What are the common cold work defects? What are the causes of cold rolled product defects?

Cold working refers to the processing technology of plastic deformation of metals at a temperature lower than that of recrystallization, such as cold rolling, cold drawing, cold forging, stamping, cold extrusion, etc. The cold work deformation resistance is large, and the hardness and strength of the workpiece can be improved by using work hardening while forming the metal.

It usually refers to the cutting of metal, that is, the cutting tool is used to cut off the excess metal layer from the metal material (blank) or workpiece, so that the workpiece can obtain a certain shape, dimensional accuracy and surface roughness processing method. Such as turning, drilling, milling, planing, grinding, broaching, etc. In metal technology, corresponding to hot working, cold working refers to the processing technology that causes plastic deformation of metals at a temperature lower than that of recrystallization, such as cold rolling, cold drawing, cold forging, stamping, cold extrusion, etc.

The cold working deformation resistance is large, and the hardness and strength of the workpiece can be improved by work hardening while forming the metal, but the plasticity will be reduced. Cold working is suitable for processing metal parts with small cross-sectional size and high requirements for size and surface roughness.

Generally speaking, the "processing" in cold and hot working often refers to plastic deformation. For the plastic deformation of metals, there is a specific temperature called the recrystallization temperature, above which the deformation process is called hot working (deformation), and the processing below this temperature is cold working (deformation). There is no work hardening in hot work, or work hardening is eliminated at any time.

Effect on the microstructure after thermal processing :(1) Improvement of ingot microstructure. Eliminate voids, refine grains, and reduce segregation; Improve strength, plasticity, toughness.

2) Formation of fibrous tissue (streamlines). The second phase or inclusions are distributed in a fibrous manner along the deformation direction, and the mechanical properties along the streamline direction are better than those perpendicular to the streamline direction (3) The final rolling temperature and deformation amount are well controlled, and the metal obtains a good recrystallization structure. The characteristics of thermal processing (1) deformation and labor-saving, sustainable processing with large deformation; (2) improve the internal quality and performance of materials; (3) With the increase of deformation, the strength and hardness increase and the plastic toughness decreases, and it is difficult to continue processing (often increase the recrystallization annealing process).

Its characteristics can be summarized in comparison with thermal processing.

1) Piercing and cutting The sharper tool cutting edges used by the operator, such as the chips in the metalworking workshop and the working turning, milling, planing, drilling, disc saw, etc., are like fast knives, which can cause injury to the unprotected parts of the human body.

2) Object strike: Falling objects from high altitudes, debris flying out along the tangential direction when the workpiece or grinding wheel rotates at high speed, punches and shearing machines in reciprocating motion, etc., can cause injuries to personnel.

3) Strangulation Rotating belts, gears and working shafts can all cause strangulation.

4) Scalds: With the processing of the chips, the chips are splashed on the exposed parts of the human body, resulting in burns.

With the help of metallographic talents, the cause of waste products such as milling, hardening, grinding cracking and low-speed machining is not light. Some of these scraps are rare (e.g., milling and quenching), and some are very common (e.g., grinding cracking), but in any case, that type of scrap will seriously affect the quality and productivity of the product, so it is important to study their metallographic characteristics and do a good job in this aspect.

Fold. In the positive stroke of the frame, the metal enters the gap between the grooved blocks, forming ears on the side surfaces of the working cone. During the return stroke of the frame, these ears are pressed into the surface of the working cone by the groove block. The defect that is formed is folding.

Since the tube is rotated once in a rolling cycle during rolling, it is folded in a spiral distribution on the surface of the tube.

The gap between the rolling groove blocks is too large, the gap distribution is uneven, the width of each part of the hole type is not enough, the size of the mandrel does not match the shape of the hole type, the uneven feeding amount or the pipe material advances and the pipe material stops rotating, etc., these reasons will promote the formation of side ears on the working cone and the formation of folds on the surface of the pipe.

If the gap between the rolling blocks is large, the gap should be readjusted. When the width of each part of the hole type is not enough, you can find out the place where the metal is "gnawed" by the hole flange, and grind the hole shape with an air grinding wheel to increase the opening of the smaller part of the hole type.

The size of the mandrel does not match the shape of the hole, which will cause the metal to be pressed down intensively and the ears will appear. In order to eliminate this phenomenon, the mandrel tapered bus bar can be replaced with a mandrel with a large slope. In the case of uneven feed sizes or in the case of a sharp increase in the amount of tubes, the causes of their occurrence should be eliminated.

