Read the mould
before the metal does.
A single strength number cannot describe how a chemically bonded sand will hold, sag and let go once the metal hits it. The hot distortion curve can, and the VHD I draws it, point by point.
A number says it is strong. It does not say how it fails.
Green compression, tensile and hardness each give one figure. Two sands can read the same on each of them and still behave differently in the mould, one veining, one cracking, one clinging through shakeout.
The hot distortion test heats a bonded specimen on one side and records how far it deflects, second by second. The shape that traces out is a fingerprint of how that sand will expand, soften, cure and finally give way against molten metal.
“The brilliance of the hot distortion curve is its ability to describe, in detail, the characteristics needed to make a quality casting.”Adapting Hot Distortion · technical review
Four regions, four things the sand reveals.
Heat one face of a cured specimen and the probe first rises, then sags, then steadies as the binder cures, then drops away as it burns through. Each stretch of the curve maps to a property that can be acted on.
Upward deflection
The base sand expands on the hot face and pushes the probe up. Reads out grain shape, distribution and compacted density.
Thermoplastic relaxation
The binder softens and the specimen sags. This plasticity, in the right amount, is what holds off veining and thermal cracking.
Thermosetting
Heat cures the binder and the slope eases. Reads out cure rate, degree of cure and hexa content.
Degradation & failure
The binder burns through and the specimen fails. Time-to-failure is the hot strength, and it drives collapsibility and shakeout.
See the VHD I trace a curve.
A cured specimen, heated on one face, and the probe recording the deflection second by second.
Alike on the bench tests. Different where it counts.
A shell foundry compared a new base sand against its standard. Grain fineness, hot tensile, LOI, clay, moisture, melt point, all matched. The hot distortion curves were the exception, differing in Region 2 and in time-to-failure.
In production the prediction held: the tighter Region 2 showed up as fewer thermally cracked moulds, and the shorter time-to-failure as cleaner shakeout, less core sand left in the casting before blast cleaning.
From a research curve to a shop-floor control.
Older hot distortion instruments left the lab with a shape and no easy way to say whether it was normal. Break the curve into deflection at each second and the method opens up: average many runs into a normal curve, set a tolerance band around it, and read each new run against that band. The VSync datalogger on the machine captures each run and syncs it to the cloud, so the batch history sits ready in the analytics suite to build that normal curve from and to compare against.
- A normal curve to work against.
Average many runs of a binder or sand system and keep it as the standard. - Limits, not opinions.
The ±3σ band separates common-cause scatter from a real shift. - Batch against batch.
Overlay runs to compare a new binder lot, a mixer change or a supplier. - In the cloud.
Each curve is logged by VSync and readable from a browser.
Lab-grade curve. Shop-floor simple.
Prepare the specimen, start the test, and the VHD I heats, measures and logs the full curve on its own. Results sit on-board and sync to the cloud through VSync for a record the quality system and the customer can inspect.
| Test | Hot distortion of chemically bonded sand (shell, no-bake, cold box, core) |
|---|---|
| Specimen | Standard transverse bar, 1/4 x 1 x 4 in, heated on one face |
| Range · least count | ±7 mm distortion · 0.01 mm |
| Output | The full hot distortion curve, logged point by point |
| Analysis | Average curve, ±3σ tolerance band, batch-vs-batch overlay, time-to-failure |
| Standards | BIS / AFS methods · NABL-traceable calibration |
| Data | On-board logging · wired network · VSync cloud, viewable from a browser |
| Size · weight | 685 × 390 × 360 mm · about 40 kg |
| Power | 230 V AC, 50 Hz standard; other supplies such as 110 V, 60 Hz on request |
See the curve on your own sand.
Book a demonstration, or ask for sample curves and a quotation. We will run the VHD I on a bonded sand sample and show the curve, the tolerance band and the record it leaves in VSync.