PROBLEMS RELATED TO MIX RATIO
Symptoms
- Soft Cure
- Brittle
- No Cure
- Insufficient Physical Properties
- Cracking
- Excessive Shrinkage During Cure
The mix ratios for Epoxies and Polyurethanes are usually
specified as ratios by weight and/or volume. These ratios are determined by
product chemistry. The reactive parts are the resin and hardener, being the
liquid components of the formulation. The fillers, if present, do not take part
in the reaction.
The mix ratio specified for filled systems takes into
consideration the amount of fillers present in a given volume of the homogeneous
material. If the fillers settled to the bottom of the container and the material
is not mixed thoroughly, product taken from the top of the container will be
"liquids rich". In this case, applying the specified mix ratio will
result in an off ratio product that will not cure or if it cures, will be
deficient in cured properties.
DO THE FOLLOWING TO QUICKLY CONFIRM
THAT THE MATERIAL (RESIN AND HARDENER) IS GOOD:
-
Take a clean plastic container.
-
Place the container on a gram scale and tare.
-
Mix the resin in its container thoroughly and pour 200grms
into the empty container on the scale.
-
Thoroughly mix the hardener in its container.
-
Weigh the appropriate amount of hardener, as indicated on the
data sheet, into the plastic container on top of the resin.
-
Thoroughly mix the resin/hardener together, scraping the
sides of the container to make certain that all the hardener is thoroughly and
evenly dispersed in the resin.
-
Pour any excess material out into another container, leaving
only the amount of product indicated on the data sheet (next to the heading "Gel
time").
-
Gel the mixture according to the cure instructions on the
data sheet. Check the sample after the specified gel time.
Results:
If, after the specified gel time, the sample is solid and
firm throughout, the product is reacting as it should and the problem is
elsewhere.
If, after the specified gel time, the sample is soft
throughout, re-check the mix ratio that was used to prepare the sample. If the
correct mix ratio was used and the sample was gelled at the specified
temperature, there is something wrong with the product and the supplier should
be contacted.
Soft spots evident within the gelled sample indicate that the
resin and hardener were not mixed thoroughly enough and the test should be
repeated.
SOME HANDY CONVERSION FORMULAS:
Calculate the Sg (specific gravity) of the mixed material
| Weight of Part "A" + Weight of Part "B"
(according to stated mix ratio) |
|
|
| Weight of "A"
+ Weight of "B" |
= |
Sg Of Mixed Material. |
| Sg of Part "A"
Sg of Part "B" |
|
|
To convert Mix Ratios from "Parts by Weight" to
"Parts by Volume"
| PBW of Part "A"
X Sg of Part "B" |
= |
Part By Volume of Part "A"
to |
| PBW of Part
"B" Sg of Part "A" |
|
1 Part by Volume of Part "B" |
* PBW = Parts by Weight (from the stated mix
ratio on Technical Bulletin) Sg = Specific Gravity (as specified on the
Technical Bulletin)
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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