工业脚轮用改性PP加TPU包胶，选型最容易只看轮面耐磨，忽略包胶层与轮芯之间的界面。这篇把脚轮的两条寿命线拆开：一条是长期静压下的轮面平点，一条是 PP 非极性表面与极性软料之间那道剥离。含判据表、验证顺序，以及三种不该用改性PP的情况。
"脚轮用了半年，推起来咯噔咯噔。拆下来一看，轮面磨平了一小块——可那台设备半年里基本没动过。"
"轮面还好好的，包胶层先鼓起来一圈，用手一抠能抠开一道缝。"
说这两句话的，一个做自动化产线，一个做医疗推车。放在一篇里讲，是因为它们指向同一件事：
脚轮有两个寿命，一个在轮面，一个在界面。而多数人只盯轮面。
轮面磨平了只是换轮子，界面脱开了是整批退货。
一、工业脚轮的失效现场：轮面磨平是换轮子，界面脱开是整批退货
结论先说：这个件的第一件事不是选料，是把两个寿命分开看——承压寿命与界面寿命，量法完全不同。
脚轮最典型、也最容易被漏掉的失效，是长期静压下的永久压痕，行业里叫平点。
现场是：设备停在原地不动，少则几天、多则一个季度，弹性体轮面被压出一个平面。再推动时，每转一圈就"咯噔"一下——轮面已经不是圆的了。
这不是磨出来的，是压出来的。 磨耗要跑里程，平点只需要时间和载荷。它还常被误判成轴承坏了。
公开的脚轮资料里有一条很直接的判断：热塑性橡胶（TPR）轮面在静载超过约 113 kg 时就容易平点，重载设备长期停放应改用聚氨酯或酚醛轮（B 级，脚轮行业公开技术资料）。这是"静载"而不是"动载"在决定选型的例子。
第二条寿命线在界面，也就是包胶层与轮芯之间那道结合面。
它的现场是：轮面外观没大问题，但包胶层鼓包、边缘起翘、或沿圆周分层。切开看，软料整片从硬芯上干净地揭下来。
"揭得很干净"听起来像剥离彻底，实际是缺陷。
二、工况六维拆解：脚轮的载荷维里，藏着三个不同的量
结论先说：脚轮必须把静压、滚动、冲击三种载荷分开报——只报一个"额定载荷"，等于什么都没报。
| 维度 | 脚轮的实际工况 | 对材料的要求 |
|---|
| 温度 | 常温车间 −20~80℃；烘箱、食品线旁 80~120℃；冷库 −20~−40℃ | 轮面耐温是硬线，聚氨酯类长期上限常在 80℃ 一档 |
| 载荷 | 三份：① 长期停放的静压；② 推行的滚动载荷；③ 过门槛的冲击 | 三份分开报。静压查压缩永久变形，冲击查轮芯开裂 |
| 介质 | 清洗剂、油污、水、盐雾；食品线与药厂还有消毒剂 | 高温高湿下聚酯型聚氨酯可能水解，优先聚醚型 |
| 寿命 | 推行里程（公开试验常见 100 km / 500 km 级）+ 投放年限 + 停放时长 | 里程算磨耗，停放时长算平点，两个数都要给 |
| 外观 | 色标稳定、不留黑印、纹路清晰 | 软轮护地面也易留印，需单独约定 |
| 合规 | 出口走脚轮标准体系；电子车间要导电或抗静电 | 标准档位先确认，各类别要求的试验项不一样 |
六个维度里，载荷这一维最容易报错——客户通常只给一句"单轮承重多少公斤"，但这一个数压不平三种工况。
业内通行的折算是：四轮车按三轮算——地面不可能完全平，总有一个轮子吃不上力；工作载荷一般再控制在额定的八成以内（B 级，脚轮行业公开技术资料）。
温度维还要多说一句。公开资料对"高温下承载掉多少"的口径并不一致：有资料说超过约 65℃ 就按 0.8 的系数折减，也有资料说80℃ 以上承载下降 35%~50%（均为 B 级，脚轮行业公开技术资料）。
两份数字不该互相替代。口径不一致时，正确做法不是挑一个用，而是把它当成必须实测的信号。
三、材料路线对比：轮面、轮芯、支架是三块，不是一块
结论先说：脚轮上改性PP 的身份往往不是轮面，而是轮芯、支架和防尘盖——把这三块分清楚，比比较材料本身重要。
| 路线 | 拿到什么 | 代价 | 负责哪一块 |
|---|
| 耐磨改性PP（矿物或耐磨助剂填充） | 轻、成型自由、摩擦系数可调 | 刚性与抗冲有上限；硬度拉高对地面不友好 | 中低载荷轮面；防尘盖 |
| 玻纤增强PP | 刚性、尺寸稳定、承载上一个档 | 各向异性、熔接线偏弱、偏脆 | 轮芯、支架（可做机械锁扣） |
| PA6 / PA66（含 MC 尼龙） | 承载高、耐磨、耐温可到 120℃ 级 | 吸水尺寸变化、成本高、低温偏脆 | 重载轮芯；高温轮面 |
| 浇注聚氨酯（CPU） | 承载高、耐磨、无痕、省力 | 温敏（约 80℃ 软化、−20℃ 以下偏脆）、怕水解 | 轮面主力 |
| 铸铁 / 钢 | 承载与耐温天然够 | 重、伤地面、噪声大 | 重载轮轮体 |
读成一句话：这个件上很少存在"一种料包全场"。
一个典型工业脚轮，轮面是聚氨酯或橡胶，轮芯是玻纤增强 PP 或 PA，支架是玻纤增强 PP 或金属，防尘盖是改性PP。改性PP 的位置多半在后面几块，而不是轮面本身。
用改性PP 做轮面的合适区间是：单轮工作载荷不高、地面平整、不要求极低滚动阻力，但有轻量与成本要求。超出这个区间不是不行，是代价不合适。
四、★ 选型判据表：剥离强度、承载与平点，每项都带验证方法
结论先说：这张表里第四列才是关键——卡住你的通常不是"该看哪一项"，是"拿什么测、测到多少算过"。
| 指标 | 门限值（典型） | 验证方法 · 标准号 | 常见失效 | 通行解法 |
|---|
| 包胶界面剥离强度（90°） | 公开经验门槛：优良级 >15 N/mm，且破坏模式须为内聚破坏 | ISO 813:2019（90° 剥离；宽 25 mm、厚 6 mm，速度 50±5 mm/min，按 N/mm 计） | 包胶层鼓包、边缘起翘、分层脱开 | 增容层 + 表面处理 + 机械锁扣冗余 |
| 剥离强度（180°，参照口径） | 由供需双方约定；须记录破坏类型 | GB/T 15254-2014（180° 剥离；宽 25±0.5 mm，速度 100±10 mm/min，弃前 25 mm，单位 kN/m；破坏类型 R/RC/CP/M） | 同上 | 速度与宽度统一后再比数 |
| 静压永久变形（平点） | 卸压后不得有可见平面，推起不得有周期性振动 | EN 12527:1998 / ISO 22878:2004 静态试验项 | 长期停放后启动周期性"咯噔" | 提高硬度档；静置位加支撑脚或垫块 |
