Rolling machine for band saws. Band saws Technical requirements for band saws
11. Preparation of band saws: rolling, sharpening of teeth, repair of saws.
Rolling is an operation, as a result of which useful internal stresses are preliminarily created in the saw blade (before installation in the machine), increasing the transverse rigidity of the saw, created by its tension on the machine pulleys. With symmetrical rolling, three to five tracks are rolled in width from the middle to the edges: the extreme tracks are at a distance of 10 ... 15 mm from the tooth cavity line and from the rear (rear) edge of the saw. The correctness of rolling is controlled by transverse curvature (deflection arrow at the width of the tape) with a special template. The deflection of a normally rolled saw is 0.15 ... 0.3 for cylindrical pulleys of the machine, 0.4 ... 0.6 mm for barrel-shaped pulleys (higher values \u200b\u200bare related to thinner and wider saws).
The sharpening of the teeth of band saws is carried out on TchL machines with corundum wheels of a flat 45 ° conical profile (ZP) with a grain size of 40 ... .25 on a bakelite (B) bond with a hardness of C1 - ST1. The wheel thickness is 0.2,..0.33 tooth pitches. Good quality provides the following mode of sharpening: circumferential speed of rotation of the circle
20.. .25 m/s; infeed in one pass 0.02.. .0.06 (up to 0.1) mm; number of passes 4.. .6 (up to 7).
The finishing of the teeth consists in grinding the front and back faces with a fine-grained whetstone, fixed in a special holder. The durability of a saw with adjusted teeth increases by 15...20%. Finishing is performed using a manual device.
Repair of band saw blades includes localization of cracks, cutting out defective zones of the blade and preparation of segments of inserts. Localization is subject to single cracks with a length of not more than 10-15% of the width of the saw, but not more than 15 mm. Localization is carried out by drilling holes with a diameter of 2 ... 2.5 mm at the end of the crack.
In the presence of single long cracks, as well as group cracks (4–5 pieces over a length of 400–500 mm) and two teeth broken in a row, the defective place is cut out. The length of the cut should be at least 500 mm in order to avoid difficulties when straightening.
12. Installation of band saws: tension methods, guides, adjustment of pulleys.
1. The cutting edge of the saw should protrude beyond the edge of the saw pulley by a tooth height.
2. The shift of the tape along the pulleys is prevented by adjusting the position of the axis of the upper pulley (together with the pulley) in the vertical (tilt forward - backward) and horizontal (turn left - right) planes. The angle of inclination of the pulley forward (on the worker) is 0.2–0.3 °.
3. The tension force of the saw, N, total for both branches of the tape, is set depending on the width and thickness of the saw:
where σ is the tensile stress in the section of the tape (50–60 MPa); a, b- width and thickness of the tape, mm.
4. The gap between the guides and the saw should be 0.1–0.15 mm. The contact of the saw with the guide devices is only allowed when sawing out curved parts.
5. During operation, the band saw should not have wave-like movements and make vibrating sounds. The tension force should be minimal to exclude these phenomena.
6. Do not allow the saw to run idle for a long time. During long stops of the machine, the tension from the saw should be removed.
7. It is necessary to regularly clean the saw blade from resin, dirt, sticking sawdust.
8. In some cases, good results are obtained by lubricating saws with water, soapy water, a mixture of diesel fuel and engine oil by drop or spray method.
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. Control of the initial or current state of the band saw allows you to clarify the amount of work required and correct the mode of execution of the technological operation for the entire blade 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 grinding machine; 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 connector plane 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 correctly 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.
The 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 connection, 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 bump 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 a band saw joint are tensile strength, bending resistance, hardness of the seam and heat-affected zones, and joint thickness. 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 with the right hand using a ruler-template in the concave zone of the blade near the line of contact with the calibration 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 ensure 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 of the saw up to 1 m 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 the 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; to eliminate the negative effect of the notch on cracking when flattening 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 fabric and prevent the unstable state of the change in the stress state of the fabric 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 toothed edge of the saw is a complex profile consisting of mating curved and straight sections, to remove metal from a thin surface it is necessary that the combination of movements of the grinding wheel and the saw makes 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 oscillating 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 machine, designed for sharpening saws of various 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 PKhFLB, produced 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, with the smallest value for thin saws and hard rocks. 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 a loose contact between the back face and the supporting surface of the anvil due to the 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 formed on a manual molding type PI - 35, produced complete with a conditioner PI - 34 - 1. The molding is intended for the formation of 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) the 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 briefly switching on the electric motor of the cutting mechanism (until the saw stabilizes its position during its idle operation), 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.
