储能液冷管路接头用什么 PP？液冷件和一般电气件最大的不同，是它要长期泡在乙二醇型冷却液里，老化是"全程不间断暴露"而不是偶发飞溅。这篇把六维工况、耐冷却液改性 PP 的选材路线、浸泡验证判据与验证顺序讲透，并说明哪三种工况下这个件不该用改性 PP。
"储能液冷接头，我们这个件泡了两年就开始渗，拆开看料没裂，但表面发粘、绝缘也掉了——你们改性PP能扛住吗？"
这是我在展会上被问得最多的一句话的变体。问的人大多已经踩过一次坑：试模、装机都顺利，跑了一段时间才发现冷却液那一侧先出问题。
液冷件和一般电气件最大的不同，就在这"泡"字上。它要长期、不间断地泡在乙二醇型冷却液里，老化是全程暴露，不是飞溅。
下面按工况、路线、判据、验证四层往下拆。
一、开篇先说结论：液冷接头的第一道门槛是耐冷却液，不是强度
储能液冷系统的管路接头，失效现场几乎都长一个样：冷却液侧先出问题。
最常见的两种——一种是接头本体或密封配合面在长期浸泡后开裂、发粘，导致缓慢渗漏；另一种是力学看着没事，但浸泡后体积电阻率或绝缘电阻掉下来，绝缘性能不满足要求。后者最隐蔽，因为外观完好，往往要等测试或现场报错才发现。
所以选这个件的材料，第一句话不该问"强度够不够"，该问"它能不能在长期泡冷却液这件事上扛住"。强度是后话，耐冷却液才是硬指标。
一个内行细节：液冷件的"介质暴露"和汽车保险杠的"雨雪飞溅"完全不是一个量级。飞溅是间歇的、可逆的，擦干就恢复；冷却液浸泡是连续的、不可逆的，缓蚀剂、金属离子、水分会持续和材料发生作用。把"耐冷却液"当成"耐一点液体"来选，是这类件最常见的选型错位。
二、工况六维拆解：全程不间断浸泡，是液冷件和其他件的根本区别
液冷管路接头的工况，拆成六个维度。把六个数报齐，方向基本就出来了。
| 维度 | 液冷接头实际工况 | 对材料的要求 |
|---|
| 温度 | 冷却液运行温度常见 40-65℃，峰值可能到 80-95℃；停机降温，接头经受反复热胀冷缩 | 耐热氧老化 + 耐水解，热变形温度留余量 |
| 载荷 | 泵启停造成压力脉动（约 0.x-数 bar 量级）；快插接头还有插拔力与密封面压紧 | 尺寸稳定 + 密封面抗蠕变 |
| 介质 | 乙二醇型冷却液（通常 30-60% 乙二醇 + 水 + 缓蚀剂 + 金属离子），全程不间断浸泡 | 耐乙二醇长效冷却液 + 耐水解 |
| 寿命 | 储能设备设计寿命常 ≥10 年 | 长期连续老化，不是偶发飞溅 |
| 外观 | 密封面平面度、无开裂发粘、颜色稳定 | 尺寸与外观都稳定 |
| 合规 | 体积电阻率 / 绝缘电阻满足该件电气要求 | 浸泡后必须复测电气项 |
六个维度里，介质这一维是"一票否决"性质的。原因很直接：冷却液是全程包裹接头的，其他维度出问题多是可返工，介质这一维出问题是从内部慢慢烂，等到发现往往已经渗漏或绝缘失效。
据行业公开资料（B 级，复材应用技术《聚丙烯材料性能分析与典型应用》），汽车散热器水室、膨胀箱等长期接触乙二醇型冷却液的件，材料通行做法是共聚 PP 混增韧体系，关键难点是"长期高温冷却液浸泡导致老化开裂"，选材要重点看耐水解与耐热氧老化。储能液冷接头面对的是同一类介质，逻辑相通。
三、材料路线对比：耐冷却液改性PP、玻纤增强PP与PA66/PPS/金属，是分工不是高低
改性PP 用在这个件上，基体基本走共聚 PP，再混增韧、补耐水解与耐热氧老化稳定体系。但液冷接头不是只有这一条路，几条路线是分工关系。
| 路线 | 拿到什么 | 适用边界 | 注意点 |
|---|
| 耐冷却液改性 PP（共聚 PP + 增韧 + 耐水解/耐热氧稳定） | 低成本、轻量、耐乙二醇浸泡、绝缘好 | 中低温、非承压或低压液冷回路接头 | 重点看长期耐热氧与耐水解；快插密封面要尺寸稳定 |
| 玻纤增强 PP | 刚性、尺寸稳定、抗蠕变更好 | 需要结构支撑的接头本体 | 纤维可能轻微影响密封面光洁与接触表现，需验证 |
| PA66-GF | 更高耐热、抗蠕变、承压更好 | 较高温度或较高压力回路 | 成本更高，吸湿影响尺寸，需控湿 |
| PPS | 耐高温、耐化学腐蚀更强 | 强腐蚀性冷却液或更高温度 | 成本高，加工窗口窄 |
| 金属接头（黄铜/不锈钢） | 承压与耐温边界最高 | 系统承压主回路 | 重、成本高，需注意电化学腐蚀 |
这几条没有"谁更好"。判断标准只有一个：这个接头处在回路的哪一段、温度压力介质各到什么量级。 低压支路的快插接头，耐冷却液改性 PP 是性价比路线；承压主回路或强腐蚀配方，就该让位给金属或 PPS。把不同边界的件硬塞进同一种材料，才是出问题的根源。
敢否定一个常见做法：有人为了"更耐用"，直接给液冷接头上玻纤增强 PP，认为纤维越多越抗造。这是错的。玻纤对接头本体的刚性有帮助，但密封配合面恰恰不希望表面有纤维露头，而且玻纤体系在长期冷却液接触下的表现要单独验证，不能默认"加了玻纤就更耐冷却液"。该加玻纤的是接头本体，不是密封面那一侧。
四、★ 选型判据表与耐冷却液浸泡验证：六项指标都带验证方法
下面这张表是全篇最该收藏的部分。注意第三列"验证方法·标准号"——选型时最常卡住的不是"看哪个指标"，而是"拿什么测、测到多少算过"。
| 指标 | 门限值（参考） | 验证方法 · 标准号 | 常见失效 | 通行解法 |
|---|
| 耐冷却液浸泡（拉伸强度保留率） | ≥85%（下降 ≤15%） | GB/T 11547-2008 / ASTM D543 浸泡后按 GB/T 1040 测 | 长期浸泡后强度塌 | 共聚 PP + 耐水解/耐热氧体系 |
| 耐冷却液浸泡（断裂伸长率保留率） | ≥70%（下降 ≤30%） | 同上 | 发脆、开裂 | 增韧体系 + 稳定剂 |
| 质量变化率（吸液/析出） | 控制在 ±2% 以内且趋于稳定 | GB/T 11547-2008 浸泡前后称重 | 持续增重、助剂析出 | 基体与助剂耐抽出 |
| 尺寸变化率（关键配合面） | ≤1%，密封面可更严 ≤0.5% | GB/T 11547-2008 量关键尺寸 | 密封面变形泄漏 | 低收缩 + 尺寸稳定 |
| 外观（开裂/发粘/变色） | 无开裂、不发粘、无明显粉化 | GB/T 11547-2008 目视 | 粉化、发粘 | 耐水解耐热氧 |
