Quality analysis of rebar
Improving product quality is the way to rejuvenate the country, and it is the efficiency and competitiveness of enterprises. The steel rolling process deeply realizes that as the production unit of the end product, the strict management of quality and the enhancement of quality awareness are particularly important. Especially at present, iron and steel enterprises have encountered unprecedented difficulties in production and operation, and the production pace has slowed down, so the steel rolling process should strengthen the process control, enhance the quality awareness of employees, and improve the product quality level as the top priority to strictly control risks, enhance market competitiveness, and improve the efficiency of enterprises.
The production of steel rolling process is a process from heating - rolling - finishing - product storage and so on. Problems in each process may affect the improvement of product quality, so the process carefully analyzes the factors that affect the quality of products, and strictly controls each link, so that there is inspection, implementation and assessment; For each quality defect, a team should be organized, starting from me, to carefully analyze the causes, formulate measures, exchange training and education between teams, and improve the quality awareness of all employees and the ability of employees to deal with accidents; Establish and constantly improve the quality management system of the two production lines and maintain effective operation and continuous improvement, the vast majority of quality defects have been effectively solved, and the majority of employees can realize that "quality safety, our common responsibility". In response to the quality problem of surface scarring defects during the night shift on November 20, 2008, the process formulated the following measures to educate employees to improve quality awareness and eliminate similar quality defects due to rolling. Specific measures are as follows:
1, starting from all aspects of steel rolling production, and constantly optimize the production process.
2, constantly improve the process discipline, starting from the red blank size inspection of rolling steel, strengthen the implementation of supervision and management.
3, improve the cause analysis and treatment of quality defects, organize each employee to study, training, on-site guidance, from the source to eliminate the factors that may produce quality defects.
4, continuous rolling theory training, monthly training on the causes of seven quality defects on the finished product surface, improve the ability of employees to analyze and solve problems.
5, serious assessment system, every quality defect should be organized analysis and assessment, in a real sense to enhance the quality awareness of employees.
The following is the quality defect analysis of rolled steel products:
I. Types of finished product defects and their measures
1, folding: Folding refers to the surface of the steel along the rolling direction of the approximate longitudinal crack of the defect, there is a certain inclination Angle, generally in a straight line, with oxide sheet.
Reason analysis:
1) Ear, bump (groove wear or cutting guide wear) or severe scratch before the finished hole.
2) Before the finished hole, a roll drops meat or twists the rolled piece (improper guide adjustment).
3) There are grooves on the surface of the billet (the depth to width ratio is too large) or scratches.
Treatment measures:
Some of the surface folding of the finished product can be found in the sample post, and some are slightly or the surface welding is not easily found, and can only be found by doing a tensile test or bending test.
1) Check the shape of the finished product to determine the alignment of the frame guide or groove wear to replace the groove or adjust the guide.
2) The surface of the casting billet shall not have deep grooves or scratches and inclusions.
2, unilateral (or wrong side) : refers to the steel bar on the same section of the two sides of the longitudinal rib height is not the same, the difference is obvious.
Reason analysis:
1) The size of the roll gap on both sides is inconsistent.
2) The inlet guide is not in line with the groove.
3) Improper adjustment of finished product inlet guide, resulting in material dumping.
4) The wear of the groove before the finished product is uneven, and the incoming material changes.
5) The shape of the finished product before the slitting rolling process is not standardized.
6) Groove processing defects, the upper and lower groove openings are inconsistent.
7) The upper and lower rolling groove is not aligned, or the rolls are moving.
8) Uneven wear of finished rolling groove.
Treatment measures:
1) Most unilateral is due to the import guide is not generated, should first adjust the import guide.
2) Check the rolling groove before replacing the finished product.
3) When the wrong edge is checked, the rolling groove is aligned or there is no string roll, and the mill is adjusted or replaced.
3. Scarring (or warping) : A thin piece of scar-like metal on the surface of steel is called scarring. Some parts are connected with the matrix and are lingual; Some are not connected to the matrix and are scaly. Scarring defects directly affect the appearance quality and mechanical properties of steel.
Reason analysis:
1) In the rolling process, the previous pass has sand holes or damage for some reason (rolling groove meat), when the rolled piece forms a convex block on the back surface of the pass, and after rolling, periodic rooting and scarring on the surface of the finished product.
2) In the rolling process, the external metal falls on the surface of the rolled piece, and is brought into the pass deformation area, pressing into the surface of the rolled piece, resulting in scarring, such scarring is not rooted and irregular.
