In humid environments (such as underground garages, high-humidity areas during the rainy season, and coastal salt spray environments), automobile control cables is prone to mold spots due to mold growth, which can lead to insulation corrosion, increased resistance, and even short-circuit faults. Mold spot treatment should take into account both "eliminating existing mold" and "inhibiting future growth", while avoiding damage to the cable insulation material. The following is a systematic explanation from four aspects: the causes and assessment of mold spots, the treatment process of mold spots, the selection and spraying of fungicides, and long-term protection strategies

I. Mechanism and Evaluation of Mold Spot Formation

The core conditions for mold growth

Mold growth requires the simultaneous satisfaction of "four elements" :

• Moisture: Environmental humidity > 75%RH or condensation on the cable surface;

• Nutrient sources: Organic substances in the cable insulation layer (such as PVC plasticizers, rubber hydrocarbons, polyester/polyether components in TPE), surface oil stains or dust;

• Temperature: 20-30℃ (optimal breeding temperature);

• Oxygen: A regular atmospheric environment is fine.

The insulating layer (PVC, rubber, TPE, etc.) of automobile control cables contains a lot of the above organic substances and is prone to absorb moisture in a humid environment, making it an ideal "culture medium" for mold.

2. Classification of mold spot severity and priority of treatment

Mold spot grade, manifestation characteristics, risk level, handling priority

Grade I (mild) : Scattered white/green mold spots on the surface that have not penetrated the insulation layer should be cleaned in time

Grade II (moderate) large-scale mold spots (diameter > 5mm), slight discoloration of the insulation layer (turning gray), cleaning + anti-mold treatment

Grade III (severe) Mold spots penetrate the insulation layer (internal mold can be seen when scratched), the insulation layer becomes brittle/cracked, and the cable needs to be replaced (cannot be completely repaired).

Ii. Mold spot treatment process: Cleaning and drying

1. Selection of cleaning agents: Balancing sterilization, mold removal and material compatibility

The cleaning agent should meet the requirements of "efficiently killing mold (spores), dissolving mold spots and organic matter, not corroding the insulation layer, and having low residue". The specific selection should be based on the cable insulation material:

The recommended cleaning agent for insulating materials, its working principle, contraindications and precautions

PVC chlorine-containing disinfectant (5% diluted sodium hypochlorite)

Quaternary ammonium salts (0.1% benzalkonium bromide) chloride destroys mold cell membranes

Cationic surfactant bactericidal concentration < 5% (to avoid PVC swelling), thoroughly neutralize after cleaning (sodium carbonate solution)

Rubber (EPDM) peroxide type (hydrogen peroxide 3%)

Silicon-based anti-mold cleaner oxidizes and decomposes mold organic matter

Physically removes mold spots. Avoid strong acidic cleaners (such as hydrochloric acid) to prevent damage to the rubber vulcanization layer

TPE enzyme preparation cleaner (protease + amylase compound)

Ethanol (75%) Enzymatic hydrolysis of organic matter mold spots

Fast evaporation, low residue. Avoid strong polar solvents (DMF) to prevent TPE swelling

General operation skills

First, remove the surface mold with a soft-bristled brush or compressed air (0.3MPa), and then wipe it with a non-woven fabric soaked in detergent.

For severe mold spots, soak in a cleaner for 10 to 15 minutes (if the cable is undamaged), and then rinse off the residue with deionized water after soaking.

2. Thorough drying: The key to preventing mold regrowth

If moisture remains after cleaning, mold may recur within 24 to 48 hours. It is necessary to ensure that the insulation layer is completely dry.

• Natural drying: When the ambient temperature is 25℃ and the humidity is less than 60%, lay the cable flat (avoid bending) and let it stand for 48 to 72 hours.

• Forced drying: Use a hot air gun (≤60℃) to blow evenly at a distance of 20cm from the cable, or maintain the temperature in an oven (50-70℃) for 2-4 hours (the temperature of the insulation layer needs to be monitored to avoid aging due to temperature exceeding 80℃).

• Drying verification: Measure the moisture content inside the insulation layer with a hygrometer (it should be less than 5%), or test the insulation resistance with a megohmmeter (it should be restored to more than 90% of the initial value after drying).

