前年梅雨季，一家做燃油蒸发系统的客户寄来两个碳罐外壳。
两个都是玻纤增强的改性尼龙件，黑色，剖开之后内壁发黏，指甲一刮能刮下一层薄薄的糊状物。
他的原话我记得很清楚：
>"壳没裂，也没漏。就是装车放两个月，内壁黏手，还带一股很冲的汽油味。这算不算我们的问题？"
这句话里其实藏着三个可以分开的变量：装的是什么油、内壁接触的是液态还是蒸气、以及在多少度下放。
我回了三句问话：当地是不是乙醇汽油？内壁有没有液态油积存？EGR 侧有没有冷凝液下来？
三句问完，方向就有了。碳罐材料难就难在——它同时面对"油"和"酸"两种介质，而这两种介质的攻击方式完全不同。
油是往里渗、把东西抽出来；酸是直接切分子链。怕的东西不一样，解药也不一样。
一、工况六维：介质这一维，要拆成两条
温度分两个区。 碳罐本体随环境走，-40℃ 到 80℃ 之间波动，靠近排气管的位置会更高。
EGR 阀件是另一个量级：废气侧本体温度可达 150–200℃，某些工况更高。
介质要拆开看，这是这个件最容易被搞混的一处。
碳罐内壁接触的是燃油蒸气，不是液态汽油。蒸气里还带着乙醇、水汽和少量有机酸。
EGR 一侧更狠：废气冷凝之后会生成亚硫酸、硝酸一类的酸性冷凝液，pH 常在 2–4。
pH 2 是什么概念？柠檬汁大约就是 2.2。也就是说，那件要在一个酸度接近柠檬汁的环境里待上十几年。
压力是交变的。 碳罐要做泄漏诊断，系统会加 -3 到 +5 kPa 的微正负压，一天里反复几十次。
寿命按法规走。 蒸发排放按 15 年 / 24 万公里考核，期间任何一次泄漏诊断失败都可能直接触发故障码。
外观与重量也是指标。 碳罐挂在车身上，支架受力，外壳还要过跌落；同时它又有减重压力。
合规要注意一条。 蒸发排放、渗透率、耐燃油，这三项都有法规原文。要在定点前拿到适用版本的原文，不能只拿一份物性表。
一个数字换算：乙醇汽油里乙醇按体积约 10%，它比汽油更容易吸水。
一只 500 毫升容积的碳罐，长年累月进出的是"油 + 醇 + 水"三种分子的混合物，而不是单纯的汽油蒸气。
渗透率按天算，法规口径通常在毫克量级——比一滴水的百分之一还小。所以这个件是"薄壁 + 高阻隔要求"的组合。
二、材料路线：碳罐壳和 EGR 阀件要分开选
把两个件放在一张表里看，才看得出为什么要分开。
| 路线 | 长期耐温 | 耐燃油蒸气 | 耐酸性冷凝液 | 代价 |
|---|
| PA6-GF30 | 100–120℃ | 一般 | 弱 | 成本低、成型成熟 |
| PA66-GF30 | 130–150℃ | 较好 | 中 | 吸湿尺寸漂移较大 |
| PA66-GF35 | 130–150℃ | 较好 | 中 | 熔接线强度随玻纤上升而下降 |
| PA6T-GF30 | 150℃ 以上 | 较好 | 中上 | 工艺窗口窄、成本高 |
| PPS-GF40 | 200℃ 量级 | 好 | 好 | 成本高、韧性低、模具要求高 |
| 多层阻隔 / 金属罐 | — | 视结构 | 视结构 | 不是单一材料方案，结构与成本要重排 |
看这张表，重点不在"哪个强"，在分工。
碳罐外壳的主流思路是 PA66-GF30 这一类：壁厚不大、要焊接、要控成本，耐蒸气够用就行。
EGR 阀件要单独看。它的温度与酸性冷凝液两件事叠在一起，PA66 体系在长期高温 + 酸的环境里会有一段比较吃力的区段。
这时候要么把 EGR 侧的件单独升到 PA6T 或 PPS 体系，要么在结构上把冷凝液导走。
一句话：碳罐壳和 EGR 阀件往往不是同一个料号，把它们并成一个料号省下的管理成本，常在验证阶段还回去。
三、选型判据表（这一页最该收藏）
| 指标 | 方向性门限 | 验证方法 / 标准 | 常见失效 | 通行解法 | 对应助剂体系 |
|---|
| 耐乙醇汽油（体积变化） | 60℃×1000h 后体积变化 ≤5% | ISO 1817 / ASTM D471 | 溶胀、内壁发黏 | 基材选型 + 控制小分子用量 | 润滑剂（低抽出型） |
| 浸泡后力学保留 | 拉伸保留 ≥70% | ISO 527-2 / GB/T 1040.2-2022 | 脆化、开裂 | 稳定化体系 + 结晶度控制 | 抗氧剂（受阻酚 + 亚磷酸酯复配） |
