Mixing system makes glass powders more even

Edited by the Engineeringtalk editorial team Dec 11, 2007

The new Thinky ARE-250 from Intertronics incorporates both planetary mixing and centrifugal degassing in one unit.

Cera Dynamics had relied for many years on a manual mixing system for its research and quality control of specialist glass powders, but embarked on a search for a process solution that would be more effective, more consistent, quicker and simpler.

The glass powders produced by Cera Dynamics are tailored to customer need - primarily for dental fillers and restorers, they vary from 0.5 to 10um average particle size.

For testing purposes the glass powder needs to be mixed with a high viscosity acrylic resin monomer to check for high transparency and low discolouration - but the manual process, while well understood, continued to give problems of nonhomogeneity and air inclusion, both of which preclude colour checking of the glass.

The search for an improved system led Dr Philip Frampton to the industry standard vacuum mix machine - excellent for 100 to 200g but not suitable for 10g samples - also to a purely planetary mixer which was found to enfold too much air - and ultimately to the new Thinky ARE-250 from Intertronics, which incorporates both planetary mixing and centrifugal degassing in one unit.

Tests with the Thinky equipment involved mixing 60% glass with 40% acrylic by weight in viscosities varying from "thick honey to stiff bubble gum", according to Dr Frampton.

Empirical investigation supported by advice from the Intertronics engineers rapidly determined suitable program parameters based on viscosity and these samples were then pressed and cured into standard GBP 2 coin sized discs for comparison with established colour standards.

Dr Frampton explains: "Cera Dynamics are one of probably only four or five companies in the world operating at the top level in this technology and we were looking to improve the mixing stage as a first step to overall improvement of our glass grinding process".

"Intertronic's expertise and supply of the Thinky mixer has allowed us to achieve that initial goal in a single operation - so now we have a reliable quality control process we can move to purchase of a spectrophotometer".

"This will enable us to refine our operation further toward development of an even cleaner and finer grinding process".

The Thinky ARE-250 Mixer allows for the process of mixing and bubble removal to be carried out simultaneously.

It mixes, disperses and degasses materials in seconds to minutes, in a sealed or lid-less container such as a jar, beaker, syringe barrel, or cartridge.

The noncontact mixing principle makes it possible for formulation of compounds from very small amounts such as 0.5ml to production quantities of 310g.

The ARE-250 may be used to formulate and mix adhesives, sealants, moulding compounds, lubricants, slurries, coatings, inks, paints, abrasives, bio chemicals, cements, medical compounds, cosmetics/personal care materials, detergents, conductive pastes, dental materials, foods, construction materials or any other materials which are hard-to-mix, hard-to-degas, or hard-to-wet.

The Thinky ARE-250 Mixer works by revolving and rotating the container in a planetary manner at various speeds with both overall and planetary rotational speeds independently pre-programmable.

Centrifugal force presses the material outwards to the inner wall of the container.

Other forces cause the material to move downwards in a spiralling direction along the slope of container wall.

The material then moves back to the centre of the container and up to the top.

As a result, material circulation from top to the bottom generates kneading effects, forcing trapped air out of the material.

This ensures no cross-contamination between batches, no damage to material from rollers, mixing blades or propellers and no unit cleaning between batches, as well as allowing re-mixing of separated materials to prolong shelf life.

Consequently, process cycles may be reduced, lowering costs and improving yield rates.

The whole noncontact programmable approach greatly improves consistency of quality and improves formulation irrespective of operator skill levels.