Abstract:
A ventilated air cooled cutting system for a circular saw that produces a thinner kerf than previously achievable. The air cooled cutting system is comprised of a saw blade having a thin blade cutting portion and a thick hub portion. The blade cutting preferably is ground from a plate, while the hub portion remains substantially the thickness of the starting plate material. The thicker hub portion serves as a heat sink to conduct heat away from the thinner blade cutting portion. Cooling holes are provided in the hub portion to provide convection cooling of the hub portion. The thicker hub portion also provides rigidity or stiffness to the blade so that it is better able to withstand torsional forces experienced during the cutting operation. If additional cooling is required, a spacer collar having a series of axial and radial apertures can be fitted to the hub portion to force cooling air through the hub portion in order to enhance cooling.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention is directed to a ventilated air cooled cutting system having the ability to generate a thin cut in a material without overheating, and specifically, to a saw blade having a thin kerf with an integral cooling system to prevent overheating. 
     2. Description of the Prior Art 
     Within the wood processing industry, it has always been desirable to cut wood with the thinnest possible kerf, the kerf being the width of a cut made by a cutting tool. This is due to the fact that a larger kerf destroys more product while producing more waste as sawdust, while a thinner kerf produces a higher yield with less waste. A thinner saw blade is required in order to produce a thinner kerf. While thin kerfs of about 0.080 are produced by some band saw blades, band saws have a much slower cutting speed, making them less efficient. 
     Although it has been desirable to design a circular saw blade as thin as possible for a particular application, problems with designs have arisen physically limiting the ability minimize blade thickness. One of these problems is the generation of heat produced by the cutting action of circular saw blades as well as the torsional forces produced during the cutting operation. Of course, there are several variables that contribute to the generation of heat and production of torsional forces. Included among these variable are feed rates, species of wood being cut and condition of the cutting equipment. Nevertheless, when critical amounts of heat and torsion are produced, the saw blade can fail. 
     Typically, as blades are made thinner to reduce the kerf, they are less able to withstand torsion than thicker blades. In addition, the thinner blades have less mass and unlike thicker blades which can act more like a heat sink, having a higher heat capacity and more heat transfer capabilities, thinner blades have a tendency to become hotter faster. This tendency, coupled with the higher torsional forces, results in an undesirable shortening of the blade life. 
     Various solutions have been attempted to solve these problems. One proposed solution is set forth in U.S. Pat. No. 213,439 to Miller dated Mar. 18, 1879. This solution sets forth a blade having ventilating holes. While such a blade design can improve the transfer of heat, assuming the cooling holes are not clogged with sawdust, the design does not address the problem of torsion. Similar solutions are set forth in U.S. Pat. No. 88,949 to Emerson dated Apr. 13, 1869; U.S. Pat. No. 212,813 to Miller dated Mar. 4, 1879; U.S. Pat. No. 1,083,645 to Wettstein dated Jan. 6, 1914; U.S. Pat. No. 3,872,763 to Kayahara dated Mar. 25, 1975; and U.S. Pat. No. 4,776,251 to Carter dated Oct. 11, 1988. While these patents set forth apertures having varying geometries and arranged in various patterns to provide cooling for blades, they do not address the problems related to torsion associated with blades as they become thinner. 
     A second approach to improving saw blade operation is to reduce vibration by drilling slots in the blades. An added advantage to these slots is the ability to dissipate heat. This approach is set forth in U.S. Pat. No. 2,563,559 to Sneva dated Aug. 7, 1951; U.S. Pat. No. 3,107,706 to Heinemann dated Aug. 12, 1960; U.S. Pat. No. 3,730,038 to Farb dated May 1, 1973; U.S. Pat. No. 4232,580 to Stewart dated Nov. 11, 1980; and U.S. Pat. No. 4,240,315 to Tuomaala dated Dec. 23 1980. However, this approach may allow for use of a thinner blade due to reduced vibration and improved heat dissipation, it does not address the problem of shortened blade life associated with torsional effects. 
     What is lacking in the art is a blade that produces a thinner kerf, while providing sufficient cooling to prevent heat buildup in the blade, yet has sufficient strength to withstand torsion during cutting, so that blade life is not shortened. 
     SUMMARY OF THE INVENTION 
     The present invention is a cutting system comprising an air cooled cutting system that includes a circular saw blade that produces a thinner kerf, while having improved cooling capabilities, yet has sufficient strength and stiffness so that torsional effects of cutting do not adversely affect the life of the saw blade. The saw blade of the present invention preferably is formed from plate stock and has a blade cutting portion and a hub cooling and strengthening portion. 
