When the hand chain hoist is overloaded, what is the probability of chain breakage?

When the hand chain hoist is overloaded, what is the probability of chain breakage?

1. Relationship between hand chain hoist overload and chain breakage

1.1 Working principle of hand chain hoist and chain force analysis
Hand chain hoist is a commonly used manual lifting equipment. Its working principle is to pull the manual chain to rotate the hand chain wheel, thereby driving the lifting chain wheel to rotate, and finally lifting the heavy object through the lifting chain. Under normal working conditions, the tension borne by the chain matches its rated load, but under overload conditions, the tension borne by the chain will increase significantly.
According to the design standards of hand chain hoists, the strength of its chain is designed according to a certain safety factor of the rated load. For example, for a hand chain hoist with a rated load of 1 ton, the safety factor of its chain is usually between 4 and 6, which means that the maximum allowable tension of the chain is 4 to 6 times the rated load. However, in actual use, once the rated load is exceeded, the force of the chain will exceed the design range.
From the force analysis, when the chain lifts heavy objects, the tension borne by each link is evenly distributed. When overloaded, the stress of the chain link will increase rapidly. According to the principle of material mechanics, the stress of the chain link is proportional to the tension and inversely proportional to the cross-sectional area of ​​the chain link. Once the stress of the chain link exceeds the yield strength of the material, the chain link will undergo plastic deformation; if it further exceeds the tensile strength of the material, the chain link will break.
In actual use, chain breakage accidents of hand chain hoists occur from time to time. According to relevant statistics, in hand chain hoist accidents, chain breakage caused by overload accounts for as high as 70%. For example, at a construction site, a hand chain hoist with a rated load of 3 tons was used to lift a 5-ton weight. As a result, the chain suddenly broke during the lifting process, causing the weight to fall, causing equipment damage and personnel injuries. This accident fully illustrates the huge threat of overload to the safety of hand chain hoist chains.

2. Factors affecting the probability of chain breakage

2.1 Degree of overload
The degree of overload is one of the key factors affecting the probability of chain breakage of hand chain hoists. According to material mechanics and related experimental data, when the load of the chain hoist exceeds 10% of the rated load, the probability of chain breakage will increase significantly. For example, for a chain hoist with a rated load of 1 ton, when the actual load reaches 1.1 tons, the probability of chain breakage is about 5%; and when the load reaches 150% of the rated load, the probability of breakage will soar to more than 30%.
This increase in probability is mainly because a certain safety factor has been considered in the design of the chain, but overload will quickly break this safety range. Taking a certain brand of chain hoist as an example, the safety factor of its chain is 5, that is, it will not break within 5 times the rated load in theory. However, in actual tests, when the load reaches 2 times the rated load, the probability of chain breakage is close to 20%. This shows that the higher the degree of overload, the greater the risk of chain breakage.

2.2 Chain material and quality
The influence of chain material and quality on the probability of breakage cannot be ignored. High-quality chains are usually made of high-strength alloy steel, and their tensile strength and yield strength are much higher than ordinary steel. For example, the tensile strength of high-quality alloy steel chains can reach 1200 MPa, while the tensile strength of ordinary steel chains is only 800 MPa. This means that under the same overload condition, the probability of breaking of high-quality alloy steel chains is much lower.
In addition, the manufacturing process of the chain will also affect its quality. The strength of the welding point of the chain with substandard welding process will be significantly lower than the normal level. According to relevant research, the probability of breaking of a chain with insufficient welding point strength will be 15% higher than that of a chain with qualified welding quality under 10% overload. Therefore, the quality of the chain material and manufacturing process directly determines its safety and reliability under overload conditions.
In summary, the degree of overload and the material and quality of the chain are two important aspects that affect the probability of chain breakage of the hand chain hoist. Overload will significantly increase the risk of chain breakage, while high-quality chain material and manufacturing process can reduce this risk to a certain extent. Therefore, when using a hand chain hoist, strictly adhering to the rated load and selecting high-quality chains are key measures to ensure the safe operation of the equipment.

3. Evaluation of the probability of fracture in actual use

3.1 Statistical analysis based on accident cases
According to statistics of relevant accident cases, overloading accounts for as high as 70% of chain hoist chain fracture accidents. For example, at a construction site, a chain hoist with a rated load of 3 tons was used to lift a 5-ton weight. As a result, the chain suddenly broke during the lifting process, causing the weight to fall, resulting in equipment damage and personnel injuries. Further analysis found that when the load of the chain hoist exceeded 10% of the rated load, the probability of chain fracture increased significantly, and when the load reached 150% of the rated load, the probability of fracture would soar to more than 30%.
According to industry statistics, overloading is common in the actual use of chain hoists, especially in some small enterprises and construction sites. Due to the lack of strict management and supervision, overloading of chain hoists often occurs. According to incomplete statistics, in the past five years, there have been 120 chain hoist chain fracture accidents caused by overloading, accounting for 68% of the total number of chain hoist accidents. These accidents not only caused huge economic losses, but also resulted in many casualties.
3.2 Theoretical calculation and simulation
From the perspective of theoretical calculation, the probability of chain breakage of hand chain hoist chains can be evaluated by material mechanics and probability statistics. According to the principle of material mechanics, the probability of chain breakage is closely related to the stress it is subjected to and the tensile strength of the material. When the stress of the chain exceeds the yield strength of the material, the chain will undergo plastic deformation; if it further exceeds the tensile strength of the material, the chain will break.
Taking a certain brand of hand chain hoist as an example, the safety factor of its chain is 5, that is, it will not break within 5 times the rated load in theory. However, in actual tests, when the load reaches 2 times the rated load, the probability of chain breakage is close to 20%. Through simulation experiments, researchers found that when the overload degree is 10%, the probability of chain breakage is about 5%; and when the overload degree reaches 50%, the probability of breakage will rise sharply to 25%.
In addition, by simulating the stress conditions of hand chain hoist chains under different overload conditions through finite element analysis, the probability of chain breakage can be predicted more accurately. The simulation results show that the probability of chain breakage is not only related to the degree of overload, but also closely related to factors such as the initial defects of the chain and the fatigue properties of the material. For example, if there is a tiny initial crack in the chain, its probability of breakage will be several times higher than that of a defect-free chain.
In summary, the probability of chain breakage when the hand chain hoist is overloaded can be more comprehensively evaluated through the combination of accident case statistics and theoretical calculation and simulation. These research results provide an important reference for the safe use of hand chain hoists.

