CVJ Boots & Steering Bellows TPU Compound | Flexible, Fatigue-Resistant
CVJ Boots & Steering Bellows TPU Compound
TPU compounds designed for automotive CVJ boots and steering system bellows, where parts experience
high-cycle repeated bending, continuous vibration, and long-term exposure to grease / lubricants, low temperature, and outdoor aging factors.
This page focuses on the most common failure modes in bellows and boots, plus grade positioning and injection / blow molding recommendations to reduce trial risk.
Many CVJ boot and bellows failures are not caused by a single property “being low”, but by an imbalance between
fatigue resistance, grease compatibility, and low-temperature flexibility—especially on thin-wall corrugated geometries where stress concentrates at the valleys and fold lines.
fatigue resistance, grease compatibility, and low-temperature flexibility—especially on thin-wall corrugated geometries where stress concentrates at the valleys and fold lines.
Dynamic Fatigue
Repeated Bending
Grease / Lubricant Resistance
Low-Temperature Flexibility
Ozone & Weathering
Injection / Blow Molding
Repeated Bending
Grease / Lubricant Resistance
Low-Temperature Flexibility
Ozone & Weathering
Injection / Blow Molding
Typical Applications
- Outer & inner CVJ boots – corrugated boots exposed to grease, road splash, and continuous bending during steering and suspension travel.
- Steering rack bellows – repeated folding with outdoor aging exposure, requiring crack resistance and stable flexibility over time.
- Drivetrain / chassis protective bellows – thin-wall flex parts where tear propagation and fatigue cracking are the main risks.
Quick Grade Selection (Shortlist)
Choose “Balanced Fatigue” when
- Dynamic bending fatigue is the main concern
- General grease resistance is required (standard grease exposure)
- You want a wider, more forgiving injection / blow molding window
Choose “Severe Condition” when
- Low-temperature flexibility is critical (cold climates)
- Grease / lubricant exposure is aggressive or long-term
- Ozone / weathering risk is higher and validation cost is high
Note: Final selection depends on boot/bellow geometry, wall thickness, grease type, target temperature range, and the molding route (injection or blow molding).
Common Failure Modes (Cause → Fix)
For CVJ boots and steering bellows, most issues appear at the fold lines and valleys. Use the table below as a quick diagnostic:
| Failure Mode | Most Common Cause | Recommended Fix |
|---|---|---|
| Cracking at valleys after repeated bending | Fatigue resistance margin too low; stress concentration amplified by thin-wall geometry | Move to a fatigue-optimized grade family; confirm flex-cycle testing on molded parts at target thickness |
| Softening / swelling after grease exposure | Grease incompatibility; prolonged contact extracts/plasticizes the system | Use a grease-resistant compound family; validate volume change and retention of tensile/tear after grease aging |
| Brittleness or cracking in cold weather | Low-temperature flexibility insufficient; stiffness increase raises local strain at fold lines | Choose low-temp flexible positioning; verify cold-flex and crack resistance on finished parts at target temperature |
| Surface ozone/weather cracks over time | Outdoor aging package not balanced; ozone / UV exposure accelerates surface micro-cracking | Improve ozone/weathering resistance package; validate aging + fatigue together (aging can reduce fatigue margin) |
| Short shot / weld-line weakness on corrugations | Melt too cold, shear too high, venting/mold balance issues; moisture can worsen defects | Dry thoroughly; stabilize melt temperature; optimize gating/venting; adjust injection speed/packing or blow molding parison control |
For bellows and boots, the most reliable route is to validate fatigue + grease + low temperature + aging together on real molded parts. A “pass” on pellets or simple plaques is not enough for corrugated geometries.
Typical Grades & Positioning
| Grade Family | Hardness | Design Focus | Typical Use |
|---|---|---|---|
| TPU-AUTO CVJ Balanced Fatigue | 80A–95A | Dynamic fatigue resistance with practical grease compatibility and stable molding window | General CVJ boots and steering bellows with standard grease exposure and broad processing tolerance |
| TPU-AUTO CVJ Severe Condition | 85A–98A | Grease resistance + low-temperature flexibility + ozone/weathering stability stacking (project-dependent) | Cold climates, long-term grease exposure, or higher aging risk where retest cost is high |
Note: Exact hardness and package choice should be confirmed based on boot/bellow geometry, wall thickness, grease type, and required temperature range.
Key Design Advantages
- High-cycle fatigue resistance positioned for repeated bending on corrugated geometries.
- Grease / lubricant resistance to maintain mechanical properties after long contact aging.
- Low-temperature flexibility to reduce crack initiation risk in cold weather service.
- Ozone & weathering stability to improve long-term surface integrity under outdoor exposure.
- Injection and blow molding adaptability for stable filling, surface quality, and repeatable production.
Processing & Recommendations (3-Step)
1) Dry
Dry compounds thoroughly before molding. Moisture can reduce surface integrity, weaken weld lines, and narrow the process window.
2) Control Heat & Shear
Avoid overheating and excessive shear. Stable melt temperature and controlled shear reduce degradation and improve fatigue consistency on thin-wall corrugations.
3) Validate on Real Parts
Validate on molded boots/bellows at target wall thickness with grease aging and cold-flex checks. Corrugated geometry amplifies weakness not visible on plaques.
- Injection molding: Ensure sufficient filling/packing on corrugations; manage weld lines and venting to avoid weak fold points.
- Blow molding: Control parison temperature and sag; stabilize cooling to maintain uniform wall thickness and consistent fold behavior.
- Aging awareness: Grease and ozone exposure can reduce fatigue margin; run combined validation if long-life requirements exist.
Is this page for you?
You will benefit most if:
- Your CVJ boot / steering bellow cracks at fold lines after repeated bending
- Your part softens or swells after grease / lubricant aging
- Cold weather increases stiffness and triggers cracking or tearing
- Outdoor exposure leads to ozone/weather cracks over time
- You need a clear grade shortlist to reduce trial and retesting risk
Request Samples / TDS
If you are developing CVJ boots or steering bellows and want to reduce selection risk,
contact us for a recommended shortlist and technical data sheets based on your part geometry,
target service condition, grease type, temperature range, and molding route.
To get a fast recommendation, send:
- Part type (CVJ boot / steering bellow), geometry highlights, and target wall thickness range
- Grease / lubricant type (if known) and exposure pattern (continuous contact or splash)
- Target temperature range (especially low-temp requirement) and expected service life
- Molding route (injection or blow molding) and any key constraints (cycle time, surface quality, etc.)
