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.
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.
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).
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).
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.
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.
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.
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).
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.
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).
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.
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.
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.
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).
VELCO GmbH, 42551 Velbert, Germany