Flash point of bitumen is the temperature at which, its vapour will ignite temporarily during heating when a small flame is brought into contact with the vapour. The knowledge of this point is of interest mainly to the user, since the bitumen must not be heated to this point. The flash point tells the critical temperature at and above which suitable precautions are required to be taken to eliminate the danger of fire during heating. This temperature, however, is well below that at which the bitumen will burn. The latter temperature is called the fire point.
It is the lowest temperature at which the vapour of a bituminous material momentarily takes fire in the form of a flash, under specified conditions of the test.
It is the lowest temperature at which bituminous materials ignite and burn under specific conditions of the test.
(Also Read: Introduction to Bitumen as Pavement Materials)
This method covers the determination of the flash and fire points, by Cleveland Open Cup Tester, of petroleum products and other liquids, except fuel oils and those materials having an open cup flash point below (79o C) as determined by the Cleveland Open Cup Tester.
a) Cleveland Open Cup Apparatus
This apparatus consists of the test cup, heating plate, test flame applicator and heater, thermometer support, and heating plate support, all conforming to the following requirement:
Test Cup – of brass conforming to the dimensional requirements shown in Figure 3. The cup may be equipped with a handle.
Heating Plate – A brass, cast iron, wrought iron, or steel plate with a centre hole surrounded by an area of plane depression, and a sheet of the hard asbestos board which covers the metal plate except over the area of plane depression in which the test cup is supported. The essential dimensions of the heating plate are shown in Figure 2, however, it may the square instead of round, and the metal plate may have suitable extensions for mounting the test flame applicator device and the thermometer support. The metal bead may be mounted on the plate so that it extends through and slightly above a suitable small hole in the asbestos board.
Note: The sheet of the hard asbestos board which covers the heating plate may be extended beyond the edge of the heating plate to reduce drafts around the cup. The F dimension given is intended for gas apparatus. For electrically heated apparatus the plate shall be of sufficient size to
cover the top of the heater.
(Also Read: List of Tests for Bitumen as per Indian Standard)
Test Flame Applicator – The device for applying the test flame may be of any suitable design, but the tip shall be 1.6 to 5.0 mm or 0.06 to 0.20 in. in diameter at the end and the orifice shall have an approximate diameter of 0.8 mm or 0.031 in. The device for applying the test flame shall be so mounted to permit automatic duplication of the sweep of the test flame, the radius of the swing not being less than 150 mm or 6 in. and the centre of the orifice moving in a plane not that 2.5 mm or 0.10 in. above the cup. A bead having a diameter of 3.8 to 5.4 mm or 0.15 to
0.21 in. maybe mounted in a convenient position on the apparatus so the size of the test flame can be compared to it.
Heater – Heat may be supplied form any convenient source. The use of a gas burner of alcohol lamp is permitted, but under no circumstances are products of combustion or free flame to be allowed to come up around the cup. An electric heater controlled by a variable voltage transformer is preferred. The source of heat shall be centred under the opening of the heating plate with no local superheating. Flame-type heaters may be protected from drafts or excessive radiation by any suitable type of shield that does not project above the level of the upper surface of the asbestos board.
Thermometer Support – Any convenient device may be used which will hold the thermometer in the specified position during a test and which will permit easy removal of the thermometer form the test cup upon completion of a test.
Heating Plate Support – Any convenient support will hold the heating plate level and steady may be employed.
One form of the assembled apparatus, the heating plate, and the cup are illustrated in Figures 1, 2 and 3 respectively.
Filling Level Gauge – A device to aid in the proper adjustment of the sample level in the cup. It may be made of suitable metal with at least one projection, but preferably two for adjusting the sample level in the test cup to 9 to 10 mm (0.35 to 0.39 in.) below the top edge of the cup. A hole 0.8 mm (1/32 in.) in diameter, the centre of which is located not more than 2.5 mm or 0.10 in. above the bottom edge of the gage, shall be provided for use in checking the centre position of the orifice of the test flame applicator with respect to the rim of the cup. (Figure 4 shows a suitable version.)
A shield 460 mm (18 in.) square and 610 mm (24 in.) high and having an open front is recommended.
(Also Read: Softening Point Test of Bitumen As Per IS: 1205-1978)
Preparation of apparatus
a) The apparatus is supported on a level steady table in a draft-free room or compartment. The top of the apparatus is shielded from strong light by any suitable means to permit ready detection of the flash point. Tests in laboratory heed (Note 1.) or any location where drafts occur are not to be relied upon.
