Environmental Adaptability and Reliability (serialized) - Biological Tests

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3.2 Biological tests;

3.2.1 Mold test

Mold testing is a project of climate and environmental testing. Used to assess the ability of products or materials to resist mold invasion. It is similar to general environmental testing, considering the environmental conditions where the product is most susceptible to mold damage during actual transportation, storage, or use. The experiment is conducted in a laboratory using artificial simulation to create the most suitable environment for mold growth.

To determine the product's ability to resist mold erosion, it is necessary to develop a test method that is similar to the actual working conditions and can determine the erosion effect of mold and provide a correct evaluation. It will provide a basis for the selection, structure, and design of products to ensure safe and reliable operation in a climate environment with a large amount of mold present

failure mechanism

The direct harm of mold is the organic components in the materials it feeds on, leading to structural damage, decreased strength, and changes in physical properties. The indirect harm of molds is the secretion of metabolic excreta, organic acids, and other ionic compounds by molds, which cause electrolysis or aging effects. Some catalysts also promote oxidation or decomposition, indirectly leading to damage to materials and components. Failure mode caused by mold growth:

---Causing electronic or electrical equipment malfunction

---Reduce the electrical performance of insulation materials

---Causing corrosion and blockage of the fuel system

---Breaking the seal

---Causing corrosion of metal parts

---Etch the glass

The impact of the environment on mold

Low pressure and mold: The combination of these two factors will not increase the impact of the two themselves;

Solar radiation and mold: Because solar radiation generates heat, this combination cannot have an impact, just like the combination of high temperature and mold. In addition, the ultraviolet rays in unfiltered solar radiation have a significant bactericidal effect;

Salt mist and mold: This is a compatible combination;

Humidity and mold: Humidity helps the growth of molds and microorganisms, but does not increase their impact;

High temperature and mold: The growth of mold and microorganisms requires relatively high temperatures, but above 71 ℃ (160 ℉), mold and microorganisms cannot grow;

Low temperature and mold: Low temperature affects the growth of mold. At temperatures below zero, mold remains in a state of suspended animation

Fungus test method

1. Classification of mold tests:

♦ Natural exposure test: Direct exposure to selected humid and hot environments. There are methods for indoor and outdoor exposure tests and buried soil tests.

♦ Laboratory manual acceleration test: commonly used methods include wet chamber suspension method and inorganic salt agar plate method.

2. Selection of bacterial strains

♦ Aspergillus niger

♦ Aspergillus flavus

♦ Aspergillus variegatum

♦ Penicillium funiculosum

♦ Fusarium globosum


3. Preparation of test samples

♦ The mold test shall not use samples that have undergone salt spray, sand dust, and other tests.

♦ The test samples are generally not cleaned.

♦ The test sample needs to undergo a visual inspection before being tested, paying special attention to contaminated surfaces, defects, and any other conditions that may affect mold growth, and making detailed records.

♦ When performance testing is required for the test sample, it should be conducted according to the technical conditions of the test sample before testing, and the original data should be recorded.

♦ The test samples are generally placed on the sample rack of the mold box (room) in the state delivered by the entrusted testing unit (or according to relevant standards)

♦ Place the control sample vertically near the test sample, but do not come into contact with the test sample.

♦ Inoculate both the experimental and control samples simultaneously.

4. Control of mold test conditions

♦ temperature

♦ relative humidity

♦ wind speed

temperature control

♦ For a constant mold test, the temperature should be controlled at 29 ± 1 ° C;

♦ Control the alternating mold test at 30 ± 1 ° C for the first 20 hours; Control the relative humidity at a temperature of 25 ± 1 ° C for the next 4 hours

♦ For a constant mold test, the relative humidity should be controlled between 95% -99% C;

♦ For the alternating mold test, the first 20 hours were 95 ± 5%; The relative humidity for the next 4 hours is 100%


Wind speed control

♦ The wind speed in the working space of the wind speed control test equipment should be controlled between 0.5m/s-2m/s. The wind speed of the test chamber should ensure uniform temperature and humidity inside the test chamber. If the wind speed is too low, a temperature gradient inside the box will affect the growth of mold; If the wind speed is too high, the spores will fall off, causing the suspended sample to shake and shake off the spores, especially in the early stages of spore germination.

5. Inspection during the test process

♦ The first seven days are a critical period for the growth and development of mold spores. After seven days, check the mold growth of the control sample. When the mold coverage area reaches more than 90%, it indicates that the test conditions are suitable. Otherwise, it indicates that the test conditions are not suitable, and the test should be conducted again.

♦ After seven days, the degree of mold growth on the control sample should gradually increase in the experiment to prove its effectiveness. On the contrary, if the test proves invalid, the test should be invalidated.

6. Rating of test results

♦ Growth site

♦ Coverage area

♦ colour

♦ Growth form

♦ Growth density

♦ Growth thickness

♦ The impact on the chemistry, physics, or structure of the test sample is divided into five levels: 0, 1, 2, 3, and 4.


7. Determine whether the tested product is qualified or not

♦ After the mold growth level is given, it is necessary to determine whether the tested product is qualified or not. It is also necessary to consider the product technical conditions, manufacturing process, product usage environment, and usage requirements to comprehensively determine whether the mold resistance performance of the tested product is qualified or not. The product professional standards will make regulations based on the specific situation of the product profession.

8. Test cycle

Test with poor or rapid mold resistance for 7-14 days

Mildew resistant or slowly growing test samples for 3-4 weeks

Inspect the appearance of the sample for 28 days

84 days of performance inspection

9. Application objects of mold test

♦ Mold testing is a means of identifying the ability of products to resist mold damage. Equipment stored, operated, and used in humid and hot environments should undoubtedly undergo this type of testing assessment. After testing, its anti mold ability and degree of mold growth can be determined.

