1846 British engineer Bessemer (Bessemer) propose to the rotating direction on the two roll seam metal injected into the melt production envisaged slab; however, after years of trying without success. Later, on the basis of continuous cast aluminum and brass on the wire rod, it is thought Bessemer contemplated. Finally, in 1951, Hunter-Douglas of the United States made a two-roll continuous casting mill and first cast it into an aluminum strip.

The research on continuous casting and rolling technology of aluminum strip in China began in the early 1960s. In January 1964, the twin-roller-type aluminum strip blank continuous casting and rolling simulation test was carried out. From July to September, the casting and rolling were successively rolled into widths of 250mm and 400mm. In 1978, the twin-roll inclined casting mill was developed. In July 1979, it was developed into a φ650×1300mm casting mill. In 1981, it was developed into a φ650×1600mm casting mill and put into trial production. In May 1982, it was developed into φ980×1600mm. Ultra-type casting and rolling mill, and in August 1983 passed the expert group organized by the Science and Technology Department of the Ministry of Metallurgical Industry.

At present, the world's leading companies in the production of twin-roll aluminum strip continuous casting mills are: Italy's FATA Hunter; France's Novelis PAE, which produces JUMBO 3C and 3CM caster; there are eight Chinese companies, such as the Sino-Japanese joint venture (North China Aluminum Co., Ltd. and Japan's Kobe steel Corporation) of Zhuoshen companies, such as Shanghai Jie Electrical and Mechanical heavy Industries Co., Ltd. Shanghai-day heavy machine type, in color Technology Engineering Technology Company, Hangzhou Dingrui Machinery Manufacturing Co., Ltd., Hongye Technology Co., Ltd., etc. By the end of 2010, there were about 1,060 twin-roller aluminum strip continuous casting mills in production worldwide, of which China had about 520 units, accounting for 49.1% of the world's total, or about half of it in mainland China. However, the average production capacity of China's cast rolling mills is only 8.5 thousand tons / year, while abroad is about 11.5 thousand tons / year;

China's cast rolling mills are mostly medium and small, accounting for about 60% of the total, and the installed capacity is relatively low.

1. Casting and rolling process and casting and rolling

The continuous casting and rolling of the aluminum strip blank eliminates the ingot casting and hot rolling process, and reduces the production cost; the equipment is simple, the land occupation is small, the investment is small, the construction period is short, and the process is simple and the maintenance is convenient. These are the main advantages. However, there are also some shortcomings, such as slow casting speed, low production capacity, 6××× series, 2××× series, 7××× series, partial 5××× series and 8××× series alloys. Can not be produced; from the aluminum alloy varieties, the alloys that can be produced only account for about 20% of the total varieties, but the amount of plate and strip that can be produced accounts for more than 75% of the total. In addition to 2××× series, 7××× system plate strips, thick plates, CTP substrates, tank materials and electrolytic capacitor foil strips, etc., not only thick plates (26mm) can not be produced, but are larger than 2mm sheets cannot be produced.

(1) Casting and rolling process

The overall appearance of the casting mill is shown in Figure 1. The production process is shown in Figure 2. Aluminum melt diameter "four treatments" (alloying, composition and temperature homogenization, purification, grain refiner addition), from the feed nozzle to the two roll gap, continuous casting into strip, cut off the head The part is rolled into a cold rolled strip.

Figure 1 Modern double-roller aluminum strip casting mill

1-degassing system; 2-filter system; 3-level control; 4-cast nozzle;

5-casting mill; 6-spraying system; 7-shearing machine; 8-belt roll

Figure 2 Casting and rolling production process flow chart

(2) Casting and rolling area

The casting zone consists of a solid phase zone, a solid solution zone and a liquid phase zone (L = L ₁ + L ₂ + L ₃ ), which refers to the area between the center of the two rolls connected to the leading edge of the casting nozzle (Fig. 3); It has been fixed before the start of casting and rolling, determined by the thickness of the cast strip, the roll diameter, the alloy, the equipment capacity and the thickness of the leading edge of the casting nozzle. The general principle of length setting of casting and rolling zone is: thickening of cast-rolled plate thickness, shortening of casting and rolling zone; increase of roll diameter of casting roll, increase of casting and rolling zone; increase of thickness of casting nozzle lip, growth of casting and rolling zone; equipment rolling The production capacity is large, and the casting and rolling zone is growing; the pure aluminum and soft alloy casting and rolling zones are slightly longer, and the hard alloy casting and rolling zone is slightly shorter.

h ₀ - strip thickness; h-melt solidification thickness; L-casting zone;

L ₁ -solid phase zone; L ₂ -solid solution zone; L ₃ -liquid zone

Figure 3 Schematic diagram of casting and rolling zone

(3) casting rolls

The casting roll consists of a roll sleeve, a roll core and a cooling water passage, as shown in Figure 4.

