US2415647A - Preformed structural material - Google Patents

Description

Patented Feb. 11, 1947 PREFORMED STRUCTURAL MATERIAL Roger A. MacArthur and Harold W. Grelder, Wyoming, Ohio, assignors to The Philip Carey Manufacturing Company,

Ohio

a corporation of No Drawing. Application July 12, 1939, Serial No. 283,972

8 Claims. 1

This invention relates to preformed structural materials and the manufacture thereof. It relates especially to improved structural materials adapted for the fabrication of space enclosures, the structural material being in the form of preformed rigid sections or slabs adapted for the construction of non-load bearing partitions, walls and ceilings and to the manufacture of such preformed structural materials.

It is a purpose of this invention to afiord structural material in the form of sections, panels, sheets or the like that is light in weight, mechanically strong, highly fireand water-resistant and has effective heat insulation properties. It is a further purpose of this invention to afford structural material of the character referred to by methods of manufacture which are economical.

One use for which structural material embodying this invention is particularly well adapted is use in fireproof ship construction, the structural material being used for panels or sheet-like slabs used in fabricating cabin and bulkhead enclosures. It is an advantage of certain structural materials embodying this invention that they, according to tests that have been made. are adequate to meet the requirements or the Maritime Commission with respect to iireand water-resistance and with respect to strength for withstandin the impact of high pressure water streams from fire hoses. In addition to being fire-resistant and water-resistant and having requisite mechanical strength, it is an important feature of structural materials according to this invention that they are light in weight. ticularly when the structural material is used in ship construction, it is desirable that the material be light in weight, inasmuch as ships cannot economically carry heavy structural loads particularly above the water-line, where stability is affected. It is also an advantageous property oi structural materials made according to this invention, that they can be produced in accurate dimensions and with a smooth surface and can be readily treated with a wide variety of decorative surfacing materials so as to produce many different kinds of decorative effects. The structural material of this invention is also advantageous, particularly in ship constructions, due to its heat insulation efliciency. structural material has low conductivity to heat, it retards the spread of fire through panels by heat conduction therethrough.

Structural materials having the desirable characteristics and properties mentioned above Par- Since the can be produced by forming an aqueous mass containing a major proportion of finely-divided normal magnesium carbonate crystals and subjecting the formed mass to relatively high prom sure. the formed and compressed mass thereai ter being heated while moist so as to convert the normal magnesium carbonate in the material to basic magnesium carbonate. During this operation and under the conditions of pressure obtained and described more in detail below the normal magnesium carbonate breaks down and decomposes and is converted to the form of basic magnesium carbonate particles that are firmly bonded together in the form of a rigid mass. Notwithstanding the high pressure used and the compression of the mass, the resulting product is remarkable for its lightness in comparison with structural materials of comparable strength which have heretofore been produced. Moreover, the new structural material has substantially greater heat insulation characteristics than structural materials of comparable strength that have heretofore been produced.

In order to give a better understanding of the practice of this invention, this invention will be described in connection with. illustrative methods or manufacture which may be employed according to this invention.

As above-mentioned, the major proportion of the materials used in making the new structural material consists of normal magnesium carbonate crystals in a finely-divided form. Normal magnesium carbonate crystals in finely-divided form and of desirable characteristics for use according to this invention may be made according to the process that is described in our copending application Serial No. 225,140, filed August 16, 1938, for Manufacture of normal magnesium carbonate and heat insulation material containing same which application resulted in Patent No. 2,396,915, dated March 19. 1946. For example, according to a preferred practice as described in the said application, magnesium bicarbonate solution produced from dolomitic rock (a mixture of calcium and magnesium carbonates) is treated under such conditions as to pro duce finely-divided crystals or normal magnesium carbonate of the chemical formula MgCOiBI-hO. This can be done, ii. desired, by continuously heating magnesium bicarbonate solution at atmospheric pressure at a temperature between about F., and about 158 F. The physical characteristics of normal magnesium carbonate crystals produced by the method referred to above or by any other methodcan be improved for the purposes of this invention by disintegrating naturally occurring needleshaped crystals of normal magnesium carbonate so as to produce a multiplicity of finely-divided particles of normal magnesium carbonate of unordered shape. Such disintegration of naturallyoccurring normal magnesium carbonate needle crystals is described more in detail in our application Serial No. 283,738, filed July 11, 1939, for

Formed article and magnesium carbonate thereg.

fore and the manufacture thereof, executed on even date herewith, which application resulted in Patent No. 335,242, dated November 30, 1943.

