{"id":7608,"date":"2026-10-27T01:14:33","date_gmt":"2026-10-27T01:14:33","guid":{"rendered":"https:\/\/uplastech.com\/nylon-pa-injection-molding-guide\/"},"modified":"2026-10-27T01:14:33","modified_gmt":"2026-10-27T01:14:33","slug":"nylon-pa-injection-molding-guide","status":"publish","type":"post","link":"https:\/\/uplastech.com\/ar\/nylon-pa-injection-molding-guide\/","title":{"rendered":"Nylon (PA6 \/ PA66) Injection Molding: Moisture, Conditioning and Dimensions"},"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-nylon-part.jpg\" alt=\"Black glass-filled nylon injection moulded gears and a natural nylon bush on a metrology bench with a micrometer\" width=\"1536\" height=\"909\"><figcaption>Glass-filled PA66 gears and an unfilled natural nylon bush. The gears hold tolerance because the glass restrains moisture uptake; the natural bush will grow 0.3 mm over a season and is measured wet, not dry.<\/figcaption><\/figure>\n<div class=\"toc\"><\/div>\n<h2 id=\"why\">The material that changes size after it leaves you<\/h2>\n<p>Polyamide \u2014 nylon 6 and nylon 66 \u2014 is the workhorse engineering plastic for anything that needs toughness, wear resistance, temperature resistance and resistance to oils and fuels. Gears, bushes, cable ties, connectors, under-bonnet parts, power-tool housings and conveyor components are all nylon.<\/p>\n<p>It also has a property that causes more quality disputes than any other in injection moulding: <strong>it absorbs water and grows.<\/strong> A dry PA66 part left in a normal room reaches equilibrium at 1.5 \u2013 2.5 % moisture and grows by 0.3 \u2013 0.6 % in every dimension. That is 0.3 mm on a 50 mm part. If the drawing does not say whether the tolerance applies to the dry part or the conditioned part, the drawing is incomplete.<\/p>\n<div class=\"callout\">\n<p><strong>The number to design around:<\/strong> unmodified PA66 grows <strong>0.3 \u2013 0.6 %<\/strong> between the dry-as-moulded state and equilibrium at 23 \u00b0C \/ 50 % RH. Glass-filled grades grow 0.1 \u2013 0.2 %. This is not shrinkage \u2014 that happens in the tool \u2014 it is moisture uptake in service, and it continues for weeks after moulding.<\/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>Moisture uptake at equilibrium<\/th>\n<th>Used for<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>PA6 unfilled<\/td>\n<td>Tough, good surface, cheaper<\/td>\n<td>2.5 \u2013 3.0 %<\/td>\n<td>Bushes, general parts<\/td>\n<\/tr>\n<tr>\n<td>PA66 unfilled<\/td>\n<td>Higher strength and HDT than PA6<\/td>\n<td>1.5 \u2013 2.5 %<\/td>\n<td>Gears, structural parts<\/td>\n<\/tr>\n<tr>\n<td>PA6 \/ PA66, 30 % GF<\/td>\n<td>Modulus 9 \u2013 10 GPa, HDT 200 \u00b0C+<\/td>\n<td>0.8 \u2013 1.5 %<\/td>\n<td>Brackets, housings, fans<\/td>\n<\/tr>\n<tr>\n<td>PA66, 30 \u2013 35 % GF, heat stabilised<\/td>\n<td>Continuous 150 \u00b0C<\/td>\n<td>0.8 \u2013 1.2 %<\/td>\n<td>Under-bonnet<\/td>\n<\/tr>\n<tr>\n<td>PA6, impact modified<\/td>\n<td>Notched Izod 80 \u2013 120 J\/m<\/td>\n<td>2.0 \u2013 2.8 %<\/td>\n<td>Power tools, sports goods<\/td>\n<\/tr>\n<tr>\n<td>PA66, mineral filled<\/td>\n<td>Low warp, good surface<\/td>\n<td>1.2 \u2013 1.8 %<\/td>\n<td>Automotive