WO1987002286A1

WO1987002286A1 - Endless jointless saw blade and process for producing the same

Info

Publication number: WO1987002286A1
Application number: PCT/SE1985/000391
Authority: WO
Inventors: Bror Elofson
Original assignee: Bror Elofson
Priority date: 1984-04-18
Filing date: 1985-10-11
Publication date: 1987-04-23
Also published as: SE446380B; SE8402160L; SE8402160D0

Abstract

An endless saw blade, which is jointless and subsequent to its original heat treatment is not subjected to a continuous heating to annealing in any way, as well as the method of producing the same from an annular blank without a joint by means of rolling it to an endless band of the desired length and thickness and later tooth punching according to a special practice before the blank is subjected to a continuous treatment according to a practice known per se.

Description

ENDLESS JOINTLESS SAW BLADE AND PROCESS FOR PRODUCING THE SAME

5 TECHNICAL FIELD

The present invention relates to endless saw blades and specifically relates to endless saw blades, which are produced without joints, as well as a process for producing the same.

10 PRIOR ART

Endless saw blades are available in several designs. It is economical to purchase endless saw blades by the meter, with completed but not set and sharpened teeth. It is expensive to buy the completed saw blade as a welded ring, sharpened and swayed or set. Various tooth

15 shapes and tooth pitches are marketed. The thickness of the blade may be from about half a millimeter to about three millimeters. The width of the blade may be from a few millimeters to about 4 decimeters.

The user selects the dimensions of the blade, tooth type and tooth 20 pitch as well as, in case the user buys joined bands, band length, with respect to the band saw he uses as well as the saw function to be performed by the saw blade.

If expressed as meters of sawn product equipments for cross-cutting 25 from logs and dry-cleaving from material produced in the stem saw after seasoning are the important fields of applications. For cross-cutting blades having a width of up to 300 mm and a thickness of about 1.5 mm are used, while the blade for dry-cleaving is less than 130 mm and has a thickness of about 1 mm. It is important in both

30 cases to produce straight saw cuts. The feed of the lumber past the teeth is about 1 m/s, when production sawing takes place.

A normal tooth pitch for endless saw blades is from a few millimeters to 60 mm. Endless saw blades having less than 150 teeth are not common --' on the market. The tooth design may vary due to different front edge angles, relief angles and tooth base designs. When endless saw blades are employed in a normal manner, sharpening is a frequent maintenance measure. A special method of extending the time between the necessary resharpenings is to coat the saw teeth with a harder material, e.g. stellite. It may also be necessary to repair cracks in the blade and damaged saw teeth, which is accomplished after cleaning and inspection and marking out of such cracks and damaged teeth; straightening and stretching; as well as joining of broken endless saw blades.

The stress of an endless saw blade is caused by the following factors: the tensile stress, which ensues, when the runners are unscrewed and the saw blade is stretched; the bending of the material each time a point on the material passes the runners; stretchning forces, which are caused by pressure from the guides; heat movement due to heating caused by friction against guides and against the sawn material; compressive forces caused by the feed movement, which tend to push the blade aside; forces on each tooth during the cutting movement. These factors have different effects on the saw blade, but band stretching and runner diameter as well as tooth base design are quite important as far as the strength of the material goes. When satisfactory saw blades are used for a prolonged period of time in well-adjusted machines, the weakest points of the material prove to be the tooth bases and the welding joint.

Great demands on skill are made, when band saw joints are welded. The following must be observed: The tooth pitch must be the same across the joint as along the rest of the saw blade; the material must be hardened and tempered in conjunction with the welding; the joint must be ground to the correct thickness after the welding; the saw blade must be straightened and/or stretched after the welding. All of these operations must be conducted with the same precision and success in order not to lower the life of the blade. Joining by soldering is insignificantly simpler, but in return it renders a hardening of the material after joining impossible. The requirement that the saw blade i_S weldable without losing its excellent properties or requiring a too complicated heat treatment after the welding is somewhat opposed to the requirement that the material displays maximum strength as to the various types of mechanical stress which result during the sawing.

From the user's point of view it certainly is of great economical value to be able to eliminate one of the weak points of band sawing, namely the reduced strength of the weld joint and the time needed to repair a broken weld joint respectively.

Swedish patent specification 59 100, granted to V C Coryell in 1925, relates to a method of producing endless metal bands, which are to be used as driving belts. Such driving belts have been commercially obtainable for quite a long time and thus the production of endless metal bands by rolling may be assigned to the concept of prior art. As far as is known, the idea of producing endless saw blades by means of the same rolling technique has not been introduced before. By means of such a rolling technique to produce endless metal bands it is possible without difficulty, by varying the rolling parameters and the starting material, to produce, by rolling, such endless bands having arbitrary thicknesses and lengths. In order to attain the maximum strength of the material the final rolling out to the desired dimensions ought to be done by cold-rolling, while for technical and economical reasons it is advantageous to keep the material hot during the main part of the reduction by rolling process.

