|Title of Invention||
"LIGHT-METAL PART BLANK TO BE CAST INTO A LIGHT METAL CASTING"
|Abstract||A light-metal-part blank which is to be cast into a light-metal casting, with a roughness of 30-601m on its external surface that will be surrounded by the material of the light metal casting component, the topography of this surface being made up of dug-out portions of material or raised portions of material running out to a point in a shape that of a pyramid or lancet, the bases thereof blending directly into the base structure of the blank.|
|Full Text||Light-metal-pait blunk to be cast
The invention relates to a light-metal-part blank which is to be cast into a light-metal casting, and to a method for producing the said blank, as is known, for example, from DE 44 38 550 Al in the instance of a cylinder liner cast into a crankcase.
Casting separately manufactured cylinder liners into light-metal crankcases makes it possible to optimize the running properties of the reciprocating piston in the cylinder liner, irrespective of the material of the crankcase. It has been possible, even already, to achieve notable success in this connection. However, problems with casting the cylinder liners into the light-metal crankcase may arise due to the fact that the bonding the outside of the liner with the crankcase material is inadequate. When the engine is running, materially imperfect bonding may cause the emission of waste heat from the reciprocating-piston engine to be impeded and, in particularly unfavourable instances, may even lead to a loosening of the cylinder liner in the crankcase. As regards other parts to be cast in, for example forged rotor recesses in a cast piston, good bonding is indispensable, if only for reasons of strength.
DE 43 28 619 C2 goes into the problems involved in good material bonding of the light-metal components during casting in, in particular in the instance of a cylinder liner to be cast in, and arms at achieving a pore-free material union between the outside of the liner and the case material by means of controlled preheating of the cylinder liner. The cylinder-liner blank preheated to a specific temperature, for example 450°C, and introduced into the casting mould has its surface melted (incipiently) by the inflowing melt of the case material, and an intimate bond with the case material is thereby made. A high melt flow directed parallel to the contact surface further assists this effect, not only by bringing about increased ncipient melting as a result of a better heat exchange, but also by washing off the 3xide skin, which is always present, from the contact side of the liner. This intensive relative flow of the melt can be ensured by various measures. The said publication mentions, in this respect, a clever choice and distribution of the gates or an agitation of the melt or even an induction of electrical eddy currents which cause fluid flows in
the melt. A disadvantage of this method is that the liner blanks preheated to temperatures which bring about reliable incipient melting are difficult to handle, especially during the casting of multi-cylinder crankcases. With the gradual introduction of the individual preheated liners into the casting die, either different liner temperatures have to be allowed for, due to cooling, during the casting operation or heating elements have to be provided in the casting die so that the liner blanks already introduced are kept hot, thus making the casting die more complicated and adversely affecting the dissipation of heat from the solidifying cast workpiece. At all events, it is necessary to install a preheating furnace, which incurs further investment costs and, above all, regular power-supply costs. Moreover', the high preheating temperatures may lead to undesirable structural changes in the material of the cylinder liner, which may adversely influence the running properties of the latter. In any case, tribologically relevant structural changes are obtained if the liner blank, while being cast in, is melted down nearly into the region of the running surface. It must be taken into account here that a machining oversize of at least about 1 mm is provided on the inside of the liner blank. In order, therefore, to prevent the liner blank from actually melting through at all locations, a correspondingly thick-walled blank would have to be provided. For reasons of a cylinder spacing which is as small as possible, however, it is desirable to have as thin-walled a cylinder liner as possible. On the other hand, if, for whatever reason, the liner is not sufficiently preheated, that is to say by way of precaution or through carelessness, then, at least in die casting, only very short periods of time are available for filling the mould and until solidification commences, so that the incipient-melting measures of the type discussed cannot take effect or can take effect only very incompletely in the short periods of time available here.
The present invention seeks to improve the relevant generic blank of a light-metal structural part to be cast in, and the corresponding production method, to the effect that, even without preheating, the blanks, while being cast in, make an intimate material union over a wide area with the cast material of the cast-round part.
Accordingly there is provided a light-metal-part blank which is to be cast into a light-metal casting, with a roughness of 30-60jim on its external surface that will be surrounded by the material of the light metal casting component, the topography of this surface being made up of dug-out portions of material or raised portions of material running out to a point in a shape that of a pyramid or lancet, the bases thereof blending directly into the base structure of the blank.
