What are the wire drawing technology?
In an era of increasingly fierce competition, the competitive pressure to produce products that satisfy customers at the lowest cost has promoted the continuous advancement of wire drawing technology. Metal wire is a common product form, usually referring to wire, wire or rod.
With the continuous development of the economy, demand and production are also booming unprecedentedly. Although the thinnest metal wire has reached a few microns, and the highest steel wire strength has exceeded 4000MPa, we are still facing changing demands and competition from non-metallic materials, so we need faster and better wire drawing technology.
- Historical Review of Wire Drawing Technology
The earliest known metal wires were polywires made by the Egyptians around 2750 AD. In the archaeology of the Terracotta Warriors and Horses of Qin Shihuang in Xi’an, my country, it was found that a large number of stone armors used copper wires, which may be the earliest evidence of metal wires in China.
From 400 to 1100 AD, metal wire technology began to develop in many countries, and it began to be drawn by hand or horse-drawn. Slowly, some technologies were invented later, such as winches, swings, ratchets, and gravity was used.
In the 17th century, Europeans began to use hydraulic wire drawing.
The invention of the steam engine in 1769 replaced the manual drawing technology and hydraulic drawing.
The promotion of motor technology in the 20th century provided a new impetus for the leap of wire drawing technology.
In 1632, the craftsman who developed the steel wire needle accidentally discovered that the residual layer of human urine on the steel wire played the role of lubricating the steel wire, and found that lubrication can reduce power requirements.
In the early days, some people tried stone molds, and later there were iron molds. From the description made by Song Yingxing, a native of Jiangxi in the Ming Dynasty, in “Tiangong Kaiwu” written by Fenyi in 1637, it can be found that iron molds are used to draw wires: “Every needle is first hammered into thin strips. Use an iron ruler to taper into thin strips. The thread eye is drawn from a strip of iron to form a thread, which is cut inch by inch to form a needle… “. In 1970, there were still old workers in Xinyu pulling wires by hand on a bench vise. Jewelry craftsmen in Guizhou still draw silver threads by hand.
In 1834, the German Wilhelm Albea invented the wire rope. At the same time, he set up a telegraph line in the UK and began to make submarine telegraph lines.
The invention of the electric motor led to the appearance of the single-drum wire drawing machine. In order to improve efficiency and quality, 2 or even 3-pass drawing (sliding wire drawing) has been realized on the single-drawing machine, and horse-riding wire starter and water-cooling technology have been adopted, and the mold technology has been continuously improved.
In 1993, when the author visited the United Steel Wire Rope Company in Kansas, I saw that they were still using single-drawing machines, but one person operated 6 sets, and the coil weight was about 1 ton, so the efficiency was not low. Inverted single drawing machine and horizontal reel drawing machine are still widely used, suitable for processing steel wire products with few passes and medium and large sizes, and it is easy to realize large-scale heavy production.
With the development of AC motor and control technology, the continuous wire drawing machine was invented in the early 20th century, which reduced the labor cost and increased the wire drawing speed.
MORGAN is one of the early major wire drawing machine manufacturers. In the late 1930s Marchal Richard Barcro invented the B-B wire drawing machine (double product line), which improved cooling and reduced torsion problems. The equipment was particularly popular with wire rope factories, and by the time the company went out of business in 1976, thousands of them were in use.
The wire drawing machine that appeared later was a looper type. In the late 1970s, the KOCH company in Germany invented the linear tuning roller SEN-SOR ARM wire drawing machine.
The narrow slit cooling technology invented around 1970 provides very favorable conditions for the increase of wire drawing speed.
Improved reel design, air cooling outside the reel, rotary die, and direct water cooling are all technologies that improve the performance of the wire drawing machine.
Since the 1990s, horizontal continuous wire drawing machines have appeared, mainly due to the need to reduce labor intensity and facilitate maintenance. When drawing filaments, it can be arranged in two rows, which reduces the floor space, and the large ones have been developed to a reel with a diameter of 1 270 mm.
While avoiding the torsion of the steel wire, the linear wire drawing machine has achieved excellent pass and speed coordination. Faster speed, better quality, easy operation and maintenance, flexible mold matching, and reduced energy consumption due to the development of electrical technology.
With the development of digital technology, the working status of a group of wire drawing machines can be monitored through a computer.
