TECHNICAL FIELD

This invention relates to a cutting assembly.

BACKGROUND ART

The present invention will be discussed in relation to use on single or double face corrugated paperboard, corrugated cardboard, paper and the like. However it should be appreciated that principles of the present invention can be applied to cutting assemblies for use in cutting other materials, particularly sheet materials such as plastic film and metal foils.

Typically, sheet materials are cut by what is known as a slitting knife assembly. The slitting knife generally consists of a rapidly rotating disc having a thickness of approximately 5-10 mm and having a sharp edge on the outer circumference. Generally, the sheet material is fed horizontally on a conveyor past the slitting knife which passes through the sheet material to cut same.

Many cutting assemblies have air operated stones attached to continuously keep a fine cutting edge.

One cannot run many of these blades close together as the board will bind on the thicker body of the blade and damage the paper flutes in the corrugated medium. Hence there is a limit as to how close the blades may sit together. Generally these blades are used only for trimming the waste edge off corrugated board while in a manufacturing process, or breaking a wide deckle of 2400mm into smaller sheets for further processing. This assembly can only produce strips above a minimum width. There are also scissor action blades that are two blades on separate shafts with a ' bevelled edge about 45 degrees. The two flat edges run face to face and offset so they cross over by 10mm. When paper is fed between them they shear the paper. One problem with this type of assembly is that they produce a rough edge. The blades also require a lot of sharpening and they do not use air stones and must be removed to sharpen.

Unfortunately, there are a number of problems associated with this assembly.

Firstly, the blade has to be a certain thickness to be strong enough to push through the corrugated sheet material. In particular, where the corrugated sheet material is cardboard or paperboard, the thick blade causes significant wastage of material. Where the blade has teeth large amounts of dust can be created from the cuts being made into the corrugated paperboard.

Another problem with such an assembly is that the blade needs to be sharpened at regular intervals, which adds considerably to the maintenance schedule. It should be appreciated that every time the assembly line has to be shut down, say for sharpening, potentially a considerable amount of money is lost due to the inability to maintain product throughput.

Therefore, it would be desirable if there could be provided a cutter or cutting assembly that addresses the aforementioned problems.

It is an object of the present invention to address the foregoing problems or at least to provide the public with a useful choice.

All references, including any patents or patent applications cited in this specification are hereby incorporated by reference. No admission is made that any reference constitutes prior art. The discussion of the references states what their authors assert, and the applicants reserve the right to challenge the accuracy and pertinency of the cited documents. It will be clearly understood that, although a number of prior art publications are referred to herein, this reference does not constitute an admission that any of these documents form part of the common general knowledge in the art, in New Zealand or in any other country.

Throughout this specification, the word "comprise", or variations thereof such as "comprises" or "comprising", will be understood to imply the inclusion of a stated element, integer or step, or group of elements integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.

Further aspects and advantages of the present invention will become apparent from the ensuing description which is given by way of example only.

DISCLOSURE OF THE INVENTION

According to one aspect of the present invention there is provided a cutting assembly for cutting sheet material including:

• at least one blade which is attached to a first spindle to rotate therewith;

• a support sub-assembly which supports the sheet material during the cutting operation;

the cutting assembly characterised in that the support sub-assembly includes at least one space which can receive a portion of at least one blade during at least part of the cutting operation, wherein the blade is in the form of a disc having a thickness of substantially 0.15mm - 0.25mm.

According to a further aspect of the present invention there is provided a blade wherein the blade is in the form of a disc having a thickness of substantially 0.15mm - 0.25mm.

According to a further aspect of the present invention there is provided a cutting assembly substantially as described above wherein the support sub-assembly is in the form of at least one radial member.

In general the radial member may be either: a roller, or at least one collar which is ring shaped, the roller/collar attached to a second spindle to rotate therewith, wherein the roller/collar includes at least one radial slot therein. In some embodiments the radial member may be a stationery (non-rotating) rod.

