Hydraulic Power Pack for Inspection Rewinding Machine: Straight Edged Finished Reels
A hydraulic power pack for inspection rewinding machine guiding drives the cylinder that keeps the printed web on one line, so the finished reel leaves the machine with flat, straight sides. Krishna Engineering Works builds the power pack and its web aligner unit in Ahmedabad for inspection rewinders of all types, including high speed machines.
Why does an inspection rewinder need a guide?
An inspection rewinder needs a guide because the reel it produces is the one the customer receives. This is the last machine in the converting chain. The printed, laminated or slit reel is unwound, checked under a viewing light or camera, cleared of faults and rewound to the diameter, direction and tension the customer has specified.
A reel with a stepped or wandering side is rejected on sight, whatever the print quality. It also runs badly on the customer’s packing machine, where the web position is taken from the reel edge. The guide is the part of the machine that turns an acceptable reel from the press into a tidy one.
The loads are light and the errors are usually small, so the job is less about force than about steadiness, cleanliness and working comfortably next to people.
Unwind guiding or rewind guiding?
Guide at the unwind when the web path is short, and at the rewind when the path is long or the edge must be exact. Inspection machines are compact, so many are guided at the unwind only: the web leaves the stand on line, crosses the inspection table and winds up straight because nothing in between disturbs it.
| Arrangement | How it works | Suits | Limit |
| Unwind guide only | Cylinder shifts the unwind stand, sensor fixed on the frame | Short web paths, table type machines | Drift arising after the sensor is not corrected |
| Rewind guide only | Sensor travels with the rewind stand, the stand follows the web | Machines where the unwind is fixed | The web position on the table is not controlled |
| Both, on one reservoir | Double power unit with two servo valves | Long paths, cantilevered shafts, demanding reel standards | More to set at each job change |
Where both ends are guided, the unwind guide keeps the print steady under the viewing position and the rewind guide looks after the reel face. Each has its own servo valve, sensor and cylinder, and they can share one tank as a double power unit. The general logic of the three guiding positions is on the web guiding system page.
What decides how straight the reel edge is?
Reel edge quality is decided by where the sensor sits, how freely the stand moves and how steadily the valve corrects. The power pack rarely lacks force or speed on this machine. Small details of the installation make the difference.
- Distance from sensor to reel. At the rewind, the sensor should read the edge as close to the winding point as the layout allows. Web that travels a long way after the sensor can move again before it lands on the reel.
- A firm lay on roller. A contact roller pressing on the reel traps the web where it lands. Without it, air drawn into the reel at speed lets the top layers slide sideways.
- Tension. A web that is slack at the edge flutters in the sensor and the guide follows the flutter. Steady, even tension gives a quiet signal.
- Sensitivity. Set it high enough that the edge is held, and low enough that the stand does not tremble. A trembling stand prints its own fine pattern on the reel face.
- Shaft grip. If the core slips sideways on the shaft, no guide can keep up. Check that the shaft holds the core firmly across its length.
Guiding printed webs by the edge
The guide follows the physical edge of the web, not the print. For a finished reel that is the right reference, because flat sides are what is being asked for.
An air sensor reads the edge by the air it blocks, so the design, the colours, clear windows in the print and metallised areas make no difference to the signal. The operator does not have to reset anything when the job changes from one printed design to another, which suits a machine that may handle many short jobs in a shift. The hydro-pneumo web aligner works this way, with the sensor air pressure adjustable from 5 to 28 mbar.
A photoelectric sensor is the other option. The electro-hydro web aligner unit uses a photocell sensor for the edge, with an AC motor, an electrical panel board to operate the complete unit, a hydraulic cylinder, an adjuster and an oil pipe. It works well on opaque printed webs. On films with clear, unprinted edges the setting needs more care.
One limit should be understood. If the print on the incoming reel is not parallel to the edge, edge guiding gives a straight reel in which the print still wanders. Following a printed line needs a line sensor, a different technique that the client’s web guide system site describes among the sensor types.
Running quietly and cleanly beside operators
An inspection rewinder is worked at arm’s length for a whole shift, so the power pack must be a good neighbour. The operator stands at the table, watches the web and handles the finished reels, often in a clean packing area.
A few points of general practice keep the unit unobtrusive.
- Sound. A small power pack in good order gives a steady hum. A change to a harsh or rattling note usually means the pump is drawing air through a loose suction joint or a low oil level, or the suction strainer is blocked. Treat a change in sound as a maintenance signal.
- Placement. Stand the tank on a firm, level floor, not on the sheet metal of the machine guard, which acts as a sounding board. The 5 metre oil and air pipes allow it to sit behind the machine, away from the operator’s side.
- Oil. Finished reels and oil must never meet. Route the oil pipe below the web path, never above it, and stand the tank where a drip cannot reach reels waiting on the floor.
- Joints. Wipe every joint dry after fitting and look again after the first day. A joint that stays dry for a day normally stays dry.
- Rod. Keep the cylinder rod clean and lightly oiled only by its own seal. A wet rod means the seal needs attention.
- Warmth. The motor and tank give off gentle heat. Leave air space around them and do not stack cartons against the tank.