| 耐酸性冷凝液 | pH 2–4、80℃×500h 后力学保留 ≥70% | GB/T 11547-2008 耐液体化学试剂 | 表面龟裂、粉化 | 基材升级或结构导流 | — |
| 内壁析出物 | 表面无粘性析出，质量变化可控 | 浸泡后外观 + 称重 | 发黏、气味残留 | 控外润滑总量、换低抽出体系 | 润滑剂（低抽出型） |
| 焊接强度 | 熔接线强度 ≥ 本体 60% | 件级剖检 + 拉伸 | 焊缝渗漏、泄漏诊断失败 | 控玻纤含量 + 焊接工艺 | 偶联剂（纤维 / 树脂界面） |
| 渗透率 | 按适用法规口径 | 件级密闭室法 | 蒸发排放超标 | 壁厚 / 阻隔结构设计 | — |
| 尺寸稳定 | 0.3% 量级以内 | ISO 294 / 调湿前后实测 | 装配干涉、支架应力 | 强制调湿或低吸水基材 | — |
| 低温冲击 | -40℃ 落锤不脆裂 | ISO 179-1 / GB/T 1843-2008 | 拆装或磕碰开裂 | 增韧体系 + 结构圆角 | — |
怎么用这张表：先看表里最靠前的两行——耐乙醇汽油与耐酸性冷凝液。
这两行决定基材，剩下的都是工艺与结构能补的。顺序反过来，就会一直在换牌号。
提醒一句：耐介质数据一定要说明"浸泡的是哪种介质、多少温度、多少小时"。只写"耐油"两个字的数据，没有可比性。
四、四条常见失效，和它们的真实根因
失效一：内壁发黏、有糊状析出，件本身完好。
根因不是"料被溶了"，多数是小分子助剂被燃油蒸气抽出来，在表面富集。
脱模剂、低分子量润滑剂在常温汽油里还算老实，到了 60℃ 的蒸气里就容易被带走。
助剂侧的一条归因：这类发黏，常常是外润滑与脱模组分用量偏高、分子量偏小造成的。解法是把它换成长链或高分子量体系，并把外润滑总量压下来。
这里要否定一个常见做法：有人看到发黏，下意识就认为"润滑不够了，加点润滑剂"。
方向正好反了——加得越多，抽出来越多，表面越黏。
失效二：焊缝渗漏，泄漏诊断报码。
碳罐多是焊接成型，熔接线强度通常只有本体强度的六成上下，而玻纤含量越高，熔接线越弱。
排查顺序是：先看焊线位置与焊接参数，再看玻纤含量，最后才怀疑基材。
失效三：EGR 阀件表面龟裂、一掰就断。
这是酸 + 高温的联合作用。为什么酸会这么厉害？
聚酰胺的主链是酰胺键，在酸的催化下会水解断裂——分子链被一段段切短，宏观上就是强度垮掉。
温度每上去一截，这个反应就快一截。所以 EGR 侧的寿命温度，是比碳罐侧硬得多的门槛。
失效四：同一批件黄得深浅不一。
这不是"料不稳定"。更可能是抗氧剂在混料阶段没被搅匀，颗粒之间的分散程度不一样。
遇到这种情况，先查混料工序和母粒化那一步，别急着换牌号。
五、加工与验证：这类件的顺序要改一下
干燥。 尼龙必干燥。含水率超标时，在料筒里就会水解降解，件出来强度已经打了折。
模具与焊接。 碳罐的外形和焊线位置要一起定。焊线避开高应力区、避开壁厚突变处。
浇口与取向。 玻纤沿流动方向排队，焊线两侧的纤维方向如果不对称，焊接后应力会自己找地方释放。
验证顺序建议这样排：
1. 调湿后尺寸与外观（干态数据只做过程记录）
2. 介质浸泡：乙醇汽油 + 酸性冷凝液两组，分别做
3. 浸泡后力学保留率与质量变化
4. 焊接件剖检 + 泄漏诊断台架
5. 渗透率件级测试
6. 整机装车与法规工况
顺序不能换。介质浸泡不过，后面的台架数据都没有解释意义。
一个容易被漏掉的细节：浸泡试验要拿带焊线的成品件做，不要只拿样条。
样条测的是材料，成品件测的是材料和结构一起。碳罐的失效常常出在焊线上，样条给不出这个答案。
六、边界：什么时候单层塑料做不到
其一，要求近零排放级渗透。 单层聚酰胺的阻隔能力有上限，要做到更低渗透，要看多层结构或其他阻隔方案，而不是继续在配方里加东西。
其二，EGR 侧长期温度超过 200℃。 这个区段里常规改性尼龙不合适，要往 PPS 体系或金属走。
其三，件要长期接触液态燃油而不是蒸气。 液态浸泡比蒸气苛刻得多，用量与温度条件都要重新算。
其四，年用量小到摊不平模具与法规验证成本。 这类件的验证要跑法规工况，周期和费用都不算小。
把这四条摆出来，是为了让项目在立项阶段就知道自己要花多少时间和多少钱。
补一节：介质浸泡试验怎么做才算数
