Densometers are the accepted standard for measuring the porosity of materials such as papers, wovens, plastics and membranes. All Densometers measure the time required for a given volume and of air (25cc to 400cc) to flow through a standard area of material being tested under light uniform pressure. Certain models, such as the S-P-S Tester, are also used to measure surface smoothness and material softness. Manual and automatic units available. Conform to TAPPI T-460, ASTM D-726-58 & APPITA/AS 1301-420, BS 5926, CPPA D-14, ISO 5636/5, D-202-77, SCAN P-19 & P-53.
The Densometer test measures the time required for a given volume of air (25cc to 300cc) to flow through a standard area of material tested, under light uniform pressure. The air pressure is supplied by an inner cylinder of specific diameter and standardized weight, floating freely within an outer cylinder partly filled with oil to act as an air-seal. The sample material is held between clamping plates having a circular orifice area of 1.0 (standard), 0.25 or 0.1 square inch (optional).
Densometer readings may be evaluated on both a direct or indirect basis dependent upon the material and test purpose. They are a direct test of materials which are intended to either resist or permit the passage of air. Indirectly, they are used to measure other physical properties which affect the flow of air through a porous sheet.
In manufacturing and printing, to control the selection of materials affording the appropriate degree of liquid (ink, varnish, sizing) absorption.
To test filters, porous bags & materials where controlled porosity is essential.
To test insulating materials for air resistance.
To supplement other physical tests enabling regulation or strength of manufacturing process to give the desired formation, appearance or strength since there is a close correlation in a given material between air permeability and these other properties.
High Pressure Densometers are the accepted standard for measuring the porosity, air-permeability or air-resistance of materials having low permeability. Typical materials include coated papers, plastics and membranes. High Pressure units are recommended whenever a standard unit would yield excessive measurement times. Manual and automatic units available. Conform to TAPPI T-536-88 and ASTM D-726-58, Method B.
The densometer test measures the time required for a specific volume of air (2.5cc to 30cc), at a constant pressure of 12.2 inches W.C., to flow through a standard area of the material being tested. The air pressure is supplied by a weighted inner cylinder floating freely within an outer cylinder which is partially filled with oil to act as a seal. The sample material is held between clamping plates having a circular orifice area of 1.0 square inch (standard).
High pressure units are recommended whenever a standard unit would yield excessive measurement times. Porosity readings with the high pressure densometer are much faster than those taken with a regular densometer. This difference can be as great as twenty-five times faster since higher air pressure is used and air volumes are one-tenth those measured with a standard densometer. Readings also can be affected by using different adapter plates with smaller orifices on all models.
The new oil-filled high pressure densometers replace older mercury-filled models yet feature identical performance, continued reliability and accuracy. The only difference is the physical height of the unit (27″ with inner cylinder down).
Obsolete Models 4120 & 4200 contain mercury which may pose personal safety hazards. These instruments can be converted to oil by replacing the entire upper cylinder assembly. The conversion must be performed at our Troy, NY factory and includes packaging for and disposal of the mercury. Please refer to No. 4050-C Product Bulletin for details.
The essential difference between these instruments is that the Permeometer tests materials primarily designed to allow air flow, while the Densometers typically test materials of lower permeability where air flow is a secondary characteristic. The means of instrument operation and resulting units of measure are related but stated differently. The Permeometer measures actual flow in cubic feet per minute, per square foot of material (at 0.5″ W.C gage pressure drop). The Densometers measure the time required to force a known volume of air through one square inch of material (at 1.22″ to 12.2″ W.C. gage pressure).
Some crossover models exist for materials of “borderline porosity”, in particular those which can be tested on the Model 4118 Textile Densometer (with 5 oz. cylinder) and Model 4301 Permeometer. The choice of instrument is typically based on the permeability of the sample and which device provides more useful data. Generally speaking, a Permeometer cannot be used to test ordinary papers.
There exists a linear relationship between material test results for Gurley low, standard and high pressure Densometers. The benchmark for these instruments is what is commonly referred to as “Gurley Seconds”, which denotes to the time needed to pass 100cc of air through 1.0 square inch of material at standard pressure. Depending on the time it takes to pass air under these conditions, a user may prefer to increase or decrease the test time (after all – who wants to wait) by increasing or decreasing the pressure and/or orifice size. For example, if a sample takes 2,500 Gurley Seconds (i.e., 100cc using 1.0 sq.in. and standard pressure) on a standard Densometer (Model 4110 or 4190), the same sample would only take 100 seconds on a high pressure Densometer (Model 4150 or 4250) using the same orifice and 10cc of air. Please refer to the following chart for more information. Note that the Model 4340 Automatic Densometer and Smoothness tester does not wait for the air to displace; the Model 4340 uses mass flow technology for instantaneous results. Still, the Model 4340 mirrors the output of all Gurley manual Densometers regardless of the orifice or volume used.
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