Description of 16 common defects of cold rolled strip stock
The billet used in cold rolled strip mill is hot rolled strip, the billet itself is of poor quality and incorrect process operation often has various defects. It will have a great impact on the quality of our cold rolled products.
(1) Iron oxide rolled into
Hot-rolled strip steel surface adhered to a layer of iron oxide, its color is mostly gray-black or red-brown, the distribution area has a large and small, there are lumps and strips, rolled into the depth of the difference between shallow and deep. The cause is the high rolling temperature of the formation of recycled iron oxide is pressed into the surface of the strip or heating time and heating temperature is too high to cause oxidation atmosphere and generate iron oxide in the rolling pressed into. The thickness of the generated iron oxide, usually depends on the heating conditions, steel quality, the opening and final rolling temperature.
(2) Bending (commonly known as sickle bend)
The length of the strip direction in the horizontal plane to the side of the bend. The reason is that the roll type processing is incorrect or roll slit adjustment is not flat exercise strip extension inconsistent, in addition to the strip billet itself on both sides of the uneven heating temperature will also promote the rolling extension is not the same, there are two sides of the amount of pressure adjustment such as improper, both sides of the roll tile wear is not a guide guard device is not installed correctly, etc. will lead to the bending of the strip in the rolling.
(3) Cracked edge
Strip edge rupture serious strip edge is torn into jagged, and there are obvious metal fragments. The reasons for this are complex: both related to steel quality, and heating, rolling process. Boiled down to the main roll roll design is unreasonable, roll adjustment is not correct, low-temperature rolling, followed by the strip steel chemical composition is not suitable or brittle billet, and then the edge of the billet cracks or billet over-burning, etc., are the reasons for the cracked edge.
The surface of the strip has lower than the rolling surface of the longitudinal and transverse scratch grooves, varying in length and location, generally continuous or intermittent distribution in the full length of the strip or local. Longitudinal scratches are mostly rolling guide plate or rollers have sharp angles and strip contact formation or in the winding process scratches, transverse scratches due to the strip in the cold bed transverse or in the process of transport caused by abrasions.
The surface of the strip is different in shape, the size of the crater, the crater is not periodic. The reason is that the rolls, pinch rolls produce sticky rolls or adhesion of iron oxide, if foreign objects fall on the surface of the strip, after rolling off will also form pits on the surface of the strip, in addition to the strip in the process of stacking with hard objects, or with a hard sharp corner of the material pad bottom will also form the indentation of the strip.
(6) Roll marks
Strip steel surface strip or sheet-like periodic roll indentation, the indentation part of the brighter, but no obvious convexity and concave feeling. The reason is that the roll material is bad, low hardness and easy to damage, high hardness of the strip steel or rolling without attention to the roll surface to produce branding or sticky iron chips.
(7) Thickness is not uniform
The thickness of each part of the strip is not consistent. Uneven thickness has a longitudinal (length direction) and transverse (width direction), that is, in the same longitudinal section appears head, middle and tail parts of the thickness inconsistency and in the same cross-section on both sides and the middle or both sides and other parts of the thickness inconsistency. The reason is the uneven heating temperature of the strip or each pass under the pressure distribution is unreasonable, resulting in inconsistent plastic deformation of the strip roll roll configuration or roll bending deformation will also cause periodic thickness unevenness in addition to the thickness of the strip itself inconsistent as well as rolls and two shaft tile wear serious will make the strip thickness uneven.
