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PROBLEM |
PROBABLE CAUSE |
POSSIBLE FIX |
|
Inconsistent Colour |
- separation caused either during transit
or storage. |
Stir thoroughly to disperse
pigment(s). De-air mix after stirring. |
|
No gel or
will not cure click below for steps in
troubleshooting:
Curing and Gellation Problems
|
-Incorrect mix ratio. |
Mix individual components separately to disperse fillers.
De-air after mixing. Confirm that the correct weight of resin and hardener
are being mixed. |
| -Resin and
hardener not mixed well enough |
-Mix thoroughly
scraping the sides of the container. |
| -Incorrect resin
or hardener used |
-Not all
hardeners react with all resins. Check and confirm that the correct
components are being mixed together. |
| -Missing resin or
hardener component |
-Check for
blocked lines or inoperative valves on dispense equipment. Confirm that
all the required components are present in the mix. |
| -Insufficient
heat applied or the pot life has not expired. |
-Some systems
require the application of heat to start the reaction. In these cases the
reaction is extremely slow or does not start without the application of
heat. Apply heat as stated on the technical data sheet. |
|
Pot Life is shorter than expected or is
shorter than stated on the Technical Data Sheet. |
-The mix is off
ratio. |
-Confirm that the
mix is not short on resin or over catalyzed. Make certain that the fillers
are properly dispersed. Make certain that all supply lines are clear from
blockage and material is not leaking past the seals on dispense equipment.
|
| -The processing
temperature is too high |
-The application
of heat will speed the reaction. Hot embedded components, mixed material
that has been heated to reduce viscosity or high ambient temperature will
all shorten pot life. The problem may be solved by cooling the heat source
before processing. |
|
-The amount mixed at one time is too large |
-Choosing the
correct hardener is critical where there is a requirement to mix large
amounts of material at one time for processing. The exothermic reaction is
usually mass dependent. The higher the mass the more heat is generated
causing a faster reaction. Cooling the mix may help but choosing a slower
hardener is better. (Also see Lead/Lag problems under "Soft spots") |
| |
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|
|
|
PROBABLE CAUSE |
POSSIBLE FIX |
|
Pot Life is longer
than expected or is longer than stated on the Technical data Sheet. |
-The mix is off ratio.
Click for details:
Mix Ratio Related Problems |
-Confirm that the mix is not resin rich or short on
hardener. Make sure that the fillers are properly dispersed.Make
certain that all supply lines are clear from blockage and material is not
leaking past the seals on dispense equipment. |
|
-The processing temperature is too low. |
-Cool ambient temperatures allow the heat generated by the
reaction to be transferred to the surrounding air or a cold bench top.
Removing some of the heat generated by the reaction will lengthen pot life
and slow the curing process. Insulate the part from the cold or choose a
more aggressive hardener. |
|
-The amount of material being mixed at one time is too
small. |
-Smaller masses generate less heat and slow the reaction.
Heat the mix or the components being processed or choose a more aggressive
hardener. |
|
Soft Gel or Cure
Click below for detailed troubleshooting:
Epoxy/Urethane Curing and Gellation Problems |
-Not cured long
enough. |
-Insufficient time or temperature. Smaller masses or
assemblies that contain components, such as metallic inserts which can
sink away heat from the curing material will cause the gel time to
lengthen. Apply moderate heat or allow for a longer gel time. |
|
-Incorrect mix ratio (could be due to settled fillers).
Click below for details:
Epoxy/Urethane Mix Ratio Related Problems |
-By far the most
common cause of this problem. Make certain that the fillers are dispersed
within the mix, the resin and hardener are present in the correct amounts.
