Main Influencing Factors and Control of Heat Treatment Quality of Fasteners

Main Influencing Factors and Control of Heat Treatment Quality of Fasteners

Heat treatment can make high-strength fasteners to obtain the design requirements of a certain strength, good plasticity, toughness and low notch sensitivity and high bending strength, to avoid relaxation phenomenon and other comprehensive mechanical properties and performance, so as to ensure the quality and reliability of fasteners, improve the market competitiveness of fastener products.

Heat treatment process has a crucial influence on high-strength fasteners, especially their intrinsic quality. Therefore, in order to produce high-quality high-strength fasteners, it is necessary to have advanced heat treatment process and heat treatment process control.

Heat treatment process is characterized by changing the internal structure of the material to make a variety of fasteners to obtain the required performance and quality, the process usually does not change the shape of the material or fasteners. Because the quality characteristics of the products given by heat treatment are often not intuitive internal quality (such as tensile strength, reduction of area, elongation, etc.), in order to ensure the quality of heat treatment in production, fasteners or samples with the furnace are generally tested through special instruments and equipment. However, due to the limitation of inspection sampling rate and inspection parts, for fasteners of each specification or even fasteners of each furnace, the inspection is local or individual, it is difficult to do the heat treatment quality of 100% of the detection. Therefore, all test results cannot fully reflect the heat treatment quality of the entire batch of fasteners or the entire fastener.

Due to the heat treatment production according to the furnace batch input or continuous production once the heat treatment quality problems, the previous efforts are abandoned, resulting in a great loss. If there is a heat treatment defect, it is easy to cause serious mechanical failure, resulting in incalculable loss. Therefore, it is particularly important to strictly control the whole process of heat treatment production and implement comprehensive quality management. It is of special significance to carry out the ISO9000 series certification work in the fastener industry and has received widespread attention. Heat treatment production is the same as other production processes without the four elements of man, machine, material and method (Man,Machine,Material,Method, 4M for short). Environmental protection is not considered here for the time being. They are all the main factors affecting the quality of heat treatment products, affecting and restricting each other, and finally determining the quality of heat treatment of fasteners.

The following reference ISO9000:2000 version of the standard requirements, the heat treatment 4M management points are analyzed and the corresponding control measures are put forward to ensure the quality of heat treatment of fasteners.

1, participants (person)

The departments involved in heat treatment production generally include equipment maintenance department, tooling management department, measurement management department and procurement and supply department, as well as production, technology and inspection department (including metallographic testing). In order to control the quality of heat treatment products, it is necessary to mobilize all members of all departments and implement full participation. Quality control is process control, not just rely on a few people or a few departments can do. In order to achieve full participation in fastener heat treatment quality control. First of all, the responsibilities and authorities of all types of personnel must be clarified, and employees must bear the responsibility of solving problems when exercising their rights. Secondly, enterprises should organize job training in a planned way, improve employees' operational skills and quality control skills, and carry out qualification certification for important positions (such as high-frequency induction heating). Heat treatment production is highly professional, employees only have sufficient knowledge, skills and experience, in order to be competent, to achieve full participation. Secondly, it is necessary to carry out various forms of quality awareness, communication awareness, professional ethics and professionalism education, improve the quality of employees, promote mutual education and mutual learning, and jointly improve the quality of fastener heat treatment. In addition, enterprises should actively create conditions to encourage employees to innovate and develop, to achieve continuous improvement.

2, equipment tooling (machine)

Heat treatment production equipment tooling more types, but also often use some precision measuring instruments, to provide equipment, tooling, measurement security, improve the reproducibility and reliability of the heat treatment process is based on the fastener heat treatment quality assurance, but also to the operator safety considerations. The operator is required to strictly abide by the operating procedures of equipment, tooling and measuring tools, and implement civilized operation and maintenance. The maintenance personnel of heat treatment equipment shall do a good job in daily maintenance and regular maintenance of the equipment, and timely carry out improved maintenance of the equipment, strictly implement the management system of tooling station equipment, require the operator to correctly use the tooling according to the system and process requirements and return it in time, and require the tooling management department to do a good job in the distribution, storage, maintenance and verification, adjustment, repair and replacement of the tooling. Strictly implement the measurement management system, require the operator to use and maintain the measuring instruments correctly according to the quality requirements of the system and fastener heat treatment, and require the measurement department to do a good job in the calibration, maintenance and identification of the measuring instruments according to the regulations. Because sometimes a little error temperature control instrument will affect the operator's judgment.

