Project Overview
Boro Foundry partnered with Steel Warriors, a UK charity transforming knives seized from the streets into outdoor calisthenics gyms.
Steel Warriors’ mission is to create a UK-wide network of gyms that help young people build confidence and pursue positive goals, and strengthen local communities.
The project combined steel casting expertise, complex melt control and powerful social impact — taking dangerous, unpredictable scrap material and turning it into a force for good.
The Challenge
This project presented a highly unusual foundry and metallurgical challenge.
The raw material supplied for melting consisted of confiscated knives, meaning Boro was working with inconsistent and unknown steel compositions, rather than standard, controlled feedstock.
Before the material could be processed, the knives required refining to remove potential contaminants, including plastic handles and other metal fittings such as brass and aluminium. These contaminants had to be carefully removed to ensure the final components could meet the required specification, which included:
- Duplex stainless steel performance
- High corrosion resistance without paint protection
- High strength for load-bearing use
- Good elongation and durability
- Reliable performance in outdoor environments
Duplex stainless steel was selected because it offers excellent corrosion resistance alongside high mechanical strength — almost twice that of typical austenitic stainless steel — while maintaining the elongation needed for demanding structural use.
The Solution
Boro developed a bespoke melting process that allowed the unknown compositions of knife steel to be blended with other raw materials and alloying additions to meet the required Duplex stainless steel specification.
Developing a Controlled Melting Process
This was not a standard batch production process. The chemistry of multiple knife batches had to be tested to allow Boro to calculate how much of each furnace charge could be made up from knife steel, and how much needed to be corrected with additional elements.
Each melt was analysed and adjusted, with different alloying additions made depending on the chemical composition of the knives in that specific melt. This was a challenging process requiring significant metallurgical expertise, fast decision making and close control at all times.
Airset Floor Moulding and Pattern Adaptation
The gym components were produced using airset floor moulding.
Boro adapted the original customer-supplied pattern equipment to produce four impressions per mould, increasing yield and production efficiency. Boro also fabricated steel mould supports and handling frames to improve production times, making the moulds easier to manage and safer to handle during manufacture.
The resulting bars measured approximately 75mm x 75mm in section, and around 1.5m – 2.7 metres in length.
Testing and Quality Control
Due to the variability of the input material from batch to batch, testing was critical.
Each batch of cast bars underwent rigorous testing during and after production to ensure that the finished components would be fit for purpose. Chemical analysis was used throughout the melting process to make sure the specific alloy adjustment was achieved, and the cast bars were also mechanically tested to confirm that they met the required performance standards for outdoor gym use.
Collaboration and Design Practicality
Boro and Steel Warriors collaborated closely on this project, working together during the design phase to simplify the gym component designs where possible, (helping each gym remain unique while keeping the parts cost-effective and practical to manufacture), and during the manufacturing process, where Boro helped Steel Warriors understand the material refining process and its impact on production and the final product.
The Outcome
Boro successfully produced Duplex stainless steel gym bars that met the required specification and were delivered in time for the construction of the Finsbury Park and Ruskin Park gyms.
The project later supported further Steel Warriors installations, including Langdon Park, Carpenters Estate, HMP Brixton and the Gymshark Regent Street store.
By combining foundry expertise, metallurgical testing and practical production engineering, Boro helped Steel Warriors transform seized knives into durable outdoor gym equipment with a powerful social purpose.
Community Impact
The finished installation is now actively used by local communities, demonstrating the real-world impact of the project:
The Key Takeaway
This project demonstrates Boro Foundry’s ability to support customers through technically challenging and highly unusual manufacturing projects.
From developing a bespoke melt process for variable scrap material, to adapting pattern equipment and testing every batch, Boro helped turn an innovative idea into a repeatable, real-world manufacturing solution.
It is a clear example of how advanced steel casting and metallurgical expertise can solve complex engineering challenges while supporting meaningful community impact.
Working with Challenging Materials or Unconventional Designs?
Not every project starts with perfect inputs. Whether you’re dealing with variable materials, complex specifications, or unique requirements, the right approach can make all the difference.
Get in touch with Boro Foundry to explore practical, engineered solutions for your next casting project.
