Hydraulic Power Pack for Paper Machine and Paper Converting Sections
A hydraulic power pack for paper machine duty supplies the oil pressure that moves heavy paper reel stands and steering frames sideways, so the sheet stays on line through winders, rewinders, sheeters and coaters. Krishna Engineering Works builds these power packs in Ahmedabad, in a 0.5 HP and a 1 HP standard model, with air sensing for dusty paper halls.
Where is a power pack used on a paper machine?
A guiding power pack is used wherever a paper web leaves a reel or is wound onto one, which in a paper mill means the sections after the dry end and every converting machine that follows. The wet end and the dryer section hold their wires and felts on line with their own guide devices, and those are a different duty. The power pack described here guides the paper itself.
| Section | What the cylinder moves | Why guiding is needed there |
| Rewinder or salvage winder unwind | The stand carrying the parent reel | Parent reels come off the machine with uneven ends and must be presented square to the slitters |
| Sheeter or cutter unwind | Each reel stand, or a steering frame after the stands | Several webs are cut together and all must lie on one edge line |
| Off-machine coater or size press unwind | The unwind stand | The sheet must enter the applicator on line, so the coated margin is even |
| Coater or supercalender rewind | The rewind stand, with the sensor carried on it | The finished reel needs flat, square ends for transport and storage |
| Paper converting machines (ruling, laminating, core and tube, bag lines) | The unwind stand or a pivoting roller frame | Print, glue lines and folds refer to the edge of the sheet |
Paper converting is where most of these units are fitted. The same drive is used on every position in the table: the standard hydraulic power pack with motor, pump, tank, filters and servo valve, piped to one cylinder.
How does paper behave as a guided web?
Paper is stiff, hardly stretches and tears from the edge, and all three properties change how the guide is set. A film can be pulled sideways and will give a little. A paper sheet will not: if it is pushed across a roller faster than it can follow, the slack side goes baggy, a crease forms and the crease becomes a break.
Three rules follow for paper.
- Correct at the source. Shifting the reel stand moves the whole sheet without bending it, which is the gentlest correction there is. A steering frame should be the second choice, and it needs a long entering span.
- Keep the gain moderate. A guide set too lively on a stiff sheet produces a wavy edge on the next reel. Slow, steady correction suits paper better than a fast snap.
- Protect the edge. A nick at the edge of a paper web is where a break starts. The sensor must never touch the sheet, and the sheet must never run against a fixed guide plate.
Moisture also plays a part. A reel that has taken up moisture on one side during storage runs with one slack edge, and no guide can cure that. The guide holds the sheet on line. Flatness has to come from the reel.
What force do heavy paper reels need?
Heavy paper reels need the push that overcomes the friction of the loaded stand on its rails, and on paper duty that push decides the model more often than speed does. Paper is dense. A reel of board or kraft at full diameter outweighs a film reel of the same size several times over, and the stand that carries it is built to match.
The cylinder does not carry the reel. It slides the stand, so the load is the moving weight multiplied by the friction of whatever the stand runs on. Using general engineering figures for friction, the table shows the push for a reel and stand with a combined moving weight of 2,500 kg.
| How the stand runs | Friction, general practice | Push for 2,500 kg | KEW-17, 260 kg | KEW-30, 389.5 kg |
| Wheels or rolling linear bearings on clean rails | About 2 to 4 percent of weight | 50 to 100 kg | Enough, with margin | Ample |
| Plain slides, clean and greased | About 10 percent | About 250 kg | At its limit | Enough, with margin |
| Plain slides carrying paper dust | 15 percent or more | 375 kg or more | Not enough | At its limit |
The force figures are the maximum operating forces of the two standard models with a cylinder of 50.8 mm diameter: 260 kg at a line pressure of 14 bar and 389.5 kg at 21 bar. The relation between pressure, piston area and force is that of any hydraulic cylinder.
The last row of the table is the one to remember in a paper mill. Dust mixed with grease turns into a stiff paste on plain slides, and a stand that moved freely when it was installed can double its resistance within months. This is why the larger model is the normal choice for paper reels, and why the rails deserve as much attention as the hydraulics.
When is the larger model the right choice?
The KEW-30 is the right choice when any of the points below apply.
