ASTM C518 thermal conductivity meets the standard process of PC41 spray-coated polyurethane insulation layer in cold chain storage
ASTM C518 thermal conductivity meets the standard process of PC41 in cold chain storage polyurethane spray insulation layer
1. Introduction: A contest about “cold”
In this fast-paced era, cold chain logistics has become an indispensable part of modern life. Whether it is fresh fruits and vegetables, or exquisite ice cream desserts, they need to be transported and stored in a low temperature environment. And in this race against time, insulation materials play a crucial role. Just like wearing a warm coat for cold food, it can effectively isolate external heat and keep the food in good condition at the right temperature.
Among many insulation materials, Polyurethane (PU) stands out for its outstanding performance and becomes a star player in the cold chain warehousing field. However, choosing the right material is not enough, and how to ensure that its insulation effect meets international standards is the real challenge. This is the topic we are going to discuss today – the ASTM C518 thermal conductivity compliance process of PC41 polyurethane spray insulation layer.
ASTM C518 is an internationally versatile standard test method for determining the thermal conductivity of materials under steady-state heat flux and temperature difference. Simply put, it is a ruler for measuring insulation performance. Only by passing this standard inspection can we prove that our insulation layer truly meets the industry requirements. So, how to achieve this? Next, we will comprehensively analyze the application of PC41 in cold chain warehousing and its compliance process from theory to practice.
In order to let everyone better understand this process, this article will use easy-to-understand language, combined with vivid and interesting metaphors and rigorous data support, striving to be both professional and fun. At the same time, we will also refer to a large amount of domestic and foreign literature to provide readers with detailed background knowledge and specific operation suggestions. Whether you are an industry expert or a beginner, you can benefit greatly from it. Now, let us enter the world of polyurethane together and unveil its mysterious veil!
2. Basic characteristics of PC41 polyurethane spray insulation layer
(I) Definition and Classification
PC41 is a rigid polyurethane foam (Rigid Polyurethane Foam) specially used for cold chain storage, produced by reaction of isocyanate and polyol. According to the parameters such as density and closed porosity, PC41 can be divided into many types, including high-density type, low-density type and enhanced type. These types of choices depend on the specific usage scenario and requirements.
Taking cold chain storage as an example, PC41 is usually used as a thermal insulation material for cold storage walls, roofs and floors. Its main function is to prevent external heat from entering the cold storage, thereby maintaining a stable low-temperature environment. If the cold storage is compared to a huge refrigerator, then the PC41 is the “thermal insulation wall” of this refrigerator, it is like a solid barrier.Keep hot air out.
(II) Interpretation of core parameters
1. Density
Density is one of the important indicators for measuring PC41’s performance, usually expressed in kg/m³. Generally speaking, the higher the density, the greater the mechanical strength of the material, but the thermal conductivity will also increase accordingly. Therefore, in practical applications, a balance point needs to be found. The following are several common density ranges and their applicable scenarios:
| Density range (kg/m³) | Features | Applicable scenarios |
|---|---|---|
| 30-40 | Light weight, low thermal conductivity | Roof insulation |
| 40-60 | Excellent comprehensive performance | Wall insulation |
| 60-80 | High strength, strong compressive resistance | Floor insulation |
2. Thermal conductivity
Thermal Conductivity is the core parameter for measuring the insulation properties of a material, usually expressed in units of W/(m·K). For PC41, the lower its thermal conductivity, the better the insulation effect. According to the ASTM C518 standard, the thermal conductivity of a qualified PC41 should be less than 0.024 W/(m·K). This means that even if the temperature outside changes drastically, the interior of the cold storage can remain relatively stable.
3. Coverage rate
Closed cell ratio refers to the proportion of the volume of closed air bubbles in the material. Higher closed porosity helps reduce moisture penetration and improve thermal insulation effect. The closed-cell rate of high-quality PC41 is generally above 95%, which makes it able to resist the influence of humid environment and extend its service life.
4. Compressive strength
Compressive strength reflects the performance of the material when it is subjected to external pressure. This is especially important for ground insulation. For example, when forklifts frequently enter and exit the cold storage, the ground insulation layer must have sufficient compressive resistance to avoid deformation or damage.
| parameter name | Unit | Typical value range | Remarks |
|---|---|---|---|
| Density | kg/m³ | 30-80 | Adjust to use |
| Thermal conductivity | W/(m·K) | <0.024 | Complied with ASTM C518 standard |
| Closed porosity | % | >95 | Providing excellent waterproofing |
| Compressive Strength | MPa | 0.2-0.8 | Depending on the application scenario |
(III) Advantages and limitations of PC41
Advantages:
- High-efficiency insulation: Due to its ultra-low thermal conductivity, PC41 can achieve ideal insulation effect at a smaller thickness.
- Convenient construction: Use spraying technology to quickly cover complex surfaces, saving time and cost.
- Strong durability: PC41 can maintain good performance even if exposed to humid environments for a long time.
Limitations:
- Higher cost: Compared with traditional insulation materials (such as rock wool boards), the PC41 is slightly more expensive.
- High requirements for construction technology: During the spraying process, temperature, humidity and other factors need to be strictly controlled, otherwise the final effect may be affected.
