How metal pipes are bent: technological subtleties of work performance

Pipes bent at an angle have found application in the oil and chemical industries, machine and apparatus engineering. Not a single architectural or construction project is complete without them.

All sorts of fittings can be used for turns, but then leaks can occur, and sometimes this is simply unacceptable for aesthetic reasons. Bending pipes provides a more attractive appearance and high reliability - a process that does not violate their integrity.

We will tell you how best to bend a metal pipe using both cold and hot technology. The article we presented describes the specifics of bending pipes made of various materials. The features of working with profile and ordinary round pipes are given.

Features of the bending process

Each metal has its own characteristics; without their consideration, it is impossible to give a complex shape to rolled metal. A bending pipe is affected by radial and tangential forces.

The former deform the section, and the latter contribute to the appearance of folds. The main requirement for the final result is that the pipe cross section must remain unchanged, and there should be no corrugations on the walls. Bending allows you to minimize the number of welds when laying pipelines with all kinds of bends.

Pipe bending methods

Based on the required bending angle, material and diameter of the pipe, bending can be done manually or using special equipment. There are also distinguished between hot and cold bending, with the filling of the pipe cavity and without filling it.

Here is a diagram, formulas and recommendations for calculating the parameters of pipe bending, following which is a guarantee of a good result

After the termination of the load, a phenomenon such as springing occurs, which is directly proportional to the modulus of elasticity of the material. The magnitude of the possible deformation also depends on the applied bending method and the geometry of the object.

Hot technology specifics

This method is chosen when it is necessary to bend a pipe with a diameter of 10 cm or more. Deform pipes in a hot way, either manually or using mechanisms. There is such a thing as a minimum bending radius.

The length of the zone of the pipe, which must be heated, is determined based on the diameter of the pipe and the bending angle. Moreover, the rounding cannot be less than the diameter of the pipe times 3.

Find the length of the heated area according to the formula:

L = α x d / 15

In the formula: L is the desired length in mm, α is the bending angle in degrees, d is the diameter of the pipe outside in mm, 15 is the coefficient. Suppose a pipe with a diameter of 200 mm needs to be bent at an angle of 60 °, then L = 60 x 200/15 = 800 mm, i.e. 4 diameters.

The minimum allowable bending radius for water and gas pipes in accordance with the requirements of GOST 3262-92 can be taken from the table

To bend the pipe, it must be heated to 900⁰. The optimum temperature for starting to bend is 760⁰, and at the end - 720⁰C. When burned, the strength characteristics of the material deteriorate.

The process of hot bending includes several operations:

• making a template;
• sand packing;
• plot marking;
• heat;
• bending.

In order not to deform the pipe section and on its inner part in the place of bending, sweets do not form, the inner space is filled with quartz sand.

The sand is preliminarily dried and calcined in order to remove organic impurities at a temperature of 150 to 500⁰, and then they are passed through a fine sieve with a mesh size of 3.3 x 3.3 mm. Before you start stuffing the pipe, you need to plug one end of it.

As plugs, wooden or metal plugs are used having an opening for the exit of gases. Fine and wet sand cannot be used, as the first is sintered and adheres firmly to the walls of the pipes when exposed to heat.

The second, as a result of the formation of steam, contributes to the appearance of high internal pressure, which can cause the cork to fly out.The presence of pebbles in the packing is unacceptable, they can push through the pipe wall.

The process of stuffing the pipe is very time-consuming, so it is transported to the tower and give it a slightly inclined or vertical position. Since the quality of the bend is directly dependent on the packing seal, the pipe is continuously tapped throughout the process. A muffled sound indicates good filling of the workpiece.

Before proceeding directly to the main operation, sections of future bends are drawn on a sand-filled pipe, attaching a template. Heated pipes in furnaces or furnaces. They bend both manually and mechanically.

In the latter case, special plates are used, equipped with thrust posts, with the help of which the heated pipe section is fixed and with clamps that serve to hold the pipe end on the plate. A cable is put on the opposite end of the pipe, the tension of which with the help of a winch or spire causes the pipe to bend.

