When the wavelength is not less than 200mm, the wave height should be less than 1% for steel plates with nominal width less than 1500mm, and less than 1.5% for steel plates with nominal width not less than 1500mm. When the wavelength is less than 200mm, the wave height should be less than 2mm.
arc
The sickle bend of steel plate and steel strip should not be greater than 5 mm in any length of 2000 mm. When the length of the steel plate is not more than 2000 mm, the sickle bend should be not more than 0.25% of the actual length of the steel plate. The sickle bend of longitudinally cut steel strip with a width less than 600mm should not be greater than 2mm in any 2000mm length.
flat angle
Steel plates shall be cut at right angles, and the cutting angle shall not be greater than 1% of the width of steel plates.
triangular
The steel strip shall be coiled firmly, and the height of one tower shall not exceed the following provisions.
Nominal thickness tower height
& lt 2.0mm 8mm
≥ 2.0mm12mm
Available brands, standards and uses
Brand supply standard supply size (width mm thickness mm)
The society for the prevention of cruelty to children.
q 195 GB/t 9 12 20 ~ 450 0.3 ~ 3.5
Q235-B GB/T3274
use
Widely used in construction machinery, transportation machinery, construction machinery, lifting machinery, agricultural machinery, light industry and civil industries, such as general structural parts and stamping parts.
Allowable deviation of size and shape
Brand: SPCC, Q 195, Q235-B.
Corresponding standards implemented: GB/T709
Chemical composition (wt%)
trademark
Silicon-manganese-phosphorus-sulfur-copper
SPCC 0.02 ~ 0.80≤0. 10 0. 15 ~ 0.30≤0.045≤0.050≤0.050
q 195 0.06 ~ 0. 12≤0.30 0.25 ~ 0.50≤0.045≤0.050≤0.050
Q235-B 0. 12 ~ 0.20≤0.30 0.30 ~ 0.70≤0.045≤0.050≤0.050
mechanical character
Grade yield strength RcL tensile strength Rm elongation A80mm impact test (longitudinal) Temperature℃ impact work AkvJ
Mpa Mpa %
SPCC ≥ 195 3 15~430 ≥33
q 195≥ 195 3 15 ~ 430≥33
Q235-B ≥235 375~500 ≥25 20 ≥27
Advantages of cold rolled strip steel:
① Very thin strip steel (as thin as 0.001mm); ) can be obtained that is difficult to obtain by hot rolling method;
(2) The product can have high and wide range of mechanical properties and technological properties;
(3) Various strip steels with high dimensional accuracy, small thickness deviation, uniform thickness along the width and length direction of strip steel, good shape and smooth surface can be obtained;
(4) low cost and high yield;
⑤ Fast rolling speed and high productivity.
Process characteristics of cold rolled strip:
(1) When the strip is cold rolled, due to the work hardening of the strip, it must be softened again by intermediate annealing to restore its plasticity before rolling can continue;
(2) Before rolling, the scale on the surface of the strip steel must be removed to ensure the surface smoothness of the strip steel and reduce the wear of the roll;
(3) Tension rolling ensures good shape, controls strip thickness deviation and reduces rolling pressure, which is beneficial to rolling thin products.
(4) Using process cooling and lubrication, it is convenient to control the temperature between the roller and the strip steel, reduce the friction between the roller and the strip steel, and reduce the rolling pressure, which is beneficial to shape control and prevent the strip steel from sticking to the roller.
history
1553, a Frenchman, Bou Lhuilier, made a rolling mill to roll gold and silver plates for coinage. The earliest cold rolling mill was a two-high mill, and later a four-high mill with smaller diameter and greater rigidity was adopted. In order to roll thinner and harder strip steel, six-roll, twelve-roll, twenty-roll and eight-roll (M.K.W) mills have been developed, which have smaller work rolls and greater rigidity. There is no tension in single piece rolling, the rolled piece is thicker (>: 1mm), and the speed is low (
The production of cold-rolled strip adopts coil rolling, tension winding and uncoiling devices, with high speed (up to 42m/s), high pass compression rate and flat shape. There are two kinds of rolling mills: single reversible and continuous.
Single-stand reversible four-high cold rolling mill is suitable for producing many varieties and small batches of ordinary carbon steel or low-alloy steel with thickness greater than 0.2 mm, and 20-high or 8-high rolling mills are mostly used for rolling high-alloy special steels such as silicon steel and stainless steel.
The continuous rolling mill consists of 3 ~ 6 stands. The more racks, the greater the total compression ratio and the thinner the product thickness; The faster the rolling speed, the greater the output; Suitable for ordinary carbon steel automobile plates, galvanized plates and tinned plates with large output and few specifications.
Machinery and equipment-full continuous cold rolled strip mill
In 1970s, a few fully continuous cold rolling mills were developed (Figure 2). Before the coil enters the rolling mill, the tail of the previous coil is welded with the head of the latter coil. Loops are used to store enough strip steel to ensure that the rolling mill continues rolling during welding. The rolling process is controlled by computer, and the specifications can be changed dynamically. After rolling, it is crushed and rolled with flying shear. When rolling each coil of strip steel by full continuous rolling mill, it is not necessary to wear the strip and flick the tail, which saves the time between coil changes. The annual output of each fully continuous rolling mill reaches 2 million tons. The waste products with out-of-tolerance thickness of steel coil head and tail are eliminated, and the rolling accuracy and yield of strip steel are improved.
