production apparatus which contains only one glow wire a slot 102 which is arranged in the secondary electrode 100 corresponds for example to the slot 50 52 or 54 the secondary electrode 100 has a rectangular base body on whose longitudinal faces two attachment webs 104 and 106 are arranged centrally the attachment webs 104 and 106 have a length which corresponds approximately to u2153 of the length of the base body of the secondary electrode 100 the attachment web 104 projects about 10 mm beyond the base body of the secondary electrode 100 in contrast the attachment web 106 projects only about 3 mm beyond the base body of the secondary electrode 100 the base body of the secondary electrode 100 has length of 162 mm and a width of about 36 mm an opening of the slot 102 extends close to the attachment web 106 virtually over the entire length of the base body in the exemplary embodiment the length of the slot 102 without including rounded areas at the ends of the slot 102 is 150 mm fig2 a also shows a section plane a in the center of the secondary electrode 100 the section plane a is located transversely with respect to the longitudinal axis of the secondary electrode 100 fig2 b shows the secondary electrode 100 along the cross section lying in the section plane a the thickness of the secondary electrode 100 is about 5 mm as is illustrated in fig2 b side walls 110 and 112 of the slot 102 are inclined at an angle of u2212 55 u00b0 with respect to a normal n the distance between the side walls 110 and 112 is 4 mm the secondary electrode 100 is composed of aluminum that is to say of.