DISCLOSURE OF THE INVENTION

The object of the present invention is to eliminate the above-described shortcoming of conventional endless saw blades by combining technique, known per se, of endless saw blade production with technique, known per se, of endless band production and, when doing so, utilizing automatic controll technique, known per se, in order to accomodate said two technical fields to each other.

Consequently, according to the present invention a seamless tube, which is produced according to known technique, is cut to short pieces, each of which forms a ring. It is of course also possible to produce a corresponding ring by forging or pressing. The ring shall have an inner diameter and a thickness of material, which reflects the amount of material in a finished endless saw blade with an addition for a certain degree of work up. One ring may also be used as a blank for a plurality of endless saw blades, which in this case are produced by rolling them abreast of each other so to speak, and subsequently be cut to its correct saw blade width.

The ring-shaped blank is slipped onto a roller in a rolling mill, which is equipped with various devices known in the art in order to guide the endless loop as its size increases and its thickness of material decreases. This rolling takes place in a hot condition after a stock removal operation, externally, internally and on its edges, and is interrupted, when the dimensions come close to the dimensions desirable in a finished saw blade. When the hot rolling is interrupted, the blank is again prepared in order to remove oxide scale, suitably by grinding. Pickling may also be used. Subsequently the blank is cold-rolled to its final thickness of material and band length and subsequently it is cut in a roll cutting machine to a suitable width. The next step is a hardening and tempering and subsequently tooth punching followed by swaging/setting, straighteing/stretching and grinding.

ή band, which is produced according to the present invention is much more adapted, than conventional endless saw blades, to stretching by means of "rolling", since no joint having differing dimensions and properties is present on the blade.

By applying modern rolling technique it seems to be feasible to produce bands having a final thickness on the order of 1-2 mm within about one tenth of a millimeter, while at the same time the length of the blade/band can be fixed on the order of from a few meters to about ten meters, the error being within a few per cent. The novel features of the present invention reside in how to use endless bands of high-quality steel to produce endless saw blades. The characterizing features of the endless saw production include as a first step tooth punching. Also, in this respect there is a fundamental difference between the ring-shaped saw blade blank according to the present invention and the endless or continuous rolled out band, from which a cut endless saw blade blank is produced. Thus, an endless saw blade is produced, as described above, from a cut blank by joining by means of soldering or welding, the joint being located in such a fashion, that the tooth pitch, after a completed joining, is the same across the joint as along the rest of the blade, while as far as the present invention goes, a plurality of teeth are to be placed on an endless band having a definite length. Consequently, the tooth pitch must come out exact as to the measured length of the band. In this respect one aspect of the invention leads to the following discussion. If all the teeth and tooth openings are to have the same height, depth and length, the tooth pitch must be constant and come out exact as to the length of the blade. Also, in order not to produce any errors when punching the last tooth, the feed of the band must be accurate. The number of teeth on a normal endless saw blade often is in the order of 150-300. In case the feed is subject to an error, which is not randomly distributed around the adjusted value, then the error may as a principle produce a systematic effect, the result being that the tooth pitch of every tooth is too large or too small to the same extent. This means that, for an error of about 1 per cent, which is the lower limit for the accuracy of commercially obtainable punching devices, the accumulated error, when punching 200 teeth, leads to the situation that "there is no place for" two teeth or they "are added" as compared to the computed number also in case the tooth pitch as chosen is "correct". If the desired tooth pitch is adjusted according to desires as to the properties for the saw blade without paying any regard to the length of the rolled out blank, then the error at the last tooth will be roughly half a tooth pitch. The tooth having an ordinary height and following the tooth having a reduced height (see Fig. 2) will in such a case be subjected to particularly strong forces as well as a risk that grooves will appear in the sawn material. According to conventional practice the dimensions of the teeth may vary among themselves several percent on a finished saw blade. According to the present invention tooth punching can be performed as follows:

The length of the blade is measured. The pitch is computed to go evenly into the length of the blade and approaches what is technically optimal for how the blade is used (in doing so the pitch must be adjusted by less than 1 per cent of what is optimal). The blade is punched until about 1/3 of the total number of teeth remains according to the computations of a microprocessor. Then the available space is measured between the last punched tooth and the first punched tooth and the tooth pitch distance is corrected. In doing so, the position of the blade edge in relation to the punch as well as the feed length are corrected. Subsequently 2/3 of the remaining teeth are punched and subsequently measurement and possible correction take place again. The last teeth are punched. The error as to the last pitch distance will then not be higher than 10 % of the pitch and in the normal case considerably less, while the difference between the three types of teeth (2/3, 1/6 in the middle, and 1/6 in the end) will be one or two per cent, and consequently, they may be considered being equal from a technical standpoint. The reading of the distance between two teeth or tooth bases may be made by means of optoelectronics, inductive sensors, differential transformers or similar devices producing an electrical output signal, which can be fed into the microprocessor more or less directly.

