The present invention concerns a multi colour die and a method of colouring extruded products providing a wide variety of colourings and applications to existing extruders.

Extrusion, using extruders, is an often used process for preparing products such as pet feed, aquatic feed, and numerous other products. In the extruder the material to be extruded is admitted into an extruder barrel in which a screw conveyor is provided. Rotation of the screw conveyor pressurizes the material to be extruded and propels it towards a die having one or more small openings from which the material is extruded as an extrudate. For producing pellets or the like the extrudate is then cut into specific lengths by a rotating knife.

The colour of the extruded product generally conforms to the colour of the material to be extruded, including any colour changes to the material due to the passage through the extruder. In many cases it is desired to be able to produce extruded products which are coloured differently from the natural colour of the material to be extruded. This is for example often the case with pet foods which through colouring may be rendered more aesthetically pleasing to consumers of such products. Colouring of extruded products may in a simple form comprise mixing a colorant with the material to be extruded before the material to be extruded enters the extruder, for example in a mixing chamber known as a conditioner placed upstream of the extruder. Colouring can of course also be effected after the extruded product has been produced, or as the material to be extruded passes through the die. Furthermore, it is known to inject a colorant into the extruder housing, so that the colorant is mixed with the material to be extruded by the action of the screw conveyor.

Different techniques for producing coloured extruded products, as outlined above, are disclosed in US4100618, US5773037, US4054271 , US2518124, FR2566700, EP0169126, DE3516852, US4171668, US6358547, WO2004054392 and US6942376.

The techniques described in the abovementioned disclosures in many cases require specially constructed or adapted extruders, or alternatively provide only limited possibilities as regards colouring of the coloured extruded products produced therewith. Accordingly it is an object of the present invention to provide greater possibilities for producing coloured extruded products.

It is a further object of the present invention to make possible the production of coloured extruded product with existing extruders.

At least one of the above objects, or at least one of any of the further objects which will be evident from the below description, is, according to the corresponding first and second aspects of the present invention, achieved by the multi colour die according to claim 1 and the method according to claim 16.

As the multi colour die comprises at least two secondary extruded product flows, it provides good possibilities for producing different coloured extruded products. Further, as the multi colour die receives an extruded product flow it can be simply attached to existing extruders.

The manifold chamber may comprise a central volume to which the secondary flow channels are connected.

The secondary flow channels are preferably cylindrical and/or orthogonal to the mixing chamber. Preferably the secondary flow channels are as short as possible as this gives the shortest distance between the manifold chamber and the elongated mixing chamber.

To further decrease the length of the flow path through the multi colour die, the mixing chambers are preferably arranged close to each other.

The junctions between the secondary flow channel and the manifold chamber, and between the secondary flow channel and the mixing chamber, are preferably made with rounded edges to minimize the resistance to the flow of the extruded product flow.

The mixing chamber is preferably cylindrical. The mixing chamber has a first end and a second end. The secondary extruded product flow preferably enters at the first end and leaves the mixing chamber at the second end.

The product outlets may be placed adjacent to each other or spaced apart.

In the context of the present invention expelling encompasses releasing.

The additive inlets are preferably provided at a position close to the secondary flow channel while the product outlet is often provided in a small group or separately.

Additional inlets may be positioned in other positions. The colorant may be any suitable colorant. The choice of colorant is governed by the type of extruded product flow.

The multi colour die may comprise, for each mixing chamber, a first and a second additive inlet, said first and second additive inlet preferably being positioned at different positions along said mixing chamber. This is advantageous as it allows the production of coloured extruded product having a base colour provided by a first colorant added to the first additive inlet positioned at a first position along the mixing element for which position the first colorant is uniformly mixed with the secondary extruded product flow, and an effect colour provided by a second colorant added to the second additive inlet positioned at a second position along the mixing element for which position the second colorant is non-uniformly mixed with the secondary extruded product flow, thereby producing decorative whirls or striations of the second colorant in the coloured extruded product. The motor assembly may comprise a direct drive motor or a geared motor. Further, the motor assembly may be energized by supplying it with electric energy, high pressure air, or hydraulic pressure.

The multi colour die is preferably attachable, for example by comprising a fastening flange provided around the inlet, to an extruder outlet plate or an extruder outlet nozzle or an extruder die of a conventional single or dual screw extruder.

