COOLPOLY THERMALLY CONDUCTIVE PLASTICS TCP. Design Manual

Transcription

1 COOLPOLY THERMALLY CONDUCTIVE PLASTICS TCP Design Manual 1

2 Table of Contents 1 Introduction to CoolPoly TCP 3 Thermally Conductive Plastics 3 2 Celanese Capabilities 4 Background 4 Design 4 Computer Aided Design (CAD) 4 Computational Fluid Dynamic (CFD) 4 Mold Design 4 Testing 6 Thermal: Component 6 Thermal: System 6 Prototyping 7 Rapid Prototyping 7 Standard Prototyping 7 3 Mold Design with CoolPoly TCP 8 Description 8 Tool Materials 8 Shrinkage 10 Draft 10 Venting 10 Gating 10 Fan Gate 11 Sub Gate 11 Runners 12 Runner Diagram 12 Sprues and Sprue Pullers 12 Sprue Diagram 12 Radii and Corners 13 Radii Diagram 13 Wall Thickness 13 Mold Heating 13 4 Injection Molding with CoolPoly TCP 14 Equipment Selection 14 Screw Design 14 Nozzle Design 14 Molding Conditions 14 Drying 14 Barrel Temperature 14 Melt Temperature 14 Mold Temperature 15 Cycle Times 15 Injection Speed 15 Screw Speed 15 Injection Pressure 15 Back Pressure 15 Regrind 15 Processing Tips 15 Contact Information 16 2

3 1 Introduction to CoolPoly TCP THERMALLY CONDUCTIVE PLASTICS Thermally conductive plastics (TCP) can offer the heat-transfer capability of metals and ceramics while maintaining the design, performance and cost advantages of conventional plastics. Polymers or, by their nature, plastics, are inherent thermal insulators. However, recent developments have enabled injection-molding grade plastics to have thermal conductivities in excess of 100 times the conductivity of the base resin. These thermally conductive plastics are composite materials consisting of high thermal-conductivity reinforcements in engineering and commodity thermoplastics. The advantages of thermally conductive plastics include heat transfer for thermal management, lower thermal expansion, high resistance to chemicals and expanded freedom in design. The applications for thermally conductive plastics include electronics, automotive, power electronics, motors, fiber optics, connectors, appliances, heating/ cooling/refrigeration, lighting, medical, food and sporting goods. CoolPoly thermally conductive plastics are available in either electrically conductive grades or electrically insulating grades. In addition to transferring heat, the electrically conductive grades provide EMI/RFI shielding characteristics due to their inherently good absorption of electromagnetic and radio frequency radiation. The electrically insulating grades are appropriate for applications where the material comes in contact with electrical leads or components. 3

4 2 Celanese Capabilities BACKGROUND Celanese is a leading global supplier of highperformance engineering polymers designed to drive growth and innovation across all industries. From the global production network of our Acetyl Chain, we provide materials that are critical to the global chemicals and paints and coatings industries. From our broad portfolio of Materials Solutions, we advance automotive and consumer-electronic designs and enable life-improving medical, food and beverage products. We focus the full power of our development support services, advanced products and deep technical knowledge on the success of our customers, helping redefine the limits of material performance in the most demanding applications. Our family of thermally conductive plastics for heat-transfer solutions, known as CoolPoly TCP, is available in a variety of base resins, with thermal conductivity ranging from 2 W/mK (similar to glass) to 40 W/mK. Celanese supplies thermally conductive plastic pellets produced from these resins. In support of application development, Celanese also assists in the design, modeling, testing, prototyping and tooling design of applications requiring thermally conductive plastics. DESIGN Computer Aided Design (CAD) Our design engineers can assist customers with their part design. We can import/export 3D CAD models and share ideas with customers using industrystandard CAD formats. We utilize our knowledge of CoolPoly thermally conductive plastics to help customers optimize their part design and select the right grade for their application. 3D CAD models assist in Computer Numeric Control (CNC) machining and mold design of prototype parts and prototype molds. Computational Fluid Dynamic (CFD) Celanese offers full CFD and thermal modeling for completion of static, transient and fluid flow analysis. Our engineers use the CFD tool to help customers optimize their parts for thermal performance, maximizing the conductive and convective heattransfer potential of the design. Celanese can accurately predict the thermal conductivity needed in an application. With this information, Celanese can recommend a material that meets the customer s thermal requirements and the overall performance requirements in the application. Mold Design Celanese has the ability to design any mold, no matter how simple or complex. Our resources are used to help customers design prototype molds and assist them with injection-molding training with CoolPoly TCP materials. The knowledge base and resources that Celanese has to offer for designing with CoolPoly thermally conductive plastics can significantly increase the success and speed of applications that use these materials. 4

