1、British Standard Aerospace Series : Methods for Determination of density and relative density of polytetrafluoroethylene (PTFE) tubing for aerospace a ppl cat ons IS0 title: Polytetrafluoroethylene (PTFE) tubing for aerospace applications - Methods for the determination of the density and relative d
2、ensity Srie arospatiale. Mthodes de dtermination de la masse volumique et de la densit des tubes en polyttrafluorthylne (PTFE) usage aronautique Luft- und Raumfahrt-Reihe. Verfahren zur Bestimmung der Dichte und relativen Dichte von Schluchen aus Polytetrafluorthylen (PTFE) fr die Luft- und Raumfahr
3、t e Contents Page National foreword 1 Committees responsible Back cover Method O. Introduction I. Scope and field of application 2. Definitions 3. Apparatus 4. Immersion liquids e National foreword This British Standard has been prepared under the direction of the Aerospace Standards Committee and i
4、s identical with IS0 7258-1 984 Polytetrafluoroethylene (PTFE) tubing for aerospace applications - Methods for the determination of the density and relative density, published by the International Organization for Standardization (ISO). IS0 7258 was produced as a result of international discussion i
5、n which the UK took an active part. Terminology and conventions. The text of the international standard has been approved as suitable for publication as a British Standard without deviation. 5. Specimens 6. Procedures Table Liquid systems for density gradient columns Figure Preconditioning cycle for
6、 method C procedure Page 3 3 3 7 Some terminology and certain conventions are not identical with those used in British Standards; attention is drawn especially to the following. The comma has been used asa decimal marker. In British Standards it is current practice to use a full point on the baselin
7、e as the decimal marker. Wherever the words International Standard appear, referring to this standard, they should be read as British Standard. Compliance with a British Standard does not of itself confer immunity from legal obligations. British Standards Institution British Standard M 56 : 1985 ES1
8、 M*5b O Introduction Density and relative density are frequently used to follow the variations in the physical structure of specimens and in calcula- tions of the amount of material necessary to fill a given volume. Density is the preferred property relating the mass and volume of an object, specime
9、n or material. These properties may also be useful in determining uniformity among samples or specimens. 1 Scope and field of application This International Standard specifies three methods for the determination of the density and relative density of polytetrafluoroethylene (PTFE) tubing used in the
10、 manufacture of medium and high pressure, high temperature, PTFE hose assemblies for aerospace applications : Method A - Density gradient column method without a preconditioning heating and cooling cycle. . Method B - Displacement of water and determination of change of weight method. Method C - Den
11、sity gradient column method with a preconditioning heating and cooling cycle. NOTE - The term “Apparent Specific Gravity“ is used within the PTFE hose industry for the density or relative density determined by methods A and B. The term “Relative Specific .Gravity“ is similarly used for the results o
12、f method C. 2 Definitions 2.1 density is expressed as follows : density : The mass per unit volume of material at t OC density, t OC : e, in grams per cubic centimetre or grams per millilitre For the purpose of this International Standard, t is equal to 25 OC. 2.2 relative density : The ratio of the
13、 mass in air of a given volume of material to the mass in air of an equal volume of a reference material at the same temperature; it is expressed as relative density, tlt OC : di where t is the temperature in degrees Celsius. For the purpose of this International Standard, t is equal to 25 OC. NOTES
14、 1 Throughout this International Standard, the term “relative density“ should be taken, as meaning relative density with respect to water. In this context, the English term “specific gravity“ is often used for “relative density“ when the reference material (see 2.2) is water. 2 Density in grams per
15、cubic centimetre may be converted to relative density with respect to water as follows : -et e; d =- where d is the relative density: er is the density of the specimen: e; is the density of water, at temperature t. At a temperature of 25 OC, e; = 0,997 1 g/cm3. 3 Apparatus 3.1 Methods Aand C 3.1.1 p
16、er, preferably ground glass. Density gradient tube, a suitable graduate with stop- 3.1.2 Constant temperature bath, a means of controlling the temperature of the liquid in the tube at 25 f 1 OC. A ther- mostatted water jacket around the tube is a satisfactory and convenient method of achieving this.
