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C. Wolf

Gunning Manipulators for the Hot Repair

Thursday, May 09, 2019

For many years, the gunning procedure is used for the repair of refractory linings. In combination with a gunning manipulator furnaces, ladles or RH­degasser legs can be repaired in hot condition. The advan­tages of the hot repair are: higher gunning rates giving shorter repair times, higher quality of application, less physical strain on operators, and lower risk of accidents. Via integrated TV cameras, the gunning repair can be performed from the operator pulpit, and the gunning can be recorded for quality control.

For many years, the gunning procedure is used for the repair of refractory linings. In combination with a gunning manipulator furnaces, ladles or RH­degasser legs can be repaired in hot condition. The advan­tages of the hot repair are: higher gunning rates giving shorter repair times, higher quality of application, less physical strain on operators, and lower risk of accidents. Via integrated TV cameras, the gunning repair can be performed from the operator pulpit, and the gunning can be recorded for quality control. This paper gives an overview of different designs of gunning manipulators (fixed type, crane hanging type or on mobile Diesel­driven carriage), and results from different customer sites.

General

The hot gunning repair of aggregates (con­verter, ladle, EAF, RH­snorkels, etc.) is a cost saving alternative to the shut­down and re­newal of the complete lining. This process increases the service life of a furnace con­siderably, and it further results in savings of re­heating energy. Due to the quick repair, the number of circulating aggregates, e.g. ladles, can be reduced, too.

The use of gunning manipulators is neces­sary to improve the working conditions for the operators. They further allow a more well­directed repair of the corresponding positions and higher gunning capacities than manual gunning, what reduces con­siderably the repair time and the heat loss of the aggregates. So, the steel plant saves money on refractory and has lower down­time. Moreover, the accident risk is reduced. However, melt shops are not identical, gun­ning manipulators have to be customized for optimum performance.

Ladles

A typical refractory consumption for ladles is 0,2 kg/t steel at bottom and side wall, and 0,4 kg/t steel in the slag zone. When check­ing the lining, it is often found that only the slag zone needs to be repaired. Especially at plants with secondary metallurgy, the slag zone wears out quicker. Sometimes, the top of the lining (lip ring) is damaged, because the slag removal with a break out machine has been too brute.

So, the ladle can be put back into operation very quick after gunning repair of the slag zone only: no need for replacing refractory, which is still good to go, no loss of time and energy to heat up and dry a new lining. The most convenient location for a hot repair is the tilting stand, where the slide gate is repaired. It is possible to use a manual gunning lance, but this is high physical stress in hot working areas  (Fig. 1).

Manual gunning of ladle
Fig. 1: Manual gunning of ladle

When using a gunning manipulator the gunning repair is:

•  quicker, because of higher gunning rates;
•  more efficient, because of the well dir­ected jet;
•  easier, because of no physical stress for the worker.

Depending on the plant layout, VELCO has built two different solutions for this task. Version one is a fixed installation consisting of a rotating lance that can move in/out and runs on a beam structure. The manipulator shown on the picture is in operation at a German steel shop since 1987! For each repair stand, one manipulator is required (Fig. 2–3).

Stationary ladle gunning installation
Fig. 2: Stationary ladle gunning installation
Gunning of slag zone
Fig. 3: Gunning of slag zone

Version two is a gunning lance, which is mounted on an self driven trolley that can drive from parking position to one or more repair positions. Fig. 4 shows a manipulator for the repair of laying ladles (liquid content approx. 150 t) at voestalpine Stahl in Linz/AT. The manipulator is driven in front of the laying ladle and is operated by a radio remote control. The manipulator is fed by a pressure vessel gunning machine. The sys­tem has a high­pressure water pump and an electronic water adjustment. 

Mobile lance trolley for ladle gunning
Fig. 4: Mobile lance trolley for ladle gunning

EAF

In the past years, VELCO has supplied 18 gunning manipulators for EAF. How­ever, due to the different layouts of the melt shops, no manipulator is alike. Moreover, the oper ating principles of the plants are different. A few plants have the ability to exchange the complete furnace vessel. These plants do minor hot gunning and re­place the complete lining every 4–5 weeks. But most plants have to keep the lower ves­sel in place, so the exchange of the lining is increasing the down time dramatically. Hot gunning is the solution to keep the furnace  running. When using hand lancing, typ­ically a 15–25 ft long pipe is introduced through the slag door. The gunning rate is only 100 lbs/min. Handling the pipe is hard work, and not all areas at the furnace can be reached well. Especially, the area’s next to the slag door are difficult to reach with hand lancing.