♦ Mold testing can be conducted on the entire equipment, components, and non-metallic materials, depending on the specific situation.

♦ In general, three samples of each type should be selected for testing, in order to evaluate the results based on two test samples.

♦ Mold growth is closely related to the structure, materials, and process of the product. During product design and manufacturing, measures must be taken to prevent mold damage. Evaluate and evaluate the effectiveness of mold and corrosion prevention in product trial production and finalization tests. When the design, materials, and process are basically fixed after finalization and identification, and in mass production, the general principle will not change, and there is no need to conduct mold testing again. Only when there are significant changes in the structure, materials, and processes of the product that affect environmental protection performance, a new assessment of mold testing must be conducted.


1. Mold proof design

The impact of various environmental factors on equipment and materials provides a large number of design methods to avoid or reduce these harmful effects. When designing products, it is necessary to fully anticipate the biological environmental conditions in which the product is located, understand the causes, conditions, hazards, and prevention methods of mold growth, and take corresponding measures. The anti mold measures for products should not be isolated and isolated, but must start from the material selection and structural design of the product and run through a series of processes such as processing, assembly testing, packaging, transportation, storage, and use and maintenance. Only in this way can good results be achieved.


2. Anti mold measures

♦ The anti mold measures are as follows:

(1) Use materials with good mold resistance as much as possible to maximize the time required for mold growth and minimize material damage caused by mold growth.

(2) It is necessary to avoid the formation of moldy damp pits during product assembly, such as between unsealed paired plugs and sockets or between printed circuit boards and terminal connectors in specific locations.

(3) Adopting a fully sealed structure filled with dry and clean gas is the best way to prevent mold growth.

(4) Place desiccant inside the partially sealed shell and replace it regularly or use heating to maintain low humidity inside the shell to avoid mold growth.

(5) When the zero resistance of the selected material cannot meet the requirements, anti mold agents can be used. Antimold agents can be added to paints, rubber, and plastics. Antimold agents can also be sprayed or infiltrated with carriers onto the materials or products to be protected, or fungicides can be made into tablets and placed in the shells of the products to be protected.

(6) During the assembly process, attention should be paid to avoiding contamination by hand sweat and dirt.

(7) Products with outer shells should be regularly cleaned to remove nutrients such as dust and dirt that can support mold growth, in order to prevent mold growth and damage.

(8) Natural ventilation is prone to dust accumulation, so the areas inside the product that are prone to dust accumulation should have sufficient and moderate air flow to prevent the growth of mold.

(9) To prevent mold growth during transportation and storage, moisture-proof packaging can be used.

(10) If materials and products allow, ultraviolet or ozone sterilization can also be used.

(11) Optical glass can achieve the goal of preventing mold by protecting it from moisture erosion with an anti fog, anti mold, and hydrophobic film layer.

(12) Control the environmental conditions during the product production process and improve the environmental conditions for product work and storage.

3. Antifungal agent

♦ (1) Antimold agents generally possess conditions that have a broad and strong inhibitory or killing ability against mold, while being harmless or less harmful to the human body;

Has good heat resistance and weather resistance;

Good chemical stability, insoluble in water or with minimal solubility;

No adverse effects on the physical properties and appearance of materials or products;

Economical and practical.

♦ (2) Commonly used mold inhibitors

Sodium pentachlorophenol



Zinc pentachlorophenol

Pentachlorophenol phenylmercury



Copper 8-quinolinolate

Phenylmercury acetate

S67 (Organic Tin)

S59 (Organic Tin)

Relevant standards

♦ According to the scope of application of the standard, there are roughly three types of international methods for mold growth testing.

♦ The first type is used for product (component, equipment, assembly) type standards, which include IEC, UK, France, Federal Germany, German Democratic Republic, Czechoslovakia, Hungary, India, and US military standards for mold growth test methods.

The characteristic is to use a specified set of bacterial strains when testing various products. The temperature and humidity conditions for the experiment were constant, except for the Czech and US military standards that used the alternating cycle two-stage method. The experimental period is mainly 28 days, with standards such as Federal German and US military standards for 84 days. The mold growth level of the product after mold growth is only divided into two levels according to Czech and Indian standards

'Yes' and' No 'indicate, but the Indian standard clearly states that' no mold growth is qualified '. The other standards mentioned above are all multi-level, with IEC, British, French, German and other standards ranging from level 0 to level 3, and the US military standard ranging from level 0 to level 4. However, most standards do not specify a qualification level.

♦ The second type is used for product material type standards, which include two standards: Japan and the former Soviet Union. The characteristic is to select different bacterial strains for combination based on product and material properties, and then mix them for use. According to the Japanese standard test cycle, different long mold test cycles are selected based on the difficulty of products and materials. However, for general industrial product testing, a 28 day test cycle is still selected as the assessment. The standards of the former Soviet Union stipulated 28 days of testing. The mold growth level of the product after mold growth also belongs to a multi-level system, ranging from 0 to 5 levels. This standard also does not specify the qualification level for mold growth.

♦ The third type is used for material type standards, which include ISO, ASTM, AATCC, and other standards. The ISO standard's mold growth method is for plastic (PVC) materials, the ASTM standard is for synthetic materials, and the AATCC standard is for textiles. The characteristic is the use of inorganic salt agar culture dish method. The duration of the long mold test is 21 days. The growth grade of the test sample after mold growth is still a multi-level system, and these standards have not specified a qualified grade.

Among the three types of standards mentioned above, the main technical indicators such as test equipment, test conditions, and test cycles in the first and second types of standards are roughly similar, with the significant difference being the test strain.