Tag Archives: engineering plastics

Machining Acetal Shapes

Highly precise acetal parts in a variety of sizes and complexities can be manufactured economically through machining. In the world of Engineering Plastics, Acetal (POM) stock shapes are considered to be some of the easiest to machine. On a scale of 1-10 with 1 being the easiest, many manufacturers place acetal at a 1, compared to a PBI which is often seen as a 10. In fact, machine shops that traditionally make metal parts find they can machine acetal using the same primary tools used for most of the metals they work with. As with any material, there are some good guidelines that can help ensure your success.

Best General Practices for Machining Parts from Acetal (POM) Engineering plastic and Potential Pitfalls of Machining Thermoplastic Shapes

We love engineering plastics! So we are always touting the many benefits of replacing plastics with metals. But this does not mean they are perfect in every way in every situation. There are some differences between plastics and metals that can trip you up when machining. But once you know the potential problems of machining acetal stock shapes machining them can become as easy as the metals machine shops are used to working with now.

Watch out for the heat! As a general rule keep in mind that, due to heat, thermoplastics expansion can be up to 10X greater than metals. Thermoplastics also hold heat longer than metals. Acetal is a thermoplastic material and has a lower thermal conductive aspect than most of the metals it is used to replace. Heat may not be an issue for metals but in the case of an engineering plastic shape from acetal heat build up from machining needs to be monitored and taken into account. Thermoplastics are more elastic than metals. So in general, heat buildup during the machining process can potentially lead to thermal expansion which can distort acetal parts.

If this leaves you concerned about machining plastics, not to worry! Plastics like acetal have numerous benefits that often outweigh the challenges of heat buildup and once you understand how to work with acetal you can easily machine consistently accurate, detailed high quality parts that your customers will be happy with. Be mindful of heat buildup, but also know that acetal does not typically require a coolant (except when drilling or threading). Sawing and machining can usually be set up to minimize heat buildup. (See the table below for Quadrant Engineering Plastics general recommendations for tools and speeds.)

  1. If cooling is used on acetal, compressed air is the standard method. The great thing is this has two benefits. The air cools the part and it keeps chips blown out of the way and keeps the heat built up in the chips off of the part or tools where it can add to any heat buildup. Other options include spray mists and non-aromatic, water soluble coolants.
  2. Sharper tools = Less friction = Less heat. To help reduce heat buildup use extremely sharp cutting tools.
  3. Chipping. Acetal creates chips when being machined so plan for removal of chips as you machine. Removing chips is very important in deep hole drilling. As the chips add to the heat, hole walls can heat to the melting point and clog the drill.
  4. Pieces may be flexible. Make sure the acetal is supported in a way that the material is not distorted, bent, twisted or allowed to deflect away from the tool.
  5. Make sure machining equipment is running as smoothly as possible, reduce any vibration to help aid in accuracy and part quality.
  6. Acetal shapes can be clamped but be aware of how tight.
  7. Choose the right blade for the job. Start by asking yourself what the end product is going to be.
    1. Band saws are good choice for a support groove and for cutting acetal rod and tube. Heat gets dissipated over the long blade.
    2. Circular saws are a good choice for cutting acetal sheet or blocks that have straight edges. Watch the feed speed (most acetal manufacturers have a recommendation).
  8. Choose the right tool for the job too
    1. Opt for positive tool geometries with ground peripheries
    2. For best tool life use carbide tools with ground top surfaces
  9. Is post machining annealing needed? See our previous blog post on this topic.
  10. Choose a machining cycle that will allow for evacuation of the chips from holes and cutting surfaces. For example, when drilling holes choose a cycle that allows drill to ‘peck’ or withdraw at certain points to draw chips back out of the hole.

