special issue

Technologyof Material

Plastic Materials Page 3

Choosing the Right ResinPage 5

in This issue:

2006 Issue 1 The Protomold Company, Inc.

Rapid injecTion Molding

Mechanical PropertiesPage 4

> executive view

I’ve been reading a book entitled “American Plastic: a cultural history.” No doubt, you’ll see it reviewed in a future issue of this journal; however, unlike some of the other books we’ve reviewed, this one is less about plastic itself, and more about its impact on, and integration into, our lives. But while the book focuses on what plastics do, author Jeffrey Meikle acknowledges the importance of what plastics are.

In this issue of the journal, we focus on the material aspects of plastic resin: the characteristics of various formulations and how we use them to meet a virtually endless range of human needs. Plastics have come a long way from their low-tech, labor-intensive beginnings with the 19th century introduction of celluloid. That material began as cotton, was processed into paper, and treated with nitric acid to yield crude-but-useful nitrocellulose plastic. It was largely

a hit-and-miss process — a risky one as well, since over-treatment with the acid yielded, instead of plastic celluloid, hazardous guncotton (the original plastic explosive). But even when the treatment went as planned, the resulting material was not much easier to work than the horn, bone, ivory, and tortoiseshell it replaced.

Today, we have thousands of pure resins, resin compounds, and processing methods, allowing us to easily and cost-effectively produce an almost limitless array of materials and objects. Plastics are no longer poor imitations of natural materials. On the contrary, they have superseded the limitations of materials that can be grown, raised, or mined and are limited only by our ability to define a need.

In their almost limitless incarnations, they package our food, encase our electronics, lighten our cars, and replace our body parts. They can be nearly as light as air or heavy as iron; opaque as lead or transparent as glass; rigid as stone or flexible as a leaf, but with so many functional options to choose from, the choice of material can be as demanding as the design itself. The opportunities are vast, but so is the complexity of the selection process.

Protomold’s rapid injection molding gives designers the opportunity to actually “test drive” resins in a finished prototype to make sure they are getting the functionality they want before finalizing production specifications. This issue presents an overview of some of the options, shares the experience of other designers, and points readers toward sources of in-depth information. It is, of course, impossible to do more than scratch the surface of such a vast field, but we hope we can, in some small way, expand your options and simplify your choices.

Brad cleveland President & CeO bradc@protomold.com

What comes out of the mold depends on what goes in

> Materials

Monomers are fairly boring little molecules. But start linking them into chains called polymers and all sorts of interesting things start to happen. Plastics are polymers. They come in a great variety of forms and offer a vast array of traits. Like those other polymers called proteins, what plastics do is determined largely by how they are structured.

The first factor in determining the nature of a plastic is its component elements. The most basic plastics — polypropylene and polystyrene for example — are made only of hydrogen and carbon. Add chlorine, nitrogen, fluorine, or oxygen (or silicon, phosphorus, or sulfur) and you can create plastics like polyvinyl chloride (PVC), Nylon, polyester, Teflon, and more. But constituent elements are only the beginning.

The degree of branching of the polymer chain affects melting point and tensile strength. Cross linking increases strength and can prevent melting entirely. And crystallinity can affect both melting point and opacity. Move beyond the basic chemical and structural characteristics of individual resins, and you can compound multiple resins and additives to offer whole new ranges of capabilities. Fillers can enhance bulk, weight, strength, or other characteristics.

The point is that the capabilities of plastic are, for all practical purposes, unlimited. If what you need

doesn’t exist, someone will compound it for you or may already be busy developing it. In a very real sense, the challenge isn’t getting what you want; it’s defining what you want. Here are some of the many possible variables to consider:

Mechanical properties for parts subjected to stress and deformation include:

n Strength

n Toughness

n Elasticity

n Hardness

Thermal properties for parts that will be subjected to extremes of temperature include:

n Melt temperature (range)

n Heat deflection temperature under load (DTUL)

n Coefficient of linear expansion

n Thermal conductivity

n Specific heat capacity

Electrical properties for parts used around current or electromagnetic fields include:

n Resistivity

n Dielectric constant

n Dielectric strength

n Arc resistance

Chemical properties include:

n Resistance to a variety of chemicals

n Resistance to stress cracking

n Flammability

n Toxicology

Other potentially significant properties include:

n Resistance to weathering and radiation

n Fire behavior and smoke development

n Water absorption

n Density

Mechanical properties are addressed in more detail in a separate article in this issue of the Journal. Other properties will be discussed in future issues.

the Material world

If what you need doesn’t exist, someone will compound it for you or may already be busy developing it.

