Detailed explanation of static load test of electric hoist

Detailed explanation of static load test of Electric Hoist

In industrial production and lifting operations, electric hoists are a common lifting equipment, and their safety and reliability are crucial. Static load test is a key link to ensure that the performance of electric hoists meets the standards and ensure the safety of operations. This article will explore the static load test of electric hoists in depth, including its definition, purpose, standard requirements, specific methods, data analysis, and precautions, aiming to provide comprehensive and professional knowledge for practitioners in related industries, and help international wholesale buyers better understand product quality and make wise purchasing decisions.

1. Definition and purpose of static load test
Static load test refers to applying a certain load to the electric hoist when it is in a stationary state to detect its load-bearing capacity and structural stability under the load. This is not only a test of the mechanical structural strength of the electric hoist, but also an effective way to discover potential defects that may exist in the manufacturing and assembly process of the equipment, such as the firmness of welding points and the load-bearing capacity of parts.
Its main purposes are as follows:
Verify the design and manufacturing quality: Through static load test, it can be verified whether the design of the electric hoist conforms to the mechanical principles and actual use requirements, and whether the process and material selection in the manufacturing process are reasonable, so as to ensure that the equipment can operate safely and reliably under normal working conditions.
Determine the safe working load: Accurately measure the performance of the electric hoist under different loads, so as to accurately determine its safe working load, provide a scientific basis for the safe use of the equipment, and avoid safety accidents caused by overloading and other reasons.
Ensure operation safety and equipment life: Discover and solve possible problems with the equipment, ensure that the electric hoist can work stably within the specified load range after being put into use, reduce the risk of equipment failure and damage, extend the service life of the equipment, and at the same time maximize the personal safety of operators and the safety of the surrounding environment.

2. Standards and specifications for static load tests
Different countries and regions have corresponding standards and specifications for static load tests of electric hoists. The following are some common reference standards:
International Organization for Standardization (ISO) standards: ISO 9001 quality management system standards put forward general requirements for quality control in the manufacturing process of electric hoists. All testing links, including static load tests, need to comply with the prescribed procedures and methods to ensure the stability and consistency of product quality. The ISO 4892 series of standards regulates the environmental durability test methods for plastic parts. Although it is not directly aimed at static load tests, it has certain reference value for data analysis and evaluation of static load tests of plastic parts in electric hoists under different environmental conditions.
European Committee for Standardization (CEN) standards: For example, EN 13155 "Lifting Equipment - Safety Specifications for Operation and Maintenance" clearly stipulates the static load test load, test method, and qualified standards of electric hoists, requiring that the test load is usually 1.25 times the rated load. During the test, the equipment should have no obvious deformation, cracks and other defects, and all components should operate normally and the braking system should be reliable.
American Society for Testing and Materials (ASTM) standard: ASTM A709 standard specifies the requirements for structural steel, and many key components of electric hoists such as hooks and drums are usually made of steel. The standard's provisions on steel performance indicators, test methods, etc. indirectly affect the qualification assessment of electric hoist static load tests, ensuring that the material can withstand the corresponding static load without damage.