In one embodiment the multi colour die further comprises at least two pressure sensors connected to a corresponding one of the at least two product outlets or to the second ends of the at least two elongated mixing chambers for determining the pressure of the coloured extruded product, the pressure then being input to a control circuit programmed to control the rotation speed of each of the two elongated mixing elements by controlling each of the at least two motor assemblies by actuating control mechanisms, such as a valve, connected to or comprised by each of the at least two motor assemblies. The control circuit is preferably programmed so as to control the motor assemblies so that the pressures determined in the at least two product outlets or second ends of the at least two elongated mixing chambers are the same. This helps ensure that the coloured extruded product is expelled at the same flow rate through each of the at least two product outlets. The embodiment of the multi colour die, according to the first aspect of the present invention, defined in claim 2, is advantageous as it allows the different layers of the secondary extruded product flow to flow at different speeds, thus affecting the mixing of colorant with extruded product for producing striated or striped coloured extruded products. The shear member may be movable manually or by using a hydraulic, pneumatic or electrical actuator. Generally, when the shear member is moved into the manifold chamber the shear stress on the extruded product flow increases and vice versa.

The embodiment of the multi colour die, according to the first aspect of the present invention, defined in claim 3, is advantageous as it allows the extruded product flow to bypass the mixing chambers, thus providing for cleaning the mixing chamber without interrupting the running of the extruder.

The shear member is preferably a piston. The shear member may be actuated, for movement relative to the manifold chamber, either manually or using a hydraulic, electric, or pneumatic actuator. The embodiment of the multi colour die, according to the first aspect of the present invention, defined in claim 4, is advantageous as it allows the mixing elements to be easily removed from the multi colour die for cleaning or replacement.

The aperture may comprise a first screw thread for interengagement with a second screw thread on the bearing assembly. Alternatively the multi colour die may comprise fastening members such as threaded studs or threaded bores provided adjacent to the aperture for fastening the bearing assembly.

In the context of the present invention insertion encompasses positioning.

The mixing element is preferably adapted to be insertable axially through the aperture. The first drive member may comprise one or more exterior or interior splines, a polygonal hole or rod, or a gear wheel.

The motor assemblies may comprise a motor axle on which the second drive member is positioned. Alternatively the motor assemblies may comprise a gear having an output shaft on which the second drive member is positioned.

The second drive member may comprise one or more interior or exterior splines, a polygonal rod or hole, or a gear wheel.

The bearing assembly preferably comprises a tapered roller bearing capable of taking up radial and axial forces. Each of the motor assemblies may comprise a tapered roller bearing capable of taking up radial forces only.

Each bearing assembly may comprise a seal for sealing the bearing assembly to the aperture. The bearing assemblies may be releasably attached by being attachable using screws to a screw thread, a bayonet fitting, bolts or nuts, etc. Each of the at least to product outlets may be fluidly connected to a corresponding one of the at least two mixing chambers via a corresponding coloured extruded product channel fluidly connected to the mixing chamber. Typically the coloured extruded product channel is angled in relation to the rotation axis of the mixing element.

The embodiment of the multi colour die, according to the first aspect of the present invention, defined in claim 5, is advantageous as it decreases the resistance which the extruded product has to overcome. This effect is achieved by the secondary extruded product flow not having to change direction for leaving the mixing chamber; rather, the secondary extruded product flow flows along the mixing element in the direction of the rotation axis of the mixing element and leaves the mixing chamber through the aperture and the product outlet in the die plate, thus ensuring that the secondary extruded product flow is subjected to the mixing effect of the mixing element for the greatest possible portion of its flow through the multi colour die with the least amount of change in direction.

The multi colour die, in the area around the apertures, is preferably provided with threaded holes for allowing the die plate to be bolted to the multi colour die with suitable bolts.

The mixing element is preferably adapted to be insertable axially through the aperture. The motor shaft preferably extends from the first end of the mixing chamber to the second end of the mixing chamber. The motor shaft preferably comprises a longitudinal spline or groove for matingly engaging a corresponding longitudinal groove or spline on the inner wall of the bore in the mixing element. In addition, or instead, the end of the motor shaft that is close to the aperture may be provided with a retaining arrangement such as the end being threaded for cooperation with a nut, the end being provided with a lateral bore for cooperation with a pin positioned in the lateral bore, or the like, for retaining the mixer element on the motor shaft. Suitable tightening of the nut may be used to cause the mixer element to rotate together with the motor shaft. If the retaining arrangement comprises a lateral bore and a pin, the end of the mixer element furthest from the motor assembly may be provided with axially extending protrusions for being engaged by the opposite ends of the pin, the pin thus rotating with the motor shaft and engaging the protrusions for rotating the mixer element with the motor shaft.

