{"id":7610,"date":"2026-10-27T01:14:39","date_gmt":"2026-10-27T01:14:39","guid":{"rendered":"https:\/\/uplastech.com\/pbt-pet-injection-molding-guide\/"},"modified":"2026-10-27T01:14:39","modified_gmt":"2026-10-27T01:14:39","slug":"pbt-pet-injection-molding-guide","status":"publish","type":"post","link":"https:\/\/uplastech.com\/es\/pbt-pet-injection-molding-guide\/","title":{"rendered":"PBT and PET Injection Molding: Glass Fibre, Drying and Warpage"},"content":{"rendered":"<style>\n.upl-blog{font-size:17px;line-height:1.78;color:#1f2937}\n.upl-blog p{margin:0 0 18px}\n.upl-blog h2{font-size:26px;line-height:1.3;color:#0b2b33;margin:46px 0 14px;font-weight:700;letter-spacing:-.015em}\n.upl-blog h3{font-size:19.5px;color:#0d3b47;margin:28px 0 10px;font-weight:700}\n.upl-blog ul,.upl-blog ol{margin:0 0 20px;padding-left:22px}\n.upl-blog li{margin:0 0 9px}\n.upl-blog figure{margin:0 0 34px}\n.upl-blog figure img{width:100%;height:auto;display:block;border-radius:10px}\n.upl-blog figcaption{font-size:13px;color:#6b7280;margin-top:10px;line-height:1.5}\n.upl-blog .toc{background:none;border:0;border-radius:0;padding:0;margin:0 0 34px}\n.upl-blog .toc .lwptoc{margin:0}\n.upl-blog .toc h4{margin:0 0 10px;font-size:13px;letter-spacing:.1em;text-transform:uppercase;color:#0d5563}\n.upl-blog .toc ol{margin:0;padding-left:18px;font-size:14.5px}\n.upl-blog .toc li{margin-bottom:6px}\n.upl-blog table{width:100%;border-collapse:collapse;font-size:14.5px;margin:0 0 10px}\n.upl-blog th{background:#0d3b47;color:#fff;text-align:left;padding:11px 13px;font-weight:600;font-size:13.5px;border:0}\n.upl-blog td{padding:11px 13px;border:0;border-bottom:1px solid #e8ebed;vertical-align:top}\n.upl-blog tbody tr:nth-child(even){background:#fafbfc}\n.upl-blog .tablecap{font-size:12.5px;color:#6b7280;margin:0 0 30px}\n.upl-blog .myth{background:#fff8ef;border:1px solid #f6ddbd;border-radius:8px;padding:16px 20px;margin:0 0 26px;font-size:15.5px}\n.upl-blog .myth b{color:#a85c10}\n.upl-blog .callout{background:#f2f8f9;border-radius:8px;padding:18px 22px;margin:0 0 26px;font-size:15.5px;border-left:3px solid #14707f}\n.upl-blog .faq h3{border-top:1px solid #eceff1;padding-top:22px;margin-top:0;font-size:18px}\n.upl-blog .faq h3:first-of-type{border-top:0;padding-top:0}\n.upl-blog .cta{background:linear-gradient(135deg,#0b2b33,#0d5563);color:#fff;border-radius:12px;padding:34px;margin:48px 0 30px}\n.upl-blog .cta h2,.upl-blog .cta .cta-h{color:#fff;margin:0 0 10px;font-size:24px;font-weight:700;line-height:1.3}\n.upl-blog .cta p{color:#c9dee3;margin:0 0 20px;font-size:16px}\n.upl-blog .btn{display:inline-block;background:#e07a1f;color:#fff;text-decoration:none;font-weight:700;padding:13px 26px;border-radius:8px;font-size:15.5px}\n.upl-blog .rel{border-top:1px solid #e8ebed;margin-top:40px;padding-top:26px}\n.upl-blog .rel h4{font-size:13px;letter-spacing:.1em;text-transform:uppercase;color:#6b7280;margin:0 0 14px}\n.upl-blog .rel ul{list-style:none;padding:0;margin:0}\n.upl-blog .rel li{padding:11px 0;border-bottom:1px dashed #e8ebed}\n.upl-blog .rel a{text-decoration:none;font-weight:600;font-size:15.5px}\n@media(max-width:640px){.upl-blog h2{font-size:22px}.upl-blog table{font-size:13px}.upl-blog .cta{padding:24px}}\n\/* \u5355\u7bc7\u9875\u9690\u85cf WhatsApp \u81ea\u52a8\u5c55\u5f00\u7684\u95ee\u5019\u5361\uff0c\u53ea\u4fdd\u7559\u5706\u5f62\u6c14\u6ce1\uff0c\u907f\u514d\u906e\u6321\u4fa7\u680f\u8be2\u76d8\u63d0\u4ea4\u6309\u94ae *\/\nbody.single-post .ht_ctc_chat_greetings_box{display:none !important}\n<\/style>\n<div class=\"upl-blog\">\n<figure>\n<img fetchpriority=\"high\" decoding=\"async\" src=\"https:\/\/uplastech.com\/wp-content\/uploads\/2026\/10\/im-pbt-part.jpg\" alt=\"Glass-filled PBT injection moulded electrical connector bodies with metal contacts on an inspection tray\" width=\"1536\" height=\"909\"><figcaption>Glass-filled PBT connector bodies with contacts inserted. Thin walls, tight pin positions, V-0 flame rating and a 260 \u00b0C solder excursion \u2014 this is the application PBT was designed for.