Ensuring Fully Cured, High Quality Cast Urethane Parts

Just as pilots perform a pre-flight check to verify that all systems are working properly, it is often helpful for molders of plastic parts to review material handling methods. While many of the steps involved in mixing, pouring and curing polyurethanes are regarded as standard procedure to experienced technicians – improper methodologies are a most frequent cause of calls to our technical hotline!

Weighing

Inaccurate resin to hardener ratios often result in parts with soft, uncured areas. It is important to verify correct component mix ratios on product containers before measuring out and weighing resin, hardener and any fillers or pigments being used. The scale used for weighing must also be accurate – periodic calibration is essential!

Mixing

When mixing, resin, hardener and fillers,  stir together for one to three minutes, checking the time. Container bottom and sidewalls should be scraped frequently to ensure that all components are fully incorporated.

Temperature

Shop temperature should be monitored. The gel times and cure cycles of most materials is determined at temperatures between 75-77ºF. Colder or warmer shop temperatures will affect handling of the polymer.

Curing

To attain the physical performance properties outlined on product data sheets, stated cure cycles must be followed. For many RAMPF polyurethanes, a room temperature cure schedule is provided as well as a post-cure + room temperature cure option. If the decision is made to use a heat cure, remember to:

• Heat the oven to the specified temperature
• Preheat the mold
• Remove the mold from the oven
• Pour the part at room temperature
• Wait until the part cures enough for demolding at room temperature
• Place the demolded part back in the oven to complete the elevated temperature part of the cure cycle

The physical properties, processing details and cured performance information on RAMPF technical data sheets is critical to realizing anticipated part quality and performance. Be sure to consult the data sheet before beginning every casting project!

For more information about handling methods of urethane casting resins, contact RAMPF at 248.295.0223 or e-mail rgi-officestj@rampf-group.com. We will be happy to assist you!