The following tables are a good starting point for how to set up machining of acetal materials. The information comes two US manufacturers of acetal materials – Quadrant Engineering Plastics and Engineer Plastics provide guidelines for machining the acetal materials they produce. Depending on the manufacturer acetal materials may go through a stress relieving (annealing process) as part of their manufacturing. This helps to ensure the highest possible consistent quality of materials. Testing and consulting with your local tkEP representative on manufacturer recommendations is always a good way to help prevent machining problems. tkEP representatives not only have a broad range of industry experience, many have worked hands on in the industry, and all tkEP representatives attend manufacturer training so we stay on top of current products and how to work them.

 

As you can see each manufacturer has their own insights into how acetal should be sawn, milled, drilled, or turned. Their are also some pretty broad ranges when it comes to the numbers they provide. This is because these are truly general guidelines that cover the broad range of acetal shapes. Acetal shapes can be acetal homopolymers, acetal copolymer. In addition there are filled acetals and unfilled acetals. Add that to other variations including thickness and size plus environment and it is easy to see that testing for individual applications is necessary.

To read more about acetal plastic shapes check out our online catalog. We have product information as well as a full range of shapes, sizes, and grades of acetal. Read More… For more detailed information on machining from Quadrant EPP and Ensinger Engineering Plastics we’ve included links to pdf files of their machining guides. In these guides you’ll find data for acetals as well as a broad range of other machinable engineering plastics. Last but not least, don’t forget about your friendly local tkEP representative. We are always happy to assist you with finding the right engineered plastics solution for your application. Contact us today 877.246.7700. this one number will put you in contact with your local tkEP branch, or send us a note.

Quadrant Engineering Plastics Machinist Handbook

Ensinger Engineering Plastics Machinist Guide

Extraneous Detection and Thermoplastics – An Industry Experience of the Customer

 

Thanks to Brad Nelson, a Quality Manager in the Food Industry for sharing his experience on our blog. Recalls in the food industry can cause massive losses and even worse, cause harm if people, pets or livestock are directly affected before a food contamination issue is caught. In other industries lines can be shut down and safety can be an issue. As a distributor of engineering plastics we think there is often no better way to learn than by hearing the stories of those who are willing to share their experiences and what they learned so we truly appreciate Brad sharing his experience of engineered plastic solutions with us on our blog. Knowledge of materials is more than the question of how much, it’s a question of what is the right material for an application.

Food PartBrad’s Story –

ABOUT 5 Years ago, there were a series of events that transformed some of my thinking within the Food Manufacturing Industry.  While working as a Quality Manager within the industry, we had come to find that we were having premature failures of some hanger bearings in a variety of screw-type augers.  (See image) Unfortunately the mode of detection came from an employee who witnessed the plugging up of extruder die heads.   These, of course, had been running for several days by that point, and we had no idea when the thermoplastic ‘bearings’ had begun to melt, extract themselves from their metal housings, and become a potential food safety issue.  After a long and arduous investigation, there were several hundred thousand pounds of product that were on hold and subsequently destroyed.  As one would expect, senior management was extremely concerned about repeat issues.  Through several rounds of research, we determined that the primary failure mode was a maintenance practice issue, in that they were misaligning the screws creating a slight wobble that would wear the bearing faster than normal and then begin a spin that then would heat and melt the thermoplastic.  Round one of preventative action: let’s change our maintenance practices.  Worked great!

For a time… then we came to discovery number 2.  Again, we found ourselves in a similar predicament of product destruction and direct emails from executives to “figure this out”.  Not that that helped, but it certainly adds to the stress.  We approached our supplier of the hanger bearings about different materials to use – we discovered that they were experimenting with various metal impregnations at different levels.  We were very willing to be the guinea pig at that point, and gave them the green light to manufacture various levels of impregnated material into the resin. I was a skeptic, and a fairly harsh one at that.  I made the team run through a Probability of Detection trial on various detection devices (Metal Detectors & X-ray) to see what size, shape, and mass we could detect at 100%.  We then compared this data to our MTBF (Mean Time Between Failures) data on the bearings.  We managed to find a happy medium of detectability and of life-length.

