Abrasion Resistance in PU Hoses — Why Material Choice Decides Service Life

Polyurethane hoses last 2.5 to 5 times longer than many rubber compounds and 3 to 4 times longer than soft PVC under abrasive loads. But there is polyurethane, and then there is polyurethane. The difference between standard ester TPU and NORRES BAGGERMAN’s Pre-PUR® shows up in 56 days and can cost you a full production season if you choose wrong.

When an industrial hose has to convey wood dust, sand, granulate, grain or any other abrasive fraction, what determines total cost of ownership is not the price per metre. It is service life. And service life depends on two things: how well the material resists mechanical wear, and how stable it remains when the operating environment is not a dry laboratory bench.

This article covers both. The focus is on the polyurethane compound that NORRES BAGGERMAN manufactures its hoses from, Pre-PUR®, compared with a typical commercial ester TPU. And because every supplier claims to have abrasion-resistant hoses, we go via the standard that is actually measurable: DIN ISO 4649.

DIN ISO 4649 — the only comparison that counts

DIN ISO 4649 (identical to the international ISO 4649 standard) is the recognised yardstick for abrasion resistance in elastomers and thermoplastics. The principle is simple: a cylindrical specimen is pressed against a rotating abrasive sheet of specified grade, and the volume the specimen loses during the test is measured. The result is reported in mm³, and lower numbers are better.

The standard describes two methods, A and B (with or without rotation of the specimen), and is used for quality control, comparative testing and product development. It is worth noting that the standard itself states that “no close relation between the results of this abrasion test and service performance can be inferred”. A laboratory test is not a 1:1 picture of the real world. But it is the best available common denominator, and it is the one any serious supplier uses to document its claims.^[2]

This is where the first interesting observation appears: many manufacturers of PU hoses cite DIN ISO 4649 in their material literature, but they do not publish the actual test values. NORRES BAGGERMAN does, and that gives us something to work with.

Abrasion numbers — how good is Pre-PUR® really?

The table below shows volume loss in mm³ measured against DIN ISO 4649 at 20 °C. The lower the number, the less wear:

Pre-PUR® sits at the very bottom of the scale. This is the basis for NORRES’ statement that Pre-PUR® is 2.5 to 5 times more abrasion-resistant than many rubber compounds, and 3 to 4 times better than most soft PVCs. The data behind this table is taken from NORRES’ own polyurethane technical paper and reproduced unaltered from their official material.^[1]

A few notes on reading the table correctly:

First, EPDM, NBR and SBR span large ranges, because final abrasion resistance depends heavily on the compound’s filler, vulcanisation grade and hardness. A premium NBR can hit 100 mm³, a budget compound can hit 220 mm³. PUR has a much narrower spread between compounds, and Pre-PUR® sits at the absolute best end.

Second, the PVC value of around 100 mm³ is a useful reference point: a soft PVC hose wears roughly 3.5 times faster than a Pre-PUR® hose under the same abrasive load. That is the difference between a hose that lasts one season and one that lasts four.

Third, the TPR/TPE figures should be read with caution. TPE is a category, not a material, and the 80 to 300 mm³ range really tells us “it depends on what the TPE is built from”. For concrete material selection you always have to consult datasheets, never category tables.

Polyurethane and rubber solve different problems

It is tempting to read the table as a hierarchy where PUR beats rubber. That is not the picture. PUR and rubber are different solutions to different problems, and a serious hose supplier carries both for good reasons.

Polyurethane dominates when abrasion is the dominant load, combined with a need for flexibility, low weight and transparency. Wood dust extraction, granulate transport, grain handling, dust extraction in machine shops, that is PU territory.

Rubber (SBR, NBR, EPDM) dominates where chemical resistance, heat resistance or elastic recovery are decisive. An NBR hose handles oils and fats in a way PU cannot. EPDM is superior for hot water, steam and many acid or alkali media. SBR has its place where price and general mechanical resistance matter more than maximum abrasion resistance.

NORRES BAGGERMAN is the result of NORRES (specialists in technical thermoplastic hoses) acquiring Baggerman with its strong rubber hose heritage. The combined portfolio therefore covers both areas. When this article focuses on PU and abrasion, it is because that is one specific technical topic, not because rubber is inferior. Rubber hoses have their own place in the FlexCore programme, and in many installations PU and rubber work side by side in the same plant.

Hydrolysis — when the environment is the real opponent

Abrasion resistance measured at 20 °C in a dry laboratory is one thing. What happens when the hose is installed in a food production line with steam, or in an outdoor extraction system where rainwater seeps in through the couplings, or in an agricultural application with humid air and temperature swings?

This is where hydrolysis becomes decisive. Hydrolysis is the chemical breakdown that occurs when water reacts with a material’s molecular structure. Polyurethane comes in two basic types, and they behave fundamentally differently:

Ester-based PU offers better abrasion resistance and better oil resistance, but is susceptible to hydrolysis. In humid environments the ester bonds break down, the material loses tensile strength, and the surface starts to crumble. This is well documented by material suppliers such as U.S. Plastic Corp and Freelin-Wade, and it is a point every serious PU hose manufacturer acknowledges.^[4][5]

Ether-based PU offers superior hydrolytic stability, resists microbial attack and fungus much better, and retains flexibility at low temperatures. The trade-off is that it is slightly softer and typically a little less abrasion-resistant than ester PU.

This is the classic trade-off: do you want abrasion resistance (ester) or environmental stability (ether)? NORRES’ answer is that the choice doesn’t have to be binary.

