Double Bore / 2-Hole Alumina Ceramic Tube for High-Temperature Applications

Where 2-Hole Alumina Ceramic Tubes Are Used

• Thermocouple and sensor protection in furnaces. Two thermocouple wires running inside one sheath can touch, short, or read the wrong junction temperature. Two separate bores keep each conductor isolated along the whole length, so the signal stays clean and the wires cannot contact each other inside the tube. Send the wire type and coated diameter, the junction position and the furnace temperature and atmosphere.
• Dual-wire routing where two conductors must stay apart. Many assemblies carry a pair of leads — a heater pair, a signal pair, a spark or ignition pair — and separation is a design requirement, not a convenience. One tube with two bores holds both in a fixed position and spacing, which also keeps the pair aligned during installation instead of relying on loose ceramic beads. Send the number of leads, each wire or sleeve diameter, and the spacing that must be maintained.
• Two paths in one body: sensing plus sampling or purge. Some instruments need to read temperature and draw or feed a small flow at the same point. Two bores let one tube carry the sensor in one bore while the other bore is reserved for a sampling or purge line. Whether the bores must be isolated from each other, and how the ends are sealed, is confirmed as a separate scope. Send the flow or medium, the end-sealing requirement and the fitting details.
• Analytical and laboratory instruments. Gas analysers, tube furnaces, catalyst test rigs and thermal analysis equipment all need a small insulating tube that fits a tight sample zone. Alumina does not react with the sample the way metal does, so the tube adds no contamination to a reactive atmosphere. Send the sample or gas, the working temperature and the mounting bore in your instrument.
• Replacement of an imported or obsolete part. When a supplier stops making a part or lead times grow, the fastest path is often to copy the part you already have. We work from your drawing, a sketch, or photos with measured dimensions, and confirm the mating features before quoting. Send the existing part drawing or measured dimensions, the mating parts and the critical features.
• New fixture or prototype where no standard part fits. For a first build or a one-off fixture, you may not have a drawing yet. Start from the bore count, the wire or element diameter, the length, the temperature and the atmosphere, and we review feasibility as one configuration. Send what you know; the drawing can be confirmed after the review.

Handling and Installation of 2-Hole Alumina Tubes

Alumina is a hard, brittle ceramic: it resists heat, wear and most chemicals, but it does not yield before it breaks. Almost every handling rule below exists because of that single property. Read the section that matches your stage — storage, installation, first heat-up, or in-service inspection.

• Handling and Storage

  1. Check OD, both bore diameters, center-to-center spacing and length against the mating parts first.
  2. Insert each wire or thermocouple through its own bore with the tube straight and supported, so the bore wall is not loaded sideways.
  3. Clamp on the ceramic web or outer wall, never across a bore.\
  4. Leave clearance for thermal expansion so the tube is not pinched when hot.
  5. Confirm the coated diameter of each conductor and the clearance it needs.

• Installation and sealing

  1. Bores come open unless the drawing says otherwise.
  2. Sealing the ends or isolating one bore from the other is a separate scope: state medium, temperature and pressure.
  3. Confirm the gasket or fitting material against the alumina surface.
  4. Avoid metal-to-ceramic contact under load; nothing should bear on the tube as a structural member.

• Storage

  1. Keep dry, dust-free and free of oil.
  2. Store so tubes cannot roll into each other.
  3. Keep away from hard tooling and abrasive surfaces.
  4. Handle with clean gloves to protect sealing and metallized surfaces.
  5. Mark any bore-edge chip at receipt, while the cause is still clear.

• Cleaning

  1. Use ethanol, isopropanol or deionized water; dry before re-use.
  2. Avoid HF, strong alkalis and cleaners that attack the surface.
  3. Do not bead-blast or machine a used tube without checking with us.
  4. If the tube is metallized or coated, confirm the cleaning method for that layer.

2-Hole Alumina Ceramic Tube FAQs

1. What is a 2-hole alumina ceramic tube used for?
   A 2-hole alumina ceramic tube routes and separates two inserted elements inside one ceramic body. The most common uses are thermocouple wire protection and insulation, furnace lead routing and high-temperature fixture components. The tube is supplied bare, so the assembly method, sealing and any fittings stay under your control.
2. What is the difference between a 2-hole tube and a single bore alumina tube?
   A single bore tube has one passage for one wire or element. A 2-hole, or double bore, alumina tube has two parallel passages separated by a ceramic web, so two conductors stay apart along the full length. Bore count changes the OD, web and outer-wall requirements, so the two types are quoted as different parts.
3. Can the bore diameters, spacing and length be customized?
   Yes. Custom OD runs 3–220 mm, individual bore diameter 0.25–10.0 mm and piece length up to 3000 mm, reviewed as one configuration against your drawing. Center-to-center spacing, minimum ceramic web and outer-wall thickness are confirmed together, because they limit each other on any given OD.
4. Which alumina grade should I choose?
   Grades from 95% to 99.7% Al₂O₃ are listed as selection references. Choose based on actual temperature, atmosphere, contact media and contamination limits rather than on the highest number. The grade temperature figures are material-selection references, not continuous-use ratings for a finished tube, so confirm the quoted grade for your duty.
5. Can I order a small quantity?
   Yes. One piece may be possible for a high-value item, and three pieces is the usual starting quantity. Individual buyers are welcome to ask. The actual MOQ is confirmed for the selected part and order value, so tell us the row you need and the quantity you have in mind.
6. What are the lead times for 2-hole alumina tubes?
   Planning ranges are 1–4 weeks for prototypes depending on complexity, 1–3 business days for catalog items only when in stock, and 2–6 weeks for repeat custom production depending on quantity and complexity. These are indicative production or dispatch times, not guaranteed delivery dates for this tube. Send quantity, dimensions, grade and destination for a confirmed lead time.
7. What if my size is not in the 26 listed rows?
   Unlisted geometry can be reviewed. Send the OD, both bore diameters, center-to-center spacing and single-piece length you need, with a drawing or sketch if you have one. We confirm feasibility, tolerances and price for that configuration rather than substituting the nearest listed row without telling you.