Aluminum Double Hung Windows Manufacturer China Factory Price Constant Force Balance
ALUMINUM DOUBLE HUNG WINDOWS MANUFACTURER CHINA: FULL TECHNICAL GUIDE
The aluminum double hung window is one of the most specified window types in residential and light commercial construction across North America, Europe, Australia, and New Zealand. A double hung window carries two operable sashes that slide vertically inside one common frame. Each sash moves up or down independently. When both sashes open, two air paths exist at once: warm interior air leaves through the upper opening while cooler exterior air enters through the lower opening. This natural stack effect gives a double hung window a ventilation advantage that a single hung window cannot offer, because a single hung window keeps the upper sash fixed and operates only the lower sash.
For B2B buyers sourcing from China, the critical questions concern manufacturing discipline, not window theory. Frame alloy, balance hardware, sealing strategy, interlock geometry, glazing configuration, and certification determine whether a window performs at a professional level or fails within two seasons. This article documents the construction details behind the aluminum double hung windows produced by Richocean, a manufacturer in Foshan, Guangdong, China. The text covers the 6063-T6 frame system, the constant force balance, the tilt-latch mechanism, the EPDM triple seal, the meeting rail interlock, and the ASTM E283, E330, and E331 test table. A practical FAQ, two case studies, and a factory direct price analysis follow.
1. 6063-T6 FRAME SYSTEM
Richocean extrudes every frame and sash profile from aluminum alloy 6063 in the T6 temper condition. Alloy 6063 belongs to the 6xxx aluminum-magnesium-silicon series. Its composition deliberately balances extrusion speed, surface finish, and corrosion resistance. Magnesium and silicon combine as magnesium silicide, the hardening phase that controls the mechanical response of the alloy to artificial aging. In the T6 condition the extrusion is solution heat treated, quenched, and artificially aged to a stable microstructure. Typical yield strength sits between 160 MPa and 180 MPa for the wall sections used in hung windows, with elongation above eight percent. This strength range carries glass and hardware without creep while remaining ductile enough to extrude complex multi-chamber geometry at production speed.
Wall thickness follows GB/T 8478 and the stricter requirements of the export program. Main frame walls measure no less than 1.4 mm. Sash walls measure 1.2 mm to 1.6 mm. Mullions and transoms use 1.6 mm to 2.0 mm. Wall thickness matters more in double hung windows than in casement windows because the sash slides inside the frame and must resist racking forces during tilt operation. A thin sash profile twists when a user tilts a wide sash. A 1.4 mm minimum wall prevents that twist and keeps the tilt-latch pins aligned with their jamb pockets over decades of use.
The frame geometry follows a three-chamber layout in the standard thermal break version. Two outer chambers contain the balance cartridges and the sash slide tracks. The center chamber holds the drainage channel and the reinforcement bar pocket. Drainage follows the concealed weep path: water that enters the jamb track drains down, crosses the sill, and exits through slot weeps in the sill cover. Every weep path is checked with a water pour test at the factory line, because a blocked weep path turns a good window into a leaking window no matter how good the gaskets are.
Surface treatment options cover the three mainstream systems. Anodizing (AA15, AA20, AA25 film classes) gives the metal a hard oxide layer with excellent abrasion resistance and color stability; it suits architectural projects that demand a metallic finish. Powder coating (60 to 120 microns) offers the widest color range, including wood-grain transfer finishes. PVDF fluorocarbon coating (two coats, minimum 30 microns per coat) delivers the best UV and chemical resistance and carries a 20-year film warranty on exterior exposure. All three lines run in-house at the Richocean campus, so finish color, film thickness, and salt spray results (tested to ASTM B117, 300 to 1000 hours depending on system) stay under one quality team.
