Analysis of Characteristics of Steel Barrel Rounding Process (Xin Qiaojuan)

Analysis of Characteristics of Steel Barrel Rounding Process

Lanzhou Barrel Factory Xin Qiaojuan

First, the deformation analysis of the winding process

According to the characteristics of the circular deformation, the winding process can be divided into elastic deformation, elastic-plastic deformation, and pure plastic deformation.

In the initial stage of bending of the blank, the external bending moment is not large. The value of the internal stress is less than the yield limit σs of the material, and only causes elastic deformation inside the blank, which is called the elastic deformation stage. When the value of the external bending moment continues to increase, the internal stress exceeds the yield limit, and the deformation of the blank deformation zone transitions from elastic deformation to elastic-plastic deformation and pure plastic deformation.

Fig.1 Tangential stress distribution in the deformation zone of a circular blank

It can be seen from Fig. 1 that the stress on the cross section of the blank transitions from the outer tensile stress to the inner lamination stress, and there must be a layer of metal in the middle, and the tangential stress is zero, which is called the stress neutral layer, and the radius of curvature is represented by ρσ. Similarly, the strain distribution transitions from the tensile strain of the outer layer to the compressive strain of the inner layer, and there must be a layer of metal with zero strain, that is, when the coil is deformed, its thickness is constant, which is called strain neutral layer, and its radius of curvature Expressed by ρε. This is the basis for accurately calculating the unfolded dimensions of the rolled blank. When the deformation is small, ρσ=ρε=r+t/2, that is, the stress neutral layer coincides with the strain neutral layer and is in the middle of the blank thickness. When the deformation is large, the stress neutral layer and the strain neutral layer move inward, and the displacement of the stress neutral layer is larger than the displacement of the strain neutral layer, that is, ρε>ρσ. In the barrel production, the following experience can be used. The formula determines the position of the strain neutral layer, ie:

Σσ=r+xt

Where: ρσ—the radius of curvature of the neutral layer of the strain, mm; r—the radius of the inner circle, mm; x—the coefficient related to the deformation procedure, taking x=0.33; t—material thickness, mm.

Second, the working principle of the rounding machine

The rounding machine can be divided into two types: a three-roller and a four-roller. The three-roller reeling machine can be divided into two types: symmetrical and non-opposing.

The working principle of the reeling machine is shown in Figure 2.

Figure 2 Working principle of the circular machine

Figure 2a is a cross-sectional view of a roller of a symmetrical three-roller reeling machine. The roller has a certain length in the axial direction so that the entire width of the sheet is bent.

In the middle symmetric position of the two lower rolls, there is an upper roll 1 which can be adjusted in the vertical direction so that the sheets 4 placed between the upper and lower rolls are given different bending radii. The lower roller 2 is active and mounted in a fixed bearing, and the motor is rotated by the gear reducer in the same direction and at the same speed. The upper roller is passive and is mounted in a bearing that can be moved up and down. Often manual adjustment.

During operation, the sheet is placed between the upper and lower rolls, and the upper roll is pressed to bend the sheet between the support points. When the two lower rollers rotate, the sheet material is moved due to the frictional force, so that the entire sheet is uniformly bent.

According to the above bending principle, it is known that only when the sheet is in contact with the upper roller, the required bending radius is reached, so that both ends of the sheet have a length that does not contact the upper roller and does not bend, which is called The remaining straight edge. The remaining straight side length is approximately half the distance between the two lower rolls.

Fig. 2b is a schematic view of the operation of the three-roller reeling machine, the upper roller 1 is located on the lower roller 2, and the other roller 3 is on the side, which is called the side roller. The upper and lower rollers are rotated by the same motor. The lower roller can be adjusted up and down, and the maximum distance adjusted is approximately equal to the maximum thickness of the coiled steel plate. The side roller 3 is passive and can be adjusted in the oblique direction.

When the coil is rounded, the sheet 4 is fed between the upper and lower rolls, and then the lower roll is adjusted to press the sheet to generate a certain frictional force, and then the position of the side rolls is adjusted. When the upper and lower rolls are driven by the motor, the sheets are rotated. Bending occurred.

The advantage of this asymmetrical three-roller rounding machine is that the edges of the two ends of the plate can also be bent, and the length of the remaining straight sides is much smaller than that of the counter-moving three-roller rounding machine, and the value is less than twice the thickness of the plate. Although the sheet material between the side roller and the lower roller is not bent, the speed can be completed by taking the sheet material out of the reeling machine and then turning the head to curl.

Figure 2c is a four roll reel. It is basically similar to the asymmetric three-roller reeling machine except that only the side rollers are added. 3. The bending of the edge of the sheet is performed by the two side rollers, thus overcoming the sheet on the asymmetric three-roll reeling machine. The trouble of turning around and turning around.

