Many beginners want to quickly understand high-temperature injection molding. As an industry leader, we have involved high-temperature injection molding product engineers and wrote this latest ultimate guide in 2022, which can guide everyone to quickly understand high-temperature injection molding products.
High temperature plastics are melt-processable plastics with extreme heat resistance. They are also referred to as high performance or engineering polymers due to their high heat resistance of over 200°C. Other key characteristics of these materials include outstanding strength, long-term durability, and biocompatibility. They have structural capabilities over the long-term at service temperatures greater than 150°C and short-term use at temperatures greater than 250°C.
High temperature thermoplastics are more adaptable than standard plastics due to their better mechanical properties, higher heat resistance, and higher chemical stability. They can also endure multiple cycles and doses of all radiation types and have an outstanding ability to be molded into parts with tight tolerance. Sometimes these high temperature thermoplastics are also referred to as "high performance plastics". High-temperature thermoplastics currently enjoy a rapidly growing segment of the plastics market, including in various medical applications, automotive, aerospace, etc.
1) PEEK (Polyetheretherketone)
PEEK is a semi-crystalline, high-performance engineering thermoplastic that’s resistant to chemicals, wear, fatigue, creep, and heat. This material is so strong and adaptable to harsh environments that manufacturers use it as a replacement for metal in many applications, In short durations, PEEK can endure temperature highs of up to 300°C and has an impressive melting point stretching beyond 370°C. Aside from car transmission components and aircraft exteriors, PEEK is also a regular among high-tech medical devices. Its compatibility with CNC machining and ease of machining through injection molding makes it an affordable option for most manufacturers. PEEK has many outstanding properties, including:
● Excellent friction and wear characteristics
● Extremely high tensile strength
● Self-lubricating
● Long-term creep and fatigue properties
● Low coefficient of friction
● Maximum working temperature 260°C
● High electrical integrity
● Low moisture absorption
● Resistant to high-pressure steam, fresh water, and saltwater
● High abrasion and cut-through resistance
● Low smoke and toxic gas emission
● Can be insulating, conducting, or static dissipative
● FDA approved
● Meets UL94 V-0 requirements
2) PAI (Polyamide-imide)
PAI (polyamide-imide) is the highest performing, melt-processable thermoplastic. The amorphous polymer has exceptional resistance to wear, creep and chemicals and performs well under severe service conditions up to 260°C. PAI also has superior electrical and structural characteristics at high temperatures, an extremely low coefficient of linear thermal expansion, and exceptional dimensional stability.
To meet specific requirements, PAI can be compounded with a variety of fillers, reinforcements, additives and pigments. Excellent compressive properties combined with creep and fatigue resistance make PAI a superior sealing material. Typical applications include non-lubricating bearings, seals, valves, compressors, and piston parts, bearing cages, bushings, and thrust washers. PAI material is an optimal choice for custom applications in severe service conditions. It also has many outstanding properties, including:
● Highest level of wear resistance
● Low friction
● High compressive strength
● Self-lubricating
● Low creep
● High temperature resistance
● Maintains toughness and impact strength in low temperatures
● Resistant chemical corrosion
● Superior compressive strength
● Excellent electrical insulation
● High dielectric constant
3) PEI (Polyetherimide)
Common PEI material is amber granules. An amorphous material with exceptional strength and rigidity under long term heat exposure, PEI has excellent impact strength, and flame resistance and generates very low levels of smoke when burned. PEI also has excellent hydrolytic stability and is well suited for repeated steam sterilization. PEI is available in transparent and opaque colors including glass fiber additives for improved mechanical properties.
This material's melting point of 219°C and a servicing temperature at a max continuous of 170°C makes it archetypal in designing circuit boards, airplane seat covers, fire blockers, and equipment for food sterilization. it is commonly used in applications where tight tolerances and low warp are essential due to its resilience against heat exposure. It has many outstanding properties, including:
● Excellent chemical resistance
● Superior high temperature characteristics resistance
● Precise tolerance control(this point is very important)
● Permanent operating temperature (170°C)
● High mechanical strength
● High creep resistance
● High dimensional stability
● Resistance to hydrolysis (suitable for meddical device repetitive steam sterilisation)
● Nice electrical insulation
● Radiation resistance
● Chemical resistance
4) PFA (Perfluoroalkoxy)
PFA, commonly known as Teflon, is a soft, heat-resistant, low-friction plastic with exceptional chemical resistance. It has high flexural strength, adequate weathering resistance, and good electrical insulating power in both hot and wet environments.
