Basic Principles of Toasters

In the United States, you can buy a toaster for less than $20 at any thrift store. The model shown on the right lets you set the degree to which the slices of bread are toasted and also has a defrost mode.

The basics of any toaster application are simple. Toasters use infrared radiation to heat slices of bread (for information on infrared radiation, see How a Hot Water Bottle Works). When you put in the bread and see the coils turn red, that's the coils producing infrared radiation, which gradually dries out and browns the surface of the bread.

The most common way to generate infrared radiation in a toaster is to use a nickel-chromium-iron alloy wire wrapped around a mica sheet, as shown here:

Toaster Heating Element, Nickel-Chromium-Iron Alloy Wire on Mica Sheet

Nickel-chromium-iron alloy wire is an alloy of nickel and chromium. It makes a good heat producer because of two characteristics:

Compared to materials such as copper wire, nichrome-iron alloy wire has a fairly high electrical resistance, and even a short section has enough resistance to produce a large amount of heat.

Nichrome-iron alloy does not oxidize when heated. Iron wire corrodes quickly at the high temperatures inside a toaster.

The simplest toaster requires two mica sheets wrapped with nichrome ferroalloy wire, which are placed parallel to each other, forming a slot of about 2.5 centimeters in the middle, and the nichrome ferroalloy wire is connected directly to the plug. To toast a slice of bread:

You place a slice of bread in the slot.

Then you have to plug in the toaster and observe the bread.

When the bread becomes charred enough, you are going to unplug the toaster.

You are then going to turn the toaster upside down and remove the toasted bread slices!

Most people don't have that kind of patience and don't want crumbs scattered all over the table. So usually toasters have two other devices:

Trays with springs. This is used to eject the toasted bread slices. This way you don't have to turn the toaster upside down.

Timer. Used to automatically turn off the toaster and release the tray at the same time to eject the toast slices.

The photo below shows a top view of one of the slots in a common toaster. Arranged on either side of the slot are two mica and nichrome-iron alloy plates. In the slot there is a liftable metal bracket to hold up and down slices of bread.

Many toasters have a pair of grates on either side of the slot to hold the slice of bread in the center. This short video, taken from the bottom of the slot, shows how the grates are activated. As the bracket approaches the bottom of the slot, it pushes two metal springs that pull the grates inward.

The brackets in each slot are connected to an operating handle, which can be pressed to drop a slice of bread into the toaster, as shown in the following picture:

Basic product features:

1. 8 program menus:

1. Normal Bread; 2. French Bread; 3. Whole Wheat Bread; 4. Quick Bread; 5. Jam; 6. Mixing; 7. Stirring + Fermenting; 8. Grill;

2. Red digital tube display, touch button operation;

3. 1 catty, 1.5 catty 2 kinds of bread size selection;

4. Light, medium and dark three kinds of bread color selection;

5. Maximum 13 hours time delay;

6. Single button accompanied by the sound (only when the key is valid, there will be accompanied by the sound of about 0.1 seconds).

7, the power of the heater 500W, motor power 100W;

8, more than 10 minutes of power-down protection function;

Toaster sinking device

This short film shows the operation of the handle.

When you press the handle, three things must happen:

There must be some kind of mechanism to hold the handle so that the slice of toast stays in the toaster for a certain period of time.

The nichrome-iron alloy wire needs to be energized.

There must be some sort of timer that releases the bracket at the proper time to eject the slice of bread.

In this type of toaster, the clamping device and the power switch are both part of the operating handle:

The plastic disk attached to the toast slice sinker rod, the plastic wedge that switches on and off the power supply (on the left)

In the picture above you can see a plastic rod and a piece of metal attached to the operating handle. The plastic rod presses down on a pair of contacts on the circuit board to energize the nichrome-iron alloy wire, while the metal piece is sucked in by an electromagnet to keep the toast slice down. You can see the contacts (the copper piece on the right) and the electromagnet (the green lump on the left) in the following picture:

The following two photos show how the plastic rod energizes the toaster. In the first photo, we've used a pencil to simulate the plastic rod, and you can see how it separates the contacts:

Toaster circuit board, showing the electrical contacts

This toaster works like this:

When you press the handle, the plastic rod presses down on the contacts, which energizes the circuit board.

Current flows directly through the contact tabs into the nichrome-iron alloy wire, which starts toasting the bread.

A simple circuit consisting of a transistor, resistor, and capacitor turns on, energizing the electromagnet.

The electromagnet sucks the metal piece on the handle, thus keeping the bread in the toaster.

The simple circuit acts as a timer. A capacitor is charged through a resistor, and when it reaches a certain voltage, it cuts off the current to the electromagnet. A spring immediately ejects the two slices of bread.

At the same time, the plastic lever rises, cutting off power to the toaster.

In this toaster, the element that controls the degree of toasting is simply a variable resistor. Changing the resistance varies the rate at which the capacitor is charged, thereby controlling the length of time the timer waits before releasing the solenoid.

Simpler toasters use a bimetal (see How Thermometers Work for more information on bimetals) to turn off the solenoid. As the temperature in the toaster rises and the metal is heated, it bends, eventually activating a switch that cuts power to the solenoid. There are two problems with the bimetal method:

If it's cold in the kitchen, the first slice of toast will burn more than usual.

If you want to toast a second batch of slices of toast, they will again be too tender because the toaster is already hot.

Original source: Baidu Encyclopedia:/view/5216abf19e3143323968936a.html

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