The thermal break version joins two aluminum extrusions with polyamide PA66GF25 struts and a 24 mm overall width. The struts are roll-formed into the profile before the aging step, which avoids the pull-out risk of crimped struts. The thermal break lowers the frame U-factor and raises interior surface temperature, which reduces condensation in cold climates. Buyers in southern climates can specify the non-thermal version at a lower price; buyers in Canada, the northern United States, and Europe should specify the thermal break version.
2. CONSTANT FORCE BALANCE SYSTEM
The balance system is the heart of a hung window. Its job is to counter the weight of the sash so the sash stays at any height without drifting up or down, and so a user can lift the sash with a force of roughly 2 to 5 pounds. Richocean fits each sash with a constant force balance: a cartridge that contains a coiled flat spring of spring steel, wound on a central drum, with the free end attached to a carrier that clips onto the sash.
The term constant force describes the physics of the flat coil spring. A coiled flat strip delivers a force that depends on the strip width, strip thickness, and coil diameter, not on the number of turns paid out. Because the coil diameter changes very little over the working travel, the delivered force stays nearly constant from the fully closed position to the fully open position. This is the decisive difference from a spiral torsion balance, which winds a torsion rod and changes its torque as the rod twists. Spiral balances drift: the sash settles a few millimeters after each use, and the user feels the effort change through the travel. A constant force balance holds the sash rock steady at any height, which matters for sleeping rooms, bathrooms, and any application where a sash left half open must stay half open.
Sizing is performed per sash. The design rule at Richocean is simple: total balance force equals sash weight plus a friction allowance of 1.5 to 2.0 pounds per sash. Sash weight is calculated from the actual glass configuration, sash profile weight, and hardware weight, not from a rule of thumb. A 24 by 48 inch sash with double glazing weighs roughly 35 to 45 pounds depending on glass thickness; the same sash with triple glazing weighs 10 to 15 percent more. The factory maintains a balance sizing table that maps sash weight to cartridge grade, and the final adjustment happens at assembly, where each sash is hung and test-cycled before packing.
Spring material is 65Mn spring steel in the standard grade and stainless steel 301 in the coastal and marine grade. The strip is shot-peened and pre-stressed in the coil direction, which extends fatigue life. Cartridges are test-cycled 20,000 times on a motorized rig, which equals roughly 15 years of daily use, with a force decay limit of five percent. After cycling, each cartridge is re-measured and graded; cartridges outside tolerance are scrapped, never reworked into another window. This test regime is the reason Richocean balances rarely appear in the warranty claims log.
Maintenance is simple by design. The cartridge clips into the jamb channel and engages the sash through a stainless carrier that rides in a track. Replacement takes under ten minutes per sash without removing the frame, because the cartridge slides out of the jamb track once the sash is tilted. The tilt-in feature, described next, is what makes balance service practical in the field.
3. TILT-LATCH MECHANISM
Tilt-in operation is the feature that made hung windows popular with homeowners and building owners. Each sash carries a tilt-latch mechanism in its top rail. The latch has two spring-loaded plunger pins, one on each end, that engage pockets in the jamb tracks. A user presses the lift handle (or the two latches, on wide sashes) toward each other; the pins retract; the sash pivots on its bottom pivot shoes and swings inward into the room. The interior face of the glass is then reachable for cleaning from inside the building, which eliminates the cost, risk, and scheduling burden of exterior cleaning access.
Richocean uses a die-cast zinc latch body with stainless plungers in the standard grade, and a full stainless version in the coastal grade. The latch mechanism is spring-loaded to return automatically, so the pins re-engage the jamb pockets when the sash is pushed back vertical. A safety interlock prevents the tilt action while the sash is open: the tilt latch can only be released when the sash is closed and seated in the frame. This is a legal requirement in several jurisdictions and a sensible engineering default, because a sash that tilts while open can fall out of the frame under its own weight.
Durability targets are explicit. The latch and pivot system is cycled 30,000 times on the test rig (open, close, tilt, return), with no pin wear beyond 0.1 mm and no force change beyond 10 percent. The pivot shoes are nylon with stainless pins, which gives a low-friction slide surface and avoids the metal-on-metal squeak that cheaper windows develop after one year. Each assembled window is hand-tested: the operator tilts both sashes and slides both sashes at final inspection. A window that does not tilt smoothly does not leave the line.
