System for fastening spark plugs of boilers or the like

Abstract

The invention relates to a system for fastening spark plugs ( 4 ) for boilers or the like, comprising a retainer ( 1 ) with an hole housing the ceramic body ( 104 ) of the spark plug ( 4 ) of the spark plug. According to the invention said hole axially projects for a certain length at least on one side of the retainer ( 1 ) such to form a cylindrical housing ( 5 ) for the ceramic body ( 104 ) of the spark plug ( 4 ), a cylindrical tightening ring ( 6, 8 ) being provided having such inner and external dimensions that it can be inserted by force fit between the inner wall of the cylindrical housing ( 5 ) and the external wall of the ceramic body ( 104 ) so to generate a predetermined radial tightening force of the spark plug ( 4 ) and such to obtain a tight seal between one side and the other one of the retainer ( 1 ).

1 . System for fastening spark plugs ( 4 ) for boilers or the like, comprising a retainer or a fastening plate ( 1 ) with an hole housing the ceramic body ( 104 ) of the spark plug ( 4 ), characterized in that the housing hole axially projects for a certain length at least on one side of the retainer ( 1 ) beyond the thickness thereof such to form a cylindrical housing ( 5 ) for the ceramic body ( 104 ) of the spark plug ( 4 ), a cylindrical tightening ring ( 6 ,  8 ) being provided having such inner and external dimensions that it can be inserted by force fit between the inner wall of the cylindrical housing ( 5 ) of the retainer ( 1 ) and the external wall of the ceramic body ( 104 ) of the spark plug ( 4 ) so to generate a predetermined radial tightening force of the spark plug ( 4 ) inside the cylindrical housing ( 5 ) of the retainer ( 1 ) and such to obtain a tight seal between one side and the other one of the retainer ( 1 ). 
   
   
       2 . System according to  claim 1 , characterized in that the retainer and the ring are made of different metal materials having a different resistance to deformation. 
   
   
       3 . System according to  claim 2 , characterized in that the retainer ( 1 ) is made of a metal material having a greater resistance to deformation with respect to the ring ( 2 ), the tightening ring ( 6 ,  8 ) being the member for compensating and recovering the tightening radial pressure that eventually exceeds a predetermined pressure value for the proper tightening of the spark plug ( 4 ) inside the cylindrical housing ( 5 ) of the retainer ( 1 ). 
   
   
       4 . System according to  claims 1  and  2 , characterized in that the tightening ring ( 6 ) is made of brass. 
   
   
       5 . System according to  claim 1  or  2  characterized in that the tightening ring is made of a copper-nickel alloy. 
   
   
       6 . System according to  claim 1 , characterized in that both retainer ( 1 ) and the ring ( 2 ) are made of brass. 
   
   
       7 . System according to  claim 1 , characterized in that the retainer ( 1 ) and the ring ( 2 ) are made of different metal materials and have a negligible difference in the thermoelectric potential. 
   
   
       8 . System according to one or more of the preceding claims, characterized in that the circular edge of the cylindrical housing ( 5 ) for the spark plug ( 4 ) that is coplanar with one of the two faces of the retainer ( 1 ) has an entrance flare ( 105 ) in order to facilitate the insertion of the tightening ring ( 6 ) inside said cylindrical housing ( 5 ). 
   
   
       9 . System according to one or more of the preceding claims, characterized in that stop means ( 106 ) for the insertion of the tightening ring inside the cylindrical housing ( 5 ) are provided. 
   
   
       10 . System according to one or more of the preceding claims, characterized in that said means are composed of an annular widening of one of the two circular head edges of the cylindrical tightening ring ( 6 ) that forms an abutment stop annular flange ( 106 ) for the insertion of the tightening ring ( 6 ) inside the cylindrical housing ( 5 ) of the retainer ( 1 ). 
   
   
       11 . System according to one or more of the preceding claims, characterized in that the circular end of the tightening ring ( 6 ) opposite to the one having the annular flange ( 106 ) has a beveled or rounded or tapered edge ( 206 ) in order to facilitate the insertion of the tightening ring ( 6 ) inside the cylindrical housing ( 5 ) of the retainer ( 1 ). 
   
   
       12 . System according to one or more of the preceding claims, characterized in that the tightening ring ( 6 ) is made of a material, particularly metal, having a high resistance to deformation capacity, particularly it is made of the same material as the retainer ( 1 ), and it is shaped such to have one or more areas ( 108 ,  9 ) for compensating and recover the radial tightening pressure that eventually exceeds a predetermined pressure value for the proper tightening of the spark plug ( 4 ) inside the cylindrical housing ( 5 ) of the retainer ( 1 ). 
   
