Patent GB-809991-A (GB)
Title: Apparatus for filling sheathed electrical resistance elements with granular insulating material
IPC: H01B7/16
Filed: 1957-04-25
Abstract: 809,991. Sheathed heating resistors. KANTHAL A.B. April 25, 1957 [April 25, 1956], No.13259/57. Class 39(3) In filling the sheaths of electric heating resistors with granular insulating material e.g. magnesiumoxide particles not exceeding 0.02 in. in size, the sheaths 21 are arranged vertically with a helical resistance wire 22 held centrally in the sheath between terminal pins 24, and the granules are fed from a hopper into a space between concentric tubes 140, 141 within the sheath. The outer tube 141 slides up along the inner surface of the sheath, and the inner tube 140 around the wire 22 has on its outer surface shelf-forming protusians 161 bridging the space between the tubes and offset mutually longitudinally of the tube. The protusions 161 are spaced apart and overlap so that the granules do not pass gravitationally between them except when a vibrator 110 on the sheaths 21 is active, the distance D between adjacent protusions 161 and the amount of overlap F being arranged accordingly. In Fig. 7 two rows of protusions 161 are shown diverging downwardly from a wider top end protusion 167 and the opposite ends of the rows terminate in a wide bottom protusion 168 on the opposite side of the tube 140. The rows of protusions thus extend helically along the tube and 2n rows of protusions 161 are associated with n end protusions 167, 168 at each end. The powder finally passes between spaced vertical ribs 162a on a preferably removable tip 165 of the inner tube 140. The ribs 162a are formed with shoulders 163 on which the lower end of the outer tube 141 rests. The wire is welded at its ends to terminal pins 24, which have portions 24b of reduced cross section. Each terminal has an external collar engaging a cup of polystyrene closing each end of the sheath. When the heater is finally swaged or rolled and annealed, the cup volatilizes, or if of metal it melts, and the end of the sheath is sealed by fused glass. The filling machine comprises a fixed frame 36 with a stationery cross member 91 having apertures in which the lower ends of the sheaths 21 rest and are gripped by clamps 99, 102. The sheaths are vibrated by an electro-magnetic vibrator 110 on a transverse support rod 111, which with the clamp 99 is connected to chains 68 passing over sprockets 58 so that they move together. On the support rod 111 is a guide bar 132 with apertures for the filling tubes 141, into which the insulating powder is fed from a hopper 71, the outer tubes 141 terminating short of the inner tubes 140. The hopper 71 is supported on a cross bar 72 attached to chains 64 moving over sprocket wheels 56, 62 so that it may be moved vertically. The bar 72 has openings 143 for passage of the powder. The upper terminal 24 (Figs. 4b, 6) is moved into a slot 182 and is held by a slot 181 in a tubular adapter hook 180 threaded on to a hook rod 175 secured to a fixed cross support 81. Powder is fed into the hopper 71 through tubes 76. The filling operation commences with the sheaths 21 and filling tubes arranged relatively as shown in Fig. 2. The sheaths are then fully raised around the filling tubes 141 and when the vibrator 110 is rendered active, the sheaths are slowly lowered as they are filled, the flow of powder stopping when the vibrator is rendered inactive. Specification 803,878 is referred to.