The rest of the story you ask?  Well, we found that fixing the screw alignment was only part of the failure mode for the assemblies, and found other mechanical changes necessary when it came to the longevity of the plastic components.  But, before we knew it, we discovered something else.  This time, it proved to be our metal detector on the end of the processing line.  A couple of shifts had gone by with Maintenance trying to ‘fix’ the problem of the continued rejections.  The report had surfaced in our daily production meeting.  I questioned it several times; only to receive the response back that “we didn’t find anything”.  I decided to go look for myself, and sure enough, I took some of the rejected material (> 200 lbs. worth) over to our off-line sensitized metal detector.  Shazam, I found this blueish powder in the reject bucket after just a few scoops.  Guess where that came from?  You guessed it, the hanger bearing assemblies further upstream.

Lessons learned: ‘detectable’ thermoplastics work, and they work great!  Design and Food Safety Planning are the keys to success.  Advising and training your plant floor on what to look for in failure modes is critical.  For the few pennies / dollars more per unit you pay upfront, you avoid many a headache in the future!

Guest Blogger
Brad Nelson
Quality Manager

We hope to bring more stories like this in the future. As more engineering plastics like the detectable materials Brad talked about are developed we need to understand how these can really work as part of the whole. How are engineering plastics affected by the materials around them, how can quality and maintenance teams quickly find potential part failures, and how these amazing materials can bring safer more reliable conditions. Keep up with us here on our blog and check out our online catalog at onlineplastics.com. On this site you can easily find items like Ultra Detectable materials, the latest in FDA compliant engineered plastics solutions for the food processing industry as well as many other well known plastics plus articles on industries and more.

 

Designing with Thermoplastics in Pump & Valve Components

Why are thermoplastics (engineering plastics) replacing metals and becoming a popular option for machined parts? To answer this question we’ve got a few blog posts that look at different aspects of why people are saying yes to engineering plastics. Pumps and valves have been around for about as long as humans have been constructing things to make life easier. Today pumps and valves occupy places in nearly every industry from medical, laboratory and testing equipment, to oil and gas, agriculture, transportation, buildings and more.

Designing pump and valve components from thermoplastics has the benefit of being made from materials that are corrosion resistant. But, even plastics withstand varying physical elements in different ways so it’s important to understand how plastics can also be affected by the physical elements they will be exposed to. The chart below looks at some of the most common plastic resins and gives a general guideline for how they stand up to potential corrosive elements.

 

Chart of Chemical Resistance for Common Polymer Resins / Thermoplastics

 

CHEMICAL RESISTANCE POLYMER RESINSA Deeper Look at Corrosion and What it Is
Corrosion is the deterioration of a material and its physical properties, Corrosion of a material occurs because of an undesirable reaction with its surrounding environment. In valve applications chemicals may attack the exterior as well as the interior surfaces. As you can see from the chart above both acids and alkalis will attack some materials. Corrosion begins with pitting that is not even visible to the eye. But once it begins corrosion continues to grow and eventually it leads to part failure. But even before creating a leak, pits increase turbulence which affects performance.

Corrosion is caused by more than just hazardous chemicals. As you can see from the chart of common thermoplastics above, sometimes an apparently benign fluid can react, as when sea water flows over brass.

How Can Corrosion of Machined Parts Be Stopped?

The best and most cost-effective way of controlling corrosion is preventing it. Studies have shown that an overall cost savings of 40% can be achieved when corrosion is prevented rather than treated. Prevention entails selecting an engineering plastic that will work best with the media being transported through the device. Whether you are using metals or thermoplastics, all environmental factors should be considered, including cleaning agents and things that might not be thought of as highly corrosive. In some cases a sacrificial layer could be used but these will have a finite life, and as the name implies the sacrificial material needs to be closely monitored and it will still require downtime to apply a new sacrificial layer.

Many customers that replace metal valves and gaskets with engineered plastics often note a number of positive benefits even if the initial part costs more.