If the tube stops rotating, adjust the front chuck.

Concavity. Depressions on the surface of the tube mostly occur in the pre-finishing section of the hole pattern and when the tube is not rolled on the mandrel when the frame is backstroked. The reasons for the formation of depression are: the gap between the rolling groove blocks is too large, the opening of the side wall of the pre-finished part of the hole type is too steep, the rolling groove blocks are staggered with each other in the horizontal plane, and there are defects on the surface of the rolling groove block.

Depressions are mostly found when thin-walled pipes are rolled.

When the gap between the rolling blocks is too large and the sidewall opening of the pre-finished part of the hole type is too steep, the metal fills the sidewall opening part of the hole pattern in the positive stroke of the frame and is cut by the flange of the hole type, and the metal of the cut part is pressed under the surface of the pipe during the return stroke rolling and forms a depression. The depressions on the surface of the tube are generally spiral due to the rotation of the tube.

The causes of cold-rolled product defects are: scratch causes: guide plates, roller tables, tools and rolls are not smooth, there are adhesions or angular burrs, etc., rolling scratches the surface; The operation is not careful, so that they collide with each other to form a scratched surface, and the metal pressingCause: The burr at the edge of the rolling part and the slag at the tail are pressed into the surface of the product.

Causes of non-metallic pressing: poor environmental hygiene, dust and foreign matter falling on the surface of the rolled piece; After pickling, the cleaning is not clean, and the reason for the pitting: when the pressure is orthopedic annealing, there are dust and foreign bodies on the surface of the pressing plate or backing plate, and the cause of the roll marks

The surface of the roll is seriously worn, with pits, textured surfaces, scratches, etc.; The mold shielding makes the surface of the roll pressed out of the pit by the plate corner, and the causes of surface cracking: the incoming material is unqualified, the surface cracks are not cleaned and slippery or the brittle suction layer on the surface of the incoming material is not removed, and the pressing procedure is unreasonable, the pass processing rate is small, the pass is too much, or the pass processing rate is unevenly distributed.

1. Defects in the production process of cold-rolled products:

1. Scarring (heavy skin) 2. Inclusion 3. Stratification.

Reason: The slab has non-metallic impurities, etc.

4. Iron oxide scale is pressed into 5, under-pickled 6, over-pickled.

Reason: Improper control of the pickling process.

7, flat flower 8, wrinkle 9, hole.

Causes: uneven rolling or improper leveling process.

10. Fold 11, edge damage 12, side crack 13, indentation 14, scratch, abrasion causes: the hot-rolled incoming material itself is defective and the rolling control is improper and produces 15, stains 16, rust spots.

Reason: The concentration of the leveling fluid is too low, the quality of the anti-rust oil is poor, and the oil can be applied unevenly.

17, hot scoop 18, pitting.

Reason: Frequent temperature changes in the annealing furnace.

There are also like: bonding, oxidation edge, carbonization edge, transverse stripes, parking spots, warping, edge waves, medium waves, cold abrasions, indentations, etc., and these are all defects in the production process, so most of them are related to the production process of the steel mill and the original substrate (hot-rolled incoming material).

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1. Lack of eggplant collapse generated in the production process of cold-rolled products:

1. Scarring (heavy skin).

2. Inclusions. 3. Stratification.

Reason: The slab has non-metallic impurities, etc.

4. Iron oxide scale is pressed in.

5. Under-pickling.

6. Overpickling.

Reason: Improper control of the pickling process.

7. Flat flowers.

8. Wrinkles. 9. a hole.

Causes: uneven rolling or improper leveling process.

10. Folding.

11. Edge loss.

12. Edge cracking.

13. Indentation.

14. Scratches and abrasions.

Reason: The defective incoming hot rolling material itself is caused by improper rolling control.

15. Spots.

16. Rust spots.

Reason: The concentration of the leveling fluid is too low, the quality of the anti-rust oil is poor, and the oil can be applied unevenly.

17. Hot scooping.

18. Pockmarks.

Reason: Frequent temperature changes in the annealing furnace.

There are also like: bonding, oxidation edge, carbonization edge, transverse streaks, parking spots, warping, edge waves, medium waves, cold abrasions, indentation slip width, etc., and these are defects in the production process, then most of them are related to the steel mill's production of Xinnaliang process and the original substrate (hot-rolled incoming material).

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The answer is in the message.

Answer: (1) Dimensional error (2) Shape error (3) Surface defect.