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This issue of
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An ePublication of the International Association of Plastics Distribution February 2008 | Focus: Cast Nylon |
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Roller Coasters: a Thrill of a Lifetime
REPRINTED FROM THE IAPD MAGAZINE
For many people, there is only one reason to go to an amusement park — the roller coaster! Some people call it the scream machine, and for good reason. The history of this ride reflects a constant search for greater and more death-defying thrills. In fact, Americans spend more than $4 billion annually at amusement parks, with roller coasters being the largest attraction.
What you may not realize as you’re plummeting down the track at near 80 miles an hour is that the coaster has no engine, and you are likely riding on plastic wheels. The car is pulled to the top of the first hill at the beginning of the ride, but after that, the coaster must complete the ride on its own.
The conversion of potential energy to kinetic energy is what drives the roller coaster, and all of the kinetic energy you need for the ride is present once the coaster descends the first hill. The type of composite material used for the wheels has a significant influence on this energy transfer.
Once you’re underway, different types of wheels help keep the ride smooth. Running wheels guide the coaster on the track. Friction wheels control lateral motion (movement to either side of the track). A final set, called underfriction wheels, keeps the coaster on the track while inverted or cresting a hill at negative G’s.
Advancements in roller coaster design over the years meant a need for a quieter, smoother and, of course, a much faster ride! Early attempts included natural rubber coated steel or aluminum wheels. Although the ride was much improved, durability was an issue. Today, the majority of the high speed rides utilize wheel rolling surfaces consisting of specialized urethane or cast nylon formulations. These materials provide the designer with a variety of rolling resistances, load bearing capacities and hysteresis characteristics, that meet the needs of comfort and that important factor — speed!
View the complete article online.
Article was written by by Calvin Petersen, Nylatech Inc.
In This Issue:
Application Focus: Roller Coasters
Plastic wheels keep your roller coaster on track.
Cast Nylon Parts in a Wet Environment
Yes! It can be done, and sometimes the part and application will even be better for it.
About Cast Nylons
Cast nylons provide better dimensional stability, easier machining, and higher compressive and tensile strengths than that achieved by extruding or molding nylon.
Test Your Knowledge
What do you know about nylons?
Online Plastic Resources
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name and fabrication capability searches.
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About IAPD
The International Association of Plastics Distribution, founded in 1956, is an international trade association comprised of companies engaged in the distribution and manufacture of plastics materials.
Members include plastics distributors, processors, manufacturers, resin manufacturers, manufacturers’ representatives and associated products and services, all of whom are dedicated to the distribution channel.
Cast Nylon Parts in a Wet Environment
REPRINTED FROM THE IAPD MAGAZINE
The broad size range availability and low cost of cast nylon make it the material of choice for a wide variety of applications. But can cast nylon parts really work effectively in a wet environment?
The answer is yes! If you design the part knowing the appropriate conditions, cast nylon can perform very well in moist environments. Selecting the right grade of cast nylon may also improve the performance of your part.
Cast nylon does experience expansion due to moisture absorption. This absorption factor affects your part’s mechanical properties. Tensile strength, compressive strength, hardness and friction coefficient will all decrease as moisture content rises. It is interesting to note that parts which require higher notch impact strength or resilience will perform better if they have absorbed moisture, since those properties increase as moisture content rises.
Depending on the moisture content, dimensional changes may also occur. The expansion of cast nylon due to moisture absorption is approximately 0.15 to 0.20 percent per 1 percent absorbed moisture.
In normal ambient conditions (70°F/21°C, 50 percent RH) cast nylon absorbs 1.5 to 2 percent moisture to a depth of 0.040'' to 0.080'' over the course of approximately 40 days. That means that by the time the material arrives on your dock, it will usually not absorb any more ambient moisture. This initial absorption occurs fairly quickly, but additional absorption slows progressively with the depth of penetration.
When submerged in water, cast nylon can absorb up to 6.5 percent water at saturation.
View the complete article online.
Article was written by Greg Waack, ZL engineering plastics-East.
The nylon monomer casting process differs from injection molding or extrusion in that it produces a product by anionic polymerization right in the mold, whereas extrusion and molding processes simply reshape a prepolymerized resin. This process of polymerizing in the mold produces a material with higher molecular weight and crystallinity, and therefore, better dimensional stability, easier machining, and higher compressive and tensile strengths than those achieved by extruding or molding.
The process starts with a lactam monomer; polymerization is achieved by the addition of an activator and co-catalyst which produces a chemical chain reaction to form nylon 6. Additives such as plasticizers and lubricants used to modify or improve the material’s performance are added to the molten lactam before casting. Plasticizers improve the material’s impact resistance while reducing tensile and compressive strengths. Internal lubricants reduce the material’s coefficient of friction and allow materials to perform at PV levels five times higher than unlubricated nylons without the use of additional oils or greases in application. Like plasticizers, they also tend to reduce tensile and compressive strengths.
Cast nylons are used in parts like rollers, bushings, gears, sheaves, sprockets, wear pads, star wheels and many other applications.
For more information on cast nylon and other plastic materials, IAPD’s Introduction to Plastics is an invaluable training manual. Information about it and other IAPD educational resources are available online at www.iapd.org.
What do you know about nylons? Answers are at www.iapd.org/popquiz.html.
1. Which additive improves the stiffness of nylon?
- carbon black
- PTFE
- glass
- colorant
2. Which of the following nylons cannot be cast?
- nylon 6
- nylon 6/6
- nylon 6/12
- nylon 12
Your IAPD Distributor is your choice in finding the right material for your application. Go to www.iapd.org to find a distributor in your area. You can search by company name, location or product category.
The IAPD Magazine web site at www.theiapdmagazine.com allows you to search by material, trade name and fabrication process. You can also search for fabrication capabilities.
© 2008
International Association of
Plastics Distribution
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Leawood, KS 66211 -1667 USA
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Phone: +913.345.1005 | Fax:
+913.345.1006
Designing with Plastics is published by the International Association of Plastics Distribution. While every effort has been made to ensure accuracy, IAPD encourages you to verify information with a plastics distributor to ensure you select the correct plastic products to meet your needs.
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