3, fastener material (material)

For fastener heat treatment production, although the material has been determined at the time of design and its own factor cannot be controlled, factors affecting the heat treatment quality of high-strength fasteners such as mixing, wrong material, loss, corrosion, bump and deformation will often occur in the treatment, transportation, inventory and work of heat treatment production. Relevant personnel can work carefully and effectively to avoid the occurrence of mixing, leakage, wrong material and other undesirable phenomena. The inspection department is required to do a good job in the inspection of materials, state identification (e.g. different steel numbers are distinguished by different colors of oil), and the material storage department is required to do a good job in the identification of materials, the collection, delivery, handling and storage of materials. The production department shall work carefully and carefully, do a good job in the identification, storage and storage of work-in-progress, find problems in time and notify relevant departments to deal with them in time. In the heat treatment production, many high-strength fastener material problems can be repaired and solved by the corresponding process technology as long as they are found in time. For example, the quenched bolt was later found to be ML35 steel for grade 35# steel, and the tensile strength was tested to be qualified for "release" after lowering the tempering temperature. If the deformation of longer specification bolts exceeds the standard, it can be solved by the corresponding straighter process. If the surface of the fastener is rusty, it can turn black again after pickling, and if there is more oxide skin, it can be solved by sandblasting. Of course, "after the fact" to solve the problem is a last resort, to be cautious.

4, process specification (law)

Heat treatment is an important process in the processing of high-strength fasteners, which plays a key role in improving the market competitiveness of fastener products. Heat treatment is essentially a process that improves the performance, service performance and service life of a material by strictly controlling the heating and cooling process of the material.

Heat treatment production technology is very theoretical and practical, there must be a set of suitable heat treatment process plus a more perfect operating specifications in order to control the quality of heat treatment. From the perspective of quality control, the development of heat treatment process should be based on specific high-strength fastener materials and related equipment tooling and staff operating skills to select the appropriate process parameters, heat treatment process staff must be familiar with the production site, and constantly through the practice of confirmation to improve the process and continuous improvement. For high-strength bolts above grade 10.9, nuts above grade 10 or new materials with special requirements, key control shall be implemented together with on-site constructors and operators. Original records shall be made in strict accordance with the requirements of quality control documents. If any abnormality is found, corrective measures shall be taken in time. In addition, strict process change control. Implement changes in accordance with process document control procedures.

The technical document storage department shall do a good job in the management of technical documents to ensure that the drawings, process documents and quality control documents used on the production site are complete, perfect, unified and clear. Heat treatment production operators must strictly implement the process discipline, according to the process operation, shall not arbitrarily change the parameters, temperature (time, medium, equipment, process, etc.). Management personnel, including craftsmen, constructors, inspectors, etc., are required to regularly carry out process discipline inspections at different levels, and problems found should be dealt with seriously.

5, conclusion.

In order to prevent 4M (human, machine, material, method) changes and produce fastener product quality problems, to specify the four main factors affecting the quality of heat treatment management methods change. Strengthen 4M management, personnel factor is the most critical. An excellent fastener heat treatment worker should not only have certain attainments in heat treatment process, metal materials and metallographic analysis, but also be familiar with heat treatment equipment in-depth on-site operation according to the process, that is to say, he must have rich working experience. Of course, the real enterprise like this development of a comprehensive fastener heat treatment talent is too little. In order to improve the quality of heat treatment of fasteners, including the quality of fastener products, it is necessary to train talents, and it is also the way out for the development of enterprises.

Source: Golden Spider Fastener Web