Accordingly there is also provided a method for producing a light-metal-part blank which is to be cast into a light-metal casting, whereby a blank is firstly made and processed to a desired shape and desired dimensions and the external surface of the blank that will be surrounded by the material of the casting component is blasted with a directed jet of particles made from a hard substance entrained in a flow of gas, the particles used to blast the surface being sharp-edged broken corundum, preferably pure corundum and having an average particle size (d) of preferably 70jam, and the surface of the blank blasted in this manner is roughened to a roughness of 30-60nm and the material of the blank close to the surface is dug out or opened up in a pyramid-shaped or lancet-like pattern.
According to the present invention there is provided a light-metal-part blank which is to be cast into a light-metal casting, the blank having a roughness of more than 20 um on its outer surface which is to be covered by the material of the light-metal casting, the topography of this outer surface being formed by tapering,
approximately pyramid-like or lancet-like protruding material scabs or material
accumulations, which merge directly at their base into the basic structure of the blank.
The present invention also provides a method for producing a metal blank
which is to be cast into a casting, in which method first of all a blank is produced and machined to the desired shape and desired size and, subsequently, the outer surface of the blank, which surface is to be covered by the material of the casting, is blasted with a directed jet of particles which consist of a hard material and are carried along in a flowing gas, wherein corundum, which is broken so as to have sharp edges and has an average grain size of about 70 µm is used for the particles for blasting the surface of a blank which consists of a light-metal alloy and is to be cast into a casting likewise consisting of light metal, and, thereby, the blasted surface of the blank is roughened and that material of the blank which is near the surface acquires pyramid-like or lancet-like protruding scabs or accumulations.
It is important that the outer contact surface of the blank has a topography with a multiplicity of tapering material elevations, for example of pyramid-like or lancet-like form, which merge, undisturbed, at their base, over a wide area, into the basic material of the blank. Despite the existing oxide skin, the tips of this multiplicity of small pyramid-like or lancet-like protruding material scabs or material accumulations on the contact side of the blank begin to melt immediately, in the region of their tip, when they come into contact with the melt of the cast-round part, because, on this small contact zone, the heat energy supplied by contact with the melt is sufficiently high and the dissipation of heat into the depth of the material is initially still low, so that a sufficient energy density is locally available in order to overcome the barrier of the oxide skin locally. The incipient melting which has been initiated spreads very quickly in the near-surface layer on the contact side of the blank. The pyramid-like or lancet-like protruding material scabs or material accumulations thus constitute initiating locations for the incipient-melting operation. On account of the rapid progress of an incipient-melting operation once begun and since the contact side is densely covered by such initiating locations, the locations where incipient melting has begun very quickly coalesce into a continuous near-surface incipient-melting zone. The incipient melting therefore spreads quickly over the surface area, but penetrates only relatively little into the depth of the blank wall, so that the structure remains
unaffected on the opposite side of the wall of the blank, for example on the piston running side.
The following numerous and widely differing advantages can be achieved by means of the invention;
• elimination of preheating the cast-in part, in particular the liner blank to be Cast
in, along with the associated investment and operating costs and handling
• roughening the outer or contact surface of the cast-in part achieves, at the same
tune, the effect of cleaning, which is necessary in any case, so that separate
cleaning is unnecessary; the outlay in terms of investment costs and regular costs
for roughening is approximately comparable to that for cleaning, so that
roughening requires virtually no extra outlay;
• in the case of liner blanks to be cast in, tribologically relevant structural changes
on the running side of the liner blank can be avoided with a high degree of
• it becomes possible for the cast-in part to have smaller wall thicknesses; at the
very least, smaller wall thicknesses can be controlled with greater process
reliability than in a casting-in operation with preheating of the casting;
• smaller cylinder wall thicknesses allow smaller cylinder spacings and therefore,
with the piston capacity remaining the same, shorter, lighter and more cost-
effective engines, which allow smaller engine spaces in the motor vehicle and, due
to the mass involved, lower fuel consumption for the motor vehicle driven
• in comparison with the casting in of non-roughened cast-in parts, a better
metallurgical bond which is largely of uniformly high quality over the extent of
