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Textile Machines – Rotary Printing Technology

Printing Machine

The printing machines are used to print the design on the fabric. There are 3 Types of Printing Machines

  1. Rotary Printing Technology
  2. Flat Belt Printing Technology
  3. Digital Printing

Rotary Printing Technology

Rotary Printing or Rotary Screen Printing is so named because it uses a cylindrical screen that rotates in a fixed position rather than a flat screen that is raised and lowered over the same print location. Rotary presses place the squeegee within the screen. These machines are designed for roll-to-roll  printing on fabric ranging from narrow  to wide-format  textiles.

Rotary Printing TechnologyIn Rotary Printing, the fabric travels at a consistent speed between the screen and a steel or rubber impression roller immediately below the screen. (The impression roller serves the same function as the press bed on a flatbed press.) As the fabric passes through the rotary unit, the screen spins at a rate that identically matches the speed of substrate movement.

The squeegee on a rotary press is in a fixed position with its edge making contact with the inside surface of the screen precisely at the point where the screen, substrate, and impression roller come together . Ink is automatically fed into the center of the screen and collects in a wedge-shaped “well” formed by the leading side of the squeegee and the screen’s interior surface. The motion of the screen causes this bead of ink to roll, which forces ink into stencil openings, essentially flooding the screen without requiring a floodbar. The squeegee then shears the ink as the stencil and substrate come into contact, allowing the ink to transfer cleanly to the material.
By converting the screen-printing process from semi-continuous to continuous, higher production speeds are obtained than in flat bed printing. Typical speeds are from 50-120 yards per minute  for rotary screen printing depending upon design complexity and fabric construction.  Rotary screen machines are more compact than flat screen machines for the same number of colors in the pattern. Therefore, they use less plant floor space.
Also with rotary screens, the size of the design repeat is dependent upon the circumference of the screens. This was initially seen as a disadvantage, because the first rotary screens were small in diameter. However, with today’s equipment, screens are available in a range of sizes and are no longer considered design limited. Today’s rotary screen machines are highly productive, allow for the quick changeover of patterns, have few design limitations, and can be used for both continuous and discontinuous patterns.
Estimates indicate that this technique controls approximately 65% of the printed fabric market worldwide. The principle disadvantage of rotary screen printing is the high fixed cost of the equipment. The machines are generally not profitable for short yardages of widely varying patterns, because of the clean-up and machine down time when changing patterns. Flat screen printing is much more suitable for high pile fabrics, because only one squeegee pass is available with rotary screen. However, rotary machines are used for carpet and other types of pile fabrics.  Most knit fabric is printed by the rotary screen method, because it does not stress (pull or stretch) the fabric during the process.

Rotary Printing Machines Parts

Rotary Printing machines consist of the following units,

  1. Fabric Entry Unit
  2. Sucking Device
  3. Fabric Centering Device or Segment roll
  4. Gluing Device
  5. Blanket
  6. Blanket Centering Device
  7. Printing Units or Heads
  8. Magnetic Beams
  9. Color Pump
  10. Washing Device
  11. Conveyer
  12. Conveyer Centering Device
  13. Plaiter
  14. Dryer Chamber
  15. Circulation fans
  16. Gas Burners or Oil heating System
  17. Exhaust Fan
  1. Fabric Entry unit:

Fabric entry device is the device which unrolls the fabric from the batcher and transfer the fabric to the blanket. It is consist of roller which rotates with the help of motor that is controlled by the inverter or drive. The drive can be run on Auto mode and manual mode. For the selection of the mode there is the selector switch on the entry panel. On manual mode the speed of the motor can be changed with the help of potentiometer that transmit the reference voltage to the drive or inverter. While on Auto mode the speed of the unit is synchronized with the blanket speed by the compensator.

The arm of the unit is pulled up or pulled down with the help of the pneumatic piston.

  1. Sucking Device:

The sucking device is used to suck the dust particles and fluff from the fabric. It has mostly two high power sucking blower that starts automatically when the blanket runs. It has mostly two high speeds motor for sucking blower.

  1. Fabric Centering Device and Segment roll:

This unit is constructed to keep the fabric at center of the machine and installed just before the blanket. This unit can be work on pneumatic system or electrical system.

Segment roll is used to keep the knitting fabric at center of the blanket. It has two sensors at both sides that sense the fabric position and transmit the signal to run the sliding motor. One motor is also used to rotate the segment roller which is synchronized with blanket.

  1. Gluing Device:

This device is used to put the thin film of glue on the blanket. It is consist of the electromagnetic coils or beam which attracts the rollers which are partially sink in the glue. The blanket is between the roller and the magnetic beam. There is a selector switch that can energize the coil to attract the desire numbers of segment which depend upon the width of the fabric. The magnetic beam is operated on DC power source.

