Washing Machines Theory

WASHING MACHINES

THEORY

o  Industrial washing process: •  Purposes

•  Components •  Phases (soaking, prewash, washing, chlorine bleaching, rinsing (i),

neutralization, spinning) •  Summary table

o  The importance of water: •  Characteristics (colourless, odourless, hardness, iron, alkalinity, pH)

o  Dirt: •  Types

•  Classification

o  Stains families (oxidizable, enzymatic, grease, environmental dirt, others)

INDEX

WASHING MACHINES THEORY

o  Fabrics: •  origin classification

•  Structure and properties •  Temperature classification

•  Possible causes of chemical damage

•  Possible causes of mechanical damage

o  Chemicals: •  surfactants, alkaline substances, sequestrants, optical bleaching, stain

removers-whiteners, acid neutralizers, enzymes.

o  Introducing washing machines: •  Washing machines with mechanical controls (programmer)

•  Semi-automatic •  Electronic with microprocessor (latest generation machines)

INDEX


o  Washing is the most important and frequent maintenance treatment that undergoes a textile product.

PURPOSES:

•  Both local and general fabrics dirt removal. •  Stains complete elimination. •  White linen conservation and maintenance of the coloured

fabrics brilliance.

•  Restriction of chemical-mechanical damage, depending on the washing cycles.

INDUSTRIAL WASHING PROCESS


TEMPERATURE

MECHANICAL ACTION

CHEMICAL ACTION

TIME

COMPONENTS


1.  Soaking 2.  Prewash 3.  Washing 4.  Bleaching 5.  Rinsing (i) 6.  Neutralization 7.  Spinning

PHASES


T° < 35° C t= 2-3 min. C= low dosing PURPOSE: Eliminate surface dirt, dirt which could stick on (e.g. blood) and soluble dirt.

SOAKING


T° 40-60 °C t= 10-15 min. C= active + alkaline products (bleach: Chlorine 50 °C max.) PURPOSE: Eliminate most of the dirt, making washing easier (less product consumption).

PREWASH


T° 60-90 °C t= 13-20 min. C= active + alkaline products (bleach: H₂O₂) PURPOSE: Remove all residual traces of dirt, to saponify fat, also by the action of the temperature, the emulsion.

WASHING


T° 40-50 °C t= 7-9 min. C= Hypochlorite PURPOSE: Remove all the stains (dyes and similar). NOTE: The chlorine development depends on the temperature. The higher the latter is, the faster chlorine develops. The optimum value of pH for bleaching is 8.5/9 (the higher is the value, the smaller is the spotting property).

BLEACHING (WITH CHLORINE)


T° 20 °C t= 2-3 min. C= no product PURPOSE: Remove all detergent traces.

RINSING


T° 20 °C t= 3-4 min. C= no product PURPOSE: Remove all detergent and chlorine traces and, depending on your habits, to give greater softness or stiffness to the fabric.

NEUTRALIZATION


T°= -- t= 8-10 min. C= no product PURPOSE: Eliminate water of the last washing from linen, in order to make drying and ironing easier. (The residual humidity percentage is about a 50%).

SPINNING


PHASES TIME (t) TEMPERATURE (°T) PRODUCTS

Soaking 2-3 min. < 35 °C active

Prewash 10-15 min. 40-60 °C Active + alkaline+ hypochlorite – max. 50 °C

Washing 13-20 min. 60-90 °C active + alkaline

Bleaching (with Chlorine)

7-9 min. 40-50 °C hypochlorite

Rinsing (1 or +) 2-3 min. < 20 °C ---

Neutralization 3-4 min. < 20 °C

Acid + softener/starch

Spinning 8-10 min. --- ---

SUMMARY TABLE


For washing machine wash, water must be: o  Colourless o  Odourless o  Hardness 7 °F max. o  Iron 0,1 ppm max . o  Alkalinity 250 ppm max . o  About 7 pH

THE IMPORTANCE OF WATER


o  Colourless and odourless: water must be perfectly transparent

and therefore, does not contain suspended substances, which might settle onto the linen. It must be odourless and therefore not bacteriologically contaminated.

o  Hardness: it depends from calcium and magnesium salts in water.

