US3814563A

US3814563A - Apparatus for treating elastomeric materials

Info

Publication number: US3814563A
Application number: US00280336A
Authority: US
Inventors: R Slaby; D Bredeson
Original assignee: French Oil Mill Machinery Co
Current assignee: French Oil Mill Machinery Co
Priority date: 1969-02-25
Filing date: 1972-08-14
Publication date: 1974-06-04
Anticipated expiration: 1991-06-04

Abstract

A machine for adding liquids such as oils to elastomeric materials such as rubber or various synthetic polymers is provided in the form of a continuous screw press with intermediate chambers where the material is worked under pressure. Liquid is supplied near the center of the chamber through injector bars, and is mixed into the material as it proceeds out of the chamber toward the press exit. If the elastomeric material contains water, it is first processed in the press to remove included moisture to a point where oil is compatible with rubber mixture; if the material contains volatile solvents, heated oil is mixed into the material and also used as an agent to promote release of the solvent.

Description

United States Patent Slaby et al.

1 1 APPARATUS FOR TREATING ELASTOMERIC MATERIALS [75] Inventors: Robert K. Slaby; Dean K. Bredeson,

both of Piqua, Ohio [73] Assignee: The French Oil Mill Machinery Company, Peoria, Ohio [22] Filed: Aug. 14, 1972 [21] Appl. No.: 280,336

Related US. Application Data [63] Continuation of Ser. No. 74,083. Sept. 21. 1970. abandoned, which is a continuation-in-part of Ser. No. 802.029. Feb. 25. 1969. Pat. No. 3.638.921.

[52] US. Cl 425/203, 100/75, 100/117, 100/150, 259/191, 425/208 [51] Int. Cl B29b l/l0, B29f 3/02 [58] Field of Search 100/74, 75, 117. 127, 1 28,

[56] References Cited UNITED STATES PATENTS 2.935.931 5/1960 Ginaven 100/149 X 2.975.096 3/1961 Ginaven et a1. 100/117 UX 1 June 4, 1974 2997.943 8/1961 210$ 1011 74 3.111.080 11/1963 French et al.... 100/37 3.158.900 12/1964 Heston 259/191 3.181.454 5/1965 Ginaven et :11 100/74 Primary ExaminerHarvey C. Hornsby Assistant Examiner-Philip R. Coe Attorney, Agent, or FirmBiebel, French & Bugg 5 7 ABSTRACT A machine for adding liquids such as oils to elastomeric materials such as rubber or various synthetic polymers is provided in the form of a continuous screw press with intermediate chambers where the material is worked under pressure. Liquid is supplied near the center of the chamberthrough injector bars, and is mixed into the material as it proceeds out of the chamber toward the press exit.' 1f the elastomeric material contains water, it is first processed in the press to remove included moisture to a point where oil is compatible with rubber mixture; if the material contains volatile solvents, heated oil is mixed into the material and also used as an agent to promote release of the solvent.

5 Claims, 5 Drawing Figures APPARATUS FOR TREATING ELASTOMERIC MATERIALS RELATED APPLICATIONS This application is a continuation of application Ser. No. 74,083, filed Sept. 21, 1970, now abandoned, which is a continuation-in-part of application Ser. No. 802,029, filed Feb. 25, 1969, now US. Pat. No. 3,638,921, issued Feb. 1, 1972.

BACKGROUND OF THE INVENTION The invention has special reference to a system employing a mechanical screw press for introducing liquids such as plasticizers, extenders, or anti-oxidants into elastomeric materials such as natural or synthetic rubbers, preferably during a combined drying or desolventizing process of the material. A typical liquid may be an oil such as a light process oil of the napthenic or slightly aromatic type. This oil serves as in intermolecular softener and lubricant which increases the plasticity and workability of the material so that it can be more easily formed into different shapes later in the processing. An oil is also frequently used as an extender along with carbon black for increasing the bulk of the rubber compound to provide a lower cost product without noticeably reducing any of the significant properties, and in many cases producing superior properties.