HYTOP
Fig. 5: HYTOP
Slag door gunning repair
Fig. 6: Slag door gunning repair

Fig. 5 shows the gunning manipulator HYTOP at Deutsche Edelstahlwerke in Sie­gen/DE for the repair of a 140 t EAF. This plant produces stainless steel grades. The gunning nozzle is driven into the requested working position at turned­away furnace cover. Gunned zones are the slag line, the tapping spout and the door area (Fig. 6). The manipulator is fed by three gunning machines, allowing to run three different material grades. The oper ator starts the gunning machine and controls the repair by means of joysticks on a r adio remote control. Alternatively, pre­programmed gunning programs can be run. The op­erator can pre­select positions via a touch panel (Fig. 7). Then the manipulator re­pairs automatically only the selected lo­ cations. It is possible to add a pinhole cam­era to the gunning head. So, the operator can watch the gunning repair from the control room. Moreover, the repair can be recorded for quality control.

Zone selection for automatic gunning
Fig. 7: Zone selection for automatic gunning
PNEUTOP and gunning machine
Fig. 8: PNEUTOP and gunning machine

At a Germany steel plant, the melt shop layout was so tight that no place could be found to place a gunning manipulator near to the furnace. This plant operates two in­dependent furnaces, each 100 t, within a distance of only 50 m. Here, the task was to build a manipulator which can be used for both furnaces. The manipulator PNEU­TOP is moved via overhead crane into the furnace. It is parked in a support frame lo­cated between both furnaces, and is fed by a pressure vessel gunning machine (Fig. 8). Gunning machine and manipulator are controlled by one radio remote control. The manipulator is well balanced; the gunning head is nearly as stable as the fixed arm de­sign. When coordinated properly, the crane movement of the manipulator is not influ­encing the charging of the other furnace. This customer typically guns 2–3 t of refrac­tory per repair. Using a higher gunning rate of 125–150 kg/min, the downtime could be reduced compared to hand lancing (Fig. 9–10).

Crane moved manipulator PNEUTOP
Fig. 9; Crane moved manipulator PNEUTOP
PNEUTOP
Fig. 10: PNEUTOP

 

elescopic loader MobiGUN
Fig. 11: elescopic loader MobiGUN
MobiGUN on meltshop deck
Fig. 12: MobiGUN on meltshop deck
High material loss at  manual gunning
Fig. 13: High material loss at manual gunning

A stainless steel producer in Italy has two 110 t EAF on the same meltshop floor. He requested a mobile gunning manipulator on a self driving carriage. VELCO decided to modify a commercial diesel driven tele­scopic loader (Fig. 11).

This MobiGUN parks on the meltshop deck and can access both furnaces. The gun­ning head is attached to the boom, and air cooled by an onboard compressor. For driv­ing, the boom is retracted, and the gunning head is folded in. For gunning, the boom is expanded and the gunning head is lowered to the furnace from the top. All movements of the gunning lance, the water regulation and the start/stop of the gunning machine can be activated with a single radio remote control (Fig. 12). MobiGUN needs only two connections: one to the gunning material hose and a second to the works water line.

RH degassers

The high quality demands of the automo­bile industry push the share of vacuum degassed melts. To reach a high availabil­ity of the RH degasser, the snorkel lifetime is an important factor. Due to the reaction with steel and slag, the snorkel wears out internally and externally. Often, the outside lining is damaged by the slag removal with scrapers or de­bricking machines.

Primary importance is to keep the system safe, and to avoid break outs of hot metal. But the service time is limited, as the se­quences of the steel plant have priority. The unplanned exchange of the snorkels should be avoided.

Outside gunning is a common practice. However, the workplace is exposed to heat, and the operator likes to stay away from the snorkel, so the gunning is not always well directed and has high rebound losses (Fig. 13).