The coil diameter of the dry continuous wire drawing machine is 250-1270mm, and the DC or AC motor power is 15-160kW. The working speed of the small dry wire drawing machine has reached over 25m/s, and the production capacity of the large wire drawing machine has exceeded 20,000 t/a.
Wet drawing equipment based on sliding wire drawing technology has been widely used in non-ferrous metals and small-sized steel wires, such as copper wires, aluminum wires, steel cords, steel wires for steel wire ropes, thin spring wires, etc., using water-based or oil-based lubricating liquids. The technology of drawing multiple threads at the same time has already appeared for a long time.
The speed of the water tank wire drawing machine is very high, and the number of drawing passes ranges from a few to twenty times, which can achieve a large amount of compression. The heavy-duty water tank can make the φ5.5mm high-carbon steel wire into ten products directly, but the steel wire is in the water tank. There is some twist, skill and experience required to adjust the flatness.
- Break Through the Speed Barrier
Drawing machine technology has come a long way, and some speed records reflect current achievements:
The speed of drawing electrical aluminum wire with an incoming wire of φ9.5mm can reach more than 30m/s, and the speed of drawing high-carbon steel filaments can also approach this speed; the speed record for the incoming wire of φ11mm 82B steel wire and the outgoing wire of 94.22mm is 12m/s .
High-speed production of high-quality steel wire requires comprehensive and comprehensive conditions.
The following summarizes and analyzes several factors affecting high-speed drawing and the breakthrough direction. When not specifically stated in the text, the wire refers to the steel wire.
2.1 Raw Materials
Large reel weight reduces the downtime required for piecing and is important for increasing the efficiency of wire drawing equipment.
The non-ferrous metal industry introduced advanced equipment in the 1970s, and the re-production of wire rods in the iron and steel industry began in the second half of the 1980s.
Before 1988, wire rods with a coil weight of 300kg already belonged to large coils in China, and some products were even only about 60 kg per piece. A small amount of imported equipment for metal products companies can only be effective when using imported large coils of heavy wire.
In 1988, the first high-speed wire rod factory with a coil weight of about 2 tons appeared in Ma’anshan. Later, the coil weight of about 2 tons gradually became the mainstream in China. The emergence of large-scale heavy wire rods made my country have the conditions to develop high-speed wire drawing. There are already wire rods with a weight of about 3t in foreign countries.
Raw material quality is also very important. Good wire rods seldom break, and can be drawn faster, ensuring the working efficiency of the wire drawing machine; in addition, good wire rods are the quality basis of high-quality steel wires, which can reduce product costs. When drawing PC steel wire, the number of broken wires per 100 mouths of good materials is less than once.
Steel cords are more sensitive to wire breakage due to many processing steps and thin product diameters. Modern metallurgy and steel rolling technology has improved the metal structure and wire quality, making wire drawing easier and reducing production costs.
2.2 Preparation of Wire Surface
Oxidized scale will be formed on the surface of wire rods during hot rolling, and some steel companies provide pickling services, especially for stainless steel wire rods.
In most cases, surface preparation before drawing is done by steel wire companies. Good surface preparation ensures proper friction between the metal and the die as it deforms, and is important to ensure smooth, high-speed drawing.
The most common process is still pickling + phosphating + boronization (or saponification, or soaking in lime solution). Using technologies such as vibration, ultrasonic and electrolysis, combined with some other technologies, the discharge of pollutants has been reduced under the premise of ensuring quality.
France has non-reactive coating materials instead of phosphating, which can reduce pollution problems. In order to solve environmental problems, more and more people use mechanical descaling technology, but some difficulties are encountered in practice, especially when producing finished steel wire.
Germany’s ECOFORM company has launched an online coating technology, which uses a technology similar to extrusion to coat the lubricant on the surface of the steel wire, greatly improving the lubrication effect, increasing the life of the mold and the speed of drawing.
In the application, when drawing W(C)=0.83% carbon steel wire, the diameter of the incoming wire is 5.5mm, the diameter of the outgoing wire is 2.2mm, and the finished product speed is increased from 12m/s to 20m/s. Turn the passive process that takes place in the mold into an active process that is easy to control.
2.3 Pay-off Wire Drawing Technology
After the output speed of the finished product is increased, the pay-off speed will naturally follow up. However, when the pay-off speed reaches a certain level, it is easy to have disordered wires and wire jams, which restricts the increase in speed.
