--- title: "What causes blackening and dimensional issues in PC copper inserts for power tools?" description: "A quality engineer faces batch issues with blackened and out-of-spec copper inserts in power tool housings. The analysis points to ultrasonic installation heat, leading to solutions in process control, material handling, and preventive design." url: "https://www.ok-tool.com/qa/pc-copper-inserts-blackening-issues.html" language: "en" type: "Q&A" category: "Plastic Components Q&A" datePublished: "2026-09-30" dateModified: "2026-09-30" brand: "OK TOOL" manufacturer: "OK TOOL" answerCount: 10 --- # What causes blackening and dimensional issues in PC copper inserts for power tools? ## Question I'm a quality engineer for a power tool manufacturer, and we've hit a frustrating wall with a new batch of housings. The parts use PC (polycarbonate) with ultrasonically installed brass-coated copper inserts for thread reinforcement. During our first article inspection for mass production, we're seeing inconsistent but widespread issues: a dark, almost blackened appearance around many inserts, and critical bore diameters are slightly undersized, causing assembly problems with the motor screws. This wasn't an issue in our prototyping phase. The inserts are supposed to be brass-coated for corrosion resistance and easy installation, but now they look burnt and are causing fit issues. My team is pointing fingers—production blames the insert supplier for bad plating, and the supplier says our process is too aggressive. I need to understand the root cause from a manufacturing standpoint. Is this a material defect, a process failure, or a design flaw? What specific parameters should I be investigating on the ultrasonic press, and what evidence can I look for on the parts themselves to pinpoint the blame? We need a clear, actionable diagnosis to stop the line and fix this before the entire batch is scrap. ## Answers ### Answer 1 — Best Answer The blackening and undersized bores you're describing are classic symptoms of excessive localized heat generation during the ultrasonic insertion process. This is almost certainly a process-driven issue, not a primary material defect from the insert supplier. The brass coating is very thin; its primary role is often for lubricity and slight corrosion resistance during shelf life, not as a robust thermal barrier. When ultrasonic energy is too high, dwell time is too long, or the horn contact is uneven, the intense friction between the insert's knurls and the PC melts an excessive amount of plastic. This overheated plastic can carbonize, causing the black "burnt" halo. More critically, the excessive heat transfers into the copper insert itself, causing thermal expansion. Once the insert cools and contracts within the solidified plastic, it can distort inward, making the internal thread bore undersize. To diagnose, first examine the blackened areas under magnification. Carbonized plastic will look charred and flaky, distinct from a simple plating discoloration. Check the insert's knurls for signs of plastic flash or residue, indicating excessive melt and flow. For dimensional checks, measure the bore immediately after insertion and again after 24 hours. If the bore shrinks over time, it confirms post-installation thermal contraction of the insert. On the process side, you must audit the ultrasonic press parameters. The key variables are amplitude (often set too high for speed), trigger force (which starts the cycle), weld time (the duration of ultrasonic energy), and hold time (pressure after energy stops). A process optimized for speed will often jack up amplitude and weld time, which is likely what happened between prototyping and mass production. The immediate corrective action is to requalify the ultrasonic process window. Start by **reducing the weld time and amplitude in small increments** while maintaining sufficient insertion depth. Implement a nitrogen purge or shield gas around the horn if available; this inert atmosphere can prevent oxidation and carbonization of the molten PC. For the current batch, you may salvage parts by using a calibrated tap to recut the undersized threads, but this adds cost and risk. A more robust preventive solution involves design-for-manufacturability (DFM) feedback. The insert's knurl design (aggressiveness, pitch) and the pre-molded pilot hole in the PC are critical. A slightly larger pilot hole can reduce interference and required melt volume, lowering heat generation. Specifying a