     The blade cutting portion has a preselected diameter and a first thickness. These thicknesses can vary, but can be thinner than those currently utilized in the art. The blade cutting portion is a disk having an outer periphery. A plurality of blade teeth are formed in the outer periphery of the disk to provide a cutting surface. The teeth can assume a variety of forms depending upon the type of cut required and the type of material that is being cut. Blade teeth technology is well known in the art. The blade cutting portion may optionally include slots or strobes as described in the prior art to alter the natural vibration frequency of the blade. 
     The hub cooling and strengthening portion has an outer diameter smaller than the outer diameter of the blade cutting portion and having a second thickness greater than the first thickness of the blade cutting portion. Thus, the blade undergoes a cross-sectional change at the hub. This increased thickness has the effect of acting as a heat sink for the blade. As heat is generated in the blade cutting portion, the heat is transferred by conduction to the larger mass of the hub portion. The thicker hub portion also provides the additional advantage of being a strengthening member for the saw blade. Thus, the stiffer cross-section provided by the thicker hub assists in reducing the overall torsional effects to which the blade is subjected. The hub cooling and strengthening portion includes inner diameter defining a bore through which passes a motor-driven shaft that is used to provide the rotational motion for the blade during cutting operations. Because heat will be transferred by conduction to the hub portion, it is necessary to provide additional cooling to the hub beyond that which occurs as a result of natural circulation of air across hub surfaces. This additional cooling is provided by a plurality of cooling apertures extending through the second thickness of the hub in a substantially axial direction. These apertures are positioned on a diameter located intermediate the hub portion inner diameter and the hub portion outer diameter. 
     The cutting system of the present invention may include radially oriented slots which extend inwardly from the outer periphery of the blade and terminate within the blade cutting portion. These strobes or slots are within the art to modify the vibrational frequency of the blade. These slots typically are cut in a radial position and extend between the outer periphery of the blade cutting portion and the outer diameter of the blade cutting portion. 
     If additional cooling is required for the blade portion, the diameter of the hub portion can be adjusted to increase the heat capacity of the hub portion, thereby allowing more heat to be conducted away from the blade portion to the hub portion. Additional cooling to transfer heat away from the hub portion can be achieved by providing additional cooling apertures in the hub portion positioned between the hub portion inner diameter and the hub portion outer diameter. 
     An advantage of the present invention is that a blade having a thinner kerf can be made, without adversely affecting the life of the blade. Another direct advantage is the ability to saw a workpiece while reducing the amount of waste, thereby increasing the yield. 
     Another advantage of the present invention is that a blade having a thinner cutting portion can be produced without adversely affecting the ability of the blade to withstand the torsional effects of the sawing operations. 
     Still another advantage of the present invention is that the improved design permits the thin blade to be cooled efficiently by use of a thick hub as a heat sink for conductive heat transfer, while the hub is cooled by convection cooling. This cooling helps to extend the blade life by preventing deterioration from overheating. 
     Other features and advantages of the present invention will be apparent from the following more detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the invention. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 is a side view of a circular saw blade having a blade cutting portion and a hub cooling and strengthening portion of the present invention; 
     FIG. 2 is a side view of a spacer collar of the present invention; 
     FIG. 3 is a perspective view of a Brewer system incorporating the low kerf blades of the present invention. 
     Whenever possible, the same reference numbers will be used throughout the figures to refer to the same parts. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to FIG. 1, which is a side view of a circular saw blade that comprises one embodiment of the cutting system of the present invention. A saw blade  10  includes a blade cutting portion  12  and a hub cooling and strengthening portion  14 . The blade portion has a preselected outer diameter that forms the outer periphery or circumference  16  of blade cutting portion  12 . This outer diameter will vary depending on the use of the blade, and typically will vary from about 7 inches for small saws to about 40 inches for large saws such as are found in large saw mills. In the most preferred embodiment, this diameter will vary from about 8-14 inches. A plurality of blade teeth are formed in the outer circumference of the blade. The design and the methods of forming the blade teeth on the outer circumference of the blade are well known in the art and are not within the scope of this invention. The blade portion has a predetermined thickness, which may vary from 0.045 inches to about 0.240 inches. Preferably the blade portion thickness is in the range of from about 0.050-0.100 inches. In the best mode of practicing this invention, the thickness of the blade portion has been varied from about 0.060-0.070 inches. The thicknesses of the blade are determined by the ultimate use of the blade, as well as by the method of manufacturing the blade as will be explained subsequently. However, blades currently used in saw mills typically produce kerfs larger than 0.100 inches. It can be seen that blades made in accordance with the present invention can produce kerfs from about 0.100 inches to as low as 0.045 inches, which is a significant improvement over the current state of the art. Blade cutting portion  12  also includes optional slots or strobes  17  for vibrational damping. While two strobes  17  are shown, any number of strobes as practiced in the art may be used. 
