232 改性尼龙失效案例速查表
开篇先讲个现场
我们办公室有一排铁皮档案柜，最下层那格放着十几只透明收纳盒，每只盒子里装着一个失效件：开裂的齿轮、磨出亮面的轴套、鼓包的接插件外壳、发脆掉渣的接线板。每个盒子上贴一张手写标签，写着客户行业、失效时间、最后认定的原因。这一柜子东西，是我们这些年在选型和售后上交过的学费。
新同事入职，老同事带他认的第一件东西不是产品样本，而是这排柜子。因为样本告诉你材料能干什么，柜子告诉你材料栽过什么跟头。做选型的人如果只看过前者，判断里就少了一层敬畏；只看过后者，又容易畏手畏脚不敢推荐。两样都看过，才敢在电话里说这句能换、那句不能碰。
这篇速查表就是把这排柜子搬到了纸面上。八类失效按发生频率排列，每一类给三个东西：现场长什么样、根因通常藏在哪、排查先动手量什么。读法建议是先扫现象，再对根因，最后照着排查动作清单走一遍——三步都做完，八成的问题能自己定位出来，剩下两成拿着清单去找材料商，沟通成本也会低很多。
先说清楚一个前提：失效很少是单一原因。我们柜子里贴的标签，一半以上写着两个原因，比如水解加上装配应力，比如蠕变叠加高温。所以下面每一类里给的排查动作，都会提醒你别在第一个发现的原因上停下。
失效一：脆性断裂
表象：件在没有明显变形的情况下突然断开，断口平整。常见原因：材料干态（未调湿，最常见）；低温（低于脆化温度）；分子量降解（加工温度过高或反复回料）；
老化（热氧或紫外老化后变脆）。排查顺序：先测含水率，再确认使用温度，再查熔指判断是否降解。
失效二：蠕变变形
表象：件在长期载荷下慢慢变形，最终失去功能或卡死。常见原因：玻纤含量不足；选了 PA6 而工况需要 PA66；温度高于预期（高温下蠕变加速数倍）；
结构设计刚度不足。排查顺序：先确认实际工作温度，再核算蠕变模量，最后看结构设计。这类失效往往在装完半年后才暴露
失效三：环境应力开裂
表象：件在使用一段时间后出现细密裂纹，裂纹多从应力集中处起始。常见原因：残余应力 + 化学介质共同作用；注塑残余应力大（保压过高、模温过低）；装配应力（过盈配合过紧）；
介质侵蚀（油、溶剂、洗涤剂）。排查顺序：先看裂纹起始点，再查装配和工艺，最后做介质相容性验证。
失效四：水解降解
表象：件在热水或湿热环境下强度下降、表面发粘、有裂纹。常见原因：没用耐水解牌号；温度超出材料上限；介质 pH 偏离（碱性加速水解）。排查顺序：测熔指（水解后熔指显著升高），确认温度和 pH，评估是否需要换 PPS 或 PPSU。这是洗碗机、热水器、冷却系统的高发失效。
失效五：热氧老化
表象：件在高温下长期使用后变色（发黄发褐）、变脆、表面龟裂。常见原因：没加抗氧剂或加量不足；加工温度过高造成初始降解；长期温度超出材料 RTI。
排查顺序：确认长期工作温度，检查抗氧体系，测熔指和色差。电机、发动机周边的件高发。
失效排查的三条通用纪律
八类失效讲完，再补三条不分类型的通用纪律。头一条是先保住证据：失效件不要扔、不要掰开看个究竟，断口本身就是最诚实的证人，掰开搓圆之后证词就没了。第二条是问时间线：装了多久开始出问题、出了问题之后多快蔓延，潜伏半年的和装机当天的，指向的根因完全不同。
第三条是问变更：这期间换过供应商没有、改过模具没有、工艺参数动过没有，多数失效的开关都在某次变更里。三条纪律都不花钱，但能让排查少走一大半弯路。
失效六：紫外老化
表象：户外件表面粉化、失光、变色、强度下降。常见原因：没加耐候体系；耐候剂已迁移析出；颜料不耐光。排查顺序：看表面粉化程度，查耐候体系配方，做氙灯老化对比验证。户外件必加炭黑或耐候三件套。
失效七：磨损与异响
表象：滑动件磨损、间隙变大、产生异响。常见原因：没做耐磨改性；PV 值超出材料上限；对磨件表面粗糙度过高；磨料进入摩擦面（沙尘）。
排查顺序：核算实际 PV 值，检查对磨面粗糙度，确认有无磨料。耐磨改性要根据磨损类型选填料。
一次三线并查的复盘
档案柜里有只盒子标签写着两行原因：水解叠加装配应力。那是个净水器三通件，客户认定是料不耐水，供应商认定是客户装歪了，两边僵了两个月。我们介入后按三条线并查。证据线：把失效件断口拍照送检，断口上有明显的水解脆化特征，同时也发现了应力集中处的银纹。
时间线：装机三个月开始渗漏，符合水解渐进的节奏，若是装配过应力当场就会裂。变更线：那批料比上一批提前了三个月投用，恰逢雨季，仓储湿度上去了。三条线汇合，结论是两方各占一半：料用了普通牌号没做水解防护，仓储又没控湿。
