Differences Between the Manufacturing Process of Capillary Quartz Tubes and Ordinary Quartz Tubes

This is a very fundamental question. The manufacturing process of capillary quartz tubes is similar in principle to that of ordinary quartz tubes, but due to their miniaturized dimensions, extremely high precision requirements, and sometimes more complex structures, the requirements in almost every production stage are far more stringent than for ordinary quartz tubes.

You can understand capillary quartz tubes as a “high-precision, miniaturized” upgrade of standard quartz tubes.

Below are the detailed differences between the two across each production stage.

Core Differences Comparison Table

Core Differences Comparison Table	Ordinary Quartz Tubes	Capillary Quartz Tubes	Reason & Impact
Raw Material Purity	High purity is sufficient, and high-quality natural quartz sand may be used.	Extremely high purity is required, often using synthetic quartz sand(produced by silicon tetrachloride vapor deposition)	Capillary tubes are commonly used in analytical instruments and optical applications. Even trace impurities can severely affect optical performance and the accuracy of analytical results.
Forming Process	Mainly produced by the direct-pulling method: molten quartz is drawn through a mold directly into the required size. The process is relatively simple.	Mainly produced using a two-step method: first prepare an inner liner tube and an outer jacket tube, then assemble them and perform secondary drawing.	It is extremely difficult to draw ultrafine tubes in one step with acceptable yield. The two-step method allows better control of concentricity, ID/OD ratios, and wall-thickness uniformity.
Size & Precision	Wide range of sizes: outer diameters from a few millimeters to several hundred millimeters.	Precision requirements are lower, with tolerances typically ±0.1 mm or larger.	Application scenarios demand this precision. For example, chromatography requires extremely consistent inner diameters and coating thickness to maintain separation efficiency.
Process Control	Control parameters such as temperature and drawing speed allow moderate fluctuation.	Control parameters must be extremely precise: temperature-field uniformity, draw speed, feed speed, and internal pressure must be precisely maintained in real time.	Even minor process fluctuations can cause dimensional inconsistency, ellipticity issues, or internal defects, resulting in batch scrap.
Production Environment	Manufacturing in a clean workshop is sufficient.	Often produced in ultra-clean rooms (Class 1000 or Class 100).	Prevents airborne particles from contaminating the inner wall or becoming embedded in the tube wall—fatal defects for microfluidics and optical applications.
Post-Processing & Inspection	Relatively simple: annealing, cutting, basic end-face treatment, and standard dimensional checks.	Extremely complex and demanding: 1.Stricter annealing to eliminate micro-stresses 2.Precision end-face polishing similar to optical fiber processing 3.High-end testing using laser micrometers, microscopes, interferometers to check geometry, roundness, straightness, and internal defects	Ensures the mechanical strength, optical performance, and fluid behavior required for capillary applications. Normal inspection methods cannot meet the required precision.
Ability to Produce Special Structures	Primarily only standard round tubes can be produced.	Capable of complex shapes such as square, rectangular capillaries, and photonic crystal fibers/capillary tubes (with periodic internal air-hole arrays).	Through stacking processes, hundreds of micro-capillaries can be bundled into a specific pattern and then redrawn to achieve specialized optical or fluid-dynamic properties.

Easy Analogy for Understanding

Producing Ordinary Quartz Tubes is like pulling noodles:
The goal is to make a strand of roughly uniform thickness. The process is straightforward and does not require extreme precision.

Producing Capillary Quartz Tubes is like carving a miniature ivory ball:
You must first prepare flawless materials (high-purity liner and jacket tubes), assemble them under a microscope, draw them under highly stable conditions in an ultra-clean environment using precision drawing towers, and finally inspect them using high-magnification optical instruments. Every step requires near-nanometer-level control.

Conclusion

The manufacturing of capillary quartz tubes is not simply a scaled-down version of ordinary quartz tube production. Instead, it is an advanced manufacturing process requiring fully upgraded raw-material purity, equipment precision, process control, environmental conditions, and inspection standards.

The core differences are the significantly higher demands for precision and consistency.