PFA is unique because it’s almost completely chemically inert and highly insoluble in most solvents, making it ideal for high-temperature applications. PFA has one of the highest melting points of any thermoplastic at 327°C and a very large operating temperature range. It’s thermally stable enough to be used anywhere between -200°C and +260°C. common PFA raw material is clear granules.
5) PBI (Polybenzimidazole)
Polybenzimidazole (PBI) has the highest heat and wear resistance, strength, and mechanical property stability of any engineering thermoplastic on the market today. it is a unique and highly stable linear heterocyclic polymer. PBI have no known melting point, don’t burn, and don’t stick to other plastics. This material has a maximum continuous service temperature of 398°C in inert environments, 343°C in air, and short term exposure potential up to a blistering 537°C. PBI high temperature material offers an excellent combination of properties:
● Highest compressive strength of any unfilled resin
● Excellent tensile and flexural strength
● Good fatigue properties; low creep
● Excellent hardness
● Low coefficient of friction
● Outstanding Tg and heat deflection temperature (HDT)
● Relatively low coefficient of thermal expansion
● High volume resistivity
● High plasma resistance
6) PPA (Polyphenylene sulfide)
PPA is a member of thermoplastic synthetic resins in the polyamide (nylon) family. It retains its high strength and stiffness up to 280°C, With a high melting point of over 300°C. They maintain mechanical integrity after thousands of hours at elevated temperatures and in high humidity and chemically aggressive environments. So we often talk about it as“high-temperature NYLON”.
PPA material use fiber reinforcements, heat stabilizers, impact modifiers, flame retardants, minerals and other additives to achieve a broad range of performance, price and processing options. PPA has a long history of replacing metals (die cast Al and Mg) in automotive applications needing to withstand high temperatures, humidity and exposure to aggressive chemicals.
This material is a major contributor to lightweight solutions, reduces fuel consumption, improves safety, and delivers energy efficiency. Typical applications include thermostat housings, clutch cylinders, charge air coolers, heater cores, water pumps and automotive powertrain components, the housing for high temperature electrical connectors and many other uses battery pack cases. This PPA material has many benefits, including:
● Nice chemical resistance
● Creep and fatigue resistance
● Small warpage
● Good dimensional stability
● Sensitivity to moisture absorption
● Higher strength and stiffness at elevated temperatures
7) PPS (Polybenzimidazole)
(PPS) is a semi-crystalline, high-heat polymer with physical properties that make it suitable for precision-molded components that must withstand high heat, mechanical stress, and chemical corrosion. The molecular structure of PPS also makes the material inherently flame retardant, as it tends to charge during combustion rather than burn.
It is classified at UL 94 V-0 without having to use flame retardant additives, and its limiting oxygen index of 50% makes it one of the most flame-resistant plastics. It has excellent dimensional stability, making it possible to mold complex parts to extremely tight tolerances with high reproducibility. Those parts will maintain their dimensional stability even at high temperatures and in harsh chemical environments.
The material features superior hydrolytic stability, high stress cracking resistance, high modulus, and high creep resistance. The material’s combination of dimensional stability, heat resistance, and corrosion resistance make it an effective lightweight substitute for metals. The benefits of such substitution can include improved corrosion resistance compared to metal, reduced manufacturing costs, and improved fuel efficiency due to reduced part weight. Its unique combination of properties gives it a wide range of applications in the electronics, automotive, aerospace, and chemical industries.
It has many outstanding properties, including:
● Excellent hydrolytic stability
● Meeting UL 94 V0 requirement
● Precision molding to tight tolerances with high reproducibility
● High stress cracking resistance
● Long term and short term thermal stability
● Dimensional stability
● High modulus and creep resistance
● Nice electrical insulation
● Chemical resistance
● High mechanical strength
8) Liquid crystal polymers(LCP)
Liquid crystal polymers (LCP) are halogen-free high performance polymers with very high dimensional stability and high flowability. Heat resistance up to 240 °C, short term up to 340 °C. With an ultra-high level of mechanical strength, the LCP also has the unique property that the thinner the product, the greater its mechanical strength per unit of cross-sectional area. Due to its very low coefficient of thermal expansion, it is comparable to steel and ceramics, and has inherent flame retardation (UL 94 V-0). Fiberglass reinforced plastics also are widely used in the market.
