22.05.2015

Purpose and types band saws

Band saws are the cutting tool of band saws: carpentry, dividing and log saws. The saws used in these machines differ only in size, tooth profile and are divided into three types: carpentry (narrow), dividing (medium) and log saw (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 sawing of boards, beams, logs and board wood materials.

Design of band saws

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 dimensions 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 maintain the total tooth pitch at the soldering point.
Band saw thickness depends on the diameter of the saw pulley and must satisfy the dependencies

The value of bending stresses depends on the ratio of the thickness of the saw and the diameter of the pulley, which in the general balance of stresses have a large specific value. The magnitude of the stress from the bending of the saw

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

The tensile strength at the soldering point does not exceed 70-80 kgf/mm2. Therefore, with a minimum margin of safety equal to 2, the stresses in a working saw should be less than 35-40 kgf / mm2. In this regard, tend to use the smallest possible thickness of the saw and large diameters of the saw pulleys.
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. When choosing the width of joiner's band saws when sawing out 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 saw width

Wider saws will flex in cross section, causing them to gouge and even slip off the pulleys.
For sawing parts with a very small radius of curvature, jigsaw machines are used, in which jigsaws are used as a cutting tool. 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 face: α = 5/10°, β = 40/45°. The dimensions of carpentry, dividing and log saw band 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 back edge (Fig. 41.6). Reciprocating saws with tooth profile I are used when sawing hard and frozen soft woods, with tooth profile II - when sawing soft woods. The dimensions of the teeth of band saws depend on their thickness, width and sawing conditions.

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

For reciprocating and log saw band saws, the tooth dimensions are (mm):

For saws with a set tooth, 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 decreases and the pressing force in the horizontal plane decreases, which shifts the saw from the pulley. However, with an increase in the front angle γ, it is necessary to take into account the properties of the material being sawn and the strength of the tooth, which depends on its dimensions and the angle of sharpening β. The angle γ should be kept within 20-35°.

Band saw soldering

Welding of band saws is carried out in case of preparation of new saws from a rolled band, repair of 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 is half the distance between the tops of adjacent teeth of the soldered saw. To do this, before cutting, the saw is marked with a ruler, square and scriber.
Marking and cutting out defective places (when repairing a saw) must be done according to the scheme shown in Fig. 42. The width of the seam B depends on the thickness of the saw s and is approximately taken equal to 105. After marking, the saw is cut along the marked lines ab and cd with scissors or a chisel. The cut ends are straightened with a hammer on the anvil and cleaned with a file. The ends of the saw are soldered with an overlap. To keep the thickness of the soldered seam equal to the thickness of the saw, its ends are beveled (chamfered) within the marked strip. Chamfering is performed manually with a file on a special device, or on milling or grinding machines. The honed ends are carefully cleaned with sandpaper and degreased.
The ends of the saws are soldered in special presses with soldering bars, electric soldering machines or flames. blowtorch. Presses with soldering bars are heated up to 830-1000°C in PM-6 muffle furnaces. The ends of the saw to be soldered are installed in a soldering press, and solder is laid between them in the form of a plate with a thickness of 0.075-0.15 mm, together with a flux - dehydrated borax. The flux is necessary to protect the soldered surfaces from oxidation, as well as their better wetting. Then, heated soldering bars are inserted into the press and tightly pressed with screws to the place of soldering. After melting the solder and cooling the bars to a dark red color, they are removed, and the place of soldering 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 already heated to a temperature of 650-700 ° C. Silver solders P-Sr-45, P-Sr-65 or brass L62 with a temperature of melting point 605-905 ° C. After cooling, the soldering site 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 soldering place is rolled.

To connect the ends of the tape, you can use the method of butt welding using ASLP-1 devices. The ends of the saws are cut at an angle of 90 ° C, fixed in the clamps of the welding machine, brought into contact and the current is 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 shifted even more tightly by moving the clamps until they are welded. This method has not yet been widely used, since it requires special equipment.

Straightening and rolling of band saws

At editing band saws detect and repair defects in the same way as when editing frame saws. Given the large length of the saws and their small thickness, defects should be eliminated with great care, mainly with the help of a rolling machine. The less the band saw is dressed correct hammers the longer its service life. Therefore, dressing should be resorted to in case of emergency, replacing it with rolling if possible.
Rolling band saws is performed in two ways.
The first way: symmetrical rolling is performed similar to rolling of frame saws and consists in lengthening the middle part of the blade (Fig. 43, a). Rolling starts from the middle part of the blade and ends, not reaching 10-15 mm on one side to the line of tooth troughs, on the other - to the rear edge of the saw. Rolling, straightening and quality control of the preparation of the saw is carried out on special tables equipped with a rolling machine, an anvil, a test plate and supporting rollers for moving the saw. The degree of rolling is determined by the arrow of transverse curvature when the saw is bent using a short test ruler. The sag should be approximately 0.2-0.4 mm for straight rim pulleys and 0.3-0.5 mm for convex ones. Larger deflection values ​​apply to wider and thinner bandsaws. An accurate check of the cross-curvature of the saw can be made with a convex template with a radius of curvature corresponding to a correctly machined saw. In addition, the straightness of the rear edge of the saw is checked by placing it on a test bench. flat plate and applying to the edge of a long straight ruler.
The second method of rolling band saws is called cone rolling (Fig. 43, b). Rolling starts at a distance of 15-20 mm from the line of tooth cavities. Closer to the rear edge of the saw, the pressure of the rollers is increased. The last track of the rolling rollers must be located no further than 10 mm from the rear edge. As a result of this, the cutting edge is shorter than the rear and, when pulled, receives greater stresses than the rest of the saw. The back edge of a saw that is tapered and placed on a flat proofing plate will be located in an arc of a circle with the center placed towards the teeth. The value of the convexity of this edge over a length of 1 m serves as a characteristic of the degree of rolling. The bulge arrow is determined by 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 big values refer to wider saws. If a part of the blade along the length of the saw has a convexity greater than required, this place must be rolled with an increase in the pressure of the rollers from the rear edge to the cutting one. 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 heating is uneven across the width of the blade.