In some cases it may be necessary to select a different hardener. Dispense
machines with heated feed lines are prone to filler settling if the heated
resin or hardener is left stagnant for longer periods of time. This could
result in an off ratio mix. |
| -Insufficient
mixing. |
-Check that the fillers are properly dispersed and that the
hardener is thoroughly mixed into the resin. Concentrated pockets of resin
and/or hardener will not react with anything and remain soft. Insufficient
number of elements in static mix heads or improperly sized feed lines will
also result in uneven mixing. |
| -Incorrect cure/gel
temperature. |
-Some systems require the application of heat to start the
reaction. The gellation process will not commence or will not complete
without heat. Warm the mix and/or warm the components and/or place the
potted assembly into an oven if necessary. |
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|
PROBABLE CAUSE |
POSSIBLE FIX |
|
Blemishes due to
shrinkage |
-Significantly different wall thicknesses |
-Good part design allows for reasonably uniform wall
thickness in the encapsulant. During the curing process the thicker
sections solidify first and the shrinking material will replenish itself
from those areas that have not been cured to the same degree. Blemishes
and cosmetic defects will occur in areas where the material cures last
(thinner section). Provide uniform wall thickness or cool the thick
sections so that all areas gel at the same time. |
|
-Incorrect heat profile |
-Most often evidenced with heat cure in metallic moulds.
This requires experimentation to determine the correct heat profile.
Ideally, the material should gel half way between the insert and the inner
surface of the mould. This will require determining the correct difference
between the temperature of the insert and the temperature of the mould. |
|
-Insufficient reservoir |
-Epoxies and Polyurethanes shrink during cure. Surface
defects and a weakened structure will result if the shrinking material is
not able to replenish from a reservoir of cooler material. |
|
Cavities in the
castings |
-Excessive
localized shrinkage |
-Localized
shrinkage usually occurs over cooler areas of the curing mass. Cavities
form if the top layer of the compound, being next to the hot mould, skins
over and cures while the area below remains cooler allowing adjacent
material to draw from it to replenish shrinkage. Adjust the heat profile
to make all areas more uniform in temperature. |
| -Air entrapment |
-It is essential
to remove the air that is inevitably introduced while mixing the resin and
hardener together. The trapped air will attempt to rise to the surface as
it is heated during the reaction. The distance the bubbles will travel
depends on the viscosity of the material and the speed of gellation.
Bubbles which are unable to reach the surface before gellation will be
trapped in the structure. Trapped air reduces the structural integrity and the
electrical properties of the material. Depending on the circumstances,
some unacceptable surface blemishes could result. The easiest fix is to
de-air the mix under 29" vacuum prior to use.
Alternately, warming the mix will aid in releasing trapped air. |
| -Trapped volatile
ingredients |
-Bubbles and
blemishes can result from using a resin or a hardener that is
inappropriate for the application at hand. Some systems have been designed
for use in thin film applications and could contain volatile components
that will flash off during cure. These volatiles may be trapped in the
structure if the system is used in casting applications with heavier wall
thicknesses. The only solution is to select a different resin/ hardener
combination. |
|
|
PROBABLE CAUSE |
POSSIBLE FIX |
|
Surface
blemishes and cosmetic defects |
-Bubbles on
surface |
-If the
component being manufactured has a complex or intricate shape with a
number of corners and curvatures, there is a good chance that the air will
not be able to rise and escape fast enough from the mould cavity prior to
gellation. This will result in small surface cavities that are
cosmetically unacceptable. Increasing the number of strategically placed
vent openings will go a long way to help eliminate this problem. Filling
the tool or potting container more slowly will also have a major impact
(keep in mind the pot life). Pouring the compound into one corner only and
letting it rise slowly will also help to eliminate the problem. In severe
cases, the only solution may be to apply vacuum after the part is poured
but be careful not to strip the volatile components from the formulation
as these vapours can also be the cause of surface blemishes. If the
product has a long pot life it is possible to warm the mix to reduce the
viscosity thereby making the release of air easier. |
|
-Surface blemishes caused by
shrinkage |
-There are 3 key factors to
look at. 1) The mix temperature should not be too high since the gellation
process will be too fast resulting in increased shrinkage. 2) The mould
and insert temperatures should relate to each other so that the material
gels toward the center. 3) There should be enough of a reservoir
containing cooler material to replenish the curing product as it shrinks. |
|
-Skinned over cavities near
the surface |
-Chances are the tool or the
container is too hot. The material gels extremely fast adjacent to the
surface while the cooler material below acts as a reservoir. Cooling the
mould or container would be the first step. Cooling the mix could also
help. |
|
-Irregular patterns on the
surface |
-The probable cause is too
much or un-evenly applied mould release on the surface of the tool. If the
mould release is silicone suspended in a solvent carrier, the cause could
be that the silicone is not properly dispersed in the carrier. Applying
the mould release in an evenly sprayed fine mist is best. |
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|
|
PROBABLE CAUSE |
POSSIBLE FIX |
|
Cracking |
-Improper Mix |
-Make certain that the fillers (if any) are dispersed
thoroughly throughout the material. Ensure that there are no pockets of
unmixed hardener present in the mix. Unevenly dispersed fillers or
hardener will cause changes in the shrinkage profile causing the product
to cure with "built in stresses". |
| -Mix off ratio.