Outside gunning of RH snorkel
Fig. 14: Outside gunning of RH snorkel
Outside gunning of RH snorkel
Fig. 15: Iside gunning of RH snorkel
Water-cooled inspection camera
Fig. 16: Water-cooled inspection camera
inside picture of RH snorkel
Fig. 17: inside picture of RH snorkel

Some steel plants have a service car, where a platform for hand gunning is attached to. Nevertheless, inside gunning is not possible because of the danger of dripping of hot steel or slag from the RH vessel.

Gunning manipulator with two lances for inside and outside repair
Fig. 18: Gunning manipulator with two lances for inside and outside repair

Hence, using a gunning manipulator is bene ficial for the outside repair because the gunning is better directed and the physical stress on the workers is reduced (Fig. 14). A manipulator is essential for the inside re­pair of the RH snorkel (Fig. 15). If gunning is performed well, the consumption is in the range of 0,5 kg/t steel. Typically, gunning takes place after 6–8 treatments.

For inspection and documentation of the wear pattern, it is possible to attach a cam­era on the manipulator (Fig. 16). Instead of the gunning lance, a water­cooled camera is driven into the snorkel. It can be made a video of the snorkel or the lower vessel area. Using the positioning encoders of the manipulator, the area in the video can be exactly determined (Fig. 17). The video can be stored, and the wear can be docu­mented. By this the optimum lifetime can be determined. The inspected areas can be precisely repaired with the manipulator. Typical manipulators have a lance for the inside repair, and a rotating base to reach the second snorkel. When inside and out­side repair is requested, most manipulators have two gunning lances based on a frame that can rotate 180° (Fig. 18). One lance can repair the inside of snorkel A, while the other is doing the outside repair of the snor­kel B. When finished, the main base rotates, so snorkel A is repaired at the outside and snorkel B at the inside.

Salzgitter Flachstahl GmbH/DE makes use of a gunning installation manufactured by VELCO GmbH for the refractory mainte­nance process of the snorkels at their new RH plant. Hereby, SZFG fulfil the increased demands on productivity, occupational health and safety and humane working conditions.

Inside gunning at SZFG (l.) ... and after gunning (r.)
Fig. 19: Inside gunning at SZFG (l.) ... and after gunning (r.)

The maintenance of RH snorkels constitutes a necessity for the safe operation of a RH plant. These must be cleaned (deskulled) from slag in regular intervals, and after­wards furnished with a protective layer in­side and outside by using the gunning tech­nique. Two snorkel maintenance carriages are used for snorkel cleaning, and each is provided with a snorkel deskulling device. The platform of these carriages can be used for manual gunning, too. The snorkel main­tenance carriages move on rails, and each one is dedicated to one RH plant.

Automatic gunning installation consisting of gunning manipulator and gunning machine on snorkel service car, and pressure vessel on ground, connected by hose swing
Fig. 20: Automatic gunning installation consisting of gunning manipulator and gunning machine on snorkel service car, and pressure vessel on ground, connected by hose swing

A snorkel service carriage is installed be­tween the snorkel maintenance carriages on the same rails. It can be used for both RH plants. The snorkel service carriage is equipped with a gunning manipulator with two lances (1× for inside gunning and 1× for outside gunning) (Fig. 19 a–b), and a gunning machine with two outlets, one each for inside, respectively outside gunning. The feeding of gunning material to the snorkel service carriage is carried out pneumatically by means of a pressure vessel machine and a pipe/hose system. The refilling of gunning machine with material is done automatically and dust­free. A recoupling of any hose is not required. In the first phase of construction, the pressure vessel machine is filled by big bags, in a subsequent phase this can be mod­ified to a silo filling (Fig. 20). The required compressed air, gunning water respectively electrical energy, are fed to the snorkel ser­vice carriage via hoses, respectively drums. A manual coupling is not required. The operator can either use automatic programmes or may control the maintenance process via a radio remote control (manually).

Christian Wolf
VELCO GmbH, 42551 Velbert, Germany
E­mail: This email address is being protected from spambots. You need JavaScript enabled to view it.

Keywords: robots, gunning repair

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