The invention relates to a method of improving a circular saw blade and a circular saw blade improved by this method.

Circular saw blades are multi-tooth cutting tools designed for cutting diverse materials, in particular metals, light alloys, plastics, wood and woodgrain materials, depending on the type of the saw blade.

Uniform and stepped thickness multi-tooth circular saw blades are commonly used for cutting diverse materials. The simplest example of such saw blades is an uniform thin disc having teeth cut out along its circumference. Such saw blades operate in specific conditions. If a saw blade is too thick the amount of the processed material (kerf loss) and energy consumption are increased which is disadvantageous. However, in view of the forces generated during the cutting and the required quality of the cut surfaces, the saw blade may not be too thin because its stiffness would be too low. Considering the above, as well as in view of varying transversal loads and the fact that the circular saw blade operates in a narrow slit (kerf) of the cut material, the design of the saw blade should be precisely adjusted to the requirements of a specific cutting process.

The main factor affecting the quality of the cut surfaces (or the cutting process performance) is the effective transversal stiffness of a blade (ETS), i.e. the transversal stiffness near the external rim of the blade (ERB) during its operation. The transversal stiffness of a blade should be understood as its stiffness in a direction perpendicular to the plane of the blade. The ETS of an operating blade near the ERB depends on its static bending stiffness and on the level of hoop stresses in this area (stress stiffness).

The rotational hoop stresses, i.e. resulting from the rotation of the blade and centrifugal forces are positive (tensile), while the thermal hoop stresses, i.e. resulting from the temperature gradient caused by the heat generated in the cutting process are negative (compressive) .

Generally, the magnitude of rotational stresses and the thermal stresses depend on the rotational velocity of the blade and its diameter, thickness and the material the blade is made of as well as on the feed speed of the material being cut, the diameter of the clamping discs, the geometry and number of teeth, the size of additional openings, such as noise dampening openings, cooling openings, compensation openings, cleaning openings etc.

Considering the sign of the each stress, the increase of the rotational stresses increases the ETS, while the increase of the thermal stresses reduces the ETS. In particular, in an uniform thickness blade (i.e. an isotropic blade having the same radial and hoop stiffness in the plane of the blade) the rotational stresses in the ERB area are several times lower than those near the internal edge of the blade, while the thermal stresses are the highest in the ERB area. Consequently, in the ERB area the resultant stresses (low rotational stresses and high thermal stresses) are usually such that additional pre-tension of the blade in this area is necessary in order to ensure a required ETS.

Conventionally, in order to improve the performance of a circular saw blade, the body of the blade is pre-tensioned so that initial tensile hoop stresses are induced near the external rim of the blade and compressive stresses are generated in the central ring. Such a distribution of the initial stresses in the blade counterbalances, at least in part, the compressive thermal stresses arising during the cutting. The pre-tension may be induced by various procedures, e.g. mechanical or thermal, known in the industry. However, these procedures are rather difficult and laborious.

Another disadvantage of the pre-tensioning is that its effect is not permanent - the pre tension must be monitored and possible losses of tension must be repaired (i.e. the pre tensioning must be restored).

One of the reasons that the performance of the cutting process may deteriorate is that wood chips are incorrectly removed from the slit formed in the material during the cutting. It happens when only a part of the formed wood chips is thrown outside. The rest of the wood chips remains in the slit and travels between the teeth to the blade body which results in additional friction causing an increase of the blade temperature, in particular in the ERB area. Additionally to lowering the quality and precision of the cut surfaces, it also reduces durability of the blade. In order to improve the efficiency of chip removal, openings of diverse shapes and sizes are provided in saw blade designs.

Basing on computer analyses and numerous experiments, the inventors have established that introduction of grooves having specific geometry and arrangement into the body of a circular saw blade enables controlling the level of the rotational stresses and the thermal stresses in the saw blade. Namely, these inventive grooves significantly reduce the radial stiffness (RS) and slightly reduce the hoop stiffness (HS) in the plane of the saw blade.

The introduction of the inventive grooves results in the circular saw blade becoming orthotropic with the ratio RS / HS being reduced. The reduction of the RS / HS causes in turn the high rotational stresses to be shifted from the internal edge of the blade towards the external rim thereof (to the ERB area). Simultaneously, the thermal stresses are reduced and in consequence the resultant stresses in the ERB area are increased. The computer simulations performed by the inventors have showed that when the RS is about 20% or less than the HS, then the sum of the rotational and thermal stresses in the ERB area reaches a level that makes pre-tensioning not necessary, meaning that the introduction of the inventive grooves completely replaces the pre-tensioning procedures.

