Repair of bearing seats. Why are the bearing seats sagging? The ball bearing dangles in the housing repair

Landings

The importance of a correct fit

If a rolling bearing with an inner ring is only fitted with an interference fit on the shaft, a hazardous annular slip can occur between the inner ring and the shaft. This sliding of the inner ring, called "slip", will cause the ring to slip relative to the shaft if the interference fit is not tight enough. When slippage occurs, the fitted surfaces become roughened, causing wear and significant damage to the shaft. Abnormal heating and vibration can also occur due to abrasive metal particles entering the bearing.

It is important to prevent slippage by firmly tightening the ring that rotates with sufficient tension, either to the shaft or to the housing. Slip cannot always be eliminated by axially tightening through the outer surface of the bearing ring. however, as a rule, it is not necessary to provide an interference fit for rings that are only subject to static loads. Landing is sometimes done without any interference on both the inner and outer rings to accommodate certain operating conditions or to facilitate installation and disassembly. In this case, lubrication or other applicable methods should be considered to prevent damage to the fitting surfaces due to slippage.

Loading and landing conditions

Load application	Bearing operation		Load conditions	Landing
	Inner ring	Outer ring		Inner ring	Outer ring
	Rotational	Static	Inner ring rotational load, outer ring static load	Interference fit	Free fit
	Static	Rotational
	Static	Rotational	Outer ring rotational load, inner ring static load	Free fit	Interference fit
	Rotational	Static
Load direction is not detected due to direction change or unbalanced load	Rotational or static	Rotational or static		Interference fit	Interference fit

Landings between radial bearings and housing bores

Load conditions			Examples of	Body bore tolerances	Outer ring axial displacement	Notes (edit)
One-piece housings	Heavy loads on a bearing in a thin-walled housing or heavy shock loads	Hubs car wheels(roller bearings), hoisting crane, impellers	P7	Impossible	-
	Car wash wheel hubs (ball bearings), vibration screens	N7
	Light or fluctuating loads	Conveyor rollers, rope pulleys, idler pulleys	M7
	Load direction not defined	Heavy shock loads				Traction motors
Non-split or split housings		Normal or heavy loads	Pumps, crankshafts, main bearings, medium and large motors	K7	Usually impossible	If axial displacement of the outer ring is not required
		Normal or light loads		JS7 (J7)	maybe	Axial displacement of the outer ring is necessary
	Loads of all kinds	General bearing applications, railway axle boxes	H7	Easily possible	-
	Normal or heavy loads	Insert bearings	H8
	Significant rise in the temperature of the inner ring in the shaft	Dryers for paper	G7
One-piece housings	Precise function is desirable under normal or light loads	Grinding spindle rear ball bearings, high speed centrifugal compressor pivot bearings	JS6 (J6)	maybe	For heavy loads, use a tighter fit than K. When required high accuracy, very tight tolerances should be used for fit
		Load direction not defined	Grinding spindle front ball bearings, high speed centrifugal compressor stationary bearings	K6		Usually impossible
	Precise functioning is desirable and high rigidity with fluctuating loads	Cylindrical Roller Bearings for Machine Tool Spindle	M6 or N6	Impossible
	Minimum noise required	Appliances	H6	Easily possible	-

Notes to the table:

1. This table applies to cast iron and steel housings. For housings made of light alloys, the fit should be tighter than in this table.
2. Not applicable for special landings.