the contact surface can be achieved between the cast-in part and the cast-round
• as a result, where cylinder liners are concerned, as measurements have shown,
higher manufacturing accuracy, in particular less manufacturing related cylinder
warping, can be achieved, because a cylinder liner which has good materialing
with bond the crankcase is more rigid than a liner essentially only positively
due to the better metallurgical bonding of the liner to the case material, it is possible to achieve higher rigidity, a cylinder wall which is uniform in the circumferential and axial directions, that is to say homogeneous, and, when the cylinder head is being assembled, with a gasket interposed, less assembly-related cylinder warping;
by virtue of the high-strength material bonding of the cylinder liner in the crankcase, there is no need for retaining collars on the end faces of the liner, with the result that the liner is designed particularly simply from a manufacturing point of view and can thus be produced cost-effectively;
as regards cylinder liners, due to the better metallurgical bonding of the liner to the case material, better heat transmission which is more uniform over the surface area, a more uniform temperature profile of the cylinder liner in the circumferential and axial directions and less thermally related cylinder warping can be achieved when the engine is running;
moreover, the temperature level of the well bonded-in cylinder liner as a whole is lower than in cylinder liners which are cast in without being roughened, and this, when the engine is running, has a favourable effect on the oil evaporation rate and therefore on the oil consumption and on the content, in the exhaust gas, of hydrocarbons produced by the lubricating oil;
higher manufacturing-related dimensional accuracy, less assembly-related cylinder warping and less operation-related thermal warping of the cylinder liners in turn make it possible to achieve a smaller piston clearance, which has a favourable effect on the content, in the exhaust gas, of hydrocarbons produced by the fuel; furthermore, the high dimensional accuracy of the running surface causes the piston to vibrate to a lesser extent and thus results in smoother running of the engine;
however, the high dimensional accuracy of the running surface also results in a better sealing effect of the piston rings and therefore lower blow-through losses and a lower oil consumption, that is to say higher efficiency, lower fuel consumption and lower emissions, particularly of hydrocarbons produced by the oil.
An embodiment of the invention is now described below with reference to
the drawing, in which:
Figure 1 shows a partial sectional view of a reciprocating-piston engine with a cylinder liner cast therein,
Figure 2 shows a detail of the blank of the cylinder liner for the reciprocating-piston engine according to Figure 1,
Figure 3 shows a metallographic cross-section through the wall of the blank according to Figure 2 in a near-surface region - detail III according to Figure 2 - showing the nature of the roughness of the outer surface,
Figure 4 shows a scanning electron microscope photograph of an outer surface detail - detail IV in Figure 2 - of the blank according to Figure 2, showing the topography of the surface,
Figure 5 shows a metallographic cross-section through the cylinder wall of the
crankcase according to Figure 1 in the boundary region between the cast-in
cylinder liner and the basic case material - detail V according to Figure 1 -
at a location where there is good material bonding between the cylinder
liner and the basic case material,
Figure 6 shows a metallographic cross-section similar to that according to Figure 5, but with a magnification lower by the factor 10 than that of Figure 5 and at a location where there is a porous bond between the cylinder liner and the basic case material,
Figure 7 shows a metallographic cross-section similar to that according to Figure 6 and with the same magnification as Figure 6, but at a location without any bonding between the cylinder line and the basic case material,
Figures 8a to 8f show a series of ultrasonic reflectance photographs of the running surfaces of cast-in cylinder liners of a six-cylinder crankcase which were roughened on the outside, according to the invention, before being cast in, showing the distribution of the bonding between the cylinder liner and the basic case material over the laid-out generated surface of the cylinder liner, the cross-hatched region, which represents good material bonding, taking up proportionally a large surface area,
Figures 9a to 9h show, for comparison, a similar series of ultrasonic reflectance photographs of a crankcase which is of basically the same design, but has
eight cylinders, in which the liner blanks were lathe-turned with cutting on
the outside in a conventional way, the cross-hatched region, having good
bonding, taking up proportionally a small surface area, Figure 10 shows a method arrangement for blasting the outer surface of the liner
blank with particles, Figure 11 shows an enlarged detail of a few particles of hard material which are
broken so as to have sharp edges and are used in the surface blasting
according to the invention, and Figure 12 shows a graph with different frequency distributions of the size of the
blasting particles in the new state, after use and after the blasting material
has been treated.
