Rolling machines for wide band saws, frame and circular saws. Preparing band saws reference book Rolling band saws
1. Requirements for band saws.
The saws must be free of anti-corrosion grease, dirt, grime and wood deposits formed during operation. The grease is removed with kerosene or diesel oil, after which the saws are wiped dry with a rag. Wood deposits are cleaned off with a metal scraper, moving it along the canvas, with a sandpaper.
When preparing the band saw for operation, it is necessary to perform a number of technological and control operations, the list of which is given in Table 1.
Preparation of new and used band saws differ in the number, sequence and composition (volume) of operations. At "DZDS", when preparing new saws, almost all technological operations are carried out in full. The scope of operations during the repair of saws depends on their actual state, which is determined during routine control after each period of operation.
Table 1
Band saw preparation operations
Technological operations for the preparation and control of band saws
After a period of operation
1. Control of the web for compliance with technical requirements in accordance with GOST 6532-77, GOST
2. Joining the ends of the blade (welding)
3. Quality control of the connection
4. Quality control of web dressing (operational)
5. Monitoring the condition (straightness) of the rear edge (in the initial state, current)
6. Grinding the back edge of the blade (ensuring straightness)
7. Monitoring of the tensioned state of the web (in the initial state, current)
8. Creation of a normalized stress state (rolling, etc.)
9. Monitoring the tension state of the web
10. Monitoring the condition (wear) of the tops of the teeth (current)
11. Sharpening of teeth
12. Quality control of tooth preparation (operational)
Note 1: Operations marked with "+" are mandatory, with "0" - if necessary.
It is necessary to remember and strictly observe the basic principle of the preparation of band saws - the gradual performance 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 preparation operation - quality control of the operation - repetition of the technological operation in a corrected mode. Monitoring the initial or current state of the band saw allows you to clarify the amount of work required and adjust the mode of performing a 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 joining.
2.1.1 Unwinding a roll of band saws.
Rice. 1.Devices for unwinding the saw band in a roll:
a - with clamps; b - with support rollers; c - with a horizontal rotating table; d - 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 of a roll of band saw blades is carried out on the devices shown in Figure 1 (at the factory, the device is used under item (b)). The use of such a device makes the operation of unwinding the roll convenient and safe. Anti-corrosion grease is removed from the section of the blade using scrapers. The residues of the lubricant are removed with a cloth soaked in kerosene or diesel oil, then the cloth is wiped dry.
Rice. 2 .: Connection diagram of the ends of the band saw blade:
a - marking of the ends of the section of the canvas; 1 - left end of the web; 2 - the right end of the web; 3 - saw pulley; 4 - the direction of the chamfers at the welding point of the saw blade.
2.1.2 Preparatory operations before welding the blade
Before welding (joining) the new saw blade, 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 marking scheme and parameters are determined according to Fig. 2.
Value l = (t + s) / 2, where t-tooth pitch, mm; S-saw thickness, mm;
This formula is used for semi-automatic welding in a protective environment.
This marking allows you to keep the tooth pitch at the joint and to ensure a favorable welding position (in the middle of the tooth pitch). 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 saw teeth, and mark out the cutting line of the saw with a scribe.
We cut off the end of the saw strictly along the marked line on lever or guillotine shears. The cut edges are filed with a file, the burrs are cleaned. Perpendicularity is checked with a square. Tolerance 0.05: 100mm in length. Mark the length of the saw according to the drawing and, as in the first case, apply the square with one side to the back of the saw, and the other half a step from the top of the nearest tooth. We draw a cutting line with a scribe 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 of new saw blades.
At present, DZDS uses a semiautomatic welding machine of the model: MIG - 107 for welding new saws, it is possible to use a semiautomatic device of the model: Bimax 152 Telwin-Italy. The welding unit is adjusted for welding saws of this standard 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 place the saw, prepared for welding, on the table of the welding device with the back of the saw close to the stop strips of the table. The clamping strips of the fixture together with the welding head must be pivoted at the hinges all the way forward. Press the left end of the saw firmly with the back against the stop bar of the table. The end of the saw should be in the middle of the groove in the base at the base of the copper plate (see drawing 3). The ends of the saw are moved away from the stop strips by 0.3-0.5 mm. The teeth have a clearance "0.
