The Conversion of Corra Gator-Boardy

Part 1: Feed Section
This is the first installment of a series by Jim Brown, a corrugated equipment specialist with more than three decades of experience. Articles will outline what the board experiences during the conversion process, but from an unusual perspective: that of the board itself, in the form of our imaginary narrator, Corra Gator-Boardy. Corra’s journey will include six adventures:

1. Feed section
2. Print sections
3. Die cut section
4. Slotter section
5. Folder section
6. Counter-ejector section

The series creates an engaging way for those within the corrugated industry to gain insight into processes outside their area of specialty, as well as to offer the next generation of professionals or those in related industries a chance to gain more understanding of the process as a whole.

Ride along with Corra in a series of six mini-adventures on her way from a flat corrugated board to an amazing, corrugated container. Learn about the mechanisms and devices that will launch her into the machine, color her panels, cut out her unique shapes, form her dimensions, hold her together, and prepare her for market.

Corra Gator-Boardy began her life as two outer layers of kraft paper glued to a fluted center with starch water and steam (Fig. 1). She was then quickly cut to length by the corrugator cutoff knife, where she officially became a corrugated board.

From there she traveled through the box plant conveyors with many others, destined to become something special. Corra had learned all about her imminent experience: how in the flexo-folder-gluer converting machine she would pass from the feed section, through the printers, die cutter, slotter, folder-gluer, and counter-ejector to finally become a valuable corrugated container. It sounded very exciting, but it was a little scary. She did not know exactly what she would be experiencing during this multi-step process.

ADVENTURE #1: THE FEED SECTION

Corra was carried up from the plant conveyor onto the prefeeder. The prefeeder shingled her and the rest of the board into the feed section hopper. The hopper is the area between the left- and right-side guides and the feed gates. Corra dropped into the hopper. Her forward movement was stopped sharply by the pair of shiny feed gates. Her belly was pressed against a series of cast aluminum support grates covered with thin, stainless steel wear strips. She was next to be fed into the converting machine.

She saw the machine operator press the feed button. The 100-horsepower motor that was driving the gear train for the entire machine was just about to engage the feed unit. She could hear the air from the vacuum blower whirring around her.

Fig. 2

Suddenly, the grates dropped her onto a series of urethane wheels supported on several rows of stationary wheel shafts (Fig. 2), and she could see that there was just enough gap below the feed gates to allow her to move forward when the time was right. Without warning, the wheel shafts began to rotate very quickly, and she was accelerated violently from zero to 1,000 feet per minute!

With vacuum pulling her down as well as the weight of the pile of board above her, she was hurled forward into the first nip. A nip is the gap between any two rollers in the machine, the first of which is the feed roll nip. The upper feed roll is covered with soft urethane that grips the board and provides pressure against the lower feed roll. The lower roll is steel with a straight knurl on its surface, a fine series of grooves that run across it (Fig. 3). The pressure between the rolls is adjusted by raising and lowering the upper roll, creating a gap just slightly smaller than the thickness of the board, but not so much as to crush the flutes inside.

Fig. 3

Operators can raise or lower any of the adjustable shafts in the machine using a pair of matched, eccentric housings. The shaft ends are supported on bearings that are fitted into the hole (bore) of the housings, except the bore is machined off center in the housings on purpose. That way, when the housings are rotated in the frames, the adjustable roll moves through an arc, which opens and closes the nip.

The feeder transmission provides both the lifting and lowering motion of the grates as well as intermittent rotary motion of the wheel shafts, all in perfect timing. It is driven by the machine’s main drive and subsequent gear train. The input shaft runs at constant velocity. There are lowering and lifting cams inside, which are round with a gradual lump on them. A cam follower bearing runs on the edges of the cams and is attached to a linkage that, in turn, raises and lowers the grates. A small, external air cylinder (interrupter cylinder) lifts the cam follower off the cams to interrupt the grate motion, which stops the machine from feeding more board.

For the intermittent rotational motion of the wheel shafts, there are custom shaped, adjustable position cam lobes on the input shaft. These cam lobes mesh with a cam follower wheel on a parallel shaft. As the input shaft rotates the cam lobes, the engagement and disengagement of the lobes in the cam follower wheel creates an intermittent rotational motion, which is then transferred by gears to the wheel shafts. This is commonly known as an indexing box (Fig. 4).

Fig. 4

The timing is set so that the wheel shafts are stationary as the next board is dropped onto the feed wheels. Once the full weight of the board is released onto the wheels, the intermittent motion begins. This on-and-off motion keeps the wheels from spinning during the moment of contact with the board. Then it accelerates very quickly to board speed, and repeats the process for each sheet that is fed.

What an amazing device, Corra thought. It accelerates the bottom board from zero to board speed as fast as 400 boards per minute. That’s over six boards per second!

Once Corra is launched into the feed roll nip she is travelling at the correct machine board speed, and begins a more comfortable, constant velocity ride through the machine. The feeder’s job is now complete and prepares to feed the next board in the hopper.

UP NEXT: THE PRINTERS

Corra’s next adventure will take her through the printers, a calmer experience that will paint her in living color. Join us in the next adventure to learn precisely how that happens and where she is heading after that.