The reciprocating-piston engine partially illustrated in Figure 1 contains a die-cast crankcase 2, in which cylinder jackets 4 which are free-standing at the top (of so-called open-deck design) are arranged, each for receiving a cylinder liner 6, in which a piston 3 is guided so as to be movable up and down. A cylinder head 1 having the devices for charge exchange and charge ignition is mounted at the top of the crankcase 2, with a cylinder-head gasket being interposed. A cavity for forming a water jacket 5 for cylinder cooling is provided around the cylinder jacket 4, inside the crankcase.
The cylinder liner 6 is produced beforehand as an individual part from a preferably hypereutectic aluminium/ silicon alloy, by a method which is not of any more interest here, and is then cast as a blank into the crankcase 2 and finish-machined together with the crankcase.
It is important, when the cylinder liner is cast into the crankcase, that a good, undisturbed material bond is made between the liner material and the case material over as large a proportion of the surface area as possible. For this purpose, the blank 9 has, on its outer surface 10, which is to be surrounded by the material 16 of the light-metal crankcase 2, a specific minimum roughness of 20 µm, preferably of 30 to 60 µm,, the topography of this surface being formed by tapering, approximately pyramid-like or lancet-like protruding material scabs or material accumulations 11. The outwardly tapering material elevations 11, of random shape and size and distributed approximately uniformly over the surface 10, merge, undisturbed, at their
base, over a wide area, into the basic material of the cylinder liner. When the melt of the case material meets the outer surface 10 of the cylinder liner, despite an oxide skin, the tips of this multiplicity of small material elevations begin to melt immediately, because, on this small contact zone, the heat energy supplied by contact with the melt is sufficiently high and the dissipation of heat into the depth of the material is initially still low, so that a sufficient energy density is locally available in order to be capable of overcoming the barrier of the oxide skin locally. The incipient melting which has been initiated spreads very quickly in the near-surface layer on the contact side of the. lines blank. On account of the rapid progress of an incipient-melting operation once begun and since the contact side is densely covered by such initiating locations, the locations where incipient melting has begun very quickly coalesce into a continuous near surface incipient-melting zone. The incipient melting therefore spreads quickly over the surface area, but penetrates only relatively little into the depth of the liner wall, so that the structure remains unaffected near the piston running side of the liner, a machining oversize of at least 1 mm having to be taken into account here too. During the casting-in operation, despite a low temperature level of the cylinder liners introduced into the casting die, a good material bond is made over a wide area between the cylinder liner and the crankcase. By virtue of the low temperature level, for example room temperature, the cylinder liners can be handled and stored without difficulty. Good bonding during casting-in even occurs when the cylinder liners introduced into the casting die are indirectly cooled via the die-side centring mandrel, onto which they are slipped in a specific position. By virtue of this cooling, for example due to a flow of water through the centring mandrel, not only can the cooling times of the casting be reduced and therefore productivity increased, but it is also possible to keep the liner structure temperature well below the melting temperature, heating even below the melting temperature sometimes bringing about a change of structure.
The quality of the good material bond which can be achieved will be explained in more detail below with reference to Figures 5 to 9. The series of Figures 5, 6 and 7 shows three fundamentally distinguishable bond qualities in a metallographic cross-section taken from the contact zone 17 between a cast-in cylinder liner and the basic case material - detail V according to Figure 1.
Figure 5 shows, in a very high magnification indicated by an extended scale, good material bonding between the cylinder liner and the basic case material, the said bonding being indicated by cross hatching in the illustrations of Figures 8a to 8f and 9a to 9h. The illustration of Figure 5 clearly reveals the undisturbed transition of the material 15 of the cylinder liner into the material 16 of the crankcase at the former contact zone 17.
Figure 6 shows a metallographic cross-section similar to that of Figure 5, but with a magnification lower by the factor 10, as can be seen from the scale indicated, at a location where there is a porous bond between the cylinder liner and the basic case material, the extent of which bond is illustrated by dots in the illustrations of Figure 8a to 8f and 9a to 9h. Here, small locations where there is good bonding alternate with more extensive regions of a front-like contrast between the different materials, air inclusions also being incorporated in these regions.
In the metallographic cross-section according to Figure 7, shown with the same magnification as Figure 6, a location without any bonding between the cylinder liner and basic case material can be seen; such regions are left white in the illustrations of Figures 8a to 8f and 9a to 9h. A small gap with a width of at least 1 fim and a plurality of air inclusions can be seen here at the contact zone 17.
