2.Max permissible PV value
The bushing can run for a short time when achieves its max PV value. It's the running service life requirement that decides the requirement for the value. In bushing design,we require that Boundary and non-lubricating state the max permissible PV value shall be smaller than the value gained by multiplying the max permissible load pressure and the max permissible running velocity.
1.Inside diameter of the bushing
Generally,the inside diameter of the bushing depends on the diameter of its mating axis.
2.Length of the bushing
The length of the bushing depends on the size of the pressure-shouldering surface.The longer the bushing,the less pressure at the surface,for the onger bushing, the load on the bushing is relatively lessened. But simultaneously, it may result in deviation contact or lower cooling efficiency and thus shorten the service life of the bushing. On the contrary, if the length of the bushing is too short,lubricating grease may quickly flow out of the bushing.Therefore,it hardly forms a grease film and capability of the bushing is accordingly debased./p>
A comparison of L/d's effect on the bushings,especially oil lubricating bushings
|Short bushing（d＞L）||Comparison items||Long bushing(d＜L)|
Force on the oil film
|Can not be too high||
Can be high
Safety aqainst beating deviation
Shock absorbing ability
The main advantage of standard composite self-lubricating bushings rest with their thin wall thickness.Standard thickness can be 0.5mm2,0.75mm2;,1.0mm2,1.5mm2,2.0mm2,2.5mm2.
In thickness design of the non-standard gliding bushing,the designer could consult thefollowing proportion of SB and D.
A)For thin wall thickness gliding metallic bushing,proportion between SB and D equals to 0.03~0.06.
B)For thin wall thickness gliding metallic bushing, proportion between SB and D equals to 0.08~0.12
C)For plastic gliding bushing,proportion between SB and D equals to 0.1~0.12
In order to make fixing easier and avoid deviation load,the bushing must be inner and outer chamfered in the direction of its length.Dimension of the chamfer are showing in the following form.
|Wall thickness||Out Chamfer Dimension||Inner Chamfer Dimension|
Shock absorbing ability
1.The mating housing must be chamfered for easier mounting.
For cylindrical bushing,its mating housing must be chamfered according to the formula:
fGx200±5.Value of fG depends on dH, the diameter of the housing.
|Diameter of the housing dH||Chamfered FG|
As to the housing mating for flanged bushings,it requires the housing being chamfered big enough to avoid he deformation at the flanged circle.The housing mating shall be chamfered according to the formula:fGx450 ±5°
|Diameter of the housing dH||Chamfered FG|
Surface roughness,hardness and plating of the mating axis will have great influence on the capability of the self-lubricating bushing.High-quality surface of the mating axis can prolong the life of the bushing while rough surface will shorten the life of the bushing.
1.Surface roughness of the mating axis
When self-lubricating bushings being used in the condition of fluid lubrication and the surface of the mating axis is faily rough,the convex points on the bushing and its axis will cut the oil film and thus the surface of the axis and the bushing will directly contact with each other.therefore,to improve he capability of the bushing, it requires polishing the surface of the mating axis as smooth as a mirror, thus can reduce the clearance of the oil film and make the film work well.
For most self-lubricating bushings applied in the condition of dry friction or marginal lubrication,a controlled roughness from 0.32 to 1.25 is acceptable and there is no need to polish the surface of the mating axis as smooth as a mirror.
2.Hardness of the mating axis
f there is no hard article in the lubricating condition,good performance can be achieved by using bushing materials and hardness recommended in the following form.If not,it would be better to use the harder material for the mating axis.
|Material quality of the axis||Hardness|
SS41(Q255B)Common Structural steel
S25C(25#)Carbon Structural Steel
The left column shaft hardness of the material,and so on
SUS.SUH anti-erosion steel(in high temperature and water),and chrome plated steel,etc.
The left column shaft hardness of the material,and so on
Under running condition with heavy load and rapid swing,the mating axis must be heat-treated.
The after treatment hardness will be decided by the material of the axis.
3.Surface treatment of the mating axis
Aim of this treatment:
a) Improve anti-erosion quality
b)Strengthen surface hardness
c)Smooth the surface and enhance lubricating capability
f the mating axis was plated, it can not only improve the anti-erosion capability but also will enhance the lubricating capability, as with a plated coating,friction can be effectively decreased.Hard oxides and other impurities caused by the axis rust constitute one of the main abrasion causes. Therefore,we recommend the user to have the mating axis chrome plated. If the bushings are going to be used in sea water or similar erosive conditions,their mating axis must be chrome plated for 2 or 3 layers.
4.Structural design of the mating axis
Surface roughness and keen-edged burrs or dents on the surface of the mating axis will destroy the gliding layer.Please see the following illustration for the qualified mating axis.
Influences on the service life
Wear and service life of the slide bearings are dependent on the following:
·Specific bearing load
·Roughness depth of the mating surface
·Mating surface material and Temperature etc.
