发动机舱护板、空滤壳用改性PP，最容易翻车的不是刚性不够，是长期高温油浸后的老化开裂。这篇把机舱件的六维工况、耐乙二醇长效冷却液与耐水解判据、HDT 与长期使用温度的门限区分、以及验证顺序和换料风险讲清楚。
有家做二级配套的技术员甩过来一张照片：发动机舱下护板拆下来，固定点一片片掉渣，用手一掰就断。"是不是你们料太次？"
我说，先别急着怪料。你先告诉我，这块护板贴在机舱哪个位置、边上挨着什么、泡了几年。
机舱护板与空滤壳用改性PP，第一判据从来不是"硬不硬"，是"泡了几年还脆不脆"。
下面按工况、路线、判据、验证四层往下拆。
一、开篇痛点：客户原话与最常见的失效现场
客户原话有两种。一种是"护板用了一年多，固定点开始掉渣、一掰就断，是不是料太次？"另一种是"空滤壳拆下来，卡扣位置发脆，拧两颗螺丝就裂"。
最常见的失效现场有两个：
第一，长期高温油浸后变脆开裂。 机舱里，下护板贴着油底壳和排气侧，常年泡在机油蒸气、冷却液渗漏、制动液飞溅里，夏天机舱内部是持续高温、局部短时更高。PP 本来不挑极性介质，但时间是杀手——热氧老化慢慢把抗氧剂耗尽、分子链切断，外观看着还好，一受振动或拆装就碎成渣。
第二，护板固定点撕裂。 石击、振动、夹紧力长期叠加在卡扣根部，材料一旦因老化变脆，应力集中点先崩。这不是单纯"强度不够"，是"老化后强度塌了 + 应力集中"的组合。
一个内行细节：机舱不是匀温箱。同一块护板，靠排气侧和靠进气侧的热负荷差很多；老化评价若只信标准试棒，会高估寿命。真正有代表性的数据，要从真实安装位置的取向取样——靠热源一侧的料，老化拐点来得更早。
二、工况六维拆解：至少四个维度要给具体数字
机舱护板与空滤壳的工况，拆成六个维度，把六个数报齐，方向基本就出来了。
| 维度 | 这个件的实际工况 | 对材料的要求 |
|---|
| 温度 | 机舱持续高温（长期按 100-120℃ 级环境设计）；局部短时峰值可到 140℃（空调风道/风扇叶类件公开资料给出"短时间可承受 140℃ 热负荷"口径） | 必须区分持续温度与短时峰值温度两本账 |
| 载荷 | 石击（碎石冲击类试验）、振动、固定点夹紧力；非结构承力 | 韧性与抗应力开裂，不是刚性 |
| 介质 | 机油/油汽、制动液、乙二醇冷却液飞溅、融雪盐、维修清洁剂 | 耐水解 + 耐油汽 + 耐化学 |
| 寿命 | 整车生命周期（行业通行按 10 年/15 年或 10 万公里级设计） | 长期老化后性能不塌 |
| 外观 | 护板多为非外观面；空滤壳要求装配面平整、卡扣不崩缺 | 尺寸与卡扣完整性 |
| 合规 | 整车禁用物质、VOC 管控（机舱件相对内饰宽松，但仍在规范内） | 按件企清单核对 |
六个维度里，温度和介质是两条硬线。原因很直接：机舱件的失效九成以上是从"热氧老化 + 油浸"开始，而不是从刚性或外观开始。所以选型第一句不是问价格，是问"你的件贴在机舱哪个位置、挨着什么介质、要扛几年"。
文字版结论：六维里持续温度和短时峰值温度必须分开算——靠排气侧的护板，短时 140℃ 可能顶得住，但长期 120℃ 持续烘烤是另一本账；空滤壳受的是进气热和曲轴箱喘气带来的油汽，温度低一些，但介质更刁。把两本账混成一一个数，是机舱件选料翻车最多的起点。
三、材料路线对比：三条路线并列，不做"谁更好"的结论
改性PP 的基体是聚丙烯，机舱护板与空滤壳主要落在三条路线上，没有谁更好，只有谁的工况对得上。
| 路线 | 拿到什么 | 代价 |
|---|
| 抗冲共聚 PP + 增韧（共聚 PP 混增韧体系，参照散热器水室/膨胀箱公开路径） | 耐水解、耐热氧老化、韧性好；对油汽与冷却液较安定 | 刚性靠填充补，耐热上限受基材档位限制 |
| 共聚 PP + 矿物（滑石粉）填充 | 补刚性、降收缩、控成本；不显著加重翘曲 | 韧性略降、表面一般，需配合增韧 |
| 长玻纤 PP（PP-LGF） | 高刚性高耐热（玻纤保留长度 >3.1 mm 临界长度；拉伸 50–80 MPa、弯曲 80–120 MPa、常温缺口冲击 15–40 kJ/m²、HDT 120–180℃、密度 1.0–1.2、收缩 0.3–0.8%） | 各向异性、表面浮纤，对石击和外观不友好 |
分法很朴素：
- 大面积护板、空滤壳壳体 → 路线一 + 路线二组合，拿韧性、耐水解、尺寸稳定
- 要挂装、要承力的支架位 → 路线三，拿刚性和耐热
- 靠排气侧短时高温区 → 路线一基础上强化耐热氧体系，不靠填充硬顶
这里有个公开案例值得借：机舱前端模块用长玻纤集成化后减重约 30%（福特 Super Duty 前端模块减重 1.4 kg 可作旁证）。但那是结构集成的思路，不等于大面积护板该上长玻纤——护板如果上长玻纤，翘曲和浮纤会先于强度出问题。
金句：配方不是全都要，是一道排序题。 这个件最怕的是油浸老化，那就把耐水解和耐热氧排第一，刚性和成本往后让。
四、★ 选型判据表：五列，每项都带验证方法
下面这张表是全篇最该收藏的部分。重点看第三列"验证方法·标准号"——机舱件选料最常卡住的，不是"看哪个指标"，而是"拿什么测、测到多少算过"，尤其耐介质和老化这两项。
| 指标 | 门限值（典型） | 验证方法 · 标准号 | 常见失效 | 通行解法 |
|---|
| 负荷变形温度 HDT | ≥100℃（参照 GB/T 24149.1-2009 汽车 PP 专用料通行门限） | GB/T 1634.2，0.45 MPa 负荷下 | 误当长期使用温度，服役变形 | 只作短时判据，长期温度另算 |
