Custom Quartz Furnace & Diffusion Tubes

Quartz Glass builds quartz furnace and diffusion tubes as complete assemblies — main tube, ports, flanges, and end design — sized to match your equipment or reproduce a worn original part.

Roundness, concentricity, and straightness follow the same grinding-stage limits as our Large-Diameter Tubes line — see that page for the full breakdown.

Furnace Tube Configurations and Process Layouts

A furnace tube isn't just a length of tubing. It has a heated length (the section inside the furnace zone) and an overall length (heated section plus the unheated ends that pass through the furnace door or mount to a flange). These two numbers are usually different, and both matter.

Common layouts:

• Open-both-ends process tube — for horizontal diffusion or oxidation furnaces, load door at one or both ends
• Closed-end tube — for furnaces that load from one side only, such as boat-style diffusion setups
• Vertical furnace liner — heated length centered in the tube, with extended unheated sections top and bottom for flange mounting

Tell us your heated length and overall length separately — sizing off overall length alone is the most common cause of a tube that doesn't sit right in the furnace.

Ports, Flanges and End Designs

Ports, flanges, and end design aren't separate add-ons — they're fixed to specific positions on the main tube, and moving one affects the others. Treat them as one assembly, not parts to spec individually.

• Ports — gas inlet/outlet, thermocouple wells, or vacuum taps, welded into the tube wall at a position set by your equipment
• Flanges — ground flat quartz flange for an O-ring seal, or a quartz-to-metal transition flange, welded to one or both ends
• End design — open square-cut end, closed dome end, or a stepped end machined for an O-ring groove

Replacing an existing tube? Send the equipment model and, if you have it, the old part or its drawing. We can work from a worn sample as well as a print. At minimum we need main tube OD/ID and wall, heated length, overall length, port OD and position, and flange type — matching only the overall length usually isn't enough.

Hot Working, Port Welding and Tube-to-Flange Assembly

The main tube is cut and end-formed first — closing an end, or leaving it open and square. Ports are then welded into the wall at their specified position, followed by flange welding at the tube ends. Every weld gets a controlled anneal afterward; skipping it is the main cause of delayed cracking at a weld joint.

Before shipment we check: main body dimensions, port position, coaxiality between tube and ports, end-face condition, weld seams, overall assembly length, and visual defects.

Can Quartz Glass match an old or worn tube exactly? Yes — send the part or a drawing and we'll confirm which dimensions carry over and which need re-specifying (wall thickness and port position are the two most likely to drift from a worn original).

50–300 mmTypical Process OD

2–10 mmWall Range

3,000 mmGeneral Length Envelope

2–3 mm/m by ODDrawn Stock Bow

≥99.99%Natural SiO₂ · synthetic ≥99.999%

<10 ppmLow-OH Option

Specifications

Furnace & Diffusion Tube Specifications

Parameter	Reference Capability / Requirement
Main Tube OD / ID	Defined by furnace bore, carrier clearance and wall section
Wall Thickness	2–10 mm typical process series; larger transparent stock alternatives specified separately
Heated Length	Dimensioned from the furnace hot-zone layout
Overall Length	5–3,000 mm general fabrication envelope
Port Diameter & Position	Specified from a common end or flange datum
End Design	Ground end / quartz flange / O-ring groove / open or closed end
Annealing	Stress-relief annealing after welding, port forming and major hot work
Material	Low-OH semiconductor grade or JGS2-class fused quartz

Standard Series

Reference Furnace-Tube Size Families

Reference Size	Wall	Length	Equipment / Process
Ø80–100 mm	2–3 mm	≤1,500 mm	Laboratory and compact thermal furnaces
Ø120 / 142 mm	3–5 mm	≤2,000 mm	Diffusion and oxidation equipment
Ø150 mm	3–5 mm	1,200–2,000 mm	Reference replacement furnace tube
Ø180 / 200 mm	5–8 mm	≤2,500 mm	PV and semiconductor thermal processing
Ø250 / 300 mm	5–10 mm	Drawing review	Large CVD, annealing and process chambers
Ported / flanged	By drawing	Datum-controlled	Replacement assemblies and OEM furnace designs

Configurations

Furnace Tube & End Configurations

Open-End Process TubeStraight chamber for loading boats and process carriers

Closed-End Furnace TubeFormed end for atmosphere isolation and thermal processing

Side-Port Diffusion TubeGas inlet, exhaust and sensor ports located from a datum

Quartz-Flanged AssemblyWelded or machined flange for equipment connection

O-Ring Seal EndGround sealing diameter and groove geometry to drawing

Multi-Port ChamberMultiple branches for gases, pressure and thermocouples

Replacement Furnace TubeMeasured from a sample or OEM datum drawing

Large-Diameter Outer TubeHeavy-wall outer chamber for crystal and PV furnaces

Material Selection

Quartz Grades for Furnace Atmospheres

Electric-Fused QuartzGrade-specific UV cut-offOH 5–150 ppm; heat treatment can adjust OH. General-purpose continuously drawn stock. Confirm UV boundary by grade datasheet.

