The potential of enhanced venting materials

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As long as conventional wisdom was the guideline on an original mould design, new venting materials would only be used to retrofit an existing mould to solve the worst problems. Although retrofitting is not difficult - a simple installation of the material in the core side, close to the problem area and opening the back side to the atmosphere - oftentimes, waterlines or other obstructions prevent placement of the material in the right spot.

Using the material in the original design and build of the mould enables it to be installed in the most effective area(s). It makes me wonder how many moulders still are producing substandard parts because they are fighting venting problems that would not exist if they had designed the original mould using an enhanced venting steel.

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Eliminating flow lines, haloing around the edges

The advantage of using an enhanced venting steel in an original installation was the basis of collaborative experiment among an automotive OEM, a moulder and a mould builder. The challenge was eliminating flow lines and haloing around the edges of automotive texture standards plaques.

The standard mould design for these 8.5-by-11-by-0.125-inch-thick plaques required a full edge gate (10 by 0.060 inches) and land vents 0.5-inch wide by 0.002-inch deep located every 0.5 inch around the perimeter (50% of the parting line). A new cavity was built with the same gate, but the only venting was a 10.5-inch piece of porous venting steel opposite the gate. Parts were run side by side to ensure identical temperatures for the mould, resin and machine.

The results of using porous metal inserts and no additional venting were chronic flow lines disappeared, ghosting at the edge of the plaques was eliminated, virtual elimination of material splay, reduced injection pressure, increased injection speed, 10°F decrease in nozzle temperature, nearly 4% reduction in shot size, and appropriate gloss and appearance.

Still, there has been no revolution in the industry. However, we’ll continue the fight with education on how to use enhanced venting steels from original part and mould design. Maybe a design contest would work, asking for the most creative solution to a moulding challenge using porous metal in the original mould design. First prize could be 5 pounds of venting steel. Maybe this will get the revolution started.

Reprinted with permission from MoldMaking Technology, Gardner Business Media, Ohio, US, moldmakingtechnology.com

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