Engineering behind "Washing Machine"

Clothes washing machines

If there's one household appliance most of us simply could not do without, it's the clothes washer. If you've ever been without your machine for a few days or weeks, you'll know just how hard it is to wash clothes by hand. Although clothes washers look pretty straightforward, they pull off a really clever trick: with the help of detergents, they separate the dirt from your clothes and then rinse it away. But how exactly do they work?.

The parts of a clothes washer

The basic idea of a clothes washer is simple: it sloshes your clothes about in soap suds for a while and then spins fast to remove the water afterward. But there's a bit more to it than that. Think of a clothes washer and you probably think of a big drum that fills with water—but there are actually two drums, one inside the other.

The inner drum is the one you can see when you open the door or the lid. In a front-loading clothes washer, common in Europe, the drum stands upright. You push your clothes inside the door from the front and the whole drum rotates about a horizontal axis (like a car wheel). The drum has lots of small holes to let water in and out and paddles around the edge to slosh the clothes around. In a toploader, more common in the United States and Asia, you open a lip on top and drop your clothes into the drum from above. The drum is mounted about a vertical axis but doesn't actually move. Instead, there's a paddle in the middle of it called an agitator that turns the clothes around in the water.

There's a second, bigger drum outside the inner drum that you cannot see. Its job is to hold the water while the inner drum (in a front-loader) or the agitator (in a toploader) rotates. Unlike the inner drum, the outer drum has to be completely water-tight—or you'd have water all over the floor!

The two drums are the most important parts of a clothes washer, but there are lots of other interesting bits too. There's a thermostat(thermometer mechanism) to test the temperature of the incoming water and a heating element that warms it up to the required temperature. There's also an electrically operated pump that removes water from the drum when the wash is over. There's a mechanical or electroniccontrol mechanism called a programmer, which makes the various parts of the clothes washer go through a series of steps to wash, rinse, and spin your clothes. There are two pipes that let clean hot and cold water into the machine and a third pipe that lets the dirty water out again. All these pipes have valves on them (like little doors across them that open and shut when necessary).

The washing machine program

All the important parts of the clothes washer are electrically controlled, including the inner drum, the valves, the pump, and the heating element. The programmer is like the conductor of an orchestra, switching these things on and off in a sensible sequence that goes something like this:

1. You put your clothes in the machine and detergent either in the machine itself or in a tray up above.
2. You set the program you want and switch on the power.
3. The programmer opens the water valves so hot and cold water enter the machine and fill up the outer and inner drums. The water usually enters at the top and trickles down through the detergent tray, washing any soap there into the machine.
4. The programmer switches off the water valves.
5. The thermostat measures the temperature of the incoming water. If it's too cold, the programmer switches on the heating element. This works just like an electric kettle or water boiler.
6. When the water is hot enough, the programmer makes the inner drum rotate back and forth, sloshing the clothes through the soapy water.
7. The detergent pulls the dirt from your clothes and traps it in the water.
8. The programmer opens a valve so the water drains from both drums. Then it switches on the pump to help empty the water away.
9. The programmer opens the water valves again so clean water enters the drums.
10. The programmer makes the inner drum rotate back and forth so the clean water rinses the clothes. It empties both drums and repeats this process several times to get rid of all the soap.
11. When the clothes are rinsed, the programmer makes the inner drum rotate at really high speed—around 80 mph (130 km/h). The clothes are flung against the outside edge of the inner drum, but the water they contain is small enough to pass through the drum's tiny holes into the outer drum. Spinning gets your clothes dry using the same idea as a centrifuge.
12. The pump removes any remaining water from the outer drum and the wash cycle comes to an end.
13. You take your clothes out and marvel at how clean they are!
14. But there's still the problem of drying your wet clothes to figure out.

Why do washing machines need so many programs?

Your machine doesn't know what you put into it and can't automatically tell how carefully to wash something like a delicate woollen jumper—because it doesn't know that's what it's got to do! The only things under its control are the amount and temperature of the water, the speed of the spin, the number of times the drum oscillates, the number of rinses, and so on. No-one wants to wash clothes in a scientific way: "I think I need 5.42 litres of water at exactly 42°C, I'll need to wash for exactly 34 minutes, and I'll need 200 spin revolutions when I'm done." That would give us literally an infinite number of possibilities, which is too much like hard work. Recognizing this, machine engineers try to make life easy by offering a few preset programs: each one uses a slightly different combination of these variables so it washes safely within the tolerance of different fabrics.

