In the optimization of dual-seal structures, which sealing combination is most effective?

The dual-seal combination of "metal hard seal + flexible PTFE packing seal" is presently the most widely applicable and successful solution validated in the industry for hot runner high-temperature and high-pressure applications.

Why does this combo work the best?

The outer metal hard seal, which typically uses 304/316 stainless steel gaskets, directly bears the high pressure and performs the primary pressure blocking function. This is a clear division of work and mutual backup. Because of its extreme stiffness, the cover is securely sealed and molten material under high pressure cannot seep in. The metal hard seal's microscopic gaps are filled by the inner PTFE flexible packing seal, which also shields it from extreme heat. The flexible packing can achieve double protection even in the event of a small leak in the metal seal by preventing additional molten material from seeping in.

PTFE can endure temperatures exceeding 300°C for prolonged periods of time without melting and failing at high temperatures like regular rubber; the metal hard seal itself has good pressure resistance, meeting both high temperature and high pressure requirements at the same time. Combining the two has no compatibility issues and is appropriate for hot runners operating in the 100–200 MPa working pressure range.

Comparing Other Frequently Used Combinations:
"Rubber Seal + Metal Seal: Rubber is not heat-resistant and will deteriorate quickly; it is not advised.Bimetallic Hard Seal: The mounting surface must be machined with incredibly high precision because even little irregularities can result in leaks. Compared to combination solutions, it is more expensive and less dependable."Flexible Packing + Flexible Packing" is unable to tolerate high pressure. The flexible packing will be forced out under high pressure, hastening the seal's failure.

A "metal bevel self-tightening seal" can be used in place of the metal hard seal in extremely high-pressure situations above 200 MPa. The dual seal's pressure resistance and dependability are further enhanced by the bevel's automatic compression of the sealing surface under high pressure, which makes the seal tighter.