Castle connections. Connections of metal blanks Methods for joining joints of galvanized sheets

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Details Category: Sheet metal

Connecting parts from sheet metal.

There are several ways to connect sheet metal parts. The simplest of them is seam seam connection. It is obtained in the following way. At a distance of 6 ... 8 mm from the edge of the sheets to be joined, mark the fold lines and bend the sheets at a right angle (see the figure on the left a). Then the edges of the blanks are folded (see the figure on the left b), connect them into a lock (see the figure on the left in) and bend the sheets near the seam with a wooden block, as shown in the figure G so that the connection is not disconnected.

The connection of parts with a seam seam is used in the manufacture of buckets, drainpipes and ventilation pipes, tin cans, as well as when covering the roofs of houses with roofing steel.

Factories do this work. tinsmiths on the folding machines. Variants of such machines are shown below.

In addition to joining with a seam seam, sheet metal parts can be joined using rivets.

Rivets used to create the so-called one-piece "connections. Usually thin metal sheets are connected with rivets, facade plates are fastened, as well as rather heavy structures.

Rivets have been used as fasteners since time immemorial. It is enough to visit any archaeological museum to see this with your own eyes. For example, ancient warriors wore armor, the metal plates of which were connected exclusively with rivets. And if you remember that rivets were used as the main (almost the only) fastener in the construction of the Eiffel Tower and the Aurora cruiser, you involuntarily imbued with respect for the people who invented fasteners so familiar today.

Rivets - these are fasteners consisting of a mortgage head and a rod. They are made of mild steel, copper, aluminum, brass. There are rivets with semicircular(a), secret(b), flat(in), semi-hidden(G) heads (see figure on the left).

To connect parts with rivets, first mark the centers of the holes for the rivets. Then holes are punched with a punch or drilled.

The dimensions of the rivets depend on the thickness of the parts to be joined. It is recommended to take the rivet diameter equal to twice the thickness of the thinner part. The length of the rivet rod consists of the thickness of the parts to be joined and the length of the protruding part (it is equal to 1.25-1.5 of the rivet diameter), on which the closing head is formed.
Often, two workpieces to be joined are drilled at once, clamping them with a clamp or in a vice. Hole diameter D must be 0.1 ... 0.3 mm larger than the rivet diameter d(see figure on the right a).
The rivet is inserted into the hole (Fig. b), and the length of the protruding part of the rivet should be (1.3 ... 1.6) d. The mortgage head is placed in the support recess( 2 ) (rice. in) and hammer blows on the tension ( 1 ) bring together the connected parts one to another. Then with circular hammer blows ( 3 ) rivet the protruding head (Fig. G) and give it the correct shape by crimping ( 4 ) (rice. d).

When making a riveted connection, it is necessary to check the reliability of the hammer nozzle on the handle.
The workpiece must be securely fixed in a vise.
You can not stand behind the back of the worker.

Rivet joints are used in aircraft construction, shipbuilding, for connecting parts of bridges, and in the manufacture of metal utensils. In industry, workpieces are riveted using pneumatic riveting hammers or special riveting machines.
Undoubtedly, rivets have a lot of undeniable advantages. But standard, so-called "full-bodied" rivets also have a rather significant drawback - to create a truly reliable connection, great attention must be paid to the quality of work with them. Considering that the rivet must be held tightly on the other side during riveting, this is a rather laborious task. However, progress does not stand still. The development of riveting technology has led to the emergence of blind rivets that solve this problem.

Installation tool(see figure on the left) for working with blind rivets is relatively inexpensive, and the convenience of their use is very high. Mechanical engineering, the construction industry, the automotive and furniture industries, and enterprises in the electronics manufacturing industry actively use the blind rivet, since the single-sided fastening technology is definitely more convenient and more reliable than other fastening methods.

One way traction(exhaust) rivet consists of two parts: corps and rod. The body of the rivet is made of various materials: aluminum, steel, stainless steel, copper, alloy MONEL(Ni/Cu=70/30). The core of blind rivets is made of steel or stainless steel.

Design features: the rivet has a convex or countersunk head. Rivet installation only requires access from one side of the material.
Mounting: drill the materials to be fastened, mount the rivet using a special tool.

From characteristics blind rivets, attention should be paid to the geometric dimensions (diameter and length of the rivet body). The type of rivet can be regular with collar (D heads= 2D rivet body, fig. 1 ), With enlarged bead (D heads= 3D rivet body, fig. 2 ), secret(rice. 3 ) and deaf with water and gas tight body(rice. 4 ).

Removable connections. This refers to the connection of workpieces with bolts, self-tapping screws, rivets. Such connections are easy and quick to perform, as well as durable.

Bolts, screws, nuts. To connect two workpieces with bolts, it is necessary to drill holes in them. To do this, take a drill, the diameter of which is slightly larger than the diameter of the bolt. For example, for an M10 bolt, a 10.5 mm hole is drilled. Such a gap (0.5 mm) will make it possible to compensate for possible inaccuracies in the position of the holes of both workpieces to be joined, especially in cases where there are several connection points, and the workpieces are long. Both workpieces must be joined together and drilled in one go. The immobility of the connection is provided by nuts, washers and spring rings - Grover's washers (Fig. 62).

Rice. 62. :
1 - spring washer; 2 - washer

A washer placed under the bolt head prevents its rotation, and the spring ring, resting with one sharp “tooth” against the nut and the other against the workpiece, prevents the nut from spontaneously unwinding. If the head of the bolt (screw) should not protrude above the surface of the part, bolts (screws) with a countersunk head are used. In this case, the hole for the screw is first drilled through both workpieces, and then countersinked with a drill or countersink.

Screws (screws) - self-tapping screws. When using them, nuts are not needed. Such a screw cuts a thread for itself in both workpieces and tightens them (Fig. 63).