Pre-PUR® — the trade-off resolved in the compound

Pre-PUR® is not a generic material. It is a patented combination of ester and ether polyurethanes, with stabilisers and additives tuned so the hose draws benefits from both:

• Abrasion resistance at ester level (25 to 30 mm³ per DIN ISO 4649)
• Hydrolysis resistance approaching pure ether PU
• Microbe resistance
• Flexibility maintained at low temperatures (−40 °C is typical for AIRDUC®, PROTAPE® and BARDUC®)
• Better hot air aging properties than standard PU

NORRES backs the compound’s hydrolysis resistance with a comparative test at 80 °C in water over 56 days. It is an accelerated hydrolysis test that effectively simulates years of use in a humid environment. The result:

That is the kind of difference that, in practice, separates a hose that fails mid-harvest from one that stays in service for five to six years without complaint. The figures come from NORRES’ own tests, and we should be honest about that, but the method (hydrolysis in water at 80 °C) is industry standard for accelerated aging and is used by virtually every supplier of thermoplastic elastomers.

What do competitors publish?

If we compare what other major European PUR hose manufacturers publish, the picture looks like this:

Merlett (Italian manufacturer, now part of Continental/ContiTech) is the most direct competitor on the Scandinavian market. Their SUPERFLEX series is the real alternative to NORRES’ AIRDUC and PROTAPE programmes. On their datasheets, abrasion resistance is given as a star rating (up to 5/5), not as mm³ values per DIN ISO 4649. That means a buyer cannot compare specific abrasion numbers directly between a Merlett SUPERFLEX and a NORRES AIRDUC. The comparison has to go via product testing or via the supplier’s own stars.^[7]

On conductivity, the difference becomes measurable and interesting. NORRES and Merlett both have an antistatic and an electrically conductive series:

At the antistatic level, the two manufacturers are comparable. On the electrically conductive variant, NORRES sits a full order of magnitude lower in surface resistance (<10³ vs. ≤10⁴ Ω). That is not an arbitrary spec, it is decisive when selecting a hose for ATEX zone 0/1 and zone 20/21, where charge has to dissipate faster than in zone 22. NORRES also specifies the ATEX zone classification per product (zone 0, 1, 2 for gases/liquids and zone 20, 21, 22 for dusts) and references DIN 26057 Type 2/3/4. Merlett’s datasheets on the conductive series only cite ATEX “according to the directions for use”.^[9]

On hydrolysis resistance, Merlett markets their ET variant as “resistant to hydrolysis in 60 °C warm water”. NORRES documents Pre-PUR® at 80 °C — a higher temperature and therefore a more aggressive accelerated aging test.

Masterflex (German manufacturer, Master-PUR series) explicitly states that their polyester PU is “more abrasion-resistant in comparison to polyether polyurethane according to DIN ISO 4649”, but they too do not publish concrete mm³ values on their datasheets. The comparison is qualitative, not quantitative — same as with Merlett.^[6]

This does not mean the competition has inferior products. Continental stands behind Merlett, and that is a respectable technical heritage. It means a buyer who has to specify a hose for a plant investment of several hundred thousand euros has a measurable basis of comparison on the NORRES hoses that is harder to establish on the alternatives. That makes it easier to document the choice to QA, the safety officer, or the auditor — especially when the hose sits in an ATEX zone where the zone classification and surface resistance must be precisely documented.

Where does this knowledge sit in the FlexCore system?

Abrasion resistance is a material question, but it is never the only thing that determines service life. The construction, whether the hose is a spirally welded profile hose (AIRDUC®), a foil strip hose (PROTAPE®), an axially extruded wall (NORFLEX®) or a full plastic build (NORPLAST®), matters just as much for whether the hose can function at all in the application.

You can dig deeper into the six base constructions under hose constructions, where AIRDUC® and PROTAPE® are the two most widely deployed in abrasive suction applications. For material resistance against specific chemicals, acids, bases, solvents, food ingredients, refer to the chemical resistance table, which covers more than 1,400 substances against 16 materials. For ATEX zones or TRGS 727 assessed installations, the formal documentation is in ATEX & TRGS zones.

So which hose should I choose for abrasive media?

There isn’t one right answer, there is the right answer for your application. As rules of thumb:

For dry, abrasive suction (wood dust, plastic granulate, grain) an antistatic PROTAPE® or AIRDUC® in Pre-PUR® is the typical choice. Low weight and high flexibility make it easy to handle, and abrasion resistance is at the absolute top of the field.

For food and pharma applications with humid media or steam cleaning, Pre-PUR®’s hydrolysis resistance becomes especially important, and this is where the food-grade variants (FDA and EU 10/2011 compliant) are relevant. The specific articles certified for food contact are listed in the technical datasheets per product.

For elevated temperatures (continuous above 90 °C, peaks up to 125 °C), specific variants with reinforced heat resistance are required. Pure PU hoses are not the right choice, and the high-temperature programme at NORRES BAGGERMAN is built on different materials such as silicone and special fabric reinforcements.

For outdoor or high-humidity environments, the ether component of Pre-PUR® is precisely why the hose holds up at all. A pure ester TPU will typically be the wrong choice here, even if it looks better on paper from an abrasion standpoint.

The shortest possible summary

If you take one thing from this article: abrasion numbers alone do not solve the choice of an industrial PUR hose. Paper-grade abrasion resistance means little if the material is broken down by the environment it has to operate in. Pre-PUR® is engineered so you don’t have to choose. Abrasion resistance is measurably top-tier (25 to 30 mm³ ester, 27 to 32 mm³ ether per DIN ISO 4649), and hydrolysis stability holds up where PVC and standard ester TPU fail.

It is that combination that lets a complete suction system from the FlexCore programme be documented as having a lower total cost of ownership over its service life, even when the price per metre is not the lowest on paper.