Profile pipes are widely used in private and industrial construction. They create gazebos, greenhouses, garages, outbuildings, billboards. Designs are not only classic rectangular, but can also have a variety of configurations. Therefore, it is very important to correctly calculate the maximum allowable bend of the pipe. This will provide the building with strength, durability and will preserve its original shape.
When making structures from profile pipe, you can not bend it "by eye" - you should make the appropriate calculations
Properties and features of profile pipe products
Profile pipes are called, whose cross section differs from round. The most common options are square and rectangular products. That fact gives them special popularity, that the final design created on their basis has rather small weight. Moreover! Due to the specific shape, fastening of pipe elements to various surfaces and to each other considerably simplifies.
These construction products are made of a wide range of alloys and metals. However, low-alloy and carbon steel profile pipes are most often used. Each metal is characterized by such a natural quality, as a point of resistance. It happens as the maximum, and minimal. The first, in particular, is the cause of deformation of constructed structures, leads to inflections, which can result in evils.
Performing a bend, it is important to take into account such characteristics, as a type of product and its density, crossing, size, as well as the flexibility of the material and its rigidity. Knowing all these properties of metal, the performer will be able to understand, how the structure will behave during operation.
in addition, should be remembered, that when bending the product, its internal parts are compressed, which leads to an increase in their density and decrease in size. The length of the outer layer increases accordingly, it becomes more stretched, but less dense. In this case, even after the end of the process, the initial characteristics of the middle sections are preserved.
When bending the pipe you need to take into account the properties of the material, of which it is made, its size and wall thickness
Importantly! Stress when bending the pipe profile will necessarily occur even on the most distant from the neutral zone segments of the product. The layers will feel especially high pressure, located in close proximity to the above neutral zone.
How the strength of the material affects the allowable bending radii
Current GOSTs in our country regulate in detail the characteristics and properties of the elements, which are used in calculating the bending strength of the pipe. First of all, in this context, the minimum radius is considered, on which it is allowed to bend a profile pipe product. It depends on the flexible execution conditions. If this procedure is carried out with heating or with stuffing of a cavity of a pipe with sand, the value of the outer diameter begins with the mark 3,5 DN (DN means a conditional passage).
If, when the contractor has the use of specialized equipment (example, pipe bending machine), which allows you to perform the sequence of necessary operations without heating, or other additional measures, then the minimum diameter is 4 DN.
If it is necessary to perform a fairly steep bend, the diameter should be equal to the minimum 10 DN, as this procedure will be performed in other ways, mainly, at high temperatures.
Of course, the values required by state standards can be slightly reduced, but then the calculation of the profile pipe for bending must be very careful. Deviations from GOST are possible, if with the bending method used the wall thickness is guaranteed to change from the initial to 15%. Only then can you be sure, that bending to smaller values will not significantly affect the strength of the structure in the future.
It is possible to bend a pipe on the maximum admissible for it radius only by means of the special machine tool or the device
Applied formulas and tables
To correctly calculate the bending strength of the pipe, it is necessary to know the length of the part. This is done according to the following formula:
D = 0,0175? R? IN + р1, where
D is the length of the workpiece; P is the radius of curvature of the pipe (mm); In - the required bending angle; p1 is the distance to hold the workpiece, required when using special equipment.
Next, we estimate the value of the area to be bent according to the following formula:
D1 = ?? IN / 180 (R + DN / 2), where
D1 - the length of the bend sections; ? - known mathematical constant; In - the angle of bending (degrees); DN - diameter on the outer surface of the pipe (mm).
In GOST №617 / 90 and №494 / 90 contains the smallest values of the main characteristics, on the basis of which the calculation of the bending strength of the profile pipe product is performed.
Useful to know! This approach - the regulation of minimum values - provides the convenience of the master, as well as the greatest safety when performing work and, of course, during operation of structures, in particular, erected of brass and copper profile.
Main characteristics, which are used in the process of calculating the bending strength of the pipe, are given in the table below.
Table 1
| The bending radius is minimal | The minimum length of the free part | Outer diameter |
| 90 | 60 | 30 |
| 72 | 55 | 24 |
| 36 | 50 | 18 |
| 30 | 45 | 15 |
| 24 | 35 | 12 |
| 20 | 30 | 10 |
| 16 | 25 | 8 |
| 12 | 18 | 6 |
| 8 | 12 | 4 |
| 6 | 10 | 3 |
The data in this table refer to brass and copper pipe products. And the calculation of the bending load on the profile pipe, made of steel, carried out in accordance with the data, below (GOST №3263 / 75).
