GB2041284A - Plasticising and impelling Particulate Materials - Google Patents

Abstract

A rotor having at least one peripheral annular channel (24) is rotatable relative to a stator surface of a surrounding stationary housing to impel material in the channel from an inlet (28) through the housing, to a circumferentially spaced outlet (36), through which plasticised (liquid) material is discharged by pressure developed by the material being impelled against a first stationary surface (34) which projects into a channel downstream of the outlet (36). A second surface (40), upstream of the outlet (36), has a clearance with the walls of the channel (24) and restrains advance of (unmelted) material (39) in the centre of the channel while permitting liquid material (25) to be dragged towards the first surface (34). The channel space (46) between the first and second surfaces (34 and 40) enables the discharge pressure to be generated in an accumulated pool (42) of the liquid material. The second surface (40) may be provided on an extension along the channel of part of the member (32) which defines the first surface or may be provided on a further member (38), which may be of various different configurations, and may act as a scraper against one channel wall. <IMAGE>

Description

SPECIFICATION Machine and Method for Processing Particulate Materials which Become Liquid in the Course of Processing This invention is concerned with a machine and a method for processing particulate materials which become liquid in the course of processing, for example plastics and polymeric materials.

In the specification of our United States Patent No. 4,142,805 are described machines and methods for processing plastics and polymeric materials. The machines comprise a rotor having at least one annular processing channel and a stationary element providing a surface cooperative with the channel to form an enclosed annular processing passage: the stationary element of the machines described in Patent No. 4,142,805 comprises a housing in which the rotor (having a cylindrical surface in which the channel is formed) is mounted for rotation, the housing having an internal cylindrical surface coaxial with the rotor.Inlets are provided in the housing through which material to be processed may be supplied to the (or each) annular processing passage and an outlet leads from the (or each) annular passage circumferentially spaced from the inlet to that passage downstream of the inlet in the direction of rotation of the rotor. The machine described in the aforementioned specification further comprises a blocking member disposed in the (or each) annular passage near the outlet, disposed between the outlet and inlet in the direction of rotation of the rotor.In the operation of the machine, in carrying out the method described in the aforementioned specification, materials supplied through the inlets which is, or becomes in the course of processing, a viscous liquid is dragged by walls of the processing channel as the rotor rotates towards the blocking member which is constructed to obstruct material in the processing channels so that there is relative movement between opposed side walls of the processing channel and the body of material in the channel, the side walls operating to drag forward material in contact with the walls against the blocking member for processing and discharge through the outlet, material discharged through the outlet being in the form of a viscous liquid.The methods and machines are described in the aforementioned specification as useful for, inter alia, melting or plasticating plastics materials, conveying, pumping or pressurising liquid material, mixing, blending, dispersing and homogenising plastics and polymeric materials, devolatilising materials, in bringing about structural change in materials by chemical reactions e.g. polymerisation, cross linking or foaming. Reference is directed to the aforementioned specification for further information on the machines and methods described therein.

One such machine described in the aforementioned U.S. specification comprises mixing structures extending part way into one or more of the processing channels positioned between the inlet and outlet to the channel (considered in the direction of rotation of the rotor). One such mixing structure described is a dam which creates a void of material on its downstream face i.e. the face of the dam nearest to the outlet. A port opening from the void thus created can be used to allow volatile materials to escape or as an inlet for adding further materials to the materials being processed.

In the specification of our copending Patent Application Serial No. 2,007,585 is described a machine similar to that described in the aforementioned U.S. patent specification but additionally comprising spreader means in at least one of the annular processing channels. The spreader means is disposed to obstruct a major portion of the channel and spaced from the side walls of the channel a distance selected to control the rate at which the material to be processed passes the spreader means under the developed pressure and dragging action of the side walls as the rotor rotates, to spread on the side walls layers of viscous liquid material, leaving a central portion of the channel between the spreader means and the outlet (considered in the direction of rotation of the channel) free from material to be processed.A port opens into this central portion of the channel for passage of material to or from the central portion; for example, this provides a large surface area to volume ratio for efficient devolatilisation of material. The liquid material passing the spreader means is collected in a pool by a surface of the blocking member for discharge. Reference is directed to the specification of the aforementioned United Kingdom patent application for further information.

The machines and methods described in the specifications of the aforementioned patent applications are generally suitable for processing particulate materials e.g. plastics or polymeric materials, especially when relatively low speeds of rotation of the rotor with respect to the housing (and accordingly lower melting rates) are involved. However, when higher speeds of rotation are used to achieve higher melting rates, the quality of discharged viscous liquid material can be affected. For example with some particulate materials processed at higher melting rates, the discharged liquid material has been found to contain insufficiently melted particulate material.

One of the objects of the present invention is to provide an improved machine for processing particulate materials which become liquids in the course of processing.

A machine in accordance with the invention for processing particulate material which becomes liquid in the course of processing comprises a rotor having an annular processing channel, the rotor preferably having a cylindrical surface in which the processing channel is formed having opposing side walls extending inwardly from the cylindrical surface. The machine further comprises a stationary element providing a surface cooperating with the channel to form with the channel an enclosed annular processing passage; in a preferred machine the stationary element comprises a housing having an internal cylindrical surface coaxial with the rotor.The machine further comprises an inlet in the stationary element for feeding particulate material to the annular passage and an outlet in the stationary element from the passage, circumferentially spaced from the inlet downstream of the inlet in the direction of rotation of the rotor. A machine in accordance with the invention further comprises a first surface disposed in the annular passage between the outlet and inlet in the direction of rotation of the rotor, conveniently adjacent and just downstream of the outlet, the first surface providing a material collecting surface in the processing channel. A machine in accordance with the invention further comprises a second surface disposed in the annular passage upstream of the outlet preferably closer to the first surface than to the inlet.The second surface is preferably spaced apart from the first surface by a minor portion of the length of the annular passage; suitably the angle between these surfaces is between 100 and 900, preferably between 150 and 400. The second surface has a shape generally corresponding in cross-section to the processing channel, but smaller, to provide a clearance, preferably between 0.03 and 0.125 inches (about 0.76 and 3.18 mm), between the walls of the processing channel and sides of a member providing the second surface.

