A sealing ring costs pennies, but its failure stops a hydraulic press, drops the pressure in a cylinder and floods the assembly with oil. When a rubber ring hardens, cracks and starts leaking every few months, the maintenance crew replaces it again and again while the line stands idle. TIMOL polyurethane rings have wear resistance 2-5 times higher than standard rubber, hold pressure without permanent deformation and work in the range from -60 to +100 °C. Below we look at exactly where such rings are used, how they outperform rubber, silicone and PTFE, how to choose the hardness and order manufacturing to a drawing.
Where polyurethane rings are used
Polyurethane rings go where you need tightness under pressure and resistance to friction at the same time. These are seals for hydraulic and pneumatic cylinders, shut-off valves, flanged pipeline joints, rod and piston groups, and assemblies working in water, oil and mildly aggressive solutions. The ring is pressed against the surfaces and provides a tight fit, while the elasticity of polyurethane compensates for micro-irregularities and runout.
In moving assemblies the ring is subject to constant friction against the rod or cylinder. This is exactly where polyurethane beats rubber the most: for abrasion per DIN 53516, polyurethane shows 38-39 mm³, whereas SBR rubber reaches 100-200 mm³, meaning rubber wears several times faster for the same rod stroke. In static joints the ring acts as a sealing gasket, and here what matters is the material’s ability to hold its shape under prolonged compression without permanent deformation.
Free casting technology makes it possible to produce a ring of any cross-section: round, rectangular, oval, chamfered or with a complex profile to suit a specific seating. Ready-made size variants and manufacturing to drawing are presented in the catalogue of polyurethane products.
Why polyurethane outperforms rubber, silicone and PTFE
Polyurethane combines wear resistance, strength and elasticity in a proportion unattainable for classic sealing materials. Rubber is tight but wears out and ages quickly; PTFE is chemically inert but has low wear resistance; silicone withstands temperature but is weak in tension. Polyurethane covers all three weak points at once.
Compared with NBR rubber (abrasion 80-150 mm³) and SBR (100-200 mm³), polyurethane loses only 38-39 mm³ in the abrasion test. The tensile strength of polyurethane is 39-87 MPa versus 10-25 MPa for nitrile rubber, so the ring does not tear at the edges and holds tension better. Silicone rubber covers a wide temperature range, but its abrasion is 150-350 mm³ and tensile strength only 5-12 MPa, so as a working seal under pressure it is no competitor. PTFE has minimal friction and chemical inertness, yet its abrasion of 200-500 mm³ and tendency to creep under load make it suitable rather for anti-friction sliding rings than for loaded seals.
Another advantage of polyurethane is mechanical memory. After the pressure is removed, the material returns to its original shape, whereas rubber over time develops permanent deformation and stops sealing. This directly extends the maintenance interval.
Comparison table of materials for sealing rings
| Material | Abrasion DIN 53516, mm³ | Working t, °C | Hardness | Tensile strength, MPa | Rebound elasticity, % |
|---|---|---|---|---|---|
| Polyurethane TIMOL | 38-39 | -60…+100 | 85A-95A | 39-87 | 34-61 |
| NBR rubber | 80-150 | -30…+100 | 40A - 90A | 10-25 | 20-45 |
| SBR rubber | 100-200 | -40…+80 | 40A - 80A | 8-20 | 30-55 |
| Silicone rubber | 150-350 | -60…+230 | 20A - 80A | 5-12 | 40-65 |
| PTFE | 200-500 | -200…+260 | 50D - 65D | 15-35 | n/a |
The table shows why in loaded moving seals polyurethane has no equal among elastomers: the lowest abrasion (38-39 mm³) is combined with the highest tensile strength (39-87 MPa). Silicone and PTFE win only on temperature range, so they are chosen narrowly for heat-resistant or chemically aggressive conditions where wear is not the deciding factor.
Engineer’s tip: for moving hydraulic cylinder seals, take a hardness closer to the upper end of the range (65-70 Shore D for loaded rods) so the ring does not extrude into the gap under high pressure. For static sealing rings, where you need to compensate for flange unevenness, choose softer grades in the 70-90 Shore A zone. And always check the cross-section radius and groove width before ordering: the ring should fill the seating without excessive compression.
How to choose a ring for a specific assembly
Selection begins with the geometry of the seating. For a ring with a round cross-section you need the inner and outer diameters, the cross-section radius and the groove dimensions. For rectangular and shaped rings a profile drawing is needed. These dimensions determine the tension and tightness of the joint.
Next, the operating conditions are assessed. Working pressure and rod travel speed determine the hardness: the higher the pressure, the harder the ring needs to be to avoid extrusion into the gap. The medium temperature should fit within the range of -60 to +100 °C, in which polyurethane retains elasticity and does not become brittle. The type of medium, that is oil, water, weak acid or salt solution, affects the choice of polymer formulation.
Installation is considered separately. The ring is fitted into a groove or onto a seating surface with the recommended tension, without twisting or damaging the edges. A correct chamfer at the cylinder entry and a clean surface free of burrs extend the seal’s service life. Technical recommendations on selection and installation are collected in the reference information section.
Manufacturing polyurethane rings to size
Rings of non-standard size variants are produced by free casting into a mould to the customer’s drawing or sample. First the cross-section geometry, hardness and formulation for the medium are agreed, then the tooling is made and the polyurethane is poured. Polymerisation takes place at a controlled temperature, after which the product is checked for dimensional conformity.
This approach makes it possible to reproduce even a discontinued or imported ring for which a replacement is hard to find. It is enough to provide a sample or an old ring for measurement. The order quantity is flexible: from a single part for an urgent repair to serial batches for scheduled maintenance of an equipment fleet.
To order rings for your assembly or get advice on the choice of hardness and material, reach out through TIMOL plant contacts. The engineers will help select the profile, calculate the tension and arrange manufacturing to your requirements.