  1. Blanket:

It is the major and most important part of the machine because fabric is printed on it.This unit has one motor (AC or DC) which rotates the blanket and coupled with the encoder or Resolver for the feedback. The speed of the blanket rotation is controlled with the help of inverter. Inverter for the blanket unit is the master inverter which transmits the speed reference to all of the inverters to synchronize the machine. There are two safety limit sensor installed left and right side at near gluing device and washing device. When blanket is getting out and cross the limits at color side and operator side, then the blanket limit sensor activates which stops the machine and protect from any damage of blanket.

There is one blanket washing device which has one motor that is coupled to brushing roller and it is removed the glue and other printing colors from the blanket.

  1. Blanket Centering Device:

To control the movement of the blanket there is a centering guide roller which changes it position with the help of guiding motor. This motor is controlled by the feeler which senses the blanket position and makes the contact to run the guiding motor clock wise and counter clock wise, according to the position.

  1. Printing Units and Heads:

Printing heads are that part of the machine in which screen are mounded and used to print the design on fabric. There are maximum 12 to 21 colors in our machines. Each head represent a single color and it is a complete unit.

There are two types of head one is called open bearing and other is closed bearing. To run the screen there is an individual motor for each unit in Zimmer and in Reggiani there is one motor for all units. To adjust the unit as per design we also have two motors one is the cross repeat motor and other is the diagonal repeat motor. The both of the motors are control to adjust the design on fabric.

There is a sensor for the color level which is place under the screen that is used to operate the color pump. Each unit have seperate color pump. Each pump used to transfer the color from its color can to the screen.

Unit can be move upward and downward with the help of pneumatic system.

  1. Magnetic Beam:

There are two type of magnetic beam one is the coil type and other is the bar type. It is operated by using the variable DC power supply (40 to 90Vdc). As we increase the voltage the attraction power of the magnetic beam is increased so we have to set the voltage as per the quality of the fabric.

  1. Conveyor:

It is used to transfer the fabric form the blanket to trolley through the dryer chamber. It is consist of a motor and its speed synchronized with blanket by using photo sensor which is mounted at the end of the blanket. We can also operate it manually by the help on Potentiometer or HMI

There is a conveyor centering device which controls the movement of conveyor. This centering device works on same principle of blanket centering device.

  1. Dryer Chamber:

There are two type of dryer chamber in our printing machines which are as follows,

  1. The chamber in which natural gas is used for the heating.
  2. The chambers in which hot oil is used for the heating.
  1. Circulation fan:

There are 4 circulation fan on Zimmer II machine and 9 circulation fan on Zimmer I and 6 circulation fan on Reggiani Machine. It is used to circulate air inside the chamber. Each circulation fan has pressure switch when fan is started pressure switch transmit the signal that the fan is running and make us sure that circulation fans are working properly. These are operated on two speeds mode (single / double). Circulation fan take few minutes to switch the motor form single speed mode to double speed mode. Circulation fans are helpful to maintain the desire temperature in dryer temperature. If the circulation fan motors become faulty immediately change it. There is one air pressure switch installed on each chamber that provides the signal that the circulations fan is throwing the air.

  1. Exhaust fan :

It is used to emit out the gases and moisture form the chamber. The speed of it can be controlled manually on single and double speed. The speed of the exhaust fan can be changed form the screen or the operating panel. There is a pressure switch inside the exhaust duct of Zimmer machine which ensures the system that the exhaust in working or not. (Burners and oil heating system of the dryer should not be activated if the exhaust is not running.)

  1. Burner:

There are four burners installed on Zimmer II machine. Each chamber has a complete unit of burner. Each unit of burner consist of blower motor, motorize valve for gas controlling, ignition & sensing rods and flame controller. When circulation fan & exhaust fan generates the activation signal then 1st of all the blower of the burner is turned ON and it is also generate the signal to the burner controller that all the things are right. After the above process the ignition transformer ignited and pilot of the burner is lit. When the flame is hold the motorize valve comes to its minimum position and start to maintain the temperature. Burner units also have the safeties, in case of any abnormal behavior of the burners the main gas inlet valve switch OFF.

In Zimmer I & Reggiani machine, there is an oil heating system. Each chamber has a motorized valve for oil which is controlled by temperature controller.

  1. Plaiter:

There is used to put the fabric in the trolley. It has a DC motor at Zimmer I & Reggiani machine which is controlled by DC drive while in Zimmer II AC motor is used for it which is controlled by inverter and all of them are synchronized with machine by the help of compensator potentiometer.

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