**3. Fogging Test Technology for Automotive Interior Materials**
**3.1 The Danger of Fogging**
Volatile substances found in automotive interior materials can evaporate when exposed to heat and then condense on the windshield, creating a fog-like layer. This phenomenon, known as fogging or "knotting," occurs when volatile compounds condense on glass surfaces inside the vehicle. The condensed material is referred to as the "condensing component."
Fogging can impair visibility through the windshield, especially under poor lighting conditions, which poses a serious risk to driving safety. Additionally, these condensing components are often harmful organic volatiles, making the fogging level an indicator of the amount of such substances present in the materials. As a result, automotive manufacturers in developed countries have established strict limits on fogging levels for interior materials.
**3.2 Development of Fogging Test Technology**
In the 1970s, major European automobile manufacturers began researching the fogging characteristics of interior parts. By the early 1980s, the German Automobile Standards Drafting Committee and the Synthetic Materials Standards Committee formed a working group focused on fog formation. They systematically studied test methods and reproducibility. In 1992, DIN 75 201 was published, titled *"Determination of the windscreen fogging characteristics of trim materials in motor vehicles."*
Subsequently, the American Society of Automotive Engineers (SAE) and the International Organization for Standardization (ISO) revised DIN 75 201, resulting in standards such as ISO 6452 and SAE J1756. Based on these standards, leading automotive companies worldwide have developed their own internal specifications for fogging testing, setting clear requirements for the fogging performance of interior components.
**3.3 Test Method Principle**
The fogging process involves the evaporation of volatile substances from automotive interior materials when heated. These vapors then condense on a cooled surface, forming a visible layer. This vaporization-condensation process is the core of the fogging test.
During the test, a sample is placed in a fog cup, covered with a seal ring and a glass plate (or a pre-weighed aluminum foil), and a cooling system is installed. The fog cup is heated in a thermostat, causing the volatile substances to evaporate and condense on the cooled surface. After the condensation process, the glass plate or aluminum foil is removed. The gloss value of the glass is measured using a gloss meter and compared with its initial value to determine the fogging value. Alternatively, light transmittance is measured before and after the test to calculate haze. For the condensation weight method, the aluminum foil is weighed before and after the test to determine the mass of the condensed volatile substances.
**3.4 Test Equipment**
The primary equipment used in fogging tests includes a fogger, a gloss meter, and a high-precision balance. The fogger consists of a temperature-controlled chamber, a cooling system, and a fog cup. The structure of the fogging tester is illustrated in Figure 3-1. Depending on the test method, either a glass plate or an aluminum foil is used.
- **Temperature Control Chamber**: Heats the fog cup to a specified temperature (typically 60–120°C) with an accuracy of ±0.5°C and reaches the target temperature within 20 minutes.
- **Cooling Section**: Cools the glass or aluminum foil to a controlled temperature (usually 20–60°C) with an accuracy of ±1°C. The cooling surface must be flat and made of non-corrosive material.
- **Fog Cup**: Made of glass or stainless steel, with a smooth surface. The size varies depending on the standard being followed.
**3.5 International and Foreign Standards and Requirements**
Several international and national standards govern the measurement of fogging in automotive interior materials. Key standards include:
- **ISO 6452**: *Rubber- or plastics-coated fabrics – Determination of fogging characteristics of trim materials in the interior of autos.*
- **DIN 75201**: *Determination of the windscreen fogging characteristics of trim materials in motor vehicles.*
- **SAE J1756**: *Test procedure to determine the fogging characteristics of interior automotive materials.*
These standards provide detailed procedures for measuring fogging and are widely adopted by automotive manufacturers globally.
**3.6 Standards and Requirements for Major Foreign Automobile Companies**
Major global automakers have also established their own internal standards for fogging testing. Examples include:
- **Volkswagen**: PV3920 (Measurement of haze value of non-metallic interior materials), PV3015 (Determination of condensed components).
- **Mitsubishi**: ES-X83231 (Standard test method for fogging of interior materials).
- **Nissan**: NES M0161 (Test method for fogging of interior materials).
- **Peugeot Citroën**: D45 1727 (Indoor cabin and accessories material atomization – water and gas condensation).
- **General Motors**: GM9305P (Determination of fogging characteristics of automotive interior materials).
- **Ford**: Follows SAE J1756 as a reference.
- **Toyota**: TSM0503G (Test method for glass fuzziness of non-metallic materials).
The main parameters measured in these tests include the gloss retention of the glass, the reduction in light transmittance (haze), and the mass of the condensate. These metrics help ensure that interior materials meet safety and quality standards.
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