| 电气（体积电阻率/绝缘电阻） | 满足该件绝缘等级 | 浸泡后按 GB/T 1410 / GB/T 10064 复测 | 力学没掉但绝缘掉了 | 浸泡后必复测电气项 |
文字版结论：六项规定里电气复测这一项最容易被漏掉。力学没掉、外观没裂，但浸泡后绝缘电阻掉下来，在液冷件上是真实存在的失效模式——因为冷却液里的离子、缓蚀剂会慢慢改变材料表面与体积内的导电通路。把这张表当体检单，缺一项不判合格，比装机跑两年再回头找原因省钱得多。
4.1 耐冷却液怎么验：浸泡条件写清三项，判据按"项 + 门限 + 方法"摆
这是本篇的核心。耐冷却液不是"泡一下看看"，而是一套可操作的验证方法。先定浸泡条件，再定判据。
浸泡条件三项必须写清：
- 介质配比：按实际冷却液配方配，例如 50% 乙二醇 + 50% 水 + 对应缓蚀剂；加速筛选可提高乙二醇浓度或提高缓蚀剂占比
- 温度：按运行温度上限取，或加速时取高于运行温度一档（如运行 65℃ 取 80-95℃ 加速）
- 时间：筛选阶段短周期（如数百小时加速），确认后再做接近寿命量级的长期浸泡
测试方法按 GB/T 11547-2008《塑料 耐液体化学试剂性能的测定》（修改采用 ISO 175:1999，现行，A 级）或 ASTM D543-21《Standard Practices for Evaluating the Resistance of Plastics to Chemical Reagents》（A 级）的浸泡体系，报告质量、尺寸、外观、强度的变化。
判据写成"项 + 可接受变化门限 + 方法"，每一项给一个参考区间并说明依据：
| 验证项 | 可接受变化门限（参考） | 方法与依据 | 门限依据 |
|---|
| 拉伸强度保留率 | ≥85%（下降 ≤15%） | GB/T 11547 / ASTM D543 浸泡后按 GB/T 1040 测 | 接头承受装配与脉动应力，强度塌即渗漏风险 |
| 断裂伸长率保留率 | ≥70%（下降 ≤30%） | 同上 | 伸长对老化更敏感，是开裂前兆 |
| 质量变化率 | 控制在 ±2% 以内且趋于稳定 | GB/T 11547 浸泡前后称重 | 持续增重 = 吸液/助剂析出，预示长期劣化 |
| 尺寸变化率 | ≤1%，密封配合面建议 ≤0.5% | GB/T 11547 量关键尺寸 | 尺寸变即密封失效 |
| 外观（开裂/发粘/变色） | 无开裂、不发粘、无明显粉化 | GB/T 11547 目视，可配显微 | 目视最直观但最晚报警 |
| 电气复测（体积电阻率/绝缘电阻） | 仍满足该件绝缘等级 | GB/T 1410 / GB/T 10064，浸泡后复测 | 力学没掉但绝缘掉了，是液冷件最易被漏的失效 |
文字版结论：上面这些门限是行业选材的筛选参考值（B 级），不是某份强制国标；具体数值要按你实际用的冷却液配方、运行温度和设计寿命来约定，最好和冷却液供应商一起确认。但"浸泡后必须复测电气项"这一条没有商量余地——力学过了不代表绝缘过了。
五、常见失效与根因：力学没掉、绝缘掉了，最容易被漏掉
失效一：长期浸泡后缓慢渗漏。 根因多在耐水解/耐热氧体系没做到位，或增韧剂在长期介质里逐步迁出。先查浸泡保留率，再查体系，顺序反了会白换几轮料。
失效二：外观没裂但绝缘掉了。 这是液冷件最隐蔽的一种。冷却液里的离子、缓蚀剂改变材料导电通路，力学指标全绿，绝缘电阻却已不达标。只在装机后测试或现场报错时才暴露，所以选材阶段就必须把电气复测排进验证流程。
失效三：快插接头反复插拔后密封面变形。 根因不是初始尺寸不合格，是材料在多次插拔后回弹/蠕变导致密封面贴合变差。只看初始尺寸会漏判，必须做插拔循环后的密封面复测。
失效四：热胀冷缩导致接头处应力集中开裂。 根因在温度循环下材料反复伸缩，转角或薄壁处应力集中。这通常是结构设计与材料耐疲劳一起看的问题，不是单换料能解决的。
敢否定一个常见做法：有人把"泡完没裂"当成耐冷却液合格。这是错的。没裂只说明外观项过了，拉伸保留率、尺寸变化、尤其是电气项可能早已越线。耐冷却液的判据是六项的组合，不是"看着没坏"一个直觉。
六、验证顺序：先泡再测力学、再测电气、最后上整机
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。
`
① 选材阶段浸泡筛选 短周期、高浓度、加温加速
↓ 先淘汰不合适的体系，此时还没花模具钱
② 力学保留率 拉伸 / 断裂伸长 / 质量 / 尺寸 / 外观
↓ 任一不过，退回上一级重新选材
③ 电气复测 体积电阻率、绝缘电阻（浸泡后必做）
↓ 力学过了不代表绝缘过了
④ 整机压力循环 + 热循环 热胀冷缩 + 泵启停压力脉动
↓ 模拟真实服役，最后一道
`
文字版结论：验证顺序必须是 浸泡筛选 → 力学保留率 → 电气复测 → 整机循环。加速筛选的价值就在"还没投模具前淘汰不合适的体系"，别把这道关留到整机阶段才发现。
七、反向诚实：这三种工况，液冷接头不该用改性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 |
|---|
| 长期冷却液温度 120℃ 以上 | PP 的耐热氧老化上限就在那条线附近，长期高温连续浸泡会逐步开裂 | 换 PA66-GF / PPS / 金属接头 |
| 系统承压主回路（高压） | PP 的刚性与抗蠕变有限，承压密封难长期保持 | 金属或增强工程塑料 |
| 长期接触强腐蚀性冷却液配方（非乙二醇体系、高缓蚀剂或氧化性组分） | PP 对冷却液配方的耐受有边界，强腐蚀会加速劣化 | PPS / 专用耐蚀材料 / 金属 |
规律很清楚：温度、压力、介质腐蚀性，任意一项越过了 PP 的边界，这个件就不该用改性 PP 硬撑。 遇到这种情况，我们的做法是先把这条讲清楚，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、换料风险清单：密封面与插拔寿命是隐藏项
决定试耐冷却液改性 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 | 新料收缩率与现料的差，长件/密封面最敏感 | 尺寸超差、密封面漏 |
