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Author Archives: KevinP

  1. Failure Analysis of Thermoplastic Parts

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    “The part failed!” All plastic parts suppliers have received this frantic call and while you want an explanation and immediate solution, it’s critical to find out exactly what went wrong before beginning to determine how to address the problem.

    First, it’s important to know that most failures are due to a series of events. The part may have broken, but what happened before it failed? For example: a crane operator disconnecting the “boom safety slip”, causing severe side loading on the outside sheave rim.  The sheave fails, but the disconnection actually caused the failure.

     

    SOME TYPICAL FAILURE MODES:

    Heat – The #1 enemy of thermoplastic wear parts and must be properly managed.  An immediate signal is when excessive heat the material brown. This is often caused by excessive speed and/or pressure.

    Pressure –Pressure alone can cause initial failure which is often seen as distortion at the “over-pressure” point. Remember that plastics are subject to creep over time, especially with relatively low increases in temperature –the safe design criteria for a material is 25% of its ultimate compressive strength

    • Additionally, look for misalignment that results in localized pressure

    Shock or Impact – This typically results in a “glass fracture” of the material, especially with more crystalline materials such as extruded moly filled nylon or PET based materials

    Chemical Attack – Some materials are susceptible to steam, solvents, oils or acids – if so, the surface exposed usually has a distinct appearance

    UV Exposure – Some materials become brittle, especially in very thin cross sections. This is usually first seen as surface discoloration.

    • NOTE – “black” doesn’t automatically mean UV stabile unless it’s specified as a UV grade

     

    CONTRIBUTING CAUSES

    Inadequate Design

    • Taking a “robust” design and scale it back to achieve cost or part uniformity goals, reducing safety factor
    • Not taking into consideration the abnormal conditions that a component may face. A common example being heavy equipment which can be in service in Northern Alaska or in Arizona.
    • not allowing for growth due to heat, moisture, etc
    • inappropriate attachment method

    Misapplication – A part may work in one application but may not be right for another and lead to failure. For example, nylon sheaves that work for a pipe lifting winch installed where steel sheaves should be used on a top-head rotary mechanism with high fleet angles and severe loads.

    “Less Than Optimal” Material Choice – The concept of “should good enough” leaves no margin for error.  Think of this one- substituting oil filled nylon for solid lubricant filled nylon– both “lubricated”, but the limiting PV (pressure x velocity) drops from~15,000 to ~6,000.

    Mating Surface Issues – Qualifying parts against a given surface then using another in the real world can have consequences.  An OEM once got a deal on steel which matched the necessary physical requirements but had so much scale that it severely abraded the nylon wear pads almost immediately.

    Raw Material Issues –On rare occasions a mill can ship material that doesn’t meet normal standards.  It’s usually caught in fabrication, but not always. Again, with proper safety factors this should not result in catastrophic part failure

     

    Need help with a plastic part issue? Call the pros at WS HAMPSHIRE, we know what to ask to address the issue! You’re in the right place!

     

    Tom Connelly is a self proclaimed “Street Engineer” with over 40 years in the plastics industry.

  2. ANNEALING OF THERMOPLASTICS – WHAT IS IT, WHY DO IT?

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    ANNEALING OF THERMOPLASTICS – WHAT IS IT, WHY DO IT?

    Thermoplastic stock shapes and parts are produced by several methods – all create some level of stress in the material, which needs to be reduced for several reasons. The process most of these shapes undergo is called “annealing”.

    The process is straightforward but isn’t “easy” You heat the material to a temperature below its glass transition point, hold it there for time that is dependent on the material and thickness, then cool it. Both the heating and cooling must be done slowly, or the material will be thermally shocked which can cause, instability (rather than stability).

    In plastics, extruded and injection molded shapes have the highest process-induced internal stress and require extensive annealing. Before cast nylon was available in FDA natural, companies would use extruded 101 (6/6) nylon rod up to 6” in diameter, and it wasn’t unusual even for thoroughly annealed 6” rod to explode every so often when contacted by a tool.

    Compression molding is usually used to produce materials that cannot be melted – most often PTFE (“Teflon®”) based material, and UHMW-PE. These materials are “fused” under pressure and heat, similar to powder metallurgy. Despite this lower stress process, thick sections still require some extra attention to relieve stress.