According to another aspect of the present invention there is provided a cutting assembly substantially as described above wherein the assembly is adapted so the first and second spindles rotate at a speed which is faster than the speed at which the sheet material is conveyed to the cutting assembly. Preferably, the first and second spindles are driven and rotate at the same speed. In a preferred embodiment the first and second spindles may be meshed to one another. Preferably, the first and second spindles counter-rotate in a direction which corresponds with the direction in which the paperboard is being conveyed. For example, if the paperboard is conveyed to the cutting assembly from a right hand direction the blade will rotate in a clockwise direction and the second spindle and support assembly will rotate in a counter-clockwise direction.

According to one aspect of the present invention there is provided a cutting assembly for cutting sheet material including:

• at least one blade; and

• at least one support sub-assembly positioned opposite the blade; the cutting assembly characterised in that the support sub-assembly includes a slot or other space configured to receive at least part of the blade during at least part of the cutting action.

According to another aspect of the present invention there is provided a method of cutting a sheet material using a cutting assembly having:

• at least one blade; and

• at least one support sub-assembly positioned opposite the blade, wherein the support sub-assembly includes a slot or other space configured to receive at least part of the blade;

the method including the steps of:

a) causing the sheet material to move through the blade to cut the sheet material; and

b) supporting the sheet material on the support sub-assembly during the cutting process;

wherein a proportion of the blade is passed through the sheet material and into the slot or other space during the cutting process, and wherein the blade is in the form of a disc having a thickness of substantially 0.15mm - 0.25mm.

The term space refers to any empty area such as a slot, groove, or gap.

The sheet material may be any material that the present configuration can be used in relation to. Reference however shall be made to the sheet material as being paperboard as it is initially problems in this industry that the present invention was designed to overcome. It is envisaged that the blade may be of a much thinner configuration than that previously used.

Previously, the thickness of slitting knives was in the order of 5-10 mm. This led to multiple problems including producing inordinate amounts of dust, inefficient use of material, and high maintenance with the blades having to be sharpened frequently.

In preferred embodiments the blades may be discs.

In contrast, the present invention makes use of a blade to be used which is as thin as possible. Preferably, the blade thickness is less than substantially 0.25mm. Preferably, the blade may be at least 0.05mm in thickness. Most preferably, the blade may have a thickness of 0.15mm. The inventor has found if the thickness of the blade falls within this range, the blade avoids most of the above problems encountered with conventional slitting blades. In particular blades that fall within the newly identified range are able to maintain a cutting edge without the need for sharpening. This surprising result is due to the thickness of the blade being sufficiently thin for the edge of the disc to form the cutting edge.

It is envisaged that in preferred embodiments the blade is made from spring steel, although other suitably strong materials can be utilised. In a preferred embodiment the blade may be coated with a thin film of titanium dioxide. This coating allowing the blade to self clean.

One advantage of the blades of the present invention is the blades may never require sharpening due to the minimal thickness (i.e. thinness) of the edge of the blade creating the cutting edge.

The support sub-assembly may come in a variety of forms provided it is sufficiently solid to be able to support the paperboard during the cutting motion: In preferred embodiments the support sub-assembly may be in the form of at least one collar and a spindle. In preferred embodiments the collar may preferably be fixed to the spindle so as to rotate therewith. However, in some other embodiments the collar may be adapted to rotate about said spindle.

In some embodiments the support sub-assembly may be in the form of a roller and a spindle. More preferably the roller may have at least one slot therein which receives the blade(s). In some embodiments the roller itself may be configured to also be the spindle.

Again the support sub-assembly may be made out of various materials, in preferred embodiments the support sub-assembly is made from mild steel, however stainless steel would also work well.

It is envisaged that the slot or space within the support sub-assembly may be sufficiently wide to receive the blade and provide sufficient tolerance to:

- stay sufficiently clean to allow the blade to freely rotate without being impeded by fibre and glue build up in the slot;

- minimise lateral over flexing of the blade which could lead to the blade breaking.

