January 30, 2023
The cold wave weather swept across the country, and the temperature in most areas plummeted. China has experienced the strongest cold wave in 2022. Recently, the Central Meteorological Observatory issued a blue warning of cold wave. Most of China will usher in a new round of cold wave. During this period, the temperature will drop by 4-8°C successively, and the temperature in some areas will drop by more than 10°C.
However, what makes the doors, windows, curtain walls and walls bond together, and what blocks us from the first ray of cold wind in winter?
Of course it is - sealant!
As an important auxiliary material widely used in the bonding and sealing of building curtain walls, doors and windows, interior decoration and other fields, sealant silently highlights its presence in every detail. So today, let us take a look at how to properly apply winter silicone structural sealants——
Winter Construction Issues
The temperature in winter in the north is generally below zero, and the temperature and humidity vary greatly. The sealant is prone to the following problems:
1) When the temperature is too low, the wettability between the silicone structural sealant and the substrate surface decreases, and there may be imperceptible fog or frost on the substrate surface, which affects the adhesion between the silicone structural sealant and the substrate.
2) Under low temperature and low humidity conditions, the curing speed and bonding speed of silicone structural sealants are slower than normal, which will lead to longer curing time and affect construction.
Precautions for construction in low temperature environment
Too low temperature greatly restricts the performance of the sealant, but the sealing performance is undoubtedly a part that cannot be ignored in winter. If you want to avoid such problems, you must adapt to the current situation.
It should be noted that at present, there are two types of architectural silicone structural sealants used in curtain wall construction according to their components: one is a single-component silicone structural sealant, and the other is a two-component silicone structural sealant. The curing mechanism and factors affecting the curing of these two types of silicone structural sealants are different, and the construction methods in low temperature environments are also different.
According to the curing characteristics of silicone structural sealant in low temperature environment, the following points should be paid attention to when working in low temperature environment:
Construction environment guarantee:
According to JGJ 102-2013 "Technical Specifications for Glass Curtain Wall Engineering" in 9.1 General Processing, the environmental temperature and humidity conditions of silicone structural sealant injection should meet the requirements of silicone structural sealant products. Take the requirements of Baiyun brand silicone structural sealant products in the construction process of the Winter Olympics as an example. The environmental requirements for the use of this product must be: a clean environment with a temperature of 10°C to 40°C and a relative humidity of 40% to 80%, and Construction is not permitted during rain or snow.
When constructing in a low-temperature environment, heating measures need to be taken to ensure that the construction temperature is higher than 10°C; while in construction in a low-temperature environment with an ambient temperature slightly lower than 10°C, a small-area sealant test must be carried out before use, and peeling and bonding must be carried out Conduct a performance test to confirm that the silicone structural sealant is cured and bonded well, and the curing time should be extended appropriately according to the situation. When necessary, it is necessary to choose to use xylene to wash and prime the coating to speed up the bonding speed and reduce the risk of poor bonding due to low ambient temperature.
Beware of poor bonding during the sizing process:
1) Before construction, it is necessary to do an adhesion test in advance, and strictly follow the method recommended by the adhesion test for construction.
2) The batches of materials (aluminum, glass, sealant, cleaning agent, primer, etc.) used in the construction process are complicated, and there may be differences in different batches. Contact test.
3) During the construction process, the method of cleaning or applying the primer solution must conform to the construction process, strictly follow the "secondary rag method" for cleaning, and apply the primer solution in time after the cleaning solvent evaporates; the primer solution should be thin and uniform, pay attention to To ensure the connection of the next process, it is best to inject the sealant within half an hour after applying the primer.
4) The sealant injection process needs to ensure that the mixing ratio is correct, and pay attention to the uniform mixing of components A and B. These two items can be confirmed by the butterfly test and the pull-off test, respectively. It is also necessary to pay attention to sufficient exhaust when changing barrels.
If the exhaust is not sufficient, part of the silicone structural sealant will be mixed with a large number of dense air bubbles, that is, "bubble sealant". The bonding effect between the bubble sealant and the base material (aluminum, glass, etc.) is very poor. If the adhesive strip is pulled by hand, the adhesive strip will be separated from the base material, and at the same time, a layer of black marks will be left on the base material.
5) After the on-site plate production is completed, the plate needs to be moved horizontally to the maintenance area for maintenance. Misalignment between the aluminum frame and the glass is not allowed during the handling process, otherwise it will affect the bonding quality of the silicone structural sealant.
The maintenance environment and maintenance time must ensure that the tapping of single components is qualified:
After the silicone structural sealant is injected, the curing process needs to be in a clean and ventilated environment, the temperature is kept at 10-40°C, and the humidity is kept at 50-90%. When the temperature and humidity of the curing environment are low, the curing time should be extended appropriately.
This situation is obvious in the one-component silicone structural sealant: that is, the curing state of the one-component structural adhesive sealant has a clear relationship with the curing time. Under the same environment, the longer the curing time, the higher the degree of curing.
▲Under low-temperature curing conditions, the injection depth of the single-component structural sealant is 10mm, and the time required for complete curing changes from 10 days to 15 days, and the curing time is extended
If necessary, take measures to increase the ambient temperature and humidity. The final result is subject to the rubber tapping test, in order to fully determine the curing time of the finished unit. After the finished rubber tapping test is qualified (see the figure below), it can be installed and transported.