3) The rolled piece slips in the pass, causing the metal to accumulate on the surface around the deformation area, which is caused by the re-rolling. Due to poor scoring on the roll surface, high raised metal is formed on the surface of the rolled piece, and regular scarring occurs during re-rolling.
4) Due to poor scoring on the roll surface, a higher raised metal is formed on the surface of the rolled piece, and regular scarring occurs during re-rolling.
5) The surface of the billet is skinned and the bubble is broken close to the metal surface.
6) There is residue on the surface of raw materials.
Treatment measures:
1) Strictly implement the groove changing system, and the post workers strengthen the spot inspection of the post to find the groove defects in time (generally observe the running condition of the red blank in the normal production process or put the wooden board on the red blank for inspection), and replace the groove in time when the problem is found.
2) After the scarring defect is found, each position shall carefully inspect the rolling line area of each frame (especially the coarse and medium rolling) to remove the abnormal debris such as the scraper.
3) In the previous process, the quality of the casting billet is strictly avoided to avoid defects such as heavy skin, subcutaneous bubbles, surface residue and inclusion.
4, bending: the longitudinal uneven phenomenon of steel is called bending.
Reason analysis:
1) The water cooling is not uniform.
2) The cutting advance setting is improper.
3) Cold bed rack deformation or rack installation size changes.
Treatment measures:
1) Adjust the water cooling.
2) Adjust according to the specification size, water temperature and rolling speed within the allowable range of the equipment.
3) Check and adjust the straightening plate and rack of the cold bed.
5, size overshoot: section geometry does not meet the requirements of the standard, collectively referred to as size overshoot. Including inner diameter overdifference, longitudinal rib overdifference, transverse rib overdifference, rib spacing overdifference and so on.
Treatment measures:
1) When the inner diameter and longitudinal rib are out of step, timely adjust the roll gap of the finished frame, adjust the tension and adjust the material shape of each frame before the finished product.
2) When the transverse rib is abnormal (height is not enough), first observe whether it is caused by the difficulty of grooving, if the excess is small, it can be met by adjusting the shape and tension of the finished material, if the requirements are not met by online adjustment, it is necessary to find the reason from the rolling groove processing parameters or processing quality.
3) When the rib spacing is not enough, it is generally due to changes in the rolling groove processing parameters or processing quality problems, but it can also be slightly compensated by adjusting the tension before the finished product.
6, crack: the surface of the material has a different shape of the fracture, or in the process of mechanical experiment on the surface of the steel cracking phenomenon. In serious cases, it cracks during the rolling process or water cooling process and is divided into two or more layers. Such defects are likely to affect the mechanical properties of steel.
Reason analysis:
1) The billet contains a large number of subcutaneous bubbles, residual shrinkage holes and serious non-metallic inclusion defects, cracking in the rolling process.
2) Billets with high sulfur and phosphorus content are easy to form transverse or longitudinal cracks in the process of severe deformation.
3) The billet is overburned when heated.
4) Serious uneven temperature in the rolling process.
5) Local quenching in the cooling process.
Treatment measures:
1) The quality of the casting billet is stable and the composition is controlled within the required range.
2) Strictly implement the temperature system and insulation system to ensure the heating quality of the billet and avoid overburning of the billet.
3) Low temperature steel rolling is strictly prohibited.
7. Scratches (or gouges) : defects similar to longitudinal cracks on the surface of the material along the axial direction of the material.
Reason analysis:
1) Uneven groove wear or groove scratches are easy to produce scratches.
2) When the groove has serious cracks, it is easy to produce scratches.
3) Improper roll turning, there are knife marks resulting in scratches.
4) There is a scraping iron in the exit or guide groove of the finished mill or there are sharp objects left to scratch the rolled pieces.
5) Due to the deviation of the outlet or guide groove installation, the above is not smooth, and one side of it has long-term friction with the rolled piece.
Treatment measures:
1) After the appearance of scratches, it is necessary to carefully check the full perimeter of the rolling groove, including the rolling groove before the finished product. When uneven groove wear is found (mainly due to uneven water cooling or non-standard material shape on the last pass) or scratches (mainly due to outlet installation or guide tip hanging iron), timely replacement of the groove, if there is uneven wear or adhere to foreign debris before the finished product, clean or replace the groove in time.
2) When there are scratches on the surface of the finished product, it is necessary to stop the machine in time to check whether the import and export guide of the finished product frame has a scraping iron and its installation quality, check the no different debris in the guide groove and the friction of the finished product, and check whether the transport roller table is locked.
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