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- What are HPU seals?
What are HPU seals?
HPU stands for hydrolysis-resistant PU and is a further development of polyurethane (PU, DIN abbreviation: PUR). PU is produced on a large industrial scale from dihydric and higher alcohols (diols or polyols) and dihydric and higher isocyanates.
The mixing ratio of the components to each other allows a wide range of properties to be set: from the well-known construction foam to thermoplastic elastomers. So it is a very versatile sealing material. Read more about seals and our seal know-how.
HPU (thermoplastic polyurethane) is a special PU variant, as it combines excellent mechanical properties with high chemical resistance and hydrolysis stability. The production of HPU is very economical, so that it has a very good price/performance ratio. As a result, it is almost universally used in sealing technology with different seals. It is ideal for demanding dynamic loads.
Modern further developments of HPU are HPU solid and HPU-MOS2. HPU solid has even improved mechanical resistance, and can be used where PTFE seals reach their limits.
HPU-MOS2 is a lubricant-filled HPU that combines the mechanical strength of HPU with high self-lubrication.
Properties of HPU seals
HPU is a versatile sealant with outstanding mechanical properties. Its tear strength, tensile strength, and elongation at break are exceptionally high, while compression set is minimal. It is especially wear-resistant, highly elastic, and capable of withstanding significant dynamic loads. Additionally, HPU has low gas permeability, making it ideal for both static and dynamic sealing applications (rod seals, piston seals, wipers, guide rings, backup rings, and O-rings).
Moreover, HPU can be easily processed through turning, milling, and grinding, facilitating the creation of custom-sized seals and special seals with unique geometries and profiles.
The operating temperature range for HPU is wider than that of PU, spanning from -20°C to 115°C (-4°F to 239°F), with special grades available for lower temperatures.
HPU exhibits good chemical resistance. Unlike standard PU, it is hydrolysis-resistant and withstands dilute acids and alkalis, seawater, and hot water up to 90°C (194°F). It is also resistant to fats, oils, mineral oil-based hydraulic fluids, aliphatic hydrocarbons such as propane, butane, and fuels (gasoline, diesel, kerosene). Additionally, HPU is compatible with pressure fluids from HFA and HFB groups.
Thanks to its FDA approval for specific grades, HPU is frequently used in the pharmaceutical and food industries.
Generally, HPU is produced in a cost-effective manner, offering an exceptional price-performance ratio. This cost efficiency, coupled with superior performance, makes HPU a favored material in dynamic sealing technologies (hydraulic seals and pneumatic seals).
When should HPU not be used as a sealing material?
Despite all the positive properties, even HPU reaches its limits with certain chemicals. It is not compatible with particularly corrosive liquids such as concentrated acids and bases.
Some solvents such as aromatic hydrocarbons (benzene and toluene) and polar solvents such as ketones (e.g. acetone) and chlorinated hydrocarbons (e.g. dichloromethane, chloroform) attack HPU. Hot steam above 100°C (212°F) must also be avoided.
Where are HPU seals used?
Due to its outstanding mechanical properties, HPU is also ideally suited for dynamic sealing applications. Accordingly, it is one of the most commonly used materials for hydraulic seals: piston seals, rod seals, scrapers, guide rings are routinely made of HPU.
Because of its resistance to water, even at higher temperatures, HPU is the ideal material in the field of water hydraulics.
HPU with FDA approval is also often used in the pharmaceutical and food industries, as there is practically no abrasion due to the wear resistance and thus enables very long service lives. What exactly are hydraulic seals?
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What is HPU solid and HPU MOS2?
The versatility of HPU is even enhanced by the further developments of HPU solid and HPU MOS2. These are special HPU qualities that are achieved by fine-tuning the raw materials during production or special additives (resulting in so-called "compounds", composite materials).
HPU solid
HPU solid is a variant of HPU, created by a different mix of monomers during manufacturing. It exhibits superior mechanical properties: being harder, more wear-resistant, and more abrasion-resistant than standard HPU. It is capable of withstanding high pressures up to 400 bar (5801,51 PSI). Its chemical resistance largely matches that of regular HPU.
A key application for HPU solid is in scenarios where the sliding properties of PTFE are needed but its mechanical resilience is surpassed, such as in gap extrusion, cold flow, potential shear forces, compression, and complex installations.
HPU-MOS2
HPU-MOS2 is a compound consisting of HPU and MoS2 (molybdenum disulfide). It combines the mechanical strength of HPU with the sliding properties of MoS2, so it can be considered a lubricant-filled plastic.
HPU-MOS2 is used when dynamic mechanical loads occur and high self-lubrication is required, e.g. in pneumatic applications.
HPU seals, HPU solid and HPU-MOS2 seals at Kofler - Dichtungen
At Kofler - Dichtungen you get HPU seals and gaskets and complete seal sets according to your requirements. We carry a variety of HPU seals in standard sizes such as flat gaskets, profile seals, O-rings, as well as elements for hydraulic seals: piston seals, rod seals, guide rings, scrapers.
For the most demanding applications, we supply you with custom-made industrial seals made of HPU, HPU solid and HPU-MOS2. For further information and seals, such as Simmerring seals, and much more, you can contact us at any time. Our sealing experts are looking forward to your inquiry.
Get in touch with us!
We perform best under pressure! Personalized advice for the highest demands and a fast delivery guarantee ensure your satisfaction. Contact our sealing experts.
We look forward to your inquiry."