<\/figcaption><\/figure>\n<div class=\"toc\"><\/div>\n<h2 id=\"why\">Why PBT owns electrical connectors<\/h2>\n<p>Polybutylene terephthalate is a semi-crystalline polyester that does one job better than anything else in its price bracket: it holds thin walls, tight dimensions and a flame rating through a soldering process. Almost every connector body, bobbins, relay base, sensor housing and terminal block in a modern appliance is glass-filled PBT.<\/p>\n<p>PET is the same chemistry with a different chain length and crystallisation behaviour. It is cheaper and tougher in some grades, but it crystallises slowly, which makes it harder to mould and mostly confines it to extrusion, blow moulding and bottles \u2014 though glass-filled PET is used for automotive and electrical parts where its higher melting point is worth the difficulty.<\/p>\n<div class=\"callout\">\n<p><strong>The number that governs PBT:<\/strong> glass-fibre loading of <strong>15 \u2013 30 %<\/strong>, which brings shrinkage down from 1.7 \u2013 2.3 % to 0.3 \u2013 0.8 % and raises HDT from 60 \u00b0C to 200 \u00b0C+. Unfilled PBT is almost never used for structural parts; the filler is what makes the material useful, and it is also what causes the warpage.<\/p>\n<\/div>\n<h2 id=\"grades\">Grades<\/h2>\n<table>\n<thead>\n<tr>\n<th>Grade<\/th>\n<th>Key property<\/th>\n<th>Used for<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>Unfilled PBT<\/td>\n<td>Tough, good surface, low HDT<\/td>\n<td>Cosmetic parts, low-temperature<\/td>\n<\/tr>\n<tr>\n<td>PBT + 15 % GF<\/td>\n<td>Balance of flow and stiffness<\/td>\n<td>Thin-wall connectors<\/td>\n<\/tr>\n<tr>\n<td>PBT + 30 % GF<\/td>\n<td>Modulus 9 \u2013 10 GPa, HDT 205 \u00b0C<\/td>\n<td>Structural electrical parts<\/td>\n<\/tr>\n<tr>\n<td>PBT + 30 % GF, V-0<\/td>\n<td>UL94 V-0 at 0.8 mm<\/td>\n<td>Connectors, bobbins, chargers<\/td>\n<\/tr>\n<tr>\n<td>PBT + GF, hydrolysis resistant<\/td>\n<td>Retains strength after 1,000 h at 85 \u00b0C \/ 85 % RH<\/td>\n<td>Automotive under-bonnet, appliances<\/td>\n<\/tr>\n<tr>\n<td>PBT + GF, low warp (mineral\/glass)<\/td>\n<td>Isotropic shrinkage<\/td>\n<td>Flat parts, long thin parts<\/td>\n<\/tr>\n<tr>\n<td>PBT + GF, impact modified<\/td>\n<td>Notched Izod 90 \u2013 130 J\/m<\/td>\n<td>Parts with snap fits or latches<\/td>\n<\/tr>\n<tr>\n<td>PBT\/ASA, PBT\/PC blends<\/td>\n<td>Improved surface, lower warp<\/td>\n<td>Automotive exterior trim<\/td>\n<\/tr>\n<tr>\n<td>PET + 30 % GF<\/td>\n<td>HDT 220 \u00b0C, higher melting point<\/td>\n<td>Under-bonnet, higher temperature<\/td>\n<\/tr>\n<tr>\n<td>PET + GF, nucleation added<\/td>\n<td>Faster crystallisation<\/td>\n<td>Makes PET mouldable at reasonable cycle times<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p class=\"tablecap\">Table 1 \u2014 PBT and PET grade families. The flame-retardant and hydrolysis-resistant variants are the two that matter most in electrical work.<\/p>\n<h2 id=\"drying\">Drying: the same trap as PC, one step milder<\/h2>\n<p>PBT and PET are polyesters, and polyesters hydrolyse. Water at melt temperature cleaves the ester bond, reducing molecular weight. The limits are less severe than polycarbonate's but the mechanism is identical.