According to one preferred method of practising this invention, finely-divided normal magnesium carbonate crystals of the character referred to above are made up into a slurry with water which contains about 2% pounds or normal magnesium carbonate per gallon. If the normal magnesium carbonate crystals as produced are combined with an excess of water, the excess of water can be removed by settling or filtering, or both. The slurry of the concentration mentioned is agitated by any suitable means and is mixed with, for example, about 0.65 pound or asbestos fiber (such as the grade testing 0-0-10-6 according to the standard screen test method of the Quebec Asbestos Producers Association) per gallon of slurry. The slurry is then run by gravity (or under a pressure head) into a filter mold of suitable size such as a mold 4 feet wide by 8 feet long and 3 inches in depth, the bottom or top of the filter mold, or both, being adapted to allow drain age of the water therefrom. The formed slurry is then pressed at a pressure of about 300 lbs. per square inch by some suitable pressing means such as a platen press applied to a movable wall of the mold whereupon excess water is expelled until the slurry contains about pounds of normal magnesium carbonate crystals and about 1.3 pounds of asbestos fiber per gallon and is in the form of a slab or sheet conforming to the shap of the filter mold.

After the slab has been formed and highly compressed it is removed from the mold and is subjected to a hardening treatment by heating it toa temperature above about 160 F., and preferably at a temperature of about 180 F., to about 300 F., under such conditions that the slab remains moist during the conversion of the normal magnesium carbonate into basic magnesium carbonate that is caused by the elevated temperature. Preferably, a minimum of water is lost from the slab durin the time that the slab is hardening or setting. The loss of water from the slab during the hardening or setting can be minimized by causing the hardening or setting of the slab to occur while it is in an atmosphere of steam. After the hardenin or setting of the slab the finished slab will contain about 2 /4 pounds per square foot, 1" in thickness, of basic magnesium carbonate. and will contain as solids about 75% of basic magnesium carbonate and about 25% of asbestos fiber. Following the hardening or set ting of the slab the slab is dried preferably at an elevated temperature in order that the drying may be accelerated, the temperature, however, being maintained below about 550 R, in order to prevent decomposition of the basic magnesium carbonate in the slab.

The density of the slab produced in the manner mentioned above is only about 3 pounds per square foot, 1 inch in thickness (36 pounds per cubic foot). By way of comparison a, slab or corresponding strength using Portland cement as a binder, e. g., a slab containing about by weight of asbestos fiber and about 75% by weight of Portland cement and set after compression at about 1000 pounds per square inch is about 10 pounds per square foot 1" in thickness (120 pounds per cubic foot). The extremely low density of the new structural material produced according to this invention is startling and indicates the value of the new product for use in the manufacture of light weight panels meeting the stringent requirements of the Maritime Commission and having the other advantageous characteristics mentioned above.

When a composition containin a major proportion of normal magnesium carbonate crystals is molded under the conditions abovementioned, it is found that the molded article will retain its shape during drying and that there is little or no drying shrinkage of articles formed from the composition. This is a very great advantage in the practice of this invention. It is thus possible to make slabs or other formed articles which,

after drying of the wet formed articles, require a minimum of mechanical trimmin and waste of valuable ingredients of the structural material.

