In response to ongoing personal protective equipment (PPE) shortages caused by the coronavirus (COVID-19) pandemic, Big-nano, a manufacturer of nanofibre filter media based in Ontario, Canada, has collaborated with the UK’s Renishaw to help create a local supply chain for protective masks.
Taking advantage of the Additive Manufacturing process, Renishaw used a RenAM 500Q AM machine located in Canada to build a new titanium nozzle for Big-nano’s liquid blowing process, enabling the production of N99 quality fabric while reducing maintenance and downtime.
In 2018, Big-nano developed a fine liquid blowing technique for the production of nanofibre, allowing easy, scalable production. Its technique streams high-velocity gas through a needle, while a polymer liquid solution is simultaneously accelerated to the tip of the same nozzle. When the two streams interact, polymer is brought from a molten to fibre state, producing a poly (vinyl alcohol) non-woven fibre mat.
Nanofibres are steadily gaining popularity in drug delivery systems, medical implant devices, water & air filtration, and protective clothing applications. After the coronavirus caused a shortage in PPE, Big-nano saw an opportunity to contribute.
“The coronavirus pandemic demonstrated to nations worldwide that some products like PPE should be manufactured locally for the national interest,” explained John Rawlins, co-founder of BIG-nano. “Supply chains around the world broke down in a way that no one anticipated. The call by the Canadian government to work on PPE locally in a way that is secure for our communities interested us. It was something immediate and good that we could do, so we stepped up to that challenge.”
The gold standard for healthcare workers, N95 and N99 masks are produced using a fine mesh of polymer fibres to filter airborne particles: 95 and 99%, respectively. Nanofibres are particularly effective at achieving a high percentage of the particle filtration necessary to protect wearers from COVID-19.
The initial challenges facing the company were making its technology practical to implement in large scale manufacturing, while maintaining N95 quality. Big-nano’s first design for its equipment was monolithic, meaning that a single component failing would require expensive maintenance and downtime on the entire machine. In particular, the nozzle sustains substantial pressure and temperature changes, which led the team to prioritise its redesign.
“The nozzle consists of a compressor system, which heats the air, and an extruder, which melts the polymer,” stated Rawlins. “That polymer is then brought into the extruder to meet the heated gas. The nozzle does the work of processing the polymer from molten to fibre state; it really is the heart of the whole system.”
“Our original design was highly efficient, which allowed us to make nanofibre at microfibre prices. The drawback was that it was arranged in an unconventional way,” he continued. “Our design was also very complex, which meant that we had to collaborate with an engineering partner that had experience with thermal dynamics and pressurised and heated fluids.”
When approaching Renishaw, Big-nano emphasised the importance of scalability, easy maintenance and quality consistence. On top of this, the urgent issues driving the manufacturing of N95 masks meant that the project had to be completed as quickly as possible.
“We realised machining the nozzle for our jetting process would mean we couldn’t complete the project in time, so we looked to Additive Manufacturing for a solution,” Rawlins stated. “Renishaw brought valuable Additive Manufacturing expertise we didn’t have in-house, giving us the ability to produce prototypes for a new nozzle design quickly, despite their complexity.”
“Big-nano presented us with a project that was a challenging but clearly valuable application of AM,” stated Carl Hamann, Additive Applications Specialist at Renishaw. “We were under time pressure to produce new prototypes to improve upon a design with complex internal geometries. We chose to use a RenAM 500Q machine, as the multi-laser system would quadruple build speed.”
The RenAM 500Q features four high-power 500 W lasers, which can address the entire build plate. The machine also comes with automated powder and waste handling systems that enable consistent process quality. Renishaw’s machine met Big-nano’s requirements, meaning engineers minimised build time while ensuring consistent part quality.
“We couldn’t take the original design for the machine and build it using AM directly. It was too large and consisted of numerous large blocks of metal that could more easily be machined,” Hamann continued. “Instead, we selected components that would bring the most benefit and redesigned them for the AM process. This led us to change the design of the machine to a modular one that can be disassembled and refitted with AM parts indefinitely.”
A modular design brings significant advantages for time-sensitive manufacturing, as it means that if the nozzle were to fail or wear over time, a substitute could be quickly built with AM and installed, reducing both maintenance costs and overall downtime. In addition, Renishaw produced the part in titanium to further minimise maintenance while retaining its ability to consistently achieve N95 standard.
“In order to go rapidly from one iteration to the next, we tested components with aluminium prototypes. This allowed us to design, produce, test and improve three iterations in just three weeks,” explained Hamann. “This introduced some new challenges as aluminium is more susceptible to thermal expansion than titanium. Cycling of cold and hot temperatures took its toll on the tool, but fortunately rapid prototyping allowed us to find better ways of cycling the polymer and gas.”
“I was particularly impressed with the turnaround for each iteration of the nozzle. In three weeks, we achieved what could otherwise have taken up to nine months,” Rawlins added. “Every process has instabilities; the central aspect of our design is to understand how they would affect the end-product and minimise any factors that could prevent us from reaching N95 quality. For us to achieve this more than nine times faster than expected is unprecedented.”
As it stands, Renishaw and Big-nano are still collaborating in order to perfect their system. The team’s goal is to make the nozzle larger to increase nanofibre throughput, thus allowing larger volumes of mask production.
“While we initially aimed for N95 quality, our improved AM design can produce N99 nanofibre,” Rawlins stated. “This is a very welcome surprise, since we, initially, were concerned with maintaining N95 quality in a scalable way. It goes to show how effective AM prototyping can be.”
“Coronavirus is going to pose challenges in indoor spaces, as it appears people are most likely to catch it in confined spaces. For heating, ventilation, and air conditioning (HVAC) equipment to protect workers in office spaces effectively, they must be substantially upgraded. While doing so with hardware improvements could work, we think that we could achieve comparable results by retrofitting nanofibre in current filtration systems. This could save users substantial hardware costs.” Rawlins added, “We are now looking past PPE and considering new applications where nanofibre could benefit society.”