Hot-cast industrial polyurethanes

MDI · TDI · PPDI · NDI

POLYURÉTHANES INDUSTRIELS COULÉS À CHAUD — GUIDE DE SÉLECTION

At Soremag, we hot-cast our polyurethane rollers and molded parts. The diisocyanate (MDI, TDI, PPDI, NDI) forms the rigid backbone — thermal resistance, load and fatigue — while the polyol (ester or ether) governs resistance to water, chemicals and solvents.

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Soremag workshop: hot casting and hardness testing of polyurethane rollers of various colors

Soremag workshop — hot casting and hardness testing of polyurethane rollers and molded parts.

General data.

The values in this sheet are recognized material-level trends; actual performance depends on the formulation, hardness, curative and post-cure — several recipe developments can target different properties. Soremag formulates to spec.

Why polyurethane? (vs rubber)

On a roller (covering)

Abrasion:
typically lasts 3 to 4× longer than rubber in abrasive environments — less downtime.
Load:
carries far heavier loads without crushing — heavy industry (metallurgy, mining).
Non-marking:
leaves no marks (unlike black rubbers) — paper, textile, finished goods.
Cut / tear:
resists better, and a nick does not propagate as it does on rubber.
Chemistry:
better resistance to oils, greases, ozone and some solvents.

On a molded part

Hardness range:
from very soft (Shore A) to plastic-hard (Shore D) while keeping elasticity.
Metal adhesion:
bonds to metal inserts far better than rubber — cored wheels, motor mounts.
Reduced tooling:
cast at low temperature and atmospheric pressure → cheaper molds (resin, aluminum).
Machinability:
hard parts can be machined (milling, turning) almost like metal for tight tolerances.

Choosing the right system: ester vs ether

Polyester (ester)

Superior mechanical robustness: cut, tear, sliding abrasion, sealing against oils, fuels and aliphatic solvents. Good dry aging. Weak point: sensitivity to hot water (hydrolysis).

Polyether (ether)

Preferred in wet or washed environments: remarkable resistance to hydrolysis and microbial attack, higher rebound, low heat build-up, low-temperature flexibility. Pure mechanical strength and hydrocarbon resistance lower than ester.

Hot cast vs cold cast — the Soremag process

Hot cast

The Soremag industrial standard

Prepolymers and curatives heated (≈ 70–120 °C), mixed, then cured several hours in an oven.
Extreme mechanics
(abrasion, tear, impact) and superior dynamics: handles hysteresis where a cold-cast PU would melt.
Massive load capacity
without permanent set · very high hardness (up to Shore D) with impact resistance.

Cold cast

For context

Two liquids (A + B) curing at room temperature — simple, economical, fast demolding.
Ideal for prototyping, soft molds, static parts and electronic potting.
But low dynamic durability: wears or degrades quickly in industrial settings.

The verdict —

for a conveyor roller or a part subject to friction, impact or heavy loads, hot casting is the way to go: it's our standard. Cold casting, while simpler, would wear out fast under dynamic stress. This hot-cast mastery is what sets Soremag apart.

Chemical & environmental resistance

	MDI ester	MDI ether	TDI ester	TDI ether	PPDI	NDI
Cold water (short contact)	G	VG	G	VG	VG	G–VG
Immersion / constant humidity	P–F	E	P–F	E	VG	F–G
Hydrolysis / hot water	P	VG	P	VG	VG	F–G
Steam	NR	P	NR	P	F–G	F
Oils & greases	VG	G	VG	G	VG	VG
Diesel & fuels	G–VG	F–G	G–VG	F–G	G–VG	G
Aliphatic solvents	G–VG	F–G	G–VG	F–G	G–VG	G
Aromatic solvents	P	P	P	P	F–P	F–P
Ketones, MEK, chlorinated solv.	NR	NR	NR	NR	P–NR	P–NR
Weak dilute acids	G	F–G	G	F–G	G	G
Strong acids	NR	NR	NR	NR	NR	NR
Ozone	G–VG	G–VG	G–VG	G–VG	G–VG	VG
Low temperature (flexibility)	F	VG	F	VG	G–VG	F–G
Continuous heat	G	G	G	G	VG	G–VG

E Excellent

VG Very good

G Good

F Fair

P Poor

NR Not recommended

Physical & mechanical properties

	MDI ester	MDI ether	TDI ester	TDI ether	PPDI	NDI
Abrasion	VG	G–VG	VG	VG	E	E
Cut	VG	G	VG	G–VG	E	E
Tear	VG	G	VG	G–VG	E	E
Tensile strength	VG	G–VG	VG	G–VG	VG	E
Rebound / resilience	F–G	VG	F–G	VG	VG–E	E
Low hysteresis (heat build-up)	F	G–VG	F	G–VG	VG–E	E
Dynamic fatigue (flex)	F–G	VG	G	VG	E	E
Compression set	G	G–VG	G	G–VG	E	E
Load capacity	G–VG	G–VG	G–VG	G–VG	G–VG	E
Heat resistance (service)	G	G	G–VG	G–VG	E	VG
Dimensional stability	G	G	G	G	VG	VG–E
Castability	VG	VG	VG	VG	F	F–P
Material cost	$	$	$	$$–$$	$$$	$$$

Material cost: $ economical → $$$ premium.

Low hysteresis = E means little heat build-up (advantage).

Selection rules

Water rule

Constant humidity, frequent washdowns, hydrolysis

→ POLYETHER (MDI ether or TDI ether)

Oil rule

Oils, greases, diesel, aliphatic solvents

→ POLYESTER (TDI ester or MDI ester)

Dynamic-load rule

Heavily loaded rollers, heavy wheels, high speed

→ NDI first, otherwise PPDI

Thermal & fatigue rule

Continuous service > 90 °C, extreme flexing

→ PPDI

Choosing by need:

economical wear part (no water) → MDI/TDI ester · standard roller or idler → MDI/TDI ether · scrapers, wiper blades, abrasive & oily environments → TDI ester · heavy material-handling wheel / NVH → NDI · high-performance seals and thermal resistance → PPDI · ketones, chlorinated solvents or strong acids → polyurethane is not suitable (consider FKM, PTFE…).

Soremag expertise & formulation

Each system is available in many hardness and recipe variants; FDA / food-contact and antistatic / conductive grades on request. All these systems are based on aromatic isocyanates and yellow under UV with no notable loss of mechanical properties. Handling is regulated (diisocyanates — REACH training required). Non-contractual document — indicative values; testing under real conditions recommended.

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