22.05.2015

Purpose and types band saws

Band saws are the cutting tool of band saw machines: carpentry, dividing and log saws. The saws used in these machines differ only in size and tooth profile and are divided into three types: carpentry (narrow), dividing (medium) and log saws (wide). The first two types are produced in accordance with GOST 6532-53, and log saws - in accordance with GOST 10670-63 “Band saws for sawing logs and beams.” Band saws are used for curved and longitudinal cutting of boards, beams, logs and slab wood materials.

Band saw design

The design of band saws is characterized by the dimensions of the blade (width B of the band, including teeth, thickness 5, length L), profile and size of the teeth of the cutting edge. The dimensions of the band saw blade mainly depend on the design of the band saw machines: the distance between the axes of the saw pulleys k, their diameter D and width.
Band saw length can be determined by the formula

Since the tape is supplied by the manufacturer in rolls, when cutting the estimated length it is necessary to take into account the soldering allowance, and at the soldering site maintain the overall tooth pitch.
Band saw thickness depends on the diameter of the saw pulley and must satisfy the dependencies

The magnitude of bending stresses, which are of great specific importance in the overall stress balance, depends on the ratio of the thickness of the saw and the diameter of the pulley. The magnitude of stresses from saw bending

The magnitude of bending stresses at s/D=0.001 will be

Temporary tensile strength at the welding site does not exceed 70-80 kgf/mm2. Therefore, with a minimum safety factor of 2, the stress in a working saw should be less than 35-40 kgf/mm2. In this regard, they strive to use the minimum possible saw thickness and large saw pulley diameters.
The width of the band saw blade depends on the width of the saw pulleys and can exceed the latter only by the height of the teeth. Choosing the width of carpentry band saws when cutting curved parts, it is additionally necessary to take into account the radius of curvature R mm of the cut and the widening of the teeth on the side Δs mm. Then the width of the saw

Wider saws will bend in the cross-section, causing them to cut and even slip off the pulleys.
For cutting parts with a very small radius of curvature, they are used jigsaw machines, in which as cutting tool jigsaws are used. Dimensions of jigsaws: L = 130/140 mm, B = 2.3/8 mm, s = 0.26/0.5 mm, t = 0.6/1.5 mm. Angular parameters of a tooth with a straight back edge: α = 5/10°, β = 40/45°. The dimensions of carpentry, dividing and log saws are given in table. 25.

Each type of GOST saw has its own tooth profile. For example, for dividing saws there are two: profile I - with an elongated cavity and profile II - with a straight rear edge (Fig. 41.6). Dividing saws with tooth profile I are used when sawing hard and frozen softwood, with tooth profile II - when sawing soft wood. The sizes of band saw teeth depend on their thickness, width and cutting conditions.

For carpentry band saws with a width of 10-60 mm, the dimensions of the teeth are determined by the following approximate expressions (mm):

For dividing and log sawing band saws, the tooth sizes are equal (mm):

For saws with set teeth, the pitch is reduced by 25-30%. The angular values ​​of the tooth profiles provided by GOST are shown in Fig. 41. The front angle of the teeth must be made as large as possible, since in this case the cutting power is reduced and the pressing force in horizontal plane, moving the saw from the pulley. However, when increasing the rake angle γ, it is necessary to take into account the properties of the material being cut and the strength of the tooth, which depends on its size and the sharpening angle β. The angle γ should be maintained within 20-35°.

Band saw soldering

Soldering of band saws is carried out in the case of preparing new saws from rolled tape, repairing saws in the presence of significant cracks (over 0.12V) or breakage. It includes the following operations: marking, trimming, chamfering, soldering, heat treatment of the soldered seam, its cleaning and straightening. Proper soldering requires that the seam be halfway between the tops of adjacent teeth of the soldered saw. To do this, before cutting, mark the saw using a ruler, square and scriber.
Marking and cutting out defective areas (when repairing a saw) should be done according to the diagram shown in Fig. 42. The width of the seam B depends on the thickness of the saw s and is approximately taken to be 105. After marking, the saw is cut along the marked lines ab and cd using scissors or a chisel. The cut ends are straightened with a hammer on an anvil and cleaned with a file. The ends of the saw are soldered with an overlap. To maintain the thickness of the soldered seam equal to the thickness of the saw, its ends are beveled (chamfered) within the marked strip. Chamfering is done manually using a file on special device, either on milling or sharpening machines. The sharpened ends are thoroughly cleaned with sandpaper and degreased.
The ends of the saws are soldered in special presses with soldering bars, electric soldering apparatus or flame blowtorch. Presses with soldering bars are heated to 830-1000 ° C in PM-6 muffle furnaces. The ends of the soldered saw are installed in a soldering press, and solder is placed between them in the form of a plate 0.075-0.15 mm thick along with flux - dehydrated borax. Flux is necessary to protect the surfaces being soldered from oxidation, as well as to improve their wetting. Then heated soldering bars are inserted into the press and pressed tightly to the soldering site using screws. After the solder has melted and the bars have cooled to a dark red color, they are removed, and the soldering area is cooled in the cold section of the press. After some time, the saw is tempered for 1-2 minutes using the same bars, but heated to a temperature of 650-700 ° C. For soldering, silver solders P-Sr-45, P-Sr-65 or brass L62 with a temperature of melting 605-905° C. After cooling, the joint is cleaned of scale and filed on both sides with a personal file to a thickness equal to the thickness of the saw blade. Then the place of soldering is rolled.

