What Is a Bimetallic Strip?

A bimetallic strip (thermostat bimetallic strip) is a strip made of two or more layers of metal with different coefficients of expansion through composite processing.

Generally, hot rolling, cold rolling, and hot pressing are used for compounding, and low-melting alloys can also be cast onto high-melting solid metal layers for compounding. The composite method depends on the nature of the component metal and the application conditions of the bimetal. The high expansion coefficient layer in the bimetallic belt is called the active layer, mainly including iron-nickel-chromium, iron-nickel-manganese, manganese-nickel-copper alloy, etc .; the low expansion coefficient layer is called the passive layer, mainly iron-nickel Alloys, etc.

According to different application conditions, bimetal strips are divided into general series, high sensitivity type, temperature type and resistance type. Because the bimetal belt has the function of bending due to "thermal-temperature" changes, it can be used for temperature indication, control, compensation and load control. The main performance indicators for measuring the function of the bimetallic belt are specific bending (curvature change per unit thickness of the bimetallic belt when the temperature changes by 1 ° C), resistivity, elastic modulus, and linear temperature variation range. Bimetallic strips used in severely corrosive environments. The surface can be galvanized with tin or coated with stainless steel to enhance corrosion resistance.

Design of CVT with bimetallic belt transmission

Metal belt type continuously variable transmission (CVT) is an ideal automobile transmission that can automatically and continuously change the speed ratio according to the driving conditions of the vehicle. At present, the metal steel belt can withstand a torque of about 450 N · m, which cannot meet the requirements for the use of medium and large-sized city buses and trucks.

The bimetallic belt drive CVT belongs to a belt-belt compound transmission scheme, which can realize stepless speed change over the entire section. The bimetallic belt drive CVT can achieve a maximum torque carrying capacity of about 900 N · m, which basically meets most cities Passenger and truck torque requirements. At home and abroad, there are few studies on the arrangement of bimetallic belt CVT. Zeng Pan proposed a bimetallic belt type continuously variable transmission structure, in which the two pulley sets share the same input shaft and output shaft. Hao Jianjun et al. Invented a bimetallic belt stepless variable speed transmission with a synchronous structure to realize the synchronous control of the speed ratio of two pulleys ^[1] .

Manufacturing technology of bimetal strip aluminum alloy bearing bimetal strip

Thin-walled bearing bushes (hereinafter referred to as bearing bushes) are one of the main vulnerable basic parts of internal combustion engines. They have a large variety and large output. With the improvement of internal combustion engine technical indicators (such as speed, power, etc.), bearing bushes are required to have high bearing capacity. The bearing capacity of white alloy (tin-based or lead-based white alloy) bearing bushes has not been able to meet the requirements, which has promoted the successful development and application of copper-based alloy bimetal strip (continuous casting or sintering) manufacturing technology. However, due to the poor surface properties (such as compliance, embedding, etc.) of these alloy bearing bushes, it is necessary to provide a lead-tin binary alloy or ternary alloy surface coating with a thickness of about 0.02 to 0.05 mm. In order to improve the bearing surface performance to meet the requirements of bearing reliability, obviously, this will increase the manufacturing cost of the bearing, and will lead to the emergence of environmental protection and other issues. Therefore, it has prompted domestic and foreign bearing companies and scholars to research and develop Manufacturing technology of AlSn20Cu bearing alloy (Sn is 17.5 22%, Cu is 0.7 1.3%, and the rest is Al) with medium bearing capacity and good surface properties, and its bimetallic strip manufacturing technology.

Studies have shown that when AlSn20Cu alloy is directly cast on the steel strip, the low melting point aluminum-tin eutectic in the alloy will be deposited on the bonding surface and affect the bonding quality; if the alloy is directly rolled and laminated on the steel strip, its low melting point Aluminum-tin eutectics are also deposited on the bonding surface, so a pure aluminum foil or nickel gate layer is used as the intermediate bonding layer between the AlSn20Cu alloy and the steel layer.

Its manufacturing process is summarized as follows:

(1) Aluminum-tin alloy casting: Attention should be paid to degassing and refinement during the casting process;

(2) Cold-rolled alloy strips: alloy ingots are rolled into alloy strips at room temperature. The parameters and times of rolling are determined according to the size of the ingot, the thickness and width of the alloy strip;

(3) Annealing of alloy strips: Generally, the annealing temperature is about 350 ° C, and the temperature is maintained for 5-7 hours;

(4) Brushing of steel strip: commonly used steel strip materials are 08A1, 08F, etc. After cleaning, degreasing, drying and other pretreatment, the steel strip is brushed with steel wire, and the surface of the compound is matte, which helps the compound Improved bonding surface quality;

(5) Brush the alloy strip and compound it with pure aluminum foil: The alloy strip is polished after degreasing, and rolled on both sides with a composite aluminum foil with a thickness of about 0.06 to 0.08 mm;

(6) Steel strip annealing: In a reducing atmosphere, it is annealed by heating at 260-300 ° C for 4-8 hours to maintain uniform hardness;

(7) Annealing of alloy strips: annealing in a reducing atmosphere after heating at 260 to 300 ° C for 6 to 10 hours and brushing;

(8) Rolling and compounding of bimetal strips: Generally, two rolls can be used. The rolling deformation of each roll is about 50%. Among them, the ratio of the reduction of the steel strip to the reduction of the alloy strip is about It is 1: 4, and the total rolling deformation is about 50% to 65%; the rolling process can usually be performed at room temperature, and the hot rolling method can also be used, and the hot rolling temperature can be controlled to 200 to 500 ° C;

(9) Bimetal strip annealing: The bimetal strip after rolling and compounding is recrystallized and annealed at a temperature of 350 ° C for 4-8 hours;

(10) Inspection, imprinting and anti-rust treatment are combined into the warehouse.

The AlSn20Cu alloy-steel bimetal strip manufactured by the rolling method can meet the requirements for the manufacture and use of bearing bushes, and is suitable for mass production. At present, AlSn20Cu bearings have been widely used in 85, 95, 100, 105, 110, 135 and other series diesel engines and crankshaft bearings of automobile engines such as Dongfeng brand ^[2] .