Rebar bending machine is one of the essential equipment for rebar processing. It is mainly used for bending rebar in various construction projects. Rebar bending machine is usually used in conjunction with cutting machine and its application is very wide. With the effect of national investment, especially the country’s vigorous development of high-speed rail construction, the production and sales of rebar bending machine have grown rapidly. Similar to other rebar cutting machines, hoop bending machines, and straightening and cutting machines, Changge City, Henan Province has formed a production base for this type of machinery. Most domestic products can meet the needs of use.
However, the quality of some products cannot meet the requirements of national standards. The production status and quality level of local steel bar bending machines in Changge, Henan reflects the current status of domestic steel bar bending machines.
Steel bar bending machine product structure
The structure of steel bar bending machines of various manufacturers is basically the same. The transmission schemes of steel bar bending machines are as follows
2 types: belt-two-stage gear-worm gear transmission! and belt-three-stage gear transmission!
The transmission efficiency of a steel bar bending machine using a worm gear drive is not as good as that of a gear-driven bending machine. In other words, under the same drive motor power conditions, a gear-driven bending machine is easier to bend steel bars of the same diameter. However, the self-locking characteristics of the worm gear drive make the positioning accuracy of the bending process higher.
Currently, bending machines using a belt-two-stage gear-worm gear drive scheme are widely used and hold a high market share. The components above the work panel are identical in these two types of steel bar bending machines. Figure 1 shows the structure of the commonly used belt-two-stage gear-worm gear drive bending machine.
Product quality differences of steel bar bending machines
At present, the structure and production process of mechanical transmission steel bar bending machines are very mature. The quality differences of products from various manufacturers are mainly reflected in the following points:
1) The shape and materials of the chassis of each manufacturer vary greatly. A steel bending machine with too little material will have poor overall rigidity and lack aesthetic appeal.
2) Only a small number of manufacturers pay attention to the surface quality of the working disc and other accessories, and use rubber sleeves to seal the working disc and other accessories.
3) Some steel bar bending machine manufacturers use non-standard motors. The output power of these motors is relatively small, and they are prone to heating during continuous operation and cannot bend steel bars of the specified diameter.
4) The gears, worm gears, etc. of the transmission system have differences in processing quality, material selection, heat treatment process, etc.
5) A large number of manufacturers do not pay attention to the quality of the exterior coating of bending machines. A small number of manufacturers use plastic spraying, and the visual effect is good.
The development and improvement direction of bending machine technology
Lightweight design can save resources, effectively reduce the production and transportation costs of bending machines, and improve the cost performance and market competitiveness of products.
The lightweight design technology of steel bar bending machine mainly includes the following points.
1) Use finite element technology to lightweight the worm gearbox or gearbox
The manufacturing cost of the worm gear or gearbox housing of a rebar bending machine accounts for a significant portion of the overall machine cost. Further weight reduction would not only save production costs but also allow for thinner panel materials. Without precise theoretical data, blindly reducing the weight of the worm gear or gearbox housing could lead to cracking during use. Currently, worm gear or gearbox housings are mostly made of cast iron. By establishing a finite element analysis model, force analysis results can be obtained without the need for physical housing fabrication. Based on these results, the housing can be optimized and its geometric parameters refined. Reducing product weight and production costs is crucial for enhancing product competitiveness.
2) Optimize the gear transmission of the transmission system. In the design of the steel bar bending machine, the gear transmission of its transmission system can be optimized.
Using a minimum total center distance as the objective function, optimization techniques are used to determine the gear parameters that meet transmission requirements. This type of problem is easily solved using the optimization toolbox provided by Matlab. The constraints of the optimization design model primarily include performance constraints and boundary constraints. The established performance constraints primarily include requirements for tooth root bending strength and tooth surface contact strength. Boundary constraints include estimating the module range of the gear pair based on the transmitted torque; estimating the range of teeth on the transmission gear and the transmission ratio range, taking into account factors such as smooth transmission and the minimum pitch diameter of the shaft gear; and ensuring that the high-speed gear does not interfere with the low-speed shaft during design.
Technical status and improvement direction of domestic steel bar bending machines
3) Optimize the worm gear structure of the transmission system. The lightweight design of the steel bar bending machine can also be achieved by optimizing the worm gear structure of the transmission system.
Under the condition of ensuring the same load-bearing capacity, the minimum center distance between the worm wheel and the worm is taken as the objective function. The constraints under this model also include performance constraints and boundary condition constraints. Performance constraints include: the requirements for the contact strength of the worm wheel tooth surface; the limit of the bending strength of the worm wheel tooth root; and the limit of the worm stiffness. Boundary condition constraints include: the range of the number of teeth of the worm wheel and the worm; the range of the module of the worm wheel and the worm; the range of the worm diameter coefficient, etc. The model can also be conveniently optimized using the optimization function toolbox provided by Matlab or other optimization solution technologies.