Which product should I start with if my web wanders at the rewind?

Start with the web aligner unit if one position needs correction and the stand can move sideways. It arrives as a complete kit with power pack, sensor, adjuster, filters, pipes and cylinder. If the stand cannot move, a tracking roller assembly placed before the rewind steers the web instead, driven by the same kind of power pack.

What is the difference between a web aligner unit and a web guiding system?

A web aligner unit is a set of hardware for one guiding position: power pack, sensor, adjuster, pipes and cylinder. A web guiding system is the complete loop, including the frame or stand that the cylinder moves and the choice of guiding position. In practice an aligner unit becomes a guiding system once it is fitted and set up on the machine.

Are spare parts available for KEW power packs and aligners?

Yes. Krishna Engineering Works keeps spares for its hydraulic power packs and hydro-pneumatic web aligner units readily available. When you order, quote the model of the power pack and name the part, such as the sensor, adjuster, air filter, oil filter, pipe or cylinder, so that the correct item is sent the first time.

Can I buy the power pack without the sensor and cylinder?

Yes. The hydraulic power pack is offered as a drive unit on its own, which suits machine builders who fit their own frames and plants that replace an existing unit. Krishna Engineering Works invites bulk enquiries from machinery manufacturers. State the cylinder size and the sensing method you use, so the unit is matched to them.

How do I calculate the force of a hydraulic cylinder?

Multiply the line pressure by the piston area. Pressure in bar times area in square centimetres gives force in kilograms force, to a close approximation. Real cylinders deliver a little less because of seal friction and pressure losses in the pipes and valve, which is why published operating forces sit below the simple calculated value.

What decides the follow-up speed of a power pack?

Follow-up speed is decided by pump flow and cylinder bore. The pump delivers a fixed volume of oil each minute, and the piston can only travel as fast as that volume fills the cylinder. The KEW-17 gives 30 mm/sec at 3.4 l/min and the KEW-30 gives 40 mm/sec at 5.8 l/min on the published cylinder size.

What is the difference between the KEW-17 and the KEW-30?

The KEW-30 is the larger unit in every respect. It has a 1 HP motor against 0.5 HP, a 30 litre tank against 17 litres, a pump flow of 5.8 l/min against 3.4 l/min, and a line pressure of 21 bar against 14 bar. It therefore corrects faster and pushes harder, and it weighs 60 kg with oil against 40 kg.

How often should the oil in a hydraulic power pack be changed?

There is no single interval, because oil life depends on temperature, cleanliness and running hours. As general practice, check the level and colour weekly, and change the oil and filter element when the oil darkens, smells burnt, turns cloudy or after a major repair. A unit that runs cool and clean keeps its oil far longer than one in a hot, dusty corner.

Why does a hydraulic power pack run hot?

A power pack runs hot when more energy is turned into heat than the tank can shed. The usual causes are a low oil level, a unit boxed in without air flow, a pressure setting higher than the load needs, or a worn pump that slips internally. Restore the level, give the tank free air on all sides and check the pressure.

Can the power pack stand away from the cylinder?

Yes, within reason. The web aligner version is supplied with 5 metre oil and air pipes, so the pack can sit beside the machine, clear of the web and the operator. Longer runs add pressure loss and delay, which makes the guide slower and less stable, so keep pipes as short and as straight as the layout allows.

Why is the tank so much larger than the pump flow?

The tank is sized to hold several minutes of pump flow so that the oil rests between passes. During that time air bubbles rise out, dirt settles and heat passes into the tank walls. On the KEW models the tank holds about five times the flow per minute. A tank that is too small sends hot, aerated oil straight back to the pump.

Hydraulic Power Pack for Plastic Processing Machine

Hydraulic Power Pack for Plastic Processing Machine: Film and Sheet Guiding

A hydraulic power pack for plastic processing machine duty supplies the oil flow and pressure that move an unwind stand, a winder or a steering frame, so that film or sheet stays on its line. Krishna Engineering Works builds these units in Ahmedabad for film, sheet and woven fabric lines, with air or photocell edge sensing.

What does the power pack do on a plastic processing machine?

The power pack is the muscle of the edge guide. A sensor watches the edge of the film, a servo valve on the power pack turns the sensor signal into oil flow, and a cylinder shifts whatever carries the web until the edge is back at the set point.

“Plastic processing machine” covers a wide family: lines that make film and sheet, and machines that print, coat, laminate, slit or convert them into bags and sacks. They share one need. The web must arrive at the knife, the sealing bar, the coating die or the winder in the same sideways position on every metre, and plastic webs do not stay there on their own.

This page is the overview for that family. It shows where a guide earns its place on each machine and which hydraulic unit fits the duty. The unit itself is taken apart component by component on the hydraulic power pack page.

Where does a film or sheet line need a guide?

A guide is needed immediately before any point where the edge position decides quality. The table lists the usual points on common plastic processing machines, as general practice in the industry.