  • Reduced maintenance
  • Reduced Downtime 
  • Reduced incidence of part failure
  • Longer lasting parts
  • Overall cost savings
  • Smooth surfaces allow for increased velocity and precision control of flow

Customers with ultra-high purity such as medical device, food processing, or water treatment applications to name a few, require very smooth interior surfaces with absolutely no place for contamination to lurk and with no risk of particles breaking free and joining the fluid. Even microscopic pitting can be cause for parts to be replaced because the pitting can allow for bacteria contamination. Once pitting occurs it is virtually impossible to clean a valve or gasket to the high standards required for high purity applications.

The highly smooth surfaces that can be achieved with machined thermoplastic materials can also reduce turbulence in fluids being transported. This allows for fluids to flow at higher velocities and allows for precision control of pumps.

Beginning with careful material selection, research and talking to experienced plastic professionals can lead to designing pump and valve components that can improve performance and increase life from day-to-day to your most demanding applications.

Do you have questions about material selection for seals and valve gaskets like:

What are the lower cost and lighter weight options to metal-to-metal sealing?

We are having thermal degradation issues with plastics in valve components, can we improve this?

Our seals and gaskets have to withstand higher and higher operating pressure. What  materials have higher compressive capabilities and creep resistance?

These are all questions I am able to assist you with. Feel free to contact me at the information below.

 

 

Montague-Sml-DSC_0304Kendall Montague
Industry Segment Manager

thyssenkrupp Materials NA
AIN Plastics Division

 

Kendall Montague is a veteran of the plastics industry with 16+ years experience working with OEM and MRO engineers assisting in developing thermoplastics material selection as well as custom design and fabrication using CNC equipment.

Active Member with the Energy & Polymer Group – Houston
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Bayer Material Science Now Covestro

As a distributor of Engineering Plastics AIN Plastics has had a long and great relationship with Bayer Material Science. Now, we here at AIN are pleased to be carrying on this same great relationship with Covestro. The company formerly known as Bayer Material Science is now a legally independent company that is still a full subsidiary of Bayer AG.

As a distributor we are looking forward to working with the same great materials and people and we are eager to see what the future brings now that Covestro stands on its own. Although some things remain the same, the change to Covestro is more than a pretty new logo. It is an opportunity that has been embraced by the Bayer team to reflect on it’s goals and it’s purpose and with that has come a new vision that Covestro released along with their new logo:

Covestro Logo Blk Txt CMYK“Making the World a Brighter Place”

In a recent press release Covestro’s CEO Patrick Thomas stated “We fulfill this vision by inspiring innovation and driving growth through profitable technologies and products that benefit society and reduce environmental impacts.”

As has been the case in the years leading up to the change, Covestro and AIN Plastics have worked with customers throughout just about every industry from high tech aerospace, defense and automotive to the demanding applications of medical device, food processing, orthotics and prosthetics and on into fine art preservation and architecture. It’s a broad range and Covestro has the high quality materials needed to supply them all. In addition, one of the things that has made the AIN Plastics / Bayer partnership so successful is our shared focus on continuous growth of industry knowledge that we bring to our customer service. As a company Covestro employs approximately 14,000 workers around the globe and according to news reports that number may be increasing soon. The US headquarters will remain in Pennsylvania where they are already sporting the bright new logo on signs around the property.

AIN Plastics is looking forward to our continued partnership with Covestro. As a top manufacturer of polycarbonate resins, sheets and shapes AIN Plastics is happy to continue stocking and selling their materials. Our team will be on the front line of learning about new Covestro materials and applications in the months and years to come, and as always, everyone at AIN Plastics will be eager to assist customers in finding that just right engineering plastic for their application.

 

 

 

For more information and articles about Bayer Material Science’s transition to Covestro see these links:

Bayer US Website

Pittshurgh-Post Gazzette

Wall Street Journal

 

See you in the blogosphere again soon!

