Mechanical Engineer

Cocoon is driving the circular economy between steel and cement by turning steel slag into a low‑carbon cement substitute.

We're backed by leading climate and hardware tech investors, including Gigascale, Wireframe, and Celsius Industries. In under two years, we've gone from concept to deploying our breakthrough technology at one of the largest steel producers in the US. We’re doubling the team in 2026 to tackle the next wave of technical challenges as we scale towards our first permanent production plant.

As part of Cocoon, you’ll own end‑to‑end development and validation of our mechanical systems, working alongside engineers, scientists, researchers, and technicians to develop and scale our technology. The role will be challenging; design, build, and validate new systems, giving you the chance to materially cut emissions from two of the most carbon‑intensive industries in the world.

We’re looking for a Mechanical Engineer to lead the design, build, and validation of mechanical systems and test rigs that underpin Cocoon’s next‑generation slag activation technology. You’ll work closely with engineers, material scientists, researchers, and technicians to mature R&D outputs into robust, scalable system designs.

This role spans experimental design, detailed mechanical engineering, supplier coordination, and hands‑on testing in the UK and overseas. You’ll own end‑to‑end development and validation work streams — from concept through commissioning — and play a key role in scaling our technology toward our first industrial plant.

• Lead mechanical engineering for R&D work streams, owning delivery from concept to validation.
• Design experiments, methods, and associated test rigs to validate and advance core technologies.
• Develop mechanical designs for hydraulic systems, industrial instrumentation, and bulk material handling systems.
• Use simulation, first principles, and engineering judgement to validate designs.

• Source components and manage subcontractors for delivering designs and test rigs.
• Manage the build and delivery of test rigs; create assembly documentation and direct manufacturing and installation activities.
• Lead validation and testing activities in the UK and overseas, from requirements definition through commissioning and testing.
• Create documentation for validation and compliance activities (DFMEA, risk registers, operating instructions, test reports).
• Support testing campaigns at Cocoon’s London R&D facility, UK pilot facilities, and US partner sites.
• Collaborate closely with the process engineering team to translate R&D outputs into system specifications for industrial deployment.
• Provide technical direction to engineers, technicians, and suppliers.
• Contribute to scaling technologies from R&D toward pilot and industrial deployment.
• Travel extensively during test campaigns to support installation, commissioning, and testing activities.

• Hold a Master’s degree in engineering and have at least two years of industry experience in mechanical, hydraulic, or electromechanical systems.
• Have experience defining experiments, designing test rigs, and managing validation testing.
• Are comfortable owning complete development and validation work streams in a fast‑moving environment.
• Bring strong problem‑solving skills and enjoy hands‑on troubleshooting and prototype building.
• Communicate clearly with technical and non‑technical stakeholders and can lead work delivered by others.
• Knowledge of industrial automation, instrumentation, or PLCs.
• Understanding of process engineering (material handling, heat transfer, unit operations).
• Experience with high‑temperature fluid handling or metallurgical systems.
• Experience scaling technologies from TRL 4/5 to TRL 8/9.
• Background in steelmaking or related heavy industrial environments.

• A hands‑on engineering role at the centre of Cocoon’s scale‑up journey.
• Ownership of real hardware development and validation work.
• Close collaboration with a multidisciplinary, mission‑driven team.
• Competitive salary, stock options, and flexibility where possible.

If you’re excited about designing, building, and validating first‑of‑a‑kind mechanical systems — and helping decarbonise heavy industry — we’d love to hear from you.

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