Installing band saws in the machine

The normal operation of a band saw depends not only on the quality of the preparation of the saw, but also on its correct tension and installation in the machine. For this, the following conditions must be met:
1. The band saw during installation and operation should 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 should be sufficient to ensure its rigidity in the lateral direction and, on average, be at least 5-6 kgf/mm2.
3. Guide vanes for the saw must be fitted and adjusted to the saw with a gap not exceeding 0.1-0.15 mm.
To prevent the saw blade from moving along the pulley due to the horizontal components of the cutting forces, the discrepancy between the resultant tension of the saw and its center line, heating the saw, etc., a number of preventive measures are used. Saw pulleys are made with convex rims, while the bulge is not located in their middle, but closer to 25-40 mm to the cutting edge. Flat pulleys to prevent slipping of the tape are tilted (on the worker) relative to the horizontal axis at an angle of 10-15 ", and the saws are rolled into a cone. In addition, most modern machines allow you to turn the upper pulley around its vertical axis due to the lateral displacement of the front support of the pulley shaft. Such a turn (with the working branch outward) allows you to hold the saw with strong heating and cutting during inside. Guide vanes make it possible to protect the saw from strong lateral bends, slipping from the pulleys and dampen resonant vibrations. In the process of work, it is necessary to carefully monitor the cleanliness of the surfaces of the saw pulleys, promptly cleaning them from dust, sawdust, resin, etc.

Technical requirements for band saws

Limit deviations in the dimensions of band saws should not exceed the values ​​\u200b\u200bspecified in Table. 26.

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

1. Requirements for band saws.

Saws must be cleaned of anti-corrosion grease, dirt, tarring and wood deposits formed during operation. The grease is removed with kerosene or solar oil, after which the saws are wiped dry with a rag. The deposits of wood are cleaned with a metal scraper, moving it along the canvas, with a sandpaper.

When preparing a band saw for operation, it is necessary to perform a number of technological and control operations, a list of which is given in table 1.

The preparation of new and used band saws differ in the number, sequence and composition (volume) of operations. At "DZDS" in the preparation of new saws, almost all technological operations are carried out in full. The composition of operations for the repair of saws depends on their actual condition, which is determined during the current control after each period of operation.

Table 1

Band saw preparation operations

Technological operations of preparation and control of band saws

After a period of operation

1. Checking the web for compliance with technical requirements in accordance with GOST 6532-77, GOST

2. Joining the ends of the web (welding)

3. Connection quality control

4. Quality control of the dressing of the web (operational)

5. Control of the state (straightness) of the rear edge (in the initial state, current)

6. Grinding the back edge of the blade (ensuring straightness)

7. Control of the tension state of the web (in the initial state, current)

8. Creation of a normalized stress state (rolling, etc.)

9. Control of the tension state of the canvas

10. Monitoring the condition (wear) of the tips of the teeth (current)

11. Teeth sharpening

12. Quality control of tooth preparation (operational)

Note 1: Operations marked with a “+” sign are mandatory, with a “0” sign - if necessary.

It is necessary to remember and strictly observe the basic principle of preparing band saws - the gradual implementation of technological operations. In fact, each preparation operation is performed repeatedly in a closed cycle: control of the initial or current state of the saw - technological operation of preparation - quality control of the operation - repetition of the technological operation in the corrected mode. Monitoring the initial or current state of the band saw allows you to refine the volume necessary work and correct the mode of execution of the technological operation for the entire web or its individual sections.

2. Technological operations in the preparation of new saw blades.

2.1 Preparing new saw blades for splicing.

2.1.1 Unwinding a roll of band saws.

Rice. 1. Devices for unwinding a band saw in a roll:

a - with clamps; b - with support rollers; c - with a horizontal rotating table; g - with external ties (unwinding from the inside); 1 - base; 2 - a roll of a band saw blade; 3 - clamp; 4 - lower support roller; 5 - threaded rod; 6 - removable frame with rollers; 7 - rotating table; 8 - vertical roller; 9 - screed on the outer surface of the roll.

Unwinding a roll of band saw blades is carried out on the devices shown in Figure 1 (the device under item (b) is used at the factory). The use of such a device allows you to make the operation of unwinding the roll convenient and safe. Anti-corrosion grease is removed from the piece of fabric with scrapers. The remains of the lubricant are removed with a cloth soaked in kerosene or solar oil, then the canvas is wiped dry.

