A paper says the pellets were pressed at 300 MPa. The press on your bench is rated in tonnes, and its gauge reads in MPa, but a different MPa. How hard do you pump? The answer depends on one more number, the diameter of the die, and without it neither the tonnage nor the gauge reading says anything about what the powder feels. The calculator below converts between press force, gauge reading and pressure on the sample for any die, and checks the frame the same way whichever of the three you start from. The rest of the page explains the three quantities and where the conversion stops being valid.
In one paragraph: three different quantities are called pressure on a pellet press. Force, in tonnes, is the rating of the machine. Gauge pressure, in MPa, is the oil pressure in the hydraulic cylinder and converts to force through the piston area, with a different factor for every press model. Sample pressure, in MPa, is force divided by die area, and is the only one of the three that describes the experiment. Convert to sample pressure before comparing presses, reproducing a method or loading a die, and keep it below 800 MPa on a standard steel die.
1. The calculator
Choose what you know: the force, a target pressure, or the gauge reading on a PressPro™ manual press. Enter the die size and read the rest.
The calculator reports three things separately, because they are separate conditions. The calculation is arithmetic and is valid for any numbers. The frame check compares the force with the rating of the frame: 30 MPa on the gauge of a 2 T frame works out to 2.4 t, which that frame cannot deliver, whatever the pressure on the sample turns out to be. The die-chart band places the sample pressure on the PressPro™ die pressure chart for steel dies; a pressure in the normal-use band does not clear the frame, and neither replaces the rating of your own die.
2. Three quantities, one word
- Force (tonnes). What the piston pushes with. A 15 T press delivers up to 15 tonnes-force, about 147 kN, whatever is on the worktable.
- Gauge pressure (MPa). The pressure of the oil in the cylinder. It is proportional to force, and the constant is the piston area. A press with a larger piston reaches the same force at a lower oil pressure, which is why a 30 MPa reading means 15 t on one PressPro™ frame and 40 t on another.
- Sample pressure (MPa). Force divided by the cross-section of the die bore. This is the pressure quoted in methods and papers.
Because the piston is always much larger than the die, the sample pressure is always much higher than the gauge reading. On a 15 T press with an 80 mm piston and a 13 mm die the ratio of the two areas is 38: a gauge reading of 20 MPa is 757 MPa on the pellet.
3. Formulas and worked examples
force (t) = sample pressure (MPa) × die area (mm²) ÷ 9800
sample pressure (MPa) = gauge pressure (MPa) × piston area ÷ die area
From a method to a force
A method asks for 300 MPa on a 20 mm pellet. The bore area is π × 20² ÷ 4 = 314 mm². Force = 300 × 314 ÷ 9800 = 9.6 t. A 15 T press does it comfortably; a 10 T press only at the very top of its range.
From a force to a pressure
A common KBr method applies about 8 t to a 13 mm die.1 The bore area is 133 mm², so the pellet sees 8 × 9800 ÷ 133 = 590 MPa. To give a 7 mm pellet the same pressure takes 590 × 38.5 ÷ 9800 = 2.3 t.
From a gauge reading to a pressure
The gauge on a 12 T PressPro™ infrared press reads 20 MPa. On that model 1 MPa of gauge pressure is 0.4 t, so the force is 8 t and a 13 mm pellet is at 590 MPa. Read the same 20 MPa on the 40 T frame, where 1 MPa is 1.33 t, and the force is about 26.7 t: about 2000 MPa on a 13 mm die, far into the severe-overload band of the die chart.
4. Gauge factors for PressPro™ manual presses
These are the conversion factors printed on the PressPro™ data sheets. They apply to the manual powder presses, the manual infrared and XRF presses and the manual isostatic presses built on the same frames.
| Frame | Piston | Printed gauge range | 1 MPa on the gauge | 1 t of force |
|---|---|---|---|---|
| 2 T | Ø32 mm | 25 MPa | 0.08 t | 12.5 MPa |
| 3 T | Ø35 mm | 28.8 MPa | 0.1 t | 9.6 MPa |
| 5 T | Ø45 mm | 31.4 MPa | 0.16 t | 6.28 MPa |
| 12 T | Ø70 mm | 30 MPa | 0.4 t | 2.5 MPa |
| 15 T | Ø80 mm | 30 MPa | 0.5 t | 2 MPa |
| 24 T | Ø95 mm | 34 MPa | 0.7 t | 1.42 MPa |
| 30 T | Ø110 mm | 31.5 MPa | 0.95 t | 1.05 MPa |
| 40 T | Ø130 mm | 30 MPa | 1.33 t | 0.75 MPa |
| 60 T | Ø150 mm | 34 MPa | 1.76 t | 0.56 MPa |
Each frame is specified by a pair: its force range and the gauge range that goes with it, so the end of the gauge range is the rated force. The two conversion factors in the table are that ratio, rounded. On most frames the rounding is under 1 %. On the 3 T frame it is 4 %: 0.1 t per MPa is 0.104 rounded to one figure, and the more exact factor is the other one, 9.6 MPa per tonne, which puts 3 t at 28.8 MPa, the end of that gauge. The calculator converts with the printed ranges, and on the 3 T frame it also shows what the rounded factor would give.
The pointer gauges on these presses carry both scales, tonnes and MPa, and resolve 1 MPa. The digital gauges resolve 0.01 t or 0.01 MPa. The electric and automatic PressPro™ presses show force in tonnes directly, to 0.1 t, and the automatic models calculate the sample pressure on screen once the die size has been entered, so no conversion is needed at the bench.
