Magnesium Oxide is a popular mineral supplement and is often used as an antacid or laxative. Tablet forms include enteric coated tablets for extended release and chewable varieties. Magnesium Oxide formulation typically has a small particle size, is abrasive and alkaline (pH approximately 10.3) which can be reactive to tool steels.
Black marks are easy to spot on white tablets. They may appear on magnesium oxide tablets either on the sideband or the tablet face. They can be irregular blotches, rounded or black streaks.
Black Mark Troubleshooting
- A single, irregularly shaped mark on the sideband is likely due to contact with the scraper blade during tablet ejection. Adding a piece of plastic (such as Delrin) in front of the scraper blade helps to protect the tablets.
- Scorch marks (excessive heat) are typically seen as black vertical streaks on the sideband. This may be a sign of high tablet ejection pressures from tip binding or sensitivity of the formulation to the die bore surface finish. Moving away from Tungsten Carbide as a die material can be helpful.
- Oil droplets tend to be more rounded and randomly dispersed only on the top tablet face. Use bellows or dust cups to catch contaminates falling from the upper guides and reduce oiling rate as necessary.
Tooling issues associated with Magnesium Oxide most commonly involve premature wear, tip binding and corrosion.
- Switch tooling material to AISI 440C or M340 stainless steel as they provide a good combination of corrosion resistance and wear resistance
Tip Binding Troubleshooting
- Reduce lower punch tip straight from 3/16” to 4mm
- Increase tip relief from 0.010” to 0.020”
- Increase lower punch barrel diameter from 0.7450 / 0.9950” to 0.7480”/0.9980” if press turret is compatible
- Adjust tip to die bore clearance
- Use stainless steel tooling (AISI 440C or Bohler M340 stainless)
- Remove tooling promptly from press after completion of batch
- Clean tooling immediately after removal from press
- Clean below 50° Celsius for shortest period possible
- Ultrasonic baths – use a cleansing agent such as Alconox
- Pre-rinse in de-ionized water – not tap water
- Final rinse in 100% Isopropyl alcohol (IPA)
- Minimize time between washing and drying
- Dry with a cloth – do not air dry
- Oil tools after cleaning
For more information on compression tools from Wilson Tool, please contact our Tooling Technicians or visit wilsontool.com/tablet.
June 23, 2022