There are many types of armor plates to choose from, each with their own pros and cons. Today we’re going to look at the differences between steel armor plates and ultra high molecular weight polyethylene (UHMWPE, or PE for short) plates.
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Steel armor is called a lot of things, but fragile isn’t one of them.
Steel armor is tough. People have dropped them, run them over with forklifts, and dumped mag after mag of rounds into them, and they just kept on going. Steel armor plates are very affordable for the level of protection offered.
But ballistic steel plates aren’t without their challenges, the most notable being weight, bullet fragmentation, and ineffectiveness against armor piercing or some super high-velocity ammunition.
Polyethylene (PE) plates are made from ultra high molecular weight polyethylene (UHMWPE), which is a ballistically resistant plastic. PE plates are made of many layers of the PE material that have been compressed and heated until it forms a hard monolithic plate.
Compared to steel, PE plates have a lot of things going for them. PE plates weigh less, float, and are effective against high velocity, non-AP or ‘green tip’ ammo.
The downsides of polyethylene plates are that they’re significantly thicker than steel, much more expensive than steel, and can lose ballistic integrity if they get too hot.
Steel vs. PE: The Breakdown
* Level III+LW = III+ Lightweight** Level III+LW stops M193 to 3,000 FPS bullet velocity
*** Prolonged exposure to below -15F (-26C) or over 150F (65.6C), or any surface melting from heat could cause PE plates to fail. If damaged, replace the plate
One of the other significant differences between steel and PE armor is in the area of backface deformation, which is the area displaced on the backside of armor when a bullet strikes it. The NIJ standards allow for up to 44mm (about 1.73″) of backface deformation, but steel armor tends to handle it much better than PE plates.
For more information on backface deformation, visit our YouTube channel, where we have several videos showing examples of different levels of backface deformation.
So which should you buy? As with most everything in the industry, the answer is “it depends.” Armor is a compromise between protection, price, and profile (weight/thickness). Both steel and PE have their pros and cons.
HDPE (high-density polyethylene) and UHMW (ultra-high molecular weight polyethylene) are both thermoplastic polymers made from ethylene monomers. The two plastics are indistinguishable based on appearance. The raw materials for both plastics are the reactive gases ethylene and hydrogen. These are polymerized in the presence of a catalyst, which differs depending on which plastic is being produced: a Ziegler-Natta catalyst for HDPE, or a metallocene catalyst for UHMW.
HDPE can be injection molded or blow molded, or formed into sheets and then further shaped using thermoforming, vacuum forming, or plastic welding techniques. It is a great option for manufactured chemical and water tanks. UHMW is a highly durable, affordable, and abrasion-resistant material used in a variety of wear applications. This article will compare the properties, applications, and costs of HDPE and UHMW.
High-density polyethylene, or HDPE, is a type of thermoplastic polymer. Compared to other polyethylene types, it has a high density (0.95 g/cm3). The polymer chains can be closely packed in this substance because the degree of polymer chain branching is quite low. HDPE is fairly hard and offers good impact resistance. HDPE’s properties are unchanged by exposure to temperatures of up to 120°C and are autoclavable as a result. Some of HDPE's key characteristics are: high impact resistance, autoclavability, opaque/translucent appearance, high strength-to-weight ratio, low liquid permeability, and good chemical resistance.
To produce HDPE, ethylene monomers, a Ziegler-Natta catalyst, hydrogen, and a comonomer are polymerized with a solvent. The solvent's main role is to carry heat away from the reaction sites where polymerization occurs. An external circulation heat exchanger then removes excess heat from the reaction chamber. The separation/drying process receives the reacted slurry. Transferring the slurry to a high-speed centrifuge allows the separation and recycling of the inert solvent from the newly-formed HDPE particles. The HDPE particles are dried under an atmosphere of high-temperature nitrogen and steam, which removes any remaining solvent, and leaves a dry, uniform HDPE powder behind.
In the powder dryer, the solvent is evaporated using high-temperature nitrogen and steam, which dries the wet powders. The scrubber recovers the solvent that has evaporated. The dried HDPE powder is transferred to an extruder, which melts and pelletizes the powder into the final raw HDPE material. Typical applications of HDPE include: containers for liquids, plastic shopping bags, pipe fittings, trays, and cutting boards. For more information, see our guide on What is High Density Polyethylene.
