GB2042406A - Machine for impelling viscous liquid material e.g. plastics - Google Patents

Abstract

The material is impelled within an annular peripheral channel (20) or adjacent channels of a rotor (10) which rotates within the surrounding cylindrical surface (14) of a station (12), to impel the material between a stator inlet (28) and circumferentially spaced outlet (29), against a stationary blocking member (19) which extends into each channel (20) to build up pressure in the liquid which causes it to flow through the outlet (29). Seals to militate against leakage from the channels are provided between rotor and stator surfaces between which there is a narrow clearance (50), the seals comprising oblique channels (26) formed in one of the surfaces, and acting, during rotation between the surfaces, to force the liquid back along the oblique channels (26) into the impelling channel. The leakage pressure, and penetration, along the channels (26) increases between the inlet (28) and the outlet (29). Power loss in driving the rotor is reduced, by a scraper (31) which removes liquid from the bends (27) between the channels (26), at a location of maximum penetration beyond the outlet (29) and of low pressure adjacent the inlet (28). <IMAGE>

Description

SPECIFICATION Machine and method for processing viscous material This invention is concerned with a machine and a method for processing materials which are, or become in the course of processing, viscous liquids, for example plastics and polymeric materials.

In the specification of our United States patent No. 4142805 is described machines and methods for processing plastics and polymeric materials. The machines comprise a rotor having at least one annular processing channel, mounted for rotation in a housing having an internal surface coaxial with the rotor, the channel and coaxial surface together defining an enclosed annular processing passage. 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 specifications further comprises å 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, material 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 so constructed to hold the material in the processing channel 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, the material discharged through the outlet being in the form of a viscous liquid. The methods and machines are described in the aforementioned specifications as useful for, inter alia, melting or plasticating plastics materials, conveying, pumping or pressurising liquid materials, mixing blending dispersing and homogenising plastics and polymeric materials, devolatilising materials, and bringing about structural change in materials by chemical reactions e.g.

polymerisation, cross linking or foaming. Reference is directed to the aforementioned specifications for further information on the machines and methods described therein.

Because of the versatility and adaptability of the basic individual processing passage, a plurality of passages are conveniently employed in preferred machines of the type described in the aforementioned specification, usually with one or more passages performing a different operation or function. For example, one or more of the individual passages could be assigned the function of receiving and transporting material from one passage to another, or of melting or of mixing or of devolatilising or of discharging polymeric or plastomeric material(s). The particular function assigned an individual passage usually determines the pressure characteristics of that passage. For example, some assigned functions, e.g. melting or discharging, can imply the generation of very high pressures.Other functions, e.g. devolatilising can involve the generation of much lower pressures while mixing operations may involve intermediate pressures. Also, the distribution of pressure along the circumference of each passage can vary depending upon the function or operation assigned the passage. For some functions, pressure may increase linearly around the complete circumference (from inlet to outlet) or around only a portion of the circumference or for some purposes pressure characteristics involving one or more pressure rises followed by one or more sharp drops along the circumference are required. Moreover frequently, individual processing passages having particular pressure characteristics e.g. high pressure, are positioned or arranged beside or between units having completely different pressure characteristics e.g. low pressure.

In most instances, therefore, it is desirable to provide effective sealing for some or all of the individual processing passages of a machine having a plurality of processing passages, to prevent unwanted leakage of material from at least some of the passages.

The unwanted leakage for example can be external leakage from one or both of the end passages of a multi-passage processor. Also, unwanted leakage can occur internally between adjacent individual processing passages. In all cases however, leakage of espe cial concern occurs at a clearance between the surface of the rotor and the stationary interior surface of the housing, especially at those portions of the passage where high pressures are generated.

External and internal leakage problems are especially complicated in machines having a plurality of processing passages because of the different radial pressures usually established at different points around the circumference of the passage(s). For example, commonly the pressure at the inlet of a passage is low while the pressure at the blocking member can be extremely high. In fact, the difference in radial pressures can be great enough to cause deflection of the rotor thereby imposing an undesirable constraint on the tolerances available for the requisite clearance between the peripheral surface of the rotor and the stationary interior coaxial annular surface of the housing.

One of the objects of the present invention is to provide an improved machine for processing materials which are, or become in the course of processing, viscous liquids, the machine comprising improved sealing means.

According to the invention there is provided a machine for processing materials which are, or become in the course of processing, viscous liquids comprising a rotor for processing the material mounted for rotation in a housing. The rotor comprises a surface, preferably a cylindrical surface, having at least one annular processing channel, the walls of which where the surface is cylindrical extend inwardly from the surface. The housing in which the rotor rotates comprises a stationary internal surface, preferably a cylindrical internal surface, complementary to and spaced slightly apart from the surface of the rotor and cooperating with the surface of the rotor to form with the annular processing channel (or channels) an enclosed annular processing passage (or passages).The machine further comprises inlets through which material to be processed may be admitted to the (or each) annular passage and an outlet 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 in the operation of the machine; for some purposes the outlet is preferably positioned a major portion of a complete revolution from the inlet considered in the direction of rotation of the rotor.The machine further comprises a blocking member disposed in the (or each) annular passage between the outlet and the inlet in the direction of rotation of the rotor to hold a body of material being processed in the (or each) annular channel so that there is relative movement between side walls of the (or each) annular channel and the body of material, the side walls operating (as the rotor rotates) to drag liquid portions of the material in contact with the side walls downstream towards the blocking member whereby pressure is built up in the liquid as the blocking member is approached.

A machine according to the invention also comprises sealing means militating against leakage of liquid material from the (or each) processing channel comprising a surface portion of the rotor at one side of the (or each) processing channel containing the liquid under pressure: in a preferred machine in accordance with the invention the rotor surface is cylindrical and the surface portion of the rotor is an annular peripheral surface portion extending around the rotor at one side of the annular channel. The sealing means of a machine in accordance with the invention further comprises a stationary surface portion of the housing adjacent said surface portion of the rotor and spaced apart therefrom by a narrow clearance.A machine in accordance with the invention further comprises a plurality of sealing channels in one of said adjacent surface portions, the construction and arrangement being such that the liquid to be processed can penetrate the channels, the width of the said one of the surface portions and the number, angle and geometry of the channels being selected so that penetration of the clearance and the channels by the pressurised liquid (outward from the processing channels containing pressurised liquid) is opposed by an inward force applied to the liquid in the sealing channels as the surface portions are relatively rotated.