这一节是我最想让你带走的部分。这类件的验证，介质做错了，等于没做。
介质要按实际装车地区的油来配。 有的地区是纯汽油，有的地区是乙醇汽油，两者的攻击性不一样。
温度要按长期值取。 用 23℃ 泡 1000 小时，和一个夏天车里 60℃ 的环境，测的不是同一件事。
要称重，不能只看外观。 体积变化、质量变化、浸泡后力学保留，三样一起记录。
要用带焊线的成品件做。 样条给不出焊线那一问的答案。
| 试验项 | 介质 | 温度 / 时长 | 看什么 |
|---|
| 耐乙醇汽油 | 乙醇汽油 E10 | 60℃×1000h | 体积变化、质量变化、外观 |
| 浸泡后力学 | 同上浸泡后取样 | 浸泡后测 | 拉伸保留率 |
| 耐酸性冷凝液 | pH 2–4 混合酸液 | 80℃×500h | 力学保留、表面状态 |
| 渗透率 | 件级密闭室法 | 按法规工况 | 日渗透量 |
| 焊接件验证 | 成品灌装件 | 同上 | 焊线是否析出、渗漏 |
再补一条时间线，让这件事有"发生过"的样子：
`
换料 ├── 上线顺利：料价省了，首件检验合格
│
第 2 个月
├── 内壁摸上去略黏（当时判为清洗不彻底）
├── 气味偏大（当时判为装配密封问题）
└── 第 14 个月整车报泄漏码 → 追溯批号 → 换低抽出体系
`
那些被忽略的信号，当时看着都不像问题。 等它变成故障码，验证已经来不及做了。
另外回答一句常被问的：这套试验要不要买设备？
介质浸泡不需要昂贵设备，恒温箱加天平就够。真正花掉的是时间——一组浸泡就是一个多月。
而它决定了后面所有台架数据有没有解释意义。这个顺序，值得把工期让出来。
换料风险清单（从原方案换过来，要动的几项）
| 环节 | 要动什么 | 容易漏的点 |
|---|
| 模具 | 收缩率随玻纤含量变，壳体与盖要同步修 | 焊线位置的壁厚突变 |
| 干燥 | 按实测含水率定窗口，用除湿干燥机 | 回用料掺入带进的水分 |
| 料温 / 模温 | 模温按焊接面平整度与纤维排布联合调 | 只抄牌号推荐值，不看件 |
| 焊接 | 焊接参数随基材与玻纤含量重定 | 沿用原方案的焊接曲线 |
| 调湿 | 强制调湿 + 复测尺寸 | 按平均壁厚估时间，厚壁处没吸透 |
| 介质验证 | 乙醇汽油与酸性冷凝液要分两组做 | 只做汽油一组，漏掉酸 |
| 渗透率 | 件级测试，不能拿样条替代 | 用样条数据推算件级渗透率 |
| 验证顺序 | 尺寸 → 介质 → 焊接 → 渗透 → 整机 | 前一项未过就往下走 |
一页纸汇报表（给要向上汇报的人）
`
项目：汽车碳罐外壳 / EGR 阀件 · 材料路线评估
结论方向：碳罐壳与 EGR 阀件建议分开选材，能否落地取决于介质验证结果
一、必须守住的三条
1. 介质验证分两组：乙醇汽油、酸性冷凝液，不能只做一组
2. 焊线避开高应力区，焊接件必须做剖检
3. 渗透率按件级测，不接受样条外推
二、前置条件（任一不满足则建议暂缓）
· EGR 侧长期温度在 200℃ 以内
· 渗透率目标在单层聚酰胺可覆盖的范围内
· 有跑法规工况的验证预算与周期
· 年用量足以摊平模具与验证成本
三、下一步动作
1. 确认装车地区的燃油品类（是否乙醇汽油）
2. 取 EGR 侧冷凝液实测 pH 与温度
3. 做 60℃ 乙醇汽油浸泡，看体积变化与析出
风险提示：本路线的主要不确定性在内壁析出与焊缝渗漏，不在初始强度。
`
读者常问的两句
问：和进口料比，国产路线差在哪？
按公开资料口径，进口牌号在这类件上的优势主要是长期浸泡数据的完整性、批次稳定性记录，以及配套的排放法规测试经验。
国产路线的差距更多在"数据配齐程度"上。哪些件上已经成熟、哪些件目前仍不建议，要靠件的验证结果说话，不能一概而论。
问：碳罐壳能不能用回料？
方向是"要看用在哪个件上"。结构件、安规件、安全件不建议碰回料；碳罐属于蒸发排放法规件，一旦失效就是排放超标。
如果只是支架、护板这类非法规件，用锁定批号的料并做小批验证，是可以谈的。关键不在"能不能用"，在"用在哪一件上"。
问：碳罐壳体的壁厚能不能再减薄？
减壁厚对碳罐是双刃的。壁薄了，重量和材料成本都下来，但渗透率会上去——渗透与壁厚大致是反比关系。
