断路器壳体换料，最容易出现的情况是灼热丝过了、CTI 掉一档。这篇讲清无卤切换的三条路线、判据表怎么读、同一个壳体不同腔位为什么分着选料，以及换料要重排的验证顺序。
断路器壳体换料这件事，前年冬天在一家做小型断路器的厂里撞上了。
他们接到一笔出口订单，目标市场要求无卤，要把原来的阻燃体系整个换掉。
寄来的两个壳件是白色的，巴掌大小，深腔多筋，用泡沫垫着，边角上还留着灼热丝试验烧过的痕迹。
电话里采购说得很直接："灼热丝那边过了，CTI 反而掉了一档，安规卡住了。"
我先反问了三句：换的是基材，还是整套阻燃体系一起动？壁厚和原来一样吗？那份 CTI 报告是干态测的，还是湿热处理后测的？
他想了一下，说体系换了，壁厚没动，报告上的测试状态没写。
这个问题点出了壳体换料最容易顾此失彼的地方——阻燃和耐电痕化这两项，提升方向常常是相反的。
下面这条时间线，是他们那批壳体的真实经过。
起点是无卤切换送测，灼热丝过了，采购认为这事成了；潜伏阶段是手上那份 CTI 数据一直看着没问题，因为它是干态测的；爆发是按污染等级送安规时，湿热态 CTI 掉了一档，认证停住；结算是回查，体系换了、壁厚没动、测试状态没写清——三件都是"没写下来"的事。
壳体换料的账，最贵的一笔常常记在测试条件上。
一、壳体换料前的工况六维
壳体看着是结构件，实际是电气安全的最后一道屏障，工况要拆成六样看。
温度这条，稳态和瞬态要分开。配电箱里的长期温度多在 40–70℃，接线端子附近更高一档；短路瞬间电弧的温度上千度，但那是极短时，考的是材料在这几秒里不持续燃烧。
载荷这条有两组。一组是操作机构的操动力，机械寿命几千到上万次；另一组是装配时自攻螺钉的扭矩，塑料凸台的滑丝扭矩要留余量。
介质这条最容易被漏。粉尘、湿气、清洗剂、沿海盐雾，四样叠在同一个件上；CTI 考的就是"电压 + 湿气 + 表面污染"同时出现时的表现。
寿命这条按十年算，还要算上电气寿命的循环次数。老化对阻燃与电气性能的影响，往往比对力学的影响更明显。
外观这条对电气件是硬指标。色差、熔接线浮纤要管，表面粗糙度也要管——表面越粗，越容易积污吸潮，CTI 跟着往下走。
合规这条最长：UL94 按最小壁厚报 V-0、灼热丝按 GWIT 与 GWFI 分档、CTI 按污染等级分档、球压按温度点报、出口还要加无卤清单。
| 维度 | 换料时要问的数 | 漏了会怎样 |
|---|
| 温度 | 长期温度区间、短路瞬态时长 | 球压与耐温档选错 |
| 载荷 | 操作次数、自攻螺钉扭矩 | 凸台滑丝、卡扣断 |
| 介质 | 污染等级、湿度、盐雾 | CTI 掉档 |
| 寿命 | 年限、电气寿命循环 | 老化后电气失守 |
| 外观 | 色差、浮纤、表面粗糙度 | 装配退回、CTI 下滑 |
| 合规 | 壁厚、阻燃与灼热丝档、无卤清单 | 送测卡住重来 |
六样里，壁厚和目标市场这两项要先定。它们定不下来，后面选什么体系都是临时方案。
二、无卤切换的三条路，先摆开代价
换料不是把阻燃等级做高就行，是把三条路的代价摆清楚。
| 路径 | 怎么换 | 代价 | 适合什么情况 |
|---|
| 换体系不动基材 | 溴锑体系换到磷氮体系 | 加量大、韧性掉一档、流动变差 | 结构成熟，只想解决法规 |
| 换基材不动体系 | PA66-GF 换到高温基材 | 料温模温整套要改 | 温度余量或尺寸要提 |
| 体系与基材一起动 | 无卤 + 高温基材 | 周期最长、验证最重 | 出口高要求、薄壁件 |
三条没有谁更好，只有哪条跟你的壁厚和认证节奏兜得住。
头一条最省事，但有个连带效应常被低估：阻燃剂的添加量一上去，流动性和韧性通常一起往下走。壳体是薄壁深腔件，流动性下降直接带来填充不足和熔接线偏弱。
第二条的风险在工艺。基材一换，料温、模温、干燥全要重设，照抄旧档位的产线最容易栽在第一炉。
第三条最贵，但在"薄壁 + 无卤 + 高 CTI"三个条件叠在一起时，往往才是能走通的那一条。
一个常见误判是"阻燃等级余量做得越大越保险"。对壳体不成立——余量做大意味着添加量做大，韧性、流动、CTI 一起受损。刚过线的那一档，常常才是好做的件。