| 承载能力 | 须标口径（静态/动态、温度）；四轮按三轮折算，工作载荷 ≤ 额定 80% | ISO 22883:2004 / EN 12532:1999 + ISO 22878 试验方法 | 轮面压陷、轮芯开裂、轴承卡死 | 加大轮径或轮宽、提高硬度档、换轮芯材质 |
| 高温承载折减 | 约 65~82℃ 起折减（系数 0.8 起）；>120℃ 聚氨酯类轮面基本不可用 | 供应商温载曲线 + 件上实测温度 | 高温软化、压痕加深、脱芯 | 换耐高温配方，或改走尼龙 / 铸铁轮 |
| 轮面耐磨与硬度 | 同方法、同砂纸等级下比磨耗量，跨方法不可换算；邵氏 A 软轮 60~75A、常规轮 80~95A | GB/T 9867-2008（等同 ISO 4649:2002）；GB/T 531.1 / GB/T 2411 | 轮面磨薄、掉块；软轮平点、硬轮伤地面 | 按地面选硬度档 + 耐磨助剂或矿物填充 |
六项里最该放第一位的是两行剥离强度，量的是同一件事，只是两种量法。第二该看静压永久变形，它是被漏得最多的一项。
第一，两种剥离方法的结果不能互相换算。
| 对照项 | ISO 813:2019（90°） | GB/T 15254-2014（180°） |
|---|
| 剥离角 / 试样宽度 | 90° / 25±0.1 mm | 180° / 25.0±0.5 mm |
| 试样厚度 | 6±0.1 mm | 2.0±0.2 mm |
| 剥离速度 | 50±5 mm/min | 100±10 mm/min |
| 取值方式 | 最大力 ÷ 宽度 | 弃前 25 mm 后取平均力 ÷ 宽度 |
| 结果单位 | N/mm | kN/m |
| 破坏类型记录 | 有（八类） | 有（R / RC / CP / M） |
速度差一倍、厚度差三倍，出来的数当然不一样。比剥离强度之前先比方法。 另外 ISO 813 不适用于硬度高于约 85 IRHD 的胶料。
第二，剥离强度必须和破坏模式一起看。
破坏模式大致四类：软料本体撕裂（内聚破坏）、软料与胶黏剂分离、胶黏剂内部破坏、胶黏剂与硬芯分离。只有第一类是好的。
后三类本质都是"界面先投降"——数值可能不低，但那是材料自身强度撑出来的。所以验收条件要写全：剥离强度 ≥ 某个数，且破坏模式为内聚破坏。
第三，剥离强度会随时间与环境退化，所以要复测。 湿热后再剥一次、冷热循环后再剥一次，这两次的数比首次更接近真实寿命。
五、常见失效与根因：三个现象，三条根因
结论先说：三条里真正属于"料不行"的比例不高，多数是"静载被当成动载""界面被当成外观问题""结构问题被当成材料问题"。
失效一：长期停放后轮面压出平面。
根因是压缩永久变形，不是磨损。四个变量：单轮静载、环境温度、轮面硬度、连续停放时长。客户通常只报第一个。
公开的标准解读摘要显示，ISO 22883:2004 覆盖的手推与牵引工业类（≤4 km/h）里，静态试验并非必做项（B 级）。
这就形成一个错位：标准不强制验的那一项，恰好是这类件最常出的失效。 看到"动态载荷合格"就放心，是有风险的。
失效二：包胶层鼓包、边缘起翘、分层脱开。
包胶本身有两条工艺路：包胶注塑（软料直接注在硬芯上）与机械嵌合（软料件后装、靠结构咬合）。前者成败看界面，后者成败看结构。
起点是极性。PP 非极性、自身表面能很低，公开的包胶技术资料说得很直接：PP 是常用的最难粘的基材之一，通用弹性体牌号在 PP 上通常会失败（B 级，包胶行业公开技术资料）。
表面能低，软料熔体在 PP 表面"铺不开"，容易成珠缩回；只有极性相近的材料之间，才有分子链缠结与互扩散。
所以"参数调到极限也救不回来"——不是参数问题，是搭配问题。 四条解法，各有代价：
- 加增容层：加一道过渡层。代价是多一道工序，工序稳定性直接决定批次一致性。
- 机械锁扣：打孔、开槽、做倒钩。代价是模具复杂、锁扣处应力集中。
- 换极性基材：轮芯换到 PA、ABS 上。代价是——那就不是本篇的料了。
- 换软料体系：PP 与 SEBS 基弹性体极性接近，可直接包胶，二次注塑建议 170~220℃ 一档；PP 基的 TPV 因化学相近也常配（B 级）。
"必须聚氨酯轮面 + 必须PP 芯"这个组合，天生站在最难的一格——这时候更值得谈的是结构，不是配方。
敢否定一个行业习惯做法：验收包胶件，很多人第一句问的是"硬度够不够软"。
>
这句话问错了。包胶件能不能长期用，第一件要验的是剥离强度，不是硬度。
>
公开的包胶加工资料里有两个数：界面处理到位的组合，90° 剥离强度可做到 15~22 N/mm 量级；靠成型收缩与表面粗糙硬撑的组合，会掉到 2 N/mm 以下（B 级，属加工方经验口径）。差了将近一个数量级，硬度调得再准也没有意义。
失效三：轮面磨损、掉块与推起来费劲。
粗糙混凝土对轮面的作用接近砂纸；金属屑、碎石嵌入轮面后被反复碾压，会从微切口扩展成掉块。"推起来费劲"的归因则常在轮径、轴承、轮面硬度三处。
这里纠正一个直觉：耐磨不是"硬度越高越好"，也不是"填充越多越好"。 矿物填充能提高硬度与承载，也可能增加对磨面的磨损；
玻纤能提高刚性，在粗糙地面却更容易崩边。归因顺序是：先看地面与碎屑管理，再看载荷与轮径，最后看配方。
六、验证顺序：先做包胶界面剥离，再做承压与永久压痕
结论先说：验证顺序不能按"从易到难"排，要按"最可能一票否决"排——界面剥离排第一位，因为改界面比改配方贵得多。
依据是公开的脚轮标准体系：ISO 22878:2004 / EN 12527:1998 把试验方法拆成十几项，含轮子游隙、转向游隙、电阻、制动疲劳、动态试验、静态试验、接触压力、冲击、长距离跑合、滚动阻力、转向阻力等；
应用要求另写在 ISO 22879~22884 / EN 12528~12533 各档里（A 级，ISO / EN 标准）。先确认自己按哪一类验，再排顺序。
`
① 包胶界面剥离（一票否决性最强）
按 ISO 813:2019 做 90° 剥离（或按 GB/T 15254-2014 做 180°），看单位宽度剥离力 + 破坏模式
↓ 破坏模式为"界面干净分离"（RC 或 M 类）→ 直接退回
退回动作是改增容层 / 表面处理 / 机械锁扣，不是加厚包胶层
