When designing for Porcerax II venting steel, the following guidelines should be considered:
Depending on the emissions or gas residue given off during the molding process, the molder will have to evaluate whether to use a 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 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 gases close the pores. This can still be a feasible method if disposable inserts are used. Where extreme venting is needed, a 20-micron pore size is recommended. The 20-micron grade was developed to be used with a milled finish. When milled properly this process with the 20-micron material leaves a pore that is partially open (about 40-50 %). However, using the 20-micron pore size material and maintaining the 20-micron pore size, by EDM or polishing after milling, will vent better than 7-micron, but it will also clog faster.
Size of Area to be Vented
The producing mill recommends that at least 10% of the core and 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 core and cavity area, the lower the back pressure will be in the cavity. Due to the larger surface area, the insert will not require cleaning 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.
Note:Porcerax is typically inserted on the core side of the mold in the problem area in order to hide insert lines.
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. 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 (#9 to a #2-3 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. Certain procedures must be followed to prevent the possible, irreversible damage to the internal pore structure of the material. The texturing house selected for this procedure must be advised that they will be texturing porous, venting steel. The pores must be thoroughly cleaned and sealed prior to texturing. This insures the acid used to etch the surface does not run through the material corroding the interior structure. Performed properly, texturing Porcerax II will give the molder an unmatched finish in terms of definition.
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 come into contact with Porcerax II.