The slab or other formed article produced in the manner described hereinabove by way of exempliflcation is adapted to receive many different kinds of surface treatment. If desired, the surface may be sanded so as to be extremely smooth. The capacity of the product to be tinished by sanding is of great practical advantage. Alternatively the slab may be coated with some coating composition such as paint or varnish that is adapted to harden on the surface. The slab may also be treated with a material such as sodium silicate which is adapted to react chemically with magnesium carbonate. Slabs or other articles composed of the new structural material likewise lend themselves admirably to combination with decorative and/or reinforcing material which, if desired, can be bonded thereto as by some suitable adhesive. For example, there may be bonded to the formed structural material a layer of sheet metal, wood veneer, asbestos-cement lumber or the like as may be required or desirable. In this manner panels, etc., can be produced having a foundation slab of the new structural material and a surface layer of some other type of material as may be desired.

The structural material may likewise be produced by other novel methods adapted to afford better structural characteristics and improved orientation of the reinforcing fiber therein and resulting in increase in strength characteristics. According to one such method a paper making machine such as a Fourdrinier type machine commonly used for making paper may be used, but in such case the calender and drying rolls are replaced by an accumulator roll whereon the mixture of fiber and normal magnesium carbonate particles are accumulated until a water-laid sheet of desired thickness is formed. The use of such accumulator rolls in paper making machines is well known at the present time and further reference thereto herein is not regarded as necessary. In making a water-laid sheet on a paper making machine, finely divided normal magnesium carbonate is made in the form of a thin suspension corresponding in dilution to a paper making furnish wherein a filler is used. If desired, one can, of course, include additions to the stock such as diatomaceous silica or casein to improve the formation of the furnish on the paper machine. In making the water-laid paper the mixture of normal magnesium carbonate crystals and asbestos fiber is run onto a traveling belt suitably made largely of wool and is passed over suction boxes adapted to receive excess water. The paste of water-laid asbestos fiber and normal ma nesium carbonate on the belt is then passed und r the accumulator roll onto which the layer 0 water-laid material is transferred and wrapped until it becomes of suitable thickness. The laminated layer that is formed on the accumulator roll and which conveniently has a thickness of about 1"; to about inches is removd and subjected to pressure oi the order hereinabove described to press excess water from the formed sheet and to afi'ord a highly compressed product. If a single sheet only about of thickness is made up on the accumulator roll and is pressed, the resulting product is very thin and while it is suitable for many purposes such as fire-resistant veneer, it is usually desirable to produce a slab having a high degree of structural strength and such a slab may be produced by superposing several sheets built up on the accumulator roll and pressing the superposed sheets together to form a slab of desired thickness. Depending upon the number of sheets that are superposed, the thickness can be built up to any desired degree. In compressing the material thus formed it is not necessary to use a filter mold, inasmuch as the slab has sufllcient integrity to retain its shape when excess water is squeezed therefrom.

Another way of making a slab of substantial thickness and strength using sheets formed on an accumulator roll of a paper making machine is to individually press the sheets after formation on the accumulator roll and then bond the individually formed and compressed sheets together using some suitable adhesive such as sodium silicate or an adhesive containin rubber or casein. In this manner a product resembling plywood and having a high degree of structural strength can be produced.

Another method by which a sheet may be water-laid on a paper making machine involves the use of one or more screen covered paper making cylinders of usual type caused to rotate in a vat or vats that contain a dilute slurry comprising flber and normal magnesium carbonate. In such case the cylinder or cylinders pick up a layer of water-laid concentrated paste of fiber rupture and normal magnesium carbonate which can be 55 built up to desired thickness by transferring the said layer on the cylinder or cylinders to a travelling felt and subsequently transferring said layer to an accumulator roll, substantially as described above for a Fourdrinier type machine, and usin methods well known to the paper making art.

According to a further method of practising this invention, a mixture oi normal magnesium carbonate crystals in dry condition may be mixed with some suitable fiber such as asbestos fiber and with or without added filler and the dry mixture spread upon a suitable mold or support, e. g., a felt sheet containing wool. The dry mixture is built up in this way to any desired thickness and is then moistened with water. The moist mixture thus produced can then be compressed as by the use of a platen press in the manner described hereinabove.