exterior<\/td>\n<\/tr>\n<tr>\n<td>PA12 \/ PA11<\/td>\n<td>Lowest moisture uptake, flexible<\/td>\n<td>0.8 \u2013 1.2 %<\/td>\n<td>Fuel lines, precision parts<\/td>\n<\/tr>\n<tr>\n<td>PA6\/6T, PPA<\/td>\n<td>High temperature, low moisture<\/td>\n<td>0.3 \u2013 0.6 %<\/td>\n<td>Lead-free solder reflow, automotive<\/td>\n<\/tr>\n<tr>\n<td>Cast PA (MC nylon)<\/td>\n<td>Very high molecular weight<\/td>\n<td>2.0 \u2013 2.8 %<\/td>\n<td>Large bushes, sheets \u2014 not moulded<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p class=\"tablecap\">Table 1 \u2014 Polyamide grades. PA12 and PPA exist mainly to solve the moisture problem.<\/p>\n<h2 id=\"moisture\">Moisture: drying, then re-absorbing<\/h2>\n<p>There are two completely separate moisture issues with nylon, and confusing them is the root of most problems.<\/p>\n<table>\n<thead>\n<tr>\n<th>Issue<\/th>\n<th>When<\/th>\n<th>Target<\/th>\n<th>Consequence if wrong<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>Too wet at the hopper<\/td>\n<td>Before moulding<\/td>\n<td>&lt; 0.1 % (PA6), &lt; 0.08 % (PA66)<\/td>\n<td>Hydrolysis: molecular weight drop, brittle parts, silver streaks<\/td>\n<\/tr>\n<tr>\n<td>Too dry in service<\/td>\n<td>After moulding<\/td>\n<td>Conditioned to 1.5 \u2013 2.5 %<\/td>\n<td>Part grows, but also becomes tougher \u2014 dry nylon is brittle<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p class=\"tablecap\">Table 2 \u2014 The two moisture problems. They have opposite targets.<\/p>\n<table>\n<thead>\n<tr>\n<th>Drying method<\/th>\n<th>PA6<\/th>\n<th>PA66<\/th>\n<th>PA66-GF30<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>Desiccant dryer, 80 \u00b0C<\/td>\n<td>4 \u2013 6 h<\/td>\n<td>4 \u2013 6 h<\/td>\n<td>3 \u2013 4 h<\/td>\n<\/tr>\n<tr>\n<td>Desiccant dryer, 100 \u00b0C<\/td>\n<td>2 \u2013 3 h<\/td>\n<td>2 \u2013 3 h<\/td>\n<td>2 h<\/td>\n<\/tr>\n<tr>\n<td>Vacuum dryer, 90 \u00b0C<\/td>\n<td>1.5 \u2013 2 h<\/td>\n<td>1.5 \u2013 2 h<\/td>\n<td>1 \u2013 1.5 h<\/td>\n<\/tr>\n<tr>\n<td>Hot air oven, 90 \u00b0C<\/td>\n<td>6 \u2013 8 h<\/td>\n<td>6 \u2013 8 h<\/td>\n<td>4 \u2013 6 h<\/td>\n<\/tr>\n<tr>\n<td>Dew point requirement<\/td>\n<td>\u221220 \u00b0C<\/td>\n<td>\u221220 \u00b0C<\/td>\n<td>\u221220 \u00b0C<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p class=\"tablecap\">Table 3 \u2014 Drying schedules. Over-drying above 110 \u00b0C oxidises nylon and yellows it.<\/p>\n<p>Note the second row of Table 2: dry nylon is <em>brittle<\/em>. A freshly moulded, bone-dry PA66 part will snap where the same part conditioned for two weeks will bend. This is why nylon parts are often conditioned deliberately \u2014 either by leaving them in a humid chamber, or by boiling them in water for 30 \u2013 60 minutes, which accelerates uptake to near-equilibrium in an hour.<\/p>\n<table>\n<thead>\n<tr>\n<th>Conditioning method<\/th>\n<th>Time to equilibrium<\/th>\n<th>\u0627\u0644\u0645\u0644\u0627\u062d\u0638\u0627\u062a<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>Ambient, 23 \u00b0C \/ 50 % RH<\/td>\n<td>2 \u2013 6 weeks (depends on wall)<\/td>\n<td>Uncontrolled; not a process<\/td>\n<\/tr>\n<tr>\n<td>Humidity chamber, 70 % RH<\/td>\n<td>1 \u2013 2 weeks<\/td>\n<td>Controllable and repeatable<\/td>\n<\/tr>\n<tr>\n<td>Hot water, 80 \u2013 100 \u00b0C<\/td>\n<td>1 \u2013 4 h<\/td>\n<td>Fast; can relieve stress too<\/td>\n<\/tr>\n<tr>\n<td>Steam autoclave<\/td>\n<td>1 \u2013 2 h<\/td>\n<td>Fastest; risk of over-absorption<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p class=\"tablecap\">Table 4 \u2014 Conditioning routes. Hot water is the practical answer for production.