The inventive grooves, designed mainly to increase the hoop stresses in the ERB area, also improve the effectiveness of the wood chips removal. As the side surfaces of the saw blade are also increased because of the grooves, heat dissipation from the cutting operation area is improved too.

In view of the above, an inventive method of improving a circular saw blade is provided, the circular saw blade comprising a body having circumferential cutting teeth, the method including grooving the saw blade body, and being characterized in that grooves are formed on both sides of the body, and in that said grooves have a depth smaller than the thickness of the saw blade body and extend in a direction different from the radial direction of the circular saw blade, said grooves being comprised in evenly distributed angular grooved sections covering at least a part of each surface of the body in which grooved sections each radial cross- section of the body comprises at least two grooves, each of said two grooves being located on a different side of the body, so that each groove on one side is located in a part of the body that is free of the grooves on the opposite side of the body.

Preferably, the angular grooved sections formed on the same side of the body sum up to a 360° angle. The grooves formed in the body of the circular saw blade preferably have in a surface plan view the shape of rings and/or fragments of rings concentric with the circular saw blade.

The grooves formed in the body of the circular saw blade may have in a surface plan view the shape of sections of rings non-concentric with the circular saw blade.

Preferably, the grooves formed in the body of the circular saw blade have in a surface plan view the shape of straight stripes extending along the sides of at least one polygon having its center coincident with the center of the circular saw blade.

Preferably, the grooves are formed on the area of the body of the circular saw blade that is located between 0,5 and 0,8 of its radius.

The grooves may be formed having a substantially rectangular cross sectional shape.

Preferably, the grooves are formed in which the distance between the edges of the neighboring grooves located on the opposite sides of the body is not less than a dimension that is equal to the thickness of the body minus the depth of the groove.

Preferably, the formed grooves have a depth equal to about half the thickness of the body.

Preferably, the neighboring angular grooved sections comprising the grooves having in a surface plan view the shape of sections of rings or the shape of straight stripes overlap on the angular areas covering an angle of at least 3°.

According to the invention a circular saw blade is also provided comprising a body having circumferential cutting teeth and being characterized in that the body of the circular saw blade comprises grooves having a depth smaller than the thickness of the saw blade body and extending in a direction different from the radial direction of the circular saw blade, said grooves being comprised in evenly distributed angular grooved sections covering at least a part of each surface of the body, in which grooved sections each radial cross-section of the body comprises at least two grooves, each of said two grooves being located on a different side of the body, so that each groove on one side is located in a part of the body that is free of the grooves on the opposite side of the body.

Preferably, the angular grooved sections on the same side of the body sum up to a 360° angle.

The body of the circular saw blade preferably comprises the grooves having in a surface plan view the shape of rings and/or sections of rings concentric with the saw blade.

The body of the circular saw blade may comprise the grooves having in a surface plan view the shape of sections of rings non-concentric with the saw blade.

In another variant, the body of the circular saw blade may comprise the grooves having in a surface plan view the shape of straight stripes extending along the sides of at least one polygon having its center coincident with the center of the circular saw blade.

Preferably, the grooves are formed on an area of the body of the circular saw blade that is located between 0,5 and 0,8 of its radius.

The grooves preferably have a substantially rectangular cross sectional shape.

The distance between the edges of the neighboring grooves located on the opposite sides of the body is preferably not less than a dimension that is equal to the thickness of the body minus the depth of the groove.

The depth of the grooves preferably equals about half the thickness of the body. Preferably, the neighboring angular grooved sections, comprising the grooves having in a surface plan view the shape of sections of rings or the shape of straight stripes, overlap on the angular areas covering an angle of at least 3°.

The grooving of the saw blade body by the method according to the invention contributes to the improvement of the saw blade and its performance. According to the invention the grooves are arranged in such a way that the radial cross-sectional profile of the body acquires somewhat wave-like shape, which is because the grooves are located alternately on both sides of the body, at least over a part thereof.

Consequently, the radial stiffness of the body is reduced which results in the increase of the hoop rotational (tensile) stresses and the reduction of the hoop thermal (compressive) stresses during the operation of the saw blade. Hence, the resultant hoop stresses are increased and stiffen the saw blade in the transversal direction (the ETS is increased).

