Five feats for a flawless film-line foundation
With a little extra attention from the very beginning, every line startup can turn a profit from Day One.
By Consulting Technical Editor Eldridge Mount -- Converting Magazine, 6/1/2009 12:00:00 AM
Many new film lines are built and commissioned every year, and the large majority come online producing in-specification product in a short period of time, if not right at the start. There are, however, lines where nothing seems to go right, especially at the point where saleable production is required.
A Windmoeller & Hoelscher blown-film line at Superior, WI-based Charter Films. (Photo by Julie Sturzyk)
Among the questions raised at that point: 1) Why is this happening? 2) Whose fault is it? 3) How do we correct the problem? And especially 4) Who pays for the changes? As you can imagine, this is not a happy time, but with a little extra attention from the very beginning, every new film-line startup can be resounding success.
So, what is the genesis of the few times when a line starts poorly? In my experience, it's usually related to the lack of a clear description of what the line is supposed to do—or a poor specification. First, you generally get what you ask for, and if you ask for a film line, you get a film line. But, if what you really wanted was a line to produce a barrier-coextrusion for deep-draw thermoforming, you may end up with a line for cast-polyethylene (PE) or cast-polypropylene (PP) film for bread bags. It's all in how you ask (See sidebar below).
Saleable goods from the start
Assuming you have specified the line well, how then can you make sure it produces saleable goods as soon as possible? There are five startup 
steps every business owner, general manager, project manager and process engineer should follow when installing and starting a new film line (See sidebar below). These five steps should be performed in sequence and not all at once: 1) The “Smoke Test;” 2) Safety and shutdown test; 3) Moving-parts operation test; 4) Actual performance measurement; and 5) In-spec product manufacture and measurement.
The five steps can be done in sequence as each component is installed, prior to shipping to your location and in combination with other installed components. Step 4 may be the most critical as it determines if the line will produce finished material at the rate and quality you need for maximum productivity and profit.
Five steps—sounds almost too simple—but they are necessary to insure that all is well when product production is scheduled and new capacity is needed. A poor line startup benefits no one, except perhaps your competitors.
Who's responsible for all of these checks? Ultimately, you, the purchaser, but how and who conducts the checks and pays for necessary modifications (etc.) is likely a partnership with the supplier (if a turnkey) or critical-component suppliers. At times there may be multiple entities responsible for the final outcome. This must be clear in your contract for the supply and installation of the line and various technology components. If it isn't clear who's responsible for a poor start (it could be you), then you can only hope for honest suppliers who stand behind their equipment—or perhaps you'll have to rely on the courts. Make sure the manufacturers did not supply a terrific line for the production of a product you did not really want.
Fire extinguisher at the ready
So now, let's look at the purpose and conduct of each of the five steps.
First, the “Smoke Test.” The purpose of Step 1 is to find wiring or installation errors as well as components that are “weak,” of poor quality, broken or destined to fail early. This is important for electronic systems where components either fail early or at very long times and which may take a long time to receive replacements. Nothing is more frustrating or costly than waiting two weeks for a replacement circuit board which had a resistor burn up while your full production staff is ready to work.
Next, after everything is assembled, Step 2 begins with checking all the emergency-shutdown systems and e-stop circuits before putting the line into operation. This means all of them and requires a disciplined, deliberate approach. These systems protect operators and equipment from harm, and as such there can be no compromises.
Try and start the line with each safety circuit activated (should not start) and power down the line by activating each one. Nothing is more terrifying than punching an e-stop and having nothing stop—or more frustrating than to have one activate when it shouldn't.
“Start your engines!”
Now, we're ready to “start the engines” in Step 3. Lubricate everything and check oil levels. Confirm that 1) everything that should turn turns; 2) that if they shouldn't turn, they don't; and 3) that they turn in the right direction. Also, check that lubrication is working, parts don't make noises, components don't run at high power and don't shake. I think you can get the picture.
Take initial vibration signatures if you plan to monitor vibration or initial torque and power readings without a load. Now's a good time to check roll alignment and bearings and to look for bent shafts. To run an extruder with the screw installed, uncouple the drive or better don't install the screw yet so the gearbox can be checked. Verify all motor speeds and readout accuracy and calibrate all tension-measuring systems.
Step 4 of the process confirms the performance of all parts and subsystems, checking the design of the line components to determine if output will meet your expectations. Determine if all parts were designed properly, what needs to be replaced or redesigned. This may be the most important step. The preceding tasks make Step 4 possible, and the final step depends on the successful completion of this one.
In film-process lines, key functions to check include extrusion, quenching, web transport and winding. The extruders supply the melt for film formation, the quenching system cools the molten combination to create the film at a given line speed, and web transport carries film to the winder where it is collected in rolls. There are other systems such as edge pinning and trim-removal systems to inspect, but they complement and often don't restrict performance. Still, they must be checked against your performance expectations.
Up to snuff?
