ººRental laundries need to operate at maximum productivity and minimum cost to keep profitable in the current market. The most successful companies will be those who discard the old concept of laundering being a batch operation and train their teams to think in terms of the complete rental flowline.
The true rental flowline starts in the sorting area with a steady flow of correctly classified and sequenced work coming forward. The next step is the tunnel washer which relies for its productivity both on the sequence from the sorting area and availability of downstream plant.
Next comes the membrane press which reduces work down to the desired moisture retention, and then the dryer, if one is free. Ironing is the next stage, and here work is either handled immediately or joins a never-ending queue of barrows which are filling the laundry floor and starving other operators of work.
From this flowline there is a steady feedback of stained re-wash, ideally identified before ironing, and a similar flow of crease re-wash from misfeeds and folder snarl-ups.
This flowline is the animal which the laundry manager has to keep moving.
Most washing lines are designed to handle four batches of linen, followed by two batches of towels. This flow pattern is based on brand new equipment and even then the design is frequently tight, with barely enough tumble-drying capacity.
Most washing lines start to run short of drying capacity within six to 12 months, so if this sequence is maintained interruptions start to creep in as washers go on “hold” until a dryer becomes free.
In extreme cases, we find laundries which run five or even six batches of linen to two batches of towels. They then find they have a long run of towels at the end of the day, after the ironer team has left.
Reducing the batch cycle time was seen as the way to raise washing machine productivity, until quite recently and some machines now operate with cycle times below 80 seconds. While this will wet the work it does not allow for much washing.
Reducing the cycle time is usually the wrong decision, unless the machine is giving 100% of the theoretical batches per hour and this is being achieved with work in the right sequence, with no towels left at the end of the day. Otherwise the laundry must find other ways of raising washer productivity.
There is nothing magic about a 50kg batch size being fed to a 50kg machine. Occasionally underloading is necessary, but generally machine capacity can be raised to 52kg or even 55kg without problems. This should be done in conjunction with the machine supplier who may well have designed the main tubular construction for a slightly larger batch size.
When new, most continuous batch washers are designed to work with cold rinse water and do not have integral heat recovery. But over the next two or three years all major suppliers are expected to bring in washers with consistently low water consumption and built-in heat recovery.
The secret is to maintain a temperature from the last compartment in the work going forward around 50C to 55C, whilst keeping the pre-wash temperature to 35C to 38C to avoid setting protein stains.
There are various techniques for doing this but most involve a combination of small heat exchanges. The benefits of hot rinsing can be seen mainly at the press and tumble dryers. The benefits of integral heat recovery are a reduction of 20 % to 30% in the steam required.
The secret of a smoothly operating washing flowline lies in good press extraction. The key parameter is the percentage moisture in the work going forward from the press, calculated relative to the
bone-dry weight.
For many years a moisture retention of 58% for towels and 54% for sheets was the accepted norm but the latest press designs with programmable controllers and high pressure units are consistently beating 50% moisture retention, even for terry towels. Working to this 50% figure will not just shorten drying cycles and save energy (it is 15 times cheaper in energy terms to remove water by press than in the tumbler) but will reduce the frequency of ‘waits’ with the washer idling until a tumbler becomes free.
Tuning points
The points to watch when tuning a press are the time at pressure, the ultimate pressure achieved and the press temperature. Time spent tuning down the various waiting times in the press cycle to give maximum time at pressure will generally improve moisture retention and repay the effort many times over.
If the odd batch of towels starts sticking to the underside of the press membrane, this should be seen as a warning of difficulties ahead. Solving the problem may require attention to the press profile, or to the wash chemistry, or even to both.
The problem is just as serious as allowing a ‘sharp’ in the work which will have immediate and disastrous effects on the membrane. Hot rinsing at too high a temperature and allowing the membrane to go above say 55C will also create problems However, this is still a bit of a grey area because there is no date on membrane life at 60C as against 40C .
Even with warm rinsing and superb press extraction, optimising drying times can still be difficult. For a dryer needs expert tuning to produce as-new drying times, especially for towels.
Raising inlet air temperature above the safe limit with a direct gas-fired drive will not help as it results in hard, harsh towelling. The temperature at the start of the cycle is probably more important than the temperature at mid cycle. Every batch of towelling should be properly cooled with 7% or 8% moisture left so it feels soft. A programmable controller and some experimentation are worth the cost and time.
Most dryers, when new, can dry terry towels in around 18 minutes, but a 15-minute cycle is usually achievable if the washing, the press and the dryer are fine tuned by the engineer. Towel drying needs to be in the 15-minute to 18-minute range for the rental operators to remain competitive and productive, but this alone is not sufficient to get the work through in the right sequence if the original specification was tight.
