## 4 Conclusions  
Herein, we present a fabrication and performance study of a stainless-steel pump impeller manufactured by BJ printing of a sand mould followed by casting. The main conclusions of the work can be summarized as follows:  
Figure 13: _Recipe 3_. (**a,b**) Dependence of pump average (current) on pump pressure and polyol flow for two consecutive production cycles. (**c,d**) Tank level, polyol flow, and pump pressure, read continuously for a complete production cycle. KSB impeller (**a,c**), BJ impeller (**b,d**).  
* Reverse engineering of the original impeller allowed creating a polyamide copy, used to validate the CAD design by metrological characterization, with a dimensional accuracy of 99.6%.
* This work is another example of the advantages of BJ sand printing in creating multi-component moulds able to recreate complex features of the original part.
* The casted material showed an essentially homogeneous surface, with a very small proportion (<0.5%) of shrinkage voids. The microstructure was similar to that of the original impeller, with 6.3% of ferritic phase.
* The operational performance of the produced impeller was tested in a real scenario by installing the impeller in a centrifugal pump. The pump operated in a polyol/polyglycol plant, and a series of process parameters related to the pump behaviour were measured continuously for three production recipes varying in final concentration and viscosity.
* For example, at 500 cSt of product viscosity, the average current consumption of the pump was 9.34 A, as compared with 9.41 A measured with the original impeller, with standard deviations of 0.3% and 2.7%, respectively, for a wide interval of pressures (4-6 bar) and flows (2000-6000 L/h).
* The parameters were also comparable when measured during a complete production cycle. This indicated that both impellers had equivalent performance, thus validating the fabrication strategy from an operational point of view.  
Therefore, this work demonstrated that the implementation of additive manufacturing technologies in chemical process engineering is a useful solution for fabricating spare parts of high added value that are difficult to replicate with other technologies, with consequent economic benefit. Further work should focus on comparing the initial mechanical and morphological properties of the BJ impeller with those obtained after one year of operation in order to understand possible changes induced by the stress associated with continuous operation. In addition, a next step will involve the fabrication of an impeller by direct metal 3D printing and an economic study of the possible wider implementation of both 3D printing technologies in the chemical plant.  
Conceptualization: F.H and A.F.; methodology and experimentation, F.H.; data curation, F.H.; writing--original draft preparation, F.H.; writing--review and editing, A.F.; supervision, A.F. All authors have read and agreed to the published version of the manuscript.  
This work received no external funding.  
Not applicable.  
All data are included in the article.  
We thank [PERSON] (Dow Industrial Solutions, Production Leader Polygyclol/Utilities Plant), [PERSON] (Dow Chemical Senior Technology Manager, Rotating Equipment), [PERSON] (Dow Chemical, Improvement Manager), and [PERSON] (Leitat, Energy and Engineering Department) for their valuable support and contributions to the finalization of this work.  
The authors declare no conflict of interest.