One-stop Bending Solutions For Wires, Tubes And Pipes
One-stop Bending Solutions For Wires, Tubes And Pipes
Fully automatic pipe bending machines can automatically complete pipe shaping and forming tasks with complete working procedures. This brings greater convenience to pipe bending, saves manpower, and reduces operational risks. Automated management and control also ensure smooth bending.
In the pipe forming system of fully automatic pipe bending machines, the core difference between cold bending and hot bending lies in whether the pipe is preheated. This key operation directly determines the technical path and application boundaries of the two processes.
1. Cold Bending with a Fully Automatic Pipe Bending Machine
The cold bending method involves a fully automatic pipe bending machine operating at room temperature (typically room temperature, without additional heating). The machine’s pre-programmed tooling (such as a clamping die or bending die) applies force to the pipe, gradually conforming the pipe to the die’s curvature without altering the metal’s crystal structure. Throughout this process, the pipe remains “cold,” preserving the metal’s original physical and chemical properties (such as corrosion resistance and mechanical strength) from high temperatures. No subsequent cooling is required. The fully automatic system can directly complete the entire process, from feeding, clamping, bending, to unloading. This method is particularly well-suited for batch processing of standardized pipes, such as the mass bending of standard steel pipes in the shipbuilding industry.
2. Hot Bending with a Fully Automatic Pipe Bending Machine
The hot bending method requires a heating step before bending. The fully automatic tube bending machine’s accompanying heating device (such as a medium-frequency induction heater or flame heater) first heats the tube to be bent to a specific temperature (usually within the metal’s “plastic deformation temperature range,” such as approximately 600-900°C for carbon steel). This softens the metal’s internal crystal structure and reduces its yield strength. The machine then drives the die to complete the bend. The heating temperature must be strictly controlled: too low a temperature will make the tube difficult to deform and prone to cracking; too high a temperature can lead to metal oxidation and coarsening of the grains, which in turn reduces the tube’s performance. After bending, some tubes require slow cooling or tempering to restore mechanical properties. Therefore, the automated hot bending process requires the integration of additional modules such as temperature monitoring and thermal insulation cooling, making the process significantly more complex than cold bending.
Comparison of Key Characteristics of Cold and Hot Bending Methods for Fully Automatic Pipe Bending Machines
In actual application, the two processes exhibit distinct characteristics, which directly influence industry choices. This is particularly true in the shipbuilding industry, where stringent requirements for pipe quality are crucial. This comparison of characteristics is a key factor in process selection.
| Comparison Dimension | Cold bending method | Hot bending method |
| Influence of metal properties | 1. Due to “work hardening” caused by stress at room temperature, the hardness and tensile strength of the pipe after bending are significantly improved (10%-20% higher than hot-bent pipes); 2. It does not damage the original metal structure, and the corrosion resistance and fatigue life are basically the same as those of the raw material; 3. No oxide scale is generated, and the inner wall of the pipe is smooth, eliminating the need for subsequent cleaning processes such as pickling and rust removal. | 1. High-temperature heating may cause metal oxidation, forming a surface oxide scale (approximately 0.1-0.3mm thick), requiring additional treatment. 2. Uneven heating or rapid cooling can easily lead to coarse grains and internal stress concentration, potentially reducing pipe toughness (for example, the impact toughness of alloy steel pipes may decrease by 5%-15% after hot bending). 3. When hot bending is used on special materials such as copper pipes, high temperatures may cause “hydrogen embrittlement” (hydrogen gas penetrates the metal and forms microcracks), directly affecting safety. |
| Bending the boundaries of capability | 1. Limited by the yield strength of metal at room temperature, it is impossible to bend elbows with a “small curvature radius” – the conventional cold bending radius must be ≥ 1.5-3 times the outer diameter of the pipe (for example, for a steel pipe with an outer diameter of 50mm, the minimum cold bending radius is approximately 75mm); 2. It is difficult to achieve “continuous bending” or “bending without straight pipe sections”. A straight pipe section of at least 1-2 times the pipe diameter must be retained between two adjacent elbows, otherwise the pipe will easily crack at the bend; 3. It has poor adaptability to brittle materials (such as some high-alloy steel pipes) and is prone to wrinkling or breaking during cold bending. | 1. After high-temperature softening, the metal’s plasticity is significantly enhanced, enabling the production of elbows with “extremely small curvature radii.” The hot-bending radius of carbon steel and alloy steel pipes can be as small as 0.7-1.5 times the outer diameter (e.g., a 50mm outer diameter steel pipe has a minimum hot-bending radius of only 35mm). 2. It supports “continuous bending,” eliminating the need for straight sections between adjacent elbows, enabling the single-step forming of complex pipe shapes (such as “U-shaped” and “S-shaped” pipes). 3. It is suitable for special pipes with poor cold ductility and excessively thick or thin walls, such as thick-walled alloy pipes and thin-walled stainless steel pipes, avoiding collapse during cold bending. |
| Equipment and cost | 1. The equipment structure is relatively simple, requiring no heating or cooling modules, resulting in low initial investment costs. 2. The fully automated process requires no additional heating energy, and the unit processing cost is only 60%-70% of that of hot bending. 3. High production efficiency: The processing time for a single pipe is 30%-50% shorter than that of hot bending, making it suitable for mass production. | 1. The equipment is highly complex, requiring integrated heating, temperature control, and cooling systems. The initial investment cost is 40%-60% higher than that of cold-bending equipment. 2. The heating process consumes a lot of energy (for example, medium-frequency heating consumes 50-100 degrees of electricity per hour), and additional costs for scale treatment and tempering are required, resulting in a high unit processing cost. 3. The process involves multiple steps (heating – bending – cooling – post-processing), resulting in lower production efficiency than cold-bending, making it more suitable for small-batch, customized pipe processing. |