Plastic Materials: the View from 15,000 meters

TM

COvEr phOTO: INSECT IN NATURAL AMBER, ONE OF THE FEW PLASTIC RESINS PROTOMOLD DOESN’T USE.

> Plastic on Plastic

Hi, Professor Plastic here. Recently someone asked me to name the strongest plastic I could think of. I’m rarely lost for a snappy answer, but

“strength” is a general term covering

a variety of properties and a subject to which entire engineering courses could be devoted, so I simply explained that:

n Two sets of strength measurements are most commonly used for plastics. “Tensile” is pulling, as in pulling on a rope until it stretches and ultimately breaks. “Flexural,” is bending, as in bending a pencil until it curves and breaks.

n “Modulus” is a measure of stiffness. Two commonly used types of modulus are tensile, which is resistance to stretching, and flexural, which is resistance to bending. An easily-stretched thermoplastic rubber like TPE has a low tensile modulus.

n “Yield” is the point to which materials can be stretched or bent and still return to their original shape. Beyond this point, they are permanently deformed. This is the “yield point” or “elastic limit.”

n Yield point and breaking point can vary independently. A “brittle” material elongates or bends very little before it breaks. An elastic material can stretch or bend a lot without breaking and still return to its original shape. A ductile material can also

stretch or bend without breaking but does not return to its original shape.

n There are two types of strength: “yield” and “ultimate.” Yield strength is the amount of stress required to bring a sample to its yield point. Ultimate strength is the amount of stress required to break it.

n The above measures apply energy to a material relatively slowly. Impact resistance measures material behavior when energy is applied quickly (as it would be in a crash or from a sudden blow). It measures the amount of energy the material absorbs when it is broken by a blow from a “pendulum hammer.”

n Then there’s hardness, which measures resistance to permanent surface indentation, and abrasion, which measures loss of material to scraping or rubbing.

n Finally, there is high temperature strength, which is strength at a standard elevated temperature.

So, in picking a resin, you have to consider: how much stress it will have to handle, whether the stress will pull or bend the material, how gradually or suddenly the stress will be applied, whether the material will need to resist rubbing or indentation, and whether it will have to withstand heat. Protomold’s resin guide (www.protomold.com/designguidelines/resininfo) can give you a general idea of the material properties of various resins, but for detailed information, you can consult the books or sites mentioned elsewhere in this issue.

Of course, there are other resin properties to consider, but those are for a future issue.

> case study

Electric utilities have always been concerned with the quality — voltage, harmonics, and disturbances — of the power they supply, and are more so now with the increased demand by sensitive electronic equipment. Power Monitors Inc. (PMI) is a leading supplier of instruments for evaluating power quality, and one of their most

popular products is the Flex CT. This flexible probe is wrapped around single or bundled wires to measure, by induction, the characteristics of current in the wires and feed that information to a scanner for analysis.

“We needed a new, smaller flexible probe for use in tight spaces,” says Manager of Hardware Engineering Glen Shomo. “One of the challenges was the connector that holds the ends of the flexible probe in place while measurements are taken. Alignment has to be very precise and, because of the high voltages, it has to be operable by a user wearing protective gloves.”

Shomo’s team selected a self-locking, two-part design with side latches that are pressed to disengage the ends of the probe. Rapid prototyping (RP) was used to determine the size and shape of the components, but couldn’t help with tests of functionality. “In our design, the flexibility of the resin itself provides the ‘spring’ for the latches, but RP materials are too brittle,” says Shomo.

“RP couldn’t tell us whether an injection molded version of the connector would operate properly in the field.”