     The hub cooling and strengthening portion  14  is integral with the blade portion  12 , but is thicker than the blade portion  12 . The thickness of hub portion  14 ,which typically is dependent on the thickness of the starting material, can be selected to be in any range. This selection must be balanced by the limitations regarding overall blade rigidity. Hub portion thickness is chosen so that to be thicker than blade portion  12  in order to provide additional rigidity or stiffness to the saw blade in order to counterbalance torsional effects as the blade rotates and cuts. If additional cooling is required a thicker stock of starting material may be selected, although torsional considerations are also a factor in selection. Typically, the hub cooling and strengthening portion  14  has a thickness of between 0.060 to about 0.250 inches. The upper limit of ¼″ is currently dictated by the availability of the preferred starting material, which typically is plate. However, as plate is manufactured in larger sizes, or as other thicker forms of material become economically feasible, the thickness may be increased. Hub cooling portions have been tested in the range of about 0.090-0.110 inches with blade portion thicknesses in the range of 0.060-0.70 inches. Hub portion  14  includes an inner diameter  20  which forms a bore through which passes a motor-driven shaft that is used to provide the rotational motion for the blade during the cutting operations. This diameter will vary depending upon the size of the shaft onto which the blade is designed to fit. Since an arbor may also be used to mate up with a saw blade, this diameter may also be sized to fit a preselected arbor diameter. Hub portion  14  also includes an outer diameter  22  and is the transition from the thinner blade cutting portion to the thicker hub cutting portion. This diameter  22  can vary depending upon the amount of mass required for heat transfer requirements and torsional considerations, but typically is within 10 to 40% of the blade portion outer diameter. A first series of holes  24  is positioned on a first diameter  26  intermediate between hub portion inner diameter  20  and outer diameter  22 . In FIG. 1, these holes  24  are shown as elongated in the preferred embodiment as will be explained, with their major diameter extending in a circumferential direction. However, this geometry is optional, and these holes can assume any geometrical configuration. A plurality of cooling apertures  28  are located on a second intermediate diameter  30  positioned between first intermediate diameter  26 . Additional cooling holes at additional locations, such as cooling holes  32  located on third intermediate diameter  34 , may optionally be provided when additional cooling is needed. Cooling holes  32 ,  34  provide additional surface area to facilitate convective cooling of hub portion  14 . 
     Hub portion also includes an aligning means. In FIG. 1, the aligning means is shown as slots or keyways  36 ,  38 . The aligning means may assume other forms, and only keyways are shown in FIG.  1 . 
     When additional cooling is needed for a blade, the cutting system can be fitted with a spacer collar  40  having a predetermined thickness. In certain embodiments, which will be discussed, spacer collar  40  also provides a function in addition to cooling. Spacer collar  40  has an inner diameter  42  and an outer diameter forming an outer circumference  44 . The size of inner diameter  42  is subject to the same considerations as inner diameter  20  of hub portion  14 . Spacer collar  40  includes a plurality of cooling apertures  45  that are aligned on a first intermediate diameter  47  positioned between inner diameter  42  and outer diameter of the spacer collar and extend substantially axially through the thickness of the spacer collar. This diameter  47  corresponds to first intermediate diameter  26  of hub portion  14 , and cooling apertures  45  are positioned so as to align with holes  24 . As noted above, in the preferred embodiment, holes  24  are elongated, which makes alignment of holes  24  with cooling apertures  45  simpler, as the elongated holes allow for some tolerance mismatch. Thus, in the preferred embodiment, the axially oriented cooling holes  45  are circular in cross-section have a diameter approximately corresponding to the minor diameter of elongated holes  24 . 
