Apr 11, 2017

Hard Case: Composite-Based Transmission Case

Hard Case: Composite-Based Transmission Case Delivers Hard-to-Beat Performance in Lawn Tractors, Snow Throwers.

Every fan of the sport of boxing knows what it means to say someone has a “glass jaw.” It’s a negative term, used to describe a boxer who goes down easily in a match, usually due to a hard punch to the jaw.

Hardier fighters often get labeled as “iron-jawed” by the sporting press. A more modernized term might be “glass-composite jawed.”

Glass composites, in other words, can make for a hardy material.

Gear-heads can debate endlessly over the relative values of composite (read: plastic!) versus metal construction for mission-critical parts such as engine intake manifolds and transmission cases in moving vehicles of all types: cars, motorcycles, lawn tractors and so on.

On at least one point, that of glass-composite-based transmission casings for lawn tractors, General Transmissions (GT) lands a knockout punch on critics who may argue that such components are best left to the metal merchants.

GT’s composite-based transmission housings, found on both the RS 800 and RT 400 continuously variable transmissions (CVTs), are built to go the distance for lawn tractor and snow-thrower owners. As GT describes it, the company first proved out its practice of using composite parts in transmissions designed for traditional walk-behind mowers. The concept stood the test of time: manufacturers have built and sold more than 20 million walk-behinds worldwide equipped with GT plastic-composite-engineered transmissions. The CVT transmissions withstand the elemental forces of high heat and withering cold without so much as a whimper. Moisture never seeps through these impenetrable shells and ordinary lawn debris – pebbles, twigs, shards of ice – bounce harmlessly off their sturdy frames.

GT borrowed a page from the playbooks of the automotive industry in producing a composite-based transmission for lawn tractors and snow throwers. To wit, automakers know that the fewer moving parts to any component, the better. Even a product as basic as a transmission housing – nothing new there in terms of functionality – benefits if parts are kept to a minimum. To that end, GT locks its injection-molded housing components in place with a small battery of bolts for maintenance-free performance throughout the life of the machines to which they are attached. 

The result is a pound-for-pound advantage for GT transmissions over the more traditional metal-made housings of the competition. Using composite materials allows GT to offer up a lighter-weight transmission component, which translates into less strain on the engine – and more power to the wheels for tasking jobs such as maneuvering lawn tractors up sharply sloped inclines, or powering a snow-thrower through compacted snow.

The automotive industry pioneered the use of hardened composite materials for use in exterior body panels, beginning in the 1940s – really at the dawn of the plastic age. And make no mistake: as much as today is the “digital age,” it is also the “plastic age.” Plastics in a sense make the digital age possible. Few people would want to haul around a steel-encased cell phone, certainly. 

Carmakers have long understood the advantages of using plastic and composite-based materials to boost vehicle performance. Consider that the first Chevy® Corvettes, introduced in 1953 by General Motors, featured fiberglass exterior body panels, as opposed to the more standard sheet metal shells of the day.

In today’s world, the automotive industry embraces plastics and composite materials as key to delivering more fuel-efficient, environmentally friendly products. The automakers are under constant regulatory pressure to improve their efficiency ratings, motivating them to explore alternatives to metal components at every stage of vehicle development. Driven to build lighter-weight cars and trucks, the industry has embraced plastics and composite materials to such a degree that about 10 percent of the total weight of cars today consists of synthetic materials. Plastics composites compose much of the typical car’s interior today, along with some portion of the body panels, bumpers and even engine hoods, roofs and rear lift-gates.

The plastics industry is also picking up the pace on introducing components made of composite materials in areas such as the powertrain. Some late model Audi® R8 sports cars incorporate a transmission oil pan made of glass fiber-reinforced Durethan® thermoplastic material. The composite-based oil pan is lighter in weight and lower in height than the metal pan it replaced.

Industry insiders see the automotive industry adopting composite materials for an ever-increasing number of powertrain components. Over the next decade, the industry could see the gradual adoption of composite-made piston cylinder housing. Fully composite engine blocks may not be far behind. And as the automotive industry goes, so goes the outdoor power equipment industry, in many cases.

But one supplier to the outdoor power equipment industry, General Transmissions, has the automotive industry beat when it comes to making composite-based transmission parts.

When NASA’s planned Orion spacecraft blasts off sometime in the next decade, it will be equipped with an all-composites heat shield capable of withstanding temperatures as hot as 5,000 degrees Fahrenheit.

