GB2288879A - A rheometer for measuring viscosity of material with automatic cleaning facility - Google Patents

Abstract

A rheometer for measuring the viscosity of material, comprises a chamber 20 which is cleaned automatically following a measuring process and which contains a releasable die 24 and receives material from supply cells 34, 36, 38. A tamping piston 72 packs material into the chamber, and during measuring heated material is forced through the die by a loading/test piston 70. For cleaning, the die is released and a plug 84 is driven by the tamping piston to clean the chamber 20. Heating means 22 compensates for heat loss and maintains the material in a known state. The rheometer 2 is also provided with automatic die changing means 14, which allows different dies 24 to be used. A microprocessor controls the functions of the rheometer including cleaning, tamping, heating and die changing. The plug may expand through heat, may be resilient, may be made of wood, phosphor bronze, ceramics or polymeric material, or may be a spring (104, fig. 5). Means (80, fig. 1) cleans pistons 70, 72. <IMAGE>

Description

IMPROVEMENTS IN AND RELATING TO RHEOLOGY This invention relates to improvements in and relating to rheology, in particular to improvements in apparatus and methods for measuring the viscosity of materials.

It has long been very important to know how a material will flow in order to determine how it may be processed. Many operations in industry depend upon the predictability of the flow of materials. Viscosity measuring instruments, such as rheometers, are used to monitor the flow characteristics of a material as it is being extruded, or as it flows. Measurement of flow characteristics may occur as a continuous process by taking a bleed of flowing material and extrude it through a die of known geometry at a known flow rate, or pressure. Alternatively the process may be performed as a batch process in which samples of material are tested in isolation from processing of the material.

Using the change in pressure over the die, the geometry of the die, and the flow rate through the die, the viscosity of the material can be calculated, usually automatically by the machine --(shear viscosity is shear stress, derived from the pressure drop, divided by shear strain rate, derived from volume flow rate).

The viscosity of a material can alter with flow rate, and with temperature. In order to measure the changes in viscosity of a material over a large range, or of different materials having different viscosities, it is necessary to use dies of different geometries each die giving an acceptable "window" of measuring capability. To change a die in a rheometer it is necessary to remove an old die and replace it with a new die of different characteristics. Furthermore this involves a rheometer being used repeatedly to perform such measurements.

In one known kind of analysis of a processed solid material using a simplified rheometer of the kind known as a melt flow indexer, the material is provided in granule or powder form and is pushed into a melting cylinder which is usually a steel barrel. The material is usually tamped down into the heated barrel which melts it. Heating elements are provided associated with the barrel. A melt typically occupies approximately 60% of the volume of the granulated or powder material. A piston pushes the melt through a capillary die provided at the bottom of the barrel.

The material is tamped down to increase thermal conduction between granules of material to improve the rate of melting, and to improve the uniformity of the melt.

After each measurement operation traces of material may be left in the barrel. The traces may be present in a consistency or a form falling within a range extending from an oil-like material to a toffee-like material. Residue of material left in the barrel may cause blockage of the rheometer the next time it is used or contamination of the next sample which may, of course, be a material of a different composition. Therefore the barrel must be cleaned after each measurement operation. This may, for example, require a cleaning operation every ten minutes whilst the rheometer operates. The rheometer may be in operation all day or longer. The cleaning operation is conventionally performed manually.

In conventional melt flow indexer rheometers the operation of a piston pushing melt material through the die, removal of the piston from the barrel, cleaning of the piston barrel and die, and insertion of another batch of material into the barrel and tamping of the material are performed manually, sequentially, and in that order. This is time consuming.

The heating elements in rheometers are conventionally disposed around the barrel. It is critical to the determination of flow characteristics that the temperature of the melt be uniform and accurately determined. Heat can escape by radiation and convection from the lower end of the barrel. Although heating elements extending to the bottom of the barrel may alleviate the problem of heat loss, this may also interfere with insertion and removal of the die. One known expedient is to insulate this area with PTFE insulators. Whilst this is reasonably effective it does limit the upper working temperature of the rheometer to 2500C. Above this temperature PTFE degrades thermally.

According to a first aspect of the invention we provide a rheometer comprising a die, a material holding chamber, and cleaning means; in which the cleaning means is adapted to clean the material holding chamber automatically.

Preferably the cleaning means comprises a plug and means for urging the plug through the material holding chamber so as to clean the chamber. The plug may be cylindrical. The plug may have a generally uniform outer surface. The plug may have a rough or smooth surface. The plug may have a stepped surface having raised and sunken regions adjacent one another.

Preferably the plug has at least one raised region adjacent a sunken region. There may be a sunken region to either side of the raised region. A raised region may be a ring. A sunken region may be a ring. The plug may have the form of a series of rings of alternating wider and narrower diameter.

The cleaning plug may be provided in delivery means adapted to deliver the plug to the entrance to the rheometer bore. The delivery means may comprise a plug-holding bore in a body, the plug being provided in the plug-holding bore before it is introduced into the rheometer bore. The plug-holding bore may be a through bore.

Preferably the material holding chamber is an elongate bore, most preferably defined in a barrel.

The cleaning means may be adapted to change diameter when inserted into the material holding chamber. The plug may be resilient. It may be adapted to be compressed from a wider diameter to a narrower diameter. Alternatively the plug may be adapted to expand in the material holding chamber. This may be achieved by thermal expansion of the plug, or a part of the plug, when exposed to an increase in temperature.

The plug may be of complementary shape to the material holding chamber so as to be a tight interference sliding fit in it. The plug may be adapted to thermally expand in the material holding chamber such that the outer surface of the plug is in bearing contact with the inner surface of the material holding chamber. The plug may comprise a body portion and a split ring surrounding a region of the body portion. The plug, or elements of the plug adapted to be in contact with the material holding space, may be made of phosphor bronze.