3. Preparation for static load test
Sufficient preparation is the basis for ensuring the smooth conduct of static load tests and obtaining accurate results. The specific preparations are as follows:
Test site selection: A flat, solid, open site without external interference should be selected as the test site. The site's ground bearing capacity should meet the total weight requirements of the electric hoist and the test load, avoiding situations such as equipment tilting and sinking due to uneven ground or insufficient load that affect the test results. At the same time, there should be enough space around to facilitate operators to perform test operations, load loading and unloading, and set up safety protection measures.
Test load preparation: Standard weights, prefabricated weight blocks or other equipment with known weights can be used as test loads, but the weight of the test load must be accurate and the error range must be within the specified limit (usually no more than ±1%). For electric hoists with a larger range, preparing the corresponding test load may require a certain amount of cost and space. At this time, equipment such as hydraulic loading systems that can accurately control and apply loads can also be used to replace physical loads, but the accuracy and reliability of the loading system must be ensured.
Equipment inspection and maintenance: Before the test, the electric hoist should be thoroughly and carefully inspected, including appearance inspection to check whether there are obvious deformation, cracks, wear and other defects on the surface of the equipment; functional tests should be performed on key components such as motors, reducers, brakes, hooks, wire ropes, etc. to ensure that they operate normally, without jamming or abnormal sounds; check whether the bolts and nuts at each connection are tightened, and whether the welds are firm. At the same time, according to the equipment maintenance manual, the electric hoist should be maintained as necessary, such as lubrication and cleaning, to ensure that the equipment is in good working condition and eliminate test interference factors that may be caused by equipment failures.
Installation and calibration of test instruments: Prepare test instruments for measuring various parameters of electric hoists under static load, such as displacement sensors, strain gauges, pressure sensors, dynamometers, etc., and install them correctly at the corresponding measurement positions. For example, displacement sensors can be installed in key parts such as hooks and drums to measure the deformation during loading; strain gauges are attached to the surface of components prone to stress concentration to monitor their strain. After installation, all test instruments are calibrated to ensure that their measurement accuracy meets the test requirements and that test data can be accurately obtained.
Development and implementation of safety protection measures: Since there are certain safety risks in the static load test process, such as load falling, equipment tipping, etc., which may cause casualties and property losses, strict safety protection measures must be formulated. Set up a warning area and prohibit irrelevant personnel from entering the test site; equip operators with necessary personal protective equipment, such as safety helmets, safety belts, protective gloves, goggles, etc.; install protective devices on key parts such as the hook and lifting mechanism of the electric hoist to prevent accidental load shedding; at the same time, prepare emergency rescue equipment and equipment, such as fire extinguishers, first aid kits, etc., and ensure that on-site personnel are familiar with the emergency handling process so that they can respond quickly and effectively in the event of an accident.

4. Specific methods of static load test
Gradual loading method: This is one of the most common static load test methods. Divide the test load into several equal parts, usually divided into 3-5 loading stages, and apply a certain proportion of the load in each stage, such as applying 30% of the rated load first, and then increasing it to 60%, 90%, 125%, etc. in sequence. Keep the load stable for a period of time (generally not less than 10 minutes) in each loading stage, observe the response of each component of the electric hoist, and record the displacement, strain, stress and other data displayed by the test instrument. The advantage of the step-by-step loading method is that the performance changes of the equipment under different load levels can be clearly observed, which is convenient for timely detection of potential problems, and the test data can be analyzed and processed more carefully, so as to accurately evaluate the load-bearing capacity and structural performance of the electric hoist. However, the test cycle of this method is relatively long, the operation process is relatively cumbersome, and it requires more manpower and material resources.
One-time loading method: Unlike the step-by-step loading method, the one-time loading method is to directly apply the test load to the electric hoist at one time, and maintain it for a certain period of time (usually 10-30 minutes) after reaching the specified static load test load, and then conduct a comprehensive inspection and data collection of the equipment. The advantage of this method is that the test process is simple and fast, saving time and resources, and improving the test efficiency to a certain extent. However, the disadvantage is that it is impossible to obtain detailed performance change information of the equipment at different load stages, and it is difficult to detect some minor defects or abnormal conditions that may appear in the early stage of loading in time. Therefore, the comprehensiveness and accuracy of the test results are slightly insufficient compared with the step-by-step loading method.
Cyclic loading method: For some electric hoists that need to simulate complex working conditions such as frequent lifting and braking during actual use, the cyclic loading method is a more effective test method. In the test, the electric hoist is subjected to multiple loading and unloading cycles according to the predetermined load spectrum. The load in each cycle can be fixed or varied within a certain range, but the maximum load should not exceed the load value specified in the static load test. Through cyclic loading, the fatigue performance and structural stability of the equipment during long-term use can be more truly reflected, and potential problems such as fatigue cracks and loose connection parts caused by cyclic stress can be discovered in time. However, the test equipment for the cyclic loading method has high requirements, and it is necessary to be able to accurately control the application and unloading process of the load, and the test time is often long, which also puts higher requirements on the technical level of the test personnel and the reliability of the equipment.