Figures 8a to 8f, on the one hand, and Figures 9a to 9h, on the other hand, show ultrasonic reflectance photographs (more details of these are given below) of the running surfaces of cast-in cylinder liners of a 6-cylinder crankcase and 8-cylinder crankcase, respectively, the said cylinder liners being treated differently on the outside before being cast in, Figures 8a and 9a being assigned to the first cylinder, 8b and 9b to the second cylinder, etc., and Figure 8f being assigned to the sixth, and Figure 9h to the eighth, cylinder of the crankcase. Both instances are concerned with engines having a V-shaped arrangement of the banks of cylinders, which is why the reflectance photographs of the individual cylinders are arranged in two rows. The long sides of the rectangles correspond respectively to the upper and the lower end of the cylinder running surface. The short sides correspond to the generatrix of the running surfaces which is directed towards the front side or control housing side of the internal combustion engine; the vertical centre line of the rectangular generated surface is directed towards the rear side of the engine, where the transmission is arranged. The
vertical one-quarter dividing lines and the three-quarter dividing lines of the photographs must be imagined as lying at the sides of the rows of cylinders. Specifically, the above-mentioned dividing lines of the reflectance photographs which are directed towards the middle of Figures 8 and 9 correspond to the generatrices directed towards the middle of the V-engine, that is to say to those on the inlet side, whereas the dividing lines directed towards the edge of the figures correspond to the outer generatrices - on the outlet side.
Such ultrasonic reflectance photographs are taken under water, the water serving as a propagation and contact medium between ultrasonic source or ultrasonic receiver, on the one hand, and the object to be examined, on the other hand. The water and the wall material constitute, as it were, a more or less homogeneous propagation medium for the ultrasound, the said propagation medium being disturbed by defects in the metal, for example gaps lying transversely to the propagation direction or contact locations where there is no material union. Only a small fraction of the ultrasound can bridge defects of this kind, whereas the majority of the primary sound energy is reflected at such defects. An ultrasonic transmitter, which at the same time is an ultrasonic receiver, is arranged at a specific height, and with specific orientation, centrally in the middle of the cylinder liner to be tested. The ultrasonic transmitter emits a very short ultrasonic signal in a highly directional manner and the ultrasonic receiver receives the echo reflected from the cylinder wall, the intensity of the echo, rather than the transit tune, being recorded. As a result of this type of ultrasonic examination, non-metallic inclusions within the object to be examined are detected by an increase in the intensity of the reflected sound, similarly to the way in which dust particles, smoke or the like can be made visible in a gas by a beam of bright light. At locations where there is fault-free, good material bonding between the cast-in cylinder liner and the crankcase - according to Figure 5 - the emitted ultrasonic pulse passes through the fault-free wall virtually without any echo; the intensity of the echo is very low here. At locations disturbed by air inclusions and small gaps - Figure 6 - the intensity of the reflected ultrasound is very much higher, whereas, in the case of gaps extended over a wide area - Figure 7 - a very high proportion of the emitted ultrasound is reflected. By means of such a test arrangement, the entire surface of a cylinder liner can be scanned line by line with high local resolution, thus resulting in
ultrasonic reflectance photographs over the laid-out generated surface of the cylinder liner, as can be seen in Figures 8a to 8f and 9a to 9h.
The ultrasonic reflectance photographs according to Figures 8a to 8f show good bonding between the cylinder liner and the basic case material. These cylinder liners where roughened, according to the invention, on their outside 10 before being cast in. The cross-hatched region, which represents good material bonding, takes up proportionally a large surface area, about 80 to 95%, here. Only in the case of a few cylinders do zones located on the transmission side or inlet side contain locations which have poor bonding, these relatively small locations being of tolerable size. No location on the circumference of the cylinder liner is entirely without material bonding to the case material. If the region of material bonding is only short in the axial direction, this is restricted to the region of a single, locally small location on the circumference of a few cylinders. Moreover, these images are not reproduced either as regards the individual cylinders of one crankcase or as regards crankcases cast in succession. It is certainly possible, here, to achieve further improvements by means of optimizing measures, particularly as regards the guidance of the melt.
