manufacturing process of Refrigerator

       manufacturing  process of Refrigerator 

Refrigerator 

A refrigerator is a cooling apparatus. Commonly known as fridge too.  . Cooling is a popular food storage technique in developed countries and works by decreasing the reproduction rate of bacteria. The device is thus used to reduce the rate of spoilage of foodstuffs.

A refrigerator maintains a temperature a few degrees above the freezing point of water. Optimum temperature range for food storage is 3 to 5 °C (37 to 41 °F). A similar device which maintains a temperature below the freezing point of water is called a "freezer".

The History of the Refrigerator

Prior to the development of artificial refrigeration techniques during the 1800s, people utilized a variety of means to chill and preserve foodstuffs. For centuries, ice served as the principal refrigerant. The relatively quick evaporation of a liquid creates an expanding volume of gas. As water vapor rises, its kinetic  energy  increases  dramatically, in part because the warm vapor is drawing in energy from its surroundings, which are cooled by this process.

The Indians and Egyptians took advantage of this phenomenon by placing wide, shallow bowls filled with water outside during the cool nights. As some water quickly evaporated, the remaining water cooled, forming ice. With this method, it was possible to create sizeable chunks of ice that could then be used to cool food.

The first known attempt to develop an artificial refrigerator took place in Scotland at the University of Glasgow. There, in 1748, William Cullen revived the ancient Indian-Egyptian practice of freezing liquid by means of evaporation, although he accelerated the process by boiling ethyl ether into a partial vacuum (ethyl evaporates more quickly than water).

[An Oldman's refrigerator, more like an icebox with its refrigerating mechanisms on top]

 

Raw Materials

Refrigerators today consist of several basic components: the exterior cabinet and door, the inner cabinet or liner, the insulation inserted between the two, the cooling system, the refrigerant, and the fixtures. The cabinet and door are made of aluminum or steel sheet metal that is sometimes prepainted. The metal is generally purchased in a coil that is either fed directly into the manufacturing process or cut to size and fed sheet by sheet. The inner cabinet is made of sheet metal, like the outer cabinet, or of plastic. The insulation that fills the gap between the inner and outer cabinets consists of fiberglass or polyfoam.

 The components of the cooling system (compressor, condenser, coils, fins) are made of aluminum, copper, or an alloy. The tubing is usually copper, because of that metal's ductility its ability to bend without breaking. Freon remains the most commonly used refrigerant, and almost all of the large interior fixtures (door and cabinet liners) are made from vacuum-formed plastic; smaller fixtures (butter compartments, egg trays, salad crispers) are purchased as small plastic blanks or in pre-formed pieces.

Design

The refrigerator is based on two basic laws of physics:

·          One ,That heat flows from warmer material to cooler materials and never the reverse;

·          Two, that decreasing the pressure of a gas also decreases its temperature.

Refrigerators work by removing the warmth from the air within their interior compartments and relaying that heat to the air outside. The coolant (freon) accomplishes this transfer as it passes through a circuit, moving from the evaporator to the condenser. Beginning in the evaporator, which lies inside an insulated cabinet, the freon is heated. Because it has been made to boil, the freon draws heat from the air within the refrigerator. Having absorbed this heat, the freon is then routed to the condenser. In this set of copper coils (usually mounted at the back or on the bottom of the refrigerator), the freon condenses—returns to a liquid state—transferring its heat into the outside air as it does so. After cooling, the freon then returns to the evaporator, where it is once again heated and begins to absorb heat from the food stored within the refrigerator. Sometimes, to increase their surface area (and thus facilitate thermal transfer), the evaporator and the condenser are fitted with metal fins.

For defrosting, a coil is wrapped around the freezer unit. When the timer reaches defrost, the refrigerant is passed through this coil while it is hot to raise the temperature and melt the ice. The coil is generally positioned away from any ice makers to prevent the ice cubes from melting and freezing together.

 

Manufacturing Process

 

 

Outer cabinet and door

• The outer cabinet and door, made of sheet metal, are either welded or clinched together. Pieces of sheet metal are either welded or clinched together. Clinching is a process closely resembling stapling in that the two pieces are crimped together under pressure, though no additional pieces such as staples are added. If the part of the cabinet is to be visible, it will be welded and ground down to appear as one piece. The extent to which the welding process is automated depends on the company and the number of refrigerators being produced.