The three most common types of LCP are semi-aromatic copolyesters, co-polyamides, and polyester co-amides. These polymers contain rigid rod-like or plate-like repeating units with high aspect ratios, so-called mesoprystal groups, capable of self-assembling into anisotropic liquid crystals (mesophases) upon cooling or external fields. Three very common LC mesophases are nematic, smectic A, and smectic C. The nematic mesophases show only a one-dimensional orientation order along the long (rod) or short (disk) molecular axis. This is usually the flow direction during LC resin processing. On the other hand, the smectic mesophase shows a two-dimensional orientation order. These LCS have much in common with crystalline polymers whose molecules are arranged in layers (sheets). The long axis of the (rod-like) molecule is either perpendicular to the plane (smectic A) or tilted at an Angle (smectic C).
This material has many core properties:
● High flowability
● Vibration absorption
● Thin and strong
● Non-halogen
● Flame resistance
● High elastic modulus
● Solder heat resistance
● Metal-like linear expansion rate
LCP materials are useful for a range of applications, including:
● Circuit board (PCB) parts
● Parts for electric motors
● Cookware
● Semiconductor handling devices
● Chip carriers
● Mobile SIM card
● Coiling parts
High temperature materials (like all polymers) comprise two molecular structures: amorphous(randomly ordered) and crystalline (highly ordered). For practical purposes, thermoplastics are either amorphous polymers or semi-crystalline polymers which have both amorphous and crystalline regions.
One of the major differences between the two types is how they respond to temperature. Both amorphous and crystalline high temperature thermoplastics are used in the automotive, aerospace, medical, and electrical electronic industries where demanding properties are required.
By using special reinforcing materials, such as glass fiber, heat distortion resistance and rigidity can be improved even further than that shown by the base polymer. Additives such as fluorocarbon or graphite particles will considerably improve sliding friction characteristics. The rigidity and toughness of the high temperature material are improved remarkably by recombination and modification.
4. High Temperature plastics of characteristics and properties
High temperature plastics are characterized by their high heat resistance, strength, long-term durability, and biocompatibility. In their molecular structure, it is the use of rigid aromatic rings that yields their temperature resistance. High temperature plastic material boasts continuous operating temperatures of over 200°C. Their high-temperature resistance provides many valuable characteristics over other materials such as metal. These include:
● Physical and dimensional stability
● Resistant high and low temperature
● Resistant to harsh chemical and hydrolysis
● Increased design flexibility
● Excellent corrosion resistance
● Excellent noise and vibration damping
● Self-lubricating Function
For any type of high temperature plastic, its mechanical properties, chemical resistance, electrical conductivity, material fatigue, and many other attributes can be affected by increased temperatures. We must consider this point when we choose material in early of part development.
High temperature plastic materials also offer lightweight, corrosion resistance, high dimensional stability, and design flexibility for a wide range of applications in the electrical/electronics, medical, aerospace, and telecommunications industries.
1) Medical devices
Plastic continues to replace standard materials for medical devices due to its greater design flexibility and cost-effective characteristics. Some of the common high temperature thermoplastics employed in the medical field applications include:
● Polyetheretherketone (PEEK) is commonly used as a replacement for stainless steel, and other metals in several medical applications.
● Liquid Crystal Polymers (LCP) are used to replace metal in medical device applications for microsystem technology and minimally invasive surgery.
● Polysulfones (PSU) and polyethersulfones (PES) are commonly used to manufacture parts and membranes of dialyzers, surgical theater luminaries, sterilizing boxes, secretion bottles, reusable syringes, and infusion equipment.
● Polyetherimide (PEI) is used for a myriad of disposable and reusable medical devices.
2) Automotive
Increasing market demands for energy efficiency and fuel economy in the automotive industry are generating significant interest among design engineers to replace metals with high performance thermoplastics material. High temperature thermoplastics have continuous operating temperatures of more than 150°C.