The die plate may be attached directly to the multi colour die or alternatively it can be attached to the multicolour die via an annular carrier comprising at least two flow channels, the annular carrier being adapted for fluidly connecting one end of said flow channel with said mixing chamber via said aperture, and the other end of said flow channel with said product outlet in said die plate. The die plate is adapted, to be releasably attached to the multi colour die, in that the position of the at least two product outlets on the die plate and the dimensions of the die plate are chosen such that when the die plate is attached to the multi colour die, each product outlet is placed in fluid connection with the corresponding mixing chamber.

The embodiment of the multi colour die, according to the first aspect of the present invention, defined in claim 6, is advantageous as it allows one of the at least two secondary flow channels, mixing chambers, mixing elements, additive inlets, and/or product outlets to be blocked, and accordingly separated from the extruded product flow, for cleaning while the coloured extruded product may continue to be produced using the other one of the at least two secondary flow channels, mixing chambers, mixing elements, additive inlets, and/or product outlets. When one of the secondary flow channels are blocked, the corresponding parts of the multi colour die, i.e. the corresponding secondary flow channel, mixing chamber, mixing element, additive inlet, and/or product outlet may be cleaned either in situ, also known as clean-in-place (CIP) by flushing a cleaning fluid or water through and around the part using the additive inlet and product outlet as inlet/outlet for the cleaning fluid or water. Alternatively the corresponding additive inlet and/or mixing element may be removed from the multi colour die and cleaned ex situ.

Another reason for blocking one of the at least two secondary flow channels is when the multi colour die is used to produce at least two differently coloured extruded products and a desired amount of one of the two differently coloured products has been produced.

In the context or the present invention selectively blockable encompasses blockable.

Further, independently blockable is to be understood as having the meaning that one of the at least two secondary flow channels may be blocked without the other of the at least two secondary flow channels being blocked.

The embodiment of the multi colour die, according to the first aspect of the present invention, defined in claim 7, is advantageous as it provides a simple way of gaining access to the secondary flow channels for blocking them. The additive inlets preferably comprise a first screw thread interengageable with a second screw thread provided on the additive aperture. Preferably the minimum diameter of the additive aperture is larger than the minimum diameter of the corresponding secondary flow channel. Preferably the blocking member is adapted to extend from the additive aperture to a position in the secondary flow channel close to the manifold chamber. The embodiment of the multi colour die, according to the first aspect of the present invention, defined in claim 8, is advantageous as it provides a secure fastening of the blocking member and a precise positioning of the blocking member, the first end preferably comprising a first screw thread interengageable with a second screw thread in the additive aperture.

The embodiment of the multi colour die, according to the first aspect of the present invention, defined in claim 9, is advantageous as it allows both of the secondary flow channels to be blocked allowing the mixing chambers and the mixing elements to be cleaned.

The embodiment of the multi colour die, according to the first aspect of the present invention, defined in claim 10, is advantageous as hydraulic motors have higher torque than similarly sized electric motors thus providing a good mixing. Further, hydraulic motors are not damaged if stalling, such as due to a seizure of the mixing element or due to damage to the mixing element.

The embodiment of the multi colour die, according to the first aspect of the present invention, defined in claim 11 , is advantageous as it provides an inexpensive and effective mixing element. The mixing element may for example advantageously be formed of a plurality of metal plates having a central hole and a plurality of cylindrical spacers arranged one after the other on a central axle or body. Preferably the metal plates are elongated and/or laser cut.

The mixing blades may be rod shaped, rectangular, spiral shaped or twisted.

The embodiment of the multi colour die, according to the first aspect of the present invention, defined in claim 12, is advantageous as it allows different flow rates and/or flow speeds for the different secondary extruded product flows. This allows the production of different amounts of the differently coloured secondary extruded product flows.

The radially extending mixing blades configured for propelling the corresponding secondary extruded product flow may be twisted so as to define propeller blades, or may comprise flights.

