Analysis of Common Problems in Structural Sealant Service

1 Introduction

Structural adhesive is high strength, can withstand a larger load, and anti-aging, fatigue resistance, corrosion resistance, stable performance in the life expectancy, suitable for structural adhesive bonded to the adhesive. Mainly used for metal, ceramics, plastics, rubber, wood and other materials or different materials between the bonding, can be part of the replacement welding, riveting, bolting and other traditional forms of connection. Silicone structural sealant is the key material used in the whole or semi-hidden frame glass curtain wall. It is directly related to the durability and safety of the curtain wall structure by connecting the plate and the metal frame, bearing the wind load and the self load load of the glass. One of the key aspects of glass curtain wall safety. It is a linear polysiloxane as the main raw material of the structural sealant, in the curing process, the cross-linking agent and the base polymer to form a three-dimensional network structure of the elastic material. (Si-O specific physical and chemical properties: bond length 0.164 ± 0.003nm, thermal dissociation energy of 460.5J / mol, which is obviously higher than that of CO (superscript 2 +). The Si-O bond in the molecular structure of silicone rubber can be larger in the common chemical bond 358J / mol, CC 304J / mol, Si-C318.2J / mol), compared to other sealants (such as polyurethane, acrylic acid, polysulfide sealant, etc.), the resistance to ultraviolet light and resistance to atmospheric aging, In a variety of weather conditions can be maintained for 30 years without cracking, no deterioration, in a wide temperature range with ± 50% resistance to deformation displacement.

However, with the increase in the amount of silicone sealant used in the application, there will be a variety of problems in practical applications, such as: B component with the phenomenon of agglomeration of particles, B component separation and delamination, pressure The disk does not go down or turn the phenomenon of glue, glue machine out of the plastic slow, butterfly chip colloidal particles, the surface dry pull off time too fast or too slow, colloidal crust or vulcanization phenomenon, glue the process of “plastic “Colloid can not be normal curing, curing a few days after the sticky hand, after curing hardness is not normal, and the substrate bonding surface needle hole, glue folder with bubbles, poor adhesion with the substrate, and accessories are not compatible Wait. In the following, we will analyze the possible causes of the common problems in the process of structural glue service, and give the corresponding solution ideas, expect to provide reference for practical problem analysis.

2. Analysis of common problems in structural adhesive service

2.1 The B component has the phenomenon of agglomeration of particles

If the B component of the phenomenon of agglomeration of particles agglomeration, there are two reasons: First, the use of the former upper layer has been the phenomenon, which is due to poor packaging, B component of the cross-linking agent or coupling agent For the active compound, easy to react in the air of water, the batch should be returned to the manufacturer. Second, in the course of the use of downtime, re-boot when the phenomenon of particles agglomeration powder, indicating the pressure of the plastic plate and rubber seal is poor, should be linked with the equipment to solve the problem.

2.2 glue machine out of the plastic slow

Products in the initial use, the gumbing machine during the process of glue is too slow phenomenon, there may be three reasons: ⑴ A component of poor mobility, ⑵ pressure plate is too large, ⑶ gas pressure is not enough. When determining the reason for ⑴ or cause ⑶, we can solve the pressure by adjusting the glue gun pressure; when it is determined that the second reason, the order matching the caliber barrel can solve the problem. In the normal use of the process if the glue speed slowed down, it may be mixed with the filter and the filter is blocked, once found, you need to clean up the device in time.

2.3 pull off time too fast or too slow

The breaking time of the structural glue refers to the time when the colloid is mixed into the elastomer by the paste, and is usually tested every 5 minutes. There are three factors that affect the dry curing of the plastic sheet: (1) the influence of the proportion of A and B components; (2) the temperature and humidity (in which the temperature is the main); (3) the formula of the product itself is defective.

The solution for the reason ⑴ is to adjust the proportion of the ratio, increase the proportion of B component can shorten the curing time, hardening and hardening of the adhesive layer; and reduce the proportion of curing agent, will extend the curing time, the layer becomes soft, toughness and strength reduce. In general, the volume ratio of A: B components can be adjusted between (9 ~ 13: 1), the high proportion of B component is fast, the time is short, the reaction is too fast will affect the time of dressing and stopping the gun, Too slow will affect the colloid of the whole dry time, pull off the time is generally adjusted between 20 to 60 minutes, the proportion of solidification after the colloid performance is basically the same. In addition, when the construction temperature is too high or too low, we can appropriately reduce or increase the proportion of B component (curing agent), so as to achieve the purpose of adjusting the colloid surface and curing time. If the product itself is a problem, you need to replace the product.