<\/p>\n<div class=\"myth\">\n<p><b>Myth: \"the part measured 50.00 mm, so it's in tolerance.\"<\/b> If it was measured an hour after moulding, it was still dry. Three weeks later it measures 50.25 mm and the customer rejects it. Every nylon drawing must specify the conditioning state \u2014 dry as moulded, or conditioned to 23 \u00b0C \/ 50 % RH \u2014 and the two give different nominal dimensions.<\/p>\n<\/div>\n<h2 id=\"processing\">Processing window<\/h2>\n<table>\n<thead>\n<tr>\n<th>\u0627\u0644\u0645\u0639\u0644\u0645\u0629<\/th>\n<th>PA6<\/th>\n<th>PA66<\/th>\n<th>PA66-GF30<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>\u062f\u0631\u062c\u0629 \u062d\u0631\u0627\u0631\u0629 \u0627\u0644\u0630\u0648\u0628\u0627\u0646<\/td>\n<td>230 \u2013 260 \u00b0C<\/td>\n<td>270 \u2013 295 \u00b0C<\/td>\n<td>280 \u2013 300 \u00b0C<\/td>\n<\/tr>\n<tr>\n<td>Barrel profile<\/td>\n<td>220 \/ 235 \/ 245 \/ 250 \u00b0C<\/td>\n<td>250 \/ 270 \/ 285 \/ 290 \u00b0C<\/td>\n<td>260 \/ 280 \/ 295 \/ 295 \u00b0C<\/td>\n<\/tr>\n<tr>\n<td>Mould temperature<\/td>\n<td>60 \u2013 90 \u00b0C<\/td>\n<td>70 \u2013 100 \u00b0C<\/td>\n<td>80 \u2013 100 \u00b0C<\/td>\n<\/tr>\n<tr>\n<td>Injection pressure<\/td>\n<td>70 \u2013 110 MPa<\/td>\n<td>80 \u2013 130 MPa<\/td>\n<td>90 \u2013 150 MPa<\/td>\n<\/tr>\n<tr>\n<td>Injection speed<\/td>\n<td>\u0633\u0631\u064a\u0639<\/td>\n<td>\u0633\u0631\u064a\u0639<\/td>\n<td>Moderate \u2014 fibre breakage<\/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<td>60 \u2013 80 %<\/td>\n<\/tr>\n<tr>\n<td>Back pressure<\/td>\n<td>0.5 \u2013 1.0 MPa<\/td>\n<td>0.5 \u2013 1.0 MPa<\/td>\n<td>0.3 \u2013 0.8 MPa<\/td>\n<\/tr>\n<tr>\n<td>Residence time<\/td>\n<td>&lt; 8 min<\/td>\n<td>&lt; 6 min<\/td>\n<td>&lt; 6 min<\/td>\n<\/tr>\n<tr>\n<td>\u0627\u0644\u0627\u0646\u0643\u0645\u0627\u0634<\/td>\n<td>1.2 \u2013 2.0 %<\/td>\n<td>1.0 \u2013 2.0 %<\/td>\n<td>0.2 \u2013 0.5 %<\/td>\n<\/tr>\n<tr>\n<td>Regrind<\/td>\n<td>Up to 25 %<\/td>\n<td>Up to 25 %<\/td>\n<td>Up to 15 % (fibre shortening)<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p class=\"tablecap\">Table 5 \u2014 Processing windows. PA66 needs roughly 35 \u00b0C more melt temperature than PA6 for the same viscosity.<\/p>\n<p>Mould temperature is the lever that controls crystallinity, and therefore strength, wear resistance and dimensional stability. A PA66 part moulded at 40 \u00b0C has a thin amorphous skin, low crystallinity in the core, and poor wear resistance; the same part at 90 \u00b0C is fully crystalline and performs as the datasheet says. For gears and wear parts, a hot mould is not optional.