4. EPDM TRIPLE SEAL SYSTEM
Sealing strategy decides the weather performance of a hung window, and hung windows are harder to seal than casement windows because two sashes move inside one frame. Richocean uses an EPDM (ethylene propylene diene monomer) triple seal system with three continuous sealing planes on every operable perimeter.
The first plane is the outer jamb seal: a compression bulb of EPDM, fitted into the frame jamb, that presses against the sash stile when the sash is closed. The second plane is the mid-seal: a second bulb (or a dense pile on the standard grade) that runs the full sash perimeter and also seals the slide track against air bypass. The third plane is the inner seal, at the interior edge of the sash, which completes the three-line defense. On the sill, a dedicated sill weatherstrip drains water outward through the weep slots while a vinyl sill nosing protects the frame corner. On the meeting rail, sealing is handled by the interlock described in section five.
EPDM is chosen over PVC, TPE, and neoprene for three reasons. First, EPDM survives UV and ozone exposure without cracking; PVC weatherstrip hardens and shrinks within a few seasons in direct sun. Second, EPDM keeps its compression set resistance from minus 40 degrees Celsius to plus 120 degrees Celsius, so the seal continues to press against the sash in winter cold and summer heat. Third, EPDM is available as a continuous extrusion, which lets the factory splice the corners with molded corners rather than butt joints. A molded corner cannot open up; a butt joint always can.
Seal geometry is a compression bulb, not a wipe seal, on the exterior faces. A compression bulb is forgiving of the small dimensional differences that occur across a production run, and it recovers when the sash is opened and closed. The bulbs are co-extruded with a hollow profile that collapses under closing pressure and springs back when released. Bulb hardness is specified at 60 Shore A plus or minus 5, a balance between soft enough to seal at low closing forces and firm enough to survive 30,000 cycles without tearing. The triple seal result, measured on the test rig, is air infiltration below 0.06 cfm per square foot at 1.57 psf, which places the window in the R3 performance class of ASTM E283 (details in section six).
5. MEETING RAIL INTERLOCK
The meeting rail is the horizontal member where the upper sash and the lower sash meet at the middle of the window. It is the most vulnerable joint on a hung window: it is a seam between two moving parts, invisible from outside, and it sits directly in the path of wind-driven rain. Richocean closes this seam with a positive interlock. The lower edge of the upper sash carries a downward flange; the upper edge of the lower sash carries a matching upward groove. When both sashes are closed, the flange seats into the groove and the two rails lock together across the full width of the window.
The interlock performs three jobs. First, it blocks the air path. Without an interlock, the two rails leave a visible slit through which air and sound pass; with the interlock, the air path is a labyrinth that must turn twice before it reaches the interior. Second, the interlock blocks the water path. Rain that runs down the exterior face of the upper sash is captured by the flange and channeled outward to the jamb drainage system, never inward across the sill. Third, the interlock resists forced entry from the exterior. A pry bar that attacks the meeting rail meets the interlocking metal before it can reach the latch cam. On the security grade, the interlock is paired with two cam locks that engage the flange and pull the rails together, which also reduces sash rattle in high wind.
The interlock geometry is part of the extrusion die, so its dimensions hold to plus or minus 0.1 mm across every profile from the same die. That consistency matters: a loose interlock rattles, and a tight interlock binds the sash. The standard seal sits inside the groove: a small EPDM bulb that compresses when the rails lock, which gives the meeting rail its third line of defense against both air and water. Assembly workers check interlock engagement on every window by closing both sashes and passing a 0.05 mm feeler gauge along the joint. The gauge must not enter at any point.
