WO1995023662A1

WO1995023662A1 - Lubrication of casting rolls

Info

Publication number: WO1995023662A1
Application number: PCT/GB1995/000392
Authority: WO
Inventors: Peter George Grocock; Philip Milroy Thomas; David Tucker
Original assignee: Davy Mckee (Poole) Limited
Priority date: 1994-03-03
Filing date: 1995-02-24
Publication date: 1995-09-08
Also published as: GB9404109D0

Abstract

A roll caster has provision to reduce sticking of the cast strip to the or each roll. An applicator (5) engages with each roll (1) and over the length of the roll which corresponds to the width of the strip to be cast a layer of parting agent of substantially uniform thickness. The applicator may include felt blocks (8) which seal against the roll with a slot (10) between the blocks containing the liquid parting agent (14).

Description

LUBRICATION OF CASTING ROLLS

This invention relates to a caster for casting metal strip and which includes at least one casting roll. In particular, the invention relates to a method of, and apparatus for, applying a parting agent (lubricant) to the or each roll.

Roll casting is an established technology for the production of metal strip. In one such process, molten metal, such as aluminium or aluminium alloy, is fed into the bite of a pair of cooled counter-rotating rolls. The molten metal solidifies in contact with the casting rolls and then undergoes a hot deformation before exiting the caster as solid strip having a gauge for example in the range 6-10mm,

A major problem of the casting process is the tendency of the cast strip to stick to one or both of the casting rolls. It is known-that the application of a parting agent, such as a suspension of colloidal graphite in water, to the casting rolls is beneficial in reducing this sticking. The parting agent is usually applied to the casting rolls in the form of a fine spray,

The spraying of the parting agent may result in a non-uniform layer of parting agent being deposited on the surface of the rolls and this is undesirable because the thickness of the parting layer affects both the rate at which heat is removed from the solidifying strip and the friction conditions in the roll bite. In areas that remain under-coated, there is a tendency for sticking to occur whereas, in areas where there is an excess of parting agent, the rate of heat removal is diminished and defects can result.

The problem of sticking becomes more serious as the as-cast thickness of the strip is reduced. At as-cast gauges less than approximately 4mm it is essential that the layer of parting agent is as uniform as possible and it has been demonstrated that strip of less than 1mm can be produced provided the parting agent is applied uniformly. It has also been demonstrated that, as the rotational speed of the caster is increased, the rate of application of the parting agent has to be increased, otherwise sticking can result.

According to a first aspect of the present invention, in a method of casting metal strip in a caster which includes at least one rotating casting roll, molten metal is introduced into contact with part of the length of the periphery of the or each roll and prior to the contact of the molten metal with the roll, a layer of parting agent of substantially uniform thickness is applied to only that part of the roll which is to be contacted by the molten metal.

According to a second aspect of the present invention, a caster having at least one casting roll for casting metal strip and the or each roll having an applicator which engages the peripheral surface of the roll and applies a layer of parting agent of substantially uniform thickness to the roll only along that part of the length of the roll which is to be contacted by the molten metal.

In order that the invention may be more readily understood it will now be described, by way of example only, with reference to the accompanying drawings in which:

Figure 1 is a diagrammatic side elevation of a two roll caster in accordance with the invention,

Figure 2 is a perspective view of one of the rolls of Figure 1,

Figure 3 is a sectional end view of the lubrication applicator shown in Figure 2.

Figure 4 is a view from below of the applicator shown in Figure 2 and

Figure 5 is a sectional end view similar to Figure 3 but of an alternative embodiment of the invention.

Referring to Figure 1, a twin roll caster has two counter rotating spaced apart cooled rolls 1, 2 and a nozzle 3 for introducing molten metal into the gap between the rolls to produce a cast strip 4. To prevent sticking of the cast strip to one or other of the rolls, parting agent is applied to the surface of each roll to act as a lubricant. According to the present invention a layer of parting agent of substantially uniform thickness is applied to that part of the length of each roll which is to be contacted by molten metal. To this end each of the rolls has a lubrication applicator 5. The device 5 engages the roll on a part of its periphery which is at that time, upstream of the part against which the molten metal engages so that a layer of parting agent is applied to the roll before the molten metal comes into contact with it,

Referring to Figure 2. each applicator 5 comprises an elongate member 6 of channel section which faces the roll surface and parting agent (lubricant) is introduced into the channel through feed pipes 7 spaced apart along the length of the channel. The channel 6 can be divided into sections with each section being separated from its neighbour and each section receiving lubricant through a separate pipe 7 with a valve 7 ' so that the amount of lubricant can be varied.