1-roll core; 2-roller sleeve; 3-cooling water channel

Figure 4 Cast roll structure

1, the roller cover

The sleeve is in the outer layer and it is in contact with the liquid metal. Due to repeated alternating heat and cold, it eventually leads to defects such as surface thermal fatigue cracks, which need to be re-ground after each use period, which is a wearing part.

2, the roll core

The core of the roll is the core component of the casting roll, through which it supports the sleeve and achieves circulating water cooling.

3, cooling water channel

The cooling water channel, also known as the cooling water channel, is a circulating water channel formed by machining the roller core. Due to the long-term passing of cooling water, it is easy to scale, rust or break. Generally, it is necessary to re-weld and grind when changing the sleeve.

4, roll core and roll cover material

The core material commonly used at home and abroad is steel, including: 45, 35CD4, 34CrMo4, SCM432, 23CD4, 23CrMo, 35CrMo, SCM440 and so on. Widely used steels are 23CrMo and 35CrMo. The hardness is between 280 and 400 HB.

The roller sleeve is affected by bending stress, torsional stress, surface friction and periodic thermal impact. It requires: good thermal conductivity, low linear expansion coefficient and small elastic modulus, high strength and hardness, good. High temperature resistance, thermal fatigue resistance and thermal deformation resistance. In addition to the above performance requirements, the overall cost is also considered.

Commonly used roll sleeve steel materials at home and abroad are: 3MoV, 32Cr3MoV, 20Cr3MoWV, 35CrMnMo, 45MnMWV, CrNi3MoV, etc., hardness range HB 380 ~ 420, room temperature tensile strength is 950 ~ 1400N ∕ mm ² , 600 ° C tensile strength is 550 ~750N∕mm ² .

Second, the copper roller cover

The copper roller sleeves introduced by Germany's Came Company (KME) have been put into practical use in production, and have achieved good economic benefits, which is worth introducing and promoting. However, the application of copper roller sleeves has not yet entered a perfect stage of maturity, and there are still some problems to be developed.

The biggest disadvantage of the steel sleeve is that its thermal conductivity is low, about 25W ∕m·K, while the Cu-Co-Be alloy Elbrodur B95 is about 250W/m·K, the former is only 1/10 of the latter. Therefore, the productivity of the steel sleeve casting mill is low, and FIG. 5 shows the relationship between the thermal conductivity and the tensile strength between the copper sleeve and the steel sleeve.

1-Elbrodur NiB alloy; 2-Elbrodur B95 alloy; 3-steel

Figure 5 Thermal conductivity and tensile strength of cast roll sleeve material

(1) Development of copper roller sleeves

From the day of the twin-roller aluminum strip continuous casting mill, metallurgical engineers and scientists thought of the high thermal conductivity of copper alloys. After years of trials, the copper alloys were not able to achieve the intended purpose. In this area, a lot of experimental research work has been done by Granges and Pechiney. Although it has not been put into practical use, it has gained some experience and many problems. However, on the small narrow-width casting and rolling, Aliusuiss (which was acquired by Alcan in 1999) was successfully applied for the first time. The aluminum alloy AlSn12 for automotive bearings was produced by a copper roll casting mill. There is a fairly wide range of solidification temperatures.

The main shortcomings of the copper roller sleeves used are summarized as follows:

· Hardness is not high;

·Under the temperature of the casting and rolling process, the strength is low, especially the fatigue strength is not high; in addition, the ability to resist thermal stress is not strong;

· The limitation of the shrinkage fit between the copper sleeve and the steel roll core is unsatisfactory, resulting in uncontrollable sliding of the sleeve on the roll core;

· Compared with conventional steel sleeves, copper sleeves have a short life and low economic efficiency.

In order to overcome the above shortcomings, the world's largest copper producer, Germany's Came Group (KME), has invested considerable effort in the scientific research of copper rollers since 1998. After nearly four years of research and development, it has made breakthrough progress. To this day, most of the factors that restrict the application of copper sleeves have been overcome, and a small part has not been completely solved, but it has also been greatly improved.