<\/p>\n<h2 id=\"design\">Design rules<\/h2>\n<table>\n<thead>\n<tr>\n<th>\u0627\u0644\u0645\u064a\u0632\u0629<\/th>\n<th>Rule<\/th>\n<th>Why nylon is different<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>Wall thickness<\/td>\n<td>1.0 \u2013 3.5 mm<\/td>\n<td>Thick walls have a moisture gradient for months<\/td>\n<\/tr>\n<tr>\n<td>Wall uniformity<\/td>\n<td>Within 15 %<\/td>\n<td>Differential moisture uptake causes warpage after moulding<\/td>\n<\/tr>\n<tr>\n<td>Draft<\/td>\n<td>0.5 \u2013 1\u00b0<\/td>\n<td>Nylon releases well and is slippery<\/td>\n<\/tr>\n<tr>\n<td>Ribs<\/td>\n<td>0.5 \u00d7 wall<\/td>\n<td>Thicker ribs hold moisture differently and swell<\/td>\n<\/tr>\n<tr>\n<td>Bosses<\/td>\n<td>Wall 0.6 \u00d7 nominal<\/td>\n<td>Boss cores stay hot; voids form<\/td>\n<\/tr>\n<tr>\n<td>Gate<\/td>\n<td>Large; avoid restrictive gates on GF grades<\/td>\n<td>High shear degrades melt and breaks fibres<\/td>\n<\/tr>\n<tr>\n<td>Tolerance<\/td>\n<td>Do not specify below &plusmn;0.1 mm on unfilled PA<\/td>\n<td>Moisture movement exceeds the tolerance<\/td>\n<\/tr>\n<tr>\n<td>Metal inserts<\/td>\n<td>Design for 1 % differential growth<\/td>\n<td>Nylon grows; metal does not \u2014 inserts can split the boss<\/td>\n<\/tr>\n<tr>\n<td>Sharp corners<\/td>\n<td>Internal R \u2265 0.5 \u00d7 wall<\/td>\n<td>Nylon is notch sensitive when dry<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p class=\"tablecap\">Table 6 \u2014 Nylon design rules. The tolerance row is the one that causes the most arguments.<\/p>\n<h2 id=\"gears\">Gears and wear parts<\/h2>\n<p>Nylon is the default material for moulded gears and bushes, and the reasons are specific: it has a low coefficient of friction, it tolerates shock loads, it runs without external lubrication in many applications, and it damps noise.<\/p>\n<table>\n<thead>\n<tr>\n<th>Requirement<\/th>\n<th>Grade<\/th>\n<th>Design note<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>Low load, quiet running<\/td>\n<td>PA66 unfilled<\/td>\n<td>Cheapest; swells most<\/td>\n<\/tr>\n<tr>\n<td>Higher torque<\/td>\n<td>PA66 + 30 % GF<\/td>\n<td>Stronger but more abrasive to the mating gear<\/td>\n<\/tr>\n<tr>\n<td>Mating pair<\/td>\n<td>PA66 gear + POM pinion<\/td>\n<td>Dissimilar materials reduce wear and noise<\/td>\n<\/tr>\n<tr>\n<td>High speed<\/td>\n<td>PA46 or PPA<\/td>\n<td>Better heat resistance at the tooth flank<\/td>\n<\/tr>\n<tr>\n<td>Wet environment<\/td>\n<td>PA66 + GF, or POM<\/td>\n<td>POM absorbs less water and holds tolerance better<\/td>\n<\/tr>\n<tr>\n<td>Food contact<\/td>\n<td>PA66 natural, food grade<\/td>\n<td>Check the colourant<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p class=\"tablecap\">Table 7 \u2014 Gear material selection. Never run nylon against nylon in a loaded pair \u2014 it welds and tears.<\/p>\n<p>Gear tolerances need a note: a moulded nylon gear is normally specified to AGMA 8 \u2013 9 or DIN 9 \u2013 10, not to the precision of a machined gear. If the application needs better, the gear is machined from cast nylon or from POM.