CA2072422A1 - Continuous grease lubrication system for metal casting moulds - Google Patents

Abstract

Abstract A lubricating system is described for continuous grease lubrication of a casting mould surface. The mould is one for effecting solidification of molten metal into a formed metal product including means adjacent to an inlet portion of said mould for feeding said molten metal into the mould and means for delivering a lubricating grease to a surface of said mould contacting the molten metal to substantially prevent adhesion of any solidified metal on said surface. It has a lubricating grease delivery system comprising at least one grease delivery channel arranged generally parallel to the mould surface, inlet means for delivering a flow of grease into said channel, a plurality of uniformly spaced restrictive flow passages extending across between said delivery channel and grease outlet holes adjacent the molten metal for delivery of grease to the mould surface, and means for feeding grease in either solid or liquid form to said delivery channel.

Description

Continuous Grease Lubrication System for Metal Casting Moulds Background of the Invention This invention relates to continuous metal casting systems, and more particularly to lubricating systems for continuous grease lubrication of a casting mould surface.
Casting moulds are used to shape molten metal and to extract heat from the metal to form a solid casting or ingot.
These moulds have two basic characteristics. The first is to extract heat to effect solidification, and the second is to provide a parting agent or lubricant to prevent adherence between the molten metal and the mould. The distribution of the lubricant over the surface of the inner mould wall has a substantial effect on the surface quality of the ingot.
Lubricated moulds are typically used in vertical direct chill (D.C.) casting systems with or without insulated or hot tops and in horizontal casting systems. Direct chill casting is widely used for the casting of aluminum and other like metals and in this system, the molten metal is poured into the inlet end of an open ended mould while liquid coolant is applied to the inner periphery of the mould to maintain heat transfer thereby initiating solidification of the metal as an ingot. Also, the same or a different coolant is normally applied to the exposed surface of the ingot as it emerges from the outlet end of the mould to continue the cooling effect on the solidified metal. A typical example of a direct chill casting mould is that described in Wagstaff, U.S. Patent 4,421,155 issued December 20, 1983. Other examples include Harrington et al., U.S. Patent 3,612,151 and Bryson, U.S.
Patent 3,713,47~.
It is also commonplace in D.C. casting to use a lubricating oil as parting agent or lubricant on the mould surface. The oil is typically castor oil, rapeseed oil, other vegetable or animal oils, esters, paraffins, synthetic liquids, etc. A problem with the use of oil as a lubricant is that substantial amounts are required to achieve uniform distribution and it is difficu:Lt subsequently to separate the oil from the cooling water used in D.C. casting.

