CASTABLE MOUNTING
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CASTABLE RESIN PROPERTIES
Following cutting or sectioning the specimen is typically mounted. Mounting provides the following advantages:
- Convenient means to hold the specimen
- Provides a standard means to mount multiple specimens
- Protect edges
- Provide proper specimen orientation
- Provides a means to label and store the specimens
Castable resins are cross-linked polymers which are typically cast or potted at room temperature.
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Castable Resins |
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Room temperature mounting |
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Liquid and hardener |
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Mounting container required |
PROCESS DESCRIPTION (Castable Resins)
Castable resins are monomer resins which utilize a catalyst or hardener for polymerization. Polymerization results in cross-linking of the polymer to form a relatively hard mount. Castable resins are advantageous for mounting high volumes of samples because the cumulative amount of time required to compression mount can be significantly higher than by multiple specimen mounting with castable resins.
Castable Mounting Resins include:
- Epoxy Resins
- Acrylics (Castable)
- Polyesters (clear)
EPOXY |
ACRYLIC |
POLYESTER Resin |
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Type |
Epoxy resin and hardener |
Acrylic resin and powder |
Polyester resin and hardener |
Peak Temperature |
100-375° F |
150 ° F |
100 ° F |
Shore D Hardness |
82 |
80 |
76 |
Cure Time |
30 minutes to 8 hours |
5-8 minutes |
6-8 hours |
Comments |
Moderate hardness, low shrinkage, transparent |
Very fast curt, translucent, some shrinkage |
Transparent, water clear |
EPOXY RESINS
The most common and best performing castable resins are epoxy based. Epoxy resins are typically two part systems consisting of a resin and a catalyst (hardener). Mixing ratio's vary from 10-parts resin to 1-part hardener to 5-parts by weight of resin to 1-parts by weight of hardener and it is important that the recommended ratio of resin to hardener be maintained.
| Epoxy | Standard Epoxy | Quick Mounting Epoxy | Low Viscosity Epoxy |
| Characteristic | Lower cost | Fast cure | Lower viscosity, clearer, lower exotherm, low shrinkage |
| Cure Time | 1 hour | 30 minutes | 2 hours |
| Mixing ratio (weight) (resin : hardener) |
5:1 | 10:1 | 10:1 |
| Peak Exotherm -20 grams -30 grams |
300° F 350° F |
350° F 375° F |
120° F 150° F |
| Color | Clear to slight yellow tint | Slight yellow tint | Clear |
| Viscosity | Medium | Medium | Low |
| Shrinkage | Moderate | High | Low |
Curing time is dependent upon a number of variables including:
- Volume of mount (larger mounts cure faster)
- Thermal mass of specimen (larger specimens require longer curing time)
- Specimen material
- Initial resin temperature (higher temperatures cure faster)
- Ambient temperature (higher temperatures cure faster)
- Relative humidity and shelf life (absorption of water)
As a general rule, curing is on the order of 30-45 minutes to 24 hours for ready to grind epoxy resins (Shore D hardness approximately 80). Note that these epoxy resins typically will continue to harden over a longer period of time.
The curing time can be altered by modifying or controlling the resin temperature. For example, an 8-hour resin system can be cured in 30-45 minutes by pre-heating the resin to approximately 120°F (50°C) prior to mixing and then curing at room temperature. This procedure initiates the catalytic reaction sooner; however, this may also increase the maximum exotherm temperature.
Also the resin curing cycle can be slowed or reduced by decreasing curing temperature by forcing air over the curing mounts, placing the mounts into a water bath, or curing in a refrigirator. In this case, care must be taken not to kill the reaction, however if this does occur or the resin is too soft after curing, heating it to 100-120°F for several hours should push the reaction to completion and the mount should be hard after cooling to room temperature.
Advantages of Epoxy Resins
- Low shrinkage
- Relatively clear
- Relatively low exotherms
- Excellent adhesion
- Excellent chemical resistance
- Good hardness
ACRYLICS (Castable) - are fast curing resin systems which are useful for rapid specimen mounting. Typical acrylic mounts are ready for use within 10-15 minutes. Fillers are added to increase hardness and to reduce shrinkage.
Acrylic resins are also less sensitive to mixing ratio's and therefore tend to produce more consistent repeatable results as compared to epoxy resin.
Characteristics of Acrylics
- Rapid mounting
- Very repeatable and consistent
- Moderate shrinkage
- Good hardness
- Semi-transparent
- High odor
- Can be submerged in water during curing to reduce exotherm heat and shrinkage
| Acrylic | CASTAMOUNT | Acrylic |
| Characteristic | Fast, clear, low shrinkage | Fast, hard |
| Cure time | 8 minutes | 10 minutes |
| Mixing ratio (volume) Powder : Liquid |
3:2 or 2:1 for lower viscosity |
5:2 |
| Color | Semi-clear | Gray |
POLYESTERS - are typically used when a very clear mount is required.
