All modern rolling mills have to be able to remove the rolls quickly, especially the work rolls.  The work rolls wear and get damaged from time to time.

A shuttle table is used to remove the rolls.  One set of rolls can be positioned on a shuttle table while another set is being removed.  Once the rolls are removed from the mill and put onto the shuttle table, the shuttle table moves over and new rolls can be inserted into the rolling mill.  This is accomplished with hydraulic cylinders and spindle clamps located on the rear of the rolling mill.

Before removing the rolls, spindle clamps located on the rear of the mill are used to clamp the universals or spindles accurately so when new rolls are put back in they line up perfectly with the spindles.  Spindles can be spherical gear type enclosed in grease or they can be large, forged “U” type universals.  Many older rolling mills have a four-leaf design, which make noise when the rolling mill is running, especially at low speeds.

Load Cells

Load cells are positioned between the hydraulic cylinder top chocks.  Load cells not only tell the operator what the separating force is at each pass, but they can be automatically applied to control the hydraulic pressure accurately for skin pass rolling.

Above all, load cells allow for quick set up. Without strip going through the rolling mill, the rolls can be brought together and by simply pushing a button, the rolling mill is zeroed in.  Load cells are also used to accurately control tension at any speed.  Load cells are placed in passline roll housings.  This system is more consistent than using torque at the tension reels.

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Many plastics and rubbers are made on a rolling mill. This is sometimes referred to as a calendar mill.  Many plastics used in automotive brake pads are rolled on a rolling mill.  There are many types of plastics that are rolled, such as polyurethane and polypropylene.  The rubber is mixed in the rolling mill.  The rubber can be pure rubber or any polyurethane type of rubber.  Because polyurethane rubber can be in a non-liquid state, it is best to mix it with a rolling mill or calendar mill with many passes.

Ceramics

Ceramic can be used for many purposes such as corrosion resistant, high tensile products.  Ceramic is made into a powder and sometimes put through a rolling mill to make a ceramic sheet or product.  Ceramic can handle considerably higher temperatures than metal.  Sometimes ceramic is mixed with metals and plastics where heat and strength are needed.  Fiberglass plastics, as an example, are a mixture of glass fiber and plastic resin.  This type of material is made in many different forms, depending upon the purpose, which could be acid resistant, heat resistant, light weight, and low cost.  Many ceramics are molded, but some are put through a rolling mill to make a sheet.

Ceramic may even include pure powder carbon.  American Steel Products Company has been successful in rolling powdered carbon for the electronic industry.  Powdered carbon strip is used in electronics as a high temperature conductor of electrons.  Carbon strip is rolled down to a thickness of .001” with a tolerance of ± .00008”.

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2-High Rolling Mill

3-High Rolling Mill

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Coolant nozzles with valves are placed approximately every 2” across the width of the work roll or back up roll or both.  If there is a wavy center, it means that the center is expanding and more coolant is applied in the center.  This allows the roll to change its shape by thermal expansion.  The roll can actually change its shape anywhere along the surface of the roll with coolant.  Instead of observation of the outgoing shape by the operator, it can be done with a shape roll.  Shape rolls are usually a series of rollers that measure the deflection across the width of the strip.  These rollers are air actuated and each shape roll can be every 2”.  If the shape roll detects center buckle or stretched edges, it deflects the strip under tension and is measured accordingly.  This gives a reading on the screen as shown above.  Some shape rolls use a common shaft with rolls every 2” using air bearings.  As the roll is under pressure, air is measured under each air bearing and gives a reading every 2” across the width of the strip.  All shape rolling can be done by observation or automatically.  An automatic shape roll system is very expensive because it needs to operate the nozzles to change the shape of the rolls at any speed.  The air for the air bearings must be highly filtered for this purpose.

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An advantage of an AC to DC drive or rectifier is the cost.  Drives can be upgraded utilizing older DC motors.  The rectifier system from AC to DC has substantially reduced in cost, and the drive itself is usually less expensive than an AC variable frequency drive.  Another advantage of a DC drive is that it can be regeneration.  The uncoiler or tension reel can generate a substantial amount of electrical power that can be put back into the machinery so the electrical power generated by the uncoiler tension reel can be utilized at the recoiler tension reel.  Another advantage is that DC drives do not require large resistors or sometimes no resistors depending upon the electrical utility.  This is because the breaking system on a DC drive can go into the electrical utility for regeneration quickly and bring the drive down to stop quickly without resistors.

Many mills and components still prefer DC variable speed, variable torque drives.  These are energy efficient as they only require the amount of energy required to do the work.  If a motor has 5,000 HP and only 1,000 HP is needed to do the final pass, it will only use 1,000 HP.

Another benefit of modern electronic DC technology is the fact that you eliminate many relays and expensive conduit and wiring, as controls can be sent from the control console to the motor through small cables instead of a hundreds of wires.

All new variable speed drives can be controlled through Human Machine Interface (HMI) touchscreen controls.  Electrical controls and circuits to a rolling mill require experienced rolling mill electrical engineers to design a system based on information obtained from an experienced rolling mill engineer.  Of course, speed, tension, thickness, lineal feet, part number, run time, roll replacement/change and any variable involved can be put into a modern HMI touchscreen.

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The flattener with pinch rolls flattens the material.  Only the top rolls in the flattener are driven, and the lower rolls spin freely.  The material is fed through the pinch rolls of the flattener, across the breaker roll, across the shape roll, through the crop shear, and across an apron through the work rolls.  As soon as the material is through the work rolls, the work rolls can come down to take a small reduction.