To connect the ends of the tape, you can use the electric butt welding method using ASLP-1 devices. The ends of the saws are cut at an angle of 90° C, secured in the clamps of the welding machine, brought into contact and the current turned on. As soon as the ends of the saws are heated to a plastic state, the current is turned off, and the ends of the saws are moved even more tightly by moving the clamps until they are welded. I haven't received this method yet wide application, since it requires special equipment.

Straightening and rolling of band saws

At editing of band saws, defects are identified and eliminated in the same way as when straightening frame saws. Given the large length of the saws and their small thickness, defects should be eliminated with great care, mainly using a rolling machine. The less the band saw is trimmed with the right hammers, the longer its service life. Therefore, straightening should be resorted to in case of emergency, if possible replacing it with rolling.
Rolling Band sawing is done in two ways.
The first method: symmetrical rolling is performed similar to rolling of frame saws and consists of lengthening the middle part of the blade (Fig. 43, a). Rolling begins from the middle part of the blade and ends, not reaching 10-15 mm on one side to the line of the tooth cavities, on the other - to the rear edge of the saw. Rolling, straightening and quality control of saw preparation are carried out on special tables equipped with a rolling machine, anvil, test plate and support rollers for moving the saw. The degree of rolling is determined by the arrow of transverse curvature when bending the saw using a short ruler. The deflection should be approximately 0.2-0.4 mm for pulleys with a straight rim and 0.3-0.5 mm for pulleys with a convex rim. Higher deflection values ​​apply to wider and thinner band saw blades. An accurate check of saw lateral curvature can be carried out using a convex template with a radius of curvature corresponding to a properly machined saw. In addition, check the straightness of the rear edge of the saw by placing it on a test flat plate and applying a long straight ruler to the edge.
The second method of rolling band saws is called cone rolling (Fig. 43, b). Rolling begins at a distance of 15-20 mm from the tooth cavity line. Closer to the rear edge of the saw, the pressure of the rollers is increased. The last mark of the rolling rollers should be located no further than 10 mm from the rear edge. As a result cutting edge It turns out to be shorter than the rear one and, when tensioned, receives greater stress than the other parts of the saw. The rear edge of a saw that has been beveled and placed on a flat test plate will be in a circular arc with the center pointing toward the teeth. The amount of convexity of this edge over a length of 1 m serves as a characteristic of the degree of rolling. The convexity arrow is determined using a test ruler with an indicator along the entire length of the saw. The convexity arrow should be equal to 0.3-0.5 mm over a length of 1 m, while large values refer to wider saws. If part of the blade along the length of the saw has a convexity greater than required, this place must be rolled with increasing pressure on the rollers from the rear edge to the cutting edge. On the contrary, if the convexity is small, roll with increasing pressure of the rollers from the cutting edge to the rear. The second rolling method is the best for wide band saws, especially when the heating is uneven across the width of the blade.