Click below for details:
Epoxy/Urethane Mix
Ratio Related Problems |
The mix ratio is based on product chemistry. If it is
incorrect there will be a change in the crosslink density. Any change in
the crosslink density will cause changes in tensile strength and the
elongation properties of the cured material. The combination of tensile
strength and elongation is key in preventing cracking. |
|
-Improper/insufficient cure |
-Most, if not all, compounds are brittle just after
gellation, before they are fully cured. All products must be cured at the
specified temperatures for the specified length of time to develop full
strength. In some cases, where a step cure is specified, full cure is not
achieved until after all the stages are complete. Curing at temperatures
other than those specified will result in less than optimal properties.
Cracking can occur if the cast component is subjected to mechanical or
thermal stresses prior to full cure. |
| -Residual built
in stresses due to improper heat profile during cure |
-Whether the system is cured at room temperature or with
the application of heat, it is important to have a uniform heat profile so
that curing takes place at a uniform rate throughout the part. For
example; zoning in a curing oven will cause the material to cure at
different rates in different areas of the part. The area that cures first
will want to replenish its shrinkage for adjacent cooler material. This
will result in built in stresses within the cured mass.
- Almost all products will cure in a more "relaxed state"
if the final cure temperature is above their Tg (glass transition
temperature). |
| -Inadvertent
thermal cycling prior to full cure |
- Almost all materials are brittle after gellation. Care
must be exercised not to subject components to undue mechanical or thermal
stresses while in this state. For example; gelling a product in an oven
and then storing the parts at room temperature prior to final post cure
would in fact be thermal cycling. |
| -Weakened areas
due to embedded sharp edges |
- Internal components, having sharp corners or sharp
pointed edges, will cause the formation of internal micro cracks as the
material shrinks during gellation. These internal cracks will propagate
further during post cure and will represent seriously weakened areas in
the encapsulant. These cracks will eventually propagate to the surface
with the application of mechanical stresses or thermal cycling. It is best
to eliminate the undesirable contours or at least cushion these surfaces
prior to encapsulation if possible. |
| -Improper
adhesion to internal components |
- Non-uniform adhesion to internal components can result in
built in stresses. The curing material can pull away from contaminated
areas as it shrinks during gellation. This will result in varied strength
within the structure. The ultimate bond strength of the particular layer
will be governed by the weakest link (i.e. the bond strength of the
contaminant to the substrate vs. the bond strength of the compound to the
contaminant). Typically areas with oily contaminants are the worst
offenders but residual mould release, grease and various chemicals will
also cause problems. |
| -Weakening due to
excessive shrinkage during cure. |
- The areas that gel last will act as reservoir to
replenish the shrinking material in adjacent areas. This could leave the
area that gels last in a weakened state, with built in stresses, just
looking for an excuse to crack. More uniform wall thickness and evenly
heated mass should fix this problem. - In some
cases, choosing another material or a different hardener may be necessary
to reduce the amount of shrinkage during gellation and cure. Filled
materials and slower hardeners tend to shrink less. |
| -Large
differences in the coefficient of thermal expansion between the embedded
components and the encapsulant. |
- Large differences in thermal expansion between the
embedded component and the encapsulant, if not compensated for, either
through the formulation or through mechanical means, could result in
cracking. Employing different types of fillers and/ or hardeners can solve
this problem. Alternately, mechanical cushioning around embedded
components may be the only solution. In some cases, utilizing a system
with higher filler content or a slower reacting hardener may solve the
problem . Compounds with higher elongation characteristics may also be
sufficient. It is best to contact the material supplier for a
recommendation |
| -Insufficient
tensile strength |
- Most often results in cracking during thermal cycling
since the material "breaks" usually at the higher temperature. Part design
has a major effect on the amount of tensile strength that is required for
the application. Part design that includes smooth, rounded corners with
heavier encapsulant wall thickness usually fare better. Alternately, an
encapsulant with a more favorable combination of tensile strength and
elongation may be required. |
| -Insufficient
elongation |
-
See above |
| -Insufficient
filler content (due to filler settling or layering during cure) |
-
Evenly dispersed fillers are critical to avoid cracking.