Rice. 63.

The hole is pre-drilled in two workpieces at once, having previously been set in the desired position. The hole diameter is equal to the screw diameter minus two thread heights. A part made of sheet metal (or other material) must be fixed to a lining of wood or chipboard before drilling. If the metal is thin (tin), there is no need to drill holes: it is enough to punch them with a center punch; sheets of greater thickness should be drilled. It is essential that the thickness of the lower workpiece does not exceed 2.5 mm; in addition, the screw must pass through, otherwise there will be no pressing effect.

hairpins are metal rods with threads at both ends. They are used in cases where it is necessary to attach another part to a thick or massive workpiece. A hole is drilled in the workpiece, a thread is cut in it for a stud. The depth of the hole must exceed the length of the cut part of the stud. Otherwise, it cannot be unscrewed.

Permanent connections. Rivets are used to fasten elements of products of small thickness, mainly from sheet materials. They consist of a rod and a mortgage head (Fig. 64). The most common are the rivets shown in fig. 65. Before connecting the parts, holes are pre-drilled in them, then a rivet is inserted and its end is riveted to form a closing head. The material of the rivets must be homogeneous with the material of the parts to be joined. This is necessary so that electrochemical corrosion does not occur and stresses caused by different coefficients of thermal expansion do not occur.

Rice. 64. :
1 - mortgage head; 2 - rod; 3 - closing head

Rice. 65. :
a - with a flat head; b - with a countersunk head; in - with a semi-secret head; g - conical rivet with head

Tools for hand riveting are support, tension and crimp. Based on the freedom of access to the closing and to the embedded heads of the rivet, there are two methods of riveting - direct (open) and reverse (closed). Using direct method hammer blows on the rivet rod are applied from the side of the closing head. The order of operations is as follows (Fig. 66): the rivet is inserted into the hole (a), a massive support (2) is placed under the mortgage head, and a tension (1) is put on top of the rod, and the connected parts are upset by hammer blows on the tension (b); by uniform blows of the hammer at an angle to the end of the rod, the closing head (c) is preliminarily formed, a crimp is installed on this head, and the closing head (2) is finally formed by uniform blows (with support on the support).

Rice. 66. :
a - laying the rivet; b - upsetting parts with a stretch; c - preliminary formation of the closing head; d - final formation of the closing head; 1 - stretch; 2 - support; 3 - crimping

AT reverse method blows are applied to the mortgage head. The rivet rod is inserted into the hole from above, the support is placed under the rod - first flat - for the preliminary formation of the closing head, and then - the support with a semicircular head - for its final formation (if the head should be semicircular). The mortgage head is hit through the crimp, thereby forming the closing head with the help of support. However, we note that the riveting obtained by this method is of lower quality than when using the direct method.

Riveted joints with breakable stem. The disadvantage of the traditional rivets described above is that access to the back side is required when riveting. This is not necessary with breakaway rivets, which are both easy to handle and economical. However, in fairness, it should be noted that the connections on them are somewhat less durable, and to work with them, special rivet tongs are needed, equipped with replaceable guide elements. Usually pliers are sold complete with rivets (which, of course, are also sold without pliers). Rivets are inserted into the hole, just as they work with tongs, being on one (front) side of the connection. Installing a breakaway rivet is easy. As with any similar connection, a hole must be drilled under it, the diameter of which is equal to the diameter of the sleeve (the hollow part of the rivet). Then the sleeve is inserted into the hole until it stops with the flange against the surface of the sheet, and the sleeve should protrude with reverse side not less than 3 mm. After that, the protruding rod is captured with riveting tongs. From the back end, the rod has a spherical head, which, when the handles of the tongs are compressed, is drawn into the body of the rivet and crushes its protruding part (Fig. 67).

Rice. 67. :
a - the rivet is inserted into the hole; b - rivet after breaking the rod

After that, the end of the rod is torn off. This type of rivet has, in addition to the mentioned lower strength, other disadvantages: a) the rivets protrude from the back; however, no protrusions are visible inside the hollow products; b) these connections are leaking.

Adhesive connections. Bonding is a fairly common method for obtaining permanent joints. The quality, i.e., the durability of adhesive joints, depends on the quality of the preparation of the surfaces to be bonded and the type of load on the adhesive joint. First of all, the surfaces must be free of rust, grease and treated with a coarse sandpaper, grit 60 or 80. Cantilever parts with a small area of \u200b\u200bsupport, subjected to heterogeneous loads (say, shear and rotation), should not be glued together, since in such conditions the adhesive joint will certainly fragile. The same can be said about the bonding of parts under load, causing their delamination. On the other hand, glued joints will be strong if the parts to be joined are sheared relative to each other or stretched during operation. Adhesives for metal are single- and multi-component. The former, including contact maple, usually retain their elasticity for a long time and are prone to shrinkage. They are used most often to connect parts with a large area of glued surfaces and experiencing small loads. They glue very well synthetic-based multicomponent adhesives: GIPC-61, epoxy (EDP, EPO, EPTs-1), as well as BF-2, Moment, Phoenix, Super Glue.

