CA1069549A - Method of removing an article from a chamber having a reduced pressure therein - Google Patents

Abstract

ABSTRACT

A method of removing an article from a chamber having a reduced pressure therein by connecting the chamber to a pool of liquid by a barometric leg is disclosed. The method provides a conveyor in said barometric leg and allows said article to float up into engagement with said conveyor so that the force exerted on the article by the conveyor moves the article down into the pool of liquid and out into the atmosphere.

Description

GENERAL STATEMENT OF INVENTION j ' 11 A need has existed for a method of removing materials ¦
12 from pressures lower than atmospheric pressure'on a continuous 13 basis. Earlier teachings show me hods of acc~mplishing this 14 task, b~t only at the expense of grasping the material, which will .
henceforth be,called a "workpiece", and applying sufficient tensil-16 force on the workpiece to withdraw it from the reduced pressure.
17 Certain of these earlier ~eachings show the workpiece being with- ¦
18 drawn through a "vacuum seal" such as a rubber diaphragm; others ¦
19 show the work~iece being pulled out of the reduced pressure down through a barometric leg, around a pulley and into the atmosphere.
21 A11 these earlier tea~hings have merit for certain applications., , , - Some workpieces will not tolerate the tensile orce ,23 nec,essary to extract the workpiece from reduced pressure. One 24 example of this kind of workpiece is thermoplastic foamj freshly extruded polystyrene foam at or below densities of about 1.5 pound 26 per cubic foot (PCF) is very soft an,d,fragile such that it is 27 adversely affected when withdrawn from reduced pressure by virtue 28 of its own tensile strength. ;
This invention teaches a method of extracting a work-piece from reduced pressures through a liquid seal providing only ¦
81 that the work piece is lighter than the liquid such that the work-¦
¦piece i uoyed up, or float-, when i=mersed in the liquid. ¦
~' ~. - ~1 . ~ 1'' .: , ' . ' .. . .
- .
- , ' '~ '~ :, , ' .. . . . . .
:. . ,. .: .
, ", : ., . - ..

106~549 This unique and novel method applies no tensile forces on the workpiece so that the most ~ragile workpiece may be recovered through the practice of this invention.
The basic principle of the invention is simply that the workpiece is gently submerged in the liquid as the workpiece leaves the domain of reduced pressure and is submerged further and further until, finally, at some depth in the liquid the r pressure being experienced by the workpiece is equal to atmospheric pressure whereupon the workpiece is released into the atmosphere.
Everyone is familiar with the fact that water will be "sucked up" into a pipe if the lower end is placed in water - and the upper end is evacuated of air; the more air which is evacuated, the higher the water will rise until finally, at a height of 34 feet, the water stops rising. Essentially all air has been exhausted above the water in the pipe at this point.
The height of water, 34 feet, corresponds to the pressure of the atmosphere since it is atmospheric pressure pushing water up the pipe which causes the water level to rise.
When the experiment just described is performed with liquid mercury, the highest level will be only about 30 inches rather than 34 feet. This is because mercury is much denser than water. A reduced pressure equal to one inch of mercury is also equal to about 1.13 feet of water, two inches of mercury to 2.26 feet of water and so forth.
All the heights mentioned in the preceeding two paragraphs are vertical heights. The vertical height will be the same for the same degree of reduced pressure whether the pipe is vertical or is inclined or is bent or is a big pipe or a little one or is a combination of big and little pipes.
The term "barometric leg" is oftentimes used to indicated a pipe containing a liquid above which some degree of reduced pressure is maintained; this convenient terminology will be - 2 -~LB6~5~9 hereinafter employed.
According to the invention, there is provided a method of conveying a foam extrudate article of substantial length without subjecting it to substantial stress through a pool of liquid having a density greater than the density of the article, com-prising the steps of: providing a pool of liquid having a conveyor therein, the conveyor having an inclined underside terminating in a gradually upwardly extending curve of significant radius, and permitting the article to float up into engagement with the underside of the conveyor for movement therewith through the liquid.
According to another aspect of the invention, there is provided a method of producing a low density foam comprising the steps of: extruding continuously a foamable extrudate into a vacuum chamber at atmospheric pressure to form a low density foam of substantial length, providing a barometric leg connected to the vacuum chamber and terminating in a pool of liquid open to atmosphere from which liquid is drawn into the barometric leg when the vacuum chamber is at least partially evacu-ated, the density of the liquid being greater than the density of the foam, providing a conveyor in the barometric leg to support and move the foam, the convegor ex-tending from proximate the vacuum chamber into the pool of liquid and terminating in the pool in a gradually upwardly extending large radius curve, and conveying the extrudate from the vacuum chamber without substantial stress sufficient to deform the extrudate through the liquid in the barometric leg into the pool of liquid and out of the pool by permitting the extrudate to float up into engagement with the conveyor for movement therewith.
According to a further aspect of the invention, there is provided a foam extrusion apparatus for producing a low density foam of substantial length comprising:
a vacuum chamber, means to evacuate the vacuum chamber, means through which a foam is extruded continuously into the vacuum chamber when at least partially evacuated, a pool of liquid, the density of the liquid being greater than the density of the foam, a barometric leg connected to the vacuum chamber and terminating in the pool whereby liquid is drawn into the leg from the pool when the vacuum chamber is at least partially evacuated, conveyor means in the barometric leg for supporting , ~ .

