A bent profile pipe is an indispensable element in the design of arbors, sheds, greenhouses, fences, even garages. Thick-walled profiles of large cross-section are used in the construction of roofs of buildings. The reliability and attractive appearance of the structure being built depends on how well the profile bends.
In contrast to a pipe with a circular cross-section, bending a profile with a square or rectangular one is more difficult. Due to the presence of sharp corners from which the profile pipe was cast, in some cases it is necessary to partially bend the profile. The following approaches are used.
- Acting on the pipe from the inside with pressure. It can be any free-flowing or liquid medium. It will help the pipe to take the correct shape when bent, without punctures and "wrinkles" on the inside.
- Heating the profile to a temperature close to that at which the steel softens.
When bending the pipe, the profile is affected by a compressive force from the inside of the bend and a tensile force from the outside. The sides lose the correct arrangement given to them at the factory.
If you do not observe the bending radii, the profile will burst from the outside and / or rush inward from the opposite side. The influence is also exerted by the thickness of the walls, the dimensions of the section. A damaged product cannot be restored.
What do you need?
The fastest way is to use a profile or pipe bender. Cold bending a pipe up to 10 mm - both square and round is similar to bending a rebar. It is enough to observe the rule - at least 15 outer radii of a round pipe or at least 15 values of the greater width of a rectangular pipe. Bending a square profile will require If there is no access to an industrial pipe bender, in which bending along the radius is set very accurately, then a grinder and a welding machine will help. But "broken" bending is an extreme measure.
Cold bending is also possible with a simple device made from another pipe (or fittings) and a special bracket with a large gripping area that allows you to bend round or square pipe gradually. This method is used when a perfect, even fold is not required.
Homemade profile pipe bender - in the simplest case, a plate with holes, into which pins are inserted. They are positioned so that the bendable tube passes between them, but in advance they are lined up on both sides in a curve. Another option is a lever with an oval template, which acts as a kind of pattern, consisting of plane-parallel planes. A special roller wheel is also used, rolled over the zone of future bending: the depth of deflection is regulated by the applied force. All methods of homemade bending require some skill and experience.
It will not be difficult to bend a 40x20 or 20x20 profile at home. All the methods listed below are suitable for this. Narrow professional pipes (less than 20 * 20), especially thin-walled, bend using a primitive grip or even on any curved and smooth surface.
The main thing is not to bend the product along a radius less than 10-15 sides (width values) of the professional pipe, not to make sudden movements. So, for size 40 by 20 cm, the bending radius is not less than 0.3 m.
A grinder (or an angle grinder manual power tool with a cutting disc for metal) allows you to bend a profile pipe with your own hands using cuts. They are equidistant from each other when there are more than two of them. One cut will only make a sharp, rectangular bend. The more cuts, the smoother the bend. It will take the form of a regular broken line. The cuts are needed so that excess metal on the inside does not form folds that give the pipe an unsightly look.
The angle of each cut is determined by the total bending angle divided by the number of gaps cut. In order for the professional pipe to take on a neat appearance, and rainwater does not flow inside, the cuts should be with an acute angle at the outer wall of the pipe, and not rectangular. For example, an arched pipe that has a bend angle of 180 degrees requires 20 cuts for each of them at 9 degrees. This can be achieved only on a large-sized profile and using thinner discs - or make cuts with a hacksaw for metal, and not with a grinder.
There is no need to warm up the professional pipe for this. The cuts are marked and made in accordance with the bending radius requested by the customer. In this case, one of the walls - the outer one - remains intact, which will allow the structure not to fall apart, but the pipe loses its strength. To obtain the original steel pipe strength, the resulting joints are welded using welding.
This method is referred to as cold pipe bending. Heat treatment (welding) is carried out after folding - and not before it, as it happens in the cases described below. The disadvantage is the ribbed outer and inner surfaces of the fold, which eliminates tight contact with curved structures, for example, when applying composite or plastic roofing sheets over a frame assembled from such pipes.
