554 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS 2O O__ I 20 ø I0 ø 0 ø i0 ø 20 ø Degrees of rotation Figure 4. Velocity profile across spray cone 5 cm from the actuator for a Precision Standard RTBU actuator. Experimental points: ¸, 359 kN m-2 A, 290 kN m-S X, 221 kN m-S O, 152 kN m -•. Figure 3 shows that the velocity is very high close to the actuator and falls rapidly with increasing distance from the actuator. For the high pressure packs (290 and 359 kN m -•') the velocity 10 mm from the orifice is of the order of 6000 cm s -•. At 250 mm the velocity falls to betweeen 100 and 500 cm s -• depending on the pack pressure. The velocity profiles across the spray cone (Fig. 4) show that the velocity rises to a maximum at the centre of the spray cone. Both figures show that the maximum velocity in the cone increases with increasing pressure of the aerosol pack. Figure 5 shows the velocity profile across the spray cone for a 221 kN m -•' pack fitted with a Precision two-piece actuator. From a know_ledge of the diameter of the actuator orifice and the discharge

FACTORS CONTROLLING THE ACTION OF HAIR SPRAYS--Ill 555 20 ø I0 ø 0 ø I0 ø 20 ø Degrees of rotation Figure 5. Velocity profile across spray cone 5 cm from the actuator for a Precision 2-piece actuator. The pressure was 221 kN m -a. rate of the aerosol it is possible to calculate the discharge velocity of the sprays. Table III shows data for the Precision Standard actuator which had an orifice diameter of 0.041 cm. The formulation density was taken as 1.1 g cm -a. The final column of Table III shows the values of the maximum velocity of the sprays at a distance of 20 mm. The measured velocities are several times greater than the calculated values. This evidence suggests that the product does not emerge from the can as a continuous jet but as a mixture of liquid and propellant gas. The expansion chamber which precedes the atomizer probably allows partial evaporation of propellant before the Table III. Comparison of calculated and measured discharge velocities for the standard RTBU actuator Calculated Measured velocity Pressure Discharge rate velocity 2 cm from orifice (kN m -a) (g s -x) (cm s -•) (cm s -x) 152 0.92 645 1700 221 1.03 722 2600 290 1.11 778 3900 359 1.15 806 5200