Tuning the ironer for top performance

23 May 2016

Launderers who don’t keep their ironer in peak condition risk poor performance and missed productivity targets. Richard Neale of LTC Worldwide explains

The ironer line is the workhorse of the laundry and keeping it running at optimum performance is fundamental to maintaining production and achieving target productivity. It is therefore surprising to learn that in many organisations the ironer line is only working at 60-70% of design performance.
This is sometimes addressed by running the ironer faster to try to get more out, then finding that some of the textiles do not dry properly at the higher speed. Instead of addressing this, many follow the temptation to increase the conditioning time in the tumble dryer, especially for pillowcases (which are more difficult to dry because they feature two and sometimes three layers of wet fabric).
The correct solution is to 'tune' the ironer to do the work of drying and crease removal properly at high speed, so that it is possible to reduce down to thirty seconds or so the time spent in the dryer. If the tumble dryer is replaced by a cold shaker or a sheet picker, then even more economies can be realised. The economies to be achieved by 'tuning' the ironer come mainly from the much higher thermal efficiency of the ironer as compared to the tumbler. It still takes five times more energy to iron moisture from a sheet than it does to squeeze it out on a membrane press, but the tumbler takes fifteen times more energy, with much wastage going out of the flue with the hot air exhaust.
This month we look at exactly what is meant by tuning the ironer.

Minimising moisture retention
The ironer can only work efficiently and effectively if as much moisture as possible is squeezed out in hydro-extraction. Whereas a membrane press working at 24bar might only be able to achieve 56% moisture retention (m.r.) for towels and 54% m.r. for cotton sheets, modern presses operating at and over 50bar can get down to as low as 45% for sheets. This is helped by the latest drainage techniques, which enable the squeezed moisture to flow away quickly within the stage time.
The first check to make before going anywhere near the ironer is to measure the moisture retention being achieved for towels and for
cotton sheets. If this does not fall within the above guide-lines, then the hydro-extraction stage needs attention first. An ironer, however well-tuned and maintained, will not deliver its design performance if the work is too wet.

Adjusting the bed temperature
Steam-heated ironer beds have an inside temperature fixed by the pressure of the steam in the chests. Polyester, polycotton and cotton-rich textiles are designed for a bed temperature of 150C (equivalent to 4bar steam), although in practice, most withstand 165C (6bar) before they start to glaze and soften and distort. Cotton will tolerate up to 200C, although recent research work carried out by Hohenstein in Germany indicates that the lower the ironing temperature the greater the textile life.
The outside metal temperature of the bed shown on the temperature gauge (or implied by the steam pressure gauge) should be cross-checked with a digital thermometer with a surface probe. The check should extend to all beds, both sides and centre. The temperatures should match to within three degrees. If there are any differences greater than this, then look for air entrapment and condensate flooding on steam heated ironers and poor circulation or internal deposits on thermal oil units. There is no point continuing with ironer tuning until the bed temperatures are correct and uniform.

Setting up the feeder
The feeder is supposed to present the textile item to the ironer perfectly square to the direction of travel, with a straight and flat leading edge. The laydown onto the feed-bands should leave a minimal distance (say 10cm) between the trailing edge of the previous item and the leading edge of the current one, when it enters the first nip. Achieving this might require the leading edge of the current item to actually overlap the trailing edge, so that when the differential speeds of the ironer and the feed-bands is taken into account the right separation is actually achieved at the nip itself. It is vital to get this bit right, because if the bed coverage is allowed to drop below the optimum, then daily production will be lowered, often by as much as 10%. In some laundries this can make the difference between managing with one ironer and having to man-up a second one.
With the right bed coverage and the correct bed temperature the heat-transfer in the ironer should now be approaching the design performance figure.

Maintaining the ironer rolls
The rolls are supposed to be perfectly cylindrical, with a diameter which exactly matches the semi-circular cross-section of the beds in which they turn. Getting the diameter exactly right requires careful specification of the ironer cladding or 'clothing' and it might vary for each roll. Many ironers are made with the roll diameter increasing slightly, going from front to back. It is generally preferable to use two turns of strong, slightly thicker clothing, rather than three turns of the older traditional material. This usually gives better porosity of clothing and greater strength and stability in use.
When renewing the clothing, a careful check should be made of the underlying springs, because it these which gives the roll its main resilience to accommodate different thicknesses of textile items and to maintain perfect bed contact. The springing should be free of rust, with no broken springs or flattened areas of poor contact. Damaged springing should be replaced. The clothing thickness and resilience then allows fine tuning of roll diameter and roll-to-bed contact. Too great a diameter and the roll with 'bridge' the bed, touching only at the upper parts. Too small a diameter and the roll will 'bottom, with a narrow arc of contact at its lowest point. Both are disastrous for output.

Vacuum suction
As the moisture is evaporated it is drawn by vacuum through the porous clothing into the centre of the hollow roll (via small holes drilled into the metal cylinder) and away to atmosphere. This is a vital part of the entire operation. If the vacuum is inadequate, then drying of the textiles slows noticeably and they will come out damp, with 'rough-dried' patches. Even more seriously, the leading edge will not be taken cleanly into each nip and the consequent 'stutter' will create a leading corner crease and spoil a perfect finish. The reason for the 'stutter' is failure of the vacuum to dry the roll surface, lowering the coefficient of friction between this and the textile so that the fabric is not grabbed cleanly into the nip.
The target suction force for the vacuum is between 30 and 90 Pascal (Pa), with the strongest vacuum being delivered to the first roll, where most evaporation occurs. The vacuum should be checked with a properly calibrated vacuum gauge, checking for uniform vacuum across the entire width of each roll. Poor vacuum can result from build-up of wax in the vacuum pump and in the ductwork downstream of this. Curing poor vacuum will result in better drying and better finished quality.
If the problem is blinding of the clothing surface with either starch or wax, then further action is required before the clothing is replaced. Starch blinding is caused by incorrect starching in the washing machine. The starch solution should be added at the manufacturer's recommended dosage and in liquor at the right temperature. This is 50C for some starches, although more modern types are designed for cold absorption. The starching time should be long enough for the starch to build into the cloth, rather than sitting on the surface. Too much starch for too short a time at the wrong temperature will produce starch residues on the leading edge of the first bed of the ironer, with consequent blinding.
If the rolls are being blinded by wax, then the special waxing cloth should be run once every eight hours with the correct amount of wax sprinkled evenly across the width of the cloth, under the trailing flap. The cloth should then be re-run every two hours with no further wax additions. If the ironer is being waxed by hand-scattering of wax directly onto the beds, then the required minimal application will be exceeded and wax blinding of the clothing inevitable, the vacuum will be stifled and work still damp.

Many laundries have at least one more ironer than they need. Some could lose half of them if only they could get design performance out of those which are left. There are few more important tasks for the laundry engineer than tackling this problem on every site. The benefits will be seen in finished quality, in energy consumption per kg produced and in the improvements in towel productivity as tumbler minutes are trimmed by reducing or eliminating conditioning of ironed flatwork.

Tuning the ironer

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