Everyone knows well, that the windows in apartments are wooden or plastic and very rarely aluminum. In public buildings, eg, schools and hospitals - windows must be aluminum, at least in terms of fire safety, but usually, again, and there they are also plastic. And where are the steel windows and why?
Steel windows - luxury windows
Steel windows are elite windows in the full sense. They are being installed to replace the steel windows of a century ago in historic buildings., to preserve their architectural style for posterity.
Steel windows are used not only in historical buildings ... What can I say, good steel windows are strong, nice and warm - quite expensive. Therefore, they can only be installed in luxury apartments., hotels and residences, especially in those, that they are trying to look presentable and old-fashioned.
From wooden windows to steel windows
Steel windows have been around since the 1860s, but really became popular in the world, Firstly, in USA, only after 1890 of the year. Two factors contributed to the increased demand for steel windows at the time instead of the then dominant wooden windows.. First of all, then they learned to roll steel profiles of a more or less complex configuration and, Secondly, a series of urban fires have led to an increased use of wooden windows, especially in high-rise industrial and office buildings.
Steel rolling progress - steel windows progress
Like the process of rolling rails, steel window profiles rolled from hot steel rods in several passes, until we got pretty primitive, at present, corner profiles. These steel window profiles were about 3 mm and width 25-40 mm. These profiles were applied to all elements of the window: frame, sash, impost and so on. Combined with safety glass with wire mesh on the inside, these windows were truly safe windows in the event of a fire.. At that time, such windows were installed almost exclusively in brick and concrete buildings..
Steel windows - and fencing, and supporting structures
Besides fire safety, these steel windows have other advantages.. Their robust steel frame allows the installation of significantly larger windows in buildings, than wood and aluminum, not to mention plastic. Besides, steel windows can be installed in the form of a continuous strip of windows - their steel structures are not only enclosing, like other windows, but also fully perform the functions of supporting structures. This greatly influenced the design of industrial and public buildings of those times - they were designed to be spacious and with large windows..
Aluminum windows instead of steel ones
The widespread use of rolled steel profile windows continued up to 1940-50 years, when cheaper and more corrosion-resistant aluminum windows began to gain popularity. Currently, aluminum windows are gradually giving way to plastic windows., especially in household, home sector. In public buildings, aluminum windows have a certain priority over plastic windows for the same fireproof, as well as sanitary, considerations.
Modern steel windows
In modern steel windows, mainly cold-rolled profiles and profiles are used., bent from steel sheet. The steel grades used range from ordinary low carbon steels type St3, 10 and 20 with varying degrees of deoxidation, as indicated in GOST 23344-78, to various types of stainless steels.
Thermal conductivity of aluminum and steel
The thermal conductivity coefficient of low carbon steel is about 55 W /(m∙TO), which is four times lower, thermal conductivity coefficient 210 W /(m∙TO) aluminum alloy 6063 (AD31), which is used in window profiles. The thermal conductivity coefficient of stainless steel is even lower - about 14 W /(m∙TO). but, even with such a big, seemingly, advantage over aluminum, it is impossible to use steel profiles without thermal decoupling in winter conditions even in temperate latitudes. Strict building regulations apply in North America and Europe, which prescribe to use only windows from "warm" profiles in buildings, which provide windows with a certain minimum of heat loss in winter conditions.
Warm steel window profiles
An example of modern steel window profiles with thermal break can be the system profiles of the American company Dynamics Windows (picture 1). The construction of such a "warm" steel profile is similar to the construction of similar "warm" aluminum profiles. "Warm" profile consists of cold-rolled steel outer and inner sections, which are firmly connected to each other along the entire length through a thermal insulation insert (thermal insert) - usually one or two profiles made of special durable plastic, eg, polyamide or polyurethane. In this way, in a finished window made of such profiles, the outer and inner metal parts of the window are completely thermally insulated from each other. The thermal conductivity coefficient of polyamide is about 0,30 W /(m∙TO), and polyurethane - 0,12 W /(m∙TO).
Figure - Cross-section of a steel window frame from Dynamics Windows. Dimensions are in US - inches (1 inch = 25,4 mm). The "net" width of the thermal decoupling - the width of the thermal insert without taking into account the sections clamped in steel profiles - is about 30 mm, which is close to the maximum width in modern European "warm" aluminum window systems.