In the context of the present invention propelling encompasses pumping. The embodiment of the multi colour die, according to the first aspect of the present invention, defined in claim 13 is advantageous in that it allows for a rational construction of the mixing element. Each hollow cylindrical mixing screw section, of which there are typically five for each mixing element, may be identical and are inexpensive to produce and easy to exchange. Further, where the mixing blades are twisted to provide a propelling effect to the secondary extruded product flow, this effect may be varied by changing the direction of the individual hollow cylindrical mixing screw section.

The hollow cylindrical mixing screw section is preferably circular cylindrical, with a circular cylindrical bore; however, it, and the central bore, may alternatively be square cylindrical for use with a central body having a square cross section. The embodiment of the multi colour die, according to the first aspect of the present invention, defined in claim 14, is advantageous in that it provides a simple way of transferring rotation of the central body to the hollow cylindrical mixing screw section if the central body and the central bore have circular cross sections. The embodiment of the multi colour die, according to the first aspect of the present invention, defined in claim 15, is advantageous as it allows different levels of mixing for the different secondary extruded product flows. Thus, one of the secondary extruded product flows may be mixed with the colorant at a high speed, corresponding to a high level of mixing, resulting in a uniformly coloured extruded product, while the other may be mixed with the colorant at a low speed, corresponding to a low level of mixing, resulting in a non- uniformly coloured extruded product for example having stripes or whirls of the colorant. In the context of the present invention independently driveable at different speeds encompasses one of the at least two motor assemblies rotating the corresponding one of said at least two mixing elements at a first rotational speed and the other of the at least two motor assemblies rotating the mixing element corresponding to that motor assembly at a second rotational speed different from said first speed.

Further, the first or second speed may be zero, i.e. corresponding to the motor assembly not rotating the corresponding mixing element. The embodiment of the multi colour die, according to the first aspect of the present invention, defined in claim 16, is advantageous as it allows different flow rates and/or flow speeds for the different secondary extruded product flows. This allows the production of different amounts of the differently coloured secondary extruded product flows. The gear pump is preferably provided in the mixing chamber. The gear pump may comprise two intermeshing gears. In the context of the present invention controlling one of the secondary extruded product flows encompasses affecting the flow rate of one of the secondary extruded product flows.

The embodiment of the multi colour die, according to the first aspect of the present invention, defined in claim 17, is advantageous as it allows a higher number of differently coloured extruded products to be produced. Preferably at least two is four; however, at least two may be more such as 5, 6, 7, 8 or more.

The embodiment of the multi colour die, according to the first aspect of the present invention, defined in claim 18, is advantageous as it provides a better mixing by preventing the extruded product flow from rotating with the mixing element. The screw thread is preferably male, i.e. protruding from the inner wall of the mixing chamber, but may alternatively be female. Preferably the mixing blades on the mixing element have the same pitch and number of flights as the screw thread on the inner wall of the mixing chamber.

Claim 19 defines an extruder assembly comprising embodiments of the multi colour die according to the first aspect of the present invention. A knife unit allows the production of pellets from the coloured extruded product.

The knife may be mounted on a rotating disc. The knife unit, the multi colour die and the extruder may be releasably attached to each other.

The invention and its many advantages will be described in more detail below with reference to the accompanying schematic drawings, which for the purpose of illustration show some non-limiting embodiments, and in which:

Fig. 1 shows an extruder and an embodiment of a multi colour die according to the first aspect of the present invention,

Fig. 2 shows the embodiment of the multi colour die according to the first aspect of the present invention,

Fig. 3 shows further embodiments of various parts of the multi colour die according to the first aspect of the present invention, and Fig. 4 shows a further embodiment of the multi colour die according to the first aspect of the present invention. In the below description, one or more 'signs added to a reference number indicates that the element referred to has the same or similar function as the element designated the reference number without the 'sign, however, differing in structure.

Additionally, where useful for discussing two or more identical elements, a subscript Arabic numeral is used to designate such further identical elements.

When further embodiments of the invention are shown in the figures, the elements which are new, in relation to earlier shown embodiments, have new reference numbers, while elements previously shown are referenced as stated above. Elements which are identical in the different embodiments have been given the same reference numerals and no further explanations of these elements will be given. Fig. 1 shows an extruder 10 and an embodiment of a multi colour die 50 according to the first aspect of the present invention.