要减，先把渗透率目标算清楚，再用件级测试确认。另外薄壁对填充和熔接线强度更敏感，模具方案要跟着复核一遍。
结语
回到开篇那三句问话。为什么这三句能把方向定下来？
因为它问的是三件事：问油（是不是乙醇汽油，定介质组）、问状态（液态还是蒸气，定严苛程度）、问温度（定材料体系）。
这三句问完，才轮到牌号出场。
如果你手上正有碳罐或 EGR 阀件要定料，把三样东西发过来就能给方向：装车地区的燃油品类、长期工作温度、渗透率或排放法规口径。
这里做塑料的人多，做改性尼龙的也密——件不一样，料就不一样。
我们做的事很具体：把 PA6、PA66、PA46、PA11、PA12、PA6T、PA9T 和尼龙合金这些树脂，改成某个件真正能用的样子；顺带做改性 PPO、PPS 和热塑性弹性体。
配方里的助剂体系按件的工况配——常规助剂常备现货，特殊型号按需配套；你报工况和牌号，料和助剂一次配齐。
也经营各大化工巨头的尼龙树脂、副牌料和大包料，另长期收尼龙原料、水口回料与各类尼龙废料，有正规处置渠道。
碳罐这类件的选料与试模，可以一起聊。
During the rainy season the year before last, a customer who makes fuel evaporation systems sent over two carbon canister shells.
Both are glass fiber reinforced modified nylon parts, black in color. After being cut open, the inner wall feels sticky, and a thin layer of pasty material can be scraped off with a fingernail.
I remember his exact words very clearly:
"The shell isn’t cracked, and it’s not leaking. But after being loaded on the truck for two months, the inner wall feels sticky and has a strong gasoline smell. Does this count as our problem?"
There are actually three separate variables hidden in this sentence: what kind of oil is being stored, whether the inner wall is in contact with liquid or vapor, and at what temperature it is placed.
I replied with three questions: Is the local fuel ethanol gasoline? Is there any liquid oil accumulated on the inner walls? Is there any condensate coming down on the EGR side?
After asking three questions, the direction became clear. The difficulty of carbon canister materials lies in the fact that they simultaneously face two media: 'oil' and 'acid,' and the modes of attack of these two media are completely different.
Oil seeps in and draws things out; acid directly breaks the molecular chains. The things to be afraid of are different, and the antidotes are also different.