    Other materials are cast – several nylons, urethanes are examples. You pour the different base materials, and they react to become that material in the mold. With nylon, again, heavier sections require special handling. And, with cast nylon, secondary annealing also bakes off the residual unreacted monomer, which attracts excess moisture, and makes the nylon ma harder.

    Occasionally, when machining parts that have unique designs – deep pockets, large cross-section differences – it’s appropriate to “rough” machine the part, reanneal it, then finish machine to print.

    Is “slow-cooling” of cast nylon really “annealing”? – yes and no. Yes, in that the product is placed in an insulated box which cools the material more slowly = lower stress. No, in that there is no heat introduced to further align the molecules & really reduce the stress. Mills that slow cool usually find that the physical properties will indeed fall within the stated ranges – but there is no such range for internal stress, only the machinist will find that out.

    Are there different methods of annealing plastics? Yes.

    • OIL – Originally, engineering plastic stock shapes were annealed in an oil bath, which remains the most effective way to anneal. However, it’s expensive to maintain, and you have to machine away the oil stained surface before you can sell the material. Also, the EPA and OSHA weren’t fans & chased that method to Europe, where it is used sparingly.
    • AIR – Domestic mills then turned to using “air” annealing, often with a nitrogen atmosphere to prevent surface oxidation (“browning”), is the primary method today. It is used both “free state” and with added pressure (on plate only).
    • “IN-LINE” – in the 1990’s, technology was developed to anneal extruded materials “in line” immediately after extrusion, when residual heat in the material aids the process. Heaters in-line with the extruder add calories, the material continues through a slow-cooling zone. This process is extremely line speed & temperature sensitive, and is not as effective as air annealing, but it is faster and less expensive.

    Here at WS Hampshire, we qualify all our source materials to insure you get parts that meet your requirements. Call us to discuss your needs – you’re in the right place!

     

    Tom Connelly is a self f proclaimed “Street Engineer” with over 40 years in the plastics industry.

  3. Acetal- Why Two Types?

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    Acetal, an extremely popular engineering thermoplastic also known as POM (polyoxymethylene), comes in two basic types: homopolymer (POM-H) and copolymer (POM-C). While either one will work in over 95% of the applications, it’s important to know the differences.

    Historically, homopolymer (widely known by its DuPont tradename “Delrin®) was the preferred type in North America; in Europe, it was copolymer. The difference was with sourcing – here, we “grew up” with DuPont, in Europe they had Hoechst-Celanese and BASF.

    Copolymer traditionally had cost and processing advantages over homopolymer, advances in extrusion technology in the early 1990’s led to North America’s transition to copolymer.

    So, what are the actual differences in the materials?

    Functionally, either will work satisfactorily in most applications. Both are FDA compliant, machine very well and have similar properties, though POM-C has better chemical properties.  Homopolymer’s more basic structure gives it higher physical properties, making it the correct choice for such applications as gears and “keels” (structural support) for artificial feet

    Property

    POM-HPOM-C
    Tensile strength PSI11,0009,500
    Flex Strength PSI13,00012,000
    Compressive Strength PSI15,00013,500
    Heat Deflection Temp (⁰F) 264 PSI250220

    Despite POM-H’s advantage in physical properties, its disadvantages are significant:

    • Centerline porosity (low density area due to the way the more crystalline POM-H cools) – this often requires buying oversize material to prevent porous surface exposure in final form)
    • Formaldehyde outgassing – POM-H’s backbone is anhydrous formaldehyde, and the odor generated during machining & occasionally in service is very noticeable and can be an irritant
    • Size Limitation – due to the difficulty in processing POM-H, it cannot be made in very large cross-sections rod or plate, and not in tubes at all
    • Cost – the resin is 10%-15% higher in cost than POM-C, and costs more to make shapes

    Copolymer’s primary advantages:

    • Uniform density, eliminating the centerline porosity issue (in food service, porosity = mold)
    • Better steam / Hydrolysis resistance – up to 180F
    • Less formaldehyde outgassing – most of the formaldehyde is transformed into trioxane.
    • Less inherent stress – takes less pressure to process
    • Size Availability – rod up to 24” diameter, plate up to 10” thick, and extruded tubing; it can be made by extrusion and compression molding
    • Medical Applications – certain POM-C resins have USP approval for medical uses such as orthopedic trial implants
    • Colors – an extension of medical needs, POM-C is readily available in standard & custom colors

    NOTE: POM-H stock shapes are also available in modified versions, including three PTFE (“Teflon®”) filled grades, glass filled, UV stabilized and several different viscosity grades.