So, how do we check an extrusion system for design-rate compliance? First, inspect and measure the screw profile, compare it to the screw design to verify it was manufactured properly (It's your screw; you can and should have a drawing of it from the supplier). Measure the output, melt temperature and stability, motor power and pressure stability as a function of screw speed for at least one set of barrel temperatures. Output should be linear with screw speed. An output curve with a decreasing slope vs. screw speed indicates a screw that is losing output and should be replaced.
Quenching capacity and/or heat-transfer coefficients can be measured several ways during film manufacture or directly. Points of interest: Water-flow rate, water-temperature rise across the roll and final film temperature. Film properties will be dependent on the thermal history of the polymer, so if you're adding capacity with the new line, measure the thermal history of it and compare to the first line to get the same product performance.
Web-handling and winding performance are a little harder to measure, but the transport of film without wrinkles and creases or film stretching are key items. For winding, there will be a film-formulation component which cannot be ignored, but overall for winding, I prefer the use of roll density (kgms/m3). Ultimately, the real proof of winding is slitting yield.
Getting up to speed
Having performed all line-component checks, it's now time for Step 5: Put the line into production. Focus on getting the line up to speed and begin adjusting settings to optimize film properties and quality. This initially includes getting the film gauge flat by setting the average die-gap and edge-pinning systems to obtain stable edge profiles and film formation while adjusting the die. For coextrusion systems, adjust extruder temperatures to control melt viscosity to eliminate any melt disturbance which might be present. Knowing melt temperature as a function of output rate will be critical to maintaining acceptable coextrusion stability.
With film on the winder, line performance can be fine-tuned and film properties optimized. If the film is not on the winder, it's just not possible to fine-tune the properties. Optimizing film properties may take the form of additive-concentration changes for surface properties or refinements of barrier-layer thicknesses for barrier properties. Mechanical properties will be primarily controlled by polymer selection and on extrusion conditions and casting conditions.
Overall, concentrate on the first four steps, and the last step should be easy. The real goal of Steps 1-4 is to permit the routine formation of film and having it on the winder so that properties can be refined. In the few cases where a new line startup doesn't go well, it's generally the case that one or more of the first four steps were not done. Worst cases: There was no clear concept of what the line was supposed to do in the first place, or the line wasn't designed to optimize the manufacture of the desired product.
Additional photography courtesy of Davis-Standard
Creating new-line specs: Asking for what you want
The best way to avoid the heartbreak of a poor new film-line startup is to first have a clear idea of what you want the line to do. This is not as silly as it sounds. The more care taken at the earliest stages of line design will pay dividends as it allows for a more meaningful, purpose-driven, engineering design of the line.
What's involved? I like to start with a design or business-expectation conversation with the key stakeholders in the company. The statement that I want a film line producing good film at 2,000 kg/hr is pretty empty in terms of equipment-design strategy. You would be surprised at the range of meaning that 2,000 kg/hr takes, depending on who you talk to from the engineering department to the general manager or owner. (Trust me).
So, pick a business: barrier cast or blown film, stretch film, OPP or any other product. Ask what is the market, what physical dimensions are needed for the product (roll widths and lengths) and what is the existing marketplace need (one supplier, demand for thinner films, lower cost, higher quality, better barrier or toughness, etc.). This requires what I call a “fitness for use” analysis.
Then, make a clear statement of your product focus. For instance: “To produce a multilayer, barrier film for meat packaging, while meeting or exceeding competitive films' performance and generating a rate of return on investment (ROI) of XX percent.” Don't forget to do a factual ROI (See Figure 1 below). Your business has to be better than bank returns, or you're not worth the risk.
Film A: Barrier film with two nanolayer barriers surrounding a scrap layer. For example, polyethylene (PE)/nanolayer barrier structure/scrap-PE blend/nanolayer barrier structure/PE sealant
Film B: Five-layer, single-barrier layer film without scrap utilization. For example, PE/adhesive/barrier resin (Nylon or EVOH-based)/adhesive/PE sealant
Margin x Output = Profit and percent ROI = Profit/Capital Investment
ROI-B & ROI Target & ROI-A equals kill Film B and build line to produce Film A.
Next, do a property analysis of commercial or competitive films which are successful in the market. Obtain product property sheets and also measure the key physical and thermal properties of the film based on how it is used. For barrier packaging, there will be a definite barrier requirement and perhaps a thermoforming or heat-shrinkable requirement (suggesting the need to orient). Determine the material composition and estimate the material cost of the film.
At this point, you can develop a barrier and a manufacturing cost model for the conversion of the polymers into a film with the desired barrier properties. This will permit the determination of the economic viability of the project or the output level at which the desired profitability is reached.
Now, you are finally in a position to talk to equipment suppliers. Discuss the line's requirements in terms of machine size and output level, the number of layers needed and the number of layer structures to make a credible entrance into the market. Ask for a machine capable of producing Film A at a rate of XX kg/hr with a material efficiency of 96 percent and a slitting yield of 85-95 percent for rolls of a specific width and length. Then, you have a measurable target which defines success.