Third, the volume of circular classification

A method in which a round sheet is fed while being fed on a reeling machine as a continuous bending process. Compared with the bending and bending, the radius of the winding circle is generally quite large. Generally speaking, the curvature of the workpiece (on a certain section) is equal, so the winding process is widely used in the cylinder. The manufacture of steel drum parts such as a shape, a partial cylindrical shape, a conical shape, and a partial conical shape. Further, since the position of the roller can be appropriately changed with respect to the feed amount of the sheet, it is also possible to manufacture a quadrangular shape, an elliptical shape, and other non-circular cross-section steel drum parts. Figure 3 shows the circular classification of the roll.

Figure 3 The barrel of the steel drum is round

Fourth, the form of the rounding machine

1. The form of the general reeling machine: There are many forms of the reeling machine, and the classification methods are listed in Table 1.

Table 1 Classification of common rounding machines

Classification

Winding machine form and category

Roller orientation

Divided into horizontal and vertical

Press the upper roller type

Closed

The upper roller has a central roller

Open

Upper roller without central roller

According to the number of rollers and the arrangement

Four rolls

Three rolls

The three rollers are divided into a pair of shifting and asymmetrical

Press the roller position adjustment method

Up-regulation

Vertical up-regulation (mechanical or hydraulic adjustment)

Horizontal and vertical adjustment (mechanical or hydraulic adjustment)

Down mode

Asymmetric down-regulation (mechanical or hydraulic adjustment)

Symmetrical down regulation (liquid first adjustment)

Horizontal down mode (hydraulic adjustment)

The vertical reeling machine rolls are arranged vertically. The advantage of this rounding machine is that it has a small footprint; when rolling a large-diameter thin-walled cylinder, it can also prevent the steel drum from collapsing due to its own weight. The main disadvantage of the vertical rounding machine is that the steel plate will rub against the ground during the rolling process. Therefore, for large-diameter thin-walled cylinders, the curvature of the upper and lower ends will be uneven, resulting in different roundness; in addition, after the cylinder is rolled up The lifting height is high, and the factory building is required to be higher.

In order to overcome this deficiency, the remaining straight side of the symmetrical three-roller reeling machine has been developed, and a three-roll reeling machine capable of directly performing pre-bending work has been developed.

Figure 4 Pre-bending three-roller rounding machine

Figure 4 is the working process of the horizontally up-regulated (inclined) three-roller rounding machine. First adjust the upper roll to the left end, roll the left part of the sheet and roll it round, and then adjust the upper roll to the right end. Roll the right side of the round sheet and roll it round. Finally, the upper roller moves to the middle position for rounding. This type of reeling machine has a higher working efficiency, but the structure is more complicated.

2, three roll round machine

The two-roller rounding machine is ideal for mass production of shaped products. Especially for the thin steel plate barrel round, the most ideal.

As shown in Fig. 5, the two-roll reeling machine is composed of a rigid roller and an elastic roller. In the two-roll reel, the slab is continuously wound around the rigid roller due to the pressure of the elastic roller to form a cylindrical shape. The hardness of the urethane synthetic rubber roller suitable for the present processing method is Shore hardness A85°-95°.

Figure 5 Working principle of the two-roller reeling machine

Fig. 6 shows the test values ​​of the roller reduction amount (the amount of depression of the urethane synthetic rubber roller) and the diameter of the molded article. The amount of reduction reaches a certain critical value. After the sheet is applied to the roller, even if the reduction of the roller is increased above the critical value, the variation of the diameter of the workpiece is very small. Therefore, the amount of deformation that is slightly more than the critical reduction is a reasonable reduction. Although it is less than the critical reduction amount, it is not impossible to manufacture various cylindrical members having different diameters depending on the adjustment of the roller reduction amount. However, since it is not stable enough, this method is generally not employed. In order to change the diameter of the workpiece, as shown in Fig. 5, a circular roller is specially formed on the steel roller by a guide wheel of an appropriate diameter.

Fig.6 The measured value of the relationship between the roller reduction and the diameter of the reel in the two-roll bending

Compared with the three-roll and four-roll reel, the advantages of the two-roll reel are:

(1) The tip end is not bent, and the processing speed is fast;

(2) There is a possibility of high-precision forming in one stroke;

(3) The slab does not cause cracking and irregular warping even after being punched, cut, undulated, etc.;

(4) No wrinkles are generated, and scratches are not caused on the surface of the barrel;

(5) If the reduction of the roller is large, even if the pitch of the two rollers changes and the diameter of the bucket does not change, the accuracy of the equipment is not high, and a simple device is used. .

On the other hand, the disadvantages of the two-roll reel are:

(1) It is not suitable for multi-product small batch production because it is necessary to make a guide roller for each change of the diameter of the workpiece;

(2) It cannot be processed as a thick plate (maximum processing thickness is 6-9 mm).

Five, the relative position of the reeling machine roller

If the roller radius and relative position of the reeling machine are known, the position at which the roller should be adjusted can be calculated according to the radius of the sheet to be bent.

