In LCNi May/June issue, we looked in some detail at identifying machine problems and how to recognise them.
We are now going to focus attention on computer controls and the sequences they deliver, because many units are operating with non-optimum programmes and putting this right can make dramatic improvements to performance, overnight.
Back in the day when cleaning machines were controlled by slotted card type, electro-mechanical systems, programming errors were very common. We occasionally checked out machines that were delivering process times and structures that literally beggared belief. The introduction of modern, machine computer controls virtually eliminated the common problems generated by worn/damaged cards, faulty card drive mechanisms and worn components; but while we would all like to think that computer controls are infallible, we should, after two post office computer scandals (and, on occasion, the failure of our own personal computers) be aware that even today computers can still let us down.
Cleaners should always be aware that computers are only as good as the machine that they are controlling and while modern machines have good safety systems such as a still overfill prevention, there is no feedback to the computer from critical machine components such as control valves and drive systems. Unexpected problems such as sticking valves, slipping belts and compressed air leaks, over which the computer has no control, are still common. It is therefore down to management to ensure that machine processes are monitored and checked by the operator regularly and that machines are maintained in line with manufacturers and suppliers’ maintenance schedules.
First steps
The machine manufacturers all have their own specific computer controls and with some, the machine supplier may, in the interest of the cleaner, restrict access to certain areas of the control system. Machine computer controls are fairly straightforward, but it is important that you study the manual supplied with the machine and develop a good understanding of how it works and how to access the various fields relating to the program structures. Some computers may have set programs for, say, filter cleaning, that cannot be changed, but the cleaner can develop and save their own programmes if required, with cleaning processes structured to the cleaner’s specific requirements. New machines normally come with correctly installed, suitably structured industry programmes, but over time these can be inadvertently or deliberately changed by staff or engineers, all of whom are unlikely to have the theoretical knowlege required to ensure that a programme is correctly constructed for a particular classification in terms of, for example, time, dip levels, temperature and mechanical action.
Make no mistake, computer programme errors, such as an incorrect temperature setting, can result serious fabric damage.
To check an installed programme, refer to your machine manual for the computer instructions and access the programme you wish to review. You will find you can then step through the programme in detail stage by stage and check the following.
- The dip levels.
- Slow speed cage rotation – rotation speed and whether continuous or intermittent
- The stage times
- The drain time
- Spin speed and time
- The drying temperature
Bear in mind that not all machine computer controls have the capability to control features such as variable highspeed/ low speed revs per minute (rpm) or to provide intermittent cage rotation.
Computer programming
Those with an aptitude for IT will probably find inserting their own specific programs into the computer control unit fairly straightforward, but bear in mind that however confident you are in your ability, disaster can still be lying in wait just around the corner. In addition to a very careful review of the programme you have inserted (and adjusting it if necessary) it is imperative that you also monitor (in real time) the actual machine process delivered by your new programme. You should carefully check every aspect of the process structure. We have had direct experience with serious programming errors in new programs developed by acknowledged experts, because they had failed to monitor the process in real time after programming.
Examples of typical industry standard hybrid programmes
The following outline programme structures are suitable for perc and hydrocarbon solvents but, for optimum soil and stain removal, cleaning times (for which garments are tumbled in a dip or flow of solvent) may need to be extended. As a guide, for normally to heavily soiled items, cleaning time may need to be increased by as much as 15 – 20 minutes for robust items. Longer cleaning times are necessary because hydrocarbon has only one third of the solvent power of perc and weighs in at approximately 0.8 kg/ litre compared to perc at 1.6kg/litre. The low specific gravity of hydrocarbon means that mechanical action is substantially reduced, depending on machine capacity and for any given cleaning time.
Solvent condition
When developing your own programmes, it is important to bear in mind that at least 2.5 litres of solvent must be distilled per kilogram of work processed in order to maintain the base tank solvent in good condition. In the types of hybrid processes described, that are in common use today, the ratio of solvent/kg dry textiles is mainly governed by the height of the first stage dips. You can verify the ratio by checking the volume of solvent taken from the working tank to generate low, medium or high dips against the capacity of your machine.
Factors influencing cleaning Efficiency
Should you decide to have a go at developing your own programmes for, say, extremely fragile or very heat sensitive items you need to know the physical effects of variations in cleaning time, dip levels, cage speed, and intermittent slow speed cage rotation. This is very important as, for example, too much mechanical action on silk garments may cause severe fabric damage.
Examples of typical programmes for different Classifications
1. Programme for normal robust items (labelled ) – Darks, Mediums and Lights
- 3 ½ min medium circulating dip from base tank. Drop to still – extract for ½ min.
- 8 min filter wash medium dip from distilled tank + detergent. Drop to base tank extract for 2 ½ min.
- Dry at 60C for perc.CESS:
2. Programme for delicate Items (labelled ) – Darks, mediums and Lights.
- 2 min medium circulating dip from base tank. Drop to still – extract for ½ min.
- 5 min filter wash, medium dip from distilled tank + detergent. Drop to base tank – extract for 2 ½ min.
- Dry at 50C for perc.
3. Programme for white items (labelled or ). The base tank solvent must be in good condition – no more that a very light straw colour with no cloudiness.
- 6 min filter wash, medium dip from base tank. Drop to still – extract for ½ min.
- 2 min medium circulating dip from distilled tank + detergent. Drop to base tank – extract for 2 ½ min.
- Dry at 50C for perc.
When developing programme 3, it is critical that when the pre-coat circuit is employed in the first stage, the filter is producing crystal clear solvent before the cage inlet opens.
Check in the relevant sight glass.
Avoid damage due to mechanical action
- Cleaning time – doubling the cleaning time doubles the amount of mechanical action.
- Dip level – a low or no dip gives the greatest mechanical action, a high dip gives the least.
- Cage Speed – normal slow speed cage rotation provides the most mechanical action; very slow rotation where items just tumble around in the bottom of the cage gives very low action.
- Intermittent normal slow speed rotation – substantially reduces mechanical action in line with the dwell period.
Important note: very specific processes have been developed by wetcleaning machine manufacturers, which are absolutely critical to the safe, water-based processing of personal wear items, many of which are not specifically designed to be cleaned using water. We would therefore strongly advise against any attempt to alter or modify the manufacturer’s set wetcleaning programmes.