三、换料判据表：这张表决定你复验哪几项
把前面的约束落成能核对的指标。下表门限是方向性建议，不是验收标准；实际数值必须由你的件、你的壁厚和实测确定。
| 指标 | 方向性门限 | 验证方法 / 标准 | 换料后常见失效 | 通行解法 | 对应助剂体系 |
|---|
| 灼热丝起燃温度 | 按件内位置 850℃ 或 960℃ | IEC 60695-2-13 | 起燃、熄弧时间超 | 换阻燃体系、提分散 | 阻燃体系（协效） |
| 漏电起痕指数 CTI | 按污染等级，湿热后测 | IEC 60112，调湿态 | 掉一档、安规卡 | 低吸湿 + 不易碳化 | 抗氧剂（抑制降解） |
| 球压 | 125℃ 或按客户规范 | IEC 60695-10-2 | 受热压痕、变形 | 往上提耐温档 | 抗氧剂（耐温上限） |
| 拉伸与冲击保持 | 热老化后 ≥七成 | ISO 527 / ISO 179 | 熔接线裂、卡扣断 | 提模温、改浇口 | 润滑剂（影响熔接线） |
| 熔接线强度 | 按壳体应力另定 | 短射取样 + 拉伸 | 装配跌落从熔接线裂 | 提高模温、改浇口 | 润滑剂 |
| 老化后电气 | 阻燃与 CTI 不掉档 | 热老化后复测两项 | 出厂合格、后期失守 | 稳定化体系 + 重测 | 抗氧剂 |
怎么读这张表：先看头两行。
灼热丝和 CTI 是一对，换料时最常出现"过了一头、掉了另一头"。所以这两项要在同一批样上一起测，不要串行做——串行做的时间成本太高。
第三列是给采购的：CTI 报告要写清是干态还是湿热后、按哪个壁厚测；灼热丝的接触时间也要写。条件不写清，后面就是一轮扯皮。
最后一行最容易省，也最容易出事。老化后的阻燃与 CTI 复测，是把"出厂合格"变成"十年合格"的那一步。
四、换料后四种失效，和它们真正的原因
失效一：灼热丝过了，CTI 掉一档。
根因在体系选择上。提高阻燃效率的很多手段会把电痕化表现往下拉，卤系尤其明显。所以这不是"换了个牌号变差了"，是两项指标天生互相拉扯，配方要在中间找平衡点。看到 CTI 掉档先看体系，别急着怀疑基材。
失效二：熔接线开裂，多发生在装配跌落或操作循环之后。
壳体的结构特点是深腔、多孔、局部有加强筋，料流会在很多位置汇合，熔接线特别多。玻纤含量越高，本体刚性提升越平缓，熔接线强度下降越陡——整壳数据很好看，一跌落就从那条线裂开。它要结构和工艺一起动。
失效三：同一批壳体，灼热丝成绩忽好忽坏。
这不是"料不稳定"。阻燃体系对工艺波动敏感：温度高了添加剂分解，低了分散不均，批间成绩就漂。追查下去，常见的是不同班组的料筒温度设定差了一截。这一条有助剂侧的账，也有纪律的账。
失效四：老化后 CTI 掉档，出厂数据却是合格的。
CTI 会随吸湿和老化下降，机理是阻燃剂慢慢迁移、表面状态变化。所以送安规之前，先按老化后的状态自己测一遍，能省一轮整改；这一项掉不掉，取决于稳定化体系配得够不够。
五、加工与验证：壁厚和料温是两道窄门
壁厚要在选料之前定下来，不是选完料再回头改结构。
同样的阻燃等级，薄壁件的难度远高于厚壁件——阻燃剂要在更少的材料里起作用，还要兼顾流动性与熔接线。壁厚从两毫米压到一毫米出头，添加量的负面作用会被放大。
料温窗口也比通用料窄。温度高了，阻燃体系开始分解；温度低了，分散不匀，件表面和内部的表现不一致，CTI 与灼热丝的成绩都会漂。所以换料后要把加工窗口贴在机台上，按窗口锁参数。
模温对熔接线的影响，在壳体上比在其他件更直接。模温低，熔接位置愈合差，就是一条暗伤。具体抬到多少，按你的件试出来。
验证顺序建议这样排，不要换：
1. 材料级：灼热丝初筛、调湿态 CTI、球压
2. 工艺窗口：变料温与模温，打对比件看熔接线与外观
3. 件级：装配跌落、操作循环、卡扣与凸台
4. 老化后复测：热老化样件再做一次阻燃与 CTI
5. 送安规：按目标市场与污染等级出报告
为什么把老化后复测排在送安规之前？因为安规看的是长期表现，提前自己走一遍，比送去被打回来省时间。
六、边界：这几种壳体，换料先收手
这一段可能比前面几段更值钱，因为它帮你在开工前止损。