The extruder 10 comprises an extruder base 12 for supporting the different components of the extruder 10. On the base 12 is mounted an electric motor 14 connected via a gear transmission 16 and a coupling in a coupling enclosure 18 to a screw conveyor (not shown). Material to be extruded is fed through a hopper inlet 20 in fluid communication with the interior of an extruder barrel 22 within which the screw conveyor revolves driven by the electric motor 14. The material to be extruded is then compressed and propelled by the screw conveyor towards an extruder outlet plate or die 24, which is affixed to the extruder barrel 22 for closing the downstream end of the extruder barrel 22. The extruder outlet plate comprises an extruder outlet nozzle 26, only shown in fig. 1 C, through which the material to be extruded is extruded as an extruded product flow 2 illustrated as a multitude of circles in fig. 2F. Further shown in fig. 1 is a knife unit 30 comprising an electric motor 32 and a knife housing 34 which houses a rotating knife suitable for cutting the extruded product flow 2 from the extruder 10 into pieces. A knife unit outlet 36 then allows the cut pieces to be collected.

A traverse beam 40 carries lifting devices 42, 42, and 42 ₂ for suspending the extruder outlet plate 24 and the knife unit 30 for allowing assembly and disassembly of the extruder outlet plate 24 with the extruder barrel 22, and further allowing assembly and disassembly of the knife unit 30 with the extruder outlet plate 24 as in a conventional extruder.

A further lifting device 42 ₃ carried by the traverse beam 40 carries a first embodiment of a multi colour die 50 according to the first aspect of the present invention. The multi colour die 50 is interposed between the extruder outlet plate 24 and the knife unit 30. In fig. 1A and 1 C the multi colour die 50 is shown attached to the extruder outlet plate 24 and the knife unit 30; however, the multi colour die 50 may easily be separated from the extruder outlet plate 24 as needed for cleaning of the extruder outlet plate 24 and the extruder outlet nozzle 26, see fig. 1 B. Fig. 1 B further shows how the multi colour die 50 may easily be separated from the knife unit 30 as needed for cleaning of the knife unit 30.

As is clear when studying fig. 1 B the multi colour die 50 represents an add-on part to the conventional setup of the extruder 10 and the knife unit 30; thus, the multi colour die 50 may be added to an existing extruder 10 for providing the capability of producing a coloured extruded product without requiring modifications to the extruder 10 or the knife unit 30. This allows that where only a portion of the total production of extruded product from an extruder is to be a coloured extruded product, the multi colour die 50 may be attached and detached to the extruder as needed. In operation of the extruder 10 the material to be extruded is fed into the hopper inlet 20. The electric motor 14 is energized causing the screw conveyor to rotate for compressing and propelling the material to be extruded towards the extruder outlet nozzle 26. The material extruded through the extruder outlet nozzle 26 however first enters the multi colour die 50 where it is coloured, as described further below, before the coloured extruded material is cut by the knife unit 30.

Turning to figs. 2 the multi colour die 50 is now described as follows. The multi colour die 50 comprises a fastening flange 52, for allowing the multi colour die 50 to be attached to the extruder outlet plate 24, and an inlet 54, see fig. 2D, for the extruded product flow 2 from the extruder outlet nozzle 26. A main tube 56 having a first end 58 and a second opposite end 60 is attached via its first end 58 to the fastening flange 52. The main tube 56 defines a main channel 62 fluidly connected to the inlet 54 for receiving the extruded product flow 2 from the inlet 54 and directing it to a manifold chamber 64 comprising a movable shear piston 66 which by being moved into the manifold chamber 64, i.e. being moved towards the second end 60 of the main tube 56, imparts shear stress upon the extruded product flow 2. The shear piston 66 enters the manifold chamber 64 through a purge aperture 68 fluidly connectable, when the shear piston 66 is withdrawn, i.e. moved away from the second end 60 of the main tube 56, to the exterior of the multi colour die 50 via the purge outlet 70. The manifold chamber 64 is fluidly connected to four secondary flow channels, one of which is designated the reference numeral 72. The secondary flow channels 72 split up the extruded product flow 2 into four secondary extruded product flows, one of which is designated the reference numeral 2'. The manifold chamber 64 and the secondary flow channels 72 are defined in a secondary flow block 74, most clearly seen in fig 2C. Each secondary flow channel 72 opens up into a corresponding elongated mixing chamber, the one shown in the figures being designated the reference numeral 76. The elongated mixing chambers 76 are defined by the secondary flow block 74, a corresponding mixing tube 78, and a product block 80 attached to the secondary flow block 74 via the mixing tubes 78. The elongated mixing chamber 76 comprises opposite first and second ends 82 and 84 whereby the secondary flow channel 72 is fluidly connected to the first end 82.