Connections of metal parts by soldering. Soldering is the process of obtaining a permanent connection metal materials and parts from them with molten solder. Solder is a metal or alloy whose melting point is much lower than that of the products being joined. Depending on the melting temperature, the following types of solders are distinguished: soft (low-melting) - melting point is not more than 450 ° C, hard (medium-melting) - 450-600 ° C; high-temperature (high-melting) - over 600 °C. For homework, as a rule, soft tin-lead solders of the POS brand are used. Marking them means the following: the figure in the brand of solder is the tin content in percent; so, in POS solder 90 - 90% tin, in POS 40 - 40%, etc.; the letters following the brand designation (i.e., after the letters "POS") mean the addition of an element that forms the special properties of the solder: POSSU4-6 - solder with the addition of antimony, POSK50 - cadmium, POSV33 - bismuth. To protect the surfaces to be joined (previously well cleaned) from oxidation, a soldering flux is used - a substance that cleans surfaces and solder from oxides and contaminants and prevents the formation of oxides, as well as increasing the flow of molten solder. Each flux is effective only in a certain temperature range, beyond which it burns out. Solder is chosen depending on the properties of the metals to be joined, the solder, the strength requirements of the brazed joint, and some other conditions.

Amateur craftsmen usually use acid-free fluxes - rosin and fluxes based on it with the addition of alcohol, turpentine, glycerin and other inactive substances - and active (acid-free) fluxes made on the basis of zinc chloride, rosin and other substances. It should be borne in mind that after soldering, flux residues and decomposition products must be removed immediately, as they contribute to corrosion.

Soldering tool. It includes a soldering iron (Fig. 68), a blowtorch (Fig. 69), a soldering torch (Fig. 70).

Rice. 68.

Rice. 69. :
1 - burner; 2 - air balloon; 3 - handle for regulating the flame; 4 - heating tray; 5 - pump; 6 - handle; 7 - fuel tank

Rice. 70. :
a - with open flame heating; b - heated in a closed chamber

A soldering iron is used to heat the place of soldering and melt the solder. The working part of the soldering iron is a copper tip heated from external sources. When soldering small parts, for example, parts of radio circuits, use tips in the form of a screwdriver weighing 0.1-0.2 kg; for soldering larger products (say, sheets of metal roofing) - heavy tips in the form of a hammer weighing 0.5-10 kg. Heating of soldering irons is carried out in different ways - both in the flame of a burner, and with the help of electric current (electric soldering irons). The latter (domestic) are produced in various capacities - from 25 to 100 W, depending on the purpose of the application. Heating can take place with ordinary heat (in a few minutes) or with forced speed. In the latter case, electric soldering irons are called soldering guns; they are used for small soldering work (soldering electrical wires, for example). Before starting soldering, the soldering iron tip must be tinned, i.e. clean with a file or sandpaper, heat, dip in flux, apply to solder and hold until it begins to melt. This must be repeated several times - until the working surface of the tip is covered with an even layer of solder.

A blowtorch is a light, portable burner (Fig. 69) with a directed flame that runs on alcohol, gasoline or kerosene. Its functions are heating the tip of the soldering iron when soldering with hard or soft solder, melting solder, as well as heating metals when bending, straightening, etc., removing residues of old varnishes, paints, oils from wooden bases, metal parts, plaster. The soldering torch (Fig. 70) is also a lightweight portable torch with a directed (open or closed) flame. It works on liquid gas - propane or butane, which comes from a cylinder or from chargers. A soldering torch is designed for hard soldering (and, of course, soft solder), heating metal parts during their editing and bending, and melting old paint. When working with a soldering torch, it is necessary to use a refractory lining - tiles made of artificial stone, fireclay, bricks, etc.

Technique and technology of soldering. According to the type of solder used, two types of soldering are distinguished: soft, or soft soldering, and hard, or hard soldering. The choice of one or another type is determined by the magnitude of the loads to which the soldered workpieces will be subjected. Highly loaded surfaces are connected by hard soldering. The solder in this case is thicker than with soft soldering. It must be taken more so that it can penetrate into all the cracks. At the end of hard soldering, the seam is cleaned with a file. Since hard soldering requires heating up to 450 ° C and above, it can only be done with a sufficiently powerful soldering torch. Soft soldering is performed with a soldering iron and a flame at a temperature of 180-400 ° C. Where possible, joining should be performed with an overlap or overlap, which increases the contact area of the workpieces with each other. A gap of 0.1-0.5 mm should be left between the parts to be joined. First of all, you need to select the type of solder joint (Fig. 71).

Rice. 71. :
1 - flat thin-walled; 2 - tubular and complex shape; 3 - wire

At home, most often when soldering, parts are connected by soldering at the joint, for example, when connecting galvanized steel pipes.

Surface cleaning. The places of the future connection must be completely cleaned of all foreign formations - dirt, grease, rust, etc. The cleaning procedure is carried out mechanically or by chemical means. In the first case, sandpaper, scraper or grinding is used; in the second - carbon tetrachloride. Surfaces ready for soldering should be clean, smooth, free of scratches and dents.

Tinning. Before proceeding with soldering, the cleaned joints must be thoroughly tinned, that is, covered with a thin layer of solder, since the solder lies better on a tinned surface. At the places of future soldering, you first need to apply a thin layer of flux or solder paste. The soldering iron must be well tinned. Heating it, they collect solder, transfer it to the place of soldering and distribute it in an even layer. When connecting large surfaces, this procedure is repeated several times or a different method is used: a certain number of pieces of solder are evenly placed on the junction and melted; at the same time, the soldering iron must be dipped into flux or solder paste from time to time. Galvanized places do not need to be tinned.

Soldering. The parts to be joined are installed in a position convenient for soldering and fixed with a vice, clamps or other devices. Then the place of soldering is evenly heated with a soldering iron to the required operating temperature. At the same time, it is important to control the degree of heating of the soldering iron and the surfaces to be joined: if these surfaces were heated weakly, then the connection will be unreliable; if the soldering iron is overheated, it does not hold solder well. When the operating temperature is reached, the flux is melted first and then the solder. Once all the flux has melted, the preheated solder is transferred to the gap. When in contact with a part heated to the desired temperature, the solder melts and penetrates into the gap. After that, the soldering iron is used only to maintain the working temperature.