PMI needed to get the new product to market in time for their busy fourth quarter, so they turned to Protomold for fast turnaround on injection molded prototypes that would be tough, springy and sufficiently flame retardant to meet US and international safety standards. A trusted consultant recommended Valox® resin from GE. “We submitted a 3D

CAD design to Protomold and in a week we had finished parts for accelerated lifecycle testing,” says Shomo. “The Valox parts were tough and durable, but they didn’t stand up as well as we hoped they would.”

“I called Dave Nyseth, a Protomold customer service engineer on a Friday and described the problem.

He suggested four other resins that might meet our requirements; three days later I had new prototypes on my desk in all four resins. The winner was FRPP301, a flame resistant polypropylene. On paper, the original Valox material looked promising, but we had no way of knowing until we tried it. That’s the beauty of rapid injection molding: you can try

materials, actually see how they work, and validate a design in a matter of days.”

“The best part was that Protomold’s parts were of excellent quality so we

ordered 500 pieces and immediately started filling

orders with them. We are having steel molds produced offshore for ongoing production, but that could take months. In the meantime, we’ll keep reordering from Protomold to meet demand until that long-run production comes online.”

choosing the right resin at Power Monitors Inc.

“ That is the beauty of rapid injection molding: you can try materials and validate a design in a matter of days.”

Mechanical Properties

You think you’re tough? Let’s see how tough you really are.

Tough? Strong? Hard? What’s the difference?

> Book review > info in Print and online

It all began with a manual on plastics created for IBM by a student at the University of Wyoming. Today, under the leadership of that same former student, Mike Kmetz, IDES is a worldwide provider of plastic-related information. Of the company’s services, Protomold customers are likely to find most use for the company’s two handy reference books and three online services designed to help with resin selection.

The books, Pocket Specs for Injection Molding (772 pages) and Pocket Performance Specs for Thermoplastics (992 pages), are clearly directed toward users with large pockets to match their large information needs. For those without such large pockets, IDES offers online services including The Plastics Web™, a free search engine that focuses on web sites pertaining directly to plastics.

For those in need of resin, IDES offers two versions of a data service called Prospector. Prospector X5 is a free service providing detailed data sheets on over 60,000 resins. Prospector Pro is a subscription service that enables users to search on any of over 400

material properties to find resins that match. It also allows the user to compare side by side the specifications of different resins. Both services provide links to suppliers’ resin data sheets.

Nathan Potter, marketing manager of IDES, differentiates the two services as follows. “If you know the resin and you want to know its characteristics, use Prospector X5. If you know the characteristics you need and want to find a resin to match, that’s a job for Prospector Pro.”

FRee tRial oF PRosPeCtoR PRo

IDES has generously offered a free trial of Prospector Pro for readers of Protomold’s Rapid Injection Molding Journal. This shared account can be found at www.ides.com/login and will be operational until July 28, 2006.

Enter the username: protomold and password: guest.

We strongly urge you to take advantage of this powerful search program and to explore the array of other plastic-related information that can be accessed from the IDES home page at www.ides.com.

ides: the Plastics Information Management Company

If there could ever be a definitive work on plastic materials, this volume would certainly be a contender. While not large enough to require wheels, it makes up in density for what it may lack in sheer volume. Like Vince Lombardi’s oft-quoted address to the Green Bay Packers, which began “Gentlemen, this is a football,” Domininghaus begins with the basics.

Chapter one starts simply, with the statement “Plastics are macromolecular organic materials manufactured by modification of natural products or by synthesis from suitable intermediates.” But like an Atlas rocket at launch, what may seem to begin slowly rapidly gains momentum. Within five pages, the author has gotten specific enough to point out that processes for manufacturing PE-LD [linear low-pressure polyethylene] “use high pressures of 1000 to 3000 bar and

temperatures of 80 to 300° C with oxygen or peroxide catalysts. Under these conditions branched polyethylene molecules with side chains of varying length, degree of crystallinity 40% to 50% and density between 0.915 and 0.93 g cm-3/0.0338 lb/in3 are produced.”

