Abrasion Elastomers

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Abrasion elastomers

General

Abrasion is the loss of material on the surface of test specimens or components due to abrasive mechanical stress, which occurs when surfaces act on each other. The wear behaviour of elastomers is influenced not only by the molecular structure of the elastomer but also by the composition of the compound and the type of stress. The chemical composition of the elastomer also determines the glass transition temperature T_g and the hysteresis properties, i.e. the viscoelastic properties. Elastomers or rubber compounds with low T_g, combined with low hysteresis, tend to have lower abrasion resistance. Fillers, additives and the type of crosslinking also influence abrasion behaviour. For example, active fillers such as carbon black and silica reduce abrasion. The type of load on the elastomer component, the temperature and the condition of the contact surface also play a significant role in evaluating the wear properties. If the component is subjected to the impact of sharp-edged particles, as occurs when conveying granules, blasting material or bulk material (see also: density), the wear behaviour differs significantly from that resulting from dynamic loading, such as a tire.

Borderline cases of wear

Since wear occurs as a result of frictional contact between two friction partners, the wear behaviour of elastomers depends not only on the material properties, but also on the interactions that occur and the magnitudes of the stress collective. Friction and wear are therefore system properties and not purely material properties.

Four limiting cases are defined for the wear of elastomers:

• Abrasive wear (wear caused by flowing sharp particles, e.g. on a carrier belt or tire on a rough road or "full braking"),
• Adhesive wear (wear caused by rubbing or sliding pushing particles, e.g. tires on a flat road),
• Deformational wear (wear due to fatigue, as a result of shear, compression, tension, bending),
• Tribochemical wear (degradation due to frictional heat).

In practice, several mechanisms are usually involved in the wear process at the same time, but in different proportions. Both the processes that occur in a material during abrasive stress and the quantitative characterization of the abrasion properties are to be regarded as very complex. Thus, abrasion as a deformation-mechanical process is associated with crack resistance, crack growth and fatigue. Elastomers primarily exhibit the mechanisms of abrasion and fatigue wear.

Method of DIN abrasion

The characterization of the abrasion properties of elastomers can be carried out with the aid of a wide variety of different test methods. The simplest method for determining abrasive wear is the so-called DIN abrasion according to DIN 53516 (withdrawn) or DIN ISO 4649. According to DIN ISO 4649, the method for determining abrasion is divided into two procedures. Method A works with non-rotating test specimens and in method B the abrasion is determined on rotating test specimens. According to DIN 53516 (withdrawn), only stationary test specimens are used. The procedure, the specimen geometry and the determination of the abrasion are the same for both standards. The test specimen made of the elastomer to be tested is guided under a constant contact force and at a constant velocity (40 min^-1) over a fixed friction distance (40 m) over a test emery board located on a rotating cylinder (Fig. 1).

Characterization of abrasion with parameters

The abrasion according to DIN 53516 (withdrawn) (see Eq. 1) is then determined by determining the loss of mass of the test specimen, taking into account the attack sharpness and nominal attack sharpness of the test abrasive sheet and with the aid of the density.

Fig. 1:

Abrader type Zwick 6103 for tests according to ISO 4549 or ASTM D 5963

$A={\frac {\Delta m\cdot S_{0}}{\rho \cdot S}}$

(1)

with:

A	Abrasion in mm3
$\Delta$m	Mass loss in mg
ϱ	Density in g cm-3
S0	Target impact sharpness (200 mg)
S	Sharpness of impact in mg

According to DIN ISO 4649, the relative volume loss (see Eq. 2) and the abrasion resistance (see Eq. 3) are determined as follows:

$\Delta V_{rel}={\frac {\Delta m_{t}\cdot \Delta m_{const}}{\rho _{t}\cdot \Delta m_{r}}}$

(2)

with:

Δmt	Mass loss of the tested elastomer in mg
Δmconst	Defined mass loss of the reference elastomer in mg
ϱt	Density of the tested elastomer in mg/mm3
Δmr	Mass loss of the reference elastomer in mg

and:

$I_{AR}={\frac {\Delta m_{r}\cdot \rho _{t}}{\Delta m_{t}\cdot \rho _{r}}}$

(3)

with:

Δmt	Mass loss of the tested elastomer in mg
Δmr	Mass loss of the reference elastomer in mg
ϱt	Density of the tested elastomer in mg/mm3
ϱr	Density of the reference elastomer in mg/mm3

The methods for determining abrasion can be subdivided as follows:

• Simple indentation methods with hard bodies (e.g. pico-abrasion according to ASTM D 2228)
• Simulation methods of practical application with the closest possible approximation to real conditions (e.g. DIN abrasion, LAT 100 (according to Grosch), Akron Abrader)
• Test equipment that reflects the variation of load, speed and temperature (e.g. LAT 100 (according to Grosch), Akron Abrader, flat track tire test rig (Fa. iABG), drum test rig)
• Testing under real conditions (e.g. tire test)

In order to evaluate the wear properties of tread compounds, the DIN abrasion test is the preferred method in the tire industry, since sample preparation and test performance are simple and the time required is low compared to methods under real conditions.

See also

• Ageing elastomers
• Surface testing technology
• Scratch resistance
• SHORE Hardness – Material development elastomers

References

• Röthemeyer, F., Sommer, F.: Kautschuktechnologie. Carl Hanser Munich Vienna (2001), pp. 518–520 (ISBN 978-3-4461-6169-6)
• Scholz, K.-G.: Elastomere in tribologischen Systemen. Expert Verlag (2011) (ISBN 978-3-8169-2911-6)
• Friedrich, K.: Friction and Wear. In: Grellmann, W., Seidler, S. (Eds.): Polymer Testing. Carl Hanser Munich (2022) 3rd Edition, pp. 198–214 (ISBN 978-1-56990-806-8; see AMK-Library under A 22)
• Grellmann, W., Heinrich, G., Cäsar, T.: Crack initiation, wear and molecular structure of filled vulcanized materials: In: Grellmann, W., Seidler, S.: Deformation and Fracture Behaviour of Polymers. Springer-Verlag Berlin Heidelberg New York (2001) 479–492 (ISBN 3-540-41247-6; see AMK-Library under A 7)
• DIN 53516 (1987-06): Testing of Rubber and Elastomers – Determination of Abrasion Resistance (withdrawn; replaced by DIN ISO 4649)
• DIN ISO 4649 (2021-06): Rubber, Vulcanized or Thermoplastics – Determination Abrasion Resistance Using a Rotating Cylindrical Drum Device (ISO 4649:2017-09)
• ASTM D 2228 (2004; reapproved 2019): Standard Test of Rubber Property – Relative Abrasion Resistance by the Pico Abrader Method
• ASTM D 5963 (2022): Standard Test of Rubber Property – Abrasion Resistance (Rotary Drum Abrader)
• Reincke, K., Grellmann, W., Ilisch, S., Thiele, S., Ferner, U.: Structure – Properties Correlations of SSBR/BR Blends. In: Grellmann, W., Langer, B.: Deformation and Fracture Behaviour of Polymer Materials. Springer Series in Materials Science 247, Springer, Berlin Heidelberg (2017) pp. 398–408 (ISBN 978-3-319-41879-7, see AMK-Library under A 19)