Mixer and Extruder Types — Where Helical Gears Are Used
Three distinct machine types in the mixing and extrusion industry use large-module helisel dişli drives, each with different load characteristics:
Internal (Banbury) Rubber Mixer
An internal mixer kneads rubber compounds between two counter-rotating rotors inside a closed chamber. Rotor speed: 15–40 RPM. The critical load event — frozen charge restart — occurs when mixed compound solidifies during an unplanned shutdown. Restarting against the frozen charge generates torque peaks of 3–5× rated torque at essentially zero speed. The helisel dişli output shaft torques reach 150,000–600,000 N·m on large 600-litre machines. This is the most demanding peak torque event in any industrial gearbox application.
Twin-Screw Extruder
Co-rotating or counter-rotating twin screws process plastics, food compounds, or adhesives in continuous operation. Screw speed: 100–600 RPM (higher than rubber mixers). Output torque per screw: 1,000–30,000 N·m. Shock events: metal contamination in feed (tramp iron) causes instantaneous load spikes. The helisel dişli distribution gearbox must distribute equal torque to both screws — requiring matched output helisel dişliler and a common input pinion.
Planetary or Sigma Blade Mixer
Chemical, pharmaceutical, and food mixers rotate a blade or anchor impeller at 10–60 RPM. Output torques are moderate (5,000–50,000 N·m) compared with rubber mixers, but the gearbox must handle frequent batch processing with variable filling levels — creating a varying load profile that requires accurate service factor assessment. The helisel dişli gearbox typically includes a mechanical torque limiter to protect the mixer vessel and drive from overload during a material jam.
Service Factor — Why KA Reaches 3.0–4.0 in Rubber Mixer Drives
The service factor for mixer and extruder helisel dişli drives is the highest of any application category in regular industrial service, for two independent and cumulative reasons:
| Load Event | Torque Multiple | Duration | Frequency | KA Contribution |
|---|---|---|---|---|
| Normal mixing cycle peak | 120–150% rated | 10–30 s per cycle | Every batch | KA ≈ 1.50 base |
| Sudden temperature drop (compound stiffening) | 150–200% rated | 2–5 min | Several times per shift in cold weather | +0.25–0.50 to KA |
| Normal cold startup with partially cured charge | 200–300% rated | 5–20 s | Every shift startup | +0.50–0.75 to KA |
| Frozen charge restart (worst case) | 400–500% rated | Up to 30 s until charge breaks loose or protection trips | Rare but must be survived | Governs static tooth fracture check |
Recommended KA values for mixer/extruder helical gear drives (AGMA 2101 / Korea Ever-Power field data):
Twin-screw extruder (DOL motor, no tramp protection): KA = 1.75–2.25
Chemical/pharmaceutical planetary mixer: KA = 1.75–2.50
Rubber mixing mill (open mill, 2 rolls): KA = 2.00–2.50
Internal (Banbury) rubber mixer (fluid coupling): KA = 2.50–3.00
Internal rubber mixer (DOL motor, no fluid coupling): KA = 3.00–4.00
Note: The frozen charge torque peak (400–500%) must additionally be checked against
the tooth root static bending stress limit using the static safety factor S_F_stat ≥ 1.0
at the peak overload — separate from the fatigue KA check at rated torque.
Material and Module Selection for Mixer Helical Gears
Büyük modül helisel dişli for rubber mixer gearbox — 42CrMo4 forged, induction hardened HRC 50–55, module M24. At output torques of 150,000–500,000 N·m and rotor speed 15–30 RPM, the required module and face width are determined by the frozen charge restart torque (400–500% of rated), not the normal operating load, making this one of the highest unit-load helisel dişli applications in industrial manufacturing
Section Size and Heat Treatment Constraints
A rubber mixer output shaft helisel dişli at M32 with z = 30 teeth has a pitch diameter of approximately 1,000 mm and a blank cross-section of 900–1,100 mm diameter. This section size is beyond the hardenability capability of 20CrMnTi (which reliably hardens through sections to approximately 300–400 mm diameter). The correct material choice depends on the required surface hardness and the available heat treatment:
42CrMo4 + Induction Hardening
The standard choice for large-section mixer helisel dişliler (OD 500–2,000 mm). The blank is QT to HB 280–320 through-section, then individual teeth or tooth zones are induction hardened to HRC 50–55. The QT core at HB 280–320 provides the toughness needed for frozen charge restart impacts. Induction hardening acts locally — no through-section thermal distortion. σ_H lim = 820–950 MPa; σ_F lim = 340–380 MPa at tooth root.