Various modifications of the above-described method of making the teeth roughly the same of course are possible. A continuous measurement of each feed step after punching and a continuous correction of the feed length with the required length in order to maintain the sum of tooth pitches of the punched teeth at the expected value are, from a technical standpoint, as easy or difficult to perform as the above-described method. On the whole it is difficult to measure correctly and to make the mechanical components perform in such a reproducible manner as possible.

It is interesting in this connection to elucidate the principles of correcting the pitch distance. During a normal tooth punching the tooth opening is removed in order to form the tooth tip, when the next tooth opening is punched (see Fig. 2). In case only the feed length is changed, a tooth is obtained, which is not as high as the tip height of the rest of the teeth. If instead only the position of the blade edge is changed before the punching, a tooth is obtained, which has the right tip height but has a smaller groove opening.

The basic rule is that the dimensions of two adjacent teeth must not differ by more than a few per cent, in order not to considerably overload any one tooth as compared to the average.

The dimensions of the individual teeth also must not deviate by more than a few per cent from the average in order to be able to peform the swaging and the grinding in automatic machines.

Additional advantages and characterizing features as to the present invention will be set forth in the accompanying description of a preferred embodiment as well as in the attached claims.

BRIEF DESCRIPTION OF THE DRAWINGS

A preferred embodiment will be described and reference be made to the following drawings, in which:

Fig. 1 is a schematic list of operations for producing the saw blade blank from a seamless tube;

Fig. 2A-C are schematic pictures of a few saw teeth, which have been punched with the same and different feed and tooth depth in the same punching device. DESCRIPTION OF A PREFERRED EMBODIMENT

A ring is cut from a seamless tube, the internal diameter of which is larger than the smaller roller in a single roll mill. The material of the tube is selected to afford the best combination of edge sharpness, setability and fatigue in a saw blade produced therefrom. The ring is machined externally and internally and on its edges and subsequently it is heated to its rolling temperature. Subsequently the ring is hot-rolled to dimensions, which as to thickness of material and loop length are 1-10 % higher and lower respectively than the desired values of the finished endless saw blade. In order to remove oxide scale before cold-rolling, which has been formed when held in a furnace during the hot-rolling, the blank is ground externally and internally. After cold-rolling to the desired thickness of material and length, considering the dimensions of the finished blade, the blank is cut to that width, which is needed before a tooth punching. The blank is hardened and subsequently tempered according to the recommendations of the steel manufacturer.

Punching is performed after a measurement of the length of the blade and a computation of the optimal pitch distance. In doing so, the total feed after every tenth tooth is controlled and when need arises the feed length is corrected in order to achieve that result that the total feed corresponds to the expected value. At the end of the punching the length of the remaining unpunched portion is controlled and the feed is corrected, with the result that also the last punched tooth will reach a full height and be surrounded with normal tooth openings. Fig. 2A shows a few teeth, which have been punched with the same feed and tooth depth. Fig. 2B shows, a few teeth, the last punched of which has been punched after a shorter feed movement than the rest. Fig. 2C shows how the tooth depth must be corrected in order to compensate for a shorter feed movement.

The measurements are performed by means of a laser source and a photodetector together with a differential transformer, which yields the standards of measurement. The measurement of the length of the blade blank is performed in the punching machine, in which the band is mounted around two wheels having an adjustable mutual distance. When the wheels have been brought apart until a predetermined band pressure has been obtained, the distance between the wheel axles is determined and this length is computed to the total length of the blade blank. By making one of the wheels function as a roller in a "printing roll mill" a stretching of the band can be accomplished in the same machine after a tooth punching and a possible tooth base warping, which also can be integrated with the punching operation.

Subsequently the teeth are set and sharpened in automatic machines, which are adjusted to the current pitch length.

Straightening and stretching may, if need arises, be performed in a conventional manner.

Claims

1. A method of producing endless saw blades, c h a r a c t e r i z e d in that an annular blank without a joint, produced by forging, pressing or by cutting a seamless tube, subsequent to machining of the external and internal surfaces of the blank as well as its edges, is heated to its rolling temperature and is rolled out in a hot condition, is surface conditioned in order to obtain the desired surface fineness for a subsequent cold-rolling, is- cold-rolled to its desired thickness and length, is cut to its desired width, is heat treated and tooth punched.

2. A method according to claim 1, c h a r a c t e r i z e d in that the tooth pitch of the blade is determined by measuring the length of the blade and computing that pitch distance, which is close to what is optimal for the chosen tooth design and saw blade use at the same time as it goes evenly into the blade length, after which the feed per tooth and, if need arises, the depth of the tooth is corrected in the punching machine, the result being that the computed tooth pitch is attained, after which the teeth are punched with a continuous measurement of the resulting pitch distances and their average value and a correction of the punching parameters in accordance with the measurement result.

3. An endless saw blade, c h a r a c t e r i z e d in that the blade is jointless and has not been heat treated in any way to annealing after hardening and tempering.