Hydraulic Power Pack for Extruder Machine and Extrusion Line Guiding
A hydraulic power pack for extruder machine lines drives the cylinder that keeps film, sheet or coated substrate on line at the unwinds and at the winder, for as long as the extruder keeps running. Krishna Engineering Works builds the power pack and its web aligner units in Ahmedabad for extrusion coating, lamination and film lines.
Where does an extrusion line need a guide?
An extrusion line needs a guide wherever a web is fed to the die or the nip, and again where the finished web is wound. The extruder itself makes a melt, not a web, so the guiding positions are in the web handling sections around it.
| Line | Guiding position | What the guide protects |
| Extrusion coating | Substrate unwind, ahead of the die and chill roll nip | The melt curtain lands on the same band of the substrate, so the uncoated margin or the overcoat at the edge stays constant |
| Extrusion lamination | Second unwind | The second web meets the first edge to edge at the nip |
| Extrusion coating and lamination | Before the edge trim and at the winder | Trim width stays even and the reel builds with flat ends |
| Blown film | After the collapsing frame and nip, ahead of the winder | Sideways drift of the layflat, caused by bubble movement, is removed before winding |
| Cast film and sheet | After the chill section, before the trim knives and at the winder | The edge bead is trimmed evenly and the reel is wound straight |
In extrusion coating the substrate guide is the one that earns its keep first. The melt curtain is fixed in space by the die. If the paper, film or foil below it drifts by a few millimetres, the coating runs off one edge onto the chill roll or the pressure roller and leaves the other edge bare. Guiding the substrate removes the cause.
How is the winder guided on an extrusion line?
The winder is guided either by moving the reel to follow the web or by steering the web into a fixed winder, and the construction of the winder decides which.
Moving the winder
Where the winder stands on a carriage, the cylinder shifts the carriage and the edge sensor travels with it. The sensor reads the incoming web, and the power pack moves the winder until the sensor finds the edge again. Each layer is then laid on the one below. This is the classic rewind arrangement, and it works well on centre winders for narrow and medium widths.
Steering the web into a fixed winder
Many extrusion line winders cannot be moved. Turret winders with automatic changeover, surface winders and wide two station winders are heavy, fixed to the floor and tied to cutting and transfer gear. On these the web is steered just before the winder by a tracking roller assembly, a pivoting roller frame driven by a servo cylinder from the power pack. The load on the cylinder is small, so the frame answers quickly.
The frame needs a free span of web on its entry side and should sit as close to the winder as the layout allows. A long run of unsupported film after the frame gives the web room to drift again.
Guiding ahead of the edge trim
On coating lines and cast lines the edges are trimmed in line. If the web wanders under the trim knives, one trim becomes wide and the other thin, and a thin trim breaks. A guide ahead of the knives lets the trim be set to what the edge bead or the overcoat needs and no more. Where the trim knives are close to the winder, one steering frame serves both purposes.
Why does continuous duty change the demands on the power pack?
Continuous duty changes the demands because an extrusion line is not stopped for small things. Starting an extruder means heating, purging and scrapping material until the web is stable, so plants run for days between planned stops. The guide runs with it, and its pump turns all of that time.
In a guiding power pack the pump delivers its flow continuously, and whatever the cylinder does not need returns to the tank. The energy in that returned oil becomes heat. The tank is there to give the heat away and to let the oil rest: on the two standard models the tank holds about five minutes of pump flow, with 17 litres for 3.4 l/min on the KEW-17 and 30 litres for 5.8 l/min on the KEW-30. Over a long run the oil reaches a steady temperature that depends on the air around the tank.
Three consequences follow for an extrusion plant.
- Service has to fit the stops. Filter cleaning, oil changes and seal work are planned for die cleaning, screen changes and product changeovers, since the guide cannot be opened while the line runs.
- Small faults must be caught while running. A slow weep at a fitting or a rising oil temperature can be seen and noted without stopping, then dealt with at the next stop.
