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Posted by Satyendra on Dec 3, in Technical 0 comments Rolling of steel in Hot Strip Mill Hot strip mills in these days are either conventional hot strip mills or strip mills for rolling thin slabs. The primary function of the conventional hot strip mill HSM is to reheat the semi-finished steel slabs rolled or continuously cast to the rolling temperatures and then to roll them thinner and longer through a series of rolling mill stands driven by large motors and finally coiling up the lengthened steel sheet for its easy handling and transport.
The hot strip mill supplies coils for Hsm 220 rolling mill, strip shearing and slitting units as well as a finished product for shipment directly to the customers. Most material is transported out of the mill area by an automated coil handling system to the storage aisle. Attributes imparted to the strip by the hot rolled strip mill include surface quality, thickness, width, and flatness control as well as strip profile.
The main sub-processes are i heating of steel slabs in the reheating furnace, ii descaling of the heated slab and its sizing in sizing press, iii rolling in the roughing mill and secondary descaling, Hsm 220 rolling in the finishing mill, v control cooling of the hot rolled strip and vi coiling of the rolled strip.
Reheating of the slab Critical to the hot strip mill is the reheating furnace. Modern hot strip mills are equipped with state of the art walking beam reheating furnaces which have replaced and outperformed older pusher type reheating furnaces.
The furnace needs aroundkcal of fuel gas per ton of slab for the heating of the slab from room temperature to a temperature range of deg C to deg C. The inspected slabs as per rolling schedule are placed one at a time on the furnace charging roller table in the slab yard and positioned in front of the charge door on the reheating furnace.
When space is available in the furnace, the pusher arms push the slab into the furnace. Once inside, the slabs are supported around 2. Two independent sets of skids, one fixed and one walking, take turns supporting the slab as it is walked through the furnace by a massive sub-frame energized by a pair of large hydraulic cylinders.
Depending on the furnace design, the interior of the furnace is divided into several five to ten zones for temperature control.
The preheat and heating zones combust a mixture of fuel gas and preheated combustion air with the burners on the roof and on the side walls of the furnace, both above and below the skids, to heat the slab nearly to its discharge temperature.
Most of the preheating of the steel slab is achieved by the hot exhaust gases rushing past the slabs on the way to the recuperators. Whatever heat is left in the exhaust gases preheats the incoming combustion air to around deg C to deg C in the recuperators.
In the heating zone the steel is primarily heated by radiation by the hot furnace walls. In the soak zone, the burner sizes and locations are such so as to maintain a uniform temperature within the zones to equilibrate any cold spots in the slabs.
Refractory dividers help to physically distinguish the zones, and thermocouple temperature sensors throughout the furnace interact with the automatic burner control systems to maintain the target temperatures in each zone. Complex computer models calculate the targeted roughing mill exit temperature to obtain a furnace discharge aim temperature.
Estimating the temperature profile through the thickness of each slab in the furnace on an ongoing basis, the computer aids the operator in selecting the production rate and zone set-points that maximize production of steel slabs uniformly heated to as close to the target temperature as possible.
After the rolling process begins, as the steel exits the roughing mill, its temperature is fed back to the furnace, updating the computer models and informing the furnace operator as to the temperature uniformity. The reheating furnace has usually two extractors. These extractors can act independently of one another to remove double-charged slabs one at a time or in combination to extract the longer slabs.
The hot slab is placed on the entry roller table which carries it into the roughing mill through a scale breaker. Descaling and sizing of slab Descaling of heated slab is a must in the hot strip mill for attaining good surface quality of the hot rolled strip.
Descaler operation need to be optimize in order to ensure maximum scale removal and hence enhanced cleaning at minimum cooling of the heated slab.
After leaving the reheating furnace, the slab passes at a speed ranging from 0. These headers are usually equipped with advanced nozzles to spray water effectively.
The descaler is normally of closed design to prevent water from escaping and there is optimized water flow inside the descaler. Modern hot strip mills are equipped with a sizing press in place of an edger.Welcome To Tony’s Tackle T– Bay.
ashio-midori.com email [email protected] Seaside, Eastbourne, East Sussex BN21 2NU Tel: Rolling of steel in Hot Strip Mill. Hot strip mills in these days are either conventional hot strip mills or strip mills for rolling thin slabs.
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