| 浇口与排气 | 玻纤/填充料流动差异 | 充填不足、熔接线、浮纤 |
| 料温与模温 | 耐冷却液体系加工窗口 | 表面缺陷、密封面不光 |
| 干燥 | 看具体体系定 | 银丝、气泡 |
| 保压与脱模 | 收缩差异带来变形 | 顶白、变形 |
| 色差 | 外观件先确认色板 | 批次争议 |
| 验证顺序 | 浸泡筛选 → 力学 → 电气 → 整机 | 风险全压在最后一步集中爆发 |
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。跳过小样浸泡直接试模，等于把成本提前花出去；跳过短周期筛选直接整机，一次失败就是整批损失。
九、一页纸汇报对照表：直接贴进评审会
| 场景 | 推荐路线 | 关键指标 | 验证标准 | 需先确认的条件 |
|---|
| 储能低压液冷支路接头 | 耐冷却液改性 PP（共聚+增韧+耐水解耐热氧） | 浸泡后强度/伸长保留率、尺寸、绝缘 | GB/T 11547 / ASTM D543 + GB/T 1410 | 冷却液配比、运行温度、设计寿命 |
| 快插式接头（多次插拔） | 同上 + 尺寸稳定体系 | 插拔后密封面变形、插拔力保持 | 插拔循环 + 尺寸复测 | 插拔次数要求、密封结构 |
| 需承压或较高温回路 | PA66-GF / PPS | 耐热、抗蠕变、承压 | 对应工程塑料标准 | 压力等级、峰值温度 |
| 主回路 / 强腐蚀配方 | 金属或 PPS | 承压、耐蚀 | — | 系统压力、冷却液配方 |
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、自产能力位（B0档）+ FAQ
储能液冷接头这类件，行业上最常见的早期失效是长期冷却液浸泡后的缓慢渗漏与绝缘下降，而这两类问题里，由材料耐介质体系引起的比例并不低。公开资料把这类件的判据写得很清楚：要耐乙二醇长效冷却液、耐水解、耐热老化，基体走共聚 PP 混增韧，难点在"长期高温冷却液浸泡导致老化开裂"。
行业通行的做法是把三件事一起定：共聚 PP 选档、增韧体系加量、耐水解与耐热氧稳定剂配齐。三者的配平关系，才是这类件真正的技术难点——单看任何一项都没意义。
关键不在"谁的料更耐泡"，在基材档位、增韧体系、耐水解/耐热氧稳定剂、密封面尺寸稳定性四件事能不能同时对上。
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）粒子里的共聚基材 + 增韧 + 耐水解耐热氧稳定方向，按件的冷却液配方、运行温度与寿命要求给到对应的改性方案，主要用来解决上面说的"长期泡冷却液后渗漏与绝缘下降"这两件事；配方按件的工况调，可以配合做小样比对与试模，件级客户多品种小批量的需求也能接。
| 工况 | 关键判据 | 科隆常规供应 |
|---|
| 储能液冷接头（非承压回路） | 耐乙二醇冷却液、耐水解、耐热老化 | 共聚 PP + 增韧 + 耐水解/耐热氧稳定方向 |
| 快插接头密封面 | 尺寸稳定、插拔后不变形 | 低收缩 + 尺寸稳定改性 PP 方向 |
| 玻纤增强接头本体 | 刚性、抗蠕变 | 玻纤增强 PP 方向（配合尺寸控制） |
常见问答
问：我们原来用 PA66-GF 做接头，换成改性 PP 能降成本吗？
答：能降成本是事实，但前提是这个接头处在低压、中低温回路。先过浸泡筛选与电气复测两关，确认耐冷却液和绝缘都满足，再谈替换；承压主回路不建议换。分工问题，不是单纯比价格。
问：冷却液浸泡后看着没裂，是不是就安全了？
答：不一定。力学没掉但绝缘电阻掉下来，在液冷件上是真实存在的失效。选材阶段必须把体积电阻率和绝缘电阻的浸泡后复测排进流程，不能只看外观。
问：快插接头反复插拔，密封面怎么看它不变形？
答：看的是插拔循环后的密封面尺寸与变形，不是初始尺寸。初始尺寸合格不代表插拔几十次后还贴得住，这条要单独验证。
问：能不能直接给一个标准的浸泡条件？
答：没有放之四海皆准的浸泡条件。介质配比、温度、时间要按你实际用的冷却液配方、运行温度和设计寿命来定；我们按 GB/T 11547 / ASTM D543 的框架配合你把条件设出来，再做短周期加速筛选。
想提醒一句：件出问题，最常见的错法是先换料。渗漏、绝缘下降、密封面变形——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。
最后说三句
第一，液冷接头选材的第一句话是"它能不能长期泡冷却液"，不是"强度够不够"。 六维工况里只有介质是全程不间断暴露，一票否决。
第二，耐冷却液的判据是六项的组合，不是"看着没坏"一个直觉。 力学没掉但绝缘掉了，是液冷件最容易被漏的失效；浸泡后必须复测电气项。
第三，验证顺序比验证项更重要。 浸泡筛选 → 力学保留率 → 电气复测 → 整机循环，加速筛选必须放在投模具之前。
下一篇我们讲储能电池包壳体——那个件最怕的不是泡冷却液，是 V-0、耐温与绝缘三件事同时卡你。
关于我们
样品寄出去之后，我们一般还会多问一句："打算怎么试？"
因为试法不对，好料也能试出坏结果。薄壁件的干燥、玻纤料的模温和螺杆、阻燃料的停留时间——任何一项没到位，结论都会跑偏。
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。
What type of PP is used for energy storage liquid cooling pipeline joints? The biggest difference between liquid cooling components and general electrical components is that they need to be immersed in ethylene glycol-based coolant for a long time, and aging is 'continuous exposure throughout the entire process' rather than occasional splashes. This article explains the six-dimensional working conditions, the material selection route of coolant-resistant modified PP, the immersion test criteria and sequence, and also states under which three conditions this component should not use modified PP.
