This application is definitely in the high volume category, and these processors typically use 10 station, 33 or 55 ton machines. The tools are usually 4/8 cavities, and on average run on a 30 second injection cycle with a cooling time of 5-6 minutes. Based on the above assumptions, one can conservatively estimate a daily production of a minimum of 10,000 brushes which translates into an annual production of 2,500,000 based on 20 hours x 250 days. Gas assisted molding is not a suitable technology for this application because the bristles must be inserted into solid material and not holes. These manufacturers also tend to take full advantage of the individual programming of each station in order to produce a wide variety of different articles simultaneously.
A comparison with single station molding is not possible because the production economics of these thick parts have dictated the use of rotary presses for the past 20 years. Broom blocks or industrial foam moved to rotary injection in the early 1970's, and rotary co-injection is a natural outgrowth of this preference.
Co-injection has also allowed these manufacturers to move from the industrial cleaning markets into the home products market with the appearance characteristics possible in terms of "soft touch" or hard and shiny first class finish without need of lacquering. With paintbrushes, co-injection again provides distinct advantages in terms of the surface appearance which can be achieved, either hard and glossy or "soft touch".
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