GB2303053A - Cutting devices - Google Patents

Abstract

A meat cutting device (16) in a butchers' mincing machine is star shaped and has cutting inserts (22, 23, 24, 25) brazed on the arms (18, 19, 20, 21) of the star shape. The cutting inserts (22, 23, 24, 25) are strip shaped, narrow in the direction of cutting and of material which is hard, wear resistant and does not cause galling of the back plate of the mincing machine. The material of the arms (18, 19, 20, 21) which supports the cutting inserts wears more readily than the insert material so that the contact area of "land" of the inserts against the backing plate does not increase as the insert wears down.

Description

CUTTING DEVICES This invention relates in generai to cutting devices, that is devices which employ cutting edges and in particular devices which employ cutting edges which operate in a shearing action, that is where a blade executes a shearing action against a counter surface such as a foot plate or other blade or backing plate.

For example, in the field of commercial mincing machines, mincing meat, a star shaped rotating cutting device has cutting edges provided on each of the arms. the cutting edges are usually provided in a ctittinn blade which is an integral part of the casting or forging forming the arms and the whole cutting device This approach, however, requires a compromise between the requirement for strength with toughness, i.e. resistance to fracture by shock impacts, on the on. hand, and resistance to weor and dulling of the cutting edges, on the other hand.The latter requires properties antaqonistic to toughness, i.e. hardness and high temperature retention of hardness, i.e. at which heat-treatment-induced hardness will be annealed, for example. Problems of galling the backing plate also tend tu dliW when a compromise is adopted and the metals of the cutting device and back plate are similar.

The toughness is required because sometimes a piece of bone, or metal and even bullets enter the mincing machine and strike the fast rotating cutter blades ard the machine must survive such episodes at least without shattering of the cutting device The retention ot hardness at high temperatures is required because tests have shown that if tho machine is run even only for a few minutes without hlhricstion between the cutters and backing plate the edges of the cutters rise to very high temperatures at which annealing occurs, with loss of hardness which will be followed by accelerated wear.

To obviate this compromise some designs in double acting cutters have resorted to bolting the cutting blades onto the forged or cast cutter body, an optimum steel being selected for each component.

The bolting has, however, been unsuccessful as sometimes the bolts come loose then causing catastrophic damage to the machine.

Although it would seem obvious that various strategies like use of lock nuts, locking glues and regular inspection would address the problem it is found in practice that lock nuts do not provide the desired reilebility and users of the products are not willing to carry out regular inspection and in neglecting to do so lead to the failures.

In response to these problems hard cutting inserts have been braised onto the arms of the cutter In single action cutters, haviny a shape dictated by lead and lag angles according to oood practice Materials are selected which maintain the sharpness of the edge longer than could be achieved without hardened inserts. However, both types of cutter do require sharpening after a period of service and the cutter must be removed from the machine and sent to an enginoodng shop for appropriate sharpening. Since this pubs the machine Out of action the production of a machine is interrupted with a resulting loss to the business.Since operators are reluctant to incur a loss to the business this usually means that the sharpening is delayed longer than it should ba Use of the machine with blunt cutters .rQsufts in minced meat of poor quality because the meat is not cut cleanly but partially mashed and heated by the tendency to increase the pressure between the cutter and backing plate in a (misguided) effort to continue mincing with a blunt cutter.

In particular in accordance with requirements in cutting technology while the lead angle of the cutting blade is close to orthogonal to the cutting direction the lag angle is an acute angle to provide body behind the cutting edge for sufficient strength. This has the disadvantage that when wear progresses the force required to preserve appropriate pressure of the cutting device against the backing plate rises. Consequently the heat generation increases until temperatures are attained at which annealing of the cutting blade results in softening and faster wear; without heat treatment the cutting d.v:r.e in fact is not fit for further servica This condition commonly results from the decision to delay sharpening or redressing of the cutting blade beyond the advisable stage due to the reluctance to place the machine out of service.The reduced quality of i;it caused by the mashing effect and overheating of blunt cutters is related to discolouration of the meat, reduced moisture and reduced shelf life.

The object of this invention is to provide a better solution to these problems than in current designs.

The present invention is based on two key elements, primarily that a cutting edge is provided with an insert material of superior hardness and resistance to tempering due to rising temperature, (or other capacity to preserve an effective cutting edge) the cutting insert having a cross sectional shape which is narrow in thp direction of cutting and elongated orthogonolly so that it has the form of a flat strip cutting on the edge, and secondarily that this cutting insert is mounted in a mounting arm which provides a suitable trailing angle from the cutting edge uf d material less resistant to wear than the material af the cutting .dge.