For the energy storage liquid-cooled connector, this part started leaking after being soaked for two years. When we disassembled it, the material wasn't cracked, but the surface became sticky and the insulation came off—can your modified PP withstand this?
This is a variation of the question I was asked the most at the exhibition. Most of the people asking had already experienced a pitfall once: molding and assembly went smoothly, but after running for a while, they found that the coolant side developed problems first.
The biggest difference between liquid-cooled components and general electrical components lies in this word 'soak.' They need to be soaked in ethylene glycol-based coolant for a long time without interruption, with aging occurring through full exposure, not splashing.
Next, break it down four layers according to operating conditions, routes, criteria, and verification.
1. Start with the conclusion: the first threshold for liquid cooling connectors is coolant resistance, not strength.
The pipeline joints of the energy storage liquid cooling system almost look the same at failure sites: the coolant side fails first.
The two most common types are: one is that the connector body or the sealed mating surface cracks or becomes sticky after long-term immersion, causing slow leaks; the other is that mechanically it looks fine, but after immersion, the volume resistivity or insulation resistance drops, and the insulation performance does not meet the requirements. The latter is the most hidden, because the appearance is intact, and it is often only discovered through testing or on-site error reporting.
So when choosing the material for this part, the first question shouldn't be 'Is the strength enough?' It should be 'Can it withstand being soaked in coolant over a long period?' Strength comes later; resistance to coolant is the hard metric.
A detail only an insider would know: the 'media exposure' of liquid-cooled parts and the 'rain and snow splashes' on a car bumper are not comparable at all. Splashes are intermittent and reversible—you can just wipe them off and it's fine; coolant immersion is continuous and irreversible, and inhibitors, metal ions, and moisture will keep interacting with the material. Choosing 'coolant resistance' as if it just means 'resistant to a little liquid' is the most common selection mistake for these types of parts.