5 Figure 1 Temp 1.230e ae e e e e e e e e e e e+002 Celanese utilizes both part and mold design support to optimize part performance using CoolPoly TCP compounds. 5

6 TESTING Celanese performs thermal, mechanical, physical and electrical testing on all compounds. Thermal heat-transfer-related testing is done at the material, component and system level. Mechanical, physical and electrical testing is done at the material level. Thermal: Component In addition to material testing, Celanese can perform component-level thermal testing to help customers evaluate the performance of their part in CoolPoly thermally conductive plastics compared with other materials or other plastics. The measured thermal resistance R (ºC/W) of a part or assembly can be performed under the following conditionsn: Free convection R = ƒ [power (W)] Forced convection R = ƒ [power (W), air speed (cfm)] Component-level thermal resistance data can help provide a quantitative assessment of the design (geometry or shape) of the part and and its material attribute of thermal conductivity, and how this affects the performance. The customer applies this data to the process of their designs in the design process. Thermal: System Using infrared (IR) imaging technology, Celanese can perform system-level testing to help customers develop solutions using CoolPoly plastics. The images below present IR-intensity plots of two plaques under the same conditions, mounted to a 5W heater. The plaque on the left is conventional plastic, while the plaque on the right is a CoolPoly TCP material. The temperature gradient ( T) across the conventional plaque is 24 C while the T across the CoolPoly TCP plaque is only 4 C. These IR thermographs show how IR-imaging works to visually present heat in a system test, and also how poorly conventional plastics conduct heat. Radiation R = f[power (W), T surrounding ( C)] Small, enclosure-dependent Figure 2 Runner Diagram Interface material R = ƒ [power (W), thickness (t), pressure (P)] Conventional Plastic vs. CoolPoly Thermally Conductive Plastic 6

7 PROTOTYPING Celanese has an extensive and modern tooling shop to produce prototype parts and prototype injection-mold tooling. Our tool room is staffed with experienced toolmakers and machinists. Our equipment inventory includes multiple 3-axis CNC mills, sinker-die EDMs, lathes, grinders, TIG welding and support equipment. Rapid Prototyping To help customers quickly get a feel for how their part will work using thermally conductive plastics, Celanese offers rapid prototyping options, such as machining parts from solid rods or plaques to building a prototype shape mold. It is important to understand that the performance of machined prototype parts and parts molded from a prototype tool will differ. Machined prototypes provide a basis for thermal evaluation, but not an accurate representation of the mechanical properties. Machined parts lack the mechanical integrity of injection-molded parts. Standard Prototyping With a fully equipped tool room and injection-molding facility, Celanese can help customers prototype their application prior to production. From building the prototype mold to injection molding the prototype parts, Celanese can give full support to any application. With decades of experience working in thermally conductive plastics, Celanese knows how to quickly and successfully prototype parts to help ensure the success of the application. Celanese can provide customers a one-stop prototype development center. Celanese offers the support of our resources to customers developing prototypes onsite or at other facilities. From mold designs to mold trials, Celanese supports customers by ensuring maximum benefits of thermally conductive plastic in their application. 7