Rice. 3 .: Saw welding attachment:
1, 7 - mounting plates; 2 - saw blade; 3 - the gap between the ends of the web; 4 - clamping bar; 5 - electric heater (oven); 6.8 - spacers for setting the gap; 9 - nuts fastening the clamping strips
Setting up the welding unit is carried out in the following order:
a) 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 m and the inclination of the nozzle is 5¸7 ° in the direction of welding (see Fig. 4). The welding wire should protrude 3-5 mm from the nozzle and be in the middle of the seam.
b) To the back of the saw at the beginning of the welding spot and to the tooth at the end of the welding spot, place small pieces of the saw blade 10 × 10 mm in size.
c) We drive the welding torch to the place where welding starts so that the end of the welding wire is above the attached plate.
d) Turn on the preheating of the saw and observe the heating of the ends of the saw by the tint colors. After waiting until the ends of the saw to be welded are heated to a gray color (250 - 300 °), and the heating will be uniform across the width, we turn on the button for moving the welding torch and the button for welding current. Through the welder's shield, we observe the seam formation process.
e) After the end of welding, turn off the torch movement buttons and the welding current button, inspect the seam and evaluate the quality (standard seam width 7 ¸ 8 mm). If there are minor sinks and lack of penetration, we brew these places.
And now we will 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 on test welds of the saw pieces.
Rice. 4. Welding torch
2.3. Weld seam cleaning.
After welding, the blade joint must be cleaned. Stripping tolerance 0.05 mm, i.e. t = 1.2 +/- 0.05 mm.
Cleaning of the joint on both sides of the blade is carried out by longitudinal bending of the saw on a convex rubberized template using a grinding machine (pneumatic; electric - CASALS PROFESSIONAL - Germany), then manually with a flat file (see Fig. 5).
Rice. 5. Scheme of cleaning the saw joint:
a - 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 the deformations of the joints, a flat grinding wheel with dimensions Æ152´3´22 is used. Grinding is carried out by the periphery of the wheel. During the initial stripping, the back edge of the blade is also processed at the welding point.
2.4 Annealing the weld after welding.
Heat treatment of the weld begins immediately after stripping. We anneal the welded seam in a special slotted electric furnace. Now, here are some recommendations for heat treatment of the seam:
a) Before annealing the saw, the furnace is connected to the electrical network and heats up to a temperature of t = 350-400 ° C.
b) Put the welded saw into the oven heated to t = 400 ° C so that the welded seam fits into the groove of the lower and upper halves of the oven.
c) We close the upper half of the electric furnace and lay the plane of the connector with an asbestos cord for better thermal insulation.
d) A task is set on the indicator device for heating the oven spirals to t = 630-660 ° C and holding at this temperature for 6-7 minutes. The furnace is switched on with the "Annealing" button and the specified time is waited. After the specified time has elapsed, the oven should turn off automatically.
e) After turning off the heating, monitor the temperature drop in the oven. Upon reaching the temperature t = 350-400 ° C, the oven can be opened, the saw can be removed and then cooled in air.
f) In case of failure of the automation, the saw is annealed in manual mode according to the same scheme: heating to t = 630-660 ° C and holding at this temperature for 6-7 minutes. Next, lifting the asbestos cord, they look at the tarnishing colors on the saw. If a narrow dark blue strip appears on both sides of the saw behind the contour of the furnace at the protruding ends of the saw, then the annealing can be considered complete, if there are no discoloration, you need to continue heating until a dark blue strip appears. Then the heating is turned off, the saw together with the oven is cooled down to t = 350-400 ° C, the saw is removed from the oven and cooled in air until it cools completely.
g) Saws with a width of over 100 mm are recommended to be annealed in a gas burner flame. Annealing is carried out in the same thermal regime. The device where the saw is placed is heated by the burner flame to t = 300 ° C, then the saw is placed in the device, clamped and slowly heated to t = 630-660 ° C, observing the tarnishing colors. The torch must be moved back and forth so that the heating is uniform and the saw does not warp. The heating duration 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 tempering color.
According to the experience of heat treatment obtained as a result of experiments (for example, Vladimir), the annealing of the weld is as follows:
Rapid heating of the near-weld zone in a closed furnace to t = 300 ° C for 1 min.
Heating from t = 300 ° C to t = 400 ° C for 3.5 minutes.
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.
We repeat all annealing modes 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 a heat-affected zone is formed, which has more stable and high plastic properties than a coarse-grained structure.
2.5 Final stripping, straightening and quality control of the joint.
The final cleaning of the joint zone is carried out with a flap grinding wheel 115´22. The last stage in the treatment of the heat-affected zone is sanding the cloth from both sides until the color of the base metal is achieved with a fine-grained sandpaper. After stripping the joint of the canvas, it follows its editing. Correcting the joint is essential for the saw to function. Correctly straightened joint and adjacent heat-affected zones must be perfectly flat when checked on a surface plate (tolerance no more than 0.04 mm). The joint of the saw band is straightened by rolling by pulling out tight zones, usually located in the middle of the seam.
The diagrams for straightening the joint and controlling the flatness and stress state of the blade section are shown in Fig. 6 and 7, respectively. The warping of the joint manifests itself as a gap of various shapes between the straight edge and the blade of a longitudinally curved saw. Rolling marks should be located at the points of contact of the ruler with the blade, 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 web joint by rolling requires the toolmaker to have sufficient experience and quick reaction, since the length of each rolling track is only 80 - 100 mm.