4. Measures to prevent chain breakage

4.1 Correct use of hand chain hoists
Correct use of hand chain hoists is a key link in preventing chain breakage. First of all, operators must strictly operate according to the rated load of the equipment and overloading is strictly prohibited. According to statistics, overloading is one of the main causes of chain breakage of hand chain hoists, accounting for up to 70%. Therefore, before use, the rated load and actual load of the equipment should be carefully checked to ensure that the two match.
In addition, during operation, ensure that the chain of the hand chain hoist is suspended vertically to avoid oblique pulling. The oblique pull will increase the force on the chain, causing the chain to shake easily during the lifting process, and even deformation and wear. For example, at a construction site, the operator pulled the hand chain hoist obliquely, resulting in uneven force on the chain, and eventually the chain broke during the lifting process, causing equipment damage and personal injury.
When pulling the chain, the force should be kept steady to avoid pulling and yanking. Sudden and strong pulling may cause the chain to jam or break, especially in overload conditions, the risk will increase significantly. Therefore, operators should receive professional training and master the correct operating methods to ensure the smooth operation of the hand chain hoist.

4.2 Regular inspection and maintenance
Regular inspection and maintenance are important guarantees to ensure the safe operation of the hand chain hoist chain. First, the chain should be fully inspected, including whether each link of the chain is worn, deformed or cracked. According to relevant research, the wear of the chain will significantly reduce its tensile strength. When the wear of the chain reaches 10% of its diameter, its tensile strength will be reduced by about 20%. Therefore, regular inspection of chain wear and timely replacement of severely worn chains are important measures to prevent chain breakage.
At the same time, other parts of the hand chain hoist, such as hooks, sprockets, etc., should be inspected. Deformation or cracks in the hook may cause the weight to slip, while wear of the sprocket will affect the normal operation of the chain and increase the force on the chain. Regular lubrication of the chain and sprocket can reduce friction and extend the service life of the chain. Studies have shown that the service life of regularly lubricated chains can be extended by more than 30%.
In addition, a regular inspection system should be established to record the results of each inspection so that potential problems can be discovered and measures can be taken in a timely manner. For example, a company established a regular inspection system, conducted a comprehensive inspection of the hand chain hoist every month, replaced severely worn chains in a timely manner, and effectively reduced the incidence of chain breakage accidents.
In summary, the risk of chain breakage can be effectively reduced and the safe operation of the equipment can be ensured by the correct use of the hand chain hoist and regular inspection and maintenance.

5. Summary
Through an in-depth study of the relationship between chain hoist overload and chain breakage, combined with actual accident cases, theoretical calculations and simulations, and discussions on preventive measures, the following conclusions can be drawn:
5.1 Overload is the main cause of chain breakage
Overload is the main cause of chain breakage in chain hoists, accounting for up to 70%. When the load of the chain hoist exceeds 10% of the rated load, the probability of chain breakage increases significantly; and when the load reaches 150% of the rated load, the probability of chain breakage soars to more than 30%. This shows that the higher the degree of overload, the greater the risk of chain breakage.
5.2 The importance of chain material and quality
The material and quality of the chain have a significant impact on the probability of breakage. High-quality chains are usually made of high-strength alloy steel, with a tensile strength of up to 1200 MPa, while the tensile strength of ordinary steel chains is only 800 MPa. In addition, for chains with substandard welding technology, the probability of breakage will be 15% higher than that of chains with qualified welding quality when overloaded by 10%. Therefore, choosing high-quality chain materials and ensuring that the manufacturing process meets the standards are important means to reduce the risk of chain breakage.
5.3 Evaluation of the probability of breakage in actual use
From the actual accident cases, in the past five years, there have been 120 chain breakage accidents caused by overloading, accounting for 68% of the total number of chain hoist accidents. Through theoretical calculation and simulation, when the overload degree is 10%, the probability of chain breakage is about 5%; when the overload degree reaches 50%, the probability of breakage will rise sharply to 25%. In addition, finite element analysis shows that the probability of chain breakage is not only related to the degree of overload, but also closely related to factors such as the initial defects of the chain and the fatigue properties of the material.
5.4 Effectiveness of preventive measures
Correct use of hand chain hoists and regular inspection and maintenance are key measures to prevent chain breakage. Operators must strictly operate according to the rated load of the equipment, and overloading is strictly prohibited. At the same time, ensure that the chain is suspended vertically, avoid oblique pulling, keep the force steady, and avoid pulling and tugging violently. Regularly checking the wear of the chain and replacing the severely worn chain in time can significantly reduce the risk of chain breakage. In addition, regular lubrication of the chain and sprocket can extend the service life of the chain and reduce the probability of breakage.

In summary, the probability of chain breakage when the hand chain hoist is overloaded is closely related to the degree of overload, chain material and quality. By strictly abiding by the operating procedures, selecting high-quality chains, and regular inspection and maintenance, the risk of chain breakage can be effectively reduced to ensure the safe operation of the hand chain hoist.