Custom CNC Machining Extension Spring OEM Double Hook Tension Spring

توضیحات

What is an Extension Spring?

An extension spring is a type of coiled mechanical spring designed to operate with a tension load. Unlike compression springs which get shorter under load, extension springs extend or stretch when a force is applied. They are typically characterized by having some form of hook, loop, or end configuration at each end, which is used to attach the spring to the components that are pulling it apart. The primary function of an extension spring is to provide a return force to components that have been extended or separated, storing energy as it is stretched and releasing it when the force is removed to bring the components back to their original position.

Materials

The material chosen for an extension spring is critical to its performance, especially considering it is often under constant tension. Common materials include:

• High-Carbon Steel: The most common and cost-effective choice (e.g., Music Wire ASTM A228), offering good strength and fatigue resistance for a wide range of general-purpose applications.

• Oil-Tempered Steel: Used for larger, heavier-duty springs where high initial tension and larger wire diameters are required.

• Stainless Steel: Grades 302 and 304 are popular for their good corrosion resistance and non-magnetic properties, ideal for marine, food processing, and medical applications. Grade 316 offers even higher corrosion resistance.

• Alloy Steel: Chrome Vanadium (ASTM A231) and Chrome Silicon (ASTM A401) are used for high-stress applications requiring excellent fatigue life and high-temperature performance.

• Non-Ferrous Alloys: Copper alloys like phosphor bronze and beryllium copper are used for their electrical conductivity, corrosion resistance, and non-magnetic properties.

Surface Treatments

Surface treatments protect extension springs from corrosion, reduce friction, and can improve fatigue life.

• Electroplating: Zinc plating (most common) provides a good level of corrosion resistance and a shiny finish. Cadmium plating offers excellent corrosion resistance but is less common due to its toxicity.

• Powder Coating: Provides a thick, durable, and decorative protective layer, excellent for harsh environments and when a specific color is needed.

• Oxide Finishes: Black oxide coating provides mild corrosion resistance and an attractive black finish while minimizing dimensional change.

• Shot Peening: A critical process for high-fatigue applications, it bombards the spring surface to create compressive stresses, helping to prevent crack initiation and propagation.

• Passivation: A chemical treatment for stainless steel springs that removes free iron from the surface, enhancing the natural corrosion-resistant oxide layer.

Specifications

Key specifications that define an extension spring’s geometry and performance include:

• Wire Diameter: The thickness of the wire used to form the coil.

• Outside Diameter (OD): The diameter of the spring measured from the outside of the coils.

• Body Length: The length of the coiled portion of the spring without the hooks, in its unloaded (free) state.

• Hook/Loop Type: The style of the end configurations (e.g., machine hooks, full loops, side loops, extended hooks), which determines how the spring attaches to other components.

• Initial Tension: The built-in force that must be overcome before the coils begin to separate. This is a unique feature of many extension springs.

• Spring Rate (Stiffness): The force required to extend the spring a given distance per unit of extension (e.g., N/mm or lbs/in).

• Maximum Extended Length: The length beyond which the spring should not be stretched to avoid permanent deformation (yielding).

Application Fields

Extension springs are used in countless mechanisms where a pulling force is required. Common application fields include:

• Automotive: In brake systems, throttle mechanisms, carburetors, and seat recliners.

• Industrial Manufacturing: In counterbalance systems, garage doors, farm machinery, and assembly line equipment.

• Consumer Products: In trampolines, washing machines, toys, exercise equipment, and vise-grip tools.

• Aerospace: In cargo door mechanisms, flight control systems, and hatches.

• Furniture: In pull-out sofa beds, reclining chairs, and folding mechanisms.

An Excellent Case: The Garage Door Counterbalance System

A quintessential and excellent application of extension springs is in the counterbalance system of a standard residential overhead garage door.

When the door is closed, the springs are fully extended and store significant potential energy. As the door opens, the springs contract, releasing energy to lift the door with minimal effort from the motor or user. When closing, the springs are stretched again, controlling the descent and storing energy for the next cycle.

This case highlights the spring’s core function: efficiently managing tensile loads by storing and releasing energy. The system ensures safe and easy operation, reduces motor workload, and demonstrates the durability required for thousands of reliable cycles. The entire mechanism depends on the springs—without them, the system fails.