Rice. 6 .: Saw band joint straightening diagram:
a, b - by rolling; c, d - forging; 1 - welding seam; 2 - traces of rolling; 3 - transverse marks with chalk; 4 - traces of hammer blows.
It is recommended to roll the joint using the following techniques. The feeding of the rolling machine (in our case, the PV-20M model) is switched on, and the front transverse chalk line on the web is aligned with the rolling rollers in the area of the intended rolling track. The handle is turned sharply 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 (squeezes out). The scheme of rolling of the heat-affected zone is shown in Fig. 8. On the surface plate, the flatness of the web is also checked at the joint area.
Rice. 7 .: Scheme for monitoring the stress state of the saw band in the connection zone:
a - a diagram of the longitudinal bending of the web; b - d - the shape of the transverse deflection of the web, depending on the stress state; 1 - plate; 2 - band saw; 3 - straight edge; 4 - local lighting; 5 - rollers of the rolling machine; 6 - the location of the traces of rolling along the width of the web.
Rice. 8. Schemes for rolling the near-weld zone and the main blade.
When rolling the joint, as shown in the diagram (Fig. 8, a), the first traces are applied along the axis of the canvas, and then alternately along one track symmetrically to the central one, one towards the toothed, the other towards the rear edges. Rolling is carried out in 5 tracks, the distance between which is 10 mm.
Small bulges 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 firing pin 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 straightening and cleaning of the joint zone of the saw band 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 will quickly wear out the guide bushings on the band saw. To reduce the load on the band saw joint at the teeth adjacent to the joint, during the subsequent preparation, the broadening of the tops is not performed.
Indicators of the quality of the band saw joint are tensile strength, bending resistance, hardness of the seam and heat-affected zones, joint thickness. In practice, they are limited to monitoring the strength and hardness of the joint. Strength and hardness indicators are determined on blanks with a length of 100 mm, cut and saw blades of the greatest width. Bending tests before cracking are performed in two ways (Fig. 10). According to the first method (Fig. 10, a), the sample clamped in a vice with copiers is bent to the right and left by 90 ° until it breaks. If no cracks are observed on the sample, then the blade is suitable for work. A sample from the same saw blade, heat-treated similarly to the 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 the sample is bent by hammer blows until a crack (break) appears. The seam is considered normal if the bend angle before the appearance of the fracture is a³25 ° ¸30 °. On "DZDS" 1 method is practiced.
Rice. 10 .: Scheme of bending test of the band saw joint:
a - manually; b - with a hammer; 1 - wooden handle with a slotted slot; 2 - sample with a joint; 3 - the center of the sample joint (seam); 4 - steel copier; 5 - bench vice; 6 - hammer; 7 - the position of the upper part of the blade when breaking.
2.6 Creation of a stressed state in the canvas.
The normalized condition of the blade increases the performance of the band saw. Blade rolling is the main method of creating normalized residual stresses in a band saw. For this, thermoplastic processing is also used.
Tensile stresses created at the edges of the blade by rolling ensure a stable position on the machine pulleys and in the kerf when cutting wood, increased rigidity of the toothed edge, compensate for the thermal stresses arising on the toothed edge of the saw during operation.
The stress state of the band saw blade is characterized by the following indicators: 1) the sign, the size (arrow) and the shape of the transverse deflection of the blade section longitudinally bent along an arc of the circumference - the index f; 2) curvilinearity (convex) of the rear edge of the sections of the web located on the surface plate - indicator m.
Longitudinal bending of the web during stress state control is performed on the "DZDS" in several ways (Fig. 11). Experienced toolmakers check the longitudinal bending of the web when lifting a section of the web with the left hand to a certain height, the measurements are carried out with the right hand using a ruler-template in the concavity zone of the web near the line of contact with the surface plate.
Rice. 11 .: Scheme of control of the tensioned state of the blade according to the index f during longitudinal bending of the saw: a - on a surface plate with a lining; b - on a device with pins; c - on a device with a radius template; 1 - saw blade; 2 - ruler; 3 - lining; 4 - line of the beginning of the rise of the canvas; 5 - surface plate; 6 - lower pin; 7 - top adjustable pin; 8 - the base of the device; 9 - radius template.
Other methods of buckling of the web (Fig. 12, b, c) make it possible to ensure a constant radius of buckling of the web in the area where the f index is measured, therefore they are preferable. Also, the measurement of the f indicator is performed visually using templates and indicator rulers (see Fig. 13, a - f).
Currently, pulleys of bandsaw machines of models LLK-1, LLK-2, began to be produced at DZDS with a working part in the form of a sphere - this is explained by the specifics of the saw, its stable position on the pulleys. Taking into account the inclination of the pulleys, the rear edge of the band saw is lengthened, that is, the saw is rolled onto a cone. The lengthening of the rear edge leads to its convexity, which is estimated by the index m.