<\/p>\n<h2 id=\"defects\">Defects and causes<\/h2>\n<table>\n<thead>\n<tr>\n<th>\u0627\u0644\u0639\u064a\u0628<\/th>\n<th>\u0627\u0644\u0633\u0628\u0628<\/th>\n<th>Fix<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>Brittle parts<\/td>\n<td>Over-dried, over-heated, or too much regrind<\/td>\n<td>Check moisture (not too low), melt temperature and regrind ratio<\/td>\n<\/tr>\n<tr>\n<td>Silver streaks<\/td>\n<td>Moisture above 0.15 %<\/td>\n<td>Dry longer or hotter; check dew point<\/td>\n<\/tr>\n<tr>\n<td>Bubbles in thick sections<\/td>\n<td>Moisture, or voids from shrinkage<\/td>\n<td>Dry; increase hold pressure and time<\/td>\n<\/tr>\n<tr>\n<td>Warpage weeks after moulding<\/td>\n<td>Differential moisture uptake from uneven walls<\/td>\n<td>Uniform walls; condition before inspection<\/td>\n<\/tr>\n<tr>\n<td>Dimensions drifting in service<\/td>\n<td>Moisture uptake<\/td>\n<td>Specify conditioned dimensions; use GF grade or PA12<\/td>\n<\/tr>\n<tr>\n<td>Flash<\/td>\n<td>Low viscosity at high melt temperature<\/td>\n<td>Lower melt; check clamp tonnage<\/td>\n<\/tr>\n<tr>\n<td>Short shots on GF grades<\/td>\n<td>High viscosity, cold mould<\/td>\n<td>Raise melt and mould temperature; enlarge gates<\/td>\n<\/tr>\n<tr>\n<td>Yellow \/ brown parts<\/td>\n<td>Over-heating or long residence<\/td>\n<td>Lower melt 10 \u00b0C; reduce barrel residence<\/td>\n<\/tr>\n<tr>\n<td>Cracks around inserts<\/td>\n<td>Insert expansion plus dry, brittle nylon<\/td>\n<td>Condition the part; increase boss wall; pre-heat inserts<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p class=\"tablecap\">Table 8 \u2014 Nylon defects. \"Brittle\" and \"wet\" can both be true at once \u2014 they are different faults.<\/p>\n<h2 id=\"gradient\">The moisture gradient: why thick parts keep moving<\/h2>\n<p>Moisture enters nylon from the surface. On a 1 mm wall, equilibrium is reached in a few weeks and the whole section moves together. On a 5 mm wall, the outside reaches equilibrium in weeks while the core is still dry, and the part continues to change shape for months.<\/p>\n<table>\n<thead>\n<tr>\n<th>Wall thickness<\/th>\n<th>Time to 90 % of equilibrium at 23 \u00b0C \/ 50 % RH<\/th>\n<th>Time at 70 % RH<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>1 mm<\/td>\n<td>2 \u2013 3 weeks<\/td>\n<td>1 \u2013 2 weeks<\/td>\n<\/tr>\n<tr>\n<td>2 mm<\/td>\n<td>5 \u2013 8 weeks<\/td>\n<td>3 \u2013 5 weeks<\/td>\n<\/tr>\n<tr>\n<td>3 mm<\/td>\n<td>10 \u2013 16 weeks<\/td>\n<td>6 \u2013 10 weeks<\/td>\n<\/tr>\n<tr>\n<td>5 mm<\/td>\n<td>6 \u2013 10 months<\/td>\n<td>3 \u2013 5 months<\/td>\n<\/tr>\n<tr>\n<td>8 mm<\/td>\n<td>18 \u2013 30 months<\/td>\n<td>10 \u2013 18 months<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p class=\"tablecap\">Table 9 \u2014 Moisture diffusion times for unfilled PA66. Thick sections are never in equilibrium in service.<\/p>\n<p>The engineering consequence is that a thick nylon part should be designed as a <em>dry<\/em> part with generous tolerances, or made from a glass-filled grade, or made from PA12. Specifying &plusmn;0.05 mm on a 5 mm thick unfilled PA66 part is not achievable in any state, because the part is a different size in every month of its first year.<\/p>\n<div class=\"callout\">\n<p><strong>The practical rule:<\/strong> if the wall is under 2 mm and the drawing specifies the conditioning state, unfilled PA is workable. If the wall is over 3 mm, or the tolerance is tighter than &plusmn;0.1 mm, move to a glass-filled grade. Above 5 mm, move to PA12 or accept that the tolerance applies only at one defined moisture content.