1、Overview
When the stainless steel pipeline needs to change the direction or point-of-use path design requirements during the layout of the project works, it is necessary to use stainless steel elbow connection, the angle of which is 45 °, 90 °, etc. Elbow forming production can be used in different ways: bending stainless steel elbow forming, push bending forming and compression bending forming.
2, stainless steel elbow production process
Stainless steel elbow production process is as follows.
Incoming billet an inspection a forming a cleaning a shaping a chamfering a word a polishing a cleaning a drying a deburring a finished product inspection a packaging into storage
3, around the moving bend forming
(1) with a core bend
Core bending is the use of mandrels in the bending machine so that the tube material along the bending die bending around the bending method of forming. The working principle of cored bending is shown in Figure 5-1, bending mold 4 fixed in the bender spindle and rotate with the spindle, one end of the stainless steel billet 6 by the clamping block 3 pressed in the bending mold. In the stainless steel billet and bending tire mold near the tangent point, the outside of the bend is equipped with a pressure block 1, the inside of the bend is equipped with anti-wrinkle block 5, while the billet is plugged inside the mandrel 2. When the bending mold rotation, the stainless steel billet is bent around the bending mold gradually bent into shape. The bending angle of the stainless steel elbow is controlled by the block (not shown in the figure), when the bending mold to the stainless steel pipe bending angle required, then hit the block, so that the bending mold to stop rotating. The following will be the design and manufacture of the main components of the mold to explain.
A mandrel
Mandrel is an important part of the core bending device, its role is to support the wall from within the stainless steel pipe billet, to prevent deformation of the stainless steel pipe section and wall wrinkles. Common round-head mandrel and multi-ball mandrel structure form as shown in Figure 5-2.
Round-head mandrel shape is simple and easy to manufacture. However, because the mandrel and the wall contact area is less, so the effect of anti-sectional deformation is poor, usually used for stainless steel pipe fittings bending requirements are not high. Mandrel commonly used 3Cr2W8V material manufacturing, heat treatment hardness of 52 – 56HRC.
Flexible shaft multi-ball mandrel is a flexible shaft to a number of bowl-shaped spheres in series, can achieve the swing of space in any direction, suitable for thin-walled tube single, multiple and space bending forming of stainless steel pipe fittings.
The use of multi-ball mandrel bending, in the process of bending by the oil cylinder to draw out the mandrel, but also the pipe fittings can be rounded. The main disadvantage of multi-ball mandrel is the manufacturing trouble, mandrel materials and heat treatment requirements and single ball mandrel the same.
In the mandrel bend, the shape, size and working position of the mandrel, the quality of stainless steel pipe bend has a greater impact. The size of the round-headed mandrel and the working position into the tube is shown in Figure 5-3.
In order to make the mandrel smoothly inserted into the stainless steel billet, mandrel diameter d (mm) – generally should be smaller than the billet diameter of about 0.5 -1.5 mm, that is
d = D1 – (0.5 – 1.5)
The cylindrical length L of the mandrel is
L= (3-5)d
When the diameter d of the mandrel is large, the coefficient takes a small value, and vice versa takes a large value.
The working position of the mandrel should be a distance e ahead of the bending centerline. generally speaking, the size of e should be based on the diameter of the stainless steel billet, the bending radius and the size of the gap between the billet inner diameter and the mandrel, and then adjusted appropriately according to the actual production situation. e value can be calculated according to the following formula.
e = √2 (R + D1/2) z a z2 (5-1)
where D1 – billet inner diameter, nim.
R – central layer bending radius, mm.
z – the gap between the inner wall of the stainless steel pipe billet and the mandrel, mm, z = D1 – d0
The site is also commonly used in a ball-headed bar, its use and manufacturing ease just between the above two mandrels. The parts diagram of the ball mandrel is shown in Figure 5-4.
B anti-wrinkle block
Near the cut point and not into the bending deformation zone of the stainless steel billet material, its appearance is not supported by the bending tire model groove, even with the mandrel, stainless steel bending may still be wrinkled here, it should be installed as shown in Figure 5-5 anti-wrinkle block. The front end of the anti-wrinkle block is rounded edge shape, inserted between the bending mold and the billet, the front end should be close to the wall and the bending mold tangent, effectively filling the gap between the bending mold and the bending stainless steel billet, thus playing a role in supporting the wall from the outside to prevent wrinkling.
