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 Smooth-On offers a variety of liquid plastic products, each with different characteristics and properties. Why so
many? Like our rubber products, the applications for these plastics are almost endless.
Applications include:
• Making Models and Prototypes
• Reproducing Sculptures or Patterns
• Industrial Such As Making Vacuum Molds
• Special Effects (Plastics can be pigmented or painted)
Viscosity Review:
0=water; 2,500=motor oil; 100,000=molasses.
(Viscosities for liquid plastics are generally lower than viscosities of liquid rubber products.) Unfilled resins can have viscosities as low as 60 cps (such as
Smooth-Cast™ 300 & 320). These resins pour like water and do not entrap air. Cured castings are virtually bubble free. Resins that are filled (C-1508tm and
Smooth-Cast™ 385) have higher viscosities (3,000 - 4,000 cps), but give superior physical performance. If you require high impact or heat resistance, you would choose a filled system. Ask Smooth-On or your distributor which resin is best for your application.
Pot Life (Working Time)
- Smooth-On makes resin systems that have very short working times
(Smooth-Cast™ 300 and 320 each give a pot life of no more than 3 minutes), or resins with long working times (Crystal
Clear™ 204 gives a pot life of 90 minutes).
Be Aware! Know the pot life of the plastic product you are using. If you are using a fast-cast resin such as
Smooth-Cast™ 320, you have 2 ½ - 3 minutes to mix and pour liquid into the mold. If you are not careful, your liquid plastic could set up in your mixing container! Read the technical bulletin.
Durometer (The 'Shore D' scale) -
As the 'Shore A' scale is used to measure the hardness of rubber, the 'Shore D' scale is used to measure the hardness of most plastics.
The 'Shore D' scale begins at 45, which is the equivalent of Shore 95A. At this hardness, the plastic is semi-rigid and has some flexibility. These plastics have exceptional impact resistance.
General purpose casting resins (Smooth-Cast 300, 320) have a Shore hardness of 70D-75D. Tooling resins (C-1508, Smooth Cast 385) have a hardness range of 80D to 90D.
If a material is harder than 90D (such as a Smooth-On castable epoxy), its hardness is measured on a Barcol or Rockwell scale.
| Rubber |
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ShorexA |
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Very Hard |
| 00 |
20 |
30 |
40 |
50 |
60 |
70 |
80 |
90 |
95 |
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45 |
55 |
65 |
75 |
85 |
| VeryxSoft |
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Shore D |
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Plastic |
Mixing & Pouring SC-320
SC 320 (mix ratio is 1A:1B by volume) is a fast cure general-purpose casting resin. Pot life is about 3 minutes and demold time is about 10 minutes. As the technical bulletin will tell you, do not delay between mixing and pouring.
Parts A and B are dispensed in equal amounts and mixed for 90 seconds. Using the same mixing technique as used for mixing rubber, we scrape the sides and bottom several times.
After thorough mixing, pour resin into the mold at the lowest point. Letting the mixture rise from the lowest point in the mold will displace air and help minimize bubbles in the cured casting.
After 5 - 7 minutes, the resin will change color and solidify (depending on mass). In about 10 minutes, the casting can be removed from the mold (again, depending on mass).
Notice that the casting reflects all of the detail texture, etc. from the mold. A perfect reproduction of the original.
Pressure Casting
Although Smooth-On resins pour like water and readily de-air, bubbles can sometimes occur due to mold configuration or other factors. The only way to ensure 100% bubble free castings every time is to pressure cast the resin. Needed: Air Compressor with hose, Pressure Tank large enough to accommodate your mold and withstand 100
PSI.
How It Works - Mix and pour resin into the mold as directed above. As soon as the mold cavity is full, place the entire mold into a pressure tank. Place the lid on the pressure tank and attach air hose. Apply pressure by turning on the air supply. (60 PSI - 4.22 kg./mc2 or 4.15 bars). Let resin cure. Instead of vacuuming the air out of the mixture, the bubbles are pressurized out of the resin. The cured casting is 100% bubble free. Every time.
Painting The Finished Casting
• Remove the release agent using acetone (or sandblast).
• Wash with a strong dishwasher detergent.
• Apply two coats of an auto body primer (available at any auto
supply store).
• Paint with acrylic or other suitable paint.
Sections
of How to Make Molds and Castings
Moldmaking Materials
Moldmaking Process
Moldmaking
Problems and Solutions
Other Pourable Mold Configurations And
Techniques
Making A Brush-on Rubber Mold
Using Liquid Plastics
Making A Hollow Casting Using 3-D
Brush-On Mold
Spraying Mold Rubber
Mold Making Review
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Smooth-On