Factors Affecting the Quality of High-speed Wire Rod Laying Head

The laying head is the key equipment of high-speed wire rod production. It is arranged after finishing rolling mill, which plays an important role in winding the wire into a certain diameter coil and then spreading it on the air-cooled roller. The quality of the coil produced by the spinner has a great influence on the subsequent winding and packaging processes, especially for the products after packaging.

1. The main factors affecting the quality of wire rod

In the production of a high-speed wire rod mill, the coil quality of the laying head is often unsatisfactory, that is, the coil is oval, the coil is larger or smaller, and the stack is disordered and uneven on the air-cooled line, especially when rolling small-size wire rod. From the spinneret's work process, the spinneret's speed and the laying head is the main influencing factor.

(1) Spinneret

The spinneret is installed on the spinning disk, which is a spiral curve with a spatial cone shape. Although the curves of various manufacturers are different, they can be divided into three sections: first, the initial section is straight, and the wire rod does not undergo plastic bending deformation; The second is the deformation section in which the wire is deformed plastic with the bending shape of the spinneret; Thirdly, the wire rod continues to deform and form a stable coil. The shaping section is very important for the shape of the spinning coil. The end section of the exit of the spinneret is generally at an angle with the spinning pan surface to make the outgoing coil produce forward speed. Then, the overall and horizontal surface of the spinneret is 10 °～ 20 °, and the coil can be ejected smoothly from the spinneret and spread on the air-cooled roller table. 

The angle of the pipe mouth of most spinnerets is not adjustable. Therefore, when the rolling speed changes, the horizontal forward speed of the coil is different, which will cause the coil falling on the air cooling roller table to deviate from the set best condition, that is, the unsatisfactory ring shape will appear. Therefore, the first section of the air cooling roller table is designed to be adjustable in height, so that the vertical distance from the spinning plate to the air cooling roller can be adjusted. By adjusting the height of the roller table, the coil can be correctly laid on the roller table. However, in actual production, it is difficult to master due to the lack of operation experience, which leads to the coil falling down obliquely. When producing a small-scale wire rod, the front of the coil is faster than the rear because of the high horizontal speed. When the adjustment height is not the case, the coil will be inclined and placed on the roller table. Because the wire rod is thin and soft, the coil is easy to form an ellipse.

(2) Speed control of the laying head

The diameter of the coil ejected by the spinneret is not constant and the size is not a moment, which will also affect the appearance quality of the bales. Therefore, it is very important to ensure the coil diameter of the spinneret is constant. When the wire passes through the spinneret, the motion state changes from linear motion to circular motion, and the line speed is VW. at this time, the rotating line speed of the pipe mouth of the spinneret is VL. if the size of VW and VL are equal and the direction is opposite, the synthetic speed of the wire rod in the spinneret mouth relative to the earth is 0. Because of the downward inclination of the spinneret, Therefore, the wire rod will be parabolic in three-dimensional coordinates (the vertical direction is free-falling), so that the curvature radius of the wire when it is ejected is constant, namely the coil diameter.

To ensure that different wire specifications can meet the requirements of VL=VW in the whole process of wire drawing, to stabilize the coil diameter, generally, there are two clamping rollers in front of the spinner. There are two clamping systems: one is to clamp the wire in the whole process, and the micro tension control method is adopted to match the speed of the finishing mill, pinch roller and spinner; The second is tail clamping, small-size wire rod adopts tail speed reduction clamping, in order to prevent the phenomenon of rising speed when the tail out of the fine rolling mill, while the large-scale wire rod adopts tail speed up clamping to promote the wire to smoothly exit the spinner and form a circle. When VL≠VW, the velocity of the coil relative to the earth in the direction of the disk surface is not 0, that is, the coil has an angular velocity relative to the earth, so there will be a certain offset in the falling process. When VL>VW, the relative angular velocity direction is consistent with the spinning direction of the spinneret, and the coil will be left (see the rolling line); When VL<VW, the relative angular velocity direction is opposite to the spinning direction of the spinneret, and the coil will be shifted to the right. When the coil is left or right, it will collide with the side plate of the air-cooled wire and damage the wire surface.

2. Common failures and treatment methods in production

(1) Spinning machine tail-flick

It refers to the phenomenon that the tail of the wire rod can not be ejected smoothly from the spinneret and collides with the spinning surface of high-speed spinning. The reason is that the throwing angle of the pipe mouth is small, and the forward speed of the wire rod is not enough to make the tail leave the spinning surface. The solution is to adjust the throwing angle of the spinneret properly, but for the tail clamping process, it is necessary to ensure the clamping roller is reliable.