Lisa Anderson

Marketing Manager
ThyssenKrupp Materials, NA
AIN Plastics Division


lisa_anderson_001CroppedAbout Lisa Anderson

Ms. Anderson has been ThyssenKrupp Materials AIN Plastics Division for over 3 years. She brings 20+ years of advertising, award winning graphic design, social media and marketing. She has worked in book publishing, advertising agencies, printing, manufacturing, and the apartment industry. Ms. Anderson has a Bachelor of Fine Arts in Studio Arts from Calvin College, Grand Rapids, MI.

What’s That Plastic?

Have you ever come across a plastic material, a sheet, rod, or tube, in your shop or warehouse with no label and no way to determine exactly what it is? This can be a difficult challenge due to incredible number of variations that include all the machinable engineering plastics plus all the fillers and additives used to enhance or improve aspects of an engineering plastic’s performance under specific conditions.
However, there are some things you can do to get off to a good start on narrowing down the options.
We’ve put together a handy infographic on some simple do it yourself tests and how the most popular engineering plastics will react to them.

In addition to these methods take a look at our blog post on using the Burn / Flame Test to Identify Plastic Materials

 

A Plastics Guy in the Glass Industry

One of the most fascinating things about the Engineering Plastics Industry is that these materials are used in every industry, at least every industry I’ve come across so far, and that’s a lot! So when I recently visited a glass manufacturing plant I wasn’t entirely surprised to find they had a need for plastics.

As Old as Humans 
Glass was discovered by stone-age hunters in the form of obsidian long before it was first manufactured in any form. The first manufactured glass that we know of dates to Mesopotamia in the 16th century BC. In this day and age it’s hard to imagine a world without our automated glass manufacturing techniques. All you have to do is look at skyscrapers in any city. The beautiful glass that you see on the outside is engineered and produced to some amazing standards.  The same is true of the safety glass in every automobile on the road.  Without automated lines that take the sand, sodium carbonate, and calcium carbonate (soda ash and lime) through the process, cars would not be the same. Modern glass has improved safety, part life, and given designers a freedom to create a virtually endless array of shapes.

Modern-Day Glass Factories
Where do plastics enter into the modern-day glass factory? Inside glass plants, technology has led to many innovations that keep prices down and the design capabilities endless.  Automation allows glass to be consistently formed, tinted, laminated, and packaged, and all at high speeds compared to earlier methods. In this process the conveyors rather than humans handle the glass from furnace to delivery on the factory floor.  To keep the lines moving, glass is sent across conveyor lines while it is still at extremely high temperatures. This has created some challenges on the manufacturing side to be able to move the glass in a way that is gentle enough that the fresh material is not scratched, marred or broken. This is where Engineering Plastics offer benefits to the glass manufacturer as it can minimize these issues.

Glass Stops
Illustrations---Glass-HandlingOver the years glass plants have made stops, a small piece that acts as a ‘bumper’ of sorts. Glass hits the stop which helps to cushion and redirect hot glass as it moves along conveyor lines. Some plants have used phenolics or other plastics to make glass stops. Although these materials work, customers tell us they need to be replaced often as the high temperature of the glass degrades the plastic stops. DuPont™ Vespel® is a unique family of polyimide materials that many glass manufactures have moved to  because of their ability to withstand the high temperatures and impact of hot glass.  As one of the highest performing materials for high temperature environments, engineers have designed rollers, stops, fingers, and wear strips out of DuPont™ Vespel®.  In addition to performing well under extreme heat DuPont™ Vespel® has been noted for its ability to handle the constant impact of glass without deformation or causing marring, scratching, or breakage of the glass. While this material is not inexpensive, customers continue to specify DuPont™ Vespel® due to benefits that include  –

  • Reduced downtime of lines to replace stops
  • Reduced furnace downtime to cool and reheat while production lines are down
  • Minimize product loss due to scratches or other damage
  • Decrease downtime to clean up after product breakage occurs

In a recent application in an auto glass factory, we replaced a graphite based material used to make glass stops with DuPont™ Vespel® SCP-5050.  The customer reported the service life of the stops improved over 5000%! It’s a great reminder to me as we look at engineering plastics that it’s not all about the initial cost of the material, it’s about the savings and improvements to your manufacturing process that can happen when you choose the right engineering plastic for the job. So, feel free to call up your local plastics professional when you are looking for improvements. We may or may not be the right fit, but if we are, you’ll be glad you made the call.

