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As an important energy-saving product, insulating glass has been widely used. There are more than 500 large and small insulating glass companies in the world, with a production capacity of nearly 30 million ㎡, and the product quality has also been greatly improved. Especially in China, the insulating glass production line of well-known brands at home and abroad have been introduced, with strong technical force, advanced technology and equipment, strict control of the raw materials used, and a relatively complete product quality management system. Its product quality is not much different from foreign countries. However, other small and medium-sized glass deep-processing enterprises, especially the quality of hand-made insulating glass, fluctuate greatly. Judging from the entrusted inspection of insulating glass in recent years, most of the unqualified samples are hand-made, mainly manifested as dew point rise, ultraviolet radiation fogging and glass bursting, and other phenomena.    

There are 5 performance tests for insulating glass, including initial dew point, sealing, ultraviolet irradiation, high temperature, and high humidity, and climate cycle. Jinan LIJIANG Glass will briefly analyzes the problems and causes of each inspection.

1. Initial dew point    

The main test is whether the air in the insulating glass is dry, and the national standard stipulates that the dew point is equal to or lower than -400℃ to be qualified.    

The reasons for the unqualified initial dew point are:    

(1) The molecular sieve used is unqualified or has failed. If the container containing the molecular sieve is not tightly sealed, the molecular sieve will easily fail. At this time, activation treatment should be carried out, that is, heating in an oven at 3000℃ for more than 3h.    

(2) The air humidity in the production workshop is too high.    

(3) After the aluminum frame is loaded into the molecular sieve, the pieces cannot be assembled in time, and the molecular sieve will fail to absorb water if the time is too long.

Figure 1 The dew point performance testing of insulating glass 1

Figure 1 The dew point performance testing of insulating glass 1

2. UV radiation    

This test mainly tests whether the insulating glass sealant contains organic volatiles that affects sight. After the insulating glass sample is continuously irradiated by a 300W UV lamp for 168 hours, it is stored at a temperature of 23±2℃ for a week. The inner surface of the insulating glass should not appear foggy, oily, or other contaminants.    

Reasons for disqualification are:    

(1) The content of organic volatiles in the sealant is too high.    

(2) The aluminum strip has not been decontaminated.

3. Seal inspection    

This test is used to test the softness and hardness of the insulating glass sealant and whether there is leakage. The sample is kept for 2.5h under the condition of 10±0.5KPa lower than the ambient air pressure, and the thickness growth deviation is less than 15%, which is qualified.    

Problems in testing are air leaks or excessive thickness growth deviations.    

Reasons for failure are:    

(1) The operator is not careful so the sealant is not well sealed.    

(2) The uneven mixing of the sealant or the inaccurate weighing affects the curing of the sealant.    

(3) The width of the sealant layer is too narrow.

Figure 2 Measure the step difference of insulating glass with right square and feeler gauge 1

Figure 2 Measure the step difference of insulating glass with right square and feeler gauge 1

4. High temperature and high humidity test    

This test mainly tests whether the adhesive force of the sealant, the water vapor transmission rate, and the effective adsorption capacity of the molecular sieve meet the standard requirements. The samples were subjected to 224 cycles under high temperature and high humidity test conditions (humidity>95%, and the temperature varied regularly between 25-55°C). In each cycle, the gas in the insulating glass has to undergo an expansion and contraction, so there is a higher requirement for the adhesive force of the sealant. In addition, due to the high humidity, the water vapor transmission rate of the sealant should be below, and the molecular sieve should have a strong adsorption capacity.

Problems that often arise in testing are increased final dew point and glue opening.    

The reason is:    

(1) Unqualified sealant has been used or the shelf life has been exceeded. After the high temperature and high humidity test, the glue is separated from the glass, and water enters.  

(2) The glue is unevenly mixed and not fully cured.    

(3) The effective adsorption capacity of the molecular sieve is low or the exposure time in the air is too long. The operator is not careful, the sealant is not well sealed, and there are air leaks. Because the molecular sieve not only absorbs the moisture in the air sealed in the spacer layer during production so that the initial dew point is qualified but also continuously absorbs the moisture diffused into the spacer layer through the adhesive layer so that the final dew point also meets the requirements.    

(4) The glass is not cleaned, resulting in a decrease in adhesion.

(5) During manual gluing, because too much glue is mixed at one time, part of the glue is vulcanized, so the increase of air bubbles in the glue layer affects the bonding strength.

(6) Unreasonable mix of raw materials. When using silicone rubber to make insulating glass, it must be used in conjunction with butyl rubber, because the water vapor transmission rate of silicone rubber is high.

5. Climate cycle test    

This is an aging resistance test, which is an investigation of the comprehensive performance of insulating glass. It simulates the four-season climate (cold, hot, wind, rain) in a year. Each cycle has to go through three stages heating, natural cooling, and forced cooling, and a total of 320 cycles are carried out. The easy problem during the inspection is that the insulating glass bursts. , glue opening and final dew point rise. In addition to those mentioned in high temperature and high humidity, 

the main reasons also include:    

(1) The sealant does not maintain good elasticity under low-temperature conditions.    

(2) The volatile solvent content in the sealant is too high (should not exceed 1.5%).    

(3) The original glass sheet itself is not well annealed.    

As a deep-processed product supplier of insulating glass, insulating glass is expensive. Once it is damaged after installation and use, it is difficult to replace it. Therefore, the raw materials of insulating glass should be carefully selected, and the production process should be carried out in strict accordance with the operating procedures. Only in this way can the overall quality of insulating glass be improved.


For more information about Jinan LIJIANG Glass insulating glass processing equipment and insulating glass processing accessories, please click here to learn more. 

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