ARRANGED TO EXTEND FORWARDLY OF THE BLADES

Technical Field

The present invention relates to die face cutter assemblies for extruders .

Background

Within the breakfast cereal, snack foods , pasta production, and pet foods sectors extrusion is used to cook and form a range of direct expanded and half products being both an economical as well as very versatile manufacturing process. Typically , extruders are offered by a great number of manufacturers in both single screw format as well as twin screw format - the latter divided into either co-rotating screw or counter-rotating screw types. The end products that can be produced by extrusion utilise the inherent mechanical shear action of the screw to work the ingredients by forcing them in a contained cylinder - the extruder barrel - against a restrictive die causing work to be done by frictional energy. This frictional energy causes heating which can be useful to cook the extrudate in the case of starch-based ingredients. Since the extrudate is subjected to high internal pressure as it is forced towards the die, when the extrudate passes through the die the extrudate is suddenly reduced to atmospheric pressure causing rapid expansion. This expansion in volume is typically of the order of many times the size of the die aperture and gives rise to the category of end products known as“direct expanded” products. This process is widely known and adopted in a variety of fields and industry sectors. For example this may include but is not limited to animal feeds such as aqua-feeds, pet foods, and pet treats. The food industry includes snack foods and breakfast cereals, protein snack foods and meat analogues, and ingredients such as pre-gelatinised starches and encapsulated flavours. It also has other wide ranging non-foods applications such as environmentally friendly packaging whereby expanded starches are formed into individual expanded pieces as loose fill protection in transporting delicate and easily damaged goods . Typically, as these extrudates exit the die they are cut by a rotating knife assembly at the point of exiting the die face to form discrete pieces. The knife assembly typically comprises several individual knife blades attached around the circumference of a single rotating cutter shaft. It follows that the cutting efficiency is paramount and is dependent on both the sharpness of the blades, the number of blades in procession around the working diameter of the die face and the speed of rotation, as well as ensuring the geometry of the path of the rotating knife blades is maintained to keep the blades intimately close to the die face at all times to ensure consistent and accurate cutting. Over the years there have been a variety of designs put forward and many designs that claim to control the consistent and accurate cutting of the extrudate as it exi ts the die face from an extruder.

However, during start up and shut down of an extruder the extrudate must be very fluid in order to pass through the die easily to prevent stalling of the drive train which would otherwise occur. Gradual incremental increases of power are required to establish the final extruder operating process conditions , this is achieved by gradually increasing the dry mix ratio compared to the liquid ingredients. Thus start up and shutdown of the extruder are typified by either increasing or decreasing the dry to liquid ingredient ratio depending on whether starting up or shutting down so that a higher liquid ratio is used at start up and conversely at the final stages of shutdown. It is during this stage that the die face cutter is required to be stationary or not attached to prevent contamination of the blades with under-developed extrudate which is produced when the extrusion process is not at the normal production conditions. At startup this is even more important when considering food hygiene as uncooked ingredients may otherwise contaminate the entire die face cutter assembly as well as the surrounding cutter containment (sometimes referred to as the “cutter cage” or “cutter housing”).

The present invention relates generally to those extruders that employ a translating rotary knife assembly that is not attached to the die itself i.e. not being rigidly fastened in any way directly to the die plate or die assembly. In this case the extruder can be started without the die face cutting device attached to the die thus improving the quality of the production by removing sources of contamination. It also provides a more acceptable operator environment as the operator does not have to be in the immediate area around the die of the extruder in order to translate the die face cutter into the production position to commence the cutting operation , this is by virtue of not having to rigidly fasten the die cutter assembly to the die itself. Existing extruder manufacturers using this approach have chosen to translate the rotary cutting devices across the die face (i.e. parallel to the die face itself) or pivot the rotary cutting devices in an arc across the die face (i.e. pivoting up and away but still parallel to the die face itself). Both types are difficult to maintain any cutting consistency as wear on the assemblies lead to inaccurate blade to die face geometric alignment. Thermal expansion experienced during operation also causes an adverse effect on cutting performance. We seek to provide a novel extruder cutter in which the knives are at all times during normal operation maintained at a substantially consistent setting distance relative to the die face, largely irrespective of the presence of wear in the translating mechanism itself and largely irrespective of the thermal expansion of the extruder barrel and die assembly as the extrusion process continues after start up.