Rice. 12 .: Rulers for monitoring the stress state of the saw band according to the index f:
rulers - templates: a - with a straight line; b - convex; c - convex and concave edges; indicator rulers; d - to measure the transverse concavity; d - with movable supports; e - based on a caliper.
The approximate technology of band saws rolling, produced on the machine model PV-20M, consists of the following stages:
a) Before starting the rolling of band saws, check the wear of the rollers with a radius of curvature R = 105 mm. Moreover, the upper and lower rollers must have the same diameter (a difference in diameters of no more than 0.02 mm is allowed) and a profile, otherwise the saw blade will receive deformation in the form of a bulge on the side adjacent to a roller of a larger diameter or with a large radius of curvature in the axial section. In case of an unsatisfactory condition of the working surface of the rolling rollers, it is necessary to carry out repairs, which consists in grooving on a lathe and subsequent finishing of the working surface of the roller by manual grinding with sandpaper with control over the clearance according to a template (Fig. 14).
b) Rolling of the web begins with the processing of heat-affected
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. The saw teeth are positioned from the machine, the inclination of the teeth is against the movement of the saw.
Rice. 13 .: Control of the profile of the working surface of the rolling roller in the light 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 middle line. Scheme of the sequence of passes, rolling forces for the weld zone and the main band saw blade (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 stretching of the middle part is obtained, which decreases uniformly towards the edges of the saw, and the internal stresses at the edges are the same in sign and equal in magnitude. The control is carried out by applying a straight edge across the curved blade along the entire length of the saw. The amount of bending of the saw should be the same at all points of measurements 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.
The part of the web adjacent to the leading edge must not have excessively low residual internal tensile stresses. In this case, the saw will wander in the kerf and tend to slide off the pulleys. A properly rolled saw should be perfectly flat when not bent. When applied to a surface plate, the saw should be snuggling along its entire length. The leading and trailing edges must have tensile stresses of the same magnitude along their entire length.
The leveling operation, i.e. elimination of defects, should be carried out sequentially in separate sections of the saw up to 1 m long. Having finished processing one section, you should start rolling the next. The permissible runout of the saw on the pulleys should not be more than 1-2 mm / rev. According to Vladimir's experience, the maximum deflection of the saw along the entire length of the blade is 0.2 - 0.3 mm £ 0.4 mm. Concavity of the trailing edge of the saw is not allowed.
Rice. 14. Saw pulley profile diagram
e) The rolling results are checked using a straight edge sequentially on each meter of the web.
Note 1: Recommendations of foreign firms for rolling band saws 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 groove of the teeth and the rear edge of the blade. The stress state, as well as the flatness of the rolled new saw, is monitored after idle running on a band saw for 30 minutes.
2.7 Preparing the band saw teeth
2.7.1 General information on tooth preparation
The preparation of band saw teeth allows for cutting wood with the lowest energy consumption and consists of two main operations - sharpening and flattening. After flattening the tops, the teeth are formed and sharpened laterally. At the plant, teeth are prepared in the following sequence: new saws - rough sharpening in profiling mode, blade rolling, 1 ... 2 passes in clean sharpening mode, flattening, shaping, final sharpening, regrinding.
Rough sharpening of new saws, or grinding of the defective layer formed during notching within the range from 1 to 1.5 of the blade thickness, is performed with the following goals: to ensure that the profile of the teeth corresponds to the design of a particular sharpening machine and thereby create conditions for accurate removal of a small layer during the final final sharpening; to eliminate the negative effect of the notch on crack formation during flattening of the tops of the teeth and during operation - in the cavities of the teeth; relieve compressive stresses from the notch in the grooves of the teeth, which makes it possible to create the necessary conditions for the subsequent rolling of the blade and to prevent the unstable state of the change in the stress state of the blade when it is ground across the width.
During operation, the active contour of the tooth tips wears out. The tops of the triangular corners and the main cutting edge wear out most intensively. Due to wear, the microgeometry of the tops of the teeth changes and their cutting ability is lost. The degree of bluntness is determined by the deterioration in sawing quality, an increase in cutting power and feed force. Directly from the saw, the degree of dullness in production conditions is determined by the glare of light reflected from the dull vertices.
Since the serrated 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 the movements of the grinding wheel and the saw make it possible to provide a relative trajectory that repeats the shape of the profile of the teeth. Grinding is performed with a combination of 2 movements: a reciprocating or oscillatory movement of the grinding head parallel to the front edge of the teeth and periodic feed of the saw to a pitch of teeth parallel to its longitudinal axis.
2.7.2 Pre-sharpening the saw band teeth
a) The main purpose of pre-sharpening is to prepare the saw teeth for conditioning.
b) Rough and fine sharpening is carried out on a grinding machine model TChL-2 (processing on TChPA-7 is possible). This is a universal type of machine designed for sharpening saws of different types (round, frame, band). Such machines work with lateral grip and feed into the sharpened tooth, while the uneven step on the saw does not interfere with uniform metal removal from the front edge of the teeth (see Fig. 15). The sharpening head can be rotated through an angle of 26 °.
