EP1704000B1 - Method for lubricating milling material - Google Patents

Description

The invention relates to a method for rolling stock, in particular for hot strip rolling in a finishing train or a casting mill, in which a lubricant, directly on the surface of the work rolls or indirectly on the surface of the support rollers with transfer to the surface of the work rolls, applied before the rolling stock enters the nip of a roll stand, forming a strong adhesive lubricant film on the work roll surface, which leads in the nip as an intermediate layer between the roll and rolling to reduce friction.

The use of a nip lubrication in high-load finishing lines during hot rolling is known. However, the lubrication is delayed delayed on the tape head after the tapping in entspechenden scaffold and switched off some time before the unthreading of the tape end again. Such a procedure, depending on the lubricating effect, has a detrimental effect on the rolling process.

From the DE 21 05 975 is a device for automatic oil supply to a hot mill stand known through which a workpiece passes. The apparatus comprises an oil spraying means for the rolling stand, means for supplying oil to the spraying means, means for initiating operation of the oil feeding means shortly after the leading end of the workpiece passes through the rolling stand, and means for stopping the operation of the oil feeding means just before the rear End of the workpiece reaches the mill.

In Scripture US Pat. No. 6,266,985 B1 a method is described according to which, during hot rolling, the corners and the ends of the rolling stock to be rolled are subjected to a lubricant.

From the DE 20 22 923 For example, a method and apparatus for applying a lubricant to a workpiece in a hot strip mill is known wherein lubricant and atomizing air are dispensed from a plurality of spray nozzles in a four-roll stand provided with two work rolls and two back-up rolls. The spray nozzles are arranged across the width of at least one of these support rollers. As soon as the workpiece enters the work rolls, the lubricant is applied to the back-up rolls and from there to the work rolls. The lubricant and atomizing air flow to the nozzles is shut off as soon as the workpiece leaves the work rolls.

The starting point for the promotion of lubricant is the puncture in the scaffold under consideration. A disadvantage of this method or this device is that first a closed Schmierstoffim must form on the back-up roll surface, which is transmitted in the gap back-up roll / work roll on the work roll surface. From here, the lubricant enters the nip. It takes too much time (several seconds) for the lubricant to reach the rolling stock, depending on the roller peripheral speed and roller diameter. In such a method or in such a device, the tape head is not supplied with fresh lubricant during threading, which leads briefly to higher rolling forces.

Basically, no rolling is possible without friction in the nip, since only with sufficient friction, the rolling stock is detected and pulled through the nip. It must always be ensured that the so-called gripping and pull-through conditions are met.

With respect to a minimum required friction gripping condition - this describes the conditions at the beginning of the rolling - much more critical than the pull-through condition. In the pull-through condition, the roll gap is completely filled with rolling stock.

If one of the two conditions or both conditions are not met, slipping occurs, ie slippage between the roller and the rolling stock.

In addition to the friction coefficient, which describes the friction itself, the grip angle and the rolling speed play a role. As the rolling speed increases, the gripping capacity decreases. For the gripping angle, which is dependent on the thickness of the incoming rolling stock, the relative reduction in thickness during rolling and the diameter of the rolls, it is said that it must always be smaller than the friction angle to allow slip-free rolling. With conventional acceptance distribution, the gripping angle in finishing lines decreases from the first to the last stand. After that, the biggest gripping problems, a slippage at the beginning of the rolling stock, occur in the first finishing stand.

Since the gripping condition at the beginning of the rolling stock is more difficult to fulfill than the pull-through conditions in the rolling stock, the roll gap lubrication is used so that the lubrication is switched on only after a puncture in the respective frame and is switched off some time before the removal of the rolling stock. In this way, enough work roll overruns remain to completely burn the lubricant on the roll surface. This will avoid that the gripping at the beginning of the subsequent rolling stock is compromised.

The described lubrication strategy results in two different load levels within the rolling stock, provided that the preliminary sliver or the thin slab enters the finishing train with homogeneous properties over the length and without speed-up.

A high load level at the beginning and at the end of the rolling stock (without lubricating effect) and a low rolling force level in the remaining area of the rolling stock (lubrication active).

By reducing the rolling force with active lubrication, which can be up to 50% and more, the deflection of the work rolls changes. This simultaneously changes the flatness condition (mainly in the rear scaffolds) and profile (mainly in the front scaffolds) of the rolling stock.

If a work roll bending is available as an actuator in the respective scaffolding, the setting limits are nevertheless reached more frequently in the case of large rolling force reductions. A more unstable run of the rolling stock, especially in Dünnbandwalzungen is the result.

It is customary to limit the rolling force reduction to a value of about 20%.

The invention is therefore based on the object of specifying a method for applying a lubricant to a working or support roller surface, which enables an improvement of the rolling process, leads to a reduction in the wear of the rollers and lowers the energy consumption of the finishing train.

This object is achieved by the characterizing features of claim 1. Advantageous embodiments of the invention are specified in the subclaims.

If a lubrication system, which conveys the lubricant from a reservoir via lines and nozzles to the working or support rollers, already 5 to 15 sec. Switched before entry of the rolling stock in the rolling stand, all dead times are compensated in the lubrication system, so that on In any case, before the tapping has formed a closed lubricating film on the work roll.

The decisive advantage of the method according to the invention is that over the entire length of the rolling stock a constant rolling force level for the respective framework results because a lubrication over the entire length of the rolling stock is maintained.