    Have questions? We can help! The experts at WS HAMPSHIRE are ready to assist you to find the right material for your requirements! Call us – you’re in the right place!

     

    Tom Connelly is a self proclaimed “Street Engineer” with 40+ years in the plastics industry.

  4. PEEK – The ‘Swiss Army Knife’ of Plastics

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    Polyetheretherketone (PEEK) is an engineering thermoplastic with an unusual combination of properties- high mechanical strength, fatigue and creep resistance, excellent chemical resistance, and the ability to perform in high temperatures. It is so robust and does so many things well, it is the most utilitarian ‘Swiss Army Knife’ in the high performance material thermoplastic group.

    First synthesized in 1978 by Victrex, it quickly became an excellent alternative to imidized materials (VESPEL® PI, Torlon® PAI).  Offering lower cost and superior chemical and hydrolysis (steam) resistance, PEEK is an ideal material for seals, bearings and insulators in oil/gas/chemical processing and other high temperature/pressure applications. PEEK offers higher strength than fluoropolymers (Teflon®) at room and elevated temperatures.

    There was only one resin source at the time, so pricing was high and general industry acceptance was slow.  In recent years, new sources have introduced PEEK based materials, reducing the price and accelerating application development, making it attractive to more markets.

    Processing techniques have also increased with shapes now being available via injection molding, extrusion, and compression molding.

    Unfilled PEEK has the highest toughness and elongation of all the PEEK materials, and by itself has good bearing & wear properties. The most popular filled grades are 30% glass filled, 30% carbon fiber filled and a bearing grade with a carbon/graphite/PTFE additive package.

    The addition of fiber reinforcement gives PEEK dimensional stability approaching that of metals.

    Here’s a brief comparison of the properties of extruded PEEK variant shapes (at 73⁰F):

    PROPERTY

    Unfilled PEEK30% Glass Filled PEEK30% Carbon Filled PEEKBearing Grade PEEK

    Tensile Strength

    16,000

    14,000

    19,000

    11,000

    Elongation %

    4025

    2

    Flexural Strength

    25,00023,00026,000

    27,500

    Heat Deflection Temperature ⁰F

    320450518

    383

    Coefficient of Thermal Expansion

    2.61.21.0

    1.7

    Dynamic Coefficient of Friction

    .32n/a.20

    .21

    Relative Wear Rate375

    n/a

    150

    100

     

    PEEK products are found in highly critical applications from High-Performance Liquid Chromatography columns to food applications as unfilled PEEK is FDA and USDA compliant. It is one of the few plastics compatible with ultra-high vacuum applications, which makes it suitable for aerospace applications ultra-pure specialty grade PEEK is considered an advanced biomaterial used in medical implants, used with a high-resolution magnetic resonance imaging (MRI), and for creating a partial replacement skull in neurosurgical applications.

    Have a need for high performance at high temperatures? Call the experts at WS HAMPSHIRE to walk you through the candidate material selection process. You’re in the right place!

     

    Tom Connelly is a self proclaimed “Street Engineer’ with over 40 years in the plastics industry.

     

  5. How to use a Technical Data Sheet.

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    COMPOSITE MATERIAL TECHNICAL DATA SHEETS –

    WHAT THEY ARE, WHAT THEY AREN’T & HOW TO USE THEM

    One of the most frequent request we get is to provide a Technical Data Sheet (TDS) for a given material. But do you know what you are getting, and how to use it?

    First – a list of what a TDS is NOT:

    • “absolute values” – they are averaged values from many data points
    • “minimum values” – – same comment
    • “QA values” – these are not “go / no go” values

    Technical Data Sheets are a comparative tool that allows you to see the general differences between materials in an organized format and is best used to compare materials from the same source!  Many mills use the resin data for their TDS, as it is the “lowest common denominator” – and there is a relatively limited pool of resin suppliers.