With the exception of being burnt,the service life of self-lubricating bushing depends on the abrasion degree of the bushing's inner diameter.In conditions like dry friction,boundary lubrication and oil lubrication,the abrasion of thesame bushing will be different.Main factors that may influence he service life are:character and direction of the load,lubrication condition,running speed,environment temperature, hardness of the mating axis,oughness of the mating surface,material of the mating axis, air quality around etc. Therefore, it's difficult to calculate the actual abrasion quantity.Regardless the factors like influence from the load and speed, difference caused by running direction, kinds of lubricating oil,mating clearance,oughness and impurities penetration degree,the abrasion W can be calculated by the following formula.
Abrasion coefficient K gained under different lubrication conditions in the laboratory.Consult the following form for K value.
|Lubrication conditions mãŽ¡(N/mãŽ¡.m/s·Hr)|
|Periodical lubrication(marginal lubrication)||
|Oil lubrication(fluids lubrication)||
Before the bushing is pressed into the housing:as the outside diameter of the bushing is bigger than the inside diameter of the housing,strong pressure can be available in the housing. And also this kind of fixing can assure the roundness of the bushing and make the bushing well fixed, voiding abrasion caused by sliding of the bushing in the housing.The interference can be calculated by the following formula:
Min interference Min OD of the bushing-Max ID of the housing
Min interference Max OD of the bushing-Min ID of the housing
Afer bushing mounting,providing that there is no expansion of the housing,the calculation can be carried out by the following formula.
Min ID of the bushing d=Min ID of the housing D-2xMax thickness of the bushing S
Max ID of the bushing d=Min ID of the housing D-2xMin thickness of the bushing S
t's necessary to have an approptiate clearance between the inner surface of the bushing and the axis after bushing mounting.The matching learance can be calculated by the following formula:
Min clearance Δ min=Min ID of the bushing after fixing d min-Max diameter of the axis djmax
Max clearance Δ max=Min ID of the bushing after fixing d max-Min diameter of the axis djmin
1.Formula for calculation the pressing-in force when fix the bushing
t:Thickness of the bushing after polymer laymers had removed(mm)
b:Height of the bushing(mãÅ½¡)
D:OD of the bushing(mm2)
Note:In this case,value of friction coefficient between the bushing backing and the Housing is around 0.15.
Calculating the pressing-in force F used to press KDB100 2015(standard)the housing Φ23+0.0210
Pre-known:Wall thickness S=1.5mm2,thickness of the polymer layer=0.3mm2,thickness of the base plate t=1.5-0.3=1.2mm2;height of the bushing b=15;OD of the bushing D=23mãÅ½¡, surplus=0.014mãÅ½¡, surplus=0.075mãÅ½¡
Therefore,the pressing in force for fixing F=1880~10040 N
1) Fixing methods for cylindrical bushings
Diameter of the pressing-in arbor is 0.1 ~ 0.3mm smaller than the diameter of the bushing. It's better to have the core axis heat-treated.For easier fixing,we can add a light coating of oil on the bushing backing. Make sure not to fix the bushing into the housing by hammering its end surface.When he diameter of the bushing is more than 55mm, necessary measures must be taken to calibrate the seam position of bushing.
2)Fixing methods for flanged bushings
For flanged bushings,the radius at the flanged folds must be taken into account. A sufficiently large chamfer must be provided on the housing to prevent flanged bush fouling in the area of theradius.Fixing methods for the flanged bushings are similar to that for cylindrical bushings.However, he diameter of the convex part on the pressing-in arbor for flanged bushings needs to be a little bigger.
For the first running after bushing was fixed,the bushing shall be worked under situations of light load and low speed,which will have the following
1)Smooth the surface of the bushing and its mating axis and smooth the partial convex part that shoulder load.
2)Rectify fixing tolerance caused by bushing deformation;smooth the surface and increase contact surface.
Bushings will initially be roll packed or plastic bag packed and then will be secondly packed in carton or wooden box.Packed bushings shall be stored in clean and rust-resistant environment.
Avoid storing bushings in the following places
1)Place vertically in the sun
2)Place of high temperature and moisture
3)Place with water and other acid or alkali erosive liquids.
4) Do not place heavy articles on the carton to avoid bushing deformation
1.Methods for checking the outside diameter
1)Load checkin(DIN 1494-2:Test A)
The checking rig consists of two checking block halves. Align the "zero" position of the checking blocks by a setting plug dch. 2 and make the bush's split place at the upper halve of the checking blocks and then add the same checking load Fch on both of the checking halves.Read the moving distance of the halves displayed on the distance indicator and record the readingΔz.
2)Measuring of gauge (DIN 1494-2:Test B)
The checking is carried out by two ring gauges,a "GO" ring gauge and a "NO GO" ring gauge.It must be possible to press the bushing in "GO" ring gauge with hand pressure(max 250N).With the same force it must not be possible to press the bushing in "NO GO"ring gauge.
