GB2425979A - Dressing the blades of a tobacco cutting apparatus - Google Patents

Abstract

An apparatus for sharpening cutting blade 11 comprises a grind wheel 12, which is moved over a blade 11. The grind wheel 12 is occasionally indexed towards the blade 11 to compensate for wear. A diamond dressing tool 13 is arranged to abut the grind wheel 12 to cut the grinding surface thereof back to a predetermined height. A sensor 16 is positioned adjacent the dressing tool 13 and the grind wheel 12 is arranged to pass over the sensor 16 following dressing to grind a head of the sensor 16 back to the dressed height. The sensor 16 is connected to an alarm. If the dressing tool 13 breaks or wears, the grinding surface of the grind wheel 12 will not be cut back to the predetermined level following indexing and will grind the head of the sensor 16 back beyond the predetermined limit, thereby causing the sensor 16 to trigger the alarm.

Description

Machining Apparatus This invention relates to machining apparatus and more

particularly but not solely to apparatus for machining the blades of tobacco cutting apparatus.

Tobacco leaves are generally processed by an apparatus, which cuts the leaves into strands of tobacco, which are then suitable for tobacco products such as cigarettes and cigars. International Patent Application W02004/080215 discloses one such apparatus in which the tobacco leaves are compressed between a pair of converging conveyors. The compressed tobacco lamina is advanced towards a drum, which is provided with a plurality of elongate knives that cut shreds from the lamina as the drum rotates. The cut shreds fall into a hopper for collection.

The single most critical aspect governing the quality of tobacco products is the method by which the tobacco is cut and thus it is important to maintain the sharpness of the knives on the drum. Hitherto, this has been achieved by providing the apparatus with a sharpening device, which moves to and fro along the axis of the rotating drum. The sharpening device comprises a conventional motorised grind wheel formed of silicon carbide or aluminium oxide particles, which are vitreously bonded together by clays.

In use, the bond wears away as the abrasive particles wear, so that the worn particles are released and new sharp particles are exposed. It will be appreciated that the grind wheel wears rapidly and decreases in size.

Accordingly, an indexing and dressing system is provided to compensate for this wear so that the blades are sharpened to the correct height.

Generally grind wheels are indexed and then dressed to the correct height using an industrial diamond, which is positioned at the correct height such that the grinding face of the wheel is cut back as the indexed grind wheel passes over the diamond. Thus, it will be appreciated that the height of the diamond defines the grinding height of the grind wheel and ultimately the position of the cutting edge of the rotary blades.

Industrial diamonds can occasionally fracture during use, with the result that the blades are not dressed to the correct height. A disadvantage of this is that the blades may be over ground, thereby causing the tobacco shreds to be to be cut too coarsely. However, a major disadvantage is that the undressed grind wheel may completely grind the blades away and damage the expensive drum on which the blades are mounted.

We have now devised a machining apparatus which alleviates the abovementioned problems.

In accordance with the present invention, there is provided an apparatus for machining a cutting tool or blade, the apparatus comprising a grindstone having a grinding surface, means for moving said grindstone over the tool or blade to be machined, means for indexing said grindstone towards said tool or blade to compensate for wear of said grinding surface, means for dressing said grindstone comprising a projection having an outer end arranged to abut said grindstone during dressing and to cut said grinding surface thereof back to a predetermined height for machining, and a sensor positioned adjacent said projection, said grindstone being arranged to pass over said sensor following dressing and to grind a head of said sensor back to the dressed height, said sensor being connected to an alarm device arranged to generate an alarm signal if said head is ground back beyond a predetermined limit.

In use the dressing means cuts the grinding face of the indexed grindstone back to the correct height for machining the tool or blade. If the projection of the dressing means breaks or wears too much, the grinding face will not be cut back to the predetermined level and the indexed grindstone will grind the head of the sensor back beyond the predetermined limit and an alarm signal will be generated.

The alarm signal can provide a visible or audible warning to the user that the dressing means has broken or worn. Alternatively or additionally, the signal may halt the apparatus to alleviate the risk of damaging the tool or blade.

