Method of Continuously Grinding the Teeth of Saw Bands and Saw Blades

The present invention relates to a method of continuously grinding teeth into a number of adjacent saw band blanks. The method involves reciprocatingly moving, in a direction transverse to the longitudinal direction of the saw bands, a rotating grinding wheel. The present invention also relates to a device for performing the grinding method.

Saw bands manufactured by the process of grinding saw teeth into steel band material are previously known. According to De-C-3.022.292 the saw teeth are ground into a steel band by two grinding wheels, arranged one after the other, which are provided with helical cutting grooves. The first grinding wheel produces a rough tooth form, while the second grinding wheel finely grinds and sharpens the teeth. As the teeth are manufactured by this "helical grinding operation", where the grinding wheels are in continuous contact with the saw band, the rotational velocity of the grinding wheels will determine the feed velocity of the steel band.

Another known saw tooth grinding device is disclosed in German patent No. 853.702. In this device, milled saw teeth are ground by means of two or more grinding wheels arranged in a spaced apart manner. The first wheel grinds the breast of the teeth and the following wheel grinds the backs of the teeth. The grinding device requires synchronization between the feeding of the band and the successive raising of the grinding wheel from the saw band. Such a synchronization requirement results in a complicated and therefore expensive mechanical device. Further, with such a device, it is only possible to machine the saw bands one at a time. In this manner, the capacity for production will be greatly reduced.

The object of the present invention is to provide a method of grinding saw teeth whereby a large number of blank saw bands can simultaneously be provided with teeth. It is a further object of the invention that such grinding is accomplished in one work phase whereby the teeth simultaneously receive their respective positive or negative hook and their final shape. These objects have been achieved through a method wherein the grinding wheel, at the start of every reciprocating grinding movement, is adjusted (lowered) a predetermined distance corresponding to the wear of the grinding wheel after one grinding cycle is accomplished. The grinding wheel, as it moves towards the band material, passes a stationary abrasing wheel which reshapes the grinding wheel. The step-by-step movement of the saw bands for feeding the blank band members is controlled by the return stroke of the grinding wheel to its initial position. The grinding wheel passes over the saw bands twice and then returns to its initial position and is set for grinding a new set of teeth after it is reshaped by the abrasing wheel.

The device for performing the above described method can be characterized as follows: the grinding wheel is arranged at the beginning of each grinding cycle to be displaced towards a stationary abrasing wheel. The abrasing wheel is arranged in the path of the grinding wheel in front of the holding mechanism for the saw band material. The abrasing wheel has a shape complimentary to that of the saw tooth shape. Prior to each new grinding cycle, the grinding wheel is adjusted to compensate for the wear it experienced during the prior grinding cycle. Additionally, the feeding and holding mechanism for the saw band blanks is arranged to index upon the return stroke of the grinding wheel at the termination of a grinding cycle.

FIG. 1 is a side view of a grinding device according to the present invention;

FIG. 2 is a plan view of the grinding device shown in FIG. 1 with the safety device for the grinding wheel removed;

FIG. 3 is an end view of the grinding device;

FIG. 4 is an enlarged view of the details of the grinding wheel and the mechanism for holding and indexing the blank saw bands;

FIG. 5 shows the grinding cycle during the movement of the carriage in a first direction;

FIG. 6 shows the grinding cycle with the carriage moving in an opposite direction to the first direction (the reshaping movement);

FIG. 7 shows a view analogous to FIG. 5, for the grinding and shaping of every second tooth for saw teeth with a small pitch;

FIG. 8 shows a view analogous to FIG. 6 for the grinding and shaping of saw teeth with a small pitch as in FIG. 7.

With reference to FIGS. 1-4, the present invention will be described. The invention is made up of a box shaped stand 11 equipped with guiding rails 12 for a slide 13, which supports an L-shaped stand 14 with guides 15 for displaceable carriage 16. The inclination angle of the displaceable carriage 16 is adjustable, so that production of teeth with positive or negative hook is possible. The carriage 16 supports a bearing device 17 for grinding wheel 18, which is driven by electric motor 19.

Slide 13 is displaced in the direction of arrow 20 by means of motor driven actuator 22. In FIG. 1, the grinding wheel 18 is shown with continuous lines in its most worn position, and is shown in dash and dot lines in its new condition. The grinding wheel 18 is also shown with dotted lines in one of its end positions, which is also the initial position.

Stand 11 contains mechanism 23 which holds and indexes a stack of steel bands 24. Such a stack of steel bands may contain up to 80 blanks which are successively unwound from a roll. Each roll is placed on one side of the grinding device in an unreeling device. Similarly, on the other side of the grinding device, the bands are placed in a reeling device.