III. Principles and methods for testing thermal conductivity of ASTM C518
Since it is mentioned that PC41 needs to meet the ASTM C518 standard, we have to understand the specific content of this test in depth. The full name of ASTM C518 is “Standard Test Method for Steady-State Thermal Transmission Properties by Means of the Guarded-Hot-Plate Apparatus” (a standard test method for measuring steady-state heat transfer characteristics through protective hot plate devices). Doesn’t it sound a bit difficult to pronounce? Don’t worry, we explain it in simpler language.
(I) Test principle
ASTM C518 is based on steady-state heat transfer theory and calculates its thermal conductivity by measuring the temperature difference and heat flow on both sides of the sample. Suppose we have a sandwich cookie with a layer of cream (representing insulation material) in the middle, and then heat and cool on the upper and lower two cookies respectively.. If we know how much heat is input and the temperature difference between the upper and lower biscuits, we can calculate the thermal conductivity of the cream. Similarly, the thermal conductivity of PC41 can also be obtained through a similar method.
(II) Test device
The test device mainly includes the following parts:
- Hot plate: As a heat source, a constant heat is provided to the sample.
- Cold plate: absorbs heat from the sample and maintains a low temperature environment.
- Protective panels: Surround the hot and cold panels to prevent heat loss at the edges and ensure accurate test results.
- Temperature Sensor: Monitor the temperature changes on both sides of the sample in real time.
The entire device is like a precision balance, accurately weighing the flow of heat.
(III) Test Steps
- Sample Preparation: Cut PC41 samples of a certain size (usually 300mm×300mm×50mm) and ensure that the surface is flat and free of defects.
- Installation and debugging: Place the sample between the hot plate and the cold plate, and adjust the device to the initial state.
- Data Collection: After starting the device, record the temperature and heat flow data over a period of time.
- Result calculation: According to the formula λ=Q/(A·ΔT), the thermal conductivity coefficient λ is calculated, where Q is the heat flow, A is the sample area, and ΔT is the temperature difference.
It should be noted that in order to ensure the reliability of the test results, each group of experiments is repeated at least three times and the average value is taken as the final result.
IV. Key control points of PC41 spraying process
To make PC41 meet the requirements of ASTM C518 standard, not only high-quality raw materials are required, but also exquisite construction technology is required. Here are a few key control points we have summarized:
(I) Raw material ratio
Polyurethanes are produced by the reaction of isocyanate and polyols, so their proportions directly determine the performance of the final product. Generally speaking, the isocyanate index (Index) should be within the range of 100±5. Too high index can cause the material to become brittle, while too low can affect the closed porosity.
(II) Environmental Conditions
Spraying operations are very sensitive to ambient temperature and humidity. The ideal working conditions are as follows:
- Temperature: 15-25℃
- Humidity:<85%
If the environment is too humid, it may cause condensation on the surface of the foam, which will affect the insulation effect.
(III) Spraying technology
The following aspects need to be paid attention to during the spraying process:
- Spray gun distance: Maintain an appropriate distance (about 60cm) to ensure uniform coating.
- Spraying angle: Perpendicular to the surface of the substrate to avoid uneven thickness due to angle deviation.
- Layered Spraying: The thickness of a single spray should not exceed 20mm, otherwise it may lead to poor internal curing.
(IV) Maintenance time
After the spraying is completed, sufficient time is required to allow the material to cure fully. Usually, subsequent construction can be carried out after 24 hours, but it may take about 7 days to complete curing.
5. Case analysis: Application in a cold chain warehousing project
In order to more intuitively demonstrate the application effect of PC41, we selected a practical case for analysis. The project is located in a city in southern China, with a total area of about 5,000 square meters and a designed temperature of -18℃.
(I) Project Background
The customer hopes to create a modern frozen warehouse for storing all kinds of frozen foods. After many comparisons, PC41 was finally selected as the insulation material. The main reason is its excellent insulation performance and convenient construction method.
(II) Implementation process
- Substrate treatment: Carry out comprehensive cleaning of walls, roofs and floors to ensure that the surface is clean and oil-free.
- Spraying Construction: In accordance with the above process requirements, spray PC41 layer by layer, with a total thickness of 100mm.
- Quality Test: After the construction is completed, a third-party organization is invited to conduct thermal conductivity tests in accordance with the ASTM C518 standard. The results show that all areas meet the design requirements.
(III) Effectiveness Assessment
After a year of actual operation, the cold storage performed well, and its energy consumption was reduced by about 20% compared to the traditional insulation solution. The customer is very satisfied with this and plans to continue to promote the application of PC41 in other projects.
VI. Conclusion and Outlook
Through the detailed analysis of this article, we can see that the PC41 polyurethane spray insulation layer has shown great potential in the cold chain warehousing field with its excellent performance. However, to give full play to its advantages, we must strictly control each and every time during the construction process.link. In the future, with the continuous advancement of technology, I believe that PC41 will shine in more fields.
Later, I borrow a classic saying as the end: “Success is not the end, courage is the real power to move forward.” May every practitioner be brave enough to move forward in his position and jointly promote the development of the industry!
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