# Structure of small gear and big gear ring of high temperature resistant blind valve

The loosening of the valve clamping part adopts the gear ring transmission mode. The gear ring transmission ratio is constant, the transmission power is large, the efficiency is high, and the service life is long. It is a stable and reliable transmission mode, and the small opening angle of the big gear ring rotation can transfer the larger opening distance. The big gear ring is directly pushed by the push rod device to transfer the torque, and the pinion drives the screw to rotate to loosen or clamp the valve plate.

Taking the valve with diameter of DN800 and pressure of 0.05 MPa as an example, the gear ring is designed and checked.

The designed lead screw is tr80 × 16, and the torque T transmitted by the big gear ring is the total torque transmitted by the clamping lead screw

T = Ftan( φ + ρ＇) d2/2

T — transmission torque of big gear ring, NMM

F — axial load of lead screw, n

D2 — pitch diameter of lead screw thread, mm

φ – angle of thread rise, °

ρ ‘- equivalent friction angle, °

The axial load F of the lead screw, i.e. the medium force and sealing force of the valve, is calculated to be 235 kn. The pitch diameter D2 of the thread of the lead screw tr80 × 16 is 72 mm. The rise angle of the thread is calculated to be 4.046 ° and the equivalent friction angle is calculated to be 5.323 ° by substituting the value t = 1.394 × 106 nm.

Referring to the existing gear transmission structure of blind valve with the same diameter and pressure or similar, the main dimensions of pinion and big gear ring are preliminarily determined by analogy.

The torque transmitted by the pinion is t / 3nmm, and the circumferential force FT on the indexing circle of the pinion is calculated as follows:

Ft，= 2T /3d1

Substituting the value, ft = 5.5 kn.

Check the tooth root bending fatigue strength of the pinion, and calculate the bending stress σ F as follows:

σ F — calculated bending stress, MPa

FT — the circumferential force on the indexing circle of the pinion, n

B — tooth width (b = 40mm)

Ka — service factor (KA = 1.25)

KV — dynamic load coefficient (kV = 1.0114)

KF β – tooth load distribution coefficient (KF β = 1.14)

KF α – load distribution coefficient between teeth (KF α = 1.0)

YFS — composite tooth profile coefficient (YFS = 4.36)

Y ε β — coincidence degree and helix angle coefficient of bending strength calculation (Y ε β = 1.0)

Substituting the value, we get σ f = 114.05 n / mm2.

The calculated allowable bending stress σ FP is:

σ FP — allowable bending stress, MPa

σ Fe — basic value of bending fatigue strength of gear material, 320 MPa

Ynt — life factor of bending strength calculation, 1.6

Y δ relt — sensitivity coefficient of relative root fillet, 0.95

Yrrelt — relative surface condition coefficient, 0.9

YX – dimension coefficient of bending strength calculation, 0.95

Sfmin — minimum safety factor of bending strength, taking 1.25

Substituting into the numerical value, σ FP = 332.7mpa. After checking, it can be seen that if σ f < σ FP, the modulus of pinion M = 8 can meet the service conditions. The circular force on the teeth of the big gear ring is the same as that on the pinion, so only the pinion can be checked. 