US3680975A

US3680975A - Roll pump for highly viscous material

Info

Publication number: US3680975A
Application number: US2854A
Authority: US
Inventors: William F Smith; John H Mitchell; William M Edwards; Phillip W Cox
Original assignee: Dow Chemical Co
Current assignee: Dow Chemical Co
Priority date: 1970-01-14
Filing date: 1970-01-14
Publication date: 1972-08-01
Anticipated expiration: 1989-08-01

Abstract

Highly viscous material, e.g., a molten plastic, is rapidly removed from a reservoir with a roll pump positioned in an opening of the reservoir. The roll pump has a shaft extending through the opening into the reservoir and rotatable within a stationary feed member, e.g., a modified double right helix mounted within the reservoir near the opening. The helix is sufficiently open to the viscous material such that the latter flows through the helix to the shaft. The turning shaft and the open stationary member cooperate to direct the viscous material near the shaft through the opening in the reservoir.

Description

United States Patent Smith et al. 45 Aug, 1, 1972 [54] ROLL PUMP FOR HIGHLY VISCOUS 1,859,290 5/1932 Davis ..222/241 .MATERIAL 2,467,682 4/ 1949 Megargee ..415/72 [721 inventors: William F. Smith; John H. Mitchell, FOREIGN PATENTS OR APPLICATIONS both of Lake Jackson; William M. Ed d Freeport; illi w 20,573 7/1929 Netherlands ..415/72 Brazoria of Tex Norway l 3 [73] Assign: Chemical Company Primary Examiner-Henry F. Raduazo I Mlch' Attorney-Griswold & Burdick, R. G. Waterman, L. J. 22 Filed; Ja 14, 1970 Dankert and M. S. Jenkins Highly viscous material, e.g., a molten plastic, is if i "415/ %,23932 g g rapidly removed from a reservoir with a roll pump g i 12 12 positioned in an opening of the reservoir. The roll 1 e o c 413/183 71 pump has a shaft extending through the opening into the reservoir and rotatable within a stationary feed member, e.g., a modified double right helix mounted [56] References C'ted within the reservoir near the opening. The helix is suf- UNITED STATES PATENTS ficiently open to the viscous material such that the latter flows through the helix to the shaft. The turning 2,910,726 11/1959 Parshallet a1. ..18/12 SM Shaft and the open stationary member cooperate to Van Z0 di t th viscous t i l near th th gh th 3,559,240 2/1971 Kosmsky et a1 ..415/72 opening in the reset-vein I 161,621 4/1875 Maxim ..415/72 1,814,175 7/1931 Miller ..415/74 9 Claims, 4 Drawing Figures ROLL PUMP FOR HIGHLY VISCOUS MATERIAL BACKGROUND OF THE INVENTION This invention relates to apparatus for pumping highly viscous materials, and more particularly, to a pumping apparatus for removing such materials from a reservoir or other container.

In the production of plastic polymers and their fabrication into a wide variety of shaped articles, e.g., films, bottles, sheets, containers, etc., it is often necessary to remove molten polymer from a hopper or similar feed reservoir through an opening in said reservoir of somewhat smaller diameter than the reservoir. It is often desirable to move the highly viscous polymer into a second vessel or a polymer transfer or compression apparatus enclosed in a vessel having smaller diameter than that of the reservoir. For example, in the production of polymers such as polyolefin, polyamides and the like, the raw polymer product often contains volatile impurities which are advantageously separated from the polymer with a polymer devolatilizing apparatus, often called a devolatilizer. In such apparatus, the raw polymer product is heated in a container of relatively large diameter to a molten state and worked, usually by stirring, to urge the impure vapors from the molten polymer. Following devolatilization, it is usually desirable to move the molten polymer into a polymer transfer or compression means for fabrication. The column or conduit which usually encloses the transfer or compression device is generally of somewhat smaller diameter than that of the devolatilizer, thereby creating difficulty in the moving molten polymer from the devolatilizer to the transfer or compression device.

In view of these problems, it would be highly desirable to provide a pumping apparatus capable of rapidly removing highly viscous materials from a reservoir through an opening in the reservoir of somewhat smaller diameter than the reservoir.

SUMMARY OF THE INVENTION In accordance with the present invention, rapid removal of a highly viscous material from a reservoir through an opening of smaller diameter than that of the reservoir is accomplished by a roll pump positioned proximate to said opening. The roll pump comprises (a) a drive means for rotating a body; (b) a rotatable body connected to the drive means and extending through the opening of the reservoir to a distance within the reservoir sufficient for the body to contact viscous material therein, the outside diameter of said body being such to permit passage of said viscous material through the space between said body and the portion of said reservoir defining said opening; and (c) a stationary feed means mounted within said reservoir and proximate to said body and said opening. Rotation of the body causes the feed means to scrape viscous material from said body and to force said scraped viscous material through the space or spaces between said body and the portion of said reservoir defining said opening. Advantageously the rotatable body is rotatably disposed within the feed means.

