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PACE Technologies metallographic Compression Mounting consumables
Metallographic Compression Mounting Information



Metallographic Compression Mounting

Compression mounting is a very useful mounting technique which can provide better specimen edge retention compared to castable mounting resins. Compression mounting resins are available in different colors and with various fillers to improve hardness or conductivity.

Several compression mounting characteristics include:

TERAPRESS metallographic compression mounting press

Compression mounts are quick and easy to produce, requiring several minutes to cure at the appropriate mounting temperature. Most of the time required in compression mounting occurs during the heating and cooling cycles. When choosing a compression mounting machine, the most important features include its maximum heating temperature and how intimately the heater and water cooler are connected to the mold assembly. The better compression mounting machines have heaters which can reach temperatures of at least 200°C ( 450°F). For faster turn around time, water cooling is essential.


Compression mounting resins include:
Phenolic (bakelite) compression mounting resin Diallyl phthalate metallographic compression mounting resin
Glass-filled metallographic epoxy compression mounting resin Metallographic conductive compression mounting resins


PACE Technologies metallographic Compression Mounting consumables
Compression Mounting Resin Properties

There are a variety of compression mounting materials. The two main classes of compression mounting materials are thermoset and thermoplastics. Thermoset resins require heat and pressure to cross-link the polymer and the reaction is irreversible. Thermoplastic, on the other hand, can theoretically be remelted.

See the following tables for more specific information for the various compression mounting resins.

Phenolics Acrylics Epoxy
(glass filled)
Diallyl
Phthalates
Cost Low Moderate Moderate Moderate
Ease of use Excellent Moderate Good Good
Availability of colors Yes No No Yes
Cycle times Excellent Moderate Good Good
Edge retention Fair Good Excellent Excellent
Clarity None Excellent None None
Hardness Low Medium High High

TIP: Compression mounting at higher then the recommended minimum temperature generally improves the properties of the mount.

TIP: A useful tip for marking or identifying a specimen is to mold the label inside of the mount. If the entire mount is an acrylic, just place the label on top the mount and cover it with a little acrylic powder. To label other compression mounting resins, add a thin layer of acrylic over the other mounting material and then position the label on this layer. Finish off the mount with another layer of acrylic.

Metallographic acrylic compression mounting

Phenolics Acrylics Epoxy
(glass filled)
Diallyl
Phthalates
Form Granular Powder Granular Granular
Specific gravity
(gm/cm3)
1.4 0.95 1.75-2.05 1.7-1.9
Colors Black, Red, Green, Orange, White Clear Black Blue
Shrinkage (compression)(in/in) 0.006   0.001-0.003 0.001-0.003
Coefficient of Linear Thermal Expansion
(in/in/°C 10-6)
50   28 19

Chemical resistance

Glycol, petrochemicals, solvents, some acids and bases Alcohol, dilute acids & alkalies, and oxidizers Solvents, acids, alkalies Solvents, acids, alkalies
Molding temperature 200°C (392°F) 220°C (428°F) 200°C (392°F) 200°C (392°F)

Hardness

  Rockwell M63 Barcol 72  

Curing time
(1/2" mount @ temp.
and pressure)

8-10 minutes 12-15 minutes 8-10 minutes 8-10 minutes

Note Phenolics:
-In general, phenolics are used because of their relatively low cost. In addition, phenolics are available in a variety of colors.

Undercured phenolic compression mounting resin mounts

TIP: Use different color phenolics to color code jobs, specimens types, or for different testing dates. For example, changing the phenolic color each month will show which samples or jobs are getting old.

TIP: If the color dye in the mount bleeds out when rinsing with an alcohol, this is an indication that the mount was not cured either at a high enough temperature or for the proper length of time.

Acrylics: The main application for compression mounting acrylics is based on their excellent clarity. This is particularly important for locating a specific feature within the specimen mount.
Cotton ball effect in compression mounted acrylic resins

TIP: A common problem, know as the “cotton ball” effect, can occur with thermoplastic resins if they are heated to too high a temperature too fast so a liquid layer forms around the unmelted resin giving it the appearance of a cotton ball in the middle of the mount. To avoid this problem mount at a lower temperature (120-140°C), however, to correct this problem after the fact, simply put the mount back into the mounting press and either increase the time. Eventually this will eliminate the “cotton ball.”

Epoxies / Diallyl Phthalates:
Glass-filled epoxies and diallyl phthalates are compression mounting resins used to provide a harder mounting support edge next to the specimen. These resins are commonly used to support the edges of coatings, heat treated samples and other specimens requiring better flatness. The following figure shows the polished interface between a glass-filled epoxy and tungsten carbide specimen. Note that there is no noticeable gap between the specimen and the mounting material, therefore showing that glass-filled epoxies provide excellent support to the specimen edge even for extremely hard specimens.

Edge retention for glass-filled metallographic mounts
Polished edge for tungsten carbide mounted in glass-filled epoxy.

