To the naked eye, it is nearly impossible to spot the microscopic signs of abrasive wear and corrosion that can reduce the efficiency of pharmaceutical tablet compression tooling. The high-performance tooling used by pharmaceutical companies in the manufacture of tablets and capsules requires highly polished, scratch-free surfaces in order to maintain the surface contact necessary to compress formulation powders and develop a consistent, quality product. Unfortunately, industry-standard tooling steels such as D-series, S-series, and stainless steels (408, 440C) are all to abrasive wear and corrosion. As the working surfaces of the punches and dies roughen from wear and corrosion, a number of physical phenomena occur which act to reduce tablet productivity and increase manufacturing costs.
Increased Mechanical Interlocking –
When microscopic scratches and pits develop in tooling surfaces, the pharmaceutical powders can become trapped in these surface imperfections. As additional tablets are compressed, the powders will stick to the particles trapped in the surface and start to build-up on the surface. Unfortunately, due to the fact that these imperfections are almost invisible to the human eye, the effects of these scratches and pits are not noticed until it is too late. Occasionally, sticking and picking appear, and production must be halted to remove and clean the punches. The losses for the manufacturer quickly mount every second that production is offline.
Similarly, if tablet tooling surfaces corrode and rust layers build on the punch surface, powders will begin to stick to the roughened rust layers. Cleaning with detergents or solvents will remove the adhered powders but will not restore the original finish of the tooling surfaces. Tooling in this condition requires regular buffing and polishing to smooth out scratches and pits, and remove corrosion products in order to return surfaces to working conditions. Again, production must be stopped to remove and polish the machine tooling.
Increased Friction between Powders and Punch / Die Surfaces –
Whether due to scratching or corrosion, roughened surfaces will also increase frictional forces as formula powders flow across the punch faces during compression. Because pharmaceutical tablet production is an extremely precise process, the slightest imperfections in the process at any level will result in a growing number of additional problems down the line. Manufacturers use predetermined levels of materials that have been found to achieve the highest levels of efficiency. Once minor surface abrasions begin to appear in tooling, the predetermined levels of lubricants and glidants will no longer be effective. Higher compression forces may be required and the work of ejection will increase.
Reduced Life of Tablet Compression Tooling –
Constant restoration of worn and corroded punch faces by buffing and polishing has a significant negative impact on tool life. Buffing compounds contain abrasives that actually remove thin layers of the metal surface in order to polish-out scratches and pits. Repeated buffing can reduce the critical punch dimensions in the land area at the punch tip, thus reducing the fit between the punch and die. Constant buffing also results in rapid degradation of the aspect ratios of embossed features on the punches. In both cases the usable life of the punch is dramatically reduced.
Rather than continue the cycle of abrasive wear, restoration, and subsequent further degradation, pharmaceutical manufacturers have additional options for maintaining the surface integrity of high performance tooling. There are a number of different performance coatings available, each with various advantages and disadvantages. Some precision metal coatings, such as those applied by the IBED coating process, are capable to protect and enhance tablet compression tooling surfaces and are applied at low temperature, thus eliminating the possibility of tooling dynamic distortion. The result is longer life and improved efficiency for pharmaceutical tablet compression tooling.