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Your Partner For Success Tel 514-231-8260 Thomas Tammler
What does backpressure and wear cost you?
You know - The fundamental and unavoidable facts in extrusion are
- That dimensional tolerances are controlled by pressure and temperature stability
- That more output means more money
Most consultants concentrate their efforts on increasing extruder output, with new exotic screw
and barrel designs, and other gadgets and inventions but most ignore some of the fundamentals.
While output is of primary concern, pressure and temperature stability are a close second in the
race for profitability.
Optimizing pressure and temperature stability provides two critically important benefits:
A stable extrusion output enables you to meet requirements for dimensional tolerances.
Maximum pressure stability enables you to tighten product tolerances beyond the customers
requirements minimizing raw material usage - further leading to increased profits as well.
Constant pressure = constant melt temperature and consistent mixing
You’ve undoubtedly ‘heard everything’ by now in the way of promises and benefits.
I won’t try to top any of them. Nor will I insult your intelligence.
You won’t get rich quick by reading this.
You will benefit from a better understanding of the events that take place in the typical extrusion
line and be able to identify if they apply to you’re process and what potential benefits you may
miss out on.

2. P a g e | 2
Your Partner For Success Tel 514-231-8260 Thomas Tammler
Why do so many specialists ignore back pressure?
Back pressure is influenced by a multitude of factors we will address the ones that are most
widespread and disregarded.
Screens, two characteristics are of major importance in screens and constantly overlooked.
One is the open area of the screen versus the total screen area, the larger the open area versus
the total area the higher the efficiency of the screening process and the lower the ΔP.
The second is the life of the screen since a short life requires frequent screen changes which
incurs both the screen and screen replacement costs and can cause major process fluctuations
depending on the screen change technology used.
These characteristics are economically important in the extrusion process, don’t ignore them.
Are you’re screen packs optimized?
How much are you loosing by not taking advantage of the full potential of your
equipment?
Thousands a day may be lost, don’t believe it, you’re not alone.
Effect of Output Vs. Pressure
0
5
10
15
20
25
0 500 1000 1500 2000 2500 3000 3500
Pressure ( PSI )
Output(kg/h)
10RPM
25 RPM
50RPM
75 RPM
This chart shows, the influence of the back pressure on the output of a single screw extruder can be extreme.
The measurements were made on a laboratory extruder with 40mm screw diameter and 24 L/D.
With 75 1/min output loss with a ΔP of 2500PSI (172 bar) amounts to approx. 50%.
The experiments were carried out with LDPE, MFR 2

3. P a g e | 3
Your Partner For Success Tel 514-231-8260 Thomas Tammler
The quick fix and its expense!
The natural reaction of process engineers and operators is to increase screw speed to
compensate for the evolving loss in output. While this approach is successful in accomplishing
the short term goal to regain throughput, the increase in screw speed can result in significant
increases in melt temperature causing problems in cooling and sizing the product.
These increased screw speeds can also result in product quality problems as well, especially
dimensional instability due to surging and are not addressing the core problem.
Let’s look at a real life example.
An extrusion line is producing 750 lb/h with a clean screen at 2580 psi then after 8h the screen is
changed at 4610 psi, because the back pressure is too high and contamination is pushed through
the screens, or the extruder runs now at max RPM and/or max Amperage and so on.
The operator is convinced he don’t loose anything since he runs constant speed on the takeoff so
output must be constant, maybe some gage variation when adjusting the screw speed, but not
enough to scrap any product, and the screen change is done when he cleans the die anyways so
no loss there and no justification for a constant pressure continuous filtration solution or different
screen packs. He always ran like this, why change now?
What about what he could produce but he is not since he needs the room to play, to be able to
increase the screw speed to keep output constant?
What is the real cost of increasing the screw speed?
What do I mean by that? You may have this nice piece of equipment called an extruder with this
high output screw and you are not running it at full potential most of the time.
Do you pay for extra capacity that you are not using most of the time?
Can we agree on that you should run at high output rates to make sure you recover your
equipment cost as fast as possible and make maximum profit with what you have?
If your situation is similar to the example mentioned you are not making all the profits you could
make, you are not as competitive as you could be.
By optimizing your screen packs and installing a constant pressure continuous filtration system
you may run at a higher initial backpressure, let’s say instead of 2580 psi you may run at 2800
psi, don’t be concerned by this, it is constant 24/7 with a higher retention rate and no fluctuations.
Big deal, still running 750lb/h with out the big spikes in back pressure, where is the
payback?
Before you increased screw speed to overcome the back pressure increase to keep output
constant, now you increase screw speed to increase output.
You can run your line know in a constant most advantageous pressure and output range since
you know it will not change, what would that give you on increased output in lbs/h.
How much would that be a day, a month or in a year?
You would be surprised, the numbers are mind blowing.