Alternatively the plug may be made of wood, or plastics or polymeric material such as "Tufnol" (Trade Mark) polymer.

The plug may comprise an elongate body having one or more split rings, such as piston rings, mounted on it.

The plug may be re-usable or disposable after use.

The plug may be a spring. The spring may be helical. The coils of the spring may be adapted to bear against the inner surface of the material holding chamber when located therein. The length of the spring may be reduced, in order to achieve radial expansion, when it is in the chamber to be cleaned. Some other manipulation of the spring may be used to expand it radially (for example it could be twisted).

The plug may be provided additionally with flexible cleaning material. The flexible cleaning material may be cotton, for example a pad or a patch, or a covering.

We envisage pushing or pulling the cleaning plug through the material holding chamber.

The plug may comprise an invention in its own right, and could be used with automatic cleaning or manual cleaning.

According to a second aspect of the invention we provide a method of operating a rheometer comprising the steps of pushing melt from a material holding space through a die with motive means, removing the motive means from the material holding space, cleaning the motive means, and refilling the material holding chamber; in which the operations of refilling of the holding space and cleaning of the motive means overlap in the same period in time.

Preferably the cleaning operation and refilling operation are automatic.

According to a third aspect of the invention we provide a rheometer comprising a material holding space, die means, tamping means, and motive means adapted to push material from the material holding space through the die; in which the tamping means and the motive means are different components.

Having the motive means as a separate component from the tamping means enables us to clean the motive means whilst the tamping means is performing its function.

The motive means and the tamping means may both be elongate. They may extend in the same direction. They may comprise elongate rods.

Preferably the tamping means and the motive means may be moved simultaneously. Preferably the tamping means and the motive means are both mounted on the same mounting member. Preferably the mounting member is swivelable. Preferably the mounting member is adapted to index from a first position to a second position. In a first position the motive means may be located above the material holding space. In a second position the tamper may be located above the material holding space.

Preferably in the second position the motive means may be at a cleaning station to be cleaned.

Alternatively, indexing of the motive means and the tamping means to and from respective operative positions and inoperative positions may be achieved with the tamping means and the motive means mounted on different components.

Preferably the motive means is a piston, and most preferably a piston and load cell in combination.

The cleaning and tamping may be done automatically or manually.

According to a fourth aspect of the invention we provide a rheometer comprising a die means and a material holding space; in which heating means is provided adjacent the die.

Preferably the heating means is provided below the die. Most preferably the die has a lower face and the heating means is provided beneath the lower face of the die.

Preferably the material holding space is a rheometer barrel.

The heating means may comprise one or more heaters. Preferably one or more cartridge heaters are provided below the die.

The heating means may compensate for heat loss from the bottom of the rheometer barrel.

The heating means below the die is preferably controlled by a controller which receives temperature signals. The temperature signals may include signals from the region of the die or the bottom of the material holding space.

According to a fifth aspect of the invention we provide a method of filling a material holding space in a rheometer comprising the steps of loading the material holding space with a quantity of material, tamping the material, and loading the material holding space with a further quantity of material.

Preferably several tamping operations are performed. Most preferably a tamping operation is performed after each loading of the material holding space with a charge of test material (less than the volume of the holding space). A series of tamping operations may be interleaved with a series of loading operations.

Preferably loading means may be used to load the material holding space. The loading means may comprise a carousel. The loading means may comprise a plurality of blocks. A block may comprise a plurality of supply cells. There may be about three supply cells in one block. There may be a plug-holding cell provided in the carousel, preferably in the block. The material holding space may require the contents of several cells before a test operation can be performed. The holding space may be capable of receiving the contents of an entire block of cells.

Several tampings provide a greater degree of uniformity to the compressed powdered or granulated material. Non-uniformity of material in the material holding space may be a considerable source of error.

According to a sixth aspect of the invention we provide a rheometer comprising a die, a material holding space, tamping means, sensor means adapted to measure a parameter of the rheometer, and control means adapted to control the operation of the tamping means in response to the measurement of the parameter.

The parameter of the rheometers may be pressure or load exerted by the tamping means. The sensor may, however, measure conditions in the material or even pressure or force exerted on the material holding space.

Preferably the control means is adapted to respond to a specified value, for example load. The control means may change the operation of the tamping means.

The change in the operation of the tamping means may be a change from tamping to not tamping, or it may be to reduce the pressure or load exerted by the tamping means.

It is intended that by controlling the tamping force greater uniformity of material may be achieved.

We may prefer to ensure that the test material is tamped to a predetermined load or pressure. We may ensure that the tamping load or pressure does not exceed the predetermined level.

Preferably heating occurs during the tamping operation.

The tamping pressure may be applied for a controlled predetermined time. The control means may control the tamping means to apply one of a number of predetermined tamping pressures for one of a known number of times.

According to a seventh aspect of the invention we provide, in a rheometer, die transfer means which is adapted to collect a die from a rheometer, and transfer the die to a cleaning station.

Preferably collection means are provided to collect a die from a rheometer. The collection means may be a scoop or cup. The collection means may also be adapted to collect cleaning means, such as a plug, according to a first aspect of this invention.

Preferably the collection means is mounted on indexing means, such as an arm, which is adapted to index the collection means from the rheometer to the cleaning station.

The cleaning station may be a furnace. The cleaning may be thermal cleaning. Thermal cleaning may occur by burning away a quantity of material on a die.

The furnace may have an extraction system to remove exhaust products from combustion of material.

According to an eighth aspect we provide a rheometer having automatic die changing means.

