The gas nobody sees
ends up in the casting.
When metal meets a core, the binder burns and gives off gas. If more comes off than the core can vent, it goes into the metal as blows, pinholes and porosity. The VCGD measures how much, and how fast.
Blows, pinholes and porosity start as gas.
A core is a small chemical factory sitting inside the mould. The moment the metal arrives, the binder breaks down and releases gas. Some of that gas escapes through the vents and the sand. What cannot escape pushes into liquid metal.
The trouble is that two binders can look alike on the shelf and behave differently in the mould. Resin level, coating, cure and the base sand all change what comes off. Measuring it is quicker than reading it back from scrapped castings.
Burn a gram of it, and watch what comes off.
The method is simple and the result is specific to the sand, the binder and the coating in use.
Weigh the sample
A small, weighed sample of bonded sand or a coated grain is placed in a boat.
Into the furnace
The boat is pushed into the combustion tube, held at a set temperature up to 850 °C.
Collect the gas
Gas driven off the binder is collected and its volume read against time.
Read the curve
The run is logged as a curve, giving total volume and how quickly it came off.
Total volume is half the story. Rate is the other half.
Two binders can end up at the same total and still behave differently in the mould, because the one that releases early and fast puts its gas into metal that is still liquid.
Total gas volume
How much gas the binder makes in all. The headline number, in cubic centimetres per gram.
Rate of release
How quickly it comes off. A binder that gases in a rush pushes harder on the metal than one that releases slowly.
Time to peak
When the surge arrives. Gas that peaks while the metal is still liquid is the gas that ends up in the casting.
Qualify the binder before the casting does it instead.
Compare one resin lot against the next, check a coating, set a sensible resin level, or hold a supplier to the curve agreed. When a gas defect does appear, the test shows quickly whether the core was the source.
Each run kept as a curve
The VCGD records each test as a curve and syncs it through V-Sync, so the batch history is there to compare a new lot against the normal curve, and a supervisor can look at it from a browser. See how V-Sync works →
The numbers a lab plans around.
| Test | Gas evolved from chemically bonded sand, cores and coated sand |
|---|---|
| Range · least count | 0 to 50 cc · 0.1 cc |
| Furnace | Combustion tube to 850 °C, with automatic temperature control |
| Output | The gas evolution curve, logged point by point, plus the total volume |
| Sand types | Resin coated, no-bake, cold box, CO2 and green sand |
| Supplied with | Boats, boat pusher, cork and tubing, volumetric glass apparatus |
| Data | On-board logging · wired network · V-Sync cloud, readable from a browser |
| Size · weight | 600 × 450 × 750 mm · about 31 kg |
| Power | 230 V AC, 50 Hz standard; other supplies such as 110 V, 60 Hz on request |
The exterior runs hot in use. Keep the unit in place while it is switched on and allow it to cool before moving it.
Test your own cores.
Send us a sample or book a demonstration, and we will show the gas curve the binder and coating actually produce.