The Sigma Mixer for Pencil Lead (also known as Sigma Blade Mixer, Z-Blade Mixer, or Universal Mixer) is the most widely used and reliable heavy-duty kneading mixer for manufacturing high-quality pencil lead (graphite-clay composite) in the pencil industry.
Sigma Mixer for Pencil Lead Video
Key Features & Design
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Blade Type: Double Sigma (Z-shaped) blades
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Counter-rotating, overlapping blades
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Excellent for intense kneading, folding, and shearing
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Bowl Geometry: Sigma-shaped trough (two longitudinal troughs)
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Ensures complete mixing and no dead zones
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Blade Speed: Typically one blade runs at 20–30 rpm, the other at 10–15 rpm (differential speed)
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This creates high shear and thorough dispersion of graphite and clay
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Working Capacity: 50–2000 liters (common sizes for pencil lead: 100–500 L)
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Material of Construction:
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Bowl: Stainless steel (SS304/SS316) or mild steel with hard chrome plating
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Blades: Hardened steel with hard chrome plating for wear resistance against abrasive graphite
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Drive System: Heavy-duty helical gearbox with separate motors or common motor with differential gearing
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Jacketed Design: Steam or thermic fluid jacket for precise temperature control (usually 60–90°C during mixing)
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Water jacket for cooling if needed
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Tilting Mechanism: Hydraulic or manual tilting for easy discharge
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Loading Options: Top open or vacuum loading for binder (CMC, starch, etc.)
Why Sigma Mixer is Ideal for Pencil Lead
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Achieves perfect homogeneous dispersion of graphite powder (80–90% of mix) with clay (kaolin/bentonite), binder (CMC, starch), and lubricants (wax, paraffin).
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Provides high shear force to break down agglomerates and coat graphite particles uniformly.
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Ensures consistent plasticity and extrudability of the dough.
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Prevents overheating of the mix (critical for maintaining graphite properties).
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Handles extremely high viscosity pastes (10,000–100,000 cP).
Typical Mixing Process for Pencil Lead
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Dry mixing of graphite + clay + additives
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Addition of binder solution (CMC/starch in water)
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Kneading at controlled temperature (usually 70–85°C) for 60–120 minutes
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Vacuum application (optional) to remove air bubbles
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Final dough is ready for extrusion, drying, and firing
Salient Features of Sigma Mixer Machine
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Available in Stainless Steel 316, Stainless Steel 304 and Mild Steel materials.
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Stainless Steel polish to matt & mirror finish as per customer’s requirements.
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Mild Steel finish with one coat of red oxide and two coats of epoxy paint.
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Discharge option of hand wheel operated (manual) or hydraulic operated (automatic) offered.
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Jacket for heating or cooling application can be offered.
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Mineral wool insulation with cladding on jacket.
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Tangential designed ‘Z’ blades offered for uniform mixing.
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PTFE made shaft sealing provided for food grade compatibility.
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Minimum gap between trough inner shell & blades removes possibility of sticking product.
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On demand Spray system, vacuum system
Optional Features/Accessories of Sigma Mixer
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Liquid Spray System
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Vacuum System
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Blades Cooling Arrangement
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Screw System
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Automatic Valve Discharge System
Process Operation of Sigma Mixer for Pencil Lead
In Sigma mixer tangential action of mixing and kneading obtained by ‘Z’ type (SIGMA) shaped kneading blades, which rotates very accurately at different speed towards each other causing product to be transferred from one end to another end. Discharge of the finished product is achieved by tilting the container or through the valves at the bottom or by means of an extrusion screw beside the container.
The mixing action is a combination of bulk movement, stretching, folding, dividing, and recombining of the material. The shearing & tearing action of the material against blades and the side walls causes size reduction of the solids. After the time period required for sterilizing the batch has elapsed, the heating circuit shuts of the pneumatics damper (exhaust) opens and cooling operation commences.
In the tangential design, the blades rotate in the trough meeting tangentially. The front blade generally rotates faster than the rear blade usually in the ratio of 3:2. Tangential blades are generally used for material of higher viscosities such as adhesives, rubber compounds, flush colors, dyes, and pigments.
In the overlapping design, the blades overlap above the saddle of the container. Due to the overlapping action, it is necessary that the relative position of the two blades is unchanged, and as a result, both the blades rotate at the same speed. Materials that flow freely or creep down into the blades are mixed using the overlapping blade action. This design offers a faster interchange of material from one blade compartment of the mixer to the other. Overlapping blade action is used for materials of lighter viscosities such as carbon pastes, clay coating, creams, and ointments. The overlapping blade produces a lower kneading and shearing compared to the tangential blade action.
Technical Specification of Sigma Mixer Kneader
| Model | Capacity – Liters | Motor (H.P.) | ||
| Working Capacity approx. | Gross Capacity approx. | General | Heavy Duty | |
| ASM – 50 | 50 Liters | 80 Liters | 5 H.P. | 7.5 H.P. |
| ASM – 75 | 75 Liters | 110 Liters | 7.5 H.P. | 10 H.P. |
| ASM – 100 | 100 Liters | 150 Liters | 10 H.P. | 15 H.P. |
| ASM – 150 | 150 Liters | 200 Liters | 15 H.P. | 20 H.P. |
| ASM – 200 | 200 Liters | 300 Liters | 20 H.P. | 25 H.P. |
| ASM – 400 | 400 Liters | 550 Liters | 30 H.P. | 40 H.P. |
| ASM – 500 | 500 Liters | 750 Liters | 40 H.P. | 50 H.P. |
| ASM – 750 | 750 Liters | 1150 Liters | 50 H.P. | 60 H.P. |
| ASM – 1000 | 1000 Liters | 1500 Liters | 60 H.P. | 70 H.P. |
| ASM – 1500 | 1500 Liters | 2100 Liters | 75 H.P. | 80 H.P. |
| ASM – 2000 | 2000 Liters | 2600 Liters | 80 H.P. | 90 H.P. |
| ASM – 3000 | 3000 Liters | 3800 Liters | 100 H.P. | 120 H.P. |
* Power voltage can be adjusted as per customer’s domestic power voltage requirements.
* Rights of technical improvements & modification reserved.
* Illustrations & dimensions are shown for information purpose only.
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