A particularly successful material for the cutter insert has proved to be a carbide (for example). L'hromium, tungsten, titanium, columbium, vanadium, molybdenum and mongoncsc are elements which tend to r.LiSe the forming of carbides and mixtures of complex carbides.

In prior art cutter wear, zs mentioned, produces a land or surface parallel to the direction of cutting of gradually increasing dra as the wear pracecds but with the arrangement according to the present invention ongoing wear of the cutting strip leaves the width of the strip unaltered and hence of the land or are. parallei to the direction of cutting the same, since the strip is of the same relatively narrow dimension thruuyiiout its depth.At the same time the 3supporting material behind the strip which also establishes the lag angle or leq rake wears away further than and faster than the strip itself thus preserving a clearance or slight rebate which relative to the cutting strip is just sufficient to avoid the development of a land of increasing area as wear procecds; thus the harder cutting strip remains slightly proud of the supporting material behind it giving an effect somewhat equivalent to an appropriate rake angle and thus delaying the development of the objectionable land area which requires steadily lncfeasing forces between the vulliny device and the backing plate as wear proceeds.

Embodimonte of the invontion will now bo doscribod in detail, by way of example only, with reference to the accompanying drawings in which: Figure 1 shows a prior art cutting device, in elevation, Figure 2 shows cross sections of an arm of the device in figure 1, at successive stages of wear, at A to D, Figure 3 shows similar views to figure 2, but with grinding mado to avnid;;rn increasing land area develoPing with wear, in views E to H, Figure 4 shows a cutting device in accordance with the invention, in elevation, Figure 5 shows a cross section of an arm of the device in figure 4 in accordance with the invention, at successive stages of wear in views I to L, Figure 6 shows the cutting device oi figure 4 in accordance with the invention in plan view, and Figure 7 is a cross sectional crest seotion of an arm of a further cutting device in accordance with the invention.

As shown in figure 1 a typical prior art cutting device has a four arm star shape 1 with a square hole 2 to mount on a rotating drive shaft.

The device is rotated against a backing plate in use on a mincing machine (not shown).

Typically the device is cast in a steel of good wear and cutting properties but adequate toughness and it is initially ground to a cross sectional shape on each of the arms 3 to 6 as shown In view A of figure 2. This shape presents a land or flat surface 7 which bears against the backing plate, rotating so as to cause a movement in the direction indicated by the arrow 8 against the backing plate, This means that the lead angle 9 of the lead surface 9 is in the vicinity of goe and the Idy arryle 10' of the lag surface 10 is in the vicinity of 45 , in this example. These. lead and lag angles are set in accordance with good cutting practice.In use the rotating cutting device is pressed against the backing plate so that adequate pressure is established on the land or flat surface 7 for shearing cutting action to be executed by each cutting cdgo 11.

As wear proceeds through use there is a sharpening effect in the sense that each leading edge 11 is continually kept sharp but the problem arises in that the land or flat surface 7 steadily inavredses in the cross sectional area, see views 8 to D, land 7'.

This requires an increasing force to be appiied to the device against the backing plate and while initially this may not be a difficulty as can be seen in further views of C end D the area steadily incrcases and a stage is retched when sufficient force can no longer be applied, the pressure on the land reduces and the cutting quality deteriorates. In the case, for example, of mincing meat the result is that a mash is produced rather than the mea; belng cleanly sliced ill to neat cxtrudotco. The mashed condition of the meat seriously adversely affects its quality.

Referring to the view under E, F, G and H this shows the efforts made to correct thib effect of an increasing land area. Thus figure E shows the initial correct condition comprising the land 7, the lagging surface 10 and the leading surface 9 with the cutting edge 13 and a direction of cutting movement 8.

View r shows that after the land 7 has been worn down to the position 1 4 from initial position shown by the broken lines 7 and 10 in view F the lagging surface 10 is ground down to the position 15 thereby reducing the land area to the correct level.

This process continues as shown in the views G and H.

Although the correct area of the land is thus preserved it will be noticed that the angle of the lagging surtace 15 is progressively altered and accepting that the angle shown iq the viow E is the ideal angle for best cutting performance it will be appreciated that there is a progressive deterioration in this aspect.

Apart trom this, however, the main problem in practice is that the cutting devicc must be removed frorn the mincing machine and taken out of service resulting in a loss of productivity. It is found that the rate of wear is such that the machine must be taken out of operation more than once a week. It is found typically that the cutting device must the b'i La ken to a grinding service company resulting in considerable delay. Grinding is also a fairly costly business which must be done accurately by way of machine if it is to be done correctly and the cutting functions are to be preserved reasonably well. This type of regrinding is not commonly resorted to.

