“How many tons do I need?” has no single answer, because tons are force and a method specifies pressure. The same 10 t is about 740 MPa on a 13 mm die and about 80 MPa on a 40 mm die. This guide works out the force from the die and the pressure, collects the pressures that published methods use, and explains why a press much larger than the job can be a poor choice: at the low end of its range the readout steps are coarse, some models have a printed lower limit, and the frame is heavier and larger. A sizing tool checks every PressPro™ pellet press for powder, KBr or XRF work against your range.
In one paragraph: multiply the pressure your method needs by the area of your die to get the force, at both the lowest and the highest pressure you will use. Choose a frame whose rating covers the highest force and whose lower limit and readout step suit the lowest. Published pressures run from a few megapascals for a fiber composite consolidated in a heated mold to several hundred for KBr discs and battery electrolytes, and 1760 MPa in one high-pressure XRF method, so a lab that presses 7 mm micro pellets and one that presses 40 mm XRF pellets need very different frames. Precise force matters most where a property changes steeply with pressure. Weight, footprint and power rise with tonnage, and so do the guards.
The tonnage-to-MPa calculator converts force, gauge reading and pressure for every PressPro™ frame, and the comparison of manual, electric and automatic presses explains what each kind of press controls. This page is about choosing the size of the frame.
1. Force comes from pressure and area
The loaded area is the bore of a die, or the footprint of the sample or frame mold on a platen press. Area grows with the square of the diameter, so force does too: a 40 mm die needs about 33 times the force of a 7 mm die for the same pressure.
| Die bore | 50 MPa | 100 MPa | 200 MPa | 400 MPa | 800 MPa |
|---|---|---|---|---|---|
| 7 mm | 0.20 t | 0.39 t | 0.79 t | 1.57 t | 3.14 t |
| 13 mm | 0.68 t | 1.35 t | 2.71 t | 5.42 t | 10.8 t |
| 20 mm | 1.60 t | 3.21 t | 6.41 t | 12.8 t | 25.6 t |
| 32 mm | 4.10 t | 8.21 t | 16.4 t | 32.8 t | 65.7 t |
| 40 mm | 6.41 t | 12.8 t | 25.6 t | 51.3 t | 103 t |
Calculated here. For steel dies, the PressPro™ die pressure chart gives normal use below 800 MPa, 800 to 1200 MPa as overload and above 1200 MPa as severe overload. The 800 MPa column is shown for scale, not as a target.
2. What pressure does your method need?
The pressure comes from the method, not from the press. The studies below show how wide the range is. They are examples of published practice, not recommendations.
| Work | Reported condition | Pressure on the sample |
|---|---|---|
| KBr discs for FTIR, 13 mm | 10 tons for about 1 min1 | About 740 MPa |
| KBr micro pellet, 7 mm | 1.7 tons for 3 min2 | About 430 MPa |
| XRF pressed powder, 40 mm | 100 kN3 | About 80 MPa |
| XRF pressed powder, biological samples | Conventional pellets compared with high-pressure pellets4 | 220 to 440, and 1760 MPa |
| Ceramic green bodies | Zircon bars in a double-action die5; an oxide electrolyte before sintering6 | 45 to 180 MPa; 100 MPa |
| Pharmaceutical tablets | 9 to 14 mm punches7; paracetamol and cellulose tablets8 | About 50 to 300 MPa; 80 to 320 MPa |
| Sulfide electrolyte and electrode pellets | 21 laboratories building cells from the same materials, each with its own method: positive electrodes, and separators9; an electrolyte pellet in a 13 mm die10 | 250 to 520 MPa, and up to 590 MPa; 370 MPa |
| 3D-printed carbon-fiber/PA12 composite, consolidated in a heated mold | 200 to 210 °C11 | 2 to 10 MPa |
Pressures calculated here from force and area where the source gives force. The two KBr sources print tons; we take them as tonnes-force. The 1760 MPa pellets are in the severe-overload band (above 1200 MPa) of the PressPro™ die pressure chart for steel dies. Compression molding of thermoplastic test specimens, plaques and sheets is the subject of ASTM D4703 and ISO 293; ISO 293 does not apply to reinforced thermoplastics, such as the composite in the last row.12,13
Put the two together and the spread in force is large. About 10 t on a 13 mm KBr die and on a 40 mm XRF die at 80 MPa; about 5 t for the 13 mm electrolyte pellet at 370 MPa; about 26 t for a 40 mm pellet at 200 MPa; about 1.6 t for a 7 mm pellet at 400 MPa; and about 5 t for a 100 × 100 mm plate at 5 MPa.
3. The low end of a big press
A frame rated far above the job spends its working life at the bottom of its range. Three things work against that.