   
       13 . System according to one or more of the preceding claims, characterized in that the tightening ring ( 8 ) has one or more openings ( 108 ,  9 ) for the release and recover of the radial deformation of the ring ( 8 ) when the spark plug ( 4 ) is tightened inside the cylindrical housing ( 5 ) of the retainer ( 1 ). 
   
   
       14 . System according to one or more of the preceding claims, characterized in that the tightening ring ( 8 ) has at least one, preferably a plurality of notches ( 108 ) originating from the two opposite circular head edges of the ring ( 8 ) and extend only for a portion of the axial extension of the ring ( 8 ). 
   
   
       15 . System according to one or more of the preceding claims, characterized in that said notches ( 108 ) all have the same lengthways extension, particularly said extension is comprised between about a third and about an half of the axial extension of the ring ( 8 ). 
   
   
       16 . System according to one or more of the preceding claims, characterized in that said notches ( 108 ) are arranged in alternate positions one with respect to the other, that is each notch ( 108 ) originates from a head circular edge of the tightening ring ( 8 ) opposite to the head circular edge from which the immediately next notch ( 108 ) originates. 
   
   
       17 . System according to  claim 16 , characterized in that notches ( 108 ) form there between an annular continuous intermediate band, having a small thickness with respect to the total axial extension of the ring ( 8 ). 
   
   
       18 . System according to  claim 17 , characterized in that said annular continuous intermediate band has an axial dimension comprised between 1 and 3 mm. 
   
   
       19 . System according to one or more of the preceding claims, characterized in that the tightening ring ( 8 ) at its intermediate annular band has at least an opening ( 9 ) or slot for the release and recover of the radial narrowing occurring in said intermediate annular band when the spark plug ( 4 ) is tightened inside the cylindrical housing ( 5 ) of the retainer ( 1 ). 
   
   
       20 . System according to one or more of the preceding claims, characterized in that the tightening ring ( 8 ) is of the open type. 
   
   
       21 . System according to  claim 20 , characterized in that the tightening ring ( 8 ) has reciprocal fastening means by forcing the two faced ends at the opening cut. 
   
   
       22 . System according to  claim 21 , characterized in that one of the faced ends of the tightening ring ( 8 ) placed at the opening cut has at least a recess ( 208 ), while the other opposite end has at least an extension ( 308 ) intended to engage with said at least one recess ( 208 ) for closing the tightening ring ( 8 ) on itself the dimensions of the recess and extension ( 208 ,  308 ) being such to engage one inside the other by force fit generating reciprocal contact perimetral surfaces forming a tight closing of the open notch of the ring. ( 8 ) itself. 
   
   
       23 . System according to  claim 22 , characterized in that the hooking recess ( 208 ) extension ( 308 ) of the tightening ring ( 8 ) are provided in substantially intermediate positions of the respective straight end portions of the ring ( 8 ), with which straight portions said recess and said extension connect in a rounded way. 
   
   
       24 . System according to one or more of the preceding  claims 21  to  23 , characterized in that the hooking extension ( 308 ) of the tightening ring ( 8 ) has a narrowed shape root ( 408 ) projecting in substantially circumferential direction of the ring ( 8 ) with a substantially circular shape widened part, while the corresponding hooking recess ( 208 ) placed on the opposite end of the tightening ring ( 8 ) has a shape that is substantially complementary to the one of said extension ( 308 ). 
   
   
       25 . System according to  claim 20 , characterized in that the tightening ring ( 8 ) has an axial cut forming two facing ends, the axial cut having a certain width so that the said two ends are at a predetermined distance one form the other, a first end having a central protrusion ( 308 ′) and the opposite end having a recess ( 208 ′) coinciding with the said central protrusion, the central protrusion ( 308 ′) being curved essentially the same radius as the ring and having circumferential side edges extending along a plane perpendicular to the ring axis and the recess ( 208 ′) having circumferential side edges extending along the same plane perpendicular to the ring axis as the side edges of the said central protrusion ( 308 ′) the axial width of the central protrusion and the axial width of the recess ( 208 ′) being identical such that the protrusion ( 308 ′) fits in the said recess ( 208 ′) with the side edges of the said central protrusion ( 308 ′) coming into contact with the corresponding side edges of the recess ( 208 ′), the said recess ( 208 ′) having an angular extension which corresponds essentially to the width of the axial cut. 
   