Flame-Fused Quartz · JGS2220–2500 nmOH 120–260 ppm; UV-visible optical components.

Synthetic Fused Silica · JGS1185–2500 nmSiO₂ ≥99.999%; OH ≈1000 ppm. Selected for deep-UV transmission; strong OH absorption near 2730 nm.

Vacuum-Fused / Low-OH · JGS3Grade-specific UV–IR / 260–3500 nmVacuum-fused OH <3 ppm; JGS3-class OH ≤10 ppm. Use the lot certificate and transmission curve at the working thickness.

OH content varies by grade and batch; the lot certificate is authoritative. Compare material routes and typical transmission data.

Fabrication

Cutting, Port Welding, Flanging & Annealing

• Precision CuttingOverall and heated-zone lengths referenced to one datum
• OD / ID GrindingControlled seal diameters and end interfaces
• Port WeldingBranch tubes positioned for process gas, exhaust and instrumentation
• Flange FabricationQuartz flanges, grooves and bolt patterns produced to drawing
• Stress-Relief AnnealingApplied after welding and hot forming to manage residual stress
• Final InspectionOD, ID, wall, length, straightness and port location checked after hot work

Applications

Furnace & Diffusion Processes

Semiconductor DiffusionQuartz chambers for dopant diffusion and controlled gas flow

Thermal OxidationHigh-purity process tubes for dry and wet oxidation cycles

LPCVD / CVDPorted chambers for deposition gases, exhaust and wafer loading

Annealing FurnacesControlled-atmosphere tubes with replacement end geometry

Photovoltaic ProcessingThermal tubes for silicon cell and wafer manufacturing

Crystal Growth EquipmentLarge outer tubes, sleeves and thermal-zone components

FAQ

Frequently Asked Questions

What dimensions are required for a replacement furnace tube?

Provide OD, ID or wall, overall length, heated length, port diameter and position, end design and the datum used by the equipment.

Which quartz grade is used for semiconductor furnaces?

Low-OH fused quartz is available for semiconductor and infrared processes; the final grade is selected with the temperature cycle and contamination requirement.

Can side ports and quartz flanges be added?

Yes. Port centerlines, flange faces and seal diameters should be dimensioned from one end or working datum.

Do you accept one-piece replacement orders?

Yes. One-piece prototypes and replacement tubes are welcome after the sample or drawing is reviewed.

Product Examples

Product Forms and Finished Components

Need a replacement furnace or diffusion tube?Enter the main tube dimensions and send the hot-zone, port and end-interface drawing for review.

Open the Tube Configurator

Engineering Data

Grade-Qualified Material Purity

Electric-fused / flame-fused quartz: SiO₂ ≥99.99%; synthetic JGS1-grade fused silica: ≥99.999%. Grade and lot certificate govern supplied material.

Engineering Data

Thermal Service Guideline

Transparent quartz: continuous use ≤1100 °C; short-term excursions ≤1200 °C. Opaque / milky quartz: continuous use ≤1000 °C. Load, atmosphere, support span and thermal cycling determine the application limit.

Engineering Data

Transparent Stock Tolerances · Continuous Drawing

OD band (mm)	OD tolerance (mm)	Wall tolerance (mm)	Formed length tolerance (mm)	Max wall variation (mm)	Max ovality (mm)	Max bow
<10	±0.15	±0.10	±1.0	0.10	0.15	2‰
10–15	±0.20	±0.10	±1.0	0.12	0.20	2‰
15–20	±0.30	±0.15	±1.0	0.13	0.25	2‰
20–30	±0.40	±0.15	±1.0	0.15	0.30	2‰
30–40	±0.60	±0.15	±1.0	0.25	0.40	2‰
40–50	±0.80	±0.20	±1.0	0.30	0.50	2‰
50–65	±1.00	±0.20	±2.0	0.40	0.60	2.5‰
65–85	±1.20	±0.30	±2.0	0.50	0.80	2.5‰
85–100	±1.50	±0.30	±2.0	0.60	1.00	2.5‰
100–200	±1.50	±0.50	±2.0	0.65	1.10	3‰
200–350	±2.00	±0.60	±2.0	0.70	1.20	3‰

Formed stock and finished cut parts use different length tolerances. Continuously drawn transparent stock: ±1.0 mm at OD ≤50 mm / ±2.0 mm at OD >50 mm. Rotationally fused opaque stock: ±5.0 mm. Cold-cut finished parts: standard ±0.5 mm; precision ±0.1 mm only where agreed for the finished geometry.

Engineering Data

Semiconductor Process Assemblies

CVD / diffusion tubes, gas-protection and liner tubes, insulation cylinders, small-orifice flow-control components, RTP / RTO and epitaxy parts are produced to process drawings. Special high-temperature process grades require a qualified application specification; operation above the general continuous-service guideline is evaluated against load, support and thermal cycle rather than promised for all quartz stock.