The Expert's Corner

PROBLEM:

A major manufacturer of silicone sealants waslooking to make a new, highly filled, siliconesealant. The desired product has a viscosityof over 9 million centipoise and is very “sticky”.This posed several problems for manufacturingthe new sealant with their Double PlanetaryMixer with rectangular stirrer blades:

• The "sticky" nature of this material resultsin the batch climbing up the blades into thegearbox and hood area where it is not beingmixed, and creating an unnecessary mess.
• Silica powder added to the top of the batchtakes a long time to incorporate into the batch.
• Lowering the mixer blades into the high viscositymaterial is difficult.
• The viscosity of the material is beyond thecapabilities of the mixer.

SOLUTION:

The Ross HV Planetary Blades were developedto meet the demanding requirements ofmixing extremely high viscosity materials. Thisdesign enables the Ross Double PlanetaryMixer to mix products that would normally beconsidered far beyond the capabilities of mostDouble Planetary Mixers.

HV Planetary Blades consist of two helicalblades that are designed to rotate on their ownaxes while revolving around a common centralaxis. The HV Blades each provide adownward motivation to viscous materials,which prevents the common phenomenon of viscous materials “climbing” upward and out ofthe mixing vessel, into the headspace of themixer hood.

The helical design of the HV Blades makesthem self-wiping, as there is always a downwardmoving point of contact between the twoblades. A kneading action between the bladesis created which helps to promote the dispersionof solids in viscous media. This mixingaction is very useful for the incorporation ofpowders from the surface of the batch as wellas providing good top to bottom turnover withinthe batch.

PROCESSING:

For the processing of this sealant, the siliconepolymer and other liquid ingredients are addedto the mix can. The starting viscosity of theliquid is approximately 20,000 centipoise. Thepowdered fillers are added to the surface of theliquid . Vacuum is pulled on the batch beforethe mixing begins.

The finished product is a smooth, air-free siliconesealant with a viscosity of over 9 millioncentipoise.

CONCLUSION:

The Ross Double Planetary Mixer equippedwith HV Blades is capable of mixing materialsthat are normally considered beyond the viscositycapabilities for Planetary Mixers. Theincreased viscosity range of the HV Bladesenables the Double Planetary Mixer to be aviable, low-cost alternative to Double Arm mixersfor many applications.