Summary

According to the invention there is provided a cutter assembly for an extruder, the assembly comprising one or more rotatably mounted blades, a spacer which is arranged to extend forwardly of the blades, and into contact with a surface on or adjacent to a die face of an extruder, which allows the blades to be set at a required position relative to the die face, the blades and a forward end of the spacer arranged for relative translational movement along a rotational axis of the blades.

The cutter assembly may be arranged to provide a consistent setting distance of the blades relative to the die face.

An aspect of the invention may be viewed as comprising allowing a spacing between the forward distal end of the spacer and the blades to be adjusted by translational movement.

The assembly preferably allows a spacing between the blades and the forward end of the spacer to be adjustably set.

The spacer is preferably mounted for translational movement relative to the blades.

A carriage may be provided which is connected to the blades, which enables translational movement of the blades and the spacer across or perpendicular to the die face.

The blades may be attached directly to the cutter shaft or indirectly via a hub (sometimes referred to as the“cutter hub”) which itself i s attached to the cutter shaft typically via a quick release connection such and may employ a tapered connection. The one or more blades may be mounted on the cutter hub, which is attached to the drive shaft being advantageous in that an exact similar can allow for quick change of blades should one or any blade lose the cutting edge due to wear that is typical during production conditions . The quick change may also be beneficial when changing the cutter hub to one with more blades, especially when changing the die face to a different number of apertures/insert dies.

The carriage may comprise one or more guide rails.

The spacer may comprise a generally elongate element. The spacer may comprise a rod. The cutter shaft may comprise an internal volume which accommodates the spacer.

The translational position of the cutter relative to the forward distal end of the spac er may be manually adjustable, or adjustable in an automated or semi -automated way. This may be by way of a rotatable adjuster, which is manually controlled and which may be fitted with a dial indicator to provide a measure of the adjustment for repeatability of adjustment operations .

The spacer may be substantially non-rotating (in relation to the operational rotation of the blades). The spacer may be substantially rotationally stationary (at least during operation of the cutter blades).

The spacer may be termed a reference datum. The die will typically form the spacer datum edge.

The blades may be arranged to be moveable into an operational position and into a non-operational position. This may be achieved by an actuator which causes the blades to translate from an operational position to a non-operational position and vice versa. The actuator may comprise a pneumatic actuator. The pneumatic actuator may be arranged to urge the forward end of the spacer against the die.

The pneumatic actuator may be arranged to drive the carriage which carries the blades and the spacer. The assembly may be such as to allow, in use, a rearward movement of the carriage in response to contact between a heated (and as a result expanded) die surface and the forward end of the spacer which urges the carriage rearwards (and therefore the dpacer and the blades move rearward by the same amount, maintaining the spacing between the forward end of the spacer and the die surface.

According to a second aspect of the invention there is provided an extruder which comprises a cutter assembly of the first aspect of the invention.

According to a third aspect of the invention there is provided an extruder die, the die comprising a reference surface, and the die comprising at least one aperture through which extruded material can be output, wherein the reference surface is substantially co-planar with a surface which is immediately adjacent to the least one aperture.

The reference surface is located at a substantially centrally located region of the extruder die.

The reference surface may be an external surface of the die.

The reference surface may be a surface of a boss or protrusion.

The die may comprise a plurality of apertures. The reference surface may be provided substantially centrally of the apertures. The number of blades on the cutter hub is typically a function of the plurality of apertures.

The invention may comprise one or more features described in the description and/or as shown in the drawings, either additionally to the aspects defined above or separately.

Brief description of the drawings

Various embodiments of the invention will now be described, with reference to the following drawings, in which:

Figure 1 is a perspective view of the bladed cutter assembly. Figure 2 is a top elevation cross-section of the bladed cutter assembly of Figure 1 , omitting the cutter hub for clarity and showing the spacer.

Figure 3 is an enlarged top elevation cross-section of part of the cutter assembly shown in Figure 2, highlighting the bearing housing and spacer support.

Figure 4 is a side elevation cross-section of the adjustment mechanism, showing the dial indicator which provides a measure of the adjustment for repeatability of operation.

Figure 5 is a perspective view of the assembly of Figure 1 , with the bladed cutter hub omitted.

Figure 6 is a side elevation of the assembly of Figure 1 , highlighting a set distance between the cutter blades and the die face (the main purpose of the invention).

Figure 7 is a front elevation of a typical plate die with apertures for use with the apparatus of Figure 1 , detailing the apertures of the plate die .

Figure 7a shows an example of a typical insert plate die that can be used with the apparatus of Figure 1.