A machine in accordance with the invention preferably comprises scraping means projecting into the clearance for scraping liquid penetrating into the clearance from one of the surface portions into a zone of minimum pressure in the processing channel of the rotor containing liquid so that liquid contact between the two adjacent surface portions is broken during at least part of the revolution of the rotor. Suitably the processing channel of the rotor containing liquid has a zone of one pressure and a circumferentially spaced zone of a greater pressure.

Suitably a machine according to the invention is so constructed and arranged that, in the operation of the machine, the extent of penetration of liquid does not exceed the length of any sealing channel.

According to the invention a method is also provided, of processing materials which are, or become in the course of processing, viscous liquids using a machine in accordance with the invention in which the speed of rotation of the rotor is such that the length of penetration of pressurised liquid does not exceed the length of any sealing channel. Preferably the sealing channels of a machine in accordance with the invention extend obliquely across the surface portion and are helical, the helix angle of each sealing channel being 20 or less, more preferably 15 or less. The surface portion in which the sealing channels are formed is stationary (being part of the housing) in some forms of machine in accordance with the invention, and is rotatably (being a surface portion of the rotor) in other forms of the invention.

Preferably the clearance between the surface portions is 2.5 mm or less, more preferably 1.25 mm or less.

The sealing channels are suitably arranged substantially parallel to one another.

Conveniently the sealing means of a machine in accordance with the invention may comprise nested truncated conical members of stiffly resilient material, said members having a surface adjacent outer edges thereof arranged closest to the processing channel so as to be displaceable by pressure, and means for holding inner edges of the members against displacement by pressure so that the outer edges seal with the surface portion of the housing; either the surface portion of the housing or the outer edges of the nested members have the sealing channels formed therein, in this case.

In a preferred machine in accordance with the invention the cylindrical surface of the rotor provides the annular peripheral surface portion of the sealing means, and the surface portion of the housing is provided by a portion of the cylindrical internal surface of the housing.

In an alternative form of machine in accordance with the invention the surface portion of the sealing means comprises an annular peripheral surface portion of the rotor disposed inwardly of the cylindrical surface and at the opposite side of the cylindrical surface to the processing channel, and the stationary surface portion of the housing comprises a corresponding annular surface portion extending inwardly from the cylindrical internal surface of the housing. Suitably the annular surface portions of both the rotor and the housing are perpendicular to the axis of rotation of the rotor.

Preferably a machine in accordance with the invention comprises surface portions having sealing channels disposed on either side of each processing channel, there preferably being a plurality of such processing channels each having associated sealing means.

Where a machine in accordance with the invention comprises scraping means, an upstream face of the scraping means preferably extends across the surface portion inclined at an angle to the direction of movement of the surface portion relative to the scraping means whereby to direct liquid scraped from the surface portion into the zone of reduced pressure.

There now follows a detailed description to be read with reference to the accompanying drawings of a number of machines for processing materials which are, or become in the course of processing, viscous liquids, embodying the invention, together with methods of processing material using these machines which likewise embody 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 view partly in section and with parts broken away showing a rotor and housing of the first illustrative machine, having a plurality of annular processing channels; Figure 2 is a view of part of Fig. 1 (but enlarged) showing the relationship between two surface portions providing dynamic sealing means; Figure 3 is a diagrammatic view showing further relationships between the surface portions providing the dynamic sealing means of the the first illustrative machine; Figure 4 is a diagrammatic view of a cylindrical, peripheral surface portion shown in Figs. 2 and 3, developed into a plane and having a plurality of helical sealing channels; Figure 5a is a graphic representation of the pressure profile developed around the circumference of an annular processing passage of the first illustrative machine;; Figure 5b is a graphic representation of the computed length of penetration of liquid into the helical sealing channels obtained for the pressure profile shown in Fig. 5a; Figure 6 is a fragmentary view partly in section of a second illustrative machine showing the relationship between a stationary scraper and a surface portion of a rotor carrying a plurality of helical sealing channels; Figure 6a is a top view of the rotor and scraper shown in Fig. 6; Figure 6b is a view in section on the line Vlb-Vlb of Fig. 6a; Figure 7 is a fragmentary view partly in section of the second illustrative machine showing the relationship of a stationary scraper and a surface portion of the rotor (between two adjacent processing channels) carrying a plurality of helical sealing channels; Figure 7a is a top view of the surface portion of the rotor and scraper shown in Fig.

7; Figure 7b is a view in section on the line Vllb-Vllb of Fig. 7a; Figure 8a is a graphic representation of the pressure profile developed around the circumference of an annular processing passage of the second illustrative machine (similar to that of Fig. 5a); Figure 8b is a graphic representation of the computed length of penetration of liquid into the helical sealing channels obtained for the pressure profile shown in Fig. 8a; Figure 9 is a view in section of part of a third illustrative machine; Figure 9a is an end view of a surface portion of dynamic sealing means of the third illustrntive machine; Figure 9b is a top view partly in section of the surface portion of the rotor and scraper shown in Fig. 9; Figure 10 is a view in section# of part of a fourth illustrative machine;; Figure 10a is an end view of a surface portion of the dynamic sealing means of the fourth illustrative machine; Figure 10b is a top view of the surface portion of the rotor and scraper shown in Fig.

10; Figure 11 is a scrap sectional view of a fifth illustrative machine; Figures 12 and 12a are views similar to Figs. 3 and 4 respectively but showing a sixth illustrative machine; Figures 13 and 13a are also views similar to Figs. 3 and 4 respectively but showing a seventh illustrative machine; Figures 14 and 15 are each scrap sectional views showing eighth and ninth illustrative machines; Figures 16, 17 and 18 are graphical repre- sentations showing penetration length of liquid into a plurality of helical sealing channels in machines similar to the first illustrative machine in response to different conditions e.g. the number and angle of helical sealing channels and the speed of rotation of the rotor.