Rice. 2.: Scheme of connecting the ends of the band saw blade:

a - marking the ends of the segment of the canvas; 1 - the left end of the canvas; 2 - the right end of the canvas; 3 - saw pulley; 4 - the direction of the chamfers at the place of welding of the saw blade.

2.1.2 Preparatory operations before welding the web

Before welding (joining) the blade of a new saw, preparatory operations are necessary: ​​marking, cutting the blade to size along the length of the saw, grinding the bevel at the ends of the blade. The markup scheme and parameters are determined according to Fig.2.

Value l=(t+s)/2, where t-tooth pitch, mm; S-thickness of the saw, mm;

This formula is used for semi-automatic shielded welding.

This marking allows you to keep the pitch of the teeth at the junction and provide a favorable location for welding (in the middle of the pitch of the teeth). Next, we put the square on the end of the saw to be cut so that one side of it exactly coincides with the line of the back of the saw. We place the second working face of the square at a distance of half a step (t / 2) from the top of one of the teeth of the saw, and draw a line for cutting the saw with a scriber.

We cut off the end of the saw strictly along the marked line on lever or guillotine shears. The cut edges are filed, the burrs are cleaned. Perpendicularity is checked with a square. Tolerance 0.05:100 mm length. Mark the length of the saw according to the drawing and, as in the first case, we apply the square with one side to the back of the saw, and the other at a distance of half a step from the top of the nearest tooth. We draw a cutting line with a scriber and cut off strictly along the line the second end of the saw on lever scissors. We clean the burrs with a file and, if necessary, correct the cut so that the cut line is strictly perpendicular to the back of the saw.

2.2 Welding new saw blades.

Currently, DZDS for welding new saws uses a semi-automatic welding model: MIG - 107, it is possible to use a semi-automatic model: Bimax 152 Telwin-Italy. The welding unit is set up for welding saws of this size (German saws are used at the factory: b=130 mm, HRC=41 units, t=1.2 mm.) in accordance with the manual for the unit.

We put the saw prepared for welding on the table of the welding fixture with the back of the saw close to the stop bars of the table. The clamping bars of the fixture together with the welding head must be hinged forward as far as they will go. We firmly press the left end of the saw with the back against the table stop bar. The end of the saw should be in the middle of the groove in the base at the base of the copper plate (see fig. 3). The ends of the saw are moved away from the thrust bars by 0.3-0.5 mm. Teeth clearance » 0.

Rice. 3.: Saw Welding Attachment:

1, 7 - mounting plates; 2 - saw blade; 3 - gap between the ends of the canvas; 4 - clamping bar; 5 - electric heater (furnace); 6.8 - gaskets for setting the gap; 9 - nuts for fastening the clamping bars

Setting up the welding unit is carried out in the following order:

a) We insert the nozzle of the welding torch into the special terminal clamp of the right clamping bar so that the distance from the saw is approximately mm and the inclination of the nozzle is 5¸7 ° ​​in the course of welding (see Fig. 4). The welding wire should protrude from the nozzle by 3¸5 mm and be in the middle of the seam.

b) To the back of the saw at the beginning of the welding place and to the tooth at the end of the welding place, put small pieces of the saw blade with dimensions of 10x10 mm closely.

c) We distill the welding torch to the starting point of welding so that the end of the welding wire is above the attached plate.

d) We turn on the preheating of the saw and, by the colors of tint, we observe the heating of the ends of the saw. After waiting for the saw ends to be welded to heat up to a gray color (250¸300 °), and the heating will be uniform in width, turn on the welding torch movement button and the welding current button. Through the shield of the welder, we observe the process of formation of the seam.

e) After the end of welding, turn off the torch movement buttons and the welding current button, inspect the seam and evaluate the quality (normative seam width 7 ¸ 8 mm). If there are minor shells and lack of penetration, we brew these places.

And now we give some welding modes:

Wire feed speed - mode 3 (1.5 cm / sec.)

Welding wire - copper-plated d=0.8 mm. The supply of carbon dioxide is determined by trial welding of saw pieces.

Rice. 4. Welding torch

2.3. Weld cleaning.

After welding, the web connection must be cleaned. Grinding tolerance 0.05 mm, i.e. t = 1.2 +/- 0.05 mm.

Cleaning of the connection on both sides of the blade is carried out by buckling the saw on a convex rubberized template using a grinder (pneumatic; electric - CASALS PROFESSIONAL models - Germany), then manually with a flat file (see Fig. 5).

Rice. 5. Scheme for stripping the saw joint:

a - manual grinder; b - by means of a file; 1 - tile; 2 - band saw; 3 - stand (100 mm high) on a rubber base; 4 - grinding wheel; 5 - file; 6 - rolling rollers.

To reduce deformations of the joint sections, a flat grinding wheel with dimensions Æ152´3´22 ​​is used. Grinding is carried out by the periphery of the circle. During the initial stripping, the rear edge of the web is also processed at the welding site.

