DE7100475U - ELECTRICAL MACHINE, IN PARTICULAR SMALL MOTOR - Google Patents

Description

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4.1.1971 HDP class

PAPST-MOTOREN KG 7742 St. Georgen / Black Forest

Electric machine, especially miniature motor

The invention relates to an electrical machine and in particular to a miniature motor, with a stator and a rotor, the latter having a peripheral part connected to a shaft and cooperating with the stator.

Electrical machines of this type in the form of miniature motors are used, for example, to drive small axial fans, tape recorders, turntables, office machines, etc. It is known for external rotor motors, i.e. motors in which the rotor is arranged outside the stator and rotates around it to design the squirrel cage of the rotor at the same time as a rotating housing and to establish a fixed connection to the shaft _{by means of a shaft bushing s cast into this rotor housing, which is usually made of steel;} With such an arrangement, the shaft is usually pressed into the shaft bushing in order to obtain a non-rotatable connection.

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With such an external rotor motor, the rotor has roughly the shape of a cup, the shaft being fastened in the bottom of the cup and the walls of the cup from the electromagnetically active parts are formed; the bottom of the cup consists of these known constructions the material of the squirrel cage, so usually from Aluminum. Since one is often forced to use aluminum that is as pure as possible for reasons of the lowest possible cage resistance To use it, but on the other hand it has relatively poor strength values, the rotor base has to be quite thick and provide reinforcement ribs, especially if there are air holes or air ducts in this floor Need to become. The consequence of slides is that the height of the end windings of the stator is limited, for whom only a certain one maximum axial length of the entire motor is permissible. The production of thin aluminum floors is also very important in terms of casting technology difficult. Furthermore, difficulties can arise in the permanent fastening of the shaft bushing to be arranged in the rotor base, the long-term alignment of the inside of the The rotor with the shaft is usually a critical point in such rotors with a pure aluminum housing.

In the case of internal rotor motors, that is to say motors in which the rotor is rotatably arranged inside the stator, the trend is also towards building motors with a short length. For this purpose, a fixed bearing support tube with inserted bearings is used in a known construction. The rotor is hollow inside; a shaft is firmly connected to it, and this shaft is inserted into the bearings of the bearing support tube and rotates in them. The rotor then rotates around the stationary bearing support tube and interacts on its outside via the electromagnetically effective air gap with the stator arranged around it; With this arrangement, the rotating parts of the in-rotor motor are mechanical

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The structure is analogous to that of the external rotor motor described above, so that here, too, the same difficulties as described above with regard to the mechanical Result in strength of the rotor base. In addition, this construction of an internal rotor motor, although a slight axial Has length, but is more expensive than the known constructions of internal rotor motors, in which the laminated core of the Rotor a shaft is attached by pressing or the like. And this shaft is mounted in the two end shields of the motor. It is therefore endeavored to manufacture this to cheapen the construction provided with a bearing support tube.

It is therefore an object of the invention to at least partially avoid the disadvantages mentioned.

According to the invention, this is achieved in an electrical machine mentioned at the beginning in that the peripheral part of the Rotor is connected to the shaft via a molded piece made of sheet metal. Such a fitting is preferably made from made of a suitable steel, e.g. by punching. It shows in the case of a small thickness, the required strength, so that even with a short axial length of the motor in the case of an external rotor motor, the end windings of the stator can be dimensioned sufficiently high. It also gives an excellent one and very reliable mechanical connection of the rotor to the shaft, which does not change even after a long time under the mechanical loads that occur.

In an advantageous development of the invention, the Electrical machine designed so that the shaped piece is designed as a sheet metal disc, which on its outer edge in a suitable manner with the peripheral part of the rotor and on its Inner edge is connected to a bushing, which in turn is rotatably connectable to the shaft. Such Sheet metal disc, which can be designed similar to a plate, for example, can be very easily and inexpensively using

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conventional mass production methods and is very dimensionally stable, especially if they are after another advantageous feature of the invention is curved. Sufficiently large holes for ventilation can also be made in it without difficulty are provided.

A particularly simple and advantageous construction is obtained in that the sheet metal disc has recesses on its edge is provided, and aas ?, this edge is cast into a part of the rotor and preferably a short-circuit ring of the rotor is. The disk can then be fastened in one operation with the casting of the short-circuit cage, so that there are practically no additional costs compared to the known constructions. Such pouring is also a ^ s Such a molding is much less problematic than pouring a thin aluminum floor.

