{"id":14857,"date":"2026-03-01T12:00:00","date_gmt":"2026-03-01T04:00:00","guid":{"rendered":"https:\/\/zetarmold.com\/?p=14857"},"modified":"2026-04-09T08:05:41","modified_gmt":"2026-04-09T00:05:41","slug":"unikanie-formowania-wtryskowego","status":"publish","type":"post","link":"https:\/\/zetarmold.com\/pl\/unikanie-formowania-wtryskowego\/","title":{"rendered":"Jak unikn\u0105\u0107 strumieniowania w formowaniu wtryskowym?"},"content":{"rendered":"
\n Kluczowe wnioski<\/strong>
\n \u2013 Jetting occurs when molten plastic shoots through the gate as a free stream instead of flowing smoothly against the mold wall, creating a snake-like pattern on the part surface.
\n \u2013 The primary fix is reducing injection speed during the initial fill phase to 10\u201330% of normal speed, then ramping up once the melt contacts the opposite cavity wall.
\n \u2013 Gate design is the most important mold factor\u2014switching from a pinpoint gate to a fan gate or tab gate eliminates jetting at the source.
\n \u2013 Increasing melt temperature by 10\u201320\u00b0C reduces material viscosity and promotes smoother flow entry into the cavity.\n<\/div>\n

What Is Jetting in Injection Molding?<\/h2>\n

Jetting is a surface defect where molten plastic enters the mold cavity as a narrow, high-velocity jet instead of spreading out in a smooth, expanding melt front. The result is a distinctive snake-like or worm-track pattern on the part surface, usually visible near the gate area. In our factory, jetting is one of the most recognizable defects\u2014once you’ve seen it, you never mistake it for anything else.<\/p>\n

\n \"Examples
Injection molding defects\u2014jetting creates distinctive surface patterns<\/figcaption><\/figure>\n

The jet of plastic flies across the cavity and folds back on itself as it piles up against the opposite wall. Because the jetted material has partially cooled during its flight, it doesn’t fuse properly with the material that fills in around it. This creates visible lines, rough texture, and potentially weak spots where the jetted stream meets the bulk fill.<\/p>\n

What Causes Jetting to Occur?<\/h2>\n

Jetting happens when the pr\u0119dko\u015b\u0107 wtrysku<\/a>1<\/a><\/sup> is too high relative to the gate geometry, causing the melt to squirt through the gate rather than flow against the nearest cavity wall. We’ve identified several specific conditions that create jetting.<\/p>\n

\n \"Injection
Understanding flow dynamics helps prevent jetting<\/figcaption><\/figure>\n\n\n\n\n\n\n\n\n\n\n
Przyczyna<\/th>\nMechanism<\/th>\nLikelihood<\/th>\n<\/tr>\n<\/thead>\n
Excessive initial injection speed<\/td>\nMelt accelerates through the gate and becomes a free jet<\/td>\nBardzo wysoka<\/td>\n<\/tr>\n
Small gate with large cavity behind it<\/td>\nHigh velocity through small orifice with no wall to redirect flow<\/td>\nWysoki<\/td>\n<\/tr>\n
Gate facing open cavity (not a wall)<\/td>\nNo nearby surface to contact and start fountain flow<\/td>\nWysoki<\/td>\n<\/tr>\n
Low melt temperature<\/td>\nHigher viscosity increases jet velocity through the gate<\/td>\n\u015aredni<\/td>\n<\/tr>\n
Cold slug in nozzle<\/td>\nSolid slug pushes through gate, followed by high-velocity melt<\/td>\n\u015aredni<\/td>\n<\/tr>\n
Sharp gate edges<\/td>\nAbrupt transition creates a nozzle effect that accelerates the melt<\/td>\n\u015aredni<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

The single most common cause we see is a small gate (pinpoint or submarine) directing melt into a large open cavity with no opposing wall nearby. The melt has nowhere to contact and spread\u2014so it jets.<\/p>\n

\n

<\/svg> “Jetting is purely a cosmetic defect and has no effect on part strength.”<\/b>Fa\u0142sz<\/span><\/p>\n

While jetting is highly visible as a surface defect, the jetted material doesn’t fuse well with surrounding material because it has partially cooled during free flight. This creates weak boundaries within the part, potentially reducing impact strength by 20\u201340% in the affected area. Parts with severe jetting can fail under stress at the jet-to-bulk interface.<\/p>\n<\/div>\n

\n

<\/svg> “Reducing the initial injection speed is the fastest and most effective process fix for jetting.”<\/b>Prawda<\/span><\/p>\n

By slowing the injection speed to 10\u201330% of normal during the first 5\u201315% of cavity fill, the melt enters gently enough to contact the nearest cavity wall and establish proper fountain flow. Once fountain flow is established, speed can be ramped up to normal for the remainder of the fill.<\/p>\n<\/div>\n

