The fact that silicone is known for its flexibility and resilience, many engineering teams assume it will last as long as it is used. In reality, parts often fail prematurely, due to the presence of higher temperatures, aggressive cleaning chemicals, or much more than the expected number of actuations. Cracked or hardened tips create leaks in food processing lines, blistering seals, that fail to provide proper sealing, and edges that tear automated machine parts, causing expensive downtime, scrap product, and safety hazards.
This guide offers a practical approach for testing custom silicone tips for durability in heat, chemicals, and mechanical stress. Enginers and technical buyers can make informed decisions that align with real service conditions and lessen field failures, through mapping and running targeted tests.
Start with the Real-World Stress Profile
Before tests can be conducted, it is essential to have a clear understanding of the conditions that the product is subjected to in real use—not a material data sheet. Prior to any laboratory activities, develop a one page profile of stress that covers all of the demands the silicone tip will experience.
Items that should be recorded are:
- Continuous operating temperature vs. hot spikes in cleaning, sterilization, and/or process upsets.
- Chemical exposure: concentration levels and contact times with product fluids, detergents, sanitizers, oils and solvents.
- Mechanical loads: Actuation or compression cycles per day, Compression percentages, Vibration levels, Abrasion, Impact events.
This profile will be the base for all future tests. If not, they could see good numbers in the lab but not necessarily in reality.
Prioritizing the Worst-Case Use Cases
Target testing initially for the worst case scenarios of conditions. For instance, in food processing lines, a hot fill silicone tip can be subjected to a product temperature of 95°C and alkaline CIP media, and subjected to thousands of compression cycles per day. A second high risk factor is when lab equipment tips are subjected to aggressive high temperature solvents repeatedly during cycles of autoclaving.
Working with a supplier that routinely tests high-performance custom molded silicone products under similar heat, chemical, and mechanical loads can save months of trial-and-error in your own validation program.
Heat Resistance and Thermal Aging Tests
Overall, silicone rubber can withstand a broader temperature range than most organic rubbers, but there are definite limits for specific formulations. The tests of heat and thermal aging for silicone rubber are used to help predict the performance of tips at high temperatures.
Standard thermal aging is accomplished by placing sample tips or standard test coupons at fixed high (typically 150 to 200 C for high-temperature grades, 80 to 120 C for more moderate applications) temperatures for certain durations, typically 72, 168 or 500 hours. Once aged, determine important characteristics:
- Hardness (Shore A)
- Tensile strength
- Elongation at break
- Compression set
Above all: Conduct functional tests on the real tip geometry. Is it still true to mating parts? Is it still sufficiently sealant after ageing?
Simulating Repeated Cleaning or Sterilization Cycles
Silicone tips need to withstand multiple hot water, steam and/or dry-heat cycles. Develop test protocols that simulate actual cleaning or sterilizing cycles of parts from room temperature to peak process temperature.
Monitor these indicators after a certain number of cycles:
- Optical changes like discoloration, cracking or surface crazing.
- The dimensional stability and hardness drift of bulk materials.
- Functional performance such as leak testing and actuation force measurements
Regular output from different batches ensures that parts manufactured for production will be able to be relied upon to function for the duration of their service life.
Chemical Resistance and Fluid Aging Tests
Testing silicone chemical resistance is crucial because even high quality silicone can swell or soften or break down in the presence of other liquids such as oils, solvents or strong cleaning chemicals.
Common practice is to use tips or coupons, which are immersed in typical fluids under controlled temperatures for a specified period of time (usually 24 to 168 hours or more for accelerated aging). Then evaluate:
- The mass and volume changes (swell)
- Hardness shift
- The ability to resist breakage under tension, and to stretch before tearing.
- Visual surface condition
Test fluids should be as close as possible to the actual application chemistry. In dairy processing, for instance, a tip requires evaluation to compare milk fats, alkaline cleaners and sanitizing solutions at appropriate temperatures.
Interpreting Swelling, Hardness Changes, and Surface Damage
When interpreting results, context should be used:
- If the sealing performance is not affected, moderate and recoverable swelling is acceptable.
- Incompatibility is typically indicated by permanent swelling, softening or cracking.
- Hardness increase (embrittlement) can cause cracking with flex or impact.
- Contamination from surface tackiness or erosion can lead to contamination or damage of the mating components.
After any exposure to fluid, always use material data, functional assembly and leak tests. This indicates problems not picked up by conventional coupon testing.
Mechanical Fatigue, Compression, and Wear Testing
Mechanical fatigue and compression testing of silicone tips is used to address the physical demands of service that are often repeated and that can be the determining factor for the actual service life of a silicone tip, rather than the strength of the material itself.
Common tests are:
- Compression set at high temperatures for permanent deformation and sealing force retention.
- The repetitive compression or bending motion during cyclic fatigue testing, which simulates the number of thousands or millions of actuations.
- Abrasion and wear evaluation (tip surface in contact with other surfaces during operation).
Linking Mechanical Tests to Real Failure Modes
The real world breaks as the tests break:
- Usually, lip splitting after repeated actuation can be traced back to crack growth in fatigue testing.
- If it is found that it is a leak, then it is a gradual flattening which indicates excessive compression set.
- Abrasion tests are a good way to observe edge wear in a conveyor or gripper application.
Look for expected or likely failure modes in previous or similar applications and choose the corresponding test methods. This specific testing method provides quicker, more useful results than performing all possible mechanical tests.
Building a Practical, Tiered Durability Test Plan
Test plans for silicone tip reliability should be tiered in accordance with the stage of the project and risk level.
Screening tests (early design phase):
- A single or a couple of critical fluid immersion tests
- Linear compression set tests
Qualification tests (Prior to Tooling commitment or Production orders):
- This is a thermal and fluid aging that is carried out over an extended period of time.
- Fatigue cycle counts were defined
- Test the device and all components to full function
- Clear and concise statistical sample sizes with pass or fail criteria.
Carefully record test conditions, acceptance limits, and measurement techniques. Well done, well maintained tests protocols can be treasures to reuse for future designs and comparisons with suppliers.
What to Expect from a Qualified Silicone Supplier
A good manufacturing partner doesn’t just do parts. They should give full material datasheets for heat and chemical resistance, discuss the test results of materials from similar applications and, if test results suggest they need to be improved, discuss adjusting the geometry or durometer.
The best suppliers will become partners in the development of long-term reliability performance in silicone rubber for use in harsh environments, not just an order taker.
Key Takeaways for Engineers and Sourcing Managers
- The durability of custom silicone tips is a combination of temperature, chemicals and mechanical stress – test them all three together.
- A documented stress profile provides more efficient and intelligent testing.
- Accelerated aging tests for silicone parts can be used to estimate service life, but are always confirmed by functional testing of actual tips.
- Tiered testing allows for the detection of problems at an early stage and comprehensive validation is saved for completion of designs.
- Spending time in correct durability testing tests will save so much more time in the field from failures and redesigns later.
Using these methodologies, the technical team can define and qualify silicon tips with greater assurance and ensure consistent performance even under challenging industrial, food processing or laboratory applications.
