Blow Molding Industry Terminology

Accumulator Head

A storage chamber on an extrusion blow molding machine that accumulates a shot of molten plastic and then rapidly extrudes a parison; used for large/thick-walled parts and precise weight control.

increase accumulator shot size to bring part weight into spec; accumulator head reduces parison sag on 20 L jerrycans; tune accumulator push speed to improve wall distribution.

Additive Package

The blend of performance additives compounded into a resin (e.g., UV stabilizers, colorants, slip, antiblock, antistat, reheat, scavengers) to meet application requirements.

specify additive package with 0.3% UV; reheat additive sped up ISBM cycle; additive package caused label adhesion issues.

Barrier Layer

A layer (e.g., EVOH, nylon/MXD6) in a multi-layer structure that reduces permeation of oxygen, CO2, or hydrocarbons.

6-layer HDPE/EVOH fuel tank; increase EVOH layer ratio to meet OTR spec; adhesive tie-layer failure delaminated barrier layer.

Biaxial Orientation

Molecular alignment in both axial and hoop directions during stretch blow molding that improves stiffness, barrier, and clarity.

set axial 3.0x and hoop 3.5x stretch; insufficient orientation lowered top load; colder preforms reduced biaxial orientation.

Blow Pin

A pin/needle that seals at the neck and introduces compressed air to inflate the parison or preform.

blow pin misalignment scarred neck finish; switch to needle-blow for small orifice; adjust blow pin air delay to 0.15 s.

Blow-Up Ratio

The ratio of final container diameter to initial parison/preform diameter; key variable for wall distribution and orientation.

run BUR at 2.6 to thin shoulder; high BUR caused pearlescence; reduce BUR to strengthen handle area.

Clamp Force

The force that keeps the mold closed against internal blowing pressure and pinch-off forces, typically measured in tons.

flash indicates insufficient clamp force; verify 80 tons for 4-cavity 1 L bottle; clamp drift lowered OEE.

Co-Extrusion

Simultaneous extrusion of multiple melt streams into a single multi-layer parison through a feedblock/spiral die.

3-extruder co-ex for stripe indicator; co-ex EVOH for oxygen barrier; tie-layer adhesion issue during co-ex startup.

Deflashing

Removal of excess material (flash) formed at the pinch-off/parting line using trimmers, knives, or robots.

move to inline deflashing to cut labor; redesign pinch-off to reduce deflashing time; route flash to grinder for regrind.

Die Gap

The adjustable opening at the extrusion die that determines parison wall thickness; often varied over time via parison programming.

widen die gap at shoulder region; closed-loop die gap control stabilized weight; too large die gap caused overweight base.

EBM (Extrusion Blow Molding)

Process where a molten parison is extruded, captured in a mold, inflated with air, cooled, and ejected; includes continuous, intermittent, and accumulator variants.

selected intermittent EBM for oval bottles; EBM cycle time at 14 s; converting from EBM to ISBM for clarity.

Extruder L/D Ratio

The length-to-diameter ratio of an extruder screw; influences melting, mixing, output, residence time, and degradation risk.

upgrade from 24:1 to 30:1 for PCR blending; higher L/D improved color dispersion; too long L/D increased resin degradation.

FAI (First Article Inspection)

A complete dimensional and material verification on initial production to confirm conformity to design before full release.

submit FAI with ballooned drawings; FAI revealed short neck finish; customer requires FAI before PPAP.

Flash

Thin excess plastic at the parting line or pinch-off that must be trimmed; excessive flash signals tooling or process issues.

flash spec <0.3 mm; mold wear increased flash; collect flash for regrind.

Gate (Injection Gate)

The location/style where molten resin enters a preform or IBM parison; affects vestige, crystallinity, and flow-induced defects.

center-gated PET preform; gate blush near heel; reduce gate freeze time to shorten cycle.

GPI Finish

Standardized bottle/closure neck finish dimensions defined by the Glass Packaging Institute (e.g., 28-410, 38-400).

specify 28-410 GPI on drawing; torque spec depends on GPI finish; cap supplier requested GPI finish details.

HDPE

High-Density Polyethylene commonly used in EBM for jugs and industrial containers; offers stiffness and chemical resistance.

select HDPE with MFR 0.3 g/10 min; TiO2 masterbatch for opaque HDPE; switch from HDPE to PP for hot-fill resistance.

Hot Runner

A heated manifold/nozzle system in injection molding (preforms/IBM) that delivers melt without cold runners.

hot runner balance issue caused short shots; hot-tip temperature caused stringing; hot runner PM scheduled quarterly.

IBM (Injection Blow Molding)

Process where a parison is injection molded onto a core rod, indexed to a blow station, inflated, cooled, and ejected; precise necks, small bottles.

IBM selected for pharma droppers; 12-cavity IBM wheel; short shots at the injection station.

IML (In-Mold Labeling)

Label is placed in the mold and bonded to the container during molding, eliminating post-labeling.

IML improved scuff resistance; robot mispick caused missing labels; switch to PP IML film for recyclability.

Intrinsic Viscosity (IV)

A measure of polymer molecular weight, especially for PET; impacts stretchability, top load, and processability.

PET IV 0.80 dL/g; improper drying lowered IV; low IV hurt top load.

ISBM (Injection Stretch Blow Molding)

Preforms are injection molded and then stretch-blown (single-stage or reheat 2-stage) to form bottles with biaxial orientation.

2-step ISBM for CSD bottles; single-stage ISBM for cosmetics; optimize reheat lamps for ISBM.

JIT (Just-In-Time)

Lean inventory approach delivering materials exactly when needed to reduce WIP and storage costs.

JIT resin deliveries; JIT risk during supply shocks; align molding rate to JIT schedule.