17CrNiMo6 + Gas Carburizing (Smaller Modules)
For extruder and pharmaceutical mixer gears in M8–M20 (OD 200–600 mm), 17CrNiMo6 carburized to HRC 58–62 provides σ_H lim = 1600–1800 MPa — enabling more compact, lighter gearboxes for the same torque capacity. Carburizing is feasible for sections up to approximately 500 mm diameter in 17CrNiMo6. For larger sections, 42CrMo4 induction is the only practical route.
Module and Face Width Selection
The module and face width for a mixer helisel dişli are typically governed by the frozen charge peak torque rather than the rated operating torque — the static tooth root bending check at 400–500% of rated torque with S_F_stat ≥ 1.0 sets the minimum module:
Static tooth root bending check (at frozen charge peak torque T_peak):
F_t_peak = 2 × T_peak / d₁
σ_F_static = F_t_peak / (b × Mn) × Y_Fa × Y_Sa × Y_ε × Y_β × KA_static
where KA_static = T_peak / T_rated (peak overload factor) × KA_base = 4.0–5.0
Required: σ_F_static ≤ σ_F_lim_static (ISO 6336-3 static allowable ≈ 2.0 × σ_F_lim_fatigue)
Example: 600-litre rubber mixer, T_rated = 150,000 N·m, T_peak = 600,000 N·m
With M32, z=30, b=500mm, 42CrMo4 induction, σ_F_lim_static ≈ 760 N/mm²:
σ_F_static ≈ (2 × 600,000,000)/(d₁ × 500 × 32) × geometry factors × 1.0
→ Module M32 is just adequate; M36 provides comfortable S_F_stat ≥ 1.2
Drive Architecture and the Fluid Coupling’s Role
Most large rubber mixer helisel dişli drives include a fluid coupling (hydrodynamic coupling) between the motor and the gearbox input shaft. The fluid coupling limits the transmitted torque during startup — when the motor torque would otherwise be 250–350% of rated at stall — and provides a degree of impact protection during frozen charge restart. However, the fluid coupling does NOT eliminate the frozen charge torque peak: as the coupling fills and approaches synchronous speed, it briefly passes through a torque multiplication zone that can transmit 150–200% of rated torque to the gearbox. The frozen charge peak load still governs the helisel dişli tooth root bending check even with a fluid coupling in the drive line.
Lubrication for Low-Speed, High-Torque Helical Gear Drives
Mixer and extruder helisel dişli drives operate at very low pitch-line velocities (0.5–3 m/s) where churning loss is negligible but the EHL film thickness is significantly thinner than in high-speed gearboxes. The EHL film thickness h_min ∝ v^0.68 — at v = 1 m/s, the film is approximately 8–10× thinner than at v = 10 m/s for the same oil viscosity. To compensate, mixer gearboxes specify significantly higher oil viscosity than fast-running gearboxes:
Recommended viscosity for mixer/extruder helical gear drives (DIN 51517 CLP mineral oil):
v < 0.5 m/s (extremely slow, rubber mixer final stage): ISO VG 680–1000
0.5–2 m/s (slow, typical mixer intermediate stage): ISO VG 320–680
2–5 m/s (extruder intermediate speed): ISO VG 220–320
The high viscosity mineral oils specified for slow mixer helisel dişliler have excellent boundary lubrication additive packages (extreme pressure EP sulphur-phosphorus) that protect the tooth surfaces during the brief elastohydrodynamic film breakdown events that occur at the frozen charge peak load. PAO synthetic oils are increasingly used in mixer gearboxes to extend oil change intervals (3–5 years vs 1–2 years for mineral oil) and to maintain oil flow at cold startup in winter conditions.
