Quick answer. Hot cast with MOCA needs a heated, agitated curative melt tank (115-125°C) and a 100-110°C mold, because MOCA is a solid at room temperature and only reacts fast enough once molten.
Cold cast with BDO runs a liquid curative near ambient to 40°C and an 80-100°C mold, cutting demold time. TDI prepolymer pairs almost exclusively with MOCA for cast elastomer parts; MDI prepolymer pairs more often with BDO for faster-cycle work.
A casting machine quote that lists “heated tanks” without naming the curative is incomplete. This guide breaks down what changes in tank design, mold temperature, and metering ratio when the curative or prepolymer type changes.
Why the Curing Agent Determines the Machine Configuration
4,4′-Methylenebis(2-chloroaniline), known industry-wide as MOCA or MBOCA (CAS 101-14-4), is a solid flake curative with a melting point around 104-110°C. It cannot be metered accurately until it is molten and held there.
1,4-Butanediol (BDO, CAS 110-63-4) is a liquid at room temperature, with a melting point near 20°C. It can be pumped cold or lightly warmed, which removes an entire heated-tank subsystem from the machine.
That single physical-state difference is why a MOCA-rated casting machine and a BDO-rated casting machine are not interchangeable without retrofitting the curative dosing side.
For a buyer converting an existing line, that gap decides whether the retrofit is a same-week pump swap or a full tank replacement with a longer lead time and re-piping.
Hot Cast with MOCA: Tank, Temperature, and Handling Requirements
Curative Melt Tank and Moisture Control
A hot cast machine built for MOCA needs a jacketed, agitated melt tank holding the curative at 115-125°C, well above its melting point, to keep viscosity low enough for gear-pump metering.
The prepolymer side runs cooler, typically 60-80°C, since NCO-terminated prepolymers degrade faster at MOCA melt temperatures.
Both tanks need a dry nitrogen blanket or desiccant breather. Atmospheric moisture reacts with free NCO groups and generates CO2 bubbles inside the cast part.
Mold Heating and Post-Cure Schedule
Mold plates or ovens are typically held at 100-110°C for MOCA-cured TDI prepolymer systems. Demold time commonly runs 30-60 minutes depending on part thickness and %NCO.
Post-cure is not optional with MOCA systems. Sixteen hours at 100-110°C is the industry-standard schedule to complete crosslinking and stabilize hardness, tensile strength, and compression set before the part ships.
MOCA handling carries specific regulatory weight. In the United States it has its own OSHA standard, 29 CFR 1910.1014.
That standard covers exposure monitoring, medical surveillance, and protective clothing for anyone handling the molten curative.
In the EU, MOCA sits on the REACH Annex XIV Authorisation List, meaning it cannot be placed on the market or used past its sunset date without an authorization.
A dosing station built for MOCA should include closed transfer, local exhaust at the melt tank lid, and a documented cleaning procedure for the loading area.
Cold Cast with BDO: Lower Temperature, Faster Cycle Configuration
Because BDO is already liquid, the curative side of a BDO machine is a small, low-flow precision pump feeding from an unheated or 30-40°C day tank rather than a melt tank.
This shrinks the machine footprint and removes the melt-tank warm-up step from every start-of-shift routine.
Mold temperature for BDO systems commonly runs 80-100°C, roughly 20°C below a comparable MOCA line. Demold times of 10-20 minutes are achievable on fast-gelling MDI/BDO formulations, versus 30-60 minutes for MOCA/TDI.
Post-cure schedules still apply, typically 4-16 hours at 100-110°C depending on the target Shore hardness and compression-set spec, but the shorter demold time raises mold turns per shift.
BDO is not listed on the REACH Annex XIV Authorisation List and does not carry a dedicated OSHA standard the way MOCA does, which simplifies paperwork around the dosing station.
Standard isocyanate PPE requirements on the prepolymer side still apply regardless of which curative is paired with it.
TDI Prepolymer vs MDI Prepolymer: What Changes at the Metering Station
TDI-based cast elastomer prepolymers typically run 3-9% free NCO. They have been paired with MOCA for cast urethane wheels, rollers, screens, and mining and aggregate wear parts for decades.
That pairing is still the default because MOCA’s slower gel time gives operators enough working time to fill large or thick-walled molds without air entrapment.
MDI-based prepolymers, typically 4-10% NCO, have markedly lower vapor pressure than TDI at processing temperature. That is one reason MDI systems are preferred where operator exposure control is a tighter constraint.