17、 2 3.1.3 Glass floats, a number of calibrated glass floats cover- ing the density range to be studied and approximately evenly (b distributed throughout this range. Tetrachloroethylene/ tribromomethane Bromobenzene/tribromomethane Chlorobenzeneltribromomethane 3.1.4 Pycnometer, used in determining t
18、he densities of the standard floats. 1,62 to 2.89 1,50 to 2,89 1,11 to 2,89 3.1.5 Hydrometers, a set of suitable hydrometers covering the range of densities to be measured. These hydrometers should have 0,001 density graduations. 3.1.6 Analytical balance, with a sensitivity of 0,l mg. 3.1.7 Siphon o
19、r pipette arrangement, for filling the gra- dient tube. This piece of equipment should be constructed so that the rate of flow of liquid may be regulated to 10 5 5 ml/min. 3.2 Method B 3.2.1 Analytical balance, a balance with a precision within 6 0,l mg, accuracy within 0,05 % relative (that is, O,
20、makesure that the observed movement of the float is not Clue to liquid motion by waiting at least 15 min after stirring has stopped before observing the float. 6.1,2,3 When balance has been obtained, fill a freshly cleaned and dried pycnometer (3.1.4) with the solution and place it in the 25 f 1 O C
21、 bath for sufficient time to allow temperature equilibrium of the glass. Determine the density of the solution by normal methods and make in vacuo corrections for all weighings. Record this as the density of the float. Repeat the procedure for each float. 6,1.3 Gradient tube preparation (stepwise ad
22、dition method) 6,1,3.1 Using the two liquids (see 4.1) that will give the de- sired density range and sensitivity (SI in grams per cubic centi- metre per millimetre, prepare four or more solutions such that each differs from the next heavier by 80s g/cm3. The number of solutions will depend upon the
23、 desired density range of the column and shall be determined as follows : Number of solutions to prepare density-gradient column : (1 + e2 - el) N= 80s where el is the lower limit of density range desired; e2 is the upper limit of density range desired, and S is the sensitivity, in grams per cubic c
24、entimetre per millimetre. NOTE - Round off the value of (i + e2 - e,)/80S to the nearest whole number. To prepare these solutions, proceed as follows : Using the hydrometers (3.1.51, mix the two liquids in the pro- portions necessary to obtain the desired solutions. Remove the dissolved air from the
25、 solutions by gentle heating or an applied vacuum. Then check the density of the solutions at 25 f 1 OC by means of the hydrometers and, if necessary, add the ap- propriate air-free liquid until the desired density is obtained. NOTE - In order to obtain a linear gradient in the tube, it is very impo
26、r- tant that the solutions be homogeneous and at the same temperature 4 when their densities are determined. It is also important that the den- sity difference between the solutions consecutively introduced into the tube be equal. . . 6.1.3.2 By means of a siphon or pipette 3.1,7), fill the gra- die
27、nt tube with an equal volume of each liquid starting with the heaviest, taking appropriate measures to prevent air from being dissolved in the liquid. After the addition of the heaviest liquid, very carefully and slowly pour an equal volume of the second heaviest liquid down the side of the column b
28、y holding the siphon or pipette against the side of the tube at a slight angle. Avoid excess agitation and turbulence. In this manner, the “building“ of the tube shall be completed. NOTE - Density gradients may also be prepared by reversing the pro- cedure described in 6.1.3.1 and 6.1.3.2. When this
29、 procedure is used, the lightest solution is placed in the tube and the next lightest solution is very carefully and slowly “placed“ in the bottom of the tube by means of a pipette or siphon which just touches the bottom of the tube. In this manner, “building“ of the tube shall be completed. 6.1.3.3
30、 If the tube is not already in a constant temperature bath, transfer the tube, with as little agitation as possible, to the constant temperature bath maintained at 25 f 7 OC. The bath level should approximately equal that of the solution in the tube, and provision should be made for vibrationless mo
31、unting of the tube. 6.1.3.4 For every 250 mm of length of tube, dip a minimum of five clean calibrated floats, spanning the effective range of the column, into the less dense solvent used in the preparation of the gradient tube and add them to the tube. By means of a stir- rer (for example, a small
32、coiled wire or other appropriate stirring device) mix the different layers of the tube gently by stirring horizontally until the least dense and most dense floats span the required range of the gradient tube. If at this time it is observed that the floats are “bunched“ together and not spread out ev
33、enly in the tube, discard the solution and repeat the procedure. Then cap the tube and keep it in the constant temperature bath for a minimum of 24 h. 6.1.3.5 At the end of this time, plot the density of floats against the height of floats to observe whether or not a fairly smooth and linear cume is
34、 obtained. Some small irregularities may be seen, but they should be slight. Whenever an irregular curve is obtained, the solution in the tube shall be discarded and a new gradient prepared. NOTE - Gradient systems may remain stable for several months. A daily check of the original calibration will
35、reveal when instability has been reached. 6.1.4 Measurement of density 6.1.4.1 Wet three representative test specimens with the less dense of the two liquids used in the tube and gently place them in the tube. Allow the tube and specimens to reach equilibrium, which may require 10 min or more. 6.1.4.2 When a graduated tube is used, read the height of the floats and specimens by using a line through their centre of volume. When a cathetometer is used, measure the height of the floats and specimens from an arbitrary level using a line
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