| 短时热负荷 | 短时间可承受 140℃（空调风道/风扇叶类件公开口径） | 短期受热变形/外观评价 | 局部过热变形 | 区分持续温度与短时峰值，按安装位置定 |
| 耐乙二醇长效冷却液 / 耐水解 | 长期浸泡后力学保持率与外观按件企规范（公开资料：长期高温冷却液浸泡致老化开裂） | 塑料耐液体介质试验，浸泡后测拉伸保留率/外观变化率，温度与时间覆盖实际工况 | 长期冷却液浸泡开裂 | 共聚 PP + 增韧，强化耐水解与耐热氧体系 |
| 耐油浸（机油/制动液飞溅） | 浸泡后拉伸保留率/外观变化率按件企规范；浸泡温度取机舱实际介质温度、时间按阶梯（如 500 h / 1000 h，以件企规范为准） | 同上方法，介质按实际飞溅种类 | 油汽加速助剂迁移、表面劣化 | 耐油汽助剂体系 + 带介质老化评价 |
| 长期热氧老化 | 老化后拉伸/冲击保持率与外观按件企规范，重点看拐点 | 热老化箱，周期与温度点对应服役年限 | 抗氧剂耗尽后断崖式脆化 | 耐热氧抗氧体系配平 |
| 缺口冲击（常温/低温） | 常温缺口冲击按件企；低温按安装区域 | GB/T 1043.1（简支梁） | 拆装/维修开裂 | 增韧体系 |
| 模塑收缩率 / 尺寸 | 收缩率按模具现定（护板长件敏感） | GB/T 17037 系列 | 装配间隙/卡扣对不上 | 矿物填充调收缩 |
文字版结论：七项里 HDT≥100℃ 和 140℃ 短时热负荷都是"短时判据"，不能当长期使用温度用——这是行业里最常被混用的一条；耐乙二醇与耐油浸两行，门限要落在"浸泡后保留率"上，且必须带真实介质做，单独做热老化会高估寿命；收缩率不是料自己的事，要和客户的模具一起看。把这张表当体检单，缺一项不判合格，比样件试出来再回头找原因省钱得多。
五、常见失效与根因：四个现象，四条根因
失效一：固定点撕裂 / 卡扣崩缺。 根因多半是长期热氧老化后韧性塌了，再叠加石击与振动的应力集中。先查裂纹起点位置——从卡扣根部放射状扩展，指向应力集中与蠕变；从表面任意位置起裂，才先怀疑材料韧性。顺序反了会白换几轮。
失效二：长期油浸后表面粉化、发黏。 根因是助剂被油汽萃取迁移，单独做热老化看不出问题，必须带介质做老化评价才会暴露。
失效三：装配间隙 / 卡扣对不上。 这类最常被归到"料缩了"。但收缩率本身是设计输入——换料时收缩率变了却没重新核对模具，间隙必然出问题。这是换料最典型的连带成本，不是料的缺陷。
失效四（敢否定一个常见做法）：拿保险杠的 −30℃ 低温冲击指标来卡机舱护板。 机舱护板的失效主因是热氧老化与油浸，不是低温脆裂（除非北方极寒区长期停放）。把低温冲击当第一判据，会选错体系、多花钱还解决不了真问题。同理，"HDT≥100℃ 就能长期在 100℃ 用"也是错的——HDT 是短时受载变形起点，回答不了三年后的事。
| 失效现象 | 常见误判 | 实际可能的原因 | 先查什么 |
|---|
| 固定点撕裂 | 料太脆 | 热氧老化 + 应力集中 | 裂纹起点与扩展方向 |
| 表面粉化发黏 | 材料质量差 | 助剂被油汽萃取 | 带介质老化试验 |
| 装配间隙对不上 | 料收缩大 | 换料未重核收缩率/模具 | 收缩率与模具现定值 |
| 拆装即裂 | 韧性不足 | 老化后韧性塌 + 卡扣应力 | 老化保持率 + 卡扣结构 |
表注：失效排查先定位原因类别，再决定改结构还是改配方——两个方向的成本差一个量级。
六、验证顺序：先验什么，后验什么
这一段同行几乎没人写，但它是换料能不能省钱的关键。顺序错了，成本会在最后一步集中爆出来。
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① 介质兼容与热老化小样 耐乙二醇/机油浸泡 + 热老化后的拉伸保留率、外观
↓ 不通过（保留率掉到规范线下 / 开裂）直接退回，不动模具
② 缺口冲击与刚性 常温/低温缺口冲击、弯曲模量、HDT
↓ 不过退回
③ 短射试模 充填完整、熔接线、浮纤、石击薄弱位
↓ 走通才批量
④ 装车匹配与振动耐久 卡扣装配力、振动台架、石击
↓
⑤ 批量试产 + 客户端验证
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文字版结论：验证顺序是 介质老化 → 冲击刚性 → 短射 → 装车匹配 → 批量。介质老化这一关必须放在试模之前过，因为它最可能在服役中后期一票否决；过了它再做模具侧的事，才不会白花试模费。
>
一个内行细节：浸泡后的试样要先按标准状态调节再测，表面残留介质不擦净会虚高或虚低数值；带介质老化的试样从真实安装位置取向取样，比标准试棒更接近这个件的真实表现。
七、反向诚实：这三个情况出现，这个件不该用改性PP
前面讲"怎么做"，这里讲"什么时候别做"。这一段对选型判断的价值最高。
| 出现的情况 | 为什么改性PP不合适 | 该往哪走 |
|---|
| 要求长期 150℃ 以上持续工作 | 改性PP 耐热靠填充/增韧往上抬，HDT 上限就在那条线附近，长期更受抗氧体系寿命限制 | 换更高耐热的工程塑料体系 |
| 要求 A 级外观面（外露高光免喷涂） | 机舱护板多为非外观面；若同时要求 A 级外观 + 高填充，表面细腻与刚性对拉 | 外观件与结构件分开设计 |
| 要求极高刚性且不允许任何蠕变 | PP 的蠕变是结构性的，改性只能缓解 | 承力支架走工程塑料或金属，或长玻纤增强 |
