Ensure precise fit and function with our guidelines on tolerance and operating clearance for pins and bushings.
This technical support page offers critical insights into the optimal application of pins and bushings,
covering essential factors such as PV value, movement conditions, and material selection.
Conditions of Load
PV Value
PV value is an important parameter to decide suitable bush. Amount of friction thermal energy “Q” which occurs on unit area during unit time can be calculated from loss of energy, pressure and velocity by using below equation
Q = μ × P × V ÷ J
Q: Frictional heat energy generated per unit area per unit time (unit: kcal)
μ: Coefficient of friction (dimensionless)
P: Bearing pressure (unit: N/m² or kgf/mm²)
V: Velocity (unit: m/s or m/min)
J: Unit momentum conversion constant (427 kgf·m/kcal)
Here, if friction coefficiency is constant, thermal energy is proportional to PV value.
Friction heat and radiant heat in the bearing during rotation of the shaft make the bearing maintain stable temperature.
But after prolonged operation time, the friction coefficiency shall be increased according to the change of the sliding surface condition.
The existence of foreign material, deteriorated lubricant, particles from abrasion, fatigue of material and other reasons can affect friction coefficiency As a conclusion, if the temperature of the bearing goes up, it ultimately result in damage on sliding surface or seizure.
In order to keep the low temperature of bearing , in other words keep PV value smaller, lighter load condition should be considered.
Safe designing of bearing means design for small PV value in order to get a longer bearing lifetime.
Direction of movement and PV value
In one-directional journal rotation movement, we can easily operate under adequate oil film lubrication. But in case of thrust bearing, enough caution and consideration in designing oil grooves and in choosing methods of lubrication should be applied in order to obtain suitable lubrication for the sliding surfaces. It is same in situations of interrupted, oscillating and reciprocating motion. Maximum allowed PV value (on the catalogue) are in general applied to rotation movement. In case of reciprocating motion or rotation of thrust bearing or interrupted movement, half of maximum allowed PV value should be applied. In case of oscillating movement, even lower value may have to applied.
Intervention of foreign material on bush
If dust or other foreign material meddles on the sliding surface, the oil film shall be destroyed. Hence the direct contact between bearing and shaft will result in abrasion or seizure. These foreign material which are destructive obstacle to bush function can be eliminated adding grease together with seal.
Oscillating movement
Oscillating movement is one of the most severe operational conditions for bearing, because every movement cycle passes a point where velocity becomes zero value. Hence oil film can easily be destroyed, accelerating abrasion and fatigue of material and also the particles from abrasion can remain longer time.
Ball or roller bearings which are used mainly for rotation movement may have point or line contact which have extreme contact stress on the places supporting pressure. So these bearings are not suitable on oscillating movement.
Bushings which have wide contact area are generally more suitable for these kinds of operational conditions.
Conditions of Pins coupled with
Bushes
Performance of bush is most greatly influenced by the quality of relative materials which brings friction, such as the kind of material, surface coating, roughness, etc. And when used in high temperature of more than 100℃, the diameter of pins must be adjusted considering expansion by heat.
Roughness of surface
In general, the lifetime of bush is decided by the existence of oil film which is formed on the sliding surface of bearing and relative product.
The roughness of 3~12μm is requested to achieve adequate performance of bush.
Surface Treatment
Three main purposes of treating surface of relative material are as below.
1) To improve corrosion resistance 2) To improve surface hardness 3) To improve the smoothness of the surface for better sliding
When applying plating for the purpose of above article 1), high hardness Chromium plating is strongly recommended, because it protects relative material from rusting and abrasion and improves sliding.
Tolerance of pin and bushing and
operating clearance
Generally each machinery and parts manufacturers have their own standard for tolerance of pin and bush according to their own know-how, so it is common situation that tolerance is decided according to customers’ specification.
But we hereby present our below list of tolerance of bush and pin and tolerance of housing which we apply to our manufacture obtained through our long-term experience, and the list is just for reference
| Model | Housing | Pin diameter | Bush inner diameter | Bush outer diameter |
|---|---|---|---|---|
| GST45 | H7 | f8 | C9 | u6 |
| GST40 | H7 | f8 | C9 | u6 |
| GST15 | H7 | f8 | C9 | u6 |
| GCH | H7 | h7 | C8 | u6 |
| ODP,VDP | H7 | h7 | C8 | u6 |
| GHB1,4 | H7 | h7 | H9 | u6 |
| GOL | H7 | h7 | H9 | u6 |
| GSN | H7 | h7 | H9 | u6 |
The design of operating clearance for pin and bush is the most important due to be maintained optimal clearance for the formation of oil film.
The change of size owing to the operational heat and the reduction of inner diameter after fitting the bush into housing has to be considered carefully to decide the operating clearance.
This clearance can be changed according to the various fitting conditions and shape of bush, i.e. interference of bushing and housing, the shape of boss and groove of bush, flanged bush and various material and heat treatment.etc.
So it is not easy typically to fix the clearance. For just reference, the clearance of bush and pin is used about 0.1~0.3mm commonly.
