From Wikipedia, the free encyclopedia
This article is about the appliance. For manual dishwashing, see dishwashing. For the video game of the same name, see The Dishwasher: Dead Samurai.
A dishwasher containing clean dishes
A
dishwasher is a mechanical device for cleaning dishes and eating-utensils. Dishwashers can be found in restaurants and private homes. Unlike manual dishwashing,
which relies largely on physical scrubbing to remove soiling, the
mechanical dishwasher cleans by spraying hot water, typically between 55
and 75 °C (130 and 170 °F) at the dishes, with lower temperatures used
for delicate items. A mix of water and detergent
is circulated by a pump. Water is pumped to one or more rotating spray
arms, which blast the dishes with the cleaning mixture. Once the wash is
finished, the water is drained, more hot water is pumped in and a rinse
cycle begins. After the rinse cycle finishes and the water is drained,
the dishes are dried using one of several drying methods (e.g. a heating element at the bottom of the tub, fans, Zeolites based drying, etc.). Typically a rinse aid is used to eliminate water spots for streak-free dishes and glassware.
Mechanical dishwashing devices were developed in the mid- to
late-1800s. A domestic dishwasher was invented in the 1920s, but it did
not see widespread use. Dishwashers became more common in wealthy homes
in the 1950s. By the 1970s dishwashers had become common. Present-day
machines feature a drop-down front panel door, allowing access to the
interior. The inside of a dishwasher in the North American market are
either stainless steel or plastic. Mid-to-higher end North American dishwashers often come with hard food disposal units, which behave like miniature garbage (waste) disposal units that eliminate large pieces of food waste from the wash water. Many new dishwashers feature microprocessor-controlled, sensor-assisted
wash cycles that adjust the wash duration to the quantity of dirty
dishes. Large heavy-duty dishwashers are available for use in commercial
establishments (e.g. hotels, restaurants) where a large number of
dishes must be cleaned. Washing is conducted with 65–71 °C / 150–160 °F
temperatures and sanitation is achieved by either the use of a booster
heater that will provide the machine 82 °C / 180 °F "final rinse"
temperature or through the use of a chemical sanitizer.
- 1 History
- 2 Characterization
- 2.1 Capacity
- 2.2 Size
- 2.3 Features
- 2.4 Plumbing
- 2.5 Sound damping
- 3 Detergent
- 3.1 Biodegradable detergent
- 3.2 Hand-washing detergent
- 4 Rinse aid
- 5 Dishwasher salt
- 6 Hazing of glassware
- 6.1 Limescale deposit
- 6.2 Silicate filming, etching, and accelerated crack corrosion
- 6.3 Physical abrasion
- 6.4 Devitrification
- 7 Items unsuitable for the dishwasher
- 8 Drying
- 9 Level of sanitizing
- 10 Commercial dishwashers
- 11 Robotics
- 12 Environmental impact
- 12.1 Comparison with washing by hand
- 12.2 Detergents and rinse aids
- 13 Alternative use as a cooking device
- 14 See also
- 15 References
- 16 External links
History
A hand-powered dishwasher and an early electric dishwasher both from about 1917.
The first reports of a mechanical dishwashing device are of an 1850 patent in the United States
by Joel Houghton for a hand-powered wood device. This device was made
of wood and was cranked by hand while water sprayed onto the dishes.
This device was both slow and unreliable. Another patent was granted to L.A. Alexander in 1865 that was similar to the first but featured a hand-cranked rack system. Neither device was practical or widely accepted.
The first reliable (hand-powered) dishwasher was invented in 1887 by Josephine Cochrane and unveiled at the 1893 Chicago World's Fair.
Cochrane was quite wealthy and never washed dishes herself; she
reportedly invented the dishwasher because her servants were chipping
her fine china.
Advertisement in an 1896 issue of McClure's for The Faultless Quaker Dishwasher.
In England, William Howard Livens
invented a small dishwasher suitable for domestic use in 1924. It was
the first modern dishwasher, and incorporated most of the design
elements that feature in the models of today;
[1]
it included a front door for loading, a wire rack to hold the dirty
crockery and a rotating sprayer. Drying elements were even added to his
design in 1940. It was the first machine suitable for domestic use, and
it came at a time when permanent plumbing and running water in the house
was becoming increasingly common.
[2][3]
Despite this, Liven's design did not become a commercial success, and
dishwashers were only successfully sold as domestic utilities in the postwar boom
of the 1950s, albeit only to the wealthy. Initially dishwashers were
sold as standalone or portable devices, but with the development of the
wall-to-wall countertop
and standardized height cabinets, dishwashers began to be marketed with
standardized sizes and shapes, integrated underneath the kitchen
countertop as a modular unit with other kitchen appliances.
By the 1970s dishwashers had become commonplace in domestic residences in North America and Western Europe. By 2012, over 75 percent of homes in the US and Germany had dishwashers.
[4]
Characterization
Capacity
The international standard for the capacity of a dishwasher is expressed as standard place settings.
Dishes or plates of irregular sizes may not fit properly in a
dishwasher's cleaning compartment, so it is advisable to check for
compatibility before buying a dishwasher. Most Common residential
dishwashers load between 15 and 22 Place Settings.
Commercial dishwashers are rated as plates per hour. The rating is
based on standard sized plates of the same size. The same can be said
for commercial glass washers, as they are based on standard glasses,
normally pint glasses.