Further details and advantageous developments of the invention result from the exemplary embodiments of the invention described below and shown in the drawing.

Show it

1 shows a section through part of the fan, which fan is from an electrical according to the invention Machine driven in the form of an external rotor motor is, on a larger scale; the upper half of Fig. 1 shows a section, which

runs at an angle of 9o ren,

to cut after the lower.

Fig. 2 shows a blank of a sheet metal molding according to the But punching before bending; Such a shaped piece in a curved shape is used in the engine according to FIG. 1 to connect the circumferential part of the rotor to the shaft,

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fig. 3 shows a longitudinal section through the blank according to FIG. 2 in its final, curved shape,

4 shows an individual illustration which shows a method step

when connecting a shaft bushing with the middle one

; Opening of the sheet metal molding according to FIG. 3 shows »in different

larger scale,

Fig. 5 is an illustration of the bending part with the attached

th shaft bushing, after completion of the process step shown in Fig. 3,

6 shows a blank of a second embodiment of a sheet metal molding,

7 shows a longitudinal section through the blank according to FIG. 6, in its final, curved shape.

8 shows a longitudinal section through an external rotor rotor

molded short-circuit cage, whereby the sheet metal · ■ '"-' 7 is cast into the upper short-circuit ring of this rotor,

FIG. 9 shows a representation with two different plan views of the rotor according to FIG. 9, seen along the lines IX-IX of Fig. 8,

Fig. Io a longitudinal section through another embodiment,

play of a rotor, here a rotor for an internal rotor motor,

11 shows an exemplary embodiment which shows a further connection according to the invention of the peripheral part of a rotor with shows a wave

7100475 often09.77

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12 shows a partial representation of an internal rotor motor, with a connection according to the invention of shaft and rotor, and

13 shows a further embodiment of the connection of the peripheral part of a rotor to a shaft.

14/15 show arrangements for an increased supply of cooling air in an electric motor according to the invention.

In the following description, the terms "left" and "right" each refer to the graphic representation on the individual figures.

1 shows a longitudinal section through part of an axial fan lo which is driven by an external rotor motor designated in its entirety by 11. The fan Io has an outer housing which essentially consists of a cast molding 12. On one end of this outer housing a flange 14 is attached to a mounting plate 15.

On the mounting plate 15 is by means of screws 16, of which only one is shown, a bearing support tube 17 is attached, on which the stator 13 of the motor 11 is attached. Inside the Bearing support tube 17, two plain bearings 18, 19 made of sintered material are attached, between which a piece of felt 2o is arranged, which serves as a lubricant depot. Furthermore are in a recess 23 of the mounting plate 15 two discs 24 attached, the first Thrust bearings for a shaft 25 are used. This has a recess for a snap ring 26 at its left end (with reference to FIG. 1) on, which holds four disks 27, which form a second axial bearing for 'the shaft 25 with the right end face of the plain bearing 18. The shaft 25 is thus supported by the two axial bearings 24 and 18, 27 held axially in a certain position, while the two plain bearings 18 and 19 guide the shaft 25 radially.

A stator lamination packet 3o is attached to the bearing support tube 17,

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in which windings 31 and 31 'are inserted in a known manner, their connections 32 and 32' in an insulating tube 34 guided and attached to a connection element 35 which is fastened in the cast molding 12 and which 'contains' two solder contacts 33 and 33, j are connected. The windings 31 and 31 'have winding heads, of which the left with 36 and the right with 37 are designated.

A bushing 41, which is preferably designed as a rotating part made of steel, is fastened in a rotationally fixed manner on the shaft 25. At this Bushing 41 is in turn a sheet steel 'gebi Ldetes molding 42 attached to rotate with it; this shaped piece 42 has a total of eight openings 43 for the passage of air. It's up to his Outer edge provided with bent ends in the form of sheet metal tabs 44, which in the left short-circuit ring 45 with a Outer rotor housing provided with a short-circuit cage (as peripheral part) are poured in; the peripheral part 46 also has a laminated core 47 and a right short-circuit ring 48. Between the left The short-circuit ring 45 and the right-hand short-circuit ring 48 run in grooves in the laminated core 47, bars cast in, which are indicated at 49 and which also belong to the short-circuit cage; this The cage can be made of pure aluminum, for example. "'· ■ /

Fan blades are welded directly onto the peripheral part 46, two of which are shown at 52 and 53.