higher-temperature copper alloy, like C14500 (tellurium copper), can also improve thermal stability compared to generic C11000, though at a higher cost. To prevent recurrence, establish clear process control limits. Define a maximum allowable weld time and amplitude for this material-insert combination. Implement regular checks of horn alignment and wear. Finally, update your incoming inspection for inserts to include a simple thermal test: heat a sample insert to a target temperature (e.g., 150°C) and measure bore diameter before and after to gauge its thermal expansion coefficient, ensuring it's suitable for your process. This moves the focus from blame to a controlled, repeatable system. **status:** accepted **Author:** Amy Li **Date:** 2026-09-30 ### Answer 2 From a machining perspective, the dimensional instability points to the insert's own manufacturing tolerance and its interaction with heat. The bore diameter on a brass-coated copper insert is typically machined (tapped) after plating. If the plating is uneven or too thick inside the thread, it effectively reduces the minor diameter from the start. Under heat, the underlying copper expands, and upon cooling, the combined copper and brass layer contracts, potentially distorting the thinner plated layer. You should measure the inserts pre-installation with a go/no-go thread gauge and a precise bore gage. Check for consistency across a sample from multiple supplier batches. The knurl geometry is also critical; an overly aggressive knurl designed for maximum pull-out strength will generate more heat during installation. A design with a finer pitch or lower profile knurl can reduce required insertion force and frictional heat, trading off some ultimate strength for much better process stability and dimensional accuracy. **status:** suggested **Author:** Emily Chen **Date:** 2026-09-30 ### Answer 3 Considering the end-use in a power tool, the functional failure of an undersized thread is severe, but the blackening may be more than cosmetic. In high-vibration environments, the carbonized plastic zone is a point of weakness. The bond between the insert and the PC could be compromised, leading to potential insert rotation or loosening under cyclic load. You need to validate the current batch beyond simple dimensional checks. Perform torque-out and torque-in tests per your power tool's assembly specifications. Compare the failure torque of a blackened insert joint to a good one from the prototype phase. If the strength is within spec, the issue is primarily dimensional and cosmetic. If strength is degraded, the root cause is more serious—excessive heat has damaged the polymer's structural integrity. This functional data is crucial for deciding whether to scrap, rework, or use the parts. **status:** suggested **Author:** Linda Xu **Date:** 2026-09-30 ### Answer 4 A process improvement lens looks at the entire system yield. The sporadic nature of the defect suggests inconsistent input variables. Beyond the press parameters, examine the insert feeding and presentation. Are inserts manually loaded into the horn? Variation in orientation or slight contamination (oil, dust) can change the friction coefficient dramatically. Automating the feed with a vibratory bowl feeder and an inline vision check for orientation can eliminate this variation. Secondly, the PC resin's moisture content is often overlooked. Polycarbonate must be thoroughly dried before molding. If the housing was molded with even slightly damp resin, the moisture can turn to steam during ultrasonic insertion, contributing to voids, splay marks, and localized overheating. Verify the dryer settings and resin hopper management upstream in the injection molding process. Implementing SPC (Statistical Process Control) charts on key ultrasonic parameters and correlating them with post-installation bore measurements can identify the optimal stable window. **status:** suggested **Author:** Eric Zhao **Date:** 2026-09-30 ### Answer 5 The injection molding process for the housing itself sets the stage for this issue. The pre-molded pilot hole's size, shape, and surface finish are critical. If the hole has sink marks, flash, or an inconsistent diameter due to unstable molding conditions (e.g., varying pack pressure, insufficient cooling), the interference fit with the insert will vary part-to-part. This forces the ultrasonic press to compensate automatically, often leading to over-energy on some parts. You should audit the capability (Cpk) of the