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Kevin Queensen, Mechanical Engineer, Natoli.
Why Coat Your Tooling?
In the past, applying a coating to tools was the only defence available to reduce or eliminate corrosion to the tools when compressing caustic powders, such as chlorine and other chemicals. At the time, the available tool steels used to make punches and dies were low in chrome content, largely considered the most effective alloying element to fight corrosion.
Some tool steels, such as 440C with 16-18% chrome in its chemical composition, were utilised for compressing caustic powder, but due to the carbon and high iron content in the steel, did not provide 100% protection from corrosion. Coating the tools with a surface layer of chrome provided 100% protection and became the normal method to protect the tools from corrosion.
Secondary benefits of coating tools is to enhance product release and increase wear resistance. Product sticking to the face of the tools and picking within the embossing on the punch faces is often seen as a common issue with compressing many pharmaceutical products. Chrome coating provided a good solution with regards to minimising product sticking, resulting in reduced downtime cleaning tooling and increased production.
Chrome coatings are applied with the metalworking industry standard method of electroplating. However, the electroplating utilised an electrified chromic acid bath, which is plagued with obvious environmental challenges and occasional adhesion deficiencies.
Some tool manufacturers promote coatings but may not provide full disclosure of the actual coating that is applied. Instead using branded names or internal product codes to obscure the true identity of the coating type or chemistry.
Time for a Change
In the ever-evolving landscape of modern manufacturing, finding efficient, cost-effective, and high-quality solutions is vital to support the various needs and many challenges present in the tableting and encapsulation industries. The contemporary coating solution is cathodic arc deposition, a cutting-edge arc evaporation process for coating punches, dies and encapsulation parts. This article explores the merits of adopting this innovative technology, focusing on its cost-effectiveness, time-saving benefits, superior coating characteristics, and its ability to enhance product quality.
Cathodic arc deposition is a Physical Vapour Deposition (PVD) process that involves the deposition of ions from the cathode (solid metal target) onto the surface of the tooling (anode) to form a thin film coating. The cathode is energised with a high-current, low-voltage electric arc discharge, leading to the vaporisation of metal ions. The cathode may be combined with nitrogen, oxygen, or carbon-containing gas to form compound materials. These ions condense onto the tooling to form a thin, bonded layer, greatly improving appearance and durability, with exceptional adhesion properties, enhancing performance.
Traditional manufacturing practices often involved outsourcing coating services, leading to substantial expenses and excessive lead times. By adopting in-house cathodic arc deposition, manufacturers can eliminate the need to rely on third-party coating providers. This allows your tool manufacturer to maintain dimensional integrity, provide higher quality control standards, reduce costs, decrease lead times, enhance security for branded product tooling, and pass the savings on to their customers.
In-house PVD coating capabilities allows for greater control over the deposition process ensuring high quality coverage and precise thickness of coating material is applied. Direct control of the coating process parameters, such as temperature, pressure, and ion energy ensure quality, consistency in coating thickness, uniformity, and surface finish across all production runs, ultimately allowing tool vendors to tailor solutions specific to their customer’s needs.
Enhanced Wear Resistance (TiN)
Punches, dies and encapsulation parts are subjected to significant wear during the manufacturing process. Cathodic arc deposition allows for the application of exceptionally hard and wear-resistant coatings. Titanium nitride (TiN) or chromium nitride (CrN), will increase the lifespan of these essential components by offering enhanced wear resistance. The higher surface hardness provided by these coatings imparts enhanced wear resistance without sacrificing the impact toughness and strength of the steel substrate. (Insert Photo of TiN)
Improved Corrosion Resistance (CrN)
Corrosion resistant coatings become essential when tableting or encapsulating products containing harsh or caustic compounds. Cathodic arc deposition of Chromium (Cr), Titanium (Ti) or Zirconium (Zr) metals will apply corrosion-resistant coatings to protect tooling from degradation due to corrosive agents. These coatings perform significantly better when subjected to the ASTM B117 salt spray test, which quantifies and ensures a materials’ corrosion resistance. (Insert photo of CrN)
Anti-Stick Benefits--Reduced Friction and Adhesion (Cr, CrN & ZrN)
The most prevalent challenge in the tableting industry is sticking to the tool face. Sticking occurs when the adhesive forces of powder to the tool face are greater than the cohesive forces of particles to one another. Hard Chrome (Cr), Chromium Nitride (CrN), or Zirconium Nitride (ZrN) coating applied by cathodic arc deposition will significantly reduce friction, provide low adhesion properties, and enhance surface lubricity between the tool face and the powders being compressed. Decreased friction also offers an additional benefit for heat sensitive API’s as operating temperatures are reduced, significantly diminishing product sticking and picking on the contact surfaces. This helps ensure consistent product quality and therefore minimises tool cleaning and polishing.
Adaptable Coating Solutions
Different manufacturing processes require specific coating characteristics. In-house coating capabilities allow tool manufacturers to customise coating formulations to suit unique requirements. This ensures that punches and dies are optimised for specific tasks, resulting in better product quality. The most effective way to evaluate the efficacy of a coating is to test multiple coatings within one set of tooling during a single production/test run (the only gross variable is the tooling). This is best to do early in the development process as a way to identify deficiencies in the formulation using <USP 1062> guidelines.
Conclusion
Tool vendors with in-house PVD coating capabilities have developed game-changing solutions for coating punches, dies and encapsulation parts. The cost-effectiveness stemming from reduced outsourcing and increased yields empower manufacturers to allocate resources more strategically, while providing enhanced security and control of branded tooling. Most importantly, the ability to achieve superior product quality with wear-resistant, corrosion-resistant, and low-friction coatings ensures customer satisfaction and long-term success.
By embracing this PVD coating technology, tooling manufacturers can offer a wide variety of solutions to best fit their customers’ unique needs. Ultimately, the end user will reduce their operating costs, minimise downtime, increase productivity and overall product quality.