SUMMARY OF THE INVENTION The present invention is directed to improved apparatus for treating elastomeric materials and the like by compressing the material in a first stage of a drainage type screw press to produce an increase in pressure and temperature by friction heat for removing the water (where present) by drainage and flashing off of the moisture. Apparatus of this general type, used for a different purpose in a different way, is disclosed in US. Pat. No. 3.1 1 1,080. The material is worked under pressure while liquid is simultaneously added. The liquid is readily received by the material, and can be worked and pressed into the material in the second stage of the press where the pressure may be further increased. A multi-stage mechanical screw press not only provides for eflicient drying but has been found to provide an efficient, thorough and uniform mixing of the fluid into the material. It is especially desirable for use on natural rubber in which heretofore the mixing of liquids, particularly oils, has presented many difficulties. The press has also been determined to be an efficient device of adding oil or other liquids into synthetic elastomeric polymers instead of mixing in the liquid during the coagulation step, which is the present procedure.

Accordingly, the object of this invention is to provide an apparatus wherein liquid can readily be pressed into the elastomeric material being treated, at the same time using the addition of the liquid to control the temperature of the material, to avoid overheating of the material and damage thereto, or to promote release of volatiles therefrom.

Other objects and advantages of this invention will be apparent from the following description, the accompanying drawing and the appended claims.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a somewhat diagrammatic elevational view parts shown in FIG. 1;

FIG. 3 is a sectional view showing details of the valve and injector lug for adding liquid to materials processed in the apparatus;

FIG. 4 is an enlarged fragmentary sectional view through a portion of the cage of the apparatus, illustrating the manner in which openings are provided between the bars making up the walls of the chamber; and

FIG. 5 is a view similar to FIG. 1 showing a modified form of press.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the drawing, which illustrates preferred embodiments of the invention, FIG. 1 shows somewhat diagrammatically, a continuous duty, interrupted flight, screw-type expressing machine having an inlet hopper through which materials to be worked upon and treated are supplied. The materials are received between the flights of the feed screw 12 and carried thereby from the hopper 10 into the main body of the apparatus, which is made up on an outer cage structure 15 formed by two symmetrical halves which are bolted together. One half has been removed in FIG. 1 to illustrate the interior of the apparatus.

Within this outer cage structure there are a plurality of subassemblies of sections 16, I7, 18, 19, 20, 21, 22 and 23 with sections 16-19 forming the first stage of the press and sections -23 forming the second stage. Each of these sections is formed by a framework supporting a plurality of axially extending screen bars 25 (FIG. 4), in some sections separated by suitable small spacers 26. Further details of the construction of these subassemblies are illustrated in US. Pat. No. 3,126,820. An important point, as far as the present apparatus is concerned, is that those sections of the apparatus where liquid is to be drained are provided with socalled drainage openings defined between adjacent screen bars making up the section, while the sections where injection occurs do not have such openings, at least not near the point of injection.

Within the elongated cylindrical chamber defined by the casing or cage structure, and mounted on the main shaft 30, are a plurality of collar members 32 some of which may be tapered as shown so as to decrease the cross-sectional area between the collar and the cage section walls. Intermediate these collars, and also fixed to rotate with the shaft, are pressure worms 35. These pressure worms are essentially of like constructions, with a worm body 37 and an interrupted flight 38 which preferably is notched at a number of locations, as shown in FIG. 2, to produce a more thorough shearing and working of the material in the apparatus. The main difference between'the various pressure worms is that the worm bodies 37 are of different diameter, progressively increasing generally according to the larger diameter of the preceding collar. The pressure worms take up material forced around the preceding collar, and move the material under pressure over and around the succeeding collar and on to the next pressure worm. Rotation of the shaft 30, which produces this action, is obtained from a conventional drive 40, which may include any suitable form of power together with a gear case or the like by which the desired rotation of the feed worm and pressure worms is obtained.