After the moist mass containing fiber and normal magnesium carbonate crystals has been I! of the practice of this invention given herein above, which is above about 160 F., and preferably is about 180 to 300 F., until the normal magnesium carbonate is converted into basic magnesium carbonate and until the compressed mass has set, thereby producing'an article in which high structural strength is combined with low density.

In carrying out the processes above described wherein normal magnesium carbonate crystals are formed on a paper making machine, it is especially desirable in order that the water-laid mass may have proper characteristics and uniformity, to modify by disintegration the structural characteristics of naturally-occurring needle-shaped crystals of normal magnesium carbonate as disclosed in our aforesaid application Serial No. 283,738, filed July 11, 1939, for Formed article and magnesium carbonate therefor and manufacture thereof (Patent No. 2.335

In subjecting a water-containing mass comprising normal magnesium carbonate to compression, it is preferable to effect the compression by mechanical squeezing and the pressure should preferably be applied so as to compress the mass without excessive working or manipulation or lateral movement of the mass.

In the foregoing illustrations of the practice of this invention, the solid ingredients in the com- 3-) pleted slab contained about 75% of basic magnesium carbonate and about 25% of asbestos fiber. The slabs that were formed in the filter mold as described hereinabove and compressed under a pressure of 300 pounds per square inch had a density of only about 36 pounds per cubic 4 material one inch thick and about 12 inches square was laid on horizontal parallel knife edges 10 inches apart. Load was applied vertically down on the slab through a third knife edge parallel to the supporting knife edges and midway between them. The modulus of rupture is calculated by the formula:

1.5 X breaking load in lbs. span in inches width of piece in inches (thicknessin inches The water-laid structural materials made on a paper making machine in the manner above described were iound to have a strength or about 1200 to 1400 pounds per square inch. The very high strength of the product formed in the paper making machine is believed to be due to the orientation of the fiber that results from fiber being water-laid.

It is thus seen that the structural material of this invention can be made very strong and at the same time very light and of low density. This in itself is a very great improvement in structural materials heretofore produced of the general type under consideration herein. Moreover the new structural material is fireproof and weter-resistant and has a relatively high heat insulating efllciency.

In addition to abestos fiber, other fibers may be used such as vegetable fibers, although such fibers are not as resistant to high temperatures as are mineral fibers such as asbestos fiber. The incor- 7 poration in the solids of the furnish for a paper making machine of about /2% to about 3% of vegetable fiber such as sulphite pulp or kraft pulp assists somewhat in the formation of the material.

In addition to fiber, finely-divided filler materials may likewise be used in the structural material. Thus heat resistant materials such as diatomaceous silica or exfoliated mica may be used. Preferably, the filler materials which are used are those which impart greater heat resistance to the product without increasing its weight or which have less density than the basic magnesium carbonate in the finished product. some grades of diatomaceous earth and exfoliated mica meet these requirements. Substances such as wood flour and ground cork also meet these requirements. It is preferable that the filler materials such as those mentioned to be used according to this invention in addition to fiber and basic magnesium carbonate produced by decomposition in situ from normal magnesium carbonate be porous. It is desirable to use at least about 12% of fiber in the material and preferably about 25% of fiber is used, although the amount necessary will depend on the length of fiber and the reinforcing required. As above mentioned, the improved structural material should contain at least a major proportion of basic magnesium carbonate derived by decomposition in situ of normal magnesium carbonate and preferably at least about 50% of such basic magnesium carbonate should be present in the structural material.

In the manufacture of the structural material it is desirable that the normal carbonate crystals be freed of substantially all residual magnesium bicarbonate solution likely to be present when said crystals are made by heating magnesium bicarbonate solutions. The magnesium bicarbonate may be removed by addition of a small amount of alkali, such as magnesium oxide or sodium hydroxide to the crystal slurry or by washing the crystals with water. Removal of the magnesium bicarbonate solution as stated minimizes the formation of bubbles and the structural material is made stronger.