The illustrative machines described hereinafter are for processing materials which are, or become in the course of processing, viscous liquids. Each of the illustrative machines comprises a rotor 10 mounted for rotation about an axis in a housing 12 comprising a stationary cylindrical internal surface 14 coax ial with the rotor 10. The rotor 10 comprises a cylindrical surface 26 and at least one, viz.

two, annular processing channels 20 comprising side walls 24 extending inwardly from the cylindrical surface 26. The cylindrical internal surface 14 of the housing 12 co-operates with the cylindrical surface 26 of the rotor 10 to form, with the annular channels 20, an enclosed annular processing passage. Each of the illustrative machines further comprises inlets 28 through which material to be processed may be admitted to the annular passages, and outlets 29 from each annular passage circumferentially spaced from the inlet 28 to that passage downstream of the inlet 28 in the direction of rotation of the rotor 10 by a major portion of a complete revolution.A blocking member, namely a channel block 19, is disposed in each annular passage between the outlet 29 and inlet 28 considered in the direction of rotation of the rotor 10 to hold a body of material being processed in each annular channel 20 so that there is, in the operation of the illustrative machines, relative movement between the side walls 24 of each annular channel 20 and the body of material, the side walls 24 operating (as the rotor 10 rotates) to drag liquid portions of the material in contact with the side walls 24 downstream towards the channel block 19 whereby pressure is built up in the liquid as the channel block 19 is approached. Furthermore, each of the illustrative machines comprises dynamic sealing means which will be described in greater detail hereinafter.

Whereas each of the illustrative machines comprises two annular processing channels, it will be appreciated that machines generally similar to the illustrative machines may comprise only one processing channel or any suitable number of channels according to the operation to be carried out and the materials for which the machine is intended to be used.

Likewise, whereas in the illustrative machines, each outlet is circumferentially spaced from the inlet to that passage a major portion of a complete revolution from the inlet downstream of the inlet in the direction of rotation of the rotor, the outlet from one or more of the processing channels of machines in accordance with the invention otherwise similar to the illustrative machine comprising two or more processing channels may be disposed at any convenient angular position in relation to the inlet. Furthermore, in machines in accordance with the invention comprising two or more processing channels, the outlet or outlets from one or more of the processing channels may be connected to the inlet or inlets of one or more other processing channels.Machines comprising dynamic sealing means in accordance with the invention may also have features as described in the specification of our copending patent application Serial No.

2007585.

In the subsequent description of the illustrative machines like parts are given like reference numbers for ease of identification.

The first illustrative machine comprises, as hereinbefore mentioned, a rotor 10 mounted for rotation in a housing 12, the rotor being supported on a drive shaft 16 journalled in end walls 18 of the housing 12. In the operation of the first illustrative machine as hereinbefore mentioned material supplied to the channels 20 through the inlets 28 is dragged in contact with the channel walls 24 towards the channel block 19 an end wall surface of which provides a material collecting surface; collected processed material is discharged through the outlet 29. Pressure is generated by dragging of material on the channel walls 24 towards the channel block 19 so that the pressure of material in the channel increases in the direction of rotation.

A narrow clearance 50 is established between the cylindrical surface 26 of the rotor 10 and the stationary cylindrical internal surface 14 of the housing 12. Ideally, the clearance 50 is 10 mils (about 0.25 mm) or less, preferably between 3 to 5 mils (about 0.075 to 0.125 mm). The clearance 50 should be substantially constant about the circumference of the passage. However, maintenance of such a close, constant clearance can be complicated by the differential radial pressures generated along the circumference of the channel. This imbalance of radial pressures may be sufficient to cause shaft or rotor deflection from a high pressure region toward a low pressure region. Obviously, any deflection can affect the maintenance of the desired close, constant clearance because additional clearance must be provided to compensate for the extent of any deflection. Deflection may be controlled by disposing flow director units in some processing channels in radially opposed relation to those in other channels so that the radial pressures generated in one part of a processing passage or group of processing passages are balanced by radial pressures generated in other passages. While shaft deflection control can reduce leakage, it is desirable to provide auxiliary or additional sealing means to minimise leakage to the greatest extent possible.

The dynamic sealing means of the first illustrative machine (Figs. 1, 2, 3 and 4) comprises a plurality of oblique, preferably parallel, narrow, sealing channels 27 formed in and/or carried by an annular peripheral surface portion of the rotor, viz. the cylindrical surface 26, extending round the rotor at one side of the channel 20, to provide a dynamic seal between the surface 26 and a stationary surface portion, viz. the coaxial internal surface 14 of the housing 12. The oblique sealing channels 27 are cut into the surface 26 and move relative to the smooth surface 14 of housing 12. Similar dynamic sealing means are provided at either side of the channel 20 of the first illustrative machine.

The construction and arrangement of the first illustrative machine is such that the liquid to be processed can penetrate the channels, the width of the annular peripheral surface portion of the rotor, the number, angle and geometry of the sealing channels 27 being selected so that penetration of the clearance 50 and the sealing channels 27 by the pressurised liquid is opposed by an inward force applied to the liquid in the sealing channels 27 as the surfaces 26, 14 are relatively rotated. The most important relationships between the various design parameters of the dynamic sealing means of the first illustrative machine are shown in Figs. 3 and 4.In Figs. 3 and 4 and the following description D is the outside diameter of the rotor, that is the diameter of the cylindrical portion 26, t is the width of the annular peripheral surface portion of the rotor, 8 is the helix angle of the channels 27 which are helical, W is the width of the channels 27, e is the width of the land between adjacent channels 27, H is the channel depth, 8 is used in the subsequent calculations to indicate the clearance 50, n is the number of parallel channels 27, V is the surface velocity of the cylindrical surface 26 of the rotor 10.

