周三下午，一家做包装机械的客户寄来一包衬套。
沉甸甸的一小袋，倒出来混着灰色粉末和几片碎环，最大的那片还能看出原来的圆度。他在袋子上用记号笔写了一行字：用了两个月。
电话里他说得很直接："说好自润滑的，跑两个月就松了。车间师傅说，还不如回去用加油的青铜套。"
我先问了三句：这个件是整圈转还是来回摆？对磨件是钢轴还是铝轴？现场有没有粉尘或者水洗？
他答完前两句，我就知道方向在哪了。
这篇把轴套材料这条判断链写完整，也说清哪几种工况下这件事不该谈。
先把轴套、衬套、凸轮这三个叫法理一下，它们常被混着说。
轴套和衬套基本是一回事，套在轴上、承担径向载荷、提供滑动面。
凸轮是另一个东西，它靠轮廓推动从动件，接触点的速度和压力在一个循环里一直在变。
这两类件放在同一段里讲，是因为它们都吃"无油"这条线，但判据的重心不一样：轴套看 PV，凸轮看接触点的速度峰值。
把凸轮按轴套的经验选料，失败几乎是注定的。
一、无油工况的六个维度，至少四样要落到数字
径向载荷。 常见 5–20 MPa 量级。这个数不是越高越难，而是它要和速度一起看。
线速度。 轴套常见 0.05–0.5 m/s。凸轮的接触点速度在一个循环里从零变到峰值，峰值那一瞬间才是决定性的。
PV 值。 压力乘速度。10 MPa 配 0.1 m/s，就是 1 MPa·m/s。常规自润滑尼龙的持续工作区大致在 1–3 MPa·m/s 量级，具体以牌号数据为准。
温度。 摩擦热加上环境温度。车间 40℃ 的环境里，跑一段时间套子表面到 80–90℃ 是常事。
介质。 粉尘、水洗、切削液，食品设备还有食品接触的合规语境。磨屑在很多场合是硬指标。
寿命与形态。 整圈转按运行小时算，摆动件按摆动次数算。每分钟 60 次的摆动，一年就是三千万次量级。
六样里先问齐四样：载荷、速度、摆动还是整圈转、有没有粉尘。
摆动还是整圈转，这一问的权重最大，下一节会讲为什么。
还有一样容易被漏掉：有没有水洗或者食品接触的要求。
水洗工况会把润滑转移膜冲掉，等于每隔一段时间就要重新跑合一次；食品设备还牵到对应的卫生标准语境。
这两样都不改变 PV 的算法，但会改变体系的选法。
二、三条自润滑路线，并列摆开
| 路线 | 典型做法 | 它擅长什么 | 它的代价 |
|---|
| PA6 或 PA66 + 二硫化钼体系 | 层状固体润滑剂，成本适中 | 中低 PV 下的承载与抗磨，工艺成熟 | 深色件；耐高温有限，温度一高承载迅速下降 |
| PA66 + 聚四氟乙烯体系 | 极低的摩擦系数 | 启停频繁、需要低扭矩的场合 | 力学强度可能下降；对偶件较软时容易先磨伤对方 |
| PA46 或高温体系 | 更高熔点与结晶速度 | 环境温度高、散热差的场合 | 吸湿更敏感、加工窗口窄、成本高 |
并列摆开的意思是：这三条不对应"好、中、差"，它们对应三种工况。
先看对偶件是谁。对偶件是钢，二硫化钼体系通常更稳；对偶件是铝或者软金属，聚四氟乙烯类体系把摩擦系数拉得越低，接触面贴合越紧、实际接触应力越高，铝轴反而先被磨伤。
再看摆动还是整圈转。
整圈转的轴套，轴和套之间能形成稳定的转移膜，摩擦状态相对平稳。
来回摆动的件，轴每换一次方向就要重新建立转移膜，长期处在边界润滑区。 这类工况看起来温和，实际比整圈转更磨。
最后看温度。PA6 与 PA66 的差别，还是酰胺基密度那件事：酰胺基越密、氢键越强，刚性和耐热越好，吸水率也越高。
落到轴套上，吸水率高的直接后果是尺寸会走：吸水 1% 对应大约 0.2–0.3% 的尺寸变化，一个 20 毫米的孔径就是从 20.00 涨到 20.05。
在过盈配合上，这 0.05 就是从"刚好"到"卡死"的距离。
三、选型判据表（这一页值得收藏）
下表门限值是方向性建议，不是验收标准；实际数值必须由具体项目、具体工况和实测确定。
| 指标 | 方向性门限 | 验证方法 / 标准 | 常见失效 | 通行解法 | 对应助剂体系 |
|---|
