EPDM injection molding transforms synthetic rubber into a weather-beating asset for automotive, HVAC, and medical industries.
Customers expect their car door seals to remain functional and reliable for many decades. At home, they expect their HVAC seals to remain airtight to maximize heating and cooling and reduce energy waste.
In both cases, EPDM injection molding is the solution.
What Is EPDM Rubber Injection Molding?
EPDM injection molding is the irreversible process of making rubber parts by heating EPDM at high temperature and injecting it into a mold for curing and part formation.
Unlike plastics, which cool to form parts during injection molding, rubber parts undergo curing inside the mold.
This is the so-called vulcanization process, where permanent chemical cross-links form between molecules in the material. This reformulation transforms soft rubber into tough, elastic, and heat-resistant parts.
Benefits of Using EPDM Rubber Molding
EPDM rubber molding produces parts that can withstand the most severe weather conditions, including UV rays and extreme temperatures (-50°C to 150°C).
In applications where ordinary rubber cracks after a few years of sun exposure, EPDM remains elastic and retains robustness.
Further, EPDM’s chemical resilience makes it a great material for parts used in chemical processing plants, water treatment facilities, and industrial cleaning equipment.
EPDM is resistant to water, steam, dilute acids, and alkalines. However, it performs poorly when exposed to oils, fuels, and most organic solvents.
Most importantly, rubber molding is an investment in the dimensional stability of parts. This investment pays for many years because EPDM parts don’t lose shape even when under constant pressure.
EzraMade
Get Custom EPDM Parts Now!
What Are the Common EPDM Injection Molding Materials?
Sulfur-cured EPDM
Choose sulfur-cured EPDM if you want to save money on parts and products that are used indoors or in climate-controlled environments.
Sulfur-EPDM is less costly and cheaper to injection mold. Cycle times are shorter because it flows well and cures faster.
The material blend is made by mixing raw EPDM with elemental sulfur. When the two materials are heated, sulfur to carbon (S-C) is formed. The resultant material becomes highly flexible and resistant to tear.
Common applications for sulfur-cured EPDM include:
- Garden hoses
- Simple dust covers
- Non-critical gaskets
- Applications where heat resistance is not the primary concern
Peroxide-cured EPDM
This EPDM version is more heat-stable. It is commonly reserved for high-stakes applications where sulfur-cured options cannot be reliable.
Peroxide-cured EPDM is more expensive than sulfur-cured EPDM. It is made by mixing organic peroxides into EPDM, triggering the formation of super resilient carbon to carbon (C-C) bonds.
The molding process for peroxide-cured EPDM requires more precision in temperature and pressure control. But in exchange, you get long-term durability in the most exacting applications.
Common use cases for peroxide-cured EPDM include
- Engine seals and under-the-hood applications
- Industrial boilers and autoclaves
- Potable water systems
- Coffee makers and soda dispensers
EPDM vs. Other Elastomers
| Elastomer | Heat Resistance | Chemical/PH Resistance | Oil/Fuel Resistance | Mechanical Strength | Temperature resistance (range) | Ease of Molding | Primary Applications |
| EPDM | High | Excellent | Poor | Good | -50°C – +150°C | Excellent | Weather seals, HVAC, cooling, hoses. |
| Nitrile (NBR) | Moderate | Poor (Acids) | Excellent | Very High | -35°C – +100°C | Good | Fuel lines, O-rings, hydraulic seals. |
| Silicone (VMQ) | Extreme | Moderate | Poor | Low (Tears easily) | -60°C – +230°C | Excellent | Medical, baking, and high-heat gaskets. |
| Neoprene (CR) | Moderate | Moderate | Moderate | High | -40°C – +100°C | Good | Marine gear, wet suits, and bridge pads. |
| Viton (FKM) | Extreme | Excellent | Extreme | High | -20°C – +200°C | Difficult | Aerospace, racing fuel systems. |
| Natural Rubber | Low | Poor | Poor | Extremely high | -50°C – +70°C | Good | Tires, shock mounts, heavy vibration. |
The EPDM Molding Process
At first, the material is dried and intermixed with sulfur or peroxide. It is then heated until it’s just molten enough to flow, and then it’s injected at high pressure into a heated mold.
Once every cavity of the mold is filled, curing begins. The material creates the chemical cross-links that offer the part its desired properties. After curing, the part is cooled and ejected.