1. Six Dimensions of Operating Conditions: The dimension of the medium needs to be divided into two parts
Temperature is divided into two zones. The main body of the carbon canister follows the environment, fluctuating between -40°C and 80°C, and the temperature near the exhaust pipe will be higher.
The EGR valve component is on another level: the body temperature on the exhaust side can reach 150–200°C, and even higher in certain conditions.
The medium needs to be taken apart to look at; this is the part of the piece that is most easily confused.
The inner wall of the carbon canister comes into contact with fuel vapor, not liquid gasoline. The vapor also contains ethanol, water vapor, and a small amount of organic acids.
The EGR side is more severe: after the exhaust gas condenses, it will produce acidic condensates such as sulfurous acid and nitric acid, with a pH usually between 2 and 4.
What does pH 2 mean? Lemon juice is about 2.2. That is to say, that thing has to stay in an environment with acidity close to lemon juice for more than ten years.
The pressure is alternating. To perform leak diagnosis on the carbon canister, the system will apply a slight positive and negative pressure of -3 to 5 kPa, repeatedly dozens of times a day.
Lifespan follows regulations. Evaporation emissions are assessed based on 15 years / 240,000 kilometers, and any failure in leak diagnostics during this period may directly trigger a fault code.
Appearance and weight are also indicators. The carbon canister is hung on the vehicle body, the bracket bears stress, and the shell must withstand drops; at the same time, there is also pressure to reduce weight.
Compliance requires attention to one point. Evaporative emissions, permeability, and fuel resistance—all three have legal text. You need to obtain the applicable version of the original text before the designation, not just rely on a single physical property sheet.
A numerical conversion: Ethanol in ethanol gasoline is about 10% by volume, and it is more prone to absorbing water than gasoline.
A 500-milliliter carbon canister has, for years, been handling a mixture of the molecules "oil, alcohol, and water," rather than just pure gasoline vapor.
Permeation rate is calculated by day, and according to regulations, it is usually at the milligram level—smaller than one percent of a drop of water. So this piece is a combination of 'thin-walled' and 'high barrier requirements'.
2. Material route: The carbon canister shell and EGR valve components should be selected separately
You can only see why they need to be separated when you put the two items in the same table.
| Route | Long-term heat resistance | Fuel vapor resistant | Acid-resistant condensate | Cost |
|---|
| PA6-GF30 | 100–120℃ | general | Weak | Low cost, mature molding |
| PA66-GF30 | 130–150℃ | Better | middle | Moisture-induced dimensional drift is relatively large |
| PA66-GF35 | 130–150℃ | Better | middle | The strength of the weld line decreases as the glass fiber content increases |
| PA6T-GF30 | Above 150℃ | Better | Upper-middle | Narrow process window, high cost |
| PPS-GF40 | 200℃ scale | Good | Good | High cost, low toughness, high mold requirements |
| Multi-layer barrier / Metal can | — | Visual structure | View structure | It is not a single-material solution; the structure and cost need to be reorganized. |
Look at this table, the focus is not on 'which is stronger,' but on the division of labor.
The mainstream approach for the carbon canister shell is PA66-GF30 type: not very thick walls, needs to be welded, cost must be controlled, and sufficient vapor resistance is enough.
The EGR valve components need to be looked at separately. Its temperature combined with acidic condensate creates a situation where the PA66 system will go through a relatively strenuous phase in a long-term high-temperature acidic environment.
At this point, you either separately upgrade the parts on the EGR side to the PA6T or PPS system, or structurally channel the condensate away.
In one sentence: The carbon canister shell and the EGR valve parts are often not the same part number; the management cost saved by merging them into one part number is often returned during the verification phase.