2 2072~
U.S. Patent 4,917,171, issued April 17, 1990, describes a lubricatin~ system for a continuous casting mould in which a meltable lubricant, e.g. grease, is injected through orifices in the peripheral wall of the mould. The lubricant is fed from the outside of each orifice independently, necessitating either a very small number of orifices and thus poor distribution or a large number of orifices and an unacceptably expensive system.
It is also common to apply grease manually. However, this process is generally not acceptable for aggressive alloys or for long ingot lengths. Also, with manual application there is no control over the amount of lubricant used and re-application while casting is in progress constitutes a safety hazard.
Particularly with direct chill casting where cooling water is sprayed onto the surface of the emerging ingot and flows down into a collection sump, there is today a serious problem in the disposal of the coolant water contaminated by the lubricant. Thus, before the cooling water can be discharged, the oil or grease content thereof must be reduced to less than 5 ppm in some jurisdictions if the lubricant is a vegetable based material and it must be substantially O ppm if the lubricant is a mineral oil. This means that expensive separator systems must be used for separating the lubricant from the cooling water before discharge of the water. Grease has an advantage over oil in that the grease, which is normally solid at ambient temperatures, is generally easier to separate from water than is a flowable oil.
It is the object of the present invention to provide an improved lubricant delivery system which permits the use of a grease as lubricant in continuous metal casting in as effective a manner as oil.
Summar~ of the Invention The present invention relates to a process and apparatus for casting molten metal. The apparatus comprises a mould for effecting solidification of the molten metal into a formed metal product, means adjacent to an inl~t portion of the mould 2072~22 for feeding the molten metal into the mould and means for delivering a lubricating grease to a surface of the mould contacting the molten metal to substantially prevent adhesion of any solidified metal on the surface.
S The term "grease" as used herein is intended to indicate a lubricant which is solid at ambient temperatures and which readily melts into liquid form with heating. The grease may be of an animal, mineral or vegetable source and for environmental reasons animal or vegetable greases are preferred. For instance, a vegetable shortening used in baking may be used.
The grease delivery system of the present invention basically includes at least one lubricant delivery channel arranged generally parallel to the mould surface. Inlet means are provided for delivering a flow of grease under pressure into the delivery channel and a plurality of small flow passages extend between the delivery channel and the mould surface for delivering grease in liquified form from the channel to the mould surface. When the mould is operational, the grease within the delivery channel is normally in liquified fo~m and flows either under pressure or by gravity from the delivery channel through the small delivery passages to the mould surface. The grease may be liquified while contained within the delivery channel or it may be liquified prior to entering the delivery channel. The liquifying may take place because of heat input within the mould itself or the heating may be carried out externally of the mould.
One preferred embodiment of the novel grease delivery system of the present invention includes at least two grease delivery channels arranged generally parallel to the mould surface. These include a secondary channel laterally spaced a predetermined distance from the mould surface to be lubricated and a primary channel spaced from the secondary channel.
Inlet means are provided for delivering a flow of grease under pressure into the primary grease channel.
A plurality of uniformly spaced first restrictive flow passages extend across between the primary and secondary 4 2~72422 channels and a plurality of uniformly spaced second restrictive flow passages extend across between the secondary channel and grease outlet holes at the mould surface for delivery of grease to the mould surfacP. The second restrictive flow passages have effective diameters smaller than the first restrictive flow passages and the first restrictive flow passages have effective diameters smaller than the grease channels. In this mann~r, the frictional loss from the grease flow in the secondary grease channel is negligible, e.g. less than 10%, relative to the total friction loss of the total system whereby grease delivered under pressure to the secondary grease chanrel is transferred uniformly through the second restrictive flow passages to the mould surface.
Typically the second restrictive flow passages have smaller diameters, are shorter and are more closely spaced than are the first restrictive flow passages. While the required friction losses are typically based on the diameter of the restrictive flow passages, any combination of diameters, lengths and spacings of these passages may be used to obtain the required friction losses. Because the liquified grease in the distribution plate behaves rather like a Newtonian fluid, the dimensioning of the channels and restrictors around the mould czn be obtained using the methods described in Leblanc & Newberry, U.S. Patent 5,044,535, issued July 23, 1991 and incorporated herein by reference.
During casting, the secondary channel contains the grease in liquid form and this secondary channel may either be closed to the atmosphere and pressurized or it may be open to the atmosphere by way of top vents such that the liquified grease flows by gravity from the channel through the delivery passages to the mould surface. When the system is operated in the gravity feed mode, sufficient liquified grease is added to the secondary channel to supply a complete casting procedure.
Flow rates are determined by the number of lubricant outlets and amount of grease in the channels. Flow rates cannot be regulated for the gravity feed system as they can be for a pressurized system.
The delivery channel or channels and the flow passages may be formed within a distribution plate positioned above the mould or partially in a distribution plate and partially within the mould itself or entirely within the mould itself.
In one embodiment of the distribution plate, it is placed on top of and insulated from the mould and separate heaters are provided within the distribution plate. This means that the temperature of the distribution plate can be controlled independently of the temperature of the mould itself and this assures uniform temperature within the distribution plate thereby enhancing the uniformity of grease distribution at the lubricant outlets.
In another embodiment using a distribution plate, it is mounted directly on top of the mould without any intervening insulation and the primary distribution channel is formed within the distribution plate. The secondary distribution channel is formed within the mould itself as are the first and second sets of flow passages. This arrangement is highly dependent upon the material of the mould and the top manifold plate, as well as the immediate atmosphere for determining the temperature of the grease. The efficiency of this embodiment is directly related to the distance of the lubricant outlet from the molten metal, details of which are shown in Example 2.
According to yet another embodiment of the invention, a grease recirculating system is provided externally of the mould. This recirculating system is connected to a preferably low thermal conducting distribution plate positioned on top of the mould and the grease in the recirculating system is preferably heated in the grease reservoir. With this arrangement, there are two flow arrangements, the first being a recirculating arrangement in which the grease is simply circulated while passing through the distributior. plate and a second flow arrangement in which the recirculating heated grease is discharged through the distribution plate via at least one grease channel contained in the plate and flow 6 2072~22 passages extending across between the channel and the mould surface.
The grease delivery system of this invention may be used with moulds for a variety of ingot shapes, including extrusion and sheet ingot, with or without insulated or hot tops. It is of particular value with a casting device having a mould with an inner, axially extending wall defining a mould cavity, e.g.
a direct chill casting system.
One of the important advantages of this invention is that the grease can not only be used in much smaller quantity than lubricating oils, but grease is also much simpler to separate from cooling water than is the oil. Thus, when the cooling water and grease has cooled, the grease solidifies and may easily be separated from the water by physical means such as simple filtering. Moreover, in some situations the concentration of the grease in the water will already be sufficiently low that no separation of grease is required to meet local environmental standards.
Brief Description of the Drawinqs The invention will be more fully understood from the following description of embodiments thereof, given by way of example only, with reference to the accompany drawing, in which:
Figure 1 is a perspective view of a typical peripheral direct chill casting mould;
Figure 2 is a simplified sectional elevational view of a direct chill casting apparatus;
Figure 3 is a sectional view of a grease delivery plate according to the invention;
Figure 4 is a sectional view of a further grease delivery plate according to the invention;
Figure 5 is a sectional view of a direct chill casting mould showing a modified grease distribution system;
Figure 6 is a sectional view of a direct chill casting mould showing a further modified grease delivery system; and Figure 7 is a schematic flow diagram of an external grease recirculating system;