Characteristics of Polyester
- Very clear (water clear)
- High odor
- Can be submerged in water during curing to reduce exotherm heat and shrinkage
RECOMMENDED PROCEDURES (CASTABLE MOUNTING)
- Clean and thoroughly dry specimens to remove cutting and handling residues
- Remove debris from molding cups
- Apply thin coat of mold release compound to molding cup
- Center specimen in molding cup
- Accurately measure resin and hardener
- Mix thoroughly (gentle mixing to avoid producing air bubbles)
- Optional
- Before mixing preheat resin, hardener and specimen to 30°C (85°F) to expedite curing cycle (Note: this will also increase maximum exotherm)
- Pour resin under vacuum conditions and/or apply pressure during curing cycle (advantages - better infiltration of pores and cracks, more transparent mounts and fewer air bubbles)
Vacuum/Pressure Mounting
For porous or cracked specimens the epoxy resin can aid in supporting these features. Filling these voids can be difficult depending upon their size. Smaller voids being much more difficult to impregnate than larger voids. This arises mainly from the compressibility and volume of air within the void. By applying a vacuum to the specimen and pouring while under vacuum the total pressure of this air can be reduced significantly. Subsequent curing at increased pressures will force or push the resin into the voids. Note that the vacuum time on both the resin and specimen should be kept to a minimum in order to minimize degassing of the resin.
Additionally, slight preheating of the epoxy will reduce the viscosity of the resin, however this will also expedite the curing cycle and maximum exotherm.
TROUBLE SHOOTING (CASATABLE RESINS)
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Symptom |
Cause |
Action |
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Lack of or partial curing of resin |
Improper or insufficient mixing |
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Soft or gummy resins (Grinding produces a matted finish) |
Insufficient curing of resin – primarily by too low an exotherm |
Heat mount in an oven at 90-100 F (30-40 C) for 1-2 hours and let cool. Resin should harden upon cooling |
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Bubbling, cracking, or yellowing of resin |
Too hot a curing exotherm |
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Too long a curing time |
Improper resin mixture, old hardener, or too cold a mounting temperature |
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Bubbles in resin |
Improper mixing or degassing of specimen |
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CASTABLE RESINS PRODUCT DESCRIPTION
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ACRYLICS (Castable) |
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Description |
Quantity |
Catalog Number |
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CASTAMOUNT Acrylic resin kit (1 lb) |
1 lb resin with 12 oz hardener |
AK-5000 |
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CASTAMOUNT Acrylic |
1 lb (454 gms) |
AR-5000-P1 |
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CASTAMOUNT Acrylic hardener (clear liquid) |
12 oz (0.36 l) |
AH-5000-H12 |
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SUPERMOUNT Acrylic kits (with filler) |
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Description |
Quantity |
Catalog Number |
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Glass Filled Acrylic kit (gray) |
1 lb powder with hardener |
GKAR-3000 |
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Glass Filled Acrylic powder (gray) |
5 lbs |
GRAR-3000-05 |
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Lliquid hardener (64 oz) |
2-32 oz containers |
GRAH-3000-H64 |
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EPOXY Resins |
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Description |
Quantity |
Catalog Number |
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Epoxy Resin |
32 oz (0.95 l) |
EP-3000-32 |
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Epoxy Hardener |
8 oz (0.24 l) |
EH-3000-08 |
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1-gallon pump dispenser |
each |
ED-3000-01 |
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QUICKMOUNT 2 Fast EPOXY Resin |
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Description |
Quantity |
Catalog Number |
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Quick Mount Fast Epoxy Resin |
32 oz (0.95 l) |
EPF-3000-32 |
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Quick Mount Fast Hardener |
8 oz (0.24 l) |
EHF-3000-08 |
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ULTRATHIN 2 Low Viscosity EPOXY Resin |
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Description |
Quantity |
Catalog Number |
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Low Viscosity Casting Epoxy Resin |
32 oz (0.95 l) |
ULTRA-3000-32 |
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| Low Viscosity Hardener | 8 oz (0.24 l) |
ULTRA-3000H-08 |
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POLYCAST Clear Polyester Resin |
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Description |
Quantity |
Catalog Number |
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Polyester Resin (1 gallon) |
32 oz (0.95 l) |
POLYCAST-32 |
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Polyester Hardener (1 oz) |
1 oz |
POLYHARD-01 |
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Castable Mounting Molds |
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Description |
Quantity |
Catalog Number |
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1.25" reuseable two piece plastic molds |
12/pkg |
METPREP-0125 |
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1.50" reuseable two piece plastic molds |
12/pkg |
METPREP-0150 |
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Disposable plastic mounting cups |
50/pkg |
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Reuseable Silicon rubber |
each |
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Phenolic Ring forms |
100/pkg |
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MISCELLANEOUS MOUNTING ACCESSORIES |
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Description |
Quantity |
Catalog Number |
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Mold release |
8 oz (0.24l) |
MR-1000-08 |
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Stirring sticks |
100 |
SS-1000-100 |
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Mixing cups (100/pkg) |
100 |
MCUPS-1000-50 |
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Plastic specimen mounting clips (100/pkg) |
100/pkg |
KLIP-0100 |
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Metal specimen mounting clips (100/pkg) |
100/pkg |
MKLIP-0100 | ||
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1.25" specimen storage containers (25/pkg) |
25/pkg |
STORE-0125 |
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