② 承压与永久压痕
按额定载荷静态加压、保压规定时长，卸压后量残余变形
↓ 出现可见平面或残余变形超约定 → 退回轮面硬度档与承载等级
③ 滚动疲劳（滚过障碍与门槛）
带障碍的滚动耐久，行业常用 3 mm 或 5 mm 障碍
↓ 轮芯开裂、轮面掉块、包胶层边缘起翘 → 退回轮芯材质与锁扣结构
④ 耐磨与地面保护评价
GB/T 9867-2008 测磨耗量；同一地面、同一载荷下看是否留痕
↓ 磨耗量超标或留印 → 退回硬度档与填充体系
⑤ 老化后复测（湿热 + 冷热循环）
湿热后再剥一次；冷热循环后再剥一次
↓ 剥离强度明显下降 → 退回第 ① 步重选界面方案
⑥ 整机推行验证
整机推行，测启动推力与滚动阻力 → 超约定则回到轮径、轴承与硬度档
`
六步里，第 ① 步和第 ⑤ 步是一对——先验初始界面，再验老化后的界面。顺序不能倒：先开模具做锁扣、再验剥离，一旦界面不成立，改结构的时间和费用远高于换配方。
七、反向诚实：这三种情况，脚轮不该用改性PP
结论先说：改性PP 能进来的是轮芯、支架、防尘盖这几块；一旦要求落到重载、长期高温或低滚阻驱动上，它就不该硬撑。
| 出现的情况 | 为什么改性PP不合适 | 该往哪走 |
|---|
| 要求极高承载（重载叉车轮，单轮吨级） | 承载与抗蠕变都不在这一档；轮面本来也不是 PP 的活 | 铸铁或钢轮芯 + 浇注聚氨酯轮面 |
| 要求长期高温（烘箱、热处理线配套，长期 >80℃） | 聚氨酯类轮面会软化、加深压痕甚至脱芯；PP 的负荷变形温度也在这附近 | MC 尼龙（耐温约 120℃ 级）、酚醛或铸铁轮 |
| 要求极低滚动阻力的驱动轮（AGV，>4 km/h） | 驱动轮要传扭矩、连续旋转会内部生热，热会让界面先失效 | 专用驱动轮配方 + 金属芯，按 ISO 22884:2004 那一档验 |
| 长期 −40℃ 以下低温 | PP 低温变脆；聚酯型聚氨酯也脆 | 聚醚型聚氨酯；更低温度走 MC 尼龙 |
规律是一致的：只要"两个方向相反的要求同时出现、且都超出 PP 的区间"，这个件就不该用改性PP 硬撑。 硬接下来的单子，最后都要用返工还回去。
八、换料风险清单：从轮芯到包胶层，要先确认的七件事
结论先说：换料的真正成本不在料价，在"模具、工序、界面处理"这三块——它们不写在报价单上，只会在试产时出现。
| 要动的项 | 需要确认什么 | 不做会怎样 |
|---|
| 轮芯材质与收缩率 | 玻纤增强 PP 芯的各向异性与 PA 芯差别大；包胶层尺寸跟着芯走 | 包胶层偏心、轮面不圆 |
| 界面处理工序 | 增容层、底涂或火焰/等离子处理要写进工序卡并受控 | 批次之间剥离强度忽高忽低 |
| 料温与模温 | 二次注塑温度窗口（PP 上包软料公开建议 170~220℃ 一档） | 界面没熔合、表面流痕 |
| 干燥 | 软料吸湿低但仍要干燥；水分会造成气泡与银纹 | 结合强度直接掉 |
| 色差与外观 | 色标件先定色板；无痕要求另做留印评价 | 批次色差、地面留黑印 |
| 验证顺序 | 界面剥离 → 承压与压痕 → 滚动疲劳 → 耐磨与地面 → 老化复测 → 整机推行 | 风险全部压到最后一步爆发 |
这七项里，最该先谈的是验证顺序和界面处理工序。跳过界面直接开锁扣模具，是把最贵的一步提前花掉；把表面处理放在工序卡之外，等于把剥离强度交给运气。
九、一页纸汇报对照表：六种脚轮配置直接贴进 PPT
结论先说：判断这张表合不合格只有一条——客户的技术员拿它去开会，能不能在会上把方向定下来。
| 场景 | 推荐路线 | 关键指标 | 验证标准 | 需先确认的条件 |
|---|
| 中低载荷工业脚轮、常温车间 | 玻纤或矿物增强 PP 轮芯 / 支架 + 常规轮面 | 承载、滚阻、平点 | ISO 22878 / EN 12527 | 单轮工作载荷、停放时长、地面材质 |
| 静音无痕包胶轮 | PP 芯 + 与 PP 极性匹配的软料体系，或加增容层 | 90° 剥离强度 + 破坏模式 | ISO 813:2019 | 软料体系、表面处理工序、锁扣结构 |
| 必须用聚氨酯轮面的包胶轮 | 轮芯改极性材料（PA / ABS）+ TPU；或 PP 芯 + 增容层 + 机械锁扣 | 剥离强度、老化后复测 | ISO 813；温湿循环后复测 | 是否必须 PP 芯、能否接受换芯 |
| 玻纤增强PP 芯 + 浇注聚氨酯轮面（重载） | GF-PP 芯 + CPU 轮面（化学粘接） | 承载、脱芯风险、内部生热 | ISO 22883:2004 | 单轮载荷、运行速度、连续运行时长 |
| 电子车间、防静电 | 改性PP 件（轮芯 / 支架 / 防尘盖）+ 导电轮面 | 表面电阻档、接地通路 | EN 12527 电阻试验项 | 电阻档要求、接地方式 |
十、这个件上最容易出问题的，往往不是轮面
脚轮行业最常出的两类早期失效，一类是长期停放后的轮面平点，一类是包胶界面脱开。而这两类在标准里的处境不一样：ISO 22883:2004 覆盖的手推与牵引工业类里，静态试验并非必做项；
包胶界面剥离强度也不是脚轮成品的强制项（B 级，公开发布的标准解读摘要）。也就是说，采购手上那张承载表，天然盖不住这两类失效。
判据层面能对上的是三条：界面按 ISO 813:2019 做 90° 剥离，看单位宽度剥离力和破坏模式；
承压按 ISO 22878 / EN 12527 的静态与动态试验；轮面磨耗按 GB/T 9867-2008。三条都带标准号，可以写进技术协议。
通行解法也是三条并行：轮芯做极性匹配（换材料或加增容层）+ 表面状态受控（处理或底涂进工序卡）+ 机械锁扣做冗余。
重载且长期停放的场合，在停放位加支撑脚或垫块，比在配方上硬扛更省事。
宁波市科隆新材料有限公司在这个件上常供的是自产改性聚丙烯（PP）造粒里的耐磨与增强方向：轮芯与支架按单轮工作载荷、地面条件与是否长期停放来配比，小轮体按硬度档配，防尘盖按色标与耐化学要求配。
配方按件的工况调，可以陪客户做小样比对；包胶件上还愿意按客户的包胶工序反过来调轮芯的表面状态与收缩率——因为界面这件事，从来不是单方面能定的。
常见问答
