FI76277B - FOERFARANDE OCH ANORDNING FOER SPAENNING AV SAOGBLAD. - Google Patents

Description

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Method and apparatus for tensioning saw blades. -Forfarande ocord anordning för spänning av sagblad.

The invention relates to a method and an apparatus for tensioning saw blades, in particular round blades, between rolling rollers pressed against each other.

Transverse vibration of the blade causes difficulties in the operation of the circular blade. There are several eigenfrequencies of the oscillation and, in addition, the uneven heating of the blade in use shifts the position of these frequencies so that the common points of the excitation frequencies and the eigenfrequencies are very easily hit. In this case, the vibration amplitude of the blade increases and the quality of the surface produced by sawing deteriorates. A major problem, however, is that the collision of the rotational speed with the lowest characteristic frequencies causes a collapse-like decrease in the transverse stiffness of the blade.

The lowest frequency (mode 0) is eliminated by the guides coming to the circumference of the blade. Nothing can be done to eliminate the next frequency (mode 1); only the rigidity of the blade in the axial mounting keeps this frequency sufficiently high in relation to the rotational speed. The frequencies of the following modes are clearly higher than the operating speed, but they may drop sharply if the blade circumference gets warm. In this case, the saw frame increases, the quality of the surface deteriorates and the blade eventually gets stuck in the log, badly damaged.

The eigenfrequencies corresponding to mode 2 and higher mode numbers can be shifted higher by "tensioning" the blade, Vals-obtaining a pair of centrally symmetrical circular grooves in the blade with a pair of rollers from which the blade material stretches in the direction of the blade radius, increasing the outer circumference diameter. By nesting these grooves, a considerable tangential tensile tension of the outer circumference is achieved. The heating of the outer circumference during sawing is not able to remove this tangential stress on the whole from the very beginning, so the behavior of the blade is stable even with varying loads.

Tightening the outer circumference of the blade as described increases the properties of modes 2,3,4 etc considerably. This all benefits the saw mark. Thus, tensioning the blade has become a crucial measure in the use of circular blades, the correct performance of which requires good eye and professionalism.

However, tensioning the blade as described above is a significant drawback. The natural frequency of mode 1 decreases when the pole parts of the blade are subjected to compressive stress as a counterweight to the tightened outer circumference. This cannot be compensated for with the guides either, so the heavily tensioned blade behaves more safely and better, but the sawing accuracy decreases when the rotational speed gets close to the characteristic frequency of mode 1. Sa search accuracy can only be increased by thickening the blade.

The decrease in the eigenfrequency of mode 1 during tensioning can be reduced by grouping the tension grooves into a narrower range. Even then, a strong tangential pull is obtained on the outer circumference, but the increase in compressive stress near the hub decreases. Sawing accuracy is improved, but difficult problems have been identified in practical implementation due to the rolling principle.

The aim of the method and apparatus according to the invention is to reduce or completely eliminate the above-mentioned problems. To achieve this object, the method according to the invention is characterized by the matters set out in the characterizing part of claim 1 and the apparatus according to the invention is characterized by the matters set out in the characterizing part of claim 3.

The invention will now be described with reference to the accompanying drawings, in which:

II

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Figures 1 and 2 show saw blades tensioned by the present method,

Figures 3a and 3b show an apparatus for manufacturing the saw blades of Figures 1 and 2,

Figure 4 shows a saw blade in which tension grooves have been made by both the present method and the method according to the invention,

Fig. 4a schematically shows the stresses acting in the stress groove according to the current method,

Fig. 4c schematically shows the stresses acting in the stress groove according to the invention,

Figures 5a and 5b show an apparatus for manufacturing a tension groove according to the invention,

Figure 6 shows a cross - section of a sawn steel stressed by the method according to the invention, and

Figures 7a and 7b show an alternative embodiment of the apparatus of Figures 5a and 5b.

According to Figures 1-3, in order to tension the saw blade 1 to the blade, centrally symmetrical circular shallow grooves 2 are rolled by a pair of rollers 3,4. The outer surface of the rollers 3,4 is usually smooth spherical. The rollers 3,4 are pressed against each other so strongly that at the pressing point the material of the blade has to be plastically displaced from the bottom laterally. In the direction of rolling, this is not possible, so the material flow is mainly transverse. In the longitudinal direction, i.e. tangential to the blade 1, the rolling groove 2 has a uniform yield stress at the yield point along its entire length, which is maintained by the material outside.

