Structural adhesive is a type of adhesive that has high strength, can withstand large loads, and is resistant to aging, fatigue, and corrosion. It has stable performance throughout its expected lifespan and is suitable for bonding structural components. Mainly used for bonding the same or different materials such as metal, ceramic, plastic, rubber, wood, etc., it can partially replace traditional connection forms such as welding, riveting, and bolt connection. Silicone structural sealant is a key material used in fully concealed or semi concealed frame glass curtain walls. By connecting panels and metal frames, it can withstand wind loads and the self weight load of glass, directly affecting the durability and safety of building curtain wall structures. It is one of the key links in the safety of glass curtain walls.


With the increase in the use of silicone structural sealant, various problems may arise in practical applications, such as particle agglomeration and pulverization of component B, segregation and layering of component B, inability of the pressure plate to press down or flip the glue, slow glue dispensing speed of the glue dispenser, particles in the butterfly plate glue, too fast or too slow surface drying and breaking time, glue caking or vulcanization, and occurrence of "" during the glue dispensing process; Flower glue&rdquo Colloids cannot cure properly, stick to hands after a few days of curing, have abnormal hardness after curing, have needle like pores on the surface of the adhesive with the substrate, have bubbles in the adhesive, have poor adhesion with the substrate, are incompatible with attachments, and so on. Below, we will analyze the possible causes of several common problems that occur during the structural adhesive service process and provide corresponding solutions, hoping to provide reference for practical problem analysis.
 
The dispensing speed of the glue machine is slow
When the product is first used, there may be three possible reasons for the slow dispensing speed of the glue machine during the gluing process: ⑴ Component A has poor fluidity, ⑵ the pressure plate is too large, and ⑶ the gas source pressure is insufficient. When it is determined to be cause ⑴ or cause ⑶, we can solve it by adjusting the pressure of the glue gun; When it is determined to be the (2) reason, ordering a matching caliber barrel can solve the problem. If the dispensing speed slows down during normal use, it may be due to blockage of the mixing core and filter screen. Once discovered, the equipment needs to be cleaned in a timely manner.
 
During the gluing process, there is an occurrence of; Flower glue”
Flower gum is produced due to uneven mixing of A/B component colloids, manifested as local white stripes. The main reasons are: ⑴ Blockage of component B pipeline in the glue machine; ⑵ The static mixer has not been cleaned for a long time; ⑶ The scale is loose and the dispensing speed is uneven; ⑷ Changing manufacturers or brands without adjusting equipment process parameters; For reasons ⑴ and ⑵, they can be solved by cleaning the equipment; For reason ⑶, it is necessary to check the proportional controller and make appropriate adjustments.
 
During the gluing process, the colloid may form a crust or sulfide
When the two-component adhesive undergoes local curing during the mixing process, the adhesive produced by the glue gun will exhibit skinning or vulcanization. When there are no abnormalities in the curing and dispensing speed, but the produced adhesive still has crust or vulcanization, it may be due to the equipment being shut down for a long time, the glue gun not being cleaned thoroughly, or the gun not being washed thoroughly enough. It is necessary to wash the crust or vulcanized adhesive thoroughly before construction.
 
B component has particle agglomeration and pulverization phenomenon
If component B shows particle agglomeration and pulverization, there are two reasons: one is that this phenomenon has already appeared on the upper layer before use, which is due to poor packaging sealing. The crosslinking or coupling agents in component B are active compounds that are prone to react with water vapor in the air. This batch should be returned to the manufacturer. The second issue is that when the machine is stopped during use and restarted, there is a phenomenon of particle agglomeration and pulverization, indicating poor sealing between the pressure plate and the adhesive material of the glue machine. The equipment should be contacted to solve the problem.
 
There are bubbles trapped inside the adhesive
Generally speaking, colloids themselves do not have bubbles, and the bubbles contained in colloids are most likely due to the mixing of air during transportation or construction, such as: ⑴ incomplete exhaust when replacing the glue barrel; ⑵ The components were not pressed down by the pressure plate after being loaded onto the machine, resulting in incomplete bubble removal. Therefore, when using the front row foam, it is necessary to be thorough, and the glue machine should be operated correctly during use to ensure sealing and prevent air from entering. If you suspect that the product itself contains bubbles, you can use the butterfly test to make a judgment.
 
Poor adhesion to substrate
Sealing glue is not a universal adhesive, so it cannot guarantee good adhesion with all substrates in practical applications. With the diversification of surface treatment methods and new processes for substrates, the bonding speed and bonding effect between sealants and substrates are also different.
There are three forms of interface failure between structural adhesive and substrate, one is cohesive failure, that is, adhesive strength>; cohesion; The second is adhesive failure, that is, adhesive strength<; Cohesion refers to both forms of failure. If the adhesive failure area is less than or equal to 20%, it is qualified. If the adhesive failure area exceeds 20%, it is unqualified; When the adhesive failure area exceeds 20%, it is an undesirable phenomenon in practical applications.


Reasons for non adhesion between structural adhesive and substrate
⑴ The substrate itself is difficult to bond, such as PP PE,， Due to its high molecular crystallinity and low surface tension, it is unable to form molecular chains for diffusion and entanglement with most substancesTherefore, it is unable to form strong adhesion at the interface.

⑵ The product has a narrow bonding range and can only work on some substrates.

⑶ Insufficient maintenance time. Usually, after the two-component structural adhesive acts, it needs to be cured for at least 3 days, while the single component needs to be cured for 7 days. If the temperature and humidity of the curing environment are low, the curing time needs to be extended.

⑷ A. The proportion of component B is incorrect. When using two-component products, users must strictly follow the manufacturer's required ratio to mix the base adhesive and curing agent, otherwise there may be problems in the early curing process, or in terms of adhesion, weather resistance, and durability in the later stages of use.

⑸ The substrate was not cleaned as required. Due to the presence of dust, dirt, and impurities on the surface of the substrate, it is necessary to strictly clean it before use to ensure good adhesion between the structural adhesive and the substrate.

⑹ Not applying the primer as required. Pre treatment with primer on the surface of aluminum profiles can not only shorten the bonding time, but also improve the water resistance and durability of the bonding. Therefore, in practical engineering applications, we need to use the primer correctlyStrictly avoid delamination caused by improper use.