As the shallow circular groove on the anti-wrinkle block and the outer surface of the billet contact, the work of sliding friction, it requires the anti-wrinkle block working surface should have a certain degree of hardness and low surface roughness. The anti-wrinkle block is generally made of tool steel or chrome-molybdenum steel, and the hardness reaches 50 – 55HRC after quenching.
C bending mold
Bending mold is another important part of the core bending device, the radius depends on the bending radius of the stainless steel bend. However, taking into account the cold bending bend will produce a certain amount of rebound, so the design of the bending mold radius should be slightly smaller than the required stainless steel bend radius, generally according to the following empirical data to determine, namely
When R / D = 3 -4: R1 = (0.96 -0.98) R
where R1 – bending mold radius, mm.
R – bend tube center layer bending radius, mm;
D – pipe billet outside diameter, mm.
When R / D larger, take a small value; when R / D is small, take a large value, the final correction by the test mold.
Bending tire mold in addition to the use of wheel type, there are mold column type, the mold column parts diagram is shown in Figure 5-6.
Coreless bend in the production of pipe fittings are basically not used.
(2) push bending
Push bending is the more common bending method in the bending process, mainly for bending elbows. According to the characteristics of the push bending process, can be divided into cold push bending and mandrel hot push bending two categories.
Cold push bend is in the ordinary hydraulic press or crank press with the help of the bending device on the billet push bending process, at room temperature in the state of stainless steel straight billet pressed into the mold with bending cavity, thus forming a stainless steel elbow.
Cold push bending device shown in Figure 5-8, mainly by the pressure column 1, guide sleeve 2 and bending mold 4. Bending mold by the center of the two pieces put together to facilitate its cavity processing. When bending, the billet 3 in the guide sleeve positioning, the pressure column down, the billet port to apply axial thrust, forcing the billet into the bending cavity, resulting in bending deformation.
Cold push bend is suitable for bending smaller bending radius of stainless steel elbow, can bend the minimum relative bending radius R / D ≈ 1.3; elbow cross-sectional ellipticity is small (≤ 3%-5%); the outer wall thinning amount (≤ 9%); bending device structure is simple, does not require special equipment and high productivity. However, the general requirement for the relative thickness of the pipe t / D ≥ 0.06, otherwise, the billet often loses stability due to poor stiffness, resulting in the inner side of the elbow wrinkled or twisted.
Stainless steel pipe fitting plant for the cold push bending process, the following points should also be noted.
(a) In order to reduce frictional resistance, extend the service life of the bending die and improve the surface quality of the stainless steel elbow, the billet must be lubricated. Practice has shown that the surface of the stainless steel pipe billet coated with 40 -50 oil, and then coated with a layer of graphite powder, can ensure that the bending process has a good lubrication effect.
(b) bending process, the end of the billet in the axial thrust is easy to collapse, for this reason, the billet can be placed in a core as shown in Figure 5.9, which will be launched in the bending process with the tube elbow together with the pressure column.
(c) for stainless steel thin-walled elbow, in order to prevent destabilization during the push bending wrinkle, should be filled in the pipe billet, not only easy to operate, and good anti-wrinkle effect.
(3) press bending
The use of mold pressing with straight sections of stainless steel pipe fittings, the advantage of high production efficiency, mold adjustment is simple. Stainless steel pipe fittings factory in order to prevent wall wrinkling and flattening, for the outer diameter of more than 10mm thin-walled tube, bending before the need to fill the filling material or respectively from both ends into the core head. Die bending method also has some shortcomings, such as billets and concave and convex die start contact, its tube cross-section will always have some distortion, so that the quality of the bend is not ideal. In addition, the bending radius, angle and its bending shape is also subject to certain restrictions, so the application in the production of less. Figure 5-10 for the V-shaped pipe bending die, Figure 5-l1 for the U-shaped pipe bending die, the convex die of the working surface and the shape of the billet, and placed in the middle of the left and right swing concave die.
Pressed stainless steel elbow is the use of hydraulic presses on the billet bending process method, which is divided into hot and cold pressing two kinds of pressed carbon steel elbow, alloy steel elbow, stainless steel elbow, as well as copper, aluminum elbow. Pressed elbow diameter of 25 – 406mm, wall thickness of 2.5- 40mm. bending radius of R ≥ D, generally desirable R = 1.5D.