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Structural adhesives have high strength, can withstand large loads, are resistant to aging, fatigue, and corrosion, and have a stable performance within the expected life span. They are suitable for adhesives that bear the bonding of structural parts. It is mainly used for bonding metal, ceramics, plastics, rubber, wood, etc., or between different kinds of materials, and can partially replace traditional connection forms such as welding, riveting, and bolting. The following is a detailed introduction to how to use the structural adhesive and how to use the silicone structural adhesive.

1. How to use structural adhesive?

Silicone structural adhesive should be used in a clean environment with a temperature of 5°C-405°C and a relative temperature of 40%-80%r so that a better bonding effect can be obtained.

Temporary protective tape should be attached to the area near the surface of the cleaned substrate to be bonded. If the primer is to be used, it should be applied before applying glue.

The one-component structural adhesive can be directly squeezed out of the plastic tube or sausage-type packaging by manual or pneumatic sizing. The two-component structural adhesive must be sized using special sizing and mixing equipment.

The extrusion action of the structural glue should be carried out continuously so that the glue can be extruded evenly and continuously in a cylindrical shape. The diameter of the nozzle should be smaller than the thickness of the nozzle so that the nozzle can reach half of its depth. The gun nozzle moves evenly and slowly to ensure that the interface is filled with sealant to prevent bubbles or cavities from moving too fast.

After the glue injection is completed, trimming is performed immediately. The usual method is to use a scraper to press the extra structural glue outside the interface into the interface and sequentially scrape the interface surface smoothly so that the glue contacts the side of the interface, and then remove all temporary Protective tape.

Figure 1 Using a scraper to press the extra structural glue 1

Figure 1 Using a scraper to press the extra structural glue 1

Immediately after the above process, a label with the date and number should be affixed to the unit, and the unit should be played horizontally in the curing area for maintenance. During the handling process, the aluminum frame and the upper glass should not be allowed to cause any displacement or misalignment. Otherwise, it will affect the bonding quality of the structural adhesive.

The curing area must be clean, with good ventilation conditions, and the temperature should be maintained at 5°C-40°C. The relative temperature should be kept at 40%-80%; if the temperature is lower than 50%, the maintenance time of the unit should be extended.

The single-component must be cured for sufficient time under static and unstressed conditions, including at least 21 days for single-component structural adhesive and at least 14 days for two-component structural adhesive, so that the structural adhesive can produce sufficient adhesive force. After cutting the rubber, only the unit products that pass the inspection can be shipped and installed.

The user should pay attention to the double-sided coating method when the design width of the glue joint is greater than 16mm, that is, the double-sided tape is placed in the middle of the glue joint, and the glue is applied on both sides of the tape to speed up the curing speed of the glue and avoid The air permeability of the double-sided adhesive tape is not good, which affects the deep curing of the adhesive.

Figure 2 How to use insulating glass silicone structural adhesive 1

Figure 2 How to use insulating glass silicone structural adhesive 1

2. The use and requirements of structural adhesives

2.1. Structural glue should be constructed in a specially set glue injection room. 

The glue injection room is required to be clean, dust-free, no fire, and ventilated. The indoor temperature should be controlled at 23±5°C, and the relative temperature should be controlled at 70%±5%. Glue injection operators must receive special business training and pass the actual operation assessment before they can work with a certificate. It is strictly prohibited to use expired silicone structural adhesives, and it is strictly prohibited to use silicone structural adhesives that have not undergone compatibility tests, butterfly tests, and other related inspections and have passed all inspection parameters.

2.2. Clean the glue injection area. 

Use cleaning agents, cleaning cloths, protective tapes, and other auxiliary materials in strict accordance with the requirements of standard specifications, design drawings, and process regulations. For the cleaning of the substrate at the glue injection site, for non-oily pollutants, a mixed solvent of 50% isopropanol and 50% of water is usually used; for oily pollutants, xylene solvent is usually used. The cleaning cloth should be a clean, soft, non-shedding white or natural-color cotton cloth, and the cloth should not be dipped into the container containing the detergent to avoid contamination of the entire solvent. When cleaning, use the "twice wipe" process to clean. After cleaning, the cleaned part must not be in contact with hands or other sources of pollution, otherwise, it must be cleaned again. The cleaned substrate must be injected within 15-30 minutes, otherwise, a second cleaning must be performed.

2.3. Mixing of structural adhesives. 

The two-component silicone structural glue should be mixed with a special two-component silicone glue maker. When mixing the glue, you should clean the glue maker according to the instructions of the glue maker, adjust the glue nozzle, and then follow the regulations. The mixing ratio is equipped with a two-component sealant for thorough mixing. To control the mixing of the structural adhesive, the butterfly sample and the rubber cup pull-off sample should be set aside during each mixing process, check the mixing of the structural adhesive in time, and make a record of the shift. The butterfly test is to check whether the structural glue is fully mixed, and the color of the structural glue is uniform and fully mixed to inject the glue. The butterfly sample number must be recorded during the whole process of mixing.