•  If the sheet metal was not purchased in precoated form, it is now painted. Some manufacturers use spray equipment to lay a uniform coat of paint on the metal. Others dip the parts in a paint/solvent mixture before heating them to bake the paint onto the surface.

Inner cabinet

•  The inner cabinet is sometimes made from sheet metal very similar to the outer shell. Any seams are caulked to improve insulation and looks. Some manufacturers and some models use plastic for inner liners; for example, the inner door is almost exclusively made from plastic today. The plastic liners are vacuum formed. In this process, a thick piece of plastic slightly larger than the finished part has its outer edges clamped and is then heated. The hot plastic is next pulled by vacuum into a mold and cooled. After trimming, the resulting part is ready for assembly.
•  The inner cabinet is inserted into the outer cabinet, and the two are snapped together before the fixtures are inserted. Some tubes and wires are run through the gap between the two before it is filled with insulation. A dispensing device (sometimes robotically operated, sometimes a manually operated long 'gun') inserts foam between the walls. When heated in an oven, this foam expands to add rigidity and insulation to the cabinet. A similar process is used for the doors.

 

Cooling system

•  The refrigeration components are attached to the cabinet using screws and clips. The tubing is soldered together, and a protective coating is sprayed on the joints. The order of this assembly varies between manufacturers and models. The copper tubing from which the coils (condensers and evaporators) have separately been cut, bent, and soldered is then attached to the refrigerator as a unit.
•  The seal on the refrigerator door is created by means of magnet laden gaskets that are attached to the doors with screws. Handles and hinges are also screwed onto the door before its hinges are screwed onto the cabinet. Some adjustment is allowed for proper operation of the door.

     Testing and adding accessories

•  Most manufacturers mix testing with manufacturing from this point on. The unit is leak tested with nitrogen (a safe gas that makes up about 79 percent of the air); if it passes, it is charged with refrigerant and subjected to further testing. Next, the accessories (shelves, crispers, ice trays, etc.) are added and taped down for shipping. The unit is given a final look and then packaged for shipping.

 

General technical explanation

 

ü  1: vapor Compression Cycle

A: hot compartment (kitchen)

B: cold compartment (refrigerator box) I: insulation, 1: Condenser,

ü  2: Expansion valve

ü  3: Evaporator unit

ü  4: Compressor.

An Embraco compressor and fan-assisted condenser coil

A vapor compression cycle is used in most household refrigerators, refrigerator–freezers and freezers. In this cycle, a circulating refrigerant such as R134a enters a compressor as low-pressure vapor at or slightly above the temperature of the refrigerator interior. The vapor is compressed and exits the compressor as high-pressure superheated vapor. The superheated vapor travels under pressure through coils or tubes comprising "the condenser", which are passively cooled by exposure to air in the room. The condenser cools the vapor, which liquefies. As the refrigerant leaves the condenser, it is still under pressure but is now only slightly above room temperature. This liquid refrigerant is forced through a metering or throttling device, also known as an expansion valve (essentially a constriction) to an area of much lower pressure. The sudden decrease in pressure results in explosive-like flash evaporation of a portion (typically about half) of the liquid.

 The latent heat absorbed by this flash evaporation is drawn mostly from adjacent still-liquid refrigerant, a phenomenon known as "auto-refrigeration". This cold and partially vaporized refrigerant continues through the coils or tubes of the evaporator unit. A fan blows air from the refrigerator or freezer compartment ("box air") across these coils or tubes and the refrigerant completely vaporizes, drawing further latent heat from the box air. This cooled air is returned to the refrigerator or freezer compartment, and so keeps the box air cold. Note that the cool air in the refrigerator or freezer is still warmer than the refrigerant in the evaporator. Refrigerant leaves the evaporator, now fully vaporized and slightly heated, and returns to the compressor inlet to continue the cycle.

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Many modern refrigerator/freezers have the freezer on top and the fridge on the bottom.

