When designing for Porcerax II venting steel, the following guidelines should be considered.

Resins Used
Depending on the emissions or gas residue given off during the molding process, the molder will have to evaluate whether to use 7 or 20-micron pore size. Resins such as ABS, polypropylene, soft type PVC, polyethylene, acrylic, polyurethane, and styrene work very well with a 7-micron (.0003") pore size. For low viscosity or talc-filled resins, it may be necessary to have an automated system reverse the airflow after each shot to purge the impurities from the pores. Rigid PVC resins will work, but only until the corrosive gasses close the pores. This can still be a feasible method if disposable inserts are used. The 20-micron pore size (.0008") will vent about 25% more gas than the 7 micron pore size. 

Size of Area to be Vented
The producing mill recommends that at least 10% of the cavity area be Porcerax II to insure proper venting. While this is not always possible, it is important to remember that the more square inches used in the cavity area, the lower the back pressure will be in the cavity. Due to the larger surface area, the insert will not require cleaning quite as often as a smaller piece. If Porcerax II is used as a core or cavity half, instead of as an insert, there may not be a need for parting line vents.

Note:The thinner the Porcerax or the shorter the distance air has to travel to the exhaust line the better the venting will be. Keep in mind the physical properties of Porcerax II. 

Surface Finish Requirements
Since most applications can be addressed using inserted pieces on the core side, an EDM finish is acceptable and will vent better than any other surface finish. Should EDM be impractical, a stoned or polished surface will provide the next best venting surface. The 7 micron pore size provides the best polished finish. It is important to remember that if the venting steel is used on the cavity side of a mold, the gloss level will be severely reduced (from #9 to #3 with PP), so matching should be considered. If a low gloss level on a textured part is desired, it can be accomplished with the 7-micron Porcerax II. 

Slide/Lifter Applications
Porcerax II can be used in slide or lifter applications. However, it is important to consider lubrication requirements on such a design. Lubricants will, in all likelihood, reduce or eliminate permeability in areas that coming into contact with Porcerax II.

Various designs for the bottom of a Porcerax insert pocket.

Porcerax II Pin Installation

Best results can be achieved by drilling a vent hole into the bottom of the pin (Figure #1). This procedure considerably shortens the "escape route" for gas.

Since highest permeability can be achieved with an EDM finish, it is desirable to EDM the bottom and sides of the drilled hole for better efficiency (Figure #2). Be sure all EDM fluids are cleaned out before installing the pin into the tool.

Conclusion 
The age-old venting problems that have faced molders for years have been solved using Porcerax II venting steel. Better mold cavity venting adds many benefits, from reduction of scrap to better cycle times. Whether it is a retrofit or engineered into the tool from the start, Porcerax II adds value to all molds.