Former Dip, Mould Cast, and Flat Spread
Safety. Liquid concentrates carry ammonia and metal-hygiene rules (no copper or brass in dip or leach contact). Coagulant salts and heat sensitizers are plant chemicals. See Allergy and Skin Contact.
Executive summary
Liquid latex does not have one casting method. Former dipping builds film on a shape you withdraw from a tank. Mould casting gels latex inside a cavity (plaster absorption or metal heat-gel; slush or rotational). Spreading coats fabric with doctor blades on an industrial proofing line.
Straight dips are thin per pass. Coagulant and heat-sensitized branches build thicker walls. Use this after Forming film from liquid latex. The five-question tree routes geometry, thickness, mould type, metal hygiene, and spread equipment.
Forming map
Dipping deposits on a former. Moulding replicates a cavity interior. Spreading coats fabric with doctor blades. Aqueous latex dries slower than solvent doughs, so production lines run fabric slower.
What is a former vs a mould?
A former is the positive shape you dip into latex, like a glove form or a mannequin arm. A mould is a cavity you pour or rotate latex inside, like a plaster body cast or a closed metal slush mould. Dipping builds film on the outside of the shape. Casting builds film on the inside wall of the cavity.
Spreading, dipping, and fabric impregnation were already distinct industrial routes in a 1932 process map.
Former dipping
Straight dip: about 0.01–0.05 mm dry rubber per pass. Multi-dip builds gauge. Coagulant dip: coat the former with a coacervant, dwell, withdraw a gelled shell. Above about 8 mil dry thickness, coagulant is usually the economical branch. Warm leach and staged cure follow. Rotate formers between dips.
What does coagulant mean in dipping?
A coagulant is a chemical bath, often a salt solution, applied to the former before latex. It makes the liquid rubber gel on contact so each coat builds thickness instead of running off. Coagulant is a film-building step. It is not the same as coalescence, which is how rubber particles in a water-based glue merge into a solid film after you spread the glue.
Porcelain formers resist coagulant and latex. Mount them so air is not trapped on immersion. Equipment must exclude copper, brass, and galvanized iron.
Detail: Coagulant dipping for wearable thickness.
Mould casting
Plaster: water absorption plus calcium ions gel the latex. Dry completely before cure or you get blisters. Moulds erode at sharp edges. Cheap, short life.
Heat-sensitized (Kaysam class): closed nonporous mould, biaxial rotation while heating. Handbook example: about 4 minutes at 82 °C to gel. Then cool, leach, supported dry, warm-air cure. Ammonium nitrate sensitizer is added just before use. Avoid entraining air.
Slush vs rotational. Slush: fill, dwell, pour out excess. Thickness follows compound stability and cavity geometry. Rotational: meter compound, rotate while heating. Thickness follows compound mass versus cavity area. More uniform walls. Needs rotation equipment. Do not use rotational plaster moulds; they are too heavy and fragile.
What is slush vs rotational casting?
Slush casting pours latex into a mould, lets it gel on the walls, then pours out the excess. Rotational casting spins a closed mould so latex coats the interior evenly. Rotational wants dedicated equipment and timing.
Detail: Heat-sensitized gelation.
Flat spread
Industrial spreading uses flexible rubbery polymers so the coat stays flexible at room temperature. Advantages versus solvent doughs include the absence of flammable solvents. Disadvantages include fabric shrinkage or staining and slower drying, so the fabric runs slower.
Doctor blade: a sharp acute angle gives a thin coat with little strike-through. A blunt perpendicular blade gives a thick coat and more penetration.
This is textile proofing equipment.
Decision tree (five questions)
Q1. Geometry
Positive withdrawable shape → former dip. Enclosed cavity → mould cast. Continuous fabric width → spread line.
Q2. Thickness
Thin per-pass straight dip (about 0.01–0.05 mm dry) → multi-dip. Target above about 8 mil dry → coagulant branch. Hollow thick walls → slush or rotational inside a closed mould.
Q3. Mould material
Plaster or porous → dry completely before cure. Heat-sensitive metal closed mould → heat-sensitized gel cycle. Do not run Kaysam-style rotation on an open tray.
Q4. Metal hygiene
No copper or brass in dip tanks, leach water, or mould hardware contact. Metal catalysis accelerates aging. See Liquid aging, storage, and care.
Q5. Spread equipment
Doctor-blade textile line with speed matched to aqueous dry time → spread branch. A tabletop puddle without plant blade geometry is not documented as equivalent to industrial spread.
Branch mix-ups
- Kaysam-style rotation on an open tray. Heat-sensitized gel wants a closed mould.
- Spread-blade production cards on plaster slush. Plaster must dry completely before cure.
- Straight-dip pinhole logic on a thick plaster cast. Air entrapment and dry-before-cure are different failure modes.
Pair with Liquid reinforcement and laminate zones for multi-dip builds and Liquid ventilation and ammonia during compound and dip work.
Deep dives (optional)
Deep dive: Straight dip thickness vs viscosity
Gorton data: deposit thickness scales approximately with log(viscosity) when total solids and viscosity co-vary by water dilution. Single-dip band about 0.01–0.05 mm dry. Multi-dip offsets pinhole alignment.
Deep dive: Tie-coat sequences
On smooth glass formers, coagulant-first or latex-first tie-coat sequences appear to improve wetting. A final coagulant dip is optional; industrial practice recommends it for chloroprene.
Deep dive: Kaysam cycle
Example NR compound with ammonium nitrate sensitizer. Rotation gel at 82 °C. Leach 15–27 °C. Dry 82 °C at least 3 hours, supported. Cure 104 °C for 20–60 minutes, thickness-dependent. Handbook example, not a craft recipe.
Deep dive: Slush vs rotational thickness
Slush thickness depends on colloid stability (recycled compound destabilizes unpredictably) and cavity geometry. Rotational thickness is roughly a function of compound mass and cavity area.
Deep dive: Spreading blade geometry
Knife-over-roll multi-pass heated belt, and knife-over-diaphragm for delicate fabric. Industrial plant cards. Aqueous dry rate sets line speed.