The cage structure shown is of constant diameter, and has an entrance or feed opening where the feed worm l2 enters the cage structure, and a discharge opening formed by a discharge ring 42 at the opposite end of the cage structure. This ring preferably is fastened to a rotatable helical gear 43 carried on a threaded extension 44 such that rotation of the adjusting worm gear 45 will rotate gear 43 and cause axial adjusting movement of the discharge ring 42.

The collar members 32 and the bodies of worm members 37 cooperate with the interior walls of the cage structure to provide a through annular passage for the material, with such passage varying in cross-sectional area at different locations. ln one embodiment of the invention this passage decreases gradually in crosssection, so that pressure is built up on the material in the first stage up to the space around collar member 50. This collar member includes a portion which may taper inwardly such that the annular space between it and the cage walls increases on the downstream side of this collar. Therefore, in this section and within the following chamber portion 52 surrounding the next pressure worm, the pressure on the material may be somewhat reduced by reason of the increase in volume permitting expansion of the material within the zone and consequent degassing. In this region the spacers are not used, to prevent drainage. Then, progressing toward the discharge end of the cage, the pressure collars may again increase progressively in cross-section, and the worm bodies likewise correspondingly increase in size, such that pressure is again applied to the material until it reaches the discharge collar 55 which projects at least partially into the discharge ring 42. Preferably the discharge collar is provided with a set of breaker lugs 57 arranged to cooperate with a rotatable shredder member 58 having a rotary drive 59. Material passing through the discharge opening is engaged between the shredder 58 and the lugs or teeth 57, and is cut or torn into relatively small pieces which are expelled through the discharge ring 42 into any suitable collection device.

A feature of the invention, as it applies to removing water or other liquids, concerns the relationship of the drainage or venting openings between the screen bars in the various sections of the cage structure. As the annular cros's-sectional area of the passage through the apparatus decreases, the pressure on. the material will increase. it is understood that in operation the passage between the rotatable parts and the walls of the cage structure is essentially full of compacted material which is being continuously worked and compressed. This results in substantial frictional heating along with shear action and transfer of shear energy. If desired, this heating may be regulated by flowing heat exchange fluid or liquid through suitable passages such as shown in said US. Pat. No. 3,126,820. As pressure on the material increases, the tendency is to squeeze some of the material into the drainage openings between screen bars 25, therefore it is desirable to attain a balance between the maximum size of opening for the best possible drainage and such reduction in the opening as mentioned above to avoid complete clogging thereof by materials squeezed into the openings. Where pressure on the material is first released, as in chamber portion 52 at the end of the first stage, the drainage opening size is increased, thereby assuring the best possible venting and removal of vapors and liquids. By way of example, in one form of apparatus constructed in accordance with the invention the drainage openings between screen bars 25, in the section 16, is approximately 0.060 inch in width. Comparable openings in section 17 are reduced to 0.040 inch, in section 18 the openings are reduced to 0.030 inch, and in the first part of section 19 the drainage openings are further reduced to 0.020 inch in width. In the last part of section 19 the opening size is increased to about 0.060 inch, then there are no openings in section 20. The size of drainage openings in

sections

21, 22 and 23 decreases in size corresponding to the sizes for

sections

17, 18 and 19. It has been found through operation of apparatus of this type that vapors tend to flow to the point of lowest pressure, in other words to the entrance to chamber portion 52, around collar 50 and by having larger drainage openings at this point it is possible to achieve optimum venting, thereby assuring that all vapors are quickly removed from the chamber.

As shown in FIG. 1, stationary breaker lugs, indicated by the general numeral 60, are provided to prevent rotation of the material with the collars 32 and to cooperate with the notched worm flights 38 to obtain a tearing, shearing and working action of the material. However, a feature of the invention is provided by the specific construction of the breaker lug 62 (FIG/3). The breaker lug 62 is spaced outward from the collar within the chamber portion 52. A controlled injection nozzle 63 (FIG. 2) is mounted in lug 62 for directing a plasticizing oil or other compounding liquid downstream of chamber portion 52 and substantially into the middle of the mass of material at a point where the material again is under substantial pressure.