2.4 Annealing of the weld after welding.

Heat treatment of the welded seam begins immediately after stripping. Weld seam is annealed in a special slotted electric furnace. Now we give some recommendations for the heat treatment of the seam:

a) The furnace before annealing the saw is connected to the electrical network and heated to a temperature of t=350-400°C.

b) We put the welded saw into the furnace preheated to t = 400 ° C so that the weld fits into the groove of the lower and upper halves of the furnace.

c) We close the upper half of the electric furnace and for better thermal insulation we lay the plane of the connector with an asbestos cord.

d) On the indicator device, a task is set to heat the furnace spirals to t \u003d 630-660 ° C and hold at this temperature for 6-7 minutes. Turn on the furnace with the “Annealing” button and wait for the specified time. After the set time has elapsed, the oven should automatically turn off.

e) After turning off the heating, the temperature in the furnace is monitored. Upon reaching the temperature t=350-400°C, the oven can be opened, the saw removed and further cooled in air.

f) In case of failure of automation, the saw is annealed in manual mode according to the same scheme: heating to t \u003d 630-660 ° C and holding at this temperature for 6-7 minutes. Further, lifting the asbestos cord, they look at the colors of tarnish on the saw. If a narrow dark blue strip appears on both sides of the saw behind the furnace contour on the protruding ends of the saw, then the annealing can be considered complete, if there are no tinting colors, you need to continue heating until a dark blue strip appears. Then the heating is turned off, the saw is cooled together with the oven to t=350-400°C, the saw is taken out of the oven and cooled in air until completely cooled.

g) Saws with a width of more than 100 mm are recommended to be annealed in a gas burner flame. Annealing is carried out in the same thermal regime. The fixture, where the saw is placed, is heated by the flame of the burner to t=300°C, then the saw is placed in the fixture, clamped and slowly heated to t=630-660°C, observing the tint colors. The burner must be moved back and forth so that the heating is uniform and the saw does not warp. The duration of heating at t=660°C should be 7-10 minutes. Further, reducing the flame or moving the burner away from the seam, gradually reduce the temperature to t = 350-400 ° C, and then cool the saw in air. Such annealing should be carried out by an experienced welder, since it is necessary to visually determine the annealing temperature by the color of the tint.

According to the heat treatment experience obtained as a result of experiments (example, Vladimir), the annealing of the weld is as follows:

Rapid heating of the near-weld zone in a closed furnace up to t=300°C for 1 min.

Heating from t=300°C to t=400°C for 3.5 min.

Cooling from t=400°C to t=390°C for 1 min.

Heating from t=390°C to t=405°C in 15 sec.

Cooling from t=405°C to t=390°C in 30 sec.

All annealing modes are repeated 2 times.

During annealing, recrystallization occurs - the formation of new grains. As a result of annealing, welding stresses are reduced, and a fine-grained structure of the weld and heat-affected zone is formed, which has more stable and high plastic properties than a coarse-grained structure.

2.5 Final cleaning, editing and quality control of the connection.

The final cleaning of the joint zone is carried out with a flap grinding wheel Æ115´22. The last step in the processing of the near-weld zone is the sanding of the fabric on both sides until the color of the base metal is achieved with a fine-grained sandpaper. After stripping the connection of the web, it should be edited. Dressing the joint is essential to the operation of the saw. A properly aligned joint and adjacent heat-affected zones must be perfectly flat when inspected on a surface plate (tolerance no greater than 0.04 mm). The joint of the band saw is corrected by rolling by stretching the tight zones located, as a rule, in the middle of the seam.

Schemes for straightening the connection and controlling the flatness and stress state of the blade section are shown in Fig. 6 and 7, respectively. Rolling traces should be located at the points of contact of the ruler with the canvas, which are marked with chalk (marker). The processed section of the web with a joint 80¸100 mm long, which is marked with transverse marks with chalk on the web (see Fig. 6). Straightening the sheet joint by rolling requires the toolmaker to have sufficient experience and quick response, since the length of each rolling track is only 80¸100 mm.

Rice. 6.: Scheme of editing the connection of the band saw:

a, b - rolling; c, d - forging; 1 - welding seam; 2 - traces of rolling; 3 - transverse marks with chalk; 4 - traces of hammer blows.

It is recommended that the joint be straightened by rolling using the following methods. The feed of the rolling machine is switched on (in our case, model PV-20M), and the front transverse chalk line on the canvas is combined with the rolling rollers in the area of ​​the intended rolling track. The handle is sharply turned with the left hand - the upper roller is lowered (pressed), as a result, rolling begins. When the rear transverse chalk line approaches the rolling roller, the handle is again sharply turned with the left hand - the upper roller rises (is pressed out). The scheme of rolling of the heat-affected zone is shown in Fig.8. On the calibration plate, the flatness of the web is also checked at the connection site.

Rice. 7.: Scheme for monitoring the stress state of the band saw in the connection zone:

a - scheme of the longitudinal bending of the canvas; b - d - the shape of the transverse deflection of the web, depending on the stress state; 1 - plate; 2 - band saw; 3 - calibration ruler; 4 - local lighting; 5 - rollers of the rolling machine; 6 - the location of the traces of rolling along the width of the canvas.

Rice. 8. Schemes of rolling the heat-affected zone and the main sheet.

When rolling the joint, as shown in the diagram (Fig. 8, a), the first traces are applied along the axis of the web, and then alternately along one trace symmetrically to the central one, one towards the serrated, the other towards the rear edges. Rolling is carried out in 5 tracks, the distance between which is 10 mm.

