Iron doors – construction

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In this article: What can be a steel door frame; door leaf design; how the door frame of a steel door is arranged; insulation inside the leaf of the sash; hinges and anti-burglary pins; characteristics of a reliable metal door.

Iron doors - construction

Attractive metal doors are on guard, probably, most of the apartments and houses, instilling confidence in the owners of the safety of their property. But how real this security is, is it really enough to put any metal door on the entrance and the intruders won’t come close to it? I propose to understand the design of iron doors and determine which door is most capable of withstanding burglary.

First of all – the door frame

The frame of the leaf of the metal door is made of profiled metal-roll of simple and complex shape. Simple profiles – steel strip, equal angle (shelf 30 mm or 50 mm), welded pipe made of two corners, rectangular pipe with one weld seam (40 by 60 mm, 30 by 20 mm or 20 by 40 mm). Steel strips and corners are less resistant to deformation, a rectangular pipe has twice the rigidity compared to them, because contains more stiffeners. Hot-rolled and cold-rolled profiles of complex design have a fancy geometric shape and are made of thicker metal than simple ones – the more complex their shape and the thicker the metal from which the profiling is made, the higher the strength and stiffness of the metal door leaf.

The construction of a frame from profiles of complex geometry allows you to create a sash with a cladding of thick sheet metal without significantly increasing the total weight of the structure, which was not possible in the case of creating a frame from a simple profile. At the same time, the door leaf becomes thicker, thereby minimizing the loss of strength caused by the holes for the locks, it becomes possible to position the lever lock mechanism at a maximum distance from the outer surface of the door leaf. In addition, the frame made of complex profiles allows the placement of two sealing contours around the door perimeter – one on the outside, the other on the inside..

Iron doors - construction

Metal doors of most manufacturers of the European Union and Russia are equipped with frames made of a complex profile, formed by the cold-rolled method from high-carbon steel sheets 1.2–2 mm thick. Domestic manufacturers, as a rule, purchase profiled metal for the frame abroad..

To increase the strength characteristics of the frame, it is additionally reinforced with steel stiffeners – the higher the number, the better. Stiffeners in the door leaf structure can be longitudinally oriented, transversely oriented and have a mixed orientation (transverse or vertical ones are added to the longitudinal ribs). The transverse ribs resist well attempts to squeeze the sash from the frame or push it through, the longitudinal ribs resist the bending of the upper or lower corner of the door leaf from its outer side. Accordingly, the ribs of mixed direction are equally well resistant to any attempts to squeeze the canvas.

Metal door leaf – design options

The required number of stiffeners and the final overall stiffness of the sash leaf are directly related to the thickness of the steel sheathing sheet. A sheet of hot-rolled steel is welded to the frame from the outside of the sash, Russian manufacturers usually use steel 2-3 mm thick for this purpose, Western – 1.2-1.8 mm steel. The optimum thickness of the steel sheathing is 2 mm; it is not advisable to use a sheet of greater thickness, because this measure will dramatically increase the weight of the sash and the cost of the finished door, but will not give a practical result. To prevent the lock from being hacked, it is necessary to install in front of the place of its installation (behind the casing sheet) the so-called armor plate – a steel plate 4-5 mm thick, which will be very difficult for a burglar to drill.

Iron doors - construction

The frame of a steel door is often sheathed not only from the outside, but also from the inside. Internal steel sheathing is necessary if the sash is sheathed with sheets less than 1.5 mm thick – it increases the rigidity of the leaf. However, with an external cladding of 2 mm steel and a sufficient number of stiffeners, there is no real need for it – it is quite possible to sheathe the sash from the inside with an MDF panel. Note that the inner steel cladding is able to withstand burglary from the inside of the house only under the conditions of the integrity of the steel sheet and the placement of the lock fasteners at the end of the door.

Iron doors - construction

Sheathing sheets are attached to the frame using electric arc welding. Relatively cheap models of metal doors (cost 7,000–10,000 rubles) are usually welded by hand, the seams are uneven and fragile, which reduces the resistance of such doors to burglary and over time will cause structural deformations of varying complexity, up to jamming of locks. More reliable spot welding, during which an electric weld is made at 500-700 different points. Steel doors have the greatest strength, the structural elements of which are connected by semi-automatic welding in carbon dioxide, but this technology is available only to large manufacturers..

In addition to the described profile technology for creating a door leaf, there is also a one-piece welded production method – a cold-rolled steel sheet with a thickness of 1.2 mm is bent to obtain a three-dimensional structure of the door leaf. Stiffening ribs are welded into the sash paneling formed in this way. The welded one-piece bent technology minimizes the number of deformations of the steel sheet during its processing and in the process of using the structure, and the absence of heat treatment improves the performance of the final product. However, cold-rolled steel is less resistant to cutting and drilling, so the sash cladding will be correctly done with hot-rolled sheet steel..

Door frame – manufacturing technology

Similar to the frame, it is made from simple and complex profiles – a corner, a profiled pipe and a complex structure profile.

The disadvantage of a corner box with a shelf of 50 mm and higher is that the door leaf adjoins it only along one contour – the perimeter of the projection of the outer sheathing sheet behind the box. For this reason, it is possible to form only one sealing contour of porous rubber, which seriously reduces the thermal and sound insulation characteristics of a metal door, requiring it to be installed only in tandem with an internal wooden door. On the other hand, a box made of an equal angle corner does not reduce the width of the doorway, and this is its advantage.

