Dec 12, 2017
This article will describe a multiple-device threading system, briefly touching on each device, and then describe how to troubleshoot the threading system.
Consider the following example - a ropeless threading system through a size press was provided by Valmet as an upgrade. In this example, a blow plate, pickup tray and blade, (4) Valmet Tail Threading Belt [previously called FoilForce] conveyors, (4) threading pans and a nip roller are used to thread the tail from the last dryer of a dryer section through the size press to the first dryer of the next dryer section.
The blow plate blows the tail toward the pickup tray. The pickup tray pivots to guide the tail to the blade which pivots to sever the tail. The tail then proceeds to the 1st Valmet Tail Threading Belt conveyor which guides it up under a carrying roll to the 2nd Valmet Tail Threading Belt conveyor which guides the tail to a curved fixed threading pan. The pan guides the tail up above another carrying roll to the 3rd pivoting Valmet Tail Threading Belt conveyor which guides the tail downstream above another carrying roll. The 4th Valmet Tail Threading Belt conveyor (sliding) guides the tail into the size press nip. After the size press, a pivoting threading pan catches the tail and guides it downstream through a sliding threading pan and fixed threading pan. A nip roller then nips the tail to the first dryer in the next dryer section.
The first and second Valmet Tail Threading Belt units are fixed in position. The third Valmet Tail Threading Belt unit is normally pivoted to align with the cross direction of the machine, and is pivoted into the machine direction for threading. The fourth Valmet Tail Threading Belt unit is normally slid outside of the machine, and is slid into the machine for threading.
The first and fourth threading pans are fixed in position. The second threading pan is normally pivoted downward and is pivoted into the machine direction and threading path for threading. The third threading pan is normally slid outside of the machine, and is slid into the machine for threading.
The pick-up tray pivots upward to push the tail downstream toward the blade which pivots upward to cut the tail. The tail then proceeds to the next threading device (1st Valmet Tail Threading Belt conveyor).
The two pickup tray and blade positions are:
After the tail is successfully threaded, the pick-up tray and blade are returned to their storage positions.
NOTE: If the tail fails to thread, or breaks during threading, but has not yet widened beyond the maximum tail width, a fresh end can be cut using the pick-up plate and blade.
The purpose of the Valmet Tail Threading Belt system is to speed-up the tail threading and thus improve the efficiency of the production line. The automated system not only boosts the tail threading, but also improves occupational safety. The Valmet Tail Threading Belt is a compressed air actuated and logic controlled tail threading system.
The Valmet Tail Threading Belt vacuum conveyor is based on turbo foil technology, where the basic vacuum is created using a foil, and the vacuum level can be adjusted through compressed air. The air connections required by the compressed air system are located at desired points outside the main machine frames.
The logic controlled tail threading system is started by the control station, which turns the tail threading belts/plates to the operating position and the belts automatically accelerate to the desired tail threading speed.
The speed is controlled by use of a frequency inverter (AC drive). The speed information of the machine is passed to the frequency inverter, which sets the desired speed difference between the belt and machine speed. Changes in the machine speed automatically change the speed of the belts.
The above figure shows the pivoting and sliding movements of the 3rd and 4th Valmet Tail Threading Belt conveyors in the size press area between their respective storage and threading positions.
Note that the 4th Valmet Tail Threading Belt conveyor is mounted on an existing pivoting beam/bracket that also supports the tend side of a carrying roll above the size press. In order to access the size press from above, the 4th Valmet Tail Threading Belt conveyor is moved to the storage position, then manually turned to the cross machine to a roll change position.
Threading plates/pans are simple plates which support and guide the tail across open spaces. Air nozzles direct air along the plate, carrying the tail by means of friction force.
Slight negative pressure (coanda effect) is created on the plate surface, keeping the tail close to the plate. The number of sets of air nozzles varies depending on the length of the threading plate.
All but two of the threading pans in the size press area are fixed in position. The next figure shows the movement principle of the two non-fixed threading pans.
The nip roller contacts the first dryer in the following dryer section to create a driven in-going nip to secure the tail when threading through the size press into that dryer section.
The nip roller pivots between a storage and threading location via a pneumatic cylinder. When tail threading devices are enabled, the nip roller pivots to touch the dryer and is driven by the dryer. The tail is carried into the nip between the roller and the dryer by a threading pan. After successful threading, the nip roller is moved back to the storage position. A blow pipe pivots with the nip roller and ensures the tail follows the dryer smoothly after it leaves the nip roller and dryer nip.
Troubleshooting threading system operation when several different threading devices are being used simultaneously is nontrivial. The following are general and device-specific tips for threading.
Is the plate clear of paper scraps?
Is the tail width appropriate?
Is the paper moisture appropriate?
Is air coming out of the nozzles?
Is the solenoid valve coil energized?
Solenoid valve coil is energized but still valve does not open.
Is the tail free to fall into the broke pit or to the floor?
Is the tail piling up on top of the pick-up plate?
Is the tail properly positioned?
Are blow-off nozzles positioned correctly?
Is the pick-up plate moving too slowly?
Is the paper on top of the cut-off blade (MC models)?
Is the timing of the air blows correct?
Is the Valmet Tail Threading Belt fabric rotating?
Is web escaping from Valmet Tail Threading Belt unit?
Is the tail traveling too slowly?
Is the tail torn or travelling restlessly?
Does the tail go past the nip?
Is the tail bagging at any point?
Tail is not tensioned properly on downstream winding equipment
Is the tail broken in the nip?
Is the tail coming out of the machine?
For more information on troubleshooting and/or enhancing your tail threading system, contact your Valmet representative.