# Stretch Blow Molding (SBM) of Heavy-Wall PET: Preform Heating Profiles, Stretch Rod Speed, and Base Gate Centering
TL;DR — A heavy-wall PET bottle is made from a preform: a test-tube-shaped blank is reheated, stretched lengthwise, then blown against a cooled mold so the wall ends up where the geometry calls for it. Stretch blow molding (SBM) is the route that stages those moves, and the published record backs it at the capability level and no further — the record confirms blow molding capability; process variants such as stretch blow molding are configured per project. PET is recorded as a common bottle material, heavy-wall is a geometry rather than a material grade, dropper records measure their necks across 16/410–24/400, and verification lands on wall distribution and the neck pairing through the leakage check.
Why: The Preform Is Where Heavy-Wall PET Actually Gets Thick
- The wall thickness is decided before the blowing starts. In SBM, the preform's own wall profile determines where the blown bottle ends up thick and where it ends up thin. A heavy-wall bottle is not a standard preform blown with more patience — it starts from a heavier blank geometry, and the design of that blank is the design of the wall.
- Heavy-wall is a geometry, not a material grade. The PET in a heavy-wall bottle is the PET recorded as a common bottle material; heaviness lives in the wall profile of the part, so the discussion stays on geometry and never drifts into a material claim the record does not make.
- The three stages put precision in three different places. The heating profile controls where the preform softens, the stretch rod decides how the material travels lengthwise, and the base gate region records how the blowing forces meet the mold. Each is a craft lever, and none of them carries a published number.
- The record separates capability from configuration. Blow molding is recorded as a capability of our manufacturing system, alongside injection molding and mold/tooling development. Which variant a project runs — stretch blow molding, injection blow molding, extrusion blow molding — is not a field in the record, so it stays a per-project choice.
- The catalog carries the families the capability serves. Dropper records cover 73 models in glass and PET, and a PET bottle family is part of the product record. Both start at a blank and end at a neck that must pair with a closure or pipette.
- Verification belongs to wall distribution and the pairing. A heavy wall that is measured on the wrong place, or a neck that threads clean but does not seal, returns the program — the leak check and the finish pairing close the loop.
How: Three Stages, One Geometry Route
3.1 The preform is the blueprint of the wall
In stretch blow molding, the plastic is never blown from a flat sheet; it is blown from a preform, an injection-molded blank shaped like a test tube. The preform's wall is thicker in the zones the final bottle must keep thick, and the blowing step stretches that material outward until the body has its shape. For heavy-wall PET the preform is the load-bearing document of the whole program — change the blank and you change where every gram of material lands in the finished bottle.
The preform is produced by injection molding, a recorded capability in its own right, so the blank carries its own set of quality concerns: gate witness, mold parting, short-shot control in the thick sections. The heavy-wall logic then upgrades those concerns — a thick preform section is exactly where an interior defect hides most effectively.
3.2 The heating profile sets up the stretch
Before the stretch rod moves, the preform is heated until its amorphous wall is soft enough to move. That is the heating profile: the sequence of conditions along the preform's length that decides which zone is ready to stretch and which is still holding shape. Even heating means even stretching; uneven heating shows up immediately in the blown wall as thin spots or stubborn thick bands.
This is process common knowledge, not program data. No preform temperature, no heater zone count, no dwell time is published — the profile is developed per project against the project's preform and wall targets, and it is confirmed on the project's own blanks.
3.3 Stretch rod speed and base gate centering
The stretch rod is the mechanical core of SBM: it advances through the preform's mouth and stretches the softened wall downward before the air arrives, so the material is pulled before it is pushed. Rod speed works against the heating profile — too slow and the wall cools and resists, too fast and the throat of the bottle thins or the rod pushes past the developing geometry. The value is tuned per project against the wall distribution target.
The base of the bottle records the blow's last contact with the mold: the base gate region, where the preform's injection gate sits and where the stretched material lands last. Centering the preform over the base decides whether the critical wall readings land on-axis or wander toward one corner, and whether the gate material stays contained in the bottom rather than bleeding into the sidewall. Both the rod program and the gate centering are confirmed per project — no speed, no travel, no tolerance is in the publication.