Ultra-high molecular weight polyethylene, also known as UHMW or UHMWPE, belongs to the thermoplastic polymer family. UHMW's ultra-high molecular weight (5-9 million AMU) is derived from its extraordinarily long polymer chains, all aligned in the same direction. Van der Waals forces bind each polymer chain to the others in its immediate vicinity. This increases the amount of energy it takes to separate the chains, which gives UHMW its superior toughness and impact resistance.
As with the somewhat lower-density member of the polyethylene family, HDPE, UHMW is produced by the polymerization of ethylene. Differences in the details of the chemical synthesis account for UHMW's greater density. Some of UHMW's key characteristics are: toughness, high impact resistance, crack resistance, non-adhesive properties, and non-toxic nature. Typical applications of UHMW include: star wheels, rollers, gears, screws, and sliding plates. Figure 1 are examples of UHMW plastic:
Previously published on fastradius.com on August 18,
Polyethylene is a thermoplastic with a variable crystalline structure. This popular material is used in everything from shopping bags, to pipes, to prostheses and other medical devices. With several grades, types, and formulations of polyethylene available, it’s essential to learn about each material’s properties, advantages, and disadvantages before deciding which type to use for your product. Here’s everything you need to know about ultra high molecular weight polyethylene (UHMW or UHMWPE) from its molecular structure to its many uses.
An extremely dense form of polyethylene, UHMW is a semi-crystalline thermoplastic composed of long chains. UHMW forms when ethylene molecules bond, and the resulting UHMW molecules are much longer than the molecules found in other forms of polyethylene thanks to the presence of metallocenes. These compounds can serve as a catalyst and usually consist of positively charged metal ions located between negatively charged cyclopentadienyl anions.
With compression molding, sintering, ram extrusion, or gel spinning, UHMW can be produced as a sheet, rod, strip, or tube. Though the polymerization of UHMW wasn’t commercialized until the s, it was quickly recognized as a versatile material suitable for many applications.
UHMW plastic is very strong thanks to each molecule’s impressive length and high molecular orientation. In fact, UHMWPE fibers are among the strongest and lightest on the market today. UHMW is tough, slick, and durable with high tensile strength. It’s also highly resistant to corrosive chemicals, wear, abrasion, impact, moisture, and cold temperatures.
As the name suggests, UHMWPE has a very high molecular weight between 3.1 and 100 million grams per mole. Some of UHMW’s mechanical properties include:
When considering using UHMW plastic for your next project, you should know that UHMWPE fibers are less resistant to heat than other high-strength plastics. UHMW polyethylene fibers have a melting point between 144 °C and 152 °C and shouldn’t be used for extended periods at temperatures above 80 °C to 100 °C. Also, even though UHMW plastic is known for its ability to withstand cold temperatures, it will become brittle at temperatures below -150 °C (or -240 °F).
With compression molding, sintering, ram extrusion, or gel spinning, UHMW can be produced as a sheet, rod, strip, or tube.Due to its strength and durability, UHMW is often used in belt scrapers, chain guides, idler rollers, sprockets, packaging machinery components, and gears. Other UHMW plastic uses include bearings, conveyor systems’ star wheels, guard rails, and food processing machining parts.
UHMWPE’S strong and light fibers make it an ideal material for body armor. It provides increased ballistic protection and resistance to cuts while remaining comfortable to wear. Many prostheses also contain UHMW due to its biocompatibility, strength, and wear resistance. UHMW’s abrasion and moisture resistance make it a popular choice for building docks, and its resistance to cold temperatures makes it an ideal material for snowplow blades, snowmobile skis, skid steers, and truck bed liners.
It’s challenging for many product teams to decide between HDPE and UHMWPE. After all, high-density polyethylene (HDPE) and ultra high molecular weight polyethylene (UHMWPE) are both linear versions of polyethylene plastic that are affordable as well as resistant to abrasion, chemicals, and impact.
HDPE is well suited for use in fuel tanks, piping, and outdoor furniture, and unlike UHMW, it is ideal for injection molding. However, it may crack under stress. In contrast, UHMW is incredibly dense and strong — in fact, its strength rivals steel. UHMW’s combination of high tensile strength, wear resistance, impact resistance, and self-lubrication make it an ideal material for industrial applications as well as high-performance equipment.