Fig. 2 shows the shaped piece 42 in the unbent, flat state .-. * .: directly after punching. It has at its center an opening "54, the irregular edge contours has, namely, three mutually offset by 12o ° lateral protrusions 55, the purpose described hereinafter wird.-Am edge are _between: remaining eight plate tabs or sections 44 recesses 57 stamped in such a way that the sheet metal tabs 44 have widenings 58 at their free ends, as clearly shown in Figures 2 and 3. This results in:. Excellent anchoring of the sheet metal tabs 44 in the short-circuit ring 45 .; -

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As FIG. 3 shows, the sheet metal tabs 44 are approximately rectangular
bent to the plane of the blank shown in Fig. 2,
namely they are bent about in an arc. Here is how
1 clearly shows that the diameter of the bent sheet metal tabs 44 is selected so that they are very close to the outer circumference
of the short-circuit ring 45 lie. Furthermore, the distance is theirs
Ends of the laminated core 47, which distance in Fig. 1 with "h"
is designated, chosen as large as possible. Both measures

contribute significantly to the fact that the resistance of the short-circuit ring 45 is increased by the sheet metal tabs 44 only to such an extent that in the finished engine, compared to the construction without cast sheet metal tabs 44, there is at most a slight distortion ^; reduction of the output torque results. Attempts have | However, it turns out that such a reduction is in practice within the scope of the usual specimen variation of the engines, if
the given rules for the distance "h" and the diameter | of the fitting 42 are complied with. j

To ensure a secure connection even after a long period of operation

to get between the shaft 25 and the bushing 41, one can '

tread different paths. For example, the socket 41 can be

the fitting 42 are welded, in particular by pulse;

weld, or these parts can be brazed together;

be joined, particularly by induction brazing; a '■

particularly simple method for fastening the bushing 41 in [ the shaped piece 42. its opening. 54 the - j Has shape, so is provided with the bulges 55, is in

FIGS. 4 and 5 are shown. j

Fig. 4 shows how the shaped piece 42 with the inserted socket 41 "" -I

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is placed on a holder 6o. Then a hold-down device 61

lowered, which clamps the two parts 41 and 41. - '

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Then an upsetting tool 62 is lowered from above in the direction of the arrows drawn, its working end face 62 'is conical, and this deforms the outer circumference of the bushing 41 in the manner shown in FIG the pressing down of the material creates a bead 63 and the same; I early the material of the bushing 41 in the bulges 55 (Fig. 2) j is pressed and thus a stable, non-rotatable connection between the molded piece 42 and the socket 41 is created. Together with the

The bead 63 then engages around the lower edge 64 of the bushing 41 , Shaped piece 42, so that an extremely durable connection is created, Finally, the socket 41 is drawn along the line in FIG. 5 The plane 65 shown in dash-dotted lines is turned off so that it has the shape shown in FIG. 1. - The same type of attachment can also be used in the exemplary embodiments described below. Due to the conical shape of the working Forehead 62 ', the process described is significantly supported.

Fig. 8 shows a second embodiment of one labeled 7o Rotor for an external rotor motor, for example could be used in place of the rotor 46 of Figure 1 and is of a shape similar to this. The rotor 7o has a laminated core 71 with a cast short-circuit cage, e.g. made of pure aluminum. An upper short-circuit ring 72 and a lower short-circuit ring 73 of this cage are shown. Between Rings 72 and 73 lie connecting rods which run in slots (not shown) of the laminated core 71.

In FIG. 8, ring edges 79 and 79 '-V * J are drawn in dashed lines

a tool 6Γ9, 69 'indicated in the casting position. In-this _: ^

Position these ring edges 79, 79 'from both sides in the -;

Fitting 74 "pressed in by approx. 1/1 ο mm to protect against shot-in ~ \

Seal material when pouring. . · ~ -. ^ J

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7108475 08.08: 77

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. In aem upper short-circuit ring 72 is a. Fastened sheet metal molding 74, namely by the fact that its edge is cast in this ring 72 * whereby here, too, there is a distance "h" between the end of the molding 74 and the laminated core 71, which is only filled by cast material, so as to to keep the resistance of the short-circuit ring as low as possible. The shape of this shaped piece 74 in the flat, unbent state, ie the shape of the blank, is shown in FIG. 6, and the shape in the bent state from FIG Edge eight sheet metal tabs 75, in which holes 75 are punched in order to effect a good anchoring in the short-circuit ring 72. These tabs are unbent in the manner shown in FIG. 7, and at the same time the shaped piece 74 is arched, as is shown in FIG. 7 by the angle '- * -. This gives the molded piece 74 a particularly high degree of rigidity. Here, too, a bush 78 is inserted into a central recess 77, which is used to connect to a shaft not shown in FIG.

