High Purity Quartz Round Bottom Protection Tubes for Vietnamese Heat-Treatment Equipment Manufacturer-Mia

Project Overview

• Client: Vietnamese heat-treatment equipment manufacturer

• Product: Quartz round-bottom protection tubes 

• Supplier: Lianyungang Shengfan Quartz Products Co., Ltd.

• Material: High-purity transparent fused quartz glass (SiO₂ purity ≥ 99.99%)

• Application: Thermocouple protection sheaths for high-temperature heat-treatment furnaces, diffusion furnaces, and semiconductor process equipment—used to isolate thermocouple wires from corrosive high-temperature atmospheres and prevent chemical attack and mechanical damage

• Core Processes: Precision tube drawing → End-face cutting → Flame-fused round-bottom sealing → End-port fire polishing → Dimensional inspection

Client's Original Pain Points

1. Insufficient High-Temperature Service Life of Protection Tubes

The client previously used ordinary glass protection tubes that experienced softening, deformation, and surface devitrification (opacification) during prolonged operation at 800–1100°C. This led to tube rupture, exposing thermocouples directly to corrosive furnace atmospheres, causing temperature measurement failure and unplanned equipment shutdowns. The average replacement cycle for ordinary glass tubes was only 2–3 months, severely impacting continuous production line operation.

2. Unstable Round-Bottom Sealing Quality

The former supplier employed rudimentary flame-sealing techniques, resulting in uneven wall thickness at the round-bottom section, with stress concentration points and microscopic bubbles present at the bottom. Under thermal cycling shock, the bottom seal area was the first to crack, with protection tube failure rates exceeding 20%. Additionally, some batches exhibited tube-axis misalignment at the bottom, causing incompatibility with furnace sealing interfaces during installation.

3. Insufficient Surface Finish Affecting Thermal Response Time

The protection tube outer wall surface roughness was high (Ra > 1.0μm), accelerating micro-crack propagation at elevated temperatures. The rough surface also readily adsorbed particulates from the process atmosphere, causing surface scaling that reduced thermal conduction efficiency. This resulted in thermocouple thermal response delay of approximately 15–20 seconds, compromising closed-loop temperature control accuracy.

Our Targeted Solutions & Advantages

1. High-Purity Quartz Tube Blanks for Dramatically Extended Service Life

We selected high-purity transparent fused quartz tube blanks (SiO₂ ≥ 99.99%, hydroxyl content ≤ 5 ppm), offering long-term temperature resistance up to 1200°C and short-term tolerance ≥ 1300°C, with a coefficient of thermal expansion of only 5.4×10⁻⁷/℃ and outstanding thermal shock resistance. Under continuous 1100°C operating conditions, the protection tubes exhibit no softening, deformation, or surface devitrification, with expected service life exceeding 12 months—4 to 6 times that of the previous ordinary glass tubes.

2. Precision Flame-Fused Round-Bottom Sealing Eliminating Stress Concentration

We employ an oxyhydrogen flame heating combined with graphite mold shaping process for bottom sealing. The tube body and round-bottom section are butt-joined and fully fused, achieving bottom wall thickness uniformity within ±0.2mm. After sealing, precision annealing eliminates internal stress, with no bubbles or tube-axis misalignment at the bottom. Each batch undergoes bottom stress testing and roundness measurement to ensure consistent sealing quality.

Cooperation Results & Client Feedback

1. Protection Tube Service Life Dramatically Extended

Under continuous 1100°C operating conditions, the first batch of 200 quartz round-bottom protection tubes has been in service for more than 8 months without deformation, devitrification, or bottom seal cracking. Expected service life exceeds 12 months—more than 4 times that of the former supplier's products.

2. Sealing Yield Rate Significantly Improved

The precision flame-fused bottom sealing process achieves bottom wall thickness uniformity stable within ±0.2mm, with stress concentration eliminated. Batch sealing yield rate increased from less than 80% to 98.5%, with zero rework required at the client's assembly site.

3. Installation Efficiency Substantially Enhanced

High-precision OD and length control enable direct installation of every tube into furnace sealing interfaces without sorting or selection. Single-device installation time reduced from approximately 40 minutes to 15 minutes.

4. Thermal Response Speed Optimized

The fire-polished smooth surface significantly improves thermal conduction efficiency, reducing thermocouple thermal response delay from the original 15–20 seconds to within 5 seconds—providing more precise real-time feedback for closed-loop temperature control.