A PU elastomer casting machine meters, mixes and dispenses liquid polyurethane elastomer systems into open or closed molds to produce solid, high-performance parts — wheels, rollers, screens, liners, bushings and seals. Unlike foam machines that make cellular products, casting systems handle dense, often hot-cast elastomers where mechanical strength and abrasion resistance are the goal.
This guide covers how elastomer casting works, hot vs cold systems, the machine components and specifications that matter, and how to choose for your parts. For the wider equipment picture, see our complete guide to polyurethane machines.
TL;DR
- What it makes: solid cast PU elastomer parts (wheels, rollers, liners), not foam.
- Hot vs cold cast: hot-cast (e.g. MDI/TDI prepolymer + curative) for premium properties; cold-cast for simpler parts.
- Temperature is everything: precise component and mold heating drive the cure and final properties.
- Choose by: system chemistry, shot size, ratio accuracy and degassing.
How elastomer casting works
In casting, the machine heats and meters a polyol or prepolymer stream and a curative (or isocyanate) stream, mixes them, and pours the blend into a mold. The mixture cures into a dense elastomer with no intentional cell structure. Because these systems are temperature-sensitive and often moisture-sensitive, the machine must hold tight temperature control and, for many chemistries, vacuum degassing to avoid bubbles in the finished part.
Cast PU elastomers are prized for abrasion resistance, load-bearing capacity and toughness. Material test methods for hardness, tensile and abrasion are published by ASTM, and general PU chemistry guidance is available from the Center for the Polyurethanes Industry.
Hot-cast vs cold-cast systems
| Factor | Hot cast | Cold cast |
|---|---|---|
| Temperature | Components and molds heated | Near ambient processing |
| Properties | Highest strength and abrasion | Good for less demanding parts |
| Typical parts | Wheels, rollers, mining screens | Simple liners, light-duty parts |
| Process control | Tighter temperature and timing | More forgiving |
Core components of a casting machine
- Heated tanks — temperature-controlled storage for prepolymer and curative.
- Metering pumps — accurate ratio dosing, often for high-viscosity streams.
- Mixing head — dynamic mixing suited to viscous elastomer systems.
- Degassing — vacuum conditioning to prevent voids.
- Temperature control — for tanks, lines, head and (often) molds.
- Pour control — shot timing and volume for repeatable parts.
Key specifications
- System chemistry — match the machine to your prepolymer/curative (TDI, MDI, PPDI, etc.).
- Shot size and throughput — cover your smallest and largest parts.
- Ratio accuracy — critical for consistent hardness and cure.
- Viscosity handling — pumps and lines sized for the chemistry.
- Degassing capability — essential for void-free, load-bearing parts.
How to size and select a casting system
Start from the part, not the machine. Define your largest and smallest shot weight, your fastest required cycle, and the hardness range across your product mix. Then match three things: pumps sized for your chemistry's viscosity, temperature control that holds the cure window for your prepolymer, and degassing capacity that keeps your largest pour void-free. A system that is accurate but slightly under-sized on throughput is recoverable; one that cannot hold ratio or temperature for your chemistry will fight you on every batch. If you run several chemistries, prioritize flexible temperature control and easy head cleaning over raw speed. Verify the supplier has run your specific system family in production, and ask for hardness and abrasion data from comparable parts.
Applications
- Wheels and tyres for forklifts and AGVs
- Industrial rollers and sleeves
- Mining and aggregate screens
- Liners, scrapers and seals
- Bushings, bumpers and vibration parts
See related dispensing and foaming equipment on our PU machines hub, and compare machine classes in our buyer's guide.
Common casting defects and how to avoid them
- Bubbles and voids — almost always inadequate degassing or moisture in the system; verify vacuum and dry your fillers and molds.
- Soft spots or uneven hardness — ratio drift or poor mixing; check metering accuracy and head condition.
- Premature gel — temperature too high or pot life exceeded; tighten temperature control and pour timing.
- Surface tackiness — incomplete cure or moisture exposure; review cure schedule and post-cure.
Nearly every casting defect traces to temperature control, ratio accuracy or degassing. A machine that holds all three is what separates consistent load-bearing parts from a high reject rate.
What drives the cost of a casting system
- Chemistry and temperature needs — hot-cast systems require more heating and tighter control than cold-cast, raising cost.
- Degassing capability — vacuum systems add cost but are essential for void-free, load-bearing parts.
- Shot size and throughput — larger parts and higher volume need bigger metering and tanks.
- Automation — automated pour and mold handling improve repeatability at higher capex.
As with foam machines, the real cost is scrap: a casting system that holds temperature and ratio pays back through void-free, dimensionally consistent parts and far fewer rejects.
Frequently asked questions
What is a PU elastomer casting machine?
A machine that meters, mixes and pours liquid PU elastomer systems into molds to make dense, solid parts such as wheels, rollers and liners — not cellular foam.
What is the difference between casting and foam machines?
Casting makes solid elastomers for strength and abrasion resistance; foam machines make cellular products (rigid or flexible foam). The chemistry, temperature control and degassing requirements differ.
Why is degassing important in casting?
Vacuum degassing removes dissolved air so the cured part is void-free, which is essential for load-bearing and abrasion-resistant components.
Hot cast or cold cast — which do I need?
Hot cast delivers the highest mechanical properties for demanding parts like wheels and screens; cold cast suits simpler, lighter-duty components.
Can a casting machine also make foam?
No — casting systems are built for dense, often hot, high-viscosity elastomer chemistries with degassing, while foam machines are optimized for fast-reacting cellular formulations. The metering, temperature control and mixing are different. Choose the machine for the product family you actually make.
What hardness range can cast PU elastomers reach?
Cast polyurethanes span a wide hardness range from soft to very hard, set by the chemistry and ratio. Because hardness depends on accurate metering and full cure, a machine that holds ratio and temperature is what makes a target hardness repeatable across batches.
Why does temperature control matter so much in casting?
Hot-cast chemistries cure within a defined temperature window. If component or mold temperature drifts, you get premature gel, soft spots or incomplete cure. Tight temperature control across tanks, lines, head and molds is the foundation of consistent cast parts.
Casting wheels, rollers or industrial parts? Tell us your chemistry (TDI, MDI or PPDI), your part size and hardness range, and your annual volume, and we will scope the right casting system — metering, temperature control and degassing matched to your application. Explore our PU machines range to get started, or compare machine classes in our buyer's guide.