| PV 值 | 持续工况不超过牌号上限的一半 | 台架温升 + 磨耗量实测 | 温升失控、表面熔融 | 降 PV 或改结构散热 | 材料本征 |
| 摩擦系数 | 0.15–0.25 量级（对钢，干摩擦） | ASTM D1894 / 环块试验 | 启动扭矩大、爬行 | 固体润滑体系 + 配合间隙 | 固体润滑剂 |
| 磨耗量 | 按件定，一般要求 1000h 内壁厚磨损可控 | 台架称重 + 尺寸复测 | 间隙变大、松动 | 固体润滑 + 对偶件表面处理 | 固体润滑剂 |
| 对偶件磨损 | 对偶件表面粗糙度变化可控 | 对偶件表面检测 | 轴被磨伤、异响 | 降摩擦系数或改对偶件材质 | 材料本征 |
| 干湿态尺寸差 | 差异控制在 0.1% 以内 | 调湿前后实测 / ISO 294 | 配合间隙漂移 | 调湿态交付 | 材料本征 |
| 长期热氧保留率 | 90℃×1000h 后 ≥75% | ISO 527 | 发白、脆化、掉粉 | 稳定化体系 | 抗氧剂 |
| 表面析出 | 后续涂装或印刷前确认无迁移 | 表面能测试或附着力试验 | 喷漆不上、印刷脱落 | 换非迁移体系 | 表面迁移类需一并评估 |
怎么用这张表：先看 PV 那一行，再看对偶件磨损那一行。
这两行是本类件的胜负手。摩擦系数低不等于耐磨，耐磨也不等于对偶件受得了。
表里"验证方法"那一列，对偶件磨损大多没有现成国标可依。没有标准可依时，把验证方案写进技术协议，而不是省掉这一项。
四、四类常见失效，和它们的真实根因
失效一：说好的自润滑，两个月就松了。
先看一件常被忽略的事：自润滑不等于免维护。 很多人把这两个词当同义词，于是装配之后就不再看它，直到间隙大到出问题。
正确的做法是把间隙测量写进保养规程。塑件的磨损是渐变过程，早一次发现，比早一次换料便宜得多。
失效二：加了润滑反而磨得更快。
这是本类件里最有代表性的一次失效。一个做输送线的客户，原本用普通增强尼龙做滑块，寿命一般；为了提升，换成含聚四氟乙烯的低摩擦体系。
装上三周，对磨的铝导轨先出现了明显划痕，滑块反而更早报废。
查下来是：摩擦系数降低后，接触面贴合更紧、实际接触应力上升，而铝导轨本身硬度不足。
真正该做的，是调整配合间隙、改对偶件表面处理，而不是单纯换料。
失效三：摆动件比整圈转的件先坏。
同样载荷、同样速度，来回摆的那个件磨得更快。原因是它一直处在边界润滑区，转移膜还没建起来就换方向了。
遇到摆动件，把摆角与频率报给供应商，选型结论往往和按整圈转算出来的完全不同。
失效四：表面发黏，后续喷漆喷不上。
这一条从助剂侧看，常见根因是含硅酮类的润滑组分迁移到了表面，和涂层起了冲突。
看到表面发黏、或者印刷附着力突然变差，先查润滑体系，别急着怀疑料本身。
排查顺序上有一条要直说：轴套件的失效，先怀疑间隙与对偶件，再怀疑润滑状态，最后才怀疑材料。
这一条和普通结构件是反的——结构件先看材料，运动件先看配合。
五、加工与验证：先验什么后验什么
干燥。 尼龙必干燥。含水超标会在熔融温度下水解降解，件的韧性与耐磨一起掉。普通热风干燥机对尼龙基本无效，要用除湿干燥机。
分散要均匀。 二硫化钼、聚四氟乙烯这类固体润滑组分分散不均，会在件上形成局部磨耗点。这是磨损失效里最容易被忽略的一条。
模温影响表面。 表面越光滑致密，初期跑合越顺。模温不足会造成表面粗糙，跑合期直接变长。
调湿与退火。 精密配合件建议调湿或退火后交付，减少尺寸漂移对间隙的影响。
验证顺序，建议这样排：
1. 小样物性与摩擦系数比对
2. 环块或销盘磨损试验，测磨耗量与摩擦系数曲线
3. 对偶件磨损量测定（这一步最容易漏）
4. 单件台架：跑温升与间隙变化
5. 整机寿命与工况叠加（粉尘、水洗、温度循环）
顺序不能换。 前一项不过就往下走，后面测出来的数据没有解释意义。
一个内行细节：跑合五百小时后称一次件重，减重曲线平缓的才算过关，陡增的要停下来查。
这个动作成本很低，但它能在批量失效之前给出信号。