<\/p>\n<table>\n<thead>\n<tr>\n<th>Material<\/th>\n<th>Maximum moisture<\/th>\n<th>Drying<\/th>\n<th>If too wet<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>PBT unfilled<\/td>\n<td>0.04 %<\/td>\n<td>120 \u00b0C, 3 \u2013 4 h<\/td>\n<td>Silver streaks, brittleness<\/td>\n<\/tr>\n<tr>\n<td>PBT + 30 % GF<\/td>\n<td>0.04 %<\/td>\n<td>120 \u00b0C, 3 \u2013 4 h<\/td>\n<td>Streaks, weak weld lines<\/td>\n<\/tr>\n<tr>\n<td>PBT FR<\/td>\n<td>0.04 %<\/td>\n<td>120 \u00b0C, 4 h<\/td>\n<td>Streaks plus reduced flame performance<\/td>\n<\/tr>\n<tr>\n<td>PET + 30 % GF<\/td>\n<td>0.02 %<\/td>\n<td>130 \u00b0C, 4 \u2013 6 h<\/td>\n<td>Severe hydrolysis \u2014 molecular weight collapses<\/td>\n<\/tr>\n<tr>\n<td>PET unfilled<\/td>\n<td>0.02 %<\/td>\n<td>130 \u00b0C, 4 \u2013 6 h<\/td>\n<td>Not normally injection moulded<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p class=\"tablecap\">Table 2 \u2014 Drying limits. PET is twice as sensitive as PBT and needs a hotter dryer.<\/p>\n<p>The practical point: PBT arrives in sealed foil bags with a moisture barrier, and it should stay there until it goes into the dryer. A bag left open overnight in a humid plant will pick up 0.1 \u2013 0.2 %, which is four times the limit. If the plant has no desiccant dryer and relies on a hot-air oven, the resin will stabilise around 0.05 \u2013 0.08 % on a humid day and the parts will streak.<\/p>\n<div class=\"myth\">\n<p><b>Myth: \"the streaks are just cosmetic \u2014 the part is fine.\"<\/b> With polyesters they are not cosmetic. The streaks are the visible evidence that the molecular weight has dropped. A streaked PBT connector will pass a dimensional check and fail a pin-retention or a drop test. Purge and re-dry; do not sort and ship.<\/p>\n<\/div>\n<h2 id=\"processing\">Processing window<\/h2>\n<table>\n<thead>\n<tr>\n<th>Par\u00e1metro<\/th>\n<th>PBT<\/th>\n<th>PET + GF<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>Temperatura de fusi\u00f3n<\/td>\n<td>240 \u2013 265 \u00b0C<\/td>\n<td>275 \u2013 295 \u00b0C<\/td>\n<\/tr>\n<tr>\n<td>Barrel profile<\/td>\n<td>230 \/ 245 \/ 255 \/ 255 \u00b0C<\/td>\n<td>260 \/ 275 \/ 285 \/ 290 \u00b0C<\/td>\n<\/tr>\n<tr>\n<td>Mould temperature<\/td>\n<td>60 \u2013 90 \u00b0C<\/td>\n<td>100 \u2013 130 \u00b0C<\/td>\n<\/tr>\n<tr>\n<td>Injection pressure<\/td>\n<td>80 \u2013 130 MPa<\/td>\n<td>90 \u2013 140 MPa<\/td>\n<\/tr>\n<tr>\n<td>Injection speed<\/td>\n<td>R\u00e1pido<\/td>\n<td>R\u00e1pido<\/td>\n<\/tr>\n<tr>\n<td>Hold pressure<\/td>\n<td>50 \u2013 70 % of injection<\/td>\n<td>50 \u2013 70 %<\/td>\n<\/tr>\n<tr>\n<td>Residence time<\/td>\n<td>&lt; 6 min<\/td>\n<td>&lt; 5 min<\/td>\n<\/tr>\n<tr>\n<td>Shrinkage, unfilled<\/td>\n<td>1.7 \u2013 2.3 %<\/td>\n<td>1.5 \u2013 2.0 %<\/td>\n<\/tr>\n<tr>\n<td>Shrinkage, 30 % GF<\/td>\n<td>0.3 \u2013 0.8 %<\/td>\n<td>0.2 \u2013 0.6 %<\/td>\n<\/tr>\n<tr>\n<td>Regrind<\/td>\n<td>Up to 20 %<\/td>\n<td>Up to 15 %<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p class=\"tablecap\">Table 3 \u2014 Processing windows. The PET mould temperature of 100 \u2013 130 \u00b0C is what forces it to crystallise.<\/p>\n<p>The PET mould temperature is not a preference. PET crystallises slowly, and below about 90 \u00b0C it cools into an amorphous state that is brittle, dimensionally unstable and will deform if it later sees heat \u2014 a phenomenon that shows up as parts warping in a reflow oven. A PET tool needs hot-oil mould temperature control, not water. That single requirement is why PBT dominates and PET is a specialist choice.<\/p>\n<h2 id=\"warpage\">Warpage: the main PBT problem<\/h2>\n<p>Glass-filled PBT warps because the fibres align with the flow. Shrinkage in the flow direction is 0.2 \u2013 0.4 %; across the flow it is 0.6 \u2013 1.0 %. That difference is the warpage driver, and it gets worse as the flow length increases and the walls get thinner.