6. ASTM E283 / E330 / E331 TEST TABLE
Richocean tests production windows to the three ASTM standards that define weather performance for hung windows in the North American market. The table below lists each standard, what it measures, the test condition, and the values achieved by the standard production double hung window (3-foot by 5-foot size, thermal break version, double glazing).
Test standard | What it measures | Test condition | Richocean value
ASTM E283 | Air infiltration rate through the closed window | 1.57 psf static pressure, 75 Pa | 0.05 to 0.06 cfm per square foot (class R3)
ASTM E330 | Structural resistance: deflection and permanent deformation under wind load | Positive and negative pressure up to design pressure, 60 psf (2.87 kPa) | Frame deflection below L/175 at 60 psf; no permanent deformation after unloading
ASTM E331 | Water penetration resistance under static pressure with water spray | 5.0 US gallons per hour per square foot spray, pressure held 15 minutes | No water penetration at 15 psf; interior stays dry through the test
Three notes on reading the table. First, ASTM E283 air infiltration is measured at a fixed reference pressure of 1.57 psf, which is the standard North American test condition; the class rating (R2, R3, and so on) comes from the measured rate. Second, ASTM E330 is run in two steps: the design pressure test and the test at 1.5 times the design pressure, where the window must survive without failure even if deflection is exceeded. The 60 psf figure above corresponds to a design pressure rating of plus and minus 40 psf with the 1.5 factor applied. Third, ASTM E331 is a pass-fail test: the window must show no water reaching the interior at the specified pressure. The 15 psf result covers most US wind zones; buyers in hurricane zones should request the 20 psf or 25 psf variant, which the same frame passes with sealed glass and reinforced sill clips.
Test reports are issued by third-party laboratories (SGS and Intertek, among others) and are available per project. The factory also runs its own pre-test on every production batch sample before shipping, so the shipped product matches the certified design. If a buyer specifies a size outside the tested matrix, Richocean offers an engineering recalculation and a retest before mass production begins.
7. FREQUENTLY ASKED QUESTIONS
How does tilt-in cleaning work? Pull the lower sash down to the closed position. Press the two tilt latches on the top rail toward each other. Swing the top of the sash inward; the sash pivots on the bottom pivot shoes and comes to rest at about a 15 to 20 degree angle, inside the room. Wipe the interior face of the glass and the interior faces of the frame tracks. Push the sash back vertical until the latches click into the jamb pockets. Repeat for the upper sash: slide the lower sash down, tilt it in, then slide the upper sash down past the lower sash (or tilt the upper sash in from its own position if headroom allows). The whole operation takes two minutes per sash and requires no tools. The tilt axis and pivot shoes are the only wear parts, and they are replaceable.
How do you repair or replace a balance? A constant force balance that loses tension is replaced, not repaired. The procedure: tilt the sash in, slide the sash sideways to disengage the pivot shoe from the jamb, lift the sash out of the frame. Pull the old cartridge out of the jamb track (it slides out once the sash is removed). Weigh the sash on a spring scale. Select a new cartridge from the factory sizing table for that sash weight and glass configuration. Slide the cartridge into the jamb track, hook the carrier onto the sash, re-seat the sash, and test the travel. The complete job takes under ten minutes per sash and uses only a screwdriver and a spring scale. Richocean supplies balance cartridges as spare parts with every export container, and the replacement procedure is documented in the maintenance manual that ships with each order.
Double hung versus single hung: which should I buy? The decision is ventilation, cleaning access, and price. A double hung window opens at both top and bottom, which doubles the open area at a given window size and creates the stack-effect airflow described in the introduction; both sashes tilt in for cleaning. A single hung window opens only the lower sash, so its open area is roughly half that of a double hung of the same size, and only the lower sash tilts in; the upper glass is cleaned from outside or with a reach tool. Because a single hung window carries one balance system and one tilt-latch set instead of two, its factory price is typically 12 to 18 percent lower than the double hung equivalent at the same size and glass specification. The recommendation at Richocean: choose double hung for bedrooms, living rooms, and any room where cleaning access or top-down ventilation matters; choose single hung for corridors, utility rooms, and budget-sensitive projects where the upper sash will rarely open.
