Acid silicone rubber and neutral silicone rubber common problems and solutions

Most of the sealant belongs to synthetic adhesives, its main body is polymer, its properties can be divided into three categories: body properties, process properties and use properties (product performance). The use of properties (product performance) is self-evident mainly refers to the sealant in the formation of bonding process to form the comprehensive performance of the joint, the performance depends on the functional requirements of the building joint sealant. Whether it is for the exterior protection of the building or the interior decoration of the building; Whether it is a window structure or other forms of envelope and decorative structure, they can be regarded as unit composition, then there is a joint between each unit, the vast majority of the need for building sealant to seal and fill. Reasonable design of building joint, understanding of building sealant, reasonable selection of materials and correct construction of building seal are essential to ensure the success of building joint seal. Some common problems encountered in the actual use of sealant are sorted out here, and corresponding solutions are provided for you.

1. Cause analysis of foaming

The reasons for foaming of silicone sealant in construction are many and complex, and it is difficult to use one method and one result to determine the cause of foaming. Silicone structural sealant is generally completed in the factory sealant work, the factory environment and working conditions are relatively good, easy to meet the external conditions required for silicone structural sealant curing. Silicone weather-resistant sealant is generally completed at the site to complete the sealant injection work, the site environment and working conditions are poor, silicone weather-resistant sealant in the curing process required by the external conditions are not easy to meet. Climate, environment, working conditions and other non-human factors can change the effect on the curing quality of silicone adhesive is great. Therefore, the limitations of the environment and operating conditions in which silicone weather resistant adhesive is used determine the main reason for foaming. The following is some analysis of some specific situations.

(1) The sealant is wrapped in air.

Silicone weather resistant sealant is generally completed at the site to complete the sealant work, the working conditions are poor. The worker stands on the scaffold above the sealant, the uniformity of the sealant is not easy to grasp, and the sealant seam is easy to be wrapped in air. After sizing, the surface of the sealant seam is scraped and trimmed, and the pad rod inside the sealant seam is generally selected as a closed cell polyethylene foam rod, and the air wrapped in the sealant seam is not easy to overflow. After the air compression of the sealant seam is trimmed, the outwards rising tension will be generated. The weather resistant sealant is generally wide, the thickness is small, the weather resistant sealant with high displacement ability is provided, the hardness is low, and the sealant is soft before curing. The tension of the compressed air slowly bubbles the sealant seams. This phenomenon is more likely to occur in the application of weather resistant adhesives that can provide more than ±25% of the sealant displacement capacity. On the contrary, some weather resistant adhesives with lower allowable displacement capacity have higher hardness and are relatively thick before they are cured. The tension of compressed air wrapped in the sealant seam is not easy to bubble the sealant. Therefore, the more weather-resistant sealant that can provide high displacement capacity, the more attention should be paid to the uniformity of sealant injection. General gluing of vertical sealant joints can be used from the bottom up, which can overcome some foaming phenomenon. More important is the work operator's proficiency and responsibility.

(2) The interface is wet during sealant injection.

In outdoor work, often encounter rain, especially in the southern summer, almost every day to rain, if the rain, the interface inside the wet and not dry directly sealant, such as the sun irradiation bonding substrate and sealant seam inside the temperature rise, the sealant seam inside the moisture evaporation, will be uncured, relatively soft sealant seam bubbling, sometimes polyethylene foam rod wet will also cause sealant seam bubbling. Therefore, the construction can not blindly seek progress, wait until the interface is dry, and then inject sealant, which can avoid the above situation.

(3) Deflate the foam rod

The padding rod inside the sealant seam is generally selected as a closed cell type high foaming polyethylene foam rod. Due to improper extrusion during placement, the internal air bag ruptured and released air. There will be a bubble bulge or a bulging appearance when the sealant is just injected. The second is the use of open-hole foam rod or the use of foamed ethylene foam rod to overcome the above situation. In the other case, the alcohol-based weather resistant adhesive releases methanol when it cures, and the methanol reacts with some foam rods. In such cases, the problem is solved by changing the foam rod or ketone oxime type sealant.

(4) Sun exposure when the sealant is not cured.

Silicone sealant can not be exposed to the sun before curing, especially when the sun is exposed just after the sealant is injected, which will cause honeycomb bubbles inside the sealant seam, causing the external bulge of the sealant seam, which will be more obvious when the alcohol type silicone sealant is used. Construction in the hot summer, this situation is not easy to overcome. The use of sealant to avoid the sun exposure, will overcome some of the foaming phenomenon. Specific practice: In the morning on the west or north side of the building sealant, in the afternoon on the east or south side of the building sealant. After the sealant is injected, the sealant has been cured for a period of time, the surface has crusted, and when the sun is exposed, it has a certain resistance, and some foaming phenomena can be overcome.

(5) The substrate surface temperature is too high.

When silicone adhesive is cured, the temperature of the bonded material cannot exceed 50 ° C, which has been recognized by most silicone adhesive manufacturers. When the surface temperature of the substrate exceeds 50 ° C, the sealant injection will cause the sealant seam to bubble, and the above situation will be encountered when the weather resistance of the metal plate curtain wall is caulked. In the hot liter, when the sun is exposed to the metal plate, especially the surface temperature of the aluminum plate will reach 80 ° C, and the sealant injection is very easy to cause foaming of the sealant seam. Therefore, we should choose the second half of the afternoon or cloudy days to improve the above situation.

(6) The temperature difference between day and night is large, and the interface thermal expansion and cold contraction are large.

This situation is more likely to occur when the aluminum curtain wall is injected with sealant. Aluminum plate is the linear expansion coefficient of the larger material, in the northern region of China in the spring or autumn day and night temperature difference is large, and the sun at noon direct aluminum plate, aluminum plate surface temperature can be as high as 60℃-70℃, the temperature drops to about 10℃ at night, large aluminum plate, thermal expansion and contraction is also large, the interface displacement is larger, weather resistant sealant caulking, the actual displacement of the interface is borne by the sealant seam. During the curing process, excessive and repeated expansion displacement will cause foaming of the sealant seam, so avoid the noon direct sunlight when the sealant is injected to improve some of the above foaming.

(7) Spring is dry in the north

Silicone sealant to use the moisture in the air, chemical reaction into an elastic sealing material. The amount of humidity in the air is closely related to the curing speed. The spring climate in the north of China is dry, and the curing time is very long after the silicone sealant is injected, and the silicone sealant before it is cured is extremely susceptible to the influence of the external environment, providing opportunities for various foaming phenomena.