Their high temperature resistant properties provide other performance characteristics that are valuable, these include wear and chemical resistance. High temperature plastics also provide weight savings in many applications (e.g., automotive) and as a result are often considered for metal replacement. The common application of high temperature plastic in the automotive industry include:
● Engines accessories
● Car transmissions accessories
● Automotive under-hood components such as charge air cooler end caps, radiator end tanks, turbo air ducts and resonators, oil pump wheels, EGR valves, and thermostatic casings.
● Electronic connectors
3) Aerospace
In the aerospace market, PEEK polymers are replacing aluminum and other metals in a wide range of applications. The polymer combines outstanding physical and thermal characteristics with light weight and ease of processing.
● Aircraft hardware and fasteners
● Mechanical and structural components
● Transmission and power train components
● Airplane seat covers
● Thermal isolators, sector gears, bushings, and screws
4) Electrical & Electronic
● Wiring, cabling, sleeving and electrical shielding products.
● Appliance handles
● Connectors
6. High temperature plastics processing methods
Almost high temperature plastics can be processed by the same methods as for the commodity plastics. The exception to this is PTFE, which requires special techniques due to the extremely low co-efficient of friction. In our previous article mentioned the processing methods of PTFE, including molding, CNC, etc.
Injection molding and extrusion can make most parts of high temperature plastic materials. but no matter use any process. We should be remember that it is high temperature plastic before begin your project.
7. How to select high temperature plastics
Aligning with your injection molding partner to choose the best resin for your plastic part early in the design for manufacturability process, is crucial to a part’s production success. it is best to identify potential requirements needs through design and application analysis.
For high temperature plastic, any one of these high-performance plastics can really take the heat. However, not just any material will meeting your parts requirement. Engineers must do their research to ensure they’re choosing the heat-resistant plastic that’s the best fit for their particular application. If engineers choose the wrong material, they risk compromising the functionality of their part and having to start from scratch. For new develop parts, material selection is a very important thing.
1) Operation environments
Any plastic material(include high temperature plastic) strength properties may change at extreme temperatures,moist, especially high heat. PFA--we said it is “the king of plastic”, but it’s also not perfect. plastic molecules also break down when exposed to temperatures above 260 degrees for long periods of time.
Most thermoplastic materials have a heat distortion temperature (HDT) of less than 500 F. Although excessively low temperatures can have an impact as well. Materials exposed to higher heat for longer duration will wear substantially faster than those exposed to more moderate temperatures and exposure times. Common high temperature plastic heat distortion temperature (HDT) as following:
2) Stress
High temperatures can reduce stress resistance and lead to creep strain or deformation. Be sure to select a proper material or design the component accordingly. If the appearance of the product is required, sharp corners should be avoided.
3) Degradation potential
In extended exposure to harsh environments such as high heat, materials may be subject to more rapid degradation and loss of strength and structural integrity. Plastic materials subjected to prolonged exposure to high temperatures will lose strength and toughness, becoming more prone to cracking, chipping, and breaking, at a rate in proportion to the temperature and time of exposure.
4) Chemical requirement
Resistance chemical properties must be considered if the final product is exposed to an acid or base for a long period of time, which can destroy the interaction between molecules and seriously affect the stability of the product.
5) The Cost
Almost all high temperature plastics are very expensive, so we need to be very careful when choosing materials, any failure can cost you a lot of money. Once the material is changed, many things related to it have to be changed, including the design, mold, structure and so on.
8. High temperature injection molding core considerations
Matching the right plastic to its ideal application is just one side of the coin. Engineers should also remember many considerations while machining through injection molding using high temperature plastics. these are some of the core elements that we have learned from our experience.
1) Mold temperature is critical
We all know, high temperature injection molding needs high mold temperature, traditional mold uses a cooling system, but high temperature mold needs a heating system. Since your mold needs to be cool enough before ejection and hot enough before injection, the right heat-transfer channels will go a long way to improve efficiency.
Incorporate equidistant heat-transfer channels into your mold design, thus exposing each cavity to equal levels of heating and cooling fluid. the cooling rate will significantly affect the part's dimensions and properties. If the mold temperature is below the recommended level, the part will not achieve full crystallinity and maximum tensile strength, and therefore could potentially fail in use.