Photo---Paul-Hanson---ThumbnailPaul Hanson

Sales and Marketing Manager
DuPont Vespel®
ThyssenKrupp Materials NA
AIN Plastics Division

email: paul.hanson@thyssenkrupp.com

For more information about Engineering Plastics for Glass Stops download a pdf here Flyer – Glass Handling w Vespel 01-15

For more information about AIN Plastics please visit our website at ainplastics.com

Engineering Plastics use Grows in Food Processing Equipment

iStock_000014977093LargeEngineering Plastics continue to replace metals as key components in food processing equipment. Plastics are often lighter and able to outlast traditional metal parts. A quick look through the variety of plastics available in today’s market shows an increasing number of engineering plastics that are compliant to FDA, USDA, 3A Dairy standards making them available in applications where they will come into direct contact with food. They are also being chosen for their
ability to create a quieter work environment.

With 2014 looking to be a great year for Food Processing equipment sales I wanted to share what we most find in food processing applications and why.

UHMW
UHMW continues to lead the way (by pounds sold in the United States) in the transformation from metal to plastic parts.  For more information on materials sold in the U.S. see this article by the American Chemical Council. Compared to steel UHMW is just 1/7th the weight. In addition UHMW is corrosion resistant. UHMW is a great option for room temperature applications like guides, paddles, and cutting surfaces.  Recent advances include the introduction of metal detectable versions that can be recognized by your detection systems in line.

Nylons
For bearing and wear applications, Nylon materials have been the workhorse for over 30 years.  Like UHMW, Nylon is also light weight, and provides lubrication – free operation making it a great material for producing bearings or bushings.  Gears and sprockets made of Nylon have been popular because they can reduce noise in work areas. They can also improve the efficiency of production lines conveying food and liquids in your plants by lasting longer than metals, which reduces downtime, and by allowing lines to run faster.

Acetals
For many components, Acetal is the best choice for metal replacement, and we find its popularity is growing quickly in the food processing industry.  Acetal (Delrin Homopolymer or CoPolymer brands like Acetron GP and Celcon) are very easy to machine, and their very low moisture absorption rates make them a good choice for the often wet environment of food processing.  Acetals are harder than Nylons and maintain dimensional stability where Nylons tend to be more flexible. In many applications Acetals can handle continuous use temperatures up to 210° F and they are typically compatible with most cleaning solutions, a huge plus in the food processing industry.

ERTALYTE®
A popular speciality material is Quadrant Engineering Plastics Ertalyte material.  Ertalyte has unique properties that allow it to wear like Acetal in wet environments and like Nylon in dry or unlubricated environments.  I like to think of it as giving you the best of both worlds! Ertalyte also is highly resistant to stains generated by things like tomato based sauces and green vegetables.  Ertalyte also has high dimensional stability that meets the demands of the highly precise machining tolerances required in filling pistons and fluid manifolds.

In looking to the future of food processing the demands are heavy. Companies are working hard to keep consumer prices in line while still making a profit. Food processing companies are achieving these goals by improving efficiency and creating better work environments. Plastics are an increasingly big part of the solution because their use in parts can improve line speeds, decrease maintenance downtime, and even make for a quieter work environment.

As I look at the Engineering Plastics and High Performance Materials we have here at AIN Plastics I’m pleased to see how they are being used to improve the food processing industry and I’m excited to see the new applications our customers are working on as well as the new materials our suppliers are always working on. If you have an application you’ve been scratching your head over, give us a call. We know there are lots of options and we can help you take some of the guess work out of finding out if Engineering Plastics are right for your application.

Paul Hanson

Sales and Marketing Manager
DuPont Vespel®
ThyssenKrupp Materials NA
AIN Plastics Division

email: paul.hanson@thyssenkrupp.com

For more information on Engineering Plastics visit http://www.tkmna.com/tkmna/Products/Plastics/Engineering/index.html

Machined or Molded Plastic Parts – What Are the Differences?