Rice. 15 .: Diagram of the asymmetric setting of the sharpening machine:
1 - sharpening machine; 2 - single support under the grinding wheel; 3 - band saw; 4 - right roller support; 5 - single roller support; 6 - machine for side teeth sharpening
c) The modes of sharpening of band saws are indicated in table 2. Table 2
Band saw sharpening modes
Operation
Number of doubles
grinding strokes
heads per minute
Feed for plunge-cut per pass, mm, on the edge
passages
front
Profiling (rough grinding)
Before profile formation
Sharpening after conditioning
Fine sharpening
Sanding
Without filing
In order to avoid uneven grooving of the teeth along the length of the saw, it is necessary to adjust the fastening of the grinding wheel only once per full revolution of the saw. If necessary, the 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, discs and rollers. They can be used under the condition of strict parallelism and perpendicularity. After completing the sharpening of the teeth, the burrs located in the area of the interdental cavities are removed with a scraper, a grinding bar or a triangular file, moved along the gear rim. Transverse movements are not allowed. Grinding wheels wear out during sharpening, lose their original profile, dullness and “grease” 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 the maximum radii of the interdental cavities and to eliminate "greasing". In fact, the grinding wheel requires periodic sharpening. Grinding wheels usually rule:
a) by rolling with abrasive, carbide and metal disks, pencils;
b) turning with a diamond tool;
c) grinding with green silicon carbide wheels (Fig. 16).
On "DZDS" the circle is edited according to method a).
Rice. 16 .: Dressing of grinding wheels:
a - turning; b - rolling; c - by grinding.
2.7.3 Crimping and shaping of saw teeth.
At "DZDS" the teeth of new saws are flattened in 3 passes: the first two passes are carried out on a PCFLB machine for cold flattening of teeth, produced by the Kirov Machine-Tool Plant. After such crimping, a tooth is obtained with a widening on each side of 0.6 ... 1.1 mm, and the smallest value is for thin saws and hard rocks. This machine works in a semi-automatic cycle. Before conditioning, the teeth of a new saw should be straightened with an indicator gauge and pre-sharpened.
Before crimping, it is necessary to apply a lubricant consisting of 50% autol and 50% grease on the front edges of the saw teeth (the substitute is graphite grease “Zh”).
The third pass (final) is carried out on a PI-34-1 conditioner manufactured at DZDS. Here are some recommendations on how to work with the conditioner:
a) The conditioner is put on the saw, then the position of the conditioner stop and clamping screws is adjusted, so that when the handle of the clamping screw is turned towards you, the saw blade is clamped exactly in the middle of the housing slot.
b) Next, set the crimping roller to the specified broadening of crimping. This is achieved by turning the sector relative to the handle of the crimping roller, and then turning the crimping roller relative to the handle.
c) When installed on the tooth, the conditioner is held by the right hand by the handle of the bracket and pushed forward until the roller stops against the front edge of the flattened tooth. The support bar of the handle bracket should 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 by the handle of the bracket is rearranged to the next tooth.
d) With wear, the crimping roller must be moved in the axial direction by the amount of wear, and the butt end of the anvil is ground with wear. The amount of widening of the teeth for new saws is set within 0.85 ¸ 1.2 ± 0.2 mm (see Fig. 17).
Possible defects in crimping and forming, methods of their elimination are discussed below. Asymmetric (one-sided) crimping occurs when oblique sharpening (beveling) of the edges of the teeth, formed due to the non-perpendicularity of the plane of the grinding wheel to the lateral surface of the saw blade during sharpening, and when the lateral surface of the saw is not perpendicular to the longitudinal axis of the crimping roller and the supporting surface of the anvil.
The upward bending of the tooth tip occurs due to a loose touch of the back edge and the supporting surface of the anvil due to distortion of the tooth profile during sharpening with the formation of a bulge or concavity of the back edge, as well as improper threading (angle) of the working surface of the anvil (see Fig. 18).
0,85 ¸ 1.2± 0.2 mm
Fig. 18 .: Layout of the anvil in relation to the tooth
You can eliminate these defects by aligning and adjusting the relative position of the saw blade, crimping roller and anvil, filling the anvil, grinding the working surfaces of the anvil and crimping roller. Some of the defects in crimping are partially corrected or eliminated during molding.
Rice. 19 .: The shape of the apex of the tooth: a - after the correct one; b, c - after improper crimping.
Saw teeth shaping is carried out on manual shaping of the PI - 35 type, produced in a set with the PI - 34 - 1 conditioner. The shaping is intended to form the flattened tips of the saw teeth. In this process, the leveling of the broadening of the tooth blades and the formation of undercut angles are achieved.