最后的整改也是各改各的，换成耐水解牌号加仓库除湿，三年没再出事。这个案子后来成了我们内部教材：单线看都是别人的错，三线并查才看得见全貌。
失效八：尺寸超差
表象：装不上、间隙过大、装配后变形。常见原因：吸湿膨胀（最常见）；收缩率计算错误；后结晶收缩；批间收缩率波动。排查顺序：先测含水率，再核对收缩率数据，最后查模具和工艺。PA 件的尺寸问题八成和吸湿有关。
工程实测：4 条强制测试
测试1：脆断。先测含水率——未调湿是最常见原因。
测试2：水解。水解后熔指升高 50% 以上——熔指是快速判据。
测试3：热氧老化。变色 + 脆化 + 熔指变化——高温件必查。
测试4：尺寸。PA 吸湿 2.5% 尺寸涨 0.35%——八成尺寸问题源于此。
边界声明
| 工况 | 推荐材料 |
|---|
| 突然脆断 | 测含水率 → 查温度 → 查熔指 |
| 缓慢变形 | 核温度 → 算蠕变 → 看结构 |
| 细密裂纹 | 残余应力 + 介质 → 做相容性验证 |
| 强度下降发粘 | 水解：测熔指，查温度 pH |
| 变色发脆 | 热氧或紫外老化 |
| 装不上 | 测含水率，核对收缩率 |
工程备忘
失效速查：脆断先测含水率，水解看熔指，尺寸问题八成来自吸湿。按表象反推原因是最快的排查路径。
实战案例：常见踩坑与正解
踩坑一：失效速查查到了结论但没查适用条件，直接套用出错。任何速查表都有前提，脱离前提的结论都是错的。正解：看到结论先找它成立的条件——温度、介质、时间、载荷类型，四项齐全才敢用。
踩坑二：照抄别人的选型，没考虑自己的工艺能力。同样的料，不同设备和模具打出来效果不同。正解：选型要结合自己的工艺水平，不要选超出设备能力的材料。踩坑三：把速查表当最终依据，不做实际验证。正解：速查表用来缩小范围，最终一定要打样验证。
延伸判断：选型前要先确认的三件事
失效速查在选料之前，有三件事要先问清楚，顺序错了后面全部返工。
第一：长期使用温度是多少。短时峰值温度和长期工作温度是两回事，物性表上的热变形温度是短时指标，长期工作温度一般要打七折看。
第二：接触什么介质。油、水、清洗剂、汗液、电解液，每一种都会改变料号选择，介质清单比温度表更重要。
第三：有没有认证要求。阻燃、CTI、食品接触、涉水卫生、安规认证，有认证要求的件，换料号就要重新验证，代价远高于材料差价的几十块钱。这三件事问清楚，选料就完成了一半。
把这三件事写成一张表发给供应商，比打十通电话有用——失效速查的选型沟通成本，基本都花在这几项反复确认上。
排查自检问答
问：失效件一到手该先做什么？ 先拍照、先封存、先记录发现场景，三件事做完再动手。我们见过太多把断口掰开看、用砂纸打磨、甚至装回去继续跑的现场，证据链断了之后，所有结论都只能靠猜。
问：客户和供应商各执一词，找谁仲裁？ 有资质的第三方检测。但注意先想好送检项目：断口分析、成分比对、热分析，项目选错，钱花了结论还是模糊。把这篇前面的排查清单带上再下单。
问：失效责任明确后，同批产品要不要全部召回？ 看失效模式是离散的还是系统性的。批次混料、工艺漂移属于系统性，同批都有风险；单点装配损伤属于离散，抽检确认后不必扩大。判断依据还是时间线和变更记录。
问：排查报告写多细？ 细到半年后外人不解释也能看懂。写清现象、证据、结论、整改四块，附照片和关键数据。排查的产出不是给这次用的，是给下一次省钱的。
失效件寄样四步
发现失效后要送排查的，寄样四步走。头一步拍照：整体照、断口特写、装配位置照，三个角度缺一不可，照片是排查人看的第一手现场。第二步护断口：断口不要对碰、不要用胶带粘、不要用手反复摸，用气泡膜裹住整体寄出。
第三步附信息：装机时间、失效时间、使用环境、近期变更，一页纸写清，比电话里补三次都管用。第四步留备份：寄出前对失效件整体拍照存档，有条件的留一小块残样。我们收到过很多包裹，打开一看是碎渣一把、信息全无，排查还没开始就先输一半。四步都不花钱，省下的排查周期按周算。
建立自己的失效台账
速查表用到第二个项目，就该建自己的失效台账了。格式不复杂：一行一个案例，列七个字段——日期、产品、材料牌号、失效现象、根因结论、整改动作、验证结果。台账的价值在半年后显现：同类现象重复出现的，说明整改没打中根因；
不同产品出同一根因的，说明选型标准有个共性漏洞；台账越积越厚，新项目评审时翻一翻，很多坑不用再踩第二遍。我们这排铁皮柜加电子台账维护了多年，最初只是随手记录，现在成了选型培训的活教材。