    All thermoset suppliers (phenolics) and some thermoplastics mills test the actual shapes, but these are averaged. Think about it-cast nylon can be made in .187” or 10” plate – so exactly what is its tensile strength?

    Some mills report ranges, technically more correct but makes comparing materials difficult – if one lists tensile is 13,000 – 15,000 psi and the other 14,000 psi, which is better?

    Also – there is no direct correlation between ASTM and ISO/DIN values – the test samples and methods are completely different. Within each system, comparisons are usually valid.  Information on electrical properties, flammability, etc are always consistent and useful “as is”.

    Not knowing the data source can have consequences. An airplane manufacturer specification required its supplier to use PAI rod with a minimum tensile strength of 22,000 psi. Their usual sources told them “in rod, it’s 18,000 psi”. Another source supplied a resin data sheet, listing tensile of 22,500 psi and won the order, but the parts ultimately failed. (NOTE: the key error here was with the airplane company, specifying extruded rod using resin data)

    Examples of “data reporting  & terminology license” to watch out for:

    • Heat Deflection Temperature – the ASTM specification says you can run this at 66 psi or 264 psi.
    • Moisture Absorption – Most mills report 24 hr moisture pick-up, and full saturation values – but some report “equilibrium”, a number always lower than saturation to make the material look more stable than it really is.

    Concerned or confused? Don’t be – the material experts at WS HAMPSHIRE can help you get the right information for your application evaluation. You’re in the right place!

     

    Tom Connelly is a self proclaimed “Street Engineer” with over 40 years in the plastics industry.

  6. Material Temperature Ratings- What do they Mean?

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    Material data sheets usually list several temperature values – what do they mean, and how do you use them to help select the best material for your application?

    These values are different for thermoplastics (defined as materials which can be remelted) and thermosets (materials which are crosslinked and therefore cannot be remelted). Today, we deal with the true thermoplastics.

    Melt Temperature

    Temperature when a material goes from a solid to a liquid, obviously a “limiting” value!

    Glass Transition (Tg) Temperature

    Temperature when an amorphous thermoplastic (think acrylic or ABS) becomes soft and rubbery.  This feature allows certain resins to be thermoformed, though it can be problematic in service.

    Continuous Use Temperature 

    This value is technically defined as the maximum ambient service temperature (in air) that a material can withstand while retaining 50% of its initial physical properties after long term exposure (100,000 hours, or about 11 years) with no load applied. It’s a function of thermal degradation through oxidation.

    Heat Deflection (or Distortion) Temperature

    This is the temperature at which a 1/2” thick test bar, loaded to a specified bending stress, deflects by .010″ in under a given load (either 66 psi or [more commonly] 264 psi. This is the “working load” temperature, indicating the limit a material can withstand under load.

    (NOTE – “heat stabilized” plastics have an antioxidant added, it can add to Continuous Use Temperature but does NOT help Heat Deflection Temperature!)

    So – functionally, what does this mean? Take PTFE (“Teflon®”) – everyone knows it’s a 500F material, but that is continuous use – at about 160F you can push your finger into it (Heat Deflection Temperature).

    Some Guidelines

    • In general, with the lower temperature thermoplastics the Heat Deflection Temperature is at or above the Continuous Use Temperature.
    • In general, it’s the opposite with the higher performance thermoplastics as the Continuous Use Temperature is higher than the Heat Deflection Temperature (see the PTFE example, above)
    • Most thermoplastics can withstand short term excursions beyond the values given, as long as the loads are not near the “safe load limits” for the material.  When passing the Continuous Use Temperature values – parts usually wear out long before the 11 year thermal degradation means anything.

    This last point leads to a discussion on Dynamic Modulus Analysis.  This is where viscoelastic materials’ properties change with increases in temperature.  That one is a topic for another blog post – stay tuned!

     

    Tom Connelly is a self proclaimed “Street Engineer” with over 40 years in the plastics industry.

  7. Sourcing Solutions for Composite Materials

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    You have been tasked with finding new sources for non-metallic components – where to go?