In the region of the upper edge of the individual reflectance photographs of Figure 8, there is a narrow strip without any material bonding, which is not really surprising, because the casting-round operation is carried out from the bottom upwards, in accordance with the casting position and the guidance of the melt, and the upper region is the last to be reached by the melt. However, since this poorly bonded region is located in the region of the so-called top land of the piston above the piston rings, a higher cylinder-wall temperature is plainly desirable in this region, for reasons of low pollutant emission, and any assembly-related cylinder warping is absolutely negligible.
By contrast, for comparison, the ultrasonic reflectance photographs according to Figures 9a to 9h, taken in the instance of a crankcase which is of basically the same design, but has eight cylinders, show how comparatively poor the bonding result is when the liner blanks are lathe-turned with cutting on the outside in a conventional way. Although the distributions of good and poor bonding of the parts to be cast together are reproduced relatively uniformly here, the results are nevertheless very poor. Specifically, in the reflectance photographs according to Figure 9,
the cross-hatched region, having good bonding, takes up proportionally only a very small surface area - about 20%. The locations where there is good bonding are all located on the outlet side in the crankcase in accordance with the guidance of the melt. The proportion without bonding or with disturbed bonding is very high, and, under certain circumstances, at least under specific load and/or ambient conditions, would impair proper dissipation of the waste operating heat from the internal combustion engine into the cooling water. Furthermore, the result, both in the circumferential direction and in the axial direction, would be an unequal temperature distribution in the cylinder liner and therefore highly irregular thermal deformation of the liner, which would necessitate a greater piston clearance, which, in turn, would result in a higher proportion of unburnt hydrocarbons in the exhaust gas on account of the larger volume of gap between the piston circumference and cylinder running surface. Moreover, a criticism which would have to be made of the imperfectly cast-in cylinder liners according to Figures 9a to 9h would be that, over large circumferential regions, they are not connected axially to the case material and, at these locations, they may locally give way axially under the pressure of the cylinder-head gasket, not only leading to an unequal distribution of the press-on force of the cylinder-head gasket, but also increasing the unequal deformation of the cylinder liner. Unequal shapes of running surfaces, that is to say cylinder shapes deviating in the range of a few /*m from the circular shape and from the rectilinear generated shape, have an adverse effect on smooth piston running and on a good sealing action of the piston rings. In instances where cylinder liners are cast in without incipient melting, retaining collars have already been formed externally on the end faces of the liners, the said collars being intended to ensure an axial positive connection of the liner in the crankcase and to prevent the liner from loosening axially. However, these collars can usually be produced only by means of an additional machining operation - lathe-turning with cutting in the region between the collars - and by using more raw material.
So that the roughening according to the invention can be produced on a cylinder-liner blank to be cast in, first of all a tubular blank is produced and machined to the desired shape and desired size. To roughen the outer surface 10 of the blank 9, which surface is to be surrounded by the material 16 of the light-metal crankcase 2, this surface is blasted with particles 13 which are broken so as to have sharp edges,
consist of a brittle hard material, preferably high-grade corundum, and are carried along by an air jet 12 directed by means of a nozzle 18. The air-borne particle jet is directed onto the treatment location of the surface 10 of the blank 9 approximately transversely, that is to say at an angle a of about 90 ± 45°. When they strike the blank 9, the particles roughen its surface 10 and thrust up the material in a pyramid-like or lancet-like manner to form material accumulations 11, or cause scabs of material to protrude and thereby form pointed or sharp-edged material elevations which merge at their base, over a wide area, into the basic material. The particle-bearing air jet must be optimized with regards its essential parameters, in particular with regard to the flow velocity of the particles or the velocity at which they strike the outer surface and to the particle density in the air stream, the desired surface topography of the roughened outer surface and optimum metallurgical bonding of the liner to the cast-round material being two of the main results of optimization. However, it is perfectly reasonable to expect parameter optimizations of this type from the average person skilled in the field of particle blasting.