The Orion heat shield consists primarily of a carbon-fiber based composite material, developed especially for the rigors of space travel. Massive as the shield must be to protect the craft and the space travelers inside, a carbon-based solution must have been the only feasible option for NASA engineers. Imagine the weight difference between tungsten, the metal with the highest known melting point (6,192 degrees F) and carbon (melting point, 6,422 degrees F, although carbon technically sublimates [turns into a gas] at 6,917 degrees F rather than melts).

The aerospace industry has a long history of embracing plastic components for any number of uses, ranging from cabin seating, railings, and pull-down trays to structural components such as engine nacelles (the engine housing on aircraft), engine fan casings, turbine blades and even the airframes themselves. The Boeing 787 Dreamliner family of jetliners provide a virtual showcase of advanced plastics engineering, comprised primarily of sturdy and lightweight carbon-fiber composites (lightweight in contrast to sheet-metal alternatives in any case).

Most people have heard of Kevlar®, a patented plastic compound developed by DuPont® in 1965 and used today in making bulletproof vests for police officers, among other uses. But the ever-innovative chemicals industry has now produced a composite-based bulletproof ballistic helmet that can stop a bullet fired from as close a range as three-quarters of an inch. It can also protect the wearer from multiple gun shots, making it a likely product for military personnel as well as police and other first-responders.

These are all examples of highly specialized uses of plastic materials, but plastics permeates the modern world, often under the guise of trade names that obscure a product’s plastic roots. Everyone has heard of “vulcanized rubber” automotive tires, for example. Vulcanization produces a rubbery compound (plastic) that can absorb the rude shocks of the road without breaking apart. And if you wonder how Goodyear Tires got its big edge in the marketplace, then you should know that Henry Goodyear is credited with inventing the vulcanization process in 1844.

What would domestic life be like without Saran™ wrap? Dow Chemical Co. introduced Saran Wrap in the early 1950s, giving thrifty consumers a hand up on saving leftovers from their Sunday dinners. The food industry already had a version of plastic packaging: cellophane, a tough, flexible and transparent plastic film invented by Jacques E. Brandenberger, a Swiss textile engineer, early in the 20th century.

The leisure suit craze of the 1970s almost destroyed the image of polyester, another plastic fantastic material that started finding favor with clothing-makers after DuPont brought Dacron® polyester duds onto the scene in 1951. But polyester outlasted the rise and fall of the leisure-suited legions of the Disco Era. Plastics also legged out a victory in the women’s accessories business in the 1940s, following the invention of nylon (also invented by DuPont).

Materials such as polypropylene, high-density polyethylene (commonly known as HDPE) and polyethylene terephthalate (PET) galvanized advances among industrial goods manufacturers, from the aforesaid automotive and aerospace industries to medical devices, information technology, industrial packaging, housing, oil and gas, outdoor power equipment, motorsports – almost any industry you can think of relies on plastic materials to keep it going today. 

The automotive industry looks to the plastics material makers to continue to help lighten the load of its products – and wring out production costs at the same time.  The industry steps up, taking over more and more of the content of vehicles. Look for more advances in the near future, including power train components such as gear housings and even drive shafts. One Tier One supplier is working on a carbon-fiber based vehicle sub-frame.

And then we come back to the outdoor power equipment industry, where there seems to be some debate over the viability of using a glass-composite-made transmission housing for General Transmissions’ lawn tractor and snow thrower CVTs. To that, one might argue that if we can contemplate sending a spacecraft into deep space with equipped with a plastic heat shield, certainly we can trust the plastics industry to produce a material rugged enough to withstand the earthbound challenges of protecting vital transmission parts from the everyday work of mowing the lawn or removing snow, And in fact, General Transmissions has puts its transmission housing through a battery of tests that no self-respecting owner of a lawn tractor or snow thrower would ever think of doing. GT blasts the transmission housings with temperatures as high as 258 degrees F, well in excess of what a transmission will produce under normal operating conditions. (And it’s worth noting that CVTs in general run cooler than other types of automated transmissions, such as hydrostatics and friction disk models.)

The glass-composite housing of the GT transmissions may not be literally bulletproof – but they are certainly proof against most anything that a lawn tractor owner or snow thrower owner will encounter in their day-to-day uses of the machines. (And we’re pretty sure that anyone taking up arms against a lawn tractor or snow thrower would be in violation of the manufacturer’s warranty, not to mention local firearms ordinances,)

Plastic really is fantastic, Larry and his leisure suits aside!