<\/p>\n<table>\n<thead>\n<tr>\n<th>Lever<\/th>\n<th>Effect<\/th>\n<th>Coste<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>Espesor de pared uniforme<\/td>\n<td>Large reduction<\/td>\n<td>Design change only<\/td>\n<\/tr>\n<tr>\n<td>Symmetric gating (centre gate, or two gates)<\/td>\n<td>Large reduction<\/td>\n<td>Tool change<\/td>\n<\/tr>\n<tr>\n<td>Higher mould temperature<\/td>\n<td>Moderate reduction<\/td>\n<td>Longer cycle<\/td>\n<\/tr>\n<tr>\n<td>Lower glass loading (30 % \u2192 15 %)<\/td>\n<td>Moderate reduction<\/td>\n<td>Lower stiffness \u2014 may need thicker walls<\/td>\n<\/tr>\n<tr>\n<td>Mineral\/glass hybrid filler<\/td>\n<td>Large reduction<\/td>\n<td>Slightly lower strength<\/td>\n<\/tr>\n<tr>\n<td>Longer fill time<\/td>\n<td>Small reduction<\/td>\n<td>Duraci\u00f3n del ciclo<\/td>\n<\/tr>\n<tr>\n<td>Post-mould fixture cooling<\/td>\n<td>Complete, but adds a process<\/td>\n<td>Fixture plus labour<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p class=\"tablecap\">Table 4 \u2014 Warpage levers for glass-filled PBT, in order of effectiveness.<\/p>\n<p>For a flat part, the most effective single change is usually the gate: a centre gate makes the flow radial, so the fibre orientation is symmetric about the centre and the part stays flat. An edge gate makes the flow unidirectional, the fibres align along the part, and it curls.<\/p>\n<h2 id=\"electrical\">Electrical and flame-retardant grades<\/h2>\n<table>\n<thead>\n<tr>\n<th>Requirement<\/th>\n<th>What to specify<\/th>\n<th>Watch out for<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>UL94 V-0 at 0.8 mm<\/td>\n<td>FR grade with a halogenated or halogen-free system<\/td>\n<td>Halogen-free FR grades often need higher melt temperature<\/td>\n<\/tr>\n<tr>\n<td>Comparative tracking index &gt; 600 V<\/td>\n<td>Specific CTI grade<\/td>\n<td>Standard FR grades are 250 \u2013 400 V<\/td>\n<\/tr>\n<tr>\n<td>Glow-wire, 960 \u00b0C<\/td>\n<td>GWIT\/GWFI rated grade<\/td>\n<td>Required for appliance connectors in Europe<\/td>\n<\/tr>\n<tr>\n<td>Reflow solder resistance<\/td>\n<td>PBT with high HDT, or PPA\/PA6T<\/td>\n<td>PBT can blister at 260 \u00b0C if moisture is present<\/td>\n<\/tr>\n<tr>\n<td>Hot-wire ignition<\/td>\n<td>FR grade plus wall thickness<\/td>\n<td>Thin walls lose V-0 rating \u2014 check the thickness on the certificate<\/td>\n<\/tr>\n<tr>\n<td>Hydrolysis resistance<\/td>\n<td>Hydrolysis-stabilised grade<\/td>\n<td>Standard PBT fails after 500 \u2013 1,000 h at 85\/85<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p class=\"tablecap\">Table 5 \u2014 Electrical requirements. The wall-thickness caveat on V-0 is the one that catches designers.<\/p>\n<p>That last caveat deserves detail: a V-0 rating is always quoted at a specific thickness. A grade rated V-0 at 1.5 mm is often only V-2 at 0.8 mm. If your design has a 0.6 mm wall in a flame-rated part, the certificate you were given does not apply to it. Always check the thickness column on the UL yellow card, not just the rating.<\/p>\n<h2 id=\"design\">Design rules<\/h2>\n<table>\n<thead>\n<tr>\n<th>Caracter\u00edstica<\/th>\n<th>Rule<\/th>\n<th>Why PBT is different<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>Wall thickness<\/td>\n<td>0.8 \u2013 3.0 mm; thin walls are a strength<\/td>\n<td>PBT fills thin sections well; that is why it is used for connectors<\/td>\n<\/tr>\n<tr>\n<td>Wall uniformity<\/td>\n<td>Within 20 %<\/td>\n<td>Warpage is the main risk<\/td>\n<\/tr>\n<tr>\n<td>Ribs<\/td>\n<td>0.5 \u00d7 wall<\/td>\n<td>Thick ribs warp the face<\/td>\n<\/tr>\n<tr>\n<td>Bosses<\/td>\n<td>Wall 0.6 \u00d7 nominal<\/td>\n<td><\/td>\n<\/tr>\n<tr>\n<td>Draft<\/td>\n<td>0.5 \u2013 1\u00b0<\/td>\n<td>PBT releases reasonably well<\/td>\n<\/tr>\n<tr>\n<td>Gate<\/td>\n<td>Centre or symmetric; avoid long unidirectional flow<\/td>\n<td>Fibre orientation drives warpage<\/td>\n<\/tr>\n<tr>\n<td>Pin positions<\/td>\n<td>Allow &plusmn;0.05 mm on moulded holes; drill if tighter<\/td>\n<td>Glass-filled PBT holds holes well but not to machining tolerance<\/td>\n<\/tr>\n<tr>\n<td>Snap fits<\/td>\n<td>Strain \u2264 1.5 % for glass-filled<\/td>\n<td>Glass reduces elongation at break to 2 \u2013 3 %<\/td>\n<\/tr>\n<tr>\n<td>Sharp corners<\/td>\n<td>Internal R \u2265 0.5 \u00d7 wall<\/td>\n<td>Glass-filled materials are notch sensitive<\/td>\n<\/tr>\n<tr>\n<td>Metal inserts<\/td>\n<td>Design for 0.5 % differential expansion<\/td>\n<td>PBT expands 30 \u2013 60 \u00d7 10\u207b\u2076\/K<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p class=\"tablecap\">Table 6 \u2014 PBT design rules. Glass-filled grades have low elongation, so snap fits need care.