<\/p>\n<\/div>\n<h2 id=\"glass\">Glass fibre: what you gain and what you lose<\/h2>\n<table>\n<thead>\n<tr>\n<th>\u0627\u0644\u0645\u0645\u062a\u0644\u0643\u0627\u062a<\/th>\n<th>PA66 unfilled<\/th>\n<th>PA66 + 30 % GF<\/th>\n<th>Change<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>Tensile strength<\/td>\n<td>80 MPa<\/td>\n<td>185 MPa<\/td>\n<td>+130 %<\/td>\n<\/tr>\n<tr>\n<td>Flexural modulus<\/td>\n<td>2.8 GPa<\/td>\n<td>9.5 GPa<\/td>\n<td>+240 %<\/td>\n<\/tr>\n<tr>\n<td>HDT at 1.82 MPa<\/td>\n<td>75 \u00b0C<\/td>\n<td>250 \u00b0C<\/td>\n<td>+175 \u00b0C<\/td>\n<\/tr>\n<tr>\n<td>Elongation at break<\/td>\n<td>25 \u2013 60 %<\/td>\n<td>2 \u2013 3 %<\/td>\n<td>\u221290 %<\/td>\n<\/tr>\n<tr>\n<td>Notched Izod<\/td>\n<td>50 \u2013 70 J\/m<\/td>\n<td>70 \u2013 95 J\/m<\/td>\n<td>+40 %<\/td>\n<\/tr>\n<tr>\n<td>Moisture growth in service<\/td>\n<td>0.3 \u2013 0.6 %<\/td>\n<td>0.1 \u2013 0.2 %<\/td>\n<td>\u221265 %<\/td>\n<\/tr>\n<tr>\n<td>\u0627\u0644\u0627\u0646\u0643\u0645\u0627\u0634<\/td>\n<td>1.2 \u2013 2.0 %<\/td>\n<td>0.2 \u2013 0.5 %<\/td>\n<td>\u221275 %<\/td>\n<\/tr>\n<tr>\n<td>\u0648\u0627\u0631\u0628\u062c<\/td>\n<td>Low\u2013moderate<\/td>\n<td>High (anisotropic)<\/td>\n<td>Worse<\/td>\n<\/tr>\n<tr>\n<td>Abrasion of the tool<\/td>\n<td>\u0645\u0646\u062e\u0641\u0636\u0629<\/td>\n<td>\u0639\u0627\u0644\u064a\u0629<\/td>\n<td>Requires hardened steel<\/td>\n<\/tr>\n<tr>\n<td>Weld line strength<\/td>\n<td>70 \u2013 90 % of parent<\/td>\n<td>40 \u2013 60 % of parent<\/td>\n<td>Much worse<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p class=\"tablecap\">Table 10 \u2014 The cost of glass. Stiffness and stability go up; elongation, weld strength and tool life go down.<\/p>\n<p>The weld-line row is the one that fails parts in the field. In a glass-filled material, the fibres do not cross the weld \u2014 they lie parallel to the weld line, so there is a plane of unreinforced resin across the part. A 30 % GF nylon part with a weld line in a loaded location behaves like an unfilled part there, and often worse, because the fibres create a notch. If a weld line cannot be avoided, move it out of the load path or use a mineral-filled grade where the filler is more isotropic.<\/p>\n<h2 id=\"underbonnet\">Under-bonnet: the real requirements<\/h2>\n<table>\n<thead>\n<tr>\n<th>Condition<\/th>\n<th>Test<\/th>\n<th>Grade requirement<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>Continuous heat<\/td>\n<td>1,000 h at 120 \u2013 150 \u00b0C<\/td>\n<td>Heat-stabilised PA66, or PA66\/PPA<\/td>\n<\/tr>\n<tr>\n<td>Peak heat<\/td>\n<td>1,000 h at 150 \u2013 180 \u00b0C<\/td>\n<td>PA66\/6T, PPA, or PA46<\/td>\n<\/tr>\n<tr>\n<td>Thermal cycling<\/td>\n<td>\u221240 to +150 \u00b0C, 1,000 cycles<\/td>\n<td>Heat-stabilised, impact modified<\/td>\n<\/tr>\n<tr>\n<td>Hot air ageing<\/td>\n<td>1,000 h at 150 \u00b0C, property retention &gt; 50 %<\/td>\n<td>Heat-stabilised grade only<\/td>\n<\/tr>\n<tr>\n<td>Coolant contact<\/td>\n<td>Glycol at 100 \u00b0C<\/td>\n<td>Hydrolysis-stabilised<\/td>\n<\/tr>\n<tr>\n<td>Fuel contact<\/td>\n<td>Petrol, diesel, ethanol blends<\/td>\n<td>PA12 or a fuel-resistant grade<\/td>\n<\/tr>\n<tr>\n<td>Salt spray<\/td>\n<td>500 h<\/td>\n<td>Not a nylon property \u2014 protect the inserts<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p class=\"tablecap\">Table 11 \u2014 Under-bonnet requirements. The heat-stabiliser package is what separates an automotive grade from a general-purpose one.