Care is required to make sure that the fillers remain in suspension
throughout the encapsulation process. This includes taking appropriate
precautions to prevent the fillers from layering, through settling in the
mould, prior to gellation. Moulds that are heated from the bottom are
prone to this. Thoroughly dispersed fillers and even heat throughout the
mould are the answer to this problem. Settled fillers will cause
drastically different shrinkage and stresses throughout the mass, not to
mention the differences in the resulting tensile and elongation properties
within the casting. |
|
-Insufficient heat dissipation around embedded heat
generating components |
- The strength of the cured material gradually drops as
heat is applied. The most drastic change occurs around its Tg (glass
transition temperature). If this occurs, in combination with applied
mechanical stresses, cracking could result. The most effective solution is
to provide a good metallic heat sink that is not encapsulated with the
material. Epoxies and polyurethanes are insulating materials both from the
electrical and thermal standpoint. Thermal conductivity can be improved
somewhat through formulating techniques but usually not enough to
accommodate severe requirements. |
| |
|
|
|
|
PROBABLE CAUSE |
POSSIBLE FIX |
|
Soft Spots Click below
for detailed troubleshooting:
Epoxy/Urethane Curing
and Gellation Problems |
-Incomplete Mixing.
Click below for step by step confirmation:
Epoxy/Urethane Mix
Ratio Related Problems |
-Common symptom with malfunctioning dispense equipment or
improperly mixed hand batches. Increase the mix time or trouble shoot the
automated dispense equipment. |
|
-Lead/lag problems with dispense equipment. (incorrect
amounts of resin or hardener present intermittently throughout the
dispense cycle. Most frequently evident at the beginning or toward the end
of the cycle-less often during.) |
-The most common causes are incorrect back pressures that
develop during the dispense cycle. Improperly sized or partially blocked
feed lines, an incorrectly sized mix head, defective check valves or leaky
seals will cause this problem. Confirm that the material reacts as
specified when mixed by hand in a cup. If the product is fine when mixed
by hand, it is time to overhaul the equipment. |
|
-Varying or too much back pressure in dispense equipment. |
-The soft spots appear randomly throughout the dispense
cycle. Check for leaky seals, partially blocked lines and defective check
valves. |
|
-Insufficient number of elements in static mix head.
|
-Depending on the viscosities of the components, there are
different number of mixing elements that are required to obtain a thorough
mix. Most static mix heads are designed to allow sections to be added or
removed to achieve the correct mix. Consult the supplier to obtain the
correct part. |
|
-Contaminant preventing complete cure in certain spots. |
-Certain chemical residues, coating materials etc. can
interfere with uniform gellation and cure especially if these materials
are not properly removed or fully cured and are able to mix with the
epoxy. Make certain that all these materials have been processed according
to supplier instructions and any substrates are thoroughly cleaned. |
| -Incomplete cure. |
-Material covering components that have the ability to sink
the heat generated by the curing epoxy or polyurethane away from the mix
will cure last. Surrounding areas, where this condition does not exist,
will cure first and it will be necessary to extend the time to achieve
uniform hardness throughout the encapsulant. If this time is insufficient,
the areas over the heat sinking devices may remain soft leaving the
appearance of soft spots. |