L = Ds sin 8 -e.

n As described previously the dynamic seal is achieved by providing one of the two relatively moving surface portions near or at the clearance 50 with a plurality of oblique, preferably parallel sealing channels 27. In effect, each oblique sealing channel 27 functions as a segment of an extruder screw flight with the stationary coaxial surface 14 acting as a barrel for the plurality of sealing channels 27 (which may be considered as a plurality of extruder screw channels). Accordingly, the net flow q of liquid across the width 1 of the surface 26 may be determined using the same analysis which applies to a screw extruder.Thus, the net flow q is the difference between the drag flow in one direction and the pressure flow in the opposite direction or q = qD~qp (Equation A) where: qD is the theoretical drag flow qp is the theoretical pressure flow The surface 26 of the rotor 10 of the first illustrative machine is shown diagrammatically in Fig. 4 sealing against a constant pressure (for simplicity of calculation) and the total net flow q equals zero under equilibrium conditions or, qD = qp. The drag flow qD is only a function of sealing channel geometry and the speed of operation.However, the pressure flow, qp for a given pressure is inversely proportional to the length of penetration of liquid into the channels 27, i.e. to the length of channel which is filled with liquid. Under conditions, as shown in Figs. 3 and 4, equilibrium therefore will be reached as soon as the liquid has penetrated the sealing channels to a length which reduces the pressure flow (which tries to move the liquid into the channel) to a value which is equal to the drag flow. If that length of penetration measured in the axial direction is less than the length of the sealing channel 27, no liquid will leak across the width 1 of helical sealing channel carrying surface 26.

The dynamic seal of this invention however does not operate under conditions of constant pressure as discussed above in connection with Fig. 4. Instead, Fig. 5a illustrates a typical pressure profile developed around the circumference of a processing passage of the first illustrative machine. After an initial length of relatively low pressure, the pressure in the passage increases gradually, reaches a maximum value at the end of the passage and then drops suddenly beyond an obstruction viz. the channel block 19, back to the original low level. The dynamic sealing means therefore usually works against variable pressure which repeats periodically during each revolution of channel walls 24.The length of penetration of liquid into helical sealing channels 27 for the pressure profile shown in Fig. 5a has been computed by an appropriate dynamic model and is shown in Fig. 5b adjacent the pressure profile. One can see that as soon as the pressure drops suddenly, the length of penetration of liquid in a sealing channel 27 is gradually reduced to a point roughly opposite to the onset of pressure increase. From there on, the length of penetration of liquid in a sealing channel 27 increases again. In general it can be said that the net flow q (equation A) never reaches equilibrium during any one revolution.Due to the time required to empty the liquid from a sealing channel 27 when the pressure is lowest or to refill it with the liquid when the pressure is the greatest, the length of penetration of liquid in a sealing channel lags or leads the pressure profile. For example, after the sudden drop of pressure indicated in Fig. 5, there is only a gradual reduction in the length of penetration of liquid in a sealing channel 27. However, by making the length of each sealing channel long enough so that the length of penetration of liquid never exceeds the length of the helical sealing channel(s), unwanted leakage cannot occur across the width 2 of a surface portion carrying a plurality of helical sealing channels 27.

The dynamic sealing means of the first illustrative machine has many, parallel, helical sealing channels with a relatively small helix angle 8. The small helix angle a is desirable in order to provide sealing channels 27 having minimum penetration lengths for a surface portion (bearing sealing channels 27) having a relatively narrow width t. The helix angle 8 is below 204 in the first illustrative machine.

The number of sealing channels 27 employed to provide the dynamic sealing means of the first illustrative machine is also important. Because the cylindrical surface 26 has a relatively large outside diameter D, a multiflighted sealing channel carrying surface 26 is especially desirable because the lead L of the helical sealing channel 27 is larger than the width 1, of the sealing surface 26. Accordingly, a plurality of preferably parallel helical sealing channels are formed to provide an effective dynamic seal. There is also another reason for using a plurality of helical sealing channels. For a net flow q equal to zero, pressure flow and drag flow have to be equal.

However, as the ratio of sealing channel depth H (Fig. 3) to sealing channel width W (Fig. 4) increases, for example by decreasing channel width W, the pressure flow value in Equation A decreases faster than the drag flow value.

Referring to Equation A above, it is apparent that under these circumstances, namely for decreasing channel width W, the seal becomes more efficient which means that zero net flow can be achieved at lower penetration lengths of liquid in the sealing channels 27.

Also, it is apparent from the equation for channel width W (Equation C above) that an increasing number of channels results in a reduction of channel widths. Narrow sealing channel widths W are particularly desirable in the practice of the invention because of the differential radial pressures encountered about the circumference of the annular processing passage. By using a plurality of parallel, helical sealing channels 27 having narrow widths W in the first illustrative machine, the pressure variations acting on each individual sealing channel at any time is held to a small value and each channel acts independently.

Referring again to Fig. 5b, the boundary of penetration of liquid shown represents the area over which the sealing channels 27 are filled during a complete revolution of the helical sealing channel carrying surface 26 of the rotor 10 of the first illustrative machine.

That area also corresponds to the area of stationary coaxial interior annular surface 14 which is contacted with liquid. This contact of liquid with the helical sealing channel carrying surface 26 and coaxial interior annular surface 14 creates a shearing action providing the desirable drag flow which limits the extent of penetration of liquid in the sealing channels.

However, this shearing action also provides an undesirable power loss at the seal because of dissipation of energy into heat.

It has been found that power loss arising from the dynamic sealing means can be substantially reduced by breaking liquid contact between the surface portions forming the dynamic seal, during a portion of each revolution of one of the portions providing the dynamic seal. The second illustrative machine, shown in Figs. 6, 6a, 6b, in Figs. 7, 7a, 7b and in Figs. 8 and 8a employs this discovery.

