FILLER SETTLING
The Effects of Filler Settling
Many formulated compounds contain fillers to impart
desired properties. The fillers are incorporated (mixed) into the resin and/or
hardener or both at the time the products are manufactured. Although formulators
take great care in selecting fillers and use various additives to keep them in
suspension, there will be some settling occurring under certain conditions.
Conditions conducive to filler settling:
1)
Lengthy storage under high ambient temperatures.
2)
Transportation during hot summer months.
3)
Coarse fillers in the materials (may be necessary to
impart certain desired properties).
4)
The material temperature is too high at the time of
packaging.
5)
Stagnant materials in heated lines on automatic
dispense equipment.
6)
Large container volume.
7)
Very low viscosity filled product.
The effect of filler settling on the cured product:
A)
In
the case of two component materials, the optimum mix ratio has been calculated
based on weight or volume. These calculations take into consideration that the
appropriate amount of filler is present in the mix. If the fillers have settled
and are not present in the correct amounts at the time of mixing the resultant
ratio will be incorrect. Since only the liquid components of the formula react
to cause cure, there will be too much or not enough of the liquid components
present for all the molecules to properly crosslink. At best the material will
exhibit undesired properties and at worse it will not cure at all.
B)
In the case of single component materials, filler
settling will result in improper cured properties resulting in insufficient
strength or cracking etc.
Precautions to minimize filler settling
| 1. Store materials in a cool place |
-
Storing products in a cool place will result in
less of a decrease in viscosity of the liquid components and the fillers will
remain in suspension longer.
| 2. Periodically invert unopened containers in storage |
-
Inverting containers in storage will keep the
fillers in motion minimizing settling. In addition, the small amount of fillers
settled will be “soft” and easy to remix.
-
As a rule of thumb, inverting the containers
once per week is sufficient in most cases.
| 3. Mix each component separately before use |
-
This is a highly recommended practice. The only
proviso is to minimize the inclusion of air during this mixing process. Most
products are de-aired during manufacturing for several reasons. In the case of
electrical components, any included air will have a detrimental effect on the
electrical properties and its moisture content could react with the liquid
components causing the formation of crust and altering the cure.
-
Thorough mixing of each component before use
can be achieved with special mixing blades that are designed to minimize the
inclusion of air. If the material can be de-aired after mixing, all the better.
| 4. Use re-circulating pumps on storage tanks |
-
Re-circulating pumps are an excellent way to
ensure that the fillers are properly dispersed. Some of these pumps can be
operated while the material is kept under vacuum or the material is de-aired
right after the pump shuts off.
| 5. Turn off the heat on dispense lines for long
periods of inactivity |
-
Keep product moving through heated lines. The
tubing usually contain small amounts of material allowing the temperature to
rise quickly resulting in filler settling. This could result in off ratio
product, plugged lines and erratic cured properties.
Filler
settling, from whatever cause, will result in inferior properties of the cured
material. It is important to ensure that all the fillers are dispersed within a
product before use. Taking precautions to minimize filler settling is worthwhile
insurance.
Disclaimer:
The above information is general in nature and
is based solely on experiences by Crosslink Technology Inc. The recommendations
provided herein may not be applicable in all situations. They are provided to
the recipient as part of our customer service and the user must determine the
relevance of the information to his/her application, considering any limitations
that may be applicable thereto. Crosslink technology Inc. does not accept any
liability for direct or consequential damages resulting from the the
implementations of these recommendations or the use of this information.
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