If there are barely enough dryers, then conditioning work for the ironer is a luxury and sheets and pillowcases should be in the dryer just long enough to break the cheese.
A well maintained ironer will dry a pillowcase from 54% moisture retention, so conditioning for seven minutes simply wastes dryer time and triples the energy cost. There may be a case for allowing table linen more time in the dryer as it will open it out and avoid folding over at the leading edge and sides. However, this can often be achieved just as well in a properly designed wash process.
Rental operators are uncharacteristically tolerant of consistently poor drying performance from their ironers. An engineer will take three or four months to tune an ironer, concentrating on consistency of bed temperature, correct suction through the vacuum roll and a perfect roll-to-bed fit.
Even when the engineer has finished tuning, success is not automatic. Much depends on the quality of feeding both by the operator and the feeding aid. With hand feeding, the way in which the leading edge is laid down to the feed bands and the way in which the sides are guided in is important. Training and good team leaders are needed. If an automatic feeding aid is used it must be correctly set up to give the right leading edge tension, perfect lay down to the feed bands, correct side tension and trailing edge tension.
It is not uncommon to see an engineer sitting for an hour or so watching a feeder operating before making an adjustment because the tuning has to be exactly right. Correct tuning goes hand in hand with good maintenance of belts, vacuum, spreading equipment and so on.
It is important to note the interaction between the feeder and the front roll. While creasing here might stem from washing or feeding, it is just as likely to be caused by inadequate vacuum or incorrect clothing.
The ironer will only deliver its full drying performance with 100% bed coverage. So if there are bottlenecks at the ironer, managers should make consistent efforts to achieve as near edge-to-edge feeding as possible and use all lanes.
It is far more efficient in terms of labour and productivity to operate four lanes of barely conditioned pillowcases than two lanes of nearly dry items. You will need to operate at half the speed, but the output per hour will be exactly the same. Similarly, an operator who can feed one lane at high speed, can feed two at half-speed. In this way you free up dryer minutes, and keep up the flow.
Reducing re-wash
The first stage in reducing the need for re-washing is to look at the main wash conditions. If these are correct then protein staining will be softened in the pre-wash, provided this runs between 35C and 38C. Higher temperatures will progressively increase the risk of setting the stains in the pre-wash and these will set even more firmly in the hot wash, eventually making removal impossible.
This is the prime cause of staining problems and can have side effects as the instinctive response is to increase the bleach dosage. However, doing this will only increase the level of bleach rotting of the cotton stock in the rinse zone and increase the risk of bleach getting into the recycle and into the hot wash.
If protein stains are not removed successfully then any vegetable dyes associated with the proteins will probably be locked into the cotton yarn and will tend to resist bleaching as well. EMPA test pieces are available for monitoring removal of protein and other stains. Successful rental operators strive for a score of 50% on each of the main test pieces for table linen. A 40% protein staining score is acceptable for bedlinen.
Stained re-wash items will need a dedicated process in a washer-extractor. Set proteins pose the main problem and these should be treated either by a well-designed enzyme process or by vigorous action at high alkalinity.
So only the crease re-wash needs to go through the continuous batch washer and unless there are severe problems at the ironer, there should be plenty of capacity to handle the 2% or 3% from this cause. With attention to detail, it should be possible reduce total re-wash to well below 5%, even for table linen,
The way in which the rental flowline is costed is critical. Many launderers still cost washing by dividing the price of a drum of detergent by the weight of work it will wash. The shrewdest operators, though, will cost the entire flowline and minimise every element of cost in harmony. For example, energy saving by heat recovery at the washing machine yields an improvement in tumble dryer productivity and hence overall productivity which is far more valuable than the steam saving of washing or drying.
Calculating productivity and costs on the basis of the flowline leads the management team to focus on bottlenecks rather than batches and this leads to success in solving any problems.
To judge the productivity of the tunnel washer, you need to compare the actual number of loads per hour, combined with the individual batch weights, to the theoretical maximum. In the press the percentage moisture retention is the key parameter, and to achieve maximum productivity in the dryers you will need to minimise the time taken to dry one batch of towels fully. The ironers must be tuned to handle work straight from the press at a speed which will give evaporation of moisture at a rate close to the ironer manufacturer’s original figure. All these targets have to be achieved against customer demands for improving quality.
We still have a way to go to optimise rental processing. Some ideas expressed here are still only being implemented slowly while others that would assist are still in the development stage.