建议从今天收到的第一个失效件开始记，字段宁细勿简，尤其根因那一栏，写具体原因，不写料不好三个字。
结语
这个件用什么料——选料这件事，越早问越省事。
这类件的选料与试模，可以一起聊。
232 Quick Reference Table of Modified Nylon Failure Cases
Let's start with a live scene
In our office, there is a row of metal filing cabinets, and the bottom compartment holds a dozen or so transparent storage boxes. Each box contains a failed part: cracked gears, shafts worn shiny, bulging connector housings, brittle and crumbling wiring boards. Each box has a handwritten label that notes the customer's industry, the time of failure, and the final identified cause. This cabinet contains the tuition we have paid over the years in component selection and after-sales.
When a new colleague joins, the first thing an experienced colleague shows him is not the product samples, but this row of cabinets. Because the samples tell you what the material can do, while the cabinets tell you the failures the material has experienced. If a person making selections has only seen the former, their judgment will lack a layer of respect; if they've only seen the latter, they'll be hesitant to make recommendations. Only after seeing both can they confidently say over the phone what can be replaced and what cannot be touched.
This quick reference sheet basically puts this row of cabinets onto paper. The eight types of failures are arranged according to occurrence frequency, and each type provides three things: what it looks like on-site, where the root cause usually hides, and what to measure first during troubleshooting. The suggested reading method is to first scan the symptoms, then look at the root cause, and finally go through the troubleshooting action checklist—if you complete all three steps, you can locate 80% of the issues yourself; for the remaining 20%, you can take the checklist to the material supplier, which will also reduce communication costs considerably.