pilot hole diameter on the molded housings. Also, the gate location relative to the hole can induce internal stresses. Annealing the housings before insertion can relieve these stresses and provide a more consistent base material, reducing the risk of warping or cracking during insert installation. **status:** suggested **Author:** Rachel Huang **Date:** 2026-09-30 ### Answer 6 The mold tooling for the housing plays a foundational role. The core pin that forms the pilot hole must be rigid, perfectly polished, and cooled efficiently to maintain its precise diameter cycle after cycle. Wear on this pin can cause a gradual reduction in hole size, increasing interference and installation heat over time. A switch to a harder, wear-resistant steel grade like H13 for that core pin, or adding a nitride coating, can extend maintenance intervals. Furthermore, the mold design should ensure the hole is formed in a stable, thick section of the part to avoid flexing during ejection. If the housing warps slightly after molding, the pilot hole can become oval, creating uneven contact with the insert during installation and leading to localized overheating and blackening on one side. **status:** suggested **Author:** Kevin Liu **Date:** 2026-09-30 ### Answer 7 From an assembly line view, the issue is one of tolerance stack-up. The critical dimension is the final assembled position of the motor relative to the gearbox, which depends on the thread engagement depth of the screw through multiple inserts. An undersized bore can cause the screw to bind before it's fully seated, throwing off the entire assembly alignment. Before scrapping housings, conduct a trial assembly with a selective matching process. Sort the housings by measured insert bore size and pair them with screws from the upper end of their diameter tolerance. This temporary sorting can salvage parts while the root cause is fixed. Long-term, the design should be reviewed for tolerance allocation. Perhaps the screw thread specification can be loosened, or a thread-forming screw could be specified instead of a machine screw, which can tolerate a slightly smaller pilot hole. **status:** suggested **Author:** Michael Wu **Date:** 2026-09-30 ### Answer 8 The manufacturing engineer focuses on line stability and automation. Ultrasonic insertion is a critical station that must be perfectly synchronized with the rest of the line. If the cycle time at this station is the bottleneck, there is immense pressure to shorten weld time, which can lead to compensating by ramping up amplitude, causing the overheating you see. The solution is to balance the line. Could a dual-horn ultrasonic head install two inserts simultaneously? Could the housing be pre-heated in a controlled oven to a lower, consistent temperature (e.g., 80°C), reducing the energy needed from the ultrasonic horn? This approach lowers the peak temperature spike. Also, integrating an inline laser measurement system right after the ultrasonic station to check insert flushness and bore diameter (via air gauge) provides immediate feedback to adjust parameters or reject the part, preventing a large batch of defects. **status:** suggested **Author:** David Zhang **Date:** 2026-09-30 ### Answer 9 A project management perspective emphasizes gate reviews and control plans. The fact that this defect appeared at the First Article Inspection for mass production indicates a gap in the production process validation. The prototyping process parameters were likely not robustly transferred or scaled. The corrective action now is a formal deviation process: place the current batch on hold, contain any suspect inventory, and initiate a multi-disciplinary review with insert supplier, molding, and assembly teams. A revised Control Plan must be signed off before production resumes. This plan should define the optimized ultrasonic settings, the frequency of parameter checks, and the specific post-installation inspection requirements (e.g., 100% visual check for blackening, statistical bore measurement). Any future design change, even a new insert supplier lot, should trigger a re-validation of this control plan. **status:** suggested **Author:** Daniel Yang **Date:** 2026-09-30 ### Answer 10 The core of the issue may be material selection. The common C11000 (ETP copper) insert has high thermal conductivity, which is good for dissipating heat, but it also has a high coefficient of thermal expansion (CTE). When briefly heated during installation, it expands significantly. For