The second illustrative machine is generally similar except as hereinafter described to the first illustrative machine and like numbers indicate like parts in the subsequent description. The second illustrative machine comprises a scraper 30 positioned on the inlet side of the channel block 19 (Fig. 6a) to scrape liquid off the cylindrical surface 26 (bearing helical sealing channels 27) which provides dynamic sealing means designed to militate against unwanted external leakage from the annular processing passage next adjacent one end of the rotor 10. The scraping clearance between the scraper 30 and the surface 26 of the rotor 10 must be close, preferably, sufficiently close to scrape off most of the liquid contacting the surface 26 and stationary internal coaxial, cylindrical surface 14. Accordingly, after scraping, liquid contact between the surface 26 carrying the helical sealing channels 27 and the surface 14 is broken and the sealing channels 27 remain filled with liquid-to the extent to which they were filled before the scraping. Power loss by dissipation of energy in the dynamic sealing means is thereby reduced after scraping and does not increase again until sufficient liquid has been pumped in the operation of the second illustrative machine into the helical sealing channel 27 to reestablish liquid contact between the coaxial surface portions of the dynamic sealing means provided by the surfaces 26, 14 in the second illustrative machine. Liquid material scraped off the helical sealing channel carrying surface is discharged into the annular processing passage at the region of the inlet 28 (which is a lower pressure region) at low pressures.

The second illustrative machine also com prises a scraper 31 (see Figs. 7, 7a, 7b) of a dynamic sealing means having two sets of intersecting helical sealing channels 27 and 27a on the cylindrical surface 26 between adjacent processing channels 20 of the rotor 10 of the second illustrative machine. The helices of the sealing channels of each set are opposed to each other. The scraper 31 is positioned at the inlet side of the channel blocks 19 in the adjacent processing passages (Fig. 7a) and is maintained in close scraping relationship with the surface 26 to break liquid contact between the surfaces 26, 14 and to discharge the scraped material into the inlet region of the second illustrative machine.

The dynamic sealing means between the channels 20 militates against leakage between the channels 20.

The advantages of breaking liquid contact between surface portions of the dynamic sealing means are further shown in Figs. 8a and 8b. Fig. 8a (like Fig. 5a) shows a typical pressure profile developed along the circumference of an annular processing passage of the second illustrative machine. The computed length of penetration of liquid into the helical sealing channels 27 for the pressure profile of Fig. 8a having a scraper cooperating with the surface 26 is shown in Fig. 8b. The arrangement of Figs. 6, 6a and 6b is described here but similar effects are achieved with the arrangement of Figs. 7, 7a and 7b also. Scraping is done near the inlet 28 i.e. at or near the low pressure area of the annular processing passage. The scraping breaks liquid contact between the surface portions of the dynamic sealing means but leaves the helical sealing channels 27 filled to some level with liquid.Because the layer providing liquid contact between the surface of the dynamic seal is removed, there is reduced power loss and very little penetration of liquid in the area extending from the back of the scraper 30 up to about 13 on the scale of Fig. 8b. However, once the pressure in the annular processing passages starts increasing, length of liquid penetration immediately and very closely follows the pressure profile with maximum penetration occurring rather close to maximum pressure. A comparison of Fig. 8b with Fig.

5b shows that the area of maximum liquid penetration of Fig. 8b is considerably smaller than the maximum liquid penetration area of Fig. 5b. Consequently, the scraper 30 of the second illustrative machine appears to reduce power losses without impairing the efficiency of the dynamic sealing means.

The third illustrative machine is generally similar to the first and second illustrative machines except that the surface portions of the dynamic sealing means in one of which the sealing channels are provided occupy a different part of the periphery of the rotor 10.

The third illustrative machine comprises an annular peripheral surface portion 32 of the rotor 10 having a plurality of oblique sealing channels 35 on the surface portion 32 (see Figs. 9, 9a, and 9b). The annular peripheral surface portion 32 is disposed outwardly of the cylindrical surface 26 of the rotor, at the opposite side of the surface 26 to the annular processing channel 20. The portion 32 carry ing the plurality of sealing channels 35 has width 2 (Figs. 9 and 9a). The surface portion 32 carrying the sealing channels 35 moves in rotation relative to a stationary surface portion 33 of a stationary annular element 34 fixed securely to the stationary interior surface 14 of the housing 12 and projects inwardly.The surface portion 33 is spaced from the surface portion 32 by a fixed, narrow clearance 51 which can be the same, or greater than, or less than the clearance 50 between the surfaces 26, 14 but suitably is 10 mils (about 0.25 mm) or less. While the channels 35 are (see Fig. 9a) in curved spiral form, channels of a machine otherwise similar to the third illustrative machine, may be straight but obliquely arranged without departing from the scope of the invention. Fig. 9b is a top view showing the relationship between the surface portions 32, 33 forming the dynamic sealing means of Fig. 9, and a scraper 36. The scraper 36 is fixed in the stationary annular member 34 and extends outwardly from the portion 33 to break liquid contact between the surface portion 33 and surface portion 32.The scraper 36 extends at least across the width 2, and is positioned at or near the inlet (not shown) of the annular processing passage.

The fourth illustrative machine (see Figs.

10, 1 0a and 1 0b) is generally similar to the third illustrative machine except as hereinafter described and in particular, has a smooth cylindrical surface of the rotor and a smooth flat annular peripheral surface portion 40 of the rotor disposed at the opposite side of the cylindrical surface 26 to the processing channel 20. The fourth illustrative machine comprises an annular element 39 fixed to the stationary internal surface 14 of the housing 12 (similar to the element 34 of the third illustrative machine). The element 39 has a stationary surface portion 38 provided with a plurality of helical or oblique sealing channels 37.The stationary surface portion 38 is positioned spaced apart from the annular peripheral surface portion 40 of rotor 10 by a narrow clearance 51 and has a width 2. In Fig. 1 ova is shown the annular element 39 with the plurality of sealing channels 37 provided in the width 2 of the surface portion 38. Fig. 1 Ob is a top view showing the relationship between the surface portions 38, 40 forming the dynamic sealing means of the fourth illustrative machine and a scraper 41.

The scraper 41 is fixed in the stationary annular element 39 and extends from the surface portion 38 towards the surface portion 40 to break liquid contact between surface portions 38, 40. As shown in Fig. 1 ova, the scraper 41 extends at least across the width and, as in the case of all scrapers described hereinbefore, is positioned at or near the inlet (not shown) or in a low pressure area of the annular processing passage.

