Patent Publication Number: US-4257562-A

Title: Apparatus for feeding liquid adhesive

Description:
STATEMENT OF PRIOR ART 
     In accordance with 37 CFR 1.56 and 37 CFR 1.97, applicant cites the following prior art. 
     U.S. Pat. No. 4,115,085 (BARBE). The whole document is of interest. 
     This art is the closest prior art known to applicant. 
     BACKGROUND AND SUMMARY OF THE INVENTION 
     The present invention relates to an apparatus for feeding liquid adhesives to nozzle applicators, of the type used for example in the cigarette making industry, for applying a thin layer of adhesive on the paper web which is wrapped around the tobacco rod. 
     The apparatuses of the known type substantially comprise a tank for the liquid adhesive and a pump for feeding the said adhesive under pressure to a nozzle applicator. Usually, the pump is of the peristaltic type, due to the fact that, in peristaltic pumps, the liquid adhesive does not come into contact with the driving components of the pump, which therefore reduces to the minimum the cleaning maintenance of the pump at the end of the working day, and consents its inactivity even for long periods of time, without any damages. 
     The known type apparatuses presents however at least two disadvantages. The first disadvantage derives from the fact that usually the liquid adhesive contains entrapped in it bubbles of air or other gases which, upon reaching the nozzle applicator, cause a discontinuity in the spraying of the adhesive. 
     A second disadvantage is represented by the fact that the peristaltic pumps present, due to their characteristic features of operation, a delivery having a discontinuous (pulsating) flow rate, which consequently affects the spraying of the nozzle applicator. 
     The above and other disadvantages of the known type apparatuses are eliminated by the feeding apparatus according to the present invention, which proposes the interposition, between the peristaltic pump and the nozzle applicator, of a device for expelling the gases from the liquid adhesive, which eliminates the bubbles entrapped in the adhesive, in combination with a pressure chamber for the degasified adhesive, acting as a buffer for compensating the discontinuous delivery of the peristaltic pump. 
     The characterizing features of the invention and the advantages deriving therefrom will appear evident from the following description of a preferred embodiment, made with reference to the attached drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view, partially open and cutaway, of a feeding apparatus according to the invention. 
     FIG. 2 is a longitudinal vertical section, with parts in view, of the apparatus of FIG. 1. 
     FIG. 3 is a horizontal section, with parts in view, along line III--III of FIG. 2. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     With reference to the drawings, the feeding apparatus comprises an airtight chamber 1, which is closed at one of its sides by a block 2. Said side block 2 presents a cylindrical fitting 102 to which there is connected the conduit or pipe 3. The pipe 3 is connected in its turn to the delivery of a known type peristaltic pump. In the block 2 there is also obtained a very narrow horizontal slit 202, which connects the said cylindrical fitting 102 with the interior of chamber 1 and presents a transverse section which is practically constant in height and progressively increases in width, in the direction from the cylindrical fitting 102 to its outlet into chamber 1. In a preferred embodiment, the height of the slit is from 0.3 to 0.7 millimeter, and preferably 0.5 millimeter. Above the said slit 202 there are also provided through bores 302 which put in communication the upper section of cylindrical fitting 2 with the upper zone of the interior of chamber 1. 
     The airtight chamber 1 is provided with a venting opening, closed by plug 4 or by any other suitable valve means. 
     In correspondence of the bottom of chamber 1 there is fitted the pipe 5, which leads to the nozzle applicator 6. 
     As it clearly appears from FIGS. 1 and 2, the airtight chamber 1 is arranged with a certain inclination, in such a manner as to increase the distance (height) between the outlet end of slit 202 and the surface of the liquid adhesive contained at the interior of said chamber. 
     The operation of the described apparatus is evident. The liquid adhesive pumped by the peristaltic pump arrives through pipe 3 to the cylindrical fitting 102 from which it is admitted into the chamber 1 through the horizontal slit 202. The air bubbles contained in the adhesive, by flowing through the said narrow horizontal slit 202, are laminated or broken, and therefore are in any case separated from the adhesive in correspondence of the outlet of slit 202. The greater air bubbles which could accumulate in the upper section of cylindrical fitting 102 are discharged into chamber 1 through the bores 302. 
     While the air or gas bubbles are eliminated in the above manner, it appears also evident that at the interior of chamber 1 there is built up a gas pressure, which depends from the characteristic features and delivery of the peristaltic pump. The said gas pressure acts on the surface of the liquid adhesive as a buffer which compensates the delivery variations of the peristaltic pump, thus contributing to render more uniform the spraying effected by the nozzle distributor 6. 
     The said gas pressure increases upon separation of the air bubbles from the liquid adhesive, and therefore it will be periodically necessary to relieve the said pressure by discharging air through the venting opening, acting manually on plug 4 or automatically through any suitable venting valve. 
     It is to be understood that the above description refers to a preferred embodiment, and that many variations and modifications, particularly in the construction of the apparatus, are possible.