To prevent the pipe walls from deforming, gaskets are placed in the rack-pipe space - straight or curved. The free end with a cable attached to it is secured with a stand. During the process, control the geometry of the pipe, periodically applying a template to it.

By bending the pipe at the desired angle, plugs are removed from it by burning out or simply knocked out. Sand is poured out, the pipe is cleaned and washed. Perform a final bend test using a template.

Cold bending

To change the configuration of pipes of small diameters, various hand tools are used, for large - mechanized pipe benders. At home, bending water and gas is most often required steel pipesused in the device of water supply and heating systems.

Bending of a pipe under 90⁰ is called a bend, 180⁰ - kalach, with a ledge - a duck, in the form of a loop - a bracket.

If pipe bending is rare, it is enough to stock up on the simplest devices. A metal plate with holes in which pins are installed depending on the radius (Fig. 2) or a mandrel - a vertically mounted double plane-parallel plate with variations in the angle of bend (Fig. 3)

For manual bending, there are other devices. At home, for the manufacture of a coil for heating water, a stainless steel tube with a diameter of about 20 mm is simply wound on a piece of large diameter pipe. Previously, a bracket is welded onto a large pipe, laid on supports and clamped.

The tube is tightly packed with sand and closed with corks, then inserted into the bracket and winding begins. The pipe used as a template needs to be scrolled, so efforts of at least two people will be required. Having finished winding, the coil is leveled.

On such a device, pipes with a diameter of up to 2 cm are bent. It is attached to a workbench using a plate (1) and a hub. The template roller (6) is fixed on the common axis of the plate and the hub. The movable roller (2) is fixed by a bracket (4) having a handle (3). The pipe is placed between the rollers so that its end fits into the clamp (7). The bracket through the handle is rotated around the template to obtain the desired bend angle

Bending stainless steel pipes or other material at home can be done on the simplest tool. It is advisable to apply for small amounts of work.

A simple mechanical machine for bending a pipe can be built with your own hands, especially if you have the skills of a welder and are familiar with the welding machine:

To make a primitive pipe bending device need a slab of concrete, pins made of metal and a hammer. The plate is divided into cells 40 x 40 or 50 x 50 mm. At the corners of the cells, holes are drilled with a puncher and pins are inserted into them.

The tubular product is inserted between the pins and, by applying force, bend. Accuracy with this method of bending is not ideal, but to use the workpiece at home is quite sufficient. For bending with higher accuracy, you can use a device made on the basis of a jack.

To make a hydraulic bending machine, you need a jack that can withstand a 5-ton load, a strong base and pins. The pipes are bent using shoes. The size of these elements should correspond to the parameters of the bent pipe

So that the inner lumen of the pipe does not deform, apply means that counteract this process from the inside. As internal limiters, sand is most often used. At the same time, a plug is inserted into one end of the pipe, and sand is poured through the second, then it is clogged with a cork. Next, bending is performed.

Sometimes the limiter is a spring specially made for this purpose. For winding use a wire with a diameter of 1 to 4 mm. The spring should freely enter the pipe at the bend point, leaving part of the wire outside.

The hydraulic system of hand tools, portable and stationary machines greatly facilitates the bending process and speeds up the process of pipe deformation:

After bending, the spring is removed by pulling the wire. In the case of working with a pipe having a square cross section, a wire with the same cross section is selected for the manufacture of the spring.

A bundle of wire consisting of separate segments that push one inward one at a time to the place of the future bend is also suitable for this purpose. After the operation is completed, the segments are also removed one at a time. You can manually bend a stainless pipe with a cross section of up to 4 cm and a wall thickness of 0.3 cm.

Common methods for manual bending of pipes: with run-in, by winding, on two supports, by bending with drawing. The latter method is used for seamless thin-walled pipe material. In this way, pipes of small length are bent at a small angle

To work with large diameters, you need professional equipment. There are pipe bending machines equipped with a mandrel. This structural element is an ordinary metal rod.

