First published in the Proceedings
of the Altshuller Institute TRIZCON 2000, May, 2000.
Ian F Mitchell
Ilford Imaging
UK Ltd
Summary
During the slide bead coating process a thick
edge of emulsion is laid on the extreme outer edges of the coating.
A system consisting of a separator vessel, a
vacuum pump, a holding tank and a nozzle had been designed and built to remove
the excess emulsion from the edge of the wet coating.
Continuous maintenance was needed to keep the system operating and
to stop the vacuum pump from being blocked by emulsion being carried over
during the removal process.
To overcome these problems a series of
components were added including a spray
inside the separator vessel, a filter before the vacuum pump and eventually a
second separator vessel.
This approach did not reduce the level of
maintenance or improve the systems performance,
The newly acquired Techoptimiser Professional
Edition software and the group who had been trained in its use were asked to
come up with an improved method of
Thick Edge Removal.
By using TOPE the original system was reduced from twelve components down to
just two components costing just a few pounds, requiring only occasional
cleaning and using a resource from the original system.
An additional benefit has also emerged from
the development of the new system.
The
photographic coating process.
One of the numerous methods for coating
materials that are light sensitive is the slide bead process. This method of
coating has been used successfully for many years for achieving the required
accurate level of liquid distribution across the width of the material to be
coated.
This process requires the cascade/ hopper to
be positioned extremely accurately and very close to the substrate to be coated
so that the liquid can pass down the inclined slide and pass across the coating
gap fig1.
At each outer edge of coating a thick edge is
generated by an edge guide to maintain positional accuracy of the edge of
coating on the substrate. The thick edge also maintains the stability of the
sheet of liquid passing across the gap and prevents necking from occurring
which in turn would create an uneven edge to the coating and thus generate
undue waste.
Once the thick
edge of emulsion is on the base it has served its purpose. Due to the nature
of the drying process the thick edge then has to be removed as the thick line
of emulsion requires considerably more drying than the rest of the liquid
sheet.
Edge
Suck Off
System
History
A system was designed to remove the thick
edge of emulsion from the surface of the moving web. This consisted initially a
vacuum pump, a separator vessel, a waste tank, a delivery pipe and a nozzle fig
2.
The idea behind the design was to suck the
excess thick edge from the base where it would mix with the surrounding air to
form a mixture. It would then be drawn along the delivery pipe into the
separator vessel, the liquid and air mixture would then separate. The liquid
falling onto the surface of the waste whilst the air would follow the route to
the vacuum pump.
The delivery pipe entered the separator
vessel tangentially to try and reduce the velocity of the mixture, hence giving
it more chance to separate.
In the first instance the vacuum pump became
blocked by emulsion which did considerable damage. To overcome this problem a
filter was placed between the separator vessel and the vacuum pump but although
there was some improvement after a period of time the vacuum pump again became
blocked.
At this time a spray was added into the top
of the separator vessel to try and stop the carry over from the separator
vessel into the vacuum pump.
During this period products were changing and
it became necessary to dilute the emulsion being picked up from the base with
warm water to stop the nozzle and delivery pipe from becoming clogged.
There were still problems around separation
and so yet another separator vessel with spray was added into the
configuration.
Introduction
of TRIZ and Techoptimiser to Ilford Imaging.
After two presentations by Graham Rawlinson
of Next Step Associates, a visit to a seminar given by Ellen Domb in London and
two presentations by myself to the Ilford Management Team it was decided to
purchase a single licence for the Techoptimiser Professional edition (TOPE)
This was followed by a two day training
course for eight people and after that I set up a weekly lunch time session for
that group to meet and not only solve problems but also to educate ourselves in
the tools of TRIZ.
The group were asked to look at the Edge Suck
Off System and to see if it could be improved.
The following is how the group analysed the
system. Then solved the problem using
TOPE and how there were radical changes in the groups thoughts and ideas
during the process.
What were the Objectives:-
1 To improve system performance:-
Separation of the emulsion was
not happening inside either of the vessels.
2 To reduce maintenance:-
The system had to be stripped
on a regular basis with parts being replaced because of blockage.
3 To stop the vacuum pump and filter from
clogging:-
Even with the protection of two
separator vessels the vacuum pump and filter were still becoming clogged.
4 To stop additional components from being
added to the system:-
It was quite clear that all
previous efforts had just complicated the problem. Compromise had been used
everywhere.
The
Path through TOPE to solve the problem
The first thing to do when using the TOPE
software is to fill out the objectives and limitations around the existing
system, then build a function model of the system.
By doing this you are aware of the
constraints you are working within and it is possible to argue that you have
thought about the ideal system.
All the components were built into the
function model showing useful, harmful and insufficient actions linking the various
components.
Immediately it is possible to see that there
are a series of contradictions in the existing system.
The delivery pipe has the useful effect of
transporting the mixture but the detrimental
effect of causing
the mixture to solidify during transportation
The initial function
model can be seen in fig 3.