The particles 13 of hard material which are used have an average grain size d of about 70 µm,. The size of this average essentially also determines the amount of roughness achieved. The average grain size should be greater than the sought-after roughness. With an average grain size of the blasting material, broken so as to have sharp edges, of about 70 µm,, a roughness of about 30 to 60µm, can be achieved. The value given for the average grain size is a statistical average which, as the graph according to Figure 12 is intended to illustrate, can be exceeded upwards and downwards in accordance with a bell-shaped frequency distribution 19. Admittedly, the striking of the particles 13 on the outer surface 10 also causes force to be exerted on the particles, so that at least some of them are broken up. Consequently, during particle blasting, the grain size of the particles of hard material used is shifted in the direction of smaller average grain sizes (d"), as indicated in Figure 12 by the frequency distribution 20 represented by a dot-and-dash line. By filtering off a fine fraction - the left-hand region 14 in the distribution graph according to Figure 12 - out of the particle stream constantly or repeatedly, instance by instance, and by feeding in a quantity, of approximately equal mass, of a fresh particle mixture, it is possible to achieve a frequency distribution 21 around an average particle diameter d', which is
only slightly smaller than the original average diameter d. By treating the particle mixture in this way, an approximately constant particle size and therefore approximately constant surface roughness can be achieved.
It is important, in choosing and treating the blasting material, that not only the particle size, but also the particle shape is optimum and also remains optimum by means of suitable treatment measures. Splinter-like, lancet-like, tetrahedral, pyramid-like particles with pointed corners are preferred, whereas cubic or even globular particles are unfavourable for the roughening sought after in the present instance. Insofar as the particles are broken up by striking the workpiece, it is better, under some circumstances, after being used several times, for the particles to break up completely and disintegrate into a fine fraction which can be separated out than for them merely to have their corners knocked off and to assume a pebble shape. Particles "rounded" in this way would not afford the desired roughening effect, but, as seen under the microscope, would instead leave a relatively smooth hammered structure on the blasted surface. The desired breaking behaviour can be observed, above all, in brittle materials.
1. A light-metal-part blank which is to be cast into a light-metal casting,
with a roughness of 30-60µm on its external surface that will be surrounded
by the material of the light metal casting component, the topography of this
surface being made up of dug-out portions of material or raised portions of
material running out to a point in a shape that of a pyramid or lancet, the
bases thereof blending directly into the base structure of the blank.
2. A blank as claimed in claim 1, wherein the pyramid-shaped or lancet-
like dug-out areas of material or raised portions of material, stochastic in
terms of their shape and size, are distributed more or less uniformly across
the surface as a statistical average.
3. A blank as claimed in claim 1, wherein the light metal component to
be infused is a cylinder sleeve and the light metal casting component
receiving the light metal component is a die-cast crankcase of a
reciprocating piston engine.
4. A blank as claimed in claim 3, wherein the material of the cylinder
sleeve is a hypereutectoid aluminium/silicon alloy.
5. A method for producing a light-metal-part blank which is to be cast
into a light-metal casting as claimed in claim 1, whereby a blank is firstly
made and processed to a desired shape and desired dimensions and the
external surface of the blank that will be surrounded by the material of the
casting component is blasted with a directed jet of particles made from a
hard substance entrained in a flow of gas, the particles used to blast the
surface being sharp-edged broken corundum, preferably pure corundum
and having an average particle size (d) of preferably 70µm, and the surface
of the blank blasted in this manner is roughened to a roughness of 30-60µm
and the material of the blank close to the surface is dug out or opened up in
a pyramid-shaped or lancet-like pattern.
6. A method as claimed in claim 7, wherein the jet of airborne particles
is directed at an angle (a) of 90 + 45° onto the point of the surface of the
blank being treated.
7. A method as claimed in claim 5, wherein a residual fine fraction of the
particles of hard substance used during blasting formed by the breakup of
the particles, is constantly removed and as a result of this and the addition
of a more or less equal quantity of new particles of a specific average particle
size (d), the average particle size (d1) of the material in the ongoing blasting
process remains the same.
8. A method as claimed in claim 5 wherein a tubular blank is made
firstly in order to provide a blank for a cylinder sleeve (6) to be infused in a
light metal crankcase of a reciprocating piston engine.
9. A light-metal-part blank which is to be cast into a light-metal casting
substantially as described herein with reference to, and as illustrated in, the
10. A method for producing a light-metal-part blank which is to be cast
into a light-metal casting, substantially as described herein with reference
to, and as illustrated in, the accompanying drawings.
|Indian Patent Application Number||2411/DEL/1997|
|PG Journal Number||09/2008|
|Date of Filing||26-Aug-1997|
|Name of Patentee||DAIMLER-BENZ AG|
|Applicant Address||EPPLESTRASSE 225, D-70546 STUTTGART, GERMANY|
|PCT International Classification Number||B21C 1/00|
|PCT International Application Number||N/A|
|PCT International Filing date|