Chapters two through 25 are dedicated to specific families of resins — polyethylene, propylene, vinyl, styrene, fluoropolymers, polyamides, polyester, and so on. Each chapter follows approximately the same format addressing:

n Production methods, broken down, if appropriate, by sub-types of the resin

n Structure and general properties

n Additives, including functional additives, fillers, and reinforcements

n Availability, addressing the range of forms in which the resin can be provided

n Specific physical and chemical properties (detailed below)

n Processing, addressing the range of methods by which the material resin can be used

n Typical applications

n And trade names under which the product is sold

The section covering physical properties is broken down into sub-areas including mechanical properties, thermal properties, electrical properties, optical properties, water absorption, and gas permeability. Chemical properties include chemical resistance, weathering resistance, flammability, resistance to radiation, and toxicology. Within the main text, nearly 100 charts and almost 600 graphs provide an enormous amount of data on virtually every aspect of each material’s behavior and performance. To fill any remaining gaps, the appendix provides 30 additional pages of tables. (In tribute to the book’s clear overall organization, the index for this ambitious tome is a mere five pages.)

everything You Wanted to Know about PlasticsTitle: Plastics for Engineers: Materials, Properties, Applications

author: Hans Domininghaus

publisher: Hanser Publishers, 1993

isBn: 3-446-15723-9

If none of the 60,000 resins in the IDES database is precisely what you’re looking for, you might consider contacting rTp Company, a leading provider of specialty thermoplastic compounds. As an independent company not affiliated with a particular manufacturer, rTp is unbiased and accesses resins and additives from many sources to address specialized needs. For example, a client designing a disposable pump for food and pharmaceutical applications needed a plastic that would resist both wear and chemicals, and maintain dimensional stability in wet conditions over a wide temperature range. The material also had to comply with FDA standards and be self-lubricating. rTp created a unique glass reinforced polyphenylene sulfide (ppS) material with pTFE lubrication, combining FDA-compliant polymers and additives and enabling the customer to bring their innovative product to market.

For further information, see www.rtpcompany.com.

still can’t find what you need?

and a whole lot more!

Pro-datasheet Pro-results Pro-search

HeRe...We’ve begun production at our new Maple Plain expansion facility. As planned, it will be operational in Q2 of this year, bringing our North American space to over 60,000 square feet.

tHeRe...Our aim, when we established The Protomold Company Limited in the UK, was to duplicate the success we’ve had in the U.S. We had no idea how quickly — or how literally — we’d achieve that goal. EU response to rapid injection molding has been very strong, so we are already in the process of doubling capacity at our Telford plant. That expansion should be complete by the end of Q1.

...and eveRywHeReThe spring conference season is getting under way. We hope to see you:

March 20-23, 2006National Manufacturing WeekDonald Stevens Convention CenterRosemont, IL, Booth #16,025 in the National Design Engineering section

June 4-7, 2006PTC/User World EventGaylord Texan Resort & Convention CenterDallas, TX

And thanks to all of you who visited us in Las Vegas at the SolidWorks World Conference in January.

iF you’Re a Poet, let us know itHere’s another entry to the Protomold Poetry Slam.

Dieting’s a way of life for everyone we know.

A name that means “low calorie” can earn you lots of dough.

Some marketers of cake mix think they really got it right

When they took a hint from plastics and they called it Bakelite.

If you’ve got the rhyme, we’ve got the time. Send submissions to marketing@protomold.com.

don’t FoRget The Protomold Refer-a-friend program at www.protomold.com.

Visit the Protomold Store at www.co-store.com/protomold

what’s new

www. ProtoMold.coM/Parts

the Protomold company, inc. 1757 Halgren road Maple Plain, Mn 55359

(763) 479-3680

© 2006 by The Protomold Company, Inc.

noBody’s fasTeR in The shoRT RuntM

Bringing new products to market can be a very frustrating experience, so it’s a good idea to find humor wherever you can. Please email your suggestions for future “Everything by Design” cartoons to marketing@protomold.com.

everytHing By design

youR CHanCe to win a $1000 Best Buy™ giFt CaRdSee Protomold’s print ad running in several design-oriented magazines and enter our monthly “Cool Parts” promotion for your chance to win. If you can’t find our ad, send an email to marketing@protomold.com telling us what you’re reading these days and we’ll tell you where to look. Best Buy is not affiliated with Protomold. Best Buy does not sponsor, endorse, approve or have any responsibility for this promotion. Please see back of card for terms and conditions.