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The Technology of Laundry

  • Basic Principles of Laundry
  • Obtain a Good Washing Result
  • Textiles and Programs
  • Understanding Residue Moisture
  • Ironing - How Does It Work?
  • Conclusion
Basic Principles

Applies to all washing methods

Mankind has always washed things. In ancient times washing was done in the sea, on a riverside, at the well or wherever water was available. Fortunately, however, there are now other and more convenient ways to wash. Today, machines can be used.

In order to obtain an effective washing result, some key information about the goods and the washing conditions is necessary.

A good washing result is determined by:
The nature of the textile fibres.
The nature of the dirt.
The quality and effect of the water.
The washing products, detergent, softeners, bleaching etc.
The proper washing program.
Futhermore, when washing soiled goods, some qualities must be restored by the washing process and some qualities must be preserved.

Qualities to be restored are:
Feeling, touch.

Qualities to be preserved are:
Colour and finish.
Absorption ability.
Resistance to static electricity.

These basic washing principles apply to all washing methods such as traditional wash, wet cleaning, dry-cleaning and LCO2 cleaning.

Traditional Washing

Domestic washing

Traditional washing is used for washing common linen which does not require any special treatment. Domestic and professional laundry are examples of traditional washing, where water is the washing medium in a washer extractor with detergents.

Traditional washing is used where hygienic aspects are important as the maximum temperature can go up to 90°C.

Economical aspects
To obtain an optimal washing result and washing economy the filling factor is of the utmost importance. The correct filling factor ensures that the drum is loaded with the correct amount of laundry. The filling factor varies according to the textile of the laundry, as well as to the degree of soiling.

Environmental aspects
When considering the environmental aspects of traditional washing, it is important to ensure an optimal consumption of water and energy. The detergent is also of great importance, and manufacturers are continually developing detergents which are gentle on the environment.

Washing process
The traditional washing program will wash and rinse the laundry in the following order:

  • Main wash
    One main wash is carried out at a temperature of 30°C-90°C and pH 9-11.
  • Rinse
    The laundry is rinsed, generally three times.
  • Extraction
    During the extraction, the laundry is de-watered.
  • Drying
    The laundry is dried, either in a tumble dryer or in a drying cabinet.
How it works
The equipment used for traditional washing is generally a washer extractor and a tumble dryer. Finishing equipment is selected to suit the different types of linen
Sinner's Circle

The degree of soiling matter
The appropriate washing time depends on the type of chemicals used, as well as the degree of soiling of the textiles. Obviously, heavily soiled textiles from a kitchen or manufacturing plant cannot be compared to bed linen from a hotel. Degree of soiling is therefore a very important consideration.

Depending on how the machine is to be used, a machine with flexible programs or fixed programs can be chosen.

Global variations
However, washing time also differs substantially between Europe on the one hand and the US and Japan on the other. Most of the difference is due to the different washing techniques normally used, such as relatively low wash temperatures and the absence of built-in heating units in the US and Japan as compared to Europe.

The heating itself in European washing machines consumes a great deal of time. Normally, a 60°C-85°C washing program lasts an hour. The corresponding value for American and Japanese machines used in launderettes and coin-ops is 20-30 minutes.

Obtaining a good washing result
When textiles are being washed, the process is basically a combination of mechanical and chemical processing, time and temperature. This is graphically visualised in a circle diagram, with the different parameters in varying ratios.

The purpose of the circle is to show that the total sum of these factors - mechanical and chemical processing, time and temperature - correspond to the energy required to wash a certain amount of a certain type of textile. If one washing parameter is changed, the others must be altered correspondingly.

The circle diagram shows how the parameters must be altered correspondingly, in order to achieve the same washing result.

The parameters can be explained as follows:
  • Time and temperature
    The time and temperature of the process are compiled in a washing program. The washing program determines what characteristics and consequently what field of application the actual washing process is given.

  • Mechanical action
    The mechanical action is performed by the washing machine.