TIP: Epoxies (glass-filled) and diallyl phthalates are significantly more expensive then phenolic and acrylics. In order to reduce the cost of these mounts, they can be laminated with a lower cost mounting compound such as a phenolic. The technique is to place a sufficiently thick enough layer of the glass-filled epoxy or diallyl phthalate around the specimen in order to compensate for any grinding loss. The rest of the mount can then be supported with a lower cost compression mounting compound such as a phenolic. Red phenolics are used frequently for this technique.

Phenolic and glass-filled epoxy for cost reduction of metallographic mounts

Specialized Compression Mounting Resins: - With the addition of fillers such as graphite or copper, the compression mounting compounds can be made conductive. Conductive mounts are used in scanning electron microscopes (SEM) to prevent the specimen from building up a charge. Conductive mounts are also used for specimens requiring electrolytic etching or polishing.


PACE Technologies metallographic Compression Mounting consumables
Recommended Compression Mounting Procedure
TIP: Preheat resin and sample to 35°C (95°F) to expedite the initial heating process and for increasing throughput.

PACE Technologies metallographic Compression Mounting consumables
Compression Mounting Trouble Shooting

Symptom Cause Action
Large bubbles in acrylic resins Curing temperature too high or mounting press has insufficient mounting pressure Reduce temperature (120-140°C) and increase mounting pressure
Soft surfaces on mount Mount did not completely polymerize because of polymer incompatibility with mold release or oil on the specimen surface Clean specimen and mounting machine to remove incompatible coatings. Use a compatible mold release
Voids or cracks High internal stress due to overly rapid cooling Allow mounts to cool more slowly and longer
Haze around specimen (acrylic mounts) Specimen contains moisture
Specimens contain copper or some other polymerization retarding alloy
Use a desiccator or low
temperature oven to dry specimen Coat specimens with an appropriate lacquer before mounting
Phenolic dye leaching out with alcohol rinsing Insufficient mounting temperature Increase mounting temperature or service check heater element
Distortion or cracking of specimen Autoclave pressure is too great for the specimen Reduce mounting pressure or use a castable epoxy resin


PACE Technologies metallographic Compression Mounting consumables
Product Descriptions

Phenolic Mounting Resin
Description Quantity Catalog Number Product Image
Phenolic powder - Black 5 lbs (2.3 kg)
25 lbs (11.4 kg)
CM-2001B-5
CM-2001B-25
Metallographic phenolic compression mounting
Phenolic powder - Red 5 lbs (2.3 kg)
25 lbs (11.4 kg)
CM-2001R-5
CM-2001R-25
Metallographic phenolic compression mounting
Phenolic powder - Green 5 lbs (2.3 kg)
25 lbs (11.4 kg)
CM-2001G-5
CM-2001G-25
Metallographic phenolic compression mounting
Phenolic powder - Orange 5 lbs (2.3 kg)
25 lbs (11.4 kg)
CM-2001OR-5
CM-2001OR-25
Metallographic phenolic compression mounting
Phenolic powder - White 5 lbs (2.3 kg)
25 lbs (11.4 kg)
CM-2001W-5
CM-2001W-25
Metallographic phenolic compression mounting

PACE Technologies metallographic castable mounting consumables

TRANSACRYLIC Compression Mounting Resin
Description Quantity Catalog Number Product Image
TRANSACRYLIC Resin powder (transparent) 5 lbs (2.3 kg) CM-2101A-5 Metallographic compression mounting acrylic
TRANSACRYLIC Resin powder (transparent) 25 lbs (11.4 kg)
CM-2101A-25

PACE Technologies metallographic castable mounting consumables

EPOXY (Glass Reinforced) Compression Mounting Resin
Description Quantity Catalog Number Product Image
EPOCOMP Epoxy Compression Resin powder 5 lbs (2.3 kg)
25 lbs (11.4 kg)
EP-2201A-5
EP-2201A-25
Metallographic compression mounting glass filled epoxy
EPOCOMP Epoxy FINE Compression Resin powder 5 lbs (2.3 kg)
25 lbs (11.4 kg)
EPF-2201A-5
EPF-2201A-25

PACE Technologies metallographic castable mounting consumables

Diallyl Phthalate Compression Mounting Resin
Description Quantity Catalog Number Product Image
Diallyl Phthalate Compression Resin powder (short-glass filled) 5 lbs (2.3 kg)
DY-2301A-5
Metallographic compression mounting diallyl phthalate
Diallyl Phthalate Compression Resin powder (short-glass filled) 25 lbs (11.4 kg) DY-2301A-25

PACE Technologies metallographic castable mounting consumables

Conductive Mounting Resin
Description Quantity Catalog Number Product Image
Conductive (graphite) Compression Resin powder 2.5 lbs (1.1 kg)
5 lbs (2.8 kg)
CONDUCTO-1
CONDUCTO-5
Metallographic compression conductive mounting
Conductive (copper) Compression Resin powder 2.5 lbs (1.1 kg)
5 lbs (2.8 kg)
CONDUCTO-CU1
CONDUCTO-CU5

PACE Technologies metallographic castable mounting consumables

Miscellaneous
Description Quantity Catalog Number Product Image
30 ml measuring scoop 30 ml MS-1000-30 Metallographic compression mounting
Mold release 8 oz (0.24l)
16 oz (0.47l)
MR-1000-08
MR-1000-16
Metallographic compression mounting


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