How microwave oven is made – manufacture, making, used, parts, components, structure, product, Design

Microwave Oven

Background

Microwaves are actually a segment of the electromagnetic wave spectrum, which comprises forms of energy that move through space, generated by the interaction of electric and magnetic fields. The spectrum is normally broken into subgroups determined by the different wavelengths ( or frequencies ) and emission, infection, and assimilation behaviors of diverse types of waves. From longest to shortest wavelengths, the spectrum includes electric and radio receiver waves, microwaves, infrared ( hotness ) radiation, visible light, ultraviolet radiation, roentgenogram, gamma rays, and electromagnetic cosmic rays. Microwaves have frequencies between approximately .11 and 1.2 inches ( 0.3 and 30 centimeters ) .
Microwaves themselves are used in many different applications such as telecommunication products, radar detectors, wood bring around and dry, and medical treatment of certain diseases. however, certain of their properties render them ideal for cook, by far the most common manipulation of microwave department of energy. Microwaves can pass through formative, glass, and paper materials ; metal surfaces reflect them, and foods ( particularly liquids ) absorb them. A meal placed in a conventional oven is heated from the outside in, as it slowly absorbs the surrounding air that the oven has warmed. Microwaves, on the early hand, heat food a lot more quickly because they penetrate all layers simultaneously. Inside a man of food or a container filled with liquid, the microwaves agitate molecules, thereby heating the means.

The ability of microwave department of energy to cook food was discovered in the 1940s by Dr. Percy Spencer, who had conducted research on radar vacuum tubes for the military during World War II. Spencer ‘s experiments revealed that, when confined to a metal enclosure, high-frequency radio receiver waves penetrate and excite certain type of molecules, such as those found in food. Just knock-down adequate to cook the food, the microwaves are not firm adequate to alter its molecular or genetic structure or to make it radioactive .
Raytheon, the company for which Dr. Spencer was conducting this research, patented the engineering and soon developed microwave ovens adequate to of cooking big quantities of food. Because manufacture costs rendered them excessively expensive for most consumers, these early ovens were used primarily by hospitals and hotels that could more well afford the $ 3,000 investment they represented. By the former 1970s, however, many companies had developed microwave ovens for home use, and the monetary value had begun to come down. today, microwaves are a standard family appliance, available in a broad range of designs and with a server of convenient features : rotate plates for more coherent cook ; digital timers ; autoprogramming capabilities ; and adjustable levels of cooking office that enable defrost, browning, and warming, among other functions .

Design

The basic design of a microwave oven is simple, and most operate in basically the lapp manner. The oven ‘s diverse electronic motors, relays, and control circuits are located on the outside casing, to which the oven cavity is bolted. A front jury allows the exploiter to program the microwave, and theThe oven cavity and door are made using metal-forming techniques and then painted using electro-deposition, in which electric current is used to apply the paint. The magnetron tube subassembly includes several important parts. A powerful magnet is placed around the anode to provide the magnetic field in which the microwaves will be generated, while a thermal protector is mounted directly on the magnetron to prevent damage to the tube from overheating. An antenna enclosed in a glass tube is mounted on top of the anode, and the air within the tube is pumped out to create a vacuum. Also, a blower motor used to cool the metal fins of the magnetron is attached directly to the tube.
door frame of reference has a little window to enable the cook to view the food while it is cooking. Near the top of the steel oven cavity is a magnetron—an electronic tube that produces high-frequency microwave oscillations—which generates the microwaves. The microwaves are funneled through a metal waveguide and into a stirrer fan, besides positioned near the top of the cavity. The winnow distributes the microwaves evenly within the oven. Manufacturers vary the means by which they disburse microwaves to achieve uniform cook patterns : some use double stirrer fans located on opposition walls to direct microwaves to the pit, while others use entrance ports at the bottom of the pit, allowing microwaves to enter from both the top and bottom. In addition, many ovens rotate food on a turntable .

Raw Materials

The cover or outer casing of the microwave oven is normally a one-piece, wrap-around metal enclosure. The oven ‘s inside panels and doors are made of startle or

stainless steel

and are given a coating of acrylic enamel, normally light in discolor to offer beneficial visibility. The fudge coat is by and large made of ceramic or glass. Inside the oven, electromechanical components and controls consist of timer motors, switches, and relays. besides inside the oven are the magnetron tube, the waveguide, and the scaremonger winnow, all made of alloy. The hardware that links the respective components consists of a variety of metal and plastic parts such as gears, pulleys, belts, nuts, screws, washers, and cables .

The Manufacturing

Process


Oven cavity and door manufacture

  • 1 The process of manufacturing a microwave oven starts with the cavity
    and the door. First, the frame is formed using automatic metal-forming
    presses that make about 12 to 15 parts per minute. The frame is then
    rinsed in alkaline cleaner to get rid of any dirt or oil and further
    rinsed with water to get rid of the alkaline solution.
  • 2 Next, each part is treated with zinc phosphate, which prepares it for
    electro-deposition. Electro-deposition consists of immersing the parts
    in a

    paint


    tank at 200 volts for 2.5 minutes. The resulting coating is about 1.5
    mils thick. The parts are then moved through a paint bake operation
    where the paint is cured at 300 degrees Fahrenheit (149 degrees Celsius)
    for 20 minutes.
    The chassis or frame is mounted in a pallet for the main assembly operation. A pallet is a vise-like device used in conjunction with other tools.

  • 3 After the door has been painted, a perforated metal plate is attached
    to its window aperture. The plate reflects microwaves but allows light
    to enter the cavity (the door will not be attached to the cavity until
    later, when the chassis is assembled).