5. Data collection and analysis of static load test
Data collection: During the static load test, the installed test instruments are used to collect various data in real time, including but not limited to the displacement, strain, and stress values ​​of the key components of the electric hoist, as well as the current, voltage, temperature and other parameters of the motor. At the same time, the size of the test load, loading time, loading stage and other information are recorded to ensure the integrity and accuracy of the data. In order to improve the reliability of the data, it is recommended to use a method of measuring the same parameter with multiple sensors, and average the collected data or perform error analysis to eliminate obviously abnormal data points.
Data analysis: Conduct an in-depth analysis of the collected data. First, draw a curve chart of each parameter changing with load, observe the trend and characteristics of the curve, and judge whether the performance of the equipment during loading is normal. For example, the displacement curve should show a steady growth trend and can basically return to the initial state after unloading; the strain curve should not show sudden changes or abnormal fluctuations, and its maximum strain value should be within the allowable strain range of the material; the stress distribution should meet the expectations of mechanical analysis, and there should be no excessive stress caused by stress concentration. In addition, the data can be further processed by data analysis software, such as spectrum analysis and correlation analysis, to explore the potential information behind the data and evaluate whether the performance indicators of the equipment such as structural strength, stiffness, fatigue life, etc. meet the design requirements and relevant standards and specifications. For any abnormal data or non-compliant situations found, detailed investigation and analysis are required to find out the reasons and take corresponding measures to improve and optimize, such as adjusting the equipment structure, strengthening weak parts, replacing damaged parts, etc., and then re-test and verify until all performance indicators of the equipment meet the qualified standards.

6. Qualification assessment and result processing of static load test
Qualification assessment standards: According to relevant standards and specifications, as well as the design requirements of electric hoists, the qualification assessment standards for static load tests are formulated. Generally, the following aspects are included:
Structural integrity: Under the test load, the structure of the equipment has no obvious deformation, cracks, weld cracks and other defects that affect normal use, and all connection parts are firm and reliable, without loosening, falling off and other phenomena.
Normal function of parts: The motor runs smoothly, without overheating, overcurrent, abnormal noise and other conditions; the brake is reliable, and the hook and load do not slide down significantly after braking; the hook, drum, wire rope and other parts have no excessive wear and deformation and can work normally.
Displacement and deformation are within the allowable range: The displacement and deformation of key components shall not exceed the allowable value specified in the design. For example, the deformation of the hook opening degree shall not usually exceed 0.25% of the original size, and the radial runout and axial movement of the drum shall be within the specified tolerance range, etc.
Test data meets the requirements: The various parameters obtained through data collection and analysis, such as stress, strain, etc., should meet the strength of the material and the design requirements of the structure, the stress concentration coefficient should not be too large, and the strain distribution should be uniform and reasonable.
Result processing: If all indicators of the electric hoist in the static load test meet the qualification assessment standards, the static load test of the equipment is determined to be qualified and can be put into use, and the test report is provided to the user as one of the product quality certification documents. If the test result is unqualified, it is necessary to carry out corresponding processing according to the specific situation:
Return to the factory for repair and rectification: For some problems that can be solved by replacing parts, strengthening the structure, repairing defects and other measures, the equipment will be returned to the manufacturer for repair and rectification. After the rectification is completed, the static load test will be carried out again until it is qualified.
Scrap processing: If the equipment has serious structural defects or key components are damaged, it cannot meet the qualified requirements through repair and rectification, or the repair cost is too high. From the perspective of economy and safety, it should be scrapped, and the situation should be explained to the user, and corresponding solutions should be provided, such as replacing new equipment.

7. Precautions for static load test
Personnel qualification and safety training: Personnel participating in static load test must have corresponding professional knowledge and skills, undergo strict safety training, be familiar with test procedures and operating specifications, understand possible safety risks and countermeasures, and be certified to ensure personnel safety and data accuracy during the test.
Influence of environmental factors: Environmental factors such as temperature, humidity, and wind speed in the test environment may have a certain impact on the performance and test results of the electric hoist. For example, temperature changes may cause changes in the mechanical properties of the material, affecting the strain and stress measurement results; high wind speeds may interfere with the stability of the equipment, etc. Therefore, environmental parameters should be controlled and recorded as much as possible during the test. For some test items with high requirements for environmental conditions, they need to be carried out within the specified environmental range, and the correction of environmental factors should be considered during data analysis.
Accuracy and reliability of test equipment: The accuracy and reliability of the load measurement equipment, sensors, data acquisition systems, etc. used in the test directly affect the accuracy of the test results. These equipment should be calibrated and checked before each test to ensure their normal operation, and regularly maintained and updated to ensure the credibility of the test data.
Test records and report preparation: Detailed and accurate recording of various information during the test, including test time, location, personnel, equipment number, test load, data collection results, equipment response, etc., is an important basis for the preparation of the test report. The test report should be complete in content, standardized in format, and clear in conclusion. It should be able to clearly reflect the entire process and result evaluation of the static load test, and provide users with more comprehensive equipment performance information.