Analysis of Common Problems in Structural Adhesive Services

4.1. Component B exhibits particle agglomeration and pulverization
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.
4.2. Slow dispensing speed of glue machine
When the product is first used, there may be a phenomenon of slow glue dispensing speed during the gluing process of the glue machine. There are three possible reasons: ⑴ poor flowability of component A, ⑵ excessive pressure plate, and ⑶ insufficient air source pressure. 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.
4.3. Breaking time too fast or too slow
The breaking time of structural adhesive refers to the time it takes for the colloid to change from paste to elastomer after mixing, and is generally tested every 5 minutes. There are three factors that affect the dry curing of the adhesive surface: (1) the influence of the proportion of components A and B; ⑵ Temperature and humidity (with temperature being the main factor); The formula of the product itself has defects.
The solution to cause ⑴ is to adjust the proportion of component B, which can shorten the curing time and make the adhesive layer harder and more brittle; Reducing the proportion of curing agent will prolong the curing time, soften the adhesive layer, enhance toughness, and reduce strength. The volume ratio of component A to component B can be adjusted within the range of (9-13:1). A higher proportion of component B results in a faster reaction rate and shorter fracture time. If the reaction is too fast, it will affect the time for trimming and stopping the gun, while if it is too slow, it will affect the time for the colloid to dry completely. The fracture time is generally adjusted between 20-60 minutes. After solidification, the colloid properties are basically the same within this ratio range. In addition, when the construction temperature is too high or too low, we can appropriately reduce or increase the proportion of component B (curing agent) to achieve the goal of adjusting the surface drying and curing time of the colloid. If there is a problem with the product itself, it needs to be replaced.
4.4. "Flower glue" appears during the gluing process
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 Loose scale and uneven dispensing speed; ⑷ Failure to adjust equipment process parameters when changing manufacturers or brands; 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.
4.5. 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.
4.6. Bubbles are 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: (1) 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.
4.7 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 force>cohesive force; The second is adhesive failure, which means that the adhesive force is less than or equal to cohesive force. The third is that both forms of failure exist, and the adhesive failure area is qualified if it is less than or equal to 20%. 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. There may be six possible reasons for the non adhesion between structural adhesive and substrate:
The substrate itself is difficult to bond, such as PP and PE. Due to their high molecular crystallinity and low surface tension, they cannot form molecular chains for diffusion and entanglement with most substances, thus 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.
The proportion of components A and 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 Failure to clean the substrate 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.
(6) Failure to apply 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 correctly and strictly avoid delamination caused by improper use.
4.8 Incompatibility with attachments
The reason for incompatibility with attachments is that the sealant has undergone physical or chemical reactions with the attachments in contact, resulting in hazards such as discoloration of the structural adhesive, non adhesion to the substrate, decreased performance of the structural adhesive, and shortened service life of the structural adhesive.
The above is a detailed introduction to how to use structural adhesive and how to use silicone structural adhesive. Silicone structural adhesive has excellent properties such as high strength, high stability, aging resistance, and high temperature resistance, and is widely used in the structural bonding of building curtain walls. The editor of Xianji.com once again reminds that before the construction of silicone structural adhesive, compatibility and adhesion tests of glass, aluminum and accessories should be checked. During the construction process, strict adherence to the requirements of each link should be carried out to achieve the effect of structural adhesive and ensure the quality of the project.