Managing residual creasing in rental workwear2 October 2019
Richard Neale of LTC Worldwide looks at how to keep the cost of processing workwear to an acceptable minimum, but still produce a result which is as nearly crease-free as possible
In the battle to produce an acceptable finish and keep the lid on processing costs a few enterprising and tenacious rental operators have actually managed both to save money and to improve visual quality on workwear.
The first part of this article has been written with the washer extractor user in mind, but the general principles apply equally to tunnel washers. The special features to watch for in tunnel washers are summarised in the final section.
Types of creases and how and why they occur
Pressure creases in wear usually occur around the seat of the garment – the coat of an operator seated at a supermarket till is a good example. They become more deeply embedded the longer the garment is worn and the higher the humidity in the store and from the wearer. They typically run for 10 to 150mm, with most around 25 – 100mm long.
Pressure creases in washing occur in the hot wash. They affect the garment which happens to be at the bottom of the cage during cage-reversal, so that at the end of the stage nearly every garment might display random pressure creases which are 10–100mm long. The sharpness of the creases increases with bath temperature and load factor, as might be expected.
Pressure creases in spinning occur if the final spin is too fast and if the rinse water temperature is elevated (for instance, if there is heat recovery into the main water tank, so that the laundry is rinsing with warm water).
Roping creases are as sharp as pressure creases, but they are much longer, typically up to 900mm. They occur mainly in the hot wash, especially if the rotational speed of the cage is slightly too low
Thermal shock creases look like the imprint of a crow’s foot multiplied a hundred times and they occur in patches at random on some or all garments. These are caused by failure to programme the correct cooldown sequence at the end of the hot wash.
Crumple creases occur in normal wear and with the normal washing action. They are not sharp, in contrast to the other types of crease described and they are the only type of crease that is fully removed in the tunnel finisher.
How to prevent or remove sharp creasing
Pressure creases in wear are removed by washing in a correctly loaded machine, with a hot wash that is above the temperature at which the wearer put the creases in. This is likely to be at 35 – 40C, which is easy for the laundry to exceed, unless it is trying to use an ultra-low temperature main wash. Correctly loaded means, for polycottons, using a load factor which is 60 – 85% of the load factor for 100% cotton. This means, in a washer extractor, allowing 11.5 to 16.5 litres of cage capacity per kg of dry workwear. The optimum load factor varies with the sensitivity of the fabric, but most operators aim for 85% of the cotton capacity wherever possible.
Pressure creases in the main wash are avoided by washing in a correctly loaded machine, which has been selected for its suitability for workwear. This means one which has a rotating cage which has a depth to diameter ratio which is at least greater than unity. Generally, the lower the diameter, the lower the risk of pressure creases in the wash. This is because these are formed in the hot wash by the weight of garments in the cage-reversal crushing the garment which happens to be at the bottom of the cage, up against the unforgiving cage wall. The lower the diameter, the lower the height of this pile.
For obvious reasons, this also makes avoiding overloading the machine doubly important. It also makes sense to avoid use of D-pocket or Y-pocket washer extractors, because these allow the crushing of a few garments during every rotation, in the tapering joints that feature in the D and Y configurations.
If all else fails, then the launderer has the unattractive option of increasing the main wash dip, especially if this is below the standard 100mm, but this is a last resort as it increases water, energy and chemical costs (although it does work well).
Pressure creases in the spin are avoided by tuning the spin speed, using the major benefit of the inverter drive on modern machines to enable fine adjustment. Some fabrics will withstand faster spins than others, so a separate program could be installed for these. If the rinse water has been pre-heated as part of a heat-recovery scheme, then the warm conditions in the spin will may encourage much more severe creasing.
Roping creases are caused in the hot wash by the use of too slow a rotational speed, so that the textiles roll up like a ball and roll off the lifter at the 9 o’clock and 3 o’clock positions, creating long hard creases. Sometimes these curl round the legs of overalls or round the body of a coat. The solution is to raise slightly the rotational speed (the adjustment may be in the ‘advanced’ section of the machine programming instructions), until the correct ‘lift and drop’ action from the 11 o’clock position is obtained. This will give the right pounding, stretching and abrasive action essential for good quality stain and soil removal, with no roping.
Thermal shock creases in polycotton garments, with the characteristic crow’s foot appearance, is avoided by programming the correct cooldown at the end of the hot wash. It may not be sufficient simply to tick the requirement for cooldown in the menu of programming options. To work for most fabrics, the maximum rate of temperature reduction must not exceed 4C/minute until the bath is below 52C. For a few very sensitive fabrics, this must be reduced to a maximum of 2C/minute. Note that by using a low temperature wash process, the launderer will also save significant water and time during the cooldown, which should be built into the economic analysis of the pros and cons of low temperature processing. A good low temperature process will eliminate the cooldown entirely.
Crease avoidance at the tunnel washer
Pressure creasing in washing and thermal shock in the first rinse can be eliminated by using a tunnel which has been correctly designed or modified for garment processing and following the manufacturer’s guidelines for load factor. Normally there is never any problem with thermal shock creasing in a tunnel washer, because the counterflow design of the machine encourages steady changes in temperature from stage to stage.
Roping creases are avoided by the use of the correct lifter designs, which are also a feature of the machine manufacture. If, despite this, either pressure creases or roping creases arise, it is worth trying small adjustments to the rotational speed and rock angle, because these are under the launderer’s control.
However, pressure creases in the final spin can arise for the same reason as in a washer extractor (rinse water which has been warmed by recovered heat). This can be a major problem in a highly integrated high-volume plant (with significant heat recovery), which is probably best solved by reducing the spin speed and compensating in the tunnel finisher settings for the higher moisture content at the tunnel finisher entry.
The first step in any programme of improvement is to examine the type and severity of the residual creasing and then to address this with the correct solution as a trial. It will be found that different fabrics often show different potential for creasing and different machines can give very different results, so a disciplined and methodical approach is needed! Good luck!
Optimising the tunnel finisher
The following factors affect the degree to which creases are improved in the tunnel:
Time in the barrow – the longer the time the more severe the pressure creasing.
Load in the barrow – double loads squash creases into the lower batch.
Warm or hot rinsing – increases the severity of all pressure creasing in the barrow.
Moisture content of the wet garment coming forward – The wetter it is up to say 100% moisture retention, the easier it is to relax all types of crease from the fabric.
Steam injection at the tunnel entry – This warms up the wet garment rapidly, giving more time for effective relaxation of the creasing.
Garment to peg ratio – that is whether garments are hung on every peg, every other peg or on in three. This has a greater effect on tunnel productivity than on quality, but hanging on every peg means that the garments are closer together and this usually gives a higher smoothing force down the front and back of each one and can lead to a slightly better finish.
Air recycle rate – that is the percentage of very hot and humid air from the drying zone which is recycled back into the initial conditioning zone and main de-creasing zone. Generally, the more humid the air, the greater the smoothing force exerted on the garments (because the humid air has a higher density than dry air) and hence the better the finish. The optimum setting is one which gives good commercial quality at an acceptable productivity rate.
Volumetric flowrate of air from the main fans – this is what provides the main downward smoothing force and it can be maximised by keeping the fans and ductwork clean and free from build-up of lint and grease and by clearing the main filters regularly and effectively.
It should however be noted again that whilst good, well-maintained tunnel finishers will improve all types of creasing somewhat, it is unlikely ever to remove sharp creases completely. These must be prevented by the launderer.