Introduction
A dish washer is a mechanical device that is used in the cleaning of eating utensils and dishes. They are mainly found in restaurants and homes. The existence of the dish washing device has become a staple in many homes because, unlike the manual dish cleaning process, dishwashers spray the hot water in the temperature range of 55-75 degrees centigrade on the dishes. This has made dish washing process easier and eliminates the danger of breaking utensils and injury that is associated with mechanical washing.
Design concepts
The best dish washing devices are designed to reduce the probability of inflicting injury on the user. Most cases of back pain especially in the older generation are associated with mechanical movements and this may occur by when the bottom rack of the dishes is accessed.
Operating conditions
In addition, the operating conditions of dishwashers are extremely harsh and dangerous to human safety. As such, the design should factor in the harsh operating environment of high temperature water cycle and high temperature forced air drying cycle. Moreover, the cycle involves various detergents and chemicals which might be harmful to human health if due care is not taken. The following operating conditions, which have been, put into consideration in most design concepts;
- High water temperatures of up to 1600 F
- Drying temperatures of up to 1800 F
- Mineral deposits
- High water pressure
- Large temperature differential
- Detergents with solvents and abrasives
Space
Therefore in this literature, some examples of conceptual designs will be put into focus. The first common type of designs in the market involves a swinging shelf mechanism. In this design, the bottom rack consists of an independent track and a spring driven swing system that lift the rack to allow the bottom rack to be removed. A lever is used in this design to engage and disengage the ring to allow the back and forth movement of the spring.
Fig. swinging system
Vertical lift system
The next design is the vertical lift system. In this case, the bottom rack is usually pulled out like the normal door of the dishwasher. Once the button drawer has been removed, the bottom rack is lifted vertically. The door has a lift system that is mounted on it.
Moment arm application
The third design involves a moment arm application that attaches the bottom of the rack to a pivoting arm. This arm attaches along a track on the bottom arm and allows the bottom rack to be pulled over.
Fig.2 Vertical lift design
Carousel system
Finally, a carousel system is considered that involves the connection of two racks joined by crossing brackets in a side by side manner and connected to a single track. The tracks rotate about the pin joint when they are pulled out.
Fig. 3 carousel design
Each of the designs stated above has their advantages and disadvantages. The first design is simple to build, but swinging mechanism is difficult to implement and may damage easily. The second design is complex to fit in the dishwasher while carousel does not require locking the bottom drawer, but its complexity arises at the single points of support on each side.
The following features are the standards for most dish washing devices;
CAPACITY
Place setting is the standard used to express international capacity for dishwashers. It is thus important to have a uniform capacity in order to accommodate all utensils no matter their size and shape. Commercial dishwashers are usually rated as plates per hour to illustrate the sped of the washer.Fig.4 American counter top dishwasher
According to the standard size of most dishwashers installed in kitchen cabinets has 60cm standard width and depth of 86cm. Portable dish washers are, however, small in sizes and have less than 60 cm widths. They are classified into two; standard or tall tub designs. Standard tubs designs have an attached kickplate beneath the dish washer that permit simple maintenance installation and repair.
Other design factors
Other factors note consideration in the design process involves efficient cleaning operation in a quiet manner. The motors in use are powerful and quiet, and outside of the device are highly insulated. The design in the market comprise of both single motor and double motor washers. The single motor demand more insulation while double motor dishwashers have less insulation required for quiet operation. The two motors are used for pumping water, and drainage and both operate at the same horse power. An example of a double motor dish washing machine is from Amana electronics.
External design
The external design of dish washing machines are made in a sophisticated manner and in most instances, the stand-alone models consist of a wooden cabinet that can additionally be used as a working area.
ARCHITECTURE
The basic structure of a dishwasher consists of steel frame and a steel door panel. Pieces of stainless steel are developed and fabricated in appropriate sizes. The racks that hold the dishes are made of steel and coated with tin to prevent scratching and rusting. Racks are finally dipped in plastics in the form of PVC. The inner compartment that holds the racks and the washer arms is referred to as the tub. Through injection mould, it is placed inside the plant using pellets of calcium-reinforced polypropylene plastics. The plastic is inert and strong thereby cannot react with the detergents and the heat. Other parts such as cutlery basket, detergent containers, wash tower and sprayer arms are injection molded. Motors and electrical appliances are sourced from third parties as per the designer specifications.
HOW DISHWASHER WORKS
A dishwasher is a kind of robot that performs many operations in regards to washing utensils. It essentially does the following;
It fills itself with water
It raises the temperature of water through heating
It releases the dish detergents at a specific time
It sprays water on the dishes
It drains the water on the dishes
It finally rinses the dishes with clean water and heats the air in the unit to completely dry the dishes. Dishwashers have a self monitoring mechanism that ensures that all the operations are performed correctly. For instance sensors in the unit detect the prevailing conditions and if the correct conditions are achieved, it shuts itself off.
Dishwashing cycle
The small basin in the bottom of the unit is filled with water, and heating is done here to the desired temperature (130-140 degrees F). The pump then propels the water up the jets where it is subsequently forced out of the spraying arm and sprayed against the dirty dishes. When the wash and rinse cycle are completed, the water is drained out of the basin, and the processed is executed by the pump propeller. Different models of dish washers have different locations for drained water, either in the directly into the sink or into the pipes under the sink. The final process is the drying cycle. This is optional and many users bypass it to economize power, but in this stage, the heating unit located at the bottom of the dishwasher heats the air inside the unit to dry the dishes.
