Choice of stirring elements

With the following we would like to assist you in the choice of stirrer shafts. All stated values are experienced data established by experimentation and practical testing. All stirring elements are made for clockwise rotation (view from the top of the stirring agitator).

The diameter of the stirring shaft depends on the products used as well as on their viscosity. The higher the viscosity, the larger the shaft diameter. If you are in doubt, you should choose always the larger shaft diameter, in most cases it is possible to reduce the chucking diameter.

Stirrer shafts with a diameter of 8, 10 and 16 mm are most commonly used. For standard applications up to a rotation speed of 350 rpm and a max. length of 600 mm, a shaft diameter of 10 mm will be sufficient. For stirring of high viscous products or shaft lengths over 600 mm, it should be checked whether the use of a stirrer shaft with 16 mm will make sense. Furthermore, adequate stirrer bearings and chucks at the agitor should be available.

Propeller stirrer shafts

Stirrer shaft with several, inclined, arched and partly twisted blades. Also with draught tube. Stirring effect is based on a mainly axial flow which moves away from the agitator; changes in the blade inclination or rotating direction result in a change of the flow direction.

R = (0.2 to 0.4) x D
B = (1.0 to 1.5) x R

Discoidal stirrer shafts

Stirrer shaft with a blade with several, plane or curved paddles. Stirring effect is based on a radial, outwards directed flow with axial suction from the bottom and the top. The dispersing liquid is exposed to a high shearing.

R = (0.3 to 0.4) x D
H = 0.2 x R
B = R

Impeller stirrer shafts

Stirrer shaft with three angular, arched paddles. The stirring effect is based on a radial flow which is diverted axially due to the ground level position of the stirrer.

R = (0.50 to 0.70) x D
H = (0.12 to 0.17) x R
B = (0.08 to 0.18) x R

Stirrer Shafts with rigid paddle

Stirrer with a narrow blade. The stirring effect is based on a radial and axial flow. The product is opposed to shear forces ranging from moderate to strong.

R = (0.70 to 0.9) x D
H = (0.05 to 0.1) x R
B = (0.10 to 0.2) x R

Stirrer Shafts with rigid blade

Solid, plane blade in user-defined form. Stirring effect due to different rotation speeds of the product displaced by stirring and the residual vessel content.

R = (0.4 to 0.5) x D
H = (0.9 to 1) x R
B = 0.3 x R

Stirrer Shafts with angular blades

Stirrer shaft with several inclined, rectangular, straight blades (special form a2 = 90 degrees, also curved blades). The stirring effect is based on an axially directed flow combined with an increased shear rate. Reversion of the flow can be obtained by changing the inclination of the blades or the rotation direction.

R = (0.30 to 0.40) x D
H = (0.15 to 0.25) x R
B = (0.50 to 1.00) x R

U-shaped stirrer shafts

Anchor stirrer blade adapted to the vessel’s wall, reaches from edge to edge. The stirring effect is based on a mainly tangential flow with poor axial forces.

R = (0.90 to 0.95) x D
H = (0.50 to 1.00) x R
B = (0.003 to 0.005) x R

Double impulse stirrer shafts

Stirrer shaft with two contrarily aligned blades on a radial arm. The stirring effect is based on an axial flow with poor radial forces. Analogue to the conveying direction of the blades an axial flow arises near to the shaft. The conveying direction of the outer paddles is adapted to the mixing demands.

R = 0.70 x D
H = 0.20 x R
B = 0.28 x R

What you should know about Stirrer Shafts

BOLA Stirrer Shafts consist of a PTFE-jacketed stainless steel shaft and a stirrer blade made of solid PTFE. The stainless steel core provides high mechanical stability and allows a safe fixing in the agitator.

Unbreakable

All glass stirrer shafts which are commonly used in laboratories are very fragile. Dropping, stirring solid materials or too much power transmitted from the agitator to the product can cause broken glass. Due to their solid stainless steel core, BOLA Stirrer Shafts are protected against all these possibilities of breaking.

Universal chemical resistance

Due to the thick PTFE-jacket, the product which is stirred is only exposed to PTFE. This assures an almost universal chemical resistance. PTFE-jacketed stirrer shafts can be used whenever stirrer shafts made of PP (polypropylene), glass or stainless steel are not sufficient.

Temperature resistance

Stirrer shafts made of PP (polypropylene) are deformed at temperatures exceeding +100°C and cannot be used any longer. All BOLA PTFEjacketed stirrer shafts can be used at temperatures of up to +250°C without any negative effects on their chemical resistance.

Non-adhesive

The surfaces of glass and stainless steel stirrer shafts allow adhesion of products (in particular such as dyes and glues). BOLA PTFE Stirrer Shafts, however, are non-adhesive and therefore eliminate adhesion of dyes and glues.

Interchangeability

At present, most stirrer shafts used in laboratories are made of glass. All BOLA Stirrer Shafts are available with the same diameters, lengths and surface qualities (KPG) as stirrer shafts made of glass. Thus, the user can easily replace the glass stirrer shaft with a PTFE-jacketed stirrer shaft and does not have to change agitators, couplings and guiding devices.

Safe fixing

The upper end of the BOLA Stirrer Shaft is not jacketed with PTFE and can therefore be fixed safely into the agitator or the stirrer coupling.

Solid stirrer blade

The stirrer blade is fixed tightly to the stirrer shaft and cannot be loosened by the product which is still turning after switching off the agitator. The stirrer shafts are suitable for clockwise and counterclockwise rotation.

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