This Spring Mattress Independent Bag Spring is a pocketed coil unit built for your mattress assembly line, not a generic off-the-shelf component. Each coil is individually bagged, heat-set, and compre
This Spring Mattress Independent Bag Spring is a pocketed coil unit built for your mattress assembly line, not a generic off-the-shelf component. Each coil is individually bagged, heat-set, and compression-tested to hold ±0.05 mm wire diameter tolerance and a total runout under 0.10 mm across the spring height—so your finished mattress feels even, never lumpy, even after 50,000 compression cycles. Made in China by BQUQ (20 years in CNC machining, stamping, and spring forming), we deliver these custom springs in 7 days for prototypes and 15 days for production runs, with no MOQ on first orders.
We form independent bag springs from SWC (hard drawn) or SWPB (music wire) steel, with wire diameters from 1.2 mm to 2.6 mm. Coil outside diameter ranges from 45 mm to 90 mm, and free height goes up to 200 mm. Our CNC coiling machines hold pitch tolerance at ±1.5% and total coil count variation at ±0.25 turns. This is not hand-wound—every spring is shaped on servo-driven formers that repeat within 0.02 mm, so your bagging machine never jams on an oversized coil.
After coiling, we heat-set every spring at 320°C for 20 minutes to relieve internal stress. This locks the coil geometry and prevents sagging. Final hardness is HRC 42-48, measured on a Rockwell tester on the wire cross-section—not the surface, which can be decarburized. We also offer optional tempering to HRC 50 if you need higher fatigue resistance for heavy-duty mattresses. For medical or hospitality grades, we can add a zinc-nickel plating (5-8 µm) to pass 96-hour salt spray tests.
We supply springs either as bare coils or pre-bagged in non-woven polypropylene (80 g/m² or 100 g/m²). The fabric is ultrasonic-welded, not glued, so there is no adhesive failure over time. Bag width is adjustable from 60 mm to 90 mm, and we can pre-glue the top and bottom ends for your assembly line. If you use a glue spray system, we ship with a release agent coating that ensures clean bonding without clogging your nozzles.
Every batch is sampled at 5% (minimum 10 pieces) and tested for compression set per ASTM D395. We compress each spring to 70% of its free height, hold at 50°C for 22 hours, then measure permanent height loss. Typical result: less than 3% set. We also run a load-deflection curve on each sample, reporting force at 25%, 50%, and 75% compression—you get a printed chart with every shipment. This data lets your quality team verify performance without re-testing each coil.
Bare springs get a light oil film (8-12 mg/m²) to prevent rust during transit. If you skip the oil for downstream welding, we can supply with a dry phosphate coating instead. Surface finish average Ra is 0.8 µm on the wire, which is standard for spring steel. We also offer a VCI (vapor corrosion inhibitor) wrap on request—no oil, no residue, and safe for 60 days in humid containers.
Our QC lab checks three things on every lot: wire diameter (micrometer, 3 points per coil), free height (digital height gauge, ±0.1 mm), and load at 50% compression (load cell, ±1.5%). We also do a 100% visual pass for bag tears and misaligned coils before packing. If any sample fails, the entire batch is re-sorted and re-tested—we do not ship partial lots. A full inspection report with Cpk values is emailed to you within 24 hours of dispatch.
We pack springs in reinforced cartons (each holding 500-800 pieces depending on size) with interlayer cardboard to prevent tangling. For loose coils, we use shrink-wrapped bundles of 100. Pallet load is 40 cartons max, height 1.6 m, weight under 800 kg—safe for sea freight. Prototypes ship via DHL or FedEx in 7 days; production orders by sea (15-20 days to US/Europe) or air (5 days). We handle export paperwork, including CO and packing list.
| Specification | Value / Range |
|---|---|
| Wire Material | SWC, SWPB, or 65Mn steel |
| Wire Diameter | 1.2 – 2.6 mm (±0.05 mm) |
| Coil Outside Diameter | 45 – 90 mm (±0.3 mm) |
| Free Height | 50 – 200 mm (±1.0 mm) |
| Hardness (after heat set) | HRC 42 – 48 |
| Surface Finish | Ra 0.8 µm (bare wire) |
| Total Runout | ≤ 0.10 mm |
| Compression Set (ASTM D395) | ≤ 3% after 22h at 50°C |
| Lead Time (prototype) | 7 days |
| Lead Time (production) | 15 days |
| MOQ | No MOQ (first order) |
If you are designing a new mattress line, use our standard coil mapping: edge springs (stronger gauge, 2.2 mm wire) and center support springs (1.6 mm wire) can be mixed in the same shipment. We can also make hourglass or barrel-shaped coils for zoning—just send a drawing. For engineers new to spring specs, our CNC cutting tool selection guide is useful for understanding how tooling affects coil forming, and our CNC machining tolerances guide explains the tolerance classes we reference on your drawings.
No—we accept prototype orders of 50 pieces and production orders of any size, with no MOQ for first-time customers.
Yes, send your drawing or a sample, and we will reverse-engineer the wire diameter, coil count, and heat treatment within 48 hours.
We use SPC on every batch, sampling 5% per lot and testing compression set and load-deflection, with a full report emailed before shipment.
Prototypes ship in 7 days; production orders leave our Dongguan factory in 15 days after drawing approval.
Send your drawing or a sample spring to get a firm quote within 12 hours. Email sc@bquq.com or WhatsApp +86 13713157787. We reply with pricing, a DFM check, and a suggested spring spec—no obligation.
| Parameter | Capability |
|---|---|
| Materials | SUS302/304/316, SWC piano wire, SWP music wire, 65Mn, phosphor bronze, beryllium copper |
| Types | Compression, extension, torsion, wire forms, battery springs, touch springs |
| Wire Diameter | 0.05 - 12.0 mm |
| Tolerance | ±0.02mm standard, ±0.01mm on request |
| Surface | Zinc plating, nickel, black oxide, passivation, shot peening |
| Machines | CNC spring coiling machines, torsion machines, wire forming machines |
| Prototype | 72 hours, no MOQ on samples |
| Inspection | Load test per batch, fatigue test data on request |