规律很清楚：凡是"两个方向相反的要求同时要"，就说明这个件不该用 PP 硬撑。 遇到这种需求，我们的做法是先说清楚，再谈有没有折中空间——硬接下来的单子，最后都要用返工和索赔还回去。
八、换料要动什么：一张先看再动的清单
决定试改性PP 之前，这张表建议先过一遍。客户真正的顾虑往往不是性能，是"我现在的模具和工艺要不要改"。
| 要动的项 | 需要确认什么 | 不做会怎样 |
|---|
| 模具收缩率 | 新料收缩率与原方案差，护板长件尤其敏感 | 尺寸超差、卡扣对不上 |
| 浇口与排气 | 矿物/玻纤料流动差异，排气不足易困气 | 充填不足、熔接线、烧焦 |
| 料温与模温 | 耐热体系加工窗口不同 | 浮纤、分解、表面缺陷 |
| 干燥 | 看具体体系，填充料通常不需要 | 银丝、气泡 |
| 保压与脱模 | 收缩差异带来变形与顶白 | 变形、顶出拉伤 |
| 色差 | 空滤壳装配面外观 | 批次色差争议 |
| 验证顺序 | 小样介质老化 → 冲击刚性 → 短射 → 装车 | 风险全部压到最后一步集中爆发 |
文字版结论：换料要动的是模具、工艺、色差三块，其中最该先谈的是验证顺序。跳过小样直接试模，等于把成本提前花出去；跳过短射直接批量，一次失败就是整批损失。
九、一页纸汇报对照表（可以直接贴进 PPT）
| 场景 | 推荐路线 | 关键指标 | 验证标准 | 需先确认的条件 |
|---|
| 大面积发动机舱护板 | 抗冲共聚 + 增韧 + 矿物填充 | 耐乙二醇/耐水解、热氧老化保持率、收缩率 | 介质浸泡+热老化、GB/T 1043.1、GB/T 17037 | 安装位置热负荷、接触介质种类 |
| 空滤壳（非外观） | 共聚 PP + 增韧 | 机油汽浸泡保持率、卡扣冲击、尺寸 | 带介质老化、缺口冲击 | 介质温度与时间 |
| 护板支架 / 挂装位 | 长玻纤 PP（玻纤保留 >3.1 mm） | 拉伸 50–80 / 弯曲 80–120 / HDT 120–180 | 长玻纤判据、GB/T 1043.1 | 是否接受各向异性 |
| 短时高温区护板 | 共聚 PP + 耐热氧体系 | 短时 140℃ 热负荷、HDT≥100℃ | 短期受热、GB/T 1634.2 | 持续温度与短时峰值分界 |
文字版结论：这张表的作用是让技术员能把结论直接往上报，不必重新组织语言。判断标准只有一条——客户拿这张表，能不能在一次会议里把材料方向定下来。
十、这个件上最容易出问题的，往往不是料
机舱护板与空滤壳在公开技术资料里讨论集中在三类问题：长期高温冷却液浸泡后的老化开裂、油汽加速助剂迁移导致的表面劣化、夹点与卡扣的应力开裂。三类问题指向同一个判断——机舱件的选材验证必须带介质、做长期，只做短期的样品验证会在服役中后期暴露。
公开的判据也很清楚：耐乙二醇长效冷却液、耐水解、耐热老化（共聚 PP 混增韧体系，B 级公开资料）；短时热负荷按"短时间可承受 140℃"口径区分持续与峰值；若走长玻纤，玻纤保留长度要过 3.1 mm 临界长度，否则纤维被拔出、强度发挥不出来。
行业通行的做法是把三件事一起定：抗冲共聚选档、增韧体系加量、矿物填充控收缩；承担结构功能的位置用长玻纤或填充玻纤混合体系；助剂体系按"耐热氧 + 耐油汽"组合选型，老化试验带介质做。
宁波市科隆新材料有限公司在这个件上常供的是改性聚丙烯（PP）粒子里的抗冲共聚增韧方向，按安装位置的热负荷与接触介质分档推荐，覆盖填充、玻纤增强、增韧等改性方向，主要用来解决上面说的"长期油浸老化与装配尺寸"这两件事；可按件配小样，做带介质老化的对比验证。
常见问答
问：护板和空滤壳能用同一种料吗？
答：看接触介质与温度分布。靠排气侧的护板热负荷高、油汽重；空滤壳受的是进气热和曲轴箱喘气带来的油汽。两处工况接近可以并料，差很多就得分档推荐——合并的前提是介质和温度区间真的重叠，不是图省事。
问：怎么判断该不该上长玻纤？
答：看是否真的承力挂装。大面积护板上长玻纤，翘曲和浮纤会先出问题；只有支架类承力位才划算。判断标准就是那根 3.1 mm 临界玻纤长度——保不住，加再多玻纤也是拔出的短纤维。
| 工况 | 关键判据 | 科隆常规供应 |
|---|
| 大面积发动机舱护板 | 耐乙二醇/耐水解、热氧老化保持率、收缩率 | 抗冲共聚 PP + 增韧 + 矿物填充方向 |
| 空滤壳（非外观） | 机油汽浸泡保持率、卡扣冲击、尺寸 | 共聚 PP + 增韧方向 |
| 护板支架 / 挂装位 | 长玻纤保留 >3.1 mm、HDT 120–180℃ | 长玻纤 PP 方向 |
| 短时高温区护板 | 短时 140℃ 热负荷、HDT≥100℃ | 共聚 PP + 耐热氧体系方向 |
想提醒一句：件出问题，最常见的错法是先换料。油浸开裂、卡扣崩缺、尺寸对不上——每一条的原因都不止一个。先定位，再换料；顺序反了，往往换了几轮还在原地。
关于我们
关于我们，四句话：
一、改性聚丙烯：均聚 / 无规共聚 / 抗冲共聚；
二、改性方向：填充、玻纤增强、增韧、阻燃、低气味低 VOC、耐候、免喷涂耐划伤；
三、各大石化厂 PP 树脂贸易；
四、副牌料、大包料现货。
宁波市科隆新材料有限公司，自产改性聚丙烯（PP）造粒，覆盖均聚 / 无规共聚 / 抗冲共聚三档基材，以及填充、玻纤增强、增韧、阻燃、低气味低 VOC、耐候、免喷涂耐划伤等改性方向；兼营各大石化厂 PP 树脂、副牌料与大包料。
