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Probing into the misunderstanding and preventive measures in the use of grinding wheels

I. raising problems

for a period of time, the author has encountered several wheel burst accidents in the actual safety management work when using moving grinding wheels for casting sand cleaning and grinding with grinders, which has posed a major threat to the personal safety of employees, affected the normal operation of production to a certain extent, and caused economic losses to the enterprise. The bursting of grinding wheel occurs during the idling test before formal use and during the grinding process. After the investigation, summary and repeated analysis of these two situations and similar accidents in the past, it is found that there are misunderstandings in many links of production with grinding wheels

II. Misunderstandings in the use of grinding wheels

there are the following misunderstandings in the process of submission, procurement, grinding and other use of grinding wheels:

1. Without technical analysis, the user unit put forward clear requirements for the structural characteristics of grinding wheels, resulting in some structural characteristics of grinding wheels being omitted or ambiguous in the submitted grinding wheel procurement plan

2. The purchasing personnel did not understand the specific production purpose of the grinding wheel and the basic characteristics of the grinding wheel, so they drew a gourd and purchased the wheels that did not meet the production requirements as planned

3. Operators lack excellent safety technical quality. (1) Mistakenly think that the grinding wheel has been balanced before leaving the factory, and it is not necessary to balance before use; (2) Incorrect sound knocking inspection method is adopted before installing ceramic bonded grinding wheel; (3) The size and gasket of the chuck used do not meet the national safety standards

4. The linear speed of the grinding wheel during operation is inconsistent with the rated linear speed, and the grinding wheel operation speed is too large for human reasons

III. analyze the harmfulness of mistakes and take preventive measures to standardize operation

there are various mistakes in the use of grinding wheels, such as improper selection of grinding wheel model, excessive linear speed, poor balance of grinding wheels, improper installation, incorrect operation, etc., which may lead to the breakage of high-speed rotating grinding wheels, light side delay in production, and scrapping of grinding wheels; The worst is to cause casualties, property losses of enterprises, and even bad social impact

1. The structural characteristics (specifications and models) of the grinding wheel are improperly selected. After the plan is submitted, the purchasing department may purchase grinding wheels that cannot meet the production requirements, and hidden dangers of accidents are buried from the beginning of work

for example, because the Foundry Branch did not put forward clear performance requirements for the pneumatic grinding wheel used, the relevant personnel could not even understand the meaning of the sand line speed. In the plan, only the dimensions were reported, and other properties of the grinding wheel were ignored. The 50 m/s grinding wheel should have been used in production. As a result, the 35 m/s grinding wheel was purchased and installed for use, causing the pneumatic grinding wheel to break during ultra-high speed rotation

therefore, the technical personnel of the unit using the grinding wheel analyze and demonstrate the material, process requirements, specific grinding conditions, characteristics and the speed of the grinding equipment of the workpiece processed in the production process, so as to determine the characteristics of the grinding wheel required in the production. Such as: abrasive, particle size, hardness, binder, shape, size (including grinding wheel outer diameter D, thickness h, inner diameter d) and linear speed. Accordingly, the plan submitter shall accurately and timely submit the grinding wheel procurement plan to the purchasing personnel to eliminate the hidden danger of grinding wheel cracking from the source

2. Guide relevant accident units to select grinding wheel models, and examine and standardize the production qualification and product quality of suppliers. At the same time, the procurement department is required to review the grinding wheel procurement plan received from the production unit, carefully check the characteristics of the submitted grinding wheel against the national standards, investigate and understand the specific production use of the grinding wheel when necessary, and correct the non-standard items in the plan in time, so as to ensure that the purchased grinding wheel meets the production requirements and national standards, and eliminate the hidden dangers that may be caused by the procurement process

for example, the forging branch used inferior grinding wheels without manufacturer and production certificate purchased by the electromechanical center of the third production department, which also caused a grinding wheel with an outer diameter of 400mm to break during test run. In order to prevent similar events from happening again, the remaining grinding wheels of the same batch were returned to the warehouse after investigation and study by the user and relevant departments

3. Due to the lack of knowledge about the safe use of grinding wheel or the pursuit of output, the operators cut down the safe operation steps or habitual wrong operation and other illegal behaviors, which are the biggest hidden dangers leading to the fracture of grinding wheel. In the actual production process, there are often the following situations:

first, the grinding wheel with an outer diameter greater than 200mm is used by the grinder. "Ma Zhanfeng said that after the chuck is installed, it is installed and used without static balance, because the operator mistakenly believes that the balance is only the business of the manufacturer, and the grinding wheel has been balanced when it leaves the factory. There is no need to balance when using. This is a misunderstanding of the safe use of grinding wheel

