This invention relates to a device comprising a rotary shear and associated method, for trimming materials, such as metal plates, strips or slabs.

Conventional rotary shears for slitting or side trimming typically comprise one or two pairs of disc type blades, driven via a gearing mechanism, each pair of blades being spaced apart from the other to enable the metal to be trimmed to be positioned in between, such as described in US5964136. Pinch rolls prevent the material from moving sideways, as the material moves through the blades. However, practical constraints in the operation of such shears, limits the plate thickness to about 25 mm.

In accordance with a first aspect of the present invention, a device comprises a rotary shear and a set of pinch rolls, the shear comprising a first pair of rotary blades, the pair of rotary blades positioned in a transport path for a material to be transported through the device; the set of pinch rolls comprising a first pair of pinch rolls, the pair of pinch rolls positioned in alignment with the pair of rotary blades in the transport path, wherein the pinch rolls are adapted to exert a feed force on the material; and a control unit, the control unit adapted to control the feed force exerted by the pinch rolls, according to the thickness and strength of the material.

The pinch rolls exert a feed force in the direction of travel of the material along the transport path to enable different thicknesses of material to be coped without increasing the radius of the shear excessively.

When slitting, a single set of pinch rolls and pair of rotary blades are used, positioned in the transport path according to the required position across the width of material to be slit, but when trimming, this is generally done on one or both edges of the material, so preferably, the device further comprises a second pair of rotary blades, the first and second pairs of rotary blades being positioned on opposite sides of the transport path; and a second pair of pinch rolls, the first and second pairs of pinch rolls being positioned on opposite sides of the transport path.

The arrangement is adapted according to whether the shear is a double or single edge trim shear.

In one embodiment, the set of pinch rolls comprise entry pinch rolls, upstream of the shear.

In another embodiment, the set of pinch rolls comprise exit pinch rolls, downstream of the shear. Preferably, the set of pinch rolls comprise both entry and exit pinch rolls.

Preferably, the control unit further comprises a thickness sensing circuit, or a thickness data input unit and a source of material strength data.

Thickness data may be obtained as part of the trimming operation, or may have been obtained and stored previously. The material strength may be a nominal or fixed value to be used with the thickness data, but typically, a material strength data input is also provided to input material strength data to the control unit.

In particular for side trim shearing, preferably, the first pair of pinch rolls and rotary blades are fixed at a reference position; and, the second pair of pinch rolls and rotary blades are moveable relative to the first pair to set a width for the shear.

This allows the width of the sheared material to be adapted as required.

Preferably, the control unit is adapted to set the feed force at a value greater than or equal to the difference between a horizontal component of cutting force applied by the blade and a horizontal component of frictional force between the blade and the material.

The pinch rolls enable frictional forces opposing the material as it feeds through to be overcome, so that thicker materials can be cut.

Preferably, the control unit is adapted to reduce the force applied by the entry pinch rolls when the exit pinch rolls are operational.

Preferably, the material comprises metal plates, sheets, strips, or slabs.

In accordance with a second aspect of the present invention, a method of side shear of a material comprises setting a first pair of rotary blades of a shear at one side of a transport path; and, setting a first pair of pinch rolls on the same side of the transport path; feeding the material into the shear; and exerting a feed force on the material by the pinch rolls; the feed force being controlled by a control unit, according to the thickness and strength of the material.

In accordance with a third aspect of the present invention, a method of slitting a material comprises setting a first pair of rotary blades of a shear at a position across the width of a transport path; and, setting a first pair of pinch rolls aligned with the first pair of rotary blades in the transport path; feeding the material into the shear; and exerting a feed force on the material by the pinch rolls; the feed force being controlled by a control unit, according to the thickness and strength of the material. Preferably, the method further comprising setting a second pair of rotary blades of the shear on the opposite side of the transport path; and setting a second pair of pinch rolls on the opposite side of the transport path

The first pair of blades and pinch rolls may be set to a reference position and the second pair of blades and pinch rolls may be set at a position for a required width of the material to be sheared.