<\/p>\n<h2 id=\"inserts\">Inserts and assembly<\/h2>\n<p>Most PBT parts are assembled with metal contacts, and the insert design determines whether the part survives.<\/p>\n<table>\n<thead>\n<tr>\n<th>M\u00e9todo<\/th>\n<th>Suitability for PBT<\/th>\n<th>Notas<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>Moulded-in inserts<\/td>\n<td>Good, with pre-heating<\/td>\n<td>Pre-heat to 100 \u2013 120 \u00b0C; cool the pin if the wall is thin<\/td>\n<\/tr>\n<tr>\n<td>Ultrasonic insertion<\/td>\n<td>Excelente<\/td>\n<td>The standard method for connectors<\/td>\n<\/tr>\n<tr>\n<td>Heat staking<\/td>\n<td>Bien<\/td>\n<td>Works well on glass-filled PBT<\/td>\n<\/tr>\n<tr>\n<td>Press fit<\/td>\n<td>Feria<\/td>\n<td>Glass-filled PBT is brittle; hoop stress can crack the boss<\/td>\n<\/tr>\n<tr>\n<td>Self-tapping screws<\/td>\n<td>Good in unfilled; poor in 30 % GF<\/td>\n<td>Glass causes the boss to split<\/td>\n<\/tr>\n<tr>\n<td>Ultrasonic welding<\/td>\n<td>Bien<\/td>\n<td>Needs a proper joint design; glass content reduces weld strength<\/td>\n<\/tr>\n<tr>\n<td>Laser welding<\/td>\n<td>Bien<\/td>\n<td>Requires a transmissive and an absorptive grade<\/td>\n<\/tr>\n<tr>\n<td>Adhesive<\/td>\n<td>Feria<\/td>\n<td>Surface energy is moderate; some structural acrylics work<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p class=\"tablecap\">Table 7 \u2014 Assembly methods. Self-tapping screws in 30 % GF PBT are a common field failure.<\/p>\n<h2 id=\"defects\">Defects and causes<\/h2>\n<table>\n<thead>\n<tr>\n<th>Defecto<\/th>\n<th>Causa<\/th>\n<th>Fix<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>Silver streaks<\/td>\n<td>Moisture above 0.04 %<\/td>\n<td>Dry at 120 \u00b0C for 4 h; check dew point<\/td>\n<\/tr>\n<tr>\n<td>Brittle parts<\/td>\n<td>Hydrolysis, or excess regrind<\/td>\n<td>Check moisture and regrind ratio; verify the grade<\/td>\n<\/tr>\n<tr>\n<td>Alabeo<\/td>\n<td>Fibre orientation, asymmetric cooling<\/td>\n<td>Symmetric gating; uniform walls; higher mould temperature<\/td>\n<\/tr>\n<tr>\n<td>Short shots on thin walls<\/td>\n<td>Cold mould, low speed<\/td>\n<td>Raise mould temperature and injection speed<\/td>\n<\/tr>\n<tr>\n<td>Weld line weakness<\/td>\n<td>Low mould temperature, glass accumulation at the weld<\/td>\n<td>Raise mould to 80 \u2013 90 \u00b0C; move the gate so the weld is not in a loaded area<\/td>\n<\/tr>\n<tr>\n<td>Flash<\/td>\n<td>Low viscosity, high melt temperature<\/td>\n<td>Lower melt; check clamp tonnage<\/td>\n<\/tr>\n<tr>\n<td>Blisters after soldering<\/td>\n<td>Absorbed moisture flashing at reflow<\/td>\n<td>Dry before moulding; store parts dry; consider a bake before reflow<\/td>\n<\/tr>\n<tr>\n<td>Ejector pin marks \/ white stress marks<\/td>\n<td>Over-packing, insufficient draft<\/td>\n<td>Reduce hold; add draft; increase ejector area<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p class=\"tablecap\">Table 8 \u2014 PBT defects. The blister row is a moisture problem that appears a process step later.<\/p>\n<h2 id=\"thinwall\">Thin-wall filling: what PBT can and cannot do<\/h2>\n<p>PBT's reputation comes from its ability to fill thin sections at high speed, which is what connectors need. The limit is a combination of wall thickness, flow length and glass loading.