Details of one nozzle are shown in FIG. 3. The tubular body 65 is fitted into the lug, and a valve stem 66 carries a head 68 which cooperates with a seat 69 to control flow into the chamber. The stem has a threaded part 70 which is received in a piston 71 movable in a cylinder 72. Oil under pressure is supplied to the stem side chamber 73 when it is to be injected, This automatically opens the nozzle. Valving the oil under pressure to the opposite chamber 74 will shut off the nozzle. The projecting stem 75 provides a means for locking the nozzle closed if desired, and also gives a visual indication of nozzle position.

' The liquid to be mixed with the material is supplied to a pipe or manifold from a positive displacement reciprocating cylinder pump 82. Particularly in the treatment of natural rubber and the like, a liquid such as oil may be used to provide a so-called oil extended" rubber product. This oil is provided from a suitable tank connected through pipe 86 to a conventional controlled heat exchanger 88 which heats and maintains the oil to a desired temperature. In the case of renotched pressure worm flights and the interaction of these flights with the collars and breaker bars. A bypass is provided around the heat exchanger 88, and a control valve 92 is included in the bypass, whereby cool oil from the tank can be supplied directly to the cylinder 82 if additional cooling effect should be needed.

The cylinder 82, as shown in FIG. 1, is of the reciprocating double-acting type, which receives the oil to be injected through the check valves 95 and delivers the oil through check valves 96 into a manifold 9,7 which leads to the entrance tubes 75 of the injectors. A pressure relief valve 98 is provided, which will bypass oil back to the tank 85 if the pressure increases beyond a predetermined limit. This arrangement provides posifluid is pumped through pump 103 to a conventional servo-operated reversing valve 105. This valve has pilot cylinders 106 at its opposite ends connected to the opposite heads of the motor 100, thus as the motor piston reaches one limit of its stroke, the build-up pressure will cause the appropriate pilot 106 to shift the valve thereby reversing the pressure connections to the motor 100 and reversing its direction. At the same time the return connection to tank T2 is likewise reversed. An adjustable bypass valve 108 is connected to the outlet side of pump 103, and by adjusting the pressure of the pump outlet through this valve, it is possible to increase or decrease the reciprocating speed of the motor 100, thereby controlling the rate of displacement of the pump 82.

H6. 5 illustrates a modified form of apparatus which may be used in accordance with the invention, particularly to remove volatile solvents from elastomeric polymers such as solution polymerized SBR, or material of generally the same nature. These materials contain a volatile solvent, such as hexane, but do not contain water. lt is necessary to remove this solvent, preferably in a gaseous state, and it is often desirable to compound other materials, such as oil, into the polymer. The present arrangement provides for these operations in a continuous and practically simultaneous process.

The press structure is similar to the type disclosed in greater detail in copending application Ser. No. 753,647, filed Aug. 19, 1968 entitled MECHANICAL SCREW PRESS, now US. Pat. No. 3,574,891 which is assigned to the assignee of this application. lt differs from the apparatus shown in FIG. 1 in several respects. There is an adjustable intermediate choke ring 110 in the chamber of the press, downstream from the injector nozzle 2, which can be of the same construction as shown in FIG. 3. The cage structure from the inlet, past the injector, to and around the adjustable ring 110, is closed or imperforate. Downstream of ring 110 the diameter of the worm body is decreased, providing an expansion chamber in which pressure on the material is reduced. This chamber is surrounded by spaced screen bars, allowing the volatile solvent to escape into a surrounding collection housing (not shown).