power tools, where dimensional stability under varying operational temperatures is also key, a different copper alloy might be a better fit. C14500 (Tellurium copper) has similar conductivity but better machinability and slightly improved thermal dimensional stability. For the highest performance, a beryllium copper alloy (like C17200) offers excellent strength and minimal thermal growth, but at a substantially higher cost. The trade-off analysis should weigh the incremental material cost against the scrap rate, rework labor, and assembly line downtime caused by the current issue. Sometimes, the more expensive insert is the lower total-cost solution. **status:** suggested **Author:** Sophia Wang **Date:** 2026-09-30 ## Related Resources - [Plastic Components Q&A](https://www.ok-tool.com/qa/plastic-components/) - [Plastic Components](https://www.ok-tool.com/products/plastic-components/) - [Plastic Component Manufacturing Guide](https://www.ok-tool.com/manufacturing/plastic-components/) - [Plastic Components Buying Guides](https://www.ok-tool.com/buying/plastic-components/) - [Capabilities](https://www.ok-tool.com/capabilities/) - [Custom Manufacturing](https://www.ok-tool.com/custom-manufacturing/) - [Manufacturing Knowledge Base](https://www.ok-tool.com/knowledge/) - [Plastic Components](https://www.ok-tool.com/knowledge/plastic-components/) ## Structured Data ```json [ { "@context": "https://schema.org", "@type": "QAPage", "mainEntity": { "@type": "Question", "name": "What causes blackening and dimensional issues in PC copper inserts for power tools?", "text": "I'm a quality engineer for a power tool manufacturer, and we've hit a frustrating wall with a new batch of housings. The parts use PC (polycarbonate) with ultrasonically installed brass-coated copper inserts for thread reinforcement. During our first article inspection for mass production, we're seeing inconsistent but widespread issues: a dark, almost blackened appearance around many inserts, and critical bore diameters are slightly undersized, causing assembly problems with the motor screws. This wasn't an issue in our prototyping phase. The inserts are supposed to be brass-coated for corrosion resistance and easy installation, but now they look burnt and are causing fit issues. My team is pointing fingers—production blames the insert supplier for bad plating, and the supplier says our process is too aggressive. I need to understand the root cause from a manufacturing standpoint. Is this a material defect, a process failure, or a design flaw? What specific parameters should I be investigating on the ultrasonic press, and what evidence can I look for on the parts themselves to pinpoint the blame? We need a clear, actionable diagnosis to stop the line and fix this before the entire batch is scrap.", "answerCount": 10, "upvoteCount": 5, "datePublished": "2026-09-30T12:33:49Z", "dateModified": "2026-09-30T12:41:38Z", "author": { "@type": "Person", "name": "Anonymous", "url": "https://www.ok-tool.com/qa/pc-copper-inserts-blackening-issues.html" } ,"acceptedAnswer": { "@type": "Answer", "text": "The blackening and undersized bores you're describing are classic symptoms of excessive localized heat generation during the ultrasonic insertion process. This is almost certainly a process-driven issue, not a primary material defect from the insert supplier. The brass coating is very thin; its primary role is often for lubricity and slight corrosion resistance during shelf life, not as a robust thermal barrier. When ultrasonic energy is too high, dwell time is too long, or the horn contact is uneven, the intense friction between the insert's knurls and the PC melts an excessive amount of plastic. This overheated plastic can carbonize, causing the black "burnt" halo. More critically, the excessive heat transfers into the copper insert itself, causing thermal expansion. Once the insert cools and contracts within the solidified plastic, it can distort inward, making the internal thread bore undersize. To diagnose, first examine the blackened areas under magnification. Carbonized plastic will look charred and flaky, distinct from a simple plating discoloration. Check the insert's knurls for signs of plastic flash or residue, indicating excessive melt and flow. For dimensional checks, measure the bore immediately after insertion and again after 24 hours. If the bore shrinks over time, it confirms post-installation thermal contraction of the insert. On the process side, you must audit the ultrasonic press