(2) Uneven loops of the laying head

It refers to the diameter of the coil that the spinneret spits out is different. The reason is generally related to the speed matching between the spinneret and the finishing mill. It can be solved by adjusting the advanced amount of the spinning. When producing a small wire rod, it is easy to produce a large circle phenomenon at the tail, because the tail will gradually increase speed when leaving the finishing mill, while the speed of the spinneret changes very little, so the diameter of the tail ring becomes larger; For large-scale wire rod, especially the round bar with ribs, most factories adopt tail nonpinch process to ensure the surface quality of wire rod, which will lead to the speed of wire rod end entering the spinner, and thus reduce the coil diameter. Therefore, it is suggested to clamp the tail of a large-size wire rod, and reduce the clamping pressure of the clamping roller to avoid damage to the surface.

（3） Uneven tiling

In order to make the coil evenly spread on the air-cooled roller, the other important factor is the spinning pipe, except that the speed of the roller bed must be constant. When a spinneret produces several specifications of wire, the quality of the coil is often unstable, and it is easy to spread uneven or spit the size circle. This is because wires of different specifications have different spinning speeds, which produce grooves with different trajectories in the spinning tube. Wires passing through this tube are prone to trajectory deviation. Therefore, the best solution is to replace different spinneret tubes when rolling different specifications. When rolling small sizes, one pipe can be used to match one variety, while rolling large size (e.g More than Φ10 mm) a threaded pipe can be shared when the wire rod is used.

（4） The coil is oval

When the small wire is produced and the temperature of spinning is too high, it is easy to appear circle ellipse, because of the soft wire. In addition, the air-cooled roller table height is too low, the coil falling distance of the spinneret is too large, it is also easy to appear ellipse. When the front throw angle of the pipe mouth is too large, the wire rod has a large forward split speed, which causes the coil to fall into the roller table obliquely. For the spinner without head positioning function, the coil is easy to be stuck in the gap of the roller table and the production accident occurs. Therefore, to solve these problems, we must analyze and solve the problems from three aspects: the throwing angle of the spinning pipe, the height of the roller table, and the spinning pipe's temperature.

If you are interested in the laying head or wire rod production line, please mail at marketing2@hanrm.com.

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Requirements for Roll Performance of Bar Rolling Mill

With the progress of steel rolling technology and the improvement of equipment level, the bar production line has gradually moved towards continuous, automatic and efficient production, and the requirements for wear resistance and thermal stability of rolls are also higher and higher.

All kinds of ductile iron rolls used in the past can not meet the higher requirements, especially the production line based on hot-rolled ribbed steel bars. In addition to the special requirements for the hardness and toughness of the roller for the finished stand, the slitting rolling technology is mostly adopted for the small-sized varieties, and the requirements of the pre-slitting and cutting passes on the rolls are sometimes even more stringent than the requirements for the finished rolls of the ribbed bars.

At present, the traditional cast iron roll is still widely used in most bar production lines. Centrifugal casting high Ni Cr acicular bainite ductile iron roll is generally used in the finishing mill. The single-groove steel passing capacity of the finished roll is only 50 ~ 400t / groove according to the rolling specifications and process conditions.

This means that a bar production line with a single shift (8h) output of about 1000t has to replace the rolling groove 3-5 times per shift, resulting in a long cumulative time for roll changing and groove changing, frequent adjustment of rolling mill and frequent production accidents. As a result, the operation rate of the whole production line is reduced, the technical and economic indicators such as yield are poor, the product size fluctuates greatly and the comprehensive production cost is increased.

Therefore, the development and application of high wear-resistant and long-life rolls is an important means to improve the production efficiency of the bar production line. At present, this kind of roll mainly includes centrifugal casting high-speed steel composite roll, forging high-speed steel roll ring combined roll and tungsten carbide roll ring combined roll.

The main performance indexes of the roller are core strength and wear resistance of the working layer. In addition to considering the economy and the matching of roll changing and groove changing period with shutdown time, it is more important to reasonably select rolls with different performance characteristics from the pass difference of each set of stands, the deformation characteristics of rolled pieces and the requirements of product accuracy.

The main task of the roughing stand of the bar mill is to reduce the cross-section at high temperature, which has a high rolling force and low rolling speed. Generally, the roll performance should be considered from the two aspects of ensuring the roll strength and hot cracking resistance. For general steel grades and normal rolling temperature, centrifugal casting ordinary ductile iron roll can be selected.

