Structural characteristics of the main components of the rotary screen printing machine

Structural characteristics of the main components of the rotary screen printing machine 11 Fabric feeding device The fabric feeding device consists of a fabric feeding roller,...

Structural characteristics of the main components of the rotary screen printing machine

11 Fabric feeding device
The fabric feeding device consists of a fabric feeding roller, a fabric tensioning frame, a vacuum cleaner, a tension compensator, an edge suction device and an arc-shaped electric heating plate. As shown in Figure 8-28, it is suitable for cloth There are two methods: box feeding and cloth rolling. A fully electric fabric edge detector is installed at the cloth feeding position. It has high sensitivity and can effectively control the cloth feeding position to maintain neat white edges on both sides of the fabric during printing. For some fabrics that easily cause curling, a three-roller spiral edge stripper can be installed to make the edge of the fabric enter the arc-shaped electric heating plate smoothly and stick flatly to the printing guide belt coated with thermoplastic resin through the pressing roller.

21 printing unit
(1) Rotary screen: Rotary screen is the pattern of the rotary screen printing machine. It is generally made of nickel metal plating, also known as nickel mesh. The mesh thickness is about 0.1mm, and the mesh is distributed in a hexagonal honeycomb shape. Common mesh specifications include 2316 mesh number/cm (60 mesh), 3115 mesh number/ cm (80 mesh), 3913 mesh number/cm (100 mesh), 4712 mesh number/cm (120 mesh). Both ends of the rotary screen are fixed with bulkheads to prevent the rotary screen from deforming during printing and affecting the accuracy of the pattern. The rotary screen should have a certain strength and elasticity and be able to withstand the pressure of printing paste and scraper.
(2) Pulp feeding and scraping device: The big difference between rotary screen printing and screen printing scraping devices is that during the scraping process, the scraper is fixed while the rotary screen runs continuously, resulting in scraping marks. The inner surface of the device and the rotary screen is relatively relaxed. The color paste in the mesh is squeezed through the mesh and printed onto the fabric evenly.
The slurry feeding device mainly consists of a slurry bucket, a slurry feeding pump, a scraper pipe, a scraper, a scraper clamp, etc., as shown in Figure 8-29. The scraper tube is installed inside the rotary screen, one end is closed with a top cap to prevent color paste from overflowing, and one end is equipped with a pipe joint, which is connected to the slurry pump through a plastic hose.
There is a row of uniform holes on the back side of the lower part of the scraper tube, through which the color paste flows to the inner wall of the rotary screen. The slurry feed pump can rotate forward and reverse. When it rotates forward, it sends the color paste in the slurry bucket into the scraper pipe. When it rotates reversely, it sucks the color slurry in the scraper pipe back into the slurry bucket. The amount of slurry supplied can be controlled and adjusted through the liquid level manipulator. When the rotary screen comes into contact with the fabric on the rubber blanket, the slurry feed pump automatically starts to deliver slurry. When the color paste liquid level rises to the set height and contacts the detector contact piece, the pulp feeding pump automatically shuts down and stops feeding pulp. When the color pulp liquid level drops and separates from the contact piece, the pulp feeding pump restarts to deliver pulp, so that the cylinder screen The color paste is always maintained at the specified liquid level.
There are currently three types of scraping devices for rotary screen printing machines.
①Elastic metal scraper scraping device: This device consists of a scraper frame, a scraper blade and a pulp feed pipe, as shown in Figure 8-30(a). The color paste is sent to the wedge-shaped groove between the squeegee and the rotary screen by the slurry feeding device. The squeegee is evenly clamped along the width direction by the air pipe, and elastically deforms under the action of mechanical force. When the rotary screen rotates, the color paste is squeezed by the doctor blade in the wedge-shaped groove to evenly fill the holes of the rotary screen and is squeezed towards the fabric.