Landings between radial bearings and shafts

Load conditions		Examples of	Shaft diameter, mm			Shaft tolerance	Notes (edit)
			Ball bearings	Cylindrical and tapered roller bearings	Spherical Roller Bearings
RADIAL BEARINGS WITH CYLINDRICAL HOLES
Slight axial displacement of the inner ring on the shaft desirable	Wheels on static axles	All shaft diameters			g6	Using g5 and h5 where precision is required. In case of large bearings, f6 can be used for light axial movement
Slight axial displacement of the inner ring on the shaft is not required	Idler pulleys, rope pulleys				h6
Rotational load on the inner ring or undefined load direction	Electrical Appliances, pumps, fans, vehicles, precision machine tools, metal cutting machines	<18	-	-	js5	-
		18-100	<40	-	js6 (j6)
		100-200	40-140	-	k6
		-	140-200	-	m6
	Normal loads	General bearing applications, medium and large motors, turbines, pumps, motor main bearings, gearboxes, woodworking machines	<18	-	-	js5 (j5-6)	k5 and m6 can be used for single row tapered roller bearings and single row angular contact bearings instead of k5 and m5
			18-100	<40	<40	k5-6
			100-140	40-100	40-65	m5-6
			140-200	100-140	65-100	m6
			200-280	140-200	100-140	n6
			-	200-400	140-280	p6
			-	-	280-500	r6
			-	-	over 500	r7
	High loads or shock loads	Railway axle bushings, industrial vehicles, traction motors, structures, equipment, crushing plants	-	50-140	50-100	n6	Bearing internal clearance must be greater than CN
			-	140-200	100-140	p6
			-	over 200	140-200	r6
			-	-	200-500	r7
Axial loads only			All shaft diameters			js6 (j6)	-
RADIAL BEARINGS WITH TAPERED HOLES AND BUSHINGS
All types of loads		General bearing applications, railway axle boxes	All shaft diameters			H9 / IT5	IT5 and IT7 mean that the deviation of the shaft from its true geometric shape, for example, round or cylindrical, must be within the IT5 and IT7 tolerances, respectively.
		Transmission shafts, woodworking equipment spindles				H10 / IT7

Note: This table only applies to solid steel shafts.

Choosing the correct fit, ensuring the required cleanliness and dimensional tolerances for bearing surfaces is a key factor in ensuring the durability and reliability of mechanisms.

Correct fit is essential for bearing performance.

Based on the features of the bearing, the ring that rotates should be fixed on the supporting surface motionlessly, with an interference fit, and the stationary ring should sit in the hole with a minimum clearance, relatively freely.

The tension setting of the rotating ring prevents it from turning, which could lead to wear of the bearing surface, contact corrosion, bearing imbalance, support flaring, excessive heating. So, basically, the bearing is seated on the shaft, which operates under load.

For a stationary ring, a small gap is even useful, and the ability to rotate no more than once a day makes the wear of the bearing surface more uniform and minimizes it.

Basic terms

Let's take a closer look at the basic terms and concepts that define the bearing fit. Modern mechanical engineering is based on the principle of interchangeability. Any part made according to one drawing must be installed in the mechanism, perform its functions, and be interchangeable.

For this, the drawing determines not only the dimensions, but also the maximum, minimum deviations from them, that is, the tolerances. Tolerance values ​​are standardized by a single system for tolerances, ESDP landings, broken down by degrees of accuracy (quality), are given in tables.

They can also be found in the first volume of the Handbook of Mechanical Engineer Anuryev, and GOST 25346-89, as well as 25347-82 or 25348-82.

According to GOST 25346-89, 20 accuracy grades are defined, but in mechanical engineering they are usually used from 6 to 16. Moreover, the lower the quality number, the higher the accuracy. For landings of ball and roller bearings, 6.7, less often 8 qualifications are relevant.

Within the same grade, the size of the tolerance is the same. But the upper and lower deviations of the size from the nominal are located in different ways and their combinations on the shafts and holes form different fits.

There are landings that provide a guarantee of clearance, interference and transitional ones, realizing both the minimum clearance and the minimum interference. Landings are indicated by Latin lowercase letters for shafts, large for holes and a number indicating the quality, that is, the degree of accuracy. Landing designations:

• with clearance a, b, c, d, e, f, g, h;
• transient js, k, m, n;
• with interference p, r, s, t, u, x, z.

According to the hole system for all qualities, it has an H tolerance, and the nature of the fit is determined by the shaft tolerance. This solution allows to reduce the number of required control gauges, cutting tools and is a priority. But in some cases, a shaft system is used in which the shafts have an h tolerance, and the fit is achieved by machining the hole. And this is precisely the case when the outer ring of a ball bearing is rotated. An example of such a design is the rollers or drums of belt tension conveyors.

Selection of rolling bearing fit

Among the main parameters that determine the bearing fit:

• the nature, direction, magnitude of the load acting on the bearing;
• bearing precision;
• rotational speed;
• rotation or immobility of the corresponding ring.