The mold halves 69, 69 'of the die casting tool for production of the electric motor according to the invention have circular rings Pressure webs 79, 79 ', which clamp the molded piece 74 so tightly, that a certain material deformation occurs in the vicinity of the surface of the molded part and, as a result, the formation of an undesirable, very thin cast skin on the exposed surface of the molded part 74 is prevented. These

Deformation of the material on the shaped piece 74 also has a shape-stabilizing effect

The catch pin 82 of the tool serves to center the molding 74 during the casting process.

9 shows a view of the rotor 7o in the left half 8 from above and in the right half a view according to FIG of the same rotor 70 from below, each related to Fig. 8. in the left half are those intended for balancing Holes marked 8o and 81 in the right half.

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Fig. Io shows a rotor 85 for an internal rotor motor; this rotor 85 is also designed as a squirrel-cage rotor and has an upper short-circuit ring 86 and a lower short-circuit ring 87, which is electrically operated by rods (not shown) cast in grooves in the laminated core 88 are connected to each other. The upper ring 86 has a recess 88 into which a stamped part 89 is pressed and by embossing 9o of the short-circuit ring 86 in its Laje is being held. Here, too, a shaft 91 is pressed into the inner recess of the punched part. The stamped part is a So-called fine-stamped part, the tool of which has greatly reduced cutting gaps, so that the cut surface over the thickness of the punched part is as true to size as possible (small fracture surface). In this way, the dimensions can be adhered to more precisely.

Fig. 11 shows another type of fastening for the peripheral part 93 of a rotor, only a section of which is shown is, namely a part of the laminated core 94 with a cast upper short-circuit ring 95, as well as a sheet metal disk 96, which in its center is connected to a bush 97, in which a shaft 98 is in turn pressed.

The short-circuit ring 95 is cast here so that it has a number of upwardly projecting pins, one of which is shown in FIG. 11 with dashed lines and designated by 99 is. At the points at which these pegs are located, the disk 96 is provided with holes loo, so that the disk can be placed on the ring 95. Then the pins 99 are riveted by means of a suitable device, the The rivet heads Io3 shown in FIG. 11 arise. You get thus a secure connection of the short-circuit ring 95 to the sheet metal plate 96 and thus to the shaft 98.

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Fig. 12 shows a schematic representation of a construction, which is preferably suitable for an internal rotor motor and enables »a particularly long bearing support tube to be used. The rotor is denoted by Ho and the stator by 111 here. A stationary bearing support tube is located inside the rotor Ho 112, which can be constructed and arranged similarly to the bearing support tube 17 according to FIG. 1. In the bearing support tube 112 two self-lubricating bearings 113 are arranged, and in these a shaft 114 rotates, at the upper end of which a bush 115 is attached. A hat-shaped sheet metal molding is attached to the socket 115 116 attached, with its central, raised part, while its outer edge is directly on the laminated core 117 of the Rotor Ho rests and is fixed there by casting by means of an upper short-circuit ring 118. The fitting 116 thus forms part of the laminated core of the rotor Ho in this construction.

u Fig. 13 shows a further solution according to the invention, which predominantly is intended for an internal rotor motor, but under certain conditions it is also advantageous for an external rotor motor can be used. Here, too, a bush 122 is fastened on a shaft 121, and bush 122 is on this a deep-drawn, cup-like sheet metal molding 123 securely attached, for example by one of the aforementioned methods. This Molded piece 123 is pressed into the inner bore of a circumferential rotor part designated by 124 in such a way that a frictionally engaged Connection is created, which can safely transmit the torques occurring during operation. Here is between the short-circuit rings 125 and 126 on the one hand and the molded piece 123 on the other hand each has a radial distance. The resulting annular gaps 127 and 128 are engaged during manufacture a tool that presses the laminated core 124 together.

