UHMW Sheet, TIVAR H.O.T.

TIVAR H.O.T. high-temperature UHMW sheet, sold by the full sheet.

TIVAR H.O.T. exists for one reason and it is a good one: continuous service in air of 230F against 180F for every other UHMW grade here. The maker does not expand the acronym or name the modification, and we are not going to speculate about what is in it.

The published figures: 110C / 230F continuous in air over 20,000 hours, based on thermal-oxidative degradation, with a minimum service temperature of -200C. Tensile 6,800 psi, higher than standard UHMW. Heat deflection at 1.8 MPa is still 116F, so this buys you long-term thermal survival, not load capacity when hot - the distinction matters. Dynamic coefficient of friction 0.15 to 0.30, wear rate 6 micrometers per kilometer, volume resistivity 10^14 ohm-cm.

This grade carries the clearest food-contact statement of any UHMW we researched: the maker states compliance with both EU 10/2011 and FDA 21 CFR 177.1520. That declaration is theirs, names their product, and we will supply it on request.

It is for wear parts that run warm - wash-down and pasteurizing lines, hot-fill equipment, dryer and oven-adjacent conveyors - where standard UHMW would be above its service ceiling.

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.

Friction is low but let us be accurate about it. Dynamic coefficient against dry steel is 0.10 to 0.20. PTFE is about 0.10, so PTFE equals or slightly beats UHMW - anyone telling you UHMW is slipperier than PTFE is overselling. What UHMW gives you is friction in the same range with vastly better abrasion resistance and impact strength, at a fraction of the cost. Limiting PV is about 3,000 psi-ft/min at a 4:1 safety factor.

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.

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.