This study investigates the friction welding conditions for sound friction welded joint of high density polyethylene round bar and pipe. A comparison of joining phenomena of round bar and pipe is carried out. The mechanisms of generation of polyethylene dust and its preventive means are examined.
The results of this experiment are as follows;
1) The sound friction welded joint of polyethylene round bar was obtained, when friction welding conditions were friction time t1=20s, upset time t2=60s, friction pressure P1=0.10MPa, upset pressure P2=0.10MPa, rotational speed N=60s-1 and t1=25s, t2=60s, P1=0.05MPa, P2=0.05MPa, N=60s-1. These conditions are strict, compared with carbon steel.
2) Tensile strength and elongation of sound friction welded joint of round bar were 25.2-25.4MPa and 749-757%, respectively. These were nearly equal to that of the base polyethylene.
3) In the case of round bar, unbonded area occurred if the friction pressure was more increased than the sound friction welded joint condition. The tensile strength of this joint decreased slightly but the elongation decreased remarkably, compared with the base polyethylene.
4) A good welded joint of polyethylene pipe was obtained, when the friction welding condition of friction time t1=5s, upset time t2=60s friction pressure P1=0.10-0.25MPa, upset pressure P2=0.10-0.25MPa, rotational speed N=60s-1 was given.
5) Tensile strength and elongation of sound welded joint of pipe were 23.4MPa and 520%, respectively. These were nearly equal to those of the base polyethylene.
6) There were two main causes of generating dust in the polyethylene pipe. First, polyethylene became hard in the initial friction welding because heat generation by friction welding was low. Second, polyethylene was shaved by friction pressure and rotation. Consequently, the way of preventing dust generating is to preheat the faying surface at about 393K before friction welding.