Process
A bench grinder is usually used to create the sparks, but sometimes this is not convenient, so a portable grinder is used. In either case, the grinding wheel must have adequate surface velocity, at least 23 m/s (4500 surface feet per minute (sfpm)), but should be between 38 and 58 m/s (7500–11,500 sfpm). The wheel should be coarse and hard, therefore aluminium oxide or carborundum often are employed. The test area should be in an area where there is no bright light shining directly into the observer's eyes. Moreover, the grinding wheel and surrounding area should be dark so that the sparks can be observed clearly. The test sample is then touched lightly to the grinding wheel to produce the sparks.
The important spark characteristics are color, volume, nature of the spark, and length. Note that the length is dependent on the amount of pressure applied to the grinding wheel, so this can be a poor comparison tool if the pressure is not exactly the same for the samples. Also, the grinding wheel must be dressed frequently to remove metallic build-up.
Read more about this topic: Spark Testing
Famous quotes containing the word process:
“We are in the process of creating what deserves to be called the idiot culture. Not an idiot sub-culture, which every society has bubbling beneath the surface and which can provide harmless fun; but the culture itself. For the first time, the weird and the stupid and the coarse are becoming our cultural norm, even our cultural ideal.”
—Carl Bernstein (b. 1944)
“Like a prophet, you are possibly teaching us about the workings of the divine mind, but in the process you are ruining the human mind, dear friend.”
—Franz Grillparzer (1791–1872)
“A process in the weather of the world
Turns ghost to ghost; each mothered child
Sits in their double shade.
A process blows the moon into the sun,
Pulls down the shabby curtains of the skin;
And the heart gives up its dead.”
—Dylan Thomas (1914–1953)