问：轮面我用的是聚氨酯，PP 只做轮芯，界面为什么还会脱？
答：因为问题不在轮面，在轮芯的极性。PP 非极性、表面能低，与聚氨酯这类极性软料的相容性天生不好。三条路：换极性轮芯、加增容层与表面处理、做机械锁扣。至少走一条。
问：怎么判断一个包胶件能不能长期用？
答：第一件事是剥离强度，不是硬度。按 ISO 813:2019 做 90° 剥离——内聚破坏才算结合好，"界面干净分离"就是缺陷；再做湿热与冷热循环后复测。
问：设备长期停在原地，轮面压出一块平面，这算料的问题吗？
答：优先当工况问题处理。压缩永久变形和单轮静载、温度、轮面硬度、停放时长都有关。
把"单轮静载"和"连续停放时长"一起报出来——重载静置的场合，该加大轮径、提高硬度档，或在停放位加支撑脚和垫块。
| 工况 | 关键判据 | 自产常规供应 |
|---|
| 中低载荷脚轮轮芯 / 支架 | 承载、刚性、尺寸稳定 | 玻纤或矿物增强改性 PP 方向 |
| 小轮径轮体、防尘盖 | 硬度档、色标、耐化学 | 耐磨改性 PP 方向，按地面条件配比 |
| 长期停放的重载轮 | 静压永久变形 | 增强 PP 轮芯方向 + 支撑结构建议 |
| 电子车间用件 | 电阻档、接地通路 | 改性 PP 件方向（轮芯 / 支架 / 防尘盖） |
最后说三句。
第一，脚轮有两个寿命，一个在轮面，一个在界面。 轮面磨平了是换轮子，界面脱开了是整批退货——别用一个"耐磨"盖住两件事。
第二，包胶件验收的第一项是剥离强度与破坏模式，不是硬度。 "撕下来很干净"在包胶件上不是优点，是缺陷。
第三，改性PP 在这个件上多数时候做的是轮芯、支架和防尘盖，不是轮面。
Industrial casters use modified PP coated with TPU. When selecting them, people usually only look at the wear resistance of the wheel surface and ignore the interface between the coating layer and the wheel core. This article separates the two lifespan lines of casters: one is the flat spot of the wheel surface under long-term static pressure, and the other is the delamination between the non-polar surface of PP and the polar soft material. It includes criterion tables, verification procedures, and three situations where modified PP should not be used.
The caster wheels had been used for half a year, and they made a clattering noise when pushed. When I took them apart, I saw that a small area of the wheel surface had worn flat — even though the equipment had barely been moved in the past six months.
The wheel surface is still fine, but the rubber coating has bulged up in a ring, and you can pry open a gap with your hand.
The ones who said these two sentences, one works on an automated production line, the other works on medical carts. They are mentioned together in one article because they point to the same thing:
Casters have two lifespans, one on the wheel surface and one at the interface. Yet most people only focus on the wheel surface.
If the wheel surface is ground smooth, it's just a wheel replacement; if the interface comes off, it's a full batch return.
1. Failure scenarios of industrial casters: When the wheel surface is worn flat, the wheel is replaced; when the interface separates, the entire batch is returned.
Conclusion first: The first thing about this part is not the material selection, but to look at the two lifespans separately—pressure-bearing lifespan and interface lifespan, with completely different measurement methods.
The most typical and easily overlooked failure of casters is the permanent indentation under long-term static pressure, which is called a flat spot in the industry.