8 3 Mold Design with CoolPoly TCP DESCRIPTION CoolPoly thermally conductive plastics are engineered materials. They are formulated compounds using commodity, engineering, and highperformance grade thermoplastic resins. Various additives and ingredients are compounded to impart thermal conductivity and other desirable attributes. Since CoolPoly TCP grades are based on specific polymers, basic mold design guidelines specific to the thermoplastic in question, e.g., PPS, PA, ABS, LCP and TPE are recommended as a starting point in the design process. Furthermore, the following CoolPoly TCP mold design guidelines are important and will assist the design engineer and mold designer in optimizing components made from CoolPoly TCP to meet the requirements of their applications. Our experts are available for design or processing assistance. Tool Materials Many standard-tool steels may be used with CoolPoly TCP. Since CoolPoly TCP conducts heat much better than conventional plastics, tooling materials are very important in the mold design. Stainless steel and aluminum are not recommended tooling materials, not even for prototypes. Aluminum has such a high thermal conductivity that CoolPoly TCP parts and runners will cool too quickly after injection into the mold and may freeze off before filling the cavity. On the other hand, stainless steel has a very low thermal conductivity and may cause sticking of thick-walled parts if the cooling is not fully optimized. 8

9 The following are recommendations for tool steels: Prototyping For prototype tools, P-20 and NAK-55 are recommended, depending on the number of parts to be run. Aluminum may be used, but is only advised for runs of 100 parts or less and not for thin-walled parts due to its high thermal conductivity. Parts and runners cool and freeze before the cavity is filled. Production Cores, cavities, gates and runners should have hardness greater than Rc 50 for most CoolPoly TCP grades. In some cases, hard coating of cavities is also an option to help preserve tooling finish. H-13 and D-2 are the most common tool steels used for TCP. Armaloy XADC coating or an equivalent tool coating can be used to help preserve tooling and can also aid in ejection due to its lubricating qualities. Removable gate inserts can also be used if wear is experienced near gating or other locations. For more specific information on which tool steels to use, please contact our experts for assistance. 9

10 Shrinkage Mold shrinkages for most CoolPoly TCP grades tend to be very low. In addition, tighter tolerances, lower warpage and better part stability are also possible with CoolPoly TCP compounds. Typical shrink values for CoolPoly TCP products are listed on the individual product data sheets. Draft Draft is very important when designing a part for injection molding. Even with the low shrink rates of CoolPoly TCP, a 0.5 degree min. draft is recommended. More draft is possible. With the help of our engineers, each specific application can be evaluated to help ensure its success. A draw polish is also recommended to help in the release of the part from the mold. Venting Sufficient venting is necessary to achieve quality parts with CoolPoly TCP materials. Vents should be located where the injected plastic may trap air, i.e., ejector pins, parting lines, bosses and other projections. In general, perimeter venting of the cavity/core is recommended, with additional vents provided by ejector pins and blades, as permitted by part design. Gating Gates should be designed to allow the mold to fill easily, with no interruptions to flow, and with as low a pressure as possible. Although CoolPoly TCP grades are no more abrasive than conventional engineered resins, gate inserts or hardened gate inserts may be used to prolong tool life and make tool repairs easier. Gates should be hardened as recommended in the Tool Materials section of this Design Guide (see page 8). Plating may also be used to increase wear resistance, and polishing is suggested to maximize flow. As all CoolPoly TCP grades are thermally conductive, they cool faster in the mold than conventional plastics. Faster cooling greatly reduces required cycle time (by as much as 50 percent), but may also cause the material to freeze off more quickly. Therefore, gates should be large. Cold material traps are important to ensure that only molten plastic enters the cavity. Extra attention should be placed on weld lines to ensure that they are formed in areas where minimal loads will be applied. Most traditional gate designs can be used for molding most CoolPoly TCP grades, with minor modifications. Use the following gating design recommendations (Figs 3-4) as a starting point when designing a gate-and-runner system for CoolPoly TCP parts. 10