其一，周边有强电弧的位置。接触器的灭弧区一带，壳体表面要经受电弧侵蚀，普通阻燃尼龙顶不住，该往热固性或者陶瓷化方向看。
其二，要做透明视窗的壳体。透明窗与阻燃壳体一体成型对材料是极限挑战，多数厂走双料方案，视窗单独注塑再装配；这条路的风险在界面密封，选料之前就要把方案定死。
其三，极薄壁、又要无卤、还要高 CTI 三件叠加的件。这是配方区里难度很高的一块，先考虑改结构或者放宽其中一项，别把三件事压在一次换料上。
其四，年产量极大、单价压得很低的件。这类件的账要算总，材料侧升一档的成本未必收得回来。
其五，失效点还没定位的件。壳子烧了、裂了，先分清是阻燃不够、是熔接线弱、还是装配距离偏了，三件事的解法完全不同。
把这五条写前面不是劝退，是省时间。
七、换料风险清单（从原体系换到无卤路线，要动的东西）
| 环节 | 要动什么 | 容易漏的点 |
|---|
| 模具 | 添加量变了收缩率会变，深腔件要复测 | 只换料不修模，装配紧配出问题 |
| 干燥 | 换体系后干燥窗口要重定 | 沿用旧参数，表面起雾 |
| 调湿 | CTI 必须按调湿态判定 | 拿干态数据送安规 |
| 料温 / 模温 | 阻燃体系对温度敏感，要锁窗口 | 不同班组设定不一致 |
| 保压 / 脱模 | 熔接线位置与强度要重新定 | 玻纤高、添加量大时更脆 |
| 色差 | 白色与深色件的色板分别对 | 阻燃体系换后底色会变 |
| 验证顺序 | 初筛→工艺→件级→老化复测→送安规 | 前一项没过就往下走 |
八、打样试模排程（几轮上机、每轮验什么、留样多久）
我们给壳体换料排的试模，通常分三轮，轮次之间不跳步。
头一轮·小样比对：用你的原模具打 3–5 模，验外观、填充、短射熔接线位置，同时送一组灼热丝初筛。这一轮先把"料能不能填满深腔"确认掉。留样两件，标注批号与料温模温。
第二轮·工艺窗口：固定料，变料温与模温，打两组对比件。验调湿态 CTI、球压、熔接线强度、装配跌落。这一轮决定量产参数。
第三轮·老化与安规：把热老化后的样件再做一次阻燃与 CTI，然后按目标市场送检。这一轮过了，才建议放量。留样按批封存，覆盖首批量产，便于追因。
三轮之间为什么不能跳？因为阻燃与电气成绩都依赖分散状态和吸湿状态，工艺没锁住，数据只对那一批有效。
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。
读者常问的三句
问：灼热丝和 CTI 哪个更难过？看件内位置。发热件附近灼热丝是硬门槛，带电件沿面爬电位置 CTI 是硬门槛。多数壳体两项都要过，初筛时两条线一起测。
问：无卤换了以后电气会不会变差？体系选对了不会，但吸湿性要盯，湿态介电要复测。沿海高湿市场，湿态数据比干态数据说明问题。
问：老化后复测一定要做吗？要做。阻燃与 CTI 都会随老化变化，这一项是把报告里的"合格"变成十年里的"合格"。
九、结构分件：同一个壳体，不同腔位可以分着选
这是壳体换料里最省成本的一件事，也是最多人漏掉的一件事。
同一台断路器，不同腔位的工况并不一样。接线腔温度比主腔低，但粉尘和湿气更重，按污染等级算，CTI 的要求反而更高；主腔看阻燃与球压；操作机构区看强度和熔接线；透明视窗那一段，多数走双料。
| 位置 | 主要考点 | 选料方向 |
|---|
| 主腔壳体 | 阻燃、球压、机械强度 | 阻燃增强体系 |
| 接线腔 | 污染等级下的 CTI | 调湿态 CTI 更高的一档 |
| 操作机构区 | 熔接线与卡扣强度 | 韧性与流动兼顾 |
| 透明视窗 | 透光与界面密封 | 双料方案，单独选 |
| 灭弧区附近 | 耐电弧侵蚀 | 热固性或陶瓷化方向 |
按位置分档选料，比整机一刀切更省钱，也不牺牲安全。
如果你要拿这篇去汇报，可以收成四行：
| 项 | 一句话结论 |
|---|
| 换什么 | 无卤磷氮体系先行，基材是否跟换看壁厚 |
| 动什么 | 壁厚先定、料温窗口锁死、模温重设 |
| 验什么 | 灼热丝、调湿态 CTI、球压，三项一起测 |
| 什么时候能放量 | 三轮试模过、老化后复测不掉档、安规出报告 |
我们交付的，不只是一包料。
