UHMW Sheet, Reprocessed

Reprocessed UHMW sheet in black, sold by the full sheet.

This is reprocessed UHMW - made using reprocessed resin rather than virgin. It is a recognised trade grade, not off-spec material: ASTM D6712, the specification for UHMW solid plastic shapes, explicitly covers both virgin and recycled UHMW, and every major mill offers a reprocessed line. It is the economical way to buy UHMW for general wear duty.

What it costs you is more than just the paperwork, and two of the three losses matter in exactly the job UHMW is usually bought for. Abrasion index goes from 12 to 18 on the sand-slurry scale, so roughly half again the wear. Elongation at break falls from about 450 percent to about 200, so it is much less ductile. And thermal expansion rises about 73 percent, from 11 to 19 x 10^-5 per degree F - which on a ten-foot liner panel is the difference between allowing 1.3 inches of movement and allowing 2.3. It is slightly harder and slightly stronger at yield, and notched Izod is still no break.

And the line, stated plainly: reprocessed UHMW is not supplied as FDA food-contact material, not 3-A Dairy, not USDA and not NSF. Every mill we checked says so explicitly. The 3-A standard does allow a mill's own clean in-process scrap, but that is not the same thing as bought-in reprocessed resin, and a commercial reprocessed sheet does not inherit the claim. Colors are limited too - typically black and green only. If you need food contact, traceability or dimensional stability, buy the virgin grade; we stock it in the same sizes.

It is for chute and hopper liners, wear pads, backing and guide strips, bumpers and general machined wear parts where the duty is abrasion and impact and there is no food-contact or close-tolerance requirement.

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.

Outdoor service needs a UV-stabilized grade, and color is not a substitute - black UHMW is not automatically UV-stabilized. One maker published 2,000-hour exposure data on unstabilized UHMW: its Taber abrasion index went from 2 to 182, and tensile behavior went from no break to breaking at 2,940 psi. The material that would not break now breaks. For sustained sun, specify a UV-stabilized grade and ask us.

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.

A note on how it is made, because it explains the tolerances. UHMW essentially does not flow when molten - that is literally how the ISO standard defines it - so it cannot be injection molded. It is compression molded or ram extruded into plate, sheet and rod, and parts are machined or fabricated from that stock. Sheet thickness tolerance is about plus or minus 10 percent, which is normal for the material and worth allowing for.

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.