•  0-15 °F = Fresh water •  16-25 °F = Medium hard water •  26-40 °F = Hard water •  > 40 °F = Very hard water


THE IMPORTANCE OF WATER (2)

o  PROBLEMS CAUSED BY WATER HARDNESS TO FABRICS Problems caused by the presence of calcium and magnesium to fabrics: •  Weight increase •  Greying •  Roughness to the touch •  Bad quality of washing •  Difficulty in eliminating stains •  Decrease of hygiene (easier bacteria proliferation) •  Faster fibre degradation



o  PROBLEMS CAUSED BY WATER HARDNESS TO STAINS Problems caused by the presence of calcium and magnesium to stains: •  Partial or total stopping up of the drum holes •  Lower performance of the heated elements •  Encrusted pipes •  Increased effort of the motor to spin an encrusted drum •  Bacteria proliferation in the washing machine •  System pumps greater effort



•  Iron 0,1 ppm max.: the presence of iron in water may depend on

the fact that this comes from an aquifer, where the metal is dissolved, or on corrosion of the pipes in which the feeding water of the laundry has to go through. This may cause a decrease in whiteness. A relevant presence of alkalinity, may also cause a progressive degradation of fabrics whereas oxidants, such as those used for bleaching, can provoke a violent reaction bringing to a subsequent irremediable damage of fabrics (e.g. holes).



o  Alkalinity (250 ppm max.): alkaline water causes difficulties in

rinsing and consequently even during ironing, that is to say yellowing and chalk deposits onto the wringer, preventing the linen scrolling.

o  Ph (<7): acid water requires a greater use of detergent but, due to the acidity value inconstancy, situations of overdosing or underdosing can occur.



TYPES: o  Dirt is the set of foreign substances deposited on the fiber and

inside of it, during the use of the linen.

•  Solid mineral particles: dust, sand, rust, earth, soot. •  Fat or oily: vegetal, animal, mineral. •  Micro organism: bacteria, spores, fungus, mould •  Colouring agents : fruits, coffee, tea, wine, sauces, lipstick, blood •  Soluble in water: salt, sugar

DIRT


Depending on its degree of washability, dirt can be classified into 3 3 groups: o  Washable: which can be eliminated with water and a detergent.

o  Washable with solvents: all insoluble or partially soluble substances, which can be eliminated by dry cleaning.

o  Washable through bleaching: all the colouring agents that can not be eliminated during the washing process nor by dry cleaning. They are oxidized by bleaches and therefore decomposed.

DIRT CLASSIFICATION


o  The main 4 stains families are: •  Oxidizable. •  Enzymatic •  Grease •  environmental dirt •  Others

STAINS FAMILIES


•  They are Tannin based stains (a natural colouring agent). By the time, they become fixed and more difficult to be washed.

•  E.g.: beverages (beer, coffee, tea, red wine), fruits and legumes (tomatoes etc.), spices (paprika, curry etc.)

•  On tablecloths, towels and kitchen linen (aprons, tea towels, etc.)

OXIDIZABLE


•  There are 3 types of these stains: •  Of the body (blood, sebum, urine and faeces) •  Based on proteins of natural origin (eggs,

milk, etc.) •  Based on vegetable proteins (grass, cocoa

etc.)

•  There are also enzyme stains that are the combination of vegetable and animal proteins (e.g. chocolate).

•  Usually on tablecloths, towels and kitchen linen (aprons, tea towels, etc.), sheets and sportwear.

ENZYMATIC


o  There are 2 types of grease stains.

•  Animal and vegetable Es.: dietary fats (oil, butter, sauces etc.) and cosmetics (foundation cream, lipstick, make-up etc.) Usually on kitchen linen dish cloths, aprons, tablecloth and towels, bath towels and T-shirts. •  Mineral Es.: sludge, tar, grease and motor oil. Usually on overalls, doctors white coats and bath towels.

GREASE


o  Composed by microscopic fragments, insoluble in water and solvents.

Es.: earth, mud, grass, sand, dust. These stains can be usually found on sportswear and overalls.

ENVIRONMENTAL DIRT


o  The other families of stains are:

•  Metal stains (rust, verdigris)

•  Chemical stains (ink, mercurochrome, tincture of iodine, paint, glue)

•  Others (wax, chewing-gum, mould, burning, bleach, perfume)

OTHER STAINS


ORIGIN:

o  According to the origin of the fiber, fabrics can be distinguished into natural or synthetic.

•  Cotton à vegetable fiber = natural •  Wool à animal fiber = natural •  Polyester à chemical fiber = synthetic

FABRICS


STRUCTURE PROPERTIES

COTTON -  Natural flat fiber -  91-95% cellulose composition

COTTON -  Resistant to: Alkali, Chlorine, Sodium

perborate, Temperature -  Hydrophilic -  It traps dirt particles

WOOL - 50% keratine composition - Scaly cylindrical shape

WOOL -  Stretchy -  Easily deformable -  Not resistant to: Alkali, Chlorine, Temperature

POLYESTER -  Obtained by condensation (chemical reaction) -  Cylindrical smooth fiber

POLYESTER -  Thermoplastic -  Resistant to: Alkali, Chlorine, Sodium

perborate, Acids -  Lipophilic (it absorbs fats)

STRUCTURE AND PROPERTIES


o  According to their washing process temperature, fabrics can be classified into:

•  85-90 °C à white cotton (or indelible colours), overalls (for garage), polyester/white cotton

•  50-60 °C à coloured linen •  25-35 °C à wool and delicates

TEMPERATURES CLASSIFICATION


o  The presence of metals during the washing process (Fe, Mn, Cu,

etc.)

o  Sodium hypochlorite not properly used

o  Too alkaline products based of caustic soda

o  Acid products

POSSIBLE CAUSES OF CHEMICAL DAMAGE


o  Poor care during transports (tears)

o  Loading without removing foreign bodies

o  Smudge in the washing drum (or dryer) o  Scales in the mangles o  Improper use of the linen (knives, toothpick, etc.)