六、边界：什么时候这件事根本不该谈
以下四种情况，轴套或凸轮走塑化这条路不建议推进：
其一，PV 值明显超出常规自润滑尼龙的持续工作区。 高载荷叠高速度的场合，塑料的散热跟不上，温升会先失控。这类需求要看含油金属或专用复合轴瓦。
其二，配合精度要求进入微米级。 塑料的热膨胀与吸湿膨胀都远大于金属，这个差距是材料层面的，改配方补不回来。
其三，长期工作温度超过 110℃。 常规体系在这个区间的长期数据支撑不足，要看 PA46、PPA 或金属路线。
其四，有较大冲击载荷。 多数自润滑体系的韧性有限，冲击工况下容易崩边。
把这四条写在前面不是劝退，是省时间。 样品阶段很顺、卡在批量验证上再回退的项目，回退成本比一开始就不做高得多。
还要说清一句：凸轮和轴套不能一并打包评估。 凸轮的接触点速度在循环里一直变，峰值那一瞬间的 PV 可能比轴套高一个量级。
七、自产能力位：我们能陪到哪一步
我们做的事很具体：把 PA6、PA66、PA46、PA11、PA12、PA6T、PA9T 这些树脂，改成某个件真正能用的样子。
轴套与凸轮这类件的打样，我们按轮次走。
先出小样对比摩擦系数与磨耗量，再上单件台架跑温升与间隙，然后回到整机上做工况叠加。
每一轮的样件按批留样，出了偏差，能倒回去查是哪一轮动的什么。
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。
换料风险清单（从含油金属或 POM 换过来，要动的东西）
| 换料要动的项 | 要关注什么 | 容易漏的点 |
|---|
| 模具 | 收缩率差异随体系变，配合孔径可能要做补偿 | 只按通用收缩率给，不按件做补偿 |
| 干燥 | 尼龙必干燥，含水超标会水解降解，耐磨与韧性一起掉 | 用热风干燥机顶替除湿机 |
| 配合间隙 | 塑料的热膨胀与吸湿膨胀都要预留 | 沿用金属件的 H7/f7 思路不给塑料留量 |
| 对偶件 | 表面粗糙度与硬度要一起评审 | 只改塑料这一侧，对偶件不动 |
| 料温与模温 | 模温决定表层致密度，直接影响跑合期 | 照抄牌号推荐值，不看件 |
| 调湿 | 按调湿后的尺寸验收，干态数据只作过程记录 | 按平均壁厚估时间，厚壁处没吸透 |
| 验证顺序 | 小样 → 磨损试验 → 对偶件磨损 → 单件台架 → 整机 | 漏掉对偶件磨损这一项 |
一页纸汇报表（给要向上汇报的人）
`
项目：轴套 / 衬套 / 凸轮 · 材料路线评估
结论方向：改性尼龙可作候选路线，能否落地取决于四项前置条件
一、必须守住的三条
1. 先核 PV 与温升，再谈材料牌号
2. 对偶件磨损量单列一项，和塑料侧一起评
3. 摆动件按摆动次数算寿命，不按运行小时算
二、前置条件（任一不满足则建议暂缓）
· PV 值落在牌号持续工作区的一半以内
· 配合精度不进入微米级
· 长期工作温度 ≤ 110℃ 量级
· 有粉尘或水洗工况时，有对应的防护与验证方案
三、下一步动作
1. 取实际对偶件，做销盘或环块磨损试验
2. 量调湿前后配合孔径，评估件对状态的敏感度
3. 单件台架跑 500 小时，称重看减重曲线
风险提示：本路线的主要不确定性在温升与对偶件磨损，不在初始摩擦系数。
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读者常问的两句
问：既然自润滑，是不是装配完就不用管了？
不是。自润滑解决的是"不用加油"，不解决"间隙会变"。运动件的磨损是渐变过程，把间隙复测写进保养规程，比换更贵的料更有效。
问：聚四氟乙烯体系摩擦系数最低，是不是优先选它？
不一定。摩擦系数低只是其中一项。对偶件是铝或者软金属时，低摩擦带来的贴合更紧，反而会先把对偶件磨伤。要先把对偶件的材质报清楚。
结语
轴套与凸轮的无油选型，说到底是一道配合题，不是硬度题。
判断链只有三条：
摆动形态定润滑区 → PV 与温升定体系 → 对偶件定成败。