When choosing the pay-off technology, the previous take-up technology should be considered at the same time. The pay-off can be regarded as a reverse process of the previous take-up. The selection of take-up technology should be considered systematically, mainly considering the needs of the next process. If it is a finished product, it is necessary to study the most suitable method for the customer. Usually, the take-up technology affects the cost and efficiency of the customer.
Generally, wire rods are paid out by horizontal forks or vertical cylinders. The duck tongues of the horizontal forks can reduce the problem of coils running out too fast. The use of I-beams for small diameter steel wires is the most ideal high-speed pay-off method.
The I-shaped wheel can take up the wire at high speed, and the wire arrangement is relatively neat, which is conducive to re-paying the wire. Active spool pay-off can achieve precise tension control, but it is rarely used in wire drawing. Some equipment realizes automatic disk change, such as some steel wire drawing machines of KOCH and some aluminum wire drawing machines of other companies, which obviously improves production efficiency.
Elephant nose (gooseneck) take-up is also a technology that can realize continuous operation. With some twisting of the steel wire, it can realize heavy take-up of large coils or non-stop winding of small coils. The design speed of GCR equipment has reached 28 m/s, and the diameter is 400-760mm. There is no torsion problem with the inverted take-up, and the highest design speed in foreign countries reaches 25 m/s, and it can realize large-scale heavy production.
The tension control of the take-up and pay-off line is very important. The equipment can judge whether the speed is coordinated through the tension, and the tension also affects the quality of the winding line.
Passive pay-off mainly relies on braking to generate tension, and active pay-off can use technologies such as torque motors, loopers, and tension-sensing rollers.
There is no tension control for the passive pay-off of the uncoiled pay-off, but the duck tongue of the horizontal fork is required to produce proper damping.
2.4 Lubrication
Drawing is inseparable from lubrication, and the possibility of lubrication failure is one of the important reasons for limiting the speed. Lubrication failure causes the temperature of the steel wire to rise sharply, and the metal to be drawn adheres to the die, resulting in problems such as shortened die life and product surface damage.
Commonly used lubricating materials include calcium-based or sodium-based stearate (drawing powder), lubricating oil and grease. The same lubricating material sometimes behaves differently in different factories. This is because other factors lead to different pressure and temperature in the mold, which makes the lubricant behave differently.
In addition to the lubricating technique described in 2.2, pressure dies can also achieve similar dry coating.
In the acid-free drawing, it is effective to add an online boronization device before the wire drawing machine, and it reduces the requirements for powder coating technology.
Adding an agitator to the wire drawing powder box of the wire drawing machine can avoid the tunnel effect. A powder clip is a tool that snaps onto the wire to make drawing powder easier to get into the mould. Sometimes it works well, but it can also result in too much powder being brought into the mould.
The pressure and contact form of the powder clip will affect the use effect.
Lubrication failure can be judged according to the powder output state. Normally, there is no coking, and the plasticized powder adheres to the steel wire. When there is a problem, the powder output is very hard, and the agglomeration shows high temperature black. In severe cases, severe friction will occur, the phosphating film on the surface of the steel wire will be damaged, and even drawn martensite and transverse cracks will appear.
2.5 Wire Drawing Machine
The electromechanical characteristics of the wire drawing machine, the cooling capacity, and the above-mentioned take-up and pay-off technology all affect the speed and quality of the wire drawing. High-speed wire drawing needs the support of motor, transmission mechanism, speed coordination control system, and dynamic balance effect of rotating reel.
The heat balance ability of the wire drawing system is also a key factor. The friction and deformation during the metal drawing deformation process generate heat. Modern wire drawing machines take away heat through water cooling of the mold, water cooling inside the reel, and air cooling of the external steel wire. The faster the speed, the unit time The more heat is generated, the cooling capacity of the wire drawing machine is limited. High temperature leads to aging and brittleness. It is generally recommended that the mold release temperature should not be higher than 180°C, and severe embrittlement will occur if it is above 220°C.
Italian Wire Technology Co., Ltd. proposes the following calculation method for the cooling water volume of the drawing reel:
The amount of cooling water per minute for each reel (20°C): W20=f·Pinst, where / is a coefficient of 0.7-1.0, and Pinst is the installed power. If 8 continuous wire drawing machines with 75kW motors are installed, the coefficient is 0.85, and the total supply of cooling water (not including the mold box) should be 87560*0.85=30.6 t/h.
