External Gear pumps
Most gear pumps are not made for metering applications and even if they are very good at creating high pressures and working at high flow rates, they have pretty sloppy tolerances and working at the low flowrates we wanted to use, they would not deliver a linear relationship between rotational speed and output flow rate. Also, most of the gear pumps we looked at could not tolerate the temperatures we required.
At last, we found a gear pump that would satisfy our demands, MZR-7205F from HNP Mikrosysteme GmbH. This pump could handle a 4 bar inlet pressure to enable us to use a pressure feed wax delivery system, it could handle a 30 bar differential output pressure and deliver volumes within 1% error at the relatively low flow rates we need.
At last, we found a gear pump that would satisfy our demands, MZR-7205F from HNP Mikrosysteme GmbH. This pump could handle a 4 bar inlet pressure to enable us to use a pressure feed wax delivery system, it could handle a 30 bar differential output pressure and deliver volumes within 1% error at the relatively low flow rates we need.
Together with a heating module, a thermally isolating motor coupling, a temperature control unit and upgraded seals, this pump should have been able to handle our application, but everything were not perfect.
Due to the extremely fine tolerances in the gear pump assembly it is very sensitive to particles and contamination, creating a need for a very fine (10 micron) particle filter that could clog, and effectively preventing us from reuse of wax, which was a main feature that we wanted in the Royal Wax Printer.
Progressive cavity pump
Progressive cavity pumps consists of a helical rotor and a twin helix stator that seals tightly against the rotor as it rotates, forming a set of fixed-size cavities in between. It is also called a "endless piston pump", since it is more similar to the operation of a piston pump than a rotary pump. The cavities move when the rotor is rotated, and the material is moved forward at a rate very close to perfectly linear relationship (less than 1% error) between input rotation and output volume.
This kind of pump is often mounted to different kinds of robotic platforms and used in industrial applications like sealant application, two component adhesive application, soldering paste, potting, optical bonding, paint mixing and thermal paste application.
It also has one very good edge over the gear pumps, it is not sensitive to particles in the media,
This kind of pump is often mounted to different kinds of robotic platforms and used in industrial applications like sealant application, two component adhesive application, soldering paste, potting, optical bonding, paint mixing and thermal paste application.
It also has one very good edge over the gear pumps, it is not sensitive to particles in the media,
and is often used to dispense abrasive medias due to it's inherent resistance to abrasion.
This sounded like the perfect option for our print head, but nothing is perfect. After talking with the engineers at Viscotec, they explained to us that their pumps was only made for temperatures up to 60C, and above that, they would wear excessively and potentially not seal properly, due to the different thermal expansion coefficients of the materials used.
Using a pump in our intended temperature range of 60-110C would require a custom designed rotor and stator, together with a custom heating jacket.
Initially, this seemed like a dead end, but after prolonged discussions with Viscotec and later Scanmaster, we got a offer on them making a custom made pump for our application, made to operate at the elevated temperatures, and including a custom made heater jacket. In combination with being granted extended funding for the project, this settled it and this became the main part of our print head.
This sounded like the perfect option for our print head, but nothing is perfect. After talking with the engineers at Viscotec, they explained to us that their pumps was only made for temperatures up to 60C, and above that, they would wear excessively and potentially not seal properly, due to the different thermal expansion coefficients of the materials used.
Using a pump in our intended temperature range of 60-110C would require a custom designed rotor and stator, together with a custom heating jacket.
Initially, this seemed like a dead end, but after prolonged discussions with Viscotec and later Scanmaster, we got a offer on them making a custom made pump for our application, made to operate at the elevated temperatures, and including a custom made heater jacket. In combination with being granted extended funding for the project, this settled it and this became the main part of our print head.
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