Fabric manufacturing process-3

Positive tappet shedding:

PRINCIPLE:

In this variety of shedding, the heald shaft is raised and down by the tappet.

CONSTRUCTION:

POSITIVE TAPPET SHEDDING MECHANISM

 cam and bowl is connected with each other. a lever is connected with bowl and cam. this lever is fulcrumed at a position shown in figure. and this lever is connected with tappet lever. tappet lever is connected with connecting rods, this connecting rods bend at middle and fulcrumed. this levers is connected with heald shafts.

working principle:

when tappet cam is rotates, and strike on bowl then lever is moves downward. due to fulcrum lever other side is moves backward. then tappet lever is moves backward. then heald frame is moves up word. when cam round shape position moves and not strike on bowl then lever moves up word then due to fulcrum levers other side is moves forward then tappet levers moves forward, then heald frames moves downward. and this system continuously running. 

DIFFERENCE BETWEEN POSITIVE AND NEGATIVE TAPPET SHEDDING.

1. positive tappet shedding control both side movements of  heald frames (upward and downward)
2. negative tappet shedding control half movement of heald frame (50%) down ward movement control.

General characteristics of cam(tappet) mechanism.

technical:- design capability

• simple weaves

no. of picks/repeat

• limited to 8 or 10 picks/repeat

no. of heald frames(or no. of ends/repeat

• limited to 8,10 or 12 heald shafts

OPERATIONAL MERITS AND DEMERITS

MERITS:

• Simple and robust
• inexpensive with regard to both initial cost and maintenance .
• no likely to cause faults in the fabric(reliable).
• impose no limitation on the speed of the loom (1000,1500 rpm.)

DEMERITS:

• Restricted design possibilities
• inconvenient for frequent pattern changes.
• to change the cams, or
• at least to rearrange them,
• to change the gearing of cam shaft if the new weave repeats on a different no. of picks.