How to analyze and solve the foaming phenomenon of silicone sealant during construction?
Maybe when you use silicone sealant, you will occasionally encounter a construction inconvenience, that is, there will be bubbles in the construction. The reason why the silicone sealant foams during construction is more complicated. Caused by the reasons, it is difficult to use a method or a result to determine the cause of foaming.
Silicone structural sealants are generally used in factories. They are filled in the factory. The environment and working conditions in the factory are relatively good, and it is easy to meet the external conditions required for silicone sealant curing.
1. Wrap the air in the glue injection process.
Silicone weather-resistant sealants generally perform glue injection work at the construction site, and the working conditions are poor. Workers stand on the scaffolding and glue the glue. The uniformity of the glue injection is not easy to grasp, and it is easy to wrap the air into the glue. After the glue is applied, the surface of the rubber joint is scraped and smoothed. The gasket inside the rubber joint is generally a closed-cell polyethylene foam rod. The air wrapped inside the rubber joint is not easy to overflow, and the rubber seam is compressed and compressed. The tension, the weather-resistant glue joints are generally wider, the thickness is small, the weather-resistant glue providing high displacement capability, the hardness is low, and the glue is soft before being cured. The tension of the compressed air slowly foams the seam. This phenomenon is more likely to occur in weathering adhesives that provide ±25% or more of the seam displacement capability. On the contrary, some weather resistant adhesives that allow lower displacement capacity have higher hardness and are thicker before the glue is cured. The tension of the compressed air wrapped in the glue joint is not easy to foam the rubber support. Therefore, the more weather-resistant glue that can provide high displacement capability, the more attention should be paid to the uniformity of injection. Generally, the vertical glue sewing glue can be applied from the bottom to the top to overcome some foaming phenomenon. The most important thing is the proficiency and responsibility of the work operator.
2. The interface is wet when the glue is injected.
In outdoor work, rainfall is often encountered, especially in the summer in the south. It rains almost every day. If it rains, the interface is wet and dry, and the glue is injected directly. When the sun shines on the bonding substrate and the glue joint, the interface is inside. The temperature rises, the moisture inside the glue seam evaporates, and the uncured, softer glue seams are foamed. Sometimes the moisture of the polyethylene foam pad will cause the glue joint to foam. Therefore, during construction, you should not be eager to find a solution. After the interface is dry and then injected, you can avoid the above situation.
3. The sun is exposed when the glue is not cured.
Silicone glue can't be exposed to the sun before it is cured. Especially when the glue is just finished, the sun will be exposed to the sun, which will cause honeycomb bubbles inside the glue joint, which will cause the external seam of the glue joint. Silicone glue will be more obvious. In the hot summer construction, this situation is not easy to overcome. Avoiding sun exposure when using glue injection will overcome some blistering. In the morning, glue on the west or north side of the building, and in the afternoon on the east or south side of the building. After the glue is injected, the glue is solidified for a period of time, the surface layer has been crusted, and when the sun is sun-dried, with some resistance, some foaming can be overcome.
4. The surface temperature of the substrate is too high.
When the silicone adhesive is cured, the temperature of the bonded material should not exceed 50 ° C. This conclusion has been approved by most silicone adhesive manufacturers. When the surface temperature of the substrate exceeds 50 ° C, the glue is injected, which will cause the foam to be foamed. This will be the case when the metal panel curtain wall is weather-resistant. In the hot summer, when the sun is exposed to the metal plate, especially the surface temperature of the aluminum plate will reach 80 ° C, at this time, the injection can easily cause the foam to foam. Therefore, it should be selected in the second half or cloudy days to improve the above situation.
5. The temperature difference between day and night is large, the interface thermal expansion and contraction is larger.
This situation is more likely to occur when the aluminum panel curtain wall is glued. Aluminum is a material with a large coefficient of linear expansion. In the spring or autumn of northern China, the temperature is large, and when the sun is directly exposed to aluminum at noon, the surface temperature of the aluminum plate can be as high as 60 ° C -70 ° C, and the temperature drops to about 10 ° C at night. The large aluminum plate has more thermal expansion and contraction, and the interface displacement is larger. After the weathering rubber is caulked, the actual displacement of the interface is tolerated by the rubber joint. In the curing process, the excessive and repeated telescopic displacement will occur. Causes the seam to foam, so avoid the above-mentioned foaming when avoiding the strongest direct sunlight at noon.
7. The climate is dry.
The silicone sealant is polymerized into an elastic sealing material by means of moisture in the air. The amount of humidity in the air is closely related to the curing speed. The spring climate in northern China is dry. After silicone rubber injection, the curing time is very long. The silicone sealant before uncured is extremely susceptible to the external environment and provides opportunities for various foaming phenomena.
7260 is a general purpose, single component silicone sealant which offers best sealing performance on most fields.
1.Fill and Seal doors and windows coated with aluminum alloy, titanium alloy and plastic steel.
2.Seal all kinds of glass and aluminum-plastic panel curtain walls and stone cladding.
3.Bond and seal buckled doors and windows.
The above-mentioned foaming phenomena and causes are also summarized by the technicians. I hope that it will be helpful to those who are working on the construction site. It is necessary to learn to consider the ambient temperature and other factors when determining the cause of foaming. It is possible to avoid or overcome the above situation.