   
       26 . A system according to  claim 25 , characterized in that the axial width of the protrusion ( 308 ′) of one end of the tightening ring and the axial width of the recess ( 208 ′) are such that the side edges of the protrusion ( 308 ′) and the corresponding side edges of the recess ( 208 ′) extending in circumferential direction of the ring adheres one to the other in a sealing way, at least after being forced together with the ceramic body of the spark plug ( 4 ) in the retainer ( 1 ). 
   
   
       27 . A system according to one or more of the preceding claims, characterized in that the retainer ( 1 ) is formed by a fastening plate ( 101 ) having a hole for housing the ceramic body of a spark plug ( 4 ), the said whole being coaxial with a cylindrical extension ( 5 ) at one side of the said fastening plate ( 101 ). 
   
   
       28 . A system according to  claim 27  characterized in that the fastening plate ( 101 ) has a thickness greater than the thickness of the cylindrical extension ( 5 ). 
   
   
       29 . A system according to  claim 28 , characterized in that the fastening plate has ( 101 ) a thickness of at least 3 mm, while the cylindrical extension ( 5 ) has a thickness of less than 2 mm. 
   
   
       30 . A system according to  claim 29 , characterized in that the fastening plate ( 101 ) has a thickness from about 3 mm to about 5 mm, while the cylindrical extension ( 5 ) has a thickness of about 1 mm to 2 mm. 
   
   
       31 . A system according to one or more of the preceding  claims 28  to  30 , characterized in that the trough hole in the fastening plate ( 101 ) for the ceramic body of the spark plug ( 4 ) has a greater diameter than the said ceramic body together with the tightening ring on it, while the cylindrical seat ( 5 ;  305 ) with the reduced diameter for force fitting the said ceramic body and the tightening ring is provided on one side of the fastening plate ( 101 ) outside the thickness of the fastening plate and is connected to the said hole of the fastening plate ( 101 ) with a frustoconical part ( 205 ). 
   
   
       32 . A system according to  claim 31 , characterized in that the cylindrical seat ( 5 ;  305 ) with the reduced diameter for force fitting the said ceramic body and the tightening ring has an axial extension corresponding at least to the axial extension of the tightening ring. 
   
   
       31 . A system according to one or more of the preceding claims, characterized in that the fastening plate ( 1 ) has a thickness less than 3 mm and has stiffening ribs. 
   
   
       32 . A system according to  claim 31 , characterized in that the stiffening ribs are formed by pressing or drawing. 
   
   
       33 . A system according to one or more of the preceding claims characterised in that the retainer has means for connecting electrically and mechanically an electric conductor. 
   
   
       34 . A system according to  claim 33 , characterised in that the said means for connecting electrically and mechanically an electric conductor consist in a male or female part fo an electric and or mechanical connector. 
   
   
       35 . A system according to  claim 34 , characterised in that the said means for connecting electrically and mechanically an electric conductor consist in the metallic tounge ( 401 ) forming the male part of a so called FASTOM® connector. 
   
   
       36 . A system according to one or more of the preceding  claims 33  to  35 , characterised in that the said means for connecting electrically and mechanically an electric conductor are made in one piece with the fastening plate ( 101 ) of the retainer ( 1 ). 
   
   
       37 . A system according to  claims 35  or  36 , characterised in that the said means for connecting electrically and mechanically an electric conductor are obtained in a one shot shaping and cutting operation of the retainer by means of drawing or stamping a metallic sheet. 
   
   
       38 . Method for manufacturing a locking ring by force fit for a system according to one or more of the preceding  claims 20  to  26 , characterized in that said ring is obtained by shearing a material strip from a metal material band, the hooking extension or the protrusion in a first material strip for a first ring being obtained from the material removed for manufacturing the hooking recess of the immediately next material strip, while said two material strip are rolled in a cylindrical way and then the ends of said cylindrically rolled strips are connected one with the other by force fit engagement of the hooking extension to the hooking recess or of the protrusion in the recess, the differences in dimension between the hooking recess and the hooking extension and of the protrusion in the recess necessary to the dimensional interference for the reciprocal, sealing engagement by force fit of the hooking extension and the hooking recess or of the protrusion in the recess are automatically obtained with the shearing that is carried out in such a way to cut the material band only for a thickness part and to break the material band for the remaining part of the band thickness consequently with the narrowing of the hooking recess or of the recess and the expansion of the hooking extension or of the protrusion due to the material stretching as regards the thickness part of the material band that is separated by breaking it.