The construction and arrangement of a machine in accordance with the invention is such that as the rotor is rotated in the operation of the machine liquid material is dragged through the clearance towards the first surface, the first and second surfaces being positioned to provide a space for liquid material between the first and second surfaces. The liquid material dragged through the clearance into the space forms a pool collected by the first surface sufficient that pressure is generated in the pool for discharge of liquid through the outlet.

In a machine in accordance with the invention the construction and arrangement is such that as the rotor is rotated in the operation of the machine advance of material in a central region of the processing channel is restrained by the second surface while permitting liquid material to be dragged by the walls through the clearance into the pool of liquid material collected adjacent the first surface. A machine in accordance with the invention may comprise a portion positioned in the space between the first and second surfaces, the portion occupying a part of the space to provide a region of predetermined geometry for liquid carried into the space; the geometry of this region is preferably selected to provide desired discharge pressure characteristics for liquid collected in the region.

Preferably a machine in accordance with the invention comprises means, for example a valve, for controlling discharge of liquid material from the outlet to secure a desired extent of processing. The clearance between the wall of the processing channel and the side of the member providing the second surface is also selected to apply desired conditions of shear (and stress) on liquid material dragged past the member providing the second surface.

Preferably a machine according to the invention comprises heating means for supplying heat to melt particulate material in the annular passage.

A machine in accordance with the invention also preferably comprises other means to facilitate processing. For example the member providing the second surface preferably comprises means for mixing the liquid material as the liquid is dragged past the member in the operation of the machine; suitable these means comprise recesses in the sides of the member providing the second surface.

Further, a member of a machine in accordance with the invention providing the first surface may be constructed to allow at least a limited quantity of the liquid material to pass the member providing the first surface and recirculate through the annular passage for mixing with restrained particulate material, thereby facilitating melting of the particulate material. A machine in accordance with the invention may also comprise means positioned between the inlet and the second surface to divert part of the liquid material from the walls of the processing channel to mix the liquid material with restrained particulate material in the central region of the processing channel.Furthermore, a machine in accordance with the invention may also conveniently comprise means to cause accumulation of a portion of liquid material at the second surface, so that the accumulated liquid material can be mixed with restrained particulate material. A machine in accordance with the invention may be constructed so that a scraping clearance is provided between one of the sides of the member providing the second surface and an adjacent one of the walls of the channel, so that liquid material can be accumulated at the second surface; the accumulated material becomes mixed with restrained particulate material to facilitate melting thereof.

Where a machine in accordance with the invention comprises a portion positioned in the space between the first and second surfaces, the precise configuration and construction of this portion is selected according to the geometry which it is required to provide for the pool of liquid collected by the first surface. For example a machine in accordance with the invention may comprise a blocking member providing the first surface and a further, restraining, member providing the second surface, the portion positioned in the space being provided by a section of one of said members extending towards the other of said members; alternatively the portion may be provided by a section of each of said members extending towards the other of said members. Alternatively a machine in accordance with the invention may comprise a unitary member providing the first and second surfaces, and the portion positioned in the space between the first and second surfaces.

A machine in accordance with the invention is conveniently constructed so that at least a portion of the width of the processing channel between the interior surfaces of the channel walls is between 0.75 and 1.50 inches (between about 19 mm and 38 mm). Suitably a machine in accordance with the invention also comprises means to rotate the rotor (and thus the walls of the processing channel) at a speed of between 50 rpm and 300 rpm.

In carrying out a method in accordance with the invention a machine in accordance with the invention is conveniently used. A method in accordance with the invention for processing particulate material which becomes liquid in the course of processing, using a machine in accordance with the invention, comprises the steps of introducing the particulate material through the inlet into the annular processing passage, rotating the channel in a direction from the inlet toward the outlet to establish relative movement between the rotating walls and a main body of particulate material restrained by the second surface, dragging liquid portions of the material in contact with the rotating walls through the clearance towards the first surface, and collecting the dragged forward liquid material as a pool of liquid against the first surface for controlled processing and/or discharge.In carrying out a method in accordance with the invention the processing is preferably controlled to apply preselected shear conditions to the liquid material as the material is dragged through the clearance to the first surface, for example by means hereinbefore referred to in reference to a machine in accordance with the invention.

Likewise melting of the particulate material may be facilitated in the manner described in reference to a machine in accordance with the invention.

There now follow detailed descriptions of machines embodying the invention and methods of processing particulate material utilising these machines embodying the invention in its method aspects. It will be realised that these machines and methods have been selected for description to illustrate the invention by way of example.

In the accompanying drawings: Figure 1 is a schematic, exploded, perspective view of a first illustrative machine embodying the invention; Figure 2 is a perspective view partially in section of the first illustrative machine; Figure 3 is a flattened sectional view of a processing channel of the first illustrative machine taken at a selected radius and shows movement of material in the channel; Figure 4 is an enlarged view in section of the first illustrative machine showing a processing channel thereof; Figure 5 is a cross-sectional view taken on the line 5-5 of Figure 4;; Figures 6, 7 and 8 are flattened, sectional views of channels of other machines embodying the invention generally similar to the first illustrative machine but having different restraining surface providing members taken at a selected radius and showing movement of material in the channels; Figure 9 is a view in section of a second illustrative machine embodying the invention showing a processing channel and a preferred unitary member providing a restraining surface and liquid material collecting end wall surface; Figure 10 is a flattened sectional view of the channel of the second illustrative machine of Figure 9, taken at a selected radius and showing the unitary member;; Figure 11 is a flattened sectional view of a channel taken at a selected radius of a further machine embodying the invention generally similar to the second illustrative machine but comprising a different unitary member; Figure 12 is a view in section of a third illustrative machine embodying the invention showing a processing channel; Figure 13 is a flattened sectional view of the channel of the third illustrative machine taken at a selected radius; Figures 14 and 15 are flattened, sectional views of channels taken at a selected radius of other machines embodying the invention generally similar to the third illustrative machine but comprising alternative combinations of members providing a restraining surface with members providing a liquid material collecting end wall surface, and movement of material in the channel;; Figure 16 is a flattened, sectional view of a channel taken at a selected radius of a further machine embodying the invention showing a further unitary member and movement of material in the channel; and Figure 1 7 is a flattened fractional sectional view of one side of a channel taken at a selected radius of yet another machine embodying the invention showing the action of a scraping and mixing element on a layer of liquid material carried on a channel wall.