The material passes through the rolling mill, across an exit apron, through the exit crop shear, shape roll, breaker roll, and is positioned downward onto the drum.

A belt wrapper is used to quickly thread the material around the drum of the recoiler.  Once it is threaded on recoiler drum, the outboard hydraulic support can be positioned to assure that the recoiler tension reel does not deflect regardless of tension or coil weight.  After a few wraps around the drum, the belt wrapper backs away from the recoiler tension reel, and the mill is now ready to uncoil the coil through the rolling mill onto the other recoiler tension reel at the first pass.  Once the tail of the coil is almost through the end of the rolling mill, the material can be put in reverse to the other recoiler tension reel with outboard support.  A deep reduction can now be made, one tension reel acting as an uncoiler and one acting as a recoiler.  The material goes back and forth two to five times depending upon the amount of reduction with each pass.  The coil can be removed from either tension reel by way of the pit type coil car.

As you can see, an operator needs to be equipped with considerable high technology electronics and data recorder for each coil number, each pass, including time for threading, separating force, reduction of each pass, line speed, incoming and outgoing strip tension, and any comments.  Also, maintenance schedule and unusual problems with material such as surface finish, coil removal, and reason for downtime should be included.

Modern rolling mills have many hydraulic cylinders, small AC gear motors, modern solenoid valves, flow control valves, heavy pipe, compressed fittings to prevent hydraulic oil from mixing with coolant, and many hydraulic pump and tank units with heat exchangers to assure consistent temperature to assure a minimum of thermal expansion which can cause leaks.  All functions can be observed at the control console.

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To accomplish this, the operators or machine normally make some adjustment and then come back down again with mechanical screwdowns.  Hydraulic screwdowns eliminate this.  There is no backlash with hydraulic screwdowns.  Cylinders can be almost any size necessary to create separating forces for the rolling mill.  At the hydraulic cylinder are servo valves.  The invention of a servo valve was to quickly operate a torpedo toward the direction of the ship.  Hydraulic servo valves can allow a drop of oil to move the screwdowns, or if necessary, put in large quantities of oil to position the screwdowns quickly.  The screwdowns can be operated with the automatic gauge control system.

Hydraulic screwdowns are powered with a hydraulic pump and tank unit.  The pump is usually a pressure compensated pump.  The pressure is held at all times into an accumulator so that the hydraulic pressure is ready to go to put one drop or a large quantity of oil into the hydraulic cylinders.  The hydraulic cylinders have an encoder to measure with each movement of the hydraulic cylinder, usually .0001”. Some encoders are inside the hydraulic cylinder and some are located outside of the hydraulic cylinder.  The encoder tells the position of the cylinder or the roll gap.  The usual pressure is a maximum 4,500 PSI.

Usually precision screwdowns work best at higher pressures between 3,000 and 5,000 PSI.  New servo valve technology is being developed to operate at up to 10,000 PSI.  Movement in the cylinder is done within milliseconds so that the strip coming out of the rolling mill has uniform

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Before a product is designed with carbon steels or alloy carbon steels, extensive research is done to not only look at the best consistent quality of available steel, but to look at the cost of each carbon steel product.  Seeking the advice of a welding expert to specify, and how the material should be welded, such as ERW, TIG, MIG, etc.  All alloy carbons steels become harder (100,000 to 300,000 PSI yield strength) after being rolled or reduced and annealed for further rolling and reducing.

Carbon steels and stainless steels can be made into almost any alloy.  An alloy is the mixture of almost any element.  The most common high strength, high yield alloy is a chrome moly alloy such as AISI 4140 or 4340.  These alloys are commonly used in steel plate and are quenched and tempered.  To reduce these steels, cold working or work hardening is a factor to consider because, like stainless and high carbon steels, the material increases substantially in yield strength when reducing.

One of the most useful purposes of alloy steels is in springs or any application where the material has to flex on a continuous basis without breaking.  Most steels will crystalize in time even though they are not bent beyond the yield point.  As an example, that is why a lot of machinery shafts that take a side load are made from alloy steel.  As an example, AISI 4340 is used to prevent fatigue, and the maximum stress the shaft may be under is 16,000 PSI however, the actual yield point of the material is 150,000 PSI.  Fatigue and flexing is considered when the material is used in bridge or machinery building.  The material, type of construction, welding, machining, etc. must all be considered in the final cost.

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Certain vessels require food to all be within stainless steel. When cooking in large high pressure vessels, it is necessary to have a high pressure, safe vessel to withstand substantial pressure with large safety factors therefore, the inside walls are made of stainless. The outer walls of a vessel are made of heavy carbon steel. Carbon steel can be heavy in thickness because it is easy to weld and assures a good bond for possible high pressures. The vessel is made from cladded plate.

Cladding can be copper to plastic, such as used in printed circuits. One purpose for cladded material is main bearings and connecting rod bearings for gasoline and diesel engines. Bearing material used to be Babbitt, which is a lead alloy. Babbitt was fused to the steel as an insert. Babbitt, being soft and with proper lubrication, made a good bearing however, lead is not good for the environment and better material is now used, including aluminum tin copper alloys. This soft alloy needs to be cladded to the steel. To fuse this material to steel, you need a cladding process developed by American Steel Products Company, Toledo, Ohio. Many types of bearings have been developed using rolling mills.

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