Research on the Use of Reflective Thermal Insulation Coating on Railway Tracks and Wagons in Slovak Republic

Abstract

Global warming is a process in which the temperature of the entire planet gradually increases. High temperatures affect the surface of the material and cause undesirable effects such as damage because of overheating of the material. This article describes the use of reflective thermal insulation coatings on railway tracks abroad. Part of the article describes the method of applying reflective coatings to railway tracks. The article examines, analyzes, and evaluates the effect of a reflective thermal insulation coating on the railway track and railway wagon in the conditions of the Slovak Republic.

1. Introduction

Thermal insulation coatings are thermoceramic coating materials that function on an acrylic base and are available in various color shades. These coatings consist of three main components: binder, filler, and pigment. The binder is a highly elastic acrylic resin that, when exposed to UV radiation, forms a dual-network structure. The filler is in the form of microceramic hollow spheres, which contain an inert gas filling. The pigment is typically white and in the form of titanium dioxide, which can be tinted to any desired shade if necessary [1].

The thermal insulating properties of the coating are provided by the microceramic hollow spheres with the inert gas filling. The thermal insulation coating primarily ensures high reflectivity of solar radiation that acts upon it. A total of 86% of the coating is capable of reflecting solar rays into space, thereby reducing material overheating. The binder and filler of the thermal insulation coating prevent the penetration of atmospheric water and air moisture into the material while allowing evaporation, thereby regulating the moisture content of the substrate with absorptive and diffusive capabilities and increasing the thermal resistance of the entire structure. The high elasticity of the coating prevents the formation of cracks when applied to any surface. The application itself can extend the lifespan of the material [2].

The typical product based on this technology is the IndustrySpecial coating. It is an industrial coating ready to use, based on the thermal ceramic coating technology. IndustrySpecial for tank coating is a resistant protective coating suitable for use on almost all surfaces in industrial sectors. The special composition of ThermoShield IndustrySpecial provides a wide range of energetic application areas for thermal shielding in summer [3].

The key properties of this coating are variable diffusion, high resistance to aggressive environmental influences such as smog and ozone, low emissions, free of solvents, high UV and weather resistance, reflective, very high color resistance, waterproof, expandable, and thermally comforting.

The material data are as follows [4]:

• − Sd values according to DIN 52615: dry area: sd = 0.58; wet area: sd = 0.42;
• − Density of 1.04 kg/dm³, according to ISO 2811-1;
• − Fire behavior: C-s1, d0;
• − Sunlight reflection: 84%, according to DIN 67507;
• − Chemical resistance: available upon request.

2. Application of Reflective Thermal Insulation Coating on Railway Tracks

In practice, a special machine is used for applying the reflective thermal insulation coating. The individual parts of the machine are depicted and explained in Figure 1. The machine can generally be divided into three parts as follows [5,6]:

• Rough cleaning mechanism based on the use of sandblasting: This mechanism is responsible for cleaning the surface before applying the coating. It uses the principle of sandblasting, where abrasive particles (usually sand or similar materials) are propelled at high speed onto the surface to remove dirt, debris, and old coatings and prepare the substrate for the application of the thermal insulation coating.
• Soft cleaning mechanism based on the use of high-pressure air: This mechanism utilizes high-pressure air to clean the surface further. It helps to remove any remaining particles, dust, or loose materials that might affect the adhesion of the coating. The high-pressure air is directed onto the surface, effectively blowing away the contaminants.
• Application of the thermal insulation coating: This part of the machine is responsible for applying the reflective thermal insulation coating onto the prepared surface. The coating material is typically stored in a reservoir, and it is applied using a spraying mechanism. The spraying mechanism ensures an even and uniform application of the coating onto the surface, maximizing its effectiveness in reflecting solar radiation and providing thermal insulation.

These three parts work together to achieve proper surface preparation and application of the reflective thermal insulation coating, ensuring the best possible performance and longevity of the coating.