One advantage of this is that it enables the die through which the material being tested is flowing to be changed whilst the rheometer is still on-line whilst the extruding or flow-generating of a main material dispenser is still working. Furthermore, since the die can be changed automatically we can replace a die which is, for example, blocked or partially blocked, with a fresh die in a matter of seconds, rather than minutes as was required to change a die manually and without the need for personnel to be present. However, the invention can be used with the rheometeras described in relation to the drawings, or a simplified melt flow indexer which derives from it.

The die may be changed for a similar or identical die, or it may be changed for a die having different characteristics. Changing the die for one with different characteristics enables us to test the material for different properties, or for a greater range of the same property, possibly (when used on-line) in the same operational run of the main extruding or like flow-generating apparatus from which the flow to the rheometer is taken.

Preferably the die changing means is controlled by automatic control means, such as a microprocessor, computer or the like.

The automatic die changing means preferably has a plurality of interchangeable dies of different characteristics. The rheometer can change one die from being in an operative condition to an inoperative condition, and the previously inoperative die to being operative, thereby varying the flow characteristics of the die being used.

Preferably the automatic die changing means comprises a cartridge or block having a plurality of dies and a corresponding plurality of operative positions with respect to a flow passageway of the rheometer with which the operative die is in communication. Cartridge moving means are preferably providing to move the cartridge between its operative positions. The cartridge moving means is preferably under the control of the automatic control means. The cartridge of dies preferably has dies arranged in a line, or around an arc of a circle. Cleaning plug holding means may also be provided in the cartridge.

The rheometer preferably has seal means to seal the die that is in use to the flow passageway. The seal means preferably includes clamping means adapted to urge the die against an abutment face provided on the rheometer. The clamping is preferably under the control of the automatic control means.

The rheometer may have sensing means to detect automatically when a die is blocked, the control means then preferably changing the die automatically.

According to a ninth aspect of the invention we provide a rheometer comprising a die, a material holding space and cooling means; in which the cooling means is adapted to cool the material which emerges from the die.

Preferably the material is cooled to solidify the material.

The cooling means may be one or more air jets or fans.

The cooling means may be an air ring.

Preferably the diameter of the material is measured after the material has been cooled by the cooling means. This effectively "freezes" the swell of the material as it emerges from the die and enables die swell measurements to be made more easily. The cooling means is preferably close to the die, and most preferably immediately below the die heater.

According to a tenth aspect of the invention we provide a rheometer comprising a die, a material holding space, and cutting means; in which the cutting means is adapted to cut the material which emerges from the die when the extrudate reaches a pre-determined length.

Means to vary the predetermined length may be provided.

Sensor means may be provided to measure the length of extruded material. The sensor means may be adapted to operate the cutting means automatically. Operation of the cutting means may occur in response to a signal from the sensor means.

In having pre-determined lengths of extruded material, measurements carried out on the material may be more accurate. The measurements may include the diameter of the extruded material at any point along its length. Accordingly, diameter measuring means may be provided. This may enable the swell of the material to be determined.

The cutting means may cut material to provide length of about 70mm. The cutting means may again operate once the total length of material is a second known length, for example about 120mm. Diameter may be measured with diameter measuring means which may then be movable out of the way. The diameter measuring means may operate only when the extrudate has a predetermined length, or one of a number of predetermined lengths.

Instead of measuring the diameter of the extrudate some other parameter indicative of swell might be measured. For example, the weight of a predetermined length of extrudate might be measured.

The ninth and tenth aspects of the invention may be combined together in a machine to cool, and perhaps solidify material, which may then be cut to provide pre-determined lengths of material.

Measurement of the swell of the material provides information concerning the elastic properties of the material. Once emerged from the die the material may have a viscosity within the range from an oil to a solid. It is important to define a certain length of extruded material in order to determine the weight of the extruded material, and hence the load at the point of diameter measurement.

According to an eleventh aspect of the invention we provide a rheometer comprising a die, a material holding space, and cutting means; in which the cutting means is adapted to hold the extruded material against lateral movement during cutting of the extruded material.

Preferably the cutting means comprises pincer cutters. The cutting means may have a jaw region which is adapted both to hold and to cut.

Embodiments of the invention will now be described by way of example only, with reference to the accompanying drawings of which: Figure 1 shows a side elevation of a rheometer system according to the invention; Figure 2 shows in greater detail part of the rheometer shown in Figure 1; Figure 3 shows schematically a plug cleaner for a rheometer; Figure 4 shows schematically an embodiment of a plug; Figure 5 shows an alternative embodiment of a plug; Figure 6A shows a rheometer having a die heating system; Figure 6B shows schemetically the relationship between a die and a slotted plate which holds it in place in the barrel of the rheometer; Figure 7 shows a rheometer having a simultaneous tamping and piston cleaning system; Figure 8 shows a material loading arrangement having a plurality of loading blocks; Figure 9 shows a schematic load and temperature control system for a rheometer; ; Figure 10 shows a rheometer having an extruded material cooling system; Figure 11 shows a pincer cutter, typically for use with the system of Figure 10; Figure 12 shows schematically the die changing means of the rheometer of Figure 1; and Figure 13 shows a side view of the die changing means of Figure 12.

Figure 1 shows a rheometer system 2. The rheometer system 2 has a frame 4, a material supply system 8, a force applying system 10 with drive means 12, a die changing means 14, a gas purge system 15, and a furnace 16.

The rheometer is shown in greater detail in Figure 2. It comprises a steel barrel 18 having a bore 20 running along the length of the barrel 18. The barrel 18 has a countersunk lead-in 19 to guide into the bore material to be tested or a piston.Surrounding the barrel 18 is a heater 22. The heater may be a single heating unit or a composite of several heating units as shown in this embodiment.

