be phased out in favor of HFAs, and the FDA has stated its position on the subject [24].

An aerosol container consists of a number of components. The container may be constructed of aluminum or coated aluminum (to prevent interactions with the product). Other materials have been employed, including tinplate, glass, plastic-coated glass, and polycarbonate. The valve that is attached to the opening of the container may be constructed of aluminum or tinplate, in the main, with additional components, such as valve stem and gaskets, being made of a variety of polymers or rubbers [1,3-5].

A collet is used to crimp the valve to the top of the container. The collet consists of a number of "teeth" arranged in an open circle (with gaps between them) of larger diameter than the valve ferrule. The gaps between these teeth enable them to be drawn together to form a closed circle of smaller diameter than the valve ferrule. If the valve is seated on the container and the collet is placed over the valve and the "teeth" are drawn together, the pressure applied to the valve ferrule results in a crimp that attaches the valve to the container. This is described in detail in the following.

A filling nozzle or head is used to deliver either the concentrate or the propellant to the container in a controlled and quantitative fashion.

LABORATORY OR PILOT PLANT EQUIPMENT Concentrate Product-Filling Equipment

General Description of Product Filler

Existing machines for filling concentrate products are analogous to the piston motion of a plunger within a syringe. These machines are operated pneumatically. Throttle valves on each of two inlets to the pneumatic cylinder allow the adjustment of the filling and refilling speeds. Figures 1 and 2 show the positions of these inlet valves. Where a high level of dosage accuracy is

Figure 1 Concentrate product-filling equipment in filling position.

required of the fillers, a purging device is added to eliminate all vapor trapped in the metering cylinder of the filler.

A filling nozzle connected to the outlet of the metering cylinder releases the concentrate product into the container to be filled. The appropriate filling nozzle is selected according to several criteria. These fall under these general headings:

Type of activity: pharmaceutical, chemical, other

Dosage accuracy required

Speed of filling

For pharmaceutical products, the major criterion is that of accuracy. Mass market aerosols, such as paints, insecticides, and cosmetics, prioritize speed.

Two different types of filling nozzles are usually available. Figures 3, 4, and 5 show a filling nozzle type in which the canister must be present for the filling to occur. The container mechanically operates this nozzle when the filling unit is lowered. Figures 6 and 7 show a filling nozzle that is mon LE VA LVR TO ADJUST


COMPRESSED AIR | . | AIR EXHAUST !'; " j concentrate prc duct

Figure 2 Concentrate product-filling equipment in refilling position.

operated by a servomotor. Servomotor nozzle filling occurs automatically as the concentrate product-filling pressure is increased. At the end of the filling, instantaneous closing occurs that results in no loss of product due to dripping, as shown in Fig. 8. This has been adopted for pharmaceutical purposes.

Suspension Filling. The major difficulty in filling with a suspension, which may consist of a number of components, is maintaining the homogeneity of the mixture. A recirculation loop is fitted on the installation to avoid any drug sedimentation in the tank, tubings, or filling device. During each filling cycle, this recirculation is interrupted to completely isolate the filling unit, as shown in Fig. 9. Between filling cycles, the recirculation is fully operational, which allows the concentrate product to flow freely through the filler and return to the tank, as shown in Fig. 10.

Figure 3 Filling nozzle, requiring the presence of canister for filling to occur, before filling.

The suspension concentrated product must be chilled to obtain accuracy during filling with propellant 11. Slow evaporation of propellant results in a vapor lock in the tubing and metering cylinder of the filler. This ultimately results in inaccurate filling. The simplest solution to this problem is to chill

Figure 4 Filling nozzle, requiring the presence of canister for filling to occur, during filling.

the product in a double-jacketed tank around which cold water is circulated at 2-4°C (35-40°F), as shown in Figs. 9 and 10. Figure 11 shows the approach when propellant 114 is also used in the concentrate; then not only does it have to be refrigerated, but the tank must be maintained under compressed nitrogen at 40-50 psig.

As indicated previously, a pump is necessary to render the recirculating system operational. The capacity may be small. One pint per minute

Figure 5 Filling nozzle, requiring the presence of canister for filling to occur, after filling.
Figure 6 Filling nozzle operated by a servomotor, before filling.
Figure 7 Filling nozzle operated by a servomotor, during filling.

II I Aid 11

Figure 8 Filling nozzle operated by a servomotor, after filling.

Figure 9 Suspension-filling equipment showing interrupted recirculation system during filling.
Figure 10 Suspension-filling equipment showing operational recirculation system between fillings.
Figure 11 Suspension-filling equipment for high-vapor-pressure propellant.
Figure 12 Solution-filling equipment.
Figure 13 Schematic identifying five rules for crimping. (1) Well-adapted shape of crimp collet, (2) well-adapted depth stop, (3) crimping diameter, (4) crimp height, (5) sufficient vertical force.

(0.47L/min) is sufficient. The maximum pressure provided by the pump must remain far under the servomotor filling nozzle operating pressure. When the quantity of concentrate product in the tank exceeds 1 gallon, a pump delivering a larger flow should be selected to guarantee product homogeneity. Gear pumps, diaphragm pumps, and piston pumps are recommended. Centrifugal pumps are not suitable for this purpose. Pump selection also requires consideration of possible component swelling after contact with propellant. The pump should be arranged in the system to allow gravity feed. Thus, risks of vapor-phase formation in the inlet tubing will be eliminated, as shown in Figs. 9 and 10.

Figure 14 Recommended shape for crimp collet. The angle, a, varies according to the type of bottle or can being crimped.

Solution Filling. Solutions generally do not involve products subject to fast evaporation, such as chlorofluorocarbons, and therefore they do not require chilling and recirculation. Figure 12 shows a solution-filling system.

With product fillers that are not equipped with a purging device, it may be difficult to purge all air remaining in the metering cylinder and tubings. As a result, the first hundred fillings may be inaccurate. The addition of a recirculation system prevents this inconvenience, and, in practice, fillings become more accurate after the first five actuations.

Crimping Equipment

Five rules must be observed to perform correct crimping. These rules are illustrated schematically in Fig. 13 and are described as follows.

Adapted depth rtop Unidapted depth (top

Adapted depth rtop Unidapted depth (top

Figure 15 Schematic showing correct and incorrect action of a depth stop.
Table 2 Vertical Force Applied to Valve Ferrule During Crimping and the Extent of Compression of the Sealing Gasket Required for Different Containers


Force provided,


gasket (%)

N (lb)

of the scaling

Glass bottle

578-667 (130-150)

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