MDI is also more often paired with fast-reacting BDO for CASE work (coatings, adhesives, sealants, elastomers) rather than for large, thick cast parts.
On the machine, this shows up as two different metering ratio ranges. MOCA dosing typically sits in a 5-15 phr (parts per hundred resin) window depending on %NCO, requiring a larger heated metering circuit.
BDO dosing typically sits in a 2-6 phr window, requiring a smaller pump but tighter flow-rate accuracy, since the working window is narrower and the reaction starts faster after mixing.
| Parameter | Hot Cast (MOCA / TDI prepolymer) | Cold Cast (BDO / MDI prepolymer) |
|---|---|---|
| Curative physical state | Solid flake, melts ~104-110°C | Liquid, melts ~20°C |
| Curative tank requirement | Jacketed, agitated, N2-blanketed melt tank at 115-125°C | Unheated or 30-40°C day tank, precision low-flow pump |
| Prepolymer tank temperature | 60-80°C | 50-70°C |
| Mold temperature | 100-110°C | 80-100°C |
| Typical demold time | 30-60 minutes | 10-20 minutes |
| Post-cure schedule | 16 hours at 100-110°C (standard) | 4-16 hours at 100-110°C (formulation dependent) |
| Typical curative dosing | 5-15 phr | 2-6 phr |
| Common prepolymer type | TDI, 3-9% NCO | MDI, 4-10% NCO |
| Regulatory handling note | OSHA 29 CFR 1910.1014; REACH Annex XIV | No dedicated OSHA standard; not Annex XIV listed |
| Typical parts | Wheels, rollers, screens, wear/mining liners | Fast-cycle CASE parts, seals, thinner-section moldings |
Choosing the Right Casting Machine for Your Production
Start from the resin system, not the machine brochure. If a supplier’s formulation sheet specifies MOCA, the machine needs a heated melt tank, N2 blanket, and a mold heating system rated to at least 110°C.
A BDO-configured machine cannot substitute without adding that entire subsystem, and the reverse retrofit wastes the melt tank a BDO line never uses.
Check the metering pump’s turndown ratio against the phr range you actually need. A pump sized for 5-15 phr MOCA dosing will struggle to hold accuracy at a 2-6 phr BDO setpoint, and the reverse is also true.
Ask for the mold-heating zone count and control tolerance, and treat a single “mold temperature” figure on a spec sheet as incomplete. Uneven heating across a large mold produces differential cure and warpage even when the average reading looks correct.
As a manufacturer, we build both curative-tank configurations to order. Metering pump range is set for the specific prepolymer and curative combination a buyer supplies, rather than shipped as one fixed generic tank.
Machines built for export carry CE electrical and pressure-equipment documentation. Ask for it before the tank is fabricated; adding compliance labeling after the build delays shipment.
MOQ and lead time scale with tank volume, heating capacity, and control-panel customization, so a single-tank pilot line and a multi-station production line quote differently.
Our polyurethane casting machine line covers both hot cast MOCA and cold cast BDO builds.
Our casting process guide covers the degassing and mixing steps upstream of the curative decision.
FAQ
Q: Can one casting machine run both MOCA and BDO?
Only if it is built with both a heated melt tank for MOCA and a separate low-flow pump circuit for BDO, plus full purge-and-clean procedures between changeovers. Most production lines dedicate one machine per curative to avoid cross-contamination and changeover downtime.
Q: Why does MOCA need 16 hours of post-cure but some BDO systems need less?
MOCA’s slower reaction kinetics mean the crosslink network is not fully developed at demold; the extended 100-110°C post-cure completes it. Some fast BDO/MDI systems reach a higher percentage of final crosslink density before demold, so a shorter post-cure can still meet the hardness and compression-set target on the datasheet.
Q: Is TDI prepolymer more hazardous to handle than MDI prepolymer?
TDI has a higher vapor pressure than MDI at the same processing temperature, so TDI lines generally need tighter local exhaust ventilation and vapor monitoring at the mixing head. Both require SDS-specified PPE regardless of which curative is used.
Q: What mold temperature tolerance should a hot cast machine hold?
±2°C across the mold surface is a reasonable working tolerance for MOCA systems. Wider swings show up as localized hardness variation and can shift demold time by several minutes zone to zone.
Q: Do you supply the curative dosing tank customized to a specific MOCA or BDO formulation?
Yes. Tank volume, heating capacity, agitator type, and metering pump range are configured to the %NCO and curative loading a buyer specifies, rather than shipped as one fixed generic setup. Minimum order quantity and lead time depend on tank size and control panel customization.