As seen in Figure 2, a die 24 is held at the bottom end of the barrel 18 so that the bore 20 is in communication with an aperture in the die. The die 24 is held in place by a plate 25. The plate 25 has a key-hole slot with a wider portion and a narrower portion. The plate can be slid sideways by a solenoid (not shown) and when the wider portion of the key-hole slot registers with the die the die drops out of the barrel. This can best be seen in Figures 6A and 6B.

The rheometer is provided in a chamber 7 to which the gas purge system 15 is connected. The gas purge system is adapted to pump nitrogen, or some other inert gas, into the chamber. This is used when testing some materials which react in air and enables us to test materials in an atmosphere in which they do not react or degrade.

The material supply system 8 is shown in Figures 1, 2 and 8. Referring mainly to Figure 2, the material supply system 8 is located above the rheometer barrel. A carousel disc or cylinder 26 has a series of slots 28 extending inwardly from the peripheral edge of the circular carousel 26. Supply blocks 30 are located in respective slots and project above them.

Each of the blocks 30 may be moved radially with respect to the carousel 26. The blocks 30 each comprise a series of individual supply cells 34, 36, 38 adjacent one another in a row forming the block 30. The cells are aligned radially along the carousel 26 with cell 34 farthest from the centre of the carousel 26 and cell 38 nearest to the centre. In addition to the supply cells 34 to 38 there is a cleaning plug cell 32 which contains a cleaning plug, referenced 84.

Each individual turn of the carousel 26 indexes a block 30 to register with the countersunk lead-in 19 of the barrel 18. The block 30 may move radially with respect to the carousel in a series of steps. Each step registers an individual load cell with the countersunk lead-in 19.

The supply cells 34, 36 and 38 have an open upper end but their lower ends are blocked by a plate portion of the carousel 26 (referred to in Figure 2 as numeral 25). The lower plate portion 25 of the carousel 26 has a series of through-holes 27, one in each slot 28, which register in turn with the lead-in 19 to the bore 20 as the carousel is indexed around. In this embodiment, once a supply cell is in registration with the rheometer bore the material is free to fall from the cell to the bore. The material may be pushed out by the tamping piston. A similar arrangement is provided for the cleaning plug cell 32.

In an alternative embodiment a slidable plate or grate may be located at the bottom of the supply block 30 to close the bottom end of all of the supply cells. Once a supply cell is in registration with the rheometer bore, the plate is moved to open the end of the supply cell and the material is free to fall from the cell to the bore. Of course, each supply cell may be provided with individually moveable plates or grate which may be operated independently.

The material supply system 8 is disposed adjacent to the rheometer barrel on one side. Disposed to the other side of the rheometer barrel is a piston and tamper cleaner 80.

The die changing means 14 is located below the level of the bottom end of the rheometer barrel, as is shown in Figures 1 and 2. The die changing means 14 is also shown in greater detail in Figures 12 and 13. The die changing means 14 comprises a transport arm 40, a loading ring 42, a loading cylinder 44 and an ejection cylinder 46.

The transport arm 40 is driven to rotate through 3600 about an axis 48 passing through an end 150 of the arm 40. In rotating through 3600 the arm pass underneath the rheometer 6, through the furnace 16 and underneath the loading ring 42.

Figure 13 shows the relative positions of the transport arm 40, the ring 42 and the cylinders 44 and 46. The ring 42 overlaps the transport arm 40. The cylinder 44 has a loading piston 52. The cylinder 46 has an ejection piston 54. The cylinders 44 and 46 may be electrical servos, or pneumatically or hydraulically driven (or driven in any other suitable way).

Referring back to Figure 1, the drive means 12 comprises means for producing movement of the rheometer test, or loading, piston 70 and the tamping piston 72. In this embodiment there is a screw jack and drive motor 56. The force applying system 10 is adapted to apply force to a cross head 58. The cross head runs on guide and support bars 60, 62. Mounted on the lower face of the cross head 58 is a plate 64 carrying load cells 66 and 68 which measure load in the rheometer test piston 70 and the tamping piston 72 respectively. The pistons 70 and 72 are guided and supported by a support strut 74 which is guided by a guide sleeve for movement along a support bar 76 (which in turn is carried by the head 58).

The plate 64, load cells 66 and 68, pistons 70 and 72 and strut 74 together form a swivel unit 78 which is capable of swivelling about the support bar 76. This unit is shown in Figure 7. The drive means for the swivel unit 78 is not shown in the drawings.

The swivel unit may swivel between a first position in which the loading piston is registered above the rheometer barrel and a second position in which the tamping piston is registered above the rheometer barrel.

Located beneath the rheometer barrel is a diameter gauge 122 which is moveable from a first position (referenced A in Figure 2) to a second position (referenced B in Figure 2). This is shown in Figure 1 and in slightly more detail in Figure 2.

Figure 3 shows schematically an embodiment of a barrel cleaner according to one aspect of the invention. A plug 84 is held over a bore 83 of a barrel 86 of a rheometer to clean the barrel 86. The plug is provided in a cartridge 87 which also contains sample to be tamped down (not shown). A piston 85, which in this embodiment is the tamping piston (but may be some other piston) pushes the plug through the bore 83 to clean it. The plug drops out of the open bottom end of the bore.

As a further example, in an alternative embodiment of the invention the swivel unit shown in Figure 7 may have a third piston mounted on the plate 64. In this alternative embodiment the swivel unit 78 may be adapted to swivel to an additional third position in which the third piston is adapted to be swivelled into a position above the rheometer 6.