Figure 8 is a diametrical cross-section of the aperture plate die of Figure 7, and

Figure 8a is a diametrical cross-section of the insert plate die of Figure 7a.

Detailed description

In the description which follows, there is described a novel cutter assembly 1 for an extruder. In summary, the assembly 1 comprises an independent non-rotating spacer rod which is concentric with and independently mounted within the inside of a hollow cutter drive shaft, which extends along the same centerline of the rotating knife assembly, which advantageously provides a direct contact surface with the die face but yet is not itself rigidly attached to the die itself. This in use serves as a direct contact datum reference of the die face itself and when the die face cutter has been translated either into position for normal cutting operation or is translated back to its home position for startup and shutdown. This arrangement is pneumatically forced against the die face using a pneumatic piston and cylinder arrangement against the die face, thus creating a dependable and repeatable reference to the die face itself.

Reference is first made to Figure 1 , which shows the cutter assembly 1. The assembly comprises a number of angularly spaced blades 1 1 , which are provided on a hub 10. The hub 10 is removably attached to a drive shaft 3. The drive shaft 3 is driven by a drive (not shown) which causes the blades and the cutter shaft to rotate.

With reference to Figure 3, internally of the drive shaft 3, there is provided a hollowed section which extends along substantially the entire length of the drive shaft 3. The drive shaft 3 is mounted for rotation by way of bearings or bushings 8, which are provided in a housing 9. This hollowed section of the drive shaft accommodates a spacer rod 5. The spacer rod 5 is not rotationally coupled to the drive shaft 3 and so remains substantially stationary in use whilst the drive shaft 3 is rotating. The spacer rod 5 extends along the rotational axis of the drive sh aft.

With reference to Figure 1 and Figure 2, the spacer rod 5 is provided with a forward distal end or tip 5a, which is located forwardly of the blades 1 1. In use, the forward end 5a is arranged to contact and bear against a surface 14 of a die plate (described below) which is at or adj acent to the die face of the extruder. In this way, a predetermined spacing or distance can be maintained between the die face and the blades. Reference is made to Figure 6 which shows the tip 5a contacting the surface 14, and thereby spacing the cutting edges of the blades 1 1 a distance d from the surface 14.

With reference to Figure 1 , both the blades 1 1 and the spacer rod 5 can be translated backwards and forwards on a carriage by way of a pneumatic piston and cylinder sub- assembly 7 which is positioned rearwardly of the assembly 1 , to achieve either an operational or non-operational position. The carriage comprises a plate 18 and a housing 18a. The cutter shaft being rotated by a drive hub (not shown) requires that the translating assembly itself is held stationary (i.e. does not rotate). The resulting purely translational movement is achieved by way of cut-outs in the plate 18, which move relative to the rails 19 to maintain non-rotation. The drive hub is in constant engagement with the teeth or splines 3a, which are provided on the external surface of the drive shaft 3, irrespective of operating position (i.e. operational or non- operational) .

Additionally a hand-wheel 16 with geared movement (shown in Figure 4) is used to provide fine adjustment and allows the initial calibration of the knife position relative to the die face by the operator (i.e. the distance from the tip 5a to the plane in which the cutting edges of the blades 11 are situated) and this is established by a dial indicator that measures the precise setting distance adjustment , typically in microns. In this way the rotary blade assembly maintains a required setting distance from the startup almost entirely irrespective of the thermal expansion of the main parts of the extruder, especially the barrel and the die at the discharge end of the barrel during normal extrusion process operation, even when the temperatures of these parts will have risen dramatically. When the operator rotates the wheel 16, the blades 11 are translated relative to the forward end 5a of the spacer 5.

Further reference is made to Figures 3 and 4, which better show the fine adjustment mechanism. The wheel or knob 16 is connected to a shaft 23, to which is fixedly connected a worm gear 24. The worm gear 24 engages with the teeth of a gear 25. The gear 25 is fixedly attached to a sleeve 27, which is internally threaded. The threaded portion of the sleeve 27 engages with the thread of a sleeve 26, in a region shown at 28. This rotation will result in the spacer 5 to move towards or away from the die face 14, setting the blades 1 1 to a desired distance from the die face 14.