When winding with a symmetrical three-roller (as shown in Figure 7a), the position of the upper roll can be obtained by:

Where: h - the vertical distance of the upper and side rolls, mm; R - the bending radius of the sheet, mm; t - the thickness of the sheet, mm; r1 - the radius of the upper roll, mm; r2 - - side roller radius, mm; L - half of the center of the side roller, mm.

When winding a four-roller (Fig. 6b), the position of the side roller can be obtained by the following formula:

Where: h - the vertical distance between the side roller and the lower roller, mm; r1 - the radius of the upper and lower rollers, mm; r2 - the radius of the side roller, mm; t - the thickness of the sheet, mm; R - the bending radius of the sheet, in millimeters.

Due to the rebound of the steel plate, the h value obtained in the above formula is referred to for the initial roll. The diameter of the small cylinder that can be rounded on the reeling machine depends on the diameter of the upper roller. Considering the rebound after the barrel is rounded, the smallest cylinder diameter that can be rounded is about 1.1-1.2 times the diameter of the upper roller. .

Figure 7 Calculation of roller position of the reeling machine

Sixth, the remaining straight edge and elimination method

When the sheet is wound on the rounding machine, there are always straight edges on both ends. The theoretical residual straight edge values ​​are related to the type of the reeling machine, as shown in Table 2.

Table 2 The size of the theoretical remaining straight edge

Equipment category

Rolling machine

Press

Curved form

Symmetrical bending

Asymmetric bending

Die bending

Three rolls

Four rolls

Remaining straight edge

Cold bend

L

1.5t-2.0t

1.0t-2.0t

1.0t

Hot bending

L

1.3t-1.5t

0.75t-1.0t

0.5t

This watch is suitable for all bending deformation processing.

In the table, L is half of the center distance of the side rolls; t is the thickness of the sheet. In fact, the remaining straight edge value is larger than the theoretical value. Generally, it is 6t-20t when symmetrical bending, and 1/6-1/10 when it is symmetrical bending when asymmetric bending. Since the remaining straight edges are difficult to eliminate when rounding, and causing large weld stress and equipment load, the steel drum is not round enough. For small diameter steel drums it is important.

Generally, for small batch production of thicker plates, pre-bending is required. There are several ways to bend forward:

(1) pre-made a bending die, put the bending die into the roller, and place the sheet on the bending die to roll and roll;

(2) pre-bending with a mold;

(3) Pre-bending on a four-roll crimper.

For the steel drum industry, the remaining straight edges are not long due to the thinner sheets. If the barrel can be rounded with a four-roller, the remaining straight edges can be eliminated.

Seven, the quality analysis of the volume

The quality problems of common coils include shape defects, surface crushing and cracking.

1, shape defects

When rolling a cylindrical barrel, several common shape defects include bends, cones, drums, waists, edge skews, and corners, as shown in Figure 8. The cornering (Fig. 8a) is due to the excessive adjustment distance of the upper roller (three-roller reeling machine), so that the two edges overlap too much. Using a wooden hammer to strike the edge of the barrel allows the diameter to expand and can be removed by cornering. In order to prevent the barrel from being bent, the curvature is checked with a template each time the roller is adjusted.

Figure 8 several common shape defects

Since the adjustment amounts at both ends of the upper roller or the side roller are not uniform, the center lines of the upper and lower rollers are not parallel to each other, and a tapered defect is generated (Fig. 8b). To prevent this defect, the template should be used to verify that the radius of curvature is the same across the length of the barrel. If there is a difference, the feed of the roller should be increased at the end of the radius of curvature.

The drum-shaped defect (Fig. 8c) is caused by bending due to insufficient rigidity of the roller at the time of winding. In order to prevent the bending of the roller, a support roller can be added in the middle portion of the roller.

The waist (Fig. 8d) is caused by the downward pressure of the upper roll or the pre-pressure of the lower roll, causing the roll to be reversely bent.

Skew (Fig. 8f) is due to the fact that the billet is not centered when the billet is fed, or the billet is not rectangular and causes skew defects.

The corners (Fig. 8f) are caused by inaccurate pre-bending.

2, surface crush

When rolling, the scale on the surface of the steel plate or the roller and the adhered impurities may cause crushing on the surface of the sheet. In order to reduce the hazard of scale, the following measures can be taken:

(1) Before rolling, the scale on the surface of the sheet should be removed.

(2) The rounding machine must be kept clean and the surface of the roller must be free of scale, burrs, edges or other hard particles.

(3) When winding the circle, timely attention should be paid to purging the inner and outer rust powder, dust and other materials.

3, cracking

When the sheet is rounded, the deformation of the material is large, the cold work hardening of the material, and the stress concentration can cause the plasticity of the material to deteriorate and cause cracks. In order to prevent the occurrence of cracks, for the material that is easy to be cracked, it is possible to take measures to limit the deformation; the steel plate is subjected to normalizing treatment; preheating and the like.

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