Product lines
            The mixers, in the process vessels or fermentors are the real “motors of operations” their performance controls the material and heat exchanges among phases of the process and with the vessels.
            Every process has its character and capacity; the magnetic mixers  STE.M are available in 7 sizes to cover most of different capacities, several tested profilesto cover most of the different kinds of agitation, different motors and gearmotors to cover mostof the ranges of speeds required

In the basic helical STE.M series, reported in the attached list of models, each impeller is provided with inclined blades; they produce a primary hidraulic vortex up to the free surface of the liquid, well evident; then the rotation of the fluid generates a secondary vortex down to the blades of the impeller.

The result is a powerful agitation  with high hydraulic efficiency with fast currents up and down in the vessel, very limited generation of foam and a very efficient heat exchange with the wall of the vessel.

In the centrifugal STE.M turbine series with inducer the bodies of impellers which enclose the magnets are the same of the basic helical series but the blades are vertical, except the lower edges which are curved.

The main hydraulic effect is centrifugal but a very useful suction of heavy components from the bottom is also provided.
The primary vortex is very vigorous and centered on the impeller I, it permits extremely fast dispersions of solids. Secondary vertical currents are generated in this case but some dispersion of  gas bubbles is possible.

In the series ST E.M.H of  homogeneizers the impellers are provided with adouble set of blades and work in combination with a multibored crown, the stator.

The inner blades are centrifugal, the external blades are mainly axial.
The fluidi is pumped by the inner blades torough the stator but while passing it receives twice a strong shearig effect bu the inner blades and by the external blades.
The resulting hidraulic vertical forces on the impeller are balanced by the magnetic system of the external magnetic rotor which is directly fit to the motor.
In this seriesthe external  blades  have a smaller diameter than the magnetic body of the impellers and can reach much higher speeds than the other STE.M
series.
These homogenizers can be employed alone to produce gels or ointments or for any technological process where high shearing effect is needed or can be  combined with other principles of agitation in the same vessel: anchors with scrapers, axial turbines to produce even highly viscous creams.
The advantage of the unique design of these magnetic homogenizers is that are constantly levitating,  wear-freeand prevent absolutely any contamination.
For exemple the production of sterile eye- ointments can obtain substantial advantages of industrial yield, reliability and safety.

The series of  agitators made by plastic material PEEK started from the request  of some Cients to have cheap but reliable single use impellers for applications in single use process plastic bags.

This series is limited to the smaller models STE.M.P and STE.M.A.
These agitators can reach very high speeds and a surprising hidraulic efficiency and can conveniently be adopted by many Research Centers for the chritical step of implementation to pass from the basic research into the first pilote industrial stage of sample production. This step can be in plastic bags or stainless steel vessels.
In this case the impellers can be provided with bearings as the other STE.M series to rech durations even of many years because the PEEK polimer is extremely stable up to the temperature of sterilization and has an excellent resistance to corrosion.

A peristaltic magnetic mixer or vibromixer STE.M.V is essentially a horizontal disc with several conical borings and a set of magnets guided to move vertically in a vessel by an external magnetic coupling linked to a reciprocating electrical motor.
The flux of the liquid  according to the Bernoulli law is more in the direction of the edges of the cones, consequently a primary  flux in the vessel is generated up or down according to the direction of the cones.
This agitation  can be interesting for the processes where a vigorous agitation is requested with guaranty of prevention of air or gas trapping in the product or
for gentle agitation of delicate biomass  which can be sensitive to shear-effects.
The magnetic couplings provided for this type of peristaltic movement are completely different from the rotary movements and the supports are similar but longeri. These agitators are unique and are patent pending.
Click here to see a short film with a STE.M.V.A in operation.

Characteristics
         The magnetic mixers STE.M, born in 1992 and patented in 1996 operate without mechanical seals or seals of any kind and eliminate all sources of contamination .
            The impellers are made of amagnetic  stainless  AISI 316L, containing a crown of highly performantmagnets; they rotate around a fixed shaft and a support welded to the bottom of the tank.
            The impellers are completely open on top and are continuously flushed by the fluid in operation, they are easily cleaned in place ( CIP) and sterilized in place ( Sip ) with the vessel witout dismantling and without special dedicated nozzles.
            The rotation is given by a system of external magnets  ( magnetic rotor)  moved by an electrical motor or a gearmotor.
            The magnets are mounted radially and keep the impellers continuously levitating;this eliminates the wear of mechanical thrust blocks and the relevant wear of the bearings.
            The whole system is easy and confortable in use and easy to be keptperfectly reliable and not noisy for decades.

Power calculations
         La hidraulic power of the magnetic mixers  STE.Mis evaluated according to the method of Rayleigh as  a function of the geometrical parameters of the models and of the specificied physical data of the fluids.  All results are compared with the available magnetic torque available.
            The hydraulic tests made with the various models have confirmed the assumptions for the characteristic relation between the Reynolds Number ( NRe, which summarizes the effects of the phisical data of the fluids on the hirdaulicpattern laminar / turbulent)  and the Power Number of each type of STE.M mixer:  STE.M with inclined blades or vertical blades, homogenizers with combinations of blades.

            On this base of design the power is calculated using the following formula:
            P = k . Np. µ . N³ . D³.D²                 in cui:                                                **************
            P = power in HP
            Np = Characteristic Power Number
            µ = viscosità in cPs
            N = RPM
            D = Diameter of the impeller
                       

Materials’ selections
         The magnetsemployed in the STE.M aresynterized using metals of the Lantanid series of elements also called rare earths: La, Nd, Sm in adequate mixtures to cover the process requirements; and using Cobalt or  Nickel as ligant..
            The sainless steel used for the STE.M has alow content of carbon and anyway amagnetic to avoid dispersions of magnetic field and eddy currents, generally is ASTM A240 Tp 316L or equivalent europeani.
            In process cases where materials with even higher resistance to corrosion are specified, special alloys can be adopted or very resistant plastic material like PEEK (poliether-eterchetone )can be selected as in our product line.
            The selection of materials for the bearings can be specified by the Clients according to the process conditions; where no abrasive components are present in the fluids, the traditional choice is in favour of tungsten carbidein the impellers and on the shafts; these are provided with a special hardening surface treatment by titanium nitride or titanium carbonitride; the surface hardness reaches 3000 degrees HV10 and the friction factor is the lowest available.
          The wear of our bearings, evaluated according to the most restrictive procedures   of the US Pharmacopoeia ( USP ) are several tenths less than allowed, practically negligible. This certification is available upon request.
            Where abrasive solids are present, the best selection is generally silicon carbide;   the hardness of our standard bearings, measured by the Shore Scleroscope is 2,800 . 
            In any case it is important to have a clear statement of the maximum process temperature, which is generally the temperature of sterilization.

The perfect fit of the bearings which have a very low  expansion coefficient must   remain in the stainless steel of the impellers which have a higher expansion coefficient  even at the temperature of sterilization. For this reason the impeller side bearings are mounted with interference following our standardized mill procedure.