
Common problems and solutions of neutral glue
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- Time of issue:2018-10-19 00:00
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(Summary description)
Common problems and solutions of neutral glue
(Summary description)
- Categories:Technology sharing
- Author:
- Origin:
- Time of issue:2018-10-19 00:00
- Views:
Sealants are mostly synthetic adhesives, whose main body is polymer, and their properties can be divided into three categories: bulk properties, process properties and use properties (product properties). The nature of use (product performance) is self-evident, mainly refers to the comprehensive performance of the sealant during the formation of the cementation process to the formation of the cemented joint, and this performance depends on the functional requirements of the building joint for the sealant. Regardless of the building envelope or building interior decoration; whether it is window structure or other forms of enclosure and decoration structure, they can be regarded as unit composition, then each unit will have a seam, which is extremely large. Most require construction sealant to seal and fill. Reasonable design of building joints, understanding of building sealants, reasonable selection of materials and correct construction of building seals are the indispensable whole process to ensure the successful sealing of building joints. Here are some common problems encountered in the actual use of sealants, and provide you with corresponding solutions.
1. Analysis of the cause of blistering
There are many reasons for the foaming of silicone weathering sealant during construction, and it is more complicated. It is difficult to use one method and one result to determine the cause of foaming. Silicone structural sealants generally complete the glue injection work in the factory. The environment and operating conditions in the factory are relatively good, and it is easy to meet the external conditions required when the silicone structural sealant is cured. Silicone weathering sealants are generally completed on the construction site to complete the glue injection work. The site environment and working conditions are poor, and the external conditions required by the silicone weathering seal during the curing process are not easily met. Climate, environment, operating conditions and other non-human factors have a great influence on the curing quality of silicone weathering adhesive. Therefore, the limitations of the environment and operating conditions in which silicone weathering glue is used determine the main cause of foaming. Let's make some analysis on some specific situations.
(1) Air was engulfed when the glue was injected.
Silicone weathering glue is generally completed on the construction site to complete the glue injection work, the working conditions are poor. Workers stand on the scaffold to inject glue, and the uniformity of the glue is not easy to grasp, and air is easily trapped in the glue joints. After sizing, the surface of the glue seam is scraped and pressed to make it smooth and clean. The pads in the glue seam are generally closed-cell polyethylene foam rods. The air wrapped in the glue seam is not easy to overflow. Outside the bulge tension, the weather-resistant glue seam is generally wide and small in thickness, and provides high-displacement weather-resistant glue. The hardness is low, and the glue is very soft before curing. The bulge tension of the compressed air slowly propped up the glue seam to bubble up. This phenomenon is more likely to occur in the application of weather resistant adhesives that can provide more than ±25% of the gap displacement capability. On the contrary, some weather-resistant adhesives with lower allowable displacement ability have higher hardness and are thicker before curing. The bulge tension of the compressed air wrapped in the glue seam is not easy to hold up the glue. Therefore, the more weather-resistant glue that can provide high displacement capability, the more attention should be paid to the uniformity of the glue when injecting the glue. Vertical glue joints generally can be glued from bottom to top, which can overcome some blistering. More important is the proficiency and sense of responsibility of the work operator.
(2) The interface is wet when the glue is injected.
When working outdoors, it often rains, especially in the summer in the south. It rains almost every day. If the interface is wet and not dry after the rain, the glue is injected directly, and the temperature inside the interface when the sun is shining on the bonding substrate and the glue joint As it rises, the moisture in the glue joint will evaporate, which will bulge the uncured, relatively soft glue joint, and sometimes the dampness of the polyethylene foam pad will cause the glue joint to foam. Therefore, do not blindly seek progress during construction. Wait until the interface is dry before injecting glue to avoid the above situation.
(3) Foam stick deflated
The cushion rods in the glue seams generally use closed-cell high-foaming polyethylene foam rods. When placed, the internal airbags rupture and release air due to improper extrusion. When the glue is injected, there will be bubbles or bulges. The bulging appearance, the solution to this situation, one is to cut the foam stick with the cut side facing inside, and the other is to use an open-cell foam stick or a foamed ethylene foam stick to overcome the above situation. In another case, alcohol-based weathering glue will release methanol during curing, and methanol reacts with some foam sticks. In such a situation, the problem was solved by replacing 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 it is cured, especially if it is exposed to the sun just after the glue is injected, it will cause honeycomb bubbles inside the glue joint, which will cause the outside of the glue joint to bulge. This is the case in alcohol type silicon. It will be more obvious when ketone glue is used. In the hot summer construction, this situation is not easy to overcome. Avoid sun exposure when using glue injection to overcome some blistering. The specific method is to inject glue on the west or north side of the building in the morning and on the east or south side of the building in the afternoon. After the glue is injected, the glue is cured for a period of time, and the surface layer has been skinned. When exposed to the sun, it has a certain resistance and can overcome some blistering.
(5) The surface temperature of the substrate is too high.
When the silicone adhesive is cured, the temperature of the bonded material cannot exceed 50°C. This conclusion has been recognized by most silicone adhesive manufacturers. Injecting glue when the surface temperature of the substrate exceeds 50℃, it will cause the glue joint to foam. The above situation will be encountered in the weather-resistant caulking of the metal panel curtain wall. In the hot liters, when the metal plate is exposed to the sun, especially the surface temperature of the aluminum plate will reach 80℃, the glue injection will easily cause the glue joint to bubble. Therefore, the latter half of the afternoon or cloudy days should be selected to improve the above situation.