On pipe benders, pipes with different geometries and cross-sectional sizes can be bent. This is a universal equipment, as bending of products with a wide range of diameters and from different materials is possible, starting from carbon steel and ending with non-ferrous metal pipes. The most sophisticated machines are electronically controlled

Before starting the bending process, it is placed inside to prevent deformation of the pipe walls. The mandrels included in the kit have a different section, so you can choose the right one for a certain diameter of pipe products.

Changing the configuration of non-ferrous metal pipes

There is a very useful property in non-ferrous metals - high ductility. However, they have insufficient strength. During bending, as a result of the application of compressive and tensile forces, collapse or rupture of the pipe may occur. To prevent this from happening, you must strictly follow the technology.

How to bend copper and brass pipes?

For bending copper as well as brass pipes, both hot and cold methods are used. When choosing the first as the internal filler, choose sand, the second - molten rosin. The bending technology is the same as for steel pipes.

Pipe products made of copper and brass before cold bending are subject to annealing with subsequent cooling. The temperature range for both materials is the same - from 600 to 700 ° C. The difference is in the cooling medium - copper is placed in water, and brass is cooled in air.

After completion of the process, rosin is removed by smelting it. In order to prevent rupture of the pipe, the process in no case start from the middle of the pipe, only from the ends. As bending devices, both simple tools and sophisticated machine tools are used.

Manual pipe benders work due to the physical efforts of a person, while hydraulic benders reduce these efforts to a minimum. Both those and others are equipped with interchangeable nozzles for the possibility of selecting the desired diameter.

The minimum radius for bending copper and brass pipes is regulated by GOST 617-90 and GOST 494-90, respectively. Experts do not recommend using this radius without special need. It’s always better to do with its great value

It is much easier to work with copper and brass pipes than with steel pipes, but metal deformation during bending occurs according to the same laws of physics. On a bent portion, the outer surface experiences tension, as a result of which the walls become thinner.

Inverse processes occur inside the pipe - the wall contracts and becomes thicker. There is a risk of turning the circular cross section into an oval and reducing the conditional pass, so you cannot start bending without taking measures to prevent these phenomena.

Bending aluminum pipes

The main methods of bending aluminum pipes are the same as brass or copper:

• pushing between the rollers;
• rolling;
• rolling away;
• pressure.

Before deciding on how and how to bend aluminum pipes, you need to familiarize yourself with each. The first method is used for thin-walled pipes with a maximum diameter of 10 cm, when you need to get a gentle bend with small accuracy requirements. The minimum radius is strictly regulated here. Its value is 5-6 pipe diameters.

The curvature of the plot determines the position of the deflecting roller. In this way, decorative elements of the interior are most often made. In the second way, large-diameter pipe material is bent, for which 3-roller pipe benders are used. The pipe is pulled between the drive rollers, the orientation of which determines the bending radius.

In the photo there is a stationary electric 3-roller pipe bender, but there are also manual mobile models of equipment. On it, the workpiece moves through the rollers and bends at a given angle along the entire length. On such a machine, you can change the configuration of the pipe by bending it with a ring, a spiral or making an arc of large radius

The accuracy of this method is even lower than the previous one, but the part can be subjected to repeated bending and repeating the process until the desired geometry is obtained.

Bending of aluminum thin-walled pipes can be done manually, having prepared properly:

The rollback method does not provide for the presence of an internal filler, so it is not used to obtain small radii. When choosing this method, it will not work to fulfill the strict requirements regarding the ovality of the section at the bend.

For deformation of an aluminum pipe by pressure, presses with dies mounted on them with a matrix of the desired shape are used. The given geometry is obtained as a result of the influence of pressure exerted from the outside.

In some cases, the pressure may be internal when the pipe is placed in the mold and the fluid is supplied inside with a pressure sufficient to press it against the walls.

It is not easy to bend duralumin pipes, as this material is quite hard and springy. To facilitate the process, they are fired immediately before bending at a temperature of 350 to 400 ° C, then they wait until the pipes are naturally cooled in air.