parameters. The key variables are amplitude (often set too high for speed), trigger force (which starts the cycle), weld time (the duration of ultrasonic energy), and hold time (pressure after energy stops). A process optimized for speed will often jack up amplitude and weld time, which is likely what happened between prototyping and mass production. The immediate corrective action is to requalify the ultrasonic process window. Start by reducing the weld time and amplitude in small increments while maintaining sufficient insertion depth. Implement a nitrogen purge or shield gas around the horn if available; this inert atmosphere can prevent oxidation and carbonization of the molten PC. For the current batch, you may salvage parts by using a calibrated tap to recut the undersized threads, but this adds cost and risk. A more robust preventive solution involves design-for-manufacturability (DFM) feedback. The insert's knurl design (aggressiveness, pitch) and the pre-molded pilot hole in the PC are critical. A slightly larger pilot hole can reduce interference and required melt volume, lowering heat generation. Specifying a higher-temperature copper alloy, like C14500 (tellurium copper), can also improve thermal stability compared to generic C11000, though at a higher cost. To prevent recurrence, establish clear process control limits. Define a maximum allowable weld time and amplitude for this material-insert combination. Implement regular checks of horn alignment and wear. Finally, update your incoming inspection for inserts to include a simple thermal test: heat a sample insert to a target temperature (e.g., 150°C) and measure bore diameter before and after to gauge its thermal expansion coefficient, ensuring it's suitable for your process. This moves the focus from blame to a controlled, repeatable system.", "upvoteCount": 5, "url": "https://www.ok-tool.com/qa/pc-copper-inserts-blackening-issues.html#acceptedAnswer", "datePublished": "2026-09-30T13:52:25Z", "author": {"@type": "Person","name": "Amy Li","url": "https://www.ok-tool.com/team/amy.html"} } ,"suggestedAnswer": [ { "@type": "Answer", "text": "From a machining perspective, the dimensional instability points to the insert's own manufacturing tolerance and its interaction with heat. The bore diameter on a brass-coated copper insert is typically machined (tapped) after plating. If the plating is uneven or too thick inside the thread, it effectively reduces the minor diameter from the start. Under heat, the underlying copper expands, and upon cooling, the combined copper and brass layer contracts, potentially distorting the thinner plated layer. You should measure the inserts pre-installation with a go/no-go thread gauge and a precise bore gage. Check for consistency across a sample from multiple supplier batches. The knurl geometry is also critical; an overly aggressive knurl designed for maximum pull-out strength will generate more heat during installation. A design with a finer pitch or lower profile knurl can reduce required insertion force and frictional heat, trading off some ultimate strength for much better process stability and dimensional accuracy.", "upvoteCount": 0, "url": "https://www.ok-tool.com/qa/pc-copper-inserts-blackening-issues.html#suggestedAnswer-2", "datePublished": "2026-09-30T13:47:21Z", "author": {"@type": "Person","name": "Emily Chen","url": "https://www.ok-tool.com/team/emily.html"} } , { "@type": "Answer", "text": "Considering the end-use in a power tool, the functional failure of an undersized thread is severe, but the blackening may be more than cosmetic. In high-vibration environments, the carbonized plastic zone is a point of weakness. The bond between the insert and the PC could be compromised, leading to potential insert rotation or loosening under cyclic load. You need to validate the current batch beyond simple dimensional checks. Perform torque-out and torque-in tests per your power tool's assembly specifications. Compare the failure torque of a blackened insert joint to a good one from the prototype phase. If the strength is within spec, the issue is primarily dimensional and cosmetic. If strength is degraded, the root cause is more serious—excessive heat has damaged the polymer's structural integrity. This functional data is crucial for deciding whether to scrap, rework, or use the parts.", "upvoteCount": 0, "url": "https://www.ok-tool.com/qa/pc-copper-inserts-blackening-issues.html#suggestedAnswer-3", "datePublished": "2026-09-30T13:27:07Z", "author": {"@type": "Person","name": "Linda