for example, in May, 2002, when a worker of 615 branch was working on a grinder equipped with a single crystal grinding wheel with an outer diameter of 900mm to process diesel engine crankshafts, a piece of sand worth more than 2000 yuan burst due to the above reasons. Fortunately, no casualties were caused, but the normal production was affected to a certain extent

in view of this situation, we have prepared and issued the instructions for safe use of "grinding wheel adjustment static balance" and "grinding wheel dressing" and the national standards for safety technology related to the use of grinding tools, and organized more than 200 grinders in each branch to learn. It is emphasized that the center of gravity of the grinding wheel will not coincide with the rotation axis and cause imbalance due to the asymmetry of the grinding wheel geometry, the non concentricity of the outer circle and the inner hole, the inconsistency of the tightness of each part of the grinding wheel and the eccentricity during installation. The unbalanced grinding wheel is easy to make the grinding wheel spindle vibrate or swing, and accelerate the wear of the spindle and bearing, which not only affects the processing quality, but also easily causes the grinding wheel to break. Therefore, employees are required to conduct a balance test before grinding with a grinding wheel with an outer diameter greater than or equal to 200mm on the grinder to ensure the balanced operation of the grinding wheel and the grinder spindle after installation and coordination, so as to ensure the safety in the production process

second, before installing the ceramic bond grinding wheel, some workers mistakenly used iron tools when knocking to check whether the grinding wheel has cracks with the sound inspection method. As a result of this operation, the original intact grinding wheel increases the possibility of cracks, which is not desirable. Therefore, the staff must correctly use the wooden hammer for knocking inspection

third, although chucks are installed on both sides of the grinding wheel as required, and pads are added between the chucks and the grinding wheel, the used chucks and pads are not standardized, specifically as follows:

a, the size of the chuck is large or small, which does not meet the national standards (that is, the diameter of the chuck shall not be less than one third of the diameter of the grinding wheel, and the diameter of the cut-off sand wheel shall not be less than one fourth of the diameter of the grinding wheel)

b. the liner does not use elastic materials (such as rubber plate, felt, leather, asbestos board, etc.) according to national standards

c. the thickness and size of the gasket do not meet the requirements of the national standard (that is, the thickness should be 1-1.5mm, and the diameter should be more than 1mm larger than the chuck diameter)

d, sometimes even forget to add padding

although these cases are individual behaviors, the consequences are serious. Therefore, we have also put forward specific standards for chucks and liners in the safety production learning materials to put an end to the above misoperations

4. The linear speed V of the grinding wheel is related to the number of revolutions N and the diameter D of the grinding wheel (v=d л n/(60 × 1000), d-mm, N-R/min, V-M/s). For grinding wheels with the same diameter, the higher the speed is, the greater the linear speed is, and it is necessary to supplement the pressure immediately; Only charge nitrogen into the accumulator;, The greater the centrifugal force, the greater the possibility of crushing caused by centrifugation. In this regard, there are the following wrong operations in actual production:

a. before installing the grinding wheel, the operator does not carefully check whether the rated linear speed printed on the grinding wheel matches the spindle speed of the grinding wheel, resulting in exceeding the specified rated speed during use

b. the operator does not understand the matching problem between the linear speed of the grinding wheel and the speed of the grinder (or the number of revolutions of the spindle of the machine tool). The grinding wheel is installed and used immediately after it is received

c. when replacing a new grinding wheel, the spindle speed when using the worn grinding wheel was not adjusted in time, causing the linear speed of the grinding wheel to exceed the rated linear speed

d. in order to pursue personal economic interests, the operator of the portable pneumatic grinder adjusts the governor of the pneumatic grinder to increase the grinding wheel speed without authorization

for example, in order to complete more working hours, some employees of the Foundry Branch arbitrarily increased the rotation speed of the pneumatic grinder, so that the actual rotation of the 150mm outer diameter grinding wheel that should have worked at 5500-6600 RPM reached about 8000 rpm, resulting in serious overspeed rotation of the grinding wheel and breakage

the above four conditions may cause the grinding wheel to burst during overspeed rotation, resulting in serious consequences. Therefore, before using the grinding wheel, the operator is required to:

first, check whether the linear speed of the grinding wheel is appropriate, and do not make it run beyond the rated linear speed

second, it is forbidden to increase the rotating speed of the pneumatic grinder without authorization

third, let's talk about how to calibrate and test. In the grinding process, with the wear of the grinding wheel, its outer diameter gradually becomes smaller. At this time, in order to ensure the peripheral speed of grinding, it is necessary to increase the spindle speed. When the grinding wheel is nearly worn, the spindle rotates at the highest speed. Therefore, when replacing a new grinding wheel, the spindle speed in the highest turning state must be adjusted to ensure that the peripheral speed of the grinding wheel does not exceed the rated speed. Avoid grinding wheel crushing accidents

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