US3548522A - Foamed plastic paddle or vane - Google Patents

Description

Dec. 22, 1970 c, RQPER 3,548,52fi

FOAMED PLASTIC PADDLE OR VANE Filed Oct. 2. 19s? INVENTOR.

EDWARD CULLUM ROPER V 1 W/ZL1W% ATTORNEY United States Patent l 3,548,522 FOAMED PLASTIC PADDLE 0R VANE Edward Cullum Roper, Stamford, Conn, assignor to American Machine & Foundry Company, a corporation of New Jersey Filed Oct. 2, 1967, Ser. No. 672,331 Int. Cl. B32!) 3/26, 5/18; E01h 5/00 US. Cl. 37-43 5 Claims ABSTRACT OF THE DISCLGSURE A paddle or vane having a substantially unfoamed outer skin and a foamed inner core made by molding from a polyethylene having particular properties.

This invention relates to structural paddles or vanes. More particularly, the invention relates to structural paddles or vanes comprising high impact resistant, foamed polyethylene and suitable for use on snow removing apparatus, such as a snow blower, although such paddles or vanes can be used on other devices or for other suitable purposes depending upon the particular shape in which they are constructed. However, for the sake of simplicity the invention will be disclosed as it relates to paddles or vanes suitable for use on snow removing machines.

Presently most snow removing apparatus, such as snow blowers are normally equipped with single or multiple impeller vanes or paddles. Such paddles or vanes commonly react against the force provided by the inertia of the snow which is being removed. Consequently, these vanes or paddles are subjected to constant flexural stresses and at times to extremely high flexural impact shocks when they come into contact with ice patches, hidden boulders, logs or other like obstructions. As a result of the stresses to which such paddles or vanes are subjected, they have generally been constructed of tough metals, such as steel and/or alloys thereof, aluminum and/or alloys thereof and the like. However, when constructed of such metallic materials in order to obtain good strength and high impact resistance, the vanes or paddles must be made of relatively heavy gauge material which creates problems of excessive bulk and excessive weight, especially when they are to be used on snow blowing apparatus operated by an individual and normally used in clearing driveways, walkways, steps, porches and the like around private residences.

Attempts to construct suitable metallic paddles or vanes from lighter gauge materials such as aluminum, for example, on the other hand, result in low impact resistance and low strength. Consequently, they are easily bent or distorted from their original shape when subjected to normal usage. This is so even though the light weight material is satisfactory from a viewpoint of weight in utilization in the smaller type of snow blowing device used around private residences. Accordingly, there exists a need for the provision of impeller paddles or vanes, regardless of shape, suitable for such snow blowing apparatus as mentioned hereinabove and which paddles combine the lightness in weight of the light gauge metal vanes and paddles and the structural strength of the heavy gauge metal paddles and vanes.

The present invention fulfills this need by providing a snow blower paddle or vane having a substantially unfoamed outer skin aiid a foamed inner core made by molding from a polyethylene having particular properties.

In order to understand the present invention more fully, reference is made to the following description which is to be taken in conjunction with the accompanying drawing wherein:

FIG. 1 is a view in perspective of a snow blower 3,548,522 Patented Dec. 22, 1970 paddle or vane made in accordance with the invention;

FIG. 2 is an end view of the snow blower paddle of FIG. 1, and

FIG. 3 is a view in section taken along line 1--1 of PEG. 1 showing the foamed core and unfoamed outer s 1n.

Referring more particularly to FIG. 1, the snow blower paddle or vane illustrated there and generally designated by numeral 11 is molded from a linear polyethylene containing a foaming agent and having a bulk density of .75 gram per cubic centimeter based on a linear polyethylene having a specific gravity of .96, a weight average molecular weight of about 250,000, determined in any suitable known manner, and a melt index 1 at approximately 190 C. in a range of about .14 to about .22 as determined by ASTM test method D-1238. Like paddles or vanes can also be constructed from polyethylenes having a weight average molecular weight in excess of from about 250,000 up to about 8,000,000 or more, when such materials are available and the melt indexes thereof do not exceed about .3. In contrast, polyethylenes having weight average molecular weights of about 200,000 and below and specific gravities of below about .96 as well as melt indexes of .3 and above do not result in structural paddles or vanes having suitable properties with respect to strength when subjected to flexural impact shocks.

The paddle illustrated in FIG. 1 has the shape of a compound curve. More specifically, the illustrated paddle or vane 11 is molded so that it has a substantially vertical lip 12 for attachment to an axial supporting member (not shown) on a snow blowing apparatus. The vertical lip 12 is provided with a plurality of slots 13 which cooperate with screws, bolts or like means on the axial supporting member mentioned above.