Figure 4 shows an embodiment of the plug 88. A plug body 90 comprises an end stop 92 and a series of annular discs 94 having alternating wider and narrower diameters. The end stop 92 and the narrow diameter discs 96 are comprised of stainless steel. The wide diameter discs 98 are comprised of phosphor bronze. A screw threaded rod 100 extends from one face of the end stop 92. The discs are threaded onto the screw threaded rod 100 in the order described above. The discs 94 may simply be washers able to rotate on the screw thread or may be internally screw threaded to cooperate with the screw threaded rod 100 and to lock firmly into place against one another. A retaining disc 102 is screw threaded to hold the other discs in place.

In a production version the plug may be a single piece of bronze, it may have the same geometry as that shown in Figure 4, but be turned from an integral piece of bronze.

As seen in Figure 2, the plug 84 cleans the bore 20 by scraping or wiping off any smudging of residue which may remain following a test operation. The plug has such a tight fit with the bore that any test material that may be left on the sides of the bore is swept away by the plug.

Of course, it will be appreciated that the test piston should sweep the barrel clean as far as possible, the die should be removed, and then the tamping piston will push the cleaning plug through to clean the barrel.

After a measurement operation using the rheometer 84 it will usually be desired to remove the die at the bottom of the rheometer barrel 83. Residue of the test material extruded may remain along the bore 83 of the barrel 86. A cleaning plug as described in relation to Figure 4 is brought into a position above the barrel. The plug is then inserted into the barrel 86. A countersunk lead-in at the entrance to the bore 83 may guide the plug into place.

The barrel 86 will still be hot and this heat will increase the temperature of the plug 88. Phosphor bronze is a material having a relatively high thermal co-efficient of expansion. Since the operating temperature range of the rheometer will be known as well as the diameter of the bore 83, a suitable diameter of phosphor bronze disc may be determined to ensure a close fit between the discs 98 and the bore 83 once the plug has fully warmed up. Even if the discs 98 are an interference fit in the bore 83, phosphor bronze is a good bearing material, and the odisc should be moveable longitudinally with respect to the bore 83.

The plug is pushed downwardly through the bore scraping off residual sample material as it progresses. The plug 88 may be pushed completely through the bore 83 to carry as much sample material as possible. The plug may not be attached to the rod 85 (or may be releasably attached) and preferably falls off (or is removed from) the rod 85 once it emerges from the bottom of the barrel 86 (the die having first been moved out of the way). The plug 82 is collected at the lower end of the rheometer barrel 86 as it emerges.

It may be desirable to choose the diameter of the discs 98 such that on thermal expansion in the bore, the first to enter is a close fit, the second to enter is a near interference fit, and the third to enter is an interference fit, in order to provide progressively better cleaning of the bore. Of course the plug may carry more or less than three discs.

Figure 5 shows an alternative embodiment of a cleaning plug. The plug comprises a helical spring 104.

The spring is of a width slightly greater than a bore 83 and when inserted in a bore, the coils of the spring 104 press outwardly against the bore 83. Since this embodiment would provide a rather inexpensive plug, such a helical spring plug may be disposable.

In each embodiment the principle is the same: that when the plug is inserted into the bore 83, surfaces of the plug apply pressure to or lie in close proximity to the internal surface of the bore 83. Other plugs may be made of wood, ceramics, or any other suitable material.

Another feature of the rheometer system 2 not previously described is shown in Figures 6A and 6B.

Since Figures 6A and 6B are schematic the feature will be described in relation to a third rheometer, but it will be appreciated that it is also present on the embodiment of Figure 1. The rheometer 89 of Figure 6A has a barrel 86 provided with a bore 83. A heater 106 is shown surrounding the barrel 86 and a die 108 is shown located at the bottom end of the barrel 86. A sliding plate 91 holds the die in the bore. The plate 91 has a key-hole slot (or some other arrangement with a hole wide enough for the die to pass through). A further heating system 110 is located adjacent to and beneath the die 108. The heating system may comprise one or more cartridge heaters 111. Heating in this area beneath the bottom face of the die compensates for heat loss through the base of the barrel.This is intended to give a more uniform temperature throughout the barrel 86 to provide accuracy of temperature readings.

Moreover, since the test material previously flows through the die in the region of the die we control the temperature of the very region where the flow characteristics are important.

Figure 10 shows a further embodiment of the invention. The arrangement of a barrel 86, a heater 106, and a die 108 is maintained. Additionally a cooling system 112 is included below the die to cool extruded material which emerges from the die. If the additional heating system as described above is included in this embodiment, it may be provided between the bottom of the die 108 and the cooling system 112.

The cooling system uses jets of air to cool extruded material so that it sets. The cooling system is preferably an air ring which surrounds an extruded string of test material.

Again the embodiment of Figure 1 has this feature, but it is not described or shown in Figure 1.

Figure 9 shows schematically a control system for providing more uniform tamping. A tamping piston 114 is driven by drive means 116. A load cell 118 measures the load exerted by the drive means 116 on the tamping piston 114. A controller 120 controls the force applied by the drive means and receives a signal from the load cell 118 indicative of the force. Tamping is generally performed as a multi-stage operation. As discussed earlier supply cells 34, 36 and 38 sequentially provide a quantity of material to the rheometer bore. After a quantity of material is supplied it is tamped down with the tamping piston 114. Once a pre-determined force is detected by the controller 120, the drive means 116 stops applying force (possibly after maintaining that force for a period) and the tamping piston 114 is removed. The rheometer is heated and the material is melting.A further quantity of material is supplied by another supply cell and tamping force is applied until another pre-determined force is detected and again the tamping piston 114 is removed. This procedure continues until the rheometer barrel is fully loaded. By carefully controlling the force applied during tamping the distribution of material and the properties of the material, and distribution of packaging density through the rheometer, is controlled and is more uniform.