Once the solder has cooled, you can remove the clips. The part itself is cooled in air or in cold water. Soft soldering with a flame is advisable in cases where it is necessary to connect workpieces of relatively large thickness: the flame heats them up faster than a soldering iron. Soft soldering can join most metals and their alloys, excluding light metals and alloys (for example, aluminum). To join many metals, only their own solders are required. Since soft soldering is performed at noticeably lower temperatures, the requirements for cleaning the contact surfaces are much higher.

Hard soldering flame. All metals can be joined by this method, including bronze and gray cast iron, as well as dissimilar metals, such as steel and brass. The only difference between this soldering method and soft soldering is that the process takes place at much higher temperatures. For solid flame melting, conventional acid-acetyl torches are used, and for small, thin-walled joints, gas blowtorches are used. For example, when forming a T-shaped connection, a vertically standing workpiece is fixed with a wire, while a horizontal one may not be fixed; the wire must be removed from the place of soldering. Then, with a gas burner (or a blowtorch), the workpieces are heated from the edges to the point of contact, which eliminates the possibility of warping and mutual displacement of the parts. Finally, solder in the form of a rod and wire is carefully brought to the place of soldering and metered, economically melted. In conclusion of the story about soldering, we will give the types of metal compounds that can be obtained by one or another type of soldering (Fig. 72 and Fig. 73).

Rice. 72.

Rice. 73.

Welding- this is the process of obtaining a permanent connection of parts from solid materials and products from them by melting the edges of the parts to be joined. Both homogeneous materials (for example, metal with metal) and dissimilar materials (metal with ceramics) are welded. There are many welding methods, of which arc welding is the most widely used at home, in which the edges of the parts to be joined are melted by an electric arc. This arc is an electrical discharge between two electrodes or an electrode and the workpiece. The arc plasma temperature is 6-7 thousand degrees, which makes it possible to melt almost all metals.

The welding unit consists of a welding machine with two connecting cables. At the end of one of them there is a clamp fixed to the part, at the other there is a holder into which the electrode is inserted. An electric arc occurs between the tip of the electrode and the workpiece due to the strong electric field created by the welding machine: it breaks through the air gap between the electrode and the workpiece, and as a result, a powerful electric current arises, which generates a large amount of heat when flowing through the workpiece. To excite the arc, touch the part with the tip (end) of the electrode and immediately pull it back 3-4 mm. The welding electrode is a metal rod that melts during welding and thus provides additional metal for the weld. The most common are chopped-type electrodes used in welding with both direct and alternating current. Electrodes are usually 30 or 35 cm long, 1.5: 2.25 thick; 3.25; four; 5 mm or more. For welding thicker parts, thicker electrodes and high currents are also used. Table 10 elaborates on this condition.

Table 10

The connection of two or more parts obtained by welding is called welded. In shape, such joints are divided into docking, corner, lap, tee (Fig. 74) and others; according to the position of the weld in space - to the lower, horizontal, vertical and ceiling (Fig. 75). A weld is a section of a welded joint that directly connects the parts to be welded. According to the method of execution, welds are single-pass, multi-layer, continuous (solid, intermittent, fillet, butt, spot and some others) (Fig. 76.)

Rice. 74. :
a - butt; b - angular; in - overlapping; g - tee

Rice. 75. :
a - lower; b - horizontal; c - vertical; g - ceiling

Rice. 76. :
a - butt continuous single-pass; b - butt continuous multilayer; c - angular intermittent

Features of the welding arc. In the process of arc burning under the electrode, i.e. in the part, a depression is formed filled with liquid metal, which is called a crater. Part of this metal evaporates, and when the arc is extinguished, the crater turns out to be "dry", that is, it simply represents a recess, a hole in the metal. The crater reduces the quality of the weld, and it must be filled, i.e. welded. The depth of the crater, or, as it is called, the depth of penetration is the greater, the more welding current and less arc movement speed. The crater is brewed like this. An arc is ignited on the base metal, after which it is moved through the crater to the weld bead and, having filled the crater, is moved forward again. best quality the seam is provided by the so-called normal (or short) arc, i.e. arc, the length of which does not exceed the diameter of the electrode rod. If this length is greater, then the arc is called long. It must be borne in mind that too long an arc gives seams of poor quality. There is another "bad" effect that must be eliminated - the deflection of the discharge arc under the action of the magnetic field of the discharge current, or the phenomenon of the so-called magnetic blow (Fig. 77).

Rice. 77. :
a, b - deviations of the arc; c - arc deflection compensation by electrode tilt

To reduce the deflection of the arc, a number of measures are used: change the location of the current lead, tilt the electrode towards the deflection of the arc, and reduce its length. Although an AC arc is less stable than a DC arc, welding with it has the advantage of being simpler and less expensive for welding equipment. Welding with a DC arc can be carried out by connecting the “+” of the power source to the workpiece to be welded (straight polarity) or to the electrode (reverse polarity) (it is clear that this does not matter when welding with alternating current). When burning an arc of direct polarity, the welded part heats up more, and an arc of reverse polarity heats up the electrode. In addition, the melting rate of electrodes made of low-carbon steels is 10-40% higher with reverse polarity than with direct polarity. This circumstance is taken into account by choosing direct or reverse polarity, depending on the type welding work(tack or welding), the thickness of the products to be welded, the material of the electrodes (carbon, chromium-nickel). Reverse polarity welding is also used when joining thin sheets of metal.

Arc welding technique. Before proceeding with the actual welding, it is necessary to clean the edges of the parts to be joined from dirt, rust, oil, paint and slag. Having selected the electrode corresponding to the type of weld, insert it with its free end from coating into the electrode holder, and then set the current strength switch to the position corresponding to the normal welding mode. How to ignite the arc has already been explained above. In places of its contact with the workpiece to be welded, the metal melts instantly, so welding must begin immediately after the arc is ignited. The melting process takes place in two zones, in which the metal is mixed: one at the electrode, the other at the edges of the parts. The mixing zone, when the electrode is removed, quickly solidifies due to good heat removal from it. The seam formed during cooling is called a weld bead.