Methods of bending large diameter pipes

Relatively recently appeared methods are pipe bending involving industrial and high frequency currents and bending with tension. In the first case, a high-performance high-frequency installation is used, in which a pipe with a diameter of 95 - 300 mm is heated, bent and cooled.

It consists of two parts - a mechanical one in the form of a bending machine and an electric one, including an electric part and a high-frequency installation.

The pipe is deformed only in the heated area located in the inductor zone. Changing the geometry to a predetermined size occurs under the influence of a deflecting roller. Using this method, a bend with a curvature of small radius can be obtained.

Bending using the second method is carried out on bending machines, the set of which includes a rotary table. Large tensile and bending forces act on the pipe. This gives you steeply curved bends with a constant wall thickness around the entire circumference.

The method is used for bending large-diameter pipes used in the aviation, automobile industry, shipbuilding, where high demands are placed on the pipeline. The advantage is the ability to bend pipes with a wall from 2 - 4 mm to 180⁰.

Features are flexible profile assortment

Profile pipe products have a more aesthetic appearance than their counterparts with a circular cross section, so it is often found in household structures. When bending, compression forces act on it from the inside, and tensile forces from the outside. Carefully choose a bending method before proceeding with this operation.

The profile assortment includes pipes with a cross section in the form of a square, oval, rectangle.

There are several nuances and you should not forget about them when doing flexible shaped pipes at home without special equipment:

1. The optimal length of the bent section for profiled pipes with thin walls and a section of up to 2 cm is the pipe height multiplied by 2.5.
2. For thick-walled pipes, the length of the bending zone is determined by multiplying the cross section by three. Otherwise, cracking of the material from the outside or its deformation from the inside cannot be avoided.
3. The minimum value of the radius of curvature is the bending cross section multiplied by 2.5.

Without considering these requirements, you can not even hope for a good result. Bending methods do not differ from those used when working with products with a circular cross section. In addition, you can use the method of manual bending with the implementation of transverse cuts, which are performed on three sides of the pipe.

The length of cuts and their number is determined by calculation. Suppose there is a pipe 40 x 90 mm. It is necessary to complete a full turn, i.e. bend along the wall 40 mm at an angle of 180 ° with a radius of 150 mm. First, calculate the length of the semicircle along the outer radius:

L = (2π r: 2 = 2x 3.14 x 190): 2 = 596.6 mm

For the inner radius, the calculations are the same:

LVL = (2 x 3.14 x 150): 2 = 471 mm.

The sum of the lengths of cuts on the inner radius is determined by the formula: Lout = L - Lin = 596.6 - 471 = 126 mm.

Wishing to do it yourself manual pipe bender or profile pipe bending machine with our own hands in the articles we have proposed will find a lot of useful information, diagrams and useful recommendations.

If you consider that a grinder can cut 5 mm wide, then on the bend plane with a length of 126 mm you get 25 slots, after which the pipe is bent until the edges of the cuts come into contact. The slots are brewed and the seams are cleaned.

Conventional pipe benders are not suitable for bending profile pipes. For this purpose, there are special pipe bending machines, but even with such equipment, it is almost impossible to get a right angle. It’s easier to use the weld method or use fittings.

There is another way that profile and round pipes are bent, but it can only be used in the winter. To do this, plug the tubes into the ends of the tube, fill in the water and wait until it hardens. The pipe is bent, controlling the process with a template, then the plugs are removed and the liquid removed.

Conclusions and useful video on the topic

Clip # 1. Learn how to bend a pipe using improvised tools from this video:

Clip # 2. How to bend a pipe of any section into a circle:

Clip # 3. A homemade pipe bender is a necessary thing in the household:

When performing repairs or building a house, the need to bend the pipe — round or profile — often arises. If the volume is small, you can do it yourself. Mass bending of pipe products is possible only with special equipment.

Tell us about how you bent a metal pipe for a greenhouse or other purposes. Share technological nuances known only to you with site visitors. Please write comments in the block below, post a photo on the topic of the article, ask questions.