UHMWPE is a strong, water-resistant, and biocompatible plastic that’s suitable for a wide range of applications, from docks to orthopedic implants. It’s highly versatile, durable, and easy to fabricate, making it an ideal choice for many projects. Working with an experienced manufacturing partner when selecting materials can simplify the process and elevate your final product.
When you partner with SyBridge, we’ll work with you and offer in-depth information to help you navigate the manufacturing process. Backed up by years of manufacturing experience with a wide range of materials, we can guide you to the best material that will help you achieve your manufacturing goals. Ready to get started? Contact us today.
What is UHMW-PE?
UHMW-PE stands for Ultra High Molecular Weight Polyethylene. It is the highest quality polyethylene (PE) available, engineered for tough jobs and a wide range of applications. It delivers savings in a number of difficult applications. Ultra High Molecular Weight is the secret of this polymer’s unique properties. Its high-density polyethylene resin has a molecular weight range of 3 to 6 million, compared to 300,000 to 500,000 for high molecular weight (HMW) resins. That difference is what ensures that this material is strong enough to withstand abrasion and impact better than lower level poly products. UHMW-PE’s high molecular weight means it will not melt or flow as a molten liquid. Processing methods are therefore derived from those of powder metal technology. UHMW-PE cannot be transformed and molded by conventional plastic processing techniques (injection molding, blow molding or thermoforming). Compression molding is the most common conversion process used with this resin because it produces a stronger, more consistent product.
What is TIVAR®?
TIVAR® is the brand name (from Poly-Hi) for a special formulation of ultra high molecular weight polyethylene (UHMW-PE). UHMW-PE is a unique family of high-density polyethylene with a molecular weight 3 million or higher. UHMW-PE is a high performance polymer with a high melt viscosity that can be extruded, fabricated or compression molded.
What does TIVAR® stand for?
TIVAR® is an acronym for Tough Inert Very Abrasion Resistant.
What are the key properties of TIVAR® UHMW-PE?
TIVAR® is known for its high abrasion resistance, natural lubrication, high impact strength, chemical-, corrosion-, and moisture-resistance and acoustic impedance.
Why use TIVAR®?
Due to its abrasion-, corrosion-, chemical- and moisture-resistant properties, TIVAR® is commonly used in applications where conditions may be too harsh for other materials. It is a cost-effective high performance polymer used to produce low cost, high quality parts.
How does TIVAR® compare to other materials?
In most cases, TIVAR® will out-wear materials such as Nylon, Teflon® or Acetal. It can also outperform metals such as steel and aluminum when used in the proper applications. Material performance is of course dependent on the specific environmental conditions.
Where is UHMW used?
UHMW is a self-lubricating material which exhibits excellent wear and abrasion properties as well as adding extremely high impact strength. A few of the markets which would utilize these attributes would be snowboard bottoms, package handling, packaging, food processing and automotive.
What are the benefits of UHMW-PE?
The high molecular weight is what gives UHMW-PE a unique combination of high impact strength efficient of friction and abrasion resistance that outwears carbon steel 10 to 1 making it more suitable for applications where lower molecular weight grades fail.
A
re UHMW-PE USDA and FDA approved?
Yes, UHMW-PE is both FDA and USDA approved for use in food processing and medical applications.
How do you differentiate UHMW from HDPE?
There are three tests you can perform:
What is the temperature range of UHMW?
UHMW-PE can operate continuously up to 180 degrees F and intermittently at 200 degrees F with custom blends available to enhance the temperature range up to 300 degrees F. UHMW-PE can perform without degradation at extremely low temperatures (-452 degrees F).
What are the heat characteristics of UHMW?
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The sustained high temperature use is 180 degrees F and the intermittent use is 200 degrees F.
Does UHMW degrade at higher temperatures?
Not for short times but for longer times above 200 degrees F it loses mechanical properties, abrasion and impact.
What chemicals affect UHMW?
Water solutions are generally safe except highly oxidizing chemicals such as bleach. Hydrocarbons such as gasoline, kerosene, oil and grease cause swelling. Chlorinated solvents cause swelling. Organic alcohols, ketones and acids have little effect.
How does the environment affect UHMW?
What is the flammability of UHMW?
UHMW has no UL recognition. It would be HB on UL-1 – that is slow burning (less than 3″ per minute).
How can you tell if a sample of UHMW contains regrind?
