The Earliest Bulldozers

Ever since humans began modifying the surface of the earth, there has been a requirement to move earth and rocks, particularly to fill holes or push material over an edge. While it could be accomplished using hand tools, this method required significant effort and time. The challenge was to find a mechanical solution to this labor-intensive task.

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Initially, horses were quite effective at pulling machinery and performed adequately with pull graders that spread material behind them. However, the real puzzle was how to get horses to push material forward.

The specific year of invention and the name of the inventor have faded with time, but during the mid- to late-1800s, a device was created to address this challenge. Although the details varied, the basic design involved a long beam with a perpendicular, vertical blade at one end, and an axle and teamster’s seat at the other. Horses were hitched to both sides of the beam, providing an efficient way to use horse power to push material ahead. The earliest known examples were created around 1880, and these early “bulldozers” continued to be produced into the early 1920s.

As crawler tractors began to be utilized in agriculture and logging in the late 1910s, their applications naturally extended to construction. These powerful machines proved to be superior to livestock for pulling wagons and scrapers. Reports suggest that Benjamin Holt tested a blade on the front of a steam tractor as early as 1902 and experimented with a blade on a crawler tractor in 1916.

It is believed that the first effective use of a dozer blade on a crawler tractor was created by the LaPlant-Choate Manufacturing Company in 1920 for the City of South Milwaukee garbage dump. This blade couldn’t be lifted or lowered, merely flipping up and dragging on the ground when reversing, similar to blades on horse-powered dozers.

As the concept of a tractor-mounted blade developed, so did design variations. An adjustable angle dozer was developed for moving spoil to the side. Several manufacturers referred to these as “trail builders” due to their effectiveness in cutting roads and trails along slopes. Other dozers were created for specialized tasks like land clearing, push-loading scrapers, mine reclamation, and handling large volumes of bulk materials. With the advancement of hydraulics, versatile six-way dozers that could be angled and tilted became widely used.

Over time, the crawler tractor became synonymous with its bulldozer attachment, and many models are now designed specifically for dozing tasks.

Bulldozer

Bulldozer

Background

In the 1920s, bulldozers, often referred to as dozers, rose to prominence and have been indispensable ever since. Derived from crawler tractors, these machines are crucial in almost every construction site worldwide.

The primary manufacturers of bulldozers in the United States include Caterpillar, John Deere, and Case Tractor Company. Bulldozers serve various industrial roles, such as in construction, waste management, and agriculture.

Raw Materials

Bulldozers and crawlers, known for their large blades and versatile tracks, consist of numerous structural, hydraulic, and engine parts. The core body, including the mainframe and undercarriage, is fabricated from low carbon structural steel plates and a massive casting. The cab, enhancing the operator's comfort, incorporates glass, rubber, and plastic. The engine, enduring high operating temperatures, includes many high-strength steel parts. Other crucial components like the blade, power train, and various system components are made from structural and high carbon steel. The tracks, consisting of standard-grade steel links, add to the machine's substantial weight. When filled with fuel, hydraulic fluid, coolant, oil, and other fluids, a dozer's weight increases significantly. Finally, decorative trim, decals, and paint complete its distinct appearance.

Design

Two notable features define a bulldozer: the large, vertical steel blade in front and the rotating twin tracks for movement. The blade, weighing up to 16,000 lb (7,264 kg), effectively moves materials. Attached to the frame by a long lever arm, the curved blade can tilt and move vertically under hydraulic power.

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The familiar flexible track of a bulldozer is extensively used in industrial equipment and military tanks. Farming tractors, often considered bulldozer cousins, also use flexible tracks instead of standard wheels. The steel links, sometimes over 2 ft (61 cm) long, are connected with lubricated pins to ensure smooth motion and stability. Additionally, many bulldozers feature an elevated sprocket design that enhances terrain responsiveness. Thanks to the diesel engine generating 50-700 horsepower, bulldozers can navigate rough terrains and steep slopes with ease.

Above the flexible tracks, the operator cabin houses complex hydraulic mechanisms to control the blade within a limited vertical range. The cabin design has seen numerous enhancements for operator comfort and ergonomics, including features like air conditioning, AM/FM radio, automatic seat adjustments, electronic controls, and system-monitoring equipment. In these design aspects, bulldozer engineering and research closely align with the automotive industry.

The power train, including the transmission, differential, and gears, enables track rotation. Connected to the engine crankshaft, the power train transmits power to the elevated sprocket gear. Modern bulldozers often feature independent steering, allowing each sprocket to maintain full power during turns. Recent innovations also include differential steering, hydraulic power, and planetary gear transmissions.

The Manufacturing Process

The assembly of a bulldozer, composed of numerous steel components, complex systems, and intricate assemblies, begins on an assembly line. Before the final assembly, extensive machining, fabrication, and sub-assembly occur. The process starts with engineering prints and drawings from a computer-aided drafting (CAD) program, which outlines the method for constructing each component. Some programs set up machines for fabrication cells, machining centers, and sub-assembly lines, a process known as computer-aided manufacturing (CAM). These components undergo various stages such as heat treating, annealing, or painting. An overhead conveyor system transports these pieces to the rough paint or powder coating operation and then to the main assembly line. Alternatively, pieces may be transported by lift truck, hand cart, or floor conveyor.