Let's first clarify a premise: failures are rarely caused by a single reason. More than half of the labels in our cabinet list two causes, such as hydrolysis combined with assembly stress, or creep combined with high temperature. Therefore, the inspection actions given in each category below will remind you not to stop at the first cause you find.
Failure 1: Brittle Fracture
Phenomenon: The part suddenly breaks without obvious deformation, and the fracture surface is smooth. Common causes: dry material (not conditioned, most common); low temperature (below embrittlement temperature); molecular weight degradation (processing temperature too high or repeated regrinding);
Aging (becomes brittle after thermal-oxidative or ultraviolet aging). Troubleshooting order: first measure the moisture content, then confirm the usage temperature, and then check the melt index to determine if degradation has occurred.
Failure 2: Creep Deformation
Phenomenon: The part slowly deforms under long-term load, eventually losing function or seizing. Common causes: insufficient glass fiber content; choosing PA6 when the operating conditions require PA66; temperature higher than expected (creep accelerates several times at high temperature);
The structural design lacks sufficient stiffness. Troubleshooting sequence: first confirm the actual operating temperature, then calculate the creep modulus, and finally check the structural design. This type of failure often only becomes apparent six months after assembly.
Failure Three: Environmental Stress Cracking
Appearance: After being used for a period of time, fine cracks appear, usually starting from areas of stress concentration. Common causes: combined effect of residual stress and chemical media; large residual stress caused by injection molding (excessive holding pressure, low mold temperature); assembly stress (overly tight interference fit);
Medium erosion (oil, solvents, detergents). Troubleshooting order: first look at the crack initiation point, then check assembly and process, and finally perform medium compatibility verification.
Failure Four: Hydrolytic Degradation
Phenomenon: The part loses strength, becomes sticky on the surface, and develops cracks under hot water or a hot and humid environment. Common causes: Using a grade not resistant to hydrolysis; temperature exceeding the material's limit; medium pH deviation (alkaline accelerates hydrolysis). Troubleshooting sequence: Measure melt index (melt index significantly increases after hydrolysis), confirm temperature and pH, assess whether PPS or PPSU needs to be replaced. This is a common failure in dishwashers, water heaters, and cooling systems.
Failure 5: Thermal Oxidative Aging
Appearance: The component changes color (turns yellow or brown), becomes brittle, and the surface cracks after long-term use at high temperatures. Common causes: no antioxidant added or insufficient amount; high processing temperature causing initial degradation; long-term temperature exceeding the material's RTI.
Investigation order: Confirm long-term operating temperature, check the antioxidant system, measure melt index and color difference. High occurrence around motors and engines.
Three General Rules for Failure Investigation
After covering the eight types of failures, three additional general rules that are not categorized are added. The first is to preserve the evidence: do not throw away failed components, do not pry them open to see the cause—the break itself is the most honest witness; once pried open and rolled up, the testimony is gone. The second is to ask about the timeline: how long it took to start having problems after installation, and how quickly the problems spread. The root causes are completely different for issues that remained dormant for half a year versus those that occurred on the day of installation.
Article 3 is about asking about changes: during this period, whether the supplier was changed, whether the mold was modified, whether the process parameters were altered; most failed switches are involved in some change. These three rules cost nothing, but they can save more than half of the detours in troubleshooting.
Failure Six: Ultraviolet Aging
Appearance: The surface of outdoor parts shows chalking, loss of gloss, discoloration, and decreased strength. Common causes: absence of weather-resistant system; migration and precipitation of weathering agents; pigments not lightfast. Troubleshooting sequence: check the degree of surface chalking, review the weather-resistant system formula, and perform xenon lamp aging comparison tests. Outdoor parts must include carbon black or the weather-resistant three-piece set.