The scene is: the equipment is stationary, staying in one place for anywhere from a few days to a quarter of a year, and the elastomer wheel surface is pressed flat. When pushing it again, it makes a 'clunk' with every rotation — the wheel surface is no longer round.
This is not worn down by grinding, it's pressed out. Wearing requires mileage, while leveling only needs time and load. It is also often mistakenly judged as a bearing failure.
There is a very direct judgment in the publicly available information on casters: thermoplastic rubber (TPR) wheel surfaces are prone to flat spots when the static load exceeds about 113 kg. For heavy-duty equipment that is parked for a long time, polyurethane or phenolic wheels (Grade B, according to publicly available caster industry technical information) should be used instead. This is an example of 'static load' rather than 'dynamic load' determining the choice.
The second lifespan line is at the interface, that is, the bonding surface between the coating layer and the wheel core.
Its condition on site is: the roller surface appearance has no major issues, but the rubber coating is blistering, edges are peeling, or it is delaminating along the circumference. When cut open, the soft material comes off the hard core completely cleanly.
"Revealed very cleanly" sounds like thorough peeling, but in reality, it's a defect.
2. Six-dimensional analysis of working conditions: In the load dimension of the caster, there are three different quantities hidden
Conclusion first: Casters must report static pressure, rolling, and impact loads separately — if you only report a single 'rated load,' it's equivalent to reporting nothing.
| Dimension | The actual working conditions of the caster | Requirements for the materials |
|---|
| Temperature | Normal temperature workshop −20~80℃; oven, beside food line 80~120℃; cold storage −20~−40℃ | The temperature resistance of the wheel surface is rigid; the long-term upper limit for polyurethane types is often around 80°C. |
| Load | Three parts: ① Long-term static load; ② Implemented rolling load; ③ Impact over the threshold | Submit three separate reports. Check static pressure for permanent deformation of the compressor, and check impact for wheel core cracking. |
| Medium | Cleaners, grease, water, salt spray; food production lines and pharmaceutical factories also have disinfectants | Polyester-based polyurethane may hydrolyze under high temperature and high humidity, preferably use polyether-based. |
| Lifespan | Mileage implementation (commonly 100 km / 500 km level in public trials) Service life Parking duration | Mileage counts as wear, parking duration counts as flat spots, both numbers need to be provided. |
| Appearance | Color is stable, leaves no black marks, and the texture is clear | Soft wheels can easily leave marks on the floor, requiring a separate agreement. |
| Compliance | Export caster standard system; electronic workshop must be conductive or anti-static | First confirm the standard gear level, as the test items required for each category are different. |
Among the six dimensions, the load dimension is the most prone to errors—customers usually only provide a single statement of 'how many kilograms each wheel can bear,' but this one number cannot cover the three working conditions.
The commonly accepted conversion in the industry is: a four-wheeled vehicle is counted as three wheels — the ground can never be completely flat, and there will always be one wheel that doesn't bear force; the working load is generally controlled within 80% of the rated load (Class B, publicly available technical information from the caster industry).
I need to say a bit more about temperature. Public information on 'how much load is lost at high temperatures' is not consistent: some sources say that above about 65°C, the load should be reduced by a factor of 0.8, while other sources say that above 80°C, the load decreases by 35% to 50% (all are Class B, public technical information from the caster industry).
Two sets of numbers should not replace each other. When the calibers are inconsistent, the correct approach is not to pick one to use, but to treat it as a signal that must be measured.
3. Comparison of material routes: the wheel surface, wheel core, and bracket are three separate parts, not one piece.
Conclusion first: The modified PP on casters is often not the wheel tread, but the wheel core, bracket, and dust cover—distinguishing these three parts is more important than comparing the material itself.
| Route | Get what | Cost | Which part are you responsible for? |
|---|
| Wear-resistant modified PP (filled with minerals or wear-resistant additives) | Lightweight, free forming, adjustable coefficient of friction | Rigidity and impact resistance have upper limits; increasing hardness is not friendly to the ground | Medium and low load wheel surface; dust cover |
| Glass fiber reinforced PP | Rigid, dimensionally stable, one level higher in load-bearing | Anisotropy, weak weld lines, brittle | Core wheel, bracket (can be made with a mechanical latch) |
| PA6 / PA66 (including MC nylon) | High load-bearing, wear-resistant, temperature resistant up to 120°C | Water absorption dimensional changes, high cost, brittle at low temperatures | Overloaded wheel core; high-temperature wheel surface |
| Cast Polyurethane (CPU) | High load-bearing, wear-resistant, non-marking, labor-saving | Temperature-sensitive (softens at about 80°C, becomes brittle below −20°C), prone to hydrolysis | Main force on the rollers |
| Cast iron / Steel | Naturally sufficient for load-bearing and heat resistance | Heavy, damaging the ground, loud noise | Overloaded wheel body |
Read as one sentence: There is rarely a 'single material package for the whole field' on this item.
A typical industrial caster wheel has a wheel surface made of polyurethane or rubber, a wheel core made of glass fiber reinforced PP or PA, a bracket made of glass fiber reinforced PP or metal, and a dust cover made of modified PP. The modified PP is mostly located in the rear parts, rather than the wheel surface itself.
The suitable range for using modified PP for wheel surfaces is: single-wheel working load is not high, the ground is flat, extremely low rolling resistance is not required, but there are requirements for light weight and cost. Exceeding this range is not impossible, but the cost is not appropriate.
