Play Time

It may be a cliche, but few materials match the versatility of plastic. Engineers can create various formulations that are light, strong, rugged, tough, durable, stiff or flexible, inexpensive, and manufacturable--just the sort of stuff you want to use for making children's outdoor toys.

In April, The Wall Street Journal reported a growing interest in backyard toys, including several examples of homeowners installing commercial play equipment. To answer the call of rising demand from these and their more conventional customers--schools and parks--manufacturers are increasing their ability to design and produce ever-larger and more complex plastic components. At the same time, traditional toy companies continue to respond with ever more numerous and creative products for baby boomers' kids.

Here are a few examples of the latest in outdoor toys and play equipment, and the stories behind their design.

Bigger is better. Big Foot is a prime example of what engineers can create using advanced polymers and manufacturing techniques. No, we're not talking about the mythical Sasquatch. Big Foot is the latest one-piece slide produced by GameTime (Fort Payne, AL), one of the largest producers of commercial park and playground equipment.

Big Foot features triple bedways--slides, in layman's terms--molded into a single 78 x 150-inch, 275-lb plastic part. Each slide is slightly different. One has ridges, one has bumps, and the third has banked "S" turns.

"It's the largest one-piece slide in the industry today," says William Page, GameTime's vice president of operations. Others, including GameTime, produce double slides, "but the market was calling for a product with an additional play event," he says. "They want one-piece parts, because the more parts you have to put together the more problems you have."

Seeing a future in ever larger components, the company invested in the construction of a completely new facility. And to decorate its new buildings, it purchased a few of the world's largest carousel-style rotational molding machines, Ferry Industries' (Stow, OH) Rotospeed(TM) Model RS-500s.

The RS-500 features independent arm movement to accommodate high-volume production, and provides for a complete segregation of the heating, cooling, and servicing process functions. Its 7,500-lb capacity easily accommodates Big Foot's 4,066-lb mold.

The molding tool itself is one of the largest made, claims Page. Constructed by the Wheeler Boyce Co. (Stow, OH), it's all aluminum and coated on the inside with a Teflon-based material, Stone Coat 7000 from E. L. Stone (Barberton, OH).

The use of Teflon presents some interesting process challenges. "A lot of people won't use it because of warpage," says Page. He considers overcoming the warpage issue a suitable price to pay for the high sheen Teflon imparts on the finished product.

The potential for warpage arises when a part is pulled from the mold and it releases from different areas at different times. "You can end up with a potato chip if you don't know what you're doing," Page says. GameTime addresses the warpage problem by using air to hold the plastic material firmly against the wall of the mold.

The slide is constructed of Petrothene(reg), a linear low-density polyethylene produced by Equistar Chemical (Houston, TX). It was selected for this application because Big Foot didn't need the strength of high-density polyethylene, and the improved flow helps with rotomolding. "We keep coming back to this material because it meets all our needs from a safety standpoint," says Page, "and the material's excellent flow helps us from a design standpoint."

Handling shrinkage. Big Foot wasn't the company's only breakthrough product for 1998. Leveraging the same advanced rotomolding facility, engineers created MegaRock(TM), a one-piece, boulder-like scrambling platform for tiny climbers.

"MegaRock is very interesting from a rotational molding standpoint," says Page. It's produced from the same Petrothene polyethylene used in Big Foot, and like any polyethylene, it shrinks as it cools. Typically, engineers can design a fixture to hold a component's shape as it shrinks in a critical direction. "Because of the complex shape of the rock surface, this thing wants to shrink in every direction. This was a real challenge," he says.

The climbing platform measures 115 x 76 inches and weighs 275 lb. It requires a slightly smaller mold than Big Foot, but at 4,400 lb., the mold weighs slightly more. As with Big Foot, MegaRock leverages the increased capacity of the new Ferry RS-500 rotomolding machines.

Page's engineering team worked for several weeks longer than normal to solve the shrinkage problem, ultimately applying some proprietary techniques which he won't disclose. However, much of their effort was spent adding or modifying radii in critical areas to improve material flow. The situation was exacerbated by the need to mold the skeleton of a dinosaur into MegaRock's bottom side. "My concern with the fossil was that it would get blow holes in areas near the ribs," he explains. "It didn't. The material worked great."

Littlest leaguers get a leg up. Anyone who has fungoed baseballs knows that the difficult part is getting the toss right. This coordination of hand and eye, bat and ball can easily exceed the capabilities of very young players. To help these pre-little leaguers develop their batting skills, Little Tikes (Hudson, OH) invented the 3-in-1 Baseball Trainer. Its multiple components are constructed from a variety of plastics, each selected to address a particular design requirement.

The baseball trainer itself is an outdoor toy that can be configured in three different ways depending upon the child's skill. The base and foot pedal can be used alone to pop up balls into the air for hitting. Or, the tube and tee can be attached so that balls are launched up the tube and roll out onto the tee. Lastly, the tee can be rotated 180 degrees so that an adult can operate the foot pedal for a child.