How Do You Adjust Process Parameters to Prevent Jetting?<\/h2>\n

Process adjustments are the first line of defense against jetting because they don’t require mold modifications. We’ve developed a proven sequence that resolves jetting in 80% of cases through machine settings alone.<\/p>\n

\n \"Injection
Precise machine control is essential for preventing jetting<\/figcaption><\/figure>\n

1. Use Multi-Stage Injection Speed:<\/strong> This is the most effective fix. Set the first stage (0\u201315% of fill) to 10\u201330% of normal injection speed. Once the melt has established contact with the cavity wall and formed proper fountain flow<\/a>2<\/a><\/sup>, ramp up to full speed for the remaining fill.<\/p>\n

2. Increase Melt Temperature:<\/strong> Raise barrel temperature by 10\u201320\u00b0C. Lower viscosity at higher temperature means the melt is less likely to form a coherent jet\u2014it spreads out more readily on entering the cavity.<\/p>\n

3. Increase Mold Temperature:<\/strong> Raise mold temperature by 10\u201315\u00b0C. A warmer mold surface helps the melt spread instead of solidifying on contact, promoting adhesion between the initial jet (if any) and subsequent fill.<\/p>\n

4. Reduce Holding Pressure Switch Position:<\/strong> If you’re switching from injection to holding pressure too late, the melt is still being injected at high velocity when jetting occurs. Adjust the V\/P switchover point to reduce the high-speed fill phase.<\/p>\n

5. Ensure Proper Nozzle Temperature:<\/strong> A cold nozzle can create a cold slug that blocks the gate, then breaks free as a projectile followed by high-velocity melt. Maintain nozzle temperature at or slightly above barrel temperature.<\/p>\n

What Gate Design Changes Eliminate Jetting?<\/h2>\n

If process adjustments don’t fully resolve jetting, gate design is almost always the root cause. The right gate design prevents jetting by directing the melt against a cavity wall immediately upon entry, establishing fountain flow from the start.<\/p>\n

\n \"Edge
Edge gate design directs melt flow against the cavity wall<\/figcaption><\/figure>\n\n\n\n\n\n\n\n\n\n\n
Typ bramki<\/th>\nJetting Risk<\/th>\nDlaczego<\/th>\nNajlepsze dla<\/th>\n<\/tr>\n<\/thead>\n
Pinpoint Gate<\/td>\nWysoki<\/td>\nSmall orifice creates high-velocity jet<\/td>\nSmall parts (use with slow initial speed)<\/td>\n<\/tr>\n
Submarine Gate<\/td>\n\u015arednio-wysoki<\/td>\nBelow parting line, often into open cavity<\/td>\nAuto-degating (requires speed profiling)<\/td>\n<\/tr>\n
Edge Gate<\/td>\nNiski<\/td>\nMelt directed along cavity wall<\/td>\nMost applications<\/td>\n<\/tr>\n
Fan Gate<\/td>\nVery Low<\/td>\nWide entry spreads melt across cavity<\/td>\nFlat parts, panels<\/td>\n<\/tr>\n
Tab Gate<\/td>\nVery Low<\/td>\nSacrificial tab absorbs initial jet<\/td>\nParts with high cosmetic requirements<\/td>\n<\/tr>\n
Cashew Gate<\/td>\n\u015aredni<\/td>\nCurved path reduces velocity<\/td>\nAuto-degating with reduced jetting<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

The most reliable anti-jetting gate design is one where the melt enters the cavity and immediately hits an opposing wall within 2\u20133 mm. This forces the melt to spread out and establish fountain flow. When we design new molds for jetting-prone geometries, we always specify gate orientation toward the nearest cavity wall.<\/p>\n

\n

<\/svg> “Increasing the injection speed helps solve jetting because it forces the melt to fill faster.”<\/b>Fa\u0142sz<\/span><\/p>\n

Increasing injection speed makes jetting worse, not better. Jetting is caused by excessive melt velocity through the gate. The correct approach is to decrease the initial injection speed to allow the melt to contact the cavity wall and establish fountain flow before ramping up speed for the remainder of the fill.<\/p>\n<\/div>\n

\n

<\/svg> “A tab gate or fan gate design virtually eliminates jetting by spreading the melt entry across a wider area.”<\/b>Prawda<\/span><\/p>\n

Fan gates and tab gates distribute the melt across a wider cross-section, dramatically reducing the local velocity at the gate entry point. Fan gates spread melt across the full part width, while tab gates absorb the initial high-velocity jet in a sacrificial tab that is trimmed after molding.<\/p>\n<\/div>\n

What Role Does Material Choice Play in Jetting?<\/h2>\n

Material viscosity and flow characteristics significantly influence jetting tendency. In our experience, lower-viscosity materials are more prone to jetting because they flow more easily through small gate openings at high velocity.<\/p>\n

\n \"Plastic
Material flow characteristics affect jetting susceptibility<\/figcaption><\/figure>\n