The product block 80 further comprises an aperture 86 for each elongated mixing chamber 76, the aperture 86 allowing insertion and removal of an elongated mixing element, in its entirety designated the reference numeral 90. The elongated mixing element 90 comprises opposite first and second ends 92 and 94 and a central body 96. On the central body 96 are mixing blades, one of which is designated the reference numeral 98, and cylindrical spacers, one of which is designated the reference numeral 100, alternatively threaded. The mixing blades are preferably manufactured from laser cut sheet metal. The first end 92 of the elongated mixing element 90 comprises a first drive member, shown best in fig 2G, represented by splined receiver 102. The second end 94 of the elongated mixing element 90 is journaled in a bearing assembly 104 comprising a tapered roller bearing 106 for journaling the second end 94 both radially and axially. The bearing assembly 104 is further attachable to the product block 80 for sealing the aperture 86 and positioning the elongated mixing element 90 in the elongated mixing chamber 76.

Attached to the secondary flow block 74 are four motor assemblies, one of which in its entirety is designated the reference numeral 1 10. The motor assembly 1 10 comprises a hydraulic motor 112 comprising a turbine 1 14 energized and via first and second hydraulic lines 1 16 and 1 18, and attached to the secondary flow block 74 via mounting flange 120 and motor bearing assembly 122 through which motor shaft 124 extends into the elongated mixing chamber 76 journaled radially by the motor bearing 126.

For coupling the motor assembly 110 to the elongated mixing element 90 the free end of the motor shaft 124 comprises a splined end 128, representing a second drive member, shown best in fig. 2G.

The second end 84 of the elongated mixing chamber 76 is fluidly connected to a coloured extruded product channel 130 terminating in a set of coloured extruded product outlets, one of the coloured extruded product outlets being designated the reference numeral 132. Colorant 4, represented by filled squares in fig. 2F, for colouring the secondary extruded product flow 2', is introduced via a first additive inlet 134 screwable into a first threaded additive aperture 136 formed in the secondary flow block 74. A second additive inlet 138 is likewise screwable into a second threaded additive aperture 140 formed in the product block 80. If desired, a second colorant may be added to the second additive inlet 38. As the second additive inlet 138 is positioned at the second end 84 of the elongated mixing chamber 76, the second colorant may not be uniformly mixed with the secondary extruded product flow 2' in comparison with the first colorant 4 which is added to the first additive inlet 134 which, as it is positioned at the first end 82 of the elongated mixing chamber 76, is positioned upstream of the second additive inlet 138, and the first colorant 4 therefore has a longer residence time in the elongated mixing chamber 76 providing better mixing.

If desired, a pressure sensor (not shown) may be screwed into the secondary threaded additive aperture 140. The pressure sensor measures the pressure in the second end 84 of the elongated mixing chamber 76, and the pressure measured may be used to control the speed of rotation of the elongated mixing element 90 through controlling the supply of hydraulic fluid to the motor assembly 110 with the aim of achieving the same pressure in the second ends 84 of all four elongated mixing chambers 76, and consequently the same flow of coloured extruded product 6 through each of the four sets of coloured extruded product outlets 132. Control of the supply of hydraulic fluid to the motor assembly 1 10 may be carried out by adjusting the flow using a valve interconnected between the motor assembly 110 and the first and second hydraulic lines 116 and 1 18.

As the elongated mixing element 90 turns in the elongated mixing chamber 76, the colorant 4 is uniformly mixed with the extruded product flow 2 to form the coloured extruded product 6 which then leaves the multi colour die 50 through the set of coloured extruded product outlets 132 as seven flows.

Only one of each of the in total four secondary flow channels 72, elongated mixing chambers 76, motor assemblies 1 10, elongated mixing elements 90, coloured extruded product channel 130 and sets of coloured extruded product outlets 132 of the multi colour die 50 are shown in cross sections in fig. 2; however, the other three of each are the same as is clear from fig. 2C. The coloured extruded product outlets 132 are defined by holes in a die plate 142 attached to an annular carrier 144 bolted to the product block 80. The seven holes of each set of coloured extruded product outlets 132 are connected to a corresponding one of the four coloured extruded product channels 130, each coloured extruded product channel having a cross section shaped as a quarter of an annulus when seen from the direction of the flow of coloured extruded product 6 at the die plate 142, each of the four coloured extruded product channels 130 lining up with a quarter of the die plate 142.

