When two strong surfaces
are held apart by a firm structure, the result is far more rigid than
the sum of the three constituent parts. This is the familiar principle
upon which the manufacture of corrugated board is based. Unlike solid
board, corrugated does not depend upon mere thickness for its Strength.
The composite material is light and tough, as well as rigid.
Different duties are served by varying the weight of individual components
and the profile of the fluting. Two basic sizes of used. C flute board
gives the greater beam and compression strengths because its surfaces
are more widely separated. In B flute board the contours are shallower
and closer-knit. It offers strong resistance to crushing and at the same
time helps to keep down freight and storage charges by reducing the bulk
of a case. Where exceptional rigidity and strength are needed, C flute
and B flute are combined to form BC flute, also called twin-flute or double-wall
The Corrugator is a combination of many individual machines
brought together to make one very complicated, yet synchronized, piece
of machinery which is used for the conversion of the paper into different
types of board.
The different pieces of equipment which basically make
up the Corrugator are as follows:-
- SINGLE FACER (one for B flute and one for C flute)
- DOUBLE BACKER
- HEATING SECTION
- COOLING SECTION
- SLITTER SCORER
- CHOP UNIT
- TAKE OFF
1. SINGLE FACER
This section of the machine converts the reels of inner
liner paper and fluting medium into single face fluted board.
It is fed from the reel stand on one side by the fluting
medium and from the other by a liner. This liner is normally inner liner
the outer liner is applied at the Double Backer stage.
The fluting medium is fed by way of a series of pre-heated
rollers through a steamer pre-conditioning section to the first Corrugator
roll, it is then passed between the first and second Corrugator rolls;
this action cause a the paper to be nipped, and so form the corrugations.
Before leaving the Corrugator main roll an application of starch glue
is applied to the tips of the flutes, by the glue applicator roll. The
fluting, still held in contact with the main Corrugator roll by line of
vacuum nozzles, passes over the pressure roll where it meets the liner
and so forms Single Face corrugated board. Older corrugators held the
fluting medium by single piece fingers, this is why most modern corrugators,
is described as having a "Fingerless single facer".
This single face board is then fed to the Double Backer
by way of the bridge.
This action is exactly the same for both B and C flute,
only the machine setting and tolerances vary from one to the other. It
should also be mentioned that the lower Corrugator roll remains fixed
and the upper Corrugator roll, the glue applicator roll and the pressure
roll, can all be adjusted to ensure that even corrugation, glue application
and caliper takes place.
Other refinements are also incorporated in the machine
to ensure that these factors are kept constant, such as liner tensioning
and board moisture control.
2. DOUBLE - BACKER (GLUE) MACHINE
This part of the machine prepares the single face board
and the liner (outer) before double face board is formed.
The single face board comes from the bridge through
a heater dryer unit to the glue machine where application is identical
to that at the Single Facer. It then passes from the applicator to meet
the liner, which has been fed from the reel stand through a pre-conditioner
just as it enters the heating section.
3. HEATING (DRYING) SECTION
This section is a series of 'Hot Plates' called Steam
Chests, which are kept at a temperature around 340 - 360 degrees. The
double faced board passes over the top of these chests and the effect
is to dry the board out and in turn this dries the glue to give good adhesion
of liners to fluting medium. The board is kept in contact with the plates
by a continuous belt, and the pressure applied by the belt is kept constant
by idler rolls spaced at even intervals over the length of the Heating
4. COOLING SECTION
A continuous belt takes the position of the steam chests
and the board is allowed to cool as it continues towards duplex unit for
5. SLITTING AND CREASING UNIT
The Slitting and creasing units are a positioned series
of shafts. The they are usually separated into slitting and creasing shafts.
are two slitting shafts and three creasing shafts. As the board enters
the units for creasing, and then is slit to the correct first-way size.
The bends and slit blades on these shafts can be positioned anywhere on
the shafts within the limitations of the mounting bosses, (which is the
width of that boss). Setting of the slitting and scoring units is often
computer controlled. The shafts can be raised and lowered as required,
to enable most standard first way crease to crease sizes to be manufactured
on a Corrugator with multiple shafts. Creases are of usually of the 3
point reverse or the 2 point Sauer type.
6. CHOP UNIT
This is a very complicated cutting machine, which cuts
the board into lengths as required.
The setting up of the chop size automatic and the board
length is governed by a complicated Gear assembly. The speed of the machine
and the position of the belts on the gear wheels gives the resultant board
length. The Chop unit can be of the single or multiple type. The
a single knife design has gained in popularity over recent years. This
means that only one job can be run at a time on this machine. Corrugators
that have multiple chop knives, can run more than one job, in a particular
grade, at one time. Both systems have their plus and minus points.
7. TAKE OFF
This is a series of belts which control the flow of
finished boards to the take-off section. On exiting the chop section the
pieces of board, which have now been cut to their correct board size and
had any first way bends put in, are separated and then shingled as they
start to go up the inclined belts. At the top of the belts the boards
reach the down stacker. The number of boards in the bundles at the take-off
points is regulated by gates which work automatically. When the set number
of boards is reached those still on the conveyor are held by the gates
while the completed stack is lowered to the bottom conveyor. The stacks
pass down a final conveyor system and are then automatically palletized.
A forklift then places the palletized board into a holding area prior
This is made by the Starch Plant Operator in the Starch plant, adjacent
to the Corrugator.
Basically the contents of a normal mix is:
550 Gals. of WATER
9 cwts. STARCH POWDER (normally maize)
33 lbs. BORAX
31 lbs. CAUSTIC SODA.
Single Facer - 35-40 secs
Double Backer - 60-70 sees