Uniformity of these parameters allows for greater accuracy in measurement of rheology properties of the material.

Again the embodiment of Figure 1 has this feature, but it is not shown or described.

A discussion of the operation of the rheometer system 2 of Figure 1 follows. Reference may be made to Figure 2 which shows some details more clearly. At the point where we join the test cycle the rheometer barrel has been cleaned and a clean die is provided at the bottom of the empty rheometer barrel. The piston 70 which has just forced test material out of the rheometer is not yet clean and still has material from the last measurement operation adhering to it.

The carousel 26 indexes around to bring one of the slots 28 into alignment with the top end of the bore 20 of the rheometer barrel 18. A supply block 30 is moved along the radius of the plate to bring the first of the supply cells into registration with the rheometer bore 20.

Material is loaded into the barrel sequentially from each supply cell by the tamping piston 70 moving downwards (carried by the head 58) and pushing it out.

The tamping piston 70 is, of course, first swivelled to register with the bore 20.

After each quantity of material is supplied to the rheometer bore the supply block 30 is moved away from the rheometer barrel and the tamping piston 70 is brought down to tamp the material in the barrel. The control system shown in Figure 9 operates to provide uniform tamping in the rheometer barrel.

The force and motion to the tamping piston 70 is also applied to the loading piston 72 since it is the head 58 that is moved. As each tamping operation occurs and the tamping piston is inserted into the rheometer barrel, the loading piston 72, in an uncleaned state is also brought down. The loading piston is brought into the cleaner 80 to one side of the rheometer barrel. The cleaner operates to clean the loading piston 72. Accordingly the test piston is cleaned whilst tamping occurs.

The cleaner 80 comprises a mechanism for cleaning the tips of the test piston and/or tamper piston. For example, one or more rotating brushes. The cleaner 80 cleans the bottom end face of the test piston 72.

Once the material is in rheometer barrel is fully loaded and tamped in the rheometer barrel, and has melted, it is ready to be tested. The swivel unit 78 swivels about the bar 76 and the test, or load, piston 72 is located above the rheometer barrel and the tamping piston 70 is located above the cleaner 80. The drive means 12 then pushes the test load piston 72 into the rheometer barrel and material is extruded out of the die.

As mentioned above, the die is usually heated by heating system 110 to ensure accuracy and uniformity of the temperature of the material. There is, of course, a controller and sensors for the heating system, with appropriate feedback.

The diameter gauge 122 is located in a position beneath the die. As a length of extruded material extrudes out of the die the diameter of the length of extruded material is measured periodically by the diameter gauge. The information is fed to a central processor which determines the die swell from the diameter of the aperture in the die, the length of the extruded material and the diameter of the length of extruded material. As the length of extruded material grows it passes through the cooling system 112 where it is cooled and solidified.

When the extruded material reaches a length of 70mm a pair of pincers close to cut off the end of the length of material. The action of the pincers may be initiated in response to a signal provided by a sensor which detects the extruded string of material.

The length of material is now a standard length and any measurement of the diameter of the extruded material close to the die has a repeatable, consistent, effect due to the effect of gravity on the length of the material (effectively we can calculate the load on the hanging string of extrudate at the point of measurement, measure its diameter, and calculate swell).

If we vary the length of the suspended string (by varying the position of the sensor or length cutter, or both) we can see how the swell depends upon the load.

This can provide useful information.

Figure 11 shows a pair of pincers 124 for cutting the string of extruded material to a predetermined length.

The pincers 124 are comprised of two components 126 and 128 which are pivotally attached at a pivot point 130. At one end of the pincers 124, cutting surfaces 125 and 127 on the components 126 and 128 surround a cutting region 132. The cutting action of the pincers is operated at the other end of the pincers 124. As the ends of the components 126 and 128 furthest from the cutting region 132 are brought together as shown by the arrows 134 in the drawing, the cutting surfaces are brought together. A length of material present in the cutting region 132 will be pinched by the cutting surfaces 125 and 127 and held in place against lateral movement whilst the end of the length of material is cut off. This avoids us forcing the string of extruded material sideways, as we would do if we used straight-bladed scissors.

The length of material continues to grow after the end has been cut off, and measurements of the properties of the material continue. Once the length of material is 120mm long, a sensor detects the end and the pincers are operated again to standardise the length of material to 70mum. Thus, we get diameter measurements at two known loads - 70mum and 120mm.

The system has a sensor 103 to detect when the string reaches 120mm (length D of Figure 2).

Both the length C and the length D can be varied under the control of the user, either automatically adjustable or manually adjustable. This enables us to have strings of extrudate of different known lengths and enables useful data to be obtained.

Returning to the operation of the general overall machine, as the loading piston moves deeper into the rheometer barrel, the tamping piston enters the cleaner 80 where it is cleaned of material remaining on its surface. Accordingly the tamper is cleaned whilst the loading piston is acting on material in the rheometer barrel.

At the end of the extrusion and measurement operation, the test load piston is withdrawn from the rheometer barrel. The diameter gauge 122 and cooling ring 112 are moved to a position to the left of the bottom of the rheometer barrel 18 as shown in Figure 2.

The plate 25 is slid sideways by its solenoid to align the wider part of the key-hole with the die and the die falls off to be received in hole 137 of arm 40. The transport arm 40, carrying the used die, indexes around, removing the used die from the vicinity of the rheometer barrel. A plug collecting portion (hole) 136 of the arm 40 is brought into register with the bottom of the rheometer barrel. The carousel then brings a new block 30 into line with the bore of the barrel and a cleaning plug 84 is then driven through the rheometer barrel by the tamping piston 70 to clean it as set out above. The tamping piston 72 is used to drive the plug. The plug passes straight through the barrel and falls into the plug collecting portion 136 of the arm 40.