Failure Seven: Wear and Abnormal Noise
Manifestations: Wear of sliding parts, increased clearance, abnormal noise. Common causes: No wear-resistant modification; PV value exceeds the material limit; surface roughness of friction parts is too high; abrasive particles enter the friction surface (sand and dust).
Check sequence: calculate the actual PV value, inspect the roughness of the grinding surface, and confirm whether there are abrasives. Wear-resistant modification should select filler according to the type of wear.
A review of a three-line simultaneous check
In the filing cabinet, there was a box with a label that had two lines indicating the cause: hydrolysis combined with assembly stress. It was a water purifier three-way fitting. The customer insisted that the material was not water-resistant, while the supplier claimed that the customer had installed it incorrectly, and both sides were at a stalemate for two months. After we stepped in, we investigated along three lines. Evidence line: we took photos of the fracture of the failed part and sent it for inspection. The fracture showed obvious signs of hydrolytic embrittlement, and silver streaks were also found at the stress concentration areas.
Timeline: Leakage started three months after installation, matching the gradual pace of hydrolysis; if it were assembled with excessive stress, it would have cracked immediately. Change line: That batch of material was put into use three months earlier than the previous batch, coinciding with the rainy season, and storage humidity increased. The three lines converge, and the conclusion is that both factors contributed equally: the material used a standard grade without hydrolysis protection, and storage humidity was not controlled.
The final rectification was also done individually; each person made their own changes, switching to a hydrolysis-resistant grade and adding dehumidification in the warehouse. There were no incidents for three years. This case later became our internal teaching material: looking at a single line, it was someone else's fault, but only by investigating across three lines could the full picture be seen.
Failure 8: Dimension Out of Tolerance
Manifestation: Cannot be installed, excessive gap, deformation after assembly. Common causes: moisture absorption and expansion (most common); incorrect shrinkage rate calculation; post-crystallization shrinkage; batch-to-batch shrinkage rate fluctuations. Troubleshooting sequence: first measure the moisture content, then verify the shrinkage rate data, and finally check the mold and process. About 80% of dimensional issues with PA parts are related to moisture absorption.
Engineering field measurement: 4 mandatory tests
Test 1: Brittleness. First measure the moisture content—the most common reason is that it has not been conditioned.
Test 2: Hydrolysis. After hydrolysis, the melt index increases by more than 50% — the melt index is a quick criterion.
Test 3: Thermal oxidative aging. Discoloration, embrittlement, melt index changes — a must-check for high-temperature components.
Test 4: Size. PA absorbs moisture 2.5%, size increases 0.35% - eighty percent of size problems come from this.
Boundary Declaration
| Operating condition | Recommended materials |
|---|
| Suddenly brittle and breaks | Measure moisture content → Check temperature → Check melt index |
| Slow deformation | Core temperature → Calculate creep → Check structure |
| fine cracks | Residual stress Medium → Perform compatibility verification |
| Strength decreases and becomes sticky | Hydrolysis: measure melt index, check temperature and pH |
| Discoloration and brittleness | Thermal-oxygen or ultraviolet aging |
| Can't install | Measure moisture content, check shrinkage rate |
Engineering memo
Failure Quick Lookup: For brittle fracture, first measure moisture content; for hydrolysis, check melt fingers; size issues are mostly due to moisture absorption. Using appearances to reverse the cause is the fastest way to troubleshoot.
Practical Case: Common pitfalls and correct answers
Pitfall 1: Failure quick search finds a conclusion but not applicable conditions, so applying it directly leads to errors. Every quick check table has premises; conclusions that deviate from these premises are wrong. Correct answer: When you see a conclusion, first look for the conditions that hold it—temperature, medium, time, load type. Only use it when all four are complete.
Pitfall 2: Blindly copying others' selection without considering your own process capability. The same material produces different results depending on equipment and mold. Correct answer: Selection should be based on your own process level; avoid materials beyond the equipment's capabilities. Pitfall 3: Use the quick reference sheet as the final reference, without actual verification. Correct answer: The quick reference table is used to narrow down the scope; final sample verification is necessary.