For the engine compartment shield and air filter housing, modified PP is used. The most common cause of failure is not insufficient rigidity, but aging and cracking after long-term exposure to high-temperature oil. This article explains the six-dimensional operating conditions of engine compartment parts, the criteria for resistance to long-life ethylene glycol coolant and hydrolysis, the distinction between HDT and long-term usage temperature thresholds, as well as the verification sequence and material replacement risks.
A technician from a company that does secondary support sent over a photo: after removing the lower engine compartment guard, the mounting points are crumbling, breaking apart just by hand. Could it be that your material is too poor?
I said, don’t rush to blame the material. First, tell me where this protective plate is attached in the engine compartment, what is next to it, and how many years it has been soaked.
The engine compartment guard and air filter housing are made of modified PP. The first criterion has never been 'is it hard or not,' but 'does it become brittle after a few years?'
Below, break it down layer by layer according to operating conditions, routes, criteria, and verification.
1. Opening Pain Points: The Customer's Original Words and the Most Common Failure Sites
The client's exact words are of two kinds. One is: 'The skid plate has been used for over a year, the fixing points are starting to flake off, and it breaks with a twist. Is the material too poor?' The other is: 'When the air filter housing is removed, the clip positions become brittle, and it cracks after tightening just two screws.'
There are two most common sites of failure:
First, it becomes brittle and cracks after long-term exposure to high temperatures and oil immersion. In the engine compartment, the under panels are attached to the oil pan and the exhaust side, constantly soaked in engine oil vapor, coolant leaks, and brake fluid splashes. In summer, the interior of the engine compartment is persistently hot, with even higher local temperatures for short periods. PP (polypropylene) is generally resistant to polar substances, but time is the killer—thermal and oxidative aging gradually depletes the antioxidants and breaks the molecular chains. It may look fine on the outside, but it will crumble to pieces under vibration or when removed.