The roll pump of the present invention is particularly useful in supplying molten polymer from a polymer reservoir to a second vessel such as a polymer transfer apparatus for removing the polymer to an extruder, pelletizer or other polymer fabrication means. Said roll BRIEF DESCRIPTION OF THE DRAWINGS In the drawings, various forms of the invention are shown, but it is to be understood that it is not limited to such forms since the invention as set forth in the claims may be embodied in a plurality of forms.

In the drawings:

FIG. I is a vertical sectional view of one embodiment of the roll pump as employed in a conventional polymer devolatilizer.

FIG. 2 is a vertical sectional view of a second embodiment of the roll pump as employed in a conventional polymer devolatilizer.

FIG. 3 is a vertical sectional view of a third embodiment of the roll pump.

FIG. 3A is a top view of the roll pump of FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENTS With reference to FIG. 1, the invention is shown in an apparatus which is a polymer devolatilizer in combination with a polymer transfer device. Accordingly, the apparatus of FIG. 1 has a generally upright column 3 with devolatilizing zone 5 as a reservoir for the mo]- ten polymer, feed zone 7 and transfer zone 9 in a topto-bottom alignment. Column 3 tapers conically from devolatilizing zone 5 into the feed zone 7. An inlet 4 for receiving raw polymer into devolatilizing zone 5 and an exhaust port 6 for vapor separated from the molten polymer in devolatilizing zone 5 are located adjacent to the top of column 3. Transfer zone 9 includes an opening 8 adjacent to feed zone 7 through which polymer passes from feed zone 7 to transfer zone 9, a driven screw 11 extending lengthwise of the transfer zone portion of the column 3, and an outlet I3. Screw 11, driven by a driving means 12, moves material downwardly through the transfer zone and to outlet 13 adjacent to the bottom of column 3. Outlet 13 can be connected to a polymer fabricating apparatus such as a pelletizer, an extruder or compression molding apparatus. A roll pump 15 is situated vertically in feed zone 7. The roll pump 15 has as a stationary feed means a modified double right helical member 17, the

flights

29 and 30 of which having downwardly extending flanges 25 affixed to the outer edges thereof. A circular support collar 27 is affixed about the middle of said helical member 17 at the point where one flight 29 of said member 17 ends. The remaining flight 30 extends above said collar. The helical member 17 is rigidly mounted in feed zone 7, the axis of said member 17 extending lengthwise of column 3. As a rotatable body the roll pump has a smooth surfaced shaft 19 rigidly mounted on the upper end of driven screw 11, said shaft 19 extending lengthwise from said screw 11 and upward into feed zone 7 to a point above helical member 17. The smooth surfaced shaft 19 is rotatably disposed within helical member 17 with running clearance between shaft 19 and nearest edges of

flights

29 and 30.

In operation as screw 11 is rotated to move molten polymer downwardly through transfer zone 9, shaft 19 rotates causinghelical member 17 to scrape molten polymer from shaft 19 and to force the scraped polymer downward through opening 8 into transfer zone 9.

FIG. 2 depicts a combined polymer devolatilizer and polymer transfer device similar to that illustrated in FIG. 1.- In the roll pump 15 of FIG. 2, the stationary feed means is a partially enclosed single turn right helix 170 having a single flight 29 extending from opening 8 upwardly into the feed zone to a point above shaft 19. Helix 170 has a partially enclosing cylindrical wall 31 affixed to the outer edge of flight 29, wall 31 extending generally upward from opening 8 to flight 29. In operation, shaft 19 rotates causing flight 29 to scrape molten polymer from shaft 19 and to force the scraped polymer downward through opening 8 into transfer zone 9. There is running clearance between shaft 19 and the nearest edge of flight 29.

In embodiments wherein the stationary feed means is a helical member, the pitch of the flight or flights of said member is not critical; however, the pitch is advantageously in the range of from about to about 85. It is not critical that the flight or flights be entirely open to the reservoir. In fact, it is generally desirable that the flight or flights be partially enclosed in order to inhibit the viscous material within the flights from returning to remaining mass of material from whence it came. It is only critical that the flight or flights be open with curves downward along the outside surface of the shaft 19. In FIG. 3 four scraping pieces 17b are positioned equidistance along a circle circumscribing shaft 19 such that there is running clearance between shaft 19 and scraping edges 38.

