RU2457045C1 - Method of protecting building roofing against formation of icicles on its edge - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: invention relates to roof protection against formation of icicles on its edges. Proposed method consists in application of hydrophobic coating on roof surface. Note here that coating with limiting wetting angle of over 120° is selected. Hydrophobic coating is applied in strips with their width making at least 50 mm, seeing from the edge. Water drop on surface is ball shaped to roll on roof surface with no wet traces. Boundary layer disappears on such surface.

EFFECT: higher repellent properties.

7 dwg

Description

The present invention relates to areas of the economy related to the protection against the formation of icicles on the edges of roofs of various kinds of material objects: houses, warehouse buildings, etc.

The formation of large icicles on the edges of roofs and their subsequent fall can lead to serious and tragic consequences, not to mention the fact that the fight against this phenomenon requires large material costs.

A known method of coating a metal plate (see Japan patent JP 4338960 B2, 1999, IPC B05D 5/08 - analogue). The coating is applied to obtain high antifriction properties of the surface of the material. However, the hydrophobic properties of such a coating are unknown.

There is also a method of applying a wear-resistant coating on the surface of a part (see Russian patent Ru 2381077 C1, 2008, IPC B05D 5/08 - analogue). The coating is applied by the deposition of aluminum particles on a previously prepared surface, followed by microarc oxidation of the deposited layer. Since the patent does not contain information on the hydrophobic properties of the coating, it is not possible to use the proposed method for the problem being solved.

The closest technical solution selected for the prototype is the method consisting in the fact that a hydrophobic coating is applied to the surface of a material object (see WIPO patent Wo 2009005465 A1, 2008, IPC B05D 5/08). The method is based on the production of a liquid solvent under pressure, in which a hydrophobic soluble substance is added, which precipitates (or crystallizes) after expansion of the liquid at low pressure. However, the method is practically difficult to perform, since when opening the hole in the vessel and flowing out of it into the environment at a significant pressure drop, high flow rates are realized, which does not guarantee uniform distribution of particles on the surface, and therefore, the quality of such a hydrophobic coating will be low.

The object of the invention is to protect the roof of the roof of a material object from the formation of an icicle on its edge.

The technical result in the claimed method of protecting the roof of a material object from the formation of icicles on its edge is achieved due to the fact that the method consists in the fact that a hydrophobic coating is applied to the roof surface of the material object, and the coating is selected with a contact angle of more than 120 ° , on which a spherical drop of water during rolling does not leave a wet trace, while the coating is applied with a strip, the width of which is chosen at least 50 mm, counting from the edge.

Since it is primarily advisable to use a grease (paste) as a hydrophobic coating with θ above 120 °, it is fundamentally important to apply it not on the entire roof surface, but in the form of a narrow strip along its edge. This creates normal, safe conditions for the staff to work on almost the entire roof (for example, replacing roof sheets, repairing cracks, etc.) and, in addition, significant savings are achieved in the cost of expensive coatings.

The present invention, which consists in applying a hydrophobic coating with a contact angle of more than 120 ° to the roof surface of a roof of a material object, can also significantly reduce (and at an angle θ tending to 180 °, and eliminate) the adhesion of liquid (water) to the surface and Thus, to avoid the formation of a boundary layer on the surface of the washed material object. Under these conditions, the resistance to movement of the object associated with friction in the boundary layer will tend to zero.

Figure 1 shows a diagram of the action of surface tension at the front point A of a drop of water on a hydrophilic surface (contact angle θ less than 30 °).

Figure 2 shows a diagram of the effect of surface tension at the front point A of a drop of water on a hydrophobic surface (contact angle θ greater than 120 °).

Figure 3 presents a photo (top view) of a water-filled polyethylene cover with a graphite circle.

Figure 4 shows a photo with magnification × 4 (top view) of a drop of water on an anti-wettable surface (contact angle θ was approximately 125 °, a)) and a drop of water on a contact surface (contact angle θ was approximately 30 °, b) )

Figure 5 shows a diagram of the experimental setup, with which confirmed the feasibility and effectiveness of the proposed method.

Figure 6 presents a photo of an icicle formed on the edge of the roof of sandpaper.

Figure 7 presents a photo of an icicle formed on the edge of the roof of sandpaper with a strip of modified graphite lubricant applied.

The pattern of surface tension at the front point of a water droplet on a hydrophilic surface (the contact angle θ is less than about 30 °) of a material object has the following features (Fig. 1): on a phase interface, a material object (in the following description of the object) is liquid (water) - physical and chemical processes occur, as a result of which the phenomenon of wettability occurs, which is manifested in the ability to spread a drop of liquid on the surface of an object. Wettability is quantified by the value of the contact angle θ. The surface of an object for which the angle θ is less than about 30 ° is called hydrophilic, i.e. well wettable water. The surface of an object for which the angle θ is greater than about 120 ° is called hydrophobic, i.e. poorly wettable water. It can be considered that surfaces with an angle θ from 30 to 90 ° are weakly hydrophilic, and surfaces with an angle θ from 90 to 120 ° are weakly hydrophobic.

As you know, the spreading of a drop of liquid (water) 1 on the surface of object 2 occurs until the effective types of surface tension are balanced each other: 3 - surface tension at the liquid-gas interface (σ _g-g ); 4 - surface tension at the interface of the object - the liquid (σ _about ); 5 - surface tension at the boundary of the object - gas (σ _about-g ). Since | σ _о-ж |> σ _о-г for the hydrophilic surface of the object (θ <30 °), the projection of the surface tension σ _о-ж on the X axis is negative (Fig. 1), and the surface tension σ _ж-г is located in the first a quarter. In the case of a hydrophobic surface with a wetting angle greater than 120 ° (Fig. 2), the surface tension σ _g-g passes into the second quarter, and the surface tension σ _g- at the front point of drop A changes the direction of action in comparison with the case of the wetted surface ( θ <30 °).