一份调湿态的 CTI 数据、一次老化后的复测、一张按腔位分好的选料表——这些东西不会出现在料袋上，却决定了这个壳体能不能过安规。回到开篇那三句问话：问是换体系还是换基材，问壁厚有没有变，问测试状态写没写清。
When changing the material of a circuit breaker casing, the most common situations are the fusing wire exceeding the limit and the CTI dropping by one level. This article explains the three routes for halogen-free switching, how to read the criteria table, why different compartments of the same casing are selected separately, and the verification sequence that needs to be rearranged when changing materials.
The matter of replacing the breaker housing materials happened two winters ago at a factory that makes small circuit breakers.
They received an export order, and the target market requires it to be halogen-free, so the original flame-retardant system needs to be completely replaced.
The two shell pieces sent are white, palm-sized, with deep cavities and multiple ribs, cushioned with foam, and the corners still bear traces of being burned in a hot wire test.
The purchasing person said very directly on the phone: 'The hot wire passed, but the CTI actually dropped a level, and the safety standard got stuck.'
I first asked three counter-questions: Are we changing the base material, or are we adjusting the entire flame-retardant system together? Is the wall thickness the same as before? Was that CTI report measured in a dry state, or after damp heat treatment?
He thought for a moment and said, the system has changed, the wall thickness hasn't, and the test status on the report isn't written.
This issue highlights the area where changing the casing material is most likely to have conflicting priorities—flame retardancy and tracking resistance often have opposing directions for improvement.
The timeline below shows the real course of their batch of shells.
