Document GmxLx6MjKRKMg7G8J8BREE8Xq

902 CHAPTER 60 1965 Guide And Data Book tors, the humidity in the food-storage compartment is low dimensions, both of which are influenced by competitive due to the presence in the cabinet of the cold evaporator,.. considerations. The method of computing usable cubical and therefore rapid drying of uncovered foods occurs.- The `contents and shelf area is contained in the American Standard sealed chamber maintains a high humidity because the cool B38.I-1955. ing surface is the whole surface of the chamber, operating .at .practically the same temperature as the air inside. Food desic-_ v Structure " r . 7- V cation is thus held to a minimum. Temperatures just above The external shell of the cabinet is generally a winglc fabri- freezing provide the additional advantage of inhibiting -bac-.:, i;,cated steel structure which,supports the inner,food'eompart- terial action. This combination of high humidity'and near-... A ment^ the door, and-the refrigerating mechanism.-In'general freezing temperature is optimum for extended storage of. un-. ' tiie door andbreaker stripconstructionis similar to that shown wrapped or uncovered perishable foods. . 4 miFig. 1. The door coversatile whole front of the cabinet. A Automatic ice-making is also available in some two-tem single plastic sheet serves as the inner surface for the door and perature refrigerators. As ice is removed from a storage con - th door breaker stripe. The door is formed to the contour of tainer in the freezer, the icemaker automatically refills the"' the cabinet opening and to accommodate the shelves and ice-making cavities with water from the house piping and compartments attached to it. The air gap between the breaker ejects cubes until the storage container is again full. strips' and the door panel'contributes`substantially to the Automatic Defrosting totil heat leakage of the cabinet:Therefore; this'gap should be kept 'as small as possible,:and the width of the breaker strip Another important feature in household refrigerators'is the kept'as wide as practicable. Mechanically, the overall struc rapid automatic defrosting of the evaporator. Early attempts ture of the cabinet should be strong enough* to'stand shipping! to solve the problem of removing the frost from the evaporator A cabiriet that will'withstand shipping is almost certain to be were confined to providing a manual means for modifying strong enough to withstand daily usage'. The inner food'liner the operation of the standard temperature control This modi should be so'designed', that it.does notchip or craze at the fication permitted the evaporator to operate above 32 F for a points of support. Shelves must be designeif'with adequate period of time. More recently defrost clock mpehantsma be^ strength' io that'they will hot sag under the heaviest antici came available as accessories. These devices interrupt the pated'load:'Cabinet hardware should be satisfactory for'a power supply to the refrigerator for a sufficient length of time total of approximately 350,000 door openings. ' once a day,' to. permit the day's accumulation of frost to melt from the evaporator during the early morning hours. How ever, these schemes present the problem of maintaining tem .Insulation, ,.... -,.f .... . peratures adequate for the proper storage of frozen food such ""In a domestic refrigerator insulation'usually varies from 2 as ice cream. to 3|in! in' thickness! Insulating'materialsin common use are .Another method is to have a separation between the .sub rock wool and glass wool. Other types are (1) expanded-in- freezing and main food-storage compartments. The evaporator place foam insulations: which have-good .moisture sealing used in the main food-storage compartment operates above properties, and structural .rigidity .and (2), insulations im freezing during all or a portion of the.cycle, thus permitting the accumulated frost to melt. The sub-freezing .compart .topregnated with.a gas having a thermal conductivity less than that of air. This .may'allow the.'cabinet wall .thickness' be ment has to.be defrosted by the usual methods although less reduced!' !.!V frequently than in the conventional arrangement., .Although it is desirable,to obtain an exterior cabinet shell Practically all the manufacturers now, offer one or more as nearly, vapor-tight' ,as possible, consideration should be models, including some of the two-compartment type,- which obtain rapid automatic defrosting. ,. Various means are employed to apply heat to the refrigerat? ing system to obtain rapid melting of the accumulated frbstl This heat may be supplied by direct application of electrical heat or by suitable means for introducing hot gas to the evaporator. Defrosting-periods range from 5 to 30 minutes duration. This short defrosting cycle permits no substantial rise in the frozen-food temperature or in the food-compart ment temperatures. These refrigerators permit .the safe stor age of frozen- foods over considerable periods of time while maintaining the evaporator relatively.free of frost.The defrost water may be, collected, in .a removable container inside the refrigerator or conveyed to: a, receptacle outside to the cabinet, from.which it can evaporate. Another solution is to separate the evaporator from.either (or both) the subfreezing compartment and the main food- storage compartment By. suitable air ducting arrangements the compartment is cooled by forced convection. This has the advantage of simplifying the problem of evaporator defrost ing. In the subfreezing compartment, it has the further, ad vantage of preventing or reducing frost buildup on the frozen foods. ....... CABINET DESIGN The fundamental factors.in the,dejngn of a cabinet are its usable food-storage capacity in cubic.feet,and.its,external .. : v:vRg,. 