The key condition that determines the fit is immobility or rotation of the ring. For a stationary ring, a close clearance fit is selected and gradual, slow cranking is considered a positive factor in reducing overall wear and preventing local wear. The rotating ring must be seated with a reliable interference, which excludes rotation in relation to the seating surface.

The next important factor to be matched by a bearing fit on a shaft or in a bore is the type of loading. There are three key types of loading:

• circulating during the rotation of the ring relative to the radial load constantly acting in one direction;
• local for a stationary ring with respect to radial loading;
• oscillatory with a radial load oscillating relative to the position of the ring.

According to the degree of accuracy of the bearings, in the order of their increase, they correspond to five classes 0,6,5,4,2. For mechanical engineering at low and medium loads, for example for gearboxes, class 0 is common, which is not indicated in the designation of the bearings. For higher accuracy requirements, the sixth grade is used. At higher speeds 5.4 and only in exceptional cases the second. Example of the sixth grade 6-205.

In the process of real design of machines, the fit of the bearing on the shaft and in the housing is selected in accordance with the working conditions according to special tables. They are given in the second volume of the Handbook of the mechanical engineer Vasily Ivanovich Anuriev.

For the local type of load, the table suggests the following fittings.

Under conditions of circulating loading, when the radial force acts on the entire raceway, the loading intensity is taken into account:

Pr = (k1xk2xk3xFr) / B, where:
k1 - dynamic overload factor;
k2 - coefficient of attenuation for a hollow shaft or a thin-walled body;
k3 - coefficient determined by the action of axial forces;
Fr - radial force.

The value of the coefficient k1 with overloads less than one and a half times, small vibrations and shocks are taken equal to 1, and with a possible overload from one and a half to three times, strong vibrations, shocks k1 = 1.8.

The values ​​of k2 and k3 are selected according to the table. Moreover, for k3, the ratio of the axial load to the radial load is taken into account, expressed by the parameter Fc / Fr x ctgβ.

The corresponding coefficients and the parameter of the load intensity of the bearing fit are given in the table.

Processing of seats and designation of landings for bearings in the drawings.

The bearing seat on the shaft and in the housing must have lead-in chamfers. The roughness of the seat is:

• for a shaft journal with a diameter of up to 80 mm for a class 0 bearing Ra = 1.25, and for a diameter of 80 ... 500 mm Ra = 2.5;
• for a shaft journal with a diameter of up to 80 mm for a bearing of the 6.5 class Ra = 0.63 and with a diameter of 80 ... 500 mm Ra = 1.25;
• for a hole in the housing with a diameter of up to 80 mm for a class 0 bearing Ra = 1.25, and with a diameter of 80 ... 500 mm Ra = 2.5;
• for a hole in the housing with a diameter of up to 80 mm for a bearing of the 6.5.4 class Ra = 0.63, and for a diameter of 80 ... 500 mm Ra = 1.25.

The drawing also indicates the deviation of the shape of the bearing seat, the end runout of the shoulders for their stop.

An example of a drawing, which indicates the fit of the bearing on the shaft Ф 50 к6 and form deviations.

The values ​​of the form deviations are taken according to the table depending on the diameter, which has the bearing fit on the shaft or in the housing, and the bearing accuracy.

The drawings indicate the diameter of the shaft and housing for fit, for example, Ф20к6, Ф52Н7. On the assembly drawings, you can simply indicate the size with a tolerance in the letter designation, but in the drawings of the parts, it is desirable, in addition to the letter designation of the tolerance, to give its numerical expression for the convenience of workers. Dimensions in the drawings are indicated in millimeters, and the tolerance is in micrometers.

It happens that the bearing in the crankcase has turned, its landing in the engine block or in the crankcase of some unit (gearbox or rear axle) weakens, and it is impossible to operate a car or motorcycle with such a malfunction, since the bearing seat will break even more. Such a malfunction can occur from multiple or incorrect mounting of the bearing in the bore (socket) of the crankcase, lack of lubrication (the bearing wedges and it turns), or simply from inaccurate manufacturing of the bearing bore. And the owners of any vehicle, or just some kind of machine or unit, often encounter such a malfunction. How easy it is to get rid of such a malfunction at home, without having galvanic equipment, even the simplest one (for zinc coating), we will consider in this article.