During welding, the electrode is moved along a very intricate trajectory: in the direction of its axis (to maintain a certain arc), along and across the weld. If the electrode moves too fast, the seam turns out to be narrow, loose and uneven. Slow movement can lead to overheating and burn metal. The oscillatory (zigzag) movement of the end of the electrode not only along but also across the seam leads to the formation of a wide bead. The width of a wide seam should be 6-15 mm, and a narrow ("thread") - 2-3 mm wider than the diameter of the electrode. It is easiest to weld in the lower position (see Fig. 75a).

The reliability of such a seam can be increased by welding with a thread seam on the reverse side. Multilayer welds are made by stacking many beads on top of each other; at the same time, before surfacing the next bead, it is necessary to thoroughly clean the slag from the previous bead with a hammer and a metal brush. The quality of welding significantly depends on the accuracy of the first layer. This is especially important for those structures where it is not possible to weld the reverse side of the joint. When welding horizontal seams, usually the bevel is made only at the upper part of the joint (see Fig. 75b). The arc is first ignited at the lower horizontal edge, after which they move to the beveled upper edge. It is more difficult to weld ceiling seams (see Fig. 75d), since it is necessary to keep the metal from flowing down from the crater. This can only be achieved with short arc welding. The arc current and electrode diameter when welding this type of seam should be 15-20% more than when welding seams in the lower position. Welded seams are filled in two ways: along the length and along the section. In the first method, they are performed "on the way" and back in a stepped way. Seams, the length of which is not more than 300 mm, run from beginning to end in one direction. Seams 300-1000 mm long are welded either along the way from the middle to the edges, or in a reverse-step way. The last way seams of large (more than 1000 mm) length are also welded. The reverse step method consists in the fact that a long seam is divided into sections 100-300 mm long and they are boiled in the direction opposite to the general direction of the seam. The end of each section is welded with the beginning of the previous one.

As already noted, according to the method of execution, single-layer (single-pass), multilayer, and other seams are distinguished. In multilayer, each layer is performed in one or two or three passes. In any case, the reverse step welding method is used. The butt joint (see Fig. 74a) of their elements with a thickness of 4-8 mm is performed with a single-pass seam (see Fig. 76a), and thicker parts are welded with a multi-layer (multi-pass) seam. In the latter case, welding is carried out with thread rollers-electrodes of the same diameter (Fig. 76b). At the point of rotation, the seam is welded without breaking the arc. For butt welding of parts of different thicknesses, the electrode diameter and current are selected according to the lower parameters of the welding mode recommended for parts of greater thickness. An electric arc is directed to it during welding. Butt welded joints have a number of advantages over other types of joints: the ability to weld parts of any thickness; higher strength; minimum consumption of metal; reliability and ease of control. The following butt joints are available: without beveled edges, with flanging, with one-sided bevel (V-shaped), with double-sided beveled (X-shaped). There are several types of tee joints (Fig. 78): at a right angle without beveled edges (Fig. 78a); at an angle with a bevel of one edge (b); at a right angle with a bevel of one edge (c); at a right angle with a double-sided bevel (d).

Rice. 78. :
a - at a right angle without beveled edges; b - at an angle with a bevel of one edge; c - at a right angle with a bevel of one edge; g - at a right angle with a double-sided bevel of the edges

The bevel angle in right angle joints is usually 55-60°. In this method of overlapping connections (Fig. 78b), the part is placed on the part and a seam is made along the edge of the upper element. The advantages of this connection are the ease of preparation of parts for welding and their assembly into a structure; slight shrinkage and warping. The disadvantages include increased metal consumption, the need for welding on both sides, the likelihood of corrosion, labor intensity and high consumption of electrodes. Lap joints are usually used for welding parts with a thickness of 1-10 mm from low carbon and stainless steels. The process of actually welding units and parts begins with their mutual fixation with tacks (or "rivets") - spot "seams", otherwise the elements to be joined during welding may "scatter" in different directions. Tacks must not be made in sharp corners, on circles of small radius, in places of sharp transitions, as well as near holes and at a distance of less than 10 mm from them or from the edge of the part.

Flanges, cylinders, washers, tubular connections are fixed by placing the tacks symmetrically. If it is necessary to make a double-sided tack, these dotted "seams" must be staggered. In any case, the sequence of tacks should minimize sheet warping. In addition, when performing tack welding, the welding current should be 20-30% more than necessary for welding the same materials; electrodes, on the contrary, should be chosen thinner; the length of the arc when making tacks should be small - no more than the diameter of the electrode; the arc breaks off not at the moment of formation of the crater, but after its complete filling.

Difficulties in welding. 1. Sticking of the electrode is essentially a short circuit, as a result of which the welding machine experiences an overload. The stuck electrode is removed from the seam with a sharp jerk. 2. Another defect that often occurs during welding is the removal of the arc from the weld: the methods of dealing with it are described above. 3. Welds are fragile in the following cases: when welding a multi-pass weld, slag is not completely removed from the surface of the deposited beads; too much or too little discharge current.

Arc welding safety. When carrying out welding work, there is always the possibility of injury of varying severity: electric shock, burn by an electrode or hot metal particles, burn of the retina by arc light radiation, etc. but also the survival of the welder. First of all, it is necessary to carefully check the integrity of the insulation of electrical circuits. The power supply housing must be grounded, or even better - "zeroed" (Fig. 79). Any work with the source - moving, repairing, etc. - must be carried out when it is disconnected from the network. It is especially important to pay attention to wires with a cross section selected from the calculation of 5-7A / mm 2. The electrode holders (Fig. 80) must meet all the requirements for them.