The glue cup test is used to check the mixing ratio of the two-component silicone structural gum base and curing agent.

Figure 3 The mixing of two-component silicone structural adhesives 1

Figure 3 The mixing of two-component silicone structural adhesives 1

2.4. Injection of structural adhesive. 

The structural glue must be injected mechanically, and the glue injection should be carried out to remove the air in the glue injection gap; the nozzle of the glue injection gun should be inserted into the appropriate depth, so that the glue is continuously, evenly, and fully injected into the glue gap, No air bubbles are allowed; the pressure should be adjusted at the joint to ensure that there is enough silicone structural adhesive. During the glue injection process, pay attention to the color change of the silicone structural glue to judge the change in the mixing ratio of the structural glue. Once the mixing ratio of the structural glue changes, the machine should be shut down and repaired immediately, and the glue at the changed part should be cut off. Fill up with qualified structural glue. After the glue is injected, it should be flattened with a scraper to scrape off the excess structural glue, and the exposed surface should be trimmed to make the surface smooth and without bubbles in the seam. Make a record of glue injection in time for glue injection. The finished glass components after glue injection should be sampled for cutting and peeling test to check the firmness of the bonding and the degree of curing.

3. How to use silicone structural adhesive

3.1. One-component silicone structural adhesive can be directly applied to the bonding between aluminum and glass. It hydrolyzes by absorbing moisture in the air, and the condensation reaction solidifies from the surface to the inside. The glue room is required to be clean and the temperature Not less than 23°C and relative humidity is not less than 40%, otherwise it will affect the curing and reduce the strength of the adhesive layer.

3.2. The one-component silicone structural glue is divided into acidic and neutral. When the acidic glue is cured, it releases acetic acid, which will corrode the film of the coated glass produced by the vacuum magnetic sputtering method for the hidden frame curtain wall, so it should be used. Neutral silicone structural adhesive.

3.3. Before using the two-component silicone structural adhesive, an accelerator must be added to the base rubber, and the aluminum material and glass must be fully mixed and coated in a special glue machine for bonding and curing. Two-component glues are all neutral glues.

3.4. Silicone structural adhesive has an outstanding feature. That is to say, there is a compatibility problem between the glue and the bonded aluminum, glass, and foam strips. A compatibility test is required. This kind of test cannot be done in China for the time being.

If the compatibility test results show that the structural adhesive is incompatible with one of the three materials, even during the bonding process, all the strength indicators at that time meet the requirements. After half a year or a little longer, the silicone structural adhesive will begin to discolor and change into a liquid state and lose its binding ability. The glass will fall, causing serious consequences. Therefore, to ensure the long-term bonding ability of the silicone structural adhesive, a compatibility test must be done.

4. Analysis of common problems in structural adhesive services

4.1 B component has the phenomenon of particle agglomeration and pulverization

If component B has particles agglomerated and pulverized, there are two reasons: one is that the upper layer has already appeared before use. This is because the packaging and sealing is not good, and the crosslinking agent or coupling agent in component B is all It is an active compound that is easy to react with moisture in the air, and the batch should be returned to the manufacturer. The second is to stop the machine during use, and the phenomenon of particle agglomeration and pulverization occurs when the machine is turned on again, indicating that the pressure plate of the glue spreader and the rubber material is not well sealed, and the equipment should be contacted to solve the problem.

4.2 the glue dispensing machine is slow

When the product is used for the first time, the glue output speed of the glue machine is too slow. There are three possible reasons: 

(1) The fluidity of component A is poor, 

(2) the pressure plate is too large, and the gas source pressure is not enough. 

When it is determined to be the cause (1) or cause (3), we can solve it by adjusting the pressure of the glue gun; when it is determined to be the cause (2), ordering barrels with matching calibers can solve the problem. If the glue output speed slows down during normal use, it may be that the mixing core and filter are blocked. Once found, the equipment needs to be cleaned in time.

4.3 the break time is too fast or too slow

The breaking time of structural adhesive refers to the time for the colloid to change from paste to elastomer after mixing, and it is generally tested every 5 minutes. Three factors affect the dry curing of the rubber sheet: 

(1) The influence of the ratio of A and B components, etc.; 

(2) Temperature and humidity (the influence of temperature is the main one); 

(3) The product's formula is defective.

The solution for reason (1) is to adjust the ratio. Increasing the proportion of component B can shorten the curing time and make the adhesive layer harder and brittle; while reducing the curing agent ratio will prolong the curing time, the adhesive layer will become softer, and the toughness will increase and the strength will be increased. reduce. Generally, the volume ratio of the A: B component can be adjusted between (9~13:1). The higher the ratio of the B component, the faster the reaction speed and the short breaking time. If the reaction is too fast, it will affect the time of trimming and stopping the gun. Too slow will affect the total drying time of the colloid. The breaking time is generally adjusted between 20 and 60 minutes. The performance of the colloid after curing in this ratio range is the same. 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 purpose of adjusting the surface drying and curing time of the colloid. If the problem is with the product itself, the product needs to be replaced.

