The paste-bottom packaging bag is mainly used to hold powders, granules, tablets, wadding, and thick materials, such as cement, grain, starch, feed, chemical fertilizers, chemical raw materials, ore powder, etc. In recent years, the packaging has been improved for packaging asphalt and paraffin. , paint, paint and other materials, instead of drum packaging. The application range of paste bottom bags is extremely wide, and the dosage is very large. Therefore, in the continuous improvement of packaging and technological innovation process, it is of great significance to apply and promote the bottom package bags.
First, paste bags As we all know, the traditional heavy-duty bag closure is mostly sewn sewing machine, called the bottom of the bag, and the bottom of the bottom bag is glued (including other bonding methods or thermal law) The four sides of the bags are stick together and are called bottom bags. The bottom bags are divided into valve pockets and open pockets according to the shape of the filling mouth.
1, valve pocket:
The valve pocket is a pre-seal bag type. The bag body before loading is a flat tube. The upper and lower ends of the bag are pasted, and the upper corner is filled with a filling valve port. When the material is poured in, the material itself The pressure stretches the bag into a cube and presses the wide mouth to prevent leakage. For example, a cement bag is a typical bottom bag.
The bottom of the paste bottom bag has tubular and reinforced type, top-mounted type, pocket type and other types. In order to adapt to the packaging of certain ultra-fine powders, the valve opening can be further sealed by heat sealing or on the basis of self-sealing. Made of double valve type to enhance the sealing.
The outer surface of the upper and lower bag bottoms can be attached with an additional bottom (commonly referred to as a bottom sticker). The use of the bottom bag for different purposes may be optional, and may be unilaterally or bilaterally.
The bottom of the bag can be made with a longitudinal cut type, which can increase the sticking area of â€‹â€‹the bottom of the bag by about 18%, so that the bottom of the bag can be reinforced and the bag making material can be saved.
2, open pocket:
The difference between the open-mouth bag and the valve bag is that the lower end of the bag is the bottom of the paste, and the upper end is open. After filling the filling line, the sealing is performed. The method of sealing includes sewing, sticking and nails, etc., and is suitable for large filling port packaging. Machines such as grain bags are typical open pockets.
The open pockets for small packages have a folded inner edge on both sides. The bottom of the bag is rectangular and has good self-standing properties.
Second, the characteristics of the bottom of the bag, a high-stitch bag because the bottom of the bag is sewn, the needle hole at the seam is the main reason leading to the bottom of the bag is not high, according to the research department to do the firmness At the time of the test, 60-80% of the bottom pockets were broken due to the fracture at the seam. Because the seam of the bottom seam bag generally uses 25#-26# needles, the diameter of the needles is 23mm, and the double threads are passed through the needle holes, so that the diameter of each pinhole will also be enlarged, plus the burden on filling. The gravitational effect, pinhole diameter up to 25 mm or more. There are 78-90 pinholes in the bottom of the bottom of the bag, and the average diameter of these pinholes adds up to 210 mm. This means that a 210-mm-long hole is cut at the bottom of the bag before the bag has been thrown, which occupies about 20% of the circumference of the bag, resulting in a lot of strength loss. The bottom bag completely eliminates the bottom line of the seam. Sewn pinholes have an adverse effect on bag strength.
From a mechanical point of view, taking cement packaging as an example, when a bag filled with 50 kg of cement falls parallel to the ground from a height of 1 meter, the ground's reaction force reaches 6 KN. In other words, the impact surface will act on the packaging bag with a force of 6 KN so that the cement in the bag will move and its direction will be radial. Due to the bag-like constraint, the cement in the bag impacts the top and two faces of the bag, so that the bag body is subjected to tensile stress (in all directions). Because the direction of the force is related to the geometry of the bag body, it is generally decomposed into longitudinal stress and lateral stress. According to the motion characteristics of the fluid material, such a stress distribution rule is formed: regardless of the longitudinal or transverse direction of the bag body, the stress in the middle portion is larger than the two sides; the stress in the transverse middle portion of the bag body is greater than that in the middle portion. This is the reason why the transverse tensile strength of the package is required to be high, and why the breakage of the packaging line mostly occurs in the middle section of the bag body. This point is the same for the bottom bag and the bottom bag. The difference is: the ratio of the width to the length of the bottom bag is 1:1.72 to 1.83, while the bottom bag is only 1:1.06-1.18. Obviously, both sides of the sew-bottom bag must receive greater impact. The parts of the bottom bag are basically in the state of equal strength and there is no stress concentration phenomenon, which is more reasonable in terms of structural design.
Practice has proved that the bottom bag made of different materials is 1-3 times stronger than the bottom bag.
(1) Low cost The raw material accounts for 80-90% of the cost of the bag making. Therefore, whether or not the material can be saved is crucial for selecting the bag type.
According to the calculation results of the size and surface area of â€‹â€‹the two bags of paste base bags and sew bottom bags, it is proved that because the bag-type structure of the paste bottom bags is reasonable, the material is brick-shaped after loading, and the bottom bags are pincushion-shaped. Therefore, it is equally effective. In the case of loading volume, its surface area utilization is significantly better than that of the bottom bag. Taking a cement bag as an example, the same volume of bags can be produced, saving 5-6% of the material used. For the traditional multi-layer paper bag, after the spoils are changed, the strength of the bottom bag can be increased, so that the bag can be reduced and the material can be saved by 20-25%. (To be continued)
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