4. ★ Selection Criteria Table: Peeling Strength, Load Bearing, and Neutral Point, each with a verification method
Conclusion first: the fourth column in this table is the key—the thing that usually trips you up is not 'which item to look at,' but 'what to measure and how much counts as passing'.
| Indicator | Threshold (typical) | Verification Method · Standard Number | Common Failures | Common solution |
|---|
| Adhesive Interface Peel Strength (90°) | Open experience threshold: Excellent grade >15 N/mm, and the failure mode must be cohesive failure | ISO 813:2019 (90° peel; width 25 mm, thickness 6 mm, speed 50±5 mm/min, measured in N/mm) | Blistering of the coated layer, edge lifting, delamination | Capacity expansion layer Surface treatment Mechanical latch redundancy |
| Peel strength (180°, reference diameter) | Agreed by both supply and demand sides; the type of damage must be recorded | GB/T 15254-2014 (180° peel; width 25±0.5 mm, speed 100±10 mm/min, discard first 25 mm, unit kN/m; failure type R/RC/CP/M) | Same as above | Compare the numbers after speed and width are unified |
| Static Pressure Permanent Deformation (Flat Spot) | After pressure relief, there must be no visible plane, and when pushed up, there must be no periodic vibration. | EN 12527:1998 / ISO 22878:2004 Static Test Items | After long-term storage, the startup is periodically accompanied by a 'clunk' | Increase the hardness level; add support legs or blocks when stationary |
| Load-bearing capacity | Caliber must be specified (static/dynamic, temperature); four wheels calculated as three wheels, working load ≤ 80% of rated | ISO 22883:2004 / EN 12532:1999 ISO 22878 Test Methods | Tire surface indentation, tire core cracking, bearing seizure | Increase wheel diameter or width, raise hardness grade, change wheel core material |
| High temperature load reduction | Start reducing around 65~82℃ (starting coefficient 0.8); >120℃ polyurethane tire surfaces are basically unusable | Supplier temperature load curve Actual measured temperature on the part | High-temperature softening, deepening of indentations, core shedding | Switch to high-temperature resistant formula, or change to nylon / cast iron wheels |
| Wheel Surface Wear Resistance and Hardness | Under the same method and the same sandpaper grade, the wear amount cannot be converted across different methods; Shore A soft wheel 60~75A, conventional wheel 80~95A | GB/T 9867-2008 (equivalent to ISO 4649:2002); GB/T 531.1 / GB/T 2411 | The surface of the wheel is worn thin and chipping; soft wheels leave flat spots, hard wheels damage the floor | Select hardness level according to the floor Wear-resistant additives or mineral fillers |
Among the six items, the one that should be placed first is the peel strength of the two lines, which measures the same thing, just in two different ways. The second thing to look at is the permanent deformation under static pressure, which is the one most often missed.
First, the results of the two stripping methods cannot be converted into each other.
| Reference item | ISO 813:2019 (90°) | GB/T 15254-2014 (180°) |
|---|
| Peeling angle / Specimen width | 90° / 25±0.1 mm | 180° / 25.0±0.5 mm |
| Specimen Thickness | 6±0.1 mm | 2.0±0.2 mm |
| Peeling speed | 50±5 mm/min | 100±10 mm/min |
| Value Selection Method | Maximum force ÷ Width | Discard the first 25 mm, then take the average force ÷ width |
| Result unit | N/mm | kN/m |
| Destruction Type Record | There are (eight types) | Have (R / RC / CP / M) |
A speed difference of twice and a thickness difference of three times will naturally result in different numbers. Compare the method before comparing the peel strength. In addition, ISO 813 is not applicable to rubber with a hardness higher than about 85 IRHD.
Second, peel strength must be considered together with the failure mode.
There are roughly four types of failure modes: tearing of the soft material itself (cohesive failure), separation of the soft material from the adhesive, internal failure of the adhesive, and separation of the adhesive from the hard core. Only the first type is good.
The essence of the latter three categories is all 'the interface surrenders first' — the values may not be low, but that is supported by the material's own strength. Therefore, the acceptance criteria need to be fully specified: peel strength ≥ a certain value, and the failure mode should be cohesive failure.
Third, peel strength will degrade over time and due to environmental factors, so it needs to be retested. Peel it once after humidity and heat, and once after thermal cycling; these two measurements are closer to the actual lifespan than the first one.
5. Common Failures and Root Causes: Three Phenomena, Three Root Causes
Conclusion first: Among the three points, the proportion that truly falls under 'material is inadequate' is not high; most are 'static load being mistaken for dynamic load,' 'interface being mistaken for appearance problem,' and 'structural problem being mistaken for material problem'.
Failure 1: After long-term parking, the rear wheel develops a flat spot.
The root cause is permanent deformation due to compression, not wear. There are four variables: static load on a single wheel, ambient temperature, wheel surface hardness, and duration of continuous parking. Customers usually only report the first one.
The publicly available standard interpretation summary shows that for hand-operated and tractor industrial types (≤4 km/h) covered by ISO 22883:2004, static tests are not mandatory (Class B).
This creates a mismatch: the item that the standard does not require testing for happens to be the type most prone to failure. Feeling assured just because you see 'dynamic load qualified' carries risks.
Failure 2: The coating layer is bulging, the edges are peeling, and delaminating.
There are two process routes for overmolding itself: overmolding injection (soft material is directly injected onto the hard core) and mechanical assembly (soft parts are installed later, relying on structural interlocking). The success of the former depends on the interface, while the success of the latter depends on the structure.
The starting point is polarity. PP is non-polar and has very low surface energy. Public technical materials on coating technology state it very directly: PP is one of the most difficult substrates to bond, and common elastomer grades usually fail on PP (Class B, publicly available technical materials in the coating industry).
With low surface energy, the molten soft material cannot spread on the PP surface and tends to form beads and retract; only materials with similar polarity can have entanglement and interdiffusion of molecular chains.
"So even when the 'parameters' are pushed to the limit, it can't be saved"—it's not a parameter problem, it's a compatibility problem. Four solutions, each with its own cost:
- Adding a buffer layer: add a transition layer. The cost is an additional process, and the stability of the process directly determines batch consistency.
- Mechanical latch: punching, slotting, making barbs. The cost is complex molds and stress concentration at the latch.
- Change the polarity of the substrate: switch the wheel core to PA or ABS. The cost is—well, that's not the topic of this article.
- Change soft material system: PP and SEBS-based elastomers have similar polarity and can be directly overmolded. For secondary injection molding, a setting of 170~220℃ is recommended; PP-based TPVs are also often used together due to their chemical similarity (Grade B).
"It must be a polyurethane tread and a PP core." This combination is naturally in the most challenging category — at this time, it's more worth discussing the structure, not the formula.
Dare to challenge a common industry practice: when inspecting rubber-coated parts, the first question many people ask is 'Is the hardness soft enough?'
>
This question is asked incorrectly. Whether overmolded parts can be used long-term, the first thing to check is the peel strength, not the hardness.
