Effect of preheating temperature on roller chain welding quality

Effect of preheating temperature on roller chain welding quality

Introduction
As a key component widely used in the field of mechanical transmission, the welding quality of roller chain is directly related to the performance and service life of roller chain. As an important parameter in the welding process, preheating temperature has a profound impact on the quality of roller chain welding. This article will explore the multi-faceted effects of preheating temperature on the quality of roller chain welding to help readers better understand this key factor.

1. Basic principles of roller chain welding
Roller chain welding is to connect the various components of the roller chain (such as inner chain plates, outer chain plates, sleeves, pins, etc.) to form a complete chain structure. During the welding process, the weldment needs to be heated to a certain temperature to melt and combine together. However, the temperature change during welding will affect the performance of the material, and the preheating temperature plays a vital role in this process.

2. Effect of preheating temperature on roller chain welding quality
Improvement of welding material performance
Reducing material hardness: In roller chain welding, proper preheating can reduce the hardness of the material. Materials with high hardness are prone to generate large stress during welding, leading to problems such as cracks in the weld and heat-affected zone. Through preheating, the internal structure of the material changes and the hardness is reduced, thereby improving the plasticity and toughness of the material, which is conducive to the welding process and reduces the generation of cracks.
Eliminate stress and deformation: Preheating can reduce the temperature difference between the welding area and the base material, reduce the deformation and residual stress caused by thermal expansion and contraction. For high-precision roller chains, reducing welding deformation is crucial because it can ensure the dimensional accuracy and transmission performance of the chain.
Impact on welding process
Increase welding speed: Preheating can increase the temperature of the weldment and reduce the heat loss during welding, thereby allowing the use of higher welding speeds. This is of great significance for improving production efficiency and reducing production costs.
Reduce welding defects: Preheating can evaporate the moisture on the surface of the weldment and reduce the introduction of hydrogen during welding. Hydrogen is one of the main factors that cause problems such as weld porosity, hydrogen embrittlement and cracking. Through preheating, the hydrogen content in the weld can be reduced, the generation of welding defects such as porosity and cracks can be reduced, and the welding quality can be improved.
Optimization of welding performance
Improve the performance of welded joints: Proper preheating can improve the plasticity and toughness of welded joints, making the performance of welded joints closer to that of the parent material. This is crucial to improving the load-bearing capacity and service life of roller chains.
Preventing the generation of cold cracks in welding: Preheating can reduce the cooling rate of welded joints, reduce the tendency to harden, and thus reduce the risk of cold cracks. The effect of preheating is particularly obvious when welding high-strength steel or thick-walled roller chains.

3. Reasonable selection of preheating temperature
Select preheating temperature according to material
Low carbon steel: Low carbon steel has a small tendency to harden. Generally, when the welding thickness is less than or equal to 10mm, the preheating temperature can be around 100℃; when the welding thickness is greater than 10mm, the preheating temperature can be increased to around 150℃.
Low alloy steel: The preheating temperature of low alloy steel needs to be considered comprehensively based on factors such as the composition, thickness and welding process of the material. Usually, the preheating temperature is between 100℃-300℃, and the specific temperature should be determined based on the carbon equivalent of the material and the welding process specifications.
Stainless steel: Stainless steel has low thermal conductivity and is prone to large thermal stress and deformation during welding. Therefore, the preheating temperature is generally between 100℃-200℃, and the specific temperature should be determined according to the material grade, thickness and welding process.
Select the preheating temperature according to the welding process
Manual arc welding: The preheating temperature of manual arc welding is generally between 100℃-300℃, and the specific temperature should be determined according to the welding material and welding process specifications.
Submerged arc automatic welding: The preheating temperature of submerged arc automatic welding is generally between 100℃-200℃, and the specific temperature should be determined according to the welding material and welding process specifications.
Gas shielded welding: The preheating temperature of gas shielded welding is generally between 50℃-150℃, and the specific temperature should be determined according to the welding material and welding process specifications.
Select the preheating temperature according to the ambient temperature
When the ambient temperature is below 0℃, the preheating temperature should be appropriately increased. In general, the preheating temperature should be 30℃-50℃ higher than the ambient temperature.
When the ambient temperature is higher than 0℃, the preheating temperature can be adjusted appropriately according to the welding materials and welding process specifications.

