In industrial applications, the coils of hydraulic valves (solenoid valves) must withstand harsh environments such as high temperatures, oil contamination, and high-frequency vibrations. As a result, extremely high standards are required for their space utilization (slot fill rate), heat dissipation, and electrical stability. The multi-layer winding process places extreme demands on the precision and parameter calibration of automated equipment.The following are key considerations during the multi-layer winding process:

OEM Manufacturing of Multi-Layer Wound Hydraulic Valves In Process

1. Dynamic Tension Control and Bobbin Protection

• Tension Tapering: During multi-layer winding, radial pressure accumulates toward the inner layers. If the same absolute tension is maintained for both the bottom and outer layers, the massive accumulated stress after winding dozens or even hundreds of layers can easily cause the inner wall of the bobbin to deform or even collapse, thereby affecting the subsequent insertion of the valve core. A closed-loop tension controller must be used to smoothly reduce tension in a stepped or curved manner as the number of winding layers increases.

• Wire Diameter Elongation and Resistance Consistency: Excessive winding tension can cause the enameled wire to undergo plastic elongation and become thinner. This not only damages the insulating varnish coating but also alters the coil’s final DC resistance value, directly affecting the hydraulic valve’s electromagnetic thrust and response time. The elongation of the wire should generally be strictly controlled within 0.5%–1%.

2. Winding Precision and Interlayer Transition Handling

• Orthocyclic Winding: To achieve maximum magnetic permeability and optimal heat dissipation, multi-layer coils require the utmost precision in winding alignment. The wires must be wound tightly, one turn adjacent to the next, and the path of each layer must precisely fit into the groove formed by the coils of the layer above. This requires that the stepping accuracy of the winding mechanism be highly matched to the actual wire diameter (including the thickness of the varnish coating).

• Offset Distribution of Crossover Points: When moving from one layer to the next after completing a layer, the wires will inevitably form a crossover angle. In a multi-layer structure, if the crossover points consistently overlap at the same physical location, it will cause severe bulging of the wire coil in that area (i.e., “bulging”). During equipment commissioning, fine-tuning the spindle rotation angle or the wire-laying pitch is necessary to ensure that the crossover points of each layer are evenly staggered around the circumference.

3. Enamel Coating Protection and Dielectric Strength Considerations

• Surface Finish of the Wire Path: From the pay-off reel, guide pulleys, and felt pads to the wire-laying guide pins, all physical components in contact with the enameled wire must maintain an extremely high surface finish (the use of precision ceramic parts is recommended). During high-speed multi-layer winding, even the slightest mechanical friction can accumulate over time and potentially scratch the enamel coating, leading to catastrophic interlayer short circuits.

• End Collapse and Wire Breakage: When winding reaches the edge of the bobbin and preparing to change layers, if the wire-laying reversal point is not set accurately, the wire is prone to sinking into the gap at the edge of the previous layer (shoulder collapse) or flying directly off the bobbin. The lead-in distance for the edge reversal point must be precise to the micrometer level.

• Interlayer Voltage Resistance Differences: For high-voltage proportional valve coils, the potential difference between the first and last layers is significant. In addition to using high-strength enameled wire (such as polyimide wire rated at Class 200 or higher), it may be necessary to automatically wrap insulating tape between specific layers when required.

4. Tensile Strength Design for Start and End Leads

• Hydraulic systems often operate under severe vibration. The winding (wrap) of the coil’s starting end (leading wire) and ending end (trailing wire) at the form frame pins or terminals must allow for reasonable buffer clearance, and sufficient turns must be ensured. This effectively prevents lead root fractures during subsequent injection molding (or vacuum potting) and under actual operating conditions involving vibration.