2. Six-dimensional analysis of operating conditions: Continuous immersion throughout the entire process is the fundamental difference between liquid-cooled parts and other parts
The operating conditions of the liquid cooling pipeline joints are broken down into six dimensions. Once the six numbers are reported, the direction basically emerges.
| Dimension | Actual operating conditions of liquid-cooled joints | Requirements for the materials |
|---|
| Temperature | The operating temperature of the coolant is commonly 40-65℃, with peaks possibly reaching 80-95℃; when shutting down and cooling, the joints undergo repeated thermal expansion and contraction. | Heat-resistant oxidation aging, hydrolysis resistance, margin of heat distortion temperature |
| Load | Pump start and stop cause pressure pulsations (about 0.x- several bar); quick-connect fittings also have insertion and removal forces as well as sealing surface pressing | Dimensional stability Sealing surface creep resistance |
| Medium | Ethylene glycol-based coolant (usually 30-60% ethylene glycol, water, corrosion inhibitors, metal ions), continuous immersion throughout | Ethylene Glycol Long-Lasting Coolant Hydrolysis Resistant |
| Lifespan | The designed service life of energy storage equipment is often ≥10 years | Long-term continuous aging, not occasional splashing |
| Appearance | Sealing surface flatness, no cracking or stickiness, color stability | The size and appearance are both stable |
| Compliance | Volume resistivity / insulation resistance meets the electrical requirements of this part | Electrical items must be retested after soaking |
Among the six dimensions, the medium dimension is of a 'veto' nature. The reason is straightforward: the coolant completely surrounds the joints throughout, and problems in other dimensions are often reworkable, but if there is an issue with the medium, it gradually deteriorates from the inside, and by the time it is discovered, it has often already leaked or undergone insulation failure.
According to publicly available industry information (Class B, Composite Material Application Technology "Analysis of Polypropylene Material Properties and Typical Applications"), for automotive radiator water tanks, expansion tanks, and other parts that are in long-term contact with ethylene glycol-based coolant, the common practice for materials is to use a copolymer PP toughened system. The key difficulty is 'aging and cracking caused by long-term immersion in high-temperature coolant,' so material selection should focus on hydrolysis resistance and thermal oxidative aging resistance. The situation with energy storage liquid cooling connectors involves the same type of medium, and the logic is similar.
3. Comparison of Material Routes: Coolant-resistant modified PP, glass fiber reinforced PP, and PA66/PPS/metal are a matter of division of labor, not superiority.
Modified PP is used in this part. The matrix is basically based on copolymer PP, with additional toughening, hydrolysis resistance, and thermal oxidative aging stabilization systems mixed in. However, liquid-cooled connectors are not limited to this single approach; there are several routes that have a division of labor.
| Route | Get what | Applicable scope | Points to Note |
|---|
| Cold-resistant modified PP (copolymer PP, toughened, hydrolysis-resistant/heat-oxidation-stable) | Low cost, lightweight, resistant to ethylene glycol immersion, good insulation | Medium-low temperature, non-pressurized or low-pressure liquid cooling circuit connector | Focus on long-term heat and hydrolysis resistance; plug-in sealing surfaces need dimensional stability |
| Glass fiber reinforced PP | Rigid, dimensionally stable, better creep resistance | The joint body requires structural support | Fibers may slightly affect the sealing surface's smoothness and contact performance, verification is required. |
| PA66-GF | Higher heat resistance, creep resistance, better pressure bearing | Higher temperature or higher pressure circuit | Higher cost, moisture absorption affects dimensions, moisture control needed |
| PPS | Higher resistance to high temperatures and chemical corrosion | Strongly corrosive coolant or higher temperature | High cost, narrow processing window |
| Metal fittings (brass/stainless steel) | Maximum pressure and temperature resistance boundary | System pressurized main circuit | Heavy, high cost, attention needed for electrochemical corrosion |
There is no 'which is better' for these items. The only judgment criteria are: which section of the circuit the fitting is in, and the magnitude of temperature, pressure, and medium. Quick-connect fittings for low-pressure branches, made of coolant-resistant modified PP, are the cost-effective choice; for pressurized main circuits or highly corrosive formulas, metal or PPS should be used. Forcing parts designed for different boundaries into the same material is what causes problems.
Dare to challenge a common practice: some people, in order to make it 'more durable,' directly add glass fiber reinforced PP to liquid cooling connectors, believing that the more fibers, the stronger it will be. This is wrong. Glass fiber does help with the rigidity of the connector body, but the sealing interface does not want fibers exposed on the surface. Moreover, the performance of glass fiber systems under long-term coolant exposure needs to be verified separately; it cannot be assumed that 'adding glass fiber makes it more resistant to coolant.' The place where glass fiber should be added is the connector body, not the sealing surface side.