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Transversely, i.e. radially, the outer circumference can stretch out of the way, so in that direction the tension is very small. Thus, point A in Fig. 4 shows a mainly tangential yield stress compression stress on the rolling groove according to Fig. 4a.

The stress state in the rolling groove 2 is very stable, and the tangential compressive stress at the yield point cannot be discharged anywhere. On the other hand, even a small change in the stress state in any direction always causes additional yielding, so that the stress gradually stabilizes to some extent, e.g. due to the vibration of the blade 1. The outer circumference of the blade 1 is connected to the pole part throughout and only through this rolling groove 2. Even a small transverse force of the outer circumference causes the circumference to bend into a cone and, according to Fig. 4b, a sharp bend is formed at the rolling groove 2. Even during rolling, even a small bending of the blade causes it to become strongly conical. The bend must not be straightened with anything other than a hammer.

When performing the corresponding stress breaking, the corresponding phenomenon does not occur. Fig. 4c shows the stress state around the intermittent rolling residues 5 at point B in Fig. 4. At the rolling point 5 there is a compressive stress at the yield point, as well as at the base 6 between the rolling marks in the tangential direction. Instead, these supports 6 tend to resist the radial widening of the band, so that a tensile stress is formed in them. In fact, these adjacent stresses at the yield point in different directions cause the material to move transversely so that the stress level decreases below the yield point under the effect of the next rolling impact. A steep bend in the stress zone is not formed as easily as with a uniform rolling ice 2.

Figures 5a and 5b show how one of the rolling rollers 7 and 8 is notched at its outer circumference. During rolling, the material flow can be discharged at the notches 9. In addition, when the notch 9 is at the nip, both adjacent "teeth" 10 bend the blade 8 against the blade 8. A truly plastic deflection is formed in the blade 1, allowing a large and easy flow of material from the nip 5 to the bend. Thus, already during rolling, the tangential stress in the rolling zone drops well below the yield strengths and the zone becomes completely stable. In addition, the blade becomes slightly tortuous in cross-section, as shown in Fig. 6.

An even more favorable rolling result is obtained by arranging the notch 9 alternately and interleaved according to Fig. 7. In this case, the strongly tortuous breaker is also able to release its own tensions. The structure can also be implemented in such a way that the rolling mark consists of alternating or parallel depressions in two or more rows.

Pair of rollers can also be formed by making notches 9 in each of the rollers 7 and 8. The size and location of the notches 9 in the different rollers 7 and 8 can then differ from each other.

The method preferably produces two or more parallel cut grooves in one rolling by placing two or more pairs of rollers 7,8 in parallel and / or in succession.

The above embodiments are intended only to clarify the invention, without limiting the scope of the claims. In addition to circular blades, the invention is also applicable to tensioning, for example, band and frame saws. In addition, the shape and location of the notches can be varied considerably without departing from the inventive idea.

Claims (7)

762 77 A method for tensioning saw blades, in particular circular blades, between rolling rollers (7,8) pressed against each other, characterized in that the method comprises forming a break groove in the saw blade (1) using rollers (7, 8), at least one of which (7) is provided with notches of the desired shape (9). Method according to Claim 1, characterized in that the method is used to make two or more parallel breakers using two or more pairs of rollers (7, 8) arranged in parallel and / or in succession. Apparatus for carrying out the method according to claim 1 for tensioning saw blades between press rollers (7,8) pressed against each other, characterized in that the apparatus comprises at least one pair of rollers (7, 8), at least one of which pair (7) is provided with notches (9) of the desired shape on the circumference, arranged in the desired order. Apparatus according to Claim 3, characterized in that the notches 9 in the roller are formed as a row in substantially the same row. Apparatus according to Claim 3, characterized in that the notches (9) in the roller (7) are formed in two different rows as a series alternately or parallel to the circumferential direction. Apparatus according to Claim 5, characterized in that the notches (9) in the different rows are interleaved. Il 76277 Apparatus according to Claim 3, characterized in that the apparatus consists of two or more pairs of rollers (7, 8) arranged in parallel and / or in succession.