648 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Figure 3. Wallace and Tieman Double Simplex Metering Pump, Wallace and Tiernan Div., Pennwalt Corp., Walpole, Mass. Evaluation of the Mixing Operation A typical production batch Of product when examined microscopically was found to have an average dis!•ersed droplet diameter of about 15 t•- Experiments were conducted to determine if an emulsion produced with droplets of less than 15 t• would exhibit an improved consistency and/or stability. With a Manton-Gaulin piston homogenizer • a droplet di- ameter of 0.1 to 1 t• was achieved. Such a cream upon cooling lacked consistency and stability and changed the general character of the prod- uct. On this basis, high shear blenders were concluded to be unsuitable. With the foregoing information, two types of mixers were selected for testing. They were (a) the in-line low-to-moderate shear axial flow turbine mixer and (b) an in-line static mixer (low shear). The static mixer is rather novel in that it has no moving Darts. Its action and/or effect is produced by the movement or flow of the prod- • Manton-Gaulin Manufacturing Co., Everett, Mass.

MANUFACTURING PROCESS FOR COSMEq'IC CREAM 649 Figure 4. Lightnin In-line Axial Flow Turbine Mixer. Mixing Equipment Co.. Inc., Rochcstcr, N. Y. uct through its length within which a turbulent mixing action is achieved by a re--eated splitting of the product stream. A summary of the results of product mixed with these two test units including a comparison with the Manton-Gaulin and standard batch product is listed (Table VII). Observations were made with a light microscope to determine average droplet size. Evaluation o[ Scraped-Wall Heat Exchanger The heat exchanger is used to cool the cream leaving the in-line mixer from approximately 60øC to the filling temperature of 41øC on a continuous basis. Three heat exchanger models (potentially the most costly item in a continuous process) were evaluated in a test loop (Fig. 8).