Bulges of small extent should be corrected with light blows of a cruciform hammer (Fig. 9, b), after placing a piece of paper. The blows are carried out from the center of the tuber to its edges, while the striker should be located with its elongated part either along or across the blade and never at an angle, since this causes the saw to twist.

Rice. 9.: Set of hammers for forging and straightening saws:

a - with a round striker; b - with a cross arrangement of longitudinal strikers; c - with an oblique arrangement of longitudinal strikers

Regardless of the methods used, the dressing and cleaning of the joint area of ​​the band saw is carried out very carefully. A well-finished joint should have a higher flatness than the rest of the saw blade. With a deviation from flatness within 0.1¸0.2 mm, the saw connection becomes short-lived. A band saw with this connection quickly wears out the guide bushings on the band saw. To reduce the load on the joint of the band saw, the teeth adjacent to the joint are not subjected to broadening of the peaks during subsequent preparation.

The indicators of the quality of the connection of a band saw are tensile strength, bending resistance, hardness of the seam and heat-affected zones, the thickness of the connection. In practice, they are limited to the control of strength indicators and hardness of the joint. Strength and hardness indicators are determined on workpieces 100 mm long, cut out and saw blades of the greatest width. Bending tests before the appearance of cracks are performed in two ways (Fig. 10). According to the first method (Fig. 10, a), the sample clamped in a vise with copiers is bent to the right and left by 90 ° until a break. If no cracks are observed on the sample, then the canvas is suitable for work. A sample from the same saw blade, heat-treated in the same way as a welded sample, is taken as a reference.

According to the second method, the sample is clamped in a vice so that the middle coincides with the upper edge of the jaws (Fig. 10, b). Then, with hammer blows, the sample is bent until a crack (break) appears. The seam is considered normal if the bending angle before the appearance of a break is a³25°¸30°. At DZDS, 1 method is practiced.

Rice. 10.: Scheme of testing the connection of a band saw for bending:

a - manually; b - with a hammer; 1 - wooden handle with a slotted slot; 2 - sample with a joint; 3 - the center of the sample connection (seam); 4 - steel copier; 5 - bench vise; 6 - hammer; 7 - the position of the upper part of the blade at a break.

2.6 Creating a stress state in the canvas.

The normalized state of the blade increases the efficiency of the band saw. Blade rolling is the main way to create normalized residual stresses in a band saw. For this, thermoplastic processing is also used.

Tensile stresses created on the edges of the blade by rolling provide a stable position on the machine pulleys and in the cut when cutting wood, increased rigidity of the serrated edge, and compensate for the thermal stresses that occur on the serrated edge of the saw during operation.

The stress state of the band saw blade is characterized by the following indicators: 1) the sign, magnitude (arrow) and shape of the transverse deflection of the section of the blade longitudinally bent along an arc of a circle - indicator f; 2) the curvilinearity of the (convex) rear edge of the sections of the canvas located on the calibration plate - the indicator m.

Longitudinal bending of the web during the control of the stress state is performed on the "DZDS" in several ways (Fig. 11). Experienced toolmakers check the buckling of the blade when lifting a section of the blade with their left hand to a certain height, measurements are taken right hand using a ruler-template in the zone of concavity of the web near the line of contact with the surface plate.

Rice. Fig. 11.: Scheme for monitoring the stressed state of the blade in terms of f at buckling of the saw: a - on a calibration plate with a lining; b - on a fixture with pins; c - on a fixture with a radius template; 1 - saw blade; 2 - ruler; 3 - lining; 4 - the line of the beginning of the lifting of the canvas; 5 - calibration plate; 6 - bottom pin; 7 - top adjustable pin; 8 - the base of the device; 9 - radius template.

Other methods of web buckling (Fig. 12, b, c) make it possible to provide a constant radius of web buckling in the area of ​​measurement of the f index, so they are preferable. Also, the f indicator is measured visually using templates and indicator rulers (see Fig. 13, a - f).

At present, the pulleys of band saw machines of the LLK-1, LLK-2 models began to be produced at DZDS with a working part in the form of a sphere - this is due to the specifics of the saw operation, its stable position on the pulleys. Taking into account the inclination of the pulleys, the rear edge of the band saw is lengthened, i.e., the saw is rolled into a cone. Elongation of the rear edge leads to its convexity, which is estimated by the indicator m.

Rice. 12.: Rulers for monitoring the stress state of the band saw in terms of f:

rulers - templates: a - from a straight line; b - convex; c - convex and concave edges; indicator lines; d - for measuring transverse concavity; d - with mobile supports; e - based on a caliper.

An exemplary technology for rolling band saws, produced on a machine model PV-20M, consists of the following steps:

a) Before starting the rolling of band saws, the wear of rollers with a radius of curvature R = 105 mm is checked. Moreover, the upper and lower rollers must have the same diameter (a difference in diameter of not more than 0.02 mm is allowed) and a profile, otherwise the saw blade will receive deformation in the form of a bulge from the side adjacent to the roller of a larger diameter or with a large radius of curvature in the axial section. If the condition of the working surface of the rolling rollers is unsatisfactory, it is necessary to carry out a repair, which consists in turning on a lathe and subsequent fine-tuning of the working surface of the roller by manual grinding with sandpaper with clearance control according to the template (Fig. 14).

b) The rolling of the web begins with the processing of the seam

zones with a width of 120-130 mm, for this we place the welded and cleaned saw in a special device with a rolling machine. We have the saw teeth from the machine, the inclination of the teeth is against the movement of the saw.