Installing band saws into the machine

Normal operation band saw depends not only on the quality of the saw preparation, but also on its correct tension and installation in the machine. To do this, the following conditions must be met:
1. During installation and operation, the band saw must be placed on the saw pulleys so that the cutting edge protrudes beyond the edge of the pulleys by at least half the height of the tooth, but not more than its height.
2. The tension of the saw must be sufficient to ensure its rigidity in the lateral direction and on average be at least 5-6 kgf/mm2.
3. The guide devices for the saw must be fitted and adjusted to the saw with a gap not exceeding 0.1-0.15 mm.
To prevent displacement of the saw blade along the pulley due to horizontal components of cutting forces, mismatch of the resultant tension of the saw with its center line, heating of the saw, etc., a number of preventive measures are used. Saw pulleys are made with convex rims, and the convexity is not located in their middle, but closer to 25-40 mm to the cutting edge. To prevent the belt from slipping, flat pulleys are tilted (for the worker) relative to the horizontal axis at an angle of 10-15", and the saws are rolled onto a cone. In addition, most modern machines allow you to rotate the upper pulley around it vertical axis due to the lateral displacement of the front pulley shaft support. Such a turn (with the working branch outward) allows you to hold the saw during strong heating and cutting in inner side. Guide devices make it possible to protect the saw from strong lateral bends, slipping off the pulleys and dampen resonant vibrations. During work, you must carefully monitor the cleanliness of the surfaces of the saw pulleys, promptly cleaning them from dust, sawdust, resin, etc.

Technical requirements for band saws

Maximum deviations in the dimensions of band saws should not exceed the values ​​​​specified in table. 26.

The roughness of the side surfaces of saws must be at least class 7 according to GOST 2283-57. Cracks, delaminations, scratches, and burns from grinding are not allowed. The canvas must be straightened and rolled evenly. Every 10 m on the saw there should be a mark indicating the type of saw, its dimensions, GOST. For example, for log band saws according to the scheme: “Saw PLB Bхsхt GOST 10670-63”.

Vary band saws two types: narrow saws(up to 50 mm.) and wide(from 80 mm to 250 mm)

As we know, any saw cuts with a tooth, and how the saw will cut depends on the shape and type of tooth. It is the saw tooth that determines the characteristics of the saw blade itself.

What should you choose?

Let's compare narrow and wide saws.

Torn narrow band saw not such a rare occurrence. The saw became dull, got stuck in the cut with sawdust and burst, the ring is no longer there, and a piece of torn blade is hanging on the pulleys or lying by the machine. But on wide saws This is an extremely rare occurrence!

Wide saws You may often be surprised by the appearance of cracks in the cavities of your teeth. This is often due to the selected tooth preparation parameters (depending on the type and condition of the wood and the feed speed of the saw blade into the log). But to break wide band saw, you need to put in a lot of effort.

On narrow saws to avoid jamming of the tape, carry out the so-called tooth spread. When setting the teeth, the first to the left, the second to the right, the third straight and repeat, while only the left and right teeth are sawed (the straight one only takes out its part of the sawdust), forming a cutting width in which the saw body itself will not jam.

With this preparation of teeth, each of them removes its third of sawdust (33%).

The optimal preparation is in which each tooth works 100%, but on narrow saws this is not possible due to the small height of the tooth. Thus, narrow saws severely limited in sawing speed due to the problem of removing the same sawdust! Given the cut that a narrow band has (about 2.5 mm), it at the same time does not have (unlike a wide saw) a stabilizing body, and can dangle in the cut.

As the feed speed increases, it will be pulled to the side, followed by overload, over-tension and, as a consequence, breakage. And again repair (welding), and welding is a shortening of the length, and all pulleys have restrictions on the length of the saw blade ring.

The only solution isincrease the width of the saw blade itself, not forgetting the 20/80 ratio. Wide blade narrower than 80 mm. allows you to understand the height of the tooth, for example up to 11mm.

At the same time, with a step of 35mm, the area of ​​the cavity increases by 2 times, which makes it possible to more efficiently remove sawdust, which caused us so much trouble. Such a tooth can already be prepared in a more modern way, starting with flattening its tip to create a widening in the cut and ending with the most technologically and economically advantageous, such as stellite surfacing!

After sharpening such a tooth, it begins to work at 100%, completely coping with the removal of sawdust. In this case, the wiring becomes completely unjustified.

Narrow band saw. Every third tooth works.

Wide band saw. Every tooth works.

When working on wide ribbons with almost the same cutting width, the saw does not wobble, works stably at high speeds, greatly increasing productivity.

Using wide band saws, you can fine-tune tooth parameters, changing it shape, cutting angles, as well as changing cutting width. For each species and condition of wood, you can select your own optimal parameters tooth preparation, which can add up to 25% to sawing speed and increase the yield of finished products.

