Qualify an alternative resin with a one-gaylord trial lot

When a trial lot makes sense

A trial lot is the step between a paper match and a production release. It comes after incoming inspection, which has its own checklist on incoming resin inspection. This page covers what happens next: proving an alternative grade in the part.

Printable trial-run worksheet (PDF): one page for drying, incumbent vs. trial process settings, first-article checks and sign-off.

• Adding a second source. You want a qualified backup before your main supplier slips. The same grade from another seller usually needs only a light trial. An equivalent from another producer needs the full trial on this page. See set up a backup resin source and how to qualify a second source.
• Cost-down alternative. A matched grade at a lower delivered cost only saves money if the part still passes. The trial is where the saving is proven. Compare cost per part, not per pound, because a different density changes part weight.
• Grade on allocation or discontinued. When your grade is short or going away, qualify the replacement while you still have stock to run. See allocation and force majeure, replacing a discontinued grade and PA66 shortage alternatives.
• Brand ownership change. When a resin line moves to a new owner, the grade name may stay while the production site or the data sheet changes. If either changes, treat it like a new grade and run a trial lot. Ask for the current data sheet and where the grade is made.

Looking for candidates? Start with the resin grade cross-reference and how to find an equivalent grade.

Before you order: paper review

Many failed trials could have been caught on paper. Spend an hour here before you spend a press shift.

• Data sheets side by side. Put the incumbent and trial data sheets next to each other. Check base polymer, filler type and level, melt flow, density, mold shrinkage along and across flow, tensile strength, flex modulus, impact and HDT. See how to read a resin data sheet.
• Test methods comparable. ASTM and ISO results are not directly comparable. Melt flow must be at the same temperature and load, HDT at the same stress (0.45 or 1.8 MPa), and impact on the same test (Izod vs. Charpy). Nylon values must be on the same basis, dry as molded or conditioned. If the methods differ, ask for data on the same basis rather than guessing.
• The drawing callout. Check the trial grade against the callout on the drawing, not only against the incumbent grade. The material code decoder explains callouts, and the trade name decoder shows the family behind a brand name.
• Regulatory letters. FDA food contact, NSF, RoHS, REACH or whatever your customer requires. These belong to the exact grade, not the family. See resin compliance documents.
• UL Yellow Card. If the part needs a flame rating or RTI, the trial grade needs its own UL recognition, at your wall thickness or thinner and in your color. Look the grade up in UL Product iQ. A family-level match is not enough. See UL 94 ratings explained.
• Color match. A precolored trial grade needs its own match to your color standard. If you color at the press, the masterbatch let-down ratio may need adjusting on a different base resin. See masterbatch vs. precolored resin.
• COA contents. Check which properties the trial grade's COA reports and the producer's spec range for each. See what a COA shows.

Then write down the go/no-go criteria before anyone sees parts: which dimensions, what part weight range, what cycle time, what appearance standard, which functional tests. Criteria set after the trial tend to drift toward whatever the trial produced.

How much material do you need?

Work it out from your shot, not from a guess. Count four things: purge and startup, setup while you find the process, the trial run itself (with capability samples pulled from it), and parts for tests and retains.

Example (illustrative numbers): a 4-cavity tool, 45 g parts, a 20 g cold runner, so a 200 g (0.44 lb) shot, on a 30-second cycle (120 shots an hour).

Illustrative numbers only. Use your own shot weight, cavities, cycle and run length. The order size calculator turns part weight and volume into pounds and gaylords.

In this example a 1,000 lb gaylord covers the trial with about 470 lb to spare. That is enough for a second day if the first shift raises questions, or a rerun after a process change. If the trial passes and the change is approved, the rest can run as production.

Plan on the net weight on the quote, not the box count. Light resins such as PP fill a gaylord before they reach the top of the typical range, and dense resins such as acetal are packed to a weight limit. See bulk density of plastic pellets and gaylord vs. LTL vs. truckload.

When to order two gaylords:

• Large shots. A 1 kg (2.2 lb) shot at 60 shots an hour uses about 130 lb an hour, or over 1,000 lb in an 8-hour shift.
• Extrusion. A line running 250 lb an hour can use about 850 lb on startup and purge (say 100 lb), an hour to stabilize (250 lb) and two hours of steady running for samples (500 lb), before any rerun.
• Several molds or part numbers on the same grade.
• A longer customer run. If the trial must also serve as a production-representative run for PPAP, size it to that run (see below).
• Lot-to-lot check. If you want to see two lots, ask whether two different lots are available for the grade.