Rotation of shaft 19 causes pieces 17b to scrape viscous material from shaft and force material trapped to the reservoir at some point so that the rotating body can contact the viscous material such that the material is drawn into the flights.

While the dimensions of the roll pumps illustrated in FIGS. 1 and 2 and are not critical, they are somewhat dependent on the capacity of the transfer means to be fed. Illustratively, for a transfer means having a driven screw with 3.5 inch diameter, 21 inch length and 30 flights of 0.2 inch X 3/16 inch at 1% inch lead enclosed in a column having 3.503 inch inside diameter, the rotatable shaft of the roll pump has a diameter from about l k to about 4 inches and a length of from about 2 to about 24 inches. The helically shaped member, i.e., the modified double right helical member, the partially enclosed right helix, or similar helical member, has an inside diameter from about 1 $4 to about 6 inches and length from about 2 to about 24 inches. A roll pump having these dimensions is capable of feeding molten polymer or similar viscous material having a melt flow viscosity of 0.5 decigrams/minute [ASTM D-l238-5T(E)] at a rate of to pounds/hour when the shaft is rotated at a rate of 3 to 15 revolutions per minute.

FIG. 3 illustrates a roll pump in accordance with this invention having a plurality of scraping pieces 17b as the stationary feed means and a rotatable shaft 19 rotatably disposed within scraping pieces 17b. Each scraping piece 17b has a surface 32 generally facing the direction of rotation of shaft 19, surface 32 slanting away from the direction of rotation when proceeding from top to bottom along the axis of rotatable shaft 19. Scraping pieces 17b have an outside wall 37 running generally parallel to shaft 19, and afiixed to slanting surface 32 to provide pieces 17b with scoop-like structure. Each scraping piece 17b has a scraping edge 38 in the space defined by

walls

32 and 37 and shaft 19 downward toward an opening in the reservoir.

FIG. 3A illustrates, by way of a top view, the roll pump of FIG. 3 by depicting the direction of rotation of shaft 19 and position of scraping pieces.

In respect to the embodiment illustrated FIGS. 3 and 3A, it is understood that more or less than four scraping pieces could be employed or that pieces of different shapes and sizes could also be used. In this embodiment the critical feature is that the scraping piece or pieces have a surface facing the direction of rotation, said surface slanting away from direction of rotation when proceeding along the axis of rotatable member in the desired direction of viscous material flow.

More generally defined, the roll pump of this invention comprises (1) a feed means which is a stationary member defining a static shear face and (2) a rotatable body defining a second shear face. The stationary member and rotatable body are positioned to define a shear gap such that upon rotation of the body the static shear face of the stationary member scrapes viscous material in the shear gap from the second shear face and simultaneously forces the scraped material along the axis of the rotatable body. Simultaneous with movement of the scraped viscous material, viscous material near the material removing end of the rotatable body is drawn into the shear gap to fill the space left by material previously moved along the axis of the rotatable body. In this manner the viscous material is continuously moved through the roll pump.

In all embodiments of this invention, there must be at least running clearance between the rotatable member and the stationary feed means. In the case of rather large reservoirs and large pumps, the clearance between rotatable member and feed means may be several inches. Preferably, the clearance is from running clearance to about one half inch.

The stationary member, i.e., the stationary feed means, can have any of a variety of shapes which provide a static shear face which can cooperate with the shear face of the rotatable body to move viscous material along the axis of said rotatable body. For example, in addition to the stationary feed means illustrated in FIGS. 1-3, the stationary member can be a single right helix in which case the rotatable body is disposed within the helix such that the axis of the rotatable body extends along the same direction as the axis of the helix, preferably the rotatable body and the helix are coaxial. In another embodiment the stationary feed means is a plurality of scoops similar to the scraping pieces of FIG. 3 except that the static shear faces of the scoops are in the same plane as the axis of rotation. The static shear face of the stationary member can be smooth or rough and consists of any material sufiicient to withstand the conditions used in pumping the viscous material. Although not required, it is preferred that the shear face be a smooth surface and consist of a substance, e.g., polytetrafluoroethylene and the like, which is not adhered to by the viscous material.

' agonal shaped shaft, or the like. The surface of the rotatable body can be smooth, roughened, contoured or the like and be made of any substance which the viscous material to be pumped will adhere to. A smooth surfaced shaft is generally preferred.

The roll pump of the present invention is useful in moving highly viscous materials such as molten polymers of olefins, unsaturated amides, unsaturated esters, vinyl aromatic compounds and the like and other materials which exhibit relatively high viscosities. Accordingly such viscous polymers or other viscous materials can be moved in a rapid continuous manner along either a vertical or horizontal plane. Other inherent advantages and analogous embodiments will occur readily to those skilled in the art and the extent of the invention is accordingly intended to be limited only by the scope of the appended claims.

