With any mold, the venting slot is used for two purposes. One is to get the air out of the plastic injection mold cavity when the injection of materials is happening. The other use is to get rid of all the gases created during the injection molding process. Setting up the venting slots is very important, especially if you are creating thin-walled products.
Venting slots also need attention when the mold manufacturer is creating small-sized parts or components that are meant to work with precision. The main goal is protecting the finished products from any defects such as burned surfaces or lack of filling. If you want to know how much air venting you need, the best indicator is zero presence of burn marks on the product while the mold is working at the highest injection speed
Known Venting Methods
For a mold manufacturer, there are many options to work with when you need to vent a mold cavity, regardless of your choice the main goal should be a unified front. Venting has to allow the size of the vent slot to prevent molten material from entering the slot, and it also has to prevent clogging as well. It sounds difficult, but it’s doable.
If the mold has too many slots, you will have a problem, mainly because the clamping force put against the mold cavity is going to part the surface area without vent slots in a high position, making the cavity material prone to cracks. This is a dangerous development that could ruin the project altogether.
On top of being designed in the part surface of the mold cavity, the vent slot needs to be machined at the last section of the running system. The clearance that is put in place in the ejector will let out any trapped air. Vents that are not positioned with clear specifications based on height, width, and position will bring flashing to the finished products, and the project will be ruined.
Other Considerations About Venting
The clearance design also needs to be able to prevent the same flash effect in the location of the ejector pin. It also a good reminder that not all projects are alike. While aesthetics are important on quite a few finished products, others such as gears are not affected by flash at all. For better results, you can try to eliminate the air in the runner by using a peening treatment.
Peening happens when you use silicon carbide, an abrasive agent in the part surface. After doing so, you can vent the slots in the final section of the runner system, always checking the machining slots in each section of the sub-channel. The width on these should be the same as the ones in the sub-channel, and the height could vary depending on the materials being used.