KEVOS® MAKEOS · Strength
Press Tie Rod Check (Cylinder Force, Rod Thread Stress, Stretch, Nut Engagement)
For a four-post hydraulic press, what load does the cylinder put into the tie rods, is the thread stress within limits, how much do the rods stretch, and are the nuts long enough?
Check of the tie rods of a hydraulic press frame: the press force from the cylinder bore and pressure, matching the bore a cylinder sizing gives for that force (as the hydraulic cylinder sizing tool), the load per rod, the thread tensile stress area and stress (as the metric thread tool), the elastic stretch of each rod over its length, and the nut length needed so the threads do not strip (as the thread engagement tool), against your allowable stress, stretch limit and nut height.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Cylinder bore | mm | Bore of the press cylinder. |
| System pressure | bar | Highest system pressure (relief valve setting). |
| Number of tie rods | rods | Number of tie rods sharing the load. |
| Rods | ||
| Rod thread nominal diameter | mm | Nominal diameter of the rod thread. |
| Thread pitch | mm | Thread pitch. |
| Rod length between nuts | mm | Length of rod between the nuts (the length that stretches). |
| Modulus of elasticity | GPa | Modulus of elasticity of the rods. |
| Allowable thread stress | MPa | Allowable tensile stress on the thread (lower for rods that cycle millions of times). |
| Largest rod stretch | mm | Largest stretch you accept (it shows as frame spring and uneven bolster loading). |
| Nuts | ||
| Nut height (thread engaged) | mm | Length of thread engaged in each nut. |
| Rod tensile strength | MPa | Tensile strength of the rod material. |
| Nut tensile strength | MPa | Tensile strength of the nut material. |
Method and formulas
- Press force F = p × π D² ÷ 4; the bore that gives F at this pressure (as the hydraulic cylinder sizing tool).
- Thread stress area A_s = π ÷ 4 × ((d₂ + d₃) ÷ 2)² (as the metric thread tool); stress = F ÷ (rods × A_s); stretch = (F ÷ rods) L ÷ (E × π d² ÷ 4).
- Engagement needed so the nut thread does not strip before the rod (as the thread engagement tool).
- Example: 628.32 kN of press force puts 157.08 kN on each rod: 140.14 MPa and 0.85034 mm stretch.
Limitations
- Load shared equally by the rods; off-centre work loads some rods more.
- Static stress; presses that cycle often need a fatigue check of the thread roots.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Check the tie rods of a workshop or moulding press
- Size rods and nuts for a new press frame
- Check a press after raising the system pressure
Who it is for
- Design engineers
- Hydraulic engineers
- Toolmakers
What you get
- Press force and load per rod
- Thread stress and stretch
- Nut engagement needed
Interpreting the result
- Pre-tightening the nuts above the press load keeps the frame stiff and the threads out of fatigue.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 281–286, 1867–1890, 1586–1590. Topic reference; no source tables or recommended settings are reproduced.
WORKOS tools are screening and decision-support utilities. Verify important financial, engineering, safety, legal or operational decisions using appropriate professional standards and your organisation’s approved data.
Open the Press Tie Rod Check (Cylinder Force, Rod Thread Stress, Stretch, Nut Engagement) calculator
