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Common appearance defects of rebar and preventive measures
[/vc_column_text][vc_separator border_width=”4″ css=”.vc_custom_1634717105239{padding-top: 30px !important;padding-bottom: 30px !important;}”][vc_column_text]Description：
Product quality is the top priority for the development of an enterprise, and guaranteeing the qualified products of the factory is the basic condition for the survival of the enterprise. Enterprises must survive and develop in fierce market competition. Without excellent product quality, they will eventually be eliminated in the wave of market economy. Jingye Group is a large-scale rebar production base in the world. The quality of rebar products is stable and reliable, and it is inseparable from the quality inspection of product quality inspections by quality inspectors. Through the first inspection, mutual inspection by the operators of the production workshop, and the special inspection by the quality inspection personnel, they found that the quality fluctuations were notified to the production adjustment in time, and the quality control and supervision of the production process were carried out to ensure the stability of the quality; the difference in inspection methods and methods will affect the The final judgment of the product affects the control of creating high-quality goods. After a long-term practical inspection, the Metrology and Quality Inspection Department has summarized the following common rebar appearance quality defects and preventive measures:
Keyword：
Surface cracks; Folding; Scars; Warped skin; Staggered roll
Realed product：
[/vc_column_text][vc_column_text]Surface cracks:
Cracks refer to parallel and vertical linear cracks on the surface of the steel along the rolling direction. Some cracks contain inclusions and decarburization on both sides.
Cause:
1) There are unremoved cracks, subcutaneous bubbles and non-metallic inclusions on the surface of the billet;
2) The billet has pinholes (surface pores), which will cause linear cracks when oxidized after rolling;
3) In the first few passes of rough rolling, cracks occurred in the rolled piece due to thick oxide scale.
Precaution:
1) Strict inspection and inspection, found that there are surface cracks, surface pores and inclusions of the cast slab, which shall not be cast into the furnace for rolling.
2) Reduce the time of the billet in the furnace, and try to reduce the thickness of the oxide scale.
Folding:
Cause:
1) As ears are generated in the previous pass of rolling, the subsequent rolling pieces are folded back to produce folds;
2) Before the finished product, the rolls of a rolling mill fell off, which caused bumps in the rolled piece, which would be easy to fold after rolling;
3) The K3 rolling mill has a large slitting width during slitting and rolling, which is easy to produce folding;
4) The internal defects of the billet can easily cause the rebar to fold.
Precaution:
1) Adjust the roll in time and install the guide and guard correctly.
2) 2) Improve the internal quality of the continuous casting slab.
3) Adjust the relationship between the pre-slicing rolling mill, the slitting rolling mill and the slitting wheel.
Scars:
Metal or non-metal scars on the surface of the steel that are not welded to the substrate, which appear as creases, massive scars, and sawtooth scars on the steel.
Cause:
1) The material of the blank itself is uneven and there are many impurities;
2) Roll scratches and poor surface processing.
Precaution:
1) The inspection is strictly controlled. If there are inclusions on the surface of the cast slab, the production should be notified to grind in time, otherwise it is not allowed to be put into the furnace.
2) The production should check the surface quality of the steel bar frequently. If the surface is scarred and there is a certain pattern, you must stop and check the usage of the roll and guide guard. If there is any problem, replace it immediately;
3) Strengthen the acceptance of the surface of the roll after processing.
Warped skin:
the surface of the rebar is tongue-like, block-like or scale-like raised flakes.
Cause:
1) The pass design of the rolling mill is unreasonable, and the rolled piece appears wrinkled during the deformation process to form a warped skin.
2) The billet is of poor quality and has more surface inclusions.
3) Mixing of mold powder.
4) The subcutaneous bubbles of the billet.
Precaution:
1) Optimize the pass design, so that the rolled piece does not fold during deformation.
2) Strictly inspect the surface quality of the blanks, and grind and remove the inclusions to provide qualified blanks for steel rolling.