7 2072~22 Figure 8 is a plan view of a flow circuit of the invention;
Figure 9 is a plot of lubrication consumption v. mould temperature, and Figure 10 is a plot of lubrication consumption v.
distance from the lubricant outlet.
Description of the Preferred Embodiments The device shown in Figures 1 and 2 is a mould assembly having an open ended rectangular body configuration. The mould 10 has a vertical mould face 11 which comes into contact with the molten metal. A coolant manifold 12 is fed with coolant for the purpose of cooling the mould surface 11. For casting an ingot, molten metal 15 is fed via dip tube 14 into the mould and the metal is chilled sufficiently to form an outer skin while passing the mould plate wall face 11. The ingot thus being formed is then further cooled by water sprays --13. The ingot 30 being formed is supported by a stool 31 which moves downwardly and controls the casting rate. The forming ingot moves downwardly into a pit and the bottom of the pit includes a sump for collecting the coolant 13 sprayed onto the surface of the ingot 30.
Lubrication System One embodiment of the lubricating system of this invention is illustrated in Figure 3 and is intended to provide a uniform distribution of grease on the mould face under casting conditions. In the embodiment of Figure 3, a grease distribution plate 16 is positioned on top of mould 10.
This distribution plate incudes an inner edge face 17, a top face 18 and a bottom face 19. A layer of insulation 25 is provided between the bottom 19 of plate 16 and the top face of mould plate 10. This also provides protection against lubricant penetration. The inner edge face 17 includes a downwardly projecting lip 26 which protects the insulation 25 from direct contact with the molten metal and this inner face 35 17 and lip 26 merge into mould face 11.
The distribution plate 16 includes a large primary grease channel 20 extending generally parallel to the distribution 8 2072~22 plate face 17 and mould face 11 and remote therefrom. Grease is fed into channel 20 by a grease pump (not shown) through an inlet connector (not shown). A secondary delivery channel 23 of smaller cross-sectional dimension is positioned spaced from primary channel 20 and also spaced a short distance from distribution plate inner edge 17. A plurality of restrictive passages 21 extend across between channels 20 and 23. A
plurality of small restrictive delivery passages 24 extend from channel 23 to face 17.
Heating elements 27 and 28 are mounted within plate 16 and extend generally parallel to face 17. These heating elements provide uniform heating of the channels 20 and 23 as well as the restrictive passages 21 and the delivery passages 24.
In the particular embodiment shown in Figure 3, the distribution plate 16 consists of an upper portion 16a and a lower portion 16b joined by threaded studs (not shown) and o-ring seals 29. With this arrangement, the delivery passages 24 are in the form of grooves formed either in the bottom face of upper plate portion 16a or in the top face of lower plate portion 16b.
In the embodiment of Figure 4 a lubricating plate 66 is positioned on top of a mould 65 with a layer of insulation 67 therebetween. The outer edge of the insulation 67 is protected by means of a downwardly projecting lip portion 66a of plate 66. Positioned above the plate 66 is a grease distribution plate 68. This plate has a primary distribution channel 70 and a secondary distribution channel 6g formed therein. A horizontal bore 71 extends inwardly from one edge of plate 68 and is closed by means of plug 72. This bore is connected to the upper end of distribution channel 70 and has a restriction zone 73 therein. The inner end of this restriction zone connects to a further bore 74 extending upwardly from secondary channel 69. A set of restrictive flow passages 78 extend from channel 63 to outlets in the mould face.
The plate 68 is heated by means of heating elements 75 9 2072~22 and 76 and these are sealed from contact with the grease by means of O-rings 77.
Another embodiment is shown in Figure 5 in which a manifold plate 35 is mounted directly on top of the mould 10.
This plate includes a large primary grease channel 37 parallel to and remote from the mould face 11. A plurality of insulated restrictive flow passages 38 extend downwardly within the mould 10 from channel 37 to a secondary channel 39 formed within the mould. A second set of restrictive flow passages 40 extend from the channel 39 to outlets in the mould face 11. These restrictive flow passages 40 are positioned accurately at a specific distance from the metal meniscus level, this distance being dependent on the fluid viscosity index and the temperature of the mould face. The channel 37 15 is sealed by means of studs 36 and O-ring channels 41 and 42.
With the arrangement shown in Figure 5, grease is pumped into the primary channel 37 in either solid or liquid form.
During casting, pressure is maintained within the channel 37 such that grease in liquified form is uniformly distributed 20 through the passages 38, secondary channel 39 and passages 40 to the mould face 11. When solid lubricant is pumped into channel 37, the heat from the molten metal and the temperature of the mould wall serve to meet the grease.
The embodiment of Fighre 6 is generally similar to that of Figure 5, but is designed to deliver the grease by gravity flow rather than pressurized flow. Thus, a modified form of delivery plate 45 is used, again with O-ring channels 41 and 48 to provide seals. However, in this embodiment, the secondary channel 46 is left open to the atmosphere by way of vent holes 47. When this system is used, grease is pumped into channel 46 via channel 37 and flow passages 38 such that a substantially constant level of grease is contained along the length of the channel 46. When molten metal is fed into the mould, the heat of the molten metal maintains the grease in the channel 46 at a liquid temperature and this liquid grease flows from channel 46 through restrictive flow passages 40 to the surface of the mould. The vent holes 47 serve a 2Q72~