5. Force chart: tonnes needed for a given pressure
| Die bore | 100 MPa | 200 MPa | 300 MPa | 400 MPa | 500 MPa | 600 MPa | 800 MPa |
|---|---|---|---|---|---|---|---|
| Ø3 mm | 0.07 | 0.14 | 0.22 | 0.29 | 0.36 | 0.43 | 0.58 |
| Ø5 mm | 0.20 | 0.40 | 0.60 | 0.80 | 1.00 | 1.20 | 1.60 |
| Ø7 mm | 0.39 | 0.79 | 1.18 | 1.57 | 1.96 | 2.36 | 3.14 |
| Ø10 mm | 0.80 | 1.60 | 2.40 | 3.21 | 4.01 | 4.81 | 6.41 |
| Ø13 mm | 1.35 | 2.71 | 4.06 | 5.42 | 6.77 | 8.13 | 10.84 |
| Ø15 mm | 1.80 | 3.61 | 5.41 | 7.21 | 9.02 | 10.82 | 14.43 |
| Ø20 mm | 3.21 | 6.41 | 9.62 | 12.82 | 16.03 | 19.23 | 25.65 |
| Ø25 mm | 5.01 | 10.02 | 15.03 | 20.04 | 25.04 | 30.05 | 40.07 |
| Ø30 mm | 7.21 | 14.43 | 21.64 | 28.85 | 36.06 | 43.28 | 57.70 |
| Ø32 mm | 8.21 | 16.41 | 24.62 | 32.83 | 41.03 | 49.24 | 65.65 |
| Ø40 mm | 12.82 | 25.65 | 38.47 | 51.29 | 64.11 | 76.94 | 102.6 |
Force in tonnes, calculated as pressure × bore area ÷ 9800. The 800 MPa column marks the limit of normal use on the PressPro™ die pressure chart, which gives normal use for steel dies as below 800 MPa.
Read across a row to see what a press of a given size can do with a die. A 15 T press reaches 800 MPa on anything up to 15 mm, 400 MPa on 20 mm and about 200 MPa on 30 mm. A 40 T press reaches 300 MPa on a 40 mm XRF pellet.
6. Where the number stops being valid
The die limit
PressPro™ steel pellet dies are intended for use below 800 MPa of sample pressure. From 800 to 1200 MPa the die is being overloaded, and above 1200 MPa seriously so. The calculator marks the three zones. A calculated pressure is not permission to apply it: the limit is a property of the die, and the die selection guide covers how to choose one for the pressure you need.
It is an average
Force divided by area is the mean pressure under the punch. Inside the powder the pressure is not uniform, because friction against the die wall carries part of the load and the pressure falls with distance from the moving punch.2,3 For thin pellets the mean is a good description. For tall ones it overstates what the far end receives; the powder compaction guide shows by how much.
Tonnes, tons and kilonewtons
PressPro™ presses are rated in metric tonnes-force. One tonne-force is 9.8 kN. A US short ton-force is 8.9 kN, about 9 % less, so a method written in US tons needs slightly less on a metric gauge: 10 US tons is 9.08 t. Methods that give force in kN convert at 9.8 kN per tonne.
Rectangular dies and platens
The same formula applies with the area taken as length times width. On a platen press the area is the footprint of the sample or frame mold, not the platen: 20 t on a 100 × 100 mm film is 19.6 MPa, and the same force spread over a full 300 mm platen is 2.2 MPa. The hot pressing guide has a calculator for platens.
Isostatic presses
None of this applies inside an isostatic chamber. There the sample is surrounded by liquid, and the pressure on it is the pressure of the liquid regardless of the size or shape of the part; fine silica powders have been compacted this way at up to 1 GPa.4 The area that matters is the bore of the chamber, which sets the force the press must deliver: 300 MPa in a 30 mm chamber takes 22 t. See the isostatic press selection guide.
7. Related guides and equipment
- How to Choose a Laboratory Hydraulic Press — pellet, hot and isostatic routes and the full PressPro™ range.
- Pellet Press Die Selection — die types, limits and fit.
- Powder Compaction Guide — what the pressure does inside the die.
- KBr Pellet Preparation for FTIR and XRF Pressed Pellet Preparation — typical forces for analytical pellets.
- Manual vs Electric vs Automatic Laboratory Presses — what each kind of readout resolves.
- Solid-State Electrolyte Pellet Pressing — megapascals from the literature turned into a force on your die.
- Presses that display sample pressure directly: PressPro™ automatic powder press, automatic XRF press, automatic hot press.
- How to Specify a Pellet-Press Cycle — the numbers that define a pressing cycle, and a method line another laboratory can follow.
- Small vs Large-Tonnage Laboratory Presses — how much force a method needs, and why a larger frame is not always better.
8. FAQ
How do I convert tons to MPa on a pellet press?
Multiply the force in tonnes by 9800 and divide by the die area in mm². For a 13 mm die the area is 133 mm², so each tonne is 74 MPa. There is no single conversion without the die size.
How many MPa is 10 tons on a 13 mm die?
About 738 MPa with metric tonnes, or about 670 MPa with US short tons.
Is the MPa on my press gauge the pressure on the pellet?
No. The gauge reads oil pressure in the hydraulic cylinder. The pellet sees that pressure multiplied by the ratio of piston area to die area, which is usually between ten and several hundred.
What pressure is 15 tons on a 40 mm die?
About 117 MPa.
What is the maximum pressure for a pellet die?
For PressPro™ steel dies, normal use is below 800 MPa on the sample. Dies from other makers carry their own limit, often stated as a maximum load in tonnes for that bore.
Why does the same force give different results in different dies?
Because pressure depends on area. Ten tonnes is 738 MPa on 13 mm, 312 MPa on 20 mm and 78 MPa on 40 mm.