US1184308A - Cork-board. - Google Patents

Description

L. L. BENTLEY.

CORK BOARD.

APPLICATION FILED MAY 19, 1915.

WITNESSES INVENTOH cw a r .nnion.

LOUIS L. BENTLEY, 0F BEAVER FALLS, PENNSYLVANIA, ASSIGNOR TO ARMSTRONG CORK COMPANY, OF PITTSBURGH, SY'LVANIA,

PENNSYLVANIA, A CORPORATION 01'? PENN- CORK-BOARID.

menses.

Specification of Letters Patent.

Patented May 23, 1916.

Application filed May 19, 1915. Serial No. 29,036.

diagrammatic, showing means for determining the heat conductivity of the material; and Fig. 2 is a sectional view, also partly diagrammatic, of the same.

My invention provides a cork board which combines a relatively high degree of structural strength with a relatively low weight per cubic foot.

It also provides a cork board having a relatively high resistance to heat conductivity, which is more elastic than, and which is generally superior to, the cork board heretofore known.

Cork board is used to a large extent for heat insulation purposes, and particularly in cold storage structures; and by the term cork board as used herein and in the claims I intend to cover not only boards of this'material, but also slabs, blocks, bricks, and other structural shapes.

The best cork boards heretofore on the market have had a weight per cubic foot of at least eight pounds, but notwithstanding this relatively high density, the material is not homogeneous throughout, but contains to a very considerable extent, large air spaces or voids due to imperfect contact between the separate pieces or granules of cork. The tensile strength of such product is usually not in excess of four pounds per square inch.

My improved cork board can be made with a weight of less than eight pounds per cubic foot; is much more compact and homogeneous than the old product; has a tensile strength of not less than five pounds per square inch of cross section, and has a very low heat conductivity. I have manufactured this new product with a weight per cubic foot of but little in excessof five pounds,

' and having a tensile strength of eight pounds per square inch of cross section. Heat conductivity tests of this material show a heat transmission of less than five B. T. Uis'per square foot of one inch thickness in twentyfour hours for each one degree Fahrenheit difference in temperature, under cold storage conditions.

Cork board embodying my invention will 1n all cases have a weight per cubic foot of from about four and eight-tenths pounds to seven and eight-tenths pounds; will have a tensile strength of not less than five pounds per square inch of cross section, and usually very greatly in excess of this figure and will have a heat transmission of less than that just' specified when tested by the well known hot-plate method. There are several varieties of the'hot plate method in use. The method which I consider most accurate and which should be employed in testing my improved material is shown in the accompanymg drawlng. In accordance therewith, two

pieces or slabs 2 of the material are placed upon opposite sides of an electrically heated hot plate 3, having a plurality of heating coils 4: arranged in multiple. To guard against heat losses, particularly at the edges of the test material, they are packed in a heat-insulating material 5, preferably loose kieselguhr.

6 designates cooling jackets having circulating baiiles 7, and placed one above the upper test piece and the other below the lower test piece. The two jackets have separate inlets 8 for water or brine and separate outlets 9.

The numeral 10 designates an ameter, and

11 a voltmeter in the supply circuit for the heating coils.

12 is a constant voltage voltmeter which is connected to the central portion 43* only of the middle heating coil, thus largely eliminating errors due to heat leakage at the edges.

13 is a millivoltmeter connected to a thermo-couple 142, placed in that portion of the hot plate containing the section to which the voltmeter 12 is connected:

In making a test, the following data is taken:

ET is the average temperature of the brine at the two inlets 8.

OT is the average temperature of the brine leaving the two outlets 9.

LV is the drop in voltage through the three coils 4.

CV is the drop in voltage through the portion 4: of the middle heating coil.

CT is the temperature at center of portion 4 as given by the millivoltmeter 13.

1 volt l ampere=1 watt.

1 watt in twenty-four hours=81.984 B. '1. U .s.

VoltageXamperage 8L984c=heat in B. T. U.s put in in twenty-four hours.

Then:

VoltageXamperageX81.984 thickness of test piece Degrees difference in temperaturexarea in sq. rt. of test piece Heat transmitted in B. T. U.s Iper twenty-four hours per square foot area. per inch t ickness per each degree Fahrenheit difference in temperature.

I have stated that my improved material showed a heat transmission by this test of less than five B. T. .U.s, per square foot of one inch thickness in twenty-four hours for.

each one degree F. difference in temperature, Whenthe colder surface is 20 degrees F. and the hotter surface is 100 degrees F.