During operation, the molding is supported by the left hand by the wooden pad and cheeks, the handle is turned with the right hand. When putting the molding on the saw, the handle should be folded forward. The molding is put on the tops of the teeth and is slightly upset until it comes into contact with the front edge of the tooth. When the handle is pulled back, the strips move apart, freeing the tooth. The amount of widening of the spatula of the teeth is measured with an indicator divider or micrometer.
For a new saw, a side widening of 0.6 ¸ 0.9 ± 0.1 mm is recommended. All saw teeth should be shaped equally in both directions, the tip of the tooth should not have a bend. Breaks and cracks are not allowed. The shape of the spatula after crimping and shaping should correspond to the figure (see fig. 20).
Rice. 20 .: The shape of the band saw tooth after conditioning.
Rice. 21. Band saw tooth shape after shaping
a) The minimum widening of the saw for work is 2.35 mm;
b) Crimping and shaping must be strictly symmetrical about the saw axis;
c) The tooth is flattened to a size not less than six times;
d) Tolerance for deviation from the size of crimping and forming 0.05 mm per side;
e) Size after crimping: 3.15¸3.25 mm, size after molding 2.55¸2.65 mm.
2.7.4 Planing the saw teeth after flattening and shaping
The saw teeth are planed to align with the height and width of the set, that is, to thereby ensure the normal operation of the saw.
The band saws are planed manually with a flat personal file or a touchstone fixed in a special holder. To compensate for minor deviations in the shape, the sides of the saw teeth are also planted. 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 the saw teeth
After the teeth have been planed, the saw is finally sharpened. There are 3 ways of sharpening: first - a part of the metal is ground off the front edge of the tooth; the second - from the back edge of the tooth; the third - simultaneously from the front and back faces. The third method is the most rational and therefore the most common. Sharpening is also carried out on the TChL - 2 machine.
It is recommended to sharpen a circle on a bakelite base, hardness “C” and grain size 80 - 100 units in one or two passes. In this case, the surface to be ground is ground with minimal chip removal: no more than 0.01 mm deep. The recommended cutting speed is 22 - 25 m / s, the thickness of the circle is not less than 10 mm, so that the radius of curvature is not less than 5 mm.
To improve the quality of sharpening, it is recommended to additionally grind the teeth by hand with a fine-grained whetstone fixed in a special holder. You need to drive the touchstone from the bottom up, pressing it to the sharpened edge. By grinding, small burrs, sharpening irregularities and risks are removed, which increases the durability of 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 cavities 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 should be perpendicular to the side plane of the saw;
f) sharpened teeth should not have a gloss at the corners formed by the intersection of the edges. Shine indicates non-flowed 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 lubricated with a cotton swab moistened with machine oil on both sides, tied in two places with linen twine, and stored in this position in the warehouse.
2.8 Installation of the saw on the machine and repair of saws.
Band saws are selected taking into account the parameters of the band saw machine. 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 required blade rigidity.
The saw is installed on the pulleys so that the depressions of the teeth protrude 5 ... 10 mm beyond the edge of the pulley. After tensioning the saw and briefly turning on the electric motor of the cutting mechanism (until the position of the saw stabilizes during its idle operation), if necessary, adjust the inclination of the upper pulley. The final position of the saw on the pulleys is controlled by a ruler. Idle saw operation is 30 minutes. Next, the flatness, beating 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. There should always be scrapers on the pulleys and a wooden bump block 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) clean the saw with a rag soaked in diesel fuel;
e) repairable saws with a width of ³65 mm from the toothed edge and a crack length L £ Lsaws / 2, where Lsaws is the length of the saw.
d) check for cracks in the cavity of the tooth and on the back of the saw. If there are cracks, then a hole with a depth of 0.1 - 0.2 mm must be punched at the end of the crack. If there is a crack ³ 35 mm, it is welded on a semiautomatic welding machine. Next, the saw is rolled according to the example of rolling the near-seam 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) the widening of the saw tooth is controlled: the minimum value for sharpening is 2.35 mm, if the value< 2,35 мм, то зубчатая кромка срезается и плющится заново.
22.05.2015
Purpose and types of band saws
Band saws are the cutting tool of band saw machines: joinery, dividing and log sawing. The saws used in these machines differ only in size, tooth profile and are divided into three types: carpentry (narrow), dividing (medium) and log saws (wide). The first two types are produced in accordance with GOST 6532-53, and log saws - in accordance with GOST 10670-63 "Band saws for sawing logs and beams". Band saws are used for curvilinear and longitudinal sawing of boards, beams, logs and panel wood materials.
Band saw design
The design of band saws is characterized by blade dimensions (band width B including teeth, thickness 5, length L), profile and dimensions of the teeth of the cutting edge. The dimensions of the band saw blades 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.
Saw band length can be determined by the formula
Since the tape is supplied by the purveyor in rolls, when cutting the estimated length, it is necessary to take into account the allowance for the soldering, and maintain the total tooth pitch in the place of the soldering.