For example, in one embodiment it is envisaged that for a blade of a thickness of 0.15mm, the space or slot will be in order of 2.0mm. Other dimensions are of course possible.

A narrow space or slot also ensures that most of the paperboard will be supported

- except of course in the immediate region of the cut.

An advantage of having a support sub-assembly in the form of collars is that these can be easily pulled apart for cleaning of the space if required to remove any build up.

In preferred embodiments of the present invention, the cutting assembly has multiple blades.

In most embodiments the paperboard is conveyed on a conveyor to the cutting assembly during the cutting operation. However, it should be appreciated in some embodiments of the present invention the cutting assembly may be moved in relation to the paperboard during the cutting operation.

In one preferred embodiment, the paperboard is cut in a continuous action with the conveyor pushing the paper board over the support sub-assembly in the form of a roller while a portion of the cutting blades are within the slots in the roller. The roller acts to support the paperboard while it is being cut by the cutting blades.

The inventor has found by supporting the paperboard during the cutting operation, all the forces of cutting are directed through the body of the blade in a radial direction, and not in a lateral direction which would bend the blade. Therefore, the present invention is capable of using a blade that is considerably thinner than the slitting knives previously used.

Furthermore, a thin blade (say 0.15mm) made from a suitable material (say spring steel or titanium) does not require sharpening as do thicker blades such as that used with conventional slitting knife assemblies.

Thus, preferred embodiments of the present invention may have a number of advantages over the prior art which can include:

The ability to make use of significantly thinner blades.

Obviating the need to sharpen and/or minimising the need to replace blades. The ability to reduce the amount of wasted material caused by effecting a cut into the paperboard.

BRIEF DESCRIPTION OF DRAWINGS

Further aspects of the present invention will become apparent from the following description which is given by way of example only and with reference to the accompanying drawings in which:

Figure 1 is a diagrammatic cross-sectional view of a cutting assembly in accordance with one aspect of the present invention;

Figure 2 is a 3 dimensional view from an underside perspective of a cutting assembly in accordance with one aspect of the present invention.

BEST MODES FOR CARRYING OUT THE INVENTION

Figure 1 illustrates an end view (exaggerated) of a cutting assembly generally indicated by arrow 1.

The cutting assembly includes a rotating blade (2) shown side on. Beneath the blade (2) is a support sub-assembly (3) in the form of a roller.

The blade (2) is mounted on a spindle (12), whereas the roller (3) is mounted on a spindle(13) so as to rotate therewith. Collars (14) hold the blade (2) onto the spindle (12) so that the blade rotates along with the spindle.

The roller (3) has a slot (4) which is approximately twice the width of the blade (0.2mm) (2). A portion of the blade (2) extends into the slot (4).

Supported on the upper surface of the roller (3) is a sheet of paperboard (5). In operation, the paperboard (5) is conveyed via a conveyor assembly (not shown) to the cutting assembly (1) whereby it is supported on the roller (3). The blade (2) which is spinning rapidly (say 3 or more times faster circumferentially than the paperboard) cuts the paperboard.

Figure 2 show an alternative preferred embodiment which is similar to that in

Figure 1 so like reference numbers have been used to indicate like elements. The main difference of the embodiment shown in Figures 2 and 3 is that instead of a roller (3) the support sub-assembly is in the form of a series of collars (10) that are arranged in pairs (11). The pairs of collars (11) are fixed to a spindle (13) to rotate therewith and to provide a space in the form of a gap (15) between each collar of the pair into which the a portion of the blade (2) can extend. The spindles (12) and (13) are meshed to one another to travel at the same speed via identical gears (50) and (51). The gears (50, 51) move in the direction of arrows A and B given the direction (shown by arrow C) in which the paperboard (5) is conveyed.

Aspects of the present invention have been described by way of example only and it should be appreciated that modifications and additions may be made thereto without departing from the scope of the appended claims.