Wheelbarrow

Background

A wheelbarrow is a carrier, usually having only one wheel, consisting of a tray bolted to two handles and two legs. While known mostly as a device for carrying small loads for the household gardener, a wheelbarrow is often also used in construction and industry for carrying larger loads.

The birthplace of the modern wheelbarrow was China, possibly as early as 100 B.C. One early version consisted of a large single wheel at or near the front of a platform. The load would be placed behind the wheel, and the operator would lift the heavy end and push the load. Sometimes a small basket would be used to carry the load, and if it was heavy, a second operator could pull from the front. Another type, probably invented by Chuko Liang in 300 A.D. , had a carrying surface that was basically a large wheel housing that encased the top half of the wheel. A flat platform projected out from both sides at axle level could then carry large loads, people and goods in pannier fashion while the operator steered it. Loads were higher off the ground than those carried in modern wheelbarrows. Chinese wheelbarrows were hence similar to rickshaws in that the goal was to carry heavy loads long distances. Tseng Min-Hsung in 1200 A.D. boasted that "ways which are as winding as the bowels of a sheep will not defeat it."

Unlike Chinese wheelbarrows, European wheelbarrows were designed to carry small loads over short distances. It is difficult to trace the progression of the wheelbarrow from China to Europe. Possibly, Arab traders brought it to the Middle East and Europeans learned of it during the Crusades. Ancient Greeks might have used the wheelbarrow for construction, while the Romans might have adapted it for agriculture. After Rome fell, the wheelbarrow could have remained in use in Byzantium until the Crusaders learned of it during their journeys. However, it is most likely that it was an independent invention of the late middle ages, created by putting a wheel on the two-person handbarrow already in use for carrying such items as stones or sheaves of corn.

The first use of the wheelbarrow in Europe was probably in agriculture; then, it spread to construction, transportation of goods, mining, and brick making. Some wheelbarrows had a wooden, box-like body with feet. Others had a flat slatted or wicker framework with feet. French, Flemish, and Dutch wheelbarrows usually had a rack to rest the load or basket against. Swiss wheelbarrows had solid wheels, while English ones had four feet and spoked wheels. Bohemians of the time also used spoked wheels, but no feet were used to help lower the load. To assist when moving loads, European wheelbarrows of around 1200 A.D. had leather straps that wound around the handles. Operators would slip the straps around their necks.

The wheelbarrow's advantages were that loads could be lifted and carried close to the ground, as opposed to two-person handbarrows that required carrying to be done at waist level. A wheelbarrow carrying a basket of goods could be unloaded quickly and put back into action, although it was too unwieldy at this date to be emptied by simply tilting and twisting it. One person using a wheelbarrow cuts labor costs in half, and it's easier than two people coordinating their movements as they carry a load. Wheelbarrows quickly became items crafted by carpenters to be sold to construction workers. In 1222, records for the king of England's works show that eight wheelbarrows were purchased from the town of Canterbury for construction at Dover.

The modern wheelbarrow can have one, two, or four wheels. These wheels can be either in front or beneath the load. Other conveniences include storage space compartments or side clips to carry tools. Wheelbarrows are considered a necessity for the backyard gardener as well as industry, for they are considered simple, unmotorized, yet effective ways for one person to carry a heavy load.

Raw Materials

A wheelbarrow consists of a tray or bed composed of steel, wood, or plastic. A steel brace attaches this bed to steel support legs and to a steel or plastic wheel, with a rubber tire around it. In two- or four-wheeled models, the wheels may be similar to bicycle tires, complete with inner tubes. Some handles are metal with foam or hard plastic grips, while some wheelbarrows intended for the home gardener have solid wooden handles with no grips.

The Manufacturing
Process

Because wheelbarrows exist in a variety of forms, made from many different materials, manufacturing procedures vary widely depending on the exact kind of wheelbarrow being made. Some wooden wheelbarrows are simple enough to be made with hand tools used by weekend hobbyists with modest carpentry skills. Some heavy-duty wheelbarrows, intended for industrial use, are manufactured with heavy machinery which shapes thick steel sheets. In order to discuss several different techniques used for making wheelbarrows, the following outline will describe the manufacturing of a typical garden wheelbarrow, with wooden handles, steel legs and braces, a rubber tire, and a plastic tray.