The starting point was sending the halogen-free switch for testing. The glow-wire test passed, and the procurement considered the matter settled; the latent phase was constantly monitoring the CTI data on hand, which seemed fine because it was measured under dry conditions; the outbreak occurred when submitting for safety compliance according to the contamination level, and the CTI under damp heat conditions dropped by one grade, causing certification to halt; the settlement was a retrospective check— the system had changed, the wall thickness had not, and the test conditions were not clearly documented— all three were things that 'weren't written down.'
The cost of replacing the casing is often the most expensive item recorded under the testing conditions.
1. Six-dimensional condition of the casing before material change
The casing looks like a structural component, but in reality, it is the last line of defense for electrical safety, and the working conditions need to be examined in six different ways.
For the temperature aspect, steady-state and transient should be separated. The long-term temperature in the distribution box is mostly between 40–70°C, and it is one level higher near the terminals; during a short-circuit instant, the arc temperature can reach thousands of degrees, but that is extremely brief, and the concern is that the material does not keep burning during those few seconds.
This load has two sets. One set is the operating force of the actuating mechanism, with a mechanical life of several thousand to over ten thousand cycles; the other set is the torque of the self-tapping screws during assembly, and the slipping torque of the plastic studs must have a margin.
This medium is the easiest to be overlooked. Dust, moisture, cleaning agents, and coastal salt spray all accumulate on the same component; CTI tests exactly the performance when "voltage, moisture, and surface contamination" appear simultaneously.
The lifespan is calculated based on ten years, and the number of electrical cycles must also be considered. The impact of aging on flame retardancy and electrical performance is often more pronounced than on mechanical properties.
Appearance is a strict standard for electrical components. Color differences, weld lines, and floating fibers must be controlled, and surface roughness must also be managed—the rougher the surface, the more likely it is to accumulate dirt and absorb moisture, causing the CTI to decrease.
Compliance is the longest: UL94 is reported as V-0 according to minimum wall thickness, glow wire is graded by GWIT and GWFI, CTI is graded by pollution level, ball pressure is reported by temperature point, and exports also require a halogen-free list.
| Dimension | The numbers to ask when changing materials | What happens if it leaks? |
|---|
| Temperature | Long-term temperature range, short-circuit transient duration | Incorrect selection of ball pressure and temperature grade |
| Load | Number of operations, self-tapping screw torque | Boss thread stripping, clip break |
| Medium | Pollution level, humidity, salt spray | CTI dropped |
| Lifespan | Rated life, electrical life cycles | Electrical failure after aging |
| Appearance | Color difference, floating fibers, surface roughness | Assembly return, CTI decline |
| Compliance | Wall thickness, flame retardant and hot wire grade, halogen-free list | Stuck during submission for testing, redo |
Among the six items, wall thickness and target market need to be decided first. If they can't be decided, any choice of system afterward will be a temporary solution.
2. Three paths for halogen-free switching, first lay out the costs
Changing materials is not just about increasing the flame-retardant rating; it's about clearly laying out the costs of the three options.
| Path | How to change | Cost | Suitable for what situations |
|---|
| Change the system without moving the substrate | Switch the antimony bromide system to a phosphorus-nitrogen system | Increased dosage, toughness drops one level, fluidity worsens | The structure is mature, only wants to address regulations |
| Change substrate without altering the system | Switch PA66-GF to high-temperature substrate | The complete set of material and mold temperature needs to be modified | Temperature margin or size needs to be increased |
| The system and the substrate move together | Halogen-free High-temperature Substrate | The longest cycle and the heaviest verification | High export requirements, thin-walled parts |
None of the three is better; it’s only about which one can match your wall thickness and certification pace.
The first option is the most convenient, but it has a side effect that is often underestimated: once the amount of flame retardant is increased, both fluidity and toughness usually decrease together. The shell is a thin-walled deep cavity part, so a decrease in fluidity directly leads to insufficient filling and weak weld lines.
The risk in Article 2 lies in the process. Once the base material is changed, the material temperature, mold temperature, and drying all need to be reset. Copying the old production settings is most likely to fail on the first batch.