2.4 glue the process of “plastic”

Patch is due to A / B component colloid mixed uneven produce, the performance of local white stripes. (3) the size of the loose, the glue speed is not uniform; ⑷ for manufacturers or grades not to adjust the equipment process parameters; for the reasons ⑴, ⑵, â € ¢ â,¬ â- Can be resolved by cleaning equipment; for reasons ⑶, you need to check the proportional controller, and make the appropriate adjustments.

2.5 colloid in the process of colloidal crust or vulcanization phenomenon

When the two-component glue in the mixing process occurs when the local curing, glue gun shot out of the glue will appear crust or vulcanization phenomenon. When the curing and the glue speed are no exception, and play the plastic is still crust or vulcanization phenomenon, it may be a long time to stop the device, glue gun is not clean or wash gun is not thorough, need to crust or vulcanized rubber Clean after construction.

2.6 glue inside the folder with bubbles

In general, the colloid itself is no bubbles, colloidal folder is likely to be transported or the construction process mixed with the air, such as: ⑴ replace the plastic bucket when the exhaust is not clean; (2) components in the machine after the pressure plate Not pressure down, resulting in the bubble is not complete. Therefore, before use in the bubble to be thoroughly, the use of the process should be properly operated glue machine to ensure that the seal to prevent air from entering. If you suspect that the product itself with bubbles, you can judge through the butterfly test.

1

Poor bonding with the substrate

Sealant is not a universal glue, so in practice can not guarantee that all substrates are well bonded. With the current substrate surface treatment and the diversification of new technology, sealant and substrate bonding speed and bonding effect is also different.

 2

There are three types of bonding between the structural adhesive and the substrate. One is the cohesive failure, that is, the cohesive force> cohesion; the second is the bond failure, that is, the cohesive force, the cohesive force, If the damage area is less than or equal to 20%, the bond failure area is more than 20%. When the bonding damage area is more than 20%, the undesirable phenomenon is not expected. The reason for the non-sticking of the structural adhesive and the substrate may be as follows:

⑴ use of the substrate itself is difficult to bond, such as PP, PE, because of its high molecular crystallinity, surface tension (the “surface tension” by the industry encyclopedia) low, can not form a molecular chain with most substances Diffusion and entanglement, and thus can not form a strong adhesion at the interface;

⑵ product bonding range is narrow, only part of the substrate work;

⑶ maintenance time is not enough Usually two-component structure after the role of plastic, at least 3 days of conservation, while the one-component will have to maintain 7 days, if the conservation of environmental temperature and humidity is low, you need to extend the curing time.

⑷ A, B component ratio is wrong. Users in the use of two-component products, must be in strict accordance with the requirements of the proportion of manufacturers to adjust the proportion of base rubber and curing agent, or may be in the early curing problems, or the use of late in the bond, weather resistance and durability problem;

⑸ did not clean the substrate as required. As the surface of the substrate dust, dirt and impurities will hinder the bond, so use it before the strict cleaning to ensure that the structural adhesive and substrate bonding good.

⑹ did not apply the primer as required. It is also possible to improve the water resistance of the adhesive (shortening the bonding time) by using the primer on the surface of the aluminum profile (the term “pretreatment” is provided by the industry) Encyclopedia provides) and durability [3]. Therefore, in practical engineering applications, we should use the primer properly, strictly avoid the use of improper use of degumming caused by [4].

2.8 is not compatible with the attachment

And incompatible with the attachment is because the sealant and contact with the annex produced a physical or chemical reaction, the harm caused by the structure of plastic discoloration, and the substrate is not sticky, structural adhesive performance degradation, structural adhesive life shorter.

3 Conclusion

Silicone structural adhesive (the term “silicone adhesive” provided by the industry Encyclopedia) has high strength, high stability, excellent resistance to aging, high temperature and other excellent performance, widely used in building curtain wall structure bonding. However, in practical applications due to human factors and the choice of substrate problems (can not strictly comply with the construction specifications), the performance of structural adhesives have a great impact, or even failure. Therefore, before the construction should check the glass, aluminum and accessories compatibility test and bond test, the construction process should be strictly in accordance with the requirements of all aspects, in order to achieve the effect of structural glue to ensure the quality of the project.


Post time: Feb-27-2017
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