In Figure 1, the numbered parts represent the various components of the machine that apply the reflective thermal insulation coating to the railway tracks as follows:

• Sand supply module: This part of the machine is dedicated to supplying the abrasive material, typically sand, which is used for the cleaning process.
• Air supply module: This component focuses on providing high-pressure air, which is utilized for cleaning and removing any excess materials from the surface.
• Thermal insulation coating supply module: This component is responsible for supplying the reflective thermal insulation coating material.
• Wheels: This part represents the wheels of the machine that move along the railway tracks, allowing the application process to take place.
• Nozzles for sand cleaning: These nozzles ensure the cleaning of the railway tracks using the abrasive material (sand). They direct the sand particles onto the surface to remove dirt, debris, and old coatings.
• Nozzles for air cleaning: These nozzles are designed to remove excess sand and waste materials from the surface using high-pressure air. They help ensure a clean and properly prepared surface for the coating application.
• Nozzles for applying the thermal insulation coating: These nozzles are responsible for applying the reflective thermal insulation coating onto the railway tracks. They distribute the coating material onto the surface evenly, allowing their effective heat reflection and thermal insulation.

Figure 2 shows the mechanism and principle of cleaning rails through nozzles. Figure 2 shows the individual components of the machine that ensure the cleaning of the railway tracks using sand. The letter A shows the machine wheels, which lie on the rails. The letter B indicates the body of the machine on which the sand containers are located. The letter C indicates the nozzles that ensure the cleaning of the rails. The letter D shows the dispersion of the nozzles that clean the rails. Each nozzle is tasked with cleaning 1/3 of the rail surface to ensure the overall cleaning of the rail. The letter E shows the rails themselves, and under the symbol F, there is a clamp with a screw that fastens the rails to the base.

Figure 3 shows the numbered individual parts of the machine, which ensure the cleaning of the rails with the help of pressured air. The only change in Figure 2 is the number of nozzles on the sides of the railway tracks.

Figure 4 shows the numbered individual parts of the machine, which ensure the application of the thermal insulation coating to the rails. The application of the thermal insulation coating must be conducted in two layers [7,8]. The uniform coating surface’s thickness with the prescribed tolerance is ensured by the constant coating machine’s working velocity.

Figure 5 shows the above-described special machine during the implementation of the reflective thermal insulation coating on railway tracks in Switzerland [9].

3. Utilization of Reflective Thermal Insulation Coatings on Railway Tracks Abroad

Rhätische Bahn is the largest private railway company in Switzerland. They have applied thermal insulation coatings to their railway tracks. The tracks tend to expand when they reach temperatures of 60 °C. The tracks are considered neutral when laid at temperatures ranging from 27 °C to 29 °C, depending on the climatic conditions in the region. The application of thermal insulation coatings has resulted in a temperature reduction of approximately 30% for the railway tracks during high temperatures. The coating significantly reduces the expansion force on the tracks. It is also important to consider the surroundings of the tracks (railway top), which emit a strong heat flow of up to 30 cm above the ground level [9].

Deutsche Bahn conducted a practical test of thermal insulation coatings on railway tracks on the Pfieffe viaduct in Melsungen, located in northern Hesse, on the high-speed line of Hannover. Ronald Pofalla, a member of DB’s executive board, stated: “Our passengers should have the opportunity to travel reliably by train in all weather conditions. Therefore, we ensure that the railway tracks and technologies function reliably even in very hot weather. The impacts of climate change pose a challenge for us to explore new possibilities and technologies and to venture down new paths. White rails are one of these new paths”. Deutsche Bahn recognizes the importance of addressing the challenges posed by climate change and ensuring reliable railway operations under changing weather conditions. The practical test of thermal insulation coatings on railway tracks reflects their commitment to exploring innovative solutions and technologies to improve the performance and resilience of their rail infrastructure. The use of white rails, which can be achieved through thermal insulation coatings, is one such approach being explored to mitigate the effects of high temperatures on the tracks. The Pfieffe viaduct has a track length of 812 m. The thermal insulation coating was applied at only one section of the track to compare the temperatures of the track with and without the coating. Temperature sensors were then installed, and the track temperatures were compared. The research lasted for 10 months. The evaluation of the test demonstrated that the thermal insulation coating effectively protected the track from overheating, although regular renewal of the coating is necessary. Through this test, DB proved the effectiveness of thermal insulation coatings and subsequently applied the coating to the second section of the track as well [10,11].