dual purpose of permitting gravity flow from the channel 46 and also providing a visual indication as to when the channel has been uniformly filled.
An external grease recirculating system is shown in Figure 7. This includes a grease reservoir 50 having heating elements (not shown) for maintaining the grease at a predetermined elevated temperature. An outlet (suction) line Sl extends from the reservoir to the inlet of a varia~le positive displacement pump 52. The discharge 53 from the pump travels through either line 59 or through lines 59 and 55 simultaneously depending on the positioning of a solenoid valve 54.
When the solenoid valve 54 is in closed position, hot liquified grease flows through line 59 and needle valve 60 and around a recirculating loop 61 within grease distribution plate 56. This hot li~uified grease serves to heat the distribution plate 56 prior to returning to reservoir 50.
During a casting, the solenoid valve is in the open position and this means that hot liquified grease flows through both lines 59 and 55. The proportion of flow between each of these lines 55 and 59 depends upon the adjustment of the needle valve 60. The hot liquified grease flowing through line 55 continues through distribution plate 56 and out through lubricant outlets 57. During casting, the amount of heat from the hot liquified grease generated within distribution plate 56 remains unchanged since the total flow of hot liquified grease through pl~te 56 remains the same whether solenoid valve 54 is open or closed. With this external recirculation system, the distribution plate 56 is kept hot at all times while pump 52 is running, since the heating medium is the preheated grease from reservoir 50. If the pump 52 is stopped while solenoid valve 54 is in the closed position, the grease plate 56 cools down causing the grease to solidify. This provides the advantage of reduced spillage from the lubrication plate when the mould is tilted.
The system also includes a relief valve 61 to protect the variable positive displacement pump 52 if the needle valve 60 2072~22 is accidentally closed while solenoid valve 54 is in the closed position.
The system may also include an air purge for purging the lines between casting runs and this may be connected to solenoid valve 54.
Figure 8 is a schematic plan view of a grease distribution plate 56. This uses the grease distribution channels and passages as shown in Figure 3, i.e. with a large primary grease channel 20 extending generally parallel to the edge faces of the plate 56, a secondary delivery channel 23 of smaller cross-sectional dimensions and laterally spaced from primary channel 20, a plurality of restrictive passages 21 extending across between channels 20 and 23 and a plurality of small restrictive delivery passages 24 extending from channel 23 to the mould face.
The distribution plate 56 is heated by means of the recirculating loop 61 connected to the hot liquified grease inlet line 59 and outlet line 58. The primary grease channel 20 is connected to inlet line 55.
The following examples are also illustrative of the invention.
Example 1 Tests were conducted using a system generally of the type shown in Figures 1, 2 and 3. The actual casting system used was a conventional 26"x65"x5" Supertruslot Wagstaff Mould.
Casting trials were carried out using AA 5182 and AA 3104 alloys and the grease used was Tenderflake3 household shortening. The grease was injected by means of a standard injector pump and the grease was pumped into primary channel 20 in solid form at room temperature. There it was heated to just above the melting point of 40C and the grease then moved through the passages 21, channel 23 and passages 24 in liquid form. It was found that when casting AA 3104 alloy, an entirely satisfactory lubrication of the mould surface could be maintained with a grease flow of less than 3 cc/min. When AA 3104 alloy is cast in the same Wagstaff mould using conventional castor oil as lubricant, approximately 30-40 2072~22 cc/min of the oil is required~
Example 2 Studies were conducted on the gravity flow lubricant system of Figure 5 to determine the optimum distance of the lubricant outlet 40 above the meniscus of the molten metal 15.
These were theoretical determinations based on flow down an inclined plane. It was determined that the mould temperature varies between the lubricant outlet and the meniscus, the temperature at any given level also being dependent on the alloy being cast. Three different alloys were tested, these being (1) Al-4.5 Mg-0.35 Mn, (2) 99.7 Al and (3) Al-1 Mg-l Mn.
The temperatures obtained at four different distances above the meniscus are shown in Table 1 below: -. .. . ___._ _ , l Alloy Composites I(mm) Al-4.5 Mg-0.35 Mn 99.7 Al Al-l Mg-1 Mn I