Present situation of cold rolled strip mill
In 1980, there were 466 cold strip mills with the roll length exceeding 860mm in the world, including 16 1 reversible four-high mill, 108 reversible multi-high mill and 197 continuous mill. There are 9 cold rolling mills for wide strip steel in China, including 4 reversible four-high mills, 3 reversible twenty-high mills, 1 eccentric eight-high mills and 1 continuous mills. Figure 3 shows the cold tandem mill built by Wuhan Iron and Steel Company at 1978. Table 2 shows the main performance specifications of the mill.
Process flow of cold rolled strip steel
According to the specifications of raw materials and products, there are slight differences.
Process pickling
When the coiled steel coil is placed, it is easy to form iron oxide with air if it is not treated, because the air is humid and will rust after a long time. Therefore, it is necessary to use continuous pickling line to remove the scale on the surface of hot rolled coil. Acid used to be sulfuric acid, but now it is mostly hydrochloric acid. Before pickling, it should be welded into coils, and some parts should be subjected to continuous "black annealing". After pickling, cleaning, drying, trimming and rolling.
cold rolling
The strip after pickling is rolled to the thickness of the finished product on a cold rolling mill, and generally no intermediate annealing is carried out. The total cold rolling compression ratio of five-stand tandem mill is generally 60 ~ 80%, and the main rolling thickness is 0.3 ~ 3 mm for automobile plate, enamel plate and galvanized plate. Six-stand tandem mill mainly rolls tinplate with thickness of 0. 15 ~ 0.5 mm, and the total cold rolling compression ratio is generally 70 ~ 90%. When rolling, the reduction distribution of each stand (or pass) is comprehensively formulated according to the promised pressure, power and speed of the rolling mill, considering the factors such as output and quality.
Process lubrication
It plays the role of lubrication and cooling. Generally, emulsion with good cooling performance is used, and pure oil lubricant with good lubricating performance is used when rolling thin or hard metals, such as palm oil for rolling tinplate or stainless steel.
take exercise
The purpose is to eliminate cold rolling hardening, make the steel plate recrystallize and soften, and have good plasticity. The annealing method includes coil annealing in a bell furnace and annealing in a continuous furnace. Coil annealing is divided into tight coil annealing and loose coil annealing; Continuous furnace annealing includes vertical continuous furnace annealing and horizontal continuous furnace annealing. Usually, shielding gas is introduced into the furnace. At present, bell furnace annealing is mostly used. Although the treatment period is long, it is flexible to use and saves investment because of the large number of furnaces. The output of continuous furnace annealing is large, in which horizontal continuous furnace annealing is only used to treat abnormal steel with low output, such as decarburization annealing of silicon steel.
level
The purpose is to avoid the plastic instability of annealed steel plate in stamping process and improve the quality (flatness and surface condition) of steel plate. There are two types of leveler: single stand reversible and double stand, and the flattening compression ratio is 0.5 ~ 4%. The double-stand temper mill has high efficiency and compression ratio, and can be used for secondary cold rolling to further roll thin steel plates. 0. 10 ~ 0. 15 mm coil can be produced if it is matched with a five-stand tandem mill.
Coating, cutting and packaging
Sending the steel plate to be plated to a zinc plating, tin plating or organic coating unit for treatment.
Generally, cold-rolled plates are cut after flattening. There are longitudinal shear and transverse shear. The longitudinal shears are used for trimming or slitting according to the required width, and the transverse shears are used for cutting the coiled material into individual plates according to the required length. After inspection and classification, the cut finished strip is coated with antirust oil and packaged before leaving the factory.
Technological development has improved productivity.
Mainly to improve the speed of continuous rolling mill and the weight of single coil. After years of improvement, the rolling speed is shown in Figure 5 [1930 ~ 1980], and the weight of single coil has increased from 20 tons in the 1950s to 40 ~ 60 tons in the 1970s. Due to efficient circulating oil supply and some improvements in rolling equipment, the rolling speed of a group of six-stand cold tandem mills in Japan 197 1 can reach 2500m/min. In order to control and ensure the quality, the actual speed of the general rolling mill is still 1500 ~ 1800 m/min. In the late 1960s, the automation of computer-controlled screw-down schedule formulation, parameter setting and adjustment of rolling mill, threading and unwinding, winding and unwinding, and roll change was realized, which improved the efficiency of rolling mill.
Improve product quality
In the late 1960s, automatic thickness control system (AGC) was widely installed. In 1970s, the newly-built rolling mill adopted hydraulic AGC with fast response and high precision, which reduced the tolerance of cold-rolled strip to 0.005 mm ... The hydraulic bending roll shape adjusting device was widely used in shape control, and an automatic shape control system composed of various shape detectors and roll shape adjusting devices was developed. The key to shorten the production cycle is to make each working procedure go on continuously.
Shorten the production cycle
The key is to make each process continuous. 197 1 year, Japan established the first fully continuous rolling mill. In the early 1980s, a production line was established, which connected the continuous pickling with the full continuous rolling mill, and combined the continuous annealing line with the continuous rolling mill. In order to shorten the storage time of products in each process, speed up the production cycle and realize the continuity of processes, computer planning, scheduling, equipment diagnosis and maintenance systems are being established.