The nozzle water has the useful effect of
diluting the coating solution but the harmful effect of coagulating the coating
solution.
There is the useful effect of the air aiding
the transport of the coating solution but the harmful effect of mixing with it
which, with the existing system requires it to be separated.
There is also the insufficient effect between
the separator vessel and the mixture itself and the insufficient effect that
the filter was having on the vacuum pump.
Finally there is the problem of the spray in
the top of the vessels having a harmful effect.
Initial
Ideas
From this some initial ideas of what could be
done with the system were discussed.
1
Improve separation of the emulsion within the vessel to stop the
emulsion getting past the filter and into the vacuum pump.
2 A
method to stop the mixture clogging the delivery pipe needed to be found.
3
At this point there was still much discussion within the group about
solving the problem without having analysed the situation properly.
All the links between the components were
then assigned values to show their importance within the system.
This was done by consensus within the group
and the “expert” who new the system.
Begin
to Trim
The component that came out at the top of the
list for the trimming process was the water spray as it was close to the
product and also having a harmful effect. It was not stopping the emulsion from
carrying over into the vacuum vessel.
With this removed from the system it did not
look very different from before but it would save some energy costs. The
question of improving the system performance still had to be answered so the
trimming process was continued. Discussion still centred around
methods of separating the emulsion from its carrier, the water and air
mixture.
The next component on the list was the
separator vessel. At this point the question was asked how can there be a
system to separate emulsion without the separator vessel?
There was now a radical change in our
direction of thinking. If the separator vessel could be eliminated why try and
separate the mixture at all? In its present form the material we were doing all
this work to was scrap. There must be a way of getting the material from where
it was to where it was needed, with the minimum amount of work.
We did not stop at this point and continued
with the trimming process to see if there was a way of reducing the system
itself to a much fewer number of components than it was presently built from.
Further ideas discussed at this stage
included the use of a liquid ring pump. This would be able to handle the
mixture of air, emulsion and water but would still consume a relatively high
level of energy to keep the system working. Further investigations also
suggested that there would be a considerable increase in the amount of water
that we were presently using. There was also the feeling that it would still be
far away from an ideal system
We were now at the stage of completely
removing the vacuum pump and filter and just leaving the nozzle, nozzle water
and the delivery pipe.
The system
was considerably reduced from the original starting point of eleven
components. All that was left was the nozzle through which the liquid must
travel, the delivery pipe from the nozzle to the reprocessing plant, water to
stop the emulsion from clogging the nozzle, the emulsion itself and the
surrounding environment, air.
Fig 4 shows the
trimmed model.
Towards the Ideal System
What was needed was a method of removing the
liquid from the web and sending it to our reprocessing area by only using water
and our existing nozzle.
Now with a much trimmed down system there
were still some questions to be answered that were raised at the very
beginning.
1 How to overcome “solidifies” in delivery
pipe
2 How to get the emulsion off the moving web
and into the delivery pipe with just the available resources.
By using the Prediction module in conjunction
with the 76 Standard Solutions the following concepts were developed.
Surround the emulsion, air, water mixture
with a new substance.
PTFE lined delivery pipe.
Co-axially inject water around the mixture to
keep it away from the pipe wall.
Introduce a modified substance into the
emulsion at the point of removal from the base i.e. wetting agent
Something that came up in our search was that
Rhythm co-ordination was not an option. The energy increase would cause greater
coagulation. This was something that could not be considered.
By now moving to the physical effects data
base a method needed to be found whereby a liquid could be lifted from the
surface of the moving web by using the available resources of water and nozzle.
This came in the form of the Venturi nozzle
using the Bernoulli effect. This fitted in perfectly with the requirement of
just using water and the nozzle to remove the emulsion from the base material.
After a small amount of searching a supplier
was found who was able to supply a nozzle to match the demands of the system.
This has since been thoroughly been tested
and proven to be very effective.
The issue of clogging in the delivery pipe
has been resolved by the use of water
from the venturi nozzle diluting the emulsion to a greater degree than before.
There is also the added benefit that when the
mixture reaches the reprocessing plant it does not have to be diluted further.
The water used in the venturi nozzle does this well enough not to have to
dilute it again.
Fig 5 shows the schematic of the built
system.
Conclusions:-
By using TOPE the system went from 12
components to just two components.
The venturi nozzle and the delivery pipe.
Maintenance has been virtually eliminated.
A radical change in the direction of the
groups thinking took place during the analysis.
The emulsion is still removed from the edge
of the moving substrate without detriment to the product,
We no longer have to dilute the emulsion once
it gets to the reprocessing area as the water in the venturi does that for us,
The device only costs £90
Bibliography:-
Techoptimiser Professional Edition V3.0
Training manual
The Innovation Algorithm G Altshuller
Tools of Classical TRIZ Boris Zlotin Alla Zusman
TRIZ: The right solution at the right time
Yuri Salamatov