The medium rolling mill of bar rolling mill generally adopts an ellipse round pass system, which mainly undertakes the task of extending the rolled piece and providing an accurate profile for the finishing mill. The rolling force is moderate and the pass wear is uniform. Therefore, centrifugal casting ordinary ductile iron roll or medium nickel-chromium alloy ductile iron roll is generally selected. In order to ensure the stability of the size of the exported rolling pieces of the unit, the export stand can also choose high nickel-chromium alloy ductile iron rolls or high-speed steel composite rolls.

There are many varieties of bar finishing mill, complex pass shape, uneven distribution of deformation, high rolling speed and large variation of rolling force. Therefore, the performance requirements of the roller mainly wear resistance and toughness, and both hot cracking resistance and strength are taken into account.

For the extended pass of the simple section, high nickel-chromium alloy ductile iron rolls are generally used, and high-speed steel composite rolls can also be used. For the finished front hole of round steel or ribbed steel bar, it is recommended to select high-speed steel composite roller or tungsten carbide composite roller with higher wear resistance.

As the finished hole of round steel is very small, the tungsten carbide composite roller with the best wear resistance and the high-speed steel composite roll with higher surface hardness should be selected. The finished hole of the ribbed steel bar is affected by the transverse ribs, and it is very easy to produce thermal cracks or micro-cracks during use.

In general, all transverse ribs must be turned off, and the amount of heavy vehicles is large. Therefore, the economy of the expensive tungsten carbide combined roll will be greatly affected. It is better to select a high-speed steel composite roll. Due to the serious non-uniform deformation in use, the high-speed steel composite roller with good toughness and wear resistance and moderate hardness or the tungsten carbide composite roll with good toughness and wear resistance should be selected.

Due to the existence of slitting wedge, not only good wear resistance and toughness, but also reliable hot cracking resistance are required. It has been proved that the present high-speed steel composite roll and tungsten carbide composite roll do not have this characteristic, and the phenomenon of splitting wedge spalling easily occurs in use. Therefore, only high nickel-chromium alloy ductile cast iron rollers can be used.

If you are looking for rolls of rolling mills, please contact me.
Email: marketing2@hanrm.com; Whatsapp / Wechat: +8618392033938

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Common Accidents on the Site of High-speed Steel Rolling and Measures (4)

15. What are the reasons for stacking steel between the stands of the finishing mill?

(1) The rolling guide sticks the steel;

(2) The guide wheel does not turn or the bearing burns out;

(3) The rolled piece split;

(4) The guide or the roll ring is installed incorrectly;

(5) The roll gap is not set properly or the incoming material size is not reasonable;

(6) The guide is not fastened.

16. What are the reasons for the poor wire loop of the laying head outlet?

(1) The tension between the rolling mills is too large;

(2) the alignment deviation of the water cooling section, the nozzle duct wear and corrosion cause the rolling operation to be unstable;

(3) The clamping force of the pinch roller is not appropriate due to the wear of the pinch roller ring or the failure of the cylinder link mechanism;

(4) The deviation of the bending line of the spinning tube, the spinning tube is seriously worn, and the spinning tube is sticky connected, the unbalance of the spinning tube causes the loop formation difference;

(5) Improper speed configuration of the finishing mill, pinch roll, and laying head, serious speed fluctuation of the rolling mill, causing the rolling speed to be faster or slower, resulting in uneven coil size;

(6) When the temperature of the rolled piece is high, the coil is too soft, and the coil falls on the receiving platform, and it will become an ellipse or a random circle.

17. What are the common types of damage to rolling guides in finish rolling? What are the causes? How to prevent it?

1) The guide roller bearing is broken, so the guide roller cannot rotate;

2) The guide roller is short of oil, and the bearing is locked;

3) The guide roller lacks water, causing the guide roller to not rotate or burst;

4) The guide roller shaft is broken;

5) The guide roller moves, the screw of the pin is loose;

6) The guide arm is loose.

Solutions:

1) Strictly control the size of the red billet, ensure the same size as the guide, and prevent the thickness of the material from impacting the guide roller.

2) Prevent misalignment of the roll ring, prevent twisting of the rolled piece, and the rolling guide is damaged. The bottom surface of the roll ring needs to be aligned with copper skin.

3) To prevent the roll ring from moving, due to the roll ring movement, the torsion moment is generated in the rolled piece.

4) The guide guard must be aligned to prevent excessive force on one side of the guide roller.

5) Strictly control the installation quality of the rolling guide, prevent the guide roller from moving, the guide guard arm is loose, and the cap screw is tight.

6) Strictly check whether the oil pipes and water pipes are working properly.