Xu","url": "https://www.ok-tool.com/team/linda.html"} } , { "@type": "Answer", "text": "A process improvement lens looks at the entire system yield. The sporadic nature of the defect suggests inconsistent input variables. Beyond the press parameters, examine the insert feeding and presentation. Are inserts manually loaded into the horn? Variation in orientation or slight contamination (oil, dust) can change the friction coefficient dramatically. Automating the feed with a vibratory bowl feeder and an inline vision check for orientation can eliminate this variation. Secondly, the PC resin's moisture content is often overlooked. Polycarbonate must be thoroughly dried before molding. If the housing was molded with even slightly damp resin, the moisture can turn to steam during ultrasonic insertion, contributing to voids, splay marks, and localized overheating. Verify the dryer settings and resin hopper management upstream in the injection molding process. Implementing SPC (Statistical Process Control) charts on key ultrasonic parameters and correlating them with post-installation bore measurements can identify the optimal stable window.", "upvoteCount": 0, "url": "https://www.ok-tool.com/qa/pc-copper-inserts-blackening-issues.html#suggestedAnswer-4", "datePublished": "2026-09-30T13:23:45Z", "author": {"@type": "Person","name": "Eric Zhao","url": "https://www.ok-tool.com/team/eric.html"} } , { "@type": "Answer", "text": "The injection molding process for the housing itself sets the stage for this issue. The pre-molded pilot hole's size, shape, and surface finish are critical. If the hole has sink marks, flash, or an inconsistent diameter due to unstable molding conditions (e.g., varying pack pressure, insufficient cooling), the interference fit with the insert will vary part-to-part. This forces the ultrasonic press to compensate automatically, often leading to over-energy on some parts. You should audit the capability (Cpk) of the pilot hole diameter on the molded housings. Also, the gate location relative to the hole can induce internal stresses. Annealing the housings before insertion can relieve these stresses and provide a more consistent base material, reducing the risk of warping or cracking during insert installation.", "upvoteCount": 0, "url": "https://www.ok-tool.com/qa/pc-copper-inserts-blackening-issues.html#suggestedAnswer-5", "datePublished": "2026-09-30T13:19:42Z", "author": {"@type": "Person","name": "Rachel Huang","url": "https://www.ok-tool.com/team/rachel.html"} } , { "@type": "Answer", "text": "The mold tooling for the housing plays a foundational role. The core pin that forms the pilot hole must be rigid, perfectly polished, and cooled efficiently to maintain its precise diameter cycle after cycle. Wear on this pin can cause a gradual reduction in hole size, increasing interference and installation heat over time. A switch to a harder, wear-resistant steel grade like H13 for that core pin, or adding a nitride coating, can extend maintenance intervals. Furthermore, the mold design should ensure the hole is formed in a stable, thick section of the part to avoid flexing during ejection. If the housing warps slightly after molding, the pilot hole can become oval, creating uneven contact with the insert during installation and leading to localized overheating and blackening on one side.", "upvoteCount": 0, "url": "https://www.ok-tool.com/qa/pc-copper-inserts-blackening-issues.html#suggestedAnswer-6", "datePublished": "2026-09-30T13:16:48Z", "author": {"@type": "Person","name": "Kevin Liu","url": "https://www.ok-tool.com/team/kevin.html"} } , { "@type": "Answer", "text": "From an assembly line view, the issue is one of tolerance stack-up. The critical dimension is the final assembled position of the motor relative to the gearbox, which depends on the thread engagement depth of the screw through multiple inserts. An undersized bore can cause the screw to bind before it's fully seated, throwing off the entire assembly alignment. Before scrapping housings, conduct a trial assembly with a selective matching process. Sort the housings by measured insert bore size and pair them with screws from the upper end of their diameter tolerance. This temporary sorting can salvage parts while the root cause is fixed. Long-term, the design should be reviewed for tolerance allocation. Perhaps the screw thread specification can be loosened, or a thread-forming screw could be specified instead of a machine screw, which