     Spacer collar  40  also includes a means for aligning collar with hub portion  14 . As shown in FIG. 2, the aligning means includes a large slot or keyway  46  and two small slots or keyways  48 . These keyways correspond to large keyway  36  and small keyways  38  on hub portion, and inner diameter  42  of spacer collar has the same diameter as inner diameter of hub portion  14 . In the embodiment shown in the figures, at least one keyway of spacer collar  40  is aligned with at least one corresponding keyway of hub portion  14 , and a key is inserted to prevent rotation. In a typical operation, the motor-driven shaft that fits through the inner diameters of hub portion and spacer collar has a standard key having a size corresponding to large keyways  36 ,  46  or two small keys corresponding to small keyway slots  38 ,  48 . Other alignment means to align spacer collar  40  to hub portion  14  may be used. For example, spacer collar  40  on its face may include a pin which is received by a pin hole on a mating face of hub portion  14 . Alternatively, spacer collar  40  may include a key or plurality of keys that corresponds to one or more of the keyways of hub portion  14 . In yet another arrangement, the spacer collar  40  can be designed to have a surface that slides into inner diameter  20  of hub portion  14 , with both inner diameter  20  and the spacer collar surface having a flat to prevent rotation. These represent just a few examples, as many other alignment and locking arrangements are well known in the art and can be interchanged for those discussed above. The only requirement is that spacer collar  40  be locked in position with respect to hub portion  14  so that alignment is maintained during operation. A means for positively locking either hub portion  14  or spacer collar  40  with respect to the other is preferred. 
     Space collar  40  also includes at least one substantially radially oriented cooling aperture  50  that extends from the outer circumference  44  of collar  40  and intersects at least one of the axial cooling holes  45 . In a preferred embodiment, apertures  50  are located in a plane formed by the thickness of the spacer collar, so that the apertures  50  are substantially within the plane formed by the thickness of the spacer collar. The number of cooling apertures  50  will vary, being limited by clearances and by the available space along the around and along the circumference of spacer collar  40 . The apertures  50  are positioned at an acute angle with respect to the circumference  44  of spacer collar  40 , the acute angle being measured from and less than the right angle defined by a radial line extending from a center of the spacer collar  40  and a line tangent to outer circumference  44  of the spacer collar  40 . The aperture  50  extends inward from the outer diameter of the spacer collar, intersecting at least one substantially axially-oriented cooling aperture  45 . In a preferred embodiment, a plurality of cooling apertures  50  are positioned circumferentially along spacer collar  40 . The cutting system is force-ventilated through the aligned arrangement of the spacer collar and the hub portion. This forced ventilation is in addition to cooling provided by conduction of heat to the hub portion  14 , convection of heat by away from the hub portion  14  by axial cooling holes such as holes  28 , and conduction of heat across the contact faces between hub portion  14  and spacer collar  40 . The forced ventilation occurs as cooling air is circulated through hub portion  14 , depending upon the direction of rotation of the blade, by either creating a vacuum that draws air into cooling apertures  50  as a negative pressure is created; or by forcing air through cooling apertures  50 , as a positive pressure is created. The relationship of cooling apertures with the direction of blade rotation determines whether the pressure is positive or negative. The cooling air passes through axial holes  45  and through holes  24  of hub portion  12 , drawing heat from the hub portion and the spacer collar by convective flow. In a preferred embodiment, the spacer collar  40  is made from a material having a heat transfer capability as great as or greater than the heat transfer capability of the material forming the circular saw blade. Some heat is transferred across the interface of hub portion  14  and spacer collar  40 . Improved coupling between the interfaces as well as increased contact area between hub portion  14  and spacer collar  40  results in more efficient heat transfer due to conduction. 
     Of course, once coupling and contact area have been maximized, additional conductive heat transfer can occur when spacer collar has a greater heat capacity and heat transfer coefficient than the hub portion  14 . In the best mode of practicing the present invention, the spacer collar  40  has been comprised of a material selected from the group of metals consisting of aluminum and its alloys, while the blades have been made from ferrous alloys, tool steels. 
