GB1446710A - Filtering - Google Patents

Abstract

1446710 Moving band filter P G KALMAN 29 Aug 1973 [29 Aug 1972] 40064/72 Heading BID In a filter device for molten plastics wherein one or more filter elements, e.g. bands 5 of woven steel or random metal or glass-fibre matrices, are moved intermittently across a filter passage 2 through slots in which slats are effected by semi-solid plugs 28 of the plastics being filtered or other sealant material (such as described in Specifications 1181075, 1285702, 1285703 or 1433867), the filter element(s) is supported in the passage and moved thereacross by a backing support 7 reciprocal in the direction of movement of the band, means being provided to allow the filter element to move with the support in one direction of reciprocation of the latter but to prevent movement of the band with the support upon return of the latter in the other direction. In Figure 2A, a toggle mechanism 22 is provided for reciprocating the support 7 and comprises a frame 23 pivotally connected to the support and to hydraulic cylinders 26. Toggle jaw 27 engages the solidified plug 28 and is biased towards the plug by leaf spring 29. Similarly biassed toggle jaws 210 carried on a frame 211 affixed to body 1 prevent the filter and plug from sliding back when the backing plate 7 is retracted. The filter and backing support are further supported in the filtering passage by perforated breaker plate 6. In a further embodiment (Fig. 3 not shown) the upper side of the filter band is protected by a cover plate (31), perforated in the region of the passage 2 and reciprocal with the backing plate, the filter band being sandwiched between the two, and the two sets of toggle jaws are replaced by a pair of serated jaws which grip the filter during one direction of reciprocation of the plate 7 but release it for the return movement. An alternative method of preventing return of the filter with the backing plate on the return stroke is to clamp the filter at the exit port during the retraction by means of a hydraulic or pneumatic cylinder (Figs. 4A or 4B not shown) or by means of spring loaded eccentric grippers (Fig. 4C not shown). In a further embodiment, (Figure 5 not shown), the backing support is enclosed within the body 1 and does not extend to the inlet or outlet ports and is reciproated by a push rod (51) slidably engaged in the breaker plate 6. The push rod may be replaced by a piston integral with the backing support and reciprocated by pneumatic means (Fig. 9 not shown). Figure 6 shows two filter bands 111, 112 similarly mounted for reciprocation by push rod 119. The filter apparatus in this case comprising two opposed filtering passages with a common filtrate collection chamber 113 between the filters. The linkages 117 provide for the backing supports 116 to be pushed against the filter bands in one direction of reciprocation but released therefrom on the return movement. A further method of releasing the filter band from the backing support for the return reciprocation involves raising a further support element 61 (Fig. 7) through slits in the breaker plate to lift the plate band clear of the backing support. During the movement of the filter band, the support 61 is lowered so that the filter band is clamped against the backing support 7 by hydrostatic pressure in passage 2. The further support element may be pneumatically raised and lowered (Figure 8A not shown).