Table 2
| The size of the pipe | The length of the free part (minimal) | Minimum bending radius | ||||
| conditional passage | Outer diameter | Hot camp | cold state | |||
| 100 | 114 | 230 | 340 | 680 | ||
| 80 | 88,5 | 170 | 265 | 530 | ||
| 65 | 75,5 | 150 | 225 | 450 | ||
| 50 | 60 | 120 | 180 | 360 | ||
| 40 | 48 | 100 | 150 | 290 | ||
| 32 | 42,3 | 85 | 130 | 250 | ||
| 25 | 33,5 | 70 | 100 | 200 | ||
| 20 | 26,8 | 55 | 80 | 160 | ||
| 15 | 21,3 | 50 | 65 | 130 | ||
| 10 | 17 | 45 | 50 | 100 | ||
| 8 | 13,5 | 40 | 40 | 80 | ||
Among the main parameters, which must be taken into account, determining the bending load, also includes the thickness of the walls and the diameter of the workpiece. The correlation of these two indicators is presented ??in the next table. By the way, the information contained in it can be used to calculate the load on the pipe of round cross section.
Table 3
| Diameter (mm) | Bending radius (minimum) at wall thickness | |
| Thickness is more 2 mm | The thickness is less 2 mm | |
| 60/140 | 5D | 7D |
| 35/60 | 4D | 6D |
| 20/35 | 3D | 5D |
| 5/20 | 3D | 4D |
I need to say something else. Various online calculators available on the Internet are designed to replace the manual calculation of the load of this type. They work according to the formulas laid down in them, focused on different samples of pipe products. The range of applications of the modern online calculator is very wide: starting from the simplest calculation of a round pipe for deflection, and ending with the calculation of the load on the profile pipe during its bending.
Deformation of pipes at the bend is sometimes inevitable, but it can degrade the performance of the finished structure
Technological process of bending
Any deformation leads to a decrease in the bearing capacity of the profile pipe and is accompanied by the occurrence of prolonged stresses on its walls. On the inner layer due to the compression of the metal density increases, and on the outer part of the stretch, vice versa, reduces the value of this indicator. The shape of the section also changes as expected. The combination of these factors leads to this, that the bearing capacity of the structure at the bend is significantly reduced. This is true for round pipes, as well as for rectangular and square tubular products. And, for the latter two, this phenomenon is not so pronounced, knife for round pipe.
However, in any case, a careful approach to assessing the degree of load is required, applied when bending the workpiece. Then there will be no unnecessary fractures and distortions. In terms of functional purpose, this applies, primarily round pipes, from which branches for water supply systems are made.
Useful to know! The formed folds lead to clogging, increase fluid resistance, transported and reduce the permeability of the working environment.
Therefore, the degree of oval deformation for parts with a diameter up to 20 mm should not exceed 15 percent. As the diameter increases, the value of this indicator decreases to the mark 12,5 percent. The same figures are used to determine the optimal load on the deflection of the pipe with a profile cross section, and the above values of diameters are inscribed / described in / around a rectangle (a) or square (a) car.
We apply Hooke's law
The calculation of the bending strength of a tubular product is reduced according to Hooke's law to a simple determination of the value of the maximum stress at the investigated point of the structure. It is important to consider, what material the profile is made of, because each of them has its own voltage rating.
According to Hooke's law, the force of elasticity is in direct proportion to the degree of deformation. In general, the following formula is used for calculations:
H = P / V, where
H - voltage; P is the amount of bending along the axis of influence of the applied force; V is the value of bending resistance, which is taken along the above axis.
Bending pipes, keep that in mind, that the load on the workpiece should not be too strong, otherwise the pipe will simply burst
Determining the normal value of resistance is one of the main tasks of man, who decided to erect the building from the profile. And the use of formulas to calculate the optimal level of strength, affecting the pipe, involves checking the correctness of the results. To do this, you need to know a number of rules and, of course, stick to them. They are summarized as follows:
- first, than to start calculations, it is necessary to draw at least a sketch of the future design. This way you will be insured against mistakes, caused by a misunderstanding of the shape of the building;
- to prevent deformation or destruction of the profile, complicating the operation of the facility, should take into account the material of its manufacture and wall thickness;
- calculating the bending strength of the pipe, it is necessary to carefully study the results obtained. They must not exceed the maximum set values.
Well, the basic rule sounds like this: perform calculations slowly, neatly, exactly. Apply the appropriate formulas at each stage, that do not adjust the values to those that are beneficial to yourself.