The corrosion of the inner wall of the reel has a great influence on the cooling and heat transfer. It can be found in the WAI steel wire manual [2] that the 0.25mm thick rust reduces the heat transfer capacity by 50%. Appropriate rust prevention techniques should be beneficial, but care should be taken to avoid coatings with low thermal conductivity.
Narrow slot cooling has become a popular technology in the world. There are also companies that manufacture direct water-cooled V-groove wire drawing machines. The finished steel wire made by direct water cooling is in a warm state, with good toughness and slightly lower strength. When the temperature is higher, although the drawing strength of the drawn wire is higher, at the same time, there is a loss of plasticity and toughness. Even if it is not serious, its strength cannot be maintained stably.
The experience of making prestressed steel strands shows that after the strands are stabilized, the strength of direct water-cooled low-strength low-strength steel wires will rebound, while the strength of high-strength hot steel wires will have an obvious loss of strength.
In the 1970s, Kobe Steel studied the direct water cooling of steel wire after mold release, and it took two years to put this technology into practical use. There are also companies that have tried to spray water mist next to the reel.
The inclined drum design is an effective means of improving cooling and increasing speed potential. Because the inclined reel increases the height of the accumulated wire, that is to say, the cooling time of the steel wire on the reel is increased. Increasing the number of rolls is also a design idea, which can reduce the compression rate of each pass, that is, reduce the load of the cooling system for each pass.
For high-speed production, some companies have also developed non-stop wire drawing technology, using 3 t reel heavy anti-disorder wire pay-off technology, the first 4 high-accumulation wires, automatic disc change of the shafting machine, and the capacity of the I-shaped wheel reaches 3t.
2.6 Improving the Drawing Process
Researchers in South Korea adopted the principle of equal-temperature compression rate distribution [3], that is, the predicted temperature of each channel is controlled at 166°C, which avoids the problem of insufficient utilization of the cooling capacity of the first channel in the traditional distribution method.
The result of such distribution is that the compression rate gradually decreases from the first pass, and the cooling capacity of each pass is fully utilized.
The general rule of thumb is to control the compression rate of the first pass at a low level, which can achieve a better lubricant coating effect in the first pass, but this effect is also affected by the characteristics of the lubricant, the amount of compression, the speed and the cooling capacity. Influence.
More ideally, the characteristics and performance of wire-drawing powder, equipment performance, cooling capacity, material deformation capacity and total compression rate should be considered comprehensively, and the potential of the equipment should be brought into play under the premise of ensuring quality.
The use of a pressure die can improve the lubrication effect and improve the plasticity of the material when it is drawn and deformed, which is beneficial to increase the speed.
High-speed drawing can also be achieved by installing a roller die on the wire drawing machine for drawing. When the roller drawing method is used to produce steel wire, it can obtain a stronger [110] texture than the fixed die, with uniform deformation, less heat generation, and a higher strength index. and plasticity indicators.
Technology with a registered trademark of MICROROLLING has been applied to process copper, zinc, aluminum, titanium, copper alloy, aluminum alloy, carbon steel, stainless steel, tool steel wire, gas-shielded welding wire, and flux cored welding wire. When processing medium and high carbon steel wires of φ1.8mm, the wire speed can reach 16m/s, and the soft wire speed of the same specification can reach 25m/s.
- Conclusion
In order to draw faster and better, we should pay attention to the following points:
(1) Use high-quality raw materials with as large a plate weight as possible;
(2) Prepare the surface suitable for the subsequent high-speed processing technology, and even integrate it with the wire drawing machine on the same line;
(3) Adopt appropriate take-up and pay-off technology to prevent disordered wires and broken wires, and adapt to the corresponding wire drawing speed; (4) Use appropriate lubricants to adapt to expected processing conditions;
(5) A high-speed wire drawing machine with stable control, no torsion, and excellent cooling is adopted, and the deformation process can even be realized by roller pulling;
(6) Comprehensively consider the influence of surface preparation, lubrication, cooling, mold and material properties in the wire drawing process, and make full use of the cooling and speed potential of the equipment under the premise of controlling temperature and ensuring surface quality.