Machine	Point where edge position matters	What the cylinder moves	Typical duty
Blown film line	Winder, after the layflat leaves the haul off	Winder carriage or a steering frame ahead of it	Light web, continuous running
Cast film line	Winder, after edge trimming	Winder carriage	Light web, high speed
Sheet line	Winder or stacker entry	Winder carriage	Stiff web, slow drift
Bag and pouch making machine	Unwind, ahead of the sealing and cutting section	Unwind stand	Stop and go web motion
Woven fabric coating or lamination line	Fabric unwind, ahead of the coating die	Unwind stand	Heavy roll, rough edge
Film slitter or rewinder	Unwind, ahead of the knives	Unwind stand	Heavy reel, fast correction
Printing or laminating machine for film	Unwind, before the first unit, and rewind	Stands at both ends	Continuous, solvent area

Film making lines usually need one guide, at the winder. Converting machines usually need one at the unwind, because they inherit every winding error of the reel they are fed. Machines with both an unwind and a critical rewind need two.

Why is plastic film harder to guide than paper?

Plastic film is harder to guide because it is thin, extensible and often transparent. Each of these properties affects the hydraulic side as well as the sensor.

Thin and extensible. Film stretches under small forces. A guide that jerks pulls a tight lane into the film, so the correction must be smooth and proportional. That is the strength of a servo valve feeding a hydraulic cylinder.
Gauge bands. Small thickness variations across a film build up on the reel into hard and soft bands. Such reels unwind with a slow curve to one side, and the guide has to follow that curve for the whole reel.
Transparency. Clear and lightly tinted film passes light, which makes simple optical sensing unreliable. An air jet is blocked by any solid film, clear or printed.
Static charge. Running film collects static and draws dust towards the sensor gap. A sensor that keeps itself clean has a real advantage on a film line.
Low tension. Film runs at low tension, so the web follows a moved stand without resistance. The load on the cylinder comes almost entirely from the stand and the reel, not from the web.

Thick sheet behaves in the opposite way. It is too stiff to be twisted across a short span, so a steering frame is a poor choice for it. Sheet is guided by moving the winder to meet the web, or the edges are trimmed to a fixed line and the trim absorbs the drift.

Which unit suits which plastic processing machine?

Choose the unit by the web first and the load second. Krishna Engineering Works offers two sensing methods on the same hydraulic drive, and the steering frame as a separate assembly.

Situation on the machine	Unit that suits	Reason
Clear, tinted or printed film at an unwind or winder	Hydro-pneumo web aligner	The air jet reads any solid film, whatever its colour
Dusty area around woven fabric or reclaimed material	Hydro-pneumo web aligner	Outflowing air keeps the sensing gap clear
Opaque film or coated fabric where an electrical panel is preferred	Electro-hydro web aligner	Photocell sensor for the edge, with panel board control
Neither end of the web can be moved	Tracking roller assembly with the power pack	A pivoting frame steers the web in mid machine
Two or three guides on one machine	Double or triple power unit	Two or three servo valves share one reservoir

The air sensing version is described on the hydro-pneumo web aligner page. The electro-hydro web aligner (power pack) unit comes with a photocell sensor for the edge, an AC motor, an electrical panel board to operate the complete unit, a hydraulic cylinder, an adjuster and an oil pipe. Where the web must be steered between two fixed sections, the cylinder drives a tracking roller assembly.

The hydro-pneumatic unit is supplied as a kit: a 0.5 HP motor, 5 metres of air pipe, 5 metres of oil pipe, one sensor, one adjuster, one air filter, one oil filter and one hydraulic cylinder of 6 inch stroke. The way those parts connect on the machine is shown on the web aligner unit page.

Choosing the hydraulic power pack for plastic processing machine loads

Choose the model by the push the stand needs and the speed at which the edge moves. In a hydraulic drive, pump flow sets how fast the cylinder travels and line pressure sets how hard it can push.

Model	Motor	Pump flow	Line pressure	Maximum operating force	Follow-up speed
KEW-17	0.5 HP	3.4 l/min	14 bar	260 kg	30 mm/sec
KEW-30	1 HP	5.8 l/min	21 bar	389.5 kg	40 mm/sec

The force figures are for a cylinder of 50.8 mm diameter. Tank capacity is 17 litres on the KEW-17 and 30 litres on the KEW-30, and power pack units are available in different models from 0.25 HP to 3 HP.

For most film winders and light unwinds the smaller model has ample force, because a film reel on a well kept carriage needs little push. The larger model earns its place on wide woven fabric rolls, on jumbo reels at a slitter and wherever the stand runs on plain slides. The follow-up speed matters most on fast cast film winders and on slitters fed with telescoped reels.

Heat, static and dust around plastic machinery

Heat is the main enemy of a power pack on a film or sheet line. Extruders, dies, chill rolls and dryers warm the air around them, and the oil in a small tank follows the room it stands in.