There now follow detailed descriptions of a number of machines embodying the invention together with methods embodying the invention utilising these machines. In the following description like numbers represent like parts, suffixes being used to identify specific parts in various ones of the machines embodying the invention described.

The machines embodying the invention described hereinafter are for processing particulate material, for example plastics or polymeric material, which becomes liquid in the course of processing.

Each of the machines described hereinafter is generally similar to the first illustrative machine in construction, except as will become apparent hereinafter; for conciseness, therefore, only the first illustrative machine will be described in detail. The first illustrative machine comprises a rotor 10 having an annular processing channel, the rotor comprising a number of spaced elements 12 mounted on a drive shaft 14 for rotation within a stationary element comprising a housing 16 having end plates 18 in which the shaft 14 is journalled for rotation. The rotor 10 has a cylindrical surface 20 of rotation coaxial with the rotor 10 in which the processing channels 22 are formed by opposing side walls 24 extending inwardly from the surface 20.Each of the machines comprises means (not shown) for rotating the rotor 10 which may be means commonly used for rotating extruder screws or similar polymeric processing apparatus and which are well known to those in the art. The housing 16 of the stationary element comprises a cylindrical surface 26 coaxial with and cooperating with the surface 20 of the rotor 10 to form with the channels 22 enclosed annular processing passages.

The housing 16 also comprises an inlet 28 for introduction of particulate material for processing from a suitable feeder, viz. a hopper 30, into the annular channel 22. It will be understood that suitable devices for feeding particulate plastic or polymer may be used which may be a simple gravity feed hopper as shown or may include other devices for example a screw feeder, a ram feeder, or a disc-type pre-heater feeder to name a few typically available feeder devices, suitable to the character of the particulate material and the difficulty of controlling its supply to the channels 22.

Also associated with the housing 1 6 of the first illustrative machine is an outlet 36 spaced apart from inlet 28 at least a major portion of the circumferential distance about the passage downstream of the inlet 28 in the direction of rotation of the rotor 10. Near the outlet 36 and mounted on the housing 16 is a blocking member 32 which extends into the channel 22 between the outlet 36 and the inlet 28 in the direction of rotation of the rotor 10 and provides a first surface, viz. a liquid material collecting end wall surface 34 and scraper portions in close relation to the walls 24 of the channel 22. The member 32 has a shape complementary to and fitting closely within the channel 22 into which it extends and the end wall surface 34 facing the channel 22 may be radially disposed or at another suitable angle depending upon the material and treatment desired.A shaping die 37 is disposed directly in the outlet 36 of the first illustrative machine.

The first illustrative machine also comprises a further, restraining, member 38 (Flgures 1 to 4), mounted on the housing 1 6 and extending into each of the channels. Each of the members 38 provides a second surface, viz. a restraining surface 40, in the channel 22 between the inlet 28 and the liquid material collection end wall surface 34 upstream of the outlet 36.The restraining surface providing member 38 has at least a portion of its shape adapted to fit within the associated one of the channels 22 so as to provide the surface 40 which can effectively restrain, and/or obstruct movement of any substantial portions of unmelted (or incompletely melted) particulate material beyond the surface 40; the shape of the member 38 is also such as to provide a sufficient clearance 50 between the side walls 24 of the channels 22 and sides of the member 38 to permit liquid material to be dragged by the side walls 24 past the member 38 towards the liquid material collecting end wall surface 34 while advance of material in a central region of the channel 22, mainly unmelted particulate material, is held or restrained by member 38, in the operation of the first illustrative machine in a method embodying the invention.

In the operation of the first illustrative machine in carrying out a method embodying the invention particulate material is fed from the hopper 30 into one or more of the channels 22 through the inlet 28.

As the rotor 10 turns, a main body 39 of particulate material is held by the restraining surface 40 of the member 38 in the central region of the channel 22 so that the rotating channel side walls 24 and the member 38 coact to establish relative motion between the walls 24 and the main body 39 of restrained particulate material. Portions of the particulate material are converted to the liquid state preferably by melting using heating means (not shown), for example chambers provided on the outside of each channel wall 24 so that a temperature control fluid can be introduced into each chamber for heat transfer through the walls of the channel as described in the aforementioned U.S. patent specification.Melted, liquid material in contact with the walls 24 of the channel 22 therefore is dragged by the walls 24 past the member 38 towards the end wall 34 of the member 32 where it is collected as a pool 42 for controlled processing and/or discharge through the outlet 36.

This is schematically shown in Figure 3: movement of the main body 39 of the particulate material is held back by and compacted against the surface 40 of the member 38 as a result of the relative motion between the rotating side walls 24 of the channel 22 and the restrained body 39 of particulate material. This relative motion generates friction which can cause melting of portions of the particulate material or optionally, as mentioned, the channel walls 24 may be preheated. In any case, a film 25 of melted material is formed on the side walls 24 of the channel. The film in contact with the walls 24 moves forward with the walls 24 and is vigorously sheared by motion relative to the main body 39 of restrained particulate material in the channel 22 to generate further heat by viscous dissipation. The action of the side walls 24 of the channel 22 in dragging forward the film 25 of melted material on their surfaces builds up pressure progressively along the length of travel of the side walls 24 usually reaching a maximum value in the region of the surface 40 of the member 38. In some cases however, depending on such features as the geometry, shape and position of the member 38 and the operating speed, maximum pressure may be reached elsewhere e.g. at the surface 34 of the member 32. The member 32 scrapes off melted material carried forward by the side walls 24 of the channel 22 and the scraped-off material accumulates in the pool 42 against the end wall surface 34 of the member 32 and may be discharged through the outlet 36.