In manufacturing the structural material the pressure used can be widely varied. Thus the pressure employed can be varied from 100 pounds per square inch to about 3000 pounds per square inch. The pressure employed depends somewhat upon the dimensions of the slab that is being manufac ured. In making a slab which is relatively thick, e. g., a slab that is about 1 to 3" in thickness, strength suitable for must requirements can be obtained using pressures of about 100 to 300 pounds per square inch, the minimum density of the resulting product consisting essentially of basic magnesium carbonate and about 25% of asbestos fiber in such case being about 24 pounds per cubic foot. If a slab of relatively large lateral extent is to be manufactured and which is relatively thin, e. 8., about A to V2" in thickness, it is desirable to use higher pressures which, as above mentioned, may be as high as 3000 pounds per square inch and over. In such case the density of the product consisting essentially of about 75% basic magnesium carbonate and about 25% of asbestos fiber will be about 48 pounds per cubic foot. It is thus seen that panels of desired thickness and strength may be made and that the attainment of desired properties in the product is within the control of the operator.

bestos fiber, and 10% of exfoliated mica. The

aqueous mass was molded il a filter mold under a pressure of about 400 pounds per square inch. the filter mold being adapted to make a slab about 2 feet by 2 feet. The slab was then heated while moist to about F., for 1% hours to convert the normal magnesium carbonate substantially to basic magnesium carbonate and then dried. The density of the dried product was about 2.12 pounds per square foot one inch thick and its strength as modulus of rupture was about 290 pounds per square inch.

Somewhat more generally it is desirable that preferred embodiments of this invention either consist essentially of fiber together with a major proportion of basic magnesium carbonate integrally bonded by formation by decomposition from normal magnesium carbonate in the formed article, or consist of these two materials together with about 5% to 35% of a finely-divided filler, the density of which filler is not substantially greater than the density of the basic magnesium carbonate.

It is preferable that th strength as modulus of rupture of the preformed structural material produced according to this invention be at least about 200 pounds per square inch.

While this invention has been described in connection with certain specific illustrations of the practice thereof, it is to be understood that this has been done for the purpose of exemplification and that the products mentioned above and the manufacture thereof may be varied considerably without departing from the scope of this invention as defined by the following claims.

We claim:

1. A preformed rigid article of structural material in the form of a hard, strong slab adapted for use as Wall board, paneling or the like, in the fabrication of structures such as walls and partitions, which comprises at least 12% of fiber and a major proportion of basic magnesium carbonate set in integrally bonded condition by decomposition in situ of particles of normal magnesium carbonate compressed together in a formed and compacted mass, said article having high mechanical strength, namely, having a modulus of rupture greater than about 725 pounds per square inch, and having a relatively low density for an article of such high strength, namely, having a density when dry of about 36 to 48 pounds per cubic foot.

2. A preformed rigid article of structural material in the form of a hard, strong slab adapted for use as wall board, paneling or the like in the fabrication of structures such as walls and partitions, which consists essentially of basic magnesium carbonate in major proportion. about 12% to about 25% of mineral fiber and about 5% to about 35% of finely-divided filler, said basic magnesium carbonate being integrally bonded by formation by decomposition in situ of the normal magnesium carbonate particles compressed together in a com acted mass consisting essentially of said normal magnesium carbonate particles, said fiber and said filler, said filler being porous and of not substantially greater density than the density of said basic magnesium carbonate, and the density of said structural material when dry being about 36 to 48 pounds per cubic foot, and said structural material having a modulus of rupture greater than about 725 pounds per square inch.

3. A preformed rigid article of struci .ral material according to claim 2 in which said filler is filler selected from the group consisting of exioiiated mica, diatomaceous earth, wood flour and ground cork.