Most fridge/freezers, with the exception of manual defrost models and/or cheaper models utilize what appears to be two thermostats. Only the freezer compartment is properly temperature controlled. When the freezer gets too warm, the thermostat starts the refrigeration process and a fan also starts. The air is circulated around the freezer. During this time, the fridge is also getting colder. The fridge temperature control knob is doing nothing to 'control' the temperature. This knob is only controlling the amount of air

Modern, computerized refrigerators do not use the damper system. The computers manage fan speed for both compartments (although air is still pumped from the freezer).

Quality Control

As mentioned above, all subassemblies of tubing that will contain refrigerant are pressure-tested with nitrogen. The entire unit is also leak-tested prior to charging with freon. Once charged, the unit is tested as a whole to ensure that it is capable of reaching design temperatures including those necessary during the defrost cycle. The unit is operated with sensors inside that determine the temperature changes over time. Sometimes the refrigerant pressures are also measured. The unit is then subjected to a final 'sniff test by a machine that detects refrigerant to ensure that no leaks have developed during testing.

 

By products/Waste

Metal components that are rejected are sold to metal recycling companies. Plastic components are ground into small pieces and either reused as raw material or returned to the vendor for reuse. If a unit is rejected after it has been charged, the refrigerant is drained by special equipment and reused.

Styles of refrigerators

Most households use the freezer on top and refrigerator on bottom style, which has been the basic style since the 1940s.

• Traditional style 1940s-present freezer top/refrigerator bottom (although most of the earlier models, some of the cheaper later models and still some mini-fridges use the 'freezer chest,' or what is known as the 'freezer in the fridge').
• Side by side style – introduced by Amana in 1949 but not popular until 1965–present; left side is freezer and the right is refrigerator.
• Top refrigerator/bottom freezer style – mid-1950s – present.

 

Environmental Concerns

 

In the new era  scientists began to understand that as gases in the chlorofluorocarbon (CFC) group, which includes freon, waft upward into the stratosphere (the upper layer of the atmosphere), they gradually decompose,

The space between the inner and outer cabinets is filled with foam insulation, usually polystyrene, which can be inserted manually or automatically by a robot
Because this insulation releases CFCs, which contribute to the destruction of the ozone layer, researchers are searching for substitutes. The polystyrene may be replaced by the same kind of vacuum insulation that is used in thermos bottles, since vacuum insulation is more efficient in terms of both space and energy.

Releasing chlorine atoms as they do so. The problem with this is that each chlorine atom can destroy tens of thousands of ozone molecules, ozone being the triatomic form of oxygen that comprises a protective layer in the stratosphere, absorbing much solar ultraviolet radiation that would harm animal life if it reached the earth's surface.

Unfortunately, chlorofluorocarbons are also present in the polystyrene foam that some manufacturers use as an insulator between the external case and the interior lining of their refrigerators. So, efforts to reduce the CFC emissions from refrigerators are presently continuing on two fronts, as manufacturers attempt to find alternatives to both the coolant freon and the insulator polystyrene.

 

 

Features

Newer refrigerators are

• Automatic  defrosting
• A  power  failure warning, alerting the user by flashing a temperature display. The maximum temperature reached during the power failure may be displayed, along with information on whether the frozen food has defrosted or may contain harmful bacteria;
• Chilled water and ice available from an in-door station, so that the door need not be opened.

The Future

 

In terms of freon, several intermediate steps have been taken to minimize CFC emission as researchers attempt to identify safe coolant alternatives. Refrigerator designs have been improved to reduce the amount of freon needed; leak detection systems have been installed; maintenance has been limited to trained, authorized personnel; and refrigerant is recovered and recycled whenever possible.

 Moreover, long-term replacements for freon are being explored. Thus far, the most promising among them is HCFC-22, which, although still a chlorofluorocarbon, contains an additional hydrogen atom that reduces the molecule's ozone-depletion capacity by 95 percent. While its cost (three to five times greater than that of freon) is problematic, HCFC-22 is presently undergoing tests to determine its toxicity.

CFC-containing insulation may be replaced by the same kind of vacuum insulation that is used in thermos bottles. Research indicates that vacuum insulation is more efficient in terms of both space and energy, so, at present, it appears that insulation alternatives will become viable well before freon substitutes.