I .

From the above results, it has been found that mould temperature at any given level is lowest for Al-4.5 Mg-0.35 Mn and highest for Al-1 Mg-l Mn. The results are also shown in the graph of Figure 9 for both a high viscosity lubricant (castor oil) and a low viscosity lubricant (Tenderflake~
Canola), with higher consumptions being shown for the higher viscosity lubricant than for the lower viscosity lubricant.
The lubricant consumption was also measured at the four different levels above the molten metal meniscus and those results are shown in the graph of Figure 10. These results show an increasing lubricant consumption with increasing distances above the meniscus and again higher consumptions for higher vis~osity lubricants.

Claims (21)

1. An apparatus for casting molten metal comprising: a mould for effecting solidification of the molten metal into a formed metal product, means adjacent to an inlet portion of said mould for feeding said molten metal into the mould and means for delivering a lubricating grease to a surface of said mould contacting the molten metal to substantially prevent adhesion of any solidified metal on said surface, characterized in that the lubricating grease delivery means comprises at least one grease delivery channel arranged generally parallel to the mould surface, inlet means for delivering a flow of grease into said channel, a plurality of uniformly spaced restrictive flow passages extending across between said delivery channel and grease outlet holes adjacent the molten metal for delivery of grease to the mould surface, and means for feeding grease in either solid or liquid form to said delivery channel.

2. An apparatus according to claim 1 wherein the delivery channel and passages are formed in a grease distribution plate mounted on top of the mould.