The dynamic sealing means of the fourth illustrative machine differs from the dynamic sealing means of the first, second and third illustrative machines in that the plurality of sealing channels are carried by a stationary surface portion in the fourth illustrative machine whereas the plurality of sealing channels of the first to third illustrative machines are formed in a rotating surface portion. As already discussed, in relation to the first illustrative machine, similar principles being applicable to the second and third illustrative machines, the length of penetration of liquid into each sealing channel carried by a rotating cylindrical surface portion varies progressively during each revolution because of the differential pressures encountered around the circumference of the annular processing passage, as graphically shown in Figs. 5, Sa, 8 and 8a.This variation in length of penetration of the liquid into each helical sealing channel is not encountered during each revolution with dynamic seals having a stationary surface portion carrying the sealing channels, as the fourth illustrative machine. Instead, because each sealing channel is always at a fixed position about the circumference of the processing passage, each helical sealing channel of the fourth illustrative machine is always subjected to a constant head pressure during every revolution of channel walls 24 of rotor 10 (when operating in a steady state condition).Accordingly, the length of penetration of liquid into each stationary sealing channel of the fourth illustrative machine will differ but the maximum length of penetration into any given channel will always be substantially constant so long as a constant pressure is applied to that sealing channel during each revolution of the rotor 10. Again however, so long as the length of penetration of liquid into any of the helical channels on the stationary surface portion 38 does not exceed the length of any sealing channel 37, unwanted leakage from between the surfaces will not occur.

The fifth illustrative machine is generally similar to the first and second illustrative machines and the dynamic sealing means is formed between the cylindrical surfaces 14, 26 defining the clearance 50. However the dynamic sealing means of the fifth illustrative machine functions in a manner similar to that of the fourth illustrative machine because the helical sealing channels 42 are formed in the stationary internal surface 14 of the housing 12 which is coaxial with and spaced apart from the cylindrical surface 26 of the rotor 10 by a clearance 50.Accordingly, the length of penetration of liquid into each helical sealing channel 42 carried by the stationary interior surface 14 will vary, as discussed above in relation to the fourth illustrative machine and the maximum length of penetration of liquid into any given helical channel 42 (at a fixed pressure position around the annular processing channel) will always be substantially constant so long as constant pressure is applied at that fixed position (and that the machine is operating in a steady state condition). So long as the length of penetration of liquid into any stationary helical sealing channel 42 does not exceed the length of the channel, leakage of liquid between the surface portions of the dynamic sealing means (surfaces 14, 26) at clearance 50 will not occur.

In each of the previously described illustrative machines leakage of viscous liquid material being processed e.g. molten plastics or polymeric material, at the clearance defined between the surface portions of the dynamic sealing means is controlled by the plurality of helical or oblique sealing channels carried by one of the surface portions. Such features of the sealing channels as the number, geometry, dimensions and angle are selected (as discussed previously, see especially the first illustrative machine) so that the length of liquid penetration into each sealing channel does not exceed the length of the sealing channel penetrated. Nevertheless a prime function of the dynamic sealing means is to resist the penetration of fluid into the channels to thereby restrict the amount of liquid leakage at the clearance.A degree of that control can still be achieved even though the length of penetration of leakage fluid into a channel exceeds the length of the channel penetrated. Under such circumstances, some leakage of the liquid will occur at the clearance but the helical sealing channels would still provide control over the amount of leakage and the amount would be less than that which would occur without the sealing channels.

Sixth and seventh illustrative machines are shown in Figs. 12, 12a and 13, 13a; in these illustrative machines effective control of liquid leakage at the clearance between surface portions of the dynamic sealing means can still be achieved even though penetration of liquid exceeds the length of the sealing channels.

The sixth illustrative machine (Figs. 12, 12a) comprises a plurality of helical sealing channels 27 carried on the cylindrical surface 26 of the rotor 10. However the width 2 of the surface portion carrying the channels 27 does not extend across the total width of cylindrical surface 26 and penetration of liquid into the channels 27 can exceed the length of the channels 27. The sixth illustrative machine thus also comprises a liquid penetration collecting channel 57 to collect the liquid which penetrates the channels 27 and retain the collected liquid until it can be discharged through the channels 27 at low pressure regions of the annular processing passage.

The liquid penetration collecting channel 57 preferably has about the same depth H (Fig.

4) as the channels 27.

The seventh illustrative machine (see Figs.

13, 13a) is a modification of the sixth illustrative machine shown in Figs. 12 and 12a.

Again the width , of the surface portion carrying the sealing channels 27 only occupies a portion of the total width of the surface 26. Instead, a recessed portion 59, the width of the sealing channel carrying surface portion2, and the liquid penetration collecting channel 57 are arranged across the total width of the periphery of the rotor 10. The depth of liquid penetration collecting channel is preferably the same as depth H (Fig. 4) of channel(s) 27.

The depth of the recessed portion 59 can be the same as or different from the depth of the channel(s) 27, or, in a further modification, the recessed portion 59 may be tapered downward (not shown) from the surface 26.

In a machine in accordance with the invention in which processing channels are connected, transfer passages between processing channels (connecting the outlet of one channel with the inlet of another channel) may be provided by removable flow director units which are held by the housing and include surface portions forming part of the surface of the annular housing and with the transfer channels formed in these surface portions of the flow director units. The flow director units may also carry the blocking members which extend into the processing channels of the rotor. In further machines in accordance with the invention transfer passages interconnecting processing channels and blocking members may be circumferentially and/or axially disposed to reduce bearing load to develop opposed radial forces in the processing channels.For example, the annular processing passages, blocking members and transfer pasages may be arranged to develop radial forces in at least once of the annular processing passages to oppose radial forces developed in at least one other annular processing passage to provide substantial axial balance of radial forces. Axial balance of radial forces is desirable because shaft or rotor deflection is minimised thereby providing closer and better control over clearances between the surface portions of sealing means of machines according to the invention.

As discussed previously, in machines according to the invention the surface portions of the sealing means are preferably spaced apart from each other by clearances up to 10 mils (about 0.25 mm); however, more preferably the surface portions are spaced apart from each other by clearances of 5 mils (about 0. 125 mm) or less. Accordingly, the degree of shaft or rotor deflection is a factor that should be considered indesigning sealing means of a machine in accordance with the invention.