Mechanism 23 contains a moveable holder 25. The moveable holder is displaceable in the longitudinal direction of saw bands 24 by linear actuator 26. Mechanism 23 also includes a stationary clamping attachment 27. The moveable and stationary clamping devices, 25 and 27 consist of a fixed clamping device 28, which includes hydraulic piston 29, which acts on spring loaded lever 30 which pivots around shaft 31. Spring loaded lever 30 includes adjustable gripping jaw 32 which presses the stack of saw bands 24 into engagement against fixed gripping jaw 33. Clamping attachments 25 and 27 are individually actuable according to fixed schedules. Their respective actuation schedules interact such that while stationary clamping attachment 27 is arresting movement of saw bands 24 during grinding, the moveable clamping attachment 25 moves in a direction towards a collecting position. When the moveable clamping attachment 25 has reached the collection position, the stationary clamping attachment 27 is released so that the moveable clamping attachment 25 can move the stack of saw bands an exact distance equivalent to the number of saw teeth ground.

The grinding wheel 18 moves in a linear reciprocating manner relative to the saw blanks. During its movement, grinding wheel 18 passes abrasing wheel 34. Abrasing wheel 34 is driven by motor 35 which is carried in bracket 36 attached to stand 11. The abrasing wheel 34, which has the same shape as the prospective saw, is preferably a profiled roll provided with diamonds on its cutting surface.

As the diameter of the grinding wheel 18 is reduced after each grinding stroke, means are arranged for controlling the lowering of the grinding wheel 18 to the predetermined level at which abrasing is performed. These means include a breaker, which controls the lowering of the stepping motor, so that the grinding wheel 18 is lowered an empirically determined distance which corresponds to the presumed wear. The means might also include a touchless electronic sensing and governing means which would govern the stepping motor 21 of the carriage 16.

During the initial stroke of the grinding wheel 18 it is not possible to achieve a sharp pointed saw tooth. This is not achieved until the return movement of the grinding wheel. With reference to FIG. 5, the grinding wheel is shown moving in its initial direction. The stack of saw bands 24 is then moved a few tenths of a millimeter simultaneously with the adjustment of the grinding wheel 18. This small movement allows the breasts 37 or backs 38 of the saw teeth to be ground so that they will receive sharp points. In FIG. 6 it is shown how the breasts 37 of the saw teeth are machined on the return stroke of the grinding wheel 18 to receive their sharp points.

In order to obtain this small displacement of the stack of saw bands 24 in relation to the grinding wheel, the fixing and feeding mechanism 23 is mounted on a plate 39, which is displaceable relative to plate 40. Lever 41 and linear motor 42 control the desired side displacement of fixing and feeding mechanism 23. The length of displacement is adjustable by adjusting screw 43. During the grinding movement plate 39 is fixed relative to plate 40.

The stack of saw bands 24 is kept in arrangement against a horizontally located ruler 44. Each clamping device 25 and 27 has a ruler 44 contained therein. Hold down member for the bands 45 presses the bands into contact with ruler 44. Hold down member 45 of the moveable clamping device 25 is connected to the clamping device and therefore moves in conjunction with the clamping device. The hold down member 45 consists of plastic material, e.g. polyurethane.

The grinding device operates in the following manner: the grinding wheel 18, at the start of each cycle, is located to the left of the abrasing wheel 34 in FIG. 1. The grinding wheel is then automatically lowered a predetermined distance, which depends on the wear of the grinding wheel, by means of stepping motor 21. The grinding wheel 18 then starts its linear movement (in an accelerated condition) to a position just before it contacts abrasing wheel 34. The linear velocity of the grinding wheel 18 is reduced to a suitable value for its reshaping as it passes the stationary abrasing wheel. The grinding wheel 18 is then reaccelerated to a position just before it contacts the steel bands 24. Its velocity is then reduced to a suitable grinding feed and proceeds across the entire stack of bands 24 in accordance with FIG. 5 or 7. When the grinding wheel 18 has entirely passed the stack of bands 24, the hydraulically fixed plate 39 is released from the base plate 40 and the displacement of the plate 39 is effected equivalent to the sharpening measure "t" as shown in FIG. 6, or according to tooth pitch as shown in FIG. 8. The plate 39 is again fixed and the return stroke of the grinding wheel now begins. The grinding wheel moves at a velocity suitable for sharpening the teeth by completing the grinding of the breasts and backs of the saw teeth according to FIG. 6. The grinding wheel 18 can also be positioned to grind the space between previously ground teeth as an alternative method of obtaining sharp teeth.

When the grinding wheel 18 has finished the grinding part of its stroke, its linear velocity is increased and it returns to the initial position of the cycle, whereupon a new cycle is automatically initiated. During the time lapse from when the grinding wheel has left the stack of bands 24 until it returns to the abrasing wheel 34 as part of a new cycle, a forward movement of the stack of saw bands is effected. This forward movement is performed when the clamping device 27 opens its jaws and linear actuator 26 displaces the stack of saw bands by aid of clamping device 25. Clamping device 25 clamps the stack of saw bands 24 and moves from its right position at the clamping device 27 to its left position according to FIG. 4. This movement of clamping device 25 is equal to the length of the number of saw teeth ground in one grinding cycle of the grinding wheel. The clamping jaws of the fixed clamping device 27 are then closed and the clamping jaws of the moveable clamping device 25 until it is up against the fixed clamping device 27, in which position the clamping jaws of the moveable clamping device 25 are again closed.