Continuous casting flow control · Monoblock stopper refractory and argon bore, gas-tight joint, clogging and erosion, servo mechanism and mould level control
A tundish stopper rod is a refractory rod suspended above the tundish outlet: lowering its nose into the nozzle seat closes the flow, and raising it opens the flow of steel into the submerged entry nozzle and mould. A stopper mechanism (manual or servo-driven) moves it to hold the mould level. Ask three things first: what refractory, nose shape and argon gas path the rod has, how its top joint is kept gas-tight, and how the mechanism and level controller cope with clogging and erosion that change the rod's flow characteristic.
Monoblock stopper rods for tundishes in continuous casting of steel and the stopper mechanisms that position them, including argon injection. Slide gate systems, submerged entry nozzles, tundish nozzles and mould level sensors as separate products are outside this page.
CNFX editorial research · Sources checked October 12, 2026 · 5 sources
Specify the refractory rod, argon bore and gas-tight joint
US patent 5,024,422 (one-piece stopper rod, priority 1988) gives the dimensions of a stopper rod (typ.) as about 1,450 mm long, tapering from about 150 mm diameter at the top to about 127 mm at the nose, with an axial bore of about 34 mm, made of alumina-silica-graphite refractory, for example 53% Al₂O₃, 13% SiO₂, 31% graphite and about 3% other materials such as zirconia. A metal bushing copressed into the refractory takes a hollow threaded steel rod that connects to the lifting mechanism. [1]
The patent explains that argon injected through the bore helps remove non-metallic inclusions and minimises aluminium oxide formation in the nozzle, which causes clogging with aluminium-killed steels; and that a gas-tight seal at the top joint matters because the steel flow creates a vacuum in the pouring system that can draw air down through the rod, oxidising the steel. It notes argon injection through the bore of a one-piece stopper had become the industry standard. [1]
European patent EP 2 067 549 explains that alumina build-up can change the flow control characteristics enough to interrupt casting, that the venturi effect of steel passing the nose creates a negative pressure that can suck air through untight joints, and proposes a restrictor (a bore narrowing of about 0.5–4 mm) to keep positive pressure in the rod; its calculation shows 1.5 bar back-pressure at 8 l/min of argon with the restrictor at the nose, or 12 l/min with it at the slag line. It also gives the immersed part of the rod as the lower 60-70% of its length (typ.). [2] Jinrong lists alumina-carbon and magnesia-carbon stopper rods with nose designs for bloom, billet, round, slab and thin-slab casters. [4]
Give the supplier the caster type and section, steel grades (aluminium-killed, calcium-treated), tundish depth and nozzle seat geometry, rod length and diameter, refractory (alumina-carbon, magnesia-carbon, nose material), argon requirement (flow, pressure, porous or bore nose), connection to the mechanism, casting sequence length, mechanism type (manual, hydraulic, electric servo) and the level control system it must work with.
02
Plan mechanism and level control for clogging and erosion
An IFAC 2005 paper on mould level control at Czech steelworks explains that the level can be held by varying flow from the tundish or the strand withdrawal speed, with input flow control preferred where quality requirements are high, using an electric servo actuator to move the stopper. It lists nozzle clogging, stopper erosion and stopper clogging among the disturbances. [3]
The paper describes valve clogging, from material sticking on the stopper plug and seat, as shifting the stopper characteristic to the right, steeper in the middle and flatter at the ends, and erosion, from shrinking plug or growing seat diameter, as shifting it to the left. Erosion is slow and handled by a robust controller, but a clogging layer can peel off suddenly and change the characteristic abruptly. It also found poor mechanical condition of the linkage between servo drive and stopper a source of strong non-linearity, and used mould oscillation of 3 mm amplitude as a measured disturbance. [3]
Its controller switched from PI to P action when the level deviation left a band of −2.5 to +2.0 mm. [3] Ruihua lists a tundish stopper mechanism (RHZ-S2) among its flow-control products. [5] Editorial note: ask the mechanism supplier for stroke, positioning resolution and backlash of the linkage, since the paper shows mechanical play directly degrades level control.
03
Refractory rods in one listing, the mechanism in the other
Listings include alumina-carbon and magnesia-carbon monoblock stopper rods and tundish stopper mechanisms; ask each for refractory composition, nose design, argon path and test data, or for mechanism stroke and positioning performance.
04
Nose, argon bore, bushing, mechanism and level loop
Both patents single out the joint between bushing and connecting rod, because suction at the nose can draw air in through it. [1][2]
Published examples exist only for rod dimensions, refractory and service temperature; stroke, density, thermal-shock cycles and weight have to come from the supplier's data sheet.
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Compiled and source-reviewed by the CNFX editorial team.
Each manufacturer above links to the page on that company's own website where the product is listed, with the date we checked it. How we source and review
· Page last updated 13 October 2026
Buyer questions
Why is argon injected through a stopper rod?
A US patent explains argon helps remove inclusions and minimises aluminium oxide build-up and nozzle clogging with aluminium-killed steels. [1]
Why must the stopper rod joint be gas-tight?
The steel flow creates a vacuum or venturi suction that can draw air through untight joints into the steel. [1][2]
How do clogging and erosion affect level control?
An IFAC paper shows clogging shifts the stopper characteristic one way and erosion the other; clogging layers can peel off suddenly. [3]
Sources and what still needs a direct check
Sources checked 2026-10-12. The patents describe specific inventions and their background; the IFAC paper reports one steelworks' control study. Supplier pages describe their own products.
