In electrical engineering, plastic components carry current, insulate it or enclose parts that can become hot in a fault. Housings for switchgear, connectors and insulators therefore need fire protection that works across the entire service life.
This article explains how flame retardants work, which classes and standards apply, how they affect material and processing – and what to watch when selecting them.
The key points at a glance
- Additive or reactive. Additive flame retardants are blended into the plastic, reactive ones bond chemically to the polymer. Reactive types cannot be washed out but are not available for every material.
- UL 94 is the common benchmark. Classes range from HB to V-0. V-0 is frequently required for electrical components – but the product standard of the application is what counts.
- The additive changes the material. Mineral fillers can make parts more brittle, and many systems alter flow behaviour and surface quality.
- Processing becomes more demanding. Flame-retardant compounds flow differently and can be abrasive. This affects mould design, process window and tool wear.
- Documentation is part of it. Material identification, traceability and REACH and RoHS conformity belong to supply capability, not just to the technology.
How flame retardants work
There are two basic types. Additive flame retardants are blended into the plastic without altering the polymer structure. These include halogenated compounds, phosphorus compounds and mineral fillers such as aluminium hydroxide. Reactive flame retardants bond chemically to the polymer – they cannot be washed out or outgas, but are not available for every material.
The mechanisms differ: mineral fillers such as aluminium hydroxide release water under heat and thereby cool the material. Phosphorus compounds promote the formation of a protective carbon layer that impedes oxygen access. Halogenated systems intervene in the combustion reaction in the gas phase.
Classes and standards
The most common benchmark is UL 94. The classification describes how a material behaves after exposure to flame – from HB (slow burning in horizontal position) through V-2 and V-1 to V-0, where the specimen self-extinguishes quickly and does not drip while burning. V-0 is frequently required for electrical components.
- UL 94: classification of burning behaviour, the basis for many material approvals.
- IEC 60695: series on fire hazard testing, including the glow-wire test that simulates an overheated component.
- ISO 5659-2: determination of smoke density – in enclosed spaces often as safety-relevant as the flame itself, because smoke obscures vision and can be toxic.
- REACH and RoHS: restrict the use of certain substances and are a prerequisite for marketability in the EU.
Which class is actually required does not follow from UL 94 itself but from the product standard of the respective application – for household appliances, switchgear assemblies or building services, for example. Requirements also differ between Europe, North America and Asia.
Selecting material and flame retardant together
Polyamides (PA), polycarbonates (PC) and polyphenylene sulphides (PPS) are frequently used in electrical engineering. They offer mechanical strength and process well. What matters, however, is not the plastic alone but the compound of polymer and flame-retardant system.
- PA 6 / PA 66: typically with aluminium hydroxide or phosphorus compounds – used for connectors and switch housings.
- PC and PC/ABS: typically halogen-free with phosphorus compounds – used for luminaire housings and operating elements.
- PPS: typically with silicates and phosphorus compounds – used for sensor housings and motor components.
The additive does not come without consequences: mineral fillers increase stiffness but can make the part more brittle. Halogen-free systems often require higher loading levels, which impairs flow behaviour. And every flame retardant must withstand the processing temperature of the plastic without decomposing.
What flame retardancy means for processing
Flame-retardant compounds behave differently in injection moulding from unfilled standard grades. For mould and process this means:
- Flow behaviour: higher loading levels impair flow. Gate position, flow path length and wall thicknesses must be designed accordingly.
- Tool wear: mineral-filled compounds are abrasive. This requires higher-grade, hardened tool steels and defined maintenance intervals – also relevant for moulds taken over via tool transfer.
- Process window: excessive melt temperatures or long residence times can damage the flame retardant – and with it the protective effect.
- Drying: many of the materials used are hygroscopic. Insufficient pre-drying shows up as surface defects and reduces mechanical properties.
It is therefore advisable to bring material supplier, design and processor together early – ideally before mould design begins.
Flame-retardant components at Schröder + Heidler
We manufacture technical plastic components for electrical engineering and match mould design and process control to the respective material. Because mould making and injection moulding are located at one site, adjustments after sampling can be implemented without detours.
Material certificates and documented traceability are standard – our processes are certified to ISO 9001 and IATF 16949. Release of the specific compound for your application is carried out together with you and the material manufacturer. Assembled units can be supplied via our subassembly assembly.
Frequently asked questions
Which flame retardancy class does my part need?
This is not specified by UL 94 itself but by the product standard of the application – for household appliances, switchgear assemblies or building services, for example. V-0 is frequently required for electrical components. Requirements also differ between Europe, North America and Asia.
What is the difference between halogenated and halogen-free systems?
Halogenated flame retardants intervene in the combustion reaction in the gas phase and are effective at low loading levels. Halogen-free systems based on phosphorus or minerals usually require higher loadings but release fewer toxic gases in a fire and are often easier to recycle.
Does flame retardancy change mechanical properties?
Yes. Mineral fillers increase stiffness but can make the part more brittle. Higher loading levels also impair flow behaviour, which affects gate position and wall thicknesses. Selection should therefore go hand in hand with part design.
Why do moulds wear faster with flame-retardant plastics?
Mineral-filled compounds are abrasive on gate, cavity and ejectors. This requires higher-grade, hardened tool steels and shorter maintenance intervals. Both belong in mould design, not in later maintenance.
Can every plastic be made flame retardant?
In principle many thermoplastics can be modified, but not every flame-retardant system suits every polymer. What matters is the finished compound – and that its processing temperature suits the material so the additive does not decompose.
Conclusion: the compound decides, not the plastic
Flame retardancy in injection moulding is not an afterthought but a decision that affects material, part geometry, mould and process together. Knowing the required class and the associated product standard early avoids later correction loops on the mould.
Planning a flame-retardant component for electrical engineering? Talk to us about material and mould concept.