Making the tray

• 1 A typical plastic used to make wheelbarrow trays is polyethylene. Polyethylene is formed by linking molecules of ethylene into a long chain. Ethylene is a hydrocarbon which is found in petroleum and natural gas. For industrial purposes, however, ethylene is usually obtained by heating heavier hydrocarbons, obtained from petroleum, in the presence of a catalyst. This process, known as cracking, transforms larger molecules into smaller molecules, such as ethylene.
• 2 The process of combining numerous small molecules into a long chain is known as polymerization. Ethylene can be polymerized into two types of polyethylene. Low density polyethylene, made by subjecting ethylene to very high pressure, is generally used in the form of a thin, flexible film, as in plastic bags. High density polyethylene is much stiffer and is used to make wheelbarrow trays and other rigid items. High density polyethylene is polymerized by subjecting ethylene to a pressure of about 250-500 lb per sq in (18-35 kg per sq cm) in the presence of a catalyst.
• 3 High density polyethylene can be formed into a wide variety of shapes using various techniques. For wheelbarrow trays, it is generally produced in the form of a thick sheet. This can be done by extrusion. This process involves melting granules of polyethylene into a liquid and forcing it through a nozzle. The opening of the nozzle has the width and thickness of the desired sheet. As the liquid polyethylene emerges from the nozzle it cools into a sheet that can be cut to the desired length.
• 4 Sheets of polyethylene are shipped to the wheelbarrow manufacturer and inspected. They are then shaped into trays using a technique known as vacuum forming or thermo forming. This process involves heating the sheet until it is soft. The soft plastic is then placed on top of an open box. The box contains a mold in the shape of the wheelbarrow tray. Air is removed from the box, and the resulting vacuum causes the air pressure outside the box to force the sheet against the mold. The plastic cools into the wheelbarrow tray and is removed.

Making the legs and braces

• 5 The support legs and braces are usually made of steel. Steel is made by combining iron ore and coke (a carbon-rich substance made by heating coal in the absence
  

  A typical wheelbarrow.
  of air) and heating them with very hot air in a blast furnace. The resulting mixture of iron and carbon is known as pig iron. Oxygen is blasted into molten pig iron to remove most of the carbon. The resulting molten steel is cooled into a variety of shapes.
• 6 Strips of steel arrive at the wheelbarrow manufacturer and are inspected. Sharp dies are used to punch various components out of the steel strips using large, powerful presses. Holes are punched into these components to allow them to be bolted into place.
• 7 The steel components are usually painted for protection. A degreasing solution is used to clean the components, which are then dried. Paint is applied using an electrostatic process. The steel and the paint are given opposite electrical charges. The opposite charges attract, causing the paint to cover the steel evenly and completely. The paint is then baked onto the steel in an oven.

Making the wheel and tire

• 8 The wheel may be made of steel or plastic. It is made using methods similar to those used to make other steel parts or the plastic tray.
• 9 The tire is usually made of natural or synthetic rubber. Natural rubber is made from latex, a substance secreted by rubber trees. The latex is filtered to remove foreign substances, and water is added to make the liquid latex thinner. A dilute acid is added to cause solid rubber to be deposited out of the liquid mixture. Synthetic rubber can be made from a wide variety of chemicals. The most common form of synthetic rubber is styrene-butadiene rubber. This substance is made by mixing styrene and butadiene, both derived from petroleum, in an emulsion of soap and water. The two chemicals combine to form synthetic rubber.
• 10 The natural or synthetic rubber is heated until it melts into a liquid. It is then poured into a mold in the shape of the tire. The rubber cools and the tire is removed from the mold. The tire is shipped to the wheelbarrow manufacturer and is placed around the wheel.

Making the handles

• 11 Lumber arrives at the wheelbarrow manufacturer and is inspected. The wood is stored and allowed to dry. It is then cut and shaped by woodworking equipment such as saws and lathes. Holes are drilled to allow the handles to be bolted into place. The wooden handles are then coated with varnish for protection.

Packaging and shipping

• 12 Wheelbarrows are generally not assembled until they reach the consumer. Instead, the components are packaged in strong cardboard boxes and shipped to retailers. By not being fully assembled, the wheelbarrows take up much less space during shipping and storage.

Quality Control

The most important factor in the quality control of wheelbarrows is ensuring that all the components fit together correctly. During the shaping of steel components, each part is compared to a standard part of the same type that is known to be correct. In a similar way, the plastic tray is compared to a standard tray. Wooden handles are compared to a drawing or to a sample handle. The most critical part of this comparison process is ensuring that holes are drilled in the correct positions to allow bolts to hold the wheelbarrow together.

Because a wheelbarrow is generally assembled into its final form by the consumer, it is critical that all necessary components are included in the shipping container. Instructions for assembly must also be included. Large components and instruction sheets are inspected individually to ensure that they are all present. Instead of counting all the bolts to ensure that there are enough included to assemble the wheelbarrow, the manufacturer can save time by weighing a batch of bolts on an accurate scale. A batch of bolts of the correct weight will contain the correct number of bolts.

A sample wheelbarrow can be tested by assembling it, filling it with a load, and moving it around. Factors to be considered in order to produce a wheelbarrow that will satisfy consumers include ease of assembly, ease of motion, stability, ability to be steered accurately, and ability to carry a heavy load with minimal effort on the part of the user.

The Future

The wheelbarrow has changed over thousands of years from handheld carriers with no wheels to modern lawn carts with four wheels. The increasing popularity of gardening as a hobby, combined with the aging of the American population, suggests that wheelbarrows will continue to evolve in ways that will make them more versatile and easier to use.