Category: Products > Specialty Extrusions
Sparge Tubes, OBE tubes, MgO High Density tubes, MgO hard fired tubes
Introduction: MgO ceramics have uses in extremely corrosive metallurgical applications because of the superior properties of MgO to resist attack. In most applications of this nature, a high density body is preferred for better mechanical properties and resistance.
This product line is a companion to our slip cast product line which produces a superior ceramic body but is limited to wall thickness and certain dimensional constraints. Tubes and rods in this category must be able to be made by extrusion, within fabrication limitations. Only TATEHO OZARK has the ability to extrude High Density MgO shapes, by combining our casting technology with our extrusion ability.
USES: Most tube geometries are employed as a means of introducing a gas or liquid phase into a liquid melt in metallurgical or glass processes. They may also serve limited roles as protection sleeves to protect internal components.
The potential user must be very familiar with the limitations of MgO high density tubes because they are not interchangeable with Alumina, Mullite, Zirconia, etc. in most applications.
NOT USES: Not recommended for consideration as muffle tubes, protection tubes, thermal wells, or any application:
a) where the thermal gradients exceed 50 C/inch,
b) where the heating/cooling rates exceed 200 C/hour
c) where the unit must support it’s own weight and shape above 1000 C.
Your application must provide for mechanical support (such as a refractory metal sheath) and be able to tolerate thermal shock failure if heating and cooling rates are violated.
Description: High density MgO extruded products are limited to small and medium size tubes or small rods with constant cross section and limited length.
Purity: 99.2% nominal MgO with 2% Y2O3 content. The Y2O3 is added to promote sintering and is functionally equivalent to MgO content.
Density: > 3.0 gm/cc minimum, typically 3.3 gm/cc. (Theoretical density for MgO is 3.58 gm/cc)
Porosity: Typically 8-10%, less than 1% open porosity. Not guaranteed to be gas tight.
OD sizes: Tubes – .060 to .500 OD; solid rods from .060 to .300. Default Tolerances +/- 5% (.005” min)
(Larger OD tubes might be available by slip casting, up to 5” diameter, please refer to our Slip Cast flyer).
Lengths: 10” maximum for best straightness, 16”-20”maximum for “best efforts” straightness, with a premium charge of 10%/inch (over 10” base). We do not employ conventional “hang” firing techniques, and are limited to these shorter lengths. Because of the high temperature creep properties of MgO, we do not recommend them for unsupported applications with long free spans.
Wall thickness: ID should be maximum of 75% of OD (12.5% wall) for 1-hole tubes for best roundness results. Default ID tolerances are +/- 10%, (.005” min)
Straightness: Typical Camber is less than .005 in/in. Lengths over 10” may have slight “knee” or doglegs.
Other: Surface finish may vary, but is usually smooth, but not adequate for a mechanical seal. Appearance may be mottled or blotchy because of fabrication artifacts.
Can I get closed end tubes?
Not Exactly. Monolithic closed end tubes cannot be produced by extrusion. We can obtain mechanical closure by “pinching” of the ends, or by inserting an MgO plug. These methods do not produce a hermetic seal.
Can I get double bore or four-bore tubes?
Yes, by special order. We carry a limited amount of High Density MgO inventory, and most items will require special order. Please allow 6-8 weeks for special order sizes.
Will they work for furnace muffle tubes or thermal wells?
Not Likely. Besides the disclaimer about Creep Strength under “Lengths”, MgO also has limitations due to thermal shock. We do not recommend use where there is a thermal gradient along the length, exposure to drafts, or excessive heatup or cooldown rates.