>
In the publicly available encapsulation processing data, there are two figures: for combinations with proper interface treatment, the 90° peel strength can reach the range of 15~22 N/mm; for combinations relying on molding shrinkage and surface roughness to physically support, it drops below 2 N/mm (Grade B, according to the processor's experience). The difference is nearly an order of magnitude, making precise hardness adjustment meaningless.
Failure three: Wheel surface wear, chipping, and difficulty in pushing.
The effect of rough concrete on the wheel surface is similar to sandpaper; after metal chips and gravel are embedded in the wheel surface and repeatedly pressed, they can expand from micro-cuts into spalling. The difficulty in pushing is often attributed to the wheel diameter, bearings, and wheel surface hardness.
Let's correct an intuition here: wear resistance is not 'the higher the hardness, the better,' nor is it 'the more filler, the better.' Mineral fillers can increase hardness and load-bearing capacity, but they may also increase the wear on the polished surface.
Fiberglass can increase rigidity, but it is more prone to chipping on rough surfaces. The order of attribution is: first look at the surface and debris management, then the load and wheel diameter, and finally the formula.
6. Verification sequence: first perform the encapsulation interface peeling, then perform the pressure-bearing and permanent indentation tests
Conclusion first: the verification sequence should not be arranged from 'easy to difficult'; it should be arranged according to 'most likely to result in a veto' — interface separation comes first, because changing the interface is much more expensive than changing the formula.
The basis is the public caster standard system: ISO 22878:2004 / EN 12527:1998 breaks down the test methods into more than ten items, including wheel backlash, steering backlash, resistance, brake fatigue, dynamic test, static test, contact pressure, impact, long-distance run-in, rolling resistance, steering resistance, etc.;
Application requirements should be separately written in ISO 22879~22884 / EN 12528~12533 at each level (Grade A, ISO / EN standard). First, confirm which category you are testing according to, then arrange the order.
`
① Delamination at the coated interface (the most critical veto item)
Perform 90° peel according to ISO 813:2019 (or 180° according to GB/T 15254-2014), and observe the peel force per unit width and the failure mode
↓ Damage mode is 'clean interface separation' (RC or M type) → directly return
The return action is to change the reinforced layer / surface treatment / mechanical lock, not to add a thicker cushioning layer.
② Under Pressure and Permanent Indentation
Apply static pressure according to the rated load, maintain the pressure for the specified duration, and measure the residual deformation after releasing the pressure.
↓ Visible surface or residual deformation exceeds the agreed limit → Revert wheel surface hardness grade and load rating
③ Rolling fatigue (rolling over obstacles and thresholds)
Scrolling durability with obstacles, commonly used obstacles in the industry are 3 mm or 5 mm
↓ Core cracking, wheel surface chipping, edges of the rubber coating layer peeling → Return to core material and latch structure
④ Wear Resistance and Floor Protection Evaluation
GB/T 9867-2008 Measures wear; check if marks are left under the same surface and the same load
↓ Excessive wear or leave marks → Return to hardness grade and filling system
⑤ Retest after aging (damp heat, thermal cycling)
Peel once after damp heat; peel once after a hot and cold cycle
↓ Peeling strength significantly decreases → Return to Step ① to reselect the interface scheme
⑥ Whole machine implementation verification
Implement for the whole machine, measure starting thrust and rolling resistance → if exceeding the agreed limit, return to wheel diameter, bearings, and hardness settings
`
In the six steps, step 1 and step 5 form a pair—first validate the initial interface, then validate the aged interface. The order cannot be reversed: first open the mold to make the latch, then test the peeling. Once the interface fails, the time and cost to change the structure are far higher than changing the formulation.
7. Reverse Honesty: In these three situations, caster wheels should not use modified PP
Conclusion first: Modified PP can be used for the wheel hub, bracket, and dust cover; once the requirement involves heavy load, long-term high temperature, or low rolling resistance drive, it should not be forced.
| The situation that occurred | Why is modified PP not suitable | Which way should I go? |
|---|
| Requires extremely high load-bearing (heavy-duty forklift wheels, single wheel ton-level) | Neither load-bearing nor creep resistance falls into this category; the wheel surface wasn't originally PP's job anyway. | Cast iron or steel wheel core Cast polyurethane wheel surface |
| Requires long-term high temperature (matching with ovens or heat treatment lines, long-term >80°C) | Polyurethane wheel surfaces may soften, deepen indentations, or even core out; the load deformation temperature of PP is also around this range. | MC nylon (temperature resistant to about 120°C), phenolic, or cast iron wheels |
| Drive wheels with extremely low rolling resistance (AGV, >4 km/h) | The drive wheel needs to transmit torque and rotate continuously, which will generate internal heat, and the heat will cause the interface to fail first. | Dedicated drive wheel formula, metal core, tested according to ISO 22884:2004 standard |
| Long-term below −40℃ low temperature | PP becomes brittle at low temperatures; polyester-based polyurethane is also brittle | Polyether polyurethane; use MC nylon at lower temperatures |
The rule is consistent: as long as 'two opposite requirements appear at the same time and both exceed PP's range,' this part should not be forcibly made with modified PP. For orders that are forcibly pushed through, in the end, they all have to be reworked and returned.
8. Material Change Risk Checklist: Seven Things to Confirm from the Core to the Coating Layer
Conclusion first: The real cost of changing materials is not in the material price, but in 'molds, processes, and interface treatments' — they are not listed on the quotation, and only appear during trial production.
| Items to move | What needs to be confirmed | What will happen if I don't do it? |
|---|
| Core Material and Shrinkage Rate | The anisotropy of glass fiber reinforced PP core is very different from that of PA core; the size of the coating layer follows the core. | Eccentric coating layer, non-circular wheel surface |
| Interface processing procedure | The thickening layer, primer, or flame/plasma treatment must be written into the process card and controlled | The peeling strength fluctuates between batches |
| Material Temperature and Mold Temperature | Secondary injection molding temperature window (PP overmolding soft material publicly recommended 170~220°C for one grade) | The interface is not fused, surface flow marks |
| Dry | Soft materials have low moisture absorption but still need to be dried; moisture can cause bubbles and silver streaks | Bonding strength drops directly |
| Color difference and appearance | Color-coded parts first determine the color board; for no-mark requirements, make a separate imprint evaluation | Batch color difference, black marks left on the floor |
| Verification order | Interface delamination → Load-bearing and indentation → Rolling fatigue → Wear resistance and ground → Aging retest → Full machine propulsion | All the risk is pushed to the final step before it erupts |
Among these seven items, the ones that should be discussed first are the verification sequence and the interface processing procedure. Skipping the interface and directly unlocking the mold is like spending the most expensive step in advance; putting surface treatment outside the process card is equivalent to leaving the peel strength to luck.