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7100475 08.09.77

I If you turn one with a squirrel cage

§. Rotor of an external rotor motor from the inner bore so that

I '. the groove webs are reduced in size and instead of the exposed

j | ! turned material a molded piece 123 made of soft magnetic

| ; Material of a certain wall thickness, one obtains a so-called

I called the tubular rotor rotor, in which a tubular conductor layer and

^ a cage short-circuit winding magnetically one behind the other

Jp are switched. This gives a torque characteristic

; for

J ristics that * »some cases benefit from the overburden

I- the characteristics of a squirrel cage rotor and a tubular rotor (solid I 'rotor) is put together. The shaped piece 123 is used twice in this case in a very advantageous manner. Fig. 14/15 show relief-like elevations and depressions in the shaped piece 74 which serve to increase the supply of cooling air into the engine interior when the shaped piece rotates during operation of the engine. Here, in FIG. 14, blade-like elevations 131 and 132 are arranged on both sides of the shaped piece 74 according to section AA and in different circles 131/132 and 131 '/ 132' for both directions of rotation.

FIG. 15 shows, as a variation on this, incised and bent out lobes 133/134 of greater radial width, also if for both directions of rotation.

I. The invention therefore makes it possible in a simple manner, in particular rotors I and squirrel-cage rotors of motors and \ specifically micromotors safe with the associated shaft to connect ι, said rotors even after long operating safely

I retained their shape and, due to their structure, a slight one

■: enable axial length of the associated motor. Casting technology

■. the production of electric motors according to the invention is also less problematic than the known arrangements.

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7100475 08.09.77

Claims (23)

