TABLETING
uniform corrosion can be caused by non- uniformities in the steel structure. A further example of corrosion is
‘galvanic’. Tis type of corrosion is induced when two dissimilar metals are coupled together within a conductive solution. Te difference between the metals is determined by its notability and therefore it’s corrosion potential. Galvanic corrosion is a local form of corrosion, and it is limited to the contact zone between the two metals. Te intensity of corrosion decreases by increasing the distance between the point of contact.
HOW TO STOP THE RUST Prevention is better than cure, and in this instance that statement is very true. Since it’s impossible to eliminate oxygen from the air, it is necessary to implement measures to regulate temperature and humidity and minimise moisture. Effective cleaning measures are another
effective step in corrosion prevention. Inadequate and incorrect cleaning methods can lead to corrosion. Certain formulations that contain corrosive elements can react with the tooling surfaces and cause oxidation if not cleaned properly. Terefore, it is vital that tooling
Several types of corrosion can form on tooling, all of it detrimental to the tableting process
undergoes a thorough cleaning process after compression, preferably by use of ultrasonic, and always using a corrosion inhibitor.
After cleaning and drying lubrication is another important maintenance step to consider. Tablet tooling should always be lubricated before storing to protect it from moisture and prevent corrosion. It is also important to note that drying is very important before lubrication. If moisture sits between the lubricant and the steel substrate, then filiform corrosion can occur. Two of the most effective lubricants
are oil and grease. Tere are various grades of each type of lubricant. Measured in viscosity, these grades characterise the ease at which the lubricants will flow. Oil is recommended when storing tooling for a short period of time. Tey are available as synthetic vegetable or mineral oil and are the industry’s most common forms of lubrication. For long-term tool storage, grease is the optimum choice as it is more viscous than oil adhering to the tool for a longer period of time. Tis offers greater protection for prolonged storage, however, it is worth noting that it is harder to remove from tooling than oil.
Example of corrosion on punch tip
Although using the correct maintenance and storage processes are vital to stop corrosion, it is important to note that high-quality tooling steel (normally a martensitic stainless with a high chromium content) and coating technology can have a considerable effect. Consider using specialised steels and coatings with corrosion resistance properties if a product that you are compressing has corrosive elements to its formulation. Coatings in particular have a very high resistance to oxidisation, staining and discolouration of the tablet tooling.
ADDRESS THE CORROSION CAUSE
Te consequences of corrosion can be costly, not just in purchasing additional tools, but also in production problems that could have been avoided. Poor tool care, the environment, storage, and a lack of understanding of the formulation’s characteristics will all contribute to corrosion. Selecting the right tool steel and coating is key to the successful performance of tablet compression tooling and the prevention of corrosion. It is important to consult with a tooling expert who can determine which steel and coating applications are the right fit the product and provide optimised maintenance solutions for your specific requirements.
Jack Tillotson is process development engineer at I Holland
www.iholland.co.uk
www.scientistlive.com 45
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