Of course, you can increase the diameter of the outer bearing race if you cover it with chrome or a layer of zinc, and I already wrote about this (you can read it here in). But for this you will need to make special plugs (so that the coating layer does not get on the balls, separators and inner surfaces of the clips), and you will have to tinker with chemicals.

In the same article, we will consider another, even simpler way of increasing the outer diameter of the clip, which can be carried out both in his garage and in the field by any person, even a schoolboy.

To begin with, we will consider the more common traditional methods of restoring a broken bore in a bearing, maybe some of the newbies do not know about them and they will be useful to someone. And after that we will analyze a more rare method, which most repairmen do not know about.

1 - crankcase, 2 - bushing, 3 - outer bearing race.

So, if the bearing is mounted in the crankcase of some kind of unit or its cover, and the bore is broken, then the cover is fixed through a faceplate in a lathe, and the crankcase is in a cardinate boring machine, and the bore diameter is bored by about 3 - 4 mm and after This is pressed into the bored place of the repair sleeve, in which the inner diameter is slightly larger (with allowance for finishing) and after turning, the inner diameter of the sleeve is bored to the diameter of the outer bearing race (see Figure 1).

This method is quite common, despite the fact that many craftsmen have to look for a cardinate boring or lathe and also make a device for precise fixing of the part. In addition, this method will not work if the thickness of the metal of the housing wall becomes thin after boring and does not provide sufficient rigidity to the bearing bore. And this stops many, and you will not find a competent machine operator everywhere.

Some "masters" try to do with just punching the landing surface, but it is hardly worth hoping that such a "repair" will last for a long time, usually for a couple of hours. After all, the bearing cage with this method will not lie on the entire surface of the bore, but only on scanty areas (pimples), which have a scanty area. Yes, and the numbered places are quickly crushed already during the installation of the bearing (especially in the soft aluminum crankcase), and the bearing race again begins to dangle and turn.

The most affordable and effective repair methods are when the enlarged bearing bore is not touched at all, but only increase the thickness of the bearing cage. And there are also several methods here, this is the spraying of metal with special installations, which are still very rare, this is the coating of the clip with chrome, and the more affordable at home zinc coating of the clip, which I already wrote about (link above in the text).

But there is another little-known, but very simple way to increase the size of any round metal part, and in this case, a bearing race, which is not difficult to implement at home, in the garage, and even while traveling (on the side of the road). Moreover, no special qualifications or some kind of secret skill is required, and any driver who is able to open the hood of his car will cope with this simple operation quite easily, especially if an assistant helps.

The principle of metal build-up in this simple way is based on the principle of resistance welding. And for work we need only a couple of springs, for example from a Moskvich or the Volga, a couple of pieces of thick wire (cables with a crocodile clip are suitable for "lighting") and a well-charged battery, or a welding transformer (a powerful starting Charger).

1 - battery, 2 - springs, 3 - bearing, 4 - table with supports.

And in order to increase the diameter of the outer bearing race, this bearing will need to be rolled between two springs by connecting an electric current to the springs (see Figure 3). And as I already said, springs from our domestic cars will do, but if the bearing is much larger, for example, from a truck, then the width of the springs needs to be chosen wider, from the same truck (you can find old springs at scrap metal collection points, or in auto services) ...

The length of the springs also depends on the diameter of the bearing, but as a rule, the length of one spring is about a meter, and the second can be cut off to half a meter (it will be more convenient to work this way). We connect each spring with a cable to the pole pieces of the battery or transformer, ensuring good contact.

You can use the terminals from the car to tightly connect the cables to the battery, but you can clamp the cables to the springs using bolts and washers, or powerful crocodile clamps (such as welding). Moreover, the polarity when connecting the springs can be any.

a - surfacing thickness of 0.1 mm, b - surfacing thickness of 0.25 mm, c - surfacing thickness of 0.5 mm.

Rolling is performed several times, and at the same time the surface of the outer cage is gradually covered with a large number of small welded bumps made of spring metal (see photo on the left). And it is enough to make a few rolls, and the surface of the outer bearing cage is already built up to such a diameter that the cage will no longer dangle in its broken hole.