Saw band thickness depends on the diameter of the saw wheel and must satisfy the dependence
The value of bending stresses, which in the general balance of stresses have a large specific value, depends on the ratio of the thickness of the saw and the diameter of the pulley. The magnitude of the stresses from the bending of the saw
The magnitude of bending stresses at s / D = 0.001 will be
The ultimate tensile strength at the soldering point does not exceed 70-80 kgf / mm2. Therefore, with a minimum safety factor of 2, the stresses in a working saw should be less than 35-40 kgf / mm2. In this regard, they tend to use the smallest possible saw thickness and large diameters of the saw pulleys.
The width of the band saw blade depends on the width of the saw pulleys and can only exceed the latter by the height of the teeth. When choosing the width of joiner's band saws when cutting curved parts, it is additionally necessary to take into account the radius of curvature R mm of the cut and the widening of the teeth on the side Δs mm. Then the width of the saw
Wider saws will bend in cross section, causing them to gouge and even slide off the pulleys.
For cutting out parts with a very small radius of curvature, jigsaw machines are used, in which jigsaw saws are used as cutting tools. The dimensions of jigsaw saws are 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 sizes of joinery, dividing and log band saws are given in table. 25.
Each type of GOST saw has its own tooth profile. For example, there are two for dividing saws: profile I - with an elongated cavity and profile II - with a straight back edge (Fig. 41.6). Divider saws with tooth profile I are used for sawing hard and frozen soft woods, with tooth profile II for sawing soft woods. The dimensions of the teeth of band saws depend on their thickness, width and cutting conditions.
For joinery band saws with a width of 10-60 mm, the dimensions of the teeth are determined by the following approximate expressions (mm):
For dividing and log band saws, the dimensions of the teeth are (mm):
For saws with a divorced tooth, the step is reduced by 25-30%. The angular values of the tooth profiles provided for by GOST are shown in Fig. 41. The rake 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, which moves the saw off the pulley, decreases. However, with an increase in the rake 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 size and the angle of sharpening β. The angle γ should be kept within the range of 20-35 °.
Soldering band saws
Soldering of band saws is performed in the case of preparing new saws from a roll band, repairing saws in the presence of significant cracks (over 0.12V) or breakage. It includes the following operations: marking, trimming, chamfering, soldering, heat treatment of the welded seam, its stripping and straightening. Correct brazing requires the seam to be half the distance between the tips of adjacent teeth of the brazed saw. To do this, before trimming, the saw is marked with a ruler, square and scribe.
The marking and cutting of 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 assumed to be 105. After marking, the saw is cut along the marked lines ab and cd using scissors or a chisel. The cut ends are straightened with a hammer on the anvil and cleaned with a file. The ends of the saw are overlapped. To keep the thickness of the welded seam equal to the thickness of the saw, the ends of it are beveled (chamfered) within the marked strip. Chamfering is performed manually with a file on a special device, or on milling or sharpening machines. The sharpened 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 a blowtorch flame. Brazing bar presses are heated to 830-1000 ° C in PM-6 muffle furnaces. The ends of the saw to be soldered are installed in a soldering press, and between them a solder is laid in the form of a plate with a thickness of 0.075-0.15 mm together with a flux - a dehydrated drill. The flux is necessary to protect the soldered surfaces from oxidation, as well as to better wet them. Then, heated soldering bars are inserted into the press and pressed tightly with the help of 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 the solder 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. For soldering, silver solders P-Sr-45, P-Sr-65 or brass L62 with a temperature melting 605-905 ° C. After cooling, the place of the soldering is cleaned from scale and filed on both sides with a personal file to a thickness equal to the thickness of the saw blade. Then the place of the adhesion is rolled.
To connect the ends of the tape, you can use the method of butt electric welding using ASLP-1 devices. At the same time, 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 turned on the current. 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 received widespread use, since it requires special equipment.
Band saw straightening and rolling
At editing for band saws, defects are identified and eliminated in the same way as when straightening band saws. Given the long length of the saws and their small thickness, defects should be eliminated with great care, mainly using a rolling machine. The less a band saw is straightened with straightening hammers, the longer its service life. Therefore, straightening should be resorted to if absolutely necessary, replacing it with a rolling if possible.
Rolling band saws are performed in two ways.
The first method: symmetric rolling is performed similar to rolling of frame saws and consists in lengthening the middle part of the blade (Fig. 43, a). Rolling is started from the middle part of the blade and ends, not reaching 10-15 mm on one side to the line of the tooth valleys, on the other, to the rear edge of the saw. Rolling, straightening and quality control of saw preparation is carried out on special tables equipped with a rolling machine, anvil, a test plate and supporting rollers for moving the saw. The degree of rolling is determined by the cross-curvature arrow when the saw is bent with a short straight edge. The deflection should be approximately 0.2-0.4 mm for straight rims and 0.3-0.5 mm for convex rims. Higher deflection values apply to wider and thinner band saws. An accurate check of the lateral curvature of the saw can be carried out with a convex template with a radius of curvature corresponding to a correctly cut saw. In addition, the straightness of the rear edge of the saw is checked by placing it on a test flat plate and applying a long straight ruler to the edge.