回收开头那三句追问——整圈转还是摆动、对偶件是钢还是铝、有没有粉尘——它们分别指向润滑状态、对偶件与防护三条线。
三条对完，"这个件能不能用自润滑尼龙"自然就有答案了。
如果你手上有个衬套或凸轮要定料，把三样东西发过来就能给方向：径向载荷与线速度、摆动或整圈转、对偶件材质与表面状态。
先把话讲清楚，再谈价钱。
有些件我们宁可说"这条路不合适"，也不硬接。选型错了，便宜也是贵。自润滑不是免维护，能用和不能用之间有条线，这条线我们不含糊。
我们做改性尼龙（PA6 / PA66 / PA46 / PA11 / PA12 / PA6T / PA9T 及尼龙合金）、改性 PPO / PPS / 热塑性弹性体，也经营各大化工巨头的尼龙树脂、副牌料与大包料。另：长期收尼龙原料、水口回料与各类尼龙废料，有正规处置渠道。
On Wednesday afternoon, a client who makes packaging machinery sent a package of bushings.
A small, heavy bag, when emptied, revealed a mix of gray powder and a few broken rings, the largest piece still showing its original round shape. He wrote a line on the bag with a marker: Used for two months.
On the phone, he spoke very directly: 'It was supposed to be self-lubricating, but it loosened after just two months. The workshop master said it would be better to go back to using the oiled bronze sleeve.'
I first asked three questions: Does this part rotate in a full circle or swing back and forth? For the grinding part, is it a steel shaft or an aluminum shaft? Is there any dust or water washing on site?
After he answered the first two questions, I knew which direction to take.
This article completes the judgment chain for the bearing sleeve material and also clarifies under which operating conditions this matter should not be discussed.
First, let's sort out the three terms: bushing, liner, and cam; they are often confused with each other.
Shaft sleeves and bushings are basically the same thing; they fit onto the shaft, bear radial loads, and provide a sliding surface.
A cam is something different; it drives the follower through its profile, and the speed and pressure at the contact point keep changing throughout a cycle.