It is useful to put on rubber gloves at the ends of the upper spring and wrap them with duct tape, or just wind electrical tape. This will avoid short-circuiting the springs and damage to the battery if, during rolling, the upper spring touches the lower spring with its end.

This often happens when the diameter of the bearing being remanufactured is small. And if the bearing is already of a very small diameter, then it is useful to turn the upper spring with a deflection upwards when working on the contrary.

When working with a battery, so as not to spoil it, it is useful not to protect rust on the springs at all, since rust has additional resistance that will prevent excessive current growth. But if you wish, you can also connect a rheostat, which will be able to accurately select the required current strength.

If, instead of a battery, a welding transformer is used, then of course it is better to use one on which there is a current adjustment. The welding current is set in the range of 100 - 150 amperes, and the higher the current, the faster the metal build-up will occur, but the particles being deposited will also be larger.

Therefore, it is useful to find a middle ground so that the particles of the deposited metal (inclusions) are not large, and you do not have to mess around for a long time. You can practice first on an unusable bearing. Typically, however, a normal 0.5mm increase in diameter for a 110mm bearing would require 150 amps of current and approximately five minutes of rolling. And at the same time, the bearing heats up only to 100 degrees, which means that the structure of its metal does not change.

After rolling, as can be seen in the photographs, the surface of the clip has a somewhat rough appearance, which is even better, since it will never turn in its hole again (the grip of a rough surface is better than a smooth one). But still, if someone wants to restore the surface of the outer cage in this way to the factory smooth state, then it is quite possible to make the coating twice as thick (instead of 0.5 mm, make 1 mm). And then give the bearing to the turner, who will polish the cage to a smooth state, removing about 0.5 mm from the surface.

In the way described in this article, the fit of the bearings rotated in their places was restored not only for cars and motorcycles, but also for trucks, and a lot of money was saved, since the crankcase or rear, hub, or engine block no longer needed to be changed. what I wish for you too; Good luck everyone.

Restoration of bearing seats by means of metal polymers by gluing.

The essence of this method lies in the fact that the process of restoring the seat is combined with the assembly operation of the bearing assembly. As a result, a fixed connection of the bearing and the shaft (bearing housing) is formed, which is many times superior in strength characteristics to the interference fits recommended in such cases, which more reliably protects the bearing rings from rotation, eliminating wear and ensuring more reliable operation of the unit. At the same time, the insertion, in contrast to the interference fit, does not lead to the appearance of stresses and deformations of the bearing rings, which also contributes to its more comfortable operation.

To disassemble the bearing assembly restored in this way, it is necessary to heat the layer of metal-polymer formed at the place of bonding to a temperature above 300 ° C or burn it out, for example, using a gas burner.

The main steps in the process of restoring footprints using inserts.

I.Restoration of seats with insignificant (up to 0.25 ÷ 0.3 mm in diameter), uniform wear (without preliminary machining of the restored surface).

1. Prepare the surface to be repaired in accordance with general recommendations (clean from dirt, oil, etc., roughen with emery paper, degrease).

2. Wipe down and degrease the bearing seating surface.

3. Conduct a test assembly: the bearing should be installed in the seat easily enough, without significant effort.

4. Protect the bearing cage with adhesive tape or electrical tape from possible ingress of metal-polymer into it when gluing.

5. Prepare the required dose of metal polymer.

6. Apply the required layer or layers of metal polymer to the shaft (housing) seat, thoroughly wetting the surface to be repaired.

7. Smear, literally wetting, with a thin layer of metal polymer the bearing seat.

8. Install the bearing on the shaft (in the housing), carefully pressing it against the limiting collars, bushings, and retaining rings.

9. Remove the squeezed-out excess metal polymer, clean the unprotected places on the shaft (in the housing) with acetone in case of accidental contact with the metal polymer, remove the protection from the separator.

10. After polymerization of the metal polymer, the unit is ready for further operation.

Note:

With the indicated values ​​of wear, the centering of the bearing relative to the shaft (housing) during the gluing process is ensured both by the filler particles of the metal polymer falling into the gap, and by additional methods, for example: preliminary punching of the restored surface (usually it is enough to punch the surface that is the supporting one during gluing), centering relative to other parts etc.