What is claimed is:

1. In a reservoir for highly viscous material having an opening through which the viscous material can be passed, a roll pump for pumping the viscous material through said opening, said pump comprising a. a drive means for rotating a body;

b. a rotatable body connected to the drive means and extending through said opening and into said reservoir to a distance within said reservoir sufficient for the body to contact viscous material therein, the outside diameter of said body being such to permit passage of said viscous material through the space between said body and the portion of said reservoir defining said opening;

. a stationary feed means mounted within said reservoir proximate to said body and said opening whereby rotation of said body causes said feed means to scrape viscous material from said body and to force said scraped viscous material through the space between said body and the portion of said reservoir defining said opening.

2. The roll pump according to claim 1 wherein the feed means is a stationary member defining a static shear face and the rotatable body defines a second shear face, said member and said body being positioned to define a shear gap such that rotation of said body causes said static shear face to scrape viscous material in said shear gap from said second shear face and simultaneously force scraped material along the axis of said rotatable body.

3. The roll pump according to claim 2 wherein the feed means is a generally helically shaped member.

4. The roll pump according to claim 3 wherein the helically shaped member is a right helix.

5. The roll pump according to claim 3 wherein the helically shaped member is a partially enclosed helix whereby the scraped viscous material is substantially prevented from rejoining the remaining viscous material in said reservoir.

6. [n a reservoir for highly viscous material having an opening through which the viscous material can be passed, a roll pump for pumping the viscous material through said opening, said pump comprising a. a drive means for rotating a body;

b. a rotatable body connected to the drive means and extendin throu b said 0 enin and into s 'd reservoir to a d1s%ance Wlth lIl sal d reservoir suffcient for the body to contact viscous material therein, the outside diameter of said body being such to permit passage of said viscous material through the space between said body and the portion of said reservoir defining said opening;

. a double right helix mounted within said reservoir proximate to said body and said opening whereby rotation of said body causes said helix to scrape viscous material from said body and to force said scraped viscous material through the space between said body and the portion of said reservoir defining said opening.

7. The roll pump according to claim 6 wherein the double right helix has flights partially enclosed by flanges mounted along the outer edges of said flights, and extending generally parallel to the axis of said helix.

8. The roll pump according to claim 1 wherein the feed means comprises at least one stationary scraping piece having a shear face generally facing the direction of rotation, said surface slanting away from the direction of rotation when proceeding along the axis of said rotatable body in the desired direction of viscous material flow.

9. The roll pump according to claim 8 wherein the stationary scraping piece has a surface generally parallel to the axis of said rotatable body and extending away from the shear face in the desired direction of viscous material flow.

Disclaimer 3,680,975.William F. Smith and J 07m H. Mitchell, both of Lake Jackson; William M Edwamls, Freeport, and Phillip W. 0000, BIZLZOI'lEL, Tex. ROLL PUMP FOR HIGHLY VISCOUS MATERIAL. Patent dated Aug. 1, 1972. Disclaimer filed Mar. 17, 1975, by the assignee, The Dow Chemical Company. Hereby enters this disclaimer to claims 1-4 of Said patent.

[Oyficial Gazette August 10, 1976.]

Claims

1. In a reservoir for highly viscous material having an opening through which the viscous material can be passed, a roll pump for pumping the viscous material through said opening, said pump comprising a. a drive means for rotating a body; b. a rotatable body connected to the drive means and extending through said opening and into said reservoir to a distance within said reservoir sufficient for the body to contact viscous material therein, the outside diameter of said body being such to permit passage of said viscous material through the space between said body and the portion of said reservoir defining said opening; c. a stationary feed means mounted within said reservoir proximate to said body and said opening whereby rotation of said body causes said feed means to scrape viscous material from said body and to force said scraped viscous material through the space between said body and the portion of said reservoir defining said opening.

6. In a reservoir for highly viscous material having an opening through which the viscous material can be passed, a roll pump for pumping the viscous material through said opening, said pump comprising a. a drive means for rotating a body; b. a rotatable body connected to the drive means and extending through said opening and into said reservoir to a distance within said reservoir sufficient for the body to contact viscous material therein, the outside diameter of said body being such to permit passage of said viscous material through the space between said body and the portion of said reservoir defining said opening; c. a double right helix mounted within said reservoir proximate to said body and said opening whereby rotation of said body causes said helix to scrape viscous material from said body and to force said scraped viscous material through the space between said body and the portion of said reservoir defining said opening.