- Spares must be on the shelf. A line that cannot wait for a filter element or a seal kit should hold them. The parts are listed on the web aligner spare parts page, and spares are kept readily available.
How does heat from the extruder affect the oil?
Heat from the extruder thins the oil, and thin oil changes how the guide behaves. The barrels, the die, the melt curtain and any preheating or drying section all radiate heat, and the air above an extrusion line is warm even in a cool building.
The property that matters is viscosity. As mineral oil warms it becomes thinner, more of it slips past the working clearances of the pump and the valve, and less is left to move the cylinder. The table shows the usual signs.
| Sign at the guide | What the heat is doing | Remedy |
| Guide is crisp at start-up and soft after some hours | Oil has thinned, so internal leakage has risen | Move or shield the pack, check the oil level and grade |
| Stand creeps when the line is stopped | Thin oil passes the valve and the piston seal more easily | Check seals at the next stop, lower the oil temperature |
| Oil darkens and smells burnt | Oil has been run too hot for too long | Change the oil and the filter, then find the heat source |
| Rod seal weeps after a few months | Seals harden when they are kept hot | Shield the cylinder from radiant heat, renew the seals |
| Tank too hot to keep a hand on | Tank cannot shed its heat to the surrounding air | Give the tank free air on all sides, away from hot ducts |
As general practice, mineral hydraulic oils last longest when they are kept comfortably warm and not hot, and their life shortens quickly as the temperature rises above that. A tank that is too hot to touch for more than a moment deserves attention.
Placement solves most of this. The pipes of the standard kit are 5 metres long, which lets the power pack stand at floor level to the side of the line, away from the die and outside the path of the hot exhaust. Only the cylinder and the sensor then sit near the web. Where the cylinder must work close to the die, a simple sheet metal screen between the two keeps radiant heat off the rod and its seals.
Which sensor suits film and coated webs on an extrusion line?
An air sensor suits most extrusion line webs, because the web is often clear and the air near the die is not clean. Polyethylene and polypropylene films are transparent or lightly tinted, and an air sensor detects them by the air they block, not by the light they stop.
The area around a die also carries fume. Vapours from the melt condense on cool surfaces, and a sensor lens is one of them. An air sensor works with a steady outflow of air at 5 to 28 mbar, infinitely adjustable, which keeps its sensing gap clear. How the air signal reaches the servo valve is explained on the hydro-pneumo web aligner page.
Three cautions apply on extrusion lines.
- Freshly made film is soft. Keep the sensor on a section where the film has cooled and is under steady tension, not directly after the chill roll.
- A beaded edge is not a clean edge. Before the trim, the edge of a cast or coated web is thicker and less regular than the body. Guide from it only when there is no trimmed edge to use.
- Open substrates need a different sensor. Nonwovens and open woven fabrics that are extrusion coated let air through. For these the electro-hydro web aligner (power pack) unit with a photocell sensor for the edge is the alternative.
Choosing the model for an extrusion line
The model is chosen position by position, because the unwind and the winder of an extrusion line ask for different things.
| Position | Typical load | Model usually considered | Reason |
| Substrate unwind on a coating line, paper or board | Heavy reel on a shifting stand | KEW-30 | 389.5 kg maximum operating force for a dense reel |
| Substrate unwind, film or foil | Light to medium reel | KEW-17 | 260 kg is ample on free running slides |
| Second unwind on a lamination line | Light to medium reel | KEW-17 | Same as above |
| Steering frame before a fixed winder | Light frame | KEW-17 | Speed matters more than force |
| Shifting winder carriage | Reel and carriage together | KEW-30 | Moving weight grows through the reel |
The force figures are for a cylinder of 50.8 mm diameter. The follow-up speeds are 30 mm/sec for the KEW-17 and 40 mm/sec for the KEW-30. For duties outside these two, power pack units are available in different models from 0.25 HP to 3 HP. The components and the sizing steps are set out on the hydraulic power pack page.
