Introduction
The Chalmers DST (Dynamic Stiffness Tester)
presents corrugated board manufacturers and users
with a very powerful new tool to measure the quality
of their corrugated board.
The tester measures the MD Shear Stiffness of a
sample of corrugated board which is very sensitive
to the general state of the board but especially the
state of the fluted medium. |
Figure 1: The Chalmers DST |
MD Torsional Stiffness measures how well the
corrugated board has been made, how much damage is
received during the printing and converting
process and how well it will protect its contents
in real world service environments.
The test is quick and easy to perform and will
lead to abandoning current QA tests like
thickness, flat crush, ECT and BCT. Another major
upside is the establishment of consistent quality
product that will allow the down weighting of
components. The Chalmers DST empowers
Production Staff to take control of their process.
Value Proposition for the Convertor
The Chalmers DST is the first easily used
tester to tell the convertor how well he is making
his corrugated board. The method is visible,
reliable, repeatable and understandable. The
tester is solid and can not be adjusted by staff.
Easily incorporated into existing computer data
logging systems, it will reduce the number of
tests required for board QA. Save on testing
costs. It can be used to examine the whole
manufacturing chain and isolate damage points.
Poor techniques, damaging settings or faulty
equipment can be remedied quickly.
It is designed to be used on the floor by
operators to do their own quality checks.
Improve product consistency and ownership by
operators.
By raising product quality and reducing
product variability weight can be taken out of the
components so that lighter board can do the same
job. Savings in raw material on some grades
could typically be in the order of 15%.
Lighter weight components will corrugate faster.
More production off the corrugator.
Opposition boxes doing the same job in the market
place can be analysed and board down-graded to
meet the same specs produced. Savings in raw
material etc.
The pay back for a well managed data acquisition
and product improvement system using the Chalmers
DST can be in as little as a day. One plant in NZ
saved the cost of the DST on one job. Large plants
could save millions of dollars annually.
Corrugated Board for
Corrugators
Corrugated board is made from liners and mediums
that have known properties. If you want a strong
corrugated board you use Kraft liners and semichem
mediums otherwise you use recycled fibre. Higher
liner and fluting medium weights generally make
stronger boxes.
But there are liners and liners and mediums and
mediums, especially with recycled fibre. Some are
stronger than others and we know this.
We can easily measure the strength of liner and
medium with tensile, ring crush or short span
compression testing. We can get guaranteed results
from our suppliers.
In a nutshell, we can get a reliable raw material
into our corrugators.
How come our boxes do not perform as well as they
should?
Why do we have to use such heavy components to get
reliability?
The answer of course is that we do not make the
corrugated board as well as we should. And when we
do we often damage it during printing and
converting.
Why?
Because we have no easily used tools to quantify
corrugated board quality.
Damage to corrugated board is almost always damage
to the medium.
Liner damage is uncommon, it is visible
and easily quantified.
Medium damage is common, it is invisible
and difficult to quantify.
That is until now. The Chalmers DST will rapidly
quantify the state of the fluted medium and allow
you to make better board off the corrugator using
your existing raw materials.
It will guide you to where your board is being
damaged and give you the data to fix it.
How does the Chalmers DST work?
The basis of the testing technique is as old as
physics itself and completely reliable. It uses
the simple relationship in a rotating system where
the torsional stiffness of an object fixed at one
end and twisted slightly about its axis at the
other end is equal to the square of the natural
oscillation frequency setup on release of the
twisting force multiplied by the moment of inertia
of the rotating end.
Torsional stiffness = Angular Frequency² x Moment
of inertia
Because we keep the moment of inertia constant for
every test (it is the effective rotating mass of
the system) we can ignore it and accept that
angular frequency squared is directly proportional
to the torsional stiffness.
The figure extracted from the test is the angular
frequency squared which we simplify by dividing by
100 to end up with a figure like 19.0 or 7.2, or
for a very strong board 30.9. The strongest board
we have ever tested came in at 78.9.
Who uses the Chalmers DST?
Currently there are over 70 Chalmers DSTs in continuous service around the world, mostly in Europe and Australasia.
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