1. Principle of the cone rolling
Cylinder and cone simple workpiece can be regarded as the generatrix of cylinder and cone workpiece rotated 360 degrees around the centerline of rotation in the same plane.
The generatrix of the cylinder workpiece is parallel to the rotation centerline, and the generatrix of the conical cylinder workpiece is inclined to the rotation centerline.
The principle of three-point bending is used to roll the cylinder and cone.
There are three steps in the rolling process:
Feed the workpiece into the work roller of the roll bending machine.
One roll is above the workpiece, which is called the upper roll.
Two under the workpiece are known as the lower roll.
This is three roll bending machine;
The four roll bending machine has three rollers under the workpiece.
One in the same vertical plane of the upper roller is called the middle lower roller.
The other two on both sides of the upper roll are called the side roll.
The upper roller can bend the workpiece with any two rollers of the side roller and the middle and lower rollers.
This article only discusses the symmetrical arrangement of two lower rolls or side rolls and upper rolls;
The second step is to make the work roll do the feed motion, that is, three-point bending.
In some cases, the upper roll is used to press down the feed, while the lower roll or side roll moves upward.
For the convenience of description, according to the principle of relative motion, the workpiece and the lower roller or side roll are regarded as stationary, and the upper roll is pressed down;
When rolling a cylindrical workpiece, the upper roller is parallel to the lower roller when it is pressed down; when rolling a cone-shaped workpiece, the upper roller is inclined to the lower roller when it is pressed down;
The more the reduction, the greater the curvature of the generatrix and its vicinity;
The third step is to rotate the workpiece through the rotary motion of the work roll.
At the same time, the reduction of the upper roller is kept constant, so that each generatrix of the workpiece has the same curvature or curvature distribution, and becomes a circular cylinder and a conical cylinder.
There are many methods to roll the cone with the plate rolling machine, which are suitable for different workpieces and have their own characteristics.
No matter what method is used, it is necessary to ensure that the generatrix of the workpiece coincides with that of the upper roll during the rolling process.
The conical cylinder is a fan-shaped steel plate, which is rolled in the plate bending machine of cylindrical work roll.
It is necessary to ensure that the generatrix of the workpiece coincides with that of the upper roll during the rolling process.
The motion of the fan-shaped steel plate between the work rolls can be regarded as the combined motion of the uniform motion of each point on the workpiece generatrix in the direction perpendicular to the axis of the work roll (The rotary motion of the main transmission device of the cylindrical work roll can realize this motion) and the rotation of the workpiece around a vertical line passing through a certain point on the generatrix. .
Make the big head go faster or the small head slower.
This requires an additional moment to be applied to the fan-shaped steel plate to overcome the friction between the workpiece and the work roll.
This is the key to the cone.
The rotational movement of the workpiece around the vertical line passing through this point on its own generatrix requires the smallest moment.
2. Method of the cone rolling
According to whether the thrust roller (block) is used in the rolling process, hereinafter referred to as the thrust roller, it can be divided into the thrust roller method and the non-thrust roller method.
There are the following types of non-thrust roller method:
1) Partition marking method:
Draw a number of generatrix on the fan surface of the workpiece, align each generatrix of the workpiece with the generatrix of the upper roll, and roll the workpiece near both sides of each generatrix according to the generatrix partition.
This is an approximate and discontinuous method, which is low efficiency but simple.
The rotation movement of fan-shaped steel plate around the plumb line passing through a certain point on its generatrix is realized by manual aligning the generatrix.
2) Cone roll method:
Workpieces with three tapered rollers all use cone roll method.
The taper of the tapered roller is related to the workpiece, and there is no mutual sliding between the workpiece and the roller surface;
There are also active rolls with tapered rolls (generally upper rolls) and passive rolls with segmented sleeves.
The workpiece, the roller sleeve and the roller core slide with each other.
The more the number of rolls, the less sliding between the workpiece and the sleeve.
The movement of fan-shaped steel plate is realized directly by cone roller.
The Cone roller method is the most efficient and cost-effective method, which is suitable for single variety and mass production.
3) Clamping roll method:
Generally, the four-roller bending machine can use the clamping roll method.
Tilt the lower roller, clamp the big end of the workpiece with the upper and lower rollers, and adjust the tilt amount and clamping force of the lower roller to adapt to different workpieces.