Narrow saws use simpler and cheaper equipment, and are also easier to install and tension on pulleys, which makes them gain a little position from wide saws. As we know, during operation any saw heats up, especially its cutting part. The narrow belt heats up completely, since it has a small width, and its linear expansion is compensated by the pulley tension mechanism. But in the case of using a wide tape, several problems have to be solved. Speaking in simple language, wide saws have to be pulled several times stronger than narrow ones, which is why the saw unit is used more complex and massive. Since the width of the saw is much larger than the cutting part, it does not heat up evenly (the cutting part heats up much hotter than the rest of the saw). At the same time, the cutting part lengthens and weakens, which can cause a “wave” in the cut. In this case, the guide rollers cannot reliably hold the wide belt on the pulleys, since the sawing speeds are much higher than when sawing with narrow saws, and the load on the material is higher. To get rid of these difficulties, it was necessary to complicate the design of the machines, which could not but affect the cost of the equipment, as well as the level of training of the personnel working on this equipment.

The result of this was the use of profile pulleys and their rotation relative to each other. Thus, the surface of the pulleys has several profiles, the most common of which are convex in the center of the pulley (1/2), convex with an offset to the part of the pulley where the cutting edge of the saw will be located (1/3 or 2/5) and flat ( saw rolling 1/3 or 1/2). The pulleys are not located in the same plane, but are turned towards each other. When using these features, the tensioned saw is securely fixed on the pulleys and compensates for the elongation of the leading edge when the saw heats up during operation. Placing a wide band saw on the pulleys.

Rolling w wide saws

During the rolling process, the body of the saw is rolled longitudinally with rollers harder than the saw itself under pressure. Rolling tracks are formed on it. Rolling is done depending on the profile of the pulley on which the saw will then have to work. During the rolling process, the saw body acquires a deflection corresponding to the shape of the pulley. Also, which is very important, rolling is used to stretch the rear edge of the saw, which corresponds to the rotation of the pulleys. The belt stretched on the pulleys repeats their shape, and the unfolded pulleys tighten it. During operation, the saw moves slightly back to the rear edge and tightens the front edge, compensating for the elongation of the cutting part due to heating. At correct angle turning the pulleys, rolling the saw body and tensioning it, the saw coming off the pulleys becomes impossible.

The saw can serve for a long time. But do not forget that with continuous operation the saw “gets tired”, so after a maximum of 2-3 hours of sawing it must be removed, wiped, turned inside out and hung up to rest for a day. Periodically, the saw needs to be sharpened (a dull saw stops cutting normally and can cause problems when cutting). The pulleys must be wiped so that no sawdust or other debris remains on them (check the condition of the scraper cleaners), as cracks may form in the center of the saw body. The saw also needs to be rolled over time to return it to the required shape. After grinding off the flattening or welded plate, you can re-prepare the tooth and continue working on the saw until its width becomes less than acceptable for fitting on the pulleys. Such saws, when correct use, they pay for themselves without any problems!!

Preparation band saws includes connecting their ends by welding or soldering, monitoring the stressed state of the blade, correcting defects in its shape, rolling, and final monitoring of the stressed state of the saw blade.

The stresses arising in the web as a result of welding are removed by rolling.

The stress state of the saw is controlled based on the deflection of the blade, similar to frame saws. In addition to local defects, similar to frame saws (tight place, bulge, etc.), the tape can curl, have winging, longitudinal waviness, warping, bending of the trailing edge of the blade, non-straightness. Twisting is eliminated by light forging, other defects by rolling. If the trailing edge in the joint area is not straight, the fabric is cut and re-welded or soldered.

Methods for identifying and eliminating defects in band saw blades

a, b - transverse warping; c, d - wingedness; d, f - longitudinal waviness; g, h - bend of the edge; 1 - saw, 2 - surface plate; 3 - ruler; 4 - probe; 5 - calibrated plate

More detailed information Byprices, discountsand other questions you are interested in, you will receive when contacting our specialistsby phone:

Availability complete set equipment, fixtures and measuring instruments are the first condition necessary when rolling band saws.

It is also necessary to evaluate the technical condition of the equipment used, that is, identify defects and, if necessary, bring it into a condition that meets accuracy standards.

When visiting enterprises, the author often noted the absence of certain devices and control and measuring instruments or the unsatisfactory condition of the equipment used and, accordingly, the unsuccessful practice of rolling band saws.

For example, one “craftsman” tried to roll band saws without a pressure gauge on the rolling machine. At another plant, radial and axial play of the rolling roller was discovered. The reason is wear of the bronze bushing due to lack of lubricant. The two cases mentioned refer to obvious violations, but there are also hidden defects in the technology used, which are quite difficult to identify.