8. CHINA RANKING #1: RICHOCEAN
Richocean operates from Foshan, Guangdong, the historic center of China aluminum processing industry. The campus integrates billet sourcing, extrusion, surface treatment (anodizing, powder coating, PVDF), hardware assembly, glazing, and final test under one roof, which is rare even among large Chinese window plants. Most competitors buy profiles from one factory and hardware from another, then assemble; Richocean controls every step from alloy receipt to the container door.
The ranking claim is simple to verify: export volume of hung window units, measured in completed containers per year, places Richocean first among Chinese hung window manufacturers serving the North American and European markets. The number behind the ranking is quality consistency, not volume alone. Batch rejection rates hold below 0.5 percent at third-party inspection (SGS or Bureau Veritas) on the last 120 inspected containers. On-time delivery holds above 98 percent over the same period. The factory holds ISO 9001 certification, and windows carry CE marking where required; project-specific certifications (AAMA/WDMA, NFRC simulation) are produced on request.
Buyers work with a dedicated export team that includes English-speaking engineers, not just sales staff. Drawing review, balance sizing, glass configuration, and hardware selection are handled by the engineering desk before the order is booked, which is why the first sample matches the production units. Sample lead time is 10 to 15 days, production lead time is 25 to 40 days for a 20-foot container, and a 40-foot container ships in 35 to 50 days depending on the finish and glass mix.
9. CASE STUDIES
Case study one: townhouse development in Vancouver, Canada. The developer required 640 aluminum double hung windows across 120 townhouse units, with a strict site schedule of six months and a penalty clause for late delivery. Richocean supplied the thermal break version with constant force balances, tilt-latch hardware, and double glazing with low-E coating and argon fill. The order was split into four shipments of 160 windows each, synchronized with the construction sequence of the site. Every shipment passed SGS inspection at the factory before loading; on-site rejects totaled seven windows out of 640 (1.1 percent), all replaced from the spare parts kit shipped with the container, with zero schedule impact. The developer re-ordered for phase two without a second tender, citing delivery reliability and the low reject rate as the decisive factors.
Case study two: heritage renovation in Cambridge, United Kingdom. The project involved a listed Victorian building where the planning authority required the new windows to respect the original sightlines and sash proportions. Richocean produced 70 custom double hung windows with slimmer profile sightlines (matching the original timber sash dimensions), a traditional color finish (deep green powder coat), and constant force balances sized for the heavier double-glazed units that replaced the original single glazing. The challenge was dimensional: 40 of the 70 openings had non-standard sizes, and each was measured on site and manufactured to plus or minus 2 mm. All 70 windows installed without shim-pack adjustments beyond the standard allowance. The architect report noted that the windows met the planning conditions while achieving a center-of-glass U-factor improvement from roughly 5.0 to 1.6 W/m2K. Heritage projects like this one are where the balance system earns its cost: a sash that holds its position under a heavy double-glazed unit, without drift, is a sash that will not slam shut on a windy day in a protected building.
10. PRICE ANALYSIS
Factory direct prices from China are a function of three variables: balance grade, sash ratio, and glass configuration. Understanding these variables lets a buyer target the price point without sacrificing the performance that matters for the project.
Balance grade. The standard grade is the constant force cartridge described in section two, with 65Mn spring steel and 20,000-cycle rating. The premium grade adds stainless 301 springs, a 30,000-cycle rating, and a sealed cartridge that resists coastal salt air. The premium balance adds roughly 4 to 6 percent to the window price and is worth it within 5 kilometers of the coast or in any project with a 15-year-plus maintenance horizon. The cheapest option on the Chinese market is a spiral torsion balance; it cuts balance cost by roughly 30 percent, but it drifts, and drift converts directly into warranty calls. Richocean does not offer the spiral option on export windows.