A plastic part by any other name would still be a plastic part, wouldn’t it? Yes it would. But the way those plastic parts produced; either by molding plastic parts or by machining plastic parts are dramatically different. Those differences in the process of making plastic parts can result in big differences in lead times, cost, and quality. Below are things to consider when looking at how to manufacture plastic parts and some answers that may help you to decide.

How Many Plastic Parts do you Need to Make?

MOLDED: Molded Plastic parts have been around since the first machine for the process was patented in 1872 by John Wesley Hyatt and his brother Isaiah so its easy to see how this became one of the standard processes for creating plastic parts. Mold machines are used to run mass produced plastic parts from tooth brushes to auto parts and everything in-between. Creation of the mold(s) costs thousands of dollars, requires time up front to make the mold(s) and the molds require maintenance over their life and storage when not in use.

MACHINED: Depending on the project, volumes from 25 to 5,000 parts can often be machined more cost effectively than molded. For small parts, you may have a lower final cost by using high performance screw machines that can run circles around expensive multi-cavity molds. This means shorter lead times than molded parts and little up front cost. Machined parts don’t require secondary machining to clean a part once it is ejected from the mold.

Will You Need to Make Changes to Your Part Design?

MOLDED: Parts made from molds require that the mold be made first which is more time and expense up front. In addition a mold will require maintenance over it’s service life and storage space when it isn’t in use. Changes to a mold are costly in terms of time and dollars to either change or make a new mold, depending on the changes needed.

MACHINED: Machined parts allow for shorter lead times and flexibility in making design changes because they are run directly from a CAD file. Overall, machining can be used to create very complex parts including parts with undercuts and thick walls and the materials are more homogenous across the length and width of the part.

How Important Are Tight Tolerances and Dimensional Stability?

MOLDED: Every plastic behaves differently. But in general plastic parts made from molds may not be as dimensionally stable as machined parts. There is more chance the parts will not be as homogeneous across the length and width of a part. The molding process is not ideal for large parts or where there are thick walls. Tolerances of +/- .005″ are typically the best that can be achieved in molded parts. This compares to +/- .001″ for machined parts.

MACHINED: Many of today’s high performance engineering plastics, such as DuPont Vespel, PEEK, PBI or others can take extreme temperatures of 250 or even 450 degrees and remain dimensionally stable. Many of these materials are also chemical resistant. Additionally machined parts have less internal stress and tolerances of +/- .001″ or better can be achieved.

How Large or Complex Are Your Parts?

MOLDED: Small to mid-size plastic parts can work well. Large volumes can be run fast. But large plastic parts with thick walls, or complicated undercuts can be an issue for mold design. Materials cooling at different  temperatures within a mold can result in more internal stress and a less homogeneous material. Undercuts can pose a mold design challenge with how to release the part from the mold. Plastic parts fresh from the mold may require secondary machining to remove flash, parting lines, or ejector marks, adding to production time and cost.

MACHINED: Large parts and parts with complicated undercuts can be made quickly and efficiently by machining processes. Thick cross sections will have higher, more consistent mechanical properties. Again, because there is no mold to be made, the up front investment and lead time is much shorter. Machining also handles threading extremely well and machined parts will have no parting line, ejector marks, or flash. The availability and selection of engineering plastics means many prototypes can be made in production-equivalent materials. Plastics are more often being found to be a good alternative to metals. They can often be machined on the same equipment and many high temperature engineering plastics offer features such as lightweight, flexibility, high strength, resistance to corrosion, excellent durability, high heat tolerance and chemical resistance. Some plastics, such as those for bearings even require little or no lubrication making them even more cost effective on the service end.

The moral of this blog – a plastic part by any other name is still a plastic part but how you get to create that part could make all the difference in the world. Molded plastic parts have their place, but before going down the path of investing in molds it may be worth a little time considering the questions in this blog and determining if molded or machined is the best option.

