Washing dishes is not the most rewarding task. Cooking can be creative, but cleaning up afterward seems like a waste of time and leaves the person washing complaining about "dishpan hands." The development of the dishwasher has helped relieve some of the monotony, as well as the grease and grime. It operates on a simple principle of washing dishes that have been placed on racks inside the machine with multiple jets of water. The modern dishwasher has features that cater to fine glassware or the toughest pots and pans; multiple cycles that clean, sanitize, and dry; and under-the-counter or stand-alone models for every size, use, and price range. It is far from perfect; tough foods may need personal attention before and after dishes and pans are cleaned in the dishwasher, and few owners of crystal glassware and fine china are willing to trust them to a machine. But the dishwasher, like other kitchen appliances invented and improved in the twentieth century, is a fixture in many kitchens of the twenty-first century.
The major obstacle to washing dishes has always been the availability of water. Early civilizations used limited numbers and types of dishes, utensils, and cookware and carried them to streams, ponds, or troughs of water for cleaning. The second choice was to carry the water to the dishes. Women carried water in buckets from communal water sources or from private pumps behind their homes or apartment buildings into the early twentieth century, when indoor plumbing finally brought water indoors, not only for bathing but for kitchen use as well.
The first dishwashers were patented in about 1850, but, like machines for washing clothes, they were large contraptions that used steam power and supplies of heated water to soak many dishes at a time. In some models, the dishes were held on cradles that rocked through the water; others had paddles that sloshed water around the dishes or circular racks that held the dishes and rotated to circulate them through the water. An assortment of propellers, plunging casings bearing the dishes, and plungers that drove water over the dishes were incorporated in other machines. In 1875, C. E. Hope-Vere created a machine that directed sprays of water toward racked dishes; the idea of the water jets was adopted by other inventors including A. W. Bodell, whose model was introduced in 1906. Another, the Blick machine, used a propeller that sprayed jets of water over racks filled with dishes. This basic idea is the one used today.
The first publicly displayed models were introduced in about 1915, but the dishwasher was not widely manufactured and sold to private families until about 1930. The dishwasher was not an immediate hit. The refrigerator was introduced at about the same time and swept America; but this is logical because food preservation is far more important than dishwashing. The machines were also too inefficient to completely eliminate hand work; to be fair, this was not entirely the fault of the dishwashers—soaps of the day were not suited to the task. By the 1950s, special dish-washing soaps that clean without sudsing and rinse away began to be developed especially for dishwashers, and the public began to demonstrate more interest. The automatic dishwasher is still not an absolute in every kitchen, but, by the 1970s when more women
The major components of a dishwasher are made of steel and plastic. The basic structure consists of a steel frame assembly and a steel door panel. Sheets of stainless steel are purchased and fabricated in the required pieces and shapes in the factory; both the door and the wrap-around cabinet for standalone models are purchased as coiled sheet steel that has been prefinished in several standard colors. Other small steel parts are designed in house but made by suppliers to the manufacturer's specifications.
The racks that hold the dishes are also made of steel, but it is delivered to the factory as coiled wire. To coat the rack tines to prevent them from scratching dishes, the racks are dipped in plastic in the form of powder polyvinyl chloride (PVC) or nylon.
The inner box that holds the racks and the washer arms is called the tub. It is a single piece (not counting the piece lining the inside of the door) that is injection-molded in the plant. The injection molding is done with pellets of calcium-reinforced poly-propylene plastic. This plastic is respected for its strength and for the fact that it is inert; that is, it won't react with chemicals like those in detergents and is resistant to water and heat. Many other parts including the basket for cutlery, containers for detergent, and the wash tower and spray arms are also injection molded.
Motors, pumps, and electrical controls and components are made by subcontractors in accordance with designs by the dishwasher manufacturer.
The engineers who design dishwashers are interested in improving two key features of their products. Efficient cleaning is, of course, the biggest marketing feature, but consumers are also interested in quiet operations. Cleaning systems consist of a wash tower and sprayer arms, but the openings, the power of the water pump, and positions of racks relative to the washers are all design elements. In the late 1990s, consumers became increasingly interested in the dish-washer as a tool for sanitizing dishes, so design efforts have been aimed at adding heating methods for killing germs.
Manufacturers have taken different approaches to keeping their dishwashers as quiet as possible. Maytag, for example, uses a single, powerful motor for all operations and wraps the outside of its machines with heavy insulation. By contrast, Amana Appliances has equipped its dishwashers with two motors (one to operate the water pump and another for the drainage system). Together, the two motors have the same horse-power as single-motor units, but less insulation is needed for quiet operation.
Design of the exterior of a stand-alone model is somewhat more sophisticated because it has to have an attractive outer cabinet. Usually the top of the stand-alone dishwasher is a wooden cabinet top so the machine will function as a spare work surface.