  • Chemicals
    The chemical process is performed using water combined with some sort of washing detergent.

    The washing process is divided into different phases, such as pre-wash, main wash and rinsing. In order to obtain a good washing result, it is important to acquire the correct balance between the mechanical and chemical process and the time and temperature in each washing phase.
Heat increases the chemical action
Temperature affects the washing result in several respects. A high temperature will:
  • Decrease the water surface tension.
  • Dissolve fat stains more easily.
  • Increase the bleaching effect.
In general, heat will also increase the chemical action of the detergent. The proper washing temperature depends on:
  • The type of textile.
  • Whether the textile is white or coloured.
  • The degree of soiling.
  • The textile quality.
  • Whether the laundry is infected (hospital laundry) or not.
  • Local hygiene demands.
Hygiene demands
Hygiene demands as stated in local regulations refer to a relative time and temperature for achieving the necessary hygiene standards. These standards vary from country to country, but as a rule of thumb, the following formula can be used:

Calculating relative time/temp. for a hygienic washing result
(Temperature -55) x Time > 180

There are two methods of disinfection:
  • Thermic disinfection, which is carried out with the aid of high temperature.
  • The chemothermic disinfection, which requires a chemical as well as a high temperature.

Emulsifies the dirt
Detergent loosens and emulsifies dirt from the textiles, while also ensuring the dirt remains floating in the water in order not to stick to the linen again. Occasionally, the detergent also restores the whiteness of white textiles.

Great efforts are continuously being made to develop modern detergents which have less impact on the environment.

However, this is not an easy task, since washing procedures and practice vary from country to country. Moreover, certain additives are not allowed in some countries, while permitted and used in other parts of the world.

pH-value of washing detergents

Contents of the detergent
Usually, washing detergents contain four main components:

  • Surfactants (tensides).
  • Alkaline builders.
  • Bleaching agents.
  • Various types of additive.
Each component contributes to the washing effect, and to some extent the components will provide for synergistic effects.

Furthermore, detergents are categorised as being alkaline, neutral or acidic depending on the pH value. The pH-value determines the area of use of the detergent. The illustration shows a summary of the qualities and therefore the area of application for various types of detergent.
Washing Textiles

Washing programs

Textiles are treated differently in the washing process, as each textile has its own special characteristics which must be taken into account.

The table below shows the recommended washing programs for different textiles, as well as the type of linen normally affected.

Textile fibre Temp. Gentle action Extraction
Plain fibres      
Cotton 90°C No Yes
Flax 60°?70°C No Low/No
Animal fibres      
Wool 40°C Yes Yes
Silk 40°C Yes Low/No
Cellulose fibres      
Viscose rayon 40°C Yes No
Acetate 40°C Yes No
Synthetic fibres      
Polyamide 40°C No Low/No
Polyacrylate 40°C No Low/No
Polyester 40°C (C) 60°C (W) No Low/No
Poly/Cotton 60°C (C) 90°C (W) No Low/No
Textile fibre Finishing Cool down Type of goods
Plain fibres      
Cotton Yes No Bed linen
Flax Yes No Tablecloths, bed linen
Animal fibres      
Wool Yes, but carefully No Blankets
Silk Carefully No Blouses
Cellulose fibres      
Viscose rayon Yes, but carefully No Blouses
Acetate Carefully No Lining, scarves.
Synthetic fibres      
Polyamide Not necessary No Socks
Polyacrylate Not necessary No Underwear
Polyester Not necessary No Pullover
Poly/Cotton Not necessary Yes Bed linen, shirts
Residual Moisture
Water content left in the textile
The expression residual moisture is often used when discussing efficient washing and finishing. The term refers to the amount of surplus moisture in the laundry.

When a textile is bone dry, no water at all is left in the textile. In this case, residual moisture is 0%. However, this figure is only theoretically valid, since when a textile is bone dry, it will absorb moisture from the air in the room.

