Shell Resins (Novolac Phenolic System)
High-performance thermoplastic Novolac Phenolic resins engineered for the manufacturing of high-tensile Resin Coated Sand (RCS) and Shell Moulding (Croning Process). Developed for both hot-coating and warm-coating techniques to deliver outstanding thermal stability, rapid cure kinetics, anti-peel back properties, and flawless casting finish.
Engineered Novolac Chemistry for Superior Resin Coated Sand (RCS)
Shell Resin is a specialized solid Novolac-type thermoplastic phenolic resin manufactured specifically for the foundry shell moulding and shell core-making processes (Croning process). Available in yellow-to-amber solid flakes, granules, or liquid solutions, the resin melts uniformly over pre-heated silica sand ($130^\circ\text{C} - 160^\circ\text{C}$) during the mulling process. When crosslinked with Hexamine (Hexamethylenetetramine) and lubricated with high-grade Calcium Stearate, it encapsulates every single sand grain in a smooth, tack-free, free-flowing polymeric envelope.
At BR Chemicals, our Shell Resins are synthesized with tightly controlled molecular weight distribution, strict melting point windows, and minimal free phenol. This ensures foundrymen and sand coaters achieve rapid build-up speed on heated pattern plates ($220^\circ\text{C} - 280^\circ\text{C}$), exceptionally high hot and cold tensile strengths, virtually zero peel-back, and excellent thermal degradation for effortless hollow-core shakeout after pouring.
Engineered for Cycle Speed & High-Tolerance Casting
A proven Novolac binder formulation trusted across India for dry, free-flowing sand coating, rapid curing, and high hot distortion resistance.
Rapid Polymerization
Optimized reactivity with hexamine delivers fast cure cycles and rapid shell build-up rates on heated core boxes, maximizing machine output.
Anti-Peel Back Formulation
Eliminates shell lifting, slumping, and crust cracks during the investment and rollover cycle, preventing scrap in complex tooling.
Superior Hot Strength
Resists severe thermal shock and metal static head pressure without core deformation, finning, veining, or metal penetration.
Effortless Shakeout
Engineered carbon-carbon breakdown ensures fast, residue-free core breakdown, making it ideal for thin-walled hollow cores.
Foundry Applications
- ✓ Manufacturing of Resin Coated Sand (RCS) using hot-coating muller systems
- ✓ Precision shell core production for automobile engine cylinder blocks, heads, and water pump impellers
- ✓ Shell moulding for Grey Cast Iron (CI), SG Iron / Ductile Iron castings
- ✓ Carbon steel, alloy steel, and stainless steel investment-type shell moulding
- ✓ Non-ferrous alloy castings (Aluminium, Copper, Brass, and Bronze valve bodies)
- ✓ Complex hollow cores requiring thin shell walls, light weight, and high venting permeability
The Three Pillars of the Shell Process
Novolac Phenolic Resin
A stable thermoplastic phenolic polymer available in flake or liquid form. It melts across hot sand grains without self-polymerizing until the crosslinker is added.
Hexamine (HEXA) Solution
Hexamethylenetetramine dissolved in water, providing methylene bridges upon thermal decomposition ($>130^\circ\text{C}$) to convert the thermoplastic into a rigid thermoset matrix.
Calcium Stearate Wax
Milled micronized calcium stearate added at the end of mulling to grant dry free-flowability to the sand grains and provide seamless pattern release from hot dies.
Technical Specifications
| Property / Parameter | Flake Shell Resin (Standard Grade) | Liquid Shell Resin (Solvent Grade) |
|---|---|---|
| Chemical Type | Thermoplastic Novolac Phenol-Formaldehyde | Novolac Phenolic Resin Solution |
| Physical Appearance | Pale Yellow to Amber Solid Flakes / Pastilles | Clear Reddish-Brown Liquid |
| Melting / Softening Point | 90°C – 102°C (Capillary / Ball & Ring) | N/A (Liquid at room temp) |
| Hot Plate Gel Time (@ 150°C with Hexa) | 40 – 75 seconds (Tailored to core size) | 45 – 70 seconds |
| Flow Distance (125°C Pellets) | 25 mm – 45 mm | Uniform surface wetting |
| Free Phenol Content | < 1.5% | < 2.5% |
| Hot Tensile Strength (RCS Core) | 2.0 – 3.8 MPa (After 3 min cure @ 230°C) | 2.2 – 3.5 MPa |
| Cold Tensile Strength (RCS Core) | 3.5 – 5.5 MPa | 3.5 – 5.0 MPa |
| Gas Evolution (850°C) | < 14 ml/g | < 15 ml/g |
| Standard Packaging | 25 Kg / 50 Kg Moisture-Proof HDPE Bags | 220 Kg MS / HDPE Drums |
| Shelf Life & Storage | 12 Months below 30°C in dry shaded area | 6 Months below 25°C tightly sealed |
*Values are representative of standard commercial grades. Custom softening points, gel kinetics, and anti-veining modified grades are formulated on request.
Hot Coating Instructions & Safe Storage
Recommended Hot Coating Cycle
- Pre-Heat Sand: Heat dry silica sand (AFS 50–65) to $140^\circ\text{C} - 160^\circ\text{C}$ in the sand heater.
- Resin Addition: Charge sand into the muller, add 1.8% to 3.5% Flake Shell Resin by weight of sand, and mull for 60–90 seconds until the resin completely melts and coats every grain.
- Hardener Addition: Add Hexamine aqueous solution (typically 12%–15% on resin weight dissolved in water) to initiate curing and cool the batch.
- Lubricant Addition: Add Calcium Stearate (approx. 5%–7% on resin weight) once sand breaks into lumps, mulling until free-flowing dry sand is formed.
- Discharge & Aeration: Discharge through a vibrating screen to cool below $40^\circ\text{C}$ before bagging or pneumatic transfer.
Storage & Safety Guidelines
- Moisture Protection: Store flake bags off concrete floors on wooden pallets. Novolac flakes are hygroscopic; keep bags tightly sealed.
- Temperature Control: Store below $30^\circ\text{C}$ away from boilers and direct sunlight to prevent sintering or cake formation of flakes.
- Exhaust Ventilation: Ensure efficient exhaust hoods over sand mullers and shell core machines to evacuate hexamine ammonia fumes during cure.
- Personal Protection (PPE): Use safety glasses, dust masks during sand mulling, and thermal heat-resistant gloves when handling hot shell cores.
Order Premium Shell Resins for Your Sand Coating Facility
Need high-strength flake resin, liquid solutions, or customized gel-time formulations? Connect directly with our foundry chemical specialists to receive technical data sheets, batch test reports, and factory-direct price quotes.
