Although tunnel washers are the main production units used in many larger laundries, often producing up to 95% of the total washroom throughput, the washer-extractor is still an essential part of day-to-day production in all laundries.
Tunnels are ideal for the launderer with sufficient volumes of similar classifications and soiling types to keep a the machine fully optimised for the working week.
A modest 10-stage 35kg capacity tunnel is capable of producing 28,000kg of work (at 100% efficiency) during a 40hour working week, but there are many laundries that simply do not have sufficient volumes of work to keep this size of machine working at optimum throughput.
Modern tunnel design often allows widely varying classifications to be processed in consecutive compartments without detrimental impact to the quality of the loads.
Even then, the divergent classifications should be fairly similar to minimise problems.
Launderers will also have smaller loads of work that require specialist processing. This work may include re-wash loads, heavily-soiled kitchen cloths or delicate woollen items that are handled more easily and effectively by a washer-extractor.
Saving costs on labour, water, energy and chemicals is easier with a tunnel washer as these machines have regular loads every 2 – 3 minutes, while washer-extractors have larger loads every 40 – 50minutes. However, the differences in operational costs between the two types of machinery can be minimised with careful planning, regular maintenance and good process controls. The three main objectives for the efficient washroom, irrespective of the type of washing machinery used, are productivity, cost and quality.
Managing productivity
If maximising the productivity of a washer-extractor is a top priority, the laundry must control and manage the following factors.
The degree of loading: Always ensure that all loads are weighed and the correct weight is processed each and every time.
The amount of time required to process a load of work, especially if the machine is fitted with programmable logic controllers (PLCs) or card/drum controllers, will be the same irrespective of the size of the load.
Under-loading a machine may save some time in unloading but this will be marginal.
However, if the washer-extractor is over-loaded, not only will the results be poorer but the time required to unload the machine can be disproportionately longer as larger items will often knot and tangle together.
Over-loading the washer-extractor continuously will cause progressive damage to the machine bearings, which can result in costly repairs.
Correct classification: Most, if not all, laundries classify their work by either type of item, the finishing methods used or the colour of the items to be processed.
However, the type and degree of soiling also plays a vital role in the type of wash process used and the quality of the finished items. By classifying heavily-soiled and lightly soiled work together, the launderer has the choice of either using a longer wash process so that the heavily-soiled items are all satisfactorily cleaned, but the lightly soiled items are over-washed, so wasting time, resources and materials; or using a shorter wash process designed for the lightly soiled work and then incurring the additional costs and lost production resulting from re-washing the more heavily soiled items that have not come clean.
Correct process design: A traditional wash process using a conventional rotary washing machine employed two wash stages, normally with alkali and a high titre soap (which lathers at over 60C), followed by three rinses.
During the early 1960s the washer-extractor and more sophisticated detergents came into the market along with improved automatic or semi-automatic process control units.
However, despite all these technical advances, many launderers still use the tried and tested two-wash and three-rinse program (sometimes with modifications such as the addition of a sluice for foul or infected work).
There are two basic reasons why many wash processes use the two separate wash stages. The first is to provide the correct temperature profile (below 39C to remove protein soiling and 60 – 70C for the oily ingrained soiling). The second reason is that the wash solution becomes heavily contaminated with soiling from the first wash and needs to be replenished with fresh water supply and further soap additions.
However most modern detergents are more than capable of holding the soiling in suspension throughout the complete wash cycle, unless the load’s soiling is exceptionally heavy.
A single wash stepped process will often achieve a better result saving time, water and energy.
Similarly, three rinses are often needed to achieve the required dilution of the alkali and other chemicals added during the wash stages. However, with a washer-extractor it is possible to remove significantly more contaminated water at the end of the first rinse via the use of an “inter-extract” and in this case two rinses will be sufficient.
Reducing costs
Many of the above productivity suggestions will also provide significant reductions in the washer-extractor operational costs.
The “stepped-wash” process, combined with an inter-extract, reduces water usage by up to 40%. The inter-extract is used between the first and second rinses.
Steam costs are reduced by 20% using the stepped wash process if the laundry only has a cold water supply.
But there are further ways of being able to fine-tune and trim your costs, for example by controlling your dip levels more accurately.
Many washer-extractors are supplied with dip level sensing mechanisms that either work on pressure switches or float switches – which are often pre-set at the factory – and merely shown as low, medium or high selections when preparing processes.
Work by the British Launderers Research Association in the 1950s identified optimum dip levels as pre-wash 125mm, main wash 75mm and rinses up to 375mm, depending on raw water quality. However, many laundries never check that their pre-wash and main wash dips are down to the recommended levels.
Few have tuned their rinse dips down so that the last rinse alkalinity is just under 0.04 gram/litre above that of the incoming raw water supply.
Without too much capital investment, it is possible to increase washer-extractor productivity by 20%, reduce water consumption from 32litres to 18 – 20litres per kilogram dry weight of work processed, and also reduce steam and energy costs by 15%.
Energy costs are becoming increasingly important with the imminent threat of 40 – 60% price hikes during the coming months, so it is also worth scrutinising all washing machinery thermostats to ensure that they are all functioning correctly and that temperature indicators are displaying accurately.
The probes inside the washing machine often become linted and provide false readings or the thermostat itself can be damaged.
Even small errors of 5 or 6degrees can increase steam usage levels by 10 – 15%. With some capital investment in water recovery and recycling systems as well as heat recovery it is possible to get remarkably close to the types of savings commonly produced from tunnel washers.
Improving wash quality
Wash quality will improve with the reductions in wash dips down to the correct level, for two reasons. The mechanical action will improve as the dip is lowered and the chemical concentration will increase for the same dosage of detergent.
The correct loading will make it easier to avoid polycotton workwear and polyester table linen creasing.
However, the biggest benefits in quality may come from the laundry’s detergent supplier. Now is the time to re-evaluate low temperature washing, because although detergent costs have moved with the oil price and the scarcity of phosphate ingredients, the increase has not been as great as the increase in gas tariffs.
Washer-extractor operations are amongst the most profitable in the business right now, but laundry operators need to keep up with the technology available and think their strategy through very carefully.
They should talk to detergent suppliers and take a closer look at their washer-extractor processes, controls and maintenance.
