US 3155376 A
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Description (OCR text may contain errors)
Nov. 3, 1964 w. MLLENBRUCK MIXING AND AGGLOMERATING DEVICE FOR THERMOPLASTIC MATERIAL Filed Oct. 4. 1960 @rra/evers' UnitedStates Patent 3,155,376 MIXING AND AGGLOMERATING DEVICE FOR THERMOPLASTIC MATERIAL Wolfgang Mllenbruck, Hemmingen, Kreis Leonberg,
Germany, assigner to `Werner & Piieiderer, Stuttgart- Feuerbach, Germany, a German company Filed ct. 4, 1960, Ser. No. 60,397 f Claims priority, application Germany, Oct. 17, 1959,
W 26,566 3 Claims. (Cl. 259-43) The present invention relates to devices for mixing powderized or granular material, and more particularly to devices for mixing and iagglomerating powderized thermoplastic material and a liquid such as a softener.
Devices of this kind yas heretofore known, generally comprise a cylindrical mixing vessel, the bottom of which is smoothly faired into the cylindrical wall, a rotary agitator disposed closely adjacent to the bottom and supported by a drive shaft parallel with the vessel axis, and a discharge duct. It is also knownto provide within the mixing vessel stationary baiiie pins coacting with the rotary agitator for the purpose of increasing the efficiency of the devices. None of such and similar designs have been found as eiiicient as desirable.
It is the broad object of the present invention to provide a novel and improved device of the general kind above referred to, which has a high mixing eliiciency and also a high thermal efficiency. Such efiiciency is attained by arranging the agitator and also the discharge duct in accordance with the invention.
in devices of the kind here involved lit is important that the elevation of the temperature which is required to effect agglomerati-on of the thermoplastic material is produced reliably, rapidly and uniformly. It is further important that when the agglomeration of the material has progressed to the desired extent the material is discharged from the device as rapidly as possible so that the desired granular sizeof the Iagglomerated material is preserved, or in other words that further progress of the agglomeration is arrested. t
The inventor has found that the rate 0f the circulation of the material within the mixing vessel, that is, the peripheral upward movement ofthe material and the central downward movement towards theY agitator should be as high as possible. Whenthe rate of the velocity of the material movement is high, the material experiences a correspondingly high frictional resistance while lascending along the cylindrial wall of the vessel and such resistance causes a sharp drop of the velocity in radial and tangential directions. Furthermore, a high velocity of the material movement results in a correspondingly high number of passages of the material past the agitator during any given period of time. As a consequence, the material has comparatively little time to transfer the heat ywhich is generated within the material primarily during its passage of the agitator, to the wall of the vessel and into the air filling the free space between the material and the cover of the vessel.
As is now evident, a sharply dropping velocity of the material movement and a high passing frequency at the agitator coact to afford the advantages of a short mixing time and a rapid elevation of the temperature of the material due to the powerful frictional forces active within the material.
Accordingly, it is a more specific object of the invention to provide a novel and improved device of the general kind above referred to, which is designed to impart to the material to be treated ya high circulation velocity within the vessel and to force the material past the agitator at a high rate of repeat.
It is a still further object of the invention to provide a novel and improved device of the general kind above referred to, in which the Iaforesaid high circulation velocity and high passing rate at the agitator are attained by means of a comparatively low driving force and which is very simple :and rugged in design.
As explained before, it has been attempted to increase the eiciency of mixing devices of the kind here involved by providing stationary counterbafes. Such bailles are no longer necessary in a device according to the invention and would even have an adverse effect in such device.
Broadly speaking, the invention resides in providing an agitator, including a novel and improved blade or scoop wheel capable of lifting the material within the vessel sutiicient to maintain the aforedescribed high rate of circulation velocity of the materialy even at temperatures above 80 C. The provision of the aforementioned stationary baffles would impede a high circulation velocity by constituting obstructions to a rapid ow of the material within the vessel, thus causing an increase of the required driving power and such batfies also tend to dissipate the heat generated in the material due to being thermo-conductively connected to the vessel.
Numerous tests with a mixing and yagglomerating device according to the invention have fully borne out the aforestaterl theoretical considerations. For instance, 30 kg. of suspensions-PVC (polyvinylchlorid) including l5 kg. of a softener such as dioctylphthalat fed into a cold device (device started at a room temperature of about 20 C.) were heated from 20 C. to 150 C. in about eight minutes, without any formation of heavy and undesirableA lumps.
Other and further objects, features and advantages of v the invention will be pointed out hereinafter and set forth in the appended claims forming part of the invention.
in the accompanying drawing a preferred embodiment of the invention is shown by way of illustration and not by way of limitation.
v inafter, is mounted on and driven by a drive shaft 3 disposed coaxially with the axis of the vessel. The drive shaft is shown as entering the vessel through the bottom thereof, but it can also enter the vessel from the top thereof or any other suitable driving arrangment may be provided. A discharge duct 4 communicates with the vessel. The arrangement of the discharge assembly will also be more fully described hereinafter.