Figures 3 and 4 show in more detail the applicator 5 shown in Figure 2. At each side of the channel in member 6, extending in the direction of its length, there is a generally rectangular elongate block 8 and at each end of the channel there is another generally rectangular block 9. The blocks 8 and 9 together define a slot 10 extending in the direction of the length of the channel and into which the lubrication feed pipes 7 extend. A backing plate 11 is present in the channel and bears against the blocks 8 by means of springs 12 which act between the base of the channel member and the backing plate. In use, the springs 12 urge the blocks 8 against the periphery of the roll, It is convenient for the blocks 8 to be of a felt or graphite material and for the blocks 9 to be of graphite. The blocks 8 are secured along their length to a rectangular spacer 8¹ which is located between the upper ends of the blocks in the slot 10 and which is secured to the backing plate. The blocks 8 bear against the roll and form seals therewith which keep a puddle 14 of the parting agent in the slot 10 in contact with the roll thereby applying a layer of the parting agent to the part of the surface of the roll as it comes into contact with the liquid parting agent in the slot. The block 8 which is downstream of the parting agent in the applicator acts as a wiper to even out the parting agent deposited on the roll into a layer of substantially uniform thickness.

An alternative arrangement shown in Figure 5 comprises an elongate block 13 of felt material mounted in the channel member and urged against the surface of the roll by springs 12 acting against the backing plate 11, The liquid lubricant is delivered into and impregnates the felt block which acts as a wick and transfers the liquid lubricant to the part of the surface of the roll which is contacted by the block.

In all embodiments of the invention, steps are taken to ensure that liquid lubricant is only applied to that part of each roll against which the molten metal comes into contact, i.e. along the length of the rolls which correspond to the width of the strip which is to be cast. To prevent leakage of lubricant from the ends of the channel shaped applicator, a clamping force may be applied to each end to strongly urge the blocks 9 firmly against the roll. When the width of the cast strip is to be changed, the blocks 8 and 9 in the channel can be replaced with blocks which change the length of the slot 10 to correspond to the required strip width.

Referring again to Figure 1, the applicators 5 may be used in conjunction with water boxes [not shown] which are used to apply cooling liquid to the surface of each roll. In Figure 1 the segments 15 shown in broken lines on each roll indicate the range of positions that the devices can take up dependent upon casting rate and temperature. When water boxes are used it is convenient for the devices 5 to be located at the sides of the water boxes which are away from the strip being cast. It could be dangerous to locate the device 5 on the side of the rolls adjacent the nozzle 3 in case the liquid parting agent and molten metal come into contact with each other.

The lubricant, which is conveniently a suspension of colloidal graphite in water, is applied to the device 5 at a rate based on the speed of rotation of the roll.

Claims

Claims :

1. A method of casting metal strip in a caster which includes at least one rotating casting roll, in which molten metal is introduced into contact with part of the length of the periphery of the or each roll and prior to the contact of the molten metal with the roll, a layer of parting agent of substantially uniform thickness is applied to only that part of the roll which is to be contacted by the molten metal.

2. A method as claimed in claim 1 in which a puddle of liquid parting agent is brought into contact with said part of the roll to deposit a layer thereon and thereafter the layer is wiped to ensure that the thickness of the layer is substantially uniform.

3. A method as claimed in claim 1 in which a body impregnated with liquid parting agent is urged against said part of the roll to deposit said layer on the roll.

4. A method as claimed in claim 1, 2 or 3 in which the parting agent is a suspension of colloidal graphite in water.

5. A caster having at least one casting roll for casting metal strip and the or each roll having an applicator which engages the peripheral surface of the roll and applies a layer of parting agent of substantially uniform thickness to the roll only along that part of the length of the roll which is to be contacted by the molten metal.

6. A caster as claimed in claim 5 in which the or each applicator comprises two elongate blocks urged into sealing relation with the periphery of the roll, said blocks being spaced apart to define a slot which overlies the part of the length of the periphery of the roll to which parting agent is to be applied and means for introducing liquid parting agent into the slot to form a puddle of parting agent therein in contact with the roll. - 1 -

I . A caster as claimed in claim 6 in which the two elongate blocks and two further blocks which close off the ends of the slot are located in an elongate member of channel section.

8. A caster .as claimed in claim 7 in which one or more biaεsing means are located in the member of channel section to urge the elongate blocks and the further blocks into contact with the roll.

9. A caster as claimed in claim 7 or 8 in which the elongate blocks are of felt or graphite and the further blocks are of graphite.

10. A caster as claimed in claim 5 in which the or each applicator comprises an elongate block of felt corresponding in length to the part of the length of the roll to which parting agent is to be applied, means for urging the block into engagement with the roll and means for introducing liquid parting agent into the block to impregnate the block with parting agent.

II. A caster as claimed in claim 5 comprising a pair of casting rolls, a nozzle on one side of the rolls for introducing molten metal into the bite between the rolls, and each roll having a water box associated therewith for applying cooling liquid to the surface of the roll.