Reference is made to Figure 7 and Figure 8, with their subfigures, Figures 7b and 8b, which show an example of an extruder plate die 50 or insert plate die 50b, which comprises a reference surface 14, which is provided as a boss and located substantially centrally of an array of die apertures (shown in this example as inclined slots 51) or insert dies (shown in Figure 7a as crescent-shaped dies). Reference 14 is a machined surface that typically provides a consistent reference datum. The outlet mouths of the apertures or insert dies are provided on substantially the same plane as the reference surface 14. Both are provided on the discharge side of the plate die 50 or insert plate die 50b. A circular channel or recess 53 is provided between the reference surface 14 and the outlets of the die apertures 51 or insert dies 51 a.

The above described feature may be viewed as the ability to adjust the blades relative to a known datum face (the die face) using a micrometer -like adjustment on a depth- gauge bar that allows the operator to set the desired distance between the blade s and the die face largely irrelative to the heat of expansion that would otherwise cause the die face to“grow” towards the cutter hub as temperatures increase. In use, when the die face grows due to thermal expansion , the contact between the forward end of the spacer 5 and the reference surface pushes the carriage rearwardly along the rails 19, whilst the tip 5a stays in contact with the reference surface 14 and the spacing d between the plane of the blades and the tip 5a remains constant. Here, the force of the thermal expansion is capable of overcoming the pneumatic force applied by the pneumatic piston and cylinder sub-assembly 7.

It will be clear from the foregoing that the assembly 1 have several significant advantages. Firstly, the assembly 1 not being fixedly attached to the die itself allows the assembly to move in once the extrudate has reached the desired consistency after start-up of the extruder. Conversely, during shutdown the novel design die face cutter can be moved away once shutdown has been initiated to prevent contamination or damage of the knives. The cutter assembly not being directly attached to the die itself but free to move also has an additional advantage in that the rotary knife assembly allows a quick change of knife assembly should the set of knives in operation become worn and cause inferior cutting to persist. Due to the thermal expansion of the main parts that contain the extrusion process , in particular the barrel and the die at the discharge end of the barrel through which the screws convey and mix the ingredients as they are driven against the restrictive die apertures, the die and end of the barrel can move or displace by a considerable amount - possibly many times the setting distance that typically exists between the knives and the die face. Therefore, the setting distance being set cold before the start of the extrusion process quickly bears no resemblance to the relative distance when the process is in operation anywhere between 5 to 20 minutes after start up. Also, as processing conditions are adjusted as required to optimize the extrudate characteristics which may cause the temperature of the process to change which in turn can affect the expansion of the barrel and die which then can adversely affect the setting distance. Since the carriage may comprise one or more guide rails, with time these will wear and introduce more misalignment between the plane occupied originally by the cutter relative to the die face. The same adjustment feature being subject of this same claim can therefore be used additionally to compensate for wear in these translating guide rails and guide rail rollers.

Because the blades can be moved away from the end of the barrel, other dies can be fitted at the end of the extruder barrel in order to produce extruded products that do not require face cut. Typically these include pasta or snack foods which will undergo a subsequent transformation process such as surface coating or surface drying as continuous lengths and are cut further down the process as a separate operation. It also includes co-extruded products whereby a centre-filling is injected inside a hollow tubular extrudate. In a similar way co-extruded products will undergo a subsequent transformation process such as surface coating or surface drying as continuous lengths and are cut further down the process as a separate operation. As these dies take up space which would otherwise be occupied by the die face cutter , the operating space at the end of the extruder barrel can be compromised. This is especially the case when a radial co-extrusion die is fitted, as the delivery of the centre-filling where it is to be injected inside a hollow tubular extrudate within the die is typified by a multiplicity of delivery hoses radiating around the periphery of the co -extrusion die assembly. This usually conflicts with the die face cutter even if the die face cutter is moved and parked to one side. Advantage is also gained in terms of operational gains - especially quicker changeover, better levels of hygiene , and more reliable equipment. All of which are of great importance to producers of food products with the related operational benefits.

Because of its special application as applied to extrusion and the cutting of extrudates immediately as they exit the die but with the ability to easily translate the cutter into and out of production position and back again , whilst still being able to hold the setting distance between the knives and the die face largely irrespective of the presence of wear in the translating mechanism itself and largely irrespective of thermal expansion which can cause poor cutting performance. Wear in the guide rails and rollers on which the cutter cage translates can therefore be compensated to a great extent by the fine adjustment mechanism described providing a further benefit.

It will be appreciated that embodiments of the invention may include either that the spacer rod is moveable relative to the blade assembly and/or that the blade assembly is moveable relative to the spacer rod so as to achieve a require relative spacing.