Springs
Die springs: load and balancing
Check the load by spring position and compare two layouts side by side — one blue against two greens — with the summed force, the load centre, and the moment left on the plate.
The rule this page exists to defend
At the same position, every spring takes the same compression. Since F = k · s, the ratio between forces is the ratio between spring rates — and nothing else. One blue equals two greens when k(blue) = 2 · k(green).
The classic mistake is comparing the catalogue maximum load of the two colours. Those loads are quoted at different maximum travels for each class, so equal maximum loads do not mean equal forces at your working point.
Assembly condition (the same for both layouts)
Total compression is the same for every spring in the same position — which is exactly why balancing is solved by spring rate, not by load class.Layout A
| Summed rate | 134 N/mm | |
|---|---|---|
| Force at preload | 402 N | |
| Force at end of travel | 2,010 N | |
| Load centre | X 0 · Y 0 mm | |
| BA 32050 — travel used | 29.4% | 8.1 pts of margin |
Layout B
| Summed rate | 134 N/mm | |
|---|---|---|
| Force at preload | 402 N | |
| Force at end of travel | 2,010 N | |
| Load centre | X 0 · Y 0 mm | |
| BG 32050 — travel used | 29.4% | 10.6 pts of margin |
| BG 32050 — travel used | 29.4% | 10.6 pts of margin |
- Note: The travel of this layout is limited by spring BG 32050 (light), with 10.6 points of margin. When you change the layout, this is the one that sets maximum travel — not the strongest one.
Comparison
Rate A → B
0%
134 → 134 N/mm
Force difference
0
N at end of travel
Load centre
0
mm of shift
Residual moment
0
N·m on the plate
- Note: Summed spring rates are equivalent (a 0% difference). At the same compression, both layouts deliver the same force.
For layout B to match A with 2 springs, each one needs 67 N/mm. Look for that value in your supplier's catalogue — not the load class.
The four ISO 10243 colours
Light duty — verde
The softest, with the longest allowable travel. In a mold it's the choice for ejector return, where what you want is long travel and long life, not force.
Medium duty — azul
The general-purpose middle ground. Usually the starting point when neither space nor force is tightly constrained.
Heavy duty — vermelha
More force in the same pocket, with less allowable travel. It demands checking travel before force.
Extra heavy duty — amarela
The stiffest, with the shortest travel. Only when space leaves no other way out — it's the one that most often breaks from excessive travel.
Bordignon series and the three travel levels
Each series in the B FEDER catalogue publishes three travels, as a percentage of free length. Once the spring is chosen, the three loads come from the catalogue row itself — no need to open the table.
| Series | Colour | Class | Long life | Medium duty | Maximum travel |
|---|---|---|---|---|---|
| BS | black | Extra light | 35% | 40% | 50% |
| BG | green | Light | 30% | 35% | 40% |
| BA | blue | Medium | 25% | 30% | 37.5% |
| BR | red | Heavy | 20% | 25% | 30% |
| BY | yellow | Extra heavy | 17% | 22.5% | 25% |
| BO | orange | Super heavy | 10% | 13.5% | 15% |
From Bordignon's B-FEDER-0919 catalogue. It agrees with physical monotonicity: the stiffer the series, the shorter the allowable travel.
Four things to check when changing layout
1. Summed rate, not class
It's the point above, and it's what settles the force balance. Add up k × quantity on both sides and compare that number.
2. Equal free length
If the two greens have a different L0 from the blue, in the same pocket they take different preload and don't come into load together. Balancing the rate without matching L0 gives you a plate out of square.
3. Two springs don't fit where one was
You keep the design position, but the two springs sit at P ± offset. Then adding force isn't enough: the moment has to close too. Spread them symmetrically around the original position and check the load centre in the plan view.
4. Travel is limited by the most restrictive one
Each class has its own maximum travel as a % of L0, and it shrinks as the spring gets stiffer. Swapping one blue for two greens usually gains travel margin; the other way round is what breaks springs.
Where each number comes from
All of it. The 647 springs in Mollificio Bordignon's B FEDER 0919 catalogue are here: order code, pocket Ø, pin Ø, free length, rate in N/mm and the three loads. You select series, size and length — you type none of the spring's data.
What justifies publishing a part number is the checking, not the extraction. Every row had to satisfy rate × deflection = load at all three levels, which is the decisive test because it uses only numbers from that same row: a column read out of order doesn't balance. Then each deflection had to match the percentage printed in the series header, and the length had to match what the part code carries. All 647 rows passed all three; none was discarded and none was estimated.
The pocket Ø and pin Ø of each size came from a vote across every row of that size, with no disagreement, and they match Polimold's catalogue exactly — a different manufacturer. Including the Ø63, whose 38 mm pin breaks the half-the-pocket proportion that holds for every other size: since both publish 38, it's the standard and not a typo.
What still needs care: a catalogue spring rate carries manufacturing tolerance — Polimold publishes ±10% for theirs. For fine preload, measure the spring.
Correction: an earlier version of this page claimed the spring rate couldn't be extracted because the table had been converted to vector graphics during layout. That was wrong. The cells that vanished were those set in CID fonts, with the text encoded in hexadecimal — a failure of my PDF reader, not of the file.