When designing for Porcerax II venting steel, the
following guidelines should be considered.
Due to limited physical toughness, Porcerax 2 inserts are usually
produced more than 1” thick, so relief for proper venting can be npt holes
machined then burned on the backside instead of mere EDM flat spots on the
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
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.
Porcerax II Insert Installation
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
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.