(6) The temperature difference between day and night is large, and the interface thermally expands and contracts greatly.
This situation is more likely to occur when the aluminum curtain wall is injected with glue. Aluminum plate is a material with a large linear expansion coefficient. In northern China, the temperature difference between day and night is large in spring or autumn, and when the sun shines directly on the aluminum plate at noon, the surface temperature of the aluminum plate can be as high as 60℃-70℃, and the temperature at night drops to about 10℃. Large aluminum plates have large thermal expansion and contraction, and the joint displacement is large. After the weathering glue is caulked, the actual displacement of the joint is borne by the glue joint. During the curing process, excessive and repeated expansion and contraction will cause Causes the glue joint to foam, so avoid the strongest direct sun at noon during the glue injection to improve some of the above-mentioned foaming conditions.
(7) The northern region has a dry climate in spring
Silicone sealant uses the moisture in the air to chemically react into an elastic sealing material. The humidity in the air has a close relationship with the curing speed. The climate in northern China is dry in spring, and the curing time is very long after silicone sealant is injected. The uncured silicone sealant is very susceptible to the influence of the external environment, which provides opportunities for various blistering phenomena.
2. Why is the deep curing of sealant slow?
The objective conditions of first 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. Too low temperature and high humidity will significantly slow down the deep curing. In addition, there is also the ventilation of the construction site. If the air circulation is not smooth, it will affect the deep curing. In addition, the design of the glue joint also has a great influence on the deep curing. When the width-to-depth ratio of the glue joint is not appropriate or the depth is too deep, the deep curing will be slower; in general, the deep curing will be slower, and it is not suitable for actual engineering use without quality problems (such as blistering, internal curing, etc.) As a result, the curing period of the specimens specified by the national standard is 21 days, and the thickness of the test specimens is equivalent to that in the actual project. That is to say, the complete curing time recognized by the national standards requires 21 days, and the curing time of our reaction is far less than 21 days (generally more than 5-7 days is reflected as slow drying); in addition, we believe that too fast curing of the sealant is not good for long-term use, because too fast curing is not conducive to releasing the stress caused by the temperature during the curing process. Hidden dangers. For example, the curing time of concrete is limited. If it is too fast, it will cause stress concentration and cracking.
3. Why does the sealant crack after curing?
There are very few intermediate cracks in the real adhesive strip after curing. Because there are too few cases, some objective conditions are not very clear, so it is impossible to accurately judge the cause. The cracking mentioned here mainly refers to the phenomenon of degumming on one side of the substrate caused by poor adhesion to the substrate, also called cracking.
The main reasons for this occurrence are as follows (except inferior glue):
One, the compatibility is not done well or the compatibility test is not done at all, that is, the glue and the substrate are incompatible and cause cracking.
Second, it is the reason for the construction, the surface of the substrate is not cleaned or the construction is improper, such as the construction before the solvent is dry or the cleaning is too long and contaminated.
The cracking of the sealant after curing is mostly caused by improper construction.
4. After curing, the surface of the adhesive strip is wrinkled and uneven, why?
This situation occurs more often during vertical seam sizing. The reason for this analysis should be that the wetting speed of the mortar to the substrate surface is slow in the initial stage of sizing, that is, the initial adhesion is poor, which causes the sealant to lose weight due to its own weight. Sagging causes wrinkles and unevenness; it is recommended to extend the trimming time as much as possible within the construction allowable range during construction, and change the trimming operation at the same time, use a scraper to trim the edges from the bottom of the glue seam upwards; be careful not to over-squeeze the edges when trimming, otherwise It is easy to cause the cushion foam stick to deform, and then the foam stick will gradually recover, resulting in the overall swelling of the sealant.
5. Why does the porcelain white sealant turn yellow and red?
Alcohol-based adhesives occasionally have this situation. The analysis may be caused by the unstable quality of the additives added, or it may be caused by the contamination of the accessories or other materials in contact with the cured adhesive.
6. Why does the neutral transparent glue (ketoxime type) turn yellow or even red after curing?
The ketoxime transparent glue (including the light-colored glue) will turn yellow to different degrees after curing for about 20 days, and the yellowing will increase with the increase of time. Here, the yellowing of the ketoxime transparent glue is not the existence of individual manufacturers. The problem is a product industry-wide problem, including foreign manufacturers. After analysis, it may be due to the addition of a coupling agent with amino groups.
Although yellowing is an inherent defect of current products, the curing environment has a greater impact on the yellowing. First, the ketoxime transparent glue cannot coexist peacefully with the acid glue and the alcohol glue. Within three days, the ketoxime transparent glue will turn yellow seriously. In addition, placing the cured ketoxime transparent glue in a dark and damp corner will also cause it to turn yellow until it turns red.
7. Why does the sealant have poor adhesion to some building materials (such as aluminum, aluminum-plastic panels, steel, etc.)?
Explain this phenomenon in two sentences, "the diversity of building materials, the instability of sealants".