The scrapers used for rotary screen printing include rubber scrapers, steel scrapers and polymer scrapers. Currently, steel scrapers are mostly used.
The choice of scraper should be based on the fabric variety and pattern structure to ensure appropriate slurry supply and permeability and achieve ideal printing results. The application range of commonly used stainless steel scrapers is as follows:

40mm×0.10mm (referring to the scraper blade width×thickness, the same below) is suitable for slurry feeding Patterns with low weight and fabrics with poor permeability should only be used under light pressure.
40mm×0.15mm is used for fabrics with low pulp supply and high permeability requirements, and is suitable for printing fine patterns.
50mm×0.15mm is a scraper with high pulp feeding capacity but poor penetration. It is suitable for printing on general fabrics.
55mm×0.20mm is used for fabrics that require a high amount of slurry and low penetration. It is suitable for printing on coarse ridges, suede fabrics and heavy knitted fabrics.
The amount of slurry supplied varies with the pressure exerted by the scraper, as shown in Figure 8-31. It can be seen that the amount of slurry Q increases as the pressure exerted by the scraper increases, but when the scraper pressure P increases to a certain value, the increase in Q tends to be slow. For scrapers with strong rigidity (such as 50mm×0.15mm scrapers), when the P value reaches a certain limit value, if the pressure is increased, the Q value will tend to decrease. This shows that in order to obtain a high slurry feed volume, you cannot simply increase the scraper pressure, but you should first select an appropriate type of scraper, and then obtain the best pressure state through fine-tuning. If the scraper pressure is blindly increased, not only will the desired effect not be achieved, but the friction between the scraper and the rotary screen will increase, causing damage to the rotary screen.

The relationship between the penetration of color paste into the fabric and the pressure of the scraper is linearly proportional. Generally speaking, the penetration of color paste mainly relies on mechanical extrusion in addition to the capillary effect of the fabric itself. The greater the mechanical pressure of the scraper on the color paste, the greater the penetration force. That is, when the angle between the scraper blade and the rotary screen is smaller, the penetration force is greater and the color supply amount is higher. In the same way, the more rigid the scraper blade is, the stronger the penetration of the color paste will be. Generally, the specifications of the scraper and the amount of pressure exerted by the scraper can be determined according to the following conditions:
a1 The physical state of the fabric, such as texture, weight per unit area, absorption capacity, etc.
  b1 The mesh number and opening ratio of the rotary screen adopted.
c1 Color paste composition, viscosity, and printing speed.
d1 Appearance requirements for printed fabrics, such as the fineness of patterns, level dyeing, and color amount, etc.
Reasonable selection of scraper specifications is a particularly important step in improving the printing effect of rotary screen printing. If the slurry supply amount and penetration force are too large, it will easily cause uneven coloring on large areas and blurred pattern outlines. If the slurry supply volume and penetration force are too small, the flower pattern will appear white or bloom due to poor permeability. Cause various printing defects.
Whether the fabric printing quality is excellent or not, in addition to the reasonable selection of the scraper model, the angle and pressure of the scraper must also be adjusted appropriately. The adjustment of the scraper angle and pressure depends on the thickness of the printing paste, the fabric structure, the amount of paste supplied, and the penetration requirements.
② Magnetic roller squeegee printing device: As shown in Figure 8-30(b), a metal squeegee roller is placed in the rotary screen. The diameter of the commonly used metal roller is 10~20mm. Under the printing guide belt, it is equivalent to each There is a set of electromagnets at the low position of the rotary screen. When the rotary screen and the guide belt run synchronously, the metal roller rotates around the axis of the metal roller under the action of the electromagnet, and the color paste is automatically sent from the pulp feed pipe to the space between the rotary screen and the metal roller, and the excess color paste is sucked back from the pulp pipe. . The liquid level of the color paste storage capacity depends on the diameter of the metal roller. Since the pressure of the magnetic roller scraping is relatively large, the color paste can penetrate better, and because the electromagnet can adjust its electromagnetic force in stages, the magnetic roller presses the paste. It can color uniformly along the width of the fabric. Therefore, by changing the size of the electromagnetic force and the diameter of the metal roller, it can adapt to the printing requirements of various fabrics and different patterns. Since the friction resistance between the metal roller and the rotary screen is small, the service life of the rotary screen can be greatly improved.
③ Magnetic combination scraper device: The magnetic combination scraper shown in Figure 8-30(c) is composed of a magnetically pressurized metal scraper roller and a special-shaped plate similar in shape and function to an elastic metal scraper. The special-shaped plate is close to the scraper roller and fixed next to the pulp delivery pipe. The bottom of the special-shaped plate and the metal roller are combined to form a relatively large and flat angle. Therefore, the special-shaped plate determines the amount of slurry, and the function of the metal roller is to penetrate and scrape the rotary screen. Adjusting the height position of the special-shaped plate can control the supply of color paste; adjusting the magnetic size and selecting the diameter of the metal roller can control the degree of color paste penetration. The magnetic combination scraper can be used for printing on various fabrics and can achieve excellent reproducibility.
(3) Flower alignment device: The flower alignment device allows all the circular meshes installed on the grid to quickly form a complete pattern. The flower alignment device has three types of adjustments: longitudinal, transverse and diagonal (diagonal). Mechanism, as shown in Figure 8-32.
①Longitudinal alignment: Use a plane cam differential mechanism to adjust, so that the rotary screen can obtain additional rotation, causing it to instantly lead or lag behind other rotary screens in the direction of the rotary screen to correct the deviation of the pattern at this position. Align the warp pattern of the fabric. The maximum adjustment amount for longitudinal alignment is ±20mm.