- The reel and stand together weigh more than a plain slide can carry within the force of the smaller model
- The stand runs on plain slides in a dusty area
- Two reel positions, a turret or a shafted stand with heavy brake gear move together
- The mill runs board, kraft or other dense grades at full reel diameter
Its 1 HP motor drives a pump of 5.8 l/min from a 30 litre tank, and the follow-up speed is 40 mm/sec. For reels beyond the reach of the two standard sizes, power pack units are available in different models from 0.25 HP to 3 HP.
Why does paper dust decide the sensing method?
Paper dust decides the sensing method because it settles on every surface near the sheet, including the face of a sensor. Slitting, sheeting and rewinding all shed fibre and filler, and in a converting hall the air carries it everywhere.
An air sensor is suited to this. It reads the edge with a soft jet of air at 5 to 28 mbar, infinitely adjustable, and the web is detected by how much of that jet it blocks. Because air flows out of the sensor ports all the time, dust is blown away from the sensing gap instead of collecting in it. There is no lens to coat and no window to wipe. The sensing principle is set out on the hydro-pneumo web aligner page.
The air sensor has two more advantages on paper.
- Colour and finish do not matter. White, brown, coated, printed and glossy grades give the same signal, since the sheet is sensed as a solid barrier.
- A fitter can maintain it. A blocked sensing pipe or a choked air filter is found by hand and cleared with clean air.
Its limit is porosity. Very open grades such as tissue and some filter papers let part of the air jet pass through, which weakens the signal. For those grades, and for mills that prefer an electrical panel, the electro-hydro web aligner (power pack) unit with a photocell sensor for the edge is the alternative. A photocell in a paper hall needs its lens cleaned as a routine.
Keeping dust out of the oil
Dust reaches the oil through the filler, the breather and the cylinder rod, and each of these can be protected with simple habits. Fine paper dust in the oil wears the pump and makes the servo valve stick, and a sticking valve shows itself as a guide that hunts or answers late.
| Path of the dust | What it causes | Protection |
| Open filler during topping up | Dust falls straight into the tank | Wipe the cap and the area first, pour through a clean strainer, close at once |
| Breather | Dust is drawn in each time the oil level falls | Keep the breather element clean and replace it when it is choked |
| Cylinder rod | Dust carried past the rod seal | Wipe the rod, fit a bellows where the cylinder sits under the sheet |
| Dirty oil containers | Abrasive oil from the first fill | Keep a closed can for this oil only |
| Air filter of the sensor | Weak, drifting sensor signal | Clean the element at planned stops |
Use only the stated oil grades: Servo 32, Enklo 44 or Hydro 37. The role of the oil as both the working medium and the lubricant of the pump is described under hydraulic fluid. Filter elements, seals and pipes are covered on the web aligner spare parts page, and spares are kept readily available.
Place the power pack out of the dust stream if the layout allows it. The 5 metre pipes of the standard kit let the unit stand to one side of the unwind, away from the slitter and the trim blower, with only the sensor and the cylinder at the sheet.
Which unit is supplied for paper duty?
For paper duty the unit is normally supplied as a complete web aligner set with air sensing, built on the model that the reel weight calls for. The contents of the standard set are a 0.5 HP motor, an air pipe and an oil pipe of 5 metres each, one sensor, one adjuster, one air filter, one oil filter and one hydraulic cylinder of 6 inch stroke. The set and its pipe runs are described on the web aligner unit page.
| Paper application | Sensing | Model usually considered | What decides it |
| Light converting unwinds for thin grades | Air sensor | KEW-17 | Small reels on free running stands |
| Rewinder and sheeter unwinds for writing and printing grades | Air sensor | KEW-30 | Reel weight and dust on the slides |
| Board and kraft unwinds | Air sensor | KEW-30, or a larger model on enquiry | Force for the full reel |
| Steering frame between two sections | Air sensor | KEW-17 | The frame is light, so speed matters more than force |
| Tissue and porous grades | Photocell sensor | By reel weight | The air jet passes through open paper |
Where the stands are fixed to the floor, as on many shaftless reel stands for large reels, the sheet is steered by a tracking roller assembly after the unwind. A sheeter that cuts several webs at once needs one guide for each reel. Two or three servo valves can share one reservoir for that purpose, as explained under double and triple hydraulic power units.