A coating and lamination line may have three guides: two unwinds and a winder. Double and triple power units, with two and three servo valves on the same reservoir, can feed guides that stand close together, such as the two unwinds. The winder is usually far enough away to justify its own pack with short pipes.
Bringing the guide into service at line start-up
The guide is brought into service after the web is stable, not before. The order below suits an extrusion line.
- Before heating up, check the oil level, the filters and the free movement of the stand or frame by hand.
- Set each stand and steering frame at mid travel, so the cylinder has stroke to both sides.
- Thread the leader with the guides switched off.
- Start the line and bring the coating or the film to its running width and thickness.
- Position each sensor at the edge of the stable web, with the web half covering the sensing gap.
- Switch on the unwind guide first, then the guide before the trim, then the winder guide.
- Adjust sensitivity until each correction is smooth and without overshoot.
- Note the oil temperature after the first hours of running, as a reference for later checks.
During a long run, a short daily look is enough: oil level, any weep at the fittings and the cylinder rod, the feel of the tank by hand and the cleanliness of the air filter. Change the oil and clean the oil filter at planned stops, using only Servo 32, Enklo 44 or Hydro 37.
Related machines
Extrusion lines belong to a larger family. Film and sheet machines as a group are covered on the power pack for plastic processing machines page. Solution and hot melt coaters, with their dryers, are treated on the power pack for a coating machine page, and the edge match of two plies on the power pack for a lamination machine page. The loop of sensor, power pack, cylinder and frame is explained as a whole under web guiding system.
The maker’s own converting machinery is shown on the Krishna Engineering Works main site. Power packs that have run hot for years and now creep or leak can be sent for repairs and servicing.
What to send for an extrusion line guiding quotation
Each guiding position is matched to the line. Send the details below.
- Type of line: extrusion coating, extrusion lamination, blown film, cast film or sheet
- Positions to be guided: substrate unwind, second unwind, before the trim, winder
- Substrates and films, with thickness range, and whether they are clear, opaque or porous
- Maximum and minimum web width
- Maximum reel weight at each unwind and at the winder
- Type of winder: shifting carriage, fixed turret or surface winder
- Line speed
- Distance from each guide to a cool place where the power pack can stand
- Usual length of a production run between planned stops
- For a replacement: make and model of the existing guide
Send the line data through the contact page. Machines that follow the extruder in a plant, such as slitters and printing presses, are listed under power packs by machine.
Frequently Asked Questions
Where is the guide placed on an extrusion coating line?
The first guide is placed at the substrate unwind, so the paper, film or foil runs under the die on a fixed line. A second guide is used at the other unwind on a lamination line, and a third before the edge trim or at the winder. The unwind guide controls where the coating sits on the substrate.
Can a hydraulic power pack run continuously for several days?
Yes, a guiding power pack is built to run for as long as the line does. Its pump circulates oil all the time and the tank sheds the heat. What continuous running demands is clean oil, a tank standing in free air, and filter and seal work planned for the stops that the extrusion line already takes.
How far should the power pack stand from the die?
Stand it as far from the die as the pipes allow, at floor level and out of the hot air rising from the extruder. The standard kit has pipes of 5 metres, which is enough on most lines to keep the tank in cooler air. Only the cylinder and the sensor need to be near the web.
Why does the guide become sluggish after the line has run for some hours?
The usual reason is hot oil. As the oil warms it thins, more of it leaks past the internal clearances of the pump and valve, and less reaches the cylinder. Check the oil level and grade, give the tank free air, and move or shield the pack if it stands in the heat of the extruder.
How is a fixed turret winder guided?
A fixed turret winder is guided by steering the web just before it. A tracking roller assembly, driven by a servo cylinder from the power pack, pivots to bring the edge back to the sensor. The frame needs a free entering span and should sit close to the winder, so the web has no room to drift again.
Does blown film need guiding before the winder?
Often it does. Movement of the bubble and of the collapsing frame makes the layflat drift from side to side as it comes down from the nip. A guide ahead of the winder removes that drift before the film is trimmed, slit or wound, which gives reels with flat ends and an even trim.