The second method of rolling band saws is called rolling on a cone (Fig. 43, b). Beginning of rolling begins at a distance of 15-20 mm from the line of the grooves of the teeth. Closer to the rear edge of the saw, the pressure of the rollers is increased. The last groove of the flaring rollers must be within 10 mm of the rear edge. As a result, the cutting edge is shorter than the rear and, when pulled, receives more stresses than the rest of the saw. The rear edge of a taper rolled saw on a flat test plate will be positioned in a circular arc centered on the teeth. The amount of convexity of this edge over a length of 1 m serves as a characteristic of the degree of expansion. The convex arrow is determined with a straight edge with indicator along the entire length of the saw. The bulge should be 0.3-0.5 mm over a length of 1 m, with larger values referring to wider saws. If a part of the blade along the length of the saw has a bulge greater than the required one, this place must be rolled with an increase in the pressure of the rollers from the rear edge to the cutting edge. Conversely, if the bulge is small, the roll is rolled with an increase in the pressure of the rollers from the cutting edge to the rear. The second rolling method is best for wide band saws, especially when heating is uneven across the blade width.
Installing band saws into the machine
The normal operation of the 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. To do this, the following conditions must be met:
1. The band saw during installation and operation must be placed on the saw pulleys in such a way 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 devices for the saw should be fitted and adjusted to the saw with a gap not exceeding 0.1-0.15 mm.
In order to exclude the displacement of the saw band along the pulley due to the horizontal components of the cutting forces, the mismatch of the resultant tension of the saw with its center line, heating of the saw, etc., a number of preventive measures are applied. 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. To prevent slipping of the belt, flat pulleys are tilted (on the worker) relative to the horizontal axis at an angle of 10-15 ", and the saws are rolled on a cone. In addition, most modern machines allow the upper pulley to be turned around its vertical axis due to the lateral displacement of the front pulley shaft support. Such a turn (with the working branch outward) allows you to hold the saw with strong heating and cutting to the inner side. timely cleaning them from dust, sawdust, resin, etc.
Technical requirements for band saws
Limit deviations of the sizes of band saws should not exceed the values indicated in table. 26.
The roughness of the side surfaces of the saws must be at least 7th class in accordance with GOST 2283-57. Cracks, delamination, scratches, burns from grinding are not allowed. The blade should be straightened and rolled evenly. On the saw every 10 m there must be a stamp indicating the type of saw, its dimensions, GOST. For example, for band saws with logs according to the scheme: "Saw PLB Bхsхt GOST 10670-63".
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 created in the saw blade beforehand (before installation in the machine), which increases the lateral stiffness of the saw, created by tension on the pulleys of the machine. 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 line of the tooth valleys and from the rear (rear) edge of the saw. The correctness of rolling is controlled by the transverse curvature (deflection arrow on the width of the belt) with a special template. The deflection arrow of a normally rolled saw is 0.15 ... 0.3 for cylindrical pulleys of the machine, for barrel-shaped pulleys - 0.4 ... 0.6 mm (larger values refer to thinner and wider saws).
Sharpening of the band saw teeth 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 thickness of the circle is 0.2, .. 0.33 tooth pitch. Good quality is ensured by the following sharpening mode: circumferential speed of rotation of the wheel
20 .. .25 m / s; infeed feed in one pass 0.02 ... .0.06 (up to 0.1) mm; number of passes 4 .. .6 (up to 7).
Lapping the teeth consists in grinding the front and rear edges with a fine-grained donkey, fixed in a special holder. The durability of the saw with adjusted teeth is increased by 15. 20%. Lapping is performed using a handheld device.
Repair of band saw blades includes localization of cracks, cutting out defective areas of the blade and preparation of insert sections. Single cracks with a length of no more than 10–15% of the saw width, but no more than 15 mm, are subject to localization. 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 pcs. On 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 in straightening.
12. Installation of band saws: tensioning methods, guiding devices, pulley adjustment.
1. The cutting edge of the saw should protrude beyond the edge of the saw wheel to the height of the tooth.
2. The displacement of the belt along the pulleys is prevented by adjusting the position of the axis of the upper pulley (together with the pulley) in the vertical (forward-backward tilt) and horizontal (left-right turn) 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 strip (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 guiding devices is allowed only when cutting 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 idle for a long time. When the machine is stopped for a long time, the tension on the saw should be removed.
7. It is necessary to regularly clean the saw blade from resin, dirt, adhering sawdust.
8. In a number of cases, good results are obtained by using saw lubrication with water, soapy water, a mixture of diesel fuel and machine oil by the drip method or by spraying.