As described in the aforementioned U.S. patent specification control of the rate at which processed material is allowed to discharge from the channel 22 is an important factor in determining the extent to which the material is processed and the outlet 36 is constructed and arranged to facilitate this discharge control. Control may be effected by the size of the outlet opening or by a throttling valve (not shown) or other device in the discharge outlet 36. The discharge rate may also be controlled by connecting the outlet 36 to a further processing stage, for example an extrusion nozzle or the die 37 which may provide a desired flow resistance controlling the rate of discharge from the outlet and the extent of processing of material in the channel 22.Further, in a machine in accordance with the invention otherwise similar to the first illustrative machine having more than one channel, the outlet from one channel may be lead through a conduit to the inlet of a further channel for further processing.

This arrangement is particularly valuable since the series pressure-producing and pumping action of successive processing channels is cumulative so that high outlet pressure is readily secured. It will be understood that successive channels may each have different geometry from other channels for best processing of material supplied to it. Also, material processed in and discharged from one channel or a given number of channels operating in parallel may be fed to one channel or to any suitable number of channels operating in parallel.

The function of the member 38 of the first illustrative machine and details relating to it are further shown in Figures 4 and 5. The member 38 is positioned to restrain or obstruct movement of any substantial amounts of particulate material at a position between the inlet 28 and the member 32. The member 38 preferably is positioned as far as practical from the inlet 28; however, the member 38 can be positioned anywhere between the inlet 28 and the member 32 so long as there is at least sufficient space between the member 38 and end wall surface 34 of the member 32 to collect a pool of viscous liquid which, for the particular viscous liquid involved, wets sufficient area of the walls 24 to generate sufficient discharge pressure by movement of the walls.Accordingly, the position of member 38 can vary depending primarily on the size of the melt pool 42 required in the space between the surface 40 and the end wall surface 34 to provide discharge pressure.

The size of the pool 42 needed depends on such factors as the particular viscous liquid material involved, the discharge pressure desired, the area of the walls 24 and their rate of movement.

However, the particular position selected can be determined empirically. Alternatively, the position can be determined by using the equation and teachings of the aforementioned U.S. patent specification to determine the space needed between the surface 40 and the end wall surface 34 to provide the desired discharge pressure. Suitable positions for the member 38 with respect to the end wall 34 are shown in Figure 4 (first illustrative machine) and Figure 9 (second illustrative machine) as 0 which represents the angle between the surface 40 of the member 38 and the liquid material collecting end wall surface 34. In general, the value of angle o need not be greater than about 900 and should be at least 100 with preferred values for the angle 0 being between 150 and 400.

The shape of the restraining surface providing member 38 can also vary: however, as hereinbefore mentioned, at least a portion of the shape must be capable of effectively restraining the movement of substantially all particulate (unmelted) material beyond (downstream of) the member 38 into the melt pool 42.

The member 38 of the first illustrative machine is solid throughout (as is preferred) but other members for the same purpose in machines in accordance with the invention may have openings or a portion of them may have openings so long as the openings do not interfere with the assigned restraining function: for example, a screen or a plurality of them may be used in fabricating suitable material restraining providing surface members.

The clearance 50 Figure 5 (first illustrative machine) and Figure 10 (second illustrative machine), between the sides of the member 38 and the walls 24 is a factor of some importance since it should permit only melted liquid material to be dragged past the member 38 to the melt pool 42 while the body 39 of unmelted or incompletely melted particulate material is restrained by the surface 40.

Suitable clearances 50 that can be employed are conveniently between 0.03" (about 0.76 mm) and 0.13" (about 3.18 mm) using channels 22 having widths between about 0.75" (about 19 mm) and 1.25" (about 38 mm).

Clearances 50 between the walls 24 and the sides of the members 38 which are less than the thickness of the film 25 of liquid material dragged by the walls 24 may advantageously be used; the clearance 50 can be selected depending on desired or preselected shear and stress conditions to be applied to the particular material being dragged by walls 24 past member 38 to the melt pool 42. Also, these clearances 50 can be selected in conjunction with material restraining surface providing members 38 having a leading edge or a portion of a leading edge which can scrape off some of the liquid material so that the scraped off material can be mixed with particulate material at or near the leading edge as hereinafter described in greater detail in relation to other machines embodying the invention.

In Figures 6 to 8 are shown parts of other machines embodying the invention similar to the first illustrative machine hereinbefore described except that material restraining members 38 of different configuration are used.

In the machine shown in Figure 6 the material restraining member 38a is circular in cross sectional shape and provides a material restraining surface 40a which is arcuate. The machine shown in Figure 7 comprises a restraining member 38b which provides a planar restraining surface 40b and has recesses, viz. undercuts 44, in the sides adjacent the channel walls 24. The undercuts 44 are designed to provide mixing and agitation of liquid material dragged past the member 38b. As shown in Figure 7, member 38b has a convergent, symmetrically angular downstream end portion. The machine shown in Figure 8 comprises a member 38c having a divergent symmetrically angular restraining surface 40c with respect to the direction of flow, substantially parallel sides and a planar downstream end portion.

In the machines embodying the invention shown in Figures 3, 4, 6, 7 and 8, a void of material or free space 46 is created between the channel walls 24 on the downstream side of the restraining members 38. This free space 46 is provided because the members 38, 38a, 38b, and 38c permit passage of only liquid material to the end wall surface 34 of the member 32, the liquid material dragged by each wall past the members being spread and maintained on each wall 24 as a thin film 25 until scraped off by scraping surfaces of the member 32, the material restraining surface providing members of this invention being positioned between the inlet 28 and the outlet 36 so that the particulate material is restrained at a position closer to the outlet 36 than to the inlet 28.Accordingly, the amount of free space 46 is usually considerably less than that obtained in accordance with the practice of the invention disclosed in the specification of our copending U.K. Patent Application Serial No. 2,007,585 (to which reference is hereby directed). However, if desired, the free space 46 provided between the walls 24 carrying only the thin film 25 of melted material past the member 38 to the member 32 can be used to accept or supply gaseous or volatile substances from or to the film 25. The free space 46 may also be used to introduce solid or liquid materials to the thin film 25 spread on the channel walls 24.