Second, the mounting points of the protective plate tear. Stone impacts, vibrations, and clamping forces accumulate over time at the base of the clips, and once the material becomes brittle due to aging, the stress concentration points fail first. This is not simply a 'strength insufficiency'; it is a combination of 'strength collapse after aging' and 'stress concentration'.
An insider detail: the cabin is not a uniform temperature box. The same protective panel has very different thermal loads on the exhaust side versus the intake side; if aging evaluation only relies on standard test samples, the lifespan will be overestimated. Truly representative data must be sampled according to the actual installation orientation—the material on the side near the heat source reaches the aging inflection point earlier.
2. Six-dimensional breakdown of working conditions: at least four dimensions must provide specific numbers
The operating conditions of the engine compartment guard plate and the air filter housing can be broken down into six dimensions. Once the six numbers are all reported, the direction will basically become clear.
| Dimension | The actual working condition of this part | Requirements for the materials |
|---|
| Temperature | The cabin maintains a high temperature (designed for an environment of 100-120°C over the long term); local short-term peaks can reach 140°C (public data for air conditioning ducts/fan blade components indicate they can 'withstand a thermal load of 140°C for a short time') | It is necessary to distinguish between continuous temperature and short-term peak temperature. |
| Load | Stone impact (rock impact-type test), vibration, fixed-point clamping force; non-structural load-bearing | Toughness and resistance to stress cracking, not rigidity |
| Medium | Engine oil/fuel, brake fluid, ethylene glycol coolant splashes, de-icing salt, maintenance cleaners | Hydrolysis-resistant, oil and gasoline-resistant, chemical-resistant |
| Lifespan | The full vehicle lifecycle (commonly designed in the industry for 10 years/15 years or 100,000 kilometers) | Performance does not deteriorate after long-term aging |
| Appearance | The protective plate is mostly on non-visible surfaces; the air filter housing requires the assembly surface to be flat, with no broken or missing clips. | Size and clip integrity |
| Compliance | Control of banned substances in the whole vehicle and VOCs (looser for cabin parts compared to interior, but still within regulations) | Check against the itemized inventory |
Among the six dimensions, temperature and medium are two fixed lines. The reason is straightforward: over ninety percent of cabin component failures start with 'thermal-oxidative aging and oil immersion,' not rigidity or appearance. So the first question in component selection is not about price, but 'where in the cabin will your part be installed, what medium will it be exposed to, and how many years must it last?'
Text version conclusion: In Six-Dimensional, continuous temperature and short-term peak temperature must be calculated separately—relying on the exhaust-side heat shield, short-term 140°C might withstand it, but long-term 120°C continuous baking is a different matter; the air filter housing is affected by intake heat and oil vapor from crankcase breathing, so the temperature is lower, but the medium is more demanding. Mixing these two accounts into a single number is the most common starting point for material selection failures in the engine compartment.
3. Comparison of material routes: Three routes are presented side by side, without drawing a 'which is better' conclusion
The matrix of modified PP is polypropylene. The engine compartment guard and air filter housing mainly fall under three routes; none is better, it only depends on whose operating conditions match.
| Route | Get what | Cost |
|---|
| Impact Copolymer PP Toughened (copolymer PP blended toughening system, referring to the publicly available paths for radiator water chamber/expansion tank) | Hydrolysis-resistant, heat and oxidative aging resistant, good toughness; relatively stable to oil vapor and coolant | Rigidity is compensated by filling, and the upper limit of heat resistance is restricted by the grade of the substrate. |
| Copolymer PP mineral (talc) filled | Reinforce rigidity, reduce shrinkage, control costs; without significantly increasing warping | Slightly reduced toughness, average surface, requires toughening aid |
| Long Glass Fiber PP (PP-LGF) | High rigidity and high heat resistance (glass fiber retained length >3.1 mm critical length; tensile strength 50–80 MPa, flexural strength 80–120 MPa, notched impact at room temperature 15–40 kJ/m², HDT 120–180°C, density 1.0–1.2, shrinkage 0.3–0.8%) | Anisotropy, surface floating fibers, unfriendly to stone impact and appearance |
The method of division is very simple:
- Large-area protective plates, air filter housings → Combination of Route 1 and Route 2, focusing on toughness, hydrolysis resistance, and dimensional stability
- Bracket positions that need to hang or bear weight → Route three, choose rigidity and heat resistance
- Relying on the short-term high-temperature area on the exhaust side → Strengthen the heat-resistant oxygen system based on Route One, without relying on a filled hard top
There is a public case worth referencing here: the front-end module of the cabin reduced weight by about 30% after using long glass fiber integration (the Ford Super Duty front-end module weight reduction of 1.4 kg can be used as supporting evidence). But that is the idea of structural integration, which does not mean that large-area shields should use long glass fiber—if shields use long glass fiber, warping and fiber floating will become issues before strength does.