and moving the foam through the liquid, the conveyor means having a relatively flat underside against which the foam floats up into engagement whereby the latter moves with the former, the underside of the conveyor means in the barometric leg being inclined at an acute angle to the horizontal and the friction between the article and underside of the conveyor means being sufficient to cause the foam to move along with the conveyor means, and the underside of the conveyor means terminating in the pool in a gradual upward curve, and means to drive the conveyor means for move-ment of the same and the foam through the liquid into the atmosphere.
GENERAL DESCRIPTION OF DRAWING

_ Figure 1 is a diagramatic view of the apparatus for carrying out the method according to the invention.
Figure 2 is a partial view of the barometric leg shown in Figure 1 showing individual parts moved along by the conveyor.
Figure 3 is a view of another embodiment of the invention showing protuber-ances on the conveyor to increase the force of the conveyor on the articles.
Figure 4 is a cross sectional view of the barometric leg in a pilot plant wherein a conveyor is used in the barometric leg.
DETAILED DESCRIPTION OF DRAWINGS
Now with more particular reference to the drawings, one embodiment illustrating the use of the method is seen in Figure 1. The workpiece 1 tries to float in the liquid 2. In so doing, the workpiece 1 contacts the surface of a conveyor belt 3 which is located within the barometric leg 4. The workpiece 1 exerts an upward force 5 which may be visualized in two components, force 6 and force 7. Component force 6 is perpendicular to the surface of the conveyor belt 3 thereby increasing the friction between belt and workpiece. Component force 7 tries to cause the work-piece to escape in direction 8. The smaller angle 9 becomes the smaller force 7 be-comes, and the larger force 6 becomes. Thus, for some value of angle 9--and for all lesser angles -- the tendency of the workpiece 1 to move via force 7 is overcome by the friction and the workpiece is conveyed downward in direction 10.
Angle 9 may be estimated by determining the coefficient of friction be-tween workpiece 1 and conveyor belt 3 while both are r:

~ ' ~069549 1 wetted or immersed in the liquid 2; the coefficient of friction

2 will be the tangent of angle 9. Selection of a lesser angle than 8 that calculated would provide a certain amount of assurance of performance.
It is apparent in referring to Figure 1 that the ~ conveyor belt 3 is being driven in direction 11 by means of a 7 conventional conveyor belt drive system 12, preferably a variable 8 speed electric motor with appropriate transmission. The conveyor belt 3 must be supported with suitab~e means within the barometric 0 leg 4. A preferred mode is to place idler rollers 13 at intervals along the length of the belt.
~2 The height of the liquid above the surface of the 18 pond 15 will be determined by the amount of reduced pressure withi the vacuum chamber 16. The reduced pressure is achieved through conventional controls and vacuum pump connected through a suitable 16 orifice 17 to the vacuum chamber 16.
In practice, the workpiece 1 will move from the vacuum 18 chamber 16 thence will be submerged in the liquid 2 by virtue of 19 being submerged by action of the conveyor belt 3 thence travel along with the belt on its journey downwards through the barometri~ .
~1 leg 4 thence into the pond 15 thence following the belt upward æ out of the pond and leaving the system in direction 18.
2~ Frictior. between belt 3 and workpiece 1 is the only a~ impetus which takes the workpiece along with the belt through the liquid 2. Continuity of the workpiece is not required 2B since one section of the piece has no effect on the other sections 2a There are no tensile forces pulling on the workpiece. This may be 28 appreciated in Figure 2 where it is apparent that each section 19 will move along quite independently of the others.
The origin of the workpiece 1 was not shown in Figure 1, al since the workpiece may be introduced into the vacuum chamber 16 æ in diverse ways. One origin will be illustrated in the examples.

