforations in said plasterboard being defined by the inner edges of compacted annular areas of said core material having a greater density than the remaining portions of said core, said annular areas being substantially covered by said cover sheets.

3. A perforated plasterboard having a core and fibrous cover sheets on said core, the perforations in said plasterboard being surrounded by annular depressions in the surface of the board, said depressions forming the edges of said perforations and being covered by said fibrous cover sheets which extend into said perforations and terminate in ragged edges therewithin.

4. A perforated gypsum core board in which the perforations are surrounded by annular depressions, said annular depressions forming the edges of said perforations and being covered with fibrous sheets which extend inwardly along the walls of said perforations and terminate in ragged edges, the portions of said perforation walls left uncovered by said cover sheets presenting a substantially glazed surface.

.5. A perforated plasterboard in which the walls of each perforation extend substantially at right angles to the plane of said board, each of said perforations having a larger transverse crosssectional area adjacent one side of the board than adjacent the other side thereof whereby to form an annular shoulder within the perforations.

6. A perforated gypsum core board having perforations the walls of which present a substantially glazed surface, the core portions forming said glazed surface including a farinaceous adhesive composition.

' JOHN PAGE.

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