Knit Line

A weld line where two melt fronts meet (or at pinch-off); potential mechanical and cosmetic weak point.

knit line visible on handle; increase melt temperature to strengthen knit line; Cpk failed at knit line tensile test.

Layer Ratio

The percentage distribution of each layer in a co-extruded structure.

70/5/25 HDPE/EVOH/HDPE; adjust layer ratio to meet OTR; thickness gauge caught layer ratio drift.

Leak Test

Verification of container integrity via pressure/vacuum decay, mass flow, or high-voltage methods.

inline 100% pressure-decay test; HVLD for pharma bottles; reject rate correlated with weight variation.

Melt Flow Index (MFI/MFR)

A standardized measure of polymer flow under load; inversely related to viscosity and roughly to molecular weight.

spec MFR 0.3 g/10 min for jugs; high MFR increased parison sag; blend MFR lots to stabilize weight.

Mold Venting

Small channels or clearances that allow trapped air to escape during blowing, improving surface replication and reducing burns.

add vents near logo; clean clogged vents to stop splay; vent depth set to 0.02 mm.

Neck Finish

Detailed geometry of threads, sealing surface, and tamper bead on the bottle neck; critical for closure compatibility.

38-400 neck finish; neck ovality out of spec; protect neck finish during deflashing.

NPI (New Product Introduction)

The cross-functional process to industrialize a new product, including DFM, trials, validation, and ramp-up.

run DOE during NPI pilot; gate 4 requires mold FAT; compressed NPI timeline increased risk.

OEE (Overall Equipment Effectiveness)

Composite metric of manufacturing effectiveness: Availability × Performance × Quality.

OEE improved from 58% to 72%; microstops hurt OEE; SMED boosted OEE by cutting changeovers.

Parison

The extruded molten tube captured by the mold in EBM; its temperature, thickness, and stability drive final wall distribution.

control parison sag with lower melt temp; measure parison drop time; adjust parison length for handle reach.

Parison Programming

Timed variation of die gap (via PWDS/Moog) to redistribute parison thickness along the vertical profile.

add thickness in zone 6 for base; 128-point parison profile; close-loop feedback stabilized programming.

PCR (Post-Consumer Recycled)

Reprocessed plastic from consumer waste streams; used as a layer or mono-material for sustainability targets.

25% PCR claim on label; black specks increased with PCR; FDA LNO for rPET PCR.

PET

Polyethylene terephthalate used mainly in ISBM; must be dried and reheated; good clarity and gas barrier when oriented.

dry PET to <50 ppm moisture; optimize preform reheat profile; 38 g preform for 2 L CSD bottle.

Pinch-Off

Mold feature that seals the parison and forms flash; geometry affects weld strength and leak risk.

increase pinch-off land width; pinch-off wear caused leaks; refine pinch angle to reduce stringing.

PPAP (Production Part Approval Process)

Automotive quality submission demonstrating readiness and capability (e.g., control plan, PFMEA, dimensional, MSA).

submit Level 3 PPAP; Cpk for critical dims in PPAP; customer rejected PPAP for missing PSW.

Preform

Injection-molded precursor (PET or IBM parison) that is reheated and stretch-blown into the final container.

preform weight 23 g; gate crystallinity too high; short-shot preforms detected.

Process Capability (Cp, Cpk)

Statistical indices measuring process spread and centering relative to specification limits.

weight Cpk > 1.33; neck ID Cp only 1.0; use SPC to monitor Cpk over shifts.

QMC (Quick Mold Change)

Methods and tooling (e.g., standardized hook-ups, clamps, carts) to reduce mold/format changeover time.

QMC cut changeover from 6 h to 90 min; use quick-connect water lines; combine QMC with color-change SMED.

QMS (Quality Management System)

Formalized quality processes and documentation (e.g., ISO 9001, IATF 16949, ISO 15378) ensuring consistent output.

internal audit found QMS gap; CAPA process tightened; QMS governs regrind limits.

Regrind

Ground scrap/flash reintroduced into the process; must manage contamination, properties, and lot traceability.

limit regrind to 20% in HDPE; fines caused gels; segregate regrind by color.

Resin

Base polymer feedstock used for molding (e.g., HDPE, PP, PET, PVC, PC, EVOH), typically supplied as pellets.

verify resin COA on receipt; resin price volatility hit margins; adjust drying per resin datasheet.

Screw Design

Extruder screw geometry (feed, compression, metering, barrier, mixer) that controls melting, mixing, and throughput.

barrier screw for PCR blending; Maddock mixer improved color; screw wear increased gels.

Shrinkage

Dimensional reduction as the part cools; depends on material, orientation, wall thickness, and mold temperature.

predict shrinkage in CAD; increase pack to reduce shrink marks; HDPE shrinkage ~2% typical.

SMED (Single-Minute Exchange of Die)

Lean methodology to reduce changeover times by externalizing and streamlining setup tasks.

SMED kaizen on color change; pre-heat molds externally; standardized hookups achieved SMED gains.

Stretch Ratio

Degree of axial and hoop stretching in ISBM; primary driver of orientation and final properties.

axial 3.0x, hoop 3.5x; overly high stretch caused pearlescence; tune stretch ratio to improve top load.

Takt Time

The rate at which finished goods must be produced to meet customer demand.

line balanced to 1 bottle/sec takt; increase crew to meet new takt; buffer before palletizer to absorb takt variation.

Top Load

The compressive load a container can withstand before buckling; critical for stacking and warehouse performance.

target top load 180 N; rib design improved top load; low IV reduced top load.

UN/DOT Certification

Regulatory performance testing and marking for hazardous materials packaging (e.g., UN 3H1 jerricans) under 49 CFR and related standards.

pass -18 °C UN drop test; leakproofness test at 30 kPa; apply UN marking after certification.