1 Friction alone may be less persuasive than some users of these teachings would prefer. In referring to Figure 3, it is obvious that pins, prongs, spikes, blades, 20, or other protu-4 berances may be affixed to the conveyor belt in order to secure a more firm grasp between belt and workpiece.
~ A pilot plant was constructed. The barometric leg 4 q was a length of aluminum tubing, 6 inches in diameter by 136 feet 8 long. The conveyor belt support was fabricated as shown in ~ Figure 4 because there was not room within the leg for the preferr d m ~dler rollers. Idler rollers were used for belt support beyond 11 the extremes of the leg. In referring to Figure 4, the support 21 12 was sheet aluminum bent into a triangular shaped channel, inserted 18 into the 6 inch diameter leg 22, and fastened in place with bolts 14 23 at intervals along the length of the leg. Figure 4, which is 16 a cross section, shows the conveyor belt 24 on its travel toward lB the vacuum chamber and also the belt 25 on its travel toward the 7 pond with a cross section of the workpiece 26 floating against the 18 belt and being conveyed toward the pond. The pilot plant leg was 1~ inclined from the horizontal at an angle of 1428'. The conveyor ao belt was woven polypropylene, 4 inches wide, driven by a 3/4 21 horsepower, variable speed motor through a suitable gear reducer.
22 In example I, a plastic extrusion die was placed inside the vacuum-23 chamber with the feed channel, or adaptor, for the die passing 24 through the end of the vacuum chamber opposite the end where the a$ barometric leg was fastened. Any material, or workpiece, which 26 would issue from the die would then travel the length of the vacuu a7 chamber thence encounter the conveyor belt and thence begin the 28 journey through the leg. A small conventional extruder was affixe 29 to the die adaptor and commercially available expandable polystyre e ~0 pellets were fed to the extruder hopper. The foam which issued fr m a~ the die was found to be 3.3 pounds per cubic foot (PCF) when extru ed ~2 into the atmosphere. The density was lowered to 1.8 PCF when the 1 chamber was partially evacuated of air, and the foam was recovered 2 continuously via the method of being submerged down through the 8 barometric leg as heretofore described.
In Example II, the liquid used for nearly all work in the pilot plan, which was described in Example I, was ordinary ~ water. A test was designed to illustrate that other liquids 7 would perform in the same way. A solution was made consisting of 8 57% sucrose and 43% water. The specific gravity of the solution was 1.27; this is 27% heavier than ordinary water. Expandable pellets were fed to the extruder. The density of the polystyrene 1 foam was 5.4 PCF when extruded into the atmosphere. The density 12 was lowered to 2.5 PCF when the foam was extruded into a vacuum 18 corresponding to 19 inches mercury vacuum; the identical result 14 was obtained when the liquid was ordinary water and when the t~ liquid was the heavy solution of sucrose.
lB In Example III, another thermoplastic was selected to lq illustrate that various plastic foams would be lowered in density through the practice of the invention. Commercially available expandable polystyrene pellets were used in Examples I and II.
Commerically available branched chain polyethylene pellets were 21 mixed with a powdered chemical blowing agent of which there are æ many on the market. This mixture was fed into the extruder hopper 23 The foam issuing from the dies was 41.0 PCF when extruded into 24 the atmosphere. The density of this polyethylene foam was lowered 2~ to 12.3 PCF when extruded into a vacuum corresponding to 27 inches a6 of mercury vacuum and was recovered by being submerged through the 27 barometric leg as described in Example I.
28 Examples I, II, and II used feed stocks for the extruder ~9 in which the blowing agent was incorporated within the feed, eithe impregnated in the plastic or admixed with the plastic. Another 21 series of tests was selected to illustrate another mode of adding blowing agent, Commercially available polystyrene pellets ~er~

1069549 I ~
1 fed to the extruder hopper and a liquid blowin~ agent was injecte;
2 into the extruder barrel in a manner well known and practiced .j

3 commercially. In every combination of polystyrene and liquid '¦

4 blowing agent, the density which was recovered via vacuum using I ,j the pilot plan~ described in Example I was considerably less ¦
6 than those densities obtained at ordinary atmospheric extrusion. :.
7 Dens;ties at a nominal l.O PCF were obtained many times, this is 8 lower than any practical polystyrene densities heretofore extrudec 9 The foregoing specification sets forth the invention in its preferred practical forms but the structure shown is 11 capable of modification within a range of equivalents without ¦ !, 12 departing from the invention which is to be understood is broadly ;
13 novel as is commensurate with the appended claims.
14 i .