Run the trial

1. Dry per the trial grade's data sheet, not the incumbent's. Temperature, time and dew point can differ between grades of the same family. On hygroscopic resins, check moisture after drying. See the resin drying guide.
2. Run the incumbent first, the same day. Mold a set of incumbent parts on the same press and mold, and record the settings. Ambient conditions, water temperature and the press drift from day to day, so same-day parts give the fairest comparison.
3. Purge, then start from current settings. Switch to the trial grade at the incumbent's settings, adjusted only where the trial grade's data sheet calls for a different melt or mold temperature range. Change one thing at a time and record each change and why. See purging and color changes.
4. Record a process window. Do not stop at the first good part. Find the edges: where short shots start and where flash starts, the melt temperature range that makes good parts, and a gate freeze check (part weight vs. hold time). A wide window means the grade will tolerate normal variation. A narrow one is a warning even when the parts look good. See processing parameters.
5. Center, settle, then run. Go back to the middle of the window and let temperatures and cycle stabilize before you pull first articles. Then run the planned length and pull capability samples spread through the run, from every cavity.
6. Label everything. Mark trial parts with grade, lot, cavity and time, and keep them apart from production parts.

What to log, for the incumbent and the trial:

• Melt temperature, measured with a probe on an air shot, not just barrel setpoints
• Fill time and peak injection pressure
• Transfer position, pack and hold pressure and time, cushion
• Mold temperature on both halves, cooling time and total cycle time
• Screw recovery time
• Shot weight and part weight per cavity, sampled through the run
• Defects seen, and the setting that cleared them

Part weight should scale with density. Expect roughly incumbent part weight × (trial density ÷ incumbent density). A trial part well under that figure points to under-packing or short fill; well over it points to over-packing or flash. If later lots of the new grade run differently, see when a new lot runs differently.

What to measure on first articles

Measure after parts have cooled and stabilized, often 24 hours or more. Nylon keeps changing as it picks up moisture, so measure dry as molded and after conditioning, or by your customer's method. Measure same-day incumbent parts with the same gauges and the same operator.

Typical practice only. Your drawing, your customer's specifications and any agreed standards set the real limits.

Capability. If the customer wants capability on critical dimensions, many shops use 25 subgroups of 5 parts (125 readings) per characteristic, and some customers accept 30 parts for a first look. On multi-cavity tools, study each cavity. A Ppk of 1.67 is a common target for an initial study, with 1.33 often used for ongoing production, but the customer sets the number and the sample size. Shrinkage and warp troubleshooting: warped parts and dimensional variation. Tool fit questions: running a different resin in your existing mold.

Decide and document

• Go, no-go or rerun. Judge against the criteria you wrote before the trial. Go: every check passes with margin and the process window is comparable to the incumbent's. No-go: a failed functional test, or dimensions a process change cannot bring back. Rerun: marginal results, unexplained variation, or a process change you want to confirm on the rest of the gaylord.
• Customer approval or PPAP. If the drawing names a grade or the customer approved one, a change needs their sign-off. For production automotive parts, an equivalent from another producer is a material change that normally needs customer notification and, unless the customer waives it, a PPAP submission before you ship. PPAP generally needs parts from a production-representative run: the AIAG standard's significant production run is at least 300 consecutive parts on production tooling, process and operators, unless the customer agrees otherwise. A short trial may only be the first step. Check your customer's own requirements. Medical and other regulated parts go through the customer's change control.
• Lot traceability. Record the trial lot number, its COA, press, mold, date and which parts came from it. If any trial parts ship after approval, the lot must trace to the shipment.
• Keep retains. Seal a labeled resin retain from the trial lot, and keep labeled sets of trial and incumbent parts. If a later lot runs differently, these are your reference.
• Move to production release. Update the process sheet with the settings the trial grade actually needed, the bill of materials, the approved supplier list and the control plan if you have one. On the first production order, ask for the same lot as the trial if it is still available, or confirm the lot-to-lot ranges (the producer's spec limits on the COA properties) so you know how far a later lot can move. Run incoming inspection on the first production lot and compare its COA with the trial lot's.

Ordering a trial lot from ResinBridge

Send us:

• The grade you run now, or the material callout on the drawing (a data sheet or a photo of the bag label helps)
• Annual volume, and how much you want for the trial
• Ship-to city and ZIP
• Color, and any listings or compliance letters the part needs

A polymer chemist reviews every request. We quote the grade you asked for, or a matched alternative named on the quote with its data sheet, so you can do the paper review before you order. A supplier COA comes with every prime lot. Orders start at one gaylord and go up to a railcar, shipped from 22+ partner warehouse locations, backed by 30+ years in the resin business. We aim to quote within one to three business days. If you want a later production order from the same lot as the trial, say so on the request.

Request a trial-lot quote. More on buying by the gaylord: small-quantity resin. To send the full spec in one file, use the resin RFQ template.

Common questions

Sources

• AIAG: Production Part Approval Process (PPAP)
• Prestolite Electric Supplier PPAP Handbook (AIAG-based): significant production run of 300 consecutive parts; capability 1.67 initial, 1.33 ongoing; per-cavity studies
• Production part approval process: the 18 PPAP elements (Wikipedia)
• UL Solutions: How to read the UL Yellow Card
• UL Solutions: Yellow Card plastics recognition program