Circular saws have long been used for sawing of wood as well as metal. It is known that in order to saw straight, saw blades with a thickness less than one percent of the diameter have to be provided with internal stresses comprising tensile stresses around the periphery and compressive stresses in the center, which is accomplished through tensioning by hammering or rolling of the central parts of the saw blade. A saw blade with correct tensioning can be made with a thickness down to 0.5 % of the diameter. If in addition the thickness is varied by making the central parts thicker, the peripheral parts can be made with a thickness down to 0.2 % of the diameter. Thin kerfs are economically important because of lesser consumption of raw materials and energy. Similarly, to make straight cuts with a bandsaw, compressive stresses at the edges must be avoided.

Since large circular saw blades are heavy and bulky, a need has long been felt to make them with replaceable cutting tips, to avoid removing and regrinding of the whole saw blade when one tooth is damaged. Some earlier suggested solutions are shown in the patents US 174,216, US 246,703 and US 303,787. This need has become stronger as more wear resistant but brittle materials have become available, such as sintered tungsten carbide, and have been much used as permanently brazed tips on circular saw blades and to lesser extent on bandsaws.

Replaceable tips have found little application on saws, restricted to thick circular saws for wood, and for thick slot milling cutters. The tip holder designs commonly used for lathe tools have not been possible to use on saw blades, for several reasons. Tip holders comprising screws require a substantial thickness to make room for a screw with sufficient strength, and the same holds for holders

comprising various kinds of excentrics.

Tip holders where the tip is elastically wedged produce compressive stresses in the vicinity and can thus not be used for thin saw blades, although they have been used for turning of narrow grooves and for slot milling cutters. The use of elastically wedged tips is further prevented by the heating of the tips and their vicinity relative to the rest of the saw blade during sawing, and by tungsten carbide having lower heat expansion than steel and thus needing harder wedging than what corresponds to the cutting forces. It is known that arrangements of slots or holes close to the periphery of the saw blade can lower the thermal stresses and stabilize the saw blade, as shown in patents US 1,723,843 and US 2,667,904, but the known arrangements have not been adequate to counteract the compressive stresses from wedging of replaceable tips.

The invention concerns a saw blade for use with elastically wedged replaceable tips, where neither the wedging nor the heating during sawing will produce compressive stresses around the periphery, and where consequently replaceable tips can be used on this saw blades. If some teeth are damaged, the invention allows replacement of only the damaged tips, instead of removing the whole blade for regrinding or rebrazing.

Description

A saw blade according to the invention comprises a blade body of metal with a plurality of recesses along its periphery, where the tip is wedged between clamping surfaces, according to known art described in the patent EP 095 062 or the US patents mentioned above. Other shapes of the clamping surfaces are also possible, and the clamping surfaces can be parallel or converge outwards or inwards. The tips can be made with or without a tapered entering portion, but should preferrably have at least one convex or concave locating surface guided by a corresponding locating

surface in the recess. The tips extend outside the blade body surface on at least one side.

According to the invention, the blade body is provided with 5 gullets or slots in front of and behind each recess, said gullets or slots being substantially deeper than the recess. Radially inwards of each recess is at least one tension distributing hole with closed contour not connected with the recess but separated from the recess by a bridge, said hole

10 being partly located closer to the periphery than the bottom of the gullets or slots are. The function of the tension distributing hole is letting the blade body parts between the gullets or slots act as two levers joined by the bridge. When the peripheral ends of the levers are pressed apart by

15 the wedging forces during insertion of a tip, or by thermal expansion when sawing, the bridge acts as a hinge and the inner ends of the levers approach each other causing a tangential tensile stress in the blade body. This keeps the saw blade flat and increases the resonance frequency. The

20 saw blade properties are thus improved by hard clamping or heating, in contrast to blades of prior art which strongly deteriorate in such circumstances. The tension distributing holes are preferrably shaped like inverted T:s, with one hole inwards of each recess, or L-shaped with two holes

25 inwards of each recess.