These two types of parts are discussed in the same section because they both follow the 'oil-free' line, but the focus of the criteria is different: bushings look at PV, while cams look at the peak velocity at the contact point.
Choosing cam materials based on the experience of the bushing almost guarantees failure.
1. Six dimensions of oil-free operation, at least four must be quantified
Radial load. Commonly in the range of 5–20 MPa. This number is not about higher being more difficult, but it needs to be considered together with speed.
Linear speed. Sleeve bearings commonly range from 0.05–0.5 m/s. The contact point speed of a cam changes from zero to its peak within one cycle, and it is the instant at the peak that is decisive.
PV value. Pressure multiplied by velocity. 10 MPa with 0.1 m/s equals 1 MPa·m/s. The continuous operating range of conventional self-lubricating nylon is roughly in the 1–3 MPa·m/s range, with specifics depending on the grade data.
Temperature. Friction heat plus the ambient temperature. In a workshop environment of 40°C, it is common for the surface of the sleeve to reach 80–90°C after running for a while.
Medium. Dust, washing water, cutting fluid, food equipment, and the compliance context related to food contact. Metal chips are a strict standard in many cases.
Lifespan and form. The entire cycle is calculated according to operating hours, while the swinging components are calculated according to the number of swings. With 60 swings per minute, it amounts to a magnitude of thirty million times per year.
First ask about four of the six things: load, speed, swing or full rotation, and whether there is dust.
Whether to swing or make a full turn, this question carries the most weight, and the next section will explain why.
There is one more thing that is easily overlooked: whether there are any requirements for washing with water or food contact.
Washing conditions will wash away the lubricating transfer film, which means it has to be run-in again after a certain period; food equipment also involves the corresponding hygiene standards context.
Both of these do not change the algorithm of PV, but they will change the way the system is chosen.
Two or three self-lubricating routes, arranged side by side
| Route | Typical practice | What is it good at? | Its cost |
|---|
| PA6 or PA66 molybdenum disulfide system | Layered solid lubricant, moderately priced | Load-bearing and wear resistance under medium and low PV, mature process | Dark-colored parts; limited high-temperature resistance, load-bearing capacity drops rapidly when the temperature rises |
| PA66 PTFE system | Extremely low coefficient of friction | Situations with frequent start-stop and requiring low torque | Mechanical strength may decrease; when the counterpart is softer, it is easy to wear the other party first. |
| PA46 or high-temperature system | Higher melting point and crystallization rate | Situations with high ambient temperature and poor heat dissipation | More sensitive to moisture, narrow processing window, high cost |
The meaning of placing them side by side is: these three do not correspond to 'good, average, poor'; they correspond to three different operating conditions.
First, look at what the counterpart is. If the counterpart is steel, a molybdenum disulfide system is usually more stable; if the counterpart is aluminum or a soft metal, the lower the friction coefficient of a polytetrafluoroethylene-type system, the tighter the contact surface fits and the higher the actual contact stress, making the aluminum shaft more likely to be worn first.
Then see if it swings or rotates a full circle.
The sleeve that rotates around the shaft can form a stable transfer film between the shaft and the sleeve, making the friction state relatively stable.
For parts that swing back and forth, every time the shaft changes direction, the transfer film has to be re-established, and it is continuously in the boundary lubrication zone. This type of operating condition may seem mild, but in reality, it causes more wear than full-circle rotation.
Finally, look at the temperature. The difference between PA6 and PA66 still comes down to the density of amide groups: the denser the amide groups, the stronger the hydrogen bonds, the better the rigidity and heat resistance, but also the higher the water absorption.
Falling onto the bushing, the direct consequence of high water absorption is dimensional change: 1% water absorption corresponds to approximately 0.2–0.3% dimensional change, so a 20 mm diameter would increase from 20.00 to 20.05.
In interference fit, this 0.05 is the distance from 'just fitting' to 'stuck tight'.