In the first illustrative machine a port 48 (Figure 4) is connected to the free space 46 to introduce materials to, or remove materials from, the thin film 25 of liquid material dragged past the member 38.

Volatiles in the film 25 may pass into the free space 46 and be withdrawn through the port 48 using vacuum if desired, to effect devolatilisation. Alternatively, materials may be introduced to the free space 46 through the port 48: these materials may be, for example, gases or reagents for combination with the liquid material or pigments or reinforcing materials or other solids for incorporation in the liquid material.

In the machines embodying the invention shown in Figures 1 to 8, the members 38, and the members 32, are shown as separate and distinct structural members and the cross-sectional area of the space available for the melt pool 42 is relatively large. A relatively large cross-sectional area of melt pool space can present certain advantages such as discussed before with respect to the introduction or withdrawal of materials from a free space established within a portion of the total space existing between the surfaces 40, 34 but as a general rule however, it appears that the larger the crosssectional area of available melt pool space, the larger the pool of collected melted or liquid material required to generate a satisfactory discharge pressure: for a given discharge pressure this may result in higher melt pool temperatures which may be undesirable leading to problems e.g. thermal degradation of liquid in the pool.

In the second illustrative machine embodying the invention and other machines embodying the invention hereinafter described the available space downstream of the surface 40 available for formation of the melt pool is selected to provide a region of predetermined geometry for liquid carried into the space and thus provide desired discharge pressure characteristics for liquid collected in the melt pool.

The second illustrative machine (Figures 9 and 10) is generally similar except as hereinafter described to the first illustrative machine. The second illustrative machine comprises a unitary member 52 providing both a restraining surface 40d and an end wall surface 34d positioned in the channel. The unitary member 52 can be considered to comprise a restraining surface member 38d connected to a blocking member 32d by a portion considered as a connecting section and the integral member is "T" shaped in section with planar surfaces 40d, 34d normal to the direction of flow. A part of the space between the surface 40d and the end wall surface 34d is occupied by the connecting section which therefore can control the amount of available space or volume for a melt pool 42d.Accordingly the connecting section of the unitary member 52 can be varied in configuration to provide a melt pool space having a predetermined geometry or size or volume. Melt pool spaces having a predetermined geometry, size or volume present the capability for providing preselected processing characteristics including maximised discharge pressure characteristics desired for a specified liquid material collected in the pool 42d.

As already discussed, the pressure generated for discharge of the liquid material collected in the pool is a factor that can affect the quality of the discharged melted material. However, the second illustrative machine provides a degree of control over the processing conditions applied to the liquid material collected in the melt pool 42d in terms of the shear forces applied to the collected material as well as the temperature of discharged melted material. A machine embodying the invention otherwise similar to the second illustrative machine is shown in Figure 11 and comprises a unitary member 52e providing both a restraining surface 40e and an end wall surface 34e; the member 52e is "I" shaped in section with the planar surfaces 40e and 34e normal to the direction of flow.

The third illustrative machine (Figures 12 and 13) is generally similar except as hereinafter described to the first illustrative machine and comprises a member 38f having a restraining surface 40f and a member 32f having an end wall surface 34f. However, the member 32f comprises an extension portion 56 used to reduce the available volume or space between the surface 34f of the member 32f and the surface 40f of the member 38f thereby providing a melt pool space of predetermined geometry, size, volume or configuration which also provides preselected discharge characteristics.In machines embodying the invention generally similar to the third illustrative machine further control over the geometry, volume, size and configuration of the space available for the melt pool can be obtained by adding an extension portion 57 to the member 38h (Figure 15) or by adding extension portions 57g and 56g to both the restraining surface providing member 38g and the end wall providing member 32g respectively (Figure 14).

Particulate materials which may be processed by the methods and machines of the present invention include particulate plastics materials and polymeric materials reducible by heat, mechanical energy, or by diluent to a liquid state for processing and which have sufficient stability to avoid serious degradation under treatment conditions.These materials include but are not limited to thermoplastic, thermosetting and elastomeric polymeric materials, for example polyolefins (e.g. polyethylenes, polypropylenes), vinylchloride polymers (e.g. polyvinylchloride), fluorine containing polymers, polyvinylacetate based polymers, acrylic based polymers, styrene based polymers (e.g. polystyrene), polyamides (e.g. nylons), polyacetals, polycarbonates, cellulose based plastics, polyesters, polyurethanes, phenolic and amino plastics, epoxy based resins, silicone and inorganic polymers, polysuiphone based polymers, and various natural based polymers together with copolymers and blends of those materials with each other or with solvents or diluents or with different solid and liquid additives.

Temperature of the material as supplied and during the course of processing in the apparatus may be controlled so that the viscosities and flow characteristics of the materials being processed are determinable.

In the machines embodying the invention described hereinbefore, the member 32 has been described as having the function of scraping off melted material dragged to it by the walls 24 so that a pool 42 of liquid material is collected at the end wall surface 34 for discharge. However, by carefully selecting certain clearances or by providing means to move member 32 in and out of the channel or by providing means that can otherwise permit at least some of the liquid material to bypass member 32 for recycling further improvement in processing may be achieved in machines according to the invention. Recycled liquid material can contact and mix or fuse with restrained particulate material in the channel upstream of the material restraining providing surface member.This contact and mixing and fusion of recycled liquid material with particulate material appears to have an important effect which can improve overall melting efficiency. We believe that the improved melting efficiency is a result of the viscous melted material penetrating between unmelted particles of the feed material and providing deformation for the mixture of melted and unmelted materials. Drive power accordingly can, it is believed, be converted into thermal energy at higher rates throughout the volume of the channel.

The machine embodying the invention shown in Figure 14 makes use of recycling of liquid material past the member 32g in its operation and mixing of melted liquid material with the restrained particulate material thereby takes place.

The machine embodying the invention shown in Figure 15 achieves mixing of liquid material with particulate plastic or polymeric material by establishing a back pressure in the melt pool 42h, for example by adjusting an outlet valve (not shown) or by using other discharge pressure control means (hereinbefore described). This back pressure causes accumulation of liquid material at or near the surface 40h of the member 38h. Progressive accumulation of liquid material promotes efficient mixing with the particulate material in the region of the surface 40h and thus improves overall melting efficiency.