3) Stir the molten steel evenly to fully deoxidize it to avoid subcutaneous bubbles.
Staggered roll:
The two semicircles of the rebar are staggered, and the center lines do not coincide.
Cause:
1) The roller ring is not installed in place, and the roller sleeve is struggling to cause the roller ring to not press on the oil slinger.
2) The roll shaft thrust bearing gland bolt is broken or the bearing is peeled off, causing the roll to move in the axial direction.
3) The rolling guide wheel is broken and can’t hold the material, causing the rolling material to deviate.
Precaution:
1) Reinstall the roller ring and replace the oil slinger.
2) Check the thickness of the roll ring gasket.
3) Replace the rolling guide wheel.
Bending:
The phenomenon that the steel bar is not straight in the longitudinal direction is called bending. According to the bending shape, it can be divided into “sickle bend”, “wave bend”, “elbow” and so on.
Cause:
1) Improper steel rolling operation or uneven cooling temperature of the rolled piece.
2) Improper installation of the finished product export guide.
3) The movement of the cooling bed skirt board is different, resulting in bent steel.
4) The cold shear blade is not fast, and the gap between the upper and lower shear blades is large, which leads to the shear elbow.
Precaution:
1) Improve the staff’s operating level and install the guide and guard device correctly.
2) Strengthen the maintenance and spot inspection of cooling bed equipment, so that the equipment must meet the requirements for use.
3) Cut strictly according to the number of shears, and replace the cutting blade in time according to the situation.
Bump:
The surface of the steel bar is periodically raised.
Cause:
1) There are blisters, meat loss or damage to the surface of the steel bar due to blisters, meat loss or damage to the front hole of the finished product or the finished product;
2) The roll surface is bumped by the rolled piece, and the meat falls off, causing bumps on the surface of the steel bar.
Precaution:
Roll in strict accordance with the allowable steel volume, and replace the rolls in time.
Pocked surface (pits):
There are many small grain defects on the surface of the threaded steel, which are called pocked surfaces. It is distributed periodically or continuously on the steel bars.
cause:
1) Severe rust or bad hole and groove surface occurs after the roll is turned;
2) The rolling groove is not changed for a long time, which makes the upper and lower grooves that are most easily worn in the finished pass aging and the surface is rough;
3) There is a lot of iron oxide scale adhered to the surface of the rolling groove, which is pressed into the surface of the steel bar during rolling, causing pitting on the finished product;
Precaution:
1) It is strictly forbidden to use the rolls with severe surface corrosion or poor hole and groove surface on the machine;
2) Changing rolls and grooves must be replaced in strict accordance with the roll service cycle rules;
3) Strengthen the inspection of rolling grooves and remove the oxide scale on the surface in time;
4) During controlled rolling and controlled cooling production, the quality and pressure of cooling water meet the technological requirements.
No longitudinal rib/longitudinal rib super positive difference:
The rebar has no longitudinal rib or the longitudinal rib exceeds the specified standard.
Cause:
1) The finished hole is severely worn. When the material type is constant, the rolling inner diameter becomes larger, and the amount of metal flowing to the roll gap is insufficient, which is easy to cause no longitudinal ribs;
2) The material shape before the finished hole is affected. A small material shape will cause no longitudinal ribs, and a large material shape will easily cause the longitudinal ribs to exceed the standard;
3) Improper adjustment of the roll gap of the rolling mill;
4) Influence of finishing rolling temperature;
Precaution:
1) Replace the finished hole or adjust the reduction of the finished product.
2) Adjust the shape of the hole material before the finished product, and stabilize the rolling process system.
Inappropriate appearance size:
the horizontal rib is high, and the maximum gap at the end of the horizontal rib is unqualified.
Causes: unqualified roll groove design, delay in changing rolls or pressing materials in time.
Preventive measures: Strengthen roll groove design and acceptance, and change rolls and grooves in time.[/vc_column_text][vc_column_text]One stop solution for steel industry[/vc_column_text][/vc_column][/vc_row]