 

See you in the blogosphere again soon!

Lisa Anderson

Marketing Manager
ThyssenKrupp Materials, NA
AIN Plastics Division

www.tkmna.com

Understanding Engineering Plastics

This week we decided to bring you a little bit of a different way of looking at engineering plastics. We hope you find this info graphic helpful in determining the differences between various types of engineering plastics and how factors like heat and chemicals can affect these materials.

Infographic-EngineeringPlasitcs07-13

Extruded or Cast Nylon – Material Testing Shows Differences

If you are a user of Nylon materials do you use extruded or cast nylon? Do you always use one vs. the other? Material testing shows there are differences between extruded and cast nylon materials that may warrant a good look at a Technical Data Sheet before you make your material selection.

The Top 5 Differences between the more traditional extruded nylon and cast nylon materials are:

5 – A cast nylon material inherently has less stress than extruded nylon

4 – Lower moisture absorption gives cast nylon a higher dimensional stability than extruded nylon

3 – The more crystalline structure of cast nylon gives it a higher strength than extruded nylon

2 – Cast nylon is available in smaller diameter rod than extruded nylon is when looking at premium bearing grades

1 – Cast nylon has a 20 degree higher operating temperature than extruded nylon

The table below shows a comparison chart between a typical cast nylon and a typical extruded nylon. In this case we are looking at Property Comparison of Nycast® 6pa – Natural versus Extruded Natural Nylon 6/6 

Property  Units  ASTM Test Method Nycast ® 6 pa Natural Extruded Nylon 6/6
Specific Gravity  g/cm3 D792 1.15-1.17 1.15
Tensile Strength  psi D638 10,000 – 13,500 11,500
Tensile Elongation  % D638 20 – 55 50
Tensile Modulus  psi D638 400,000 – 550,000 425,000
Compressive Strength  psi D695 13,500 – 16,000 12,500
Compressive Modulus  psi D695 325,000 – 400,000 420,000
Flexural Strength  psi D790 15,500 – 17,500 15,000
Flexural Modulus  psi D790 420,000 – 500,000 450,000
Shear Strength  psi D732 10,000 – 11,000 10,000
Notched Izod Impact  ft.lbs./in. D256 0.7 – 0.9 0.6
Hardness, Rockwell  R D785 115 – 125 115
Hardness,  Shore D D2240  78 – 83 NV
Melting Point  deg. F D789/D3418 450 +/- 10 500
Coefficient Of Linear Thermal Expansion  in./in./F D696/E831 6.1 x 10 (-5) 5.5 x 10 (-5)
Deformation Under Load  % D621 0.5 – 2.5 NV
Deflection Temperature:  264 psi deg. F D648 200-400 200
Deflection Temperature:  66 psi deg. F D648 400-430 N/A
Continuous Service Temperature  deg. F 230 210
Intermittent Service Temperature  deg. F 330 NV
Coefficient Of Friction: Dynamic  D1894 0.22
Water Absorbtion – 24 Hours  % D570 0.5-0.6 0.30
Water Absorbtion – Saturation  % D570 5.0-6.0 7
Dielectric Strength  500-600 400
Dielectric Constant 60 Cycles  3.7 3.6
1000 Cycles  3.7 3.6
100,000 Cycles  3.7 3.6

(The facts stated in the above table are based on experiments and information believed to be reliable. No guarantee is made of the accuracy, however, and the products are sold without warranty, expressed or implied, and upon the conditions that purchaser shall conduct their own test to determine suitability for their intended use.)

Although it may not always make sense to choose a cast nylon over an extruded nylon material, characteristics of cast nylons can ultimately mean longer wearing parts and in applications such as bearings, nylon wear pads, or gears, that can mean less downtime of equipment, less maintenance and improved operating costs over time.

 

See you in the blogosphere again soon!

Lisa Anderson

Marketing Manager
ThyssenKrupp Materials, NA
AIN Plastics Division

www.tkmna.com