3. An apparatus according to claim 2 wherein an insulating layer is positioned between the plate and the mould.

4. An apparatus according to claim 1 wherein at least one of said channel and passages is formed in the mould.

5. An apparatus according to claim 1 wherein the means for feeding grease to the delivery channel includes means for maintaining the grease under pressure within said channel.

6. An apparatus according to claim 1 wherein the delivery channel is arranged to feed grease to the mould surface by gravity flow.

7. An apparatus according to claim 3 wherein the distribution plate includes heating means.

8. An apparatus according to claim 1 wherein the means for feeding grease to the delivery channel comprises a grease reservoir and recirculating loop with heating means to heat the grease to the liquid state and valve means for changing the grease flow from recirculation to discharge to the mould surface.

9. An apparatus according to claim 1 wherein part of the recirculating loop passes through a distribution plate whereby the distribution plate is heated by the heated recirculating grease.

10. An apparatus according to claim 6 wherein the delivery channel has substantial height relative to its width and has vents to the atmosphere at the top thereof.

11. An apparatus for casting molten metal comprising: a mould for effecting solidification of the molten metal into a formed metal product, means adjacent to an inlet portion of said mould for feeding said molten metal into the mould and means for delivering a lubricating grease to a surface of said mould contacting the molten metal to substantially prevent adhesion of any solidified metal on said surface, characterized in that the grease delivery means comprises at least two grease delivery channels arranged generally parallel to the mould surface, including a secondary channel laterally spaced a predetermined distance from the mould surface to be lubricated and a primary channel spaced from the secondary channel, inlet means for delivering a flow of grease under pressure into said primary channel, a plurality of uniformly spaced first restrictive flow passages extending across between said first and second channels and a plurality of uniformly spaced second restrictive flow passages extending across between said second channel and grease outlet holes adjacent the molten metal for delivery of lubricant to the mould surface, said second restrictive flow passages having effective diameters smaller than said first restrictive flow passages and said first restrictive flow passages having effective diameters smaller than said lubricant channels, such that the friction loss from lubricant flow in the first lubricant channel is negligible relative to the total friction loss of the total system whereby lubricant delivery under pressure to said first lubricant channel is transferred uniformly through said second restrictive flow passages to the mould surface and heating means for heating the grease such that it is in liquid form at least in said second channel and second restrictive flow passages.

12. An apparatus according to claim 11 wherein the delivery channels and passages are formed in an oil plate mounted on top of the mould.

13. An apparatus according to claim 11 wherein at least one of said channels and passages is formed in the mould.

14. An apparatus according to claim 11 wherein the delivery channels and passages are dimensioned such that friction loss from the flow of lubricant in the first delivery channel is less than 10% of the total friction loss of the total system.

15. In a process for the production of metal ingots by the continuous casting process comprising the steps of (a) providing means for supplying molten metal to a mould adjacent the inlet portion of the mould, (b) feeding molten metal into the mould, (c) at least partially solidifying the molten metal within the mould and (d) withdrawing the at least partially solidified molten metal from the mould, the improvement which comprises providing at least one lubricant delivery channel arranged generally parallel to the mould surface, inlet means for delivering a flow of grease under pressure into said channel, a plurality of uniformly spaced restrictive flow passages extending across between said delivery channel and grease outlet holes adjacent the molten metal for delivery of grease to the mould surface, and heating said grease to liquid form and flowing said liquified grease through said channel and passages such that the friction loss from grease flow in the lubricant delivery channel is negligible relative to the total friction loss of the total system whereby the grease is transferred uniformly through said restrictive flow passages to the mould surface.

16. A process according to claim 15 wherein the friction loss from the flow of lubricant in the delivery channel is less than 10% of the total friction loss of the total system.

17. A process according to claim 15 wherein the grease is liquified by passing through a heated distribution plate mounted on top of the mould.

18. A process according to claim 15 wherein the grease is liquified by heat from the mould.

19. A process according to claim 15 wherein the grease is liquified remote from the mould and is recirculated in a loop, part of which is the mould or a grease distribution plate mounted on the mould.

20. A process according to claim 15 wherein the grease is a vegetable grease.

21. A process according to claim 20 wherein the grease is a vegetable lard or shortening.