3.4 What the record confirms: capability, material, and the geometry route
The fixed points in the published record are three. Manufacturing: blow molding, injection molding, and mold/tooling development are recorded capabilities of our manufacturing system. Material: PET is recorded among common bottle materials. Product: dropper records measure their neck window across 16/410–24/400, and a PET bottle family is part of the product record.
What the record does not carry is the variant. The blow molding entry confirms the capability only; process variants such as stretch blow molding are configured per project. The heavy-wall geometry route is the project's interpretation of the recorded material and capability — not a published attribute of either.
3.5 Verification: wall distribution first, then the pairing
Release for a heavy-wall bottle follows the bottle's own story. First the wall: the distribution target for the heavy sections is agreed per project, and the blown parts are checked against it — a heavy-wall bottle that blows thin at the shoulder has failed before any closure is fitted. Then the neck: the finish must pair inside the window the catalog measures, which for dropper bodies means 16/410–24/400.
The leakage check then takes over — a finish can thread perfectly and still fail on the seat, so pairing and seal are run as separate gates rather than one happy handshake. The neck-finish compatibility insight covers how finish classes line up with closures, the dropper-specific insight covers pipette behavior on the same bottle family, and the 12-test matrix covers the laboratory side of the same acceptance logic.
<pre class="language-mermaid"><code>flowchart LR
A[Blow molding capability<br/>recorded in the manufacturing system] –> B{SBM variant<br/>configured per project}
B –> C[Preform heating profile<br/>per project, no published values]
C –> D[Stretch rod + base gate centering<br/>per project, no published values]
D –> E[Heavy-wall PET geometry<br/>a geometry, not a material grade]
E –> F[Wall distribution check<br/>per project targets]
F –> G[Neck pairing<br/>dropper 16/410–24/400 measured]
G –> H[Leakage verification<br/>per project criteria]
H –> I[Release]
</code></pre>
What: Verified Program Data and the Verification Hooks
- Manufacturing capabilities — blow molding, injection molding, and mold/tooling development are recorded for our manufacturing system; the record confirms blow molding capability, while process variants such as stretch blow molding are configured per project, and no equipment detail is published.
- Material — PET is recorded as a common bottle material; heavy-wall is a geometry route, not a material grade, and no material-form claim is carried in the record.
- Product landscape — dropper bodies record 73 models in glass and PET; a PET bottle family is part of the product record.
- Measured neck window — dropper records measure 16/410–24/400.
- Verification hooks — the leakage check covers seal pairing; the finish-pairing logic governs how a recorded thread class lines up with its closure; laboratory coverage sits under the 12-test matrix.
- Boundary — preform heating profiles, stretch rod speed and travel, base gate centering, wall distribution targets, and all equipment parameters are configured per project and are not part of the published record.
Gotchas
- SBM is not a recorded attribute. The blow molding entry confirms the capability only; which variant produced a given bottle is not in the record, so never present stretch blow molding as the program's process.
- No heating or speed numbers exist to quote. Preform temperature, stretch rod speed, and gate centering are set per project — there are no published values because no values are published.
- Heavy-wall is a geometry, not a material grade. PET stays the recorded material; "heavy" describes the wall profile of the part, and the two must not be fused into a material claim.
- The measured window records finish classes, not wall quality. 16/410–24/400 describes thread classes on dropper records; whether a blown body hits its wall distribution target is a project check.
- Model counts do not imply process parameters. The 73 dropper models and the PET bottle family tell you the formats the capability serves — not machine counts, cycle times, or blow pressures.
- A neck that threads can still fail to seal. Pairing confirms the closure seats; leakage confirms the pairing holds — run both, in that order.
- Glass and PET dropper bodies share the window but not the process. Both record 16/410–24/400; the glass body is not a blown-polymer story, so process assumptions must not travel between the two.
- "Blow molded" does not mean "stretch blow molded." The bottle family entries in the catalog carry format and finish class; the production route behind a specific body is a project conversation.
Related Resources
- Categories: Bottles · Droppers
- Related insights: Injection Blow vs. Extrusion Blow Molding · Heavy-Wall PET vs. Glass · Neck Finish Compatibility · Dropper Pipette Viscosity Calibration · The 12-Test Lab Matrix
- Customization — stretch blow molding program configuration per project