ABS molds on any standard injection press once it is dried to 0.1 % moisture or less, at the melt and mold temperature its producer prints for the grade, such as a 220–260 °C melt and a 30–80 °C mold for INEOS Styrolution’s general-purpose Terluran GP-22, and on most producer sheets it shrinks about 0.4–0.7 % in the mold.
ABS is amorphous, so it softens over a range instead of melting at a point, shrinks little and warps little; its polybutadiene rubber phase is the part most sensitive to heat and time in the barrel. Where a part needs chemical resistance or the lowest resin cost, weigh ABS against polypropylene before the tool is cut; the material’s own limits are covered in what ABS plastic is.
Molded ABS paints, prints and vacuum-metallizes readily and overmolds onto SAN, ASA and some TPUs, but coating solvents have to be chosen so they do not stress-crack the part.
How to Dry ABS Before Molding
Dry ABS to 0.1 % moisture or less before molding, usually for 2–4 hours at 80 °C or slightly above, in a dry-air, vacuum or circulating-air dryer. Producers set the drying window per grade:
| Producer and grade | Drying temperature | Drying time | Maximum moisture |
|---|---|---|---|
| INEOS Styrolution Terluran GP-22 | 80 °C | 2–4 h | <0.1 % |
| SABIC Cycolac MG47 | 80–95 °C | 2–4 h | 0.1 % |
| Chi Mei Polylac PA-746 | 80–85 °C | 2–3 h | Not printed |
Circulating-air dryers take longer. INEOS ABS (USA) asks for dryer air at a dew point of −29 °C or below for Lustran 433. On a press with a vented barrel that vents well, INEOS Styrolution finds predrying unnecessary unless the pellets got wet in storage.
Do not hold ABS in the dryer past the producer’s limit: SABIC sets a cumulative drying time of 8 hours for Cycolac MG47 and 6 hours for its flame-retardant Cycolac FR15.
Dried ABS takes moisture back from the air, so feed the press from a closed, dried hopper and dry regrind too.
Process Settings for ABS
Melt temperature and mold temperature matter most when molding ABS: together they set gloss, weld-line strength, molded-in stress and impact strength, while pressures are set to fill and pack the part on the press in use. Every window below is a producer’s figure for its own grade, so start from the sheet of the grade in the hopper.
Melt Temperature
Mold ABS at the melt temperature its producer prints for the grade, read in the melt with a needle pyrometer: INEOS Styrolution and SABIC both list 220–260 °C for their general-purpose grades, and other producers’ windows sit lower or higher.
Barrel zone set points run below the melt target and rise toward the nozzle: SABIC’s barrel profile for Cycolac MG47 runs 190–210 °C at the rear zone and 215–240 °C at the front.
INEOS Styrolution notes that the zones can often all be set to the same temperature. Near the top of the range or on long cycles, set the feed zone somewhat lower.
None of these producer windows comes with a degradation temperature, so watch time in the barrel as well as heat: SABIC sizes each shot at 50–70 % of cylinder capacity for Cycolac MG47.
Mold Temperature
Run ABS in a warm mold, between 30 °C and 80 °C on producer sheets, toward the upper end when the part needs gloss, strong weld lines or low molded-in stress.
A warmer mold also makes ABS tougher.
The windows are mold surface temperatures, so check the cavity face with a surface probe rather than reading the water setting.
Injection Pressure and Speed
Inject ABS fast, at whatever plastic pressure the part needs to fill. INEOS ABS (USA) lists 10,000–16,000 psi of injection pressure for Lustran 433 without saying whether that is hydraulic or plastic pressure.
A hydraulic press multiplies its gauge pressure by its intensification ratio to reach the plastic pressure at the nozzle; an electric press reads plastic pressure directly. When an ABS mold moves between presses, carry over the plastic pressure.
Holding Pressure and Time
Hold ABS at about half to three-quarters of injection pressure until the gate freezes; INEOS ABS (USA) lists a holding pressure of 50–70 % of injection pressure for Lustran 248.
Back Pressure and Screw Speed
Keep back pressure low on ABS: SABIC prints 0.3–0.7 MPa for Cycolac MG47 and INEOS ABS (USA) 0–25 psi (0–0.172 MPa) for Lustran 248, neither saying whether that is gauge or melt pressure.
SABIC sets 30–60 rpm for Cycolac MG47. Set rotation so recovery finishes within the cooling time.