The third option is the most expensive, but it is often the only feasible path when the three conditions of 'thin-walled, halogen-free, high CTI' are combined.
A common misconception is 'the bigger the flame-retardant rating margin, the safer.' This does not apply to the casing—the larger the margin, the more additive is used, which negatively affects toughness, flow, and CTI together. The grade that just passes the standard is often the easiest to work with.
3. Material Change Criteria Table: This table determines which items you need to re-inspect
Implement the previous constraints into verifiable indicators. The thresholds in the table below are directional suggestions, not acceptance criteria; the actual values must be determined by your parts, your wall thickness, and actual measurements.
| Indicator | Directional threshold | Verification Method / Standard | Common failures after material change | Common solution | Corresponding auxiliary agent system |
|---|
| Incandescent wire ignition temperature | 850°C or 960°C by position within the piece | IEC 60695-2-13 | Ignition and arc extinguishing time exceeded | Change flame retardant system, improve dispersion | Flame Retardant System (Synergistic Effect) |
| Tracking Index CTI | Tested after being wet and hot according to pollution level | IEC 60112, conditioned state | Drop one gear, safety regulation card | Low moisture absorption, not easy to carbonize | Antioxidant (inhibits degradation) |
| ball pressure | 125℃ or according to customer specifications | IEC 60695-10-2 | Heat marks and deformation | Raise the temperature setting | Antioxidant (Maximum Temperature Limit) |
| Stretching and Impact Retention | After thermal aging ≥ 70% | ISO 527 / ISO 179 | Splice line crack, clip break | Mold temperature and gate modification | Lubricant (affects weld lines) |
| Weld line strength | To be determined according to the housing stress | Short shot sampling Stretching | Assembly falls from the weld line crack | Increase mold temperature and modify the gate | Lubricant |
| Aged electrical | Flame retardant and CTI without degradation | Retest two items after thermal aging | Qualified at the factory, later lost | Stabilization system Retest | Antioxidant |
How to read this table: first look at the first two rows.
The hot wire and CTI are a pair, and when changing materials, the most common issue is 'one end is over, the other end falls.' Therefore, these two tests should be conducted on the same batch of samples together, not sequentially—the time cost of doing them sequentially is too high.
The third column is for purchasing: The CTI report must clearly state whether it is after dry or damp heat, and according to which wall thickness it is measured; the contact time of the glowing wire must also be recorded. If the conditions are not clearly written, there will be a round of blame later.
The last line is the easiest to cut corners on and also the most prone to problems. Retesting fire retardancy and CTI after aging is the step that turns 'factory qualified' into 'qualified for ten years.'
4. Four types of failures after material replacement, and their real causes
Failure 1: The hot wire exceeded the limit, CTI dropped by one level.
The root cause lies in the choice of the system. Many methods to improve flame retardancy will lower the tracking and erosion performance, which is especially obvious in halogen-based ones. So this is not a case of 'it got worse just because the grade was changed'; the two indicators inherently work against each other, and the formulation needs to find a balance in between. When you see the CTI drop a level, first look at the system, and don’t rush to suspect the substrate.
Failure 2: Welding line cracking, which often occurs after assembly drops or operational cycles.
The structural features of the casing are deep cavities, porous sections, and localized ribs. The material flow converges at many points, resulting in numerous weld lines. The higher the glass fiber content, the more gradual the increase in the rigidity of the body, and the steeper the decrease in the strength of the weld lines—the data for the entire casing looks great, but it cracks from that line as soon as it drops. Both structure and process need to be adjusted together.
Failure three: For the same batch of housings, the performance of the filament fluctuates between good and bad.
This is not "material instability." Flame-retardant systems are sensitive to process fluctuations: higher temperatures mean additives decompose, lower temperatures cause uneven dispersion, causing batch performance to decline. Further investigation reveals that barrel temperature settings differ significantly between different teams. This account on the additive side also has disciplinary records.
Failure Four: After aging, the CTI drops gears, but the factory data is qualified.