At large values of the contact angle θ = 120-180 °, a qualitatively new phenomenon is essentially manifested - the phenomenon of anti-wettability, which is characterized by either the absence or a sharp reduction in the ability of a drop to spread on the surface of a material object.

An example of such an anti-wettable surface in contact with water is any surface coated with fine graphite powder.

So, if you put graphite powder on the surface of the polyethylene cover in the form of a circle (graphite circle), and then carefully pour water, then the water will fill the entire cover, except for the graphite circle. For contrast, the water was tinted. A kind of meniscus forms in the liquid when the surface of the water breaks off abruptly at the boundaries of the graphite circle (Fig. 3). In experiments, the depth of such a “dry” funnel reached approximately 3.5 mm.

Experiments were also conducted with a separate drop of water on such an anti-wettable surface. Figure 4a shows a photo of a drop of water (top view) on an anti-wettable surface (the surface of sandpaper was treated with graphite powder). The wetting angle was θ≈125 °. Here, for comparison, a photo of a drop of water on the surface of sandpaper without graphite powder is shown (Fig. 4b): the contact angle was θ≈30 °. It is seen that the size of a water drop on an anti-wettable surface is 1.6 times smaller due to the intense manifestation of surface tension.

In experiments, a drop of water on an anti-wettable surface is likened to a drop of mercury. Firstly, the drop takes a spherical shape, secondly, even with slight inclinations of the anti-wettable surface, the drop rolls like a billiard ball, and thirdly, when rolling over the anti-wettable surface, the drop does not leave a wet mark.

Experiments were conducted on the formation of icicles on the edge of the roof of the model roof and on the assessment of the effectiveness of protection in accordance with the proposed method.

For experimental confirmation of the implementation and effectiveness of the proposed method, an experimental installation with a model roof with removable roof sheets was designed and manufactured, the diagram of which is shown in Fig.5.

The experimental setup included the following parts: base plate 1, rafters 2, crate 3, removable roof sheet 4, base 5.

The study of the protection of the roof from the formation of icicles was carried out as follows.

On the roof, placed on the base plate 1 and consisting of rafters 2 and crates 3, the roof 4 was strengthened, which was a sheet 200 × 200 mm in size. Using screws, the roof support plate 1 was attached to the base 5. The angle of inclination of the roof to the horizon was chosen to be ~ 30 °. Using wire clamps, a polyethylene water bottle (not shown in FIG. 5) was fixed on the roof, in the bottom of which a hole was drilled for air supply. Another hole ~ 1.2 mm in diameter was drilled in a screw cap. The water supply was controlled by throttling the air inlet with a conical wooden stick. Thus, an automatic supply of water droplets was carried out. The distance from the lower edge of the roof to the place where drops fell from the cover was ~ 120 mm. In the experiments, the ambient temperature ranged from -8 ÷ -10 °. The total experiment time in each case was ~ 2 hours. As an experimental roof, sandpaper on a textile basis was used.

Figure 6 shows a photo of the icicle formed on the edge of the roof after the experiment: the length of the icicle was ~ 120 mm

Since it was not possible to achieve good adhesion of graphite powder to an inclined model roof (water droplets washed it off in the first minutes), a graphite lubricant (GOST 3333-80) was used as a palliative hydrophobic coating, in which the graphite content was increased from 10 to ~ 20 % (let's call it modified graphite lubricant). It can be noted that graphite grease has a wide range of operating temperatures: - 40 ÷ + 60 ° С. Experiments with a single drop of water on such a surface showed that the contact angle was ~ 90 °. A drop of water did not roll as easily as it did on graphite powder, but when displaced, it left a wet mark. In the experiments, the bandwidth of the modified graphite lubricant deposited along the edge was varied. The best results (smallest icicle length) were obtained for a strip width equal to or greater than 50 mm, counting from the edge.

At small angles of inclination of the roof, the formation of icicles can occur on the lower surface of the roof near the edge. In these cases, it is advisable to apply a strip of hydrophobic coating on the lower surface.

Figure 7 shows a photo of an icicle formed on the edge after the experiment in the case of a strip of modified graphite lubricant 50 mm wide: its length was ~ 25 mm.

From a comparison of FIGS. 6 and 7 it follows that the application of a hydrophobic coating to the roof (with a relatively low value of the contact angle θ≈90 °) has already led to a significant (approximately 5-fold) decrease in the intensity of icicle formation.

Achieved technical result is that the claimed method eliminates the formation of icicles on the edge of the roof of the material object due to the application of a hydrophobic coating with a wetting angle of more than 120 °, while the coating is applied with a strip whose width is selected at least 50 mm, counting from the edge. As a result of applying such a coating, the roof surface of the roof acquires the anti-wettability property, i.e. the adherence of water to the surface is sharply reduced. A drop of water falling on such a surface will slide off it without sticking, i.e. will behave like a drop of mercury. And the closer the contact angle to 180 °, the stronger the anti-wettability effect will be. In this case, the seemingly paradoxical effect of the disappearance of the boundary layer will appear, which, as is known, arises on the surface of an object moving in water due to the hydrophilicity of the surface.

Thus, the use of the claimed invention in the national economy of the country can give a significant economic effect, as it will allow to avoid many damage and accidents, such as falling icicles from the edges of roofs.

Claims (1)

A method of protecting a roof of a material object from the formation of an icicle on its edge, namely, that a hydrophobic coating is applied to the roof surface of the roof, characterized in that the coating is selected with a contact angle of more than 120 °, at which the spherical drop of water does not leave wet when rolling trace, while the coating is applied with a strip, the width of which is chosen at least 50 mm, counting from the edge.

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