9. One-page report comparison table: Six caster configurations directly pasted into the PPT
Conclusion first: There is only one criterion to judge whether this table is acceptable—whether the client's technician can take it to a meeting and use it to set the direction during the meeting.
| Scene | Recommended Route | Key indicators | Verification Standard | Conditions that need to be confirmed first |
|---|
| Medium and low load industrial casters, normal temperature workshop | Glass fiber or mineral reinforced PP wheel core / bracket Conventional wheel surface | Load-bearing, rolling resistance, flat point | ISO 22878 / EN 12527 | Single-wheel working load, parking duration, ground material |
| Silent traceless coated wheel | PP core with a soft material system matching the polarity of PP, or an added compatibilizer layer | 90° Peel Strength Failure Mode | ISO 813:2019 | Soft material system, surface treatment process, locking structure |
| You must use wheels with polyurethane tread. | Core modified polarity material (PA / ABS) TPU; or PP core Capacitor layer Mechanical latch | Peeling strength, retest after aging | ISO 813; Retest after temperature and humidity cycling | Is a PP core required, and is core replacement acceptable? |
| Glass fiber reinforced PP core with cast polyurethane tread (heavy duty) | GF-PP Core CPU Wheel Surface (Chemical Bonding) | Bearing, core removal risk, internal heat generation | ISO 22883:2004 | Single-wheel load, operating speed, continuous operating duration |
| Electronics workshop, anti-static | Modified PP parts (wheel core / bracket / dust cover) conductive wheel surface | Surface resistance range, grounding path | EN 12527 Resistance Test Item | Resistance range requirements, grounding method |
10. The part that most easily causes problems in this item is often not the wheel surface.
The two most common types of early failures in the caster industry are, one, flat spots on the wheel surface after long-term storage, and two, delamination at the rubber covering interface. These two types have different statuses in the standards: in ISO 22883:2004, which covers manually pushed and towed industrial types, static testing is not a mandatory item;
The peel strength of the coated interface is also not a mandatory requirement for finished caster wheels (Class B, summary of publicly released standard interpretation). In other words, the load-bearing table in the purchaser's hands naturally cannot cover these two types of failures.
At the criterion level, there are three aspects that can be matched: the interface is peeled at 90° according to ISO 813:2019, looking at the peel force per unit width and the failure mode;
Pressure tests according to ISO 22878 / EN 12527, both static and dynamic; wheel surface wear according to GB/T 9867-2008. All three have standard numbers and can be included in the technical agreement.
The common approach also involves three parallel paths: the wheel hub matches polarity (change materials or add an additional capacity layer), the surface condition is controlled (treatment or base coating is incorporated into the process card), and the mechanical latch provides redundancy.
In situations where there is heavy load and long-term parking, adding support legs or blocks at the parking spot is more convenient than trying to tough it out in the design.
Ningbo Kolon New Materials Co., Ltd. commonly supplies self-produced modified polypropylene (PP) pellets in the wear-resistant and reinforced directions for this item: the wheel core and bracket are proportioned according to the working load of a single wheel, ground conditions, and whether it will be parked for a long time; the small wheel body is matched according to hardness grade; the dust cover is matched according to color code and chemical resistance requirements.
The formulation can be adjusted according to the operating conditions of each piece, and we can make small samples with the customer for comparison; for overmolded parts, we are also willing to adjust the surface condition and shrinkage rate of the wheel core according to the customer's overmolding process—because the interface is never something that can be determined unilaterally.
Frequently Asked Questions
Question: I'm using polyurethane for the wheel surface and only using PP for the wheel core. Why does the interface still delaminate?
Answer: Because the problem is not with the wheel surface, but with the polarity of the wheel core. PP is non-polar and has low surface energy, making it inherently incompatible with polar soft materials like polyurethane. There are three approaches: change the polarity of the wheel core, add a compatibility layer and perform surface treatment, or create a mechanical lock. At least one of these should be done.
Question: How can you determine if a coated part can be used long-term?
Answer: The first thing is peel strength, not hardness. Perform a 90° peel according to ISO 813:2019 — only cohesive failure counts as good bonding; 'clean interface separation' is a defect; then retest after wet heat and thermal cycling.
Question: If the equipment has been stationary for a long time and a flat spot forms on the tire surface, is this considered a material issue?
Answer: Priority should be given to treating it as an operational condition issue. Permanent compression deformation is related to single-wheel static load, temperature, tire surface hardness, and parking duration.
Report 'single-wheel static load' together with 'continuous parking duration'—in cases of heavy load static placement, increase the wheel diameter, raise the hardness grade, or add support legs and pads at the parking position.
| Operating condition | Key criterion | Self-produced regular supply |
|---|
| Medium and low load caster wheel core / bracket | Load-bearing, rigidity, dimensional stability | Glass fiber or mineral reinforced modified PP direction |
| Small-diameter wheel body, dust cover | Hardness grade, color code, chemical resistance | Wear-resistant modified PP direction, mix according to floor conditions |
| Heavily loaded wheel that has been parked for a long time | Static pressure permanent deformation | Enhance the PP core direction support structure suggestions |
| Electronic Workshop Parts | Resistance range, grounding path | Modified PP parts orientation (wheel core / bracket / dust cover) |
Lastly, say three sentences.
First, caster wheels have two lifespans: one on the wheel surface and one at the interface. When the wheel surface is worn flat, you replace the wheel; when the interface detaches, it’s a full batch return—don’t cover up two issues with one term 'wear-resistant'.
Second, the first item in the acceptance of overmolded parts is peel strength and failure mode, not hardness. 'Peels off cleanly' is not an advantage on overmolded parts; it is a defect.
Third, modified PP is mostly used for the wheel core, bracket, and dust cover in this part, not the wheel surface.
