The type of frame deformation

Unsuitable frame will be deformed under the tension of the screen. The type of deformation manifests itself in two aspects: bending and twisting. Bending is also called beam deflection. The problem is that the wire pulls the frame inwards and bends the beam, causing the entire frame to lose its original square shape. Figure 1 shows the different shapes of bending deformation. Of course, the figures in Figure 1 are somewhat exaggerated, but these variants are everywhere in the screen shop. Fig. 1: Curving of the frame When the tension is greater than the tensile strength of the frame, bending occurs, and the beam bends so that the edge of the frame bends inwards, and some bulges outwards, depending on the direction of the tension in the bending and The size and direction of the screen relative to the frame. When bending occurs, it causes the frame to lose its original square shape, causing inconsistent pulling forces and distortion of the mesh to reduce the printable area. Whether it is a flexible frame or a rigid frame, it will be deformed. The question is how much bending deformation is acceptable. If you are printing a more demanding product, the frame will be unqualified as long as the deformation is visible to the naked eye. In addition, the deformation of the network block causes the mesh to pull in the same direction, resulting in the deformation of the mesh at the edges, which greatly reduces the smooth point or the maximum printing area of ​​the screen. Deformation of the frame can also make the tension unstable, further increasing the difficulty of color registration. Twisting causes one or more corners of the frame to lift up, the frame to bend up or down against the plane of the frame (Figure 2). Twist deformation is the same as bending deformation, which can occur on either the elastic frame or the rigid frame. Expected position of frame edges is translated as the "expected position of the frame." Figure 2: Distortion of the frame distortion is the mixing problem that occurs when the screen tension pulls a corner or corners toward the center. This problem is also accompanied by a slight rotation or distortion of the frame, which is perpendicular to the plane of the screen. In addition, the deformation of the screen and the reduction of the image area will cause the off-plate gap to become larger. The distorted frame will have an unbalanced pull force, which will affect the off-gauge gap, and the bending part will have the greatest impact. Once the frame is distorted, it is impossible to restore the level. The deformation of the poorly flat frame is first manifested in the pre-press operation, especially when screen coating is performed using an automatic coating system or a direct screen printing system (CTS) during processing. The distance between the screen plate and the automatic coating tank or the distance between the imaging heads of the direct screen imaging system is a key factor in determining the image quality of the template. When coating with an automatic coater, uneven screens result in different stencil thicknesses, and in a CTS system, such screens may cause the print heads to contact the mesh, thereby destroying the image quality (see Figure 3). . Whether it is an automatic coater or a direct screen imaging system, the contact caused by the severe deformation of the frame may even damage the device. If you are using an automatic coater or CTS, be sure to check the mesh frame carefully! CTS imaging system (top view) in the figure is translated as "CTS imaging system (top view)"; Printhead makes contact with screen mesh as "print head and mesh contact"; Printhead translates as "print head"; Position of twisted frame Translated as "position of distortion frame"; Ideal frame position was translated as "ideal frame position". Figure 3: Contact due to torsional deformation in CTS imaging systems When screens are applied by the automatic coater or CTS imaging system, distortion of the frame can cause serious problems. Taking a CTS imaging system as an example, the distorted mesh frame is likely to bring the imaging head into contact with the mesh, which will degrade the image quality. In extreme cases, the imaging head may come into contact with the frame and be damaged. Some of the data collected by the frame manufacturers indicate that when the beam is distorted, the corresponding bending deformation is about 5 times that of the distortion (Table 1), which means that the twist distance is 20% of the bending distance. They also found that the distortion Deformation should not exceed 10% of the off-plan gap, especially when printing high-resolution, dichroic overprint images. Distortion is more than 10% of the clearance clearance. In order to ensure that the control is within this ratio, the interstitial clearance must be appropriately adjusted accordingly, otherwise the consequences could be disastrous. In Other respects, it also affects ink, changing the size and accuracy of printable images and the pressure on the screen. Table 1: Frame deformation comparison frame specifications; frame thickness (mm) frame tension OD level (mm) possible bending deformation (mm) * possible distortion (mm) minimum off-plan clearance (mm) 3030; 3.0, 1.8 50030500N/cm0.20 0.04 0.40 Oblique 40/3030; 50030500N/cm0.15 0.03 0.30 4040; 2.8, 2.0 50030500N/cm0.10 0.02 0.20 4040; 2.8, 2.0 1000201000N/cm1.00 0.20 2.00 Oblique 45/35x40 1000201000N/cm0 .90 0.18 1.80 5040;3.2,2.0 1000201000N/cm0.50 0.10 1.00 Oblique 55/45x40 1016x201524N/cm4.50 0.90 9.00 6040;3.0,2.0 1016x201524N/cm3.50 0.70 7.00 Oblique 65/55x40 1016x201524N/cm2.50 0.50 5.00 *The amount of deformation is the maximum amount of deformation on each side. The data of this table is provided by Anton Hurtz Gmbh, who is a manufacturer of fine metal frames in Nettetal, Germany. This data comes from customer production practices using aluminum mesh frames. They concluded that the relative relationship between the bending deformation and the distortion is: the distortion is 20% of the bending deformation, and the deformation cannot exceed 10% of the off-plan gap. The printer often says: “Do not worry! When the screen is put on the machine Clamping is okay.” Many printers routinely put the frame of the deformed drum into a vacuum box, expecting it to flatten out during exposure. This is unwise. First, a severely deformed frame may distort the printed mounting rail, and the effect of the stencil exposure process is twofold: if the frame remains warped under the vacuum frame, the screen will be skewed by the frame and the image will be distorted If the frame is flattened under the vacuum frame, the image is made under the condition of the frame flat, but once the vacuum condition is left, the frame will return to the original deformed state if you put the original Exposure of the film and the exposure of the template compared to the image will clearly see the deformation. Therefore, to maintain the smoothness of the frame to control the deformation within 10% of the clearance from the plate, it is best to carefully and carefully, especially when the frame is selected and processed. Although not perfect, careful selection will help keep the frame within an acceptable range.