3. Selection Criteria Table (This page is worth saving)
The threshold values in the table are directional recommendations, not acceptance standards; the actual values must be determined by the specific project, specific working conditions, and actual measurements.
| Indicator | Directional threshold | Verification Method / Standard | Common Failures | Common solution | Corresponding auxiliary agent system |
|---|
| PV value | Continuous operation does not exceed half of the grade limit | Test Bench Temperature Rise Measured Wear Amount | Temperature rise out of control, surface melting | Reduce PV or change the structure for heat dissipation | Material intrinsic |
| Coefficient of friction | 0.15–0.25 magnitude (for steel, dry friction) | ASTM D1894 / Block Test | High starting torque, crawling | Solid lubrication system Cooperating clearance | Solid lubricant |
| wear amount | Determined per piece, generally requires that the inner wall thickness wear is controllable within 1000h | Test Bench Weighing Dimension Re-measurement | Gap widening, looseness | Solid lubrication Surface treatment of mating parts | Solid lubricant |
| Mating part wear | The surface roughness variation of the mating parts is controllable | Surface inspection of mating parts | Shaft is scratched and makes abnormal noise | Reduce the friction coefficient or change the material of the mating part | Material intrinsic |
| Dry and wet dimensional difference | The difference is controlled within 0.1% | Measured before and after humidity adjustment / ISO 294 | Clearance drift | Delivered in a controlled humidity state | Material intrinsic |
| Long-term thermal oxygen retention rate | After 90℃ × 1000h ≥75% | ISO 527 | Pale, brittle, powdery | Stabilization system | Antioxidant |
| Surface precipitation | Confirm no migration before subsequent coating or printing | Surface energy testing or adhesion testing | Paint does not stick, printing peels off | Switch to a non-transfer system | Surface migration types need to be evaluated together |
How to use this table: first look at the PV row, then look at the row for worn parts of the counterpart.
These two lines are the key points of this type of component. A low coefficient of friction does not equal wear resistance, and wear resistance does not mean the mating parts can withstand it.
In the column for 'internal and external' verification methods, there are generally no existing national standards for the wear of mating parts. When there are no standards to follow, include the verification plan in the technical agreement instead of omitting this item.
4. Four common types of failures and their real root causes
Failure 1: The promised self-lubrication loosened after just two months.
Let's first look at something that is often overlooked: self-lubrication does not mean maintenance-free. Many people treat these two terms as synonyms, so after assembly, they stop checking it until the clearance becomes large enough to cause problems.
The correct approach is to include gap measurements in the maintenance procedures. The wear of plastic parts is a gradual process, and discovering it earlier is much cheaper than replacing the material earlier.
Failure 2: Adding lubricant actually causes it to wear out faster.
This is the most representative failure in this type of case. A customer who makes conveyor lines originally used ordinary reinforced nylon for the sliders, with an average lifespan; in order to improve it, they switched to a low-friction system containing polytetrafluoroethylene.
After being installed for three weeks, obvious scratches first appeared on the paired aluminum rails, and the slider actually failed even earlier.
It turns out that: after the friction coefficient decreases, the contact surfaces fit more tightly, the actual contact stress increases, and the hardness of the aluminum guide rail itself is insufficient.
What really needs to be done is to adjust the fit clearance and modify the surface treatment of the paired parts, rather than simply changing the material.
Failure three: The swinging part fails before the part that rotates a full turn.
With the same load and the same speed, the part that swings back and forth wears out faster. The reason is that it is always in the boundary lubrication zone, and the transfer film hasn't formed before it changes direction.
When encountering moving parts, report the swing angle and frequency to the supplier; the selection conclusion is often completely different from the one calculated based on full rotations.
Failure 4: The surface becomes sticky, making subsequent painting impossible.
From the perspective of the additive, a common root cause is that silicone-containing lubricating components have migrated to the surface, causing a conflict with the coating.
If you notice the surface becoming sticky or the print adhesion suddenly deteriorating, first check the lubrication system before rushing to suspect the material itself.
There is one thing to say directly about the inspection order: when an axle sleeve fails, first suspect the clearance and the mating parts, then suspect the lubrication condition, and only lastly suspect the material.