<\/p>\n<table>\n<thead>\n<tr>\n<th>Wall thickness<\/th>\n<th>Flow length, unfilled<\/th>\n<th>Flow length, 30 % GF<\/th>\n<th>Minimum practical<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>0.4 mm<\/td>\n<td>25 \u2013 35 mm<\/td>\n<td>15 \u2013 25 mm<\/td>\n<td>Specialist tooling only<\/td>\n<\/tr>\n<tr>\n<td>0.6 mm<\/td>\n<td>45 \u2013 60 mm<\/td>\n<td>30 \u2013 45 mm<\/td>\n<td>Achievable with a hot runner<\/td>\n<\/tr>\n<tr>\n<td>0.8 mm<\/td>\n<td>70 \u2013 95 mm<\/td>\n<td>50 \u2013 70 mm<\/td>\n<td>Standard connector practice<\/td>\n<\/tr>\n<tr>\n<td>1.0 mm<\/td>\n<td>100 \u2013 130 mm<\/td>\n<td>70 \u2013 100 mm<\/td>\n<td>Comfortable<\/td>\n<\/tr>\n<tr>\n<td>1.5 mm<\/td>\n<td>170 \u2013 220 mm<\/td>\n<td>120 \u2013 160 mm<\/td>\n<td>Comfortable<\/td>\n<\/tr>\n<tr>\n<td>2.0 mm<\/td>\n<td>240 \u2013 310 mm<\/td>\n<td>170 \u2013 230 mm<\/td>\n<td>Easy<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p class=\"tablecap\">Table 9 \u2014 Flow length for PBT at 255 \u00b0C melt and 80 \u00b0C mould. Glass-filled grades are roughly 30 % shorter.<\/p>\n<p>Below 0.6 mm the process becomes unforgiving: the melt front freezes before the cavity fills, and every variable \u2014 mould temperature uniformity, injection speed, gate size \u2014 has to be right. That is achievable in a connector tool built for it, and it is not achievable in a general-purpose tool being pushed past its design.<\/p>\n<h2 id=\"hydrolysis\">Hydrolysis: the slow failure<\/h2>\n<p>PBT and PET degrade in hot humid environments through hydrolysis of the ester bond. This is different from the moisture problem at the hopper \u2014 it happens in service, over months, and it is invisible until the part fails.<\/p>\n<table>\n<thead>\n<tr>\n<th>Condition<\/th>\n<th>Standard PBT<\/th>\n<th>Hydrolysis-stabilised PBT<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>85 \u00b0C \/ 85 % RH, 500 h<\/td>\n<td>60 \u2013 75 % strength retention<\/td>\n<td>90 \u2013 95 %<\/td>\n<\/tr>\n<tr>\n<td>85 \u00b0C \/ 85 % RH, 1,000 h<\/td>\n<td>35 \u2013 50 %<\/td>\n<td>80 \u2013 90 %<\/td>\n<\/tr>\n<tr>\n<td>85 \u00b0C \/ 85 % RH, 2,000 h<\/td>\n<td>15 \u2013 30 %<\/td>\n<td>70 \u2013 80 %<\/td>\n<\/tr>\n<tr>\n<td>Hot water immersion, 90 \u00b0C<\/td>\n<td>Fails within 500 h<\/td>\n<td>2,000 h+<\/td>\n<\/tr>\n<tr>\n<td>Steam autoclave<\/td>\n<td>Not suitable<\/td>\n<td>Not suitable<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p class=\"tablecap\">Table 10 \u2014 Hydrolysis resistance. The stabilised grade is roughly 3\u00d7 the service life in hot humid conditions.<\/p>\n<p>The applications that need it are obvious once you know: washing-machine components, dishwasher parts, automotive under-bonnet, anything in a bathroom, anything in a tropical climate. The applications that get caught out are the ones where nobody thought about humidity \u2014 a connector in an unheated warehouse in Southeast Asia, or a sensor housing on a pump.<\/p>\n<div class=\"callout\">\n<p><strong>The test that reveals it:<\/strong> 1,000 hours at 85 \u00b0C \/ 85 % RH, then a tensile test. A standard PBT loses half its strength; a stabilised grade loses 10 \u2013 20 %. If a part is going to spend its life above 60 \u00b0C and 60 % RH, run that test on the candidate grade before the tool is cut.<\/p>\n<\/div>\n<h2 id=\"selection\">PBT, PPS or PA for a connector<\/h2>\n<table>\n<thead>\n<tr>\n<th>Requirement<\/th>\n<th>PBT + 30 % GF<\/th>\n<th>PA66 + 30 % GF<\/th>\n<th>PPS + 40 % GF<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>Continuous temperature<\/td>\n<td>120 \u2013 140 \u00b0C<\/td>\n<td>100 \u2013 120 \u00b0C<\/td>\n<td>200 \u2013 220 \u00b0C<\/td>\n<\/tr>\n<tr>\n<td>Dimensional stability in humidity<\/td>\n<td>Excelente<\/td>\n<td>Pobre<\/td>\n<td>Excelente<\/td>\n<\/tr>\n<tr>\n<td>Pin position tolerance<\/td>\n<td>&plusmn;0.05 mm<\/td>\n<td>&plusmn;0.15 mm (grows)<\/td>\n<td>&plusmn;0.05 mm<\/td>\n<\/tr>\n<tr>\n<td>V-0 without additives<\/td>\n<td>No<\/td>\n<td>No<\/td>\n<td>S\u00ed<\/td>\n<\/tr>\n<tr>\n<td>Impact strength<\/td>\n<td>Bajo<\/td>\n<td>Alta<\/td>\n<td>Bajo<\/td>\n<\/tr>\n<tr>\n<td>Relative material cost<\/td>\n<td>1\u00d7<\/td>\n<td>1.1\u00d7<\/td>\n<td>3 \u2013 4\u00d7<\/td>\n<\/tr>\n<tr>\n<td>Tooling cost<\/td>\n<td>1\u00d7<\/td>\n<td>1\u00d7<\/td>\n<td>1.3 \u2013 1.6\u00d7<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p class=\"tablecap\">Table 11 \u2014 Connector material selection. PBT wins on cost plus stability; PPS wins on temperature; nylon wins on impact only.<\/p>\n<p>The pin-position row is the deciding one for most connectors. A PA66 connector grows 0.3 \u2013 0.6 % after moulding as it absorbs moisture, which on a 40 mm connector body is 0.12 \u2013 0.24 mm of pin movement. That is more than the insertion tolerance of most terminals. PBT does not move, which is why it is the default.<\/p>\n<h2 id=\"faq\">Frequently asked questions<\/h2>\n<div class=\"faq\">\n<h3>PBT or nylon for a connector?<\/h3>\n<p>PBT, almost always. Nylon absorbs moisture and grows, which moves the pin positions; PBT does not. PBT also holds a V-0 rating more easily and is stiffer at the same glass loading. Nylon wins only where impact strength matters more than dimensional stability.<\/p>\n<h3>Why is PET harder to mould than PBT?<\/h3>\n<p>Because PET crystallises slowly. It needs a mould at 100 \u2013 130 \u00b0C with hot-oil control, and even then the cycle is longer. Unfilled PET cooled below 90 \u00b0C comes out amorphous and will deform if it later sees heat. PBT crystallises fast enough to run on a water-heated tool.<\/p>\n<h3>Can I use 50 % glass-filled PBT?<\/h3>\n<p>It exists and it is used for very stiff parts, but the elongation at break drops to about 1.5 % and the material becomes quite brittle. It also wears the tool aggressively. Above 30 \u2013 35 % glass, check whether the design can be met with ribs instead.<\/p>\n<h3>How do I stop glass-filled PBT warping?<\/h3>\n<p>Gate from the centre so the fibre orientation is symmetric, keep the wall uniform, and run the mould hot (80 \u2013 90 \u00b0C). If the part is still out, switch to a mineral\/glass hybrid grade, which shrinks more isotropically at the cost of some strength.<\/p>\n<h3>Does PBT need annealing?<\/h3>\n<p>Not usually. It is sometimes annealed at 120 \u2013 140 \u00b0C for 1 \u2013 2 hours to relieve stress in parts that will be machined or that must hold tolerance through a soldering process.<\/p>\n<h3>What is the difference between V-0 at 0.8 mm and V-0 at 1.5 mm?<\/h3>\n<p>They are different ratings for the same grade. A material rated V-0 at 1.5 mm may only be V-2 at 0.8 mm. If your part has a 0.8 mm wall, the 1.5 mm rating does not apply and the part is not compliant. Always read the thickness column on the UL yellow card.<\/p>\n<h3>Can PBT survive lead-free reflow?<\/h3>\n<p>Standard PBT is marginal at 260 \u00b0C. Grades with higher HDT, or PPA and PA6T, are the usual answer for reflow-compatible parts. If PBT is used, the part must be dry \u2014 moisture flashing at reflow temperature causes blisters that look like material failure.<\/p>\n<h3>Why do my PBT parts crack around self-tapping screws?<\/h3>\n<p>Because 30 % glass-filled PBT has about 2 % elongation at break. The hoop stress from the screw exceeds it. Use an ultrasonic insert, a heat-staked insert, or a larger boss with a thread-forming screw designed for brittle plastics.<\/p>\n<\/div>\n<div class=\"cta\">\n<p class=\"cta-h\">Designing a connector or bobbin in PBT?<\/p>\n<p>Send the drawing, the flame rating you need and the soldering process. We will tell you the right glass loading, whether the wall thickness meets the UL rating, and where the tool needs to gate to stay flat.