Description
PMC™-121 50/WET is a two-component urethane rubber designed for mold making and flexible casting.
It cures at room temperature and is suitable for applications requiring high durability, tear strength, and elongation.
The 'WET' formulation includes a release additive, resulting in a slightly oily surface that facilitates demolding, particularly useful for casting materials such as plaster, concrete, and resins.
Features
- Mix Ratio By Volume: 1A:1B
- Mix Ratio By Weight: 1A:1B
- Working time: 30 minutes
- Cure Time: 16 hours
- Shore Hardness: 50A
- Specific Gravity: 1.04 g/cc
- Specific Volume: 0.96 cm³/g
- Color: Clear Amber
- Tensile Strength: 24.1 bar
- Elongation @ Break: 500%
- 100% Modulus: 565 kPa
- Die C Tear Strength: 14.9 kN/m
- Shrinkage: < 0.001 mm/mm
- Mixed Viscosity: 1,400 mPa·s
Suitable for industrial, artistic, and construction applications, this rubber delivers reliable, durable molds that perform well under demanding conditions.
Instructions
Preparation
Store and use at room temperature (23°C).
These products have a limited shelf life and should be used as soon as possible. Use in a low-humidity environment (below 50% RH).
Mixing containers should have straight sides and a flat bottom.
Mixing sticks should be flat and stiff with defined edges for scraping the sides and bottom of your mixing container.
Good ventilation, appropriate to the size of your workshop, is essential.
Wear safety glasses, long sleeves, and rubber gloves to minimize the risk of contamination.
Sealing and Release Agents
Some materials must be sealed as urethanes are adhesive.
Models made of porous materials (gypsum plasters, concrete, wood, stone, etc.) must be sealed prior to applying a release agent. SuperSeal™ or One Step™ are suitable for sealing porous surfaces.
Sonite Wax™ or high-grade shellac is suitable for rough contours. Thermoplastics (polystyrene) must also be sealed with shellac or PVA.
Non-porous surfaces like metal, glass, and hard plastics require only a release agent. Apply a liberal coat of release agent onto all surfaces that will contact the rubber.
Spray the release agent from various angles onto your model, then spread it evenly with a soft brush. Repeat with a second light coating, and let the release agent dry for 30 minutes.
A small test application is recommended.
IMPORTANT
The shelf life of the product is reduced after opening. The remaining product should be used as soon as possible. Immediately replacing the lids on both containers after dispensing product will help prolong the shelf life of the unused product. XTEND-IT™ Dry Gas Blanket will significantly prolong the shelf life of unused liquid urethane products.
MEASURING & MIXING - Liquid urethanes are moisture sensitive and will absorb atmospheric moisture. Mixing tools and containers should be clean and made of metal, glass, or plastic. Materials should be stored and used in a warm environment (23°C).
IMPORTANT
Pre-mix the Part B before using. After dispensing equal amounts of Parts A and B into the mixing container, mix thoroughly for at least 3 minutes, making sure to scrape the sides and bottom of the container several times.
If mixing large quantities (7 kg or more) at one time, use a mechanical mixer for 3 minutes, followed by careful hand mixing for 1 minute as directed above. Then pour the entire quantity into a new, clean mixing container and repeat.
Although this product is formulated to minimize air bubbles in the cured rubber, vacuum degassing will further reduce the amount of entrapped air. A pressure casting technique using a pressure chamber can yield totally bubble-free castings. Contact Smooth-On or your distributor for further information about vacuum degassing or pressure casting.
Pouring - For best results, pour your mixture in a single spot at the lowest point of the enclosure. Let the rubber seek its level up and over the model. A uniform flow will help minimize entrapped air. The liquid rubber should level off at least 1.3 cm above the highest point of the model surface.
Curing - Allow rubber to cure overnight (at least 16 hours) at room temperature (23°C) before demolding. Cure time can be reduced with mild heat or by adding a cure accelerator. Do not cure rubber at temperatures below 18°C.
Post-Curing - After the rubber has cured at room temperature, heating it to 65°C for 4 to 8 hours will improve physical properties and performance.
Using the Mold, apply a release agent to the mold before each casting. The type of release agent to use depends on the material being cast. The proper release agent for wax, liquid rubber, or thermosetting materials is a spray release made specifically for mold making. Prior to casting gypsum plaster, sponge the mold with a soap solution to improve plaster flow and ease the release. A water-based release concentrate is recommended for releasing abrasive materials like concrete.
Performance & Storage - Fully cured rubber is tough, durable, and will perform if properly used and stored. The physical life of the rubber depends on how you use it. Shrinkage will be higher with wet vs. dry rubbers. Contact Smooth-On directly with questions about this material as it relates to your application.