② Horizontal patterning: The screw nut mechanism is used for adjustment, so that the rotary screen moves axially and the fabric is patterned in the weft direction. Alignment, the maximum adjustment amount is ±10mm.
③ Oblique alignment: Use the eccentric shaft slider mechanism for adjustment. Adjust the diagonal error on the operating side to swing one end of the rotary screen to correct the pattern deviation. The maximum adjustment amount is ±3mm.
Common defects are inaccurate flower registration and inaccurate alignment. On old-fashioned equipment, pattern matching and calibration are done by visual inspection and manual adjustment, which wastes a lot of fabric. In recent years, many improvements have been made in this area. For example, laser beams can be used to calibrate the arrangement of the screens and can also be used to correct the positioning of each screen.
(4) Guide belt positioning device: The positioning of the guide belt during operation is realized by the three-roller positioning principle. The swing of the control roller is signaled by two sets of contact rollers close to the edge of the guide belt to make the motor normal. Turn or reverse. This mechanism can ensure the smooth operation of the guide belt and the deviation range can be controlled within 4mm.
(5) The transmission device of the rotary screen and the guide belt: the rotary screen and the printing guide belt run continuously, and the transmission is simpler than the flat screen printing machine. In order to maintain the synchronous transmission of the rotary screen and the guide belt, the rotary screen and the guide belt are driven by the same motor. The transmission system is shown in Figure 8-33.

In the picture, there are several worms installed on the long axis I, which drive the circular mesh of each color respectively. At the end of the long axis I, there are a pair of The gear reduction drives the intermediate shaft II, and drives the worm shaft III through the pneumatic coupling, thereby driving the drag roller, and the friction between the drag roller and the guide belt surface drives the guide belt to run. When the working width of the rotary screen is greater than 1.85m, transmission on both sides of the rotary screen can be used to improve the printing accuracy of the rotary screen and avoid the risk of twisting the screen. Generally, the linear speed of the conductive tape is 2% to 4% faster than the linear speed of the circular mesh.
In order to eliminate errors caused by gear backlash or torsional deformation of the drive shaft, the Zimmer printing machine uses an AC servo motor, while the Stork printing machine uses a graded or stepless ring motor that directly drives the screen. One of the other improvements provided by Stork to improve accuracy is to use sensors installed on each printing head to detect metal sheets fixed to the guide belt, and use the generated pulses to precisely control the drive of a single screen to ensure that the guide belt Synchronized with the screen, this technology is patented by Stork Company, referred to as BPMS. The new RD-DD type and Donggasus type rotary screen printing machines have a single printing machine installed on each printing head.Each transmission system is equipped with a ring motor. The circular mesh can be directly connected to the ring rotor of the motor, eliminating the need for gear transmission that easily causes errors. The rotation speed can be controlled particularly accurately by combining the pulse generator and electrode measurer in the motor. To correct the angular position of the rotary screen, the transmission of the guide belt equipped with the BPMS positioning measurement system is separated from the machine head, and the two achieve precise linkage through electronic control. For this type of independently driven rotary screen printing machine, the registration accuracy between two adjacent screens can reach 0.06mm.
(6) Guide belt cleaning mechanism: After completing one printing, the printing guide belt must first wash away the yarn ends, glue, printing paste and other dirt adhering to the surface before proceeding to the next patch printing. Belt cleaning consists of pre-washing and main washing. When pre-washing, spray water first and use coarse foam to collect yarn ends and debris. The main wash consists of four spray pipes, two foam sponges and three rubber scraper intervals. The guide belt is repeatedly flushed, scraped, wiped and washed, and the water is scraped dry. The above-mentioned sponge and scraper can be easily removed from the machine for cleaning.