Sash ratio. Double hung windows cost more than single hung windows because they carry two sashes, two balance systems, two tilt-latch sets, and the interlocking meeting rail. At the same size and glass specification, expect the double hung premium to land between 12 and 18 percent over the single hung price, as stated in the FAQ. The premium shrinks at large sizes, because the frame cost is shared, and grows at small sizes, where the hardware cost dominates. Buyers who want the double hung look at a single hung budget should compare the two configurations at their exact window size before deciding.
Glass configuration. Glass is the largest single cost component in a modern hung window, typically 30 to 45 percent of the window price. The ladder runs from single glazing (cheapest, rarely exported) through double glazing (two panes, one air space) to double glazing with low-E coating and argon fill (the North American standard), to triple glazing (two low-E coatings, two gas fills, warm-edge spacers) for cold-climate projects. Each step adds roughly 15 to 25 percent to the glass cost, and therefore 5 to 10 percent to the window price. The frame system and hardware do not change with the glass specification, so buyers can hold the window price steady by fixing the glass configuration first and then comparing frame quotes on an identical glass bill of materials.
Quantity and finish also move the number. A 20-foot container of standard 24 by 48 inch double hung windows with double glazing and anodized finish prices around USD 3,200 to 4,200 per 100 windows at current factory direct rates; the same windows with thermal break, powder coat, low-E argon glass, and premium balances land roughly 25 to 35 percent higher. Those figures are indicative of the structure, not a quote; final pricing is quoted per project after drawing review, because sizes, glass, and hardware dominate the unit cost.
11. 360 SERVICE AND FOUNDER PHILOSOPHY
The 360 service model covers every step from inquiry to after-sales. Pre-sales: drawing review, balance sizing, glass configuration, sample production, and a written engineering summary before the order. Production: a production milestone report with photos at extrusion, surface treatment, and assembly; a pre-shipment inspection report; and third-party inspection (SGS or Bureau Veritas) at buyer request. Logistics: booking, consolidation, export documentation, and container loading supervision. After-sales: a 10-year warranty on frame and finish, a 5-year warranty on hardware and balances, a spare parts kit in every container, and a maintenance manual with the balance replacement procedure. Every shipment is tracked, and the export team responds to technical questions within 24 hours.
The founder philosophy at Richocean is written on the wall of the assembly hall: the window that ships is the window that was approved. The founder, who started the company as an extrusion technician in Foshan in the 1990s, insists on three rules. First, no substitution without approval: if a material or hardware component changes, the buyer is told before production, never after. Second, the test rig is the final inspector: every production batch is pre-tested against the ASTM matrix before packing, not just the sample. Third, the spare parts kit is part of the product: a window that cannot be serviced in the field is not a finished product. These rules are the practical content of the ranking: a factory that treats the approved sample as the contract will deliver a consistent window, and a consistent window is the only thing that keeps a B2B buyer in business.
12. CONCLUSION
The aluminum double hung window is a mature product, and the difference between suppliers shows up in the details that this article has covered. The 6063-T6 frame determines dimensional stability and surface durability. The constant force balance determines whether the sash drifts and whether users complain. The tilt-latch mechanism determines whether cleaning is a two-minute task or a scaffolding job. The EPDM triple seal and the meeting rail interlock determine whether the window leaks in wind-driven rain. The ASTM E283, E330, and E331 results give the buyer a numeric, third-party-verified answer to the question of weather performance. And the price analysis shows that the factory direct route from China removes the middle layers without removing the engineering.
Richocean in Foshan, China, manufactures these windows to order, tests every batch, ships with third-party inspection, and backs the product with a ten-year warranty and a spare parts kit. Buyers who need aluminum double hung windows or single hung windows at factory direct prices, with constant force balances and tilt-in sashes, can send the project drawings to the export desk for a balance sizing and a formal quotation. The ranking is earned one container at a time, and the next container starts with a drawing review.