Österreichische Bundesbahnen applied a thermal insulation coating from ClimateCoating on a section of railway track in Vorarlberg, covering the rails with white paint to reduce the temperature of the railway tracks by approximately 5 °C to 8 °C. The application of the coating aims to counteract the increased heating of the tracks due to climate change and prevent damage such as rail deformation. These measures serve as strong evidence that climate change has already taken place and that it is crucial to be more proactive in addressing its effects [12].

4. Research on the Impact of Reflective Thermal Insulation Coatings on Rail Tracks in the Conditions of Slovakia

For the research on the impact of reflective thermal insulation coatings, a sidetrack measuring 9 m in Žilina Railway Station was tested. Both the base and reflective thermal insulation coatings for the research were provided by ClimateCoating—HFR, LLC, Zilina, Slovakia. In Figure 6a, the railway tracks are shown before the application of the thermal insulation coating. The provided rails were affected by corrosion, which had to be removed before the actual application of the reflective thermal insulation coating. The removal of corrosion was conducted using an electric grinder along the all 9 m length. Figure 6b shows the rail surface before and after cleaning. The cleaning and application were carried out manually and took two days to complete. After the application of the coating, temperature measurements were conducted over a period of 1 to 5 days. Days with high temperatures were selected for the measurements (

Table 1. The summarized data from the railway track measurements.

Railway Track
Day	Date	Time	Ambient Temperature (°C)	Temperature of the Railway Track without Coating (°C)	Temperature of the Railway Track with Coating (°C)	Temperature Difference (°C)
1	2023-08-11	13:21	27.1	40.3	35.2	5.1
2	2023-08-12	12:00	24.7	44.4	28.8	15.6
3	2023-08-16	13:18	30.4	51.5	36.8	14.7
4	2023-08-17	13:10	32.5	51.5	35.7	15.8
5	2023-08-18	13:50	33.2	53.5	38.7	14.8

).

After the removal of corrosion, it was necessary to apply a base primer (RustPrimer), to protect the railway track from unwanted corrosion. Once the base primer had sufficiently cured and dried, the thermal insulation coating (IndustrySpecial) was applied to the railway track in two sprayed layers.

Figure 7 shows the final coating of the test rail.

The temperature of the tested rail was measured over a period of 5 days using the non-contact infrared thermometer, Fortum 4780401. The thermometer is suitable for the non-contact measurements of surface temperatures of objects in a temperature range from −50 °C to +800 °C with a resolution of 0.1 °C and a measurement accuracy with an uncertainty of 1.5 % from the measured value +2 °C.

Figure 8a captures a measurement of a railway track that does not have a thermal insulation coating applied. The measured rail temperature was 51.5 °C. Figure 8b captures the measurement of a rail that has an applied thermal insulation coating. The measured value of the rail temperature was 35.7 °C.

The summarized data from the measurements from different days are provided in Table 1.

Table 1 shows a record of the temperature measurements that were carried out on the rails. On the first day of measurement, the temperature difference was low, only 5.1 °C. The temperature difference was caused by the fact that the rail was only coated with RustPrimer and not with IndustrySpecial’s definitive thermal insulation coating. It can be seen that the primer alone was able to reduce the temperature of the rail by 5.1 °C. The other measurements were recorded after the final coating of IndustrySpecial was applied.

5. Research on the Impact of Reflective Thermal Insulation Coatings on Railway Wagons in the Conditions of Slovakia

The temperatures of the wagon surfaces were also measured by the non-contact infrared thermometer, Fortum 4780401. The thermometer is suitable for the non-contact measurements of surface temperatures of objects in a temperature range from −50 °C to +800 °C with a resolution of 0.1 °C and a measurement accuracy with an uncertainty of 1.5% from the measured value +2 °C.

The external and internal temperature and relative humidity (rH) measurements were performed using the Wireless Thermo-Hygrometer with three Transmitter TFA KLIMA-MONITOR (30.3054) with a measurement range of up to 60 °C and a 99% outdoor rH and with a measuring range of up to 60 °C and 90% indoor rH.