<\/p>\n<p><a class=\"btn\" href=\"https:\/\/uplastech.com\/es\/pbt-pet-injection-molding\/\">Talk to a PBT moulding engineer<\/a>\n<\/div>\n<div class=\"rel\">\n<h4>Continue reading<\/h4>\n<ul>\n<li><a href=\"https:\/\/uplastech.com\/es\/nylon-pa-injection-molding-guide\/\">Nylon (PA6 \/ PA66) Injection Molding: Moisture, Conditioning and Dimensions<\/a><\/li>\n<li><a href=\"https:\/\/uplastech.com\/es\/pom-acetal-injection-molding-guide\/\">POM (Acetal) Injection Molding: Thermal Stability and Tooling<\/a><\/li>\n<li><a href=\"https:\/\/uplastech.com\/es\/pps-peek-injection-molding-guide\/\">PPS and PEEK Injection Molding: Hot Moulds and Crystallinity<\/a><\/li>\n<li><a href=\"https:\/\/uplastech.com\/es\/overmolding-insert-molding\/\">Overmolding and Insert Molding: The Complete Design Guide<\/a><\/li>\n<li><a href=\"https:\/\/uplastech.com\/es\/injection-molding-material-selection\/\">Injection Molding Material Selection: 14 Plastics Compared<\/a><\/li>\n<\/ul>\n<\/div>\n<\/div>","protected":false},"excerpt":{"rendered":"<p>PBT and PET moulding: grade families, drying limits, thin-wall flow length, fibre-driven warpage, flame ratings by wall thickness, hydrolysis and connector selection.<\/p>","protected":false},"author":1,"featured_media":7602,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_seopress_titles_title":"PBT & PET Injection Molding: Glass Fibre, Drying, Warpage","_seopress_titles_desc":"PBT and PET moulding: grades, drying limits, thin-wall flow length, fibre-driven warpage, flame ratings by wall thickness and hydrolysis resistance.","_seopress_robots_index":"1","_seopress_robots_follow":"1","_seopress_robots_imageindex":"","_seopress_robots_snippet":"","_seopress_robots_primary_cat":"35","_seopress_robots_breadcrumbs":"","_seopress_robots_freeze_modified_date":"","_seopress_robots_custom_modified_date":"","_seopress_robots_canonical":"https:\/\/uplastech.com\/pbt-pet-injection-molding-guide\/","_seopress_social_fb_title":"","_seopress_social_fb_desc":"","_seopress_social_fb_img":"","_seopress_social_fb_img_attachment_id":0,"_seopress_social_fb_img_width":0,"_seopress_social_fb_img_height":0,"_seopress_social_twitter_title":"","_seopress_social_twitter_desc":"","_seopress_social_twitter_img":"","_seopress_social_twitter_img_attachment_id":0,"_seopress_social_twitter_img_width":0,"_seopress_social_twitter_img_height":0,"_seopress_redirections_value":"","_seopress_redirections_enabled":"","_seopress_redirections_enabled_regex":"","_seopress_redirections_logged_status":"","_seopress_redirections_param":"","_seopress_redirections_type":0,"_seopress_analysis_target_kw":"pbt pet injection molding","footnotes":""},"categories":[35],"tags":[],"class_list":["post-7610","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-injection-molding"],"meta_box":{"post-to-quiz_to":[]},"_links":{"self":[{"href":"https:\/\/uplastech.com\/es\/wp-json\/wp\/v2\/posts\/7610","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/uplastech.com\/es\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/uplastech.com\/es\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/uplastech.com\/es\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/uplastech.com\/es\/wp-json\/wp\/v2\/comments?post=7610"}],"version-history":[{"count":0,"href":"https:\/\/uplastech.com\/es\/wp-json\/wp\/v2\/posts\/7610\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/uplastech.com\/es\/wp-json\/wp\/v2\/media\/7602"}],"wp:attachment":[{"href":"https:\/\/uplastech.com\/es\/wp-json\/wp\/v2\/media?parent=7610"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/uplastech.com\/es\/wp-json\/wp\/v2\/categories?post=7610"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/uplastech.com\/es\/wp-json\/wp\/v2\/tags?post=7610"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}