Preferably the grindstone comprises a rotary grind wheel, preferably having its grinding face disposed on its axially outer end.

Preferably said moving means is arranged to cause movement of the grind wheel along a line which extends generally radially of the wheel over said tool or blade, said moving means also being arranged to move said grind wheel over said dressing means and said sensor.

Preferably the sensor comprises an internal element which extends substantially to said predetermined machining height, said alarm device being arranged to generate an alarm signal if the element is ground back to expose the internal element.

The internal element may comprise an electrical conductor or element, said alarm device being arranged to generate an alarm signal if an output signal of the sensor changes by more than a predetermined amount.

Alternatively, the internal element may comprise a fluid flow passage which is closed inside the head of the sensor and which is pressurised, said alarm device being arranged to monitor the pressure and to generate an alarm signal if the fluid pressure inside the passage changes to atmospheric.

An embodiment of this invention will now be described by way of an example only and with reference to the accompanying drawings, in which: Figure 1 is a side view of a portion of tobacco cutting apparatus in accordance with this invention, with some parts being shown in section; and Figure 2 is a sectional view through a sensor of the apparatus of Figure 1.

Referring to Figure 1 of the drawings, in a tobacco cuthng apparatus a compressed lamina of tobacco is fed from a mouthpiece towards a drum 10, which is rotatably mounted for rotation about a horizontal axis. The drum 10 is provided with a plurality of elongate blades 11 having respective cutting edges extending axially of the drum 10. The blades 11 are spaced apart circumferentially around the drum 10 and each project radially from the drum 10, such that each blade 11 cuts shreds from the lam ma of tobacco as the drum 10 rotates.

The cutting edges of the blades 11 are progressively extended by respective mechanisms within the drum (not shown) to take account of gradual wear. In use, the blades 11 need to be constantly ground to maintain their sharpness.

Also, the clearance between the tips of the blades 11 and the mouthpiece must be accurately maintained at a distance of between 0.25mm and 0.3mm, to provide a clean cut of acceptable quality.

Accordingly, the apparatus further comprises a sharpening device having a dish-shaped grind wheel 12, which is rotated by a motor (not shown) about an axis which is inclined by approximately 10 degrees to the vertical. The sharpening device is mounted on a carriage (not shown), which moves the grind wheel 12 to and fro in direction A, axially of the elongate blades 11. The lower axial grinding face of the grind wheel 12 moves across the cutting edges of blades 11 and sharpens them. The radial position of the grind wheel 12 relative to the rotating drum 10 also determines the diameter of the cutting arc and thereby defines the clearance between the tips of the blades 11 and the mouthpiece.

The grind wheel 12 is formed of silicon carbide or aluminium oxide particles, which are vitreously bonded together by clays. The bond is designed to wear away as the abrasive particles wear, so that the worn particles are released and new sharp particles are exposed. The lower grinding face of the grind wheel 12 thus wears rapidly and, in order to compensate for this wear, the wheel 12 is progressively advanced axially of itself and radially towards the drum 10 to maintain the grinding face at the same radial position relative to the drum 10.

A diamond dressing tool 13 is mounted adjacent the drum 10 on an arm 14 which extends axially towards the drum 10 from a sidewall 15 of the apparatus. The diamond dressing tool 13 extends radially outwardly relative to the axis of rotation of the drum 10 and the tip of the tool 13 is radially positioned away from the axis of rotation of the drum 10 by a distance equal to the correct radial position for the tips of the cufting blades 11. The rotating grind wheel 12 is arranged to pass over the diamond dressing tool 13 following indexing and it will be appreciated that the tool 13 removes any excess from the underside of the grind wheel 13 to set the grinding face thereof at the correct radial position relative to the axis of rotation of the drum 10.

If the diamond dressing tool 13 breaks or wears excessively, the excess will not be removed from the grind wheel 12 and there is a risk that the grinding face thereof could then be positioned to close to the drum 10, thereby causing the tobacco shreds to be to be cut too coarsely and rendering large amounts of cut tobacco unusable for downstream process apparatus. There is also a risk that the undressed grind wheel 12 may damage the drum 10 on which the blades 11 are mounted.