    There is always a web search, but that will only get you a list prioritized by how well each company can work the search algorithm.

    • Are they qualified to produce my parts?
    • Can they answer my questions?
    • Will they offer me alternative materials and help me make the right choices for MY company, not theirs?

    Look no further – we can help!

    Having offered custom non-metallic solutions in a wide range of industries for well over 100 years, WS Hampshire knows how to evaluate your application to determine the most appropriate composite material as well as what design considerations must be evaluated.

    There are often times multiple ways to make a given part, largely depending on volume, desired performance, and cost. Expertise in this area can save you money and a lot of headaches! Raw material selection is key to performance in the application and some parts can be made from sheet or tube while others can be made from a casting or extrusion. Knowing howwhen, and why to use a specific material can make a world of difference in what your part costs and how well it performs.

    With these and other sourcing considerations – the experts at WS Hampshire can walk you through how to obtain your composite parts in the most cost-effective manner.

     

    For example : A beverage OEM was buying a “U-Channel”, made in virgin UHMW. His previous source machined the part from plate, which was costly in two ways (additional material and additional machining).  The finished channel had a rough machined pattern on the inside surfaces which caused drag as bottles slid within the channel. An extruded version offered by WS Hampshire, requiring only slight secondary machining for the attachment holes. Even after amortizing the relatively inexpensive tool, the OEM saved over 30% per foot with a smooth finish and lengths longer than 10 ft were now available – a high ROI with a superior product!

     

     

  8. Positive Environmental Impacts of Plastic

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    Materials touted as “all natural alternatives” to plastic were often actually replaced by plastic decades ago because it was better for the environment.

    Plastics have been saving the planet since long before there was Earth Day, an annual event supporting environmental conservation.  Despite the massive amount of single use plastic waste that irresponsibly enters our oceans, plastics actually play an important role in protecting the environment.

    In 1869, John Wesley Hyatt used natural cellulose to create a substitute for the ivory used in piano keys, billiard balls, and similar products.  The result was a substantial  decrease in the slaughter of elephants for their tusks. Hyatt’s invention also replaced tortoise shells used for jewelry, hair combs, picture frames, and many more household items.  New plastics were then created and quickly began replacing other environmentally harmful materials.  In the 20th century, plastics began to replace paper, natural rubber, and even silk, all of which prevents deforestation.

    The reality is that plastic has saved many species from possible extinction expanding access to products for working and middle-class people.

    Plastics also replace energy-intensive iron and steel in auto manufacturing, construction and process industries.  Examples include better wearing composite stripper blades in steel mills and nylon sheaves used in construction cranes.

    Plastics Offer Safety Advantages

    From sheaves for lifting equipment to slipper blocks in steel mills to slide bars on pile driving equipment to car windows and aircraft hangar door rollers, plastics offer a greater degree of safety. Typically, about 1/7th the weight of steel, iron or bronze, installation is much easier with one person able to install components that used to take two people or even a crane. Yes, finding discarded plastic bottles along the road is irritating – but those of us with some years behind us remember all the broken glass from beer and soda bottles along the road that used to take out our tires. Glass processes at ~2800F in an extremely long process – that’s over 5 times the temperature, and vastly more energy, required than to make plastic bottles

    Plastics Actually SAVE Energy and Water Resources

    Plastics save water and energy, too. Corroding metal pipes result in the loss of ~17% of all water pumped in the United States and more than $50 billion a year in maintenance and replacement costs. Plastic piping can last more than a century and corrosion resistant plastics extended the life of pumper truck tank applications in agriculture and fire-fighting equipment.  Plastic insulation saves 40 times the energy required to make it while offering excellent shipping/fuel cost savings.

    Plastics Benefit Conservation

    Plastics are important to virtually every human activity today, including environmental conservation. Waste management and recycling is a major focus of the plastics industry as a means to continue society’s progress.

    The same spirit of innovation that created environmentally responsible replacements for ivory and tortoise shell is developing new materials, designs, and recycling methods that conserve resources and reclaim the value of used or discarded plastic.

    Recycling innovations include optical sorting, light-reflection technology to identify a variety of difficult-to-sort recyclable materials. Advanced recycling is an environmentally safe process that returns plastic to its basic chemical building blocks for reuse.