3. Selection Criteria Table (This page is the most worth keeping)
| Indicator | Directional threshold | Verification Method / Standard | Common Failures | Common solution | Corresponding auxiliary agent system |
|---|
| Ethanol-resistant gasoline (volume change) | Volume change ≤5% after 60℃ × 1000h | ISO 1817 / ASTM D471 | Swelling, inner wall sticking | Substrate Selection Control the Amount of Small Molecules | Lubricant (low extraction type) |
| Mechanical retention after soaking | Stretch retention ≥70% | ISO 527-2 / GB/T 1040.2-2022 | Brittleness and cracking | Stabilization System Crystallinity Control | Antioxidant (hindered phenol and phosphite blend) |
| Acid-resistant condensate | After pH 2–4, 80℃ × 500h, mechanical retention ≥70% | GB/T 11547-2008 Resistance to Liquid Chemical Reagents | Surface cracking and powdering | Substrate upgrade or structural flow guidance | — |
| Inner wall deposits | Surface non-sticky precipitation, controllable mass change | Appearance after soaking Weighing | Sticky, odor residue | Control the total amount of external lubrication and switch to a low extraction system | Lubricant (low extraction type) |
| Welding strength | Weld line strength ≥ 60% of the base material | Component-level inspection Tensile | Weld seepage, leakage diagnosis failure | Control glass fiber content Welding process | Coupling Agent (Fiber / Resin Interface) |
| penetration rate | According to the applicable regulations | Component-Level Sealed Chamber Method | Excessive evaporative emissions | Wall Thickness / Barrier Structure Design | — |
| Dimensional stability | within the magnitude of 0.3% | ISO 294 / Measured Before and After Humidity Adjustment | Assembly interference, bracket stress | Forced moisture conditioning or low water absorption substrate | — |
| Low temperature shock | -40℃ hammer drop does not crack | ISO 179-1 / GB/T 1843-2008 | Disassembly or impact causing cracking | Toughening System Structural Fillet | — |
How to use this table: First, look at the first two rows in the table—ethanol-resistant gasoline and acid-resistant condensate.
These two lines determine the base material, the rest can be compensated by process and structure. If the order is reversed, you will keep changing the grade.
A reminder: For data on medium resistance, you must specify 'which medium it was soaked in, at what temperature, and for how many hours.' Data that only states 'oil resistant' is not comparable.
4. Four common failures and their real root causes
Failure 1: The inner wall is sticky with pasty deposits, but the part itself is intact.
The root cause is not that the 'material was dissolved'; it is mostly that small molecular additives are extracted by fuel vapor and accumulate on the surface.
Mold release agents and low-molecular-weight lubricants behave fairly stably in gasoline at room temperature, but they are easily carried away in vapor at 60℃.
An attribution from the additive side: this kind of stickiness is often caused by a higher amount of external lubricant and release agent components, or by lower molecular weight. The solution is to replace it with a long-chain or high molecular weight system and reduce the total amount of external lubricant.
Here we need to refute a common practice: some people, upon seeing stickiness, instinctively think 'not enough lubrication, add some lubricant.'
The direction is completely reversed — the more you add, the more comes out, and the surface becomes stickier.
Failure 2: Weld seepage, leakage diagnostic code.
Carbon tanks are mostly formed by welding, and the strength of the welded seam is usually only about 60% of the body strength. Also, the higher the glass fiber content, the weaker the welded seam.
The troubleshooting order is: first check the soldering wire position and welding parameters, then look at the glass fiber content, and only finally suspect the substrate.
Failure 3: The EGR valve surface is cracked and breaks easily when bent.
This is acid, the combined effect of high temperatures. Why is the acid so strong?
The main chain of polyamide is composed of amide bonds, which can hydrolyze and break under acid catalysis — the molecular chains are cut into segments, and macroscopically, this results in a loss of strength.
For every increase in temperature, this reaction speeds up accordingly. Therefore, the lifespan temperature on the EGR side is a much higher threshold compared to the carbon canister side.
Failure 4: The same batch of items has inconsistent yellowing.
This is not 'unstable material.' It is more likely that the antioxidant was not mixed evenly during the blending stage, resulting in different degrees of dispersion among the particles.
When encountering this situation, first check the mixing process and the masterbatch step, don't rush to change the grade.
5. Processing and verification: The sequence of these parts needs to be changed
Dry. Nylon must be dry. If the moisture content exceeds the limit, it will hydrolyze and degrade in the barrel, and the strength of the molded parts will already be compromised.
Molding and welding. The shape of the carbon tank and the position of the weld seam must be determined together. The weld seam should avoid high stress areas and locations with sudden changes in wall thickness.
Gate and orientation. The glass fibers align along the flow direction, and if the fiber directions on both sides of the weld line are asymmetrical, stress will find a way to release itself after welding.
