cushion which is desirable because seat 26 is rigid adjustment of screws 43 regulates both the minimum space between hammer head 27 and anvil 22 over which web 22 travels and also the impact pressure exerted between head 27 and anvil 22 upon a web 20 during operation of such apparatus phantom lines 44 illustrate a lower position which fulcrum 34 can occupy during apparatus operation referring to fig3 there is seen an alternative apparatus similar to that in fig2 except that here the connecting rod 37 and crank wheel 38 are replaced by a double acting pneumatic cylinder assembly 46 whose piston rod 47 functionally joins with fulcrum 34 39 control valve 48 interconnects functionally with cylinder 46 via tubing 49 valve 48 is employed to control reciprocal movements of shaft 31 39 by regulating pneumatic fluid charging rates etc to cylinder 46 as those skilled in the art will readily appreciate components in the apparatus of fig3 which are like corresponding components in the apparatus of fig2 are similarly numbered but with the addition of prime marks thereto observe that the fig3 apparatus employs no heating means referring to fig4 there is seen an alternative apparatus similar to that in fig2 except that here drive shaft 31 34 is provided with a hammer head 51 having defined across the front face 52 thereof and extending in the direction of travel of web 20 34 a set of three channels 53 channels.