18. What common accidents will occur during the production of 27 high-speed roll rings with misaligned holes? How to solve it?

1) The serious slope of finished product;

2) The rolled parts are twisted, are unstable in the water-cooled channel, and are easy to get out of the waste box;

3) Due to the torsion of the rolled parts, the finished guides are easy to damage, resulting in the quality accident;

4) The guide is not easy to align.

Solution: Add copper skin to the bottom of the roller ring.

19. How to deal with the sudden stoppage of the high-speed wire mill?

1) Immediately start flying shearing machine #1, #2, and #3;

2) Emergency stop finishing and pre-finishing;

3) Notify the dispatch room to find the reason;

4) After stopping, ask an operator to the finishing mill to check the condition inside the machine;

5) Roller ring was all replaced or slowly cooled, it is strictly prohibited to cool the roller ring with water.

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6. The practice of Direct Rolling without Heating

7. What Adjustment Devices Are There in the Rolling Mill?

8. What Are the Rolling Process Systems?

9. Key Factors Affecting Rolling Mill Prices

10. Should Customers Choose Used Rolling Mill?

Reasons and Solutions for the Piling of Wire Rod Rolling

1. Piling of Steel Head

The Reason:

1) The friction of the rolling groove after changing the roll and groove is too small, causing the head of the rolled product to slip;

2) The head of the rolled product is tilted out of the rack, causing it to fail to bite into the downstream rack or the head guide position smoothly;

3) There are foreign objects in the rolling groove or guide groove;

4) The billet is severely out-of-square, unable to enter the rolling mill or take out the outlet pipe;

5) The blank is split out of the guide or wrapped around the roller.

Solution:

1) Increase the groove friction when changing rolls and grooves. Grind the grooves with the grinder or use spot welding, and turn off the cooling water of the rolls until they are completely bitten.

2) Check whether the guide base is loose and whether the rolling line is centered, and replace the old guide in time.

3) In the rolling process, timely clean up the oxide scale;

4) In the rolling process, unqualified billets are removed in time, and splitting occurs. Emergency stops should be taken as soon as possible to reduce the waste steel processing time.


2. Piling of the Middle and End of the Rolled Piece

The Reason:

1) Due to improper roll gap setting caused by improper size of rolled products, stacking steel;

2) Defects of the billet, such as inclusions, bubbles, etc., are broken during the rolling process and cause stacking of steel;

3) The speed of the rolling mill is improperly designed, and it is in the state of stacking and rolling. When the first half of the rolled product is maintained by the front rolling mill to maintain micro-tension rolling, when the tail of the rolled product leaves the front rolling mill, the tension is suddenly lost there, causing the stack at the stand tail;

4) Sudden increase or decrease in speed of the rack motor caused the stacking of steel;

5) The roll was suddenly broken or the guides were severely damaged in the first few passes, which caused the stacking of steel.


Solution:

1) After changing rollers and grooves, accurately set the groove bottom, correctly measure the diameter and speed of the rollers, and reduce speed errors

2) Strengthen the inspection of unqualified blanks;

3) Correctly adjust the tension between each frame;

4) Inspect electrical equipment and replace damaged electrical components;

5) Check the amount of roll cooling water, adjust the steel temperature, and prohibit rolling of low temperature steel and blackhead steel.


3. Piling steel between Finishing Mill Stands

The Main Reason:

1) The guide wheel does not rotate or the bearing burns;

2) splits of rolled products;

3) The guide or roller ring is incorrectly installed;

4) Improper roll gap setting or improper incoming size;

5) the roller ring is broken;

6) The broken line causes the rolling line to break automatically.


Solution:

1) Replace the guide, and strengthen the correctness of the guide installation;

2) Strengthen the blank inspection and lengthen the cutting head;

3) Recheck and adjust the roll gap;

4) Replace the roller ring and check the cooling water pipe at the same time;

5) Check the switch at the fishing line pendant, check whether there is scrap steel in the guide of the finishing mill. If there is any, it means that the previous one has piled steel in the finishing mill, and reset the roll gap in the finishing mill.

What we can do:

We are specialized in manufacturing high-speed morgan wire rod mill, high-speed rebar rolling mill, TMT rolling mill, high-speed gearbox, hard-faced gearbox.

We also provide complete design for your rolling mill workshop, not only turnkey project but also tailor-made service.

And we provide all the parts for roughing rolling mill, intermediate rolling mill process, including pinch roll, all kinds of shears, laying head, all of these crucial parts work extremely precisely and reliably.

If necessary, please feel free to contact me. Email: marketing2@hanrm.com