RECOMMENDED MOLD TEMPERATURES

2. John Wesley Hyatt, along with his brother Isaiah invented plastic injection molding in 1868 in response to a need for replacing carved ivory for billiard balls. Since that time, the industry has evolved from an art to a science, especially with the advent of computers, the sophistication of molding equipment, and the emphasis on proper training at all levels.

3. RECOMMENDED MOLD TEMPERATURES SPECIAL NOTE: Cooling lines in the mold (and heat exchanger, for that matter) MUST be kept clean and open to allow the temperature control system to operate efficiently. Tests show that a common 1/4" waterline with a scale buildup of only 0.015" (1/64") will result in a drop of 60% cooling efficiency. To clean, recondition, or maintain your waterlines you must flush them periodically with an acid solution. Even if you use chemical additives in a closed-loop water program, you must periodically flush the mold's waterlines with the acid solution.

4. Troubleshooting Defined For our purposes, troubleshooting can be defined as an activity that takes place to determine the cause of, and solution for, defects found in a molded part. This activity usually takes place while parts are being molded and occurs when the normal production of acceptable parts is interrupted by the unexpected production of one or more defective, unacceptable parts.

5. MACHINE Excessive Residence Time In Barrel Explanation: Under the best conditions, a shot size should represent 50% of the capacity of the injection cylinder (barrel). This will result in processing the material for one cycle while preparing the material for the next cycle. Thus, a mold requiring a four-ounce shot should be run in a machine that has a barrel with an eight-ounce capacity. The more material left in the barrel between shots, the greater the likelihood of thermal degradation. This degradation is what causes the black specks. Trapped Material Explanation: If any molten resin is trapped along the flow path (most notably in the heating cylinder), it will stay there until it degrades. When this happens, the degraded material becomes carbonized, then chars and becomes brittle. At that point, it will flake away from the area of entrapment and enter the melt stream appearing as black specks or streaks. Contamination in Injection Barrel Explanation: Any type of contamination in the injection barrel may be the cause of streaks, spots, and specks. It may be in the form of dust particles that fell from the ceiling into an open hopper, pellets from other materials, residual resin from an improper changeover, or even pieces of food that accidentally fell into a container of material ready to be placed in the hopper.

6. MACHINE Cycle Time Too Short Explanation: In the process of minimizing overall cycle times to reduce manufacturing costs, many molders reduce the cooling portion of the cycle. This results in the surface skin of the molded part not being fully solidified when the part is ejected from the mold. Because of this, some of the gases that are formed during molding are allowed to expand against this soft skin. Blisters are formed because the gases are not constrained. the mold. Screw Rotation Too Fast Explanation: A screw rotation speed that is too high will tend to ``whip'' air into the molten plastic. This excessive air may not be drawn out of the material during the molding process and pockets of the air may be forced to the surface of the molded part, forming blisters. Excessive rotation speed also causes a shearing action that can cause plasticizing gases to develop. These gases can also cause blisters. Low BaCk Pressure Explanation: The back pressure setting controls the density of the melt. A low setting results in a melt that is not dense enough to push out excessive gases. The gases may cause blisters.