Analysis of the causes of cracking of silicone sealant after curing.
There are three forms of silicone sealant cracking: cohesive failure, which is manifested as cracking in the middle of the glue seam; cohesive failure, which is manifested as cracking on both sides of the glue seam; mixed failure, which is manifested as the middle crack of the glue seam and the cracking on both sides. The following editors explain the reasons for the cohesive damage and adhesive damage of the sealant:
The cohesive failure of the sealant usually manifests as a crack in the middle of the colloid (the sealant in the glue seam is cured after curing), because the thinnest in the middle is pulled first. Cause Analysis:
1. Quality problem of sealant
1. With the continuous precipitation of white oil for a long time, it causes excessive shrinkage, stiffness, and loss of displacement capacity of the joint colloid, and it cannot adapt to the displacement of the thermal expansion and contraction of the substrate to cause cracking.
2. The content of the cross-linking agent in the formula is small, which is not enough to make the sealant react to form a perfect cross-linking network structure, there are structural defects, and it is easy to cause the colloid to crack.
3. The sealant is not used within the validity period.
Second, the reasons for application
1. The seam design is unreasonable, and the seam width is less than 6mm, which is easy to cause cracking.
2. A large number of bubbles formed during the sizing process can easily cause colloid cracking.
3. The uneven thickness of the sizing is easy to cause the colloid to crack in the thin place.
4. When the surface temperature of the substrate is too high or too low, the colloid is easy to crack after the glue is cured.
5. The sealant is easily cracked after curing by external force during curing.
6. Subject to large external forces or large deformation of the substrate, for example, earthquakes, typhoons, etc., the colloid may crack.
7. When the three-sided bonding phenomenon occurs, the displacement that the sealant can withstand will be limited to within ±15% of the original design displacement, which will easily cause the colloid to crack.
1. The displacement capacity of the selected sealant cannot meet the joint displacement requirements.
2. The modulus of the selected sealant does not meet the seam requirements.
3. Bonding damage.
Adhesive failure refers to poor adhesion between the sealant and the substrate, resulting in poor sealing effect. Usually manifested as peeling of the substrate and sealant. Cause Analysis:
4. Practical issues
1. Improper cleaning method of substrate surface and inappropriate use of cleaning solvents;
2. The cleaning of the surface of the substrate does not meet the requirements for applying the sealant. When the sealant is applied, the surface of the substrate is not volatile and dry;
3. The primer used is improper or the primer has failed before use;
4. Excessive primer applied on the surface of the substrate, and the surface of the substrate did not evaporate and dry when applying sealant
5. The sealant in the interface is not fully compacted during the application of the sealant;
6. The contact area between the sealant and the substrate is too small to ensure the adhesion between the sealant and the substrate (unreasonable interface design);
7. The sealant is affected by the outside during the curing process, such as wind load, thermal expansion and contraction of the substrate, etc.;
8. During construction, the ambient temperature is lower than 5 ℃, causing condensation and concealment on the surface of the substrate.