Note 1. With some samples whose vapours or products of pyrolysis are objectionable, it is permissible to place the apparatus with a shield in a hood, the draft of which is adjustable so that vapours may be withdrawn without causing air currents over the test cup during the final 56o C (100o F) rise in temperature prior to the flash point.
b) The test cup is washed with an appropriate solvent to remove any oil or traces of gum or residue remaining from a previous test. If any deposits of carbon are present, they should be removed with steel wool. The cup is flashed cold water and dry for a few minutes over an open flame, on a hot plate, or in an oven to remove the last traces of solvent and water. The cup is cooled to at least 56o C (100o F) below the expected flash point before using.
c) The thermometer is supported in a vertical position with the bottom of the bulb 6.4 mm (1/4 in.) from the bottom of the cup and located at a point halfway between the center and side of the cup on the diameter perpendicular to the arc (or line) of the sweep of the test flame and on the side opposite to the test frame burner arm.
a) The cup is filled at any convenient temperature (Note 2) not exceeding 100o C or 180o F above the softening point so that the top of the meniscus is at the filling line. To aid in this operation, a Filling Level Gauge (A7) may be used. If too much sample has been added to the cup, remove the excess, using a pipette or other suitable device; however, if there is sample on the outside of the apparatus, empty, clean and refill it. Any air bubbles on the surface of the sample (Note 3) are destroyed.
Note 2. Viscous samples should be heated until they are reasonably fluid before being poured into the cup. For asphalt cement, the temperature during heating must not exceed 100o C or 180o F above the expected softening point. Extra caution must be exercised with liquid asphalt’s which should be heated only to the lowest temperature at which they can be poured.
Note 3. The sample cup may be filled away from the apparatus provide the thermometer is preset with the cup in place and the sample level is correct at the beginning of the test. A shim 6.4 mm (1/4 in) thick is useful in obtaining the correction distance from the bottom of the bulb to the bottom of the cup.
b) The test flame is lighted and adjusted to a diameter of 3.8 to 5.4 mm (0.15 to 0.21 in.).
c) Heat is applied initially so that the rate of temperature rise of the sample is 14 o to 17 o C (25o to 30o F) per minute. When the sample temperature is approximately 56o C (100 F) below the anticipated flash point, decrease the heat so that the rate of temperature rise for the 28o C (50o F) before the flash point is 5o to 6o C (9o to 11o F) per minute.
d) Starting at least 28o C (50o F) below the assumed flash point, the test flame is applied when the temperature read on the thermometer reaches each successive 2o C (5o F) mark. The test flame is passed across the centre of the cup, at right angles to the diameter which passes through the thermometer. With a smooth, continuous motion apply the flame either in a straight line or along the circumference of a circle having a radius of at least 150 mm or 6 in. The centre of the test flame must move in a plane not more than 2.5 mm or 0.10 in. above the plane of the upper edge of the cup passing in one direction first, then in the opposite direction the next time. The time consumed in passing the test flame across the cup shall be about 1 s. During the last 17o C (30o F ) rise in temperature prior to the flash point, care must be taken to avoid disturbing the vapours in the test cup by careless movements or breathing near the cup.
Note 4. If a skin should form before the flash or fire point is reached, move it carefully aside with a small spatula or stirring rod and continue the determination.
e) The observed flash point is recorded as the temperature read on the thermometer when a flash appears at any point on the surface of the oil, but do not confuse the true flash with the bluish halo that sometimes surrounds the test flame.
f) To determine the fire point, continue heating so that the sample temperature increases at a rate of 5o to 6o C (9o to 11o F). The application of the test flame is continued at 2o C (5o F) intervals until the oil ignites and continues to burn for at least 5 seconds. Record the temperature at this point as the fire point of the oil.
(Also Read: Ductility Test of Bitumen as per IS:1208-1978)
Correction for barometric pressure
If the actual barometric pressure at the time of the tests is less than 715 mm of mercury, it is recorded and the appropriate correction is added from the following table to the flash and fire points, as determined.
Calculation and report
1. The observed flash point or fire point, or both is corrected in accordance with the above table
2. The corrected flash point of fire point or both is reported as the Cleveland Open Cup Flash Point or Fire Point, or both
The following data should be used for judging the acceptability of results (95% confidence.)
Duplicate results by the same operator should be considered suspect if they differ by more than the following amounts:
Flash point ………………………………………………………… 8 oC (15 oF)
Fire point ……………………………………………………….…. 8 oC (15 oF)
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