MATERIALS COMPARISON
Comparison between Geowell Pin and bushing’s material feature with international standards
[ Chromium molybdenum steel ]
| SCM415(KS) | Chemical Composition | C | Si | Mn | P | S | Cr | Mo | Remarks |
| 0.13 ~ 0.18 | 0.15 ~ 0.35 | 0.60 ~ 0.85 | Max 0.030 | Max 0.030 | 0.90 ~ 1.20 | 0.15 ~ 0.30 | For Surface Hardness (Application : Bush) | ||
| Heat Treatment | Quenching | 850 ~ 900℃, Oil Cooling | |||||||
| Tempering | 150 ~ 200℃, Air Cooling | ||||||||
| SCM415(KS) | Mechanical Property | Yield Point (N/mm²) | Tensile Strength (N/mm²) | elongation (%) | Reduction of Area (%) | Charpy Impact (J/mm²) | Hardness (HB) | Remarks |
| 708or More | 833or More | 16or More | 40or More | 68.3or More | 235 ~ 321 | For Surface Hardness (Application : Bush) | ||
| quivalent int'l spec | DIN | BS | AISI | NF | JIS | GB | ||
| 15CrNi5 16CrMo4 |
708M20 708H20 |
4023 | 15CD4 12CD4 |
SCM415 | 15CrMo |
[ Chromium molybdenum steel ]
| SCM440(KS) | Chemical Composition | C | Si | Mn | P | S | Cr | Mo | Remarks |
| 0.38 ~ 0.43 | 0.15 ~ 0.35 | 0.60 ~ 0.85 | Max 0.030 | Max 0.030 | 0.90 ~ 1.20 | 0.15 ~ 0.30 | Application busi, pin | ||
| Heat Treatment | Quenching | 830 ~ 880℃, Oil Cooling | |||||||
| Tempering | 530 ~ 630℃, Air Cooling | ||||||||
| SCM440(KS) | Mechanical Property | Yield Point (N/mm²) | Tensile Strength (N/mm²) | elongation (%) | Reduction of Area (%) | Charpy Impact (J/mm²) | Hardness (HB) | Remarks |
| 833 or More | 980 or More | 12 or More | 45 or More | 58.5 or More | 285 ~ 352 | Application busi, pin | ||
| quivalent int'l spec | DIN | BS | AISI | NF | JIS | GB | ||
| 42CrMo4 | 708M40 708H40 |
4140 4142 |
40CD4 42CD4 |
SCM440 | 42CrMo |
[ Carbon steel for machine structural use ]
| SM45C (KS) | Chemical Composition | C | Si | Mn | P | S | Cr | Mo | Remarks |
| 0.42 ~ 0.48 | 0.15 ~ 0.35 | 0.60 ~ 0.90 | 0.030 Max | 0.030 Max | 0.20 Under | 0.20 Under | Application bush, pin | ||
| Heat Treatment QT | Quenching | 820 ~ 870°C air cooling | |||||||
| Tampering | About 810°C Furnace cooling | ||||||||
| Quenching | 820 ~ 870°C water cooling | ||||||||
| Tampering | 550 ~650°C rapid cooling | ||||||||
| SM45C (KS) | Mechanical Property | Heat Treatment | Yield Point (N/mm2) | Tensile Strength (N/mm2) | elongation (%) | Reduction of Area (%) | Charpy impact (J/mm2) | Hardness (HB) | Remarks |
| N | 343 or More | 569 or More | 20 or More | -- | - | 167 ~ 299 | Application bush, pin | ||
| A | -- | -- | -- | -- | -- | 137 ~ 170 | |||
| H(QT) | 490 or More | 686 or More | 17 or More | 45 or More | 78 or More | 201 ~ 269 | |||
| Equivalent int'l spec | DIN | BS | AISI | NF | JIS | GB | |||
| CK45 C45 |
060A45 080M46 |
1045 1046 |
XC45 | S45C | 45 | ||||
[ High strength brass castings ]
| CAC301 (HBsC1) (KS) | Chemical Composition | Cu | Zn | Mn | Fe | AI | Residual substance | Remarks | |||
| Sn | Pb | Ni | Si | ||||||||
| 55.0 ~ 60.0 | 33 ~ 42 | 0.1 ~ 1.5 | 0.5 ~ 1.5 | 0.5 ~ 1.5 | 1.0 | 0.4 | 1.0 | - | Application bush | ||
| CAC301 (HBsC1) (KS) | Mechanical Property | Yield Point (N/mm2) | Tensile Strength (N/mm2) | elongation (%) | Remarks | |||
| 430 or More | 20 or More | 90 or More | Application bush | |||||
| Equivalent int'l spec | DIN | BS | EN | AISI | JIS | NF | ||
| CuZn34A12 | HTB1 | CC765S | SAE43 C86500 |
CAC301 (HBsC1) |
Cuzn30 - AlFeMn | |||
[ High strength brass castings ]
| CAC301 (HBsC1) (KS) | Chemical Composition | Cu | Zn | Mn | Fe | AI | Residual substance | Remarks | |||
| Sn | Pb | Ni | Si | ||||||||
| 55.0 ~ 60.0 | 33 ~ 42 | 0.1 ~ 1.5 | 0.5 ~ 1.5 | 0.5 ~ 1.5 | 1.0 | 0.4 | 1.0 | - | Application bush | ||
| CAC301 (HBsC1) (KS) | Mechanical Property | Yield Point (N/mm2) | Tensile Strength (N/mm2) | elongation (%) | Remarks | |||
| 430 or More | 20 or More | 90 or More | Application bush | |||||
| Equivalent int'l spec | DIN | BS | EN | AISI | JIS | NF | ||
| CuZn34A12 | HTB1 | CC765S | SAE43 C86500 |
CAC301 (HBsC1) |
Cuzn30 - AlFeMn | |||
[ Composite material for graphite plugged bushings & sintered bushings ]
Solid Lubricant Bush #500SP : Solid lubricant is plugged into high-strength-brass base metal
Sintered Bush : Special sintered base material of Fe or Cu