This one is the opposite of ordinary structural parts — for structural parts, you first look at the material; for moving parts, you first look at the fit.
5. Processing and Validation: What is Prior and What is Posterior
Drying. Nylon must be dry. Excess moisture can hydrolyze and degrade it at melting temperature, causing a loss of both toughness and wear resistance. Ordinary hot air dryers are basically ineffective for nylon; a dehumidifying dryer must be used.
Dispersion should be uniform. Solid lubricating components like molybdenum disulfide and polytetrafluoroethylene, if not evenly dispersed, can form localized wear points on parts. This is one of the easiest points to overlook in wear failure.
Mold temperature affects the surface. The smoother and denser the surface, the smoother the initial run-in. Insufficient mold temperature can cause a rough surface, directly lengthening the run-in period.
Moisture adjustment and annealing. It is recommended that precision fitting parts be delivered after moisture adjustment or annealing to reduce the impact of dimensional drift on clearances.
Verify the order, it is recommended to arrange it like this:
1. Comparison of Sample Properties and Friction Coefficient
2. Test on ring blocks or pin disks for wear, measuring the wear amount and friction coefficient curves
3. Measurement of wear on mating parts (this step is easiest to overlook)
4. Single-piece test bench: Temperature rise and clearance variation
5. Overall machine lifespan combined with operating conditions (dust, washing, temperature cycling)
The order cannot be changed. If the previous item is just skipped, the data measured later will have no explanatory significance.
A professional detail: After running in for 500 hours, weigh the parts once; only those with a gradual weight loss curve are considered acceptable, while those with a sharp increase need to be stopped for inspection.
This action has a low cost, but it can give a signal before mass failure.
6. Boundaries: When this matter should never be discussed
In the following four situations, it is not recommended to proceed with the route of bearing bush or cam going through plastication:
First, the PV value is significantly beyond the continuous operating range of conventional self-lubricating nylon. In cases of high load with high stacking speed, the heat dissipation of the plastic cannot keep up, and the temperature rise will become uncontrollable first. Such requirements need to consider oil-containing metals or specialized composite bushings.
Secondly, in order to meet precision requirements, it reaches the micron level. The thermal expansion and moisture absorption expansion of plastics are much greater than those of metals, and this gap is at the material level and cannot be remedied by adjusting the formulation.
Third, the long-term operating temperature exceeds 110℃. The conventional systems lack long-term data support in this range, so one needs to look at PA46, PPA, or metal-based approaches.
Fourth, there are relatively large impact loads. Most self-lubricating systems have limited toughness and are prone to chipping under impact conditions.
Writing these four points at the beginning is not to discourage, but to save time. For projects that go smoothly at the sample stage but get stuck at mass validation and then have to backtrack, the cost of backing out is much higher than not doing it from the start.
I also need to clarify one more point: the cam and the bushing cannot be evaluated together. The contact point speed of the cam keeps changing throughout the cycle, and the PV at the peak moment could be an order of magnitude higher than that of the bushing.
7. Self-production capability level: How far can we go
What we do is very concrete: we turn resins like PA6, PA66, PA46, PA11, PA12, PA6T, and PA9T into a form that a specific part can actually use.
For prototyping parts like bushings and cams, we proceed in rounds.
First, produce small samples to compare the friction coefficient and wear amount, then use a single-piece test rig to run temperature rise and clearance tests, and finally return to the complete machine to perform condition superposition tests.
Samples from each batch are kept; if there is a deviation, we can trace back to see which batch changed what.
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.
