Modem materials enable the designers to construct a lightweight helmet, far from the days of leathercap with straps 0f the 1930's.
现代材料使得设计者可以造出轻巧的头盔，这和30年代用吊带固定的皮帽相去甚远。
2
The article analyzes characteristics and abrasion factor of leathercap type pig according operation feature, and then proposes reasonable magnitude of interference.
Leathercap type pig has higher abrasion during pigging gas steel pipeline. Furthermore, various elbow bend and tee joint need different suitable length pig or else easy to cause pipeline clog.