Further improvements in sealing may be obtained in some circumstances by including in the sealing means truncated conical members of stiffly-resilient material positioned between relatively rotatable coaxial surface portions with inner edge portions of the members providing a surface adjacent and in flow resistant relation to one coaxial surface portion (e.g. of the rotor), and outer edge portions providing a surface adjacent and in flow resistant relation to the other coaxial surface portion (e.g. of the housing): Marginal portions at either the inner or outer edge portions of the members are held to enable pressure against the nested members to force the outer or inner edges respectively into sealing relation to adjacent surface portions.

The sealing means of eighth and ninth illustrative machines comprises truncated conical members 44 (see Figs. 14 and 15), carried by the rotor 10 in an orientation such that surfaces 43 of the member 44 slope towards the processing channel 20, i.e. the high pressure region. Inner edge portions 45 of the member 44 farthest from the channel 20 are held against axial movement and in sealing relation to the rotor 10 by a shoulder 46 and a retaining member, namely a ring 47. The ring 47 acts on the member 44 farthest from the channel to keep the member 44 in nested relation against shoulder 46.

Outer free edge portions 48 of the members 44 closest to the channel 20 provide a surface portion viz. a surface 49 which is in sealing relation to a surface portion viz. cylindrical surface 14 of the housing 12 so that the members 44 seal the space between the surface 49 and the internal surface 14 of the housing 12. In the eighth illustrative machine (see Fig. 14) the surface 49 comprises a plurality of helical sealing channels 52 which operate in the manner hereinbefore described to provide a dynamic seal in association with the surface 14 thus to improve sealing between the surface 49 and the surface 14. The eighth illustrative machine is especially useful if deflections of the shaft 16 require that clearances greater than about 0.005 inch (about 0.125 mm) be maintained between surface 49 and surface 14.In the ninth illustrative machine (see Fig. 15) a plurality of helical sealing channels 53 are provided on the internal surface 14 of the housing to provide a dynamic seal between surface 14 and the surface 49 which is substantially smooth.

Figs. 16, 17 and 18 are graphs showing the maximum liquid penetration length into each sealing channel versus RPM for several values of 2 of the first illustrative machine using a number of different rotors 10 of appropriate size and configuration. These graphs indicate that 10 or more channels of suitable geometry and having an axial length of about 0.5" (about 12.5 mm) can control leakage of liquid across a width 2, especially if the helix angle 8 is low, e.g. below 1 5'.

In carrying out the experiments from which the graphs in Fig. 16 were prepared, the rotor 10 has 10 helical sealing channels 27. The depth of each channel (H) was 0.1 inches (about 2.5 mm). The width of the channel bearing surface portion (z) was 0.50 inches (about 12.5 mm). The clearance between the surface portions (8) was 0.006 inches (about 0.15 mm). The flight width (e) was 0.025 inches (about 0.625 mm). The outside diameter (D) of the cylindrical surface 26 was 13.78 inches (about 350mm). The maximum pressure was 1,000 psi (about 6.9 MN/m2) and the minimum pressure was 5 psi (about 0.34 MN/m2). A number of different rotors 10 were used in preparing the first graph each having a different helix angle for the helical sealing channels 27, 8, indicated on the graphs.N indicates the speed of rotation of the rotor 10 in revolutions per minute.

In the experiments from which the graphs on Fig. 17 were produced a number of different rotors having helical sealing channels 27 of different helix angle 8 were used as indicated on the graphs; the helix angles of the sealing channels were the same as those used in preparing the graphs of Fig. 16. However, other dimensions of the rotors 10 were different from those used in preparing the graphs of Fig. 16. The rotors used in preparing the graphs of Fig. 17 each had 15 helical sealing channels 27. The sealing channel depth (H) was 0.1 inches (about 2.5 mm). The width of the channel bearing surface (),) was 0.50 inches (about 12.5 mm). The clearance (8) was 0.006 inches (about 0.15 mm). The flight width (e) was 0.025 inches (about 0.625 mm).The outside diameter (D) of the rotor 10 (namely the cylindrical surface 26) (D) was 13.78 inches (about 350 mm). The maximum pressure was 1,000 psi (about 6.9 MN/m2) and the minimum pressure was 5 psi (about 0.34 MN/m2).

The rotors 10 used in carrying out the experiments resulting in the graphs shown in Fig. 18 had a wider range of helix angle for the sealing channels 27 than did the rotors used in preparing the graphs of Figs. 16 and 17. The helix angles 8 are indicated on the graphs. The rotors used in preparing the graphs of Fig. 18 had 20 helical sealing channels 27. The depth (H) of the sealing channels 27 was 0.10 inches (about 2.5 mm). The width of the channel bearing surface portion (#) was 0.50 inches (about 12.5 mm). The clearance (8) was 0.006 inches (about 0.15 mm). The flight width (e) was 0.025 inches (about 0.625 mm). The outside diameter (D) was 13.78 inches (about 350 mm). The maximum pressure was 1,000 psi (about 6.9 MN/m2). The minimum pressure was 5 psi (about 0.34 MN/m2).

In the graphs of Figs. 16, 17 and 18 the maximum pressure generated of 1,000 psi is well above that normally expected to be generated in a passage of a machine in accordance with the invention. The maximum pressure however was selected to determine maximum axial penetration lengths of liquid into the sealing channels of the indicated geometry or dimensions under extreme operational conditions.

