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Q What should be controlled in the process of sealant construction?
A First of all, the cleaning of the substrate surface should be done well. If there is water, dust, stains and other pollution on the substrate surface, it will seriously affect the adhesion of the sealant to the substrate, resulting in the failure of sealant adhesion. Therefore, before the construction of sealant, we must use the appropriate solvent to clean the surface of the substrate, and then dry the construction.
During the construction, the nozzle should be cut into appropriate size so that the nozzle can be as wide as 1/2 of joint. Glue injection should be slow and smooth, so that the glue can fill the joints without gaps, and to ensure that the appropriate pressure to make the glue fully contact the surface of the substrate.
Environment temperature should be between 5-40 ℃, relative humidity should be between 40%—80%. Too dry or too humid weather, too low or too high temperature are unsuitable for sizing. If the surface temperature is more than 50 DEG, we should stop sizing.
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Q Sealant joint design
A The width and depth should be considered when designing the glue-line. The depth of the glue-line should be between (6-12) mm. If the glue-line is too deep, it is not conducive to the deep curing of sealant, and if the glue-line is too shallow, the sealing performance will be not good. The following factors should be considered when designing the width: (1) the area of the curtain wall ; (2) the coefficient of thermal expansion and cold contraction of the material; (3) Local temperature difference. Therefore, the possible displacement of the joint due to temperature change is calculated. The maximum possible displacement must be within the displacement capacity of the sealant.
The factors to consider when designing the sealant joint are: be convenient or construction, and can maintain good ventilation, be conducive to sealant curing, before sealant curing will not produce displacement, will not be buried in the ground or immersed in water and so on.
The design of structural adhesive joints should also consider the dead weight of the curtain wall, wind pressure and other factors, and calculate the long-term load and short-term maximum load of structural adhesive joints. According to the mandatory industry standard JCJ102-96 "Glass curtain wall Engineering Technical Specifications" issued by the Ministry of Construction, the long-term load is not more than 0.007N/mm2, the short-term maximum load is not more than 0.14N /mm2.
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Q Storage conditions of sealant
A As already mentioned, the sealant is cured by exposure to water in the air, and the storage is stable in the sealed state. However, this stability is not absolute; sealant in the storage process, the packing containing hydroxyl and cross-linking agent, catalyst will cause side reaction. This side reaction will gradually consume the system of cross-linking agent, catalyst, make it gradually fail. The phenomenon is that, with the prolongation of sealant storage time, its curing performance will be reduced when used, such as dry, sticky time prolonged or even cannot be sticky, strength deteriorates, cannot be completely cured, glue thickening and drying, etc. If this change is very weak, adhesive curing performance can also meet the requirements of users and standards, we think the sealant is still in the shelf life, if this change exceeds the limit, the curing performance of sealant cannot meet the requirements, it indicates that it has expired.
Sealant, therefore, the storage life is directly related to the system degree of side effects. Beside system formulation process, side reaction speed and storage conditions is mainly related to temperature: the higher the storage temperature, the faster the adverse events, the storage life of the product is shorter, so we have clear rules for the product storage conditions, and the storage temperature cannot be higher than 27 ° C. Of course, the lower the storage temperature is, the better. Too low storage temperature (such as below 0℃) may cause undesirable changes in the slurry state.
Another factor that needs special attention in the process of sealant storage is tightness. The packaging materials (plastic bottles, flexible packaging aluminum film, etc) must be well sealed. If the seal is not good, the sealant will cure because of contact with the air.
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Q Cause analysis of bubbling
A (1) The sealant is wrapped in air.
Silicone weather-resistant adhesive is generally completed in the site to finish the glue injection work, poor operating conditions. Workers stand on the scaffold to inject glue, the uniformity of glue injection is not easy to master, the glue seam is easy to wrap into air. Sizing surface pressure of the glue line, after finishing is bright and clean, the inside of the glue line mat rods are generally choose the polyethylene closed-cell foam, in the air is not easy to overflow to the glue line, glue line dressing compressed air, produces tension of outward, weather resistance glue line is generally more wide, the thickness of the small, weather resistance adhesive provides high displacement ability, low hardness, adhesive before curing very soft. The tension of compressed air slowly bubbles the glue seam. This phenomenon is more likely to occur in the application of weatherproof adhesive that can provide more than ±25% of the joint displacement capacity. On the contrary, some allow the displacement of the lower weathering resistance adhesive, the hardness is higher, the adhesive is relatively thick before curing. The tension of compressed air wrapped in the rubber seam is not easy to bubble the rubber brace. Therefore, the more can provide high displacement capacity of weatherproof glue, glue injection, more attention should be paid to the uniformity of glue injection. In general, the vertical glue joint can be used from bottom to top sizing, which can overcome some bubbling phenomenon. More important is the operator's proficiency and responsibility.
(2) The interface is wet when the glue is injected.