The measuring sensors were inserted into the railway wagons to measure the internal temperature and humidity. The measurements were carried out on two identical railway wagons, one of which was treated with the thermal insulation coating while the other remained in its original state. On the first day of the measurements, at 11:47, measuring sensors were inserted into the wagons before the application of the thermal insulation coating. On the second day, at 15:50, cleaning and the application of the thermal insulation coating were performed. During this day, at 19:05, temperature measurements of the railway wagon, which had already received the first layer of thermal insulation coating, were conducted. At that time, the external temperature was 29.6 °C. The internal temperature of the railway wagon without thermal insulation coating was 36.3 °C, while the temperature of the wagon with the applied thermal insulation coating was 32.8 °C. The internal temperature difference between the wagons with and without the coating was 3.5 °C. The relative humidity recorded in the external environment was 41%. The relative humidity recorded on the measuring sensor in the internal spaces of the railway wagons without the thermal insulation coating was 32%, and the railway wagon with the thermal insulation coating had a relative humidity of 36%. On the third day, at 13:41, the final measurements of both the internal and external temperatures and relative humidity were conducted. The external temperature on that day was 30.3 °C. The external wagon surface temperature was measured in two parts of the railway wagon, the roof and the wall, by the non-contact infrared thermometer. A temperature of 78.3 °C was recorded on the roof of the railway wagon without the thermal insulation coating, and a temperature of 61.2 °C was recorded on the wall of the railway wagon without the thermal insulation coating. The internal temperature of the railway wagon without the thermal insulation coating was 34.7 °C. The external temperature of the railway wagon was also measured on the roof and the wall of the structure. The temperature on the roof of the railway wagon with the thermal insulation coating was 38.7 °C, and the temperature on the wall was 34.2 °C. The internal temperature of the railway wagon with the applied thermal insulation coating was 26.8 °C. The internal temperature difference between the observed railway wagons was 7.9 °C, and the external temperature difference on the roof was 39.6 °C. The temperature difference of the wall of the railway wagon was 27 °C. The external humidity on that day was 39%, the internal humidity of the railway wagon without the thermal insulation coating was 43%, and the internal humidity of the railway wagon with the thermal insulation coating was 51%.

Table 2. Record of measurements of the railway wagons.

Railway Wagon
Day	Date	Time	Ambient Temperature (°C)	Temperature of the Wagon without Coating (°C)		Temperature of the Wagon with Coating (°C)		Relative Humidity (%)
				External	Internal	External	Internal	External	Internal 0	Internal 1
1	2023-08-03	11:47	22.4	-	44.2	-	-	56	15	-
2	2023-08-04	15:50	30.3	-	37.2	-	-	33	35	-
2	2023-08-04	19:05	29.6	-	36.3	-	32.8	41	32	36
3	2023-08-05	13:41	30.3	78.3	34.7	38.7	26.8	39	43	51

lists the complete temperature measurement process for the two railway wagons, where an examination of thermal insulation coatings from ClimateCoating was conducted.

In Table 2, the highlighted row represents the highest internal and external temperature difference recorded for the railway wagons. The internal temperature difference between the railway wagons was 7.9 °C on day 3. The external temperature difference was 39.6 °C on the roof and 27 °C on the wall of the wagons. The cell labeled “Internal 0” shows values of internal relative humidity without the thermal insulation coating, and the cell labeled “Internal 1” shows the values of internal relative humidity with the thermal insulation coating. Figure 9 displays a comparison of the internal and external temperatures of the railway wagons in the measured case.

In Figure 10, measurements of the roof temperature of the tested railway wagon are captured.

In Figure 11, measurements of the wall temperatures of the tested railway wagon are captured.

In Figure 12, there is a measuring station, which records the internal temperature and humidity from the sensors located in the ambient and in the wagon, where:

• Channel 1 records the external temperature and humidity near the railway wagon;
• Channel 2 records the internal temperature and humidity of the railway wagon without the thermal insulation coating;
• Channel 3 records the internal temperature and humidity of the railway wagon with the thermal insulation coating;
• Channel IN calculates the average values.