Why does that matter? All fabrics are different. A fabric like wool is immensely strong but has two big drawbacks (from the point of getting it clean): it's extremely hygroscopic (absorbs huge amounts of water) and loses its elasticity as the temperature increases. So if you're designing a washing machine to wash woollens, that's your starting point: don't allow the wool to become too hot (because the fibers will degrade and stretch too much) and don't agitate it excessively because it will stretch and not return to shape. With sturdier fabrics like denim, you can afford to bash them about in the drum much more—indeed, you must do so, because you need the agitation to get the detergent deep into the fibers and break up the dirt (and, of course, clothes made from denim are more likely to get dirtier than more delicate fabrics such as cashmere jumpers, which people treat more carefully).

Each program you find marked on a clothes washing machine is a best guess by the engineers as to how much agitation a particular garment/fabric is likely to need and how much it can put up with without getting damaged. If you were handwashing in a sink, you'd make those judgements instinctively, balancing the need to get your garment clean with the need to protect it from damage. While your brain/hands would do that without thinking, the washing machine does it with a certain wash temperature, so many agitations, so many spins, and a certain spin speed.

But do machines really need so many programs?

Look at the programmers in the photos above and you'll see something interesting: both machines seem to have an incredible number of programs. The mechanical programmer in the top photo offers 14 programs, seven temperatures, two spin speeds, and full or half load—and if you multiply those you'll get 392 possibilities! The electronic programmer underneath it offers 12 programs, 5 spin speeds, and various other options so, again, a good few hundred possibilities. Yet if you're like me, you probably wash almost all your clothes on a single program all the time. Even if you don't do that, it's unlikely you could think of 392 different types of clothing that need washing in 392 different ways.

Much of this is a marketing con to make you believe the machine has more features than it really does. Most machines can really do only about three or four basic washes: 1) a high-temperature, long-duration wash for white laundry that uses a fairly high spin speed and lots of water; 2) a slightly faster, lower-temperature wash for colored cottons that uses similar spin speed and water volume; 3) a synthetics wash that uses the same amount of water, agitates the laundry less, spins more slowly, and uses lower temperatures; and 4) a woollens wash that probably uses quite a bit more water, but agitates the drum less, and spins the water out relatively slowly. Any other programs are variations of these four.

It's impossible to credit any one person with the invention of the clothes washer. Like many other inventions, from cars to computers, the modern washer has evolved over hundreds of years through the systematic mechanization and automation of hand-washing techniques people have been using since ancient times. Here are a few milestones in washing-machine history; given the hundreds (perhaps even thousands) of patents covering this sort of invention, any selection is bound to be somewhat arbitrary.

• 1400s: Italian Jacopa Strada develops one of the first mechanized clothes washing machines.
• 1691: John Tyzacke (spelled Tizack in some sources) receives English patent 271 for a general-purpose machine ("an engine for oiling and dressing leathers and cloth") that can do many different things, including washing clothes.
• 1774: Hugo Oxenham invents the mangle or wringer (a pair of wooden rollers that dry clothes by squeezing water from in between them).
• 1782: Henry Sidgier develops one of the first rotating drum machines using a crank to power a wooden barrel, for which he gains English patent 1331.
• 1797: Nathaniel Briggs of New Hampshire receives one of the first US patents for a clothes washing machine.
• 1843: Jno Shugert of Elizabeth, Pennsylvania is granted US Patent 3096 for a box-type washing machine in which a lever rocks the clothes back and forth through soapy water.
• 1858: Hamilton Smith develops a more effective rotary washing machine and is awarded US Patent 21,909.
• 1901: Alva Fisher of Chicago is awarded US Patent 966,677 for the first electric washing machine, sold under the brand name Thor, which consists of an electric motor powering a more conventional drum machine. Just like a modern machine, it reverses direction periodically.
• 1937: John W Chamberlin, Jr and Rex Earl Bassett of Bendix develop the first automatic machine (in their words, a "washing and rinsing and drying machine operating automatically according to a definite cycle"), earning themselves US Patent 2,165,884.

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