<\/p>\n<p>Heat stabilisation is a real additive package, not marketing. Unstabilised PA66 loses about 70 % of its tensile strength after 1,000 hours at 150 \u00b0C; a properly stabilised grade loses 20 \u2013 30 %. The difference is a copper or organic stabiliser system that interrupts the thermal oxidation chain. It costs 10 \u2013 20 % more per kilogram and it is not optional for anything that lives near an engine.<\/p>\n<h2 id=\"faq\">Frequently asked questions<\/h2>\n<div class=\"faq\">\n<h3>Should I specify PA6 or PA66?<\/h3>\n<p>PA66 for higher strength, stiffness and heat resistance; PA6 for toughness, surface finish and cost. PA6 also processes 30 \u2013 40 \u00b0C cooler, which matters if your machine is limited. For most general parts the difference is small; for under-bonnet or high-temperature work, PA66 or a high-heat grade.<\/p>\n<h3>Why do my nylon parts measure differently a month later?<\/h3>\n<p>Moisture uptake. Dry nylon grows 0.3 \u2013 0.6 % as it absorbs water to equilibrium. Either specify and inspect in the conditioned state, or switch to a glass-filled grade where the growth is 0.1 \u2013 0.2 %, or to PA12\/PPA where it is lower still.<\/p>\n<h3>Can I boil nylon parts to condition them?<\/h3>\n<p>Yes \u2014 30 \u2013 60 minutes in water at 80 \u2013 100 \u00b0C brings most parts close to equilibrium and also relieves moulding stress. It is a standard production step for nylon gears and bushes. Do not boil glass-filled parts for long periods; the sizing on the fibre can be affected.<\/p>\n<h3>How much regrind can I use?<\/h3>\n<p>Up to 25 % on unfilled grades, 15 % on glass-filled (the fibres shorten with each pass). Regrind must be dried again, and it must be the same grade and colour. Do not use regrind in parts that will be conditioned and held to tolerance.<\/p>\n<h3>What is the difference between PA6 and PA6\/6T?<\/h3>\n<p>PA6\/6T is a semi-aromatic polyamide with a much higher melting point (around 325 \u00b0C) and much lower moisture uptake. It is used where the part must survive lead-free solder reflow (260 \u00b0C) or hold tolerance in humid conditions. It costs 3 \u2013 5\u00d7 PA66 and needs a hot-runner system rated for 340 \u00b0C.<\/p>\n<h3>Why is my glass-filled nylon part warping?<\/h3>\n<p>Fibre orientation. Glass fibres align with the flow and restrain shrinkage strongly in that direction and weakly across it, so a part with a long flow path warps. Fixes: gate from the centre, use a mineral\/glass hybrid filler, raise mould temperature, or redesign the wall to be more uniform.<\/p>\n<h3>Does nylon need a hot runner?<\/h3>\n<p>Not necessarily, but it benefits more than most materials. Nylon's high melt temperature and narrow processing window mean a cold runner wastes a lot of material and creates a lot of regrind. On a 16-cavity tool the runner can be 60 % of the shot.<\/p>\n<h3>Is nylon UV stable?<\/h3>\n<p>No. Unstabilised nylon yellows and embrittles outdoors within a year. UV-stabilised grades extend this to 3 \u2013 5 years, and carbon-black-filled grades do better. For long outdoor life, use a painted or coated part, or a different material.