Fioure 4 shows a cutting device 16 in accordance with the invention which is similar to the prior art in that it has a square hole 17 for rotatably driving the device when placed on a square shaft fitting the hole closely. Again the cutting device has four arms 18, 19, 20 and 21 giving the cutting device a star shape The difference in accordance with the invention arises in that the cutting edges are provided by the strip inserts 22, 23, 24 and 25 each in the form of a strip of hardened material provided along the leading surface of each arm. A significant aspect is that each strip is braised only on its back surface 42 and bottom surfaces 43, against which it is supported by the arm, i.e. the strip is not let into a slot or groove in the arm. These are shown in cross section in the views I through to P.An advantageous material for the inserts is a carbide, or "STELLITE" (T.M.I, which is a trade mark for a cobalt chromium tungsten alloy and whose most important characterlstic in this application is the capacity of the material to remain hard and sharp even when raised to relatively high temperatures at which other materials would often or be subject tu severely accelerated wear.

Other alloys of steel such as tool steel and p,vp.n of other metals and even ceramic or composite materials may find useful application.

As mentioned the views I to P show one of the arms in cross section.

Thus iefeiiing to the view I and arm 26 has the strip of hardened rut material 77 along the leading surface 28 of the arm in use, the direction of cutting in use being indicated by the arrow 29. Thus the lead angle is also established and the land 30 is established by the strip of hardened material. The lagging surface 31 is as in the prior art and it is notable thot the material of the arm 26 is substantially more subject to wear or in other words subject to more rapid wear than the hardened material of the strip 27.

The result of this greblel susceptibility to wear of material of thc arm is that after a period nf wear when the land 30 has been worn down to a position 32 as indicated in the view J the material immediately behind the strip of hardened material relative to the direction of motion is worn away somewhat more as indicated at 33. The result is that the strip of hardened material it somewhat proud of the material behind it and this preserves the wood cutting action of this material The lead angle remains the same and the area of the land remains the same so that the required force on the cutting knife remains the same against the backing plate.Although the accurate trailing angle af the trailing surface 31 is not neccabarily preserved at least the cutting land 32 remains proud and thus preserves to a large extent the effective cutting operation. This effect continues during progressive wear as indicated in the view L and in the view M.

By selecting the material of the arm zprnprintty this enhanced wear effect behind the cutting strip of hardened material can be increased or optimised.

Figurs G shows a plan view of the cutting device in occordonco with the invention in which the hardened material inserts are shown, These strips are, for example, braised into position in the arms of the cutting device.

The features are essentially as have been described before, the sama reference numerals are used and the description with reference to figure 4 is referred to. Figure 6 does, however, show a backing plate 40 against which the device cuts, with holes 41 for the minced meat.

Figure 7 shows the further possible embodiment of the invention by way of a cross section through one arm of a cutting device of star shape, Here the arm 36 is provided with two strips of hardened material 37 and 38 so that the cutting device can rotate between twu backing plates, one on either side of the rotating blades. A similar result can be provided by a single strip extending across the width of the arm. Apart from the fact that the device thus operates on both sides the essence of its features remains as described above. The direction of the cutting action is irldie,dted by the arrow 39 in figure 4.

Alternatively, the device can he used first on nine. star and then on the other, against a single backing plate.

Claims (6)

1. A cutting device which comprises arms with cutting edges rotting against a backing plate. the cutting arises being provided by an insert strip fixed in each arm of the cutting device, characterised in that each insert strip has a shape which is narrow in the direction of cutting and elongated orthogonally so that the insert strip has the shape of a flat strip cutting on the edge.

2 , A cutting device as claimed in claim 1, in which the arm provides a suitable lagging angle from the cutting edge of a material which is less resistant to wear than the insert material.

3. A cutting device as claimed in clairn 1 or claim 24 in which the insert strip is of a carbide material or a cobalt chromium tungsten alloy.

4. A cutting device uu claimed in any preceding claim, in which coch insert strip is braised to an arm along ite back surface and its bottom surface.

5. A cutting device as claimed in any preceding claim in which each arm has two cutting edges, facing in opposite directions each cutting edge being provided by the narrow insert strip, cutting on the edge.

6. A cutting device substantially as described herein with reference to Figures 4 to 6 or the Figure 7 of the accompanying drawings.