Dishwasher

From Academic Kids

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A dishwashing machine

The term dishwasher can represent either a person who washes (cleans) dishes (a term commonly used in the food service industry) or a machine that performs a similar function. The latter usage is discussed in this article.


A dishwasher is a mechanical device for cleaning food utensils for preparation, keeping, serving and eating and drinking. They are in restaurants and also in the more luxury kitchens of homes.

Unlike manual dishwashing, which relies largely on mechanical action to remove soiling, mechanical dishwashers use the circulation of quite hot (55-65 degrees Celsius [130-150 degrees Fahrenheit]) water and very strong detergents (most far too alkaline to be exposed to skin) to achieve its cleaning effect. The dishwasher therefore is mainly a device for spraying water on the dishes - first detergent-added water for cleaning purposes, then pure water (though sometimes with a rinsing aid added) to remove the detergent residue. Some dishwashers also contain a heating element to achieve fast drying of the dishes.

The capacity of the Dishwasher according to international standards is measured in place settings. If you have dishes or plates of irregular sizes take these to the shop and check if they will fit in the dishwasher baskets.

Contents

History

The first reports of a mechanical dishwashing device are of an 1850 patent by Joel Houghton of a hand-powered device.

Modern dishwashers are descended from the 1886 invention of Josephine Cochrane, also hand-powered, which she unveiled at the 1893 Chicago World's Fair. Cochrane was quite wealthy and was the granddaughter of John Fitch, the inventor of the steam boat. She never washed dishes herself and only invented the dishwasher as her servants were chipping her fine china.

Models installed with permanent plumbing arrived in 1920s, and electric drying elements were added in 1940.

Adoption was greatest at first in commercial environments, but by the 1970s dishwashers had become commonplace in domestic situations.

Detergent

Dishwashing detergent contains:

  • Phosphates
    - Solublises calcium and magnesium ions to prevent 'hard-water' type limescale deposits.
  • Oxygen-based bleaching agents
    - Breaks up and bleaches organic deposits.
  • Non-ionic surfactants
    - Lowers the surface tension of the water, emulsifies oil, lipid and fat food deposits, prevents droplet spotting on drying.
  • Enzymes
    - Breaks up and solublises protein-based food deposits, and possibly oil, lipid and fat deposits.
  • Anti-corrosion agents
    - Often sodium silicate, prevents corrosion of dishwasher components.

it may also contain:

  • Anti-foaming agents
    - Used as foam decreases the effectiveness of the washing action.
  • Additives to slow down the removal of glaze & patterns from glazed ceramics
  • Perfumes
  • Anti-caking agents (in granular detergent)
  • Starches (in tablet based detergents)
  • Gelling agents (in liquid/gel based detergents)

Dishwasher detergents are strongly alkaline (basic).


Hazing of glassware, prohibition on dishwashing lead crystal

Glasswares that are washed by dishwashing machine often obtain a white haze on the surface over time. This may be caused by any or all of the below processes, only one of which is reversible:

  • Limescale deposit
    - If the dishwasher has run out of the salt that recharges the ion exchange resin that softens the water, and the water supply is 'hard', limescale deposits can appear on all items, but are especially visible on glassware. It can be removed by cleaning with vinegar or lemon juice, or a proprietary limescale removal agent. The dishwasher should either be recharged with salt, adjusted appropriately for the hardness of the supply water - or possibly this is a symptom of failure of the ion exchange resin in the water softener (which is one of the more expensive components). The resin may have stopped working because it has be poisoned by iron or manganese salts in the supply water.
  • Silicate filming/etching/accelerated crack corrosion
    - This film starts as an iridescence or 'oil-film' effect on glassware, and progresses into a 'milky' or 'cloudy' appearance (which is not a deposit) that cannot be polished off or removed like limescale. It is formed because the detergent is strongly alkaline (basic) and glass dissolves slowly in alkaline aqueous solution. It becomes more soluble in the presence of silicates in the water (added as anti-metal-corrosion agents in the dishwasher detergent). In certain cases, the etching will primarily be seen in areas that have microscopic surface cracks as a result of the items' manufacturing.
  • Physical abrasion
    - Glassware placed such that it is physically touching can abrade and produce a milky surface.

Lead crystal should not be cleaned in a dishwasher as the corrosive effect of dishwasher detergent is high on such types of glass - that is, it will quickly go 'cloudy'. In addition, the lead in the crystal glass can be converted into a soluble form, which is not good for the health of subsequent users.

Sources

http://www2.whirlpool.com/html/homelife/cookin/cookdw5.htm

http://www.ccspa.org/conseducation/SDAC_autodish.html

http://www.newi.ac.uk/buckleyc/materials.htm#Glass

http://www.scienceblog.com/community/older/2003/F/20033788.html

http://www.yale.edu/ynhti/curriculum/units/1997/7/97.07.05.x.html

See also


External links

lt:Indaplovė nl:Afwasmachine fi:Astianpesukone sv:Diskmaskin

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