Equipment, devices and measuring instruments for rolling wide band saws

The Wide Band Saw Rolling Kit includes the following:

• a unit (workbench) for preparing band saws (preferably double-sided), including a rolling machine, a surface plate at least 1.5 m long, a flat anvil, a block of lifting rollers and a device for grinding the trailing edge of the band saw blade;
• a set of straightening hammers, including a hammer with a round striker, a hammer with a cross arrangement of longitudinal strikers and a hammer with an oblique arrangement of longitudinal strikers;
• a set of rulers for checking both the flatness of the blade and the straightness (convexity) of the trailing edge of the band saw blade;
• a set of templates and rulers, including an indicator, for monitoring the stressed state (degree of rolling) of the web.

It is appropriate to recall once again that the absence of any of the elements listed above will not allow high-quality rolling.

The standard equipment of the unit for preparing band saws does not include the supply of a block of lifting rollers and a device for grinding the trailing edge. Therefore, they must be manufactured and installed independently.

The lifting roller block is installed in close proximity to the rolling machine and serves to eliminate the transverse bending (groove) of the band saw blade.

The device for grinding the trailing edge of the blade is an electric motor with a grinding wheel mounted on a slide in a horizontal plane behind the surface plate. This device aligns the trailing edge, that is, eliminates its local waviness. This is a very important operation preceding the rolling of the blade, which will subsequently ensure high-quality rolling of the blade into a cone and sharpening of the teeth.

Defect detection and evaluation technical condition equipment for rolling wide band saws

First of all, it is necessary to assess the technical condition of the rolling machine, even if it is new. Practitioners say: “Why evaluate the technical condition of a new rolling machine?” The author has encountered new rolling machines in which the relative position of the rolling rollers was unsatisfactory. Therefore, even a new rolling machine should be checked.

Methods for assessing the technical condition of the rolling machine and its installation on the unit for preparing band saws are shown in the table.

No.	Controlled indicator	Allowed deviation, mm	Tool and method of control
1	Diameter of rolling rollers (upper and lower)	0,02	Micrometer. The difference in diameters of the rolling rollers is controlled
2	Parallelism of the axes of the rolling rollers in the horizontal plane	2 (at a length of 1000 mm)	Arrows 500 mm long are fixed on the shafts of the rolling rollers. In the right position, the arrows should close, then the arrows turn left. The resulting gap is measured
3	Parallelism of the axes of the rolling rollers in the vertical plane	2 (at a length of 1000 mm)	Arrows are used according to item 2, which are installed alternately vertically, first in the upper position, then in the lower position. Deviation from plumb line is measured
4	Radial runout work surface upper and lower rolling rollers	0,01	Magnetic stand with dial indicator
5	Hardness of the working surface of the upper and lower rolling rollers	2HRC	Hardness tester
6	The size of the major axis of the ellipses formed as an imprint on the plate from the top and bottom sides	5,0	A copper or aluminum plate is compressed between the rollers of a rolling machine. The pressure is removed and the major axes of the ellipses of the resulting impressions (prints) are measured with a caliper.
7	Parallelism of the plate clamped in the rolling rollers to the surface of the table plate on which the rolling machine is installed	2 (at a length of 200 mm)	Between the rollers there is a flat plate of 300x200 mm made of a saw blade. A height gauge is used to measure the difference in distances between the edges of the plate and the surface of the table plate on which the rolling machine is installed
8	Radius of the working surface of the rolling rollers in the axial section		Radius pattern
9	Assessment of the condition of the working surface of rolling rollers		Visual inspection using a magnifying glass for dents, chips and other damage
10	Installation of the working surfaces of the surface plate, anvil and lower rolling roller in the same horizontal plane	0,1	For control and installation, a 2 m long straight edge is used

Please note that the assessment according to indicators 6 and 7 is an indirect control of the condition of the rolling rollers and their relative position, but quite sufficient for the practice of rolling band saws.

To perform the test according to indicator 8, a radius template is made, which is a part of a ring machined on lathe. The gap between the working surface of the rolling roller and the template indicates wear or plastic deformation of the working surface of the rolling roller and the need to regrind it.

When assessing the condition of the working surface of the rolling roller (indicator 9), it is necessary to pay attention to risks, dents, chips and other damage - they are not acceptable.

Integral (general) assessment of the good technical condition of the rolling machine and its correct installation on the unit for preparing band saws is the flatness of the band saw blade, that is, the absence of residual deformation of the band after rolling, leading to loss of flatness of the band saw blade.

Of course, identifying defects in band saw rolling equipment is quite a complex job and requires certain skills and practice.

I hope that the material presented in the article will help technical specialists in carrying out this work. If necessary, you can contact the author for advice and technical assistance.