In fig. 2A the set of seven holes of the coloured extruded product outlets 132 connected to the coloured extruded product channel 130 is shown. The sets of coloured extruded product outlets, i.e. holes, for the other three of the four coloured extruded product channels, i.e. the other three sectors of the annular die plate 142, are not shown.

Thus, there are in total 28 holes 132 in the die plate 142. Different die plates 142 having holes with different numbers and shapes and/or dimensions may be used to obtain the desired shape and dimensions of the coloured extruded product 6.

Turning briefly to fig. 2G the removal of the elongated mixing element 90, for allowing cleaning of the same and/or cleaning of elongated mixing chamber 76 and other parts of the multi colour die 50, is shown. Another reason for removing the elongated mixing element 90, besides cleaning, is that damage has been caused to one or more of the mixing blades 98 which therefore need to be replaced, or that the whole elongated mixing element 90 needs to be exchanged due to wear or in order to fit an alternative elongated mixing element more suitable, such as by having more densely positioned mixing blades, for achieving a more uniform mixing.

The multi colour die 50 shown in figs. 1 and 2 can produce four differently coloured extruded products at the same time. If, however, a lower number of differently coloured extruded products is needed, one or more of the secondary flow channels may be blocked as illustrated in fig. 2E. Blocking further allows the corresponding secondary flow channel, elongated mixing chamber, elongated mixing element, first additive inlet, second additive inlet, coloured extruded product channel, and coloured extruded product outlet to be cleaned while production of coloured extruded products is continued using the non-blocked secondary flow channels.

In fig. 2E the secondary flow channels 72 and 72, have been blocked by stopper rods 150 and 150i, representing blocking members, inserted through the additive apertures 136 and 136,.

Each stopper rod 150 comprises an elongated body 152 having a first threaded end 154 for screwing the stopper rod into the first additive aperture 136, and a second end 156 comprising a stopper body 158 for blocking the secondary flow channel 72. For the sake of illustration all four secondary flow channels 72, 72 _t 72 ₂ , 72 ₃ and elongated mixing chambers 76, 76 76 ₂ , 76 ₃ are designated. There are no elongated mixing elements in the elongated mixing chambers connected to the blocked secondary flow channels. Fig. 3 shows further embodiments of various parts of the multi colour die 50 according to the first aspect of the present invention.

Thus fig. 3A shows an alternative embodiment of elongated mixing element 90'. The elongated mixing element 90' differs from the elongated mixing element 90 by comprising a modified central body 96' having a longitudinal ridge or spline 97. The mixing blades 98 and spacers 100 of the elongated mixing element 90 have here further been replaced by a plurality of hollow cylindrical mixing screw sections, one of which are designated the reference numeral 100' and which is also being shown in fig. 3B, threaded onto the modified central body 96' one after the other. Each hollow cylindrical mixing screw section 100' comprises a longitudinal groove 99 in the wall of its central bore 101 for engaging the longitudinal ridge or spline 97 to transfer rotation from the modified central body 96' to the hollow cylindrical mixing screw section 100'. The hollow cylindrical mixing screw sections 100' further carry pitched mixing blades 98'.

The alternative embodiment of elongated mixing element 90' shown in fig. 3A is advantageous as the hollow cylindrical mixing screw sections 100' are easily replaced or exchanged when worn or when it is desired to change the mixing action, for example by varying the pitch or shape of the mixing blades 98'.

Shown in fig. 3A is also a mounting bracket 105 for mounting the bearing assembly 104 to the product block 80. Fig 3C shows an alternative embodiment of a part of the mixing tube 78' which differs from the mixing tube 78 shown previously in that the inner wall of the mixing tube 78 is provided with a male screw thread 79. The male screw thread 79 may for example have 2 flights. The male screw thread 79 prevents the secondary extruded product flow 2' from beginning to rotate with the elongated mixing element 90 or 90', and thus helps ensure that the secondary extruded product flow 2' is properly mixed with the colorant 4.

