Feature article: PIM International, Vol.1 No. 4 December 2007, pages 47-49, 1368 words

Authors: Claus J. Joens, Elnik Systems, USA [1] and Satyajit Banerjee, DSH Technologies LLC, USA [2]

[1] Elnik Systems, Division of PVA MIMtech LLC, 107 Commerce Road, Cedar Grove, NJ 07009, USA
[2] Satyajit Banerjee, DSH Technologies LLC, USA

Introduction

Claus J. Joens (Elnik Systems) and Satyajit Banerjee (DSH Technologies, LLC) look at the benefits of laminar gas flow in batch furnaces. Laminar gas flow can offer many advantages for the MIM part producer. As well as offering a great degree of versatility and flexibility in producing a wide variety of MIM parts, the technology eliminates the need for a separate thermal debinding step.

Furnace design challenges

MIM parts are made from many different metal powders ranging from iron nickel to stainless steel, from titanium to superalloys using a variety of different binder materials to produce different feedstocks. Depending on the metal powder and the binder used, the debinding process can be carried out under atmosphere or partial pressure atmospheres of nitrogen, argon and hydrogen. The sintering process requires the same atmospheres or high vacuum for special alloys.

In order to process MIM parts from any given material the furnace was designed with a refractory metal hot zone and retort. Graphite hot zones and retorts create carbon level control problems and are not suited for hydrogen atmospheres or high vacuum. A controlled gas flow management system was developed in order to address the uneven gas flow resulting in poor temperature uniformity inside contemporary furnaces. The MIM furnace developed at Elnik Systems (Fig. 1) is very flexible allowing the processing of most materials in all the atmospheres mentioned. Typically it works under partial pressure from atmosphere 1010 mbar to 0.10 mbar and has a high degree of temperature uniformity because of the laminar flow of the gas.

The furnace may also include as an optional extra a high vacuum system reaching up to 10–7mbar. The computer controls of the furnace allow for changes to any of the conditions in any of the segments of the process via entry into an Excel spreadsheet.

Debinding cycle

The secondary binder is thermally removed inside the furnace. The rate of binder removal must be carefully controlled so that the binder vapour coming out of the part is slow enough not to crack the part. To overcome binder deposits on the cold walls of the furnace a virtually gas tight retort with plenums is constructed out of TZM molybdenum. The gas flow across the parts during debinding and sintering is of great importance. A controlled gas management system feeds the gas at a predetermined flow......

Further sections of this article include:

- Debinding cycle
- Sintering cycle
- Laminar gas flows during the debinding/sintering cycle
- Furnace controls
- Conclusion

Figures and Tables:

Fig. 1 Batch furnace for MIM tailored to offer the benefits of laminar gas flow during debinding and sintering (Courtesy Elnik Systems, a Division of PVA MIMtech, LLC)

Fig. 2 Retort with thermocouple locations (Courtesy Elnik Systems, a Division of PVA MIMtech, LLC)

Fig. 3 Retort with shelves (Courtesy Elnik Systems, a Division of PVA MIMtech, LLC)

Table 1 Temperature spread for MIM 3002 under various conditions