In one embodiment, the feed force is exerted by entry pinch rolls positioned upstream of the shear.

In another embodiment, the feed force is exerted by exit pinch rolls positioned downstream of the shear.

Alternatively, the feed force is exerted by both entry and exit pinch rolls.

Preferably, the control unit reduces the force applied by the entry pinch rolls when the exit pinch rolls are operational.

Preferably, the majority of the force is applied by the exit pinch rolls.

This helps to prevent buckling, by mainly pulling the material through the shear.

Preferably, the feed force is set at a value greater than or equal to the difference between a horizontal component of cutting force applied by the blade and a horizontal component of frictional force between the blade and the material.

An example of a rotary side trim shear in accordance with the present invention will now be described with reference to the accompanying drawings in which:

Figure 1 illustrates a conventional self-feeding rotary side trim shear;

Figure 2 illustrates operation of the conventional shear of Fig.1 in more detail;

Figure 3 illustrates a first example of a device according to the present invention, with entry pinch rolls;

Figure 4 illustrates a second example of a device according to the present invention, with exit and entry pinch rolls;

Figure 5 is a plan view of the example of Fig.4, with entry and exit pinch rolls; and,

Figure 6 is a flow diagram of the operation of a method according to the present invention, using the device of Figs.3 or 4. In the field of shearing materials such as metal plates, slabs or strips, whether continuous or pre-cut lengths, there can be problems if the thickness of the material is too great. Although the examples described below are given in the context of shearing metals, the invention may also be applicable to other non-metal materials, such as composites or plastics, where the effect of increasing thickness would otherwise prevent the shear from operating effectively. Shearing may be for side trim of one or both edges of the material, or for slitting the material longitudinally, at a chosen position across the width of the material.

Figure 1 shows a plan view of an existing rotary side trim shear device 1. The material 4 which is to be trimmed follows a transport path and enters the shear device along a roller table 5 in the direction shown by the arrow 6. The shear device 1 includes a first pair of cutting discs 2a, 2b on a fixed, or datum side of the shear and a second pair of cutting discs 3 a, 3b which can be moved to a desired width for trimming a particular piece of material. In this example, the transport path 8 for transporting the material to be sheared has a width at least as wide as the gap between the two pairs of cutting discs. The shear includes entry pinch rolls 7a, 7b which are used to guide the material strip and prevent it from moving sideways during shearing, for example, if the head end of the material is not square the shear would start cutting on one side before the other side. Like the cutting discs 2, 3, the pinch roll 7a on the datum side is fixed whilst the pinch roll 7b on the moving side moves sideways to the appropriate position for the width of the material 4 being trimmed. In addition, a scrap chopper 9 may be provided, which cuts into smaller scrap pieces the material which is cut from the edge of the material being sheared, so that this scrap can be easily transported away by conveyors.

Fig.2 illustrates operation of a conventional self- feeding rotary side trim shear 1 of Fig.1 in more detail. The example of Fig. 2a only shows one pair of blades 2a, 2b for clarity, but as indicated above, typically, a pair of blades 2a, 2b is provided at either side of the transport path 8. In the example shown, the material 4, of thickness H, moves along the transport path into the shear. For the self- feeding rotary side trim shear of Fig. 2a, the bite angle a needs to be below a certain value, typically 17 degrees, or thereabouts, otherwise the blade 2a will slip and the material 4 will not feed into the shear. Consequently the ratio of the blade radius R to the material thickness H needs to be above a certain figure. In order to cut thicker materials the blade radius R needs to increase in proportion to the thickness H in order to keep the same bite angle a.