Iii. Selection of Fungicides and Spraying Process

Core performance requirements for fungicides

• Broad-spectrum bactericidal: Inhibits common molds such as Aspergillus Niger, Penicillium, and Trichoderma;

• Material compatibility: Does not swell or corrode the insulation layer, and does not affect the insulation resistance;

• Durability: Resistant to migration and aging, with a protection period of ≥1 year;

• Safety: Low toxicity, no pungent odor, in compliance with RoHS/REACH standards.

2. Types of fungicides and applicable scenarios

The types of fungicides, representative components, advantages and disadvantages, and suitability for cable materials

Organic fungicide isothiazolinone (MIT/CIT)

benzimidazole (carbendazim) has a broad-spectrum bactericidal effect and takes effect quickly. It may migrate to adjacent components and is prone to failure after long-term use. PVC, TPE (non-food grade)

Inorganic fungicide nano-zinc oxide (ZnO)

Silver-loaded zirconium phosphate is heat-resistant, migration-resistant, and long-lasting (> 2 years). The color is slightly white, which may affect the appearance of rubber and dark insulating layers

Natural fungicide tea tree oil extract

Chitosan is environmentally friendly, low-irritating, but has a low bactericidal efficiency and a short protection period (< 6 months). It is suitable for scenarios with high environmental protection requirements

3. Anti-mold agent spraying process

Surface pretreatment

After cleaning and drying, gently sand the surface of the insulation layer with sandpaper (320 mesh) to increase roughness and enhance adhesion, and then wipe it with alcohol to remove oil stains.

Before spraying, ensure that the environmental humidity is less than 60% and the temperature is between 15 and 30 degrees Celsius (to avoid condensation water affecting the adhesion of the coating).

(2) Spraying parameters

• Tools: Electrostatic atomizing spray gun (atomizing particle size 10-20μm to ensure uniform coating);

• Distance: The distance between the spray gun and the cable should be 15 to 20cm, and spray at a 45° Angle in a cross pattern.

• Thickness: The dry film thickness should be controlled at 5 to 10μm (if it is too thin, it will be ineffective; if it is too thick, it may clog the micro-pores of the insulation layer and affect heat dissipation).

• Curing: Cure at room temperature for 24 hours, or heat at 60℃ for 1 hour (inorganic fungicides require high temperature to promote bonding with the material).

Iv. Long-term Protection Strategies and Verification

Prevention during the design and installation phases

• Material selection: Prioritize the use of insulating layers with added fungicides (such as PVC containing 0.5% zinc oxide), or mold-resistant rubber (a blend of EPDM and fungicides);

• Sealed protection: Waterproof joints (IP67 grade) are installed at the cable entrance, and the cable routing paths are sealed with corrugated tubes/heat shrink tubes to prevent direct exposure to high-humidity environments.

• Layout optimization: Avoid having cables close to damp areas (such as air conditioning drain pipes, car door drainage channels), and reserve ventilation gaps.

2. Regular maintenance and inspection

• Inspection cycle: In high-humidity environments, inspections should be conducted every three months, with a focus on areas prone to condensation such as the engine compartment and chassis.

• Rapid detection: When the insulation layer is irradiated with an ultraviolet lamp (365nm), the metabolic products of mold will emit fluorescence (facilitating the early detection of tiny mold spots).

• Performance verification:

• Insulation resistance: Measured with a 1000V megohmmeter, it should be ≥100MΩ (standard value);

• Anti-mold effect: The treated cables are placed in a constant temperature and humidity chamber (28℃, 95%RH) for 14 days of cultivation. If no new mold spots grow, they are considered qualified.

V. Precautions

• Avoid over-cleaning: Frequent use of strong solvent cleaners will accelerate the aging of the insulation layer. It is recommended to conduct deep cleaning no more than twice a year.

• Risk of fungicide migration: Organic fungicides are prohibited in food contact scenarios (such as car refrigerator cables), and inorganic or natural types should be preferred.

• Safety precautions: Wear nitrile gloves and goggles during construction. In poorly ventilated environments, wear a gas mask (especially when using chlorine-containing cleaners).

Summary

In a humid environment, automobile control cables mold spot treatment requires "thorough cleaning first (targeted cleaning agent + drying), followed by long-term protection (suitable anti-mold agent spraying)". Combining material compatibility, environmental humidity control and regular maintenance can effectively inhibit mold regrowth. The core lies in balancing "sterilization efficiency" and "material safety" to prevent permanent damage to insulation performance due to improper handling. Ultimately, long-term reliability is verified through insulation resistance tests and damp heat aging tests.