Working with thin sheet metal requires not only physical strength, but also a deep understanding of the physics of the deformation process. Galvanized steel has specific properties, such as elastic aftereffect and sensitivity of the zinc coating to overheating, which makes the task of forming products from it different from working with ferrous metal. With the wrong approach, you can easily damage the anticorrosion layer or get a product with broken geometry, which will not be hermetically connected.
In this article, we will analyze in detail the technological process of folding sheet metal of different thicknesses. You will learn what tools are needed to create high-quality drain pipes, ducts or casings with your own hands. We will pay special attention to the nuances that beginners often miss, trying to save on marking or ignoring the need for pre-flexible edges.
Features of galvanized steel with flexible
The main characteristic of the material with which to work is the presence of zinc coating. This layer protects iron from rust, but it also imposes restrictions on processing methods. When heated, for example, when using welding or hot flexible, zinc burns out, and the steel in this place instantly begins to corrode. Therefore, the answer to the question of how to fold a galvanized sheet is always based on the cold-mechanical deformation.
It is important to consider the thickness of the material, as it depends on the choice of tool and the effort that must be applied. A thin sheet (0.4-0.5 mm) is easily deformed even manually, but it is prone to the formation of cracks and a "crumpled" surface with careless handling. The thicker metal (0.7-1.0 mm and above) requires the use of specialized machines or powerful long-arm clutches to create a uniform bend radius.
⚠️ Attention: When cutting a galvanized sheet with scissors on metal, the edge is flattened, which violates the geometry of the future seam. For accurate work, it is better to use a guillotine or a SCMM with a thin disk, carefully treating the edges with a file.
Another critical point is metallicity. After bending, the sheet tends to return to its original position. This phenomenon is called springing. To get an exact angle or perfect circle, it is necessary to bend the material with a slight “failure” or, conversely, with inflection, taking into account the elasticity coefficient of a particular steel grade. Without taking into account this factor, it will not be possible to collect a sealed ventilation or drainage system.
Equipment and tools required
The quality of the final product depends on the selected equipment. For one-time work or minor repairs, you can do with a set of hand tools, which is found in the garage of most craftsmen. However, more serious equipment will be required for regular production of pipes or boxes. The main tool here are sheet-bending machines, which can be manual, hydraulic or electric.
For a homeowner, the best solution is to create the simplest leaf-bend from the channel and the loop. This design allows you to make even folds at an angle of 90 degrees or more. If your goal is to roll the sheet into the pipe, then an indispensable assistant will be a three-shaft leaf-bending machine (shafts). It provides a uniform distribution of force throughout the length of the sheet, which is critical to obtaining a perfect circle without faces.
- 🛠️ Metal scissors or an electric jigsaw with a file for cutting metal are necessary for cutting the workpiece to the specified sizes.
- 📐 Corner, roulette and core – for accurate marking of the bend lines and checking right angles before the start of the bend.
- 🔨 Kiyanka (wooden or rubber) and hammer - used for editing the edges and finalizing the shape of the product without damaging the zinc layer.
Do not forget about personal protection. The edges of freshly trimmed metal are sharp as a razor, and the zinc dust formed during grinding is harmful to breathing. Therefore, working in tight gloves and a respirator is a mandatory safety requirement, not just a recommendation.
Technology of marking and calculation of sweep
Before proceeding to the physical deformation of the metal, it is necessary to perform a competent calculation of the sweep. An error at this stage will lead to the fact that the diameter of the finished pipe will be less or more than the design, or the length of the product will not be enough for docking. The calculation is based on the thickness of the metal and the elongation coefficient in flexible conditions. To simplify, you can use ready-made tables or online scan calculators.
The marking process begins with the application of a cutting line. If you make a pipe, the length of the sweep is equal to the length of the circle plus the allowance for the seam. The inlet depends on the type of connection: for a false seam it can be from 10 to 20 mm, for a welded one (if used by a special solder) - less. The accuracy of the markup is checked several times, since “measure seven times” in working with metal means saving expensive material.
Use a color marker or kernation to apply fold lines. Pencil lines are quickly washed by hands during the work process, which can lead to an error when positioning the sheet in the machine.
For complex products, such as a box with several faces, all the fold lines are drawn on the sheet. A neutral line, the length of which does not change, runs approximately in the middle of the thickness of the sheet. It is on it that you need to navigate when installing the stops of the bending machine.
Step-by-step instruction: rolling into the pipe
Formation of a pipe from a flat sheet is a process that requires a sequence of actions. First, the workpiece is installed in rollers or clamped in a hand-held device. If a three-roller machine is used, the lower two shafts serve as a support, and the upper one, falling, creates pressure, causing the metal to bend the radius. The movement of the sheet should be smooth, without jerks, to avoid the formation of faces instead of a smooth arc.