Material Change Risk List (Items to be changed when switching from oil-containing metals or POM)
| Items to be changed | What should be paid attention to? | Points that are easy to overlook |
|---|
| Mold | The shrinkage rate differences vary with the system, and pore size may need to be compensated accordingly. | Only provide based on the general shrinkage rate, no compensation is made per piece |
| Dry | Nylon must be dry; excess moisture will cause hydrolytic degradation, and both wear resistance and toughness will decrease together. | Use a hot air dryer instead of a dehumidifier |
| Clearance | Both thermal expansion and moisture absorption expansion of plastic need to be allowed for. | Applying the H7/f7 approach for metal parts does not leave any allowance for plastic. |
| Counterpart | Surface roughness and hardness should be evaluated together | Only modify the plastic side, do not move the mating part. |
| Material Temperature and Mold Temperature | Mold temperature determines the surface density and directly affects the running-in period | Copy the recommended brand number without checking the parts |
| Humidity control | Acceptance is based on the dimensions after moisture adjustment; dry-state data is only used for process records. | Based on the average wall thickness to estimate the time, the thick-walled areas are not fully soaked. |
| Verification order | Sample → Wear Test → Pair Component Wear → Single Component Bench → Complete Machine | Missed the wear of the mating part |
One-page report sheet (for people who need to report upwards)
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Project: Shaft Sleeve / Bushing / Cam · Material Route Evaluation
Conclusion direction: Modified nylon can be a candidate route, and whether it can be implemented depends on four prerequisite conditions
1. Three Rules That Must Be Followed
1. First check the PV and temperature rise, then discuss the material grade.
2. Evaluate the wear amount of the paired component as a single item, together with the plastic side.
3. The swinging parts have their lifespan calculated based on the number of swings, not the operating hours.
2. Precondition (It is recommended to postpone if any are not met)
· The PV value falls within half of the continuous operating range of the grade
· The fit accuracy does not reach the micron level
· Long-term operating temperature ≤ 110℃ range
· When there is dust or washing conditions, there are corresponding protection and verification plans
3. Next Steps
1. Take the actual counterpart and conduct a pin plate or ring block wear test
2. Adjust the aperture before and after moisture conditioning, and assess the part's sensitivity to the condition
3. Run a single test bench for 500 hours, weigh it to observe the weight reduction curve
Risk Warning: The main uncertainties of this route lie in temperature rise and wear of the counterpart, not in the initial friction coefficient.
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Two questions readers often ask
Question: Since it is self-lubricating, does that mean once assembled, it requires no further maintenance?
No. Self-lubrication solves the problem of 'no need to add oil', but it does not solve 'gap changes'. The wear of moving parts is a gradual process, and including gap re-measurement in maintenance procedures is more effective than using more expensive materials.
Question: The PTFE system has the lowest coefficient of friction. Should it be chosen first?
Not necessarily. A low coefficient of friction is just one factor. When the counterpart is made of aluminum or a soft metal, the tighter fit caused by low friction could actually wear out the counterpart first. You need to specify the material of the counterpart first.
Conclusion
The oil-free selection of the bushing and cam ultimately comes down to a fit issue, not a hardness issue.
There are only three judgment chains:
Swing pattern determines the lubrication zone → PV and temperature rise determine the system → Mating parts determine success or failure.
Revisiting the first three follow-up questions—whether it rotates in a full circle or swings, whether the mating part is steel or aluminum, and whether there is dust—each of them corresponds to lubrication status, the mating part, and the three protective lines, respectively.
Once the three items are matched, the question of whether this piece can use self-lubricating nylon naturally has an answer.
If you have a bushing or cam at hand that needs material selection, just send over three things to get guidance: radial load and linear speed, oscillation or full rotation, and the material and surface condition of the mating part.
First make things clear, then talk about the price.
For some things, we would rather say 'this path is not suitable' than force it. If the selection is wrong, even something cheap becomes expensive. Self-lubricating does not mean maintenance-free; there is a clear line between what can be used and what cannot, and we are not vague about this line.
We manufacture modified nylon (PA6 / PA66 / PA46 / PA11 / PA12 / PA6T / PA9T and nylon alloys), modified PPO / PPS / thermoplastic elastomers, and also distribute nylon resins, second-brand materials, and bulk materials from major chemical companies. Additionally, we have long-term operations for collecting nylon raw materials, sprue regrinds, and various nylon waste, with formal disposal channels.
