เฟืองเกลียวคู่ — แรงผลักตามแนวแกนเป็นศูนย์ สำหรับระบบขับเคลื่อนเพลาขนานแรงบิดสูง

What Is a Double Helical Gear

เอ เฟืองเกลียวคู่ consists of two opposing helical sections — one left-hand helix and one right-hand helix — machined onto the same gear blank at identical twist angles. The arrangement is sometimes called a herringbone gear, though strictly speaking a herringbone has no central groove while a เฟืองเกลียวคู่ has a relief groove separating the two helix halves. Both transmit rotational motion between parallel shafts. The fundamental advantage is that the axial thrust generated by the left-hand section and the right-hand section act in exactly opposite directions, canceling one another within the gear body. Supporting bearings therefore carry radial force only, which significantly extends bearing service life and reduces shaft deflection under heavy torque.

Because axial thrust is no longer a constraint, เฟืองเกลียวคู่ can operate with helix angles between 20° and 45°. Single เฟืองตัดเกลียว are generally limited to 15°–20° before bearing thrust loads become problematic. A wider helix angle increases the overlap ratio — more tooth pairs share the load at any instant — which raises the power capacity of a given gear size and smooths vibration at high speeds. These properties make them the standard choice for crane gearboxes, marine reduction drives, industrial turbines, and rolling mill drives where both torque density and quiet operation matter. Korea Ever-Power Worm Gear Co.,Ltd supplies เฟืองเกลียวคู่ in alloy steel, carbon steel, and nodular cast iron, with hobbed or ground tooth finishes to match the required ISO accuracy class.

Technical Specifications: Double vs Single Helical Gear

The comparison below covers the principal engineering differences between single and เฟืองเกลียวคู่. Understanding these distinctions is essential when evaluating which type suits a specific power transmission requirement.

How Double Helical Gears Work

Gradual Tooth Engagement

Unlike straight-cut spur gears where the full tooth width contacts simultaneously and creates a sharp load spike, a เฟืองเกลียว tooth makes contact at one edge first, then the contact line travels diagonally across the tooth face as the gear rotates. This progressive engagement distributes the impact energy over a measurable arc of rotation, producing significantly lower noise and vibration. In the double-helix format, both tooth sets remain continuously engaged through each revolution, which essentially doubles the active contact length compared to a single-helical gear of the same face width. The practical result is a smoother output torque curve and less dynamic load amplification at the mesh frequency — a property valued in turbine gearboxes and high-speed reduction stages.

Thrust Cancellation Inside the Gear Body

ทั้งหมด เฟืองตัดเกลียว produces an axial thrust component equal to the tangential force multiplied by the tangent of the helix angle. In a standard single-helical gear at 20° helix angle, this thrust can reach 36% of the tangential load — a significant bearing load at high torque. The double-helix design routes equal and opposite thrust forces through the gear body itself. The central relief groove provides the clearance required to cut both sets of teeth independently without interference and ensures the thrust from one half does not simply transfer to the groove wall. The net axial force reaching the shaft and bearings is effectively zero, allowing the use of simpler and less expensive radial bearings rather than thrust-capable angular-contact or tapered-roller assemblies.

Double Helical Gear vs Spur Gear — Side-by-Side Comparison

A common question when specifying a gearbox is whether a เฟืองเกลียวคู่ or a เฟืองตรง is the better fit. The answer depends on speed, noise tolerance, axial space, and load requirements. The table below compares the two on the parameters that typically drive the decision.

For moderate speeds and simpler gearboxes, a standard spur gear may be the economical choice. Where noise matters, loads are heavy, or shaft and bearing configurations need simplification, เฟืองเกลียวคู่ provide clear technical advantages at a higher but justifiable cost. For a precise selection recommendation based on your torque, speed, and duty cycle, contact Korea Ever-Power directly.

Core Performance Advantages

Typical Applications

Marine Reduction Gearboxes

Shipboard gearboxes must reduce diesel or gas-turbine output speed to propeller shaft speed — often a ratio of 5:1 to 15:1 — while transmitting several thousand kilowatts. เฟืองเกลียวคู่ are standard in this duty because the zero-thrust characteristic allows the gearbox to be built without the heavy thrust collars required in single-helical arrangements. The low noise level also matters: noise transmitted from the gearbox through the hull structure affects crew comfort and, in naval vessels, acoustic signature.

Power Generation Turbines

Steam and gas turbines spin at 3,000–15,000 rpm and must be geared down to 1,500 rpm or 1,800 rpm for standard generator coupling. At these speeds, even small unbalanced forces cause significant vibration and noise. เฟืองเกลียวคู่ are the industry default for turbine step-down gearboxes because the self-balancing helix arrangement accommodates the high speeds and continuous full-load duty cycles typical of utility-scale generators. Carburized and ground tooth finishes in ISO accuracy class 5 or better are common specifications for this duty.

Heavy-Lift Cranes and Industrial Hoists

In gantry cranes, ship-loader drives, and large industrial hoists, the gearbox experiences frequent load reversals as the load is raised, held, and lowered. Reversing load direction in a gear mesh can excite backlash-related noise and impact stresses. The continuous tooth engagement of เฟืองเกลียวคู่ reduces these transient impact loads by keeping more teeth in mesh at all times, and the zero-thrust characteristic means that load reversals do not flip the direction of axial force at the bearings. The result is reduced gearbox maintenance costs over the operating life of the crane.

Selection Parameters for Double Helical Gears

Specifying a เฟืองเกลียวคู่ correctly requires confirming the following parameters before placing an order. Providing complete data upfront avoids design iterations and delays.

1. Power and torque: Rated power (kW) and peak torque (Nm) at the gear mesh, including service factor for load type (smooth, moderate shock, heavy shock).
2. Speed: Input and output shaft speeds (rpm); this determines the pitch line velocity and influences the required accuracy grade.
3. Module and tooth count: Confirm the normal module (Mn), helix angle (typically 20°–35° for standard double-helical applications), and number of teeth on pinion and gear.
4. Center distance and bore: Fixed center distance if retrofitting; bore diameter, keyway, and shaft fit tolerance for both gear and pinion.
5. Material and hardness: Carbon steel (45# or 40Cr), alloy steel (20CrMnTi for carburized applications), or nodular cast iron (QT600-3). Specify surface hardness (HRC) or core hardness (HB) as required by the duty cycle.
6. Accuracy class: ISO 1328 or AGMA class. ISO 6–8 for general industrial; ISO 4–6 for high-speed or precision drives. This determines whether hobbing or grinding is required for the tooth finish.

Related Gear Products and Drive Components

• ➜ Helical Gearbox: A fully assembled parallel-shaft helical gear reducer that packages the gear set with housing, bearings, and seals. Suitable where a bolt-on drive unit is preferred over loose gears. See our เฟืองตัดเกลียว range for matching components.
• ➜ เฟืองตัวหนอน: For right-angle drives with high reduction ratios in a single stage, a เฟืองตัวหนอน may pair with a helical first stage to achieve high overall ratio while keeping the output shaft perpendicular. Contact us for pairing recommendations.
• ➜ Double Helical Gear (Herringbone Variants): For applications requiring higher contact ratio without a central groove, herringbone-profile เฟืองเกลียวคู่ without a relief groove are available. Inquire for specifications.

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