This measuring station precisely captured the highest internal temperature difference between the railway wagons, which was 7.9 °C. The optimal relative humidity level in the space should be around 50%. The railway wagon without the thermal insulation coating had a relative humidity level of 43%, while the wagon with the applied thermal insulation coating had a relative humidity level of 51%. The thermal insulation coating reduced not only the internal and external temperatures of the railway wagon but also optimized the relative humidity level in the space.

6. Application Costs Estimation

The expected costs for applying the surface treatment in Slovakian conditions were calculated for various alternatives of the initial condition of treated rails and wagons and the resulting complexity and type of work.

Thermoshield IndustrySpecial has a coating coverage of 1.15 m² coated surface per 1 L. The average price of the coating was set at EUR 19.80 per 1 L (approx. EUR 17.22 per 1 m²). The labor costs for the coating application were estimated to be EUR 2.60 per 1 m² for the rail tracks (applied by the semi-automatic machine) and EUR 2.80 per 1 m² for the wagon surfaces (applied manually). If there is a necessity to sand the steel surface, the approximate price for 1 m² of sanded surface was estimated to be EUR 10.50 per 1 m², including the labor and material costs.

The surface of the standard rail track is approx. 0.92 m² per 1 m (920 m² per 1 km). The total estimated costs for the coating applied on new railway tracks with no need for sandblasting are estimated as

$$C_{RT,new}=920·\left(17.22+2.60\right)=\mathrm{E}\mathrm{U}\mathrm{R}18234.40\mathrm{p}\mathrm{e}\mathrm{r}1\mathrm{k}\mathrm{m}.$$

(1)

The total estimated costs for the coating applied on old railway tracks, including the sandblasting, are estimated as

$$C_{RT,old}=920·\left(17.22+10.50+2.60\right)=\mathrm{E}\mathrm{U}\mathrm{R}27894.40\mathrm{p}\mathrm{e}\mathrm{r}1\mathrm{k}\mathrm{m}.$$

(2)

The total estimated costs for the coating applied on new railway wagons with no need for sandblasting are estimated as

$$C_{RW,new}=\left(17.22+2.80\right)=\mathrm{E}\mathrm{U}\mathrm{R}20.02\mathrm{p}\mathrm{e}\mathrm{r}1{\mathrm{m}}^2.$$

(3)

The total estimated costs for the coating applied on old railway wagons, including the sandblasting, are calculated as

$$C_{RW,old}=\left(17.22+10.50+2.80\right)=\mathrm{E}\mathrm{U}\mathrm{R}30.52\mathrm{p}\mathrm{e}\mathrm{r}1{\mathrm{m}}^2.$$

(4)

The estimated prices can, of course, vary depending on the prices of the coatings, sandblasting and labor costs, as well as on the size of the applied area, especially in the case of wagons.

7. Conclusions

It has already been demonstrated abroad (especially in Switzerland) that the use of thermal insulation coatings on surfaces in railway transportation makes sense. The functionality of thermal insulation coatings has been confirmed, and the research has demonstrated excellent product properties at high temperatures. In Switzerland, the temperature testing was conducted on rail tracks. The temperature difference between rail tracks with the applied thermal insulation coating and those without was stated to be 13.8 °C [9].

In Slovakia, the application of thermal insulation coatings on rail tracks and railway wagons was utilized. The impact of the thermal insulation coatings on rail tracks showed its high effectiveness. The temperature difference between the rail tracks with the applied thermal insulation coating and those without was 15.8 °C. By using thermal insulation coatings on the railway wagon, a reduction in internal temperature would be achieved, thereby reducing the costs of air conditioning or heating of the railway wagon. The temperature difference in the internal temperature of the railway wagon—which had a thermal insulation coating on its external surface—and the wagon without it was 7.9 °C. Additionally, the average humidity of the internal wagon space was optimized by using the thermal insulation coating on the railway wagon during the summer months. The maximum temperature difference between the external surface of the railway wagon with the thermal insulation coating and the wagon without it was 39.6 °C, so the functionality of thermal insulation coatings on selected technical equipment in railway transportation has been confirmed for Slovakian railways, too.