4. The influence mechanism of preheating temperature on the welding quality of roller chain
Prevention of hydrogen embrittlement and cold cracks
Hydrogen embrittlement is caused by the penetration of hydrogen atoms into the metal during welding, which causes metal embrittlement under stress. Preheating can slow down the cooling rate of the weld, extend the insulation time of the weld at a higher temperature, and give hydrogen atoms enough time to escape the weld, thereby reducing the risk of hydrogen embrittlement.
Cold cracks usually occur during or after the cooling of the weld joint. It is due to the excessive cooling rate of the weld joint, which increases the hardness and reduces the toughness of the weld joint, thereby generating cracks. Preheating can reduce the cooling rate of the weld joint and reduce the occurrence of cold cracks.
Optimization of material properties
Preheating can make the chemical composition of the welding material more uniform and reduce segregation. This helps to improve the performance of the weld joint and make it better meet the use requirements of the roller chain.
Preheating can change the microstructure of the material, making it more prone to plastic deformation during welding, thereby improving the strength and toughness of the weld joint.

5. Measurement and control of preheating temperature
Measurement method
Thermocouple temperature measurement: Thermocouple is a commonly used temperature measurement tool with the characteristics of high accuracy, fast response and easy use. In roller chain welding, the thermocouple can be attached to the surface of the weldment or inserted into the weldment, and the preheating temperature can be determined by measuring the potential change of the thermocouple.
Infrared thermometer temperature measurement: The infrared thermometer is a non-contact temperature measurement tool with the characteristics of safety, speed and convenience. It can measure the temperature of the weldment surface at a long distance and is suitable for high temperature, dangerous or difficult to access welding environments.
Control method
Selection of heating equipment: Selecting the right heating equipment is the key to controlling the preheating temperature. Common heating equipment includes resistance heating furnace, induction heating equipment, flame heating equipment, etc. In roller chain welding, the right heating equipment should be selected according to the welding material, welding process and production requirements.
Control of heating time: Heating time is an important factor affecting the preheating temperature. Generally speaking, the longer the heating time, the higher the preheating temperature. However, in actual production, the appropriate heating time should be determined based on comprehensive considerations of factors such as welding materials, welding processes and heating equipment.
Temperature monitoring and feedback control: During the heating process, the temperature of the weldment should be monitored in real time, and feedback control should be performed according to temperature changes. The temperature of the weldment can be measured by thermocouples, infrared thermometers and other equipment, and then the temperature signal is fed back to the control system of the heating equipment to automatically adjust the heating power so that the temperature of the weldment is always kept within the set range.

6. Practical application cases
Practice of a roller chain manufacturing company
When the company produced high-strength roller chains, it was found that cracks often occurred during welding, affecting product quality and production efficiency. After analysis, it was found that insufficient preheating temperature was one of the main causes of cracks. Therefore, the company improved the preheating process, increased the preheating temperature from the original 100℃ to 150℃, and optimized the heating time and heating method. After the improvement, the incidence of welding cracks was significantly reduced, and the product quality was significantly improved.
Comparison of welding quality at different preheating temperatures
In an experiment, different preheating temperatures were used to weld the same batch of roller chains, and the quality after welding was tested. The results show that when the preheating temperature is 150℃, the strength and toughness of the welded joint are better than those when the preheating temperature is 100℃ and 200℃. This shows that the appropriate preheating temperature can optimize the welding quality, while too low or too high preheating temperature will have an adverse effect on the welding quality.

7. Future research direction of the effect of preheating temperature on the welding quality of roller chains
Research on new materials
With the continuous development of science and technology, new roller chain materials are constantly emerging. In the future, it is necessary to conduct in-depth research on the welding performance of these new materials at different preheating temperatures to determine the optimal preheating temperature range and improve the welding quality.
Innovation of welding process
The continuous advancement of welding technology will also affect the selection of preheating temperature. For example, new welding processes such as laser welding and electron beam welding are increasingly used in roller chain manufacturing. In the future, it is necessary to study the interaction between these new processes and preheating temperature and explore the optimal welding process parameters.
Development of intelligent preheating control system
With the development of intelligent manufacturing technology, it is of great significance to develop an intelligent preheating control system. This system can automatically adjust the preheating temperature according to factors such as welding materials, welding processes and environmental conditions, achieve precise control, and improve the stability and consistency of welding quality.

Conclusion
The preheating temperature is a key process parameter in the roller chain welding process and has an important impact on the welding quality. Appropriate preheating temperature can improve the performance of welding materials, optimize welding processes, improve the quality and performance of welded joints, and reduce the occurrence of welding defects. In actual production, the preheating temperature should be reasonably selected according to factors such as the material, welding process and environmental conditions of the roller chain, and advanced measurement and control technology should be used to ensure the accuracy and stability of the preheating temperature. At the same time, with the continuous development of materials science and welding technology, it is necessary to further study the influence mechanism of preheating temperature on the welding quality of roller chains in the future, so as to provide more powerful technical support for improving the welding quality and service life of roller chains.