4. ★ Selection Criteria Table and Coolant Soak Test: All six indicators include verification methods
The table below is the part of the entire text most worth keeping. Pay attention to the third column 'Verification Method · Standard Number' — the part that usually causes the most trouble when choosing is not 'which indicator to look at', but 'what to use to measure it and how much counts as passing'.
| Indicator | Threshold value (reference) | Verification Method · Standard Number | Common Failures | Common solution |
|---|
| Resistance to coolant soaking (retention rate of tensile strength) | ≥85% (decrease ≤15%) | GB/T 11547-2008 / ASTM D543 Tested according to GB/T 1040 after soaking | Strength collapses after long-term soaking | Copolymerized PP water-resistant/heat-oxidation resistant system |
| Coolant Immersion Resistance (Retention Rate of Elongation at Break) | ≥70% (decrease ≤30%) | Same as above | Becoming brittle and cracking | Toughening System Stabilizer |
| Rate of mass change (liquid absorption/desorption) | Controlled within ±2% and tends to be stable | GB/T 11547-2008 Weighing Before and After Soaking | Continuous weight gain, excipient precipitation | Resistance of the substrate and additives to extraction |
| Dimensional change rate (critical mating surface) | ≤1%, sealing surface can be tighter ≤0.5% | GB/T 11547-2008 Measuring Key Dimensions | Sealing surface deformation leakage | Low shrinkage Dimensionally stable |
| Appearance (cracking/stickiness/discoloration) | No cracking, not sticky, no obvious chalking | GB/T 11547-2008 Visual Inspection | Powdering and becoming sticky | Hydrolysis-resistant and heat-resistant oxygen |
| Electrical (Volume Resistivity / Insulation Resistance) | Meets this insulation class | After soaking, retest according to GB/T 1410 / GB/T 10064 | The mechanics didn't fail, but the insulation did. | Electrical items must be retested after soaking |
Text version of conclusion: Among the six regulations, electrical retesting is the easiest to be overlooked. Mechanical integrity is fine, appearance is not cracked, but after soaking, the insulation resistance drops. This is a real failure mode in liquid-cooled components—because the ions and corrosion inhibitors in the coolant gradually change the conductive paths on the surface and inside the material. Treat this table as a medical checkup sheet; if any item is missing, do not deem it qualified. This is much more cost-effective than installing the device, running it for two years, and then going back to find the cause.
4.1 How to test coolant resistance: clearly specify the three soaking conditions, and arrange the criteria according to 'item threshold method'.
This is the core of this article. Coolant resistance is not about 'soaking and seeing,' but a set of operable verification methods. First, establish the soaking conditions, then determine the criteria.
The three soaking conditions must be clearly stated:
- Medium ratio: Mix according to the actual coolant formula, for example, 50% ethylene glycol and 50% water with the corresponding corrosion inhibitor; to accelerate screening, the ethylene glycol concentration or the proportion of corrosion inhibitor can be increased.
- Temperature: take according to the upper limit of operating temperature, or when accelerating, take one level higher than the operating temperature (for example, if operating at 65°C, take 80-95°C for acceleration)
- Time: Short cycle during the screening phase (e.g., accelerated for hundreds of hours), then after confirmation, perform long-term soaking close to the expected lifetime.
The test method follows the immersion system of GB/T 11547-2008 "Plastics — Determination of the Resistance to Liquid Chemicals" (modified from ISO 175:1999, current, Grade A) or ASTM D543-21 "Standard Practices for Evaluating the Resistance of Plastics to Chemical Reagents" (Grade A), and reports changes in mass, dimensions, appearance, and strength.
The criteria are written as 'Item Acceptable Variation Threshold Method', with a reference range provided for each item along with an explanation of the basis:
| Verification item | Acceptable change threshold (reference) | Methods and Basis | Threshold basis |
|---|
| Tensile Strength Retention Rate | ≥85% (decrease ≤15%) | Test according to GB/T 1040 after soaking in GB/T 11547 / ASTM D543 | The joint bears assembly and pulsating stress, and strength collapse immediately poses a leakage risk |
| Elongation at break retention rate | ≥70% (decrease ≤30%) | Same as above | Elongation is more sensitive to aging and is a precursor to cracking |
| Rate of change of mass | Controlled within ±2% and tends to be stable | GB/T 11547 Weighing Before and After Soaking | Continuous weight gain = liquid/agent precipitation, indicating long-term deterioration |
| Rate of change in size | ≤1%, it is recommended that the sealing mating surface be ≤0.5% | GB/T 11547 Key Dimension Measurement | Change in size leads to sealing failure |
| Appearance (cracking/stickiness/discoloration) | No cracking, not sticky, no obvious chalking | GB/T 11547 Visual inspection, can be equipped with a microscope | Visual observation is the most intuitive but provides the latest alarm |
| Electrical Retesting (Volume Resistivity / Insulation Resistance) | Still meets the insulation rating of the part | GB/T 1410 / GB/T 10064, retest after soaking | The mechanical strength hasn't failed, but the insulation has, which is the most common type of failure for liquid-cooled parts. |
Text Version Conclusion: The thresholds above are reference values for material selection in the industry (Grade B), not any mandatory national standard; specific values should be determined according to the coolant formula you actually use, the operating temperature, and the design life, and it is best to confirm them together with the coolant supplier. However, the requirement that 'electrical items must be retested after soaking' is non-negotiable—passing the mechanical test does not mean the insulation has passed.
5. Common failures and root causes: mechanical failure, insulation failure, easiest to be overlooked
Failure 1: Slow leakage after long-term soaking. The root cause is often that the hydrolysis-resistant/heat-resistant oxygen system is not properly implemented, or the toughening agent gradually migrates out in the long-term medium. First check the soaking retention rate, then check the system; if the order is reversed, you may end up wasting several batches of material.
Failure 2: The appearance is intact, but the insulation has failed. This is the most hidden type for liquid-cooled components. Ions and corrosion inhibitors in the coolant alter the material's conductive pathways, so the mechanical indicators remain all green, but the insulation resistance no longer meets the standard. It only becomes apparent during testing after assembly or when errors are reported on-site, so the material selection stage must incorporate electrical retesting into the verification process.