Rice. 79.

Rice. 80.

And the last thing: it’s good to get acquainted (including practically) with the basic methods of providing assistance with electrical injuries. Let us pay special attention to how to deal with the actual electric arc, which is the greatest danger to the eyes, and with strong exposure causes cataracts (clouding of the lens). It is clear that welding cannot be done without a protective mask. Here the problem lies in the selection of the filter. To do this, it is recommended to carry out test welding; if in the light of the arc through the filter the joint to be welded is visible, i.e. 1-2 cm you can see where to lead the electrode - the filter is good. If the visibility is worse, then the filter is too dark, and if you can see very far, it means that the filter is too light. But even when correct selection mask light filter, inexperienced welders often “catch bunnies” from arc radiation. In the evening or at night, after working with a welding unit, a person begins to feel that his eyes are as if filled with moving coarse sand. In addition to "bunnies", you can get burns exposed parts body. To prevent such injuries, welder clothing consisting of trousers and a canvas jacket, as well as boots or boots, should be worn. Pants should be worn over shoes in order to protect the legs from burns from metal splashes and hot stubs.

Thin metal sheets are connected in different ways. The most common connection is a seam seam, which involves bending the sheets at the edges. The sequence of the seam seam is shown in Figure 135.

Rice. 135. The sequence of the seam seam

First, the sheets are bent at the edges at an angle of 90 ° by 6-8 mm (Fig. 135, a). To do this, each sheet is placed on a special table edged with a metal corner with an overhang (protrusion) of 6-9 mm and gradually, in several passes, is bent with mallets (Fig. 136). Then the sheet is turned over and the bent edges are folded with a gap of 2-3 mm (Fig. 135, b). The sheets are brought into the lock (Fig. 135, c) and securely fastened with blows of a mallet through a stepped bar (Fig. 135, d). The protrusion of the step on the seam does not allow the sheets to separate.

Rice. 136. Folding the fold: 1 - table; 2 - emphasis; 3 - foldable sheet

In this way, sheets of roofing steel are connected on the roofs of buildings, ventilation and drainpipes, buckets, cans and many other products are made.

Practical work No. 40
Joining thin metal sheets with a seam seam

Work order

Mark and cut with scissors blanks from tin for joining with a seam seam.
Mark the fold lines for the seam seam at the edges.
On a specially equipped table (workbench), following the sequence of operations, perform a seam seam.
Check the strength of the connection. Put on gloves and try to move the bonded workpieces in different directions.

New concepts

Seam seam, lock.

test questions

Where are seam joints found and why, in your opinion, are they irreplaceable?
Why are metal sheets bent gradually, in several passes?
Due to what the seam lock firmly fastens the sheets?

The edges of thin sheet metal are most often joined into a lock - by clamping one edge into the other, but occasionally other methods are used that may be needed more often in the works of a young master. These are the methods.

The edges of the sheets can simply be soldered. It is clear that this will be the most fragile way, especially if the metal sheets are thin. This will be a butt joint (1). Such a connection can be used where strength is not required, but an inconspicuous connection is needed. In thicker sheets, the butt joint is made with teeth (2). This is actually done not by tinsmiths, but by coppersmiths - craftsmen who make copper utensils, tanks, pipes, caps, etc. The butt joint can be made stronger by soldering a plate (3) on the inside. This will be a butt with an overlay. Stronger connection - overlap (4). One edge is superimposed on the other, the seam is soldered or fastened with rivets. But this connection already has a protruding edge, which is not always convenient. You can bend the edges at one edge and at the other, hook them and squeeze them with mallet blows. This will already be a simple lock (5).

The most common connection method is a double lock (6). It is done like this. In one piece, the edge is bent at a right angle, in the second, the edge is also bent, but in the other direction, and pressed against the piece, and then this edge is bent at a right angle in the opposite direction. Both bent edges are connected to each other, bent towards the first edge, and the seam is pierced with a mallet. On the reverse side, it will be smoother, which must be taken into account when joining in this way. The sequential course of work is schematically shown in the following figure:

All kinds of tin products are most often connected with a double lock.

Occasionally, tinsmiths use a connection with rivets. However, this method is more often used when it is necessary to rivet a handle, an eyelet, a strip, etc. Occasionally, the seams are strengthened with rivets into the overlay and with a simple lock. They usually rivet with small rivets, preferably with wide flat caps, in a cold way. In rough work, tinsmiths prefer rivets rolled from a piece of tin. To make them, you need to have a piece of iron with holes of different diameters, or a riveter. A diamond-shaped piece of tin is rolled up with a pounder using a hammer or round-nose pliers, inserted into a riveter, into a hole of a suitable diameter, and the head is riveted. These rivets are soft but certainly don't have the neat look of solid rivets.

Almost all work with thin metal is based on the plasticity of the metal, its ability to bend and flatten. But the master must skillfully use his tool, otherwise these same properties will go to the detriment of the work. How and why remains to be seen.

The main and very first work of the master is the ability to bend the fold, in other words, to bend the edge of the sheet. The work is simple, but also very responsible, since further processes depend on it. It is necessary to bend the fold for a variety of needs: for seam joints, and for edges, for inserting bottoms and others. It is necessary to ensure that the metal only bends, but does not flatten out at the same time. If the metal in the fold is flattened, it will expand. The fold edge will come out bent and the surface of the sheet will warp.

In rough work, where the fold is folded wide, this makes almost no difference. But where greater precision and finesse are required, it will be very noticeable. Let's explain with an example what we can do. Suppose we want to make a tube out of tin and connect it with a double lock. They unfolded the folds with an iron hammer, began to roll up the tube and connect the seam, but it turns out that it is very difficult to connect the seam; the folds turned out to be bent due to the riveting of the metal with a hammer.