In sawing of metal the cutting speed is limited and there is little risk of the tips being thrown out of the recesses by centrifugal forces, but in sawing of wood with much higher 30 cutting speed it is suitable to secure the tips with pins or tubular pegs as shown in US 1,608,182.

To make sure that all tips are cutting, the radial position _* must be well defined, which is most easily achieved by

35 tangential supporting surfaces on the tip and on the recess. >* The supporting surfaces can be located at the rear of the tip as in US 303,787, at the underside of the tip as in US 174,216 or at the front of the tip as in US 4,801,224. It

has also been suggested to make the tip with a projection as in US 246,703 to combine the radial positioning with securing against centrifugal forces, but that would lead to excessive deformation when removing or inserting the tips.

According to the invention, which is more closely described with reference to the figures 1,2,3 and 4, where figure 1 shows a tip and a recess with spacious gullets on both sides, figures 2 and 3 show a tip and a recess with narrow slots on both sides and figure 4 shows an embodiment with two tension distributing holes. The tip (11) is in all figures shown as described in US 4,801,224, where the clamping forces are applied on parallel surfaces (12,13), and the inner portion (14) of the tip is tapering to facilitate insertion. The radial position of the tip is determined by a step (15) on the front side, and below the tip (11) there is an empty part of the recess at the bottom (16) . Behind the recess is a hole (10) against which a lever is rested for removing or inserting a tip. Radially inwards of the recess bottom (16) figure 1 shows a tension distributing hole (18) , generally shaped as an inverted T with the vertical part poining towards the recess and the horizontal part in the tangential direction. The outer part (19) of the tension distributing hole is rounded to avoid crack formation, and between the outer part and the bottom (16) of the recess is a bridge (17) of the blade body material. The inner part (20) of the tension distributing hole (18) extends further in a tangential direction than the outer part (19) . In front of the tip is a front gullet (21) and behind the tip a rear gullet (22) which can be contiguous with the front gullet of the following tip. The bottoms of the gullets (21,22) should be located at a smaller radial distance to the line between the tip edges compared to the inner part (20) of the tension distributing hole and at a larger distance compared to the outer part (19).

In many applications it is unsuitable to have large gullets,

and the blade can then be made with a contour comprising radial slots in front (23) and in rear (24) of the tip as shown in figure 2. To lower the risk of crack formation the slots have terminations with larger radius, such as round holes (25) . The terminations (25) should then be located with a smaller radial distance to the line between the tip edges compared to the inner part (20) of the tension distributing holes and at a larger distance compared to the outer part (19) . The tension distributing holes (18) can also be made as slots with large radius terminations (26) .

The tension distributing hole can be made as an at least partly open hole (18) as shown in figures 1-2, or as a narrow laser-cut slot (31,34,35) with curled ends (32). Likewise, the radial slots can be terminated with either large radius holes (25) or laser-cut curled ends (32) . The tension distributing holes and slots can be left empty or filled with some easily deformable material such as synthetic resin or soft ductile metal.

Figure 4 shows an alternative embodiment where the tension distributing hole is a group of two L-shaped holes (34,35) which together give the same effect as the inverted T-shaped hole, while in addition the metal strip between the L-shapes increases the resistance to lateral forces acting on the tip during sawing.

A circular saw blade according to the invention has several tips distributed around the periphery. For sawing of metal, it is advantageous to make every second tip higher with large chamfers and short horizontal edge, and make the tips between lower with long horizontal edge, which makes all chips narrow an keeps them from rubbing or sticking to the sides of the kerf. For sawing of wood, tips with long horizontal edge can be used throughout, and to secure the tips against centrifugal forces the recess is preferrably made with a notch (33) for a tubular pegs.

The invention has been described as applied to circular saw blades, but could also be applied to other types of saw blades, such as straight blades for gang saws, power hacksaws and bandsaws, or annular saw blades. The advantages are the same in all cases: improved straightness of the cut due to internal tensile stresses along the periphery, and a possibility to exchange the damaged tips only when some damage has occurred.