(8) Scarring (also known as heavy skin)
The surface of the strip is “tongue”-like or “fish scale”-like warped sheet. Its area and thickness are not equal to the size of the profile is extremely irregular, closed and not closed, with the body of the steel and folded to the surface of the strip and not easy to fall off, there is no connection with the body of the steel but bonded to the surface of the strip, easy to fall off, there are warped and not warped, the general rolling products of the scar is not easy to warp, around the traces, the following iron oxide, caused by the steel scars easy to warp and The scars caused by steel making are easy to warp and open, and there are inclusions underneath. The reason is that there are residual scars on the ingot surface (heavy skin), pressed into the surface of the strip after rolling, or the strip surface is uneven, the cleaning depth to width ratio is not enough, the surface of the rolled part is seriously scraped and then rolled, or the finished product before a certain roll to drop the meat or have a sand eye, the surface of the strip through the bump, re-rolling after the periodic roots of the scar, or because the rolls bonded metal, the strip through the formation of pits, re-rolling if the extension of different The crater will also be deformed and scarred, in addition to rolling foreign metal falling on the surface of the strip billet is brought into the roll, rolled and pressed into the surface of the strip to form a non-rooted scar.
(9) Surface inclusions
Strip steel surface with more obvious dot, block or strip of non-metallic inclusions, its color is red-brown, light yellow and gray-white. Caused by poor slag making, steel barrel is not clean, or strip heating refractory crumbling strip steel surface adhesion of non-metallic inclusions, rolling not peeled off the surface inclusions.
Strip steel surface shows a local or continuous patch of rough surface, distributed in different shapes and sizes of craters in serious cases, similar to orange peel-like than the pockmark large and deep pockmark. The reason is that the heating process of the strip surface oxidation, rolling iron oxide into pieces or lumps pressed into the surface of the strip, in the rolling process or after pickling off the formation of small pits, commonly known as oxidation pockmark, poor quality rolls, serious wear and tear will also cause the strip pockmark, but also due to the heating process by a gas corrosion, the formation of gas corrosion pockmark.
The strip forms a double layer of metal that is partially folded to each other. The reason is that the roll type and the amount of pressure is not properly controlled to form a large wave is rolled after pressing together, or improper operation caused by local pressing together, heating temperature difference is large, local deformation is not uniform on both sides of the extension will also form folding.
There is an obvious separation of the metal structure destroys the overall continuity of the strip. In severe cases, it is divided into 2-3 layers, between layers and layers sometimes have inclusions visible to the naked eye, inclusions generated by the delamination site is not fixed. The reason is that the ingot rolling strip billet shrinkage is not cut net, so that the strip billet with shrinkage remnants, or ingots have a concentration of inclusions in addition, the chemical composition of the severe segregation may also form delamination.
(13) Red spot
The surface of the strip steel shows red, but there is a certain depth of the spot. The reason is due to the furnace ash or not removed from the red iron oxide pressed into the surface of the strip steel.
The surface of the strip is irregularly distributed with rounded bubbles of different sizes, the outer edge is relatively smooth, most of them are bulging, some are not bulging and the surface is shiny after pickling, its cross-section is layered and presents raised voids, the reason is that the steel boiling is not good, bad gas, so that the interior of the ingot billet produces serious bubbles by repeated rolling without welding up, or boiling ingot pouring temperature is too low, pouring speed Too fast, so that the gas does not have the opportunity to run out, the number of bubbles formed too much, too large, rolling failed to weld together.
The surface of the strip has different shapes of rupture, its direction is arbitrary. There is a kind of parallel to the rolling direction of the smooth crack, there is a dense fish scale or needle cracks. It often appears on the edge of the strip, and when the crack is serious, there is a clear opening, deep and long. This is mainly brought by the billet, such as billet bubble rupture and billet cracks exposed after rolling, in addition to steel sulfur, phosphorus composition out of the box or slow cooling of the strip, poor removal, etc. will cause cracks in the strip.
Both sides of the strip sometimes form a flying burr, it is a sharp and thin protruding metal on the end of such defects are mainly found in broadband steel cut into narrow strip steel strip blanks. The main reason is that the cutting edge is too blunt cutting edge is loose and improper adjustment of the cutting edge will also cause burrs.
Source: Cold Rolled Strip Supplier: www.epowermetals.com
(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)
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