The Camry Group is also the world's largest producer of copper products. It has factories in Germany, the United Kingdom, France, Italy, Spain and China. Almost all types of copper alloys can be produced. In 2008, the sales revenue was 3 billion euros. It has about 570,000 tons of copper and copper products and 6,700 employees. It is headquartered in Osnabruck, Germany. Due to the impact of the global financial crisis, the operating conditions in 2009 suffered a lot: turnover of 1.949 billion euros, investment of 38 million euros, sales of copper and copper products of about 437,000 tons, employees of 6497, equity of 423 million euros The property rights ratio is 23.9%. Kaimei Group has 8 factories and trading companies in China, namely Xinhua Youli (Beijing) Science and Trade Co., Ltd., Shanghai Youhe Co., Ltd., Tianjin Pan Asia Electronics Co., Ltd., Dongguan Youxian Co., Ltd., Shanghai Youhua Limited Company, Younier Machinery Co., Ltd. and Dalian Dashan Crystallizer Co., Ltd., etc.

1. Research and development goals

The goal of developing copper roll covers is to increase casting speed and output; improve product quality; reduce production costs; and tap the new potential of the downstream aluminum processing industry, namely to expand the types and product specifications of castable alloys. To this end, two new types of special bronzes have been successfully developed: cobalt bronze (Cu-Co-Be alloy) and nickel bronze (Cu-Ni-Be alloy), the former used to make roll mills for casters, the latter for manufacturing Net shape casting molds and other molds that need to resist high stress. The nickel bronze grade is ELBRODUR NiB, and the cast roll sleeve cobalt bronze alloy is branded as ELBRODUR B95, which can also be abbreviated as KME B95.

KME B95 alloy is an alloy optimized on the basis of cobalt bronze composition. It contains about 1% Co and 0.2% Be. Of course, it may also contain some special alloying elements. Its processing technology also has some special features. The advantages can be summarized as "four high": high hardness and strength properties, high thermal conductivity, high creep resistance, and high fatigue resistance.

The performance of KME B95 alloy has reached the expected target value.

2, manufacturing process

The manufacturing process of the copper roller sleeve (KME B95) is shown in Fig. 6.

Figure 6 copper roller sleeve manufacturing process description

(2) Performance of copper roller sleeve

The assembled casting roll sleeve is shown in Fig. 7. The equivalent stress (SEQV) after shrink assembly is shown in Fig. 8. Fig. 9 shows the temperature environment and the alternating stress subjected to the copper roll sleeve casting and rolling, and the casting and rolling The equivalent stress at time is shown in Figure 10.

Figure 7 assembled cast roll sleeve

Figure 8 Equivalent stress diagram of assembled copper roller sleeve

Figure 9 Temperature and alternating stress of copper sleeves during casting

Figure 10 Equivalent stress diagram of copper sleeve during casting

Third, KME B95 alloy

KME B95 alloy is a special alloy developed by Kaimei Group for the roll sleeve of twin-roll aluminum strip continuous casting mill. It is a kind of cobalt bronze. The average content of Co and Be is 1% and 0.2% respectively.

(1) Physical properties and mechanical properties

The physical properties of KME B95 alloy are shown in Table 1, and the mechanical properties are shown in Table 2 and Figure 11.

Table 1 Physical properties of KME B95 alloy

Table 2 Mechanical properties of KME B95 alloy

Figure 11 Relationship between tensile strength and temperature of KME 895 alloy

(2) Effect of cobalt (Co) and bismuth (Be) on copper properties

The phase diagrams of Cu-Co and Cu-Be binary alloys are shown in Fig. 12 and Fig. 13, and the aging curves of Cu-Co-Be alloy are shown in Fig. 14. At a eutectic temperature of 1112 ° C, the solid solubility of Co in copper is 8.8%, and then decreases sharply with the decrease of temperature; the phase diagram of Cu-Be binary alloy is quite complicated, and there is a peritectic reaction at the Cu end. There is an eutectoid transformation. When the peritectic reaction temperature is 866 ° C, the solid solubility of Be in Cu is 16.5 atom%, and the solid solubility at the eutectoid temperature of 600 ° C is 10 atom%. In this system, in addition to the existence of Cu-based solid solution, there are also β(Cu2Be), γ(Cu, CuBe), and the δ phase is at the end.

Figure 12 Cu-Co binary phase diagram

Pure Metal Powder

Pure metal powder for thermal spray refers to a fine powder made from a single metal, such as aluminum, nickel, or titanium, that is used in thermal spray processes. Thermal spray is a coating technique where the metal powder is heated and propelled onto a substrate to create a protective or decorative coating. The pure metal powder is typically chosen based on the desired properties of the coating, such as corrosion resistance, wear resistance, or thermal conductivity. It is important to use pure metal powder to ensure the coating has the desired composition and performance characteristics.

Tungsten Powder,Plasma Spray Powder,Pure Tungsten Powder,Tungsten Metal Powder

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