Cooling Time
An ABS part needs cooling time in proportion to the square of its thickest wall, so doubling the wall quadruples the time in the mold.
A hotter melt lengthens cooling, so a lower melt temperature with a warmer mold often holds the cycle time.
How Much ABS Shrinks
ABS shrinks about 0.4–0.8 % in the mold, and most producer sheets print 0.4–0.7 %. Each figure comes with its own test method, so compare figures only within one method.
| Producer and grade | Mold shrinkage | Method |
|---|---|---|
| INEOS Styrolution Terluran GP-22 | 0.4–0.7 % | ISO 294-4 |
| Chi Mei Polylac PA-746 | 0.40–0.70 % | ISO 294-4 |
| INEOS ABS (USA) Lustran 248 | 0.40–0.60 %, flow direction | ASTM D955 |
| LG Chem, every ABS grade in its brochure tables | 0.4–0.7 % | ASTM D955 |
| SABIC Cycolac MG47 | 0.5–0.8 %, flow direction, 3.2 mm | SABIC’s own |
Within the range, thick sections shrink more than thin ones and higher holding pressure lowers shrinkage. The most accurate figure for a new tool comes from an existing tool molding a similar part in the same material.
Post-mold shrinkage on ABS is small; INEOS Styrolution calls it usually negligible.
Uniform walls keep shrinkage even, and Bayer’s design guide for its Lustran and Novodur ABS sets ribs at 40 % of the wall thickness for minimal sink and 60 % where a slight sink is acceptable.
Molding Different ABS Grades
Within one producer’s range, the grade moves the melt and mold temperature more than the drying: flame-retardant grades run a cooler melt, heat-resistant grades a hotter one, and a plating grade may need a warmer mold. Compare a grade only against the same producer’s general-purpose grade, because the general-purpose windows already differ between producers.
High-impact and high-flow grades carry the same melt, mold and drying lines as general-purpose grades at both INEOS Styrolution and Chi Mei; glass-filled ABS takes its settings from its own sheet. PC/ABS is a blend with polycarbonate that runs to its own, hotter windows, so set it up as a different resin.
Flame-Retardant ABS
Flame-retardant ABS dries like a general-purpose grade but runs a cooler melt: SABIC tops Cycolac FR15 at 220 °C, where its general-purpose Cycolac MG47 goes to 260 °C. Keep barrel residence short as well.
Drying stays near 80 °C: SABIC prints 80–90 °C for Cycolac FR15 and Chi Mei 80–85 °C for its flame-retardant Polylac PA-765.
Plating-Grade ABS
Mold plating-grade ABS at the mold temperature its producer prints, which can be higher than for general-purpose grades: INEOS Styrolution starts the window for Novodur P2MC at 60 °C, 30 °C above its general-purpose Terluran GP-22.
Molded-in stress at the surface weakens plating adhesion, and a warm mold lowers that stress, so run the upper part of the window even where the sheet allows a cool mold.
Heat-Resistant ABS
Heat-resistant ABS runs a hotter melt than general-purpose grades at both INEOS Styrolution and Chi Mei, but the two producers change different settings besides: INEOS raises the mold floor to 60 °C for Novodur HH-112, while Chi Mei dries its high-heat Polylac PA-777E at 100–110 °C.
How Much Regrind to Add
Up to 20 % clean in-plant regrind can go back into ABS, the cap INEOS ABS (USA) prints for its Lustran grades, provided the regrind is dried and blended evenly with virgin resin.
Only regrind from properly molded parts, sprues and runners qualifies; degraded, discolored or contaminated material stays out, and parts that need virgin-level color, impact strength or purity get none. UL and other listing bodies can set their own regrind limits for listed parts.
Test the parts at any regrind share.
Common Defects and Fixes
Splay, visible weld lines and stress cracking are the defects ABS is most prone to; the others below come from the process, the tool or contamination.
On the tool side, ABS calls for:
- Vents: 0.038–0.051 mm deep, the range SABIC prints for Cycolac MG47F.
- Gates: wide enough that the melt needs no extra heat or pressure to fill.
- Cooling: circuits that hold both mold halves at the same temperature.
Splay and Silver Streaks
Stop splay on ABS by drying the resin to 0.1 % moisture or less, confirmed with a moisture analyzer, and then removing the other sources of gas:
- Dryer: hot pellets are no proof of dry resin; the supply hose should be hot, the return hose warm, and the desiccant beds replaced yearly.