PARTS OF A DISHWASHER
The dish washer contains the following main parts
CONTROL
This is located inside the door and behind the control panel. It has a timer that defines the period of time for each cycle of the cleaning of the drying process and activates each process at the right interval.
Intake valve
This is the water inlet in the dishwasher. The valve opens, and water is let in by the pressure into the unit
SPRAY ARMS
It comprises the water spraying channels onto the dishes to wet and clean them. The drain arms rotate in a circular manner to allow equal cleaning of all the dishes and their parts.
PUMP
Pump is powered by the electric motor. During the pump cycle, water is forced into the drain horse. The motor pump is placed beneath the base in the central part of the dish washer. The pump can be categorized into two parts;
Reversible pumps switch between the process of spraying water to the spray arms and pumping water to drain. This is achieved through reverse of the direction of the motor.Fig.2 Reversible pump
Direct drive pump runs the motor in one direction, and the direction of flow is determined by the solenoid that opens and closes the appropriate inlets and outlets to switch the direction of the spray arm and the drain.Fig. 3 Direct-drive
MATERIALS
A dishwasher is manufactured with materials that are not harmful to human beings. The body is made of stainless steel materials to prevent rusting. Pipe joints and material sealing are made of plastics because they are rust free. Sprinklers are made of steel, and they contain tiny perforations to achieve maximum jet pressure. Most appliances have stainless steel or plastic tubs but stainless steel is favored because it does not stain, unlike plastics. Also, it has better heat retention capacities, therefore, utilizing energy in the drying process.
Cost of materials
The cost of materials for installation of dishwasher varies depending on the quality of the dishwasher. The material prices of dishwasher range from $325-$629 for basic materials. These are the materials for dishwashers which are of low quality. The materials for better or medium quality range from between $577 to $913. The best quality of dishwasher materials is $871 to $1165. Cost of installations will also depend on the quality of the materials that have been purchased. The installation cost for basic materials range from $38-$68 while that of intermediate materials range from $62-$97. The cost for installing dishwasher using best quality materials range from $90-$136.
Models of motors and racks
Motors are electronic devices made of aluminum and steel to ensure maximum durability. Racks, on the other hand, are constructed with metals and coated with nylon. The nylon-coated models provide durable designs against chipping, peeling and scratching. Other models have adopted an extra coating of nylon at the rack tine tips to reduce wear and tear and elongate their usability. Vinyl coated racks are not common in recent times and are found only on the basic models.
SAFETY PRECAUTIONS AND USAGE GUIDELINES
Dishwasher requires the use of specified components such as detergents. The use of regular dish washing soaps will lead to dishwasher suds overflow. The effects of this are not desirable. Using the dishwashing during the day is recommended because the water pressure will be high meaning that dishes will be cleaner. Dishwashing machines perform poorly under low pressure conditions, and impacts extend of cleanliness. Pre-cleaning the dishes before inserting them on the dishwasher is not necessary. The dishwasher depends on the food particles on the dishes to maintain an appropriate pH levels in the unit. Large pieces are, however, scrapped off because they have the potential of clogging the drainage tubes. It is advisable that plastics are placed on the upper racks. The heating element in the lower rack can melt them if placed on the lower racks.
Dishes with identical shapes and make should not be placed together since they can stick to each other and result in dirt due to incomplete cleaning. The water jets cannot reach all sides in sticking bowls. Another mechanism is to place the dirtiest side of the dish facing towards the water jets. This will leave the dishes clean.
Putting too many dishes in the dishwasher at a time will not guarantee total cleanness. The buildup of overflow will prevent the jets from spraying each and every side of the dishes.
According to most dish washing machines come with standard specifications regarding the wash cycles. These may include normal, pots and rinse and hold. Normal is the default status for general dishwashing procedures while pots and pans are used for hard-soiled pans and needs longer cycles with high temperatures. However, according to the needs of the user, several other cycles can be added to improve performance and ensure energy efficiency. This includes quick wash, auto wash, sanitize, half load among others. The sanitize rinse cycle provides high temperature sanitization of up to 160 degrees as per the NSF certifications. This feature is essential for sanitizing baby bottles or plastic cups. Crystal cycle is used with glassware and delicate materials. It uses a variable speed motor that decreases the water pressure to provide maximum safety. Other models such as Miele provide cold water washing for delicate wares. Other mode such as half load uses a small amount of the water and energy to clean a small load of dishes. This customization ensures that the safety of the user is maintained at an all time as well as other variables such as energy consumption and cost.
Another important safety feature that comes with modern dishwashers is the anti-leak safety. The design consists of a safety drip pan that holds water in case of a leakage. The safety pan contains sensors that automatically shuts down the wash cycle and prevent further damage in case of a leak.
Other designs have in-built water softeners that work with special dishwashing salts to avail soft water for the washing cycles. This feature significantly reduces fogging and etching to glassware and increase the potency of the dish detergent. An in-built detergent dispenser is contained in an internal reservoir and is released automatically when the washer is activated. The dispenser can hold a thirty day worth of detergent thereby increasing convenience to the user and conserving the detergent usage.
CONCLUSION
Dishwashers are an important component for both commercial and home use. The designs of dishwashers are dependent on a host of factors including safety, efficiency, performance and power consumption. The design of individual components such as the spray arms are complex, but the understanding behind their design is fundamental for the development of a workable device. The design should be founded on the individual functioning of all the parts and the anticipated scenario. This leads to manufacture of efficient systems that optimize the resources, save energy, improve performance and, please the user.
References
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