can tolerate a slightly smaller pilot hole.", "upvoteCount": 0, "url": "https://www.ok-tool.com/qa/pc-copper-inserts-blackening-issues.html#suggestedAnswer-7", "datePublished": "2026-09-30T13:12:46Z", "author": {"@type": "Person","name": "Michael Wu","url": "https://www.ok-tool.com/team/michael.html"} } , { "@type": "Answer", "text": "The manufacturing engineer focuses on line stability and automation. Ultrasonic insertion is a critical station that must be perfectly synchronized with the rest of the line. If the cycle time at this station is the bottleneck, there is immense pressure to shorten weld time, which can lead to compensating by ramping up amplitude, causing the overheating you see. The solution is to balance the line. Could a dual-horn ultrasonic head install two inserts simultaneously? Could the housing be pre-heated in a controlled oven to a lower, consistent temperature (e.g., 80°C), reducing the energy needed from the ultrasonic horn? This approach lowers the peak temperature spike. Also, integrating an inline laser measurement system right after the ultrasonic station to check insert flushness and bore diameter (via air gauge) provides immediate feedback to adjust parameters or reject the part, preventing a large batch of defects.", "upvoteCount": 0, "url": "https://www.ok-tool.com/qa/pc-copper-inserts-blackening-issues.html#suggestedAnswer-8", "datePublished": "2026-09-30T13:12:12Z", "author": {"@type": "Person","name": "David Zhang","url": "https://www.ok-tool.com/team/david.html"} } , { "@type": "Answer", "text": "A project management perspective emphasizes gate reviews and control plans. The fact that this defect appeared at the First Article Inspection for mass production indicates a gap in the production process validation. The prototyping process parameters were likely not robustly transferred or scaled. The corrective action now is a formal deviation process: place the current batch on hold, contain any suspect inventory, and initiate a multi-disciplinary review with insert supplier, molding, and assembly teams. A revised Control Plan must be signed off before production resumes. This plan should define the optimized ultrasonic settings, the frequency of parameter checks, and the specific post-installation inspection requirements (e.g., 100% visual check for blackening, statistical bore measurement). Any future design change, even a new insert supplier lot, should trigger a re-validation of this control plan.", "upvoteCount": 0, "url": "https://www.ok-tool.com/qa/pc-copper-inserts-blackening-issues.html#suggestedAnswer-9", "datePublished": "2026-09-30T12:42:43Z", "author": {"@type": "Person","name": "Daniel Yang","url": "https://www.ok-tool.com/team/daniel.html"} } , { "@type": "Answer", "text": "The core of the issue may be material selection. The common C11000 (ETP copper) insert has high thermal conductivity, which is good for dissipating heat, but it also has a high coefficient of thermal expansion (CTE). When briefly heated during installation, it expands significantly. For power tools, where dimensional stability under varying operational temperatures is also key, a different copper alloy might be a better fit. C14500 (Tellurium copper) has similar conductivity but better machinability and slightly improved thermal dimensional stability. For the highest performance, a beryllium copper alloy (like C17200) offers excellent strength and minimal thermal growth, but at a substantially higher cost. The trade-off analysis should weigh the incremental material cost against the scrap rate, rework labor, and assembly line downtime caused by the current issue. Sometimes, the more expensive insert is the lower total-cost solution.", "upvoteCount": 0, "url": "https://www.ok-tool.com/qa/pc-copper-inserts-blackening-issues.html#suggestedAnswer-10", "datePublished": "2026-09-30T12:41:38Z", "author": {"@type": "Person","name": "Sophia Wang","url": "https://www.ok-tool.com/team/sophia.html"} } ] } }, { "@context": "https://schema.org", "@type": "BreadcrumbList", "itemListElement": [ {"@type": "ListItem", "position": 1, "name": "Home", "item": "https://www.ok-tool.com/"},{"@type": "ListItem", "position": 2, "name": "Q&A", "item": "https://www.ok-tool.com/qa/"},{"@type": "ListItem", "position": 3, "name": "Plastic Components Q&A", "item": "https://www.ok-tool.com/qa/plastic-components/"} ,{"@type": "ListItem", "position": 4, "name": "What causes blackening and dimensional issues in PC copper inserts for power tools?"} ] } ] ```