Low-temperature brittleness

Cryogenic deburring makes deliberate use of the principle of low-temperature brittleness. While the main body of a workpiece remains elastic, fine burrs become brittle when cooled to temperatures below the glass transition point and break off under mechanical action. The Shore hardness of an elastomer influences the glass transition point and therefore the cooling required:

• Soft EPDM (40 Shore A): cooling to temperatures below -120 °C required.

• Hard EPDM (80 Shore A): already brittle enough for deburring at -70 °C.

• Silicone: has high cold resistance and remains elastic even at -100 °C, which is why it requires particularly low temperatures.

Low-temperature brittleness is influenced by various factors:

• Glass transition: when the temperature falls below the glass transition point (Tg), the material changes its behaviour from elastic to brittle.

• Molecular structure: materials with rigid polymer chains or low molecular mobility are more susceptible.

• Fillers: additives such as carbon black or silica influence the low-temperature properties of the material.

• Shore hardness: harder materials generally have higher glass transition temperatures than softer ones.

The low-temperature brittleness of a material is determined using standardised methods:

Low-temperature brittleness test

• Cooling: the material is gradually cooled to low temperatures.

• Loading: the material is subjected to a mechanical load such as bending or impact.

• Fracture test: the temperature at which the material breaks is recorded as the brittleness temperature.

Standards

• DIN EN ISO 812: determination of the low-temperature brittleness of rubber.

• ASTM D746: method for determining the brittleness temperature of plastics.

Different materials react differently to low temperatures. Here is an overview:

Material	Glass transition temperature (Tg)	Susceptibility	Typical applications
NR (natural rubber)	-60 °C	Low	Tyres, seals
EPDM	-50 °C	Low	Roof waterproofing, automotive seals
Silicone	-100 °C to -130 °C	Very low	Medical products, seals, insulation
NBR	-40 °C	Medium	O-rings, hoses
PVC (polyvinyl chloride)	-20 °C	High	Window profiles, pipes

Low-temperature brittleness plays an important role in various industries:

Automotive industry

• Tyres: use of elastomers with low glass transition temperatures to prevent cracking.

• Seals: EPDM and silicone for door seals that remain flexible even at cold temperatures.

Construction industry

• Roof waterproofing: use of cold-resistant EPDM materials.

• Window profiles: use of plastic profiles with optimised properties against brittle fracture.

Medical technology

• Silicone products: highly cold-resistant tubes, seals and prostheses.

Aerospace

• Seals: special elastomers that remain stable at extreme temperatures.

• Safety: prevents material failure in cold environments.

• Efficiency: reduction of production losses through targeted material selection.

• Precision: makes it easier to plan deburring processes for elastomer parts.

• Material costs: highly cold-resistant materials are more expensive than standard materials.

• Testing effort: complex tests to determine the glass transition temperature.

• Adaptation: targeted material modifications with additives can improve the properties but increase production effort.

Material type	Cold resistance	Typical applications
Elastomers (e.g. silicone, EPDM)	Very high	Seals, hoses, prostheses
Thermoplastics (e.g. PVC, PA)	Variable	Window profiles, housings
Thermosets	Medium	Insulation, structural components

• How does low-temperature brittleness affect cryogenic deburring? Cryogenic deburring uses the effect of low-temperature brittleness to remove burrs while the main material remains flexible.

• Why is silicone so resistant to cold? The molecular structure of silicone remains flexible even at very low temperatures.

• Can the low-temperature brittleness of materials be improved? Yes, by adding plasticisers or special additives.

• Which materials are suitable for extreme cold? EPDM, silicone and special high-performance polymers such as fluoroelastomers (FKM).

Low-temperature brittleness is an important parameter when selecting materials for applications in cold environments. For cryogenic deburring, it is crucial to cool materials deliberately below the glass transition point in order to remove burrs precisely and gently. Understanding the glass transition temperature contributes to safe and efficient product development in areas such as the automotive, construction and medical technology sectors.