# 7 modi efficaci per ridurre i difetti nella produzione di custodie EVA

Canonical URL: https://evacasemanufacturer.com/it/news/7-effective-ways-to-reduce-defects-in-eva-storage-case-manufacturing
Published: 2026-02-02 12:56:00
Author: Dongguan Lianping Luggage Co., Ltd.
Publisher: LIANPING
Keywords: eva case defect reduction, custom eva case manufacturer, compression molding defects, eva shell wall thickness, zipper cycle test 5000, die cut foam density, ista 2a drop test eva case, eva case quality control
Views: 1.431
Language: it

Sette controlli in produzione che riducono gli scarti su custodie EVA personalizzate: essiccazione dei fogli, registrazione delle piastre, spessore delle pareti agli angoli, durata della cerniera, densità della schiuma e prove di caduta ISTA 2A.

Scrap on an EVA line rarely comes from one dramatic failure. It accumulates in small amounts: a lid that sits 0.5 mm proud, a corner that whitens when it flexes, a zipper that catches after three hundred pulls. Across six lines running more than 100 machines, the defects that cost the most are almost always the ones that surface late, after the shell has been trimmed, lined and packed. These are seven checks that moved the numbers at our Gaobu plant.

## Molding: four checks that catch most shell defects

1. Dry the sheet before it goes near the press. EVA sheet picks up moisture in a Dongguan summer, and a damp blank blisters under a platen at 170 to 180 °C (338 to 356 °F). We hold cut blanks in a dehumidified room for at least eight hours. The test is crude but effective: weigh a sample stack before and after a four-hour hold, and if it drops more than about 0.3%, the batch goes back.

2. Log platen temperature at the first shot, not at noon. Most of our shell variation used to come from the first 40 minutes of a shift. A press that reads 175 °C on the panel can be 12 to 15 °C lower at the corners of the platen before it soaks through. We now write a longer preheat into every setup card and record the first-shot reading, which pulled corner whitening on tool case shells from roughly 3% down under 1%.

3. Set wall thickness by the corner, not the face. Sheet at 0.18 to 0.22 g/cm³ thins out where it has to stretch around a deep draw. If the drawing only calls out a nominal 5 mm wall, the corner comes out near 3.5 mm and the case creases the first time someone sits on it. We specify the corner minimum on the mold drawing and check it with a pin gauge every 200 shots.

4. Give the shell a full day before trimming. Freshly molded EVA keeps moving for several hours as it cools and relaxes. Trim the same afternoon and you get lids that fit on the bench and gap in the carton. We stage shells for at least 12 hours, and the trimming operators can tell the difference by hand.

## Assembly: zipper, lining and the final bench

5. Treat the zipper as the wear part. On a hard shell case the zipper is usually the first thing to go, not the shell. YKK #5 and #8 coils run past 5,000 open-close cycles on our bench when the tape is set with 8 to 10 mm of seam allowance and the stitch line stays off the coil. Pull the tape too tight and you lose about a third of that life.

6. Match the lining to the contents, not to the sample book. Die-cut foam at 25 to 30 kg/m³ holds a tool set; egg-crate foam is the wrong choice for a drone controller because the peaks crush flat within a month. Velvet or a soft tricot marks less on painted surfaces, which is why we use it inside [EVA eyeglass cases](https://evacasemanufacturer.com/it/products/sub/eva-eyeglasses-case). Getting this wrong does not create a scrap part, it creates a return six months later.

7. Inspect the thing the customer inspects. Our lines run full inspection on cosmetic surfaces and AQL 2.5 on functional checks, but the number that matters is the drop test: 1.0 to 1.5 m onto concrete, six faces, three drops each, per ISTA 2A. Two shells per 1,000 go to the bench every week from every line, and when a [custom EVA case](https://evacasemanufacturer.com/it/products/category/eva-cases) fails there the batch holds. The variable being pinned down this week is glue open time on the PU leather surface for a run of [earphone cases](https://evacasemanufacturer.com/it/products/sub/eva-earphone-headphone-case), tested at 90 seconds against 120 seconds before it goes into the standard work sheet.

## FAQ

**What is a realistic defect rate for custom EVA case production?**

On a stable program, cosmetic reject rates typically sit between 1% and 3% and are caught at trimming. Functional rejects measured by drop testing are usually well under 1%. New tools and deep-draw shapes run higher for the first few thousand shots until wall thickness at the corners is dialled in, so most buyers plan a first article and a pilot run before the full order.

**How are EVA hard shell cases tested before shipment?**

Standard practice is a loaded drop test of 1.0 to 1.5 m onto concrete, six faces and three drops each, following the sequence in ISTA 2A, often paired with the vibration profile in ASTM D4169. Zippers are cycled to 5,000 open-close operations, and cartons are checked for corner crush before loading. Test reports are issued with the shipment lot number.

**What causes EVA shells to crack or whiten at the corners?**

Corner whitening usually comes from under-heated sheet, moisture in the blank, or wall thickness that drops below about 3.5 mm at a deep-draw corner. Cracking is different and points to sheet that is too hard for the geometry, typically above Shore C 70, or to a shell trimmed before it has relaxed for at least 12 hours after molding.

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