Rice. 13.: Checking the profile of the working surface of the rolling roller for clearance according to the template:

1 - mandrel; 2 - rolling roller; 3 - template.

c) We start rolling with rollers along the length of the web from its middle, and then alternately from its middle on both sides of the center line. Sequence of passes, rolling forces for the heat-affected zone and the main blade of the band saw (Fig. 8).

d) The pressure of the rollers is also reduced symmetrically from the middle to the edges of the web. As a result of such rolling, the tension of the middle part is obtained, which uniformly decreases towards the edges of the saw, and the internal stresses on the edges are the same in sign and equal in magnitude. The control is carried out by applying a straightedge across the curved blade along the entire length of the saw. The amount of bending of the saw should be the same at all measurement points and equal to the radius of the sphere of the saw pulleys (see Fig. 16). As you can see from the diagram, the optimal clearance for our saws should be in the range of 0.2 - 0.3 mm.

It must not be assumed that the part of the web adjacent to the leading edge does not have excessively small residual internal tensile stresses. In this case, the saw will wander in the cut and tend to slide off the pulleys. A properly flared saw should be perfectly flat when not bent. When applied to the surface plate, the saw must lie without squealing along its entire length. The leading and trailing edges must have the same tensile stresses along their entire length.

The alignment operation, i.e., the elimination of defects, should be carried out sequentially on separate sections saws up to 1m long. Having finished processing one section, you should start rolling the next one. Permissible runout of the saw on the pulleys should not be more than 1-2 mm / rev. According to Vladimir experience, the maximum deflection of the saw along the entire length of the blade is 0.2¸0.3 mm £ 0.4 mm. The concavity of the trailing edge of the saw is not allowed.

Rice. 14. Saw pulley profile diagram

e) The results of rolling are checked using a straightedge sequentially on each meter of the web.

Note 1: The recommendations of foreign firms for band saw rolling are close to domestic ones and boil down to the following: rolling starts from the middle line of the blade with the greatest effort; subsequent traces of rolling are applied symmetrically to the central one with a gradual decrease in the pressure of the rollers (according to the profile of the saw pulley); the distance between the tracks should be within 10 ... 20 mm; extreme traces of rolling should be located no closer than 20 mm from the line of the cavity of the teeth and the back edge of the blade. The stress state, as well as the flatness of the rolled new saw, is controlled after a blank run-in on a band saw for 30 minutes.

2.7 Preparing the teeth of the band saw

2.7.1 General information about tooth preparation

The preparation of band saw teeth allows for sawing wood with the least energy consumption and consists of two main operations - sharpening and flattening. After flattening the tops, the teeth are formed and their side sharpening is performed. At the factory, tooth preparation is carried out in the following sequence: new saws - rough sharpening in the profiling mode, blade rolling, 1 ... 2 passes in the clean sharpening mode, flattening, shaping, final sharpening, grinding.

Rough sharpening of new saws, or grinding of a defective layer formed during notching in the range from 1 to 1.5 blade thickness, is carried out with the following goals: to ensure that the tooth profile of the design of a particular sharpening machine matches and thereby create conditions for accurate removal of a small layer during final fine sharpening; eliminate negative influence notches for cracking during flattening of the tops of the teeth and during operation - in the hollows of the teeth; remove compressive stresses from the notch in the cavity of the teeth, which allows you to create the necessary conditions for the subsequent rolling of the web and prevent the unstable state of the change in the stress state of the web when it is sewn along the width.

During operation, the active contour of the tooth tips wears out. The tops of trihedral corners and the main cutting edge wear out most intensively. Due to wear, the microgeometry of the tooth tips changes and their cutting ability is lost. The degree of dullness is determined by the deterioration in the quality of sawing, the increase in cutting power and feed force. Directly on the saw, the degree of blunting under production conditions is determined by the glare of light reflected from the blunted peaks.

Since the serrated saw edge is a complex profile consisting of mating curved and straight sections, in order to remove metal from a thin surface, it is necessary that the combination of movements grinding wheel and saws made it possible to provide a relative trajectory that repeats the shape of the tooth profile. Grinding is performed with a combination of 2 movements: reciprocating or oscillatory movement of the grinding head parallel to the front edge of the teeth and periodic feed of the saw to the tooth pitch parallel to its longitudinal axis.

2.7.2 Pre-sharpening of band saw teeth

a) The main purpose of pre-sharpening is to prepare the saw teeth for flattening.

b) Rough and fine sharpening is carried out on a grinding machine model TCHL-2 (machining on TCPA-7 is possible). This is a universal type of machines designed for sharpening saws. different types(round, frame, tape). Such machines work with lateral grip and feed into the tooth being sharpened, while the uneven pitch on the saw does not interfere with the uniform removal of metal from the front face of the teeth (see Fig. 15). The sharpening head rotates through an angle of 26°.

