Common problems and solutions of silicone glue

Neutral glue

1. Foaming Cause Analysis

There are many reasons for the foaming of the silicone weathering sealant during construction. It is relatively complicated, and it is difficult to determine the cause of the foaming with one method and one result. Silicone structure sealant is generally completed in the factory. The factory environment and operating conditions are relatively good, and it is easy to meet the external conditions required when the silicone structure sealant is cured. The silicone weathering sealant is generally completed at the construction site to complete the injection work. The construction site environment and operating conditions are poor. The external conditions required by the silicone weathering adhesive during the curing process are not easy to meet. Climate, environment, operating conditions and other non-artificial changes can greatly affect the curing quality of silicone weathering adhesives. Therefore, the limitations of the environment and operating conditions of silicone weathering adhesives determine the main reason for foaming. Let's do some analysis on some specific situations.

Technology | Practical Problems and Solutions of Silicone Adhesive Technology | Practical Problems and Solutions of Silicone Adhesive

(1) Air is trapped during injection

Silicone weathering rubber is generally completed at the construction site to complete the injection work, poor operating conditions. Workers stand on the scaffold to inject the glue. The uniformity of the injection is not easy to grasp, and the air in the glue seam is easy to be wrapped. After the glue is applied, the surface of the glue seam is scraped and trimmed cleanly. Generally, closed-cell polyethylene foam rods are used for the pads in the glue seam. The air wrapped in the glue seam is not easy to overflow. The weathering rubber with external tension, generally has a wider width and a smaller thickness. The weathering rubber that provides high displacement capacity has lower hardness, and the rubber is soft before curing. The pressure of the compressed air slowly foams the glue seam. This phenomenon is more likely to occur in weather-resistant adhesives that can provide more than ± 25% of the seam displacement capacity. On the other hand, some weather-resistant adhesives with lower displacement capacity have higher hardness and are thicker before curing. The tension of the compressed air wrapped in the glue seam does not easily foam the glue. Therefore, the more weather-resistant adhesive that can provide high displacement capacity, the more uniform the injection should be paid more attention to when injecting. Vertical glue joints can be glued from bottom to top, which can overcome some foaming phenomena. More important is the proficiency and responsibility of the work operator.

(2) The interface is wet during the injection

When working outdoors, it often encounters rain, especially in the summer in the south. It rains almost every day. If the inside of the interface is wet and not wet after rain, inject the glue directly. Wait for the sun to irradiate the temperature of the interface and the substrate when bonding When it rises, the moisture in the glue seam evaporates, which will swell the uncured, relatively soft glue seam, and sometimes the polyethylene foam cushion rod is wet, which will cause the seam to bubble. Therefore, do not blindly schedule during construction, wait until the interface is dry, and then inject glue to avoid the above situation.

(3) Deflation of foam stick

The cushion rods in the glue seams are generally closed-cell high-foam polyethylene foam rods. Due to improper compression during placement, the internal airbag ruptures and releases air. There will be bubbles or bulges immediately after the glue is injected. The appearance of the bulging, the solution to this situation, one is to cut open the foam stick with the cutting side facing inward, and the other is to use open-cell foam sticks or foamed vinyl foam sticks to overcome the above situation. In another case, alcohol-based weathering glue will release methanol when cured, and methanol reacts with some foam bars. In such cases, the problem is solved by changing the foam stick or ketoxime type sealant.

(4) Sun exposure when the glue is not cured

Silicone glue cannot be exposed to the sun before curing. Especially when the glue is exposed to the sun, it will cause honeycomb bubbles to appear inside the glue seam, which will cause the glue seam to bulge. This is the case with alcohol-type silicon. Ketone gums are more noticeable when used. This situation is difficult to overcome during hot summer construction. Avoiding sun exposure when injecting glue will overcome some blistering. Specific method: in the morning on the west or north side of the building, in the afternoon on the east or south side of the building. After the glue is injected, the glue has been cured for a period of time, and the surface has become skinned. When the sun is exposed to the sun again, with some resistance, it can overcome some foaming phenomena.

(5) The surface temperature of the substrate is too high

When the silicone adhesive is cured, the temperature of the bonding material cannot exceed 50 ° C. This conclusion has been accepted by most silicone adhesive manufacturers. If the glue is injected when the surface temperature of the substrate exceeds 50 ° C, it will cause foaming of the glue seam. When weathering caulking of the metal plate curtain wall, the above situation will be encountered. In the hot rise time, when the sun exposes the metal plate, especially the surface temperature of the aluminum plate will reach 80 ° C. At this time, the glue injection will easily cause foaming of the glue seam. Therefore, the second half of the afternoon or cloudy should be selected to improve the situation.

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

This situation is more likely to occur when the aluminum curtain wall is filled with glue. Aluminum plate is a material with a large coefficient of linear expansion. The temperature difference between day and night in spring or autumn in northern areas of China is large, and when the sun directly hits the aluminum plate at noon, the surface temperature of the aluminum plate can reach as high as 60 ° C-70 ° C, and the night temperature drops to about 10 ° C. For large aluminum plates, the thermal expansion and contraction are also large, and the displacement of the interface is large. After weathering glue caulking, the actual displacement of the interface is borne by the plastic seam. During the curing process, excessive and repeated telescopic displacement will It causes foaming in the glue seam, so avoid direct sunlight at noon when the glue is strongest to improve some of the foaming conditions mentioned above.

(7) Dry weather in spring in northern regions

The silicone sealant is chemically reacted to form 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 northern part of China has a dry climate in spring. After the silicone sealant is injected, the curing time is very long. The uncured silicone sealant is extremely susceptible to the external environment and provides opportunities for various foaming phenomena.

2. Why does the sealant cure slowly?

First, the objective conditions of sizing have a greater impact on the deep curing speed. For example, the construction environment, temperature, and humidity have a relatively large impact on the curing speed. If the temperature is too low and the humidity is too high, the deep curing will be significantly slower. In addition, there is ventilation at the construction site. If the air circulation is not smooth, it will also affect the deep curing. In addition, the design of the glue joint will also have a great impact on the deep curing. When the gap width ratio is not appropriate or the depth is too deep, deep curing will be slower; in general, deep curing is slightly slower, and there is no quality problem (such as blistering, internal curing cannot be used, etc.). Impact, the national standard stipulates that the curing period of the test piece is 21 days, and the test specimen is equivalent to the sizing thickness in the actual project, which means that the full curing time required by the national standard requires 21 days, and the curing time of our reaction is far less than 21 days (usually more than 5-7 days is reflected as slow-drying); In addition, we believe that sealant curing too fast is not good for long-term use, because curing too fast is not conducive to releasing stress caused by temperature during curing. Hidden danger. If the concrete curing time is limited, if it is too fast, it will lead to stress concentration and cracking.

3. Why does the sealant crack after curing?

Real cracks are rarely seen in the middle after curing. Because there are too few cases, it is not clear about some objective conditions, so it is impossible to accurately determine the cause. Cracking here mainly refers to the phenomenon of degumming on the substrate side caused by poor adhesion to the substrate, also called cracking.

There are several reasons for this reason (except for inferior glue):

Second, there are reasons for construction. The surface of the substrate is not cleaned or improperly applied. For example, the solvent is not dried, it is applied for a long time, or it is polluted for a long time after cleaning.

4. The surface of the rubber strip is wrinkled and uneven after curing. Why?

This kind of situation occurs more frequently during vertical seam sizing. Therefore, the reason for this analysis should be that the initial wetting time of the glue is slower on the surface of the substrate, that is, the initial adhesive force is poor, resulting in the sealant due to its own weight. Sagging forms wrinkles and unevenness.