Korea Ever-Power — Large Module Mixer Helical Gear Capability
Korea Ever-Power manufacturing and inspection of large-module helisel dişliler for mixer and extruder gearboxes — M16–M50 in 42CrMo4 induction hardened or 17CrNiMo6 carburized, with frozen charge static bending check, hardness survey, and gear analyser measurement included in the order documentation
Korea Ever-Power üretiyor helisel kesimli dişliler for rubber mixer and extruder gearboxes in M8–M50, OD 200–2,500 mm, in 42CrMo4 induction hardened (HRC 50–55) and 17CrNiMo6 carburized (HRC 58–62), with the frozen charge static bending check (S_F_stat at T_peak) included in the order documentation as standard — ensuring the gear is sized for the actual worst-case event, not just the rated operating torque. As a direct helisel dişli üreticisi, Korea Ever-Power requests the fluid coupling rating (if present) and confirmed peak torque value at every mixer gear order — the two inputs that most strongly affect the required module. Browse the double helical gear product range for all module and material options.
Sıkça Sorulan Sorular
What is the difference in helical gear specification between a co-rotating and a counter-rotating twin-screw extruder?
The gear arrangement differs significantly. In a co-rotating extruder (most common for compounding), both screws turn in the same direction — the distribution gearbox uses an intermediate shaft with two identical output gears driven from a single input pinion, so the helisel dişli pair ratios are identical and torque distribution is inherently balanced. In a counter-rotating extruder, the two screws turn in opposite directions — the distribution gearbox reverses one output shaft through an idler gear, introducing an additional gear mesh that must be rated and inspected. The idler gear in a counter-rotating extruder sees twice the tooth contact frequency of the main gears (it meshes with both the driver and driven gears) and must be specified at the idler fatigue correction factor Y_M = 0.7 for reversed bending if it is a true idler.
Should the rubber mixer helical gear gearbox be specified for the frozen charge peak torque or the normal rated torque?
Both checks are mandatory and independent. The gear must pass: (1) the fatigue contact stress check at rated torque with KA = 2.5–3.0 (pitting resistance over the design service life of 40,000–100,000 hours); and (2) the static tooth root bending check at the frozen charge peak torque T_peak = 4–5 × T_rated with safety factor S_F_stat ≥ 1.0 (no fracture at the one-time peak event). For large rubber mixer helisel dişliler, the static check at frozen charge torque typically governs the module selection — the gear is larger than the fatigue rating alone would require, specifically to survive the rare frozen charge event. Korea Ever-Power performs both checks and reports both safety factors in the order documentation.
How frequently should the gear oil in a rubber mixer gearbox be changed?
With ISO VG 680 mineral oil, Korea Ever-Power recommends annual oil changes for mixer helisel dişli gearboxes in continuous production (24 hours, 350 days/year) or at 2,000 operating hours — whichever comes first. The high oil viscosity and EP additive package degrade from thermal cycling and from the mechanical shear in the high-torque low-speed contact zone. An oil analysis (viscosity, acid value, particle count, metal content) at 1,000 hours confirms whether the annual interval is adequate for the specific operating condition. Switching to PAO synthetic ISO VG 680 extends the oil change interval to 5,000–8,000 hours — often making a 3–5 year interval feasible with continued oil analysis monitoring.
Can the helical gears in an older rubber mixer gearbox be upgraded to a higher material grade without changing the housing?
Yes — replacing 42CrMo4 QT soft-flank gears (HB 280–320, σ_H lim ≈ 570 MPa) with 42CrMo4 induction-hardened gears (HRC 52, σ_H lim ≈ 900 MPa) increases the contact fatigue limit by approximately 57% without any change to module, tooth count, or centre distance. The standard module, face width, and housing geometry are all unchanged because the upgrade is in the material tier — not the gear geometry. In most cases, this upgrade also removes the need for the operating speed restriction that many older soft-flank rubber mixer gearboxes are running under because their tooth flanks have worn and the operator has reduced the mix RPM to extend gear life. Korea Ever-Power has executed this upgrade for several rubber mixer gearboxes where the original OEM parts were unavailable at acceptable cost.
Rubber Mixer and Extruder Helical Gear Specification
Provide your mixer type, rated output torque, maximum peak torque (or frozen charge estimate), output speed, and fluid coupling rating if present. Korea Ever-Power performs both the fatigue check at rated torque and the static bending check at frozen charge peak before confirming the specification.
M8–M50 · 42CrMo4 induction · 17CrNiMo6 carburized · KA 2.5–4.0 · Static bending check · Frozen charge survival · MOQ 1 piece
Editör: Cxm