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Your Partner For Success Tel 514-231-8260 Thomas Tammler
Don’t take our word for it!
The Table below shows a study by Christine Ronaghan on the effect of breaker plate pressure on
output rate and melt temperature which are also true for any other filtration system that does not
guarantee constant continuous backpressure.
Resin/RPM PSI LB/HR °F Effect per 1000 psi
increase in back pressure
Rate Temperature
PE @ 130
RPM
2178 1490 446 -11% 4.19
3133 1340 450
PP @ 138
RPM
1500 1172 492 -24% 13.58
2304 980 503
Ny6 @ 100
RPM
2143 1272 427 -4% 3.03
3133 1226 430
PET @ 75
RPM
1966 1415 572 -9 2.67
3090 1266 575
Most screen changers in use today cause extensive disturbance to your process, they range from
process interruptions and polymer degradations when slide plate or single bolt systems are used
to process fluctuations when multiple piston or duplex candle filters are employed.
All systems are subject of contaminants pushed through the screen media even so they may
break it up into smaller pieces as back pressure increases but still contaminates are introduced
into your product.
By eliminating process fluctuations you can run a thinner average thickness and achieve
significant raw material savings.
Let’s not ignore energy savings per lb/h produced since with the same amount of energy
introduced you will now produce x-amount more lbs/h more product.
But wait here is your operator again, telling you that the downstream equipment can’t handle all
the increased output rates, great what a wonderful problem to have.
Run at maximum with the existing downstream equipment, take the extra money put in your
pocket or use it to upgrade the downstream and run at full potential and make even more profits.
Companies with a few extrusion lines making relative small invests are able to maximize
what they already have; unlocking the full potential of existing equipment can recover
millions of dollars every year of lost opportunity.
Even if you don’t have the orders for the increased output yet, you can use the gain to be more
competitive, you can use the gain to do maintenance and refurbish your line before it really cost’s
you big money.
Studies have shown that reworking screws and barrels more frequently will save you money
again since you will not loose output caused by wear and keeps refurbishing costs low.
Others do have the orders and instead of buying new lines optimized existing lines at a fraction of
the time and cost.

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Your Partner For Success Tel 514-231-8260 Thomas Tammler
Don’t ignore wear!
The Table below shows how much valuable output is lost with various degrees of screw wear for
different sizes of extruders based on research by the German Plastics Institute with the following
assumptions: Screw Speed = 75 RPM Output Value = $1.70/kg
Screw size
mm
Output new
kg/h-lbs/h
Output lost
kg/h-lbs/h at
0.5 mm wear
Output lost
kg/h-lbs/h at
1.0 mm
wear
Sales lost
per day in $
at 0.5mm &
1mm wear
60 60/132 5/11 10/22 204/408
90 220/485 10/22 20/44 408/816
120 450/992 16/35 32/70 653/1306
150 900/1984 28/61 56/123 1142/2284
200 1450/3196 50/110 100/220 2040/4080
A 90 mm screw at 138 RPM did produce 892 lb/h or 21408 lb/day, with a 0.5mm wear 40 lb/h or
960 lb/day are not realized with estimated $ 3.75 sales/lb that was $3600 of unused
potential/day.
The same line was running 1/h per shift with an additional accumulative 1000 psi of backpressure
the potential gain combined was in the range of ~ $6000 total unused potential per day.
This does not take in account any $ lost on downtime, scrap or other losses caused by the non
constant pressure continues filter which where not documented.
By refurbishing the screw and barrel, optimizing the screen packs, installing a constant pressure
continuous filtration solution that allowed the processors to reduce average product thickness by
2% a total average gain of ~ $ 6000/day plus 428 lb/day of material savings were achieved.
The total cost of consulting, refurbishing and installing the constant pressure continuous
filtration solution was paid back in less then 30 days.
WHY DO YOU NEED TT-CONSULTING?
Today more then ever the extrusion industries are forced to deliver quality, consistency and
productivity. Your survival now depends on getting it right the first time. Independent consultants
can be valuable allies who help identify needs, find potential service providers, advise on provider
selection, and help plan and manage the project.
TT-consulting has the knowledge and know-how to calculate your gains and turn those numbers
into reality your competitor may profit from our services as you read this and decide if you should
contact us.
Let us call you and offer you the following guarantee:
If, after you give us the opportunity to run the numbers it turns out you will not benefit or gain
anything our consulting services are free of charge.
Thomas TammlerTT consulting
ttammler@tt-consulting.us