CTI will decrease with moisture absorption and aging. The mechanism is that the flame retardant gradually migrates and the surface condition changes. Therefore, before sending it for safety certification, first measure it yourself according to the aged state, which can save a round of rectification; whether this item drops or not depends on whether the stabilization system is adequately formulated.
5. Processing and Verification: Wall thickness and material temperature are two narrow gates
The wall thickness must be determined before selecting the material, not after selecting the material and then going back to change the structure.
With the same flame retardant level, thin-walled parts are much more difficult than thick-walled parts — the flame retardant has to work in less material while also considering flowability and weld lines. Reducing the wall thickness from two millimeters to just over one millimeter amplifies the negative effects of the additive.
The material temperature window is also narrower than that of general-purpose materials. If the temperature is too high, the flame-retardant system begins to decompose; if the temperature is too low, dispersion is uneven, and the performance of the part's surface and interior will be inconsistent, causing CTI and glow wire test results to fluctuate. Therefore, after changing the material, the processing window should be posted on the machine, and parameters should be locked according to the window.
The effect of mold temperature on the weld line is more direct on the housing than on other parts. If the mold temperature is low, the weld location heals poorly, which is a hidden defect. The specific temperature to raise it to should be determined through testing with your part.
It is recommended to arrange the verification sequence like this, do not change it:
1. Material level: initial screening with hot wire, moisture-conditioned CTI, ball pressure
2. Process window: change material temperature and mold temperature, compare parts to check weld lines and appearance
3. Component level: assembly drop, operation cycle, snap-on and boss
4. Retesting after aging: Perform flame retardant and CTI tests again on the thermally aged samples
5. Send safety regulations: issue reports according to the target market and pollution level
Why do the retests after aging come before sending it for safety certification? Because safety certification looks at long-term performance, going through it ourselves in advance saves time compared to sending it and having it sent back.
6. Boundary: For these types of shells, stop when changing materials
This section may be more valuable than the previous few sections because it helps you stop losses before starting work.
First, there are locations around with strong electric arcs. The surface of the enclosure near the contactor's arc-extinguishing area will be subjected to arc erosion. Ordinary flame-retardant nylon cannot withstand it, and attention should be given to thermosetting or ceramic directions.
Secondly, we need to make the casing of the transparent window. Integrally molding a transparent window with a flame-retardant casing is an extreme challenge for the materials. Most manufacturers adopt a dual-material solution, injecting the window separately and then assembling it; the risk of this approach lies in the interface sealing, so the plan must be finalized before selecting the materials.
Thirdly, an extremely thin-wall component that must be halogen-free and also have a high CTI. This is a very challenging part in the formula area. First, consider modifying the structure or relaxing one of the requirements, and don’t try to handle all three issues in a single material change.
Fourth, parts with extremely large annual output and very low unit prices. The accounts for these parts should be calculated in total, and the increased cost from the material side may not be recoverable.
Fifth, parts whose failure points have not yet been located. If the casing is burned or cracked, first distinguish whether it is due to insufficient flame retardancy, a weak welding line, or incorrect assembly spacing, as the solutions for these three issues are completely different.
Putting these five points at the beginning is not to discourage, but to save time.
7. Material Change Risk List (Things that need to be changed when switching from the original system to a halogen-free route)
| link; segment; part | What needs to be moved? | Points that are easy to overlook |
|---|
| Mold | If the amount is changed, the shrinkage rate will change, and deep cavity parts need to be re-measured. | Only replace the material without repairing the mold, and issues arise from tight assembly fit |
| Dry | After changing the system, the drying window needs to be redefined. | Using the old parameters, the surface is fogging up |
| Humidity control | CTI must be determined in the conditioned state | Submit dry-state data for safety compliance |
| Material Temperature / Mold Temperature | The flame-retardant system is sensitive to temperature and the window needs to be locked. | Different teams have inconsistent settings |
| Pressure Holding / Demolding | The position and strength of the weld line need to be redefined | When the glass fiber content is high and the amount added is large, it becomes more brittle |
| Color difference | The color swatches of the white and dark pieces are matched separately | The base color will change after replacing the flame-retardant system |
| Verification order | Initial screening → Process → Component level → Aging retest → Submit for safety compliance | If the previous item fails, just move on. |
8. Proofing and mold testing schedule (number of machine runs, what is checked in each run, how long samples are kept)
The trial molding for changing the material of the casing is usually done in three rounds, without skipping steps between rounds.
