Sand testing · strength

Sand strength machine (green compression strength) calibration

The universal sand strength machine turns a force into a green compression strength number. Calibration is simply proving that force is right, across the range, both ways.

By Versatile · equipment manufacturer & calibration provider · updated 2026-07-15

What the machine measures

A universal sand strength machine loads the standard AFS 50 mm × 50 mm specimen until it fails and reports the peak stress. With different accessories the same frame measures green and dry compression, shear, tensile and transverse strength. Green compression strength (GCS) is the everyday one - for most iron green-sand systems the target sits around 15-25 psi (roughly 100-170 kPa).

How it is calibrated

Calibration verifies the force path - the load cell or spring/dial system - against a traceable reference:

1. Exercise the machine and set zero.
2. Apply a series of traceable dead weights (or a calibrated proving ring / load cell) spanning the working range - typically low, mid and high points.
3. Record indicated vs applied force at each point, on the increasing load and on the return, to capture hysteresis and zero return.
4. Calculate error and, where the design allows, adjust; then re-verify.
5. Issue a certificate stating the reference used, its own certificate number and traceability, the readings and the uncertainty.

Typical green compression strength targets

Bands vary by metal, moulding method and casting geometry - treat these as orientation, not a specification.

Interval & primary checks

A production lab typically calibrates the strength machine every 6-12 months. Between calibrations a quick single-point check with a known weight catches gross drift, especially after any overload. Keep the records - see intervals & IATF 16949.

What throws GCS off

• Zero drift after overload - the single most common fault.
• Worn specimen tube - changes the area, so the stress is wrong even with correct force.
• Rammer energy off - wrong specimen density feeds every strength and permeability reading.
• Side-loading / misalignment of the specimen in the platens.

Frequently asked questions