Fig. 4 shows a further embodiment of the multi colour die 50' according to the first aspect of the present invention. The multicolour die 50' differs from the multicolour die 50 shown previously in that the coloured extruded product 6 is expelled out of the multi colour die 50' along the central axis of the elongated mixing chamber 76. This is achieved by removing the coloured extruded product channel 130 from the product block 80 and by using a larger diameter annular carrier 144' and a larger diameter die plate 142', both being dimensioned and mounted so that the coloured extruded product 6 passes through the aperture 86 through the annular carrier 144' and through the coloured extruded product outlet 132 in the die plate 142. This requires that the bearing assembly 104 is removed. Instead a modified elongated mixing element 90" and a modified motor shaft 124' are used. The modified motor shaft 124' is elongated and extends from the motor bearing 126 to the second end of the elongated mixing chamber 84 where it ends in a threaded end 125. The modified mixing element 90" comprises a modified hollow central body 96" adapted to be slid over the modified motor shaft 124'. A nut 146 is screwed onto the threaded end 125 for retaining the elongated mixing element 90" on the modified motor shaft 124'. Tightening of the nut 146 also ensures that the elongated mixing element 90" turns with the modified motor shaft 124'. Additionally the modified motor shaft 124' may be provided with a longitudinal groove or spline, and the modified central body 96" may be provided with a structure interacting with the groove or spline for transferring rotation from the modified motor shaft 124' to the elongated mixing element 90". Furthermore the modified motor shaft 124' may, as shown in fig. 4, be provided with a splined portion 128' for engaging a modified first end 92' of the elongated mixing element for transferring rotation from the modified motor shaft 124' to the elongated mixing element 90".

The multi colour die 50' shown in fig. 4 is advantageous as the extruded product flow has to travel a shorter distance thus leading to a lower back pressure, i.e. resistance. Further the elimination of the coloured extruded product channel 130 removes the angled junctions between the elongated mixing chamber 76 and the coloured extruded product outlet 132, the removal of these angled junctions further reducing back pressure, i.e. resistance.

In a variant the modified annular carrier 144' is dispensed with and the modified die plate 142' attached directly to the product block 80.

As an alternative to using the mixer element 90" a plurality of hollow cylindrical mixing screw sections 100' may be slid or threaded directly onto the motor shaft 124', the last one being and secured thereon by the nut 146, thereby also securing the remainder of the hollow cylindrical mixing screw sections 100'. In this case the motor shaft 124' could comprise a longitudinal spline similar or identical to the longitudinal ridge or spline 97 of the mixing element 90' for engaging the longitudinal grooves 99 of the hollow cylindrical mixing screw sections 100'. List of parts with reference to the figures:

2. Extruded product flow

4. Colorant

6. Coloured extruded product

10. Extruder

12. Extruder base

14. Electric motor

16. Transmission

18. Coupling enclosure

20. Hopper inlet

22. Extruder barrel

24. Extruder outlet plate

26. Extruder outlet nozzle

30. Knife unit

32. Electric motor

34. Knife housing

36. Knife unit outlet

40. Traverse beam

42. Lifting device

50. Multi colour die

52. Fastening flange

54. Inlet

56. Main tube

58. First end of main tube

60. Second end of main tube

62. Main channel

64. Manifold chamber

66. Shear piston

68. Purge aperture

70. Purge outlet

72. Secondary flow channel

74. Secondary flow block

76. Elongated mixing chamber

78. Mixing tube

79. Male screw thread

80. Product block

82. First end of elongated mixing chamber 84. Second end of elongated mixing chamber

86. Aperture

90. Elongated mixing element

92. First end of elongated mixing element

94. Second end of elongated mixing element

96. Central body

97. Longitudinal ridge or spline

98. Mixing blade

99. longitudinal groove

100. Spacer

101. Central bore

102. Splined receiver

104. Bearing assembly

105. Mounting bracket . Tapered roller bearing

. Motor assembly

. Hydraulic motor

. Turbine

. First hydraulic lines

. Second hydraulic lines

. Mounting flange

. Motor bearing assembly

. Motor shaft

. Threaded end

. Motor bearing

. Splined end

, Coloured extruded product channel. Coloured extruded product outlet. First additive inlet

. First additive aperture

. Second additive inlet

. Second additive aperture

. Die plate

. Annular carrier

. Nut

. Stopper rod

. Elongated body

. First threaded end

. Second end

. Stopper body