Extending in a substantially horizontal direction with respect to the lip 12 is the main body portion 14. Body portion 14 may also slope slightly downwardly, if desired, as it extends horizontally and slopes sharply downwardly toward each side as shown at 15. Thus, the leading edge of the main body portion takes on a concave shape as shown at 16. Accordingly, the overall shape of paddle or vane 11 forms a scoop-like construction which vastly improves the eificiency in snow removing operations.

As shown more specifically in FIG. 3, the subject vane has a foamed core and a substantially unfoamed outer skin designated by numerals 17 and 18, respectively.

The density of the unfoarned outer layer or skin 18 is at least about 1.5 times the density of the central area of the cellular core 12. The dense outer layer generally may vary in thickness or depth from about 60 to about mils at the surface of the paddle or vane. Moreover, the density of the paddle increases from the central area of the core out towards the substantially unfoamed outer skin, giving a foam bulk density of about 40 to about 48 pounds per cubic foot in the final product and a density in a range of from about 30 pounds per cubic foot to about 38 pounds per cubic foot extending from the central core to the substantially unfoamed outer skin.

This particular type of foamed structure aids in providing the necessary strength while at the same time permitting required flexibility and also results in the distribution of force on impact with a solid article.

In contrast to like paddles or vanes made of steel and aluminum, paddles of this invention molded from the particular polyethylene described showed unexpectedly high impact resistance even at low temperatures. For example, metal vanes made of 2" gauge aluminum were easily bent and broken under the impact of a 10 pound weight dropped from a height of about 4 feet at temperatures of 20 C. and lower. Like paddles made of A gauge steel were also easily bent and broken under impact when subjected to the same tests.

In contrast, the paddles or vanes of this invention, when subjected to the same tests, did not bend or shatter. Vanes or paddles made of steel having comparable strength to the paddles of this invention were of /1 gauge material and weighed twice as much as the subject paddles.

A paddle or vane in accordance with this invention can be prepared by a suitable molding process wherein the high molecular weight linear polyethylene having a gas forming agent incorporated therein is either placed directly in a heated mold and brought to thermoplastic state in the mold or is rendered thermoplastic and then injected or fed into a mold in any suitable fashion. In carrying out the practice of the invention any thermally sensitive gas forming agent which liberates gas at the desirable temperature including solids, gases or liquid gas forming agents may be utilized. Suitable agents which can be employed to expand the high molecular weight polyethylene include, for example, water, air, carbon dioxide, nitrogen, Freon, azodicarbonamide, p,p-oxy-bis- (benzene sulfonyl hydrazide), diazoaminobenzene, nitroguanidine, N,N-dinitrosopentamethylenetetramine, azobisformamide, azobisisobutyronitrile, N,N' dimethyl- N,N'-dinitrosoterephthalamide, benzene sulfonyl hydrazide, benzene-1,3-disulfonyl hydrazide, diphenylsulfon- 3,3'-disulfonyl hydrazide, 4,4'-oxy-bis-(benzene sulfonyl hydrazide), ammonia blowing agents, such as, urea, biuret, ammonium carbonate and the like, petroleum ether, butane, n-pentane, isopentane, neopentane, isobutane, hexane, heptane and the like, the perchlorofluorocarbons, such as, trichlorofluoromethane, symmetrical tetrachlorodifiuoromethane, 1,1,2-trichloro 1,2,2 trifluoroethane, symmetrical dichlorotetrafluoroethane, 1-chloro-1,1,2,2,2- pentafluoroethane, 1-chloro-1,2,3,3,4,4 hexafluorocyclobutane, 1,2-dichloro-1,2,3,3,4,4 hexafluorocyclobutane and the like. Mixtures of any two or more of the gas forming reagents can also be utilized. Among the agents mentioned above, however, azodicarbonamide is a preferred gas forming material.

The amount of gas forming agent utilized is dependent upon the extent to which it is desired to expand the thermoplastic linear high molecular weight polyethylene. Generally, in order to obtain paddles or vanes having the desirable cellular structure and consequently the desired density requirements, only a relatively small amount of the gas forming agent is needed, generally about 0.25 percent by weight, based on the weight of the thermoplastic polymer, being at least sufiicient and up to as much as about 2.0 percent by weight. In a few instances the amount of gas forming agent needed may be equal to or exceed 4 percent by weight of the thermoplastic polymer.