A machine embodying the invention employing a further method of mixing liquid material with particulate material at or near the particulate material restraining surface 40 is shown in Figure 16.

This machine comprises a unitary member 52! (see Figure 1 6) having a restraining surface 40i and an end wall surface 34i. The restraining surface 40i is angular with respect to the direction of flow and a scraping clearance is provided between one of the channel walls 24 and the adjacent side of the unitary member 52i which forms an acute angle with the surface 40i. A gap 50 is provided between the opposite side of the member and the channel wall adjacent that side forming an obtuse angle with the surface 40i. The gap 50 therefore provides a melt pool space and liquid material is collected against the surface 34i.Because of the scraping clearance, liquid material is scraped off the moving channel wall at the apex 41 of the surface 40i and this scraped off liquid material is mixed with and contacts particulate material at or near the restaining surface 40i in the manner shown in Figure 1 6.

The other channel wall, however, drags liquid material to the surface 34i where it is collected as a melt pool 42ifor processing and discharge.

Yet another machine embodying the invention in which the desirable mixing or fusion of liquid material with restrained particulate material is achieved is shown in Figure 17. This machine comprises a scraping and mixing element 60 in a fixed, stationary position adjacent the channel wall 24 and positioned between the inlet (not shown) and the material restraining surface providing members (not shown). The scraping and mixing element 60 is arranged substantially parallel to and spaced apart from the channel wall 24 by a close clearance which permits the element 60 to scrape off at least a portion of-and preferably substantially all of-the film 25 of liquid material dragged by the wall 24 to the scraping and mixing element 60.The element 60 is shaped to provide efficient mixing of the scraped off liquid material with restrained particulate material at or near the element 60. It should be understood that more than one scraping and mixing element can be positioned adjacent the channel wall(s) 24 between the inlet and the material restraining surface. Also, one or more scraping and mixing elements 60 can be positioned adjacent one or both walls 24 and spaced apart from each other along the circumferential distance between the inlet and material restraining surface to provide the desired degree of mixing of melted material with restrained particulate material.

The following examples describe methods of processing particulate material embodying the invention and comparative methods. In each of the examples the pressures (P1, P3, P4 and P5) were recorded at points "P,", "P3", "P4" and "P5, shown in Figure 4.

Example I This example is a comparative example of the processing of particulate materials by the method described in the aforementioned U,S. patent specification.

A machine generally as the first illustrative machine (shown in Figures 1 and 2) having a liquid material collecting end wall surface 34 as shown in Figure 4 but omitting the member 38, was set up with a rotor 10 having a channel width of 0.75" (about 19 mm) and an outside diameter of 7.5" (about 190.5 mm) and inside diameter of 3.75" (about 95.3 mm). The inlet 28 to the housing 16 was connected by a conduit to a supply of particulate low density polyethylene, and the outlet 36 was connected to a restricted orifice. The rotor temperature, housing temperature and exit valve temperature of the processor were maintained at 4000F (about2040C).

The results in Table 1 were obtained: Table 1 G T Melt P1 P2 P3 P4 Torque Pw N lb/hr T Disk Out psia psia psia psia lbF-in HP rpm (kg/hr) F( C) F( C) (MN/m2) (MN/m2) (MN/m2) (MN/m2) (NM) (KW) Comment 150 54 400 418 600 353 158 110 13505 32.2 Melt full (24.5) (204) (214) (4.14) (2.43) (1.08) (0.76) (1526) (24.6) of air bubbles.

200 60 400 430 730 315 152 112 12762 40.0 Some (27.2) (204) (221) (5.03) (2.17) (1.05) (0.77) (1442) (29.8) unmelted material.

Table 2 150 71.1 400 430.9 73 241 113 64 6833 16.2 Few air (32.2) (204) (222) (0.50) (1.66) (0.78) (0.44) (772) (12.1) bubbles.

200 83.4 400 447.7 59 397 110 57 7336 23.2 (37.8) (204) (231) (0.41) (2.74) (0.76) (0.39) (829) (17.3) Table 3 150 69.4 400 409 10 339 157 68 10576 25.1 Very clean (31.5) (204) (209) (0.07) (2.34) (1.08) (0.47) (1195) (18.7) melt.

200 80.3 400 438 13.7 545 201 97 16827 34 Low exit (36.4) (204) (226) (0.09) (3.76) (1.39) (0.67) (1901) (25.4) temp.

In the above tables N is speed of rotation of the rotor in revolutions per minute, G is throughput rate in pounds per hour (kilograms per hour), T Disk is the temperature of the rotor in degrees fahrenheit (celsius) T Melt is the temperature at the outlet 36 in degrees fahrenheit (celsius), Pw is the power in horsepower (kilowatts).

The pressure "P," in Table 1 is the pressure recorded at the outlet of the channel and just before the exit valve. Note that there is a progressive increase in pressure as the circumferential distance from the inlet increases with the pressure reaching a maximum at the end wall surface 34 which is adjacent the outlet 36. The presence of unmelted particulate material in the viscous liquid material discharged from the processor of this example is most likely due to the extremely high pressures ("P,") generated near the outlet 36 as is the presence of large amounts of unmelted or incompletely melted particulate material mixed with the liquid material of the pool collected at the end wall surface 34 of member 36 for discharge.

Example II This example describes a method embodying the invention. Sltbstantially the same procedure as in Example I was followed. However, a machine embodying the invention generally as the first illustrative machine but comprising a member 38a as shown in Figure 6 and of diameter 5/8" (about 15.9 mm) was positioned in the channel 22 as shown in Figure 4 so that the value of the angle 61 was 340. The minimum clearance 50 between the O.D. of the member 38a and each wall 24 was about 0.06" (about 1.52 mm).

The results shown in Table 2 were obtained.

