Augers used in in the pharmaceutical process industry demand the highest integrity with the finest overall polish finish. Fabricated augers can suffer from many defects, some of which will present problems in any application. These defects, however, are most impacting within pharmaceutical and medical applications.
Pharmaceutical augers will traditionally be manufactured in stainless steel with the helicoid flights welded onto a central core. Fabrication has a few drawbacks:
- The accuracy of the flights – Usually reliant on the “eye” of the welder/fabricator and can vary by large amounts. Variations in flight pitch and diameter affect the augers action in propelling product and can produce uneven flow patterns, affecting accuracy. Trantec Augers are manufactured using computer controlled machine tools and have accuracies within tolerances of 0.01 mm in diameter and pitch.
- Two problems associated with welding austenitic stainless steel augers are sensitisation of the weld heat affected zone and hot cracking of weld metal.
Stainless steel resists corrosion by forming a thin passive film, which is best thought of as chromium oxide (Cr2O3). Welding produces a heat zone on either side of the weld which creates chromium carbide (CR3C2), reducing the corrosion resistance in the welded area.
Hot cracking is caused by low-melting materials penetrating grain boundaries. If these compounds are present in the weld or heat affected zone, they can penetrate grain boundaries, causing cracks and shrinkage stresses as the weld cools.
Trantec’s manufactured augers, produced through our machining process, do not require any welding and don’t suffer from these defects.
Stainless Steels coefficient of thermal expansion is 30-50% greater than carbon steels. Welding stainless produces larger distortion than other metals. Fabricated augers require additional work to straighten them, which can add to their internal stresses.
Our pharmaceutical augers only require minimal post-production straightening, but mostly require no straightening at all. This is particularly important with small diameter screws.
Welding flights to a central core will require a weld on both sides of the helical strip. Even with the most skilful of welders, the welds will need grinding and dressing to produce a crevice-free finish, as required in any pharmaceutical application.
Trantec uses tooling specially selected to produce a fillet between the centre core and the flights, which is part of the original metal. Minimal dressing is required, saving time and money.
The final process in manufacturing a pharmaceutical grade auger is polishing. Mechanical polishing removes metal to impart the correct surface texture and roughness. Smooth surfaces are essential to help reduce the likelihood of product build up and subsequent “bug traps.” Smooth surfaces are easier to wipe clean manually or when using CIP (Clean in Place) or SIP (Sterilise in Place) for liquid runoff and debris removal.
Mechanical polishing is often time-consuming and involves removing metal progressively using a series of finer abrasives. The poorer the starting surface finish, the longer and more laborious the process. Fabricated augers can take many hours to hone into a fine “mirror” finish due to the poor starting condition.
Using progressively finer cutting tools and cuts, Trantec Augers often enter the polishing process at far later stages. Finishes of <0.2 Ra µm can be produced in less than an hour. These cost savings are passed on to our customers.