11 Figure 3 Fan Gate Cold-Slug Area Large fan-gates should have a radius at each end to allow for a cleaner break Fan width & thickness will vary part to part Fan Gate design recommendations for molding CoolPoly TCP materials. Figure 4 Sub Gate Sprue Cavity Surface /2 Depth of Cavity 45 deg min Ø R Sub Gate design recommendations for molding CoolPoly TCP materials. 11

12 Runners A smooth transition from runner to gate (Fig. 5) and from primary runner sections to secondary runner sections is suggested in order to minimize runner wear and to maintain good translation of the material thermal conductivity into the part. Runners should be as short as possible to prevent premature freeze-off of the plastic. Cold material traps should be used at the end of each runner branch to ensure that only molten plastic flows from one runner section to the other. Full round runner systems are recommended, as these are the most efficient for CoolPoly TCP products. However, trapezoidal runners may also be used. Runner sizes may vary depending on the part, but as a rule, the runner diameter should be no less than three-sixteenths of an inch. Hot runners may also be used with some CoolPoly TCP grades. Contact your Celanese experts for details. Figure 5 Runner Diagram Cold slug area, just prior to transition towards gate Runner Diagram design recommendations for molding CoolPoly TCP materials. Figure 6 Sprue Diagram Smooth transition from runner to gate Radial transition for change of direction Sprues and Sprue Pullers A hot sprue may be used with CoolPoly TCP products to minimize material consumption. If a cold sprue is used, it should be as short as possible, with the bushing polished in the direction of draw. A sprue puller should also be used to ensure the sprue is pulled out of the bushing. When using a sprue puller, refer to the design recommendation in (Fig.6). Z pin 10 deg R /2 Ø of Z pin R Sprue material Equals Ø of Z pin Sprue Diagram design recommendations for molding CoolPoly TCP materials. 12

13 Figure 7 Radii Diagram 1/3 T = Min. Radius Radii Diagram design recommendations for molding CoolPoly TCP materials. Wall Thickness CoolPoly TCP compounds generally have higher viscosities than neat resin systems. With their increased viscosity and rapid rate of cooling, thin-wall molding over large areas can be difficult to achieve. Talk to our engineers for guidance on specific applications. The increased thermal conductivity and rapid rate of cooling allows CoolPoly TCP grades to be molded in thicker wall sections than any other plastics. CoolPoly TCP parts cool evenly across varying thicknesses, which minimize sink marks and warpage. Ribs can be used to reduce wall thickness in some areas of a part by acting as a runner and feeding the thin sections. Ribs also increase part strength, and, most importantly, aid in the thermal performance of the application. Radii and Corners CoolPoly thermally conductive plastics tend to have increased stiffness or modulus. It is recommended that the maximum radii possible be used for all sharp internal corners and edges to reduce stress concentrations and to increase part strength (Fig 7). Mold Heating Uniform heating and cooling of molds is highly recommended. Sufficient heating and/or cooling should be provided to ensure that the mold cavities and cores maintain uniform temperature. As CoolPoly TCP products are thermally conductive, molds must be heated to higher temperatures than typically required for the base resin. Please see the CoolPoly TCP processing guidelines for specific details on suggested mold temperatures. 13