The pressure "P," in Table 2 is the pressure recorded at the point P, (Figure 4) and the melt pool space of this example was of the type shown in Figure 4. Note that again there is a progressive increase in pressure as the circumferential distance from the inlet 28 increases. However, maximum pressure is reached at or near the restraining surface 40a (Figure 6) rather than at the end wall surface 34 as in Example 1. Instead, the discharge pressure "P," generated in the space between the restrained particulate material and the end wall surface is actually much lower than the maximum pressure generated at the restraining surface. These conditions, however, uniformly and consistently provide discharged melted materials of improved quality free of unmelted particulate materials and yet are discharged as completely melted products at relatively low temperatures.

Example Ill This example describes a method embodying the invention. Substantially the same procedure as in Example I was followed. However, a machine embodying the invention generally as the second illustrative machine comprising a unitary member 52 providing a particulate material restraining surface 40d and a liquid collecting end wall surface 34d (Figures 9 and 10) was positioned in the channel. The value of the angle 61 (Figure 9) for the member 52 employed in this example was 1 50. The clearance 50 (Figure 10) was 0.03 inches (about 0.76 mm).

The results shown in Table 3 were obtained.

The pressure "P," in Table 3 is the pressure recorded at the position P, of Figure 9 and the melt pool 42d of this example was the type shown in Figures 9 and 10. As discussed above in relation to the second illustrative machine (Figure 9), the unitary members 52 provide a predetermined goemetry, size, configuration or volume for the space existing between the particulate material restraining surface 40dand the end wall surface 34d. In turn, the predetermined geometry is designed to provide preselected discharge characteristics for liquid material collected as a pool in the space. As shown by this example, the predetermined geometry of the space provides reduced discharge pressures, improved quality of discharged melted products free of unmelted material and reduced temperatures for the discharged, completely melted products.

The machines and methods embodying the invention described above give improved melting efficiency, improved control over processing parameters and improved quality of melt products. They are especially suitable for the processing of particulate materials using relatively wide channels e.g.

where the width between the opposed walls 24 is between 0.75 and 1.50 inches (about 19 and 38 mm) and having walls which can be rotated at relatively high speeds e.g. between about 50 rpm to about 300 rpm. This combination of wide channels and high rotational speeds provides efficient melting and in certain machines embodying the invention the melted liquid material is fluxed into the restrained particulate material; the mixture is under continuous deformation and shear. More mechanical energy can be converted into heat and the rate of melting increased but also improved control over the temperature and discharge pressure of the melted material is achieved.

Claims (38)

Claims

1. A machine for processing particulate material which becomes liquid in the course of processing comprising a rotor having an annular processing channel, a stationary element providing a surface cooperating with the channel to form with the channel an enclosed annular processing passage, an inlet in the stationary element for feeding particulate material to the passage, an outlet in the stationary element from the passage circumferentially spaced from the inlet downstream of the inlet in the direction of rotation of the rotor, a first surface disposed in the annular passage between the outlet and inlet in the direction of rotation of the rotor and providing a material collecting surface in the processing channel, and a second surface disposed in the annular passage upstream of the outlet the second surface being shaped to provide a clearance between walls of the processing channel and sides of a member providing the second surface, the construction and arrangement being such that as the rotor is rotated in the operation of the machine material in a central region of the passage is restrained by the second surface while permitting liquid material to be dragged by the walls through the clearance towards the first surface, the first and second surfaces being positioned to provide a space for liquid material downstream of the second surface sufficient that pressure is generated in a pool of liquid material collected in the space for discharge of liquid through the outlet.

2. A machine for processing particulate material which becomes liquid in the course of processing comprising a rotor having an annular processing channel, a stationary element providing a surface cooperating with the channel to form with the channel an enclosed annular processing passage, an inlet in the stationary element for feeding particulate material to the passage, an outlet in the stationary element from the passage circumferentially spaced from the inlet downstream of the inlet in the direction of rotation of the rotor, a first surface disposed in the annular passage between the outlet and inlet in the direction of rotation of the rotor and providing a material collecting surface in the processing channel, a second surface disposed in the annular passage upstream of the outlet the second surface being shaped to provide a clearance between walls of the processing channel and sides of a member providing the second surface, and a portion positioned in a space between the first and second surfaces, the construction and arrangement being such that as the rotor is rotated in the operation of the machine liquid material is dragged through the clearance towards the first surface into the space said portion occupying a part of the space to provide a region of predetermined geometry for liquid carried into the space in which to generate discharge pressure in the operation of the machine.

3. A machine according to either one of Claims 1 and 2 in which the rotor has a cylindrical surface, the processing channel has opposing walls extending inwardly from the cylindrical surface and the stationary element comprises a housing having an internal cylindrical surface coaxial with the rotor, the internal surface cooperating with the channel to provide the annular passage.

4. A machine according to any one of the preceding claims comprising heating means for melting particulate material in the passage.

5. A machine according to any one of the preceding claims comprising means for controlling discharge of liquid material from the outlet to secure a desired extent of processing.

6. A machine according to any one of the preceding claims in which the clearance is selected to apply desired conditions of shear on liquid material dragged past the member providing the second surface.

7. A machine according to any one of the preceding claims in which the clearance is between 0.76 and 3.18 mm.

8. A machine according to any one of the preceding claims in which the sides of the member providing the second surface comprise means for mixing the liquid as the liquid is dragged past the member.

9. A machine according to Claim 8 in which the means comprises recesses in the sides of the member providing the second surface.

10. A machine according to any one of the preceding claims in which a member providing the first surface is constructed to allow a quantity of the liquid material to pass the member providing the first surface and recirculate through the passage.

11. A machine according to any one of the preceding claims comprising means positioned between the inlet and the second surface to divert part of the liquid material from the walls of the processing channel to mix the liquid material with particulate material in a central region of the channel.

12. A machine according to any one of the preceding claims comprising means to cause accumulation of a portion of liquid material at the second surface.

13. A machine according to any one of the preceding claims in which a scraping clearance is provided between one of the sides of the member providing the second surface and an adjacent wall of the channel so that the liquid material can be accumulated at the second surface.