Fe / g J protection claims 1. Electrical machine, especially a miniature motor, its outer The rotor part is positively connected to a metal stamped part via one of its end rings and carried over this, which is rotatably connected in its center to the shaft, characterized in that the in his larger central part with the one end ring surface of a squirrel cage motor approximately aligned, designed as a disc Metal stamped part (42, 74) made of steel on the outer edge, claw-like, separated from one another by larger distances (57), to form the laminated rotor core towards (47,71) has bent, lobe-like projections (44,75), which in the one made of light metal The end ring (45,72) of the squirrel cage rotor is cast in are, wherein the bent projections (44,75) are in the vicinity of the outer circumference of the end ring (45) and / or the Ends of the bent projections (44, 75) from the magnetically active rotor part (47, 71) each have a minimum distance h. 2. Electrical machine, in particular miniature motor according to claim 1, characterized in that the tab-like projections (44, 75) are widened at their outer ends (58). 3. Electrical machine, in particular a miniature motor according to claim 1 or 2, characterized in that the tab-like projections (75) have recesses (76). 4. Electrical machine, in particular miniature motor according to one of claims 1 to 3, characterized in that the metal "stamped part (74) is slightly curved like a plate. 5. Electrical machine, in particular miniature motor according to one of the preceding claims, characterized in that the Metal stamping part (42) has a central recess (54) which, at least at one point, has a circular shape Π0475 09/08/77 having soft edge contour (54 and 55), and that a bushing (41) is brought into engagement with this edge contour (55), in that the bulges (55) are displaced by the during the upsetting process Material of the bushing (41) are filled to provide a rotationally fixed connection between the bushing and the stamped metal part (42) to form. 6. Electrical machine, in particular miniature motor according to one of claims 1 to 5, characterized in that the stamped metal part is welded, in particular pulse-welded, to a bushing that can be connected non-rotatably to the shaft. 7. Electrical machine, especially miniature motor after a of Claims 1 to 5, characterized in that the stamped metal part is connected to a bushing which can be connected to the shaft in a rotationally fixed manner is connected by brazing, preferably induction brazing. 8. Electrical machine, especially a miniature motor, after a of the preceding claims, characterized in that the Metal stamped part (74) has elevations and / or depressions (130) serving as fan elements. 9. Electrical machine, in particular miniature motor, according to claim 8, characterized in that the elevations and Wells (131,132,131 ', 132') on different circles and are arranged with opposite opening directions, each pointing in the circumferential direction. 10. Electrical machine in particular miniature motor according to one of the preceding claims, characterized in that the stamped metal part (42, 74) has ring-like embossed zones of shallow embossing depth on its surface. ΊΛ ^? Π0475 09/08/77 ta 11. Electrical machine, in particular a miniature motor with a squirrel cage rotor, which is connected to the shaft by a cage ring is connected on one side, with a separate shaped piece made of metal between the cage ring and the shaft is switched on that it is positively connected to the cage ring with this, characterized in that the molded piece is designed as an approximately hat-like part (116), the raised central part of which is connected to the shaft (114) and whose Edge part through a short-circuit ring (118) cast onto the laminated core (117) with the laminated core of the rotor (110) is mechanically connected (Fig. 12). 12. Electrical machine, especially a miniature motor with a Squirrel cage, which is connected on one side by a cage ring with the shaft, with between the cage ring and the Shaft a separate fitting made of metal is switched on in such a way that it is positively connected to the cage ring with this is, characterized in that the shaped piece formed from sheet metal is designed as a fine-stamped part (89), the is arranged between the shaft (91) and a part (86) of the rotor (85) (Fig.10). 13. Electrical machine, in particular miniature motor according to claim 12, characterized in that the fine blanking part (89) between the shaft (91) and a short-circuit ring (86) provided on the laminated core (88) of the rotor (85), and that on the short-circuit ring (86) embossments (90) are provided for fastening the fine-stamped part (8S) (Fig. 10). 14. Electrical machine, especially a miniature motor with a squirrel cage rotor, which is on one side of the active rotor part with the shaft is connected, with a separate shaped piece made of metal is switched on between this and the shaft, thereby characterized in that the shaped piece (123) is cup-shaped 71Π0475 09/08/77 I * β · β 9 is designed that the bottom of this cup-shaped molding (123) is connected to the shaft (121) and that the peripheral part of this fitting with the inside of the hollow trained rotor (124) is connected (Fig. 13). 15. Electrical machine, in particular miniature motor according to claim 14, characterized in that the rotor (124) as an external rotor rotor is formed and that its inside is turned out and that the with the inside of the rotor (124) connected peripheral part of the cup-shaped molding (123) is designed as a soft magnetic layer to a so-called to obtain mixed torque characteristics (Fig. 13). 16. Electrical machine, especially a miniature motor with a squirrel cage rotor, which is connected to the shaft by a cage ring is connected on one side, - being between the cage ring and the shaft separate fitting made of metal switched on in this way is that it is positively connected to the cage ring with this, characterized in that the shaped piece (96) has recesses (100) on its edge, so that these recesses (100) are penetrated by projections (99) of the rotor (93) are, and that on the side of the sheet metal disc (96) facing away from the rotor, these projections (99) onto the sheet metal disc are riveted (103) (Fig. 11). 17. Electrical machine, in particular miniature motor according to one of claims 12 to 16, characterized in that the shape piece (42) on its inner edge has an approximately circular recess (54) that this recess (54) one at least one point has an edge contour (55) deviating from the circular shape, and that one with the shaft (25) rotatably connectable socket (41) is brought into engagement with this edge contour (55) by an upsetting process (Figure 4) in order to achieve a to form a non-rotatable connection between it and the fitting (42). 7100475 08.09.77 '' ί i 18. Electrical machine, in particular a miniature motor according to claim 17, characterized in that the approximately circular recess (54) bulges (55) distributed on its circumference has into which the material of the bushing (41) displaced during the upsetting process (FIG. 4) flows. 19. Electrical machine, in particular a miniature motor according to claim 17 or 18, characterized in that the bush (41) in the compressed state (Fig.1,5) both broad sides of the stamped metal part or molded piece (42) engages (63,64). 20. Electrical machine, especially a miniature motor according to one of the Claims 1 to 19, characterized in that the stamped metal part or shaped piece (74, 42 etc.) has relief-like elevations and / or depressions (130). 21. Electrical machine, in particular miniature motor according to claim 20, characterized in that the e.g. beaded Elevations and depressions in different circles (131/132) and (131 '/ 132') are arranged in opposite directions (Fig. 14). 22. Electrical machine, in particular miniature motor according to claim 20, characterized in that the elevations or Depressions are formed by incised and bent out, radially wide flaps (133/134) (Fig. 15). 23. Electrical machine, in particular miniature motor according to one of claims 11 to 19, characterized in that the Fitting (74,42) with ring-like zones on the surface is of very low press-in depth. ¹ A 00475 08.09.77