The rotational movement of the fan-shaped steel plate around a vertical line passing through a certain point on its own generatrix is realized by the friction between the clamping roller and the surface of the workpiece.
This method is simple but requires experience, and when the taper is large or the workpiece is thick, it is often used in conjunction with the thrust roller.
The advantage of the non-thrust roller method is that the plate edge of the workpiece does not contact with the thrust roller, and the bevel edge can be made first and then rolled.
The integrity of the bevel edge has an impact on welding quality.
The bevel edge of the workpiece is damaged by the thrust roller method, especially for the workpiece with larger or thicker taper.
However, it is very difficult to make bevel edge on the circular workpiece after rolling.
In order to make the bevel edge first and then roll the cone, we designed the following winding device on a three roll plate bending machine with 70 × 3500 active roller as the upper roll of both cylinder and cone.
According to the taper of the wind turbine tower, a cone sleeve composed of three sections is designed for the upper roll.
The cone sleeve is firmly connected with the upper roller with a key.
The average thickness of the cone sleeve is 35mm, which is quenched and tempered, and is in dynamic coordination with the upper roller.
The surface of the two lower rollers is quenched, and a small clamping roller driven by an oil cylinder can be arranged in the space between the two lower rollers.
It should clamp the workpiece and the upper roll to prevent the workpiece from sliding with the upper roller.
The result of actual rolling is a 26mm thick, Q345 workpiece.
Because of the small taper of the workpiece, a better effect can be achieved without clamping roller.
If the upper roll is also hardened, the removal and installation of the cone sleeve will be better.
This is a combination of the cone roller method and the clamping roller method.
As the lower roll is cylindrical roll and the upper roll is covered with roller sleeve, the structure is simple and the cost is low.
There are the following types of thrust roller method:
1) A thrust roller is set on the upper roll on the overturning side:
The thrust roller is installed in the transition section between the upper roll body and the upper roll overturning side bearing through axial and radial bearings,
A part of the thrust roller is inserted into the overturning frame to limit the thrust roller from rotating with the upper roll.
The thrust roller is generally in contact with the small end plate edge of the workpiece, and the rotation movement of the fan-shaped steel plate around the plumb line passing through a certain point on its own generatrix is realized by the friction force between the thrust roller and the workpiece plate edge.
This method is suitable for the workpiece with smaller plate thickness, larger taper and smaller head thrust roller.
2) A thrust roller is set on the lower roll on the overturning side:
The thrust roller is set on the two lower roller bearing blocks on the overturning side, and is directly fixedly connected with the upper part of the lower roll bearing seat.
The working principle is the same as that of the first method, which is suitable for the workpiece with larger taper and smaller head thrust roller, and the plate thickness is larger than that of the first method.
3) A thrust roller is arranged on the frame on the overturned side:
The thrust roller is installed on the frame on the overturned side of the four roll bending machine with bolts, and the upper plane of the thrust roller is slightly higher than the lower generatrix of the upper roll.
4) A thrust roller is arranged on the overturning frame:
Thrust rollers are installed on the overturning frame and both sides of the upper roller, and short sliding keys are set between the overturning frame and the machine frame.
5) A thrust roller is set on the machine bed:
The thrust roller frame is installed on the bed with a pin, and the thrust roller is installed on both sides of the roller.
The thrust roller frame can rotate around the pin shaft, and the thrust roller can be lifted and lowered in the thrust roller frame.
6) A thrust roller is arranged on the frame at the transmission side:
On the frame on the transmission side, a large mounting plane is arranged on both sides of the upper roller.
There are optional internal thread, trapezoidal groove, pin shaft, key, etc. on the plane for fastening the thrust roller device, so that the relative position and direction of the gear device to the work roll can be changed as required.
All of them are installed on the low side of the frame.
Generally, the workpiece will not interfere with it, and the thrust roller is close to the work roll surface.
It can roll workpieces with larger taper and smaller head thrust roller.
3. Methods to improve the ability of cone rolling
In the method 2, 4, 5 and 6, there are two thrust rollers on both sides of the upper roll.
When working, the side of the plate is against two thrust rollers, the thrust roller at the feeding side exerts torque on the workpiece and the thrust roller at the discharge side guides the workpiece.