The Manufacturing Process
- A dishwasher begins to take shape with the injection molding of the tub. Two molds—the cavity relief mold for the outside of the tub and the core relief mold for the inside—have previously been etched into a steel tool, that, when fitted together, contains a void or space that is the shape of the tub. The tool halves are held together in the chamber of the injection molding machine. Pellets of polypropylene are melted in the machine at high temperature and injected by pressure into the void in the tool. The high pressure and liquid state of the plastic forces the plastic into every pocket and crevice in the mold inside the tool. The tool opens to release the tub, which is still hot.
- The warm tub is conveyed to a cooling area and cooled to a temperature that is easy for assembly workers to handle. Other plastic parts are also made by injection molding, and these smaller pieces are stored in bins (with one kind of part only per bin) that can be moved to the assembly area as needed.
- In another part of the plant, the steel components of the dishwasher are made. Outer cabinets for stand-alone models and the doors for all models are cut and stamped into shape from stainless steel in the form of coils that are prefinished on one side. Flat steel bars that will be assembled into the dishwasher's frame are sheared to length. The racks are also formed with tools that trim, de-bur, and shape wire into the racks in two welding steps. The perimeter of the rack is called the "mat," and a tool welds all the wire pieces of the mat together at the same time. Similarly, the little pieces or tines that support the dishes are welded into place simultaneously. The completed rack is taken by conveyor to a cleaning station where it is cleaned and prepared to receive its PVC coating. The PVC is in the form of a fine powder that is baked onto the rack. The coated rack is then cured to finish forming the PVC coating and to allow it to cool.
- Dishwashers are assembled at work stations along an assembly line. The workers are responsible for sets of pieces that are taken from bins alongside the workers. The frame is assembled first, and the motor or motors are attached to special mounts on the frame. The motors are provided to the line workers as completed assemblies. The tub is fitted and fastened into the frame over the motor or motors.
- With the tub in place, the interior components are installed beginning with the filtering system. The washtower and arms are attached followed by sets of rack rollers to support the racks and allow them to be rolled in and out of the machine so that dishes can be loaded easily. The racks are put in place along with the cutlery basket.
- The door assembly is completed by installing the detergent dispenser and rinse-agent cups and the controls. The door is attached to the front of the dishwasher. The exterior is completed by finishing the electrical connections and feed lines (for clean and dirty water), and the exterior is insulated to reduce noise and the effects of heat that might warp counter tops and cabinets. Insulation is prefabricated with the insulating fibers wrapped in a foil-like covering. Called "bagged insulation," it is wrapped around the machine and packed inside the toe space. Under-counter models are now complete. Stand-alone models are finished by attaching the wrap-around cabinet and wood top. Each completed machine is loaded onto a cart to be moved to the packing area.
- In the packing area, styrofoam bumper sections are placed along the edges of the machine and enclosed by a carton. Packets of instructions and other materials are placed on top of the machine in the carton, and the carton is sealed and moved to a storage area for shipping.
Quality control is assured by three basic processes. First, the assembly line workers are trained in quality issues and can reject parts or partially assembled machines. Second, the assembly process is overseen by line supervisors; when assembly is complete, quality engineers inspect the finished machine and test selected units. The most important part of the quality control process may be a design step that Amana Appliances calls a failure mode effects and analysis (FMEA). As soon as problems are observed during assembly or are reported by customers through the warranty process, corrective steps are taken. The analysis is a highly regimented learning process that continuously cycles improvements, customer feedback, and corrective actions through the marketing and design process so new models and lines benefit from any changes to the old.
Dishwasher manufacturers produce a range of lines of dishwashers and other appliances but no true byproducts. Waste is virtually eliminated by a thorough recycling program that includes metals, plastics, and paper.
All industries struggle with the issue of how to attract more customers to their product. For dishwashers, the market is still growing because it is a more open field than for other appliances. Marketers discuss this in terms of market penetration; for example, 99.8% of American households own refrigerators, but only 56.5% have dishwashers. This seems promising for dishwasher manufacturers, but it shows that potential customers who don't have dishwashers may not see that these appliances provide benefits over hand-washing dishes. To attract customers, the latest advance in dishwasher manufacture is the sanitization option with a high heat cycle to kill bacteria. Quiet operation, energy efficiency, and clean dishes without prerinsing are existing features that are continuously being improved.
Where to Learn More
Cohen, Daniel. The Last Hundred Years: Household Technology. New York: M. Evans and Company, Inc., 1982.
Weaver, Rebecca, and Rodney Dale. Machines in the Home. New York: Oxford University Press, Inc., 1992.
Amana Appliances. http://www.amana.com (August 2000).
— Gillian S. Holmes