4.4 "Confusion glue" appears in the gluing process

Flower gum is produced due to the uneven mixing of the A/B component colloids, and it appears as partial white streaks. The main reasons are: 

(1) The pipe of component B of the glue dispenser is blocked; 

(2) The static mixer has not been cleaned for a long time; 

(3) The scale is loose and the glue output speed is uneven; 

(4) The equipment process parameters are not adjusted by changing the manufacturer or the brand; 

for the reasons (1), (2), It can be solved by cleaning the equipment; for the reason (3), you need to check the proportional controller and make appropriate adjustments.

Figure 4 The mixing of the A/B component colloids 1

Figure 4 The mixing of the A/B component colloids 1

4.5 Skinning or vulcanization of the colloid during the gluing process

When the two-component glue is partially cured during the mixing process, the glue shot by the glue gun will appear skinning or vulcanization. When there is no abnormality in the curing and glue output speed, but the glue is still crusted or vulcanized, it may be that the equipment has been down for a long time, the glue gun has not been cleaned or the gun has not been washed thoroughly, and the skin or vulcanized glue needs to be rinsed Construction after cleaning.

4.6 Air bubbles are trapped in the glue

Generally speaking, the colloid itself has no air bubbles, and the air bubbles contained in the colloid are most likely to be mixed with air during transportation or construction, such as ⑴The exhaust is not exhausted when the rubber bucket is replaced; ⑵The components are pressed after the machine is put on the plate. Not pressed down, resulting in incomplete evacuation. Therefore, drain the bubbles thoroughly before use, and operate the glue dispenser correctly during use to ensure a seal to prevent air from entering. If it is suspected that the product itself contains bubbles, it can be judged by the butterfly test.

In order to avoid more air bubbles in the process of insulating glass coating process, you can use the manual two-component sealant sealing machine or automatic insulating glass sealing robot machine made by Jinan LIJIANG Glass, especially the fully-automatic sealing robot machine, which can effectively solve the problem of bubbles and glue coating and the problem of gluing unevenness.

Manual two-component silicone sealant machine
Automatic insulating glass sealing robot machine

4.7 Poor adhesion to the substrate

Sealant is not a universal glue, so it cannot guarantee good adhesion to all substrates in practical applications. With the diversification of substrate surface treatment methods and new processes, the bonding speed and bonding effect of sealants and substrates are also different.

There are three forms of failure of the bonding interface between the structural adhesive and the substrate. One is a cohesive failure, that is, adhesion & cohesion; the other is adhesion failure, that is, adhesion < cohesion. The third is both failure modes. If the bond failure area is less than or equal to 20%, it is qualified, and if the bond failure area exceeds 20%, it is unqualified; when the bond failure area exceeds 20%, it is an undesirable phenomenon in practical applications. There may be six reasons why the structural adhesive does not stick to the substrate:

(1) The substrate itself is difficult to bonds, such as PP and PE. Due to their high molecular crystallinity and low surface tension, they cannot form molecular chain diffusion and entanglement with most substances, so they cannot form a strong interface at the interface. 

(2) The product has a narrow bonding range and can only work on part of the substrate;

(3) The maintenance time is not enough. Normally, after the two-component structural glue is used, it should be cured for at least 3 days, while the single component should be cured for 7 days. If the temperature and humidity of the curing environment are low, the curing time needs to be extended.

(4) The ratio of A and B components is wrong. When using a two-component product, the user must mix the ratio of base gum and curing agent in strict accordance with the ratio required by the manufacturer, otherwise, there may be problems in the early curing, or the adhesion, weather resistance, and durability in the later stage of use problem.

(5) The substrate is not cleaned as required. Because the dust, dirt, and impurities on the surface of the substrate will hinder the bonding, it must be strictly cleaned before use to ensure that the structural adhesive is well bonded to the substrate.

(6) The primer is not applied as required. The use of primer on the surface of aluminum profiles for pretreatment can shorten the bonding time while improving the water-resistance and durability of the bonding. Therefore, in actual engineering applications, we must use the primer correctly and strictly avoid degumming caused by improper use.

4.8 Incompatible with accessories

The reason for the incompatibility with the accessories is that the sealant has a physical or chemical reaction with the accessories in contact, which causes the hazards such as discoloration of the structural adhesive, non-stick to the substrate, decreased performance of the structural adhesive, and shortened life of the structural adhesive.

The above is the detailed introduction of how to use structural adhesives and how to use silicone structural adhesives summarized by Jinan LIJIANG Glass. Silicone structural adhesives have high strength, high stability, excellent aging resistance, high-temperature resistance, and other excellent properties, and are widely used in The structural bonding aspect of the building curtain wall. The editor of Jinan LIJIANG Glass once again reminded us that the compatibility test and adhesion test of the glass, aluminum, and accessories should be checked before the construction of the silicone structural adhesive. The construction process should be carried out in strict accordance with the requirements of each link, to achieve the structural adhesive Effectiveness to ensure the quality of the project.

 For more information about Jinan LIJIANG Glass insulating glass processing equipment and insulating glass processing accessories, please click here to learn more. 

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