In place of the shredder structure shown in F l6. 1, an extruder section is provided at the discharge end of the press, including an imperforate extruder sleeve 122 which in this embodiment is of smaller diameter than the intermediate diameter of the press chamber, and a double helical extruder worm 123 operates within the sleeve 122. At the discharge of the sleeve 122 there may be a die plate 125 through which the material is discharged, and a rotating knife 126, driven from a separate motor (not shown) cuts the material extruded through the die into relatively small particles.

The solvent containing polymer is fed into the press cage and worked in the closed press section upstream of the ring 110, while hot oil is injected through the in jector 112. ln this case, the temperature of the oil is sufficiently high to promote heating of the polymer to a temperature higher than that at which the solvent changes to vapor form. However, since the material is compacted and worked mechanically within this section of the press, the hot oil is at this point merely mixed into the polymer-solvent mixture, which is increased in temperature.

As this material is forced through the ring 110, and enters the expansion chamber, the pressure on the material is reduced substantially. to the point where the pressure is quickly lower than the vapor pressure of the solvent. The solvent therefore vaporizes and flows as a gas through the vent openings of the expansion chamher into the aforementioned collection housing. The hot oil tends to promote this operation and to displace the solvent as the solvent escapes from the polymer. The change in phase of the solvent from liquid to vapor also functions to absorb some heat from the material, thereby assisting in keeping the polymer at a temperature below which damage, such as formation of gel, will occur.

The ring 110 preferably is adjustable longitudinally of the cage in order to provide control over the thickness of the annular orifice formed between the ring and the collar which it surrounds. This in turn provides a control over the pressure in the preceding section of the press, and assures that the material is not overworked to the point where undesirably high temperatures might be encountered.

This form of apparatus, therefore, provides a contin uous system in which hot compounding liquids such as oil are added to polymerized elastomericmaterials, and at the same time the volatile solvents are thoroughly removed from the material, with a high percentage of the solvent being collected and recoverable for further use in the process upstream of the press.

While the forms of apparatus herein described constitute preferred embodiments of the invention, it is to be understood that'the invention is not limited to these precise forms of apparatus, and that changes may be made therein without departing from the scope of the invention.

What is claimed is:

1. An improved screw press apparatus for continuous processing of elastomeric material and for mixing of a fluid into the material during the processing operation, comprising wall means defining an elongated chamber, means dividing said chamber into first and second stages each having an entrance and a discharge end, conveying and working means including a shaft rotatably mounted within said chamber and adapted to be power driven and a plurality of successive collars and worm bodies having flights thereon and mounted on said shaft with at least said worm bodies connected for rotation with said shaft, stationary breaker lugs extending between said worm flights for cooperating with said flights to provide a shearing and working action on the material, said conveying and working means having in each of said stages progressively increased size to decrease progressively the surrounding volume of the chamber in each of the stages for increasing toward the end of each stage the pressure on the material conveyed therethrough, drainage openings formed through said wall means in each of said stages of decreasing size along said stage in the same direction as the flow of the elastomeric material through said chamber of the press, said wall means being imperforate in said first stage immediately upstream of said expansion section, means forming an expansion section at said discharge end of said first stage and between said stages in which pressure on the material is effectively decreased, said expansion section also having drainage openings provided for escape of moisture and/or vapor released from the material, and means for injecting a compounding liquid into the region surrounded by the imperforate wall means for mixing of the liquid into the material.

2. Apparatus as defined in claim 1, wherein said injecting means includes an injector nozzle opening into said chamber to release the liquid into the mass of material in the chamber.

3. Apparatus as defined in claim 2, including a positive displacement pump means connected to deliver the liquid under pressure to said nozzle.

4. Apparatus as defined in claim 2, wherein said injector nozzle includes valve means operable from the exterior of said press to control the flow through said nozzle.

5. Apparatus as defined in claim 2, including an imperforate extruder section receiving the material from the discharge end of the second stage and having an end opposite said second stage toward which end the material is fed, and a die mounted at the end of said extruder section and having openings through which the liquid-extended material is discharged from the press.