POSSIBLE CAUSES OF MECHANICAL DAMAGE


o  During the washing process are used some chemical substances, such as:

•  Surfactants •  Alkaline substances •  Sequestrants •  Optical bleaching •  Stains removers-whiteners •  Acid neutralizers •  Enzymes

CHEMICAL PRODUCTS


o  All cleansers are based on them, they eliminate grease stains.

•  Particularly important during pigmentary dirt removal. •  Suitable for synthetic fibers washing. Strong power of fats

dispersion. •  Good detergent power, even at low temperatures.

SURFACTANTS


o  All the products that have a basic reaction in their solution can be defined as alkaline (7-14 Ph)

•  They ameliorate surfactants action. •  A big concentration of these substances can damage fabrics. •  They expand fibers increasing their wettability. •  They saponify grease dirt.

ALKALINE SUBSTANCES


o  They make soluble calcium and magnesium compounds, otherwise insoluble.

•  They increase surfactants detergent action. •  They have a strong power of dirt dispersion. •  If used at the recommended dosages, by the time, they can

descale fabrics.

SEQUESTRANTS


o  Optical bleachings increase the brightness of the white colour through a complex mechanism that changes the wavelength of ultraviolet light. In this way, they allow the fabric to emit more radiation visible to the human eye.

OPTICAL BLEACHING


o  Sodium perborate: in water, at more than 60°C, it frees oxygen that oxidizes the dyes of some of the most common stains. (tea, coffee, wine, sauces, fruits etc.) A good result of bleaching can be achieved with a cycle of 20 minutes, with at least 10 at more than 80° C.

o  Hydrogen peroxide: acting in a completely identical way to the sodium perborate.

STAIN REMOVERS OR BLEACHES


o  Sodium hypochlorite : according to pH and temperatures, it removes stains by developing oxygen. It is a stronger oxidant than perborate, because it acts at lower temperatures. When used at too high concentrations or temperatures, it damages the fibers. Its normal condition of use is with an alkaline bath at a temperature of about 50° C (max), for 7/8 minutes. It requires a neutralizer.

o  Peracetic acid: it has an effective bleaching action by developing oxygen. Already active at a temperature of 35° C (optimum 35-85° C). The optimum pH for the use of the product is between 9 and 10. It does not damage fabrics, the coloured ones in particular. If used during the washing process, it has a strong power of disinfection, due to its antibacterical action (ideal to be used in nursing homes and in hospitals. It does not require a neutralizer.


STAIN REMOVERS OR BLEACHES (2)

o  Formic acid and bacterical acid: they are weak organic acids. With normal temperatures and concentrations, their action is not harmful to the linen. They are used in the last rinse with dosages between 1/2 gr per kg of laundry, in order to neutralize the alkalinity residues of the detergent.

o  Bisulphite: it is an acid salt with a reducing action. It can have a

dual function. As a chlorine remover (very strong). As an alkalinity neutralizer (very weak). It is used during the last rinse as a chlorine remover, combined with acetic (or formic) acid and softening. Dosages are between 2/3 gr per kg of laundry.

ACID NEUTRALIZERS


o  They are particular organic substances secreted by animal or vegetable microorganisms which develop a bio-catalyst action, by increasing or accelerating a specific chemical process. They act within specific temperature and pH conditions, otherwise they are blocked or destroyed.

ENZYMES


Washing machines can be divided into 3 different types:

o  With mechanical controls (programmer) o  Semi-automatic

o  Electronic with microprocessor (latest generation machines)

INTRODUCTION TO WASHING MACHINES


o  The operator must set the wash cycle, according to the fabrics to be washed and temperature.

WITH MECHANICAL CONTROLS


o  The operator must set the wash cycle according to the fabrics to be washed and t e m p e r a t u r e . W i t h t h e technical service help, it is p o s s i b l e to c h a n g e t h e washing time parameters, temperatures and water levels, both during washing and rinsing.

SEMI-AUTOMATIC


o  The operator selects the programme (e.g. No. 1 White tablecloths) and the machine performs cleaning with the set temperatures. With the help of the instruction manual, it is possible to create washing programmes according to the fabric to be washed. This can be done by modifying various parameters: washing times, water level, both during wash and rinse, temperatures, type and time of discharge, speed and time of centrifugation.

ELECTRONIC WITH MICROPROCESSOR


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Washing Machines Theory