Physically, the above phenomenon may be explained as follows: both the low rotational (tensile) stresses and the high thermal (compressive) stresses in the ERB area of an isotropic (conventional) circular saw blade result from disadvantageous blocking of the blade deformations in the radial direction. This ERB area is being heated during the blade operation and it undergoes relatively greater centrifugal forces. The less the radial stiffness of the saw blade, the less it is blocked. As a consequence, the hoop stresses are higher in said area.

Therefore, the introduction of the grooves according to the invention in a circular saw blade results in that the body, when undergoing the radial tension caused by the thermal stresses during the operation of the blade, yields to such tension i.e. it extends radially slightly more than do conventional saw blades without the inventive grooves. For this reason, directions of the said grooves are different from the radial direction, in particular they have the perpendicular direction or a direction that is substantially perpendicular to the radial direction.

An important feature of the invention is that the increase of the hoop stresses in the ERB area (resulting from the increase of the tensile rotational stresses and the reduction of the compressive thermal stresses) and the consequent increase of the effective transversal stiffness occur during the operation of the saw blade. These effects are permanent during the life of the saw blade, i.e. they do not disappear with time and usage of the saw blade. The durability of said effects is due to the permanent existence of the grooves and not to the induced pre-tension that relaxes with time.

Additionally, it has been observed that the grooves in a circular saw blade according to the invention contribute to the reduction of noise during the operation of the blade, and importantly - because of an additional space formed by the grooves - to a better removal of wood chips from the slit in the cut material. The better removal of the wood chips contributes in turn to a more effective dissipation of heat in the working area of the cut material, and hence to the reduction of the thermal stresses.

The circular saw blade according to the invention is shown in preferred embodiments in the drawing, in which:

Fig. 1 shows the geometry of the grooves made in the plane of the circular saw blade according to a first embodiment of the invention;

Fig. 2 shows the geometry of the grooves made in the plane of the circular saw blade according to a second embodiment of the invention; Fig. 3 shows the geometry of the grooves made in the plane of the circular saw blade according to a third embodiment of the invention;

Fig. 4 shows the geometry of the grooves made in the plane of the circular saw blade according to a fourth embodiment of the invention;

Fig. 5 shows the geometry of the grooves made in the plane of the circular saw blade according to a fifth embodiment of the invention;

Fig. 6 shows the geometry of the grooves made in the plane of the circular saw blade according to a sixth embodiment of the invention;

Fig. 7 shows the geometry of the grooves made in the plane of the circular saw blade according to a seventh embodiment of the invention;

Figs. 8-12 show the geometries of the grooves made in the plane of the circular saw blade according to next four embodiments of the invention;

Fig. 13 shows the cross-section of the grooves of the circular saw blade according to the invention, the grooves having a preferred shape and dimension proportions.

The circular saw blade 1 having a body 2 and circumferential teeth 3 shown in fig. 1 is an exemplary saw blade according to the invention. As shown in fig. 1, two annular concentric grooves, respectively 4a and 4b, are provided on each respective side of the body 2 (the grooves 4b on the invisible side of the body 2 have been indicated by dashed lines). In this first embodiment of the invention the grooved angular sections I, II, III, IV (see fig. 2) sum up to 360°, so that the grooves run around the whole disc. The grooves 4a and 4b are arranged in such a way that there are four grooves in each radial cross-section of the body, each groove being located in the area of the body which is free of the grooves on the other side of the body. A preferred example of the shape of the grooves is shown in fig. 13.

Fig. 2 shows the geometry of the grooves of the circular saw blade 1 according to a second embodiment of the invention. In this embodiment eight grooves, respectively 5a and 5b, are provided on each respective side of the body 2. The grooves 5a, 5b are arranged in such a way that there are four grooved angular sections I, II, III, IV (indicated by dashed lines) evenly distributed on each side of the body. In each radial cross-section of these sections there are four grooves. In the remaining angular sections of the body, there may be more grooves, e.g. eight grooves. In this embodiment each groove has the shape (in plan view) of a fragment of an annulus that is not concentric with the body 2. As in the case of the embodiment of fig. 1, a preferred example of the shape of the grooves is shown in fig. 13 Figs. 3 and 4 show a third and a fourth embodiment respectively of the saw blade 1 according to the invention. In these two embodiments the body 2 of the saw blade 1 comprises the grooves 6a, 6b and 7a, 7b respectively, the grooves having the shape in plan view of straight stripes extending along the sides of the polygon having its center coincident with the center of the circular saw blade 1. In these two embodiments there are eight sections l-VIII on each side of the saw blade 1 (fig. 3) and six sections l-VI on each side of the saw blade 1 (fig. 4).

