Difference between revisions of "Washing of clothes"

Revision as of 15:40, 18 April 2017

Washer extractors

Washer extractors are applied for

• heavily soiled laundry
• textiles with bleeding colours
• small batches
• high quality workware
• infectous laundry
• cleanroom laundry
• medical devices
• sensitive laundry: wool blankets, curtains
• special laundry items (e.g. mattresses)
• wet clean

Design of the washing program:

• Pre wash
• Main wash
• Rinse with intermediate spin
• Neutralisation, Addition of Aids (starch, textile softener, acid)
• Final spin

Pre washing:

• Rapid wetting of laundry
• Swelling of soil
• Removal of heavy soil from the laundry
• Dissolving and swelling of spots
• Temperature: depends on amount and kind of soil -> blood 20 – 25 °C (> 30°C denaturation/fixing of proteins), fat/oil 50 – 60 °C (> 50°C good soil removal)
• Detergents: 50 – 70 % of total amount (reuse of rinse water increases detergent concentration, residues of peroxide cause denaturation/fixing of blood)
• Drain -> in sewage

Main wash:

• Removal of remaining soil
• Removal of oxidative spots
• Disinfection (thermal) at temperature > 85 °C
• Disinfection (chemical) at 40 °C (depends on disinfectant)
• Increase of textile whiteness
• Duration: approx. 10 – 15 min at temperature level
• Temperature: adapted to washing process and amount and kind of soil (e.g. thermal disinfection = 10 min at 90 °C or 15 min at 85 °C)
• Drain -> in sewage

Rinse:

• Removal of soil residues
• Removal of detergent residues (surfactants, alkali and bleaching agents)
• Duration: (total) approx. 8 – 12 min
• Temperature approx. 60 – 25 °C (without heating), depends on main wash temperature
• Drain in storage tanks
• Inactivation of bleach agents is needed if extracted water is reused

Neutralisation:

• In last rinse
• Reduction of textile pH-value for the purpose of preventing yellowing effect during drying or ironing process
• Duration approx. 2 – 4 min
• Temperature approx. 20 – 25 °C
• Formic or acetic acid in last rinse (recommended pH-values for flatwork 6,0-6,5, for fully dried laundry 6,0-6,5, for garments for tunnel finisher, flat press 5,5-6,5)

Spin:

• Mechanical dewatering by centrifugal force (g - factor up to 600, 5 - 10 min)
• Water content of laundry depends on´type of fabrics, drum, number of revolution (rpm), duration, temperature of laundry
• Intermediate spin between rinsing baths, minimisation of carry over effects of detergent residues in next rinse bath
• Problematic: wrinkling of PES/CO textiles at temperatures > 40 °C,high rpm and/or spin duration

Tunnel washers

Characteristics:

• Continuous washing process
• Counterflow principle: Constantly dilution of liquor
• Corrective: standing bath, bath exchange
• Liquor level nearly not alterable
• Low mechanics (oscillating)
• Diversification of mechanics and cycle time effects all compartments.

Schematics of a tunnel washer:

Number of compartments in a tunnel washer:

• soaking (optional): 1-2
• pre wash zone: 2-4
• main wash zone: 3 -6
• rinsing zone: 2-6
• finishing: 1-2
• dewatering

Parameters:

Pre washing

Main washing

Rinsing

Finish

Distribution of temperature in a tunnel washer

Efficiency measures

Usage of storage tanks for washer extractors:

• Use of water from last in first rinse
• Use of water from rinsing in pre- and main wash
• Last rinse with fresh water quality only
• Savings: Water up to 40 %, Steam up to 45 %, Detergents up to 30 %
• Environmentally friendly
• Economical
• Quick return on investments

Heat recovery:

The hot bath is passed through the heat exchanger and is cooled down. Fresh water is heated in the heat exchanger.

Recovery potential:

40 - 45% (pre-wash temperature < 40°C)

> 45% (higher pre-wash temperatures possible)

Examples:

Source

Leonardo da Vinci project Laundry Sustainability