Die Set FAQs
Using your Die Set:
What is the max load for my die? You can find the max recommended load on the individual product page. The steel we use has a very high yield strength of over 80,000 psi or 550 MPa. We recommend a 50 % safety margin, loads for each die set should be carefully considered before using the die to ensure safe operation. This is of particular concern with the smaller ID dies where you can reach the yield strength of the steel with a few pumps of the hydraulic press. Do note that using high pressing force does not guarantee a denser pellet. If you press too hard, you will most likely surpass the fracture stress of the compact well before you reach the yield stress of the material. The stress in your pellet will concentrate at the top side of your pellet and you will likely see cracking or "capping" at the top of your powder compact.
Do I need the prepare the die set in any way? We store our dies with a water resistant lubricant. When you get it, just give it a good clean with detergent before use. If you are storing your die for a long time or it will be exposed to moisture or humidity then you can simply spray with WD-40 or a similar product before storing.
Can I heat up my die set? Our standard die sets cannot be heated as the metal has been heat treated, heating it at all will compromise the heat treatment, making it softer, weaker and quickly lead to oxidisation. As an alternative we can make you a custom die set out of stainless steel that could be heated to around 250 °C (480F).
What is the thickest pellet I can make with my die set? As a general rule of thumb your pellet height should not greatly exceed the diameter of your pellet. This is because you get non-uniform compaction through the pellet when you go thicker than the diameter, the top will get more stress concentration than the bottom (non-moving surface). That being said, all materials are different, so you can take this rule with a pinch of salt. The maximum height of pellets you can make using our standard range (50mm height die sleeve) die sets would be between 0.6-1.0 inch pending on the material you are pressing and method of loading the die set.
- If you’re pressing long pellets (with respect to your diameter), consider lubricating your die.
- Try adding a rubber o-ring (or something flexible) between the base plate and the die sleeve, this will allow movement of both he top and the bottom plunger, improve the stress uniformity through the pellet.
- For making very long aspect ratio pellets there are other methods such as isostatic pressing which might be more suitable
What height opening does my press need to be? For our standard range have a 50mm height die sleeve and similar length plunger. Your press will need about 100-125 mm (4-5 inches) clearance for loading the die set depending on how full of powder your sleeve is a where you are using spacers.
Can I use organic solvents with my die set? Organic Solvents cannot be used with our standard die sets. We can make a custom stainless steel die set but you would need to check that the solvents you are using would be compatible with a 400 series stainless steel.
Do I need to use lubricants or binders? You do not need to lubricate your die before use for most materials nor do you have to use binders. Some people like to use a small amount on lubricant on the walls of the die as this is where there is highest friction during pressing and release which can lead to cracking. Likewise, some applications and materials use binders as common processing protocol. Both lubricants and binders can be burned out afterward when sintering above 700 °C (1290°F) leaving behind minimal residual residue (carbon).
Lubricants which you might want to consider are:
WD40, paraffin wax, stearic acid (also does the job of gumming up your powder if it's very fine), oleic acid, poly glycols, graphite, boron nitride and stearates (aluminium stearate, butyl stearate, lithium stearate, magnesium stearate, sodium stearate, zinc stearate).
Will my die rust? The steels we use for our standard die sets are high strength and high hardness and typically the steel of choice for the most demanding tooling applications – they are not stainless steels. If you don't dry it after washing or store it wet - yes it will rust. Don't worry, it happens - the good news is that it should be easy to clean off. If you so want us to make a custom die in stainless, we can do it - just complete the custom quotation form.
How do I clean and store my die set? After each use make sure die set is cleaned and dry. It is typical for small amount of powder to be left on the surface after pressing. The die set needs to be cleaned fully before the next use as the gap between the plunger and sleeve is very small. If you are storing your die for a long time or it will be exposed to moisture or humidity then you can simply spray with WD-40 or a similar product. If you are looking for a product to help with cleaning we recommend using 3M™ Creme Cleanser for cleaning our pellet die sets. It is a cream which can be used with water to clean our dies. The cream has a small amount of gentle abrasive to help remove chemicals from the surface. Use with a scourer coated sponge for best results. For inner surface of die sleeve, use with appropriate sized nylon brush.
I scratched the inside of my die sleeve or rod. Can I fix this? Potentially, yes. For small scratches you can purchase a cylinder flex hone tool (http://www.brushresearch.com/brushes.php?c1=1), attach it to a drill and clean the inside of your die sleeve or rod with some honing oil. You only need to be worried about removing the high points from the scratch that are causing interference. If the scratches are on the end they might be removed with a fine file or paper. If you use something rough, you will never get the finish back and if you remove more than 0.0005 inch and you will notice the difference in the fit.
Do you have some advice for making good pellets?
There is a lot to say here...
- Number 1 - obviously - press safely, if unsure ask someone with experience. You are able to put a lot of force through your die with a hydraulic press. Think about the force you want to apply beforehand, do not exceed the force for the die you are using, wear safety googles with side shields, use a guard between you and the press, keep other items off the press table so they don't get caught, make sure everything is inserted correctly and well located before pressing.
- Check that your press plates are parallel and sample as level as possible before pressing. Check your pressure and force gauge is working and know what your max pressing force/pressure will be. Check against the maximum loads on the product page for your pellet die diameter.
- If the die is overfilled with powder before pressing, the plunger will not locate properly.
- Always clean your die before use - this will not only stop contamination but make the die work better, with less friction.
- Higher force is not necessarily better - if you find your pellet is cracking then you should consider using less force before using more force. Please can you make sure that anyone using this die set follows the recommended forces on the product pages on our website. Make sure that the force gauge on hydraulic press is working and accurate.
- If you are having trouble with a certain material - don't worry we have all been there. Consider drying before pressing changing the grain size your materials before pressing (more grinding), tapping with a small rubber mallet after assembly and before pressing (helps the powder move around, reorganise and settle before pressing), you can also try using lubricants or binders to help get your pellet out.
Can I use more than the recommended max force? This is above the recommended safety margin and therefore poses a risk for failure. Your plunger may be able to take this force however with repeated loading there is a higher likelihood of failure. Metal doesn't show visible signs of damage so you wont know when it may break under increased force.
As always with all pressing please use a safety guard and follow all safety instructions in your lab.
What is the minimum powder particle size? The die set can take powders that are approximately 10-20 microns.
You can use the die set with nano-powders although some powder might escape around the sides of the plunger which might make it seize up (or jam) a little bit (although the parts can be released again).
Is the pressure shown on the hydraulic press pressure gauge the same as the pressure in the die? No. The pressure on the gauge is the pressure on the cylinder on the hydraulic press. If your gauge is reading in force then the force is the same as the force on the plunger. If your gauge shows pressure units then the pressure is simply the pressure underneath the ram in the hydraulic press. You need to know the ram diameter to work out the effective area and figure out the load/force. Then use this force to calculate the stress on the plunger (load divided by cross sectional area of plunger). The manual with your press should tell you either the effective area or what pressure equals what load.