The presence of a complete set of equipment, fixtures and control and measuring tools is the first condition necessary for rolling band saws.
It is also necessary to assess the technical condition of the equipment used, that is, to identify defects and, if necessary, bring it into a condition that meets the accuracy standards.
When visiting enterprises, the author often recorded the absence of some devices 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 in the absence of a pressure gauge on the rolling machine. At another enterprise, radial and axial play of the rolling roller was discovered. The reason is the wear of the bronze bushing due to the lack of lubrication. The two cases mentioned above refer to obvious violations, but there are also hidden defects in the technology used, which are quite difficult to detect.
Equipment, fixtures and instrumentation for rolling wide band saws
The kit for rolling wide band saws includes the following:
- unit (workbench) for the preparation of band saws (preferably double-sided), including a rolling machine, a calibration plate with a length of at least 1.5 m, 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 head, a hammer with a cross arrangement of longitudinal heads and a hammer with an oblique arrangement of longitudinal heads;
- a set of rulers to control both the flatness of the blade and the straightness (bulge) of the trailing edge of the band saw blade;
- a set of templates and rulers, including those with an indicator, to control the stress state (degree of rolling) of the web.
It is appropriate to recall once again that the absence of any of the above elements will not allow high-quality rolling.
The standard equipment of the machine 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 mounted independently.
The lifting roller block is installed in close proximity behind the rolling machine and serves to eliminate the transverse bend (chute) of the band saw blade.
The trailing edge grinder is an electric motor with a grinding wheel mounted on a slide in a horizontal plane behind the surface plate. With this device, the trailing edge is leveled, that is, its local waviness is eliminated. This is a very important operation preceding the rolling of the blade, which will ensure in the future high-quality rolling of the blade into a cone and sharpening of the teeth.
Identification of defects and assessment of the technical condition of equipment for rolling wide band saws
First of all, it is required 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 met 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 the preparation of band saws are indicated in the table.
| No. p / p | Controlled indicator | Permissible deviation, mm |
Tool and method of control |
| 1 | Roller diameter (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 (on 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 to the left. The resulting gap is measured |
| 3 | Parallelism of the axes of the rolling rollers in the vertical plane | 2 (on a length of 1000 mm) | The arrows according to paragraph 2 are used, which are installed alternately vertically, first in the upper position, then in the lower position. Plumb deviation is measured |
| 4 | Radial runout of the working surface of the upper and lower rolling rollers | 0,01 | Magnetic stand with dial indicator |
| 5 | The 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 |
Between the rollers of the rolling machine, a copper or aluminum plate is compressed. The pressure is removed and the large axes of the ellipses of the resulting prints (impressions) 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 (on a length of 200 mm) | Between the rollers a flat plate 300x200 mm from the saw blade is engaged. The height gauge measures the difference in distance between the edges of the plate and the surface of the table plate on which the rolling machine is installed. |
| 8 | Working surface radius of rolling rollers in axial section | Radius Pattern | |
| 9 | Assessment of the state of the working surface of the rolling rollers | Visual inspection with 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 straightedge is used |
I would like to draw your attention to the fact that the assessment according to indicators 6 and 7 is an indirect control of the state of the rolling rollers and their relative position, but it is quite sufficient for the practice of rolling band saws.
To perform a check on indicator 8, a radius template is made, which is a part of a ring machined on a 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 for its regrinding.
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.
An integral (general) assessment of the good technical condition of the rolling machine and its correct installation on the unit for the preparation of band saws is the flatness of the band saw blade, that is, the absence of residual deformation of the blade after rolling, leading to the loss of flatness of the band saw blade.
Of course, identifying defects in equipment for rolling band saws is a rather difficult job and requires certain skills and practice.
I hope that the material presented in the article will help technical specialists in this work. If necessary, you can contact the author for advice and technical assistance.
Differ 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 the tooth. It is the saw tooth that determines the characteristics of the saw blade itself.
What to choose?
Compare narrow and wide saws.
Tearing Narrow Band Saw not such a rare occurrence. The saw became blunt, clogged in a cut with sawdust and burst, there is no longer a ring, but a piece of torn canvas is hanging on pulleys or lying around the machine. But on wide saws this is extremely rare!
Wide saws can often surprise with the appearance of cracks in the cavities of the teeth. Often this is due to the selected tooth preparation parameters (depending on the type and condition of the wood and the speed of feeding the saw blade into the log). But to break wide band saw, it takes a lot of effort.
