Module 4, Washing Technology in Commercial Laundries
Washing regarded as an action is essential to achieve cleanliness and hygiene of the processed fabrics. It becomes particularly important with linen used in e.g. hospitals and factories and wherever a high standard of hygiene is a must. This determines the main goal of commercial laundries.
In general the washing process aims to:
- remove local and general soiling,
- remove stains,
- maintaining the whiteness of white work and the brightness of colour in dyed and printed goods,
- keep or restore the original condition /physical characteristics, shape etc. / of the fabric,
- avoide chemical or physical damage,
- reduce germs (e.g. bacteria, fungus but also virus) on textiles.
Transportation, Sorting and Storage of dirty Linen
Soiled linen is collected from the customer, usually by the laundry’s means of transport. The vehicles should be specially adapted for carrying laundry trolleys with bags containing dirty textile. After unloading the “dirty trolleys” should be washed and disinfected in e.g. pass-through chambers. The storage time of dirty linen should be lowered to the minimum in order to reduce development of bacteria.
The classification of work during the whole process is necessary mainly for two reasons:
- ensuring that each processed piece of linen will be properly forwarded to the section where it gets treated in a specially designed process adapted to the piece’s characteristics.
- facilitating accurate labour flow from the washer units to the appropriate finishing department.
The washing process takes place in the washing machines. It generally consists of several operations. There are breakdown (or first or pre-wash) and main wash, two or more rinses and eventually the hydro-extraction in order to remove excess of water from the linen after the last rinse. All of them are distinctively arranged with regard to the specifics of the processed loaded linen i.e. its fibre, colour, dirt etc. Pre- and main wash tasks is to achieve the general purposes of the washing process (see above).
During the operations in washing-machines /washer-extractors or tunnel batch washers/ there are four factors determining the efficiency of the process:
mechanical action: as a result of the rotating drum and movement of the linen falling down; the measure of this factor is a “falling angle” (30 - 50 deg) or peripheral speed of the drum (1, 5 - 2, 0 m/s); It is important to link them with the load ratio (1 kg load per 12 dm3 drum capacity) and the liquor ratio (5 dm3 of washing liquor per 1 kg of load).
temperature: the process is run at a certain temperature.
time of the process
chemical action /surface agents – surfactants - concentration/
The Sinner’s Circle
(more details on the washing theory in the slide presentation)
During the rinsing operation all or as much washing materials and dirt embodied in the last wash liquor are supposed to be removed (rinsed out) in the highest possible degree.
The intermediate extraction lowers remaining wash liquor in the linen and allows better dilution of the residues thanks to the larger amount of incoming water. The last hydro-extraction (centrifugal or pressed) reduces latent humidity within the linen down to app. 50%.
Having been hydro-extracted, the wet linen is conveyed to the finishing department.
Finishing process main operational tasks are:
to dry linen so that it reached the normal humidity for every sort of the fabric (e.g. cotton app 8%)
to ensure proper shape and quality of the processed pieces.
There are three main kinds of finishing processes:
- rotary drums drying
- contact drying and calendering of the flat linen – i.e. ironing
- contact drying and pressing – i.e. pressing
Rotary drying is used mostly for terry cloth garments and is maintained in tumble dryers (tumblers). The load ratio is 1: 25. The drum rotates either in one only or both directions. The water evaporates due to the high temperature caused by the hot air injected through the perforated shell of the drum. This allows to reach the desired humidity of the linen. The intake of hot air is app. 60 – 80 m3/h/kg of load. The temperature grows from the beginning 60oC up to 110oC at the end of the process. Drying time is about 15 min. Drying capacity varies from 80 up to 120 kg/h of linen per 1m3 of the drum volume. For disinfection purposes there are tumblers built in a pass-through mode in addition to the standard front-loaded ones.
Ironing makes about 60-75% of the laundry total output. The flat pieces to be processed here are fed by a feeding machine into the ironer. They are led between rotating rolls and stable heated beds. The temperature of the beds is round 165 – 180oC. The evaporated water is vacuumed out through the perforation holes on the rolls. Depending on the required capacity the ironing machines can consist of 1, 2 or 3 rolls. Due to the rotation the pieces are conveyed further into the machine. Small and big pieces of flat linen, once ironed, are length and cross folded by the synchronised units.
Pressing is a process used for most garments like shirts, overall, coats etc. A piece of garment is steamed and dried between two pressing plates. They might be positionned horizontally or vertically depending on the requirements and the built of the machine. The steam and evaporated water (vapours) are removed by the integrated suction system.
After being processed during the finishing operation the clean linen identified with regard to its user are forwarded to the clean storing section and expedited to the customers.
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