However, as the blade radius R increases the length of material which is being sheared L by the blade also increases. The cutting force is a function of the length of material being sheared L, the thickness of the material H and other parameters including the shear strength of the material and the elongation to fracture. Because the cutting force depends on the length L as well as the thickness H, cutting thicker material with a larger blade radius R results in a very large increase in cutting force and torque. Furthermore the cost and the difficulty of manufacturing the blades increases significantly as the blade radius increases.

With reference to Fig. 2, a simplified explanation of the principles of cutting with a rotary side trim shear is described below. In reality the deformation and shearing of the plate during cutting with a rotary side trim shear are quite complex, but the limitations of the prior art and the principles of the invention can be most easily understood by reference to this simplified diagram. In Fig.2, the cutting discs 2a, 2b have radius R and the material which is being sheared has thickness H. When shearing a metal plate or strip it is well known that the material fails when the blade reaches a certain point through the thickness which is approximately equal to the elongation to fracture. This is illustrated by the dashed line at distance ε.Η through the thickness where ε is the elongation to fracture.

Because the material fails once the blade penetrates more than ε.Η through the thickness the cutting force F is mainly applied in the arc between lines s and f in Fig 2. In practice, there is some additional force applied after line f, because the top blade 2a is bending the material 4 as well as shearing it, but this component can be ignored for simplicity. Another point which is ignored in this simplification is that the vertical gap between the blades is adjustable and can be increased for thicker material.

The angles al and al are:- al = acos((R-H)/R)

a2 = acos((R-(l- e ).H)/R)

The cutting force F can be approximated by the formula:- F = k.Rm.H.R.(sin(al) - sin(a2))

Where Rm is the ultimate tensile strength (UTS) of the material being sheared and k is a coefficient.

The cutting force F acts on the plate at angle a which is approximately (al + a2)/2.

The force on the plate F can be decomposed into a vertical component Fy = F.cos(a) and a horizontal component Fx = F.sin(a).

It is clear that the horizontal component Fx opposes the movement of the material into the shear. There is also friction between the blade and the material being sheared.

The friction force Ff can be approximated by:-

Ff = ^F where μ is the coefficient of friction between the blade and the material being sheared. The friction force Ff can also be decomposed into horizontal and vertical components:- Ffx = Ff.cos(a)

Clearly, if the force opposing the entry of the material into the shear Fx is greater than the friction force trying to pull the material into the shear Ffx, then the material will not feed properly. From the equations above it is clear therefore that if tan(a) > μ then the material will not feed properly. Experimentally it is found that the coefficient of friction in a typical shearing operation is typically around 0.3. This means that tan(a) must be less than -0.3 which means that the angle a must be less than about 16.7 degrees. In fact it is found that the initial feed into the shear is the worst point. At the moment when the material first enters the blades, the force is applied at angle al .

From the equations above al = π - acos(5-l) where δ = H/R. Therefore, if al < 16.7 degrees, then δ must be less than about 0.04.

A typical radius R on a modern rotary side trim shear is 750 mm. Therefore, if δ is 0.04, the maximum thickness H that can be sheared without slipping is about 30 mm and in practice a typical modern rotary side trim shear is limited to about 25 mm thickness. In order to cut 50 mm plate with a design based on the existing principles, the blade radius would need to be increased to approximately 1250 mm. However, if the blade radius is increased then the cutting force and torque increase because the area of the material being sheared - the area between s and f - increases. Therefore the aim of the invention is to increase the thickness which the rotary side trim shear can cut without increasing the radius of the blades.

The present invention addresses the problems described above by providing at least one set of pinch rolls 10, 11 at the entry or exit side of the shear 1 which are designed to exert a feed force on the material 4 to feed it through the shear. A control unit 12 controls the extent of the force exerted by the or each set of pinch rolls. Unlike conventional shears which rely on friction between the blades 2a, 2b, 3 a, 3b to self-feed the material and only use pinch rolls 7a, 7b to prevent the material moving to one side or other of the transport path, the present invention provides pinch rolls 10, 1 1 which can exert sufficient force on the material to overcome any forces opposing the feeding of the material through the shear. This force exerted by the pinch rolls 10, 1 1 is chosen to avoid buckling of the material.

