posted June 06, 2001 09:05 PM            

quote:

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Originally posted by FSD Admin:
Have a question about extrusion screw
design or processing? Why not see if someone from here or the industry might be able to give you some valuable input.
Ask away.

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Curious - are you looking for moderators?

Louis

posted March 07, 2003 07:57 PM               

quote:

---

Originally posted by FSD Admin:
Have a question about extrusion screw
design or processing? Why not see if someone from here or the industry might be able to give you some valuable input.
Ask away.

---

posted March 07, 2003 11:49 PM               

A couple of questions please:

1) When changing colors what extruder cleaning procedures do you use? How long does it take?

2) Are the extruder outputs limited by the downstream capability, or surging, or what?

3) What kind of extrusion rates do you expect?

4) Do you need to use filter screens or extruder vents to make a quality product?

Thanks, This will give us a better image of your situation.

posted March 08, 2003 07:22 PM               

quote:

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Originally posted by Tom C:
RHV,

A couple of questions please:

1) When changing colors what extruder cleaning procedures do you use? How long does it take?

2) Are the extruder outputs limited by the downstream capability, or surging, or what?

3) What kind of extrusion rates do you expect?

4) Do you need to use filter screens or extruder vents to make a quality product?

Thanks, This will give us a better image of your situation.

Tom C

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I am actually embarrassed to answer your first question. We do not use any purging agents or other types of cleaners, when we do our color changes. We simply transition from one color to another. This isn’t too bad when going from a natural to any other color; however, we will go from reds and blues to naturals and other light colors. We just allow the extruder to run several rolls of waste until the new color is all that is left. This can take as much as two hours to complete. This is not a procedure that I agree with, especially since color shade and consistency is our livelihood.

posted March 09, 2003 06:05 PM               

All lot of things go into transition from one grade or color to another. I did not hear anything about black, so be thankful.

If we assume the average transition is one hour, then it costs about $150 of resin and $150 of machine time to transition. Over a years time you will spend about $ 500,000 in transition costs. So it might be worth some investigation into better procedures if possible. Cutting the average transition to 45 minutes would save $100,000 in a year.

My initial impression is that wave sections, barrier sections, Maddock sections, and screen packs are difficult to purge.

Hopefully you have hydraulic screen changer so you can cycle in a breaker plate without screens during transition.

A simple screw design will purge faster, and if properly designed should provide an equivalent quality product. (This is without considering the mixing needs of the pigments used.)

Purging with 1 MI resin should help clean out the line quickly, and would work even better with a simple screw design. The 1 MI resin will probably not purge out at the ends of the die, and it will tend to reside in the die for a while afterwards.

Maddock sections have some dead spots which will purge slowly, or never.

The other side of the equation is production rate. Your production rates for PP on a 3 1/2" are reasonably good. However it is often surprising to see the economics behind increased production rate.

Assuming your plant is full to capacity and the product sells for $0.75/lb we can estimate your sales at $ 12MM/yr. A modest increase of 10% in output rate to 550 lbs/hr would increase sales to almost $14MM/yr. This would work out to a potential pure profit of $ 250,000.

With these examples are shown the potential of optimized production capabilities to improve profit. The payback analysis is estimated:

Engineering cost estimate: $ 10,000.00
New screws: 6 * $ 7,500 = $45,000.00
Line development time = $ 5,000.00
Developement materials = $ 5,000.00
Screw installation time and setup = $ 15,000.00

Total = $ 80,000.00 (I feel that this is a fully loaded number.)

Payback on an engineering project which will likely result in $ 350,000/yr improved profitability is less than 3 months.

A whole different analysis could be made for the pigments and whether to buy concentrates, or even liquid color.

If there are not enough new orders to fill the additional capacity, either a line could be turned off and the labor cost saved, or additional work can be found by the sales force.

The number of options, considerations, and variable involved in designing an operation for maximum profitability is huge. The resulting differences in profitability can also be huge, and therefore some study and analysis is justified. What I have tried to show here is some example of the magnitude of the number involved.

So sorry I don't think I provided any answers, just a hundred more questions. If you want to keep the discussion going, that is fine with me.

posted March 09, 2003 11:10 PM               

I run Maddocks sections, I don't have any trouble with "dead spots". We used to run a lot of Block co-polymer Styrene, which degrades badly with any extended residence time.I'm a mixing section believer though.

Running a .8-1 MI PP to speed a purge is a good way to speed up transitions from one colour to the next.

Steve H

posted March 10, 2003 03:11 PM            

quote:

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Originally posted by Tom C:
RVH,
. . . . If we assume the average transition is one hour, then it costs about $150 of resin and $150 of machine time to transition. Over a years time you will spend about $ 500,000 in transition costs. So it might be worth some investigation into better procedures if possible. Cutting the average transition to 45 minutes would save $100,000 in a year. . . .

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I would not base any cost savings on the lost "opportunity" unless you have work to fill the machine. If not, I would base it just on the lost labor / material / overhead.

Louis

posted March 10, 2003 03:31 PM               

I empathize w/ your situation; 35 color changes a week isn't easy. As well, I agree w/ TC's comments regarding the KISS principal; indeed a simple profile is a better option than the wave or barrier profiles for their ease of purge. And further, mixing when augmented w/ a mixing device is very good. I have several comments on my website (ppsincorp.com) regarding barrier profile (in the news section) which are similar to TC's. I have had alot of success designing screws for situations such as yours and would be happy to review your requirements further and offer you a quote to modify or replace your existing screws.

posted March 11, 2003 12:50 PM               

I have a question. Why would you go to others for quotations when Tom Cunningham has been quite generous with his time and has presented sizable amount of useful information. Perhaps you are not aware he is one of the most respected extrusion experts in the industry. I'm sure he can supply you with new screws with excellent designs.

posted March 11, 2003 03:23 PM               

The discussion here is about a lot of purging between jobs. From a theoretical and practicle viewpoint a typical conventional screw will purge out faster than a typical barrier screw. No other consideration is given to the comparison.

I must have missed the part about grooved feeding?