Claims (31)

1. A machine for processing materials which are, or become in the course of processing, viscous liquids comprising (a) a rotor mounted for rotation about an axis and comprising a surface having at least one processing channel, (b) a housing in which the rotor is mounted for rotation comprising a stationary surface complementary to and spaced apart from the surface of the rotor and cooperating with the surface of the rotor to form with the annular channel (or channels) an enclosed annular processing passage (or passages), (c) inlets through which material to be processed may be admitted to the (or each) annular passage, (d) an outlet 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, (e) a blocking member disposed in the (or each) annular passage between the outlet and inlet in the direction of rotation of the rotor to hold a body of material being processed in the (or each) annular channel so that as the rotor rotates pressure is built up in the liquid as the blocking member is approached, and (f) sealing means militating against leakage of the liquid from the (or each) channel, the sealing means comprising a surface portion of the rotor at one side of the (or each) processing channel and a stationary surface portion of the housing adjacent said surface portion of the rotor and spaced apart therefrom by a narrow clearance, the sealing means further comprising a plurality of sealing channels in one of said adjacent surface portions the construction and arrangement being such that the liquid to be processed can penetrate the channels, the width of the said one of the surface portions and the number angle and geometry of the channels being selected so that penetration of the clearance and the channels by the pressurised liquid is opposed by an inward force applied to the liquid in the sealing channels as the surface portions are relatively rotated.

2. A machine according to claim 1 in which the (or each) processing channel has a zone of minimum pressure, the machine comprising scraping means projecting into the clearance for scraping enough penetrating liquid from one of the surface portions into said zone so liquid contact is broken during at least part of the revolution of said rotor.

3. A machine according to either one of claims 1 and 2 in which the (or each) processing channel has a zone of one pressure and a circumferentially spaced zone of a greater pressure.

4. A machine according to either one of claims 2 and 3 in which the scraping means comprises an upstream face extending across the surface portion inclined at an angle to the direction of movement of the surface portion relative to the scraping means whereby to direct liquid scraped from the surface portion into the zone of minimum pressure.

5. A machine according to any one of the preceding claims so constructed and arranged that, in the operation of the machine, the extent of penetration of liquid does not exceed the length of any sealing channel.

6. A machine according to any one of the preceding claims in which the sealing channels are helical.

7. A machine according to claim 6 in which the helix angle of each sealing channel is 20 or less.

8. A machine according to claim 7 in which the helix angle of each sealing channel is 15' or less.

9. A machine according to any one of the preceding claims in which the surface portion carrying the plurality of sealing channels is stationary.

10. A machine according to any of claims 1 to 8 in which the surface portion carrying the plurality of sealing channels is rotatable.

11. A machine according to any one of the preceding claims in which the clearance between the said surface portions is 2.5 mm or less.

12. A machine according to claim 11 in which the clearance between the said surface portions is 1.25 mm or less.

13. A machine according to any one of the preceding claims in which the sealing channels are arranged substantially parallel to one another.

14. A machine according to any one of the preceding claims in which the surface of the rotor having said at least one processing channel is cylindrical and the sealing means comprises a truncated conical member of stiffly resilient material, said member having a surface adjacent outer edges thereof arranged closest to the processing channel so as to be displaceable by pressure, and means for holding the inner edges of the member against displacement by pressure so that said outer edges provide sealing with the surface portion of the housing and wherein either the surface portion or the outer edges have the sealing channels formed therein.

15. A machine according to any one of the preceding claims in which the surface of the rotor having said at least one processing channel is cylindrical and provides the peripheral surface portion, and the surface portion of the housing is provided by a portion of the complementary internal surface of the housing, which is also cylindrical.

16. A machine according to any one of the preceding claims in which the surface of the rotor having said at least one processing channel is cylindrical and the peripheral surface portion of the sealing means comprises an annular surface portion of the rotor disposed inwardly of the cylindrical surface and at the opposite side of the cylindrical surface to the processing channel and in which the stationary surface portion of the housing comprises a corresponding annular surface portion extending inwardly from the cylindrical internal surface of the housing.

17. A machine according to any one of the preceding claims in which the sealing means comprises surface portions having sealing channels disposed at either side of the processing passage.

18. A machine according to any one of the preceding claims in which the rotor comprises a plurality of processing channels, each having associated sealing means comprising a peripheral surface portion of the rotor and an adjacent stationary surface portion of the housing.

19. A machine according to claim 18 in which the outlet from one processing channel is connected to the inlet of another processing channel.

20. A machine according to claim 1 substantially as hereinbefore described with reference to the accompanying drawings.

21. A machine for processing materials which are, or become in the course of processing, viscous liquids constructed, arranged and adapted to operate substantially as hereinbefore described with reference to Figs. 2, 3 and 4 of the accompanying drawings.

22. A machine for processing materials which are, or become in the course of processing, viscious liquids constructed, arranged and adapted to operate substantially as hereinbefore described with reference to Figs. 6, 6a and 6b of the accompanying drawings.

23. A machine for processing materials which are, or become in the course of processing, viscous liquids constructed, arranged and adapted to operate substantially as hereinbefore described with reference to Figs. 7, 7a and 7b of the accompanying drawings.

24. A machine for processing materials which are, or become in the course of processing, viscous liquids, constructed, arranged and adapted to operate substantially as hereinbefore described with reference to Figs. 9, 9a and 9b of the accompanying drawings.

25. A machine for processing materials which are, or become in the course of processing, viscous liquids constructed, arranged and adapted to operate substantially as here inbefore described with reference to Figs. 10, 1 0a and 1 Ob of the accompanying drawings.

26. A machine for processing materials which are, or become in the course of processing, viscous liquids constructed, arranged and adapted to operate substantially as hereinbefore described with reference to Fig. 11 of the accompanying drawings.

27. A machine for processing materials which are, or become in the course of processing, viscous liquids constructed, arranged and adapted to operate substantially as hereinbefore described with reference to Figs. 12 and 12a of the accompanying drawings.

28. A machine for processing materials which are, or become in the course of processing, viscous liquids constructed, arranged and adapted to operate substantially as hereinbefore described with reference to Figs. 13 and 13a of the accompanying drawings.

29. A machine for processing materials which are, or become in the course of processing, viscous liquids constructed, arranged and adapted to operate substantially as hereinbefore described with reference to Fig. 14 of the accompanying drawings.

30. A machine for processing materials which are, or become in the course of processing, viscous liquids constructed, arranged and adapted to operate substantially as hereinbefore described with reference to Fig. 15 of the accompanying drawings.

31. A method of processing materials which are, or become in the course of processing, viscous liquids using a machine according to any one of the preceding claims, in which the speed of rotation of the rotor is such that the length of penetration of pressurised liquid does not exceed the length of any sealing channel.