Extended judgment: Three things to confirm before selecting
Failure Quick Check Before selecting materials, there are three things to clarify; if the order is wrong, rework everything afterward.
First: What is the long-term operating temperature? Short-term peak temperature and long-term operating temperature are two different things; the thermal deformation temperature on the physical property table is a short-term indicator, and long-term operating temperature should generally be discounted by 70%.
Second: What medium should it be contacted? Oil, water, cleaning agent, sweat, electrolyte—each will change the selection of part numbers. The list of media is more important than the temperature chart.
Third: Are there certification requirements? For parts with certification requirements—flame retardant, CTI, food contact, water hygiene, safety regulations—if there are certification requirements, the replacement number must be reverified, and the cost is much higher than the material price difference. If you clarify these three things, the material selection is half done.
Write out these three things in a form and send it to the supplier—it's more effective than making ten phone calls—the cost of communication for the failure check is basically spent on these repeated confirmations.
Troubleshooting Self-Inspection Q&A
Question: What should you do first when you get a failed part? Take photos first, seal the data, record the discovery scene—do these three things before you get started. We've seen too many scenes where the fracture is split open to look, sanded with sandpaper, or even put back and run again. Once the chain of evidence is broken, all conclusions can only be guessed.
Question: Customers and suppliers each have their own views—who should arbitrate? Qualified third-party testing. But make sure to think carefully about the inspection items first: fracture analysis, composition comparison, thermal analysis. If you choose the wrong item, even if you spend money, the conclusion is still vague. Bring the previous inspection checklist before placing the order.
Question: After the failure responsibility is clarified, should all products from the same batch be recalled? Check whether the failure mode is discrete or systemic. Batch mixing and process drift are systemic, and all batches carry risks; Single-point assembly damage is discrete; after sampling and confirming, there is no need to expand it. The judgment is still based on timelines and change records.
Question: How detailed should the investigation report be written? Detailed enough that even half a year later, outsiders can understand it without explanation. Clearly state the phenomena, evidence, conclusion, and rectification, along with photos and key data. The inspection output is not for this time, but to save money next time.
Four steps to sending samples of failed parts
Sending samples for inspection after discovering defects, the four steps to send samples. Step one is photography: overall photos, close-up of the fracture surface, and assembly position photos—all three angles are essential. The photos are the firsthand view of the inspector's scene. Step two: protect the fracture: do not touch the fracture joints, do not use tape to seal them, do not touch them repeatedly, and wrap the entire unit with bubble wrap before shipping.
Step 3: Attach information: installation time, downtime, usage environment, recent changes—write it all down on one page, which is more effective than making up for it three times over the phone. Step 4: Keep a backup: Before shipping, take photos of the entire damaged item for archiving, and if possible, keep a small sample. We've received many packages before; when opened, they were just a handful of fragments with no information at all, and half of the inspection was entered before the investigation even started. None of these four steps cost anything, and the savings in inspection cycles are calculated weekly.
Establish your own failure record
Quick Reference Sheet When you use the second item, it's time to create your own failure record. The format is simple: one case per line, seven fields listed—date, product, material grade, failure phenomenon, root cause conclusion, rectification actions, verification results. The value of the ledger becomes apparent after half a year: if similar phenomena recur, it means the rectification didn't hit the root cause;
If different products have the same root cause, it means there's a common loophole in the selection criteria; The ledger keeps getting thicker, and when reviewing new projects, you won't have to go through many pitfalls again. Our row of metal cabinets plus electronic ledgers has been maintained for years. At first, we just took random notes, but now they've become living textbook for model selection training.
I suggest starting with the first failed item you receive today. It's better to be detailed than simple, especially in the root cause section—write the specific reason. If you don't write the three words 'bad material', it's not good.
Conclusion
What material is used for this item—the earlier you ask about material selection, the easier it is.
For material selection and mold trials for this type of piece, you can chat together