The viscosity of hydraulic oil falls as it warms. Thin, hot oil leaks past clearances more easily, so the guide becomes soft and holds its position less firmly. Stand the power pack away from the die and the barrel heaters, out of the hot air stream from dryers, and where air can move around the tank. The pipes supplied with the kit allow the tank to stand several metres from the cylinder.

Dust is the second concern. Woven sack plants and recycling sections carry tape fibres, filler powder and granule dust, and static on the film pulls that dust towards every surface. Keep the tank cover and filler closed, wipe around the filler before topping up, and check the oil filter and the air filter of the sensor more often than on a clean film line.

Fitting a guide to an existing plastic processing machine

A guide can be added to most machines already in service, provided the stand can be made to slide. The steps below give a practical order of work.

Decide the point that the guide must protect: the knives, the sealing section, the coating die or the winder.
Make the stand or winder movable. It needs straight guide rails or wheels, low friction and enough travel on both sides of centre.
Mount the cylinder on the centre line of the moving stand, with rigid brackets and free pins, so that it pushes without bending.
Fix the sensor where the web is flat and supported, close after a roller. At an unwind it sits on the fixed frame, and at a winder it travels with the winder.
Place the power pack in a cool, clean position within reach of the pipes, fill it with the recommended oil and check the direction of motor rotation.
Bleed the cylinder, run the stand through its full travel by hand, then switch to automatic and set the sensor.

The recommended oils for the KEW units are Servo 32, Enklo 44 and Hydro 37. Do not mix grades when topping up.

Related machines in the plastic processing family

Several machines in this family have their own pages, each written around its particular duty. The winder of a film or coating extruder is covered on the page for the power pack on an extruder machine. The unwind ahead of slitting knives is covered under the power pack for a slitting rewinding machine, and the meeting of two films at one nip under the power pack for a lamination machine.

The basic process behind most of these lines is extrusion, and the full list of machine pages is under power packs by machine. Slitting machines themselves are presented on the main brand site under slitter rewinder machine.

Supply, spares and service

Krishna Engineering Works makes its power packs and aligner units in its own factory in Ahmedabad and takes a continuous trial of each unit before dispatch. The company has the capacity to supply 100 to 150 units per month and invites enquiries from machinery manufacturers who buy units in bulk.

Spares for the hydraulic power pack and the hydro-pneumatic web aligner unit are kept readily available. Older units of Indian or imported make can be sent for repairs and servicing, where worn parts are replaced with new ones.

What to send for a quotation

Send the details below, so that the sensing method and the power pack model can be matched to your machine.

Type of plastic processing machine and the point where the guide is needed
Material: film, sheet, woven fabric or laminate, with thickness range and whether it is clear
Web width range and line speed
Heaviest reel or roll, and how the stand or winder is carried
Whether the web runs continuously or in stop and go motion
Temperature and dust conditions where the power pack and sensor will stand
Number of guides on the machine, if one reservoir is to serve several
Make and model of any guiding unit being replaced

Send the enquiry through the contact page, or see the complete range on the hydraulic power pack products page.

Frequently Asked Questions

Which plastic processing machines need a web guide?

Any plastic processing machine that winds, slits, seals, prints or coats a continuous web benefits from a guide. Film and sheet lines normally need one at the winder. Bag making machines, slitters, printing machines and woven fabric coating lines need one at the unwind, because they receive reels that already carry winding errors from the previous process.

Can one power pack serve the unwind and the winder of a film machine?

Yes, when the two guides are close enough for the pipe runs to stay short. Double and triple power units carry two or three servo valves on the same reservoir, so each guide has its own valve and cylinder while sharing one motor, pump and tank. Each guide still needs its own sensor.

Is air sensing or a photocell better for transparent plastic film?

Air sensing is the safer choice for transparent film. The air jet is blocked by the film itself, so clear, tinted and printed films all give a usable signal. A photocell depends on the web interrupting a light beam, which works well on opaque film and coated fabric but less reliably on clear material.

How do I guide thick plastic sheet that cannot be steered?

Guide thick sheet by moving the winder, not the web. Stiff sheet cannot twist across a short span without buckling, so a steering frame is unsuitable. The sensor is mounted on the winder carriage, and the hydraulic cylinder shifts the carriage until it lines up with the sheet arriving from the line.

Does heat from an extruder affect the hydraulic power pack?

Yes. Heat thins the hydraulic oil, which increases internal leakage and makes the guide feel soft and slow to hold position. Place the power pack away from the die, barrel heaters and dryer exhaust, keep air moving around the tank, and use only the recommended oil grades when filling or topping up.

What size of power pack does a film winder need?

Most film winders are well served by the 0.5 HP model, because a film reel on a free running carriage needs only a modest push. Wide woven fabric rolls, jumbo reels and stands on plain slides may need the 1 HP model. Send the reel weight and the type of carriage with your enquiry.

Hydraulic Powerpack for Plastic Processing Machine