14 4 Injection Molding with CoolPoly TCP EQUIPMENT SELECTION Screw Design A general-purpose metering-type screw is preferred for injection molding of CoolPoly thermally conductive plastics. The screw consists of three sections: feed, transition and metering. Additional design-specification recommendations for the screw include the following: Screws with a low compression ratio are preferred for injection molding CoolPoly TCP materials. A 2:1 compression ratio is recommended as a starting point before going to higher ratios. Free-flowing screw tip. The passageways and flutes should provide open and smooth flow of the melt material. Free-flowing check ring and seal assembly. Ball check return valves are not recommended. Nozzle Design A general-purpose nozzle design with a minimum 7/32 inch orifice opening is recommended. This design enables unrestricted material flow. MOLDING CONDITIONS In this section, you can find a general processing overview. For more detailed recommendations regarding specific temperatures, conditions, and pressures, please reference the individual CoolPoly TCP processing guidelines. Drying Properly dried materials are important to bring out the best-use in the properties from the molded part. Improperly dried materials can cause surface blemishes as well as mechanical problems in the molded part. Celanese recommends that all materials should be thoroughly dried in a dehumidifier dryer prior to use. Drying guidelines for the base resin may also be followed. Barrel Temperature CoolPoly TCP materials heat and melt faster than conventional materials. Since CoolPoly TCP grades are thermally conductive, the heat from the barrel is transferred through the material faster than it would be with conventional plastics. For this reason, lower barrel temperatures are possible when using. Lower temperatures also help prevent material degradation due to excess heating. Running lower barrel temperatures can also result in energy cost savings. Melt Temperature In addition to lower barrel temperatures, lower melt temperatures are possible as well. In some thinwalled applications, increasing the melt temperature is recommended to help the material flow. By increasing the melt temperature, the cooling time can be increased, allowing the material to fill thin walls. 14

15 Mold Temperature As CoolPoly TCP grades cool down quickly, higher mold temperatures are required than for conventional engineered resins. The mold temperature has to be set to a temperature range, that allows the CoolPoly TCP to crystallize (or solidify) in order to reach the mechanical integrity for ejection of the part from the mold. Cycle Times Since CoolPoly TCP products are thermally conductive, the cooling time can be significantly reduced or eliminated from the cycle time in most applications. Since cooling is often the largest component in cycle times, remarkable increases in productivity and reduction of costs can be achieved. Injection Speed An injection speed of moderate to fast, about 3-7 in/sec ( mm/sec), is recommended for most CoolPoly TCP grades. Screw Speed Lower screw speeds are possible with CoolPoly thermally conductive plastics compared with conventional engineered thermoplastics. Generally a speed of rpm is recommended as a starting point. Injection Pressure It is best to consult the individual processing guidelines for recommended starting pressures. Back Pressure CoolPoly TCP products are less compressible relative to unfilled engineered thermoplastics. This allows for low back pressures. Generally, the back pressure should be kept as low as possible to ensure complete screw filling and to ensure repeatable melt cushion at transfer. Regrind Regrind can be used in most CoolPoly TCP grades. Regrind will not significantly affect the thermal conductivity of CoolPoly TCP compounds. The thermal stability of the base resin is the primary concern against utilizing regrind. Contact our engineers to discuss specific applications. Applications should always be tested with regrind prior to commercialization. Processing Tips In general, lower-injection molding machine temperatures and pressures are recommended for CoolPoly TCP products compared with conventional engineered resins. CoolPoly TCP polymers conduct heat and therefore can cool down much faster than all other plastics. Therefore, in molds and nozzle tips, higher temperatures are recommended in order to prevent premature solidification of the material. 15

16 ENGINEERED MATERIALS celanese.com/engineered-materials Contact Information Americas 8040 Dixie Highway, Florence, KY USA Product Information Service t: t: Customer Service t: t: e: Europe Am Unisys-Park 1, Sulzbach, Germany Product Information Service t: +(00) t: +49-(0) e: Asia 4560 Jinke Road, Zhang Jiang Hi Tech Park Shanghai PRC Customer Service t: f: e: Copyright 2017 Celanese or its affiliates. All rights reserved. Celanese, registered C-ball design and all other trademarks identified herein with, TM, SM, unless otherwise noted, are trademarks of Celanese or its affiliates. Armaloy and XADC are registered trademarks of Armoloy Corporation. Celanese and these materials are not affiliated with nor sponsored by Armoloy Corporation. This publication was printed March 2017 based on Celanese s present state of knowledge, and Celanese undertakes no obligation to update it. Because conditions of product use are outside Celanese s control, Celanese makes no warranties, express or implied, and assumes no liability in connection with any use of this information. Nothing herein is intended as a license to operate under or a recommendation to infringe any patents. COOL-001-CoolpolyTCPDesignManual-PM-EN-r