As mentioned hereinabove, the preparation of paddles or vanes in accordance with this invention can be accomplished by any suitable molding procedure. Howev r, one preferred procedure involves the extrusion of the thermoplastic polyethylene in a screw type injection molding apparatus under pressure at least sufficient to prevent expansion of the gas forming agent and at temperatures at least sufficient to decompose the gas forming agent and melt the thermoplastic material after which the plastic melt is injected at a lower pressure, preferably atmospheric, into a suitable mold. By this particular process the normally solid thermoplastic polymer, generally having been premixed with a sufiicient amount of solid gas forming material is fed to the extruder in the form of a flake or pellet. In the first section of the screw as the resin is rotated, it tends to stick to the barrel as it is pushed forward by the flights on the screw. Plasticization begins at that point when the resin particles start to adhere to each other, to the screw and to the barrel. Heat from the barrel as well as from the fiuxing of the polymer particles by the screw contribute to the elevation of the temperature, making it sufficiently high to melt the polymer. The term fiuxing as employed herein refers to the melting of the solid polymer particles so that they run together and coalesce with each other and are likewise forced against the surfaces of the screw and the barrel. This fluxing causes a deforming and shearing action and the heat caused thereby reduces the polymer to a molten state.

During this plasticizing process, the polyethylene goes through a phase change from a solid to a viscous melt while at the same time a compacting phase takes place as the bulk density is increased and as the pressure builds up. While under compression the homogeneous mass is prevented from expanding. The plasticization can take place in both the feed and transition or compression zones of the extruder. However, it should be complete by the end of the transition zone at which time the polymer should be in the form of a uniform melt.

The last section of the screw type extruder is the metering section in which the channel depth of the screw is at its smallest and is constant for about four turns, thereby providing a measured amount of uniform polymeric melt which is pumped out of the extruder barrel and into a suitable mold at a uniform rate. It is generally in this last section of the screw extruder that it is most advantageous to decompose the gas forming agent or in those instances where the agent is already in the form of a gas to add it to the polymeric melt.

The screw extruder is designed to provide sufficient time for heating of the polymer at each successive stage and also is designed with sufficient capacity in length to hold a number of charges. Accordingly, it is kept filled by metering the feed either by volume or by weight to balance exactly the amount delivered into the mold.

The polymeric melt is then injected by axial reciprocation of the screw into a suitable mold. The temperature of the mold is in excess of about 60 C. preferably at about C. so that on molding of the material the expanded gas formed by the gas forming agent is squeezed toward the center of the paddle or vane and leaves a well formed substantially unfoamed protective polyethylene layer around a cellular core. Paddles or vanes so produced have excellent strength as mentioned hereinabove in comparison to those made from steel and aluminum. Moreover, such paddles or vanes are remarkably light in weight and due to their strength have a greatly improved service life when compared to the life of metallic paddles. Furthermore, the subject paddles and vanes have a good hard smooth void-free outer layer. Such a surface reduces the sticking of snow to the surface of the paddle.

Numerous other advantages of this invention will be readily apparent to those skilled in the art.

It will be apparent to those skilled in the art that various modifications of the invention may be made without departing from the spirit and scope thereof. Accordingly, the invention is not to be limited except as defined in the appended claims.

What is claimed is:

1. A scoop-like paddle having a substantially unfoamed outer skin and a foamed inner core, high impact strength and structural flexibility molded from a linear polyethylene foam having a bulk density of approximately .75 gram per cubic centimeter based on a linear polyethylene having a specific gravity of about .96, a weight average molecular weight in excess of about 250,000 and a melt index 1 at approximately C. in a range of about .14 to about .22, said paddle having a density which increases from the center of the core to a maximum at the substantially unfoamed outer skin, the main body portion of said paddle having the shape of a compound curve extending substantially horizontally outwardly from a substantially vertical lip and sloping downwardly toward each side, the leading edge of said main body portion forming a concave shape.

2. A paddle as defined in claim 1 wherein the unfoamed outer skin extends inwardly to a depth in a range of 60 to 90 mils toward the center thereof.

3. A paddle as defined in claim 1 wherein the density is in a range of about pounds per cubic foot to about 38 pounds per cubic foot extending from the central core to the substantially unfoamed outer skin.

4. A paddle as defined in claim 1 wherein the bulk foam density is in a range of about 40 to about 48 pounds per cubic foot.

5. A scoop-like snow blower paddle having a substantially unfoamed outer skin having a thickness of about to about mils, a foamed inner core, high impact strength and structural flexibility molded from a linear polyethylene having a bulk density of approximately .75 gram per cubic centimeter based on a linear polyethylene having a specific gravity of about .96, a weight average molecular weight of about 250,000, a melt index I at approximately C. of about .2, a bulk foam density in a range of about 40 to about 48 pounds per cubic foot and a density in a range of about 30 pounds per cubic foot to about 38 pounds per cubic foot extending from the central core to the substantially unfoarned outer skin,

the main body portion of said paddle having the shape of a compound curve extending substantially horizontally outwardly from a substantially vertical lip and sloping downwardly toward each side, the leading edge of said main body portion forming a concave shape.

References Cited UNITED STATES PATENTS ROBERT F. BURNETT, Primary Examiner W. A. POWELL, Assistant Examiner US. Cl. X.R.

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