16' 1~ . . !
18 .
'' 1~ ' ' . ~I

21 ~
"23 . ,. . , . ,i 24 . ...
,. . , , 26 ' ;l ,.'2q . . , 3n j ~

~i

Claims (14)

I claim:

1. A method of conveying a foam extrudate article of substantial length without subjecting it to substantial stress through a pool of liquid having a density greater than the density of the article, comprising the steps of:
providing a pool of liquid having a conveyor therein, the conveyor having an inclined underside terminating in a gradually upwardly extending curve of significant radius, and permitting the article to float up into engagement with the underside of the conveyor for movement therewith through the liquid.

2. The method of claim 1 wherein the friction between the article and underside of the conveyor is sufficient to cause the article to move along with the conveyor.

3. The method of claim 1 wherein the conveyor has protuberances on its underside engaging the article.

4. The method of claim 1 comprising the steps of providing a vacuum chamber with means to evacuate it and a barometric leg connected to the vacuum chamber and terminating in the pool of liquid open to atmosphere, and wherein the conveyor extends from proximate the vacuum chamber through the barometric leg into the pool of liquid whereby the article is conveyed from subatmospheric pressure into the atmosphere.

5. The method of claim 4 comprising the step of extruding a low density foam into the vacuum chamber at subatmospheric pressure and withdrawing the same into the atmosphere by the conveyor through the barometric leg and pool.

6. The method of claim 1 wherein the foam is continuously extruded for substantial lengths thereof.

7. The method of claim 6 wherein the underside of the conveyor being inclined at an acute angle to the horizontal, and the tangent of the acute angle being at most equal to the coefficient of friction between the foam and conveyor.

8. A method of producing a low density foam comprising the steps of:
extruding continuously a foamable extrudate into a vacuum chamber at subatmospheric pressure to form a low density foam of substantial length, providing a barometric leg connected to the vacuum chamber and terminating in a pool of liquid open to atmosphere from which liquid is drawn into the barometric leg when the vacuum chamber is at least partially evacuated, the density of the liquid being greater than the density of the foam, providing a conveyor in the barometric leg to support and move the foam, the conveyor extending from proximate the vacuum chamber into the pool of liquid and terminating in the pool in a gradually upwardly extending large radius curve, and conveying the extrudate from the vacuum chamber without substantial stress sufficient to deform the extrudate through the liquid in the barometric leg into the pool of liquid and out of the pool by permitting the extrudate to float up into engagement with the conveyor for movement therewith.

9. The method of claim 8 wherein the conveyor is inclined at an acute angle to the horizontal, and the friction between the extrudate and conveyor is sufficient to cause the extrudate to move along with the conveyor.

10. The method of claim 8 wherein the conveyor comprises a plurality of rollers journalled in the barometric leg and an endless belt trained around the rollers.

11. A foam extrusion apparatus for producing a low density foam of substantial length comprising, a vacuum chamber, means to evacuate said vacuum chamber, means through which a foam is extruded continuously into said vacuum chamber when at least partially evacuated, a pool of liquid, the density of the liquid being greater than the density of the foam, a barometric leg connected to said vacuum chamber and terminating in said pool whereby liquid is drawn into the leg from the pool when the vacuum chamber is at least partially evacuated, conveyor means in said barometric leg for supporting and moving the foam through the liquid, said conveyor means having a relatively flat underside against which the foam floats up into engagement whereby the latter moves with the former, said underside of said conveyor means in said barometric leg being inclined at an acute angle to the horizontal and the friction between the article and underside of said conveyor means being sufficient to cause the foam to move along with said conveyor means, and said underside of said conveyor means terminating in said pool in a gradual upward curve, and means to drive said conveyor means for movement of the same and said foam through the liquid into the atmosphere.

12. The apparatus of claim 11 wherein said conveyor means has protuber-ances on its underside engaging the foam.

13. The apparatus of claim 11 wherein the tangent of such acute angle is at most equal to the coefficient of friction between the foam and said underside of said conveyor means.

14. The apparatus of claim 11 wherein said conveyor means comprises a plurality of spaced rollers mounted in said barometric leg and an endless belt trained around such rollers.