Readout steps
Every gauge and display has a smallest step, and on the sample that step is a pressure, larger on small dies. On PressPro™ presses:
- The pointer gauges of the manual powder frames (two-column, four-column and protective) have a resolution of 1 MPa of oil pressure. On the 60 T frame one division is 1.76 t, which on a 7 mm die is about 450 MPa, more than many methods need in total. On the 15 T frame it is 0.5 t, about 130 MPa on the same die.
- The digital gauges of the same manual powder frames read to 0.01 t, about 2.5 MPa on a 7 mm die.
- On the electric powder presses, the automatic powder presses from 10 to 100 T, the electric and automatic infrared presses and the automatic XRF presses, the screen reads force to 0.1 t. That is about 25 MPa on a 7 mm die and under 1 MPa on a 40 mm die.
The reading step of the large-tonnage automatic presses, of the manual infrared and XRF presses and of the mini infrared press is not covered here.
Printed lower limits
The automatic and electric models print the lowest force of their range. The automatic powder presses start at 0.1 t on the 10 T model and at 1 t on the 100 T model; the large-tonnage automatic presses start at 1 t. One tonne on a 7 mm die is already about 255 MPa, so a 7 mm method at 100 MPa cannot be run on those frames at all. The manual frames have no printed lower limit.
Error at the low end of a range
Bourdon-tube gauges are covered by EN 837-1, and dial and digital gauges by ASME B40.100, whose contents list a table of accuracy grades.14,15 The accuracy class of the PressPro™ gauges is not covered here. In one worked calibration, a class 1.0 Bourdon gauge with a range up to 1.6 MPa had a maximum permissible error of ±0.016 MPa, calculated from its class and applied across its scale.16 By our arithmetic that is about 1 % of a reading near the top and about 8 % of a reading of 0.2 MPa.
Related effects appear in metrology and hydraulics work:
- In the European guide to force-measurement uncertainty, the relative contribution of the indicator’s resolution grows as the force falls, and transfer standards are recommended to be used above 40 % of their capacity.17 The force-proving instruments behind such calibrations are classified under ISO 376.18
- A pressure balance built on a force transducer at a national standards laboratory lost accuracy and showed its largest relative hysteresis at the low end of its range.19
- Hydraulic jacks calibrated against a reference load cell gave a curve from gauge reading to force that did not pass through zero, so the lower end of the range had to be defined.20
- In a test cylinder, seal friction depended on the fluid pressure and the sliding speed, and was high at low speed. One seal material slid intermittently (stick-slip) over the speeds tested.21
Laboratory safety guidance makes a related point for compressed-gas systems: generally select a gauge with a range about double the working pressure.22 We found no standard that states what share of a press’s rating a method should use, and this page does not set one.
The gauge guide explains accuracy classes and how to check a press against a reference load cell.
4. When does the exact pressure matter?
Where a property changes steeply with pressure, a coarse step or an error at the low end shows in the result. Where it is flat, the same step or error matters less.
- Steep: tablet capping went from none to all tablets within less than 50 MPa in a study of tablet geometries.23 Without precompression, the in-die elastic recovery of celecoxib rose from about 4 % at 150 MPa to about 14 % at 200 MPa. With a precompression step, which removes entrapped air, the jump did not appear.24 A sulfide electrolyte reached 92.2 % relative density at 125 MPa and 97.8 % at 250 MPa.25
- Flat: zircon green density rose only from 55.5 to 59.6 % of the powder density between 45 and 180 MPa.5 In an XRF study, pellets pressed at loads from 4 to 40 t showed no clear change in line intensities; pellets pressed at low load tended to crack.26 In 3D-printed carbon-fiber/PA12 composite straps consolidated in a heated mold, the fall in porosity leveled off above about 6 MPa.11
If your method sits on a steep part of its curve, check the readout step and the lower limit at your lowest pressure.
5. What grows with tonnage
Rated force is not the only thing that changes across the range.
| Model | Rated | Size, W × D × H | Weight | Supply |
|---|---|---|---|---|
| Mini infrared press EPIM02TH | 2 T | 100 × 220 × 220 mm | 4.8 kg | Manual (hand screw) |
| Two-column manual EPPM-2P02 | 2 T | 205 × 170 × 370 mm | About 12 kg | Manual force |
| Four-column manual EPPM-4P15 | 15 T | 245 × 180 × 420 mm | About 42 kg | Manual force |
| Protective manual EPPM-PP60 | 60 T | 440 × 240 × 530 mm | About 142 kg | Manual force |
| Automatic powder press EPPA010T | 10 T | 230 × 405 × 470 mm | About 85 kg | 220 V, 400 W |
| Automatic powder press EPPA100T | 100 T | 320 × 560 × 640 mm | About 350 kg | 220 V, 700 W |
| Large-tonnage automatic EPPPE200 | 200 T | 480 × 650 × 950 mm, plus a 320 × 440 × 440 mm control box | About 850 kg | 220 V, 700 W |
Dimensions and weights as printed in the specifications (approximate weights marked “about”). Powered models run on 220 V, 50/60 Hz. On the manual models the force is generated by hand; the power of a digital gauge, where one is fitted, is not covered here.