First Round · Sample Comparison: Use your original mold to make 3–5 samples, check the appearance, filling, and short-shot weld line positions, and simultaneously send a set for initial screening with a hot wire. This round is mainly to confirm whether the material can fill the deep cavities. Keep two samples, and mark the batch number along with the material and mold temperatures.
Second Round · Process Window: Keep the material constant, vary the material temperature and mold temperature, and produce two sets of comparison pieces. Test and adjust wet-state CTI, ball pressure, weld line strength, and assembly drop. This round determines the mass production parameters.
Round 3 · Aging and Safety Regulations: Re-test the heat-aged samples for flame retardancy and CTI, then send them for inspection according to the target market. Only after passing this round is it recommended to scale up production. Store samples sealed by batch, covering the first mass production batch, to facilitate root cause tracing.
Why can't we jump between the three rounds? Because the flame retardancy and electrical performance both depend on the dispersed state and moisture-absorbed state; the process hasn't been locked in, so the data is only valid for that batch.
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.
Three questions readers often ask
Q: Which is harder to pass, the glowing wire test or the CTI? It depends on the location inside the part. Near heating elements, the glowing wire is a hard threshold; along the surface near live components, CTI is a hard threshold. Most housings need to pass both, so during initial screening, both tests are measured together.
Q: Will the electrical performance deteriorate after switching to halogen-free? If the system is chosen correctly, it won't, but you need to monitor the moisture absorption and retest the dielectric properties in a wet state. In coastal high-humidity markets, wet-state data is more indicative than dry-state data.
Q: Is it necessary to retest after aging? Yes, it is. Both flame retardancy and CTI change with aging, and this item ensures that a 'pass' in the report becomes a 'pass' over ten years.
9. Structural components: For the same housing, different cavities can be selected separately
This is the most cost-saving thing in shell material replacement, and also the thing that most people overlook.
For the same circuit breaker, the operating conditions are different in different compartments. The temperature in the wiring compartment is lower than in the main compartment, but the dust and moisture are heavier, so according to the pollution level, the CTI requirements are actually higher; the main compartment is concerned with flame retardancy and ball pressure; the operating mechanism area focuses on strength and weld lines; for the transparent window section, most use dual materials.
| Position | Main points of examination | Material selection direction |
|---|
| Main cavity housing | Flame retardant, ball pressure, mechanical strength | Flame-retardant reinforcement system |
| Wiring cavity | CTI under pollution degree | CTI with higher level of moisture conditioning |
| Operating Mechanism Area | Weld line and snap-fit strength | Balancing resilience and flow |
| Transparent window | Light transmission and interface sealing | Double plan, select separately |
| Near the arc-extinguishing zone | Arc-resistant | Thermosetting or ceramic direction |
Sorting materials according to position is more cost-effective than applying a one-size-fits-all approach to the whole machine, and it does not compromise safety.
If you want to use this article for a report, you can summarize it in four lines:
| item | A one-sentence conclusion |
|---|
| Change what | Start with a halogen-free phosphorus-nitrogen system, and whether to change the substrate depends on the wall thickness. |
| Move what | Set wall thickness first, lock the material temperature window, reset the mold temperature |
| Test what | Hot wire, moisture-conditioned CTI, ball pressure, measure all three together |
| When can the volume increase? | Three rounds of mold trials passed, re-measurement after aging shows no shifting, safety compliance report issued |
What we deliver is not just a package of materials.
A piece of humidity-conditioned CTI data, a retest after aging, a material selection sheet sorted by cavity position—these things won't appear on the material bag, yet they determine whether this housing can pass safety regulations. Returning to the three questions at the beginning: asking whether to change the system or the base material, asking whether the wall thickness has changed, asking whether the test conditions are clearly recorded.
