Editing Washing machine (section)

===World War II and after===
[[File:Hoover 0307 pulsator washing machine (1).jpg|thumb|upright|A Hoover 0307, manufactured from 1947 to 1957]]
After the [[attack on Pearl Harbor]], US domestic washer production was suspended for the duration of [[World War II]] in favor of manufacturing war [[materiel|material]]. However, numerous US appliance manufacturers were permitted to undertake the research and development of washers during the war years. Many took the opportunity to develop automatic machines, realizing that these represented the future of the industry.<ref>{{cite web |author=A. S. Campbell Company |date=1942-12-28 |title=Your Next Washing Machine (or is it?) |url=http://gogd.tjs-labs.com/show-picture?id=1129064419 |access-date=13 September 2012 |page=88 |magazine=Time}}</ref>

A large number of US manufacturers introduced competing automatic machines (mainly of the top-loading type) in the late 1940s and early 1950s. [[General Electric]] also introduced its first top-loading automatic model in 1947. This machine had many of the features that are incorporated into modern machines. Another early form of automatic washing machine manufactured by [[The Hoover Company]] used cartridges to program different wash cycles. This system, called the "Keymatic", used plastic cartridges with key-like slots and ridges around the edges. The cartridge was inserted into a slot on the machine and a mechanical reader operated the machine accordingly.

Several manufacturers produced semi-automatic machines, requiring the user to intervene at one or two points in the wash cycle. A common semi-automatic type (available from Hoover in the UK until at least the 1970s) included two tubs: one with an agitator or impeller for washing, plus another smaller tub for water extraction or centrifugal rinsing.{{citation needed|date=October 2013}} These machines, as well as other older designs like the manual rotating drum, are still available, but are typically only used in circumstances where a standard water and power hookup for a washing machine is unavailable. Many are marketed for camping due to their light weight and ability to function without a water connection. [[File:Waschvollautomat Constructa 1950er.jpg|thumb|upright|A 1950s model [[Constructa (company)|Constructa]]]]
Since their introduction, automatic washing machines have relied on [[timer|electromechanical timer]]s to sequence the washing and extraction process. Electromechanical timers consist of a series of [[Cam (mechanism)|cam]]s on a common shaft driven by a small electric motor via a [[reduction gearbox]]. At the appropriate time in the wash cycle, each cam actuates a switch to engage or disengage a particular part of the machinery (for example, the drain pump motor). One of the first was invented in 1957 by [[Winston L. Shelton]] and Gresham N. Jennings, then both [[General Electric]] engineers. The device was granted US Patent 2870278.<ref>{{cite web | url= http://www.google.la/patents/US2870278 | title = Timing mechanism for conducting a selected one of a plurality of sequences of operation | access-date = 2 November 2017}}</ref>

On the early electromechanical timers, the motor ran at a constant speed throughout the wash cycle, although the user could truncate parts of the program by manually advancing the control dial. However, by the 1950s demand for greater flexibility in the wash cycle led to the introduction of more sophisticated electrical timers to supplement the electromechanical timer. These newer timers enabled greater variation in functions such as the wash time. With this arrangement, the electric timer motor is periodically switched off to permit the clothing to soak and is only re-energized just before a micro-switch being engaged or disengaged for the next stage of the process. Fully electronic timers did not become widespread until decades later.

Despite the high cost of automatic washers, manufacturers had difficulty meeting the demand. Although there were material shortages during the [[Korean War]], by 1953 automatic washing machine sales in the US exceeded those of wringer-type electric machines.

In the UK and most of Europe, electric washing machines did not become popular until the 1950s. This was largely because of the economic impact of World War II on the consumer market, which did not properly recover until the late 1950s. The early electric washers were single-tub wringer-type machines, as fully automatic washing machines were expensive.

During the 1960s, twin tub machines briefly became popular, helped by the low price of the [[Rolls Razor]] washers. Twin tub washing machines have two tubs, one larger than the other. The smaller tub in reality is a spinning drum for centrifugal drying while the larger tub only has an agitator in its bottom. Some machines could pump used wash water into a separate tub for temporary storage and to later pump it back for re-use. This was done not to save water or soap, but because ''heated'' water was expensive and time-consuming to produce. Automatic washing machines did not become dominant in the UK until well into the 1970s and by then were almost exclusively of the front-loader design.

In early automatic washing machines, any changes in impeller/drum speed were achieved by mechanical means or by a [[rheostat]] on the motor power supply. However, since the 1970s electronic control of motor speed has become a common feature on the more expensive models.