Referring now to Figure 12, the arm 40 indexes around its axis 48 in a clockwise motion until it enters the furnace 16. The furnace burns away the material from the used die held in portion 137 and the plug thus cleaning them.

The arm 40 indexes further in a clockwise motion until it registers with the loading ring 42, the loading cylinder 44 and the ejection cylinder 46. The now-cleaned die is brought into registration with the ejection cylinder 46 and an empty location on the loading ring 42. The ejection cylinder is activated driving the ejection piston upwards which displaces the die upwardly out of the transport arm 40, and into the empty location on the loading ring 42, where it is secured. The loading ring then indexes around to bring a new die which is required for a subsequent measurement operation. Once the new die registers with the transport arm 40, the loading cylinder 46 is activated driving the loading piston downwards which displaces the new die from the loading ring and pushes the new die into the transport arm 40.

The cleaned plug may be removed from the transport arm at any stage of the clockwise motion from the furnace 16 to the loading ring 42. A pick-up may come down and retrieve the cleaned plug from the loading ring to replace it on the cleaning piston 85.

Alternatively the cleaned plug may be discarded at any stage before the next dirty plug enters the arm after cleaning the the rheometer barrel. For example the cleaned plug could be ejected by one of the loading or ejection cylinders and collected. The clean plugs to be attached to the cleaning piston 85 may be from some other source.

Claims (1)

1. A rheometer comprising a die, a material holding chamber and a cleaning means; in which the cleaning means is adapted to clean the material holding chamber automatically.

2. A rheometer according to claim 1 in which the cleaning means comprises a plug and a means for urging the plug through the material holding chamber.

3. A rheometer according to claim 2 in which the plug is cylindrical.

4. A rheometer according to claim 2 or claim 3 in which the plug has a generally uniform outer surface.

5. A rheometer according to any of claims 2 to 4 in which the plug has a stepped surface having at least one raised region adjacent at least one sunken region.

6. A rheometer according to claim 5 in which the raised regions and the sunken regions on the plug are rings.

7. A rheometer according to claim 6 in which the plug has the form of a series of rings of alternating wider and narrower diameter.

8. A rheometer according to any of claims 2 to 7 in which the plug is provided in delivery means adapted to deliver the plug to the entrance to the rheometer bore.

9. A rheometer according to claim 8 in which the delivery means comprises a plug holding bore in a body.

10. A rheometer according to any of claims 2 to 9 in which the plug is adapted to change diameter when inserted into the material handling chamber.

11. A rheometer according to any of claims 2 to 10 in which the plug is resilient.

12. A rheometer according to claim 10 in which the plug is compressed from a wider diameter to a narrower diameter when inserted into the material handling chamber.

13. A rheometer according to any one of claims 2 to 12 in which the plug is adapted to expand in the material handling chamber.

14. A rheometer according to any of claims 10, 12 or 13 in which change in diameter of the plug is achieved by thermal expansion.

15. A rheometer according to any of claims 2 to 14 in which the plug is a complementary shape to the material holding chamber so as to be a tight interference sliding fit in it.

16. A rheometer according to any of claims 2 to 14 in which the plug is adapted to thermally expand in the material holding chamber such that the outer surface of the plug is in bearing contact with the inner surface of the material holding chamber.

17. A rheometer according to any of claims 2 to 16 in which comprises a body portion and a split ring surrounding a region of the body portion.

18. A rheometer according to any of claims 2 to 17 in which the plug, or elements of the plug, adapted to be in contact with the material handling space are made of phosphor bronze.

19. A rheometer according to any of claims 2 to 17 in which the plug, is made of wood.

20. A rheometer according to any of claims 2 to 17 in which the plug of polymeric material.

21. A rheometer according to claim 20 in which the plug is made of "Tufnol".

22. A rheometer according to any of claims 2 to 21 in which the plug comprises an elongate body having one or more split rings mounted on it.

23. A rheometer according to any of claims 2 to 22 in which the plug is re-usable.

24. A rheometer according to any of claims 2 to 22 in which the plug is disposable.

25. A rheometer according to any of claims 2 to 24 in which the plug is a spring.

26. A rheometer according to claim 25 in which the plug is a helical spring adapted to bear against the inner surface of the material handling chamber when located therein.

27. A rheometer according to claim 26 in which the length of the spring is reduced in order to achieve radial expansion.

28. A rheometer according to any of claims 2 to 27 in which the plug is provided additionally with flexible cleaning material.

29. A rheometer according to any preceding claim in which the material holding chamber is an elongate bore.

30. A method of operating a rheometer comprising the steps of pushing melt from a material holding space through a die with motive means, removing the motive means from the material holding space, cleaning the motive means, and refilling the material holding chamber; in which the operations of refilling of the holding space and cleaning of the motive means overlap in the same period in time.

31. A method of operating a rheometer according to claim 30 in which the cleaning operation and refilling operation are automatic.

32. A rheometer comprising a material holding space, die means, tamping means, and motive means adapted to push material from the material holding space through the die; in which the tamping means and the motive means are different components.

33. A rheometer according to any preceding claim which comprises a material holding chamber, a die, tamping means, and motive means adapted to push material from the material holding chamber through the die; in which the tamping means and the motive means are different components.

34. A rheometer according to claim 32, or claim 33 in which the motive means and the tamping means are both elongate.

35. A rheometer according to any of claims 32 to 34 in which the motive means and the tamping means extend in the same direction.

