The O ring is a typical seal type kneading. The compression ratio and the drawing amount of the diameter of the O type circle section are the main contents of the seal program, which is of great significance to the sealing function and the service life. O type sealing ring has a good seal effect to a large extent depends on the O type ring scale and the exact match of the groove scale, constitute a reasonable sealing ring compression and tensile.

2.1. rate of contraction

The compression rate of W is commonly used to indicate that:

/d0 (d0-h) W= * 100%

Section diameter (mm) of the d0-----O type ring in the free state;

H------O type ring groove bottom and the sealing surface of the interval (groove depth), that is, after the O type circle contraction section height (mm)

In the selection of O - shaped ring of the contraction rate, we should think from the following 3 aspects:

1 to meet the sealed touch area;

2 conflict as little as possible;

3 as far as possible to prevent lasting deformation.

From these elements is not difficult to find, they exist between the opposition. The high rate of compression can be achieved by large touch pressure, but a large contraction rate will undoubtedly increase the sliding conflict and lasting. The contraction ratio is too small may be due to groove coaxiality error and O ring error does not meet the requirements, see some shrinkage caused leakage. Therefore, in the selection of O shaped circle of the contraction rate, to weigh the elements. Usually, the static seal is larger than the dynamic seal, but its extreme value should be less than 25%, otherwise the tightening stress should be relaxed, and it will happen too much. It is especially serious in the high temperature condition.

The rate of W type O sealing ring tightening selection should consider the using condition, dynamic or static seal static seal; it can be divided into radial and axial seal seal; radial seal (or cylindrical sealing) leakage of voids is radial clearance, axial seal (or plane static seal) leak gap is the axial gap. Axial seal according to the pressure medium effect on the diameter of the O ring is still outside diameter is divided by internal pressure and external pressure of the two conditions, the internal pressure to add the tensile, external pressure drop O shape circle of the initial tension. The above is not the same way of static sealing, sealing media on the effect of O circle is not the same, so the pre pressure planning is not the same. On the dynamic seal is to distinguish between the reciprocating seal is still a rotary motion seal.

1 static seal: cylindrical static sealing equipment and reciprocating motion of the same equipment, usually take W=10% ~ 15%; plane static sealing equipment to take W=15% ~ 30%.

2 on the dynamic seal, can be divided into three kinds of condition; reciprocating motion usually take W=10% ~ 15%. Rotary motion seal in the selection of the compression rate will need to think about Joule heating effect, usually, rotary motion with the diameter of the O ring diameter larger than the diameter of 3%-5%, the outer diameter of the compression rate of W=3%-8%. Low conflict motion with O ring, in order to reduce the conflict of resistance, usually are selected smaller contraction rate, or W=5%-8%, in addition, to consider the medium and temperature caused by rubber materials swell. Usually in a given contraction deformation, the maximum swelling ratio agreed was 15%, more than the scale to clarify data selection is not appropriate, should be O ring with other data, or for a given contraction deformation rate corrected.

2.2 stretch

O type ring in the seal into the groove, usually have a certain amount of tension. With the same compression rate, the size of the tensile capacity of the O ring seal and the life of the sealing function also has a great impact. A large amount of tension will not only lead to the O ring device is difficult, because together will also change the diameter d0 contraction rate decreased, that leads to leakage. Drawing amount a can be used to indicate:

Alpha = (d+d0) / (d1+d0)

D1----O diameter of the d----- (mm); ring diameter (mm).

The value of tensile capacity is 1%-5%. If the table is given the recommended value of the O type loop stretch, can be based on the size of the shaft diameter, according to the table to select the limit of O type circle of drawing. O ring contraction rate and stretching amount of the first scale

Sealing method for sealing medium tension alpha (%) compression rate w (%)

Static sealing hydraulic oil 1.03 ~ 1.0415 ~ 25

Air <1.01 15 ~ 25

Reciprocating hydraulic oil 1.0212 ~ 17

Air <1.01 12 ~ 17

Rotary motion hydraulic oil 0.95 ~ 13 ~ 8