Failure Three: The sealing surface of the quick-connect fitting deforms after repeated insertion and removal. The root cause is not an initial size defect, but the material's rebound/creep after multiple insertions and removals, which leads to poorer sealing surface contact. If you only look at the initial size, it will be misjudged; re-measuring the sealing surface after insertion and removal cycles is necessary.
Failure Four: Thermal expansion and contraction cause stress concentration cracking at joint connections. The root cause lies in the repeated expansion and contraction of the material under temperature cycles, leading to stress concentration at corners or thin-walled areas. This is usually a problem that needs to consider both structural design and material fatigue resistance, and cannot be solved by simply changing the material.
Dare to deny a common practice: some people consider 'no cracks after soaking' as qualifying for coolant resistance. This is wrong. No cracks only indicate that the appearance criteria have passed; tensile retention, dimensional changes, and especially electrical properties may have already exceeded limits. The criteria for coolant resistance are a combination of six items, not just an intuition of 'it looks fine.'
6. Verification sequence: first soak, then test mechanics, then test electrical, and finally assemble the complete machine
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 Soaking and screening during the material selection stage: short cycle, high concentration, accelerated by heating
↓ First eliminate unsuitable systems; at this point, no money has been spent on molds yet.
② Mechanical Retention Rate Tensile / Elongation at Break / Mass / Dimensions / Appearance
↓ If any fails, go back to the previous level and choose materials again
③ Electrical Retesting Volume resistivity, insulation resistance (must be done after soaking)
Passing mechanics does not mean passing insulation.
④ Whole machine pressure cycle, thermal cycle, thermal expansion and contraction, pump start-stop pressure pulsation
↓ Simulate real service, the final step
`
Text version conclusion: The verification sequence must be soaking screening → mechanical retention rate → electrical retesting → complete machine cycling. The value of accelerated screening lies in 'eliminating unsuitable systems before mold injection,' and not leaving this step to be discovered at the complete machine stage.
7. Reverse honesty: For these three operating conditions, the liquid-cooled connector 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 modified PP is not suitable | Which way should I go? |
|---|
| Long-term coolant temperature above 120°C | The heat- and oxygen-aging limit of PP is around that line, and long-term continuous soaking at high temperatures will gradually cause cracking. | Replace PA66-GF / PPS / metal joint |
| System pressurized main circuit (high voltage) | PP has limited rigidity and creep resistance, making it difficult to maintain pressurized sealing over the long term. | Metal or reinforced engineering plastics |
| Long-term exposure to strongly corrosive coolant formulations (non-ethylene glycol system, high inhibitor content, or oxidative components) | PP has limits in its tolerance to coolant formulations; strong corrosion will accelerate degradation. | PPS / Special Corrosion-Resistant Materials / Metal |
The pattern is very clear: temperature, pressure, and the corrosiveness of the medium—if any of these exceed the limits of PP, this part should not rely on modified PP. When we encounter such a situation, our approach is to first explain this clearly, and then discuss whether there is any room for compromise—any orders pushed through forcibly will ultimately have to be returned through rework and claims.
8. Material Change Risk List: Sealing surface and insertion/removal lifespan are hidden items
Before deciding to try modifying PP with coolant, it is recommended to go through this table first. The customer's real concern is often not performance, but 'do I need to change my current mold and process?'
| 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 that of existing material, with long parts/sealing surfaces being the most sensitive | Excessive size deviation, sealing surface leakage |
| Gate and Vent | Differences in the flow of glass fiber/fillers | Insufficient filling, weld lines, floating fibers |
| Material Temperature and Mold Temperature | Coolant system processing window | Surface defects, sealing surface not smooth |
| Dry | It depends on the specific system. | Silver threads, bubbles |
| Pressure holding and demolding | Shrinkage differences cause deformation | White topping, deformation |
| Color difference | Confirm the color swatch for the exterior parts first | Batch dispute |
| Verification order | Soaking Screening → Mechanical → Electrical → Complete Machine | The risk is concentrated and explodes in the final step |
Text version conclusion: Changing materials involves three aspects: molds, processes, and color differences, among which the verification sequence should be discussed first. Skipping small sample soaking and going straight to mold testing is equivalent to spending the cost in advance; skipping short-cycle screening and going straight to the complete machine means that a single failure results in the loss of the entire batch.
9. One-page report comparison table: directly paste into the review meeting
| Scene | Recommended Route | Key indicators | Verification standard | Conditions that need to be confirmed first |
|---|
| Energy storage low-voltage liquid cooling branch joint | Coolant-resistant modified PP (copolymer, toughened, hydrolysis-resistant, heat and oxidation-resistant) | Strength/elongation retention after soaking, dimensions, insulation | GB/T 11547 / ASTM D543 GB/T 1410 | Coolant ratio, operating temperature, design life |
| Quick-connect coupling (multiple insertions and removals) | Same as above Dimensionally stable system | Deformation of the sealing surface after plugging and unplugging, retention of insertion and extraction force | Plug-in and unplug cycles Dimension re-measurement | Number of insertion and removal cycles required, sealing structure |
| Circuits requiring pressure or higher temperature | PA66-GF / PPS | Heat-resistant, creep-resistant, pressure-bearing | Corresponding engineering plastic standards | Pressure level, peak temperature |
| Main Circuit / Strong Corrosion Formula | Metal or PPS | Pressure-resistant, corrosion-resistant | — | System pressure, coolant formula |
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 direction of the materials in a single meeting.
