Fasteners for thermal insulation

An important element responsible for the proper functioning of thermal insulation systems and the duration of operation of facades is dowel fastening. The issues of compliance with technical requirements when choosing and using dowel technology are relevant in hinged facade systems with an air gap, better known as "ventilated facades".The main purpose of dowels is to resist wind loads. According to existing standards, the calculation of mechanical fastening is carried out precisely from the calculation of wind loads, taking into account the shape, height and location of the building. A correct assessment of wind loads, taking into account the design of the wall, forms at the design stage a scheme for doweling insulation plates for this particular building.Often, at the design stage, the calculation of the quantity and the choice of the doweling scheme are not made, taking into account the permissible loads on this type of fastening in relation to the base of the building envelope. Such
factors as the magnitude of the wind load for a specific wind area, taking into account the average and pulsation components, no stress diagrams are plotted based on the wind load in order to determine the corresponding aerodynamic coefficients in various sections of the facade, taking into account the architectural features of buildings in terms of and factors in terms of the height of structures.When choosing dowel fasteners for thermal insulation systems, full-scale tests of fasteners for "pull-out" are often not carried out directly at the places of future work, respectively, these indicators are not taken into account when calculating doweling schemes when developing working documentation for facade work. The absence of such tests leads to significant problems at the stage of preparation for the installation of the reinforcing layer, when it turns out that the dowels used do not provide the necessary indicators for the reliability of fixing the insulation, and often simply pull out of the wall. It is clear that in these cases both the contractor and the customer there are serious problems not only of an economic nature, but also in terms of the timing of the work.When conducting field tests according to the methodology recommended by the Federal Center for Technical Evaluation of Products in Construction (FTsS Gosstroy of Russia), it is necessary to additionally take into account the factors that directly affect the obtained indicators. For example, testing at negative temperatures does not allow obtaining the correct indicators and may lead to deliberately false results.With careful consideration of this factor, it is possible to predict the behavior of dowel technology when the temperature effect changes directly in the operation of the heat-insulating system, taking into account the time factor. Accordingly, when choosing and designing heat-insulating systems, the material of the sleeve and the poppet element, as well as their joint behavior with the spacer element, becomes a significant factor when choosing and designing heat-insulating systems. under load during operation.Thus, according to the estimates of the Federal Center for Technical Assessment and a number of independent laboratories and experts, the use of dowels with polypropylene sleeves is problematic, and often unacceptable. The polypropylene brands used for the manufacture of sleeves and disc elements of dowels have serious drawbacks. The increased ability to relax predetermines a significant decrease in time of the force of expansion of the dowel in the base and, as a result, leads to a decrease in the friction force, due to which the “pull-out” indicators sharply decrease.The results of foreign tests carried out on sleeves made of polyamide, polyethylene and polypropylene showed that in less than one and a half to two years, the expansion force of the dowel with a sleeve made of polypropylene decreases by half compared to the original one, and when using a sleeve made of polyamide and polyethylene, it does not more than 25%. At the same time, unmodified grades of polypropylene are distinguished by a high brittleness temperature - + 10C - -10C. At low temperatures, its impact strength and strength are significantly reduced, which leads to the appearance of microcracks and more serious damage during the installation of dowels and, accordingly, affects not only the design characteristics of local attachment points, as such, but also the entire subsequent operation of building facades. It should also be noted that at sufficiently low temperatures, spontaneous destruction of the supporting section of the disc-shaped element is possible, which ensures tight contact of the insulation with the base. As practice shows, when carrying out the necessary measures to modify polypropylene grades to obtain satisfactory frost resistance properties, a significant increase in the cost of this product occurs.The use of dowels that are not made of stainless or galvanized steel and / or do not have an additional organic coating, with a metal spacer element during further operation leads to the release of a decorative and protective layer of corrosion products to the surface. Problems of this kind arise due to the fact that the dowel is an element that