In the example of Fig.3, a set of entry pinch rolls 10 are provided and in another embodiment, illustrated in Figs. 4 and 5 entry and exit pinch rolls 10, 11 are provided both in front of and behind (upstream and downstream of ) the shear to push and pull the material through the rotary shear. When used, the pinch rolls 10 exert a feeding force Fpx to push the material into the shear as illustrated in Fig. 3.

The pinch rolls in the present invention need to be sufficiently large to be able to exert sufficient force Fpx to overcome the difference between Ffx and Fx. This may result in larger pinch rolls than are used typically in existing rotary side trim shears because the pinch rolls operate through friction onto the material surface and so the vertical pinching force Fp has to be sufficiently large to produce the force Fpx without slipping. The friction effect of the pinch rolls which push or pull the material through the shear, also acts to prevent sideways movement of the material on the transport path.

Another feature of the present invention is that the force Fpx is adjusted according to the thickness and strength of the material. For example, considering shearing of metal plate, for thin plate Fpx needs to be very low, or even zero, or negative because even a small force would cause the material to buckle between the pinch rolls and the shear. However, because the cutting angle a is small on thin material, the material will self feed without a positive force Fpx, so this is not a problem.

When the material is thicker than the thickness which would normally self feed due to friction, then Fpx is increased to a figure greater than Fx - Ffx, but less than the force which would cause the material to buckle. Preferably, the distance xp is kept as small as is practical because this distance affects the ease with which the material buckles. The shorter the distance xp, the greater the force Fpx which can be used without buckling the material Additional features such as hold down rolls could also be used to maximise the force Fpx which can be applied without causing buckling.

Control of buckling may also be influenced by the blade diameter and by the interrelationship of the blade size, thickness of material to be cut and position of the pinch rolls.

In addition to the entry pinch rolls the shear may also be equipped with exit pinch rolls 11 as illustrated in Figs. 4 and 5. These exit pinch rolls ensure that the material continues to feed through the shear even when the tail exits from the entry pinch rolls 10. If the material is thin enough to self feed, exit pinch rolls may still be used to provide a feed force to ensure that the tail of the material continues to feed through the shear correctly, but the main focus of the present invention is to deal with the problems of thicker, non-self- feeding materials. Furthermore, when the head end of the material enters the exit pinch rolls 11 then the force exerted by the entry pinch rolls 10 can be reduced and some or all of the force required to feed the plate can be provided by the exit pinch rolls 1 1. The control unit 12 controls the torque provided by electric motors to the pinch rolls according to the requirement at any point in the travel of the material through the system.

For a given thickness, UTS, elongation to fracture etc. of the material to be sheared and the known blade radius R, the controller calculates the anticipated cutting force F, the horizontal component Fx and the friction component Ffx. The calculation may use the simplified formulae which are described here, or alternatively, a combination of calculation and on-line adaptation from measured data is used. From this the controller calculated Fx-Ffx which is the minimum horizontal force which is required to feed the plate into the blades. The reference horizontal force is then set to 120% x this figure where the 120% factor is adjustable and may depend on the thickness, UTS etc. If the material is thin enough to self feed, then no horizontal force is required to be supplied by the pinch rolls.

The control unit 12 also calculates the maximum horizontal force which could be applied by the entry pinch rolls without buckling the material and the maximum horizontal force that could be applied without the pinch rolls slipping. If the control unit calculates that reference horizontal force would cause buckling or slippage then an alarm is generated. Just before the head end reaches the blades the control unit applies the reference horizontal force to the entry pinch rolls. When the head end reaches the exit pinch rolls, the exit pinch rolls are lowered to grip the material and then the control unit distributes the horizontal force between the entry and exit pinch rolls - gradually increasing the proportion applied by the exit pinch rolls and decreasing the proportion the applied by the entry pinch rolls. Before the tail gets to the entry pinch rolls the exit pinch rolls may be providing all of the horizontal force.