In the absence of rollers, the running method can be used. The sheet is laid on a solid cylindrical mandrel (pipe of the desired diameter) and gradually squeezed around it with the help of a kiyanka or a special crimping device. This method is time-consuming and suitable for short stretches or fine metal. For long pipes, this method is ineffective, since it is almost impossible to ensure the same radius along the entire length.
☑️ Pipe folding algorithm
The key is the formation of edges for the future castle. Before rolling the sheet into a full cylinder, you need to bend the edges at an angle of 90 degrees in opposite directions (for single folder) or create a more complex profile (for double folder). This is done in the first stage, while the sheet is still flat or has minimal curvature.
| Type of connection | Leaf thickness (mm) | Seam allowance (mm) | Tool. |
|---|---|---|---|
| Single folder | 0.5 - 0.7 | 10 - 12 | Handheld, ticks. |
| Double folder | 0.5 - 1.0 | 15 - 20 | Machine, ticks. |
| To the castle (slouching) | 0.4 - 0.6 | 8 - 10 | Kiyanka, mandrel |
| Welded (sweeding) | 0.7 - 1.5 | 2 - 4 | Burner, solder |
Formation of boxes and rectangular sections
Making rectangular ducts or protective casings is technically easier than creating pipes, as it does not require the rotation of the workpiece. However, the accuracy of the angles is critical here. Any skew will lead to the fact that the sections of the box do not dock with each other during installation. Therefore, the flexibility is carried out strictly along the lines of marking using stops.
The process begins with the flexing of the edges to create a lock joint (flange). Then the sheet is consistently bent along the edges. To obtain a clear angle of 90 degrees, a punch and a leaf bending matrix are used. If the angle is sharp, when assembling boxes "lead", if blunt - there will be gaps. Corner control It is carried out by the coal after each bend.
⚠️ Attention: When bending long boxes of thin metal, the center of the edge may swell ("flapper"). To avoid this, the center of the wide edge make additional ribs of stiffness or culling edges, which gives the structure rigidity.
How do you make a stiffener?
To create a stiffness rib on a wide plane of the box, a special zig machine or manual zigs are used. The sheet is run between the rollers that squeeze the longitudinal profile. This not only strengthens the design, but also improves the acoustic properties of the duct, reducing the noise of the vibration of the walls.
Seam sealing and fixation
After the sheet is shaped like a pipe or box, it is necessary to fix the seam. For false joints, the method of “scoring” or crimping is used. The squirrels are squished together and tightly pressed along the entire length. To do this, use hand mites for folder or pass along the seam with a hammer through a wooden gasket so as not to damage zinc.
If the connection is made in a lock or using rivets, it is important to ensure that the edges fit tightly. Clearances are unacceptable, as they will lead to a loss of pressure in the ventilation system or leaks in the drain. For additional sealing of joints, special silicone-based compounds or bitumen mastics can be used, but only after mechanical fixation.
The quality of the false seam determines the tightness of the entire product. It is not enough to simply hold the hooks, you need to tightly squeeze the connection along the entire length to exclude spontaneous disclosure under pressure of air or water flow.
Frequent Mistakes and How to Avoid Them
One of the most common mistakes is to try to bend a thick sheet without preheating (unless it is provided by technology) or without using a long lever. This leads to the formation of cracks in the metal or the breakage of the tool. Always evaluate the effort: if the metal does not bend, then the wrong radius is chosen or the machine power is not enough.
The direction of metal rolling is also often ignored. Sheet metal has a fibrous structure, and it is better to bend it across the fibers (perpendicular to the direction of rolling). If you bend the sheet along the fibers, microcracks may appear on the outer radius, which will quickly lead to rupture or corrosion. You can determine the direction of rolling by sound when hit or visually by the pattern on the edge.
- ❌ Ignoring the omissions leads to the inability to dock the elements of the system.
- ❌ Using a steel hammer on zinc - destroys the protective layer, starting the rusting process.
- ❌ Haste when rolling - creates edges instead of a circle, which worsens the aerodynamic properties of the pipe.
Can a galvanized sheet be rolled up without a machine?
Yes, for thin metal (up to 0.5 mm) and small volumes, you can use the method of running around the mandrel (pipe, log) with a kiyanka. However, the quality of the round will be lower than on the machine.
What is better to cut the galvanizing so as not to damage the edge?
The ideal option is guillotine scissors. At home, it is best to use a Bulgar with a thin disc on metal, since scissors can “hide” the edge, which will make it difficult to fold.
What kind of permission to leave on a double folder?
For double folder, the total inlet is usually 15-20 mm depending on the thickness of the metal. The exact values are best taken from the reference tables for a specific flexible profile.
Why does metal burst when you're flexible?
This can be due to poor steel quality (burning during production), direction of the flex along the rolling fibers, or too small a radius of the flex for a given sheet thickness.