INJECTION MOLDING

Sink Marks and Warp: Use Endex products to remove sink marks and reduce warping. Inject a short-shot (about 10% short) with minimum holding pressure and cushion, and gradually increase the shot size until the mold is full. This allows the gas in the melt to complete the filling of the mold, with minimum pressure on the melt. With the proper level of Endex, and adjustment of the shot size, the part will have no surface effects or splay, and the injection stresses will be minimal.

Cycle Time: The internal gas pressure improves contact with the mold cooking surfaces, while the endothermic properties of Endex contribute to the cooling of the part, and this can reduce cycle time.

Temperature and Clamp: Use of Endex may also allow a reduction in processing temperatures, and a reduction in the mold clamping force.

Use of Polymer Regrind: The decomposition products of Endex do not affect the use of regrind, since there is no residual activity in the regrind.

STRUCTURAL FOAM MOLDING

Use Level: Use levels will vary with the application, but a 1% level for Endex ABC 2750 & Endex 2650 is a good starting point. The use level can then be optimized for maximum efficiency and cost effectiveness.

Venting of the Mold: In SFM, venting is usually in the range of 0.005-0.010 inches to permit fast air escape, and thus avoid compressing the foam structure. Temporary vents can be made using adhesive-backed aluminum or lead tape (available in 0.0 05, 0.010 inch thickness from 3M)

Shot Size: Start with a shot about 25% less than the mold capacity, and adjust to fill the mold over several shots.

Holding Pressure and Cushion: Since it is the gas pressure in the melt which fills the mold, the use of holding pressure will prevent the mold from filling properly. Do not use holding pressure, and ensure that the screw bottoms out (I.e. do not use a cushion during injection).

Injection Pressure and Speed: Set the injection pressure high enough to achieve the maximum available injection speed. High speed injection usually gives the best surface quality, but some resins are sensitive to the high shear generated during fast injection and the speed may have to be adjusted to suit these materials.

Back Pressure and Screw Speed: The use of back pressure (usually 100-200 psi) improves mixing and consistency in the polymer melt. Screw speed is normally 20-50 RPM.

Temperature Profile: should be set to achieve a suitable melt temperature for the polymer, however the rear zone/hopper temperature should not be so high as to cause premature decomposition of Endex, and thus loss of gas back through the hopper. A temperature range of 380 - 420°F (193 - 215°C) at the rear zone/hopper is suitable for most polymers.

Mold Temperatures: Surface finish, skin thickness and cycle time are all affected by the mold temperatures. Hot molds usually produce thinner skins, smoother surfaces and longer cycle times than cool molds. The normal range is 60 -140°F (16 - 60°C), and the polymer manufacturer’s recommendations are usually appropriate.

Use of Polymer Regrind: The decomposition products of Endex do not affect the use of regrind, since there is no residual activity in the regrind.