Due to the Walzkraftkonstanz overall higher rolling force reductions, for example, from 40 to 50%, achieve, whereby the load of the rolling mill in terms of wear and energy consumption is significantly reduced. Furthermore, the work roll wear is lowered by the higher rolling force reduction and thus extends the roll-in time (service life).

• ● konstantes Walzkraftniveau;
• ● keine mit der Walzkraft zusammenhängende Änderung des Planheitszustandes;
• ● keine mit der Walzkraft zusammenhängende Änderung des Bandprofiles,
• ● da auch die Kräfte am Anfang und am Ende des Walzgutes deutlich reduziert werden, können Gerüstvibrationen und Walzenschäden noch effektiver vermieden werden;
• ● daraus ergibt sich mehr Spielraum für Abnahmeumverteilungen und damit ergeben sich optimierte Stichpläne beim Walzen kritischer Produkte;
• ● da sich der Planheitszustand am Ende des Walzgutes aufgrund der Walzkraft nicht ändert, kann ein Verwalzen des Anfangs des Walzgutes vermieden werden.

The advantages of the method according to the invention are thus:

• ● constant rolling force level;
• ● no change in the flatness condition associated with the rolling force;
• ● no change in the strip profile associated with the rolling force,
• ● As the forces at the beginning and at the end of the rolling stock are significantly reduced, skeleton vibrations and roller damage can be avoided even more effectively;
• ● this results in more scope for redistribution and thus results in optimized pass schedules for rolling critical products;
• ● Since the flatness state at the end of the rolling stock does not change due to the rolling force, a rolling of the beginning of the rolling stock can be avoided.

Prerequisite for the application of lubrication according to the invention is that the gripping conditions are ensured at the beginning of the rolling stock.

The application of the lubricant according to the invention in a finishing train or a cast roll mill is advantageously possible from the second stand and for all subsequent stands without restriction.

• der Zustand der Walzenoberfläche nach dem Schleifen,
• der Arbeitswalzendurchmesser,
• das Arbeitswalzenmaterial,
• die einlaufende Banddicke,
• die eingestellte relative Abnahme,
• der Oberflächenzustand des einlaufenden Walzgutes ( Zunder, Temperatur, Rauheit, Material etc.),
• das eingesetzte Schmiermittel,
• die Schmiermittelmenge,
• die Walzgeschwindigkeit.

In the first finishing stand, no lubricant is generally applied due to the large thickness of the rolling stock (high gripping angle). In order to apply the lubricant according to the invention already in the second finishing stand, the present conditions of the respective system are taken into account. These include, for example

• the condition of the roll surface after grinding,
• the working roll diameter,
• the work roll material,
• the incoming strip thickness,
• the set relative decrease,
• the surface condition of the incoming rolling stock (scale, temperature, roughness, material etc.),
• the lubricant used,
• the amount of lubricant,
• the rolling speed.

If the gripping angle is in the critical range, the lubricating effect is at the beginning of the rolling stock by a smaller amount of lubricant or by a modified, i. limited properties of other lubricants.

When applying the method according to the invention for applying the lubricant to a roll surface, it is advisable to prepare the pass plan model of the finishing train for this operation. In this case, at least a doubling of the adaptation matrix should be provided so as not to adversely affect the adapted-out operation without roll gap lubrication. For physical models, the specification of different sets of friction coefficients - for lubricated and unlubricated conditions - for commissioning and for the introduction of new products and to avoid high adaptation values of great advantage.

Each friction change is associated with a change in lead, i. associated with a mass flow change or disturbance. Such a disturbance must be compensated by the control systems, which can lead to considerable difficulties in critical Dünnbandwalzungen.

A further advantage of the method according to the invention is that a constant overfeed is achieved with constant lubrication, which in turn results in a constant mass flow.

In the case of ferritic rolling, roll-gap lubrication is used to favorably influence the shearing texture on the surface. The application of the lubricant according to the invention brings about a homogeneous surface texture over the entire length of the rolling stock.

In order to avoid delays when switching on the lubrication system, the lubrication system includes the construction of a ring line with return to the lubricant tank and the installation of a switchable 3/2-way valve in front of the lubricant mixer (for example a static tube mixer).

Claims (6)

1. Method of rolling rolling stock, particularly for hot wide strip rolling in a finishing train or a casting rolling plant, in which a lubricant is applied directly to the surface of the working rolls or indirectly to the surface of the backing rolls with transfer to the surface of the working rolls before the rolling stock runs into the rolling gap of a roll stand, wherein a strongly adhering lubricating film forms on the working roll surface and which as intermediate layer between roll and rolling stock leads to a reduction in the friction in the rolling gap, characterised in that the lubricant is applied over the entire length of the rolling stock and the lubricating effect is therefore active over the entire rolling stock length.
2. Method according to claim 1, characterised in that a lubricating system which conveys the lubricant from a reservoir via ducts and nozzles to the working or backing rolls is switched on 5 to 15 seconds before entry of the rolling stock into the roll stand.
3. Method according to claim 1, characterised in that the lubricant is applied in the second and in each of the succeeding stands.
4. Method according to claim 1, characterised in that the lubricant is applied in the third and in each of the succeeding stands.
5. Method according to claim 1, characterised in that the lubricant is applied in the second and in any desired ones of the succeeding stands.
6. Method according to claim 1, characterised in that the lubricant is applied in the third and in any desired ones of the succeeding stands.