Therefore, the folds should always be bent with a wooden mallet on the sharp iron edge of a scrap, iron strip or scraper corner.

The work proceeds in this order. First of all, a fold line is drawn with a thickness gauge. The thicker the metal and the rougher the work, the wider the fold can be taken (10-20 mm, on thin sheet the fold is taken at 3-5 mm). They put the sheet on the edge of the scraper (or devices replacing it) with a fold line, with quick and accurate blows with a mallet beat off this line, first at the ends, and then along the entire length of the fold.

Then they bend the edge of the fold at a right angle, put it on the anvil with the outer side and straighten it with the inner blows of the mallet.

Suppose that you need to bend the fold of a tin cylinder.

It is clear that the diameter of the outer edge of the bent fold will be greater than the diameter of its inner circumference. Therefore, the metal must be riveted along the entire fold, stronger at the outer edge, weaker towards the cylinder.

The fold must be bent with an iron hammer. The cylinder is taken in the left hand, the width of the bend is marked from the inside with a thickness gauge and applied to the edge of the support or scrap at an obtuse angle, after which they beat the future fold with the toe of a hammer, beating off the fold line and riveting the edge. Light blows of the hammer are directed so that the outer edge is riveted more strongly. Bypassing full circle, reduce the angle of inclination of the cylinder, placing it steeper to the anvil, and continue the work in the same order. It is repeated again and again, all reducing the angle of inclination to a straight line. With such a gradual knocking out, the fold can be bent at a right angle, and it will not burst anywhere. The bent fold is placed on the stove and straightened with mallet blows.

The bottom can already be attached to such a cylinder with a fold with a double lock, only at the circle for the bottom it is necessary to bend the fold or solder the bottom with solder.

Just as they bend the fold on the cylinder, they also do it when the edge of the tin product needs to be strengthened and made thicker by rolling a wire into it. The work is carried out in the same order, but with a mallet and without beating off the sharp edge of the fold. The fold should come out smoothly, a lapel must be made on the metal, calculating the width of this lapel according to the thickness of the wire that will go in there.

The width should be taken at about three wire diameters, adding a little to the thickness of the metal. When the fold is bent at a right angle, it is bent back with a mallet, turning the cylinder on a round anvil. Then they put it on the stove, insert the wire and fix it with a few blows of the mallet on the lapel. With a mallet on a round anvil and a plate, they finally press and smooth the lapel. Turning the product edge up, straighten the rolled edge from above. If the lapel turned out to be not wide enough, it is now very easy to fix it by piercing the top with a mallet with a pull of the blow outward. On products with straight edges, rolling the wire into the edge is, of course, even easier.

Of the techniques for processing thin metal, based on riveting and drawing metal, a young master should definitely get acquainted with knocking out. By knocking out a flat plate of metal, a various convex shape is given. In this way, it is possible to knock out the bottoms and covers of boilers, hoods and a variety of streamlined parts for aircraft models, plating for ship models, etc. Above, we already had a similar job - this knocking out of a bucket.

Knocking out is a job that requires patience. You can not hit once or twice with a hammer and get a good hood. It is necessary to slowly beat with a hammer, all the time moving the product, gradually increasing the depth of drawing and finally straightening and smoothing the surface of the product with light blows.

There are basically two ways to pull. The first way is when the metal is flattened on a convex anvil, starting from the middle to the edges. The middle will be the thinnest, but the product will be convex. The work is carried out with an iron hammer. According to the second method, they are knocked out with a mallet or a hammer with a round end on a mandrel (matrix) having the corresponding shape.

As an example, we give the knocking out of the same bucket. On a wooden kolobashka or a thick board, several round recesses of various depths must be made. They are cut with a semicircular chisel, and then smoothed with blows of a round hammer. A round plate of metal is placed over the first recess and a hammer or a round mallet is knocked out until a properly rounded surface without wrinkles is obtained. The same technique is repeated in the following, deeper matrices. In conclusion, we will get a bucket along the profile of the matrix. According to a different profile and a different cutting, we could get a different shape.

Sometimes a young master will have to knock out longitudinal recesses on thin metal plates. The cross section of such a plate will turn out to be figured, and the plate will become rigid.

As in any other business, the marking and cutting of the material, the beginning of work, is a very important operation, on which further success depends. From this it is clear that this work requires special care and accuracy. The most simple work- this is cutting and making a simple open rectangular box with upright or divergent sides, with or without a toe.

From a sheet of tin cut out a rectangle of the appropriate size (a). When cutting, it is necessary to take into account the area of the bottom and the height of the walls. A thickness gauge draws a line of folds. One corner is cut off if you need to make a sock in the box. Turning the sheet over on the board, cut off the corners of the bisector of the corners with the toe of the hammer approximately to the border of the future bends of the walls (b). Turning the sheet over again, on the edge of the anvil (a piece of iron) they bend the sides with a mallet (c), but not quite. They are trimmed at the rectangular end of the anvil and bent with a mallet close to the wall (d). The cut corner for the toe remains not bent, it is slightly flattened, making a gutter out of it. The box is ready (d).

The work, as you can see, is quite simple, but it must also be done carefully.

Cutting out and manufacturing cylindrical shapes will not present any particular difficulties. For the cylinder, it is necessary to cut out a rectangle equal to the height of the future pipe, and 3.14 times the diameter of this pipe with an increase in seam rolling.

In the manufacture of conical products (bucket, funnel and others), all working methods will remain the same, only when cutting you will have to remember the geometry. All conical objects must be correctly depicted in a sweep, and this is the most important thing.