14. A machine according to any one of Claim 1 and Claims 3 to 13 when appendant to Claim 1 comprising a portion positioned in the space between the first and second surfaces and occupying a part of the space to provide a region of predetermined geometry for liquid carried into the space, in which to generate discharge pressure in the operation of the machine.

15. A machine according to any one of Claims 2, 14 and 3 to 13 when appendant to Claim 2 comprising a blocking member providing the first surface and a further member providing the second surface, the portion positioned in the space being provided by a section of one of said members extending towards the other member.

1 6. A machine according to Claim 15 wherein the portion is provided by a section of each of said members extending towards the other of said members.

17. A machine according to any one of Claims 2, 14 and 3 to 13 when appendant to Claim 2 comprising a unitary member providing the first and second surfaces and the portion positioned in the space between the first and second surfaces.

18. A machine according to any one of the preceding claims in which at least a portion of the width of the channel between the interior surfaces of the channel walls is between

1 9 mm and 38 mm.

1 9. A machine according to any one of the preceding claims comprising means to rotate the walls at a speed between 50 rpm to 300 rpm.

20. A machine according to any one of the preceding claims in which the second surface is spaced apart from the first surface and the second is closer to the first surface than to the inlet.

21. A machine according to any one of the preceding claims in which the second surface is spaced apart from the first surface so that the angle between these surfaces is between 100 and 900.

22. A machine according to Claim 21 in which the angle formed between the surface is between 150 and 400.

23. A machine according to any one of the preceding claims comprising a plurality of processing channels at least one of which comprises first and second surfaces disposed in the annular passage.

24. A method for processing particulate materials which become liquids in the course of processing comprising the steps of: (a) introducing the particulate material through an inlet into an annular processing passage comprising a channel having opposed walls and a coaxial stationary surface cooperatively arranged with the channel to retain the material in the passage, (b) providing a first surface positioned adjacent an outlet which is circumferentially spaced apart from the inlet, (c) providing a second surface spaced apart from the first surface and capable of restraining any substantial movement of the main body of particulate material fed to the passage, there being a clearance between sides of a member providing the second surface and the channel walls, the second surface being positioned in the passage to provide a space for liquid material between the second surface and the first surface to collect a pool of liquid material which can at least wet sufficient area of the wall of the channel when rotated to generate discharge pressure; (d) rotating the channel in a direction from the inlet toward the outlet to establish relative movement between the rotating walls and material in a central region of the channel restrained by the second surface, (e) dragging liquid portions of the material in contact with the rotating walls through the clearance toward the first surface and (f) collecting the dragged forward liquid material as a pool of liquid against the first surface for controlled processing and/or discharge.

25. A method according to Claim 24 comprising the step of applying preselected shear conditions to the liquid material as the material is dragged through the clearance to the first surface.

26. A method according to either one of Claims 24 and 25 comprising the step of dragging a portion of liquid material past the outlet and mixing the liquid material with the restrained particulate material.

27. A method according to any one of Claims 24 to 26 comprising the step of dragging a portion of the liquid material to the second surface and mixing a portion of the liquid material with restrained particulate material at the second surface.

28. A method according to any one of Claims 24 to 27 comprising the step of mixing a portion of the liquid material dragged from the inlet to the second surface with particulate material restrained between the inlet and the second surface.

29. A method according to any one of Claims 24 to 28 comprising the step of heating the particulate material in the passage to melt the particulate material.

30. A method according to any one of Claims 24 to 29 comprising the step of controlling the discharge of the liquid material from the outlet to secure a desired extent of processing.

31. A machine for processing particulate material which becomes liquid in the course of processing constructed arranged and adapted to operate substantially as hereinbefore described with reference to Figures 1 to 5 of the accompanying drawings.

32. A machine for processing particulate material which becomes liquid in the course of processing constructed arranged and adapted to operate substantially as hereinbefore described with reference to any one of Figures 6, 7 and 8 of the accompanying drawings.

33. A machine for processing particulate material which becomes liquid in the course of processing constructed arranged and adapted to operate substantially as hereinbefore described with reference to Figures 9 and 10 of the accompanying drawings.

34. A machine for processing particulate material which becomes liquid in the course of processing constructed arranged and adapted to operate substantially as hereinbefore described with reference to Figures 9 and 11 of the accompanying drawings.

35. A machine for processing particulate material which becomes liquid in the course of processing constructed arranged and adapted to operate substantially as hereinbefore described with reference to Figures 12 and 13 of the accompanying drawings.

36. A machine for processing particulate material which becomes liquid in the course of processing constructed arranged and adapted to operate substantially as hereinbefore described with reference to any one of Figures 14 to 17 of the accompanying drawings.

37. A method of processing particulate material which becomes liquid in the course of processing using a machine according to any one of Claims 1 to 23.

38. A machine for processing plastic and polymeric material comprising: (a) a rotatable element carrying at least one annular processing channel providing a processing surface area including opposed side walls, (b) a stationary element providing a coaxial surface cooperatively arranged with said annular processing channel to provide an enclosed processing passage, (c) an inlet in said stationary element for introducing material to said annular processing channel, (d) an outlet in said stationary element for discharging material from said annular processing channel, (e) a member associated with said stationary element and providing a first blocking surface in proximity to said outlet and extending into said annular processing channel and substantially blocking said channel, said member having a cross-sectional configuration of said annular processing channel and being positioned therein to impede further advance of liquid material carried by the processing surface area in said annular processing channel and to cooperate with said outlet to discharge said material, (f) a member providing a second blocking surface extending into said annular processing channel over substantially the full depth of said annular processing channel at a location proximate to, but upstream from said outlet whereby a space is provided between said blocking surfaces which is a minor portion of the circumferential distance of said stationary element, said second blocking surface having a cross-sectional configuration of said annular processing channel and being of lesser width in cross-section than said annular processing channel to provide a clearance between said opposed side walls and said second blocking surface providing member adapted to block advance of material in a central portion of the annular processing channel but to permit liquid material carried on said walls to pass through said clearance for collection as a pool in said space, and (g) means positioned in said space and occupying a predetermined portion of said space to provide a pool space of predetermined geometry in which material can at least wet sufficient processing surface area to generate discharge pressure.