The problem

A pipe fitting for drinking water systems, designed to be installed — often underground — by someone working on site, not in a lab.

The original design used four separate components, sold individually:

• a brass pipe connector
• a nylon ring
• a conical rubber seal
• a threaded cap

Once assembled, the cap compressed the nylon ring against the pipe, locking it in place. But the multi-step assembly, left to the installer, created a recurring problem: the nylon ring or the conical rubber seal could be left out during assembly.

On a visible fitting, that kind of mistake is caught immediately. On a fitting that ends up buried with the pipe, it only surfaces once water starts leaking — often too late, and far more expensive to locate and fix.

The solution

We proposed rethinking the product itself, not just the material.

The first step was eliminating two separate components — the nylon ring and the conical rubber seal — and replacing them with a single part: a glass-fiber-reinforced PA6.6 insert, overmolded directly with a rubber compound certified to KTW standards for contact with drinking water. No more loose parts that need to be positioned correctly one by one: the subassembly arrives exactly as it should be, with no risk of separation or misalignment.

The second step is the one we worked on the longest, and it’s also the part we’d rather walk you through in person than spell out in writing: a design solution that smartly separates two functions — mechanically retaining the pipe and sealing against leaks — so that fluid pressure, instead of being a risk to the seal, becomes a factor that reinforces it.

The third step was our own initiative: we proposed pre-assembling the entire fitting at the factory, with the new subassembly already fitted inside the connector body (the brass components remained supplied and assembled by the customer). The result for the installer: nothing to assemble, nothing to forget. Just insert the pipe and tighten.

The result

• From 4 separate components to a single overmolded subassembly that cannot be partially assembled
• A seal that performs better under pressure, not worse — the opposite of what happens with many traditional solutions
• A single supplier for the critical component, instead of two materials to manage separately
• No chance for the installer to leave a part out

The strongest validation? The solution we developed later turned out to be original enough to be patented — an indirect but concrete acknowledgment of the work behind it.

HTP designs and manufactures overmolded rubber-to-metal and rubber-to-plastic components for technical applications where mistakes aren’t an option. Got a sealing or assembly problem keeping you up at night? Let’s talk.

Foresti Alexander

L'articolo When a missed step is not an option proviene da HTP - High Tech Project.

When they called us, the project was nearly dead.

Three years of attempts, different suppliers, resources invested. And the problem was still there, unsolved. They were seriously considering giving up on the entire project.

We sat down with their technical team and listened. Not just to the stated problem — but to everything: the actual operating conditions, the system constraints, what they had already tried and why it had not worked.

The problem

The component was a machined die-cast aluminium valve with very tight tolerances and a stainless steel pin integrated into the upper section. The requirement was to overmould two sealing gaskets simultaneously — one at each end of the valve, 180 degrees apart.

But that was not all. During the discussion, a critical requirement emerged that further complicated matters: the compound had to ensure low friction under operating conditions. The part operates in a system where actuation force must be minimal — yet the seal must be reliable and consistent over time.

Two requirements pulling in opposite directions. And which explains, at least in part, why others had failed.

Why aluminium is a challenging substrate

In our line of  work, we know this all too well: aluminium is one of the most complex substrates to work with. It is not like steel. Its surface oxidises naturally, with chemical properties that vary depending on the alloy, the surface treatment, and even the storage conditions of the component.

Achieving a durable structural bond between rubber and aluminium requires: specific and controlled surface preparation, primers and bonding agents compatible with that specificalloy and the selected compound, process parameters optimised to the last detail; and a mould designed to manage the flow of the compound on both sides simultaneously.

There are no shortcuts. Every variable matters.

Three years of failed attempts

The customer — a multinational industrial group — had already faced the problem head on. For almost three years, various suppliers had attempted to develop a solution. These were large companies, with in-house resources and laboratories. The result was always the same: an inability to guarantee stable, long-lasting adhesion, or sealing issues under real operating conditions.

The project was on the verge of being abandoned.

What we did

We worked on three fronts simultaneously: selecting and optimising the compound to meet the required tribological characteristics, developing a surface treatment process specifically tailored to that aluminium alloy, and designing the mould for the simultaneous overmoulding of the two gaskets at 180 degrees, with the stainless steel pin as the central element to be managed.

It was not straightforward. But it is exactly the sort of problem we are used to dealing with.

The result

Four weeks after our first meeting, we delivered the samples in the smallest size.

I will never forget the technical team’s reaction. After three years of failed attempts, they did not expect to see those samples so soon. And above all, they did not expect them to work.

They worked.

We currently manufacture four sizes of that component using 4-cavity and 8-cavity moulds. We have been in production for over four years, maintaining consistent quality and with no issues encountered in the field.

If you are facing a similar problem

Overmoulding on aluminium is not impossible. It is complex, requires specific expertise in materials, surface treatments and process, and leaves no room for approximation.

If you have a sealing challenge that others have not been able to solve — on aluminium, special alloys, engineering plastics, or stainless steel — get in touch. The first thing we do is listen.

Foresti Alexander

L'articolo Double-seal overmoulding on aluminium: when the solution seemed impossible proviene da HTP - High Tech Project.