Golden saying: You don't need all ingredients in a formula; it's a ranking question. The thing most prone to is oil-immersed aging, so put hydrolysis resistance and heat-oxidation resistance first, and leave rigidity and cost later.
4. ★ Selection Criteria Table: five columns, each item comes with a verification method
The table below is the part of the entire article most worth saving. Focus on the third column "Verification Method · Standard Number" — the part that usually trips people up when selecting cabin components is not "which indicator to look at," but "what to measure with and what measurement counts as passing," especially for medium resistance and aging.
| Indicator | Threshold Value (Typical) | Verification Method · Standard Number | Common Failures | Common solution |
|---|
| Heat Deflection Temperature (HDT) | ≥100℃ (Refer to GB/T 24149.1-2009 Automotive PP Special Material Threshold) | GB/T 1634.2, under a load of 0.45 MPa | Mistakenly regarded as long-term operating temperature, service deformation | Only used as a short-term criterion; long-term temperature is calculated separately |
| Short-term heat load | Can withstand 140℃ for a short period (air conditioning duct/fan blade parts with open caliber) | Short-term Heat Deformation / Appearance Evaluation | Localized overheating deformation | Distinguish between continuous temperature and short-term peak, determined according to installation location |
| Ethylene Glycol Resistant Long-Lasting Coolant / Hydrolysis Resistant | After long-term soaking, the mechanical retention rate and appearance comply with item-specific standards (public information: long-term soaking in high-temperature coolant leads to aging and cracking) | Plastic liquid medium resistance test, measure tensile retention rate/appearance change rate after immersion, temperature and time cover actual working conditions | Cracking from long-term coolant immersion | Grafted PP for toughening, strengthening hydrolysis resistance and heat-oxidation system |
| Oil-resistant immersion (engine oil/brake fluid splashes) | The retention rate of elongation/appearance change after soaking is according to the company specifications; the soaking temperature is taken as the actual medium temperature in the machine compartment, and the time is based on the stepwise schedule (e.g., 500 h / 1000 h, according to company specifications). | Same method as above, the medium is according to the actual type of splashing | Migration of oil and vapor acceleration additives, surface degradation | Oil-resistant gasoline additive system with dielectric aging evaluation |
| Long-term thermo-oxidative aging | After aging, the stretch/impact retention rate and appearance should comply with the company specifications, with a focus on the inflection point. | Thermal aging chamber, service life corresponding to cycle and temperature points | Cliff-like embrittlement after antioxidant depletion | Heat-resistant oxygen and antioxidant system balancing |
| Notch Impact (Room Temperature/Low Temperature) | Room temperature gap impact according to the item; low temperature according to the installation area | GB/T 1043.1 (Simply Supported Beam) | Disassemble/Repair Cracks | Toughening system |
| Mold Shrinkage / Dimensions | Shrinkage rate is determined according to the current mold (sensitive for long protective plate parts) | GB/T 17037 Series | Assembly gap/clip does not align | Mineral-filled shrinkage adjustment |
Text version conclusion: Among the seven items, HDT ≥100℃ and 140℃ short-term heat loads are both 'short-term criteria' and cannot be used as long-term operating temperatures—this is the most commonly confused point in the industry; for ethylene glycol resistance and oil immersion, the threshold should be based on the 'retention rate after immersion,' and real media must be used, as testing with heat aging alone would overestimate lifespan; shrinkage is not just about the material itself, it must be considered together with the customer's mold. Treat this table as a physical check-up report; if any item is missing, do not deem it qualified. This saves much more money than testing a sample and then going back to find the reason.
5. Common Failures and Root Causes: Four Phenomena, Four Root Causes
Failure 1: Tear at the fixed point / broken buckle. The root cause is mostly the loss of toughness after long-term thermal-oxidative aging, combined with stress concentration from stone impact and vibration. First, check the crack initiation point — if it radiates from the root of the buckle, it indicates stress concentration and creep; if the crack starts from any point on the surface, then suspect material toughness first. If the order is reversed, you'll waste several rounds of replacements.
Failure two: after long-term oil immersion, the surface becomes chalky and sticky. The root cause is that additives are extracted and migrated by oil vapor. Testing with only thermal aging does not reveal the problem; it must be evaluated with the medium to expose it.
Failure Three: Assembly clearance / clips not fitting. This type is most commonly attributed to 'material shrinkage.' However, shrinkage itself is a design input—if the shrinkage rate changes when the material is switched but the mold is not re-verified, clearance problems are bound to occur. This is the most typical associated cost of changing materials, not a material defect.
