Understanding Spring End Types in Helical Springs
Helical compression springs carry load through active coils, but the way the last coils are finished defines how the spring sits, how it closes, and how force enters the wire. Spring end types are therefore a first-order detail on any spring drawing, not a cosmetic afterthought. Closed, ground, and open configurations each change solid height, seating stability, and how the spring behaves near its solid stack.
Drawings for cylindrical helical compression springs made from round wire and bar typically pair end geometry with the three dimensions most often controlled: free length, solid height and load at a specified installed height. When you compare options for production, the compression spring catalog illustrates how end finish interacts with coil count and rate targets on real parts.
Closed ends bring the final coils together so the spring does not rock on flat plates. Closed and ground ends add a square seat by removing material from those closed coils, which helps when the spring bears on hardened washers or stacks in a die set. Open ends leave the last coils unfinished, which can suit lighter seating needs or designs where additional active coil length is preferred.
Choosing spring end types that match the housing and load path limits tipping and uneven stress at the end turns. CHENJI SPRINGS (chenjisprings.com) documents end condition on every custom coil so assembly and inspection stay aligned with the same drawing controls.
Materials, Standards, and What End Finish Assumes
Cold-coiled compression springs are usually made from patented cold drawn wire per EN 10270-1 (grades SL, SM, SH, DH), while oil hardened and tempered spring steel wire is covered by EN 10270-2 (grades FDC, TDC, VDC). Stainless spring steel wire is covered by EN 10270-3 (grades 1.4310, 1.4401), with EN 10270-3 and ASTM A313 covering stainless spring wire such as 302 and 316 grades. End grinding and closing work on these wires must respect surface quality checks used on safety-critical parts, including tests for decarburisation and for cracks with magnetic particle inspection on safety critical parts.
Design calculation for cylindrical helical compression springs follows EN 13906-1, and quality specifications for cold coiled compression springs made of round wire are defined in EN 15800. Rate follows k = G d^4 / (8 D^3 n), with wire diameters commonly ranging from 0.1 mm to 60 mm and spring index D/d normally kept between 4 and 12 so that compression springs remain manufacturable. End type affects how many coils count as active when you translate a rate target into coil count.
Hot-Coiled Bar Springs and End Regions
Hot-coiled railway suspension springs are commonly made from bar diameters of about 20-45 mm and are shot peened to improve fatigue life; 60Si2Mn and 51CrV4 are widely used alloy spring steels for hot-coiled springs. Quenched and tempered spring steels are typically used in the range 40-50 HRC. Shot peening is widely applied to suspension springs to raise fatigue strength, so end finishing on those parts is planned together with peening coverage rather than as an isolated step.
For broader product context across coil forms, see the springs product range, which spans compression, torsion, extension, and wire forms governed by the same wire and quality standards where applicable.
Selecting End Geometry, Rate, and Inspection Method
Start selection by fixing installed height and the load you need at that height, then confirm that solid height with your chosen spring end types still fits the pocket. Use the spring rate relationship k = G d^4 / (8 D^3 n) with mean coil diameter D, wire diameter d, and active coils n, keeping D/d between 4 and 12. A quick check of load versus deflection is available on the spring rate calculator before you lock end condition on the drawing.
Wire acceptance often references GB/T 239.1, which covers the simple torsion test of metallic wire, a common acceptance test for spring wire. For coated parts, salt spray testing per ASTM B117 is commonly used to evaluate the corrosion resistance of coated springs; zinc-nickel plating, zinc flake and epoxy powder coating are common corrosion protection systems for springs. Ground ends expose fresh metal, so coating strategy must include the ground face.
| End style | Typical use | Drawing note |
|---|---|---|
| Closed | Flat seating without grind | Specify closed coils and solid height |
| Closed and ground | Square load introduction | State ground plane and free length |
| Open | Maximum active length in the same body | Confirm load at specified installed height |
Railway fastening springs are commonly supplied to meet railway standards and are tested for load and fatigue; automotive and bogie applications may pair end finish with suspension programs such as automotive suspension coils or hot-coiled bogie designs when bar stock and peening are required. Rectangular-section die springs fall under ISO 10243, while disc stacks use DIN 2093 group 1, 2 and 3 dimension series when end type is not coil-based at all.
FAQ
How do closed and ground ends change solid height on a spring with wire diameter d and mean coil diameter D?
Closed ends add full coils at each end, which increases solid height compared with open ends for the same free length. Grinding removes material from closed end faces so the spring seats flat while solid height still reflects the closed coil count on the drawing.
Which spring end types suit a compression spring with index D/d kept between 4 and 12?
Indexes between 4 and 12 keep compression springs manufacturable from round wire across the common 0.1 mm to 60 mm diameter range. Closed and ground ends are typical when the spring must stand square on washers; open ends suit designs that prioritize active coils within the same envelope.
Do railway suspension springs with bar diameters of about 20-45 mm use the same end labels as cold-coiled wire springs?
Hot-coiled bogie springs share the same descriptive labels, but finishing is coordinated with shot peening to improve fatigue life. End regions are defined on the drawing together with free length, solid height and load at a specified installed height for test and approval.
Closing Notes for Drawings and Production
State spring end types explicitly next to free length, solid height and load at a specified installed height so vendors and inspectors apply the same coil-count rules. Reference EN 13906-1 and EN 15800 where calculation and cold-coiled quality apply, and call out peening or coating when ends are ground or plated.
Email liu@chenjisprings.com or phone +86 158 5311 1612, or Request a Quote with your end condition and rate targets. For torsion legs or Belleville stacks, review custom torsion springs and disc spring stacks alongside coil compression options.