We fill with sand
Before heating the pipe, it is filled with sand. The elastic force that sand has will allow the profile to not crumple. The inside of the fold will remain smooth. To bend the pipe in this way, do the following.
- Close the ends of the pipe with wooden plugs in which the longitudinal holes have been cut. The latter are needed so that the heated air comes out of the pipe without knocking out the plugs. The length of the plugs is 10 times the profile width.
- Ignite the section of the pipe where it will bend.
- Pour medium-grain sand into the pipe . It is preferable to use sifted and well-washed sand, pre-calcined to 150 degrees.
- Check that the pipe is well sealed and mark the section of the pipe to be bent.
- Fix the pipe in a vise on a workbench.
- Heat the pipe until it is cherry red and bend it in the marked place.
- After the pipe has cooled down, remove the plugs and pour out the sand.
The bent pipe is ready for further work.
With a spring
If there is no sand at hand, there is no access to it - use a square spring, the coils of which are tightly located. The spring will prevent deformation and uneven changes in the thickness of the pipe walls, helping to keep it in shape.
The properties of high-carbon steel, from which the springs are made, do not change when ignited - it has the same elasticity as in the cold state.
Bending with the help of water just right to call "ice bend". Close one end with a tight plug, pour water, close the other end and wait for a frosty day. When the water freezes and expands, it will be much easier to bend it than in normal home conditions. At the same time, the bend will come out even, without wrinkling and tears. The disadvantage of this method is that a pipe that is too short cannot be bent, and a steel pipe (if it is not made of stainless steel) can become rusty from the inside, losing a significant part of its strength.
Do not try to make a sharp bend at a significant angle . The workpiece will break, and the spoiled section will go to scrap metal. Do not use reinforcement for bending the professional pipe by inserting a rod into the end of the pipe - it deforms its edges at the end of the profile. It is also very difficult to correct such damage. Attempts to calculate the "correct" thickness of the rod under the walls of the professional pipe will not give a result - either the profile or the reinforcement will bend.
Do not try to overheat the metal profile with an ultra-high temperature torch (for example, with a gas welding machine turned on in steel cutting mode), heating it up brighter than a red tint. Having become yellow-orange, iron (and steel too) softens, the profile is skewed.
Such damage is irreversible, damaged workpieces can only be remelted. Smelting steel is not available at home.
Do not bend the profile with jerky movements . Bending pipes too quickly will cause pipes to break. Aluminum and its alloys are especially susceptible to breakage. No rush is needed. Heat the pipe once before bending. Repeated (several or more times) heating will lead to a loss of steel strength. If individual sections of the pipe are overheated with uneven heating of the required section, then cool them until the heating color becomes uniform. Bending the overheated pipe will cause it to rupture.
If it is impossible to quickly remove wooden plugs, they can be burned out by heating the pipe ends. The burn-through and ignition temperature of wood is several times lower than the melting temperature of steel. In this case, no unpleasant consequences will come. Partial notches (thinning of the steel walls) at the bend are not allowed. When bent, such a pipe will burst - its strength is insufficient to form a smooth bend.
Do not use the tree trunk as an oval or round surface. The tree may not be able to withstand such a load. There is a separate device for this, and more than one. The 20x40 profile and other sizes, including 20x20, are too thin-walled to bend by inserting the pins inward. To obtain a wavy, twisted profile, a regular one is forged. But forging a professional pipe is not recommended for those who do not have the skills of a blacksmith, this will ruin it. Profile forging is an artistic way of processing, which is used in the manufacture of lightweight railings, gates, doors from a thinner section pipe.
To bend a professional pipe, for the appearance of which it will not be ashamed, everyone can do it independently. In total, there are more than a dozen machines and devices that replace the professional profile bending machine. The choice of the appropriate method is voluntary.
For information on how to bend a profile with your hands without a profile bender, see the next video.