| Operation and Safety | 1. The absence of high-temperature processes creates a safer operating environment, and the fully automatic system reduces the risk of human contact. 2. However, because the equipment must overcome the rigidity of room-temperature metal, pipe bending consumes greater power (20%-30% higher than hot bending). Furthermore, the pipe is prone to “springback” after bending (typically 1°-3°), requiring a preset compensation value in the program. 3. Residual stress is generated within the pipe during the bending process, potentially creating a risk of stress concentration if the pipe is subsequently subjected to uneven force. | 1. Due to the high-temperature heating process, the heating temperature and distance must be strictly controlled to avoid burns or fire risks. Fully automatic systems must be equipped with temperature alarms and fire prevention devices. 2. Metal has good plasticity at high temperatures, resulting in low bending power consumption, small springback (usually ≤1°), and easier control of forming precision. 3. The heating and cooling processes can partially release internal stress, resulting in lower residual stress than cold-bent pipes. However, caution should be exercised against “localized overheating cracking” caused by uneven heating. |
Application Scenarios of Fully Automatic Pipe Bending Machines
With the development of the shipbuilding industry, shipyards have widely adopted a variety of pipe bending machines for pipe bending. Because cold bending hardens the metal, cold-bent metal pipes are much harder than hot-bent ones. However, cold bending does not damage the metal’s original properties. Cleaning and descaling are not necessary, and thermal deformation does not occur.
Compared to hot bending, cold bending requires more bending power and significantly increases springback and residual stress. Furthermore, cold bending cannot produce sharp bends with a very small radius of curvature. Hot bending offers unmatched adaptability.
Ship piping systems (such as fuel, cooling water, and steam pipes) require extremely high safety and spatial adaptability. Therefore, the selection of cold and hot bending methods must strictly adhere to the principle of “cold bending first, hot bending when necessary.” This is highly consistent with the requirements of the Ministry’s Technical Specifications for Marine Pipe Bending.
1. Application Scenarios of Cold Bending
In the shipbuilding industry, over 80% of conventional pipe bending is done using cold bending, specifically including:
Standardized pipe processing: such as carbon steel and copper pipes with a diameter ≤100mm and a wall thickness ≤10mm, and elbows in straight pipe sections with a bending radius ≥2 times the pipe diameter (e.g., cooling water pipes in ship cabins);
High-demand pipe applications: such as copper pipes (cold bending prevents hydrogen damage and ensures pipe sealing) and stainless steel pipes (cold bending does not damage the surface passivation layer, improving seawater corrosion resistance);
Mass production requirements: For common pipes for the same ship model (e.g., deck drain pipes), the high efficiency and low cost of cold bending can significantly shorten shipbuilding cycles.
2. Application Scenarios for Hot Bending
Hot bending is only permitted when cold bending cannot meet the requirements:
Small radius bending requirements: For example, compact piping within a ship’s engine compartment requires a bend radius ≤ 1 pipe diameter (e.g., an 80mm outer diameter steel pipe needs to be bent into a 60mm radius elbow). Cold bending can easily cause cracking, so hot bending is recommended.
Complex shape processing: For example, special-shaped pipes with no straight sections requiring continuous bending (e.g., turning pipes in ship fuel systems). Cold bending cannot achieve continuous shaping, so hot bending is recommended.
Special pipe wall adaptation: For example, thick-walled alloy pipes with a wall thickness greater than 15mm (insufficient external force during cold bending can easily damage the mold), and pipes with a wall thickness less than 2mm. Thin-walled pipes (which tend to collapse during cold bending) require hot bending.
Non-standard pipe processing: For example, large-diameter (>200mm) cast iron pipes and special alloy pipes occasionally used in shipbuilding require hot bending because they lack matching cold bending dies.
Extreme-service pipes: For example, steam pipes used in ships (which must withstand high temperatures and high pressures), hot bending improves the pipe’s heat resistance through subsequent quenching and tempering, making it more suitable for cold bending.
Application Characteristics of Fully Automatic Pipe Bending Machines
Cold bending, with its core advantages of “high efficiency, low cost, and guaranteed performance,” has become the mainstream process for fully automatic pipe bending machines, particularly suitable for standardized, high-volume pipe processing. Hot bending, with its “high flexibility and wide adaptability,” fills the gap in cold bending technology, solving the forming challenges of complex and specialized pipes. In precision manufacturing fields such as shipbuilding, the two methods are not mutually exclusive; rather, they form a complementary pattern of “cold bending as the primary method, hot bending as a supplement,” depending on pipe specifications, materials, and operating conditions. Intelligent upgrades to fully automatic pipe bending machines (such as real-time temperature monitoring and stress compensation algorithms) are continuously narrowing the shortcomings of both processes, driving pipe forming technology towards higher precision and wider adaptability.
Learn More:
Application of automatic pipe bending machines in the aerospace field
How to choose a fully automatic pipe bending machine suitable for shipbuilding?
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