In the manufacture of my improved product the granulated cork is first preheated to a temperature higher than that which has heretofore been used in the manufacture of this material. The effect of this high temperature is to cause a large expansion of the cork particles, which may amount to one hundred per cent. or more. These expanded particles are then placed in the mold, and into which the mass is pressed. The molds are then subjected to a baking action at a higher temperature than that used in the preheating operation, cork being held under pressure within the molds in the meantime. The-effect of baking at a higher temperature, while the cork is under pressure, than that used in the preheating, is to cause a further expansion of the individual particles, thus creating an internal pressure inthe mass within the mold, resulting in a closing up of the voids between the granules, a better contact between the granules, and a better cementing together of the entire mass. Any suitable process of manufacture which will give these results may be employed. I prefer, however, to use the method which is described and claimed in my application Serial No. 873,962, filed N ovember 25, 1914. In accordance with that method the cork particles are first preheated to a temperature of not less than four hundred degrees Fahrenheit, and which may run as high as five hundred fifty degrees Fahrenheit. For this purpose the cork'may be fed through a heating chamber such as a shell, to which the heat is applied externally. The efiFect of preheating to this high temperature is to convert the moisture, and

1 other volatile matter within the cork into steam or vapor. The cork being brought up to this comparatively high temperature with relative rapidity the conversion of the volatile matter into steam or vapor causes a large increase in volume, due to the expansion of the cork cells. This increase may amount to more than one hundred per cent. The cork particles so treated, preferably while still at as high a temperature as practicable, are fed into a mold and are subjected to pressure therein. The molds with the material confined therein are then subjected to a baking action which preferably takes place at a temperature in excess of six hundred degrees Fahrenheit. The pressure is retained. until the material hasthoroughly set in the molds after the baking operation is completed.

Material embodying my invention is readily distinguishable from the ordinary cork board not only by the tests hereinbefore mentioned, but also by its appearance. Not only at the surface, but throughout the mass the cork particles are much closer and in more uniform contact, causing the cork board to present a more regular and homogeneous appearance.

y invention provides a cork board in which structural strength is obtained at a considerably lower weight per unit mass of material than has heretofore been possible. By the term structural strength as used herein and in the claims, I mean sufiicient strength to enable the material to be selfsupporting and to be capable of practical use. For instance, with the cork boards heretofore known, when the weight per cubic foot was less than about eight and one-half pounds, the resulting product possessed substantially no structural strength and was incapable of practical use. The invention also,

tofore on the market is quite marked in this respect. The corkboards heretofore on the market show a very irregular surface, the particles being separated from each other to a very considerable extent by intermediate void spaces. In the new product, while there is occasionally a void space between the part of one expanded particle and the part of an adjacent expanded particle, these voids are comparatively few in number both at the surface and throughout themass. It is this comparative freedom from voids and the fact that the peripheral surfaces of most of the expanded particles are in close contact with and cemented to the peripheral surfaces of adjacent particles which I have reference to in characterizing the new product as one substantially free from voids.

I claim:

1. Cork board having a weight per cubic foot of less than seven and eight-tenths pounds, and possessing suflicient structural strength for practical use in cold storage structures, substantially as described.

2. Cork board having a Weight per cubic foot of less than seven and eight-tenths pounds, and having a tensile strength of not less than five pounds per square inch of cross section, substantially as described.

3. Cork board having, under the described conditions, a heat transmission of less than five B. U.s per square foot of one inch thickness in twenty-four hours for each degree Fahrenheit difference in temperature, by the described h0t+plate test, substantially as described.

4. Corkboard having, under the conditions described, a heat transmission of less than five B. T. /U.s per square foot of one inch thickness in twenty-four hours for each degree F. d iflerence in temperature by the described hot plate test, and having a Weight per cubic foot of less than seven and eighttenths pounds.

5. Corkboard having, under the conditions described, a heat transmission of less than five B. T. U.s per square foot of one inch thickness in twenty-four hours for each degree F. difference in temperature by the described hot plate test, and having a tensile strength of not less than five pounds per square inch of cross section.

6. Corkboard having, under the conditions section and described, a heat transmission of less than five B. T. U.s per square foot of one inch thickness in twenty-four hours for each degreeF. difference in temperature by the described hot plate test, and having a Weight per cubic foot of less than seven and eighttenths pounds, and a tensile strength of not less than five pounds per square inch of cross section.

7. A corkboard having a Weight per cubic foot of less than seven and eight-tenths pounds and substantially free from voids. 8. Corkboard having a tensile strength of not less than five pounds per square inch of cross section and substantially free from voids.

9. Corkboard having a Weight per cubic foot of less than seven and eight-tenths pounds and a tensile strength of not less than five pounds per square inch of cross which is substantially free from voids.

In testimony whereof, I have hereunto set my hand.

Witnesses FRED BOYLE, F. D. MILLER.

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