Fitting the guide to a paper reel stand
A guide is fitted to a paper reel stand in the order below, and most of the work is mechanical.
- Weigh or calculate the heaviest reel, add the stand, shaft and brake, and decide the model from the push needed.
- Check the rails. Clean them, and replace worn plain slides with rolling bearings if the friction is high.
- Fix the cylinder low on the centre line of the stand, between the two rails, so that the push does not twist the stand.
- Use a rigid bracket on the floor frame and pin joints without play at both ends of the cylinder.
- Mount the sensor on the fixed frame just after the first roller that follows the reel, and let that roller move with the stand.
- Stand the power pack clear of dust and trim, within reach of the pipes, with the filler and filters easy to get at.
- Fill with clean oil, bleed the cylinder by stroking it fully several times, and check the oil level again.
- Run a reel slowly and raise the sensitivity until the stand follows the edge without overshoot.
Leave slack in the brake air line and in any cable to the stand for the full stroke. A hose that pulls tight at the end of travel acts as a spring against the cylinder and shows up as a guide that is weak in one direction only.
Related machines and further reading
Paper is guided on many of the other machines in this range. Web offset presses take paper reels at the infeed, and that duty has its own page on the power pack for an offset printing machine. Off-machine coaters share the heat and margin questions treated on the power pack for a coating machine. The sector view, with paper beside packaging, textile and metals, is on the power packs by industry page.
Standards and technical papers on winding and web handling for the paper industry are published by TAPPI. The wider range of paper converting machinery from the same maker is shown on the Krishna Engineering Works main site.
Units that have begun to creep, leak or answer slowly after years in a dusty hall can be sent for repairs and servicing.
What to send for a paper machine guiding quotation
The unit is chosen from the reel and the stand. Send the details below.
- Machine or section: rewinder, sheeter, coater, or the type of converting machine
- Paper grades and the range of basis weight
- Maximum and minimum web width
- Maximum reel weight and diameter
- How the stand is carried: wheels, linear bearings, plain slides or fixed to the floor
- Number of reels to be guided on the machine
- Line speed
- Dust conditions at the unwind, and whether porous grades are run
- For a replacement: make and model of the existing guide
Send the enquiry through the contact page. Machinery manufacturers who buy units in bulk for their paper converting machines are invited to enquire.
Frequently Asked Questions
Which power pack model is used for heavy paper reels?
The KEW-30 is the usual choice for heavy paper reels. It has a 1 HP motor, a line pressure of 21 bar and a maximum operating force of 389.5 kg on a 50.8 mm diameter cylinder. Compare that force with the push needed to slide the fully loaded stand, including friction, and keep a clear margin for dusty rails.
Why is an air sensor preferred in a paper mill?
An air sensor is preferred because paper dust cannot blind it. Air flows out of the sensor ports continuously, so fibre and filler are blown clear of the sensing gap. The sensor has no lens to clean and reads white, brown, coated and printed grades alike, since it detects the sheet as a barrier to the air jet.
Can the power pack guide tissue or other porous paper?
It can, but usually with a photocell edge sensor instead of an air sensor. Porous grades let part of the air jet pass through the sheet, which weakens the air signal. The hydraulic side stays the same: the same power pack, valve and cylinder move the stand. State the grade and its openness in the enquiry.
Does this power pack guide the felt or wire of a paper machine?
No. Felts and wires in the forming, press and dryer sections are held on line by their own guide devices, which act on a guide roll of the fabric run. The power pack described here guides the paper web, by shifting reel stands or steering frames on winders, rewinders, sheeters, coaters and converting machines.
How much does paper dust affect the force needed?
Dust can raise the force needed by half or more on plain slides. Mixed with grease it forms a stiff paste, so a stand that once needed about a tenth of its weight as push may need considerably more. Clean rails regularly, or fit rolling bearings, before deciding that the power pack is too small.
How often should the oil filter be cleaned in a paper converting hall?
Clean it at every planned stop to begin with, and set the interval from what you find. A dusty hall loads the filter faster than a clean room does. A filter that is found heavily loaded each time means dust is entering the tank, so check the filler cap, the breather and the cylinder rod as well.