𝐓𝐨𝐝𝐚𝐲'𝐬 𝐊𝐍𝐎𝐖𝐋𝐄𝐃𝐆𝐄 𝐒𝐡𝐚𝐫𝐞 : 𝐏𝐚𝐜𝐤𝐢𝐧𝐠 𝐩𝐫𝐞𝐬𝐬𝐮𝐫𝐞 𝐚𝐧𝐝 𝐡𝐨𝐥𝐝𝐢𝐧𝐠 𝐩𝐫𝐞𝐬𝐬𝐮𝐫𝐞 𝐚𝐫𝐞 𝐧𝐨𝐭 𝐭𝐡𝐞 𝐬𝐚𝐦𝐞 𝐭𝐡𝐢𝐧𝐠

 𝐓𝐨𝐝𝐚𝐲'𝐬 𝐊𝐍𝐎𝐖𝐋𝐄𝐃𝐆𝐄 𝐒𝐡𝐚𝐫𝐞

𝐏𝐚𝐜𝐤𝐢𝐧𝐠 𝐩𝐫𝐞𝐬𝐬𝐮𝐫𝐞 𝐚𝐧𝐝 𝐡𝐨𝐥𝐝𝐢𝐧𝐠 𝐩𝐫𝐞𝐬𝐬𝐮𝐫𝐞 𝐚𝐫𝐞 𝐧𝐨𝐭 𝐭𝐡𝐞 𝐬𝐚𝐦𝐞 𝐭𝐡𝐢𝐧𝐠 — 𝐚𝐧𝐝 𝐜𝐨𝐧𝐟𝐮𝐬𝐢𝐧𝐠 𝐭𝐡𝐞𝐦 𝐜𝐚𝐧 𝐜𝐨𝐦𝐩𝐫𝐨𝐦𝐢𝐬𝐞 𝐩𝐚𝐫𝐭 𝐪𝐮𝐚𝐥𝐢𝐭𝐲.

In injection molding, the cavity is typically filled to only 95–98% capacity during the injection phase. The packing phase then pushes additional material into the cavity to compensate for volumetric shrinkage as the plastic cools. Holding pressure serves a distinct, subsequent function: it maintains equilibrium pressure to prevent molten material from flowing back out before the gate freezes.

As Suhas Kulkarni of FimmTech explains, the practical distinction depends on gate geometry and system type:

- Small gates (0.040 in. or less) freeze quickly, making a combined pack-and-hold phase acceptable

- Larger gates and hot runner systems require separate pack and hold phases

- Valve-gated molds require only a packing phase — holding pressure does not apply

Machine controllers label these stages numerically (P1, P2, P3), placing the responsibility on processors to apply correct terminology and intent.

Kulkarni's full technical breakdown of each phase, including pressure behavior at the gate, is worth reading carefully. https://lnkd.in/eETRQHUP

source : Plastics Technology