In outdoor work, often encounter rain, especially in the south in summer, it's going to rain almost every day, if after the rain, interface inside is wet and hit sealant directly, such as sun adhesive base material and the glue line the inside of the interface temperature, glue line the moisture evaporation inside, will not cure the swell, comparison of soft rubber foam, polyethylene foam cushion pole wet sometimes cause glue line blister. Therefore, the construction can not blindly seek progress, wait until the interface dry, then glue, can avoid the above situation.
(3) Deflate the foam rod
Glue line inside the cushion pole is generally choose close pass high foaming polyethylene foam stick, when placed due to improper extrusion, causing internal balloon burst, releasing the air, had just finished injection glue when there are air bubbles uplift or summon up the appearance, methods to solve this kind of situation, it will cut a bubble stick, cutting face to inside, secondly, the use of open-hole foam rod or the use of foamed ethylene foam rod, to overcome the above situation. In another case, alcohol-type weatherproof adhesive will release methanol when cured, which reacts with some foam rods. In such a situation, by changing the foam rod or keto oxime type sealant, it will solve the problem.
(4) Sun exposure when the glue is not cured.
Silicone glue cannot be exposed to the sun before curing, especially just after the injection of the glue to the sun, will cause honeycomb bubbles inside the glue joint, resulting in the external swelling of the glue joint, this situation will be more obvious in the use of alcohol silicone glue. Construction in the hot summer, this situation is not easy to overcome. When using glue to avoid the sun exposure, will overcome some bubbling phenomenon. Specific practice: in the morning in the west or north side of the building glue injection, in the afternoon in the east or south side of the building glue injection. After glue injection, after a period of time of curing, the surface layer is crusted, and when the sun is exposed again, there is a certain resistance, and some foaming phenomenon can be overcome.
(5) The surface temperature of the substrate is too high.
When silicone sealant curing, the temperature of the bonded material can not exceed 50℃, this conclusion has been recognized by most silicone glue manufacturers. When the surface temperature of the substrate is more than 50℃, glue injection will cause foam joints. When the metal plate curtain wall is weatherproof and caulking, the above situation will be encountered. In the hot liters of second jin, when the sun exposed the metal plate, especially the aluminum plate surface temperature will reach 80℃, at this time the glue injection is easy to cause the glue seam blistering. So should choose the latter half of the afternoon or cloudy days to improve the above situation. (6) The temperature difference between day and night is large, and the thermal expansion and cold contraction of the interface is large.
This situation is more likely to occur when the aluminum curtain wall is filled with glue. Aluminum is linear expansion coefficient of the larger material, in the areas of northern China in spring or autumn day and night temperature difference is bigger, and at noon the sun point-blank aluminum plate, aluminum plate surface temperature can be as high as 60 ℃, 70 ℃, at night the temperature fell to around 10 ℃, large aluminum piece, heat bilges cold shrink is bigger also, interface displacement is larger, weather resistance after sealing glue, the actual displacement of the interface is by the glue line to afford, In the curing process, excessive and repeated expansion displacement will cause foaming of the glue joint, so avoid the most direct sunlight at noon when the glue injection, in order to improve some of the above foaming situation. It is dry in spring in the north
Silicone sealant should be with the help of moisture in the air, the chemical reaction into an elastic sealing material. The degree of humidity in the air is closely related to the curing speed. The climate in the north of China is dry in spring, and the curing time is very long after silicone sealant injection. The silicone sealant before curing is extremely vulnerable to the influence of external environment, which provides opportunities for various bubbling phenomena.
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Q The basic use of sealant
A 1. Silicone structural adhesive
（1） It is mainly used for metal and glass curtain wall structure or non-structural bonding assembly.
（2） It can directly connect the glass and metal component surface to form a single component, to meet the requirements of the curtain wall of fully hidden or semi-hidden frame. 3. Structural bonding and sealing of insulating glass.
2. Neutral weather resistant adhesive
（1） Suitable for all kinds of curtain wall weather sealing, especially recommended for glass curtain wall, aluminum plastic plate curtain wall, stone dry hanging weather sealing;
（2）Joint sealing between metal, glass, aluminum, ceramic tile, plexiglass and coated glass;
（3）concrete, cement, masonry, rock, marble, steel, wood, anodized aluminum and painted aluminum surface joint sealing. In most cases, primer is not required.
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Q Applicable substrate restrictions for various types of silicone sealant
A (1) Neutral sealant: alcohol-type sealant releases alcohol when curing, non-corrosive and irritating, and is applicable to most substrates, basically no substrate restrictions. Keto oxime type sealant released keto oxime when curing, and keto oxime is safe for most substrates, but also corrosive for a few substrates: corrosion of copper is more obvious, so it cannot be used for copper substrates. When used for coated glass and mirror glass, because the coating properties are unknown, it is necessary to do the compatibility test first to confirm that there is no corrosion before use
(2) Acid sealant: acid sealant will release acetic acid, and has obvious corrosion to concrete, porous stone, a variety of metal materials. It cannot be used in these substrates, and the reason it can be used for aluminum is that aluminum surface is coated with the oxide film or spraying, and has coating protection.