Failure Four (Dare to question a common practice): Using the bumper's −30°C low-temperature impact standard to evaluate the engine splash shield. The main causes of engine splash shield failure are thermal-oxidative aging and oil immersion, not low-temperature brittleness (unless it's parked for a long time in extremely cold northern regions). Using low-temperature impact as the primary criterion can lead to choosing the wrong system, costing more money, and still not solving the real problem. Similarly, 'HDT ≥ 100°C means it can be used long-term at 100°C' is also wrong — HDT is the onset of short-term deformation under load and cannot predict performance three years later.
| Failure phenomenon | Common Misjudgment | Actual possible reasons | What should we check first? |
|---|
| Fixed-point tearing | The ingredient is too brittle | Thermo-oxidative aging Stress concentration | Crack initiation point and propagation direction |
| Surface powdering and becoming sticky | Poor material quality | Additives are extracted by oil vapor | Aging test with dielectric |
| The assembly clearance does not match | Material shrinks a lot | Shrinkage rate after material change/rechecking per mold | Shrinkage rate and the current mold value |
| Breaks upon assembly and disassembly | Insufficient resilience | Toughness collapse after aging Buckle stress | Aging retention rate Snap-fit structure |
Table note: When troubleshooting failures, first identify the cause category, then decide whether to change the structure or the formula— the cost difference between the two directions is an order of magnitude.
6. Verification sequence: what is a priori, what is a posteriori
Almost no one in the industry writes this part, but it is the key to whether material changes can save money. If the order is wrong, the costs will concentrate and explode at the final step.
`
① Medium compatibility and thermal aging samples Resistance to ethylene glycol/oil soaking Tensile retention and appearance after thermal aging
↓ Fail (retention rate drops below specification / cracking) directly returned, do not move the mold
② Notch Impact and Rigidity Notch impact at room/low temperature, bending modulus, HDT
↓ But return
③ Short-shot mold test Complete filling, weld lines, floating fibers, weak spots of stone marks
↓ Only proceed after passing the batch
(4) Vehicle Fitting and Vibration Durability: Snap assembly force, vibration bench, stone strike
↓
⑤ Batch trial production Client-side verification
`
Text version of the conclusion: The verification sequence is medium aging → impact rigidity → short shot → assembly matching → mass production. The medium aging step must be completed before mold trials, because it is most likely to result in outright failure in the later stages of service; once this is passed, then working on the mold side will not waste mold trial costs.
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A professional detail: after soaking, the sample should be adjusted to the standard condition before measurement. If the residual medium on the surface is not wiped off, the values may be artificially high or low; samples aged with medium taken from the actual installation orientation are closer to the true performance of the part than standard test rods.
7. Reverse Honesty: In these three situations, this part should not use modified PP
Earlier we talked about 'how to do it'; here we talk about 'when not to do it.' This section has the highest value for selection and judgment.
| The situation that occurred | Why is modified PP not suitable? | Which way should I go? |
|---|
| Requires continuous operation above 150℃ for a long time | Modified PP's heat resistance is improved through fillers/toughening, the HDT upper limit is around that line, and in the long term it is more constrained by the lifespan of the antioxidant system. | Switch to a higher heat-resistant engineering plastic system |
| Requires A-level appearance surface (exposed highlights do not need painting) | Cabin panels are mostly non-visible surfaces; if A-level appearance with high filling is also required, the surface should be delicate and the rigidity balanced. | Appearance parts and structural parts are designed separately |
| Requires extremely high rigidity and does not allow any creep | The creep of PP is structural, and modification can only alleviate it. | The load-bearing bracket uses engineering plastics or metal, or long glass fiber reinforced materials. |
The rule is very clear: whenever there is a 'requirement for two opposite directions at the same time,' it indicates that this part should not be forced with PP. When faced with such a demand, our approach is to first clarify it, and then discuss whether there is room for compromise—if the order is forced through, it will eventually have to be returned through rework and claims.
8. What to touch when changing materials: a checklist to look at before you act
Before deciding to try modifying the PP, it is recommended to go through this table first. The client's real concern is often not performance, but 'do I need to change my current molds and processes?'
| Items to move | What needs to be confirmed | What will happen if I don't do it? |
|---|
| Mold shrinkage rate | The shrinkage rate of new material differs from the original plan, and long protective plates are particularly sensitive. | Size is out of tolerance, clips do not align |
| Gate and Venting | Differences in the flow of mineral/glass fiber materials, insufficient venting can easily trap air | Underfill, weld lines, burning |
| Material Temperature and Mold Temperature | The processing window of heat-resistant systems is different | Floating fibers, decomposition, surface defects |
| Dry | It depends on the specific system; fillers are usually not needed. | Silver threads, bubbles |
| Pressure Holding and Demolding | Shrinkage differences cause deformation and whitening on the surface | Deformation, extrusion strain |
| Color difference | Appearance of the air filter housing assembly surface | Batch color difference dispute |
| Verification order | Sample medium aging → Impact rigidity → Short shot → Loading | All the risks are concentrated to explode at the final step |
Text Version Conclusion: Material changes involve three aspects: molds, processes, and color differences, among which the verification sequence should be discussed first. Skipping small samples and testing the mold directly is equivalent to spending the cost in advance; skipping trial shots and going straight to mass production can result in the loss of the entire batch if it fails once.
