The drying box of a gravure printing machine has a large volume and complex structure. In addition, it uses thin plate materials with a thickness of 1-6mm, which are prone to various deformation problems during the manufacturing process. Therefore, it has become one of the most difficult and technologically advanced components in all riveted and welded parts.
1. Deformation issues and preventive measures during the cutting process
To prevent deformation of the drying box during the cutting process, the diagonal size of the material should also be checked while cutting, and the dimensional tolerance of the material should be strictly controlled. For example, the inner plate of the inner liner of the activity box is generally made of stainless steel, which has an expansion coefficient of 1.5 times that of ordinary steel plate, poor thermal conductivity, and its thickness is usually between 1.5 and 2mm, belonging to the category of thin plates. Therefore, when using a CNC plasma cutting machine for cutting, the inner plate will inevitably experience wave deformation.
First, the oxide film and burr around each cut plate must be removed, and then it shall be placed on the platform, and Flat noodles tapping or wooden hammer shall be used to disperse and hammer along the edge of the wave deformation part to release stress, so that the wave deformation can be flattened.
2. Deformation of ventilation pipes and preventive measures
The bending angle of ventilation pipes should generally be designed between 330 ° and 345 °, and the requirements for materials are: flat, straight, and accurate. The bending angle is realized by the bending function of the Press brake. During the bending process, the appropriate mold should be selected. In view of the inherent springback performance of the material itself, the bending angle should generally exceed the predetermined bending angle by 8 °~10 °.
In addition, it is necessary to ensure the consistency of the angle between the formed ventilation duct nozzle panel and the drying box panel. Therefore, when assembling the inner liner of the drying box, a reverse deformation method can be adopted, which is to first maintain a certain angle between the ventilation pipe nozzle panel and the drying box panel. This way, after forming, there will be a certain arc depression at the connection between the two, with a depth of 2-3 mm from the horizontal plane. After welding is completed, it can be automatically leveled.
3. Deformation issues and preventive measures during the manufacturing process of the outer plate of the drying oven
Generally, the thickness of the outer plate of the drying box is 6mm, which belongs to the category of medium thick plate. After blanking, the burrs and splashes around the plate shall be removed with a Angle grinder or slag hammer. If the deformation area of the outer plate is not large, use a hammer to strike and level it evenly; If the deformation area is large, a three roll roller machine can be used to place the outer plate on the lining plate above the roller plate and roll it in reverse.
4. The deformation problem and preventive measures of the inner liner
During the assembly process of the inner liner of the drying oven, the air nozzles at the connection between the air ducts on both sides and the middle ventilation pipe will experience protrusion and deformation. To avoid the occurrence of such deformation problems, a symmetrical manufacturing method can be used when assembling the inner liner, which is to first position weld the air ducts on both sides, and then connect the middle ventilation pipe; When welding, the previous method of welding the middle side plate and ventilation pipe on the inner side of the air chamber first, and then closing the rear fender, has been changed to the method of assembling the inner liner as a whole and then welding it as a whole, and the welding seam has been changed to a segmented symmetrical welding method.
The inner liner air chamber is one of the core components of the drying oven, mainly composed of air ducts, ventilation pipes between the air ducts, front and rear panels, upper and lower sealing plates, air inlet, circular arc plate, air distribution plate, rear panel, etc. During the assembly process of the inner duct air chamber, the ventilation pipes between the front and rear panels, air ducts, and inner and outer panels should be connected together. Then, based on the front panel of the air chamber, the assembly should be carried out in an inverted manner to ensure that the four corners of the front panel are always in contact with the platform surface. Then, the inner panel, upper and lower sealing plates, and rear panel should be assembled. After assembly, use a hammer to hammer the alternate joint to release the stress generated during welding. It is worth noting that during welding, both ends of the inner liner should be supported and fixed before conducting full position welding.
5. Deformation problem and preventive measures of the outer plate of the fixed box of the drying oven
There are many holes on the outer plate of the fixed box of the drying box for installing guide rollers, and the width of the plate is relatively narrow (usually 150mm). Therefore, the parts with holes on the outer plate of the fixed box are prone to bending and deformation. Based on years of experience, the author believes that the deformation of fixed boxes varies slightly depending on the total height of the box. According to incomplete statistics, the deformation of fixed boxes with a total height of 1.4m after assembly is approximately 2.5-3mm; After the assembly of a fixed box with a total height of 1.6m, its deformation is approximately 3-4 mm; The deformation of the fixed box with a total height of 2.4m after assembly is approximately 5-7mm. To avoid the above-mentioned deformation issues as much as possible, reverse deformation can be used when assembling the outer plate and enclosure of the fixed box. That is, before welding, hammer the upper and lower edges of the outer plate with a hammer to produce a certain amount of pre deformation. The pre deformation amount is adjusted according to the total height of the fixed box, usually about 2% of the total height. The internal stress generated by welding deformation after welding is completed will cause deformation of the outer plate, which will counteract the pre reverse deformation, thus achieving the purpose of correcting the deformation of the outer plate of the fixed box.
6. The deformation problem and preventive measures of the peripheral board
Normally, the width of the outer enclosure of the drying oven is 1000-2500mm, and the thickness of the board is generally 3mm. Due to the significant differences in width and thickness between the outer panel and the outer panel, when welding the two together, the size of the welding heat affected zone often varies due to differences in welding speed and method, resulting in uneven welding stress and uneven wave deformation of the outer panel.
To prevent the occurrence of the above deformation problems, the outer panel should be placed on the platform before welding, and hammered along the outer edge of the outer panel with a hammer to extend the plate in that area to 1-1.5mm along the fiber direction. After the welding of the outer panel and outer panel is completed, the pre deformed outer panel will be restored to its original state due to thermal shrinkage, which can alleviate the degree of wave deformation of the outer panel during the welding process.