In another example, not shown, more than one set of pinch rolls at entry and/or exit may be provided in order that there is sufficient force to move the material in the direction of travel, without damaging the surface of the material by exerting too much force with a single pair of rolls.

Fig.6 illustrates the steps that may be used in carrying out one example of a method of the present invention as applied to side trimming or slitting. For slitting the same set up is used except that only a single pair of rotory blades and entry and /or exit pinch rolls are required and these are set at a position across the width of the transport path, suitably aligned relative one another, so that the resulting slit material has the desired width in each part. A check 20 is made to determine whether there are one or two pairs of shears and pinch rolls. If only one pair of each 21, then the rotary trim shears and entry pinch rolls are set 22 at the required position across the width of the transport path for slitting. If there are two pairs 23, then the first pair of rotary blades 2a, 2b of the shear and a first pair of entry pinch rolls 10 are generally fixed at one side of the transport path 8 and the positions of the second pair of rotary blades 3a, 3b and entry pinch rolls 10 are set 24 relative to the fixed set. Typically, the second pair of rotary blades of the shear and entry pinch rolls are set on the opposite side of the transport path 8 to the fixed blades and rolls.

In both cases, the thickness and strength of the material are determined 25. This may be by measurement e.g. from sensors on the rolling line (not shown), or the data may be pre-programmed into the control unit 12. From the determined thickness and strength of the material, the feed force to be applied to the entry pinch rolls is determined 26 and control of the force exerted on the material by the pinch rolls is under control of the control unit 12. In some cases, the control may be refined by determining the difference between a horizontal component of cutting force applied by the blade and a horizontal component of frictional force between the blade and the material and then setting the feed force at a value greater than or equal to the difference.

If exit pinch rolls are provided, then on detection 27 of the plate reaching 28 the exit pinch rolls 1 1, some or all of the feed force is transferred 29 to the exit pinch rolls. On detection 30 of the plate leaving the entry pinch rolls 10, all of the force is transferred 31 to the exit pinch rolls 11 and the plate continues and exits 32 the shear. If there are 33 no exit pinch rolls then when the plate leaves 34 the entry pinch rolls is detected 35 and a check 36 is made as to whether the plate will continue to feed unaided. If so, then the plate continues and exits the shear 32 and if not 37, the shear is opened 38 to let the tail end pass through uncut.

The present invention is adapted so that the force from the pinch rolls overcomes the force opposing the feeding of the material into the shear and thus allows thicker material to be cut. The relative amount of pushing and pulling force from the entry and exit pinch rolls may be controlled by a control unit in the device, in order to avoid buckling of the material. This control is a function of the material thickness. The force needs to be sufficiently high to ensure that the material feeds into the blades, but if the force is too high then the material will buckle. The main application of the invention is to enable shearing of thicker materials. Conventionally, thin materials have been sheared without any entry or exit pinch rolls to provide pushing or pulling forces. There may be thicknesses of materials which are able to be fed without the need for any pushing force, so these materials could be sheared in a device with only a set of exit pinch rolls. However, as the material thickness increases, so more pushing force is required and so, at least initially, the majority of the force is applied by the entry pinch rolls. The exit pinch rolls are also used to assist with the feeding of the plate, since in general it is more effective to pull the material through, than to push it, but in the initial stages, thicker materials must be pushed too. Once the material is in the exit pinch rolls, most or all of the force is provided from the exit side, since there is little or no risk of buckling when the material is in tension. For materials which are not continuous, the exit pinch rolls maintain the feeding of the plate when the tail of the plate leaves the entry pinch rolls. Therefore, the control unit 12 may adjust the relative forces applied by the entry and exit pinch rolls, both horizontal and vertical force, according to the type of material, its thickness and whether the part being sheared is at the beginning, middle or end.