Improvement and Application of Band Sawing Machine

Structural Improvement of Saw Wheel

The saw wheel is a pair of wheels used to install the band saw machine and is the main component for achieving the main movement. The lower saw wheel of the band saw machine is the driving wheel, which needs to have a large rotational inertia and can act as a flywheel during operation. The upper saw wheel is passive and driven by the saw blade. It is required to be done lightly and keep in sync with the saw blade as much as possible, in order to reduce severe friction and slipping between the saw wheel and blade caused by changes in starting braking and cutting resistance, and to prevent excessive expansion and fracture of the saw blade.

(1) Quenching treatment and cold work hardening treatment are carried out on the surface of the band saw wheel to improve the strength of the saw wheel surface and reduce friction between the saw wheel and the saw blade.

(2) Applying 3-5mm thick rubber on the surface of the saw wheel can effectively reduce noise. This method is often used on small band saws in furniture factories.

(3) Change the structure of the upper saw wheel from a spoke type to a spoke plate type to make it less susceptible to vibration. The spoke type upper saw wheel adopts an integral casting structure, which eliminates or reduces the airflow rotation noise and eddy current noise generated by the rotation of the spoke type upper saw wheel, and reduces the overall noise by about 3d B (A).

Improvement of the Guide Device of Band Saw Machine

The main characteristics of the current band saw machine are high feeding speed, large saw machine specifications, and poor saw blade stability. The accuracy of sawing is low, and the stability of the saw blade depends on factors such as the tension of the saw blade, the exposed length of the saw blade, the feeding direction, and the guiding device. The saw card is a guiding device of a band saw machine, whose function is to shorten the free length of the working edge of the saw blade, improve the stiffness of the saw blade, reduce the amplitude of lateral vibration of the saw blade, and thus maintain a straight saw path. The installation position of the saw card should be close to the sawn wood.

Saw cards include upper saw cards and lower saw cards. The lower saw card is fixed on the machine base, and the upper saw card is installed on the specially designed guide rail of the machine body, which can be adjusted at any time according to the height of the saw path. The saw card in traditional sawing machines generally adopts a double resistant saw card, which is made of two pieces of hardwood and leaves a certain gap with the saw blade (usually controlled at 0.1-0.15mm, too tight will cause excessive friction, the saw blade will heat up and bend easily, and too loose will lose the function of the saw card). This structural type cannot fully ensure that the saw blade does not move during operation and has poor stability. In order to solve the gap between the inner lining of the saw card and the saw blade while hoping that the saw card can play a certain role in tensioning the saw blade, the following improvements have been made to the saw card:

① Pressure saw card: Its working principle is to compress the working edge of the saw blade outward through the lateral pressure of the saw card, causing the working edge of the saw blade to exceed the outer edge of the saw wheel by a certain distance (usually about 6-15mm), thereby forcibly straightening the saw blade. The use of pneumatic or hydraulic cylinder pressure saw card can achieve automatic retreat of the saw blade. Using it instead of the automatic retreat device used for sports cars is beneficial for improving the accuracy of the scale.

② Improving the traditional saw card to a rolling saw card: the saw blade has one side against the roller, reducing the friction between the saw card and the saw blade.

Automatic processing system for saw blade tension

In order to adapt the saw blade to the cutting stress of wood and its own thermal stress changes, prevent the saw blade from moving, and achieve stable work, the saw blade on ordinary band saw machines must undergo frequent tension treatment. The tension treatment technology is highly technical, relying on experience and tradition, and technical protection, which often leads to problems. Causing poor sawing, low sawing accuracy, and conflicts between saw machine operators and saw repairers. Therefore, many countries are developing various saw machines that can automatically handle tension.

① The automatic tension processing saw wheel form suitable for ordinary band saw machines developed by Nanjing Forestry University. After use in production, both the original and newly used saw blades do not require additional tension treatment, and can be used directly. The saw blade works smoothly, and there is no attention to the copy of the saw back and tooth root. The sawn material processing quality is good. Due to the unchanged basic structure of the original band saw machine, this technology only performs turning on the shaft surface of the saw wheel, which is easy to promote and use.

② The machining of convex edges on wheel rims is commonly used on some modern band saw machines in Europe to grind convex edges on wheel rims, mainly in two forms. One method is to add the wheel flange surface into two circular arcs and form convex edges at a distance of about 1/3 of the wheel width from the working edge; The leading edge and back of the other type of wheel flange surface are both straight lines, and the middle is processed into an arc and forms a convex edge near the leading edge.

③ There are circular grooves on the surface of the saw wheel rim, which can smoothly eliminate the air cushion that may be formed between the saw blade and the rim surface due to the squeezing of air, making the saw blade and the saw wheel in closer contact to improve the working stability of the saw blade. At the same time, these grooves form multiple support points on the surface of the saw blade in the width direction, which helps to prevent the saw blade from sliding backwards.

④ The bending of the saw wheel shaft under tension in the static axis structure of the saw wheel can cause excessive radial runout during the rotation of the saw wheel, causing periodic expansion and contraction of the saw blade, sudden stress changes, and instability. In order to solve this problem, modern band saw machines generally adopt a static axis structure, which has good stiffness and is not prone to bending, which is conducive to improving the stability of saw wheel and blade operation and can adapt to the needs of high tension band saw machines. At the same time, the static axis structure can also be made into a single support form, making it easy to apply on various joint saws.

Saw blade inspection

Saw blade cracking is a common phenomenon that is difficult to avoid in use. But it has had a negative impact on timber production. When the crack of the saw blade exceeds the specified length, it can cause accidents and threaten the personal safety of operators. So although the saw repair workers took different measures while repairing the saw, the cracks in the saw blade were avoided, but often due to improper measures, the saw blade was not easy to use and had a short lifespan, and the quality of the sawn wood significantly decreased. Previously, only three mechanical performance indicators were specified to meet the usage requirements, namely tensile strength, elongation, and hardness. However, from a safety perspective, they were not comprehensive enough, especially for the toughness indicators of fine woodworking band saw blades, where fatigue performance was not clearly reflected.

The application of repeated bending test method is an effective detection method, which has the advantages of simple testing equipment, sensitive defect reflection, convenient operation, and short testing cycle. Three defects can be detected:

a. Internal defects in steel (such as fine cracks, pinched tails, etc.).

b. Harmful impurities contained in steel (such as excessive non-metallic inclusions, grain boundary enrichment of harmful elements, etc.).

c. Heat treatment defects (such as coarse grains, quenching cracks, network carbides, and temper brittleness).

Practice has shown that defects in cold and hot processing can be detected simultaneously, and when used in conjunction with tensile and hardness tests, it can reflect good economic results, greatly reducing the incidence of band saw fracture accidents and promoting the improvement of band saw quality.