The magnetron tube subassembly

  • 4 The magnetron tube assembly consists of a cathode cylinder, a filament
    heater, a metal anode, and an antenna. The filament is attached to the
    cathode, and the cathode is enclosed in the anode cylinder; this cell
    will provide the electricity that will help to generate the microwaves.
    Metal cooling fins are welded to the anode cylinder, and a powerful
    magnet is placed around the anode to provide the magnetic field in which
    the microwaves will be generated. A metal strap holds the complete
    assembly together. A thermal protector is mounted directly on the
    magnetron to prevent damage to the tube from overheating.
  • 5 An antenna enclosed in a glass tube is mounted on top of the anode,
    and the air within the tube is pumped out to create a vacuum. The
    waveguide is connected to the magnetron on top of the protruding
    antenna, while a blower motor used to cool the metal fins of the
    magnetron is attached directly to the tube. Finally, a plastic fan is
    attached to the motor, where it will draw air from outside the oven and
    direct it towards the vanes. This completes the magnetron subassembly.


Main chassis assembly

  • 6 The chassis assembly work is performed on a pallet—a
    work-holding device used in conjunction with other tools—located
    at the station. First, the main chassis is placed on the pallet, and the
    cavity is screwed on to the chassis. Next, the door is attached to the
    cavity and chassis by means of hinges. The magnetron tube is then bolted
    to the side of the cavity and the main chassis.
    In a completed microwave oven, the magnetron tube creates the microwaves, and the waveguide directs them to the stirrer fan. In turn, this fan points the waves into the oven cavity where they heat the food inside.
  • 7 The circuit that produces the voltage required to operate the
    magnetron tube consists of a large transformer, an oil-based capacitor,
    and a high voltage rectifier. All of these components are mounted
    directly on the chassis, close to the magnetron tube.


Stirrer fan

  • 8 The stirrer fan used to circulate the microwaves is mounted on top of
    the cavity. Some manufacturers use a pulley to drive the fan from the
    magnetron blower motor; others use a separate stirrer motor attached
    directly to the fan. Once the stirrer fan is attached, a stirrer shield
    is screwed on top of the fan assembly. The shield prevents dirt and
    grease from entering the waveguide, where they could produce arcing and
    damage the magnetron.


Control switches, relays, and motors

  • 9 The cook switch provides power to the transformer by energizing a
    relay and a timer. The relay is mounted close to the power transformer,
    while the timer is mounted on the control board. The defrost switch
    works like the cook switch, activating a motor and timer to operate the
    defrost cycle. Also mounted on the control board are a timer bell that
    rings when the cooking cycle is complete and a light switch that allows
    viewing of the cavity. A number of interlocking switches are mounted
    near the top and bottom of the door area. The interlocking switches are
    sometimes grouped together with a safety switch that monitors the other
    switches and provides protection if the door accidently opens during
    oven operation.


Front panel

  • 10 A front panel that allows the operator to select the various settings
    and features available for cooking is attached to the chassis. Behind
    the front panel, the control circuit board is attached. The board, which
    controls the various programmed operations in their proper sequence when
    the switches are pushed on the front panel, is connected to the various
    components and the front panel by means of plug-in sockets and cables.


Making and assembling the case

  • 11 The outer case of the microwave is made of metal and is assembled on
    a roll former. The case is slipped onto the preassembled microwave oven
    and bolted to the main chassis.


Testing and packaging the oven

  • 12 The power cords and dial knobs are now attached to the oven, and it
    is sent for automatic testing. Most manufacturers run the oven from
    50-100 hours continuously as part of the testing process. After testing
    is complete, a palletizer robot records the model and serial data of the
    oven for inventory purposes, and the oven is sent for packaging. This
    completes the manufacturing process.

Quality Control

extensive timbre control during the industry of microwave ovens is essential, because microwave ovens emit radiation that can burn anyone exposed at eminent levels for prolong periods. federal regulations, applied to all ovens made after October 1971, limit the amount of radiation that can leak from an oven to 5 milliwatts of radiotherapy per square centimeter at approximately 2 inches from the oven surface. The regulations besides require all ovens to have two independent, interlocking switches to stop the production of microwaves the consequence the latch is released or the door is opened.

In addition, a computer controlled scanner is used to measure discharge leaks around the door, window, and back of the oven. other scanners check the seat of the magnetron tube and antenna radiation. Each scanner operation relays data to the next-on-line operation so that any problems can be corrected .

The Future

Because of their travel rapidly and convenience, microwave ovens have become an indispensable separate of modern kitchens. many developments in the microwave marketplace and allied industries are taking identify reasonably quickly. For example, foods and utensils designed specially for microwave cook have become a huge business. New features will besides be introduced in microwaves themselves, including cybernate storehouse of recipes that the consumer will be able to recall at the touch of a push button. The display and programmability of the ovens will besides be improved, and combination ovens capable of cooking with microwaves a well as by conventional methods will become a standard family product .

Where To Learn More


Books

Davidson, Homer L.
Microwave Oven Repair,
2nd edition. Tab Books Inc., 1991 .
Gallawa, J. Carlton.
The Complete Microwave Oven Service Handbook: Operation, Maintenance.
Prentice Hall, 1989 .

Microwave Oven Radiation.
U.S. department of Health and Human Services, 1986 .
Pickett, Amold and John Ketterer.
Household Equipment in Residential Design.
John Wiley and Sons, 1986 .
Raytheon Company.
Appliance Manufacturer.
Cahners Publishing, 1985.


Periodicals

Klenck, Thomas. “ How It Works : Microwave Oven. ”
Popular Mechanics.
September, 1989, p. 78 .
Roman, Mark. “ The Little Waves That Could. ”
Discover.
November, 1989, p. 54 .

Rashid

Riaz