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Silicone overmolding on stainless steel is widely used across industries such as medical devices, consumer electronics, kitchenware, industrial tools, and wearable products. By combining the durability of stainless steel with the flexibility, sealing performance, and comfort of silicone rubber, manufacturers can significantly enhance product functionality and user experience.
However, achieving a stable and long-lasting bond between silicone rubber and stainless steel is technically challenging and requires precise material selection and process control.
In actual production, poor adhesion between silicone and stainless steel often results in problems such as peeling, delamination, or separation after repeated use. These issues not only affect product quality but may also lead to functional failure, safety risks, and increased manufacturing costs.
Understanding why adhesion problems occur is the first step toward solving them effectively.
Silicone rubber and stainless steel have very different physical and chemical characteristics, which makes natural bonding difficult.
Silicone rubber has low surface energy, meaning it does not easily adhere to other materials. Stainless steel surfaces are smooth, dense, and non-porous, offering limited mechanical grip. In addition, stainless steel naturally forms an oxide layer, and any oil, dust, or residue on the surface can further weaken adhesion.
Thermal expansion differences between silicone and stainless steel during curing and use can also introduce internal stress at the bonding interface, increasing the risk of separation.
Several factors can lead to poor adhesion during silicone overmolding:
In many cases, adhesion failure is caused by a combination of these factors rather than a single issue.
Proper surface preparation is essential. Stainless steel parts must be completely free from oil, dust, and processing residues before overmolding. Common cleaning methods include ultrasonic cleaning, solvent wiping with isopropyl alcohol or acetone, and plasma or chemical cleaning.
A thoroughly cleaned surface provides the necessary foundation for both chemical bonding and mechanical adhesion.
Smooth stainless steel surfaces offer minimal mechanical grip. Controlled surface roughening increases the contact area and allows silicone rubber to mechanically lock onto the metal.
Common roughening methods include sandblasting, laser texturing, and chemical etching. When properly controlled, these processes significantly improve adhesion without compromising the strength or appearance of the stainless steel component.
Silicone primers play a critical role in bonding silicone rubber to stainless steel. A primer acts as a chemical bridge between the metal surface and the silicone material.
Key considerations include selecting a primer compatible with the silicone type (LSR, HCR, or RTV), applying the primer evenly, and allowing sufficient drying or curing time before molding. Using the wrong primer—or skipping this step entirely—often results in bonding failure.
Not all silicone rubber materials are suitable for overmolding onto stainless steel. Bonding-grade silicone formulations are specifically designed to improve adhesion to metal substrates.
Selecting the appropriate silicone material based on application requirements such as temperature resistance, flexibility, and regulatory compliance directly impacts bonding strength and long-term performance.
Even with proper materials and surface treatment, adhesion can fail if the overmolding process is not optimized. Key parameters include molding temperature, injection pressure, curing time, and mold structure.
Unstable process conditions may cause incomplete curing or internal stress at the silicone–metal interface, reducing adhesion strength. Consistent and well-controlled process settings are essential for reliable results.
After cleaning and priming, stainless steel components must be protected from contamination. Avoid direct contact with bare hands, store parts in clean environments, and conduct molding and packaging in dust-controlled workshops.
Even minimal contamination can significantly reduce adhesion performance.
Silicone overmolding on stainless steel is not a standardized process. Different industries and applications require customized solutions in terms of silicone formulation, surface treatment, primer system, mold design, and quality inspection standards.
Working with an experienced silicone manufacturer allows these factors to be optimized together, reducing development time and improving product reliability.
Poor adhesion between silicone rubber and stainless steel is a common but solvable manufacturing challenge. By combining proper surface preparation, suitable primers, correct silicone material selection, and optimized overmolding processes, strong and durable bonding can be achieved.
If you are experiencing adhesion issues with silicone overmolding, or if you are looking for customized silicone rubber product solutions, DX can provide professional support from design to mass production.
Contact us today to discuss your application and find the most suitable silicone overmolding solution for your product.
DX provides you with all-around silicone product customization services for valued customers like you.