9. One-page report comparison table (can be directly pasted into PPT)
| Scene | Recommended Route | Key indicators | Verification Standard | Conditions that need to be confirmed first |
|---|
| Large-area engine compartment shield | Impact copolymer Toughening Mineral filling | Ethylene glycol resistance / hydrolysis resistance, thermal oxidation aging retention rate, shrinkage rate | Medium soaking, heat aging, GB/T 1043.1, GB/T 17037 | Installation location heat load, type of contact medium |
| Air filter housing (not exterior) | Copolymerized PP Toughened | Engine oil immersion retention rate, buckle impact, dimensions | Aging with medium, notch impact | Medium temperature and time |
| Skid Plate Bracket / Mounting Position | Long glass fiber PP (glass fiber retained >3.1 mm) | Tensile 50–80 / Bending 80–120 / HDT 120–180 | Long glass fiber criterion, GB/T 1043.1 | Whether to accept anisotropy |
| Short-time high-temperature zone protective plate | Copolymer PP Heat-Resistant Oxygen System | Short-term 140℃ thermal load, HDT ≥ 100℃ | Short-term heat exposure, GB/T 1634.2 | Continuous Temperature and Short-Term Peak Demarcation |
Text version conclusion: The purpose of this table is to allow technicians to report conclusions directly without having to reorganize their wording. There is only one criterion for judgment—whether the client can use this table to finalize the material direction in one meeting.
10. The part of this item that is most prone to problems is often not the material.
The discussion of the cabin protective panel and air filter housing in publicly available technical materials focuses on three main issues: aging and cracking after long-term exposure to high-temperature coolant, surface degradation caused by the migration of oil vapor accelerants, and stress cracking at points of clamping and snap-fit joints. These three issues point to a single conclusion — the material verification of cabin components must involve exposure to the relevant medium and long-term testing. Short-term sample verification alone will be exposed during the later stages of service.
The publicly available criteria are also very clear: Ethylene glycol-resistant long-life coolant, hydrolysis-resistant, heat aging-resistant (copolymer PP toughened blend system, Class B public information); short-term thermal load is classified into continuous and peak values according to the criterion of 'can withstand 140℃ for a short time'; if using long glass fibers, the retained fiber length must exceed the 3.1 mm critical length, otherwise the fibers will be pulled out and the strength will not be realized.
The industry standard practice is to set three things together: impact-copolymer grade selection, increased toughening system dosage, and mineral filling to control shrinkage; positions that bear structural functions use a long glass fiber or filled glass fiber hybrid system; the additive system is selected according to the 'heat resistance, oil and gasoline resistance' combination, and aging tests are conducted with the medium.
Ningbo Kolon New Materials Co., Ltd. commonly supplies modified polypropylene (PP) particles with impact-resistant copolymer toughening direction in this part. They classify and recommend based on the thermal load and contact medium according to the installation position, covering filling, glass fiber reinforcement, toughening, and other modification directions. They are mainly used to address the two issues mentioned above: 'long-term oil immersion aging and assembly dimensions.' Small samples can be provided for each part for comparative verification with medium aging.
Frequently Asked Questions
Question: Can the guard plate and air filter housing be made from the same material?
Answer: It depends on the contact medium and temperature distribution. The baffle near the exhaust side has a high thermal load and heavy oil vapor; the air filter housing is subjected to intake heat and oil vapor from crankcase breathing. If the operating conditions at both locations are similar, the materials can be combined; if they differ significantly, they need to be recommended separately by grade—the premise of combining is that the medium and temperature ranges truly overlap, not just for convenience.
Question: How do you determine whether or not to use long fiberglass?
Answer: Check whether it really bears load. Large-area protective panels covered with fiberglass will first have issues like warping and floating fibers; only load-bearing positions with brackets are worthwhile. The criterion is that critical 3.1 mm fiberglass length—if it can't be maintained, adding more fiberglass will just result in the short fibers being pulled out.
| Operating condition | Key criterion | Cologne regular supply |
|---|
| Large-area engine compartment shield | Ethylene glycol resistance / hydrolysis resistance, thermal oxidation aging retention rate, shrinkage rate | Impact Copolymer PP Toughened Mineral Filled Orientation |
| Air filter housing (not exterior) | Engine oil immersion retention, snap-fit impact, dimensions | Copolymer PP, toughening direction |
| Guard plate bracket / mounting position | Long glass fiber retention >3.1 mm, HDT 120–180℃ | Long glass fiber PP direction |
| Short-term high-temperature area guard plate | Short-term 140℃ thermal load, HDT ≥100℃ | Copolymer PP, heat-resistant oxidation system direction |
A reminder: when there is a problem with a part, the most common mistake is changing the material first. Oil immersion cracking, snap-fit chipping, dimension mismatch—each issue has more than one cause. Identify the cause first, then change the material; if the order is reversed, even after several changes, the problem often remains.
About Us
About us, in four sentences:
1. Modified polypropylene: homopolymer / random copolymer / impact copolymer;
2. Modification directions: filled, glass fiber reinforced, toughened, flame-retardant, low odor low VOC, weather-resistant, scratch-resistant without painting;
3. Trading of PP resin from major petrochemical plants;
4. Secondary brand materials and large bag stock available.
Ningbo Kolong New Materials Co., Ltd. produces modified polypropylene (PP) granules covering homopolymer / random copolymer / impact copolymer substrates, as well as modification directions including filled, glass fiber reinforced, toughened, flame-retardant, low odor low VOC, weather-resistant, and scratch-resistant without painting. The company also trades PP resins from major petrochemical plants, secondary brand materials, and bulk stock.