It is recommended to arrange the verification sequence in this way:
1. Dimensions and appearance after moisture adjustment (dry state data is only for process recording)
2. Medium soaking: two groups of ethanol gasoline and acidic condensate, carried out separately
3. Mechanical Retention and Mass Change After Soaking
4. Welded Part Sectioning Leak Diagnosis Test Bench
5. Penetration Rate Component-Level Testing
6. Complete Vehicle Assembly and Regulatory Conditions
The order cannot be changed. If the medium is not soaked, the subsequent bench data are meaningless.
An easily overlooked detail: the soaking test should be done on finished parts with soldered wires, not just on samples.
Spline tests measure the material, while finished part tests measure both the material and the structure together. Failures of the carbon canister often occur at the weld line, which spline tests cannot reveal.
6. Limits: When a single-layer plastic cannot work
First, it requires near-zero emission-level permeability. The barrier performance of a single-layer polyamide has its limits. To achieve lower permeability, one must look at multi-layer structures or other barrier solutions, rather than continuing to add things to the formulation.
Secondly, the long-term temperature on the EGR side exceeds 200°C. In this section, conventional modified nylon is not suitable; it needs to move towards PPS systems or metals.
Third, the component needs to be in long-term contact with liquid fuel rather than vapor. Liquid immersion is much more severe than vapor, and the quantity and temperature conditions need to be recalculated.
Fourth, the annual usage is so small that the costs of spreading molds and regulatory validation cannot be justified. The validation of such parts requires running them under regulatory conditions, and both the time and cost are not insignificant.
Laying out these four items is to let the project know how much time and money it will take at the project initiation stage.
Adding a section: How should a medium immersion test be conducted to be valid
This section is the part I most want you to take away. For this type of verification, if the medium is done incorrectly, it's the same as not doing it at all.
The medium should be prepared according to the fuel used in the actual loading area. In some areas, it is pure gasoline, while in others it is ethanol gasoline, and the corrosiveness of the two is different.
The temperature should be taken according to long-term values. Soaking at 23°C for 1000 hours is not the same as being in a car at 60°C during a summer, you are not measuring the same thing.
You need to weigh it; you can't just look at the appearance. Record the volume change, mass change, and mechanical retention after soaking, all three together.
Finished parts with soldered wires must be used. The sample cannot provide an answer to the question about the soldered wires.
| Test Item | Medium | Temperature / Duration | What are you looking at? |
|---|
| Ethanol-resistant gasoline | Ethanol gasoline E10 | 60℃×1000h | Volume change, mass change, appearance |
| Mechanics after soaking | Take a sample after the same soaking | Test after soaking | Stretch retention rate |
| Acid-resistant condensate | pH 2–4 mixed acid solution | 80℃ × 500h | Mechanical retention, surface condition |
| penetration rate | Component-Level Sealed Chamber Method | According to regulatory operating conditions | Daily infiltration rate |
| Welded Component Verification | Finished filling components | Same as above | Whether the solder joint precipitates or leaks |
Add another timeline to make it look like this actually 'happened':
`
Material change ├── Smooth launch: material cost saved, first piece inspection passed
│
Month 2
├── The inner wall felt slightly sticky to the touch (at the time, it was judged to be due to incomplete cleaning)
├── The odor was relatively strong (at the time, it was judged to be an assembly sealing issue)
└── In the 14th month, the complete vehicle reports a leakage code → trace the batch number → replace the low extraction system
`
Those ignored signals didn't look like problems at the time. By the time they turned into error codes, it was too late to do the verification.
Also, to answer a frequently asked question: Do you need to buy equipment for this set of experiments?
Medium soaking doesn’t require expensive equipment; an incubator and a balance are enough. What really takes up is time—a round of soaking takes more than a month.
And it determines whether all the subsequent test bench data has meaningful interpretation. This order is worth sacrificing some construction time for.