1 ;. . .-Door and.Breaker Ship Construction Household Refrigerators and Food Freezers given to the fact that, when water vapor is migrating from the ambient air into the insulation, it is also passing from the insulation into the area around the cold evaporator. Conse quently, the design of door gaskets, breaker strips, and other parts should provide maximum barriers for vapor flow from the room air to the insulation, but, at the sometime, provide as free a passage as is practicable between the insulation and the inside of the cabinet. The effect of insulation thickness on heat leakage is not the only important consideration. Another very important'one is the maintenance of the exterior of the surface of the cabinet at a temperature sufficiently high to prevent moisture conden sation on the surface. Areas where condensation will usually occur are around the hardware or along the edge of the door opening. Good practice suggests that, with a 40 F.refrigerator interior, temperature in an SO F. room, no .external surface temperature on the cabinet should be more than 5 F below the room temperature. In some instances, particularly in two door tiesigns, it may be necessary to include,a very low, watt age heater immediately behind, certain localized areas, to raise their temperature sufficiently to prevent moisture con densation at these locations during periods of relatively high ambient humidities. These heaters are generally made of a fine resistance wire or ribbon-wound on a flexible core and en? cased in a plastic or rubber sheath. Finishes . Modem synthetic baked enamel finishes are common for refrigerators. Customarily, they are applied over a chemically . treated surface to obtain good paint adhesion and prevent spreading of the rust if scratches extend through the finish. - In addition to the synthetic enamel finishes, there are im proved vitreous enamel finishes that usually consist of one ground coat and two or three finish coats, each of-which-is fused on separately. The finish used almost universally on the -1. Hermetic (touting 2,-Cybader ;3., Pitton -. . 4. CeanocMng rod 5. CouRtor-befenco 6. Motor `. 7. Otttor booriitg 8. Pltefcui'go valve assembly 9.' Suction valve port 1 JO.. Vahe plate I l.CytisxlerJmod,' 12. Section got intofcu p/po 13. CooQng (tot \Rg.:2V';; Hermetic Motor Condenser Unit with ' ''-Reciprocating Pump . 903 food compartment liner is an acid-resistant vitreous enamel: However, suitable synthetic organic finishes.are now available for. this application. Some refrigerators have .this type of finish on the food compartment' liners. There has been a marked increase in the use of color in refrigerators. On some models it is used on the interior components such as breaker strips, shell fronts, compartment fronts, and the escutcheons and panels on the cabinet exterior. Most manufacturers now offer a wide selection of other models completely, color- styled including the food compartment liner and the-cabinet exterior. Plastics are used to a considerable extent-in present day. refrigerators,-primarily because of .their ease .of fabrica tion, low heat conductivity, pleasing, appearance, clean- ability, and resistance to moisture. - ., Low odor level is of utmost importance in the selection of a plastic for use in a refrigerator. Impact resistance, wearing qualities, electrical insulating ability, low water absorption, are other important characteristics that must be considered in selecting the plastic most suited for the particular applica tion. Polystyrene is widely used for door panels, door shelves, evaporator doors, baffles, breaker strips, drawer, pans, and many smaU items. The phenolics are generally used for laminated door panels in molded parts such as terminal boxes, and as a binder for the glass fiber insulation. The good bearing qualities of nylon are used to advantage in such applications as hinges, latches, and rollers for sliding ' shelves. Gaskets, both for the refrigerator and the evaporator doors, are generally made of vinyl or rubber. COMPRESSOR UNITS 7, Brief descriptions will be given of hermetic, reciprocating, and-rotary compressors. For;more complete descriptions see Chapter 38, Compressors. ; Hermetic Units Household refrigerators employing a mechanical compres sor utilize hermetic unit design. The motor compressor unit is an integral assembly, and is sealed into a gas-tight housing eliminating shaft seals, belts, pulleys, and open motor bear ings. The unit may be mounted on springs within the shell, or pressed tightly into it (Fig. 2). This assembly is externally supported by rubber or spring mountings. The chlorofluoromethane and ethane group of refrigerantsare almost univer sally employed in the present hermetic units. Refrigerant 12 is toe most widely used in both reciprocating and rotary compressors. However, Refrigerant 22 is used in some recipro cating compressors. Reciprocating Reciprocating, compressors are "either of the automotive type with the wrist pin in the piston, or a scotch-yoke type (Fig. 2 and Fig. 3). The advantage of the latter is the flexibility between the axis of tHe piston and the motor axis. With the automotive type, it is necessary that the wrist pin be exactly at right angles to the piston axis, otherwise noise will be in troduced due to the misalignment of parts. When parts are not built with sufficient rigidity, misalignment under load may occur even, though' no-load accuracy exists. This condi tion does not exist in .the scotch-yoke design, because it has flexibility in two directions. Rotary * Rotary compressors are generally one of tiro types;Tn one type the integral rotor and shaft assembly is'concentric with the circumference of the rotor and eccentric to'-the circum-