Iron doors - construction

Boxes of two types are created from a profiled pipe – simple and reinforced. Simple frames made from a pipe with a cross section of 60 x 40 mm are suitable for door leaves weighing up to 150 kg and a width of no more than 900 mm, their design allows only one sealing circuit. Reinforced frames are designed for a sash of 150 kg and more, they are made of profiled pipes with a section of 40 by 60 mm and 40 by 20 mm, welded to each other with the formation of two sealing contours, providing high-quality sound and thermal insulation.

From the profile of a complex structure, door frames are created that have all the characteristics of reinforced frames, but at the same time allow the door leaf to be flush with the frame when closing. This is their main advantage – the attractive appearance of the door, the impossibility of breaking the sash with a crowbar, sealing the contours of complex geometry. To seal a sash with a frame of this design, tubular and petal gaskets are used, due to which the maximum possible heat and sound insulation of the door is achieved. It should be noted that only a box made of a complex profile provides protection to the crossbars of the lock – being in the extended position, they are completely hidden by the profile lines and are not visible to the burglar.

How the door leaf is filled

If the cavity inside the door leaf is not filled with anything, then a kind of drum will come out of such a door, perfectly transmitting sounds in both directions and supplying street cold. It is possible to do without filling the sash and save on this only in one case – if there is an internal wooden door.

Iron doors - construction

Most often, manufacturers of metal doors fill the sashes with high-density mineral wool insulation or foam. In this case, the locking zone of the sash is not filled with mineral wool – there is a high probability that the fibers will get inside the lock mechanism and jam it – foam is placed in this area. Among the rare technologies for filling a metal sash is pouring concrete of a special formulation into its cavity, which increases the resistance to burglary, however, simultaneously with a serious increase in the weight of the door.

Steel door hinges

The task of the hinges in the case of iron doors is not only the normal movement of the sash, but also to prevent burglary. Depending on the manufacturer, the doors are usually equipped with hinges with an internal ball-bearing (this does not prevent burglary in any way) and hidden installation hinges (similar to those installed on car doors), which cannot be cut off, however, the leaf travel is rather limited. Foreign manufacturers of steel doors install hinges on their products that allow three-dimensional adjustment of the sash position in relation to the frame, Russian door models allow only two-dimensional vertical adjustment.

Iron doors - construction

In order to create an insurmountable obstacle for burglars who managed to cut off the hinges from the door structure with a grinder, the end sections of the sash frame adjacent to the hinges are equipped with steel pins that go into the holes specially drilled for them in the box by 20-25 mm when the door is closed. The optimal number of such pins is two for each installed lock. They will create serious problems for the burglar, forcing him to cut off and the bolts of the lock and pins.

Installation of a metal door in the opening

Usually the door frame is fixed using the mounting holes provided by the manufacturer. Fastening is carried out with steel pins (diameter from 12 mm, immersion in the wall from 150 mm and more) or anchor bolts (diameter from 10 mm, length from 150 mm). In the first case, the pins are driven into the wall, two or three on each side of the box, that part of them that remains in the doorway is riveted during the driving process or welded to the frame of the frame. The disadvantage of the pin attachment is that it is inseparable, the advantage is that the pins can be made of any length.

European manufacturers of metal doors recommend fixing the frame with anchors, the strength of which is not inferior to “domestic” steel rods. Although the anchor connection of the box looks neat and allows owners to dismantle the door quickly and easily, if necessary, the anchors have one drawback – length restrictions, in other words, they may not be long enough for strong fastening in a given wall.

Iron doors - construction

The door frame can be installed in the center of the depth of the doorway or flush with the plane of the outer wall: in the first version, installation of platbands is not required, but the door does not open more than at a right angle; in the second – you will need platbands, and they are usually not included in the door package.

Often, in metal doors, the gaps between the sash and the frame are closed with a steel sheet of the outer casing protruding beyond the box along its perimeter – it is into this gap that the burglar will try to drive a crowbar-form in order to squeeze the sash. Therefore, some manufacturers decided to remove the sheathing protrusion with the condition that the outer steel sheet was recessed into the box by 25-30 mm, while the decorative strip plays the role of a strip.

At the end

So what should be a metal door that can withstand a burglar for as long as possible? It should be sheathed with two sheets of hot-rolled steel (external – at least 2 mm, internal – 1.5 mm), have more than two internal stiffeners located vertically and two horizontal ribs near the interlocking zone (metal thickness of the stiffeners – 2 mm) … Four pins that prevent the door from being removed in the closed position, at least two complex locks (one or two crossbar cylinder and lever locks, the number of crossbars of which is at least three), an obligatory armor plate in front of the locks. It is better to place the door frame in the center of the depth of the doorway, securing it with four pins on the wide sides and three on the narrow ones. The door leaf, recessed by at least 25 mm into the frame, sheathed around the perimeter with decorative strips and with two sealing contours installed on it. The sash cavity should not be filled with paper or cardboard, as is often the case with cheap Chinese and domestic-made doors, but with hard mineral wool or foam, the total weight of the door is at least 80 kg.

Iron doors - construction

A metal door with the above characteristics will cost the buyer no less than 30,000 rubles, but it really costs this money.

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