How do you use a hanging scale?

How do you use a hanging scale?

With the continuous development of society, economy and technology, people pay more and more attention to safety issues, and the requirements for product safety are getting higher and higher. Among them, the safety of lifting machinery is one of the focuses of the AQSIQ. The reason why it has become the focus of attention is related to a number of major lifting safety accidents that have occurred in recent years. As an intermediate link of hoisting machinery, crane scale should also attract our attention. How to use the crane scale correctly so that it can read the weight safely and accurately has always been a difficult problem for many practitioners. Today SAINTBOND will teach you how to correctly understand the crane scale.

 

1. The importance of crane scale machinery safety

It has been nearly thirty years since the crane scale appeared in China. It is much later than other lifting machinery, and its application range is also smaller. It also appears as a measurement product and is managed by the measurement department. The measurement department pays more attention to the measurement performance. Therefore, the mechanical design specification and safety supervision system like hoisting machinery have not yet been formed. This is yet another reason for our attention. We know that hanging scales of 0.5t and above are usually used on cranes. The crane scale is connected to the crane on the top, and the sling rigging is connected to the bottom. As an intermediate link in the use of hoisting machinery, there should be no doubt that it should have the same safety performance as the crane and the sling, so as to ensure the safety level of the entire hoisting machinery system.

 

The manifestations of mechanical safety accidents of scale accessories are generally nothing more than the following: connection failure or broken connectors, broken load cells, and broken hooks. As a weighing instrument, the crane scale is mainly used for the measurement in the process of commodity exchange, but it is also used for process control in the industrial production process. Therefore, the object of measurement may be general commodities or dangerous goods such as molten liquid metal. . The damage caused by the safety accident of the Crane Scales Dynamometer may not only break the goods, but may have more serious consequences. Therefore, we must pay enough attention to the safety of crane scales to prevent problems before they happen.

 

2. Safety requirements for lifting machinery related parts and spreaders

The lifting machinery-related parts and spreaders connected to the upper and lower parts of the crane scale load cells, to be more specific, are various types of hooks and various types of spreaders. There are many technical standards, safety regulations, and precautions for use and maintenance of various types of hooks and various types of spreaders. They are divided into three stages: design, manufacture, and use, which can be summarized as follows:

 

1. Design stage

①The bearing structure should be simple, the force is clear, the force transmission is direct, and the influence of stress concentration is reduced.

②The influence of dynamic load, wear, corrosion, temperature, working environment and other factors on safety performance should be considered in the design.

③ The bearing structure shall have sufficient strength, rigidity and stability.

④ The material of the load-bearing structure is usually recommended to use low-alloy steel with high elongation and high impact energy.

 

2. Manufacturing stage

①The surface and interior of the bearing member should be free of defects sufficient to affect the use, and should have good fatigue resistance.

②The fiber direction of the forgings and the rolling direction of the rolled parts should be consistent with the direction of the force. The heat-affected zone formed by machining the surface by gas cutting and other methods must be eliminated.

③ Manufacturing materials and purchased parts must have technical certification documents such as the certificate of conformity of the manufacturing unit, otherwise they should be inspected and the performance can be verified before they are used.

④High-strength bolt connections should be tightened with special tools according to technical design requirements.

⑤ For products that have passed the inspection, the manufacturer shall make marks that are not easy to wear and tear at their appropriate positions, and issue a certificate of conformity. The content of the mark should at least include: rated lifting weight (limit working load), inspection mark, production number, date of manufacture, and manufacturer: the content of the certificate should include the main technical performance parameters; when the product is sold, it should be accompanied by safe use, maintenance manual.

 

3. Use stage

① Emphasize regular safety inspections during use.

② There are clear standards for scrapping.

 

3. Review the crane scale with the safety standards of lifting machinery

1. Manufacturing

The manufacturing process is also key to ensuring the safety of machinery.

 

①The influence of the quality of the material itself on the safety of the product should not be underestimated. SAINTBOND has analyzed the 40Cr bars of different manufacturers in the steel market, and the quality difference is still very obvious. For lifting structural parts, it is not only to look at their chemical composition and mechanical properties, but metallographic inspection is also necessary. For high-strength materials with notch sensitivity, the grain size of the steel and the grade of the inclusions in the steel have a more obvious influence on the fatigue life of the structural parts.

 

② The impact of manufacturing technology on the mechanical safety of the hanging crane scale is self-evident, mainly reflected in the forging, heat treatment and machining of the main stressed structural parts, and some large-scale products may have welding. Weighing instrument manufacturers are usually small in scale and often do not have the ability to forge and heat treatment. It is necessary to select qualified professional manufacturers and pay attention to strengthening the acceptance link of products. Special emphasis is placed on the processing of connecting threads. The load-bearing thread of the main force-bearing structural member in the crane scale is actually quite close to the force condition of the thread on the straight handle hook. There are detailed requirements for relevant threads and nuts in the national standard for straight shank hooks, including material, thermal processing, cutting, and inspection methods and requirements. Some crane scale manufacturers only process threads according to the requirements of ordinary fasteners, which cannot meet the safety requirements of lifting machinery.

 

③ Product identification and safe use and maintenance instructions. As a measurement product, the crane scale is clearly marked with the relevant accuracy grades and the manufacturing license of the measuring instrument, and the description of the use of the measurement is also very detailed. However, few manufacturers indicate the lifting work level of the crane scale, although the national standard of the crane scale stipulates that "the crane scale working with the crane should determine its work level". SAINTBOND has found more than once that users use common crane scales on cranes that are used very frequently, resulting in fracture accidents.

 

As for other precautions related to mechanical safety during use, there are not many clearly listed by other crane scale manufacturers. Only SAINTBOND will inform and guide customers in detail in advance on how to use the crane scale safely. Moreover, unlike other lifting slings, crane scales usually have a casing to cover part of the mechanical structure and electronic instruments. It is naturally difficult for ordinary crane workers to conduct safety inspections by conventional methods, and it is even more difficult to find potential safety hazards in general crane scales. No measures have been taken to limit the number of times of use or stipulate the period of use, which is actually a safety hazard.

 

3. Use

In addition to the safety problems mentioned above due to the lack of manufacturer's product identification and safe use and maintenance instructions, there are also user-related reasons, such as:

①During the lifting process, the force condition of the crane scale deteriorates.

②The supporting lower spreader is improper, which makes the stress condition of the crane scale worse.

③The upper hook used is too large, which restricts the free rotation of the Crane Scales sensor in the hook, which may cause the crane scale to be subjected to bending moment, which is especially unfavorable for the crane scale with threaded connection in the structure.

 

4. Summary

Crane scale is a measurement product, of course, should pay attention to measurement performance. Safety is the most basic requirement of all products and should be given enough attention. Safety issues involve all aspects of design, materials, manufacturing, use, and supervision. This article is only limited to personal opinion. It is a guide. I hope to attract the attention of the industry and take necessary measures to improve the mechanical safety standards of crane scales and improve crane scales. The safety level of the scale will promote the healthy development of this industry.