The agitator comprises a blade or scoop wheel disposed elosely adjacent to the bottom of the vessel and parallel therewith. The blade or scoop wheel comprises a hub or boss 5 seated on shaft 3, a ring 6 disposed coaxially with shaft 3 and a plurality of blades or scoops 7 and 8. The blades are circumferentially disposed and alternately of different radial length. The long blades 7 are suitably secured, for instance, by welding to hub 5 and extend from the hub close to the periphery of the vessel and more speciiically to the rounded por-tion 2 thereof. The long blades support ring 6 concentric with hub 5. The ring may be secured tothe blades in any suitable manner, such as welding. As is apparent, the ring divides each long blade 7 in a radially inward portion 7a and a radially outward portion 7b. The short blades terminate at ring 6 to which they are secured and extend from the ring outwardly close to the periphery of the vessel and more specifically to the rounded portion 2' Patented Nov. 3, 1964 3 thereof. As is apparent, the provision of alternating long and short blades leaves sufficiently clear space within the center portion of the vessel to permit a substantially unimpeded circulation of the thermoplastic material along the flow lines indicated by arrows 9 and 9 when the agitator is rotated. VEach of the blades or scoops 7 and 8 has a blade angle ,62 of 80 to 90. The angle of pitch a of the blades may be within the range of 1 to 90. The pitch of blades 7 is so selected that the height h thereof reaches about the level at which the rounded portion 2 joins the cylindrical portion 1. The radially inward portion of blades 7 has a reduced height h', preferably a height which is about one half of the height Iz. The short blades d have a reduced height in reference to the radially outward portion of blades 7. The height of blades 8 may be approximately the same as the height of h of blades '7.
The discharge duct 14 is disposed perpendicularly of the axis of vessel portion 1, or in other words, horizontally when the vessel is arranged in upright position. The duct communicates with the vessel tangenti-ally as can be clearly seen in FlG. 2 and preferably the center axis of duct 4 is tangential to an imaginary circle 11 intermediate vessel wall 1 and ring 6. The radius of circle 11 may be arbitrarily selected within the range defined by Vthe radius of cylinder wall 1 and ring 6.
The discharge duct can be opened and closed by means of a closure means which comprises a closure member 14 which is movable between a closing position 'd' and an open position 4". The surface of the closure member facing the inside of vessel 1 has a configuration such Y that said surface is substantially Hush with the correspending inner wall surf-ace of wall portion 2 when member 14 is in its closing position so that the closure member does not obstruct the circulation of the material within the vessel. In the open position 41of the closure meniber 14 the same uncovers access to a discharge conduit 13, the angle of which is so selected that the material entering duct 14 is directly guided into conduit 13 as is indicated by an arrow in FIG. 2.
' The position of the closure member 14 may be controlled by any suitable means. There is indicated a linkage 15 which in the full line position opens the discharge duct and in the dotted line position closes the duct. Of course, the opening and closing of the duct can also be controlled by pneumatic or electromagnetic means. Various such manually or automatically operated actuating means are well known in the art and do not constitute part of the invention.
While the invention has been described in detail with respect to a certain now preferred example and embodiment of the invention, it will be understood by those skilled in the art after understanding the invention, that various changes and modifications may be made without departing from the spirit and scope lof the invention, and it is intended, therefore, to cover all suchV changes and modifications in the appended claims.
What is claimed as new and desired to be secured by Letters Patent is:
l. A device for mixing and agglomerating pulverized thermoplastic material and liquid, said device comprising a cylindrical mixing vessel having 'a bottom faired into the cylindrical wall of the vessel by a rounded wall portion, a rotary agitator, and a drive shaft for said agitator disposed parallel with the axis of the vessel and supporting the agitator closely adjacent to the bottom of the vessel parallel thereto, said agitator including a hub receiving said shaft, a plurality of long blades supported on said hub in circumferentially spaced arrangement and extending from the hub close to said rounded wall portion, a ring secured to said long blades intermedi-ate the radial length thereof and disposed coaxially and substantially co-planar with said hub, a plurality of short blades secured to said ring lalternating with said long blades and extending radially outward, each of said long blades having radi-ally outward of said ring a blade angle of about to 90 anda pitch angle within the range of 1 to 90 and a height approximately equal to that of said rounded wall portion, the portionof the long blades radially inward of said ring having a reduced height and extending substantially parallel to the bottom of the vessel, each of the short blades having a height less than the radially outward height of the long blades, a discharge duct communicating with said vessel near the bottom thereof and radi-ally outward of said ring, and closure means in said duct for selectively opening and closing the same.
2. A device according to claim l wherein the height of the portion of the long blades radially inward of said ring is about half the height of the portion of the long blades radially outward of said ring, and wherein the short blades have approximately the same height as the radially inward portion of the long blades.
3. A device according tov claim l wherein said discharge duct is mounted to deine approximately a right angle with the axis of the vessel and is tangentially connected to the cylindrical portion of the vessel.
References Cited in the tile of this patent rUNITED STATES PATENTS 644,649 Walter Mar. 6, 1900 835,672 Franklin Nov. 13, 1906 2,268,038 Knittel Dec. 30, 1941 2,945,634 Beck et al. July 19, 1960 FOREIGN PATENTS 571,627 Canada Mar. 3, 1959