36. A rheometer according to any of claims 32 to 35 in which the motive means and the tamping means comprise elongate rods.

37. A rheometer according to any of claims 32 to 36 in which the motive means and the tamping means may be moved simultaneously.

38. A rheometer according to any of claims 32 to 37 in which the tamping means and the motive means are both mounted on the same mounting member.

39. A rheometer according to claim 38 in which the mounting member is swivelable.

40. A rheometer according to claim 38 to claim 39 in which the mounting member is adapted to index from a first position to a second position.

41. A rheometer according to claim 40 in which in the second position the motive means is at a cleaning station to be cleaned.

42. A rheometer according to any of claims 32 to 41 in which the motive means is a piston.

43. A rheometer according to any preceding claim which comprises a die and a material holding chamber; in which heating means is provided adjacent the die.

44. A rheometer comprising a die means and a material holding space; in which heating means is provided adjacent the die.

45. A rheometer according to claim 43 or claim 44 in which the heating means is provided below the die.

46. A rheometer according to any of claims 43 to 45 in which the material holding space is a rheometer barrel.

47. A rheometer according to any of claims 43 to 46 in which the heating means comprises one or more heaters.

48. A rheometer according to any of claims 43 to 47 in which the heating means below the die is controlled by a controller which receives temperature signals.

49. A method of filling a material holding space in a rheometer comprising the steps of loading the material holding space with a quantity of material, tamping the material, and loading the material holding space with a further quantity of material.

50. A method according to claim 49 in which a series of tamping operations are performed.

51. A method according to claim 49 or claim 50 in which a loading means is used to load the material holding space.

52. A method according to claim 51 in which the loading means comprises a carousel.

53. A rheometer according to any preceding claim which comprises a die, a material holding chamber, tamping means, sensor means adapted to measure a parameter of the rheometer, and control means adapted to control the operation of the tamping means in response to the measurement of the parameter.

54. A rheometer comprising a die, a material holding space, tamping means, sensor means adapted to measure a parameter of the rheometer, and control means adapted to control the operation of the tamping means in response to the measurement of the parameter.

55. Arheometer according to claim 53 or claim 54 in which the control means changes the operation of the tamping means.

56. A rheometer according to any of claima 53 to 55 in which heating occurs during the tamping operation.

57. A rheometer according to any preceding claim with die transfer means which is adapted to collect a die when it is moved from its operative position in the rheometer, and transfer the die to a cleaning station.

58. A rheometer with die transfer means which is adapted to collect a die when it is moved from its operative position in the rheometer, and transfer the die to a cleaning station.

59. A rheometer according to claims 57 or 58 in which collection means are provided to collect a die from a rheometer.

60. A rheometer according to any of claims 57 to 59 in which the cleaning station is a furnace.

61. A rheometer according to any preceding claim having automatic die changing means.

62. A rheometer having automatic die changing means.

63. A rheometer according to claim 61 or claim 62 in which the automatic die changing means has a plurality of interchangeable dies of different characteristics.

64. A rheometer according to any of claims 61 to 63 in which the automatic die changing means comprises a cartridge or block having a plurality of dies and a corresponding plurality of operative positions with respect to a flow passageway of the rheometer with which the operative die is in communication.

65. A rheometer according to any of claims 61 to 64 in which cleaning plug holding means are provided in the cartridge.

66. A rheometer according to any of claims 61 to 65 in which seal means to seal the die that is in use to the flow passageway are provided.

67. A rheometer according to any preceding claim comprising a die, a material holding chamber and cooling means; in which the cooling means is adapted to cool the material which emerges from the die.

68. A rheometer comprising a die, a material holding space and cooling means; in which the cooling means is adapted to cool the material which emerges from the die.

69. A rheometer according to claim 67, or claim 68 in which the cooling means is one or more air jets.

70. A rheometer according to any preceding claim comprising a die, a material holding chamber, and cutting means; in which the cutting means is adapted to cut the material which emerges from the die when the extrudate reaches a pre-determined length.

71. A rheometer comprising a die, a material holding space, and cutting means; in which the cutting means is adapted to cut the material which emerges from the die when the extrudate reaches a pre-determined length.

72. A rheometer according to claim 70 or claim 71 in which sensor means are provided to measure the length of the extruded material.

73. A rheometer according to any of claima 70 to 72 in which diameter measuring means is provided.

74. A rheometer according to any of claims 70 to 73 in which a parameter indicative of swell is measured.

75.A rheometer according to any preceding claim comprising a die, a material holding chamber, and cutting means; in which the cutting means is adapted to hold the extruded material -against lateral movement during cutting of the extruded material.

76. A rheometer comprising a die, a material holding space, and cutting means; in which the cutting means is adapted to hold the extruded material against lateral movement during cutting of the extruded material.

77. A rheometer according to claim 75 or claim 76 in which the cutting means are pincer cutters.

78. A rheometer substantially described herein with reference to Figures 1, 2, 12 and 13.

80. A rheometer with a plug cleaner substantially as described herein with reference to Figure 4.

81. A rheometer with a plug cleaner substantially as described herein with reference to Figure 5.

82. A rheometer with a heating system substantially as described herein with reference to Figures 6A and 6B.

83. A rheometer with a simultaneous tamping and piston cleaning system substantially as described herein with reference to Figure 7.

84. A rheometer with a plurality of loading blocks substantially as described herein with reference to Figure 8.

85. A rheometer with a load and temperature control system substantially as described herein with reference to Figure 9.

86. A rheometer with an extruded material cooling system substantially as described herein with reference to Figures 10 and 11.

87. A method of operating a rheometer substantially as described herein.