Single facer corrugation Machine process is a critical component to the manufacturer of the high quality combined board. If the single face web being delivered to the rest of the machine is defective, Nothing can be done in the remaining sections to repair or compensate for the damage.
The basic Single facer operation must do the following.
1. Allow for unwinding and controlling the single face liner and medium.
2. Preheat/ Preconditioning the liner and medium to prepare them for the flute forming and bonding process.
3. Form the flat medium web into its characteristic fluted shape.
4. Apply adhesive to the tip of the newly formed flute.
5. Join the medium with the single face liner
6. Transport the single face web into the bridge.
There are three main points to be considered in single facer operation.
Unwinding and tension control
At the single facer corrugation machine, a roll of liner is positioned on the one side of the station. A roll of the medium is positioned on the opposite side. Each roll is supported by a roll stand that enables the paper to unwind freely as it is pulled into the single facer corrugation machine. Typically two roll stands exist for the liner and two roll stand for the medium. This make it possible to prepare one roll for use while other roll is unwinding. When a running roll is completed or an order requires a change in paper the standby roll can be spliced in without stopping the machine.
Tension must be maintained on the paper as it unwinds to keep it tracking straight in to the single facer corrugation machine and prevent wrinkling. Constant tension is maintained by applying pressure to brake mounted on the rotating core chuck that hold the roll in position. The brake pressure requirement change as the diameter of the roll is decrease. A full diameter roll requires grater brake pressure then necessary toward the end of the roll. Early roll stands required the operator to make periodic manual adjustments of the brake tension. The roll stand used today automatically lessen the pressure as the roll diameter decrease.
Preheating & Preconditioning
Preheating and preconditioning are the process of preparing the medium and liner, respectively for the fluting and the bonding by adding heat. Heat and moisture are added to the corrugating medium in the preconditioning process to soften the fiber and make the more pliable. This enable the flutes to form without fracturing or losing there shape. Heat added to the liner to begin the gelatinization process of the adhesive.
Flute Formation and Bonding
Flute formation and bonding of the fluted medium to the single face liner occur in the single facer corrugation machine. The basic components of the single face process have remained essentially the same since the beginning of the corrugating industry. The corrugating rolls are a set of grooved heated rolls that mesh together under pressure and impart a fluted shape to the medium as it passes through the nip. A hold-down mechanism keep the fluted medium in contact with the corrugating roll while an applicator roll applies a starch-based adhesive to the flute tip. A pressure roll secures the bond between corrugation medium and the single face liner to form single face web.
Common Single Face Problem
1. Flute Fracture
This occurs during the forming of the flutes in the corrugating roller nip. It is usually observed as the single face web moves from the pressure roll nip up through the incline conveyor. Likely causes are dry medium moisture content below 6.0%, high tension somewhere in the medium path, or possibly a problem with the medium itself. Sources of high tension may be as follows:
Excessive brake at the roll stand
Squeezing the roll with the roll stand chucks
Pre-conditioner running below paper speed or not turning at all. Typically, the preconditioner should be run faster (1.0%-5.0%) then the medium so as not to induce any tension on the web.
Problems with the splicer dancer mechanism.
Potential paper problems are as follow
Low Moisture content
Incomplete pulping/ Poor stock preparation
Low tensile strength
2. Low Caliper-
low Caliper should not be confused with the crush since the flutes are supported by the lower corrugating roll during formation, adhesive application and bonding to the single face line. the following are few potential causes:
(a) Liner or medium caliper:
The caliper of the liner and medium plus the flute height profile of the corrugating rolls determines what the best single face caliper can be. With change in pressing technologies and use of high performance papers, this caliper may no longer be what people are familiar with seeing.
The caliper of the liner and medium plus the flute height profile of the corrugating rolls determines what the best single face caliper can be. With change in pressing technologies and use of high performance papers, this caliper may no longer be what people are familiar with seeing.
(b) Tension:
Similar to flute fracture, excessive tension on the medium can cause improper flute formation and low caliper. Source of tension are roll stand brakes, Slow or frozen preconditioner, squeezing the roll with the roll stand chuck, and problems within the splicer.
(c) Pressure:
Uneven or insufficient pressure exists along the corrugating roll nip, pressure roll nip or both.
(d) Heat:
Sufficient heat energy must be available to drive moisture from the medium during the flute formation and set the memory of the flutes. Wet flute are more susceptible to crushing later in process.
(e) Sufficient force holding medium to lower corrugating roll :
Wether the single facer corrugation machine has finger or its fingerless sufficient force must exist to keep the medium against the lower corrugating roll. With finger type machine, it could be improper finger adjustment, a bent finger bar, or finger with the wrong radius for a reconditioned roll. For vacuum fingerless machine this could be plugged vacuum pump. On pressurized fingerless machine this could be leaks in the chamber or air pressure problems.
force holding medium to lower corrugating roll : Wether the single facer has finger or its fingerless sufficient force must exist to keep the medium against the lower corrugating roll. With finger type machine, it could be improper finger adjustment, a bent finger bar, or finger with the wrong radius for a reconditioned roll. For vacuum fingerless machine this could be plugged vacuum pump. On pressurized fingerless machine this could be leaks in the chamber or air pressure problems.
(f) Excessive adhesive application:
This may cause wet flute and there associated problems. Check roll parallelism M/A ratio, A/LCR ratio Starch temperature and viscosity.
3. Blisters/ Delamination
These two defect are generally due to problem with heat transfer, insufficient heat available for bonding. Blister will occur somewhere within the web either continuously like a streak or intermittently. Delamination usually cover a large area in the sheet or occur at the edge of the sheet.
Zipperboard – This is generally thought of as the opposite of delamination. In this case there is often too much heat going into the liner, medium or both. Thigh heat reduces adhesive penetration into the surface of the paper.