It is hard to tell – maybe some black or other colored specks might be present. The only way to determine is by a sand slurry test. After that test, it would tend to feel stiffer or harder. There may be some increase in modules. If the resin has been reprocessed many times, abrasion and impact resistance can greatly affected.
Can UHMW be used for underwater applications?.
Yes, UHMW does not absorb water and is chemically inert.
How does UHMW protect metal from wearing away?
UHMW has the highest abrasion resistance of any thermoplastic polymer. When used as a wear liner, UHMW will not cake or stick to metal. It also offers excellent noise abatement in material handling applications.
Is it necessary to grease or oil UHMW?
No, UHMW is a self-lubricating polymer and requires no additional lubrication.
Is UHMW affected by cryogenics?
Hydrogen and nitrogen don't affect it, but oxygen could.
Are there any high performance blends that can be added to UHMW-PE?
UHMW manufacturers have done extensive research on numerous additives that can enhance a property of UHMW-PE thereby providing customized products to meet customer requirements.
Is TIVAR® H.O.T weldable?
Yes
Is TIVAR® H.O.T available in other colors?
No, only pigmented white (the standard, stock color) and black FDA can be made. For black, minimum order amounts would apply. Other colors would bleed out at higher temperatures, and therefore something you would want to avoid.
What other colors of UHMW-PE are available?
While natural (milky white) and black are standard stock colors, UHMW-PE can be produced in a variety of Pantone colors.
Does TIVAR® melt or freeze?
Although TIVAR® never actually melts, it will begin to lose its excellent properties at a temperature of 180 degrees F (82 degrees C). TIVAR® will generally perform very well down to cryogenic temperatures, but like other plastics, it will expand and contract with variations in temperatures.
Is UHMW available in a conductive or anti-static form?
UHMW can be manufactured in conductive or anti-static forms making it ideal for use in electronics and semi conductor applications.
Is UHMW UV stable?
In its natural state, UHMW-PE is not UV stable, but formulations are available to provide UV stability in natural, black or any custom color.
Many people ask: can I coat UHMW on wear surfaces?
No, you can’t coat UHMW on because of two reasons: It does not melt to form a continuous surface.; It requires pressure to weld all the unmelted particles at high temperatures.
Is there an alternative to coating parts?
Yes, wear tape is a thin film of UHMW with adhesive backing than can be bonded to the surface.
In what form are UHMW-PE film and tape available?
UHMW can be made in films .003″ through .125″ thick in continuous coil from ¼” up to 24″ wide and cut to length in pieces and in stamped parts.
What kind of tolerances can you get with TIVAR®?
Tolerance levels are dependent on the manufacturing method and part design. Contact us for specific technical data.
Can UHMW be ultrasonically welded?
Yes, again the process is much like regular HDPE. Thick sections of UHMW may be more difficult than HDPE because of lower modules. If the plastic is softer, like UHMW, more attenuation of the ultrasonic energy occurs.
Can UHMW be thermal welded?
Yes, it behaves much like regular HDPE. The minimum temperature is 400 degrees F and the minimum pressure of 300 psi is highly recommended.
What percentage of parent strength of UHMW can be attained?
0.8%.
Can adhesives be used to secure UHMW liners?
Not for most applications. The reason is the large difference between the coefficient of thermal expansion of metal and UHMW puts high stresses on the bond if the bond encounters temperature extremes.
What are my installation options for UHMW?
There are two methods of adhering – the use of pressure sensitive systems (peel and stick) and allowing UHMW-PE to be bonded using epoxy systems or contact cements. A traditional metal mechanical fastening can also be used if preferred.
Can UHMW be formed into a curved liner?
Bending or folding sheet can be done efficiently above the melt point at 300 degrees F. At that temperature, it shapes easily. However, it must be fastened in the bent or folded position until cooled.
How thick should UHMW liners be?
The minimum UHMW thickness is usually 1/4″. The liner should be thicker in impact areas and thinner in slide areas. Important notes: UHMW cannot be firmly fastened to metals because of a large difference in thermal expansion. UHMW expands five times as fast as steel and three times as fast as aluminum and about the same as wood but slightly more than concrete.
What is the best way to secure UHMW liners to metal?
Fasteners are the best way to secure UHMW to metal. The UHMW must be allowed to expand or float. Large flat head fasteners must be used. Fastener shaft holes in UHMW must be over-sized to allow for sheet expansion and contraction.
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