Rice. 15.: Scheme of asymmetric installation of a grinding machine:

1 – grinding machine; 2 - single support under the grinding wheel; 3 - band saw; 4 - right roller support; 5 - single roller support; 6 - machine for side sharpening of teeth

c) Band saw sharpening modes are shown in Table 2. Table 2

Band saw sharpening modes

Operation

Number of doubles

grinding strokes

heads per minute

Plunging feed per pass, mm, along the edge

passages

front

Profiling (rough sharpening)

Before profile formation

Sharpening after flattening

Fine sharpening

Sanding

No filing

In order to avoid uneven turning of the teeth along the length of the saw, it is necessary to adjust the fastening of the grinding wheel only once per complete revolution of the saw. If necessary, grinding wheels are balanced in accordance with GOST 3060 - 75 “Grinding wheels. Permissible unbalanced masses and the method of their measurement”. At the enterprise, the circles are balanced using the simplest devices, which are a mandrel on supports. Supports can be prisms, disks and rollers. They can be used under the condition of strict parallelism and perpendicularity. After the sharpening of the teeth is completed, the burrs located in the area of ​​the interdental cavities are removed with a scraper, a grinding block or a trihedral file, moved along the gear rim. Cross movements are not allowed. Grinding wheels in the process of sharpening wear out, lose their original profile, blunting and “loading” are also possible. When performing all operations of sharpening the teeth along the profile and from the side of the side faces, the grinding wheels must be periodically corrected with a diamond pencil, correcting the working part of the wheel with a bar. All this is done in order to obtain profiles with maximum radii of interdental cavities and eliminate “loading”. In fact, the grinding wheel requires periodic sharpening. Grinding wheels usually rule:

a) running in with abrasive, carbide and metal discs, pencils;

b) turning with a diamond tool;

c) grinding with green silicon carbide wheels (Fig. 16).

On "DZDS" editing the circle is carried out according to method a).

Rice. 16.: Dressing grinding wheels:

a - turning; b - rolling; c - grinding.

2.7.3 Flattening and shaping saw teeth.

At "DZDS" the flattening of the teeth of new saws is carried out in 3 passes: the first two passes are carried out on a cold flattening machine of the PCFLB model manufactured by the Kirov Machine Tool Plant. After such flattening, a tooth is obtained with a broadening on each side of 0.6 ... 1.1 mm, and smallest value– for thin saw blades and hard woods. This machine works on a semi-automatic cycle. The teeth of a new saw before flattening must be straightened with the control of an indicator gauge and pre-sharpened.

Before flattening, it is necessary to apply a lubricant consisting of 50% autol and 50% solid oil to the front faces of the saw teeth (a substitute is graphite lubricant “Zh”).

The third pass (final) is carried out on the conditioner model PI-34-1, manufactured by DZDS. Here are some tips for working with the conditioner:

a) The conditioner is put on the saw, then the position of the stop and clamping screws of the conditioner is adjusted so that when the handle of the clamping screw is turned towards itself, the saw blade is clamped exactly in the middle of the body slot.

b) Next, set the conditioning roller to the specified broadening of the conditioning. This is achieved by turning the sector relative to the handle of the flattening roller, and then the flattening roller is rotated relative to the handle.

c) When installing on a tooth, the conditioner is held with the right hand by the bracket handle and pressed forward until the roller stops against the front edge of the tooth being flattened. The support bar of the handle bracket must be pressed against the tops of the teeth. Then the saw tooth is flattened, by turning the handle the conditioner is released from the saw clamp and is moved to the next tooth by the bracket handle.

d) As wear occurs, the flattening roller must be moved in the axial direction by the amount of wear, and the end of the anvil is ground as it wears. The value of the broadening of the teeth for new saws is set within 0.85 ¸ 1.2 ± 0.2 mm (see Fig. 17).

Possible flattening and molding defects and ways to eliminate them are discussed below. Asymmetric (one-sided) flattening occurs during oblique sharpening (beveling) of the edges of the teeth, which is formed due to the non-perpendicular plane of the grinding wheel to the side surface of the saw blade during sharpening, and when the side surface of the saw is not perpendicular to the longitudinal axis of the flattening roller and the anvil support surface.

The upward bending of the tip of the tooth occurs due to loose contact between the back face and the anvil support surface due to distortion of the tooth profile during sharpening with the formation of a convexity or concavity of the back face, as well as improper dressing (angle) of the working surface of the anvil (see Fig. 18).

0,85 ¸ 1.2±0.2mm

Fig.18.: Scheme of the location of the anvil relative to the tooth

These defects can be eliminated by aligning and adjusting the relative position of the saw blade, flattening roller and anvil, filling the anvil, grinding the working surfaces of the anvil and flattening roller. Partially, some flattening defects are corrected or eliminated during molding.

Rice. 19.: The shape of the top of the tooth: a - after the correct one; b, c - after incorrect flattening.

Saw teeth are molded on manual molding type PI - 35, produced in a set with a conditioner PI - 34 - 1. Molding is intended for forming flattened tips of saw teeth. In this process, equalization of the magnitude of the broadening of the tooth blades and the formation of undercut angles is achieved.