In order to overcome this problem, and in accordance with the invention, a sensor 16 is mounted on the arm 14 adjacent the diamond dressing tool 13.

Referring to Figure 2 of the drawings, the sensor 16 comprises a onepiece member of metal having an externally screw-threaded body portion 18, which is engaged into an internally screw-threaded bore formed in the arm 14. The bore extends along a line, which is directed radially of the drum 10. The sensor 13 further comprises a head portion 20 which projects outwardly from the arm 14.

A duct 17 carrying compressed air extends along the arm and communicates with a bore 19 formed internally of the sensor 16. A gasket 21 maintains an airtight seal between the sensor 16 and the arm 14. The bore 19 extends axially of the body 18 of the sensor 16 and into the head portion 20 thereof.

The bore 19 terminates at a point inside the head portion 20, which is radially positioned away from the axis of rotation of the drum 10 by a distance equal to the minimum desired radius of the cutting arc of the drum 10.

In use, the rotating grind wheel 12 is arranged to pass over both the diamond dressing tool 13 and the sensor following indexing and it will be appreciated that the grind wheel 12 always grinds the head of the sensor 13 level with the tip of the tool 13.

Should the diamond dressing tool 13 break or shorten to a point where the grinding face of the wheel 13 is indexed too close to the drum 10, the excess length will cause the head 20 of the sensor 13 to be ground away, thereby exposing the duct 19. The sudden drop in pressure in the duct 17 can be sensed to halt the apparatus or raise an alarm.

The sensor head could also be of a conical shape to reduce the amount of grinding necessary.

In this manner, the risk of damaging the drum and producing unacceptably thick cut tobacco shreds is alleviated.

Claims (10)

1. Claims 1) An apparatus for machining a cutting tool or blade, the

   apparatus comprising a grindstone having a grinding surface, means for moving said grindstone over the tool or blade to be machined, means for indexing said grindstone towards said tool or blade to compensate for wear of said grinding surface, means for dressing said grindstone comprising a projection having an outer end arranged to abut said grindstone during dressing and to cut said grinding surface thereof back to a predetermined height for machining, and a sensor positioned adjacent said projection, said grindstone being arranged to pass over said sensor following dressing and to grind a head of said sensor back to the dressed height, said sensor being connected to an alarm device arranged to generate an alarm signal if said head is ground back beyond a predetermined limit.
2. 2) An apparatus as claimed in claim 1, in which the alarm signal is arranged to provide a visible or audible warning.
3. 3) An apparatus as claimed in claims I or 2, in which the alarm signal is arranged to halt the apparatus.
4. 4) An apparatus as claimed in any preceding claim, in which the grindstone comprises a rotary grind wheel.
5. 5) An apparatus as claimed in claim 4, in which the grindstone comprises a rotary grind wheel having its grinding face disposed on its axially outer end.
6. 6) An apparatus as claimed in claim 4 or 5, in which said moving means is arranged to cause movement of the grind wheel along a line which extends generally radially of the wheel over said tool or blade, said moving means also being arranged to move said grind wheel over said dressing means and said sensor.
7. 7) An apparatus as claimed in any preceding claim, in which the sensor comprises an internal element which extends substantially to said predetermined machining height, said alarm device being arranged to generate an alarm signal if the element is ground back to expose the internal element.
8. 8) An apparatus as claimed in claim 7, in which internal element comprises an electrical conductor or element, said alarm device being arranged to generate an alarm signal if an output signal of the sensor changes by more than a predetermined amount.
9. 9) An apparatus as claimed in claim 7, in which the internal element comprises a fluid flow passage which is closed inside the head of the sensor and which is pressurised, said alarm device being arranged to monitor the pressure and to generate an alarm signal if the fluid pressure inside the passage changes to atmospheric.
10. 10) An apparatus substantially as herein described with reference to the accompanying drawings.