10. Self-production Capacity Position (B0 Level) FAQ
For components like energy storage liquid cooling connectors, the most common early failure in the industry is slow leakage and insulation degradation after long-term immersion in coolant. Among these two issues, the proportion caused by the material's resistance to the medium system is not low. Public information clearly states the criteria for these components: they must resist long-term ethylene glycol coolant, hydrolysis, and thermal aging. The base material uses copolymer PP with mixed toughening, and the difficulty lies in 'aging and cracking caused by long-term high-temperature coolant immersion'.
The common practice in the industry is to decide on three things together: choosing the PP grade for co-polymerization, increasing the amount of toughening system, and matching hydrolysis-resistant and thermo-oxidative stabilizers. The balance among these three factors is the real technical difficulty for this type of part—looking at any one of them alone is meaningless.
The key is not whose material lasts longer in brewing, but whether the four aspects—substrate grade, toughening system, hydrolysis/thermal oxidation stabilizers, and sealing surface dimensional stability—can all be addressed simultaneously.
Ningbo Kolon New Materials Co., Ltd. commonly supplies modified polypropylene (PP) particles for this part, focusing on copolymer base materials, toughening, hydrolysis resistance, heat resistance, and oxidative stability. They provide corresponding modification solutions based on the part’s coolant formulation, operating temperature, and service life requirements, mainly to address the two issues mentioned above: 'leakage and insulation deterioration after long-term coolant immersion.' The formulation can be adjusted according to the part’s working conditions, and small samples and mold trials can be conducted for comparison. They can also accommodate the demands of part-level customers requiring multiple varieties in small batches.
| Operating condition | Key criterion | Cologne regular supply |
|---|
| Energy storage liquid cooling joint (non-pressurized circuit) | Ethylene glycol-resistant coolant, hydrolysis-resistant, heat aging-resistant | Copolymer PP Toughening Hydrolysis-resistant / Heat-oxidation stability direction |
| Quick connector sealing surface | Dimensionally stable, does not deform after plugging and unplugging | Low-shrinkage, dimensionally stable modified PP orientation |
| Glass fiber reinforced joint body | Rigidity, creep resistance | Glass fiber reinforced PP orientation (with dimensional control) |
Frequently Asked Questions
Question: We originally used PA66-GF for the joint. Can switching to modified PP reduce costs?
Answer: It is true that it can reduce costs, but the premise is that this joint is in a low-pressure, low-to-medium temperature circuit. First, pass the soaking screening and electrical retesting to confirm that it can withstand the coolant and meet insulation requirements, then discuss replacement; it is not recommended to replace the pressurized main circuit. The issue is about division of labor, not just comparing prices.
Q: After soaking in coolant, it looks like there are no cracks. Does that mean it's safe?
Answer: Not necessarily. Even if the mechanical properties haven't dropped, a decrease in insulation resistance represents a real failure in liquid-cooled components. During the material selection stage, the volume resistivity and re-measured insulation resistance after soaking must be included in the process, and one cannot rely solely on appearance.
Question: With the quick connector being repeatedly plugged and unplugged, how can you tell if the sealing surface is not deformed?
Answer: What is being checked is the size and deformation of the sealing surface after multiple insertion and removal cycles, not the initial size. Passing the initial size does not mean it will still fit after dozens of insertions and removals; this needs to be verified separately.
Question: Can you directly provide a standard soaking condition?
Answer: There is no universally applicable soaking condition. The ratio of the medium, temperature, and time should be determined based on the coolant formula you actually use, the operating temperature, and the design life; we will work with you to set the conditions according to the framework of GB/T 11547 / ASTM D543, and then carry out short-cycle accelerated screening.
I want to give a reminder: when there is a problem with a part, the most common mistake is to replace the material first. Leaks, insulation degradation, deformation of sealing surfaces—each of these issues has more than one cause. First identify the cause, then replace the material; if the order is reversed, even after several rounds of replacement, the problem often remains.
Finally, say three sentences
First, the first sentence in choosing materials for liquid cooling joints is 'Can it be soaked in coolant for a long time?' rather than 'Is the strength enough?' In six-dimensional operating conditions, only the medium is continuously exposed throughout, which is a deal breaker.
Second, the criterion for coolant resistance is a combination of six items, not just the intuition of 'it looks fine.' Mechanical strength may remain but insulation may fail, which is the most common failure in liquid-cooled parts; after soaking, the electrical items must be retested.
Third, the verification sequence is more important than the verification items. Soaking screening → mechanical retention → electrical re-test → whole machine circulation, accelerated screening must be done before molding.
In the next article, we will talk about energy storage battery pack enclosures — the thing that is most feared is not soaking in coolant, but getting stuck with V-0 rating, temperature resistance, and insulation all at the same time.
About Us
After sending out the sample, we usually ask one more question: 'How do you plan to test it?'
Even good material can produce bad results if the testing method is incorrect. Drying of thin-walled parts, mold temperature and screw settings for glass fiber materials, retention time for flame-retardant materials—if any of these are not properly managed, the conclusion will be skewed.
Ningbo Cologne New Materials Co., Ltd. produces modified polypropylene (PP) granules, covering homopolymer, random copolymer, and block copolymer base materials, as well as modifications including filled, glass fiber reinforced, toughened, flame-retardant, low odor and low VOC, weather-resistant, and scratch-resistant without coating; it also deals in PP resins from major petrochemical plants, off-spec materials, and bulk materials.
