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,
Custom Spring Mattress Independent Bag Spring | BQUQ Precision Manufacturing
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
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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.
Wire Diameter and Coil Geometry We Actually Hold
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.
Heat Setting and Hardness Range for Long Life
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.
Pocketing and Fabric Bonding Options
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.
Compression Testing and Set Loss Data
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.
Surface Finish and Rust Protection Before Shipment
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.
Inspection Before Every Shipment
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.
Packaging and Logistics for Your Assembly Line
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)
How Our Springs Fit Your Mattress Design
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.
Do you require a minimum order quantity (MOQ)?
No—we accept prototype orders of 50 pieces and production orders of any size, with no MOQ for first-time customers.
Can you match an existing spring spec or drawing we have?
Yes, send your drawing or a sample, and we will reverse-engineer the wire diameter, coil count, and heat treatment within 48 hours.
How do you control quality for large quantities?
We use SPC on every batch, sampling 5% per lot and testing compression set and load-deflection, with a full report emailed before shipment.
What is the lead time for a custom spring order?
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.