- Mold: look for leaking water fittings, especially above the mold, and for a mold sweating on chilled water in humid air; run the water warmer if it sweats.
- Feed lines: resin that sits an hour or more in the lines picks up moisture, so drain it at startup.
- Heat and shear: lower the melt temperature, and slow the fill or open the gate when the streaks start at the gate.
Sink Marks
Stop sinks on ABS by packing the thick section before the gate freezes:
- Holding: raise holding pressure and time.
- Gate: enlarge a gate that freezes early, or gate into or near the heavy section.
- Temperature: a lower melt temperature and a cooler mold also reduce sinks, at a cost in gloss and molded-in stress.
When settings cannot reach the section, thin the rib or boss behind the sink in the tool.
Warpage
Stop an ABS part warping by cooling it evenly, with both mold halves at the same temperature and no hot spots, and fully before ejection.
The usual causes of a warping ABS part are uneven cooling, uneven packing and molded-in stress. A warmer mold lowers that stress and, in INEOS Styrolution’s experience, the tendency to warp.
Weld Lines
Make ABS weld lines fainter and stronger by raising melt temperature, injection speed and mold temperature.
Vent where the flow fronts meet, and move the gate when the line falls on a load-bearing or cosmetic face.
Burn Marks and Black Specks
Stop burn marks on ABS by venting the gas that is trapped and compressed at the end of fill, and stop black specks by clearing the places in the barrel or hot runner where resin hangs up and degrades.
- Burn marks: clean the vents and cut them to the grade’s depth, slow the last part of the fill, and open gates narrow enough to force a hotter melt.
- Black specks: keep the melt inside the grade’s window and the shot at the producer’s share of barrel capacity, clean the screw, check ring and hot runner where resin hangs up, and purge thoroughly after a hotter-running resin.
Short Shots
Fix an ABS short shot by adding shot size, injection speed and pressure, then melt and mold temperature; when press settings run out, open the gates and add vents where the fill stops.
A job that starts shorting after a lot or grade change, with no setting changed, points to the resin’s flow, so check the new lot’s melt flow at the same test condition as the old one.
Flash
Stop flash on ABS by checking clamp force and the parting line first, then lowering injection and holding pressure, injection speed and melt temperature. Vents worn or cut deeper than the grade’s range flash too, as do worn shutoffs; weld and re-cut them.
Stress Cracking
Stop ABS parts stress cracking by molding in less stress and keeping the parts away from the chemicals that attack stressed ABS. On the press:
- Temperatures: raise the mold temperature and lower the melt temperature.
- Packing: avoid overpacking.
Solvents, plasticizers, cleaning agents, rust preventives and adhesives crack stressed ABS.
To check a part’s stress level, expose it to a mix of ethyl acetate and ethanol: the more acetate it takes to crack the part, the lower its internal stress.
Annealing helps where molding cannot remove the stress: hold the ABS parts below the grade’s heat-deflection temperature for at least 30 minutes once at temperature plus 5 minutes per millimeter of wall, then cool them no faster than 25 °C an hour.
Delamination
Stop delamination in ABS parts by finding and removing the contaminant, a polymer that does not mix with ABS in the melt; INEOS Styrolution names polyolefins, polystyrenes and polyamides. To keep it out:
- Purging: purge the barrel and hot runner thoroughly after another resin.
- Regrind and color: keep regrind streams and masterbatch carriers compatible with ABS.
- Handling: check dryers, loaders and grinders for foreign pellets.
Excess mold release on the cavity can lift the skin in the same way.
Reading the Resin Datasheet Before Setup
The processing block (melt and mold temperature, drying), the melt flow with its test condition, and the Vicat softening temperature are the lines on an ABS datasheet that set the molding window.
ABS melt flow is measured at 220 °C under a 10 kg load in ISO 19062-1, but sheets also print other conditions. Compare two sheets on melt flow only when temperature, load and unit (grams or cubic centimeters) all match.
A higher-flow grade suits thinner walls and long flow paths without a change of melt temperature.
Grades with a higher Vicat softening temperature carry hotter melt windows on INEOS Styrolution’s and Chi Mei’s sheets, though none of these sheets converts Vicat into a setting.
Treat the processing block as a starting point; some sheets carry no settings at all, so ask for the producer’s processing data with the ABS grade before the first trial.
When the lot or supplier changes on a running mold, re-check the melt flow at the same test condition against the certificate of analysis, the drying, and the first parts’ weight and critical dimensions.