According to the following calculation to determine the minimum width of the joint. Generally speaking, the filling width of elastic sealant can not be less than 6mm, and can not be greater than 30mm. It is difficult to repair the adhesive surface if the sealant is too large. The sizing thickness can not be less than 6mm, generally take half of the width (such as: 12mm wide take 6mm deep), but the sizing thickness usually does not need to be more than 10mm (such as 25mm wide glue seam take 10mm deep sizing thickness, is enough to meet the requirements). Sealant sizing width controls the maximum displacement capacity that the sealant can provide without causing sealant to break. The wider the joint, the greater the displacement capacity required. Therefore, the total joint displacement must be calculated before the optimal joint sizing width can be determined. The displacement caused by heat change is easy to calculate; However, other forms of displacement deformation must be calculated at the same time. Both calculations require the calculation of the minimum joint size. First, the possible displacement deformation is calculated, and then the joint width is derived.
Calculation of joint displacement
The possible deformation of the substrate is calculated using the following formula:
M = (MT) * S * L
Where: M represents the deformation mm of the substrate.
MT represents the maximum possible temperature of the substrate, including temperature increases due to radiation and temperature changes. If the temperature is 40℃, the surface temperature of black aluminum may reach 80℃ or more. T represents the lowest possible temperature of the substrate surface, including temperature changes due to cold wind. S represents the thermal expansion coefficient of the substrate, and the expansion coefficient of typical materials is shown in the table below. L represents the length m of the substrate.
There are two cycles of joint displacement, the diurnal cycle caused by day and night temperature changes and the annual cycle caused by winter and summer temperature changes.
Sealant needs to be able to meet these displacement cycle changes after many years without losing its elasticity, and needs to be able to meet these displacement changes, such as the requirement to meet the maximum and minimum displacement changes possible, to calculate the actual joint size required by sealant.
Joint width
After calculating the possible displacement and deformation of the substrate, the minimum joint size can be calculated as follows:
W is equal to 100 times M per second
Where: W represents the minimum seam width mm.
M represents the maximum possible joint displacement.
S represents the allowable sealant displacement deformation, expressed as a percentage, which can be provided by the product specifications.
The maximum possible displacement of the joint can be calculated according to the deformation range of the substrate. If the substrate expands, the joint will become smaller and the joint glue will be compressed. If the substrate shrinks, the glue seam will become larger. The displacement around the joint is sometimes different. For example, the bottom of the vertical plate, which is mechanically fixed at the bottom, will not move, and the heat deformation will cause the substrate to deform upward. In the figure, the substrate is supported at the bottom, so any deformation associated with the Y-axis will have an effect on the horizontal direction. Although the displacement in the X-axis direction accounts for 50% each, the displacement and deformation between the substrate A and B can reach 100%. B is fixed between the wall and only accounts for 50% of the horizontal movement. It will move in the horizontal direction along with the displacement and deformation of the wall. When the size of each piece is different, it should be considered that they will produce different displacement deformation on the joint. If the materials on both sides of the joint are different, such as glass and aluminum curtain wall, it is necessary to calculate their influence on the displacement and deformation of the joint. Each different deformation results in a deformation of the overall joint displacement. Displacement deformation can also be caused by other causes, such as the tilting of hanging panels in the installation of fixed or movable devices in the building, or the addition of floors to the structure. Porous materials such as concrete and masonry expand and contract depending on the amount of water they contain. The effect of all these changes on joint deformation should be taken into account. Usually, different construction time should also be considered to produce a certain deviation. When the base material is heated and expanded in summer, the joints will become smaller, and the working life of the sealant will be extended; In winter, the glue seam will be widened and the working life of the glue will be shortened. The above formula only calculates the minimum joint width, sealant performance and the use of the substrate will also affect the actual joint width. We require a width of no less than 6mm. There is also a maximum seam width. There are limits to expanding sealants, sizing times, and curing sealants. For silicone rubber, the maximum joint width of 40~50mm.
Weather resistance seal
Usually, the depth of the seam is half the width. If the depth is too large, the joint deformation is increased, and the surface of the sealant is prone to concave and convex phenomenon when it is displaced, resulting in excessive pressure deformation and bonding failure. If the depth of the joint is too small, the amount of glue is too little, it will cause cracking due to the formation of stress concentration or bubbles, and even lead to bonding failure. Solvent-based sealant (such as butyl adhesive) will also cause shrinkage and cracking due to plasticizer loss, therefore, the depth of weatherproof glue is not more than 12mm, width is not less than 6mm.