2) Proper Mold material--Resistance high temperature steel, high hardness steel
The mold material should withstand high temperatures without warpage. the mold material should strike a balance between abrasion resistance and machinability. High-volume production runs may need high temperature resistant mold material such as high-strength steels. in order to guarantee parts quality, the mold steel hardness should be more than HRC 50 after heat treatment. Common injection mold high-carbon steel includess S136, 316M, etc.
If the mold material is susceptible to high temperatures, it could bring about high replication of the cavity surface and increased flow resistance. Plastic injection at low pressure will most certainly stain the molds known as gate stains. We should select appropriate mold material to avoid these hitches. Design and making an injection mold for high temperature plastic is a vast and complicated topic. There are often multiple ways to achieve the same result. It is difficult and expensive to design a cost-effective mold that produces quality parts under minimal cycle times.
3) Mold add thermal baffle
We know that injection molding is a complex and delicate process, and any small detail may lead to failure. Mold temperature is one of the most important steps in the process of high temperature injection molding because the high temperature plastic material flow performance is very low, and must be heated to a high enough temperature to increase its flow, high temperature molding mold temperature could be as high as 280°C, in order to achieve this constant mold temperature, must add thermal baffle on both ends of the mold, to prevent heat loss, Increase the probability of success.
4) Proper size injection machine
The selection of a proper Injection Machine is a critical factor for molding high temperature plastics. Molding high temperature plastic needs very high temperature. Holding the melt at temperatures above a certain range may result in polymer degradation and unacceptable molding part properties.
Excessive residence time can result in resin degradation, leading to drooling, flash, plate-out, burn marks, and poor mechanical properties of the molded part. It is generally recommended that the estimated residence time should be no more than 6 min for materials such as polyphthalamide (PPA). If the cycle is to be interrupted for longer than 10 min, it is advisable to remove the resin from the molding machine barrel.
5) Barrel Temperature Control
Injection molding engineers must place strict control on the temperature of the barrel, nozzle, and mold temperature to ensure temperature stability in the barrel. The first two kinds of temperature mainly affect the plastic melting and flow of plastic, This molten material temperature will determine injection molding success or field directly. and then a temperature is mainly affecting the flow of plastic and cooling.
Different plastic have different flow performances, the same kind of plastic, due to different sources or grades, the flow performance and decomposition temperature are different, it is due to the average molecular weight and molecular weight distribution caused by different plastic. so in molding must choose a proper barrel temperature in different machines. Especially for temperature sensitive high temperature plastics.
6) Special Modified Injection Machine
Why said must be modified injection machine, have below reasons:
A. Ceramic heater bands
Regular heater brands can’t resist this high temperature, ceramic heater bands are the best choice for processing high temperature resins. because they have built-in insulation that ensures consistent operation and less heat loss.
B. Alloy screw
The regular screw must change to a better alloy screw and must be corrosion resistant. because our regular engineer plastic does not need so high temperature, when the high temperature plastic melted and temperatures up to 350-380°C will release a corrosive gas that will corrode the screw.
The above two small points look very simple, once any point mishandles, the project will be filed.
7) Pay attention to increase the molecular structure of the raw material of the glass fiber
The polymer molecular chain length of the plastic is one of the key variables that determine its properties. The molding process, if not done properly, has the potential to break the chains that existed before molding thereby reducing properties. The length of fiber additives such as glass, carbon or steel will also significantly affect physical properties
9. Summary
No matter what your experience, high temperature plastic injection molding still can be challenging.the
First step should be to ensure all your equipment can withstand the specified temperatures(heater bands, alloy screw, mold temperature control machine). Then, choose properly size machine components that will minimize residence times in the barrel while still achieving optimal injection quality. Finally, according to the reference molding temperature provided by the material supplier and our experience start to inject.
certainly, properly mold temperature also is necessary. any small temperature deviation is enough to cause extensive quality defects. Why do we pay attention so much various factors of high temperature injection molding and ensure everything is ready before the beginning? Besides the high temperature plastic is really difficult to molding, the most important is that this type of material is very very expensive and the cost of failure really is too high.
When considering the intended end use for your injection molding part, understanding key characteristics is essential to selecting the best resin. Contact an Engineer at Amazing Plastics.