2. Restoration of seats with insignificant (up to 0.1 ÷ 0.15 mm in diameter) wear.

When restoring by gluing the seats of shafts (housings) with a wear value less than 0.1 ÷ 0.15 mm in diameter (the size of the gap is commensurate with the size of the filler particles), it is necessary to pre-bore the seat by an amount of 0.5 ÷ 1.0 mm, s by cutting "ragged threads" or grooves. To ensure the centering of the bearing during gluing, boring is carried out with the remaining belts along the edges of the seat and along its length (the total width of the belts should not exceed 50% of the entire glued surface) - see Figure 1.

font-size: 11.0pt; font-family: Arial "> Fig. 1. Restoring the seat on the shaft using metal polymers by gluing the bearing:

D number. - d 1 = 0.1 ÷ 0.15 mm;

D 1 - d 2 = 0.5 ÷ 1.0 mm;

I - places of cutting "ragged threads" or annular grooves.

The rest of the recovery steps are the same as in step 1.

3. Restoration of seats with significant (over 0.5 ÷ 1.0 mm in diameter) and uneven wear.

When restoring by gluing seats with significant and uneven wear, the issues of centering and ensuring the alignment of the bearing and the shaft (bearing housing) are of particular importance. These problems can be solved in the following ways.

1. On the worn surface along the generatrix lines, metal gaskets of various thicknesses are installed (approximately 0.05 ÷ 0.08 mm thinner than the wear in this place) in the form of narrow metal strips that exceed the place of wear in length. The free ends of these strips are fixed with adhesive tape, thread, etc. near the place of gluing (preferably on a section of the shaft with a smaller diameter). A control installation of the bearing is carried out (the bearing should be installed on the seat quite easily, without significant efforts). After that, a metal polymer is applied to the place of wear (the places under the gaskets are also coated). The bearing is installed. After polymerization of the metal polymer, the leading ends of the gaskets are cut off.

2. Small holes are welded to the wear points in diameter by welding. point(to avoid overheating of the shaft) beads in the form of rings. After that, their groove is made to the nominal bore diameter of the bearing. A control installation of the bearing is being carried out. After that, the pasting is made according to the schemes described above.

3. On worn surfaces, a groove is made to install two or more centering rings. Rings (split) are fixed in the prepared grooves by welding or gluing with a metal polymer. The installed rings are machined to the nominal bore diameter of the bearing. Further insertion is made according to the schemes described above.

Other methods of bearing centering can be used in the process of restoring the seat by gluing with the help of metal polymers.

Attention!

When restoring the bearing seats by gluing, before applying the metal polymer, it is necessary to protect the existing oil channels with adhesive tape, tape.

Seats often cannot be repaired, and then the question arises of replacing the part associated with the bearing and having lost the nominal parameters of the seat. This repair option is not economically feasible enough. The way out in this situation is to repair using Dimet technology.

Let's consider examples of repair of seats by cold gas-dynamic spraying.

Motorcycle hub bearing seat.

The defect in the seat is that the outer ring of the bearing turns during operation, which gives additional loads on the axis of the inner ring and on the bearing itself.

Image 1. The seat for the outer ring of the bearing on the wheel of a motocross motorcycle.

To eliminate this problem, it is necessary to add a layer of metal to the inner diameter of the hub. The hub is made of aluminum alloy. Before applying the composition, we pre-treat the surface with an abrasive composition K-00-04-16. An additional layer is applied in the third mode of the Dimet-405 apparatus. Spraying is done with a margin. We carry out the final processing of the coating at a low feed of the cutter at high speeds.

Image 2. Stages of repair (a - applied with a margin of aluminum layer, b - the final version of the finished footprint)

Crankshaft half ring seat

The seat of the remote half-ring of the crankshaft of the cast-iron Mercedes-Benz cylinder block was repaired using the Dimet technology. The final processing was carried out with a special cutter.

Hub bearing seat

Repair of the seat of the Ford's cast-iron hub was carried out by applying an aluminum layer, 0.3 mm in size. These manipulations provided the necessary interference in the joint.

Image 1. Stages of repair (a - initial, b - final)

Electric motor bearing seat

The repair of the bearing seats in the electric motor housing was carried out with an apparatus, the composition of aluminum, the spraying mode - "3". The image shows the stages of the repair.