On the narrow saws to avoid tape jamming, carry out the so-called tooth setting. 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 sawn (the straight teeth only take out their part of the sawdust), forming a cut width in which the saw body itself does not jam.
With this preparation of the teeth, each of them removes its third of the sawdust (33%).
The best preparation is when each tooth works 100%, but on narrow saws this is not possible due to the small height of the tooth. In this way, narrow saws severely limited in sawing speed due to the problem of carrying out all the same sawdust! With the cut available for a narrow band (about 2.5 mm), at the same time it does not have (unlike a wide saw) a stabilizing body, and can hang out in the cut.
With an increase in the feed rate, it will be diverted to the side, after which an overload will follow, an overpressure and, as a result, a break. And again repair (welding), and welding is shortening 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 itselfwithout forgetting the 20/80 ratio. Wide blade already from 80 mm. allows you to understand the height of the tooth, for example up to 11mm.
At the same time, with a step of 35 mm, the area of \u200b\u200bthe cavity increases by 2 times, which makes it possible to more effectively carry out 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 hardfacing!
After sharpening such a tooth, it begins to work at 100%, completely coping with the removal of sawdust. The wiring in this case 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 kerf width, the saw does not dangle, works stably at high speeds, greatly increasing productivity.
Using wide band saws, can be fine-tuned tooth parameters, changing it shape, cutting angles, as well as changing kerf width. For each species and condition of wood, you can select your optimal tooth preparation parameters, which can add up to 25% more to the sawing speed and increase the yield of finished products.
Narrow saws use simpler and cheaper equipment, and are also easier to install and pull on pulleys than win back their positions a little. wide saws. As we know, during operation, any saw heats up, especially its cutting part. The narrow belt heats up completely, as 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. In simple terms, wide saws have to be pulled several times stronger than narrow ones, because of this, the saw unit is used more complex and massive. Since the width of the saw is much larger than the cutting part, it heats up unevenly (the cutting part heats up much more than the rest of the saw). At the same time, the cutting part lengthens and weakens, which may cause a “wave” in the cut. The guide rollers in this case cannot securely hold the wide band on the pulleys, since the sawing speeds are much higher than with narrow saws, and the load on the material side 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 personnel working on this equipment.
The result of this was the use of profile pulleys and their turn 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 that part of the pulley where the cutting edge of the saw will be (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. Placement of a wide band saw on pulleys.
We roll sh heavy saws
During the rolling process, the body of the saw is rolled longitudinally with rollers harder than the saw itself under pressure. Rolling paths are formed on it. Rolling is done depending on the profile of the pulley, on which the saw will then have to work. In the process of rolling, the body of the saw acquires a deflection corresponding to the shape of the pulley. Also, which is very important, by rolling they achieve the extension of the rear edge of the saw, which corresponds to the rotation of the pulleys. The tape stretched over the pulleys repeats their shape, and the deployed pulleys pull it. During operation, the saw moves back a little towards the trailing edge and pulls up the front, compensating for the elongation of the cutting part due to heat. With the correct angle of turn of the pulleys, the rolling of the saw body and its tension, the removal of the saw from the pulleys becomes impossible.
The saw will last a long time. But do not forget that during continuous operation, the saw “gets tired”, therefore, 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 must be sharpened (a dull saw stops sawing normally and can cause problems when cutting). The pulleys must be wiped so that there are no sawdust and other debris left on them (check the condition of the scraper cleaners), since cracks may form in the center of the saw body. Also, the saw needs to be rolled over time in order to return it to the desired shape. After grinding off the flattening or welded plate, you can re-prepare the tooth and continue to work on the saw until its width is less than the allowable fit on the pulleys. Such saws, when used correctly, pay for themselves without any problems !!
Training band saws includes joining their ends by welding or soldering, control of the tension state of the saw blade, correction of defects in its shape, rolling, final control of the tension state of the saw blade.
The stresses arising in the web as a result of welding are removed by rolling.
The control of the stressed state of the saw is carried out on the basis of the deflection of the blade, similarly to frame saws. In addition to local defects, similar to frame saws (tight place, bulge, etc.), the tape can be twisted, have wingedness, 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 is not straight in the joint area, the web is cut and re-welded or soldered.
Methods for identifying and eliminating defects in band saw blades
a, b - transverse warping; c, d - wingedness; e, e - longitudinal waviness; g, h - bending of the edge; 1 - saw, 2 - calibration plate; 3 - ruler; 4 - probe; 5 - calibrated plate
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