UHMW Rod, Static Dissipative

Static-dissipative UHMW rod, cut to length and sold by the foot.

This is the static-dissipative grade - carbon-filled UHMW, black, for places where a charge building up on a plastic wear surface is a problem. Powder and granule handling, solvent-wetted lines, electronics assembly, anywhere an ignition source or a product-quality defect can come from static.

Static-dissipative UHMW is normally specified in the 10^6 to 10^9 ohms-per-square band and measured to ANSI/ESD STM11.11. Below roughly 10^4 a material is called conductive and above roughly 10^11 insulative, though those boundaries are industry convention rather than a single standards definition - so tell us the number your specification calls for rather than the word, and we will match it. For scale, unfilled UHMW measures 10^15 or higher. ANSI/ESD S20.20 requires worksurfaces and floors to come in below 10^9 ohms.

What the carbon costs you is small, which is the good news: a couple of percent on density and on wear index, slightly higher stiffness, and the loss of color choice - these grades are black only. The abrasion, impact and friction behavior you buy UHMW for is essentially intact.

We make no food-contact claim on this line. Published positions vary grade by grade - one maker's food-grade ESD sheet declares EU 10/2011 compliance and says nothing about FDA, while several others state FDA, 3-A, USDA and NSF all No - so this is a claim that has to come from a specific mill letter, never from the category. If you need a food-contact static-dissipative grade, ask us and we will chase the certificate.

UHMW is the wear material. Molecular weight in the millions - typically 3 to 6 million g/mol, ten to thirty times HDPE - gives it an abrasion life nothing else in this price range touches, and an impact behavior that simply does not break. If something slides against it, tumbles down it, or hits it, this is the material.

On abrasion the numbers need their scale to mean anything. In the sand-slurry test where 1018 carbon steel is the 100 reference and lower is better, UHMW comes in at 10 to 12. HDPE is 110. So in that test UHMW loses roughly a ninth of the volume HDPE does, and about a tenth of what carbon steel does. That is a test result, not a general warranty - but it is why chute liners, truck beds and conveyor wear strips are made of this and not of steel.

Impact is where it is genuinely unmatched. Under the standard notched Izod test, ASTM D256 Type A, UHMW does not break - the industry had to move to double-notch methods just to get a finite number out of it, and on that method it reads around 18 ft-lb/in. Treat those as two different tests, because they are. It stays tough cold, too: brittleness temperature is below -38C and minimum service runs to -150C.

Temperature is the real ceiling and it is lower than people expect. Maximum continuous service in air is 180F. Heat deflection at 264 psi is only 116F. And the number worth pausing on: tensile strength is published at 5,800 psi at 73F and 400 psi at 150F - a 93 percent loss, and five separate grade datasheets print the same figure. We would treat anything warm and loaded as something to test rather than calculate. It melts around 270F, which is not a service temperature.

It creeps. Deformation under load runs 6 to 8 percent at 2,000 psi and 122F over six hours, and the figure the trade calls "compressive strength" - 2,400 to 3,000 psi - is itself measured at 10 percent deformation, not at failure. For a real design number use compressive stress at low strain: about 1,015 psi at 1 percent, 1,595 at 2 percent and 2,540 at 5 percent. The practical failure mode is not cracking but material flowing out from under a bolt head or a point load.

Thermal expansion is high enough to design around: 110 microinches per inch per degree F, roughly fourteen times steel. That works out to about an eighth of an inch per foot per 100F. A ten-foot liner panel moves 1.3 inches over a 100F swing, and a four-foot width moves about a third of an inch over 60F. So bolt holes want to be oversized and counterbored, fasteners must not be torqued down hard enough to stop the panel sliding, and panel joints need a gap. Ask your mill for their installation instructions - we will not invent an oversize figure for you.

Chemically it is good rather than universal. Acceptable in weak acids, alcohols, alkalis, chlorinated solvents, aliphatic hydrocarbons and inorganic salts. Limited in strong acids at pH 1 to 3, in hot water and steam, and in ketones and esters. Aromatic hydrocarbons are unacceptable. Water absorption is under 0.01 percent, so unlike nylon it does not swell or lose tolerance in a wet environment.

It cuts easily and holds tolerance badly, and those are two separate facts. Machinability rates 3 on a 1-to-10 scale, so a sharp tool and a high feed rate will get through it - the trick is clearing the swarf before it wraps. But it is elastic and it moves: diameters grow, so set to the low side; drilled holes close up, which makes taps tight; and residual stress redistributes after a cut and warps the part. For anything tight, rough it out, let it rest a day, then take a light finish cut.

It cannot be solvent cemented - nothing practical dissolves it at room temperature, which is the same property that makes it chemically resistant. Joining is by hot-gas welding with polyethylene rod, or mechanical fastening, which is how liners are normally installed. Adhesive bonding does work but needs the surface conditioned first: abrading at 100 to 120 grit is usually enough, with corona or flame treatment needed in a minority of cases, and a flexible epoxy is the right choice because it has to absorb that fourteen-fold expansion mismatch against steel.