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.
A casting machine makes solid cast PU elastomer parts — wheels, rollers, liners — rather than foam. Hot-cast systems, typically an MDI/TDI prepolymer paired with a curative, deliver premium mechanical properties, while cold-cast systems suit simpler parts at lower cost. Precise component and mold heating drive the cure and the final properties, which is why temperature control matters more here than in almost any other PU process; choosing the right machine comes down to 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.
Ground lifting: a specialized casting application
Answer: Ground lifting (also called slab jacking or polyurethane slab lifting) uses a PU elastomer casting machine to inject a fast-reacting, expanding polyurethane resin beneath a sunken concrete slab or foundation. The resin cures within minutes, expands to fill voids, and lifts the slab back to grade — a lower-disturbance alternative to mudjacking or slab replacement.
Ground lifting work differs from mold casting in three ways: injection is through small drilled ports rather than an open mold, cure speed must be fast enough to lift within minutes without over-pressuring the slab, and the machine needs a portable, heated hose system so the operator can move between injection points on site. Machines built for wheel and roller casting can be adapted for this work, but the metering, hose length and reaction-time settings must be configured for injection rather than mold pouring.
Independent guidance on polyurethane slab lifting methods and material specifications is published by the ASTM (see foamed-in-place polyurethane test standards) and by state transportation research programs such as the National Transportation Library, which has published slab-lifting field studies for pavement and foundation repair.
Operating pain points in ground lifting work
- Over-lift and cracking — injecting too much material too fast can crack or over-raise a slab. Operators need fine shot-volume control and the ability to stop mid-injection, not just a fixed pour cycle.
- Inconsistent reaction time in the field — ambient temperature swings shift cure speed outdoors far more than in a shop. Machines without tight, field-adjustable temperature control produce unpredictable lift results from one job to the next.
- Hose and port clogging — fast-reacting lifting resin can begin curing in the line if the operator pauses between ports. Heated, purge-capable hoses and a mixing head designed for quick-clean are essential for multi-port jobs.
- Portability on site — ground lifting is done at the job site, not in a plant, so tank size, hose reach and unit weight determine how much of a job can be done without repositioning the machine.
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.
Can a PU elastomer casting machine be used for ground lifting?
Yes, with a configuration built for injection: a portable, heated hose system, fine shot-volume control and a fast, field-stable reaction time. It is a distinct application from mold casting — the resin is injected through small ports beneath a slab rather than poured into an open mold.
What is the biggest operating pain point in ground lifting?
Over-lift from imprecise shot control and reaction-time drift caused by outdoor temperature swings. Machines with field-adjustable temperature control and stop-capable metering give operators the precision to lift a slab to grade without cracking it.
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.