As with any toy, durability is a primary concern. Engineers targeted a product life of 15,000 cycles. And to create a foot pedal that would survive 15,000 stomps, they injection-molded it from Chevron Chemical's (San Ramon, CA) Valtra(reg) ABS. "This component sees the highest forces," says Paul Madan, senior product engineer at Little Tikes. "It's the only part that we ran a load analysis on."

The base and tube are formed from polypropylene acquired from several different sources."They didn't need the strength of the pedal, and polypropylene is quite a bit cheaper than ABS," Madan explains.

The biggest challenge came from the tee. Not only does it have to withstand being struck by the plastic bat, it also had to hold its shape in the summer heat. "We started using PVC," he says, "but the tee would droop so far that when you launched the ball it would roll right off the end."

Engineers then turned to urethane, but had the same heat-deflection problem. And then they looked at a polyolefin elastomer, but it was too stiff. Finally, they settled on Vistaflex(reg), a thermoplastic elastomer from Advanced Elastomer Systems (Akron, OH) that had the desired durometer--mid-70s Shore A--and could be injection-molded like plastic.

Though the materials were selected, Madan's job still wasn't over. Numerous trial-and-error runs were needed to develop the internal contours of the cap at the top of the tube so that the ball would neither shoot out and off the end of the tee, nor ricochet back down the tube. Then, the baseball trainer's final seal of approval came from a small staff of in-house product testers located in what must be kiddie heaven--the toy manufacturer's own day-care center.

Plastic armor. Commercial playgrounds must withstand the pounding and rubbing of thousands of little hands and feet. It's doubtful that many see more action than the ones incorporated into McDonald's restaurants.

Such a playground at the McDonald's in Lys-les-Lannoy, France not only contains numerous plastic components, it also uses plastic on some of the metal components. Perforated sheet metal parts were powder-coated with Abcite(reg), a thermoplastic, reversible, cross-linked copolymer from DuPont Engineering Polymers (Wilmington, DE).

Powder-coating with Abcite addresses a problem which can crop up during assembly of the playground. Fastening sheet metal with screws can damage conventional coverings such as paint or shrink film, exposing the underlying metal and leading to possible corrosion. Even galvanized steel has its limits. In open-air playgrounds exposed continually to sun, rain, and pollution, deterioration of the installation can result in costly repair. A faded, rusty playground is also less than enticing to children and parents.

The factory applied Abcite using the fluidized bed dripping process. This provided good edge coverage of the perforated plates forming tower compartments that lead to the playground's slides. The coating required just a single application, and yielded a 600-micron-thick layer of the material. Essentially the same covering found on many golf balls, Abcite is nothing if not durable. But designers also liked the smooth, plastic feel it lent to the metal and its thorough edge coverage that prevents corrosion.

Polymer toughens toy Jeep. Recent Saturn commercials have touted the dent-free advantage of making automobile door panels from plastic, a benefit the makers of toy cars have known about for years. An example is the Power Wheels(reg) (Fort Wayne, IN) Jeep(reg) ride-on vehicle for children that contains injection-molded body panels made from Amoco (Alpharetta, GA) ACCTUF impact copolymer polypropylene. Engineers at Power Wheels selected the material based on its performance, processability, and reasonable cost, claims Amoco.

"We pride ourselves in setting the industry standard against which all other battery-powered ride-ons are measured," says Mike Restaino, plastics engineering manager for Power Wheels. "To remain the leader, we continually look for ways to upgrade our product as new materials and technology become available." ACCTUF, according to Restaino, provides the Jeep with a smooth surface and exceptional colorability. The material also has excellent properties at high melt-flow rates for easier molding of complicated parts and less molded-in stress.

Amoco claims that a proprietary gas phase process gives ACCTUF copolymers unique impact properties. Regardless of the reason, Restaino agrees. "The Amoco material has much better low-temperature impact resistance than other polypropylenes we've evaluated," he says. "That's very important to us because many of our products are shipped during the winter."

For more information

To speak directly to a company representative, call 1-800-828-6344 X 011 and key in the specific product code.

Thermoplastic elastomers from Advanced Elastomer Systems (M) Product Code 4348

Polypropylene from Amoco Polymers (M) Product Code 4349

ABS from Chevron Chemical (M) Product Code 4350

Polyolefin plastomer and polyethylene from Dow Plastics (M) Product Code 4351

Abcite(reg) from DuPont Engineering Polymers (M) Product Code 4352

Polyethylene from Equistar Chemical (M) Product Code 4353

Rotomolding machines from Ferry Industries (M) Product Code 4354

CYBER CONTACTS

You can reach the following companies mentioned in this feature on the Internet at the listed Web address. Please tell them that you were referred by Design News.

Advanced Elastomer Systems: www.aestpe.com

Amoco Polymers: www.amoco.com/what_we_do/chem/04_polymers.html

Chevron Chemical: www.chevron.com

Dow Plastics: www.dow.com

DuPont Engineering Polymers: www.dupont.com

Equistar Chemical: www.equistarchem.com

Ferry Industries: www.ferryindustries.com

GameTime: www.gametime.com

Power Wheels by Fisher-Price: www.fisher-price.com

Little Tikes: www.littletikes.com