4. A preformed rigid article of structural material according to claim 2 in which said filler is porous mineral filler.

5. A preformed rigid article of structural material in the form of a hard, strong slab adapted for use as wall board, paneling or the like, in the fabrication of structures such as walls and partitions, which comprises fiber and a major proportion of basic magnesium carbonate set in integrally bonded condition by decomposition in situ of particles of normal magnesium carbonate compressed together in a formed and compacted mass, said article having high mechanical strength, namely, having a modulus of rupture greater than 200 pounds per square inch, and

having a relatively low density for an article of such high strength, namely, having a density when dry of from 24 to 48 pounds per cubic foot.

6. A preformed rigid article of structural material in the form of a hard, strong slab adapted for use as wall board, paneling or the like, in structures such as Walls and partitions, which comprises at least 12% of fiber and a. major proportion of basic magnesium carbonate, said basic magnesium carbonate being set in integrally bonded condition by decomposition in situ of particles of normal magnesium carbonate compressed together in a compacted mass which comprises said particles of normal magnesium carbonate and in which said fibers are disposed in felted relation, said article having high mechanical strength, namely, having a modulus of rupture greater than 200 pounds per square inch, and said article having a density when dry of from 24 to 48 pounds per cubic foot.

ROGER A. MACARTHUR.

HAROLD W. GREIDER,

. REFERENCES CITED The following references are of record in the file of this patent:

Certificate of Correction Patent No. 2,415,647:

February 11, 1947.

ROGER A. MACARTHUR ET AL. It is hereby certified that error appears in the irinted specification of the above numbered patent requiring correction as follows:

olumn 3, line 13, for the patent number 335,242" read 2,335,242; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Oflice.

Signed and sealed this 22nd day of April, A. D. 1947.

LESLIE FRAZER,

First Assistant Oomnt'asioner of Patents.

of said normal magnesium carbonate particles, said fiber and said filler, said filler being porous and of not substantially greater density than the density of said basic magnesium carbonate, and the density of said structural material when dry being about 36 to 48 pounds per cubic foot, and said structural material having a modulus of rupture greater than about 725 pounds per square inch.

3. A preformed rigid article of struci .ral material according to claim 2 in which said filler is filler selected from the group consisting of exioiiated mica, diatomaceous earth, wood flour and ground cork.

4. A preformed rigid article of structural material according to claim 2 in which said filler is porous mineral filler.

5. A preformed rigid article of structural material in the form of a hard, strong slab adapted for use as wall board, paneling or the like, in the fabrication of structures such as walls and partitions, which comprises fiber and a major proportion of basic magnesium carbonate set in integrally bonded condition by decomposition in situ of particles of normal magnesium carbonate compressed together in a formed and compacted mass, said article having high mechanical strength, namely, having a modulus of rupture greater than 200 pounds per square inch, and

having a relatively low density for an article of such high strength, namely, having a density when dry of from 24 to 48 pounds per cubic foot.

6. A preformed rigid article of structural material in the form of a hard, strong slab adapted for use as wall board, paneling or the like, in structures such as Walls and partitions, which comprises at least 12% of fiber and a. major proportion of basic magnesium carbonate, said basic magnesium carbonate being set in integrally bonded condition by decomposition in situ of particles of normal magnesium carbonate compressed together in a compacted mass which comprises said particles of normal magnesium carbonate and in which said fibers are disposed in felted relation, said article having high mechanical strength, namely, having a modulus of rupture greater than 200 pounds per square inch, and said article having a density when dry of from 24 to 48 pounds per cubic foot.

ROGER A. MACARTHUR.

HAROLD W. GREIDER,

. REFERENCES CITED The following references are of record in the file of this patent:

Certificate of Correction Patent No. 2,415,647:

February 11, 1947.

ROGER A. MACARTHUR ET AL. It is hereby certified that error appears in the irinted specification of the above numbered patent requiring correction as follows:

olumn 3, line 13, for the patent number 335,242" read 2,335,242; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Oflice.

Signed and sealed this 22nd day of April, A. D. 1947.

LESLIE FRAZER,

First Assistant Oomnt'asioner of Patents.