<\/p>\n<\/div>\n<div class=\"cta\">\n<p class=\"cta-h\">Moulding a nylon part and fighting tolerance drift?<\/p>\n<p>Send the drawing with the conditioning state and the service environment. We will tell you whether the tolerance is achievable in unfilled PA, or whether the part needs a glass-filled grade.<\/p>\n<p><a class=\"btn\" href=\"https:\/\/uplastech.com\/ar\/nylon-pa-injection-molding\/\">Talk to a nylon moulding engineer<\/a>\n<\/div>\n<div class=\"rel\">\n<h4>Continue reading<\/h4>\n<ul>\n<li><a href=\"https:\/\/uplastech.com\/ar\/pom-acetal-injection-molding-guide\/\">POM (Acetal) Injection Molding: Thermal Stability and Tooling<\/a><\/li>\n<li><a href=\"https:\/\/uplastech.com\/ar\/pbt-pet-injection-molding-guide\/\">PBT and PET Injection Molding: Glass Fibre, Drying and Warpage<\/a><\/li>\n<li><a href=\"https:\/\/uplastech.com\/ar\/injection-molding-tolerances\/\">Injection Molding Tolerances: What Is Actually Achievable<\/a><\/li>\n<li><a href=\"https:\/\/uplastech.com\/ar\/injection-molding-material-selection\/\">Injection Molding Material Selection: 14 Plastics Compared<\/a><\/li>\n<li><a href=\"https:\/\/uplastech.com\/ar\/custom-injection-molding-guide\/\">Custom Injection Molding Guide: Process, Cost &amp; Tolerances<\/a><\/li>\n<\/ul>\n<\/div>\n<\/div>","protected":false},"excerpt":{"rendered":"<p>Polyamide moulding: the two opposite moisture targets, drying schedules, conditioning methods, the moisture gradient in thick walls, glass fibre trade-offs and under-bonnet grades.<\/p>","protected":false},"author":1,"featured_media":7600,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_seopress_titles_title":"Nylon Injection Molding: Moisture, Conditioning & Dimensions","_seopress_titles_desc":"Polyamide moulding: the two opposite moisture targets, drying and conditioning, the moisture gradient in thick walls, glass fibre trade-offs and under-bonnet grades.","_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\/nylon-pa-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":"nylon injection molding","footnotes":""},"categories":[35],"tags":[],"class_list":["post-7608","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\/ar\/wp-json\/wp\/v2\/posts\/7608","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/uplastech.com\/ar\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/uplastech.com\/ar\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/uplastech.com\/ar\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/uplastech.com\/ar\/wp-json\/wp\/v2\/comments?post=7608"}],"version-history":[{"count":0,"href":"https:\/\/uplastech.com\/ar\/wp-json\/wp\/v2\/posts\/7608\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/uplastech.com\/ar\/wp-json\/wp\/v2\/media\/7600"}],"wp:attachment":[{"href":"https:\/\/uplastech.com\/ar\/wp-json\/wp\/v2\/media?parent=7608"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/uplastech.com\/ar\/wp-json\/wp\/v2\/categories?post=7608"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/uplastech.com\/ar\/wp-json\/wp\/v2\/tags?post=7608"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}