Material Change Risk List (Transferred from the original plan, items that need to be changed)
| link; segment; part | What do you want to move? | Points that are easy to overlook |
|---|
| Mold | The shrinkage rate changes with the glass fiber content, and the housing and cover need to be adjusted simultaneously. | Wall thickness abrupt change at the weld line location |
| Dry | Set the window according to the measured moisture content, using a dehumidifying dryer | Recycled materials mixed with the water brought in |
| Material Temperature / Mold Temperature | Mold temperature is adjusted jointly according to the flatness of the welding surface and the fiber arrangement | Only copy the recommended values of the part numbers, do not look at the parts |
| Welding | Welding parameters are redefined according to the substrate and glass fiber content | Use the original plan's welding curve |
| Humidity control | Forced humidity adjustment Re-measure dimensions | Based on the average wall thickness to estimate the time, the thick-walled areas are not fully soaked. |
| Media verification | Ethanol gasoline and acidic condensate need to be handled in two separate groups. | Only do the gasoline group, skip the acid |
| penetration rate | Unit-level testing cannot be replaced with samples. | Estimate part-level penetration rate using spline data |
| Verification order | Size → Medium → Welding → Penetration → Complete Machine | If the previous item fails, just move on. |
One-page report form (for people who need to report upwards)
`
Project: Automotive Carbon Canister Housing / EGR Valve Components · Material Route Assessment
Conclusion direction: It is recommended to select materials for the carbon canister shell and EGR valve parts separately; whether it can be implemented depends on the results of the medium test.
1. Three Rules That Must Be Followed
1. Media validation is divided into two groups: ethanol gasoline and acidic condensate; you cannot do only one group.
2. Welding wires should avoid high-stress areas, and welded parts must be sectioned for inspection.
3. Penetration rate is measured per item and extrapolation beyond the sample is not accepted.
2. Precondition (It is recommended to postpone if any are not met)
· EGR side long-term temperature within 200℃
· The penetration rate target is within the range covered by single-layer polyamide
· Budget and schedule for validation under regulatory test conditions
· Annual usage is sufficient to offset mold and validation costs
3. Next Steps
1. Confirm the type of fuel in the loading area (whether it is ethanol gasoline)
2. Measure the pH and temperature of the EGR-side condensate
3. Soak in 60℃ ethanol-gasoline and observe the volume change and precipitation
Risk warning: The main uncertainties of this route lie in inner wall deposition and weld leakage, not in the initial strength.
`
Two questions readers often ask
Question: Compared with imported materials, where does the domestic route fall short?
According to public information, the advantage of imported brands in this type of component mainly lies in the integrity of long-term soaking data, batch stability records, and experience with supporting emission regulation tests.
The gap in the domestic route lies more in the 'completeness of data.' Which components are already mature and which are still not recommended at present must be determined based on the verification results of the components, and cannot be generalized.
Question: Can the carbon canister shell be made from recycled material?
The direction is 'depends on which part it is used on.' It is not recommended to use recycled material for structural parts, safety regulation parts, or safety components; the charcoal canister is a component regulated by evaporation emission standards, and if it fails, it will result in excess emissions.
If it’s just non-standard parts like brackets or protective plates, using materials with locked batch numbers and doing small batch verification is negotiable. The key is not 'whether it can be used,' but 'on which part it is used.'
Question: Can the wall thickness of the carbon canister housing be further reduced?
Reducing the wall thickness of a carbon tank is a double-edged sword. Thinner walls lower the weight and material cost, but the permeability will increase — permeability is roughly inversely proportional to wall thickness.
To reduce it, first calculate the penetration rate target clearly, then confirm it using part-level testing. In addition, thin walls are more sensitive to filling and weld line strength, so the mold plan needs to be reviewed accordingly.
Conclusion
Returning to the three opening questions. Why can these three questions set the direction?
Because it asks three things: about the fuel (whether it is ethanol gasoline, determining the medium group), about the state (liquid or vapor, determining the strictness level), and about the temperature (determining the material system).
After these three questions are asked, it's finally the turn for the brand to appear.
If you currently have a carbon canister or EGR valve parts that need material specification, sending over these three things can provide guidance: the type of fuel in the vehicle's region, the long-term operating temperature, and the permeability or emission regulation standards.
There are many people making plastics here, and those making modified nylon are also numerous—if the product is different, the material will be different.
What we do is very specific: we take resins like PA6, PA66, PA46, PA11, PA12, PA6T, PA9T, and nylon alloys, and turn them into a form that can actually be used for a certain part; we also do modified PPO, PPS, and thermoplastic elastomers along the way.
The auxiliary system in the formula is matched according to the working conditions per item — conventional auxiliaries are kept in stock, and special models are matched as needed; you report the working conditions and grade, and the materials and auxiliaries are prepared together at once.
Also operates the nylon resin, secondary-grade materials, and bulk materials of major chemical giants, and has long-term purchasing of nylon raw materials, sprue regrind, and various types of nylon waste, with formal disposal channels.
The selection of materials and mold testing for parts like the charcoal canister can be discussed together.