Mainframe core

• The mainframe core, forming the rigid inner body, is cut from steel plates and shaped to resist high impact shocks and torsional forces associated with a dozer. The structural skeleton, formed by welding steel plates to machined casting, comprises two boxed-in rail sections connected to the main casing. Performed in a fabrication cell, plates arrive ready for mounting into fixtures and are manually or robotically welded to the stationary central casting. Too massive to lift by hand, the frames are transported by overhead crane to stations where steel mounting blocks and trunions are welded on to support other bulldozer components. Once completed, the frame is rotary sanded, painted, and sent to the main assembly line.

Diesel engine and transmission

• On the assembly line, the independently manufactured diesel engine and transmission are joined with the mainframe. These engines, used in various vehicular applications, arrive fully assembled and performance-tested. The engine mounts in front of the bulldozer and connects to the transmission at the back via a long shaft supported by couplings and bearings. The transmission then connects to a series of gears and differentials, completing the power train. Bolted to the base on the main assembly line, the engine/transmission assembly is mounted on pre-welded pads.

Radiator and additional assemblies

• An engine casing on the bulldozer's front supports the radiator and hydraulic lifting cylinders. The radiator is mounted between the engine casing and the front drive shaft, connecting to water lines from the engine. Hydraulic, lubrication, cooling, and fuel system assemblies, pre-assembled and mounted on the engine or base, are brought to the main assembly line for final connections. These include tubes, hoses, and fittings linked to pumps, valves, tanks, and cylinders. Inspected for dimensional compliance at an incoming inspection station, these components are readied for assembly.

Large component assembly

As the frame, engine, transmission, and line assembly move along the production line, larger components such as the cab, hydraulic cylinders, undercarriage components, and the blade are brought in by overhead cranes, conveyors, AGVs, or lift trucks.

• The cab, typically manufactured at a different facility, and complete with electronics and controls, is mounted on steel blocks on the dozer frame. Connections are made to various controls and the power supply.
• Concurrently, the undercarriage, comprising tubular roller frames, drive sprockets, and suspension rollers, is mounted and assembled to the drive train. Sprockets, 2 ft in diameter, fit into the tracks with case-hardened teeth that rotate the track. Steering and attachment of bearings and lubrication bushings may involve outsourcing. Pre-assembled tracks are fitted around the drive sprockets and rollers after engine/transmission and undercarriage installation. The exhaust stack is supported by brackets and flanges at its base.
• Hand or guard rails and foot pegs complete main line assembly once cab controls connect to the engine and hydraulic systems, and body panels fold back for easy maintenance. Tooling and storage boxes may also be incorporated after all connections.
• Steel pins attach the front blade to hydraulic cylinders for vertical movement. Left unattached during initial assembly, these cylinders are secured post-blade assembly to fit hydraulic lines. Under-carriage arms are then attached to the blade.

Final assemblies

• More hoses, electrical lines, and fluid lines are installed, depending on the design. Components like the engine starter, batteries, and lights are connected. Once the final assembly is complete, the hydraulic lines are fitted and connected tightly. The track is finally attached to ensure smooth movement and position. Foot pegs and other ergonomic components are affixed at this stage to ensure operator comfort.

Paint

• At Caterpillar's Track-Type Tractor (TTT) division in Peoria, Illinois, bulldozers and crawlers undergo the same meticulous paint process. Applied manually with spray guns, the final layer of paint is evenly distributed over the surface, with areas that need protection covered. The paint dries quickly, after which decals and trim are added using hand templates.

Fluids

• Various fluids, including fuel, oil, and hydraulic fluid, are added to the bulldozer before it undergoes a series of mechanical tests to verify the system's operations. Once successfully tested, the dozer is transported to a staging area for any final customization before being shipped to its destination, ready for use upon arrival.

Byproducts/Waste

During the manufacturing process, wastes like machining coolants, oils, parts-cleaning detergents, paint, and diesel fuel are produced. The United States Environmental Protection Agency (EPA) enforces strict regulations to ensure proper disposal of these potentially hazardous materials. Manufacturers typically hire waste removal firms to recycle most liquid waste, and metal chips and shavings are sold to scrap dealers to minimize waste.

The Future

Continuous advancements in bulldozer component design are inevitable, focusing primarily on cab comfort and diesel engine efficiency. Component innovation and operational enhancements will likely drive changes, improving both the manufacturing process and material flow. As an indispensable earth-moving tool, the bulldozer will maintain its vital role in construction, waste management, and various industries.

Where to Learn More

Books

D7R Track-Type Tractor Specifications. Caterpillar, 1996.

D9R Track-Type Tractor Specifications. Caterpillar, 1995.

DllR Track-Type Tractor Specifications. Caterpillar, 1996.

—JasonRude

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