Thermoplastics have a lot of good attributes, but they aren’t perfect. Thicker ribs or walls will show sink marks. Surfaces can show the signs of minor impacts or scuffs.
Larger parts with thicker sections require longer cycle times to ensure there is no part deflection upon mold opening. When part designs result in molding issues, chemical foaming agents can be an effective tool to improve the finished product.
Chemical foaming agents are added to a thermoplastic compound to replace resin with gas. The foaming agent decomposes due to heat and releases gas into the melt when it’s inside the mold. Different thermoplastics react differently to different foams. When evaluating foaming agents as an option, it’s best to work with a foaming agent manufacturer to determine the right foam for your material and process Reedy Chemical is an industry leader in Foaming agents: http://www.reedychemicalfoam.com/
Hi-Tech Mold & Tool uses chemical foaming agents for three primary reasons: 1) Reducing or eliminating sink marks, 2) Part Aesthetics (post impacts/scuffs) 3) Reduce cost via weight or cycle time Above are two pictures of the same part, one before foam and one after foam. The sink marks that are caused by the thicker walls and ribs are reduced because there is less resin while it is cooling and shrinking. The foam expands while the thermoplastic is cooling thus offsetting the tendency to sink due to shrinkage.
Hi-Tech molds and assembles cases that primarily use foam to hide scuffs or impacts. Larger molded surfaces can tend to show scuffs due to minor impacts that a holding case might go thru. The foam helps to break up the aesthetics of the larger surface and thus camouflage bumps and bruises.
Chemical foaming agents can also be used to reduce cost in the molding process. The foaming agent can allow for faster fill times and shorter cooling times. Injection pressures will be reduced when using a foaming agent and the material will solidify faster due to less resin. Customers will always need to perform their own testing to ensure that a part meets their requirements, as add foam does represent a change to the material
Chemical foaming agents are one of many tools that Hi-Tech uses to optimize thermoplastic injection molding. Please contact Hi-Tech if you have any questions or would like our help on your next project.