Air sensing adds almost nothing to the noise of the machine. The jet is at very low pressure, far below plant compressed air.
What the unit includes
The hydro-pneumatic web aligner unit is supplied complete with a 0.5 HP motor, air pipe of 5 metres, oil pipe of 5 metres, one sensor, one adjuster, one air filter, one oil filter and one hydraulic cylinder of 6 inch stroke. The web aligner unit page explains each item and how they connect.
Finished reels are modest in weight compared with parent reels, so the KEW-17 power pack is the usual fit. Its figures are 3.4 l/min pump flow, 14 bar line pressure, 17 litre tank and 40 kg weight including oil. For high speed inspection machines, or for heavy laminate reels, the larger model and its higher follow-up speed can be considered. Both are set out on the hydraulic power pack page.
Setting the guide at a job change
Reset the guide in the same order at every job change, and the first metres of the reel will be as straight as the rest.
- Centre the guided stand before loading the reel, so the cylinder starts at mid stroke.
- Load the reel against the shaft stop or mark, so each reel of the job starts in the same place.
- Thread the web and take up tension by hand.
- Slide the sensor on its adjuster until the edge half covers the sensing gap.
- Switch to automatic and run slowly for a few turns. Look at the face of the new reel, not at the web.
- Bring the machine up to speed and check the reel face again with the contact roller down.
- After each stop to remove a fault, confirm that the edge is back in the sensor before restarting.
When a fault is cut out and the web is spliced, the two ends should be joined edge to edge on the table. A splice made with a sideways step shows as a ridge in the reel face, and the guide cannot hide it.
Faults seen on the reel face
Most guiding faults on an inspection rewinder can be read from the side of the reel. The table links the pattern to its usual cause.
| Pattern on the reel face | Usual cause | Action |
| Fine regular ripple | Sensitivity too high, stand trembling | Reduce sensitivity a little |
| Slow wave over many turns | Sensor too far from the reel, or guide too slow | Move the sensor closer, check filter and oil |
| Single step | Splice made off line, or edge lost during a stop | Join edge to edge, keep the edge in the sensor |
| Steps only at high speed | Air drawn into the reel | Use the contact roller, check tension |
| Gradual cone shape | Core slipping on the shaft | Check the shaft grip |
| Random scatter | Web fluttering in the sensor | Steady the tension, move the sensor nearer a roller |
If the pattern remains after these checks, the valve or cylinder may be worn. Units of Indian and imported makes can be sent for repairs and servicing, and spares are kept readily available.
Related machines
Reels that are too badly wound for inspection go first to a doctor machine, described on the page for the power pack on a doctoring rewinding machine. Where the web is slit as well as inspected, see the power pack on a slitting rewinding machine. The full list is under power packs by machine, and the main Krishna Engineering Works site shows the converting machinery range.
What to send for an inspection rewinder guiding quotation
Send the details below, so the guide can be matched to the machine and the reels.
- Machine layout: table type or vertical, and the length of the web path
- Materials inspected, and whether the edges are clear, printed or metallised
- Web width range and maximum machine speed
- Heaviest reel at unwind and at rewind
- How each stand or shaft is carried, and whether it can slide
- Whether the unwind, the rewind or both are to be guided
- Any limit on where the power pack can stand, such as a clean packing area
- Make and model of any existing guide
Send the enquiry through the contact page.
Frequently Asked Questions
Should an inspection rewinding machine be guided at the unwind or the rewind?
Guide at the unwind when the web path is short, because the web then stays on line all the way to the rewind. Guide at the rewind when the path is long or the reel face must be especially even. Machines with demanding reel standards guide both ends, using two servo valves on one reservoir.
How does the guide keep the sides of a finished reel flat?
The guide keeps each new layer landing at the same sideways position. A sensor reads the web edge, the servo valve meters oil to the cylinder, and the cylinder shifts the stand until the edge is back at the set point. Since every layer is placed on the same line, the reel builds with a flat face.
Does changing the printed design affect the edge sensor on an inspection rewinder?
No, not with air sensing. The air sensor detects the physical edge of the web by the air it blocks, so colours, clear windows and metallised areas give the same signal. Nothing is reset between designs. A photocell sensor may need its setting checked when the edge of the web changes from opaque to clear.
Is a hydraulic power pack too noisy to stand near an inspection operator?
A small power pack in good condition produces a steady hum that is normally lost in the sound of the machine. It can also stand several metres away, since the oil and air pipes supplied are 5 metres long. A harsh or rattling sound points to air in the suction or low oil.
How do I stop oil from reaching finished reels on an inspection machine?
Keep the hydraulic parts below and behind the web path. Route the oil pipe under the web, stand the tank away from where reels are stacked, wipe joints dry after fitting and check them after the first day. A wet cylinder rod or a damp joint should be attended to at once.
Can the guide follow the print instead of the web edge on an inspection rewinder?
Not with an edge sensor. The air sensor and the photocell edge sensor both follow the physical edge, which is correct for producing a straight sided reel. Following a printed line needs a line sensor arrangement. Say so in the enquiry if the print position, not the edge, is the reference.