As a result, a textile of cotton that feels dry to the touch will actually contain different residual moisture depending of the textile fibres. For cotton this is about 6-8%, wool about 12-14% and Synthetic fibres only have 2-4% at room temperature (20°C, 65%KH). This residual moisture is created just by taking the laundry out of the tumble dryer and into the room.
Calculating the residual moisture
The weight of one load of dry cotton sheets is 10 kg. The sheets are washed in a normal-spin washer extractor with a G-factor of approx 90.

When the wash is complete, the load contains approx. 9 litres of water. As a result, the total weight of the load when washed is 19 kg. The residual moisture content is 9/10, otherwise expressed as, 90%.

When the same load of laundry is washed in a high-spin machine of 350 G, the load will contain only 5,5 litres of water. The residual moisture content will be 55%.

Residual moisture content varies in textiles
Residual moisture content will vary according to textile, even though the same washing program is used.

Selection of laundry equipment and washing programs is determined after analysing the type of textile and the most effective way of drying it. For a comparison of different textiles, see the bulleted list below:
  • Synthetic fibres
  • Generally, synthetic fibres do not retain as much water as cotton or terry.
  • Polyester/cotton blends and delicate fibres
    Textiles made of polyester/cotton, or delicate fibres need only a short extraction time. The very idea with the polyester/cotton blend is to avoid finishing after drying.
  • Cotton
    Cotton can well be extracted at maximum G-factor, as cotton always requires finishing.

Water retention as a function of centrifugal force.
Time of extraction = 5 min
EW ? Normal spin • Medium spin incl • Extra spin incl • High spin incl • Heavy duty high spin • Hydro extractor

~90 G
~140 G
~220 G
~350 G
~500 G
~440-705 G

The term ?water retention? describes the ability of the textile to retain water. In this respect, it is interesting to study cotton.

When extracting cotton textiles, water retention after 5 minutes will be 50-80%. The G-factor used is 80-500 G. When changing the parameters affecting the water retention, the outcome is as follows:

Parameter Result on water retention for cotton
• Change of drum diameter, however, the G-factor stays the same. No influence
• Increase of extraction time to 10 min. -5-7 %
• Half load instead of full load. +6-8 %
• Increase of rinse water temperature to 50*C. -5-7 %
• Conditioners in final rinse. -8-10 %
• Speed ramps. No influence if extraction time is 4 min or longer.
• Water retention distribution. Higher towards drum wall

The same purpose as for a hand iron The principal functions of an ironer and press are the same as the function of a domestic hand iron. The heat of the iron removes residual water, and the pressure removes creases. Items that are typically ironed are:

  • Bed sheets.
  • Pillow cases.
  • Serviettes.
  • Tablecloths.
Textiles that are ironed are mostly flat, and are therefore called flatwork. There are two types of ironer for handling different types of linen: chest ironers and cylinder ironers. Each type of ironer can be designed with either through-feed or return-feed. Through-feeding means that the linen is fed into the ironer on one side, and out on the other. The return feed model saves space as the linen is fed both into and out of the ironer on the same side, which may be an important factor. However, this type results in a limited capacity as the same operators are required to do the feeding as well as the folding after processing. Chest ironer Small chest ironers The chest ironer reshapes the fibres in the textile. In order to do this, the moisture in the linen is heated and turned into steam. The steam "de-tensions" the fibres of the textile so that they are shaped properly. The chest ironer is used in small installations, and is generally designed with return-feed. Note that when chest ironing textiles, the residual moisture of the linen must not exceed 15-20%. The types of linen to be chest ironed are typically:
  • Table clothes.
  • Serviettes.
  • Pillowcases.

A small chest ironer from the Electrolux Laundry Systems range.

How chest ironers work

  • The textiles are placed on the feeding table.
  • Press the pedal to start the padded roller.The heated, high-polished steel-chest is pressed against the roller.
  • The textiles are processed, and fed out to the collection table in front of the ironer.

