MechChem Africa talks to Saahil Bhartu, product engineer at UMP, about the advantages offered by adopting 3D printing to manufacture complex moulds for the manufacture of polyurethane products.
Saahil Bhartu, Product Engineer at UMP presents a 3D printed design of a complex hydrocyclone helix.
UMP was founded in 1947 by Brian Christiane as a polyurethane moulding company. “Back in those days, people started putting artistic patterns into concrete, and the way that was done was to make a polyurethane stencil which, when applied to the wet concrete, creates a permanent artistic pattern. Brian Christiane started out making these patterns, but soon realised that polyurethane (PU) was a very interesting lining material,” begins Saahil Bhartu, who is the product engineer for moulded polyurethane products and 3D printing at UMP.
“Because PU is a very abrasion-resistant material, our founder realised it was ideal for lining pipes transporting mineral slurries such as coal, iron-ore and phosphate. So UMP became the first company in South Africa to develop PU-lined piping. And our business grew from there. We started doing more and more pipes, which quickly became our core business. We then started custom moulding polyurethane products, went on to include design and development, and are now a full-service engineering, design, development, casting and manufacturing company for an extended range,” he tells MechChem Africa.
“Our business is split into two, though. As well the PU side, we have taken on an increasing role in fabrication, predominantly for mining companies. This began with the fabrication of steel inserts for our lining systems and the manufacture of moulds and their supports, but we also offer fabrication services for piping and modular Bailey bridges, for example,” he says.
“We also do a lot of work for pump and hydrocyclone OEMs, as well as OEMs involved with bulk materials handling machines, such as FLSmidth, Thermo Fisher Scientific, Azmet technologies, Kwatani and Sandvik, to name a few,” he adds.
Polyurethane moulding and 3D printing
Describing the hot casting process for lining pipe with PU, Bhartu says UMP will first design an internal mould or mandrel to match the pipe section being lined. “The pipe section and mould is put onto an oven and heated. We then introduce a prepolymer and a curing agent in liquid form, and we spin the pipe. The polyurethane cures against the pipe surface due to the heat, forming a smooth lining with an even thickness.
“We can also do spray lining if the surface finish is not that important,” he says, adding that polyurethane shrinks a little on curing, “which works in our favour when it comes to removing a mould, but from a design perspective, we still have to make sure the angles used and shapes will allow the mould to be easily released once the PU has hardened.”
All sizes of pipe can be accommodated, with the largest ever done by UMP being 900 NB pipes and bends, while section lengths as long as 9.0 m can be accommodated for laying long pipelines.
PU is also used extensively for lining flat products. “For vibrating screens, for example, we do a lot of sheeting work, and we make sets of PU blocks for use as vibration dampers. If you put these blocks under the legs of rotating machinery, vibration can be completely absorbed with none being transferred into the ground or to neighbouring equipment.
“We manufacture spares for flotation cells, impellers and centrifugal pump liners and a host of products that help to protect moving steel parts such as agitators and mixers from coming into contact with abrasive slurries,” he says.
The shift to 3D printing
Describing the traditional process for manufacturing liners for pump impellers, he says that the pump OEM generally supplies a 3D CAD model of the impeller, which is used directly to design a CAD model of a matching mould. “We then machine the whole shape out of aluminium using an advanced CNC machine to make the moulds, which are used to cast bolt-on PU impeller liners.
“Particularly with the machining of largescale and complicated impeller moulds, this is a time consuming and generally expensive procedure. One has to buy a large chunk aluminium, which has to be carefully cut away to get the form needed. There is a lot of capital investment, depending on size and complexity, so to make this easier and less expensive, we at UMP started to look at different materials and manufacturing processes for making our moulds.
From a materials perspective, we found several 3D printer options. For FDM (fused deposition modelling) for example, we can use several thermoplastics with different harnesses as well nylons, carbon fibre- and glass fibre-reinforced materials. These materials all have the thermal capability and strength to be used in the PU moulding process. And the 3D printing process brings flexibility, speed and cost effectiveness on the mould manufacturing side,” says Saahil Bhartu.
Making 3D printed moulds from these materials meets all of the temperature and rigidity requirements and moulds are far cheaper and faster to make than machined aluminium moulds, though they are not quite as durable. This makes them ideal for shorter production runs or prototyping work.
UMP then started using the stereolithography (SLA) 3D printing process. A notable success using the SLA process was the manufacture of a hydrocyclone helix for the separation of cyanide and gold recovery. This is a critical process to prevent valuable gold being lost at the end of the liberation process. In partnership with a company called Azmet, which designed and patented an optimised cyclone impeller helix to minimise losses, we were charged with manufacturing a scaled down version of the impeller. The impeller was initially designed to be made in stainless steel, but it turned out to be an impossibly difficult and costly exercise to machine the exact curves needed for best separation, so we decided to cast it in polyurethane instead.
Once the prototype had proved successful, the full scale helix with a length of 900 mm had to be manufactured in polyurethane. This meant the large mould had to be designed with interconnecting pieces, so the individual parts would fit into the SLA printer and to enable the mould to be released after casting. “But while the mould design was a bit of a complex jigsaw puzzle, the whole process was so much easier. Using PU reduced the costs, made the hydrocyclone lighter and, in terms of performance, the solution is achieving 20% better gold recoveries. It was a groundbreaking project and a huge breakthrough for the direct use of 3D printing for making polyurethane products,” Bhartu tells MechChem Africa.
As a result, his 3D printing department is going from strength to strength: “We have recently got into manufacturing non-pneumatic wheels using PU, for example, basically a wheel and a tyre all in one, which can save millions on the cost of the tooling to manufacture to a steel wheel with a pneumatic tyre. We can now design a wheel and a mould and move directly on to 3D printing the mould. The whole wheel and tyre can then be cast using different grades of PU materials, with rigidity for the wheel and axle and pliability for the tyre,” he explains.
UMP is has made wheels for a German company, MöllerWerke, which makes unmanned cleaning machines. A key design aspect is that the machine has no suspension and the 860 kg load is carried on 300 mm wheels with only the tyres providing suspension. “It was quite tricky, but we were able to find a nice balance between stiffness and damping of the PU that does the job very nicely,” Bhartu explains, adding that for the small volumes needed, this could not have been cost effective without 3D-printing.
“We at UMP are now a fully-fledged design and development company that is able to do much more than just manufacturing. We are now a complete solutions’ provider that can develop, design and deliver solutions for complex modern problems. When it comes to polyurethane, we are a turnkey solutions’ company,” Saahil Bhartu concludes.