Two other things grow with the frame:
- Working space. The four-column 15 T frame has a working space 80 mm wide and 150 mm high; the protective 60 T frame, 200 by 210 mm. A die wider or taller than the working space does not fit; the tool checks both if you enter the die size.
- Guarding. The two- and four-column manual frames are open; the protective manual frames have a safety-glass guard door. The electric powder presses from 30 T up and the automatic powder presses, including the large-tonnage models, have a safety-glass door, leakage protection and an emergency stop. The 20 T electric press has leakage protection and an emergency stop but no door.
The installation and RFQ checklist covers bench space, supply, and what the press safety standards cover and exclude.
6. Press sizing tool
Enter your die bore and the lowest and highest pressure you will use. If you know the outer diameter and height of the die, add them. Choose the kind of work and of press. The tool lists every PressPro™ pellet press for powder, KBr or XRF work of the kind you choose (the hot and cold platen presses are not included), with separate results for capacity, the printed lower limit, the readout step on your die, the working space and the site data. Capacity gives your forces as a share of the rating and is a Pass or a Fail against the rating only. The readout step is a Note, or Not checked for the presses whose step is not covered here. The summary counts the models that are within the rating and the printed lower limit; the others are listed with every reason they fail.
7. A sizing sequence
- Fix the loaded area. The die bore, or the footprint of the sample or frame mold on a platen.
- Take the pressure range from the method. Both ends: the lowest pressure you will ever run and the highest.
- Convert both ends to force. Force = pressure × area ÷ 9800.
- Check the top end against the rating. The highest force must be within the rated force; the die has a rating of its own.
- Check the bottom end against the lower limit and the readout step. On a small die, a large frame may not reach down far enough, or may read in steps larger than your tolerance.
- Check the die against the working space, then the bench, the supply and the guarding.
If two manual powder frames pass, the smaller one has the finer pointer-gauge step at your pressures. If no single frame covers your range, two presses may serve better than one. The press selection guide covers the choice between pellet, hot and isostatic presses.
8. Related guides and equipment
- Tonnage-to-MPa Calculator — force, gauge reading and pressure for every frame.
- Pressure Gauge Resolution, Accuracy and Calibration — how far the reading can be trusted, and how to check it.
- Manual vs Electric vs Automatic Laboratory Presses — what each kind of press controls.
- Laboratory Press Installation and RFQ Checklist — space, supply, guarding and what to specify.
- How to Specify a Pellet-Press Cycle — pressure, hold and release in numbers.
- 7 mm vs 13 mm KBr Pellets — when a mini press is enough.
- Manual vs Automatic XRF Pellet Presses — force and readout for 32 and 40 mm dies.
- How to Choose a Laboratory Hydraulic Press — the whole PressPro™ range by purpose.
- Equipment: mini infrared press, two-column, four-column and protective manual presses, electric and automatic powder presses, large-tonnage automatic press.
9. FAQ
How many tons do I need for KBr pellets?
It depends on the die. One published method used 10 tons on a 13 mm die, about 740 MPa if the tons are tonnes-force. For a 7 mm die the same pressure needs under 3 t; one study used 1.7 tons. The KBr pellet size guide compares the two.
How many tons do I need for 40 mm XRF pellets?
One study pressed 40 mm pellets at 100 kN, about 10 t and 80 MPa; 200 MPa on the same die needs about 26 t. Check your method’s pressure and convert.
Is a bigger press always better?
No. On a manual powder frame with a pointer gauge, a larger frame reads in coarser pressure steps on a small die. On the automatic powder presses from 10 to 100 T the screen reads force to 0.1 t on every model, but the larger models print a higher lower limit, which may be above the force you need. A larger frame is also heavier and larger. Size the frame to both ends of your pressure range.
Can I use a 60-ton press for small pellets?
It can reach the force, but on a 7 mm die one division of the 60 T frame’s pointer gauge is about 450 MPa. A digital gauge or a smaller frame reads far finer.
What is the lowest force an automatic press can apply?
Each automatic and electric PressPro™ uniaxial press prints its lower limit, from 0.1 t on the 10 T automatic powder press to 1 t on the 100 T automatic powder press and the large-tonnage presses. The tool above checks it for your die.
Does a press within its rating protect the die?
No. The die has its own rating. For steel dies, the PressPro™ die pressure chart gives normal use below 800 MPa and 800 to 1200 MPa as overload. A large press can easily go past 800 MPa on a small die.