Let's take the easiest way to cut. Let's try to make a conical bucket. First of all, you need to draw its average section, along the axis. It will appear as a trapezoid; continue the sides of the trapezoid until they intersect. The intersection point is the center from which two arcs are drawn - from the long base of the trapezoid and from the short one. You will get a ring, from a part of which the surface of the conical bucket will be made. The width of this ring is the height of the bucket. You just need to remember to add to roll up the top edge and bend the bottom.

The length of the part of this ring we need is determined by the diameter of the bucket. Approximately three diameters with an addition for a double lock is what you need to take from the ring. Having set aside 3.14 diameters of the outer hole or the bottom of the bucket along the upper or lower arc, a line is drawn along the radius. Increases for a double lock are already made parallel to these radial lines. This will cut the surface of the bucket. Any conical shape is drawn in the same way, whether it is a whole or a truncated cone: the height of the figure is plotted along the radius, and the length of the scan is along the circumference.

The choice of material for the roof takes into account the individual characteristics of the building: the angle of the roof, the solidity of the foundation, the general architectural style. When choosing a finish coating, preference is often given to sheet metal. This material guarantees the durability of the roof, has a low weight and does not weigh down the structure, the processing and installation of metal is not difficult, which speeds up the entire process of roofing. In this article, we will look at how to cover the roof with iron.

What type of roofing iron to choose?

Metal sheets intended for roofing work vary appearance and coating.

Black iron - sheets or rolled steel without coating, is resistant to mechanical stress, but does not tolerate moisture. This is a budget material, but for long-term operation it needs an anti-corrosion coating.

Galvanized steel - has a smooth surface, is resistant to precipitation due to the protective layer of zinc, is indispensable for the installation of seam roofing.
Profiled metal - galvanized iron that has undergone profiling to create stiffeners. It has a trapezoidal, wavy or rectangular section. After treatment with a polymer coating, the anti-corrosion and aesthetic properties of the material increase significantly.

Stages of installation of a galvanized steel roof

Before covering the roof with iron, it is necessary to make a strong crate that will eliminate metal deflections. The basis for iron sheets is wooden beams located 20 cm apart, a continuous crate of edged boards or a step-by-step crate of boards nailed at a distance of 10 cm.

It is possible to connect sheets with galvanized iron by overlapping them and fixing them with nails with a special gasket, or in a more time-consuming and reliable way - folding. To do the job you need:

wooden mallet;
metal scissors;
workbench for preparing paintings;
metal hammer;
comb bender;
roulette;
a mixture of drying oil with minium.

Iron sheets are primed with a mixture of drying oil and red lead before starting work to increase corrosion resistance. Dried iron is cut into pieces of the desired size, for this they use metal scissors (grinder is strictly prohibited). The folded method reliably protects the joints from leakage. It is a connection of adjacent sheets of iron into a lock, made by bending the edge.

For horizontal connection, recumbent folds are performed. They are made using special machines or on workbenches using a hammer and mallet. A line is drawn at the edge of the sheet and the edge is bent with a mallet; for this work, you will need a workbench with a metal corner. On another sheet, the edge is folded over several times until a U-shape is created. The junction is sealed and bent close to the metal sheet. In this way, blanks are formed for laying on the roof, they are called paintings.

On the roof, all the paintings are connected using longitudinal standing folds. In their manufacture, a comb bender is used. Before fastening, the location of the sheets in a vertical plane is checked. The length of the workpiece is recommended to be equal to the size of the roof slope. Pictures are stacked in rows from the ridge to the gutter. A steel strip is used to seal the lying folds.

In places requiring special strength seams, use double fold. It is made by bending the edges of two sheets, followed by simultaneous folding. The recumbent seam is installed with a bend to the eaves, this allows water to flow freely along the roof. Pictures are attached to the crate with metal clamps.

The most difficult step is the collar for the chimney tube. It is pre-made, according to the shape and size of the pipe. The collar is connected with metal sheets by standing folds.

To understand how to properly install a roof using a seam connection, you should watch a video with recommendations from professionals.

Features of roofing with profiled sheet

When deciding on the size of the corrugated sheet, choose a roof slope equal in length, if it is large, focus on ease of transportation.
When counting the number of sheets, consider the angle of the roof, if it is within 15 to 30 degrees, an overlap of up to 20 cm will be required.
Before installing the corrugated board, a waterproofing film is laid. It is fastened with brackets to the rafters. Counter-rails are installed on top of it, providing a gap with metal sheets.
The polymer coating of profiled sheets should not be damaged during transportation and installation, this will lead to the loss of the anti-corrosion properties of the material.

Grades of corrugated board differ in strength and wave height. For the device of a reliable roof, two brands are used:

HC - for roofs with a significant slope angle that do not experience a high load;
H - used for capital roofing, it is distinguished by additional stiffeners.

Profiled sheets are easy to process, for laying and fastening you will need a hacksaw and a screwdriver. Stack sheets from the bottom up, starting from the right end. Solid profiled sheets are pre-fixed with one self-tapping screw and laid along the entire length of the roof. After alignment with the eaves, the final fastening is carried out with roofing screws, the heads of which are selected according to the color of the polymer coating. Horizontally, they are screwed with a screwdriver into every second wave, vertically at a distance of the crate step. The upper and lower parts are fixed with a self-tapping screw into each profile.

When using several rows of corrugated board, their transverse joints are connected with an overlap of at least 20 cm and coated with silicone sealant.

When working with profiled iron, care must be taken to prevent damage during movement. It is recommended to wear soft shoes or to make a wooden deck on the finished roof section.

Properly installed iron roofing will provide reliable protection for many years, this solid coating will withstand the action of rain and wind. Shiny or colored surface used metal sheets complement the architecture of the building.