     In one embodiment of the present invention, the low kerf, ventilated cutting system is used in conjunction with a Brewer cutting system to improve yield. A schematic of the system is shown in FIG.  3 . The cutting system is comprised of a rotating shaft  100  driven by a motor  102  and the arrow indicates the direction of movement of the motor and the rotating shaft to which the blades are attached. The cuts or kerf are shown behind the blades as they move in the direction of the arrow. A plurality of circular saw blades  110  made in accordance with the present invention are mounted on the rotating shaft  100 . Each saw blade  110  has a blade cutting portion  112  and a hub cooling and strengthening portion  114 . Each blade portion  112  has a preselected outer diameter and a first thickness as previously described. The blade cutting portion  112  has an outer periphery that includes a plurality of blade teeth, not shown in FIG.  3 . Each hub portion  114  has an outer diameter smaller than the outer diameter of blade portion  112  and has a second thickness greater than the first thickness of blade portion  112 . Hub portion  114  further includes an inner diameter defining a bore, a first series of holes positioned on a first intermediate diameter, the first intermediate diameter located between the hub portion inner diameter and the hub portion outer diameter and a plurality of cooling apertures positioned on a second intermediate diameter, the second intermediate diameter located between the first intermediate diameter and the hub portion outer diameter, as previously discussed. Also included are means for aligning each hub portion  114  with the shaft  100 . For the Brewer system, the shaft typically includes at least one key (not shown) on shaft  100  which mates with one of the keyways on the hub portion  114 . When a Brewer system includes a single key on the rotating shaft, the key generally has a width of about ¼″. When Brewer systems include two keys, the keys are usually located on the shaft 180° apart, and typically have a width of about ⅜″. Also included is at least one spacer collar  140  extending between adjacent saw blades  110 . In FIG. 3 a plurality of spacer collars  140  are shown. Each spacer collar  140  has a predetermined thickness that corresponds to the desired width of a workpiece  200  that is being sawed by blades  110 . Each spacer collar  140  has an inner diameter and an outer diameter forming an outer circumference, means for aligning each spacer collar with the rotating shaft, again using a key and keyway arrangement, although any other suitable means may be employed, and a plurality of cooling apertures. Again, the cooling apertures are positioned on a first intermediate diameter positioned between the spacer collar inner diameter and outer diameter and oriented substantially axially through the thickness of the spacer collar as shown in FIG.  2 . The spacer collar first intermediate diameter approximately corresponds to the hub portion first intermediate diameter so that the cooling apertures of the spacer collar align with the holes located on the hub portion first intermediate diameter. In a preferred embodiment, adjacent spacer collars  140  are positioned so that their planar cooling apertures are oriented in opposite directions with respect to the direction of rotation of the blades. This is desirable so that air will be forced continuously through cooling apertures of one spacer collar through hub portion holes and be sucked by the vacuum created by cooling apertures of the adjacent spacer collar. This will also prevent clogging of sawdust within either the spacer collar cooling apertures  45 ,  50  or hub portion holes  24 . As can clearly be seen in the Brewer system, as the number of blades increases to produce thinner workpieces or as the width of the original board becomes greater, less waste is produced by the thinner kerf resulting from the blades of the present invention. When the original workpiece is sufficiently wide and sufficient cuts are made, additional work pieces can be produced, thereby increasing yield. In any circumstance, less waste in the form of sawdust will be produced, as less material is ground by the thinner blades of the present invention. 
     The saw blades of the present invention are manufactured by providing material having a thickness of at least about 0.060 inches. The minimum material thickness is established by the required thickness of the hub portion. The preferred material form is plate, although other suitable forms may be used. The blade cutting portion is formed by preferably wet grinding the heavier gage material, preferably plate, to the suitable thickness. The plate may also be machined to the appropriate thickness. One problem encountered when machining blade cutting portion  12 , such as by machine lathing, is material spring back. Material normally is not removed from hub portion  14 , although it may be adjusted if needed, again by grinding or other suitable machining operation. For example, if the starting material has a thickness of 0.060 inches, then the blade cutting portion may be ground to a thickness of about 0.045, and the hub portion will have the thickness of the starting material. Similarly, if plate starting material is about 0.250 inches, the blade cutting portion should be ground to a thickness of at least 0.240 or less, and the hub portion will have the thickness of the starting material. Of course, as the blade cutting portion is reduced, the hub portion can be suitably adjusted if desired or required. A bore hole is formed in the center of the hub cooling portion, the bore hole including at least one alignment feature, such as one of the features previously discussed. Holes and alignment features may be formed by any suitable technique such as trepanning, drilling, laser ablation or laser drilling. Blade teeth are formed on the outer diameter of the blade cutting portion by well known teeth forming methods. A plurality of holes located on a first intermediate diameter of the hub cooling portion between the bore hole and a hub cooling portion outer diameter are formed by methods well known in the art as previously discussed, as are the cooling apertures on intermediate diameters of the hub portion. 
     The geometric features of the spacer collar are machined in accordance with well known manufacturing techniques. The spacer collar is comprised of a material having good heat transfer properties, at least as good as the heat transfer properties of the saw blade. Aluminum or its alloys have been found to be acceptable, although the collar can be made from a tool steel similar to or identical to the blade. The spacer collar is provided in a thickness in the range of 0.125-4.0 inches. Any suitable material form can be used. Smaller thicknesses can be stampings, while larger sizes can be extruded forms such as pipe or the like or even ring forgings. The material form is not critical. 
     Although the present invention has been described in connection with specific examples and embodiments, those skilled in the art will recognize that the present invention is capable of other variations and modifications within its scope. These examples and embodiments are intended as typical of, rather than in any way limiting on, the scope of the present invention as presented in the appended claims.