Verifying Polyethylene Hydrostatic Balance Test Calibration for Entry
Polyethylene hydrostatic testing requires degassed, temperature-corrected fluid baths and void-free plaques to prevent false 0.002 g/cm³ receiving rejections.
Archimedes Principle
Meaning
Physical law stating that any object immersed in a fluid is buoyed up by a force equal to the weight of the displaced fluid. Using the archimedes principle is the standard industrial method for determining the density of a moulded plastic part or a raw resin pellet. The measurement involves weighing the sample in air and then in a liquid of known density.
Density Verification
Precise buoyancy measurements identify voids or inclusions inside thick-walled components. When a part fails to meet its expected mass, the archimedes principle helps a quality engineer calculate whether the material contains internal gas bubbles or excessive filler content. This check happens immediately after the part reaches thermal equilibrium following the moulding process.
Liquid Selection
Distilled water or ethanol acts as the immersion medium depending on the expected density of the polymer. Because many polyolefins float in water, the archimedes principle requires a sinker or a lower density fluid like isopropyl alcohol to achieve full submersion. Accurate temperature control of the fluid remains necessary to prevent volume expansion from skewing the results during the test.
Regrind Proportion
Mixing virgin material with recycled granules changes the specific gravity of the resulting melt. By applying the archimedes principle, a facility monitors the consistency of the feedstock throughout a production run. Variations in density often signal a change in the crystallinity or the contamination level of the incoming regrind.