Design Optimization and Performance Analysis of the Pneumatic DTH Hammer with Self-Propelled Round Bit

Table 1

Air condition and bit motion at each stage.

Stage	Displacement of the piston (L)	Air condition (front chamber)	Air condition (rear chamber)	Piston motion	Bit motion
a	0 ≤ L < L5	Air intake	Air exhaust	Backhaul stage	Rotation
b	L5 ≤ L < L3	Air intake	Air compression	Backhaul stage	Rotation
c	L3 ≤ L < L4	Air expansion	Air compression	Backhaul stage	Rotation
d	L4 ≤ L < L2	Air expansion	Air intake	Backhaul stage	Rotation
e	L2 ≤ L ≤ L1	Air exhaust	Air intake	Backhaul stage	Rotation
f	L4 ≤ L < L2	Air compression	Air intake	Strike stage	Nonrotation
g	L3 ≤ L < L4	Air compression	Air expansion	Strike stage	Nonrotation
h	L5 ≤ L < L3	Air intake	Air expansion	Strike stage	Nonrotation
i	0 ≤ L < L5	Air intake	Air exhaust	Strike stage	Nonrotation

L₅, L₃, L₄, and L₂ represent a specific key location of the piston where the air conditions change at each stage, especially L₁ representing the piston’s actual strike. and represent the instantaneous mass flow rate passing through the front chamber and the rear chamber (Figure 3), respectively.