Large chest ironers
There are large bed chest ironers as well, suitable for laundries with high capacity requirements. This type of ironer is available with more than one roller, and the diameter of the roller varies from 600-1200 mm.

By adding rollers, the capacity is increased. In order to achieve high efficiency, special feeders, folders and stackers are normally used together with the ironer to obtain a high production.

A large chest ironer, from the Electrolux Laundry Systems range.

Most conventional ironers are of the bed chest type. The chest has a maximum contact surface of 180º when the roller padding is new. The large chest ironers are of the through-fed type.

How large chest ironers work

  • The sheet is clamped to the feeding machine by one or more operators.
  • The feeder then automatically stretches and positions the sheet on the feeding belt.
  • The sheet is fed through the rollers at quite a high speed. The capacity ranges up to 20-40 metres/min, depending on the size of the rollers and the degree of automatisation in the feeding and folding process.
  • When the sheet has passed through the cylinders, it is folded lengthwise and crosswise. Finally, it is stacked in an automatic stacker unit.

The smaller units can be operated manually by three or four operators who feed and fold the sheets by hand. In this case, the capacity achieved is 15-20 metres/min.

Cylinder ironer
The cylinder ironer is used to iron linen such as bed textiles and large tablecloths. The moisture content of the linen may be approx. 50% when it is fed to the cylinder ironer. The required residual moisture content can be obtained in either of the following ways:

  • The linen can be fed to the cylinder ironer directly from the washer extractor. However, this procedure requires a high-spin washer extractor, which leaves a residual moisture content of maximum 50%.
  • Unless a high-spin washer extractor is used, the linen has to be pre-dried in a separate hydro extractor and a tumble dryer until a residual moisture content of 50% is reached.

How cylinder ironers work

  • The textiles are placed on the feeding belt.
  • The belts feed the textiles into the heated high polished or stainless steel cylinder. Speed and temperature are set from the panel. The settings depend on type the of textiles to be processed and the residual moisture content in the linen.
  • The finished textiles are fed out on the discharge belt behind the ironer or on a collection tray in the front.

While the linen is being ironed, it is recommended to regularly invert heating areas and ironing areas to achieve a good distribution of heat along the cylinder.

Fully automatic cylinder ironers
There are fully automatic cylinder ironers as well, with integrated feeder, folder and stacker for use by a single operator. The ironing process is the same as for large chest ironers, but with a lower cylinder speed.

  • Optimal washing programme
    There are several different washing programs, designed to suit different textiles and types of laundry. The correct washing program ensures optimal water and energy consumption, as well as optimal washing time.
  • Designing a washing programme
    A washing program generally includes seven stages, from pre-rinse to final extraction.
  • Pre-rinse
    This can also be called the soak. During the pre-rinse, solid particles such as sand and gravel are removed, along with water-soluble dirt such as salts and proteins.
  • Wash
    The washing stage includes a pre-wash and a main wash. During the wash, dirt is loosened from the textile fibres and is kept in the water.
  • Cool down
    To avoid wrinkling, it is essential to slowly reduce the temperature towards the end of the wash.
  • Bleach
    Bleaching can be performed either together with the main wash, or as a separate process after the wash.
  • Rinse
    The rinse removes the detergent and the loosened dirt from the laundry.
  • Conditioning
    When water is softened by special equipment, the result is alkaline water. This can discolour the laundry. To avoid this, the water must be neutralised. To prevent static electricity and soften the laundry, a conditioner is also added.
  • Extraction
    During the extraction, the laundry will be de-watered. This contributes to a faster drying process in the tumble dryer.
  • G-factor
    The higher the G-factor, the more efficiently the water will be removed from the textiles. This is also a key parameter to consider when selecting the proper laundry equipment, as costs for drying and finishing can be reduced by using a high G-factor.
  • Residual moisture Residual moisture refers to the amount of water left in the textile after extraction.

This information courtesy of Electrolux Wascator
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