FAQS FOR UHMW

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.

ARE 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:

1. Burn Test – light it with a match and smell the smoke. If it smells like candle wax – that indicates polyethylene. UHMW does not drip as readily as HDPE but it will drip.
2. Oven Test – place it in an aluminum dish in a 300 degree oven. Regular HDPE will slump or melt but UHMW will not change size or shape. However, it could warp or distort due to built in stresses.
3. Saw Test – When cut with a saw, regular HDPE gives sawdust or filings while UHMW gives strings or nothing.

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?

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?

·         Wind – no effect

·         Rain or sea water – no effect

·         Sun without protection – depends on thickness and location. The thicker the better. In Florida, Arizona, New Mexico, and other desert areas – less than one year.

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.