Note: In some cases,such as the bushing with roundness problem,or the butt joints not close tightly,hand pressure with hand pressure the accuracy of the checking may be affected.
3)Measuring of rule(ISO3547-2:Test D)
For bushing with rather big diameter,their circumference can be checked out by a measuring tape.Firstly,the measuring tape is calibrated around a mandrel of diameter equal to the nominal outside diameter of the bushing. An indicating device is attached to the "free"end of the measuring tape and set to the calibration size. Secondly, move away the mandrel and take in its place with a bushing. Make sure to let the split of the bushing fully closed by pulling more strength on the tape.Finally After the bushing has been cheched,the circumference indicator readingΔZD is the difference between he calibrated value of the setting mandrel and the measured value if the bushing.Form this,the outside diameter of the bushing can be worked out.
2.Inside diameter checking methods for wrapped bushing
1)Plug gauge checking(DIN 1494-2:Test C)
Press the bush into the ring gauge,the tolerance class of which is H7,and check the inside diameter of the bushing with plug gauges.
1) Plug gauge checking(DIN 1494-2:Test C)
Check the wall thickness of the bushing a wall thickness micrometer and then calculate out the value of the inside diameter.According to ISO3547-2 make sure not to mark both the wall thickness and inside diameter on the drawing.
3.Thrust washer test method
Beside the thickness, the flatness of washer is also important for service life of washer and grinding parts'. We use very helpful test in which the washer falls through the gap between two plain parallel plates of a gauge with its own weight.The plates must be big enough to cover the whole washer.
Disc Springs, with all of their variations, are among the most widely used tension generating washers. They are used for spanning alignment holes, distributing bearing loads and for generating and sustaining the tension needed to hold assemblies together. Belleville washers provide a very high spring force for short movement and have a high energy storage capacity. In a true Belleville washer, the ratio of material thickness to rim width is held to about one in five. Crown height actually should not exceed 40% of material thickness. In application, yield strength is not exceeded and the washer returns to its full crown height when compression force is removed. Commercial Disc Springs are not held to the specific O.D./crown height/thickness ratios required of the true Belleville Disc Spring washers. Traditionally, the crown height to thickness ratio is considerably greater for commercial Disc Springs. When loaded to flat, their yield point may be exceeded. These washers, however, are often used in applications where they function entirely within their elastic range. In applications where they are loaded beyond their yield point they will act in a consistent manner over a reduced crown height. Such washers have, in effect, become reformed. By varying thickness and crown height relationships, design engineers meet a wide range of load/deflection requirement with Disc Spring washers. A crown height to thickness ratio ranging from 0.4 to 0.8, for example, produces a fairly constant spring rate (Figure 1). With a crown height to thickness ratio up to 1.4, the washer will show a positive rate of increase in the load up to 100% deflection (Figure 2). At a crown height to thickness ratio of 1.4, the Disc Spring shows a constant load over a fairly large deflection, making it useful in applications where extreme wear conditions must be absorbed (Figure 3). Where the ratio of crown height to thickness exceeds 1.4, yielding will occur and, possibly, oil canning or inverting (Figure 4).
Slotted Disc Springs
Often referred to as a diaphragm spring,the Slotted Disc Spring is used in clutch applications and other applications requiring high travel consistent within acceptable stress limits.The characteristics curve,as shown in figure 6,indicates a relatively constant load over a wide range of deflection.
Disc Springs are often stacked to enhance performance characteristics.By stacking them in parallel,load bearing characteristics are enhanced(Figure
7).when stacked in series,greater deflection or travel is achieved (Figure 8).
Combination stacking, in parallel and in series, increases both load bearing and deflection (Figure 9). Disc Springs of varying thicknesses can also be stacked to achieve specific performance
Comparing Disc Spring Stack To Coil Spring
Figure 11 clearly shows how Disc Springs,stacked in series,support the same load as a coiled spring with a substantial reduction in space required.Disc stacks may be designed for extremely high loads where coil springs are not feasible at all.
Actual Test Results versus Calculated Disc Spring Characteristics
The example, in the graph on the left, is typical of most disc springs, and underlines the necessity of limiting maximum deflection to 75 per cent to avoid sharply increasing force and stress characteristics.
As the compressed disc spring nears its ‘flattened’ condition, the reducing cone angle results in the movement of bearing point toward the centre, thus effectively shortening the ‘lever’ length and ‘stiffening’ the spring.
The ability to change the force/deflection characteristic, by way of varying the cone height to thickness ratio, is a particularly useful feature of the disc spring.
Shown above are some examples of different cone height to thickness ratios, and up to a ratio of 1.5 the disc springs may safely be taken to ‘flat’ or stacked in columns.