During operation, the molding is supported by the left hand on the wooden lining and cheeks, the handle is turned with the right hand. When dressing the mold on the saw, the handle must be pulled forward. The mold is put on the tops of the teeth and is slightly upset until it comes into contact with the front face of the tooth. When the handle is pulled back, the bars move apart, freeing the tooth. The amount of widening of the spatula of the teeth is measured with an indicator gauge or micrometer.

For a new saw blade, a widening per side of 0.6 ¸ 0.9 ± 0.1 mm is recommended. All saw teeth must be molded equally in both directions, the tip of the tooth must not have a bend. Breaks and cracks are not allowed. The shape of the spatula after flattening and molding must correspond to the drawing (see Fig. 20).

Rice. 20.: The shape of the band saw tooth after flattening.

Rice. 21. Band saw tooth shape after molding

a) The minimum widening of the saw for work is 2.35 mm;

b) Flattening and shaping must be strictly symmetrical about the axis of the saw;

c) The tooth is flattened to a size of at least six times;

d) Tolerance for deviation from the size of flattening and forming 0.05 mm per side;

e) Size after flattening: 3.15¸3.25 mm, size after molding 2.55¸2.65 mm.

2.7.4 Jointing saw teeth after flattening and shaping

The teeth of the saws are jointed to align the height and width of the set, i.e., to ensure the normal operation of the saw.

Jointing of band saws is done manually with a flat personal file or whetstone fixed in a special holder. To even out minor molding deviations, the sides of the saw teeth are also jointed. Lateral jointing of teeth is allowed only in small sizes in the range of 0.05 ¸ 0.15 mm.

2.7.5 Final sharpening of saw teeth

After jointing the teeth, the saw is finally sharpened. There are 3 methods of sharpening: the first is the grinding of a part of the metal from the front face of the tooth; the second - from the back face of the tooth; the third - simultaneously with the front and rear faces. The third method is the most rational, and therefore the most common. Sharpening is also carried out on the machine model TCHL - 2.

Sharpening is recommended to be carried out with a Bakelite-based wheel, hardness “C” and grit 80¸100 units in one or two passes. In this case, the surface to be sharpened is ground with minimal chip removal: a depth of not more than 0.01 mm. The recommended cutting speed is 22¸25 m/s, the wheel thickness is at least 10 mm, so that the radius of curvature is at least 5 mm.

To improve the quality of sharpening, it is recommended to additionally grind the teeth manually with a fine-grained whetstone fixed in a special holder. You need to drive the whetstone from the bottom up, pressing it against the edge to be sharpened. Grinding removes small burrs, sharpening irregularities and risks, which increases the durability of the saws by 15¸20% and improves the quality of the cut.

The final sharpening must meet the following requirements:

a) all teeth must have the same profile, i.e. the same pitch, height, angles and other parameters;

b) the tops of the teeth should be located in one straight line;

c) the bottom of the depressions between the teeth should have a smooth rounding. Sharp corners are not allowed.

d) saw teeth should not have twists, breaks and bluing of the tips, burrs on the edges and other defects;

e) the front cutting edge of the teeth must be perpendicular to the side plane of the saw;

e) sharpened teeth should not have a shine on the corners formed by the intersection of the edges. Shine indicates uncut areas;

g) there should be no visible scratches on the edges of the teeth and the bottom of the cavity, since they are concentrates of local stresses.

h) a sharpened saw is lightly smeared with a cotton swab moistened with machine oil on both sides, tied in two places with linen twine, and stored in this position in a warehouse.

2.8 Installing the saw on the machine and repairing the saws.

Band saws are selected taking into account the parameters of the band saw. The thickness of the band saw should be 0.0007 ... 0.001 of the saw pulley diameter. The band saw on the machine must be tensioned with a force that provides the necessary rigidity of the blade.

The saw is installed on the pulleys so that the tooth cavities protrude beyond the edge of the pulley by 5 ... 10 mm. After tensioning the saw and turning on the electric motor of the cutting mechanism for a short time (until the saw stabilizes when it is idling), if necessary, adjust the slope of the upper pulley. The final position of the saw on the pulleys is controlled by a ruler. The idle operation of the saw is 30 minutes. Next, the flatness, runout of the rear edge and the rigidity of the saw blade in the cutting zone are checked.

When sawing resinous wood, water or air cooling and saw lubrication are used. The scrapers on the pulleys and a wooden chipping block should always be in good condition to prevent sawdust from getting between the saw and the lower pulley of the machine.

Repair of band saws includes the following operations:

a) hang the used saw on the rolling stand;

b) the saw is cleaned with rags soaked in diesel fuel;

e) saws with a width of ³65 mm from the jagged edge and a crack length L£ Lsaws / 2 are maintainable, where Lsaws is the length of the saw.

d) check for cracks in the tooth cavity and on the back of the saw. If there are cracks, then you need to punch a hole with a depth of 0.1¸0.2 mm at the end of the crack. If there is a crack ³ 35 mm, it is welded on a semi-automatic welding machine. Next, the saw is rolled according to the example of rolling the near-weld zone.

e) check the transverse bending of the saw, if the deflection is £ 0.3, then the saw must be rolled (2¸3 tracks, the maximum rolling load on German saws is 14¸15 atm.

f) saw tooth broadening is controlled: the minimum value for sharpening is 2.35 mm, if the value< 2,35 мм, то зубчатая кромка срезается и плющится заново.