Figs. 5, 6 show two variants of an exemplary saw blade 1', here a wood saw blade, according to the invention. In these two variants the angular sections I, II, III, IV in which there are two rooves 8a and 8b ( 9a and 9b in fig. 6) in each radial cross-section, the grooves bypass the cleaning openings 9. In the saw blade 1' shown in figs. 5, 6 two types of openings are shown, i.e. a central clamping opening 10 and incisions for the cleaning openings 9 having side blades 11. In the embodiments shown in figs. 5 and 6, in each angular section I, II, III, IV of the body 2 there is one groove, respectively 8a and 8b on each side of the body 2, the grooves having the shape of a fragment of an annulus.

Fig. 7 shows another variant similar to those of figs. 5 and 6, but in this case the annular sections I, II, III, IV have four grooves 12a and 12b in each radial cross-section.

Other preferred embodiments of the circular saw blade according to the invention are shown in figs. 8 to 10. In the embodiments shown in figs. 8 to 10 the grooves are arranged in the area having a width E and they are located between two radiuses A and B, the radius A being equal to about 0,5 C and the radius B being equal to about 0,8 C, where C is the radius of the saw blade. Said area has been defined basing on experiments and the aforementioned calculations and numerical analysis.

In figs. 8-10 the shapes of the grooves are analogical to those shown in figs. 1-4. On the other hand figs. 11 and 12 show alternative shapes of grooves that may be made in the saw blade according to the invention. These alternative grooves have a curved trajectory, their cross-sections and dimensions being preferably as shown in fig. 13.

In all the described embodiments the number of the grooves is preferably from 2 to 6.

The circular saw blades according to the invention may be of diverse types and may have different shapes of teeth. They may also have additional openings for cleaning etc. as shown in the appended figures.

Fig. 13 shows an example of a fragment of the cross-section D-D of saw blades according to the invention that has the grooves of a particularly advantageous rectangular or substantially rectangular shape. The body of the saw blade has a thickness t, the grooves have a depth g and a width K. the thickness ti of the bottom of the grooves constitutes the difference of the dimensions t and g. In fig. 13 a dimension t ₂ is also shown constituting the distance between the edges of the grooves neighboring on the opposite sides of the body. As mentioned above, in terms of the ETS a particularly advantageous effect has been obtained when t ₂ is no less then ti, while ti « 0,5t i.e. ti equals about half the thickness of the body.

As mentioned above, the computer simulations performed by the inventors have showed that when the RS is about 20% or less of the HS, then the resultant of the rotational and thermal stresses in the ERB area reaches a level at which pre-tensioning is not necessary, meaning that introduction of the inventive grooves may totally replace the pre-tensioning procedures. In order to meet the above requirement (20% or less of the HS), the width 2a in fig. 13 must be selected adequately to the dimensions t, ti and t ₂ , namely:

where X is a positive root of the below quadratic equation:

The shapes and dimension proportions of the grooves as indicated in the example shown in fig. 13 may be applied in all the embodiments of the saw blade according to the invention described herein.

In a preferred but not limiting embodiment of the invention, the dimensions of the grooves may be e.g. the following:

- the thickness of the body t = 2,8 mm - the depth of the groove g = 1,4 mm

- the distance between the edges of the grooves t ₂ = 1,8 mm

- the difference of the dimensions t and g, ti = 1,4 mm

- the width of the groove K = 4,0 mm

- the distance 2a = 5,8 mm.

Hence, the method according to the invention involves making the suitably arranged grooves in the body 2 of a circular saw blade. The grooves may be made by means of any suitable technology known in the industry, e.g. by milling the grooves using an end mill, turning using a turning tool, by polishing or by other e.g. laser methods

The characterizing feature of the method according to the invention is arranging the grooves in the saw blade body so as to give a wave-like profile to the radial cross-sections of the body of the saw blade. In consequence, the body has lower radial stiffness during operation and higher effective transversal stiffness, as explained earlier, which constitutes an important improvement in comparison to the prior state of the art.