    And it might sound like science fiction, but enzymatic recycling — bacterial compounds that “eat” plastic waste and produce new plastic — are in the works and could become a reality.

    Let’s Focus on What Works-

    Today, innovation in life-cycle technology is the best key for the world to continue to reap the benefits of composite materials while minimizing solid waste.  Companies are now transforming windshield safety glass into new carpets and removing contaminants from recycled material to produce near-virgin-quality resins. In one case, a parking lot was paved with the equivalent of 71,000 recycled plastic bags.

    Did you know plastic bags require 70% less energy and 96% less water to manufacture than paper bags? And you can’t pave a parking lot with paper bags.

    Constant innovation is why we should never ban plastic materials or products that conserve resources and protect the environment — important to remember on Earth Day and every day!

    There are bills in Congress offering practical, bipartisan solutions. The RECOVER Act would improve collection and sorting of recyclable materials. The RECYCLE Act would fund public awareness of recycling options. The Plastic Waste Reduction and Recycling Act would develop new recycling technologies.

    When activists seek to ban or severely restrict the usage of plastic, it’s important to consider what materials would serve as replacements. More often than not, plastic actually replaced these other materials decades ago due, in part, to being more environmentally friendly. Let’s embrace innovation and build upon what works!

     

    Tom Connelly is a self proclaimed “Street Engineer” with over 40 years in the plastics industry.

  9. Nylon or Acetal- How to choose

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    Two of the most widely used engineering thermoplastics are nylon (polyamide, “PA”) and acetal (polyoxymethylene, “POM”).  The choice between the two can be difficult since their basic physical properties are similar. (FUN FACT –“Nylon” was once DuPont’s trade name for PA, but they didn’t protect it and it became the generic description!)

    For our purpose here, we are discussing these materials in general terms without differentiation of extruded vs cast in nylon and homopolymer vs copolymer in acetal.

    Material Cost

    Acetal shapes tend to be more expensive than nylon by about 10%.  The difference gets larger as size increases due to the economy of casting nylon in large shapes.

    Availability

    New technology allows acetal to be available in plate up to 10” thick and rod to 24” diameter as well as tubes up to 20” OD. Nylon is available in both small and massive shapes (78” diameter sheaves and 14 ft long slide bars have been cast in nylon). Additionally, nylon is readily available in custom profile extrusions (edge guards, clip-on wear strips) where acetal generally is not.

    Formulations

    Nylon has a wide availability of modified versions to improve wear resistance, heat stability, impact resistance and flame retardancy.  Acetal has some of these variations but less than the nylon family.

    Key Differences

    Machineability

    Both materials machine well, but nylon is known to generate chip wrap requiring spindle clearing. Both materials can be finished to excellent surface finishes

    Moisture Absorption

    Nylon picks up ~2.5% moisture atmospherically, and up to 7% at saturation.  This factor can inhibit dimensional stability and wet wear resistance. Acetal’s water absorption is 0.2% and 0.9%, respectively, which allows for closer tolerances in wet environments.

    Wear Resistance

    As a general rule is that nylon will outwear acetal by ~4:1 in dry applications and acetal will outwear nylon by the same ~4:1 ratio in a wet environment.

    Summary

    In most applications, many materials will work and the selection of the most appropriate candidate material can rest other considerations. WS HAMPSHIRE has the expertise to ask the right questions and make effective recommendations to assist you in finding the right material at the right price for your application!

     

    Tom Connelly is a self proclaimed “Street Engineer” with over 40 years in the plastics industry.

  10. You’re in the Right Place

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    Here at WS Hampshire, customization and problem solving are a way of life.  We do a little of everything with applications including wear parts in steel mills, insulation for the lighting industry, sheaves and wear pads in construction equipment and fire trucks, thermal insulation, structural fiberglass, and custom composite components for almost any aspect of industry.  Our global supply chain means that we have access to a wide variety of composite materials and can determine the best raw material and grade for your specific application.

    Our team fully understands that no two applications or customers are the same and is happy to help with a custom order for a unique project, or to build a large scale stocking program to keep your operation running.

    Whatever your needs, know that you are in the right place!

    Contact us and let us know what you are working on today.