The workpiece will deviate from its original position under the action of the thrust roller force.
Most of the time, the workpiece is in contact with only one gear wheel.
The thrust roller at the feed side exerts torque on the workpiece, and the thrust roller at the discharge side guides the workpiece, that is, the workpiece rotates too far around the center line and is blocked back by the thrust roller on the discharge side.
The two thrust rollers jointly complete the task of guiding and applying the rotary moment.
The guiding effect of two thrust rollers is better than that of one.
The rotation torque exerted by two thrust rollers on the workpiece is greater than that of one.
But the two thrust rollers are on both sides of the upper roll.
When the thrust roller of the small head of the workpiece is small, it is not easy to block the workpiece.
When two thrust rollers are used, it is better to rotate around its own axis and move up and down along its own axis.
The wear of the plate edge is small and the quenching life of the retaining wheel surface is long.
When two thrust rollers are used, it is not the friction force between the workpiece and the thrust roller, but the radial force of the contact between the workpiece and the gear wheel.
It’s more direct than friction, and it’s more efficient, so it does not have to multiply the friction coefficient.
The farther the thrust roller is from the upper roll, the longer the arm of force is, the greater the applied rotating torque is (shown in Fig. 1 and Fig. 2), and the greater the thickness of the rolled cone tube, which also requires a larger thrust roller of the small end of the workpiece.
In method 6, there are bearing blocks at both ends of the thrust roller, which is a simply supported beam with large bearing capacity,
In method 5, the retaining wheel is a cantilever beam with a relatively small bearing capacity.
In method 5, the thrust roller is on the lathe bed, and the workpiece and the frame are not easy to interfere with.
We have used method 6 on a 55 × 3200 three roll bending machine,
When rolling the workpiece with a half cone angle of 30 degrees, a 1m high bracket with large bottom and small upper part should be added between the thrust roller and the mounting plane of the frame.
Then the stop wheel is inserted into the work roll surface along the axial direction to avoid interference between the workpiece and the wide frame.
Sometimes when the workpiece is flat, if the thrust roller can not reach the workpiece, the problem can be solved by bending the workpiece first or moving the thrust roller downward.
The disadvantage of the thrust roller method is the damage to the plate edge at one end of the workpiece.
The thrust roller can rotate around its own axis and move up and down along its own axis.
The surface of the thrust roller is quenched, which can reduce the damage to the plate edge;
If possible, increasing the distance between the thrust roller and the upper roll can not only reduce the force between the thrust roller and the workpiece, but also increase the force on the thick workpiece, which requires pre-bending the longer plate end.
Friction and friction coefficient are very important factors in the process of rolling cone.
In the example of non-thrust roller method, the better effect can be achieved without clamping roller, which may be due to the different friction coefficient between the upper roll and the lower roll.
When a unit rolled 40-50 mm thick high strength steel cone tube of a large-scale project on a 100 × 4000 three roll plate rolling machine, the problem of cutting off all the bolts for the gear wheel mounting on the frame at the drive side occurred, and the project came to a standstill.
According to our field analysis and experience, it may be caused by resonance.
It is suggested to add a little lubricating oil between the workpiece and the passive roller to change the friction coefficient and vibration frequency.
This not only solves the problem but also rolls the thicker workpiece, because the lubricating oil also reduces the rotary load of the workpiece around the plumb line passing through a point on its generatrix.
It should be noted that the lubricating oil on the workpiece should be treated after coiling, so as not to affect the welding quality.
4. Estimation of cone rolling force
How much force each method needs for different workpieces requires both experience and rough calculation.
From the above analysis, it can be seen that there is only one thrust roller to apply the rotary moment to the workpiece, and the load can not be evenly divided into two thrust rollers.
The 70 × 3000 plate rolling machine of a certain unit is used to roll 60 × 2000 blast furnace shell cones with method 6.
Due to the insufficient strength of the connecting bolts between the upper and lower parts of the transmission side frame, the connecting bolts were broken in the process of rolling, and the connection of the frame was improved and rolled successfully.
In method 1, the thrust roller mainly relies on the friction between the thrust roller and the workpiece.
The positive pressure on the thrust roller is several times of the friction force, and the workpiece is easy to be damaged when it is rolled up.
Choose the appropriate method according to the size of the workpiece and different requirements.