In EPDM injection molding, the highest risk of failure comes from trapped air.
Compared to thermoplastics, rubber has higher viscosity and is more prone to air entrapment during flow. This can destroy tolerance and dimensional integrity of EPDM parts.
Engineers have several workarounds for this, including the breathing cycle technique, where the mold is slightly opened for air to escape before curing begins.
EPDM Injection Molding Temperature
Whereas plastic injection molding uses cold molds to freeze the part into shape, EPDM rubber molding uses heated molds. The mold temperature is maintained at between 160°C and 190°C for successful vulcanization.
If the mold is too cold, curing becomes incomplete. The output is a sticky mess of parts that tear during ejection or have poor mechanical strength. But if the mold is too hot, premature curing (scorching) may occur before the cavity is fully filled.
EPDM Injection Molding Grades and Their Applications
There are many different types of EDM injection molding material grades. Choose the best material based on your desired ease of processing and end-use reliability.
Standard Grades
These are mostly sulfur-cured EPDM grades convenient for cheap injection molding needs.
Common applications of standard industrial EPDM include window seals, pedal covers, and other weather-stripping in vehicles.
Standard EPDM grade parts are tough enough for tight paneling, but generally are not used in high chemical exposure environments.
High-Heat Grades
High heat EPDM grades often happen to be peroxide-cured. They can be used in environments with temperatures as high as 120°C or more.
These grades are generally harder to injection mold in comparison to standard and industrial grades. However, they offer durable reliability in engine components, radiator hoses, and heat exchanger gaskets.
Their biggest advantage is high compression resistance.
Food-Safe (FDA) Grades
Food-contact EPDM grades are cleanly engineered versions of the same material. Food-safe EPDM grades are hardened with organic peroxides.
All oils and accelerators that could leach into food are eliminated from the material, which is simultaneously made resistant to heat, pressure, chlorine, and bacteria.
Top applications for food-safe EPDM include:
- Dishwasher seals
- Coffee maker gaskets
- Municipal water valves
Low-Viscosity Grades
These are easy flow grades reserved for parts with thin walls or super complex geometries. Viscosity is measured using the Mooney scale, where a lower number equals higher flowability. Low viscosity EPDM grade helps reduce the risk of short shots where rubber doesn’t fill all sections of the cavity.
Low viscosity EPDM applications include
- Electronic seals
- Syringe plungers
- Automotive door handles
High-Damping Grades
The rubber grade is engineered to absorb shocks and vibrations. Standard EPDM materials are used for sealing, but high-damping EPDM is helpful for vibrational damping in automotive and industrial machinery applications.
The molecular friction inside this rubber has intentionally been increased using fillers like mica or hydrocarbons. When it’s pressed or vibrated, the molecular chains rub together, converting the vibration into heat.
EzraMade
Create with EzraMade EPDM Parts!
Conclusion
EPDM injection molding involves balancing the designer’s vision, the material’s properties, and the molder’s capabilities. Choose the right material grade for your product, and you’ve won half the battle. The other important thing is choosing a supplier who’s mastered design for manufacturability and process optimization to improve outcomes and cut costs.
Frequently Asked Questions (FAQ)
In EPDM injection molding, curing time is informed by the part design, specifically the wall thickness. In thicker-walled parts, heat takes longer to penetrate to the center. A 2mm gasket seal can take up to 3 minutes to fully cure. But a thick 20 mm engine mount can take up to 10 minutes to vulcanize. This also directly affects production costs as parts that stay longer on the mold have high unit costs.
No. EPDM, as a non-polar polymer, cannot withstand non-polar fluids like engine oil. The oil will penetrate through the structure of the rubber and cause it to swell and leak. Nitrile and Viton are the most recommended rubbers for safety and seal integrity in applications that involve direct contact with oils and greases. These are polar rubbers.
No. The vulcanization process during the formation of EPDM parts in the mold is irreversible. That’s why EPDM is a thermoset material, meaning the cross-links formed within the material are permanent. However, waste EPDM can be ground and reused in construction.
Sharp corners and small draft angles. Sharp corners make it difficult for molten EPDM to fill the cavity, adding to the already problematic low viscosity nature of rubber. On the other hand, when the draft angles on the walls are insufficient, the part tears and deforms during ejection. Add radii and increase draft angles to 1.5 – 3 degrees.