Size
North American counter-top dishwasher
Dishwashers that are installed into standard kitchen cabinets have a
standard width and depth of 60 cm (Europe) or 24 inches (US), and most
dishwashers must be installed into a hole a minimum of 86 cm (Europe) or
34 inches (US) tall. Portable dishwashers exist in 45 and 60 cm
(Europe) or 18 and 24 inch (US) widths, with casters and attached
countertops. Dishwashers may come in standard or tall tub designs;
standard tub dishwashers have a service kickplate beneath the dishwasher
door that allows for simpler maintenance and installation, but tall tub
dishwashers have approximately 20% more capacity and better sound dampening from having a continuous front door.
Features
Clear model of a running dishwasher
Present-day machines feature a drop-down front panel door, allowing
access to the interior, which usually contains two or sometimes three
pull-out racks; racks can also be referred to as "baskets". In older
U.S. models from the 1950s, the entire tub rolled out when the machine
latch was opened, and loading/removing washable items was from the top,
with the user reaching deep into the compartment for some items.
Youngstown Kitchens, which manufactured entire kitchen cabinets and
sinks, offered a tub-style dishwasher, which was coupled to a
conventional kitchen sink as one unit.
Today, "dish drawer" models mimic this style, while the half-depth
design eliminates the inconvenience of the long reach that was necessary
with older full-depth models. "Cutlery baskets" are also common. A
drawer dishwasher, first introduced by Fisher & Paykel in 1997, is a variant of the dishwasher in which the baskets slide out with the door in the same manner as a drawer filing cabinet, with each drawer in a double-drawer model being able to operate independently of the other.
The inside of a dishwasher in the North American market are either stainless steel or plastic. Stainless steel tubs resist hard water, provide better sound damping, and preserve heat to dry dishes faster. They also come at a premium price. Older models used a baked enamel
on steel and are prone to chipping and erosion; chips in the baked
enamel finish must be cleaned of all dirt and corrosion then patched
with a special compound or even a good quality two-part epoxy.
All European-made dishwashers feature a stainless steel interior as
standard, even on low end models. The same is true for a built-in water
softener. The flutes (Or valve meters) of the dishwasher are prevalent
in American models (With some appearing in European and Asian models
influenced by US design) due to the higher pressure of the American
water system (which averages at 90 torrs/min, as opposed to the 65
torrs/min pressure in other countries). The flutes help drain the excess
water, preventing entropy within the system due to higher pressures at a
lower volume. This is a removable fixture, as some areas require a
higher or lower discharge based on their water system.
Mid-to-higher end North American dishwashers often come with hard food disposal units, which behave like miniature garbage (waste) disposal
units that eliminate large pieces of food waste from the wash water.
One manufacturer that is known for omitting hard food disposals is Bosch,
a German brand; however, Bosch does so in order to reduce noise. If the
larger items of food waste are removed before placing in the
dishwasher, pre-rinsing is not necessary even without integrated waste
disposal units.
Many new dishwashers feature microprocessor-controlled, sensor-assisted wash cycles that adjust the wash duration to the quantity of dirty dishes (sensed by changes in water temperature)
or the amount of dirt in the rinse water (sensed chemically/optically).
This can save water and energy if the user runs a partial load. In such
dishwashers the electromechanical rotary switch often used to control the washing cycle is replaced by a microprocessor but most sensors and valves
are still required to be present. However, pressure switches (some
dishwashers use a pressure switch and flow meter) are not required in
most microprocessor controlled dishwashers as they use the motor and
sometimes a rotational position sensor to sense the resistance of water,
when it senses there is no cavitation it knows it has the optimal amount of water. A bimetal switch or wax motor opens the detergent door during the wash cycle.
European dishwashers almost universally use two or three spray arms
which are fed from the bottom and back wall of the dishwasher leaving
both racks unimpeded and also such models tend to use inline water
heaters, removing the need for exposed elements in the base of the
machine that can melt plastic items near to them. Many North American
dishwashers tend to use more basic, and old fashioned water distribution
and exposed elements in the base of the dishwasher. Some North American
machines use a large cone or similar structure in the bottom dish rack
to prevent placement of dishes in the center of the rack. The dishwasher
directs water from the bottom of the dishwasher up through this
structure to the upper wash arm to spray water on the top dish rack.
Some dishwashers, including many models from Whirlpool and Kitchenaid,
use a tube attached to the top rack that connects to a water source at
the back of the dishwasher which allows full use of the bottom rack.
Late-model Frigidaire
dishwashers shoot a jet of water from the top of the washer down into
the upper wash arm, again allowing full use of the bottom rack (but
requiring that a small funnel on the top rack be kept clear).
Some dishwashers include a child-lockout feature to prevent
accidental starting or stopping of the wash cycle by children. A child
lock can sometimes be included to prevent young children opening the
door during a wash cycle. This prevents accidents with hot water and
strong detergents used during the wash cycle.
A dishwasher should never be emptied before a complete process has
been signified to be finished by the control system, as this will often
leave the contents unwashed or still in a saturated state. It is a
common misconception that to empty a dishwasher before the end of a
cycle will save energy, as many of the contents may need to be re-run,
hence almost doubling running costs.
[citation needed]
