In the previous article Discuss the choice of secondary sealant for insulating glass① , we summarized the hazards caused by improper selection of the secondary sealant for insulating glass into two categories: one is the loss of the use function of insulating glass, that is, the loss of the original function of insulating glass; the other involves insulating glass The safety problem of the application is that the outer sheet of insulating glass falls. In this issue of Jinan LIJIANG Glass, we will focus on the second type of problem and analyze the causes and preventive solutions of the hollow glass outer sheet falling caused by the improper selection of the second sealant. The hollow glass will be introduced to you at the end of the article. The principle of the selection of the second glass sealant.
Insulating glass secondary sealant can be divided into structural sealant for insulating glass and elastic sealant for insulating glass according to whether it is suitable for structural assembly. The reason for the falling of the outer sheet of insulating glass is that the second insulating glass sealant is not selected and used according to the specification. Insulating glass secondary sealant generally uses silicone sealant, polysulfide glue and polyurethane glue, but due to polysulfide glue, polyurethane glue has poor UV resistance, and its bonding with glass (the entry "bonding" is defined by Provided by Google) If the noodles are exposed to sunlight for a long time, they will degummed. Therefore, the structural sealant for insulating glass suitable for the second sealing of the structural assembly insulating glass unit can only choose silicone sealant. If silicone insulating glass structural sealant is not used in the hidden frame and semi-hidden frame curtain wall, but silicone insulating glass elastic sealant or polysulfide glue is selected, it is likely to cause the outer sheet of insulating glass to fall.
Case 1: The outer piece of the glass curtain wall fell
Figure 1 Simulation diagram of the scene
The most direct reason for the fall of the outer sheet in this accident was the improper selection of the secondary insulating glass sealant. The silicone insulating glass structural sealant was supposed to be used, but polysulfide glue was used. The polysulfide glue undergoes ultraviolet ray aging and debonding from the glass causes the outer glass to fall.
Figure 2 The hollow glass outer sheet of the opening fan falls off as a whole (the entry "falling off" is provided by Google)
Case 2: Several outer pieces of insulating glass fell from a building in Shanghai overnight.
Figure 3 Several external insulating glass pieces of a building in Shanghai fell
The reason for the falling of the outer sheet was improper selection of the second sealant. The second sealant for the hollow glass used in the hidden frame curtain wall of the residential area did not use the silicone structural sealant.
The above two cases of the outer sheet of insulating glass falling are all caused by improper selection of the second insulating glass sealant. On the one hand, the deeper reasons for improper selection are related to the unprofessional and inaccurate construction personnel; on the other hand, it is more related to the quality problems and safety accidents caused by the blind pursuit of low prices in order to save costs.
Figure 4 The hardness of a second insulating glass sealant in a project (the entry "Injection" is provided by Google) after half a month
As shown in the figure above, the low-cost secondary sealant used in a hollow glass composite has a Shore hardness of 65 after half a month of injection, which does not meet the requirements of relevant standards and will cause hidden dangers to the safety of hollow glass.
Insulating glass secondary sealant must be used in accordance with specifications, especially the secondary insulating glass sealant used for structural assembly is directly related to safety issues. So, Jinan LIJIANG Glass would introduces several principles for the selection of insulating glass sealant.
1. Meet the requirements of the standard.
Insulating glass structural sealant should meet the requirements of category P and H in the relevant industry standard "Silicone Structural Sealant for Insulating Glass", or related industry standard "Insulating Glass Elastic Sealant for Building Doors, Windows and Curtain Walls". The insulating glass elastic sealant shall meet the requirements of category W in the relevant industry standard "Elastic Sealant for Insulating Glass" or the relevant industry standard "Insulating Glass Elastic Sealant for Building Doors, Windows and Curtain Walls".
The secondary sealant for insulating glass of hidden frame and semi-hidden frame curtain wall must use silicone structural sealant, and the interface size must be calculated according to "Glass Curtain Wall Engineering Technical Specification", the minimum bonding width cannot be less than 7mm; point support type The second layer of insulating glass sealant for glass curtain walls must use silicone structural sealant; the second layer of insulating glass sealant for large-size exposed frame curtain walls is recommended to use insulating glass silicone structural sealant; the second layer of insulating glass for doors and windows and ordinary open frame curtain walls The sealant can be insulating glass silicone sealant or polysulfide glue.
2. Do not use oil-filled sealant
As the price of raw materials rises, some manufacturers have sacrificed the performance and quality of sealant products in order to reduce production costs. Filling cheap "mineral oil" instead of expensive silicone base polymer is a common method for poor manufacturers to reduce the production cost of sealants. However, a decrease in the content of the silicone base polymer will inevitably lead to a decrease in the durability of the silicone sealant. At the same time, with the migration of "mineral oil" inside the insulating glass, it also has a great negative impact on the sealing performance of a butyl rubber, causing the insulating glass to fail prematurely. Therefore, as a practitioner with professional ethics, we must refuse to use "oil-extended glue".
In order to prevent silicone sealants from being filled with "mineral oil", the relevant industry standards "Silicon Structural Sealant for Insulating Glass" and "Elastic Sealant for Insulating Glass" stipulate that the thermal weight loss should not exceed 6.0%. However, due to the early formulation of the national standard, there was no detection method for alkane plasticizers in silicone sealants (the entry "plasticizer" is provided by the industry encyclopedia), and only obvious requirements for thermal weight loss were made. In 2015, the relevant industry standards issued by mainstream countries in Europe and the United States, "Testing Methods for Alkane Plasticizers in Silicone Structural Sealants (the entry "Plasticizing" is provided by Google)" stipulated the testing methods for silicone sealants alkane plasticizers It is recommended that users use standard methods to actively identify them, and never use hollow secondary sealant products containing alkane plasticizers.
Next, I will also share with you the simple identification method "film method" (the entry "film" is provided by Google). Glue on PE film with a thickness of 10-12 silk to qualitatively detect whether the sealant is filled with mineral oil.
The test process is as follows: On the flat PE plastic film, make a "mouth"-shaped glue, scrape it evenly to the thickness of about 1-3mm, and observe the film flatness after 24 hours. The film contacted by the oil-filled sealant will be uneven (Figure 6, left picture). The more oil-filled, the more serious the unevenness will be. The film contacted by the non-oil-filled sealant will remain flat (Figure 6, right picture).
Figure 6 "Thin film method" can easily identify whether the sealant is filled with "mineral oil"
3. Choose brand products with good reputation and good service
The choice of product brand is recommended to pay attention to product quality stability, service level, etc. Product quality stability is mainly related to production process, production control and quality control. Therefore, it is recommended to choose a sealant manufacturer with mature production technology, high degree of automation, and strict production control and quality control. The products produced by this kind of manufacturers have high quality and excellent performance, and can provide durability and service life superior to ordinary products.
The service level is mainly related to the technical service ability and level of the sealant manufacturer in the whole process of pre-sale, in-sale and after-sale. Pre-sale design consultation, drawing review, glue recommendation, solutions, etc., compatibility, adhesion, pollution test during sale, on-site training, problem solving, rubber tapping test, quality monitoring, etc., after-sale quality assurance and Return visits and other technical services covering the entire process of sealant application are a manifestation of the service level of sealant manufacturers.
In short, the second insulating glass sealant does not account for a high proportion of the cost of insulating glass, but it is very important to the quality and safe application of insulating glass. It is recommended that users must choose the right product and the good product. If blindly pursuing low prices and neglecting the correct application and quality assurance of products, it may cause quality problems for curtain wall doors and windows, and even cause major safety accidents.