Apparatus and method control dimensions of corrugated tubing by stretching tubing predetermined amount as it travels between molding unit and downstream pulling assembly running at about same rate tubing is discharged from molding unit. First counter mechanism adjacent discharge end of molding unit counts predetermined number of corrugations in tubing and immediately thereafter generates signal indicating that predetermined number has been counted. Generation of signal from first counter triggers signal from second counter mechanism indicative of number of corrugations passing pulling assembly. Signal from second counter indicates more than predetermined number of corrugations has been counted, less than predetermined number has been counted, or count substantially equal to predetermined number. When more than predetermined number of corrugations is counted speed of pulling assembly is incrementally decreased to lessen stretch of tubing, and conversely, when less than predetermined number is counted speed of pulling assembly is incrementally increased to increase stretch of tubing. Second counter mechanism is initially adjusted so that no signal is generated by second counter when tubing between molding unit and pulling assembly is stretched predetermined amount.
A pair of cooperating mold blocks for forming an enlarged coupler collar on a corrugated plastic pipe being molded therein. The mold blocks have a mold surface including a corrugated portion defined by a series of alternating ribs and valleys and a non-corrugated portion defined by a relatively smooth semicylindrical wall having a diameter greater than the diameter of the valleys in the corrugated portion and adapted for forming the relatively enlarged coupler collar. The semicylindrical wall includes a plurality of arcuately spaced projections adapted for forming inwardly projecting latching members on the wall of the plastic pipe being molded thereagainst.
A blow-molding machine for molding corrugated plastic pipe having uninterrupted annular ribs thereon is converted for forming corrugated plastic pipe having interrupting gaps or recesses in certain annular ribs of corrugated pipe being formed. Essentially the conversion is effected by positioning and securing relatively short inserts or segmental blocks in otherwise uninterrupted semicircular valleys of cooperating pairs of semitubular mold sections of dies between and against which the plastic pipe is molded.
A tubular parison of synthetic plastic material in thermoplastic condition is extruded into a travelling mold wherein it is formed into a corrugated tube. The travelling mold is formed when cooperating mold sections of two endless strings of such mold sections move together and travel for some distance in a straight path before moving apart again. Each mold section has front and rear guide rollers which travel in guide channels that are so configurated as to impart to the mold sections the aforementioned movements toward and away from each other.
A blow-molding machine for molding corrugated plastic pipe having uninterrupted annular ribs thereon is converted for forming corrugated plastic pipe having interrupting gaps or recesses in certain annular ribs of corrugated pipe being formed. Essentially the conversion is effected by inserting and releasably securing relatively short inserts or segmental blocks in otherwise uninterrupted semicircular valleys of cooperating pairs of semitubular mold sections or dies between and against which the plastic pipe is molded.
The invention relates to a method and an apparatus for the extrusion of plastic pipes. Today, plastic pipes are provided with a sleeve in such a manner that the end of the pipe is heated, whereafter the end is expanded by means of a mandrel or a pressure medium. This step requires a separate sleeve machine, and it also takes plenty of time and consumes thermal energy. According to the invention a sleeve (22) is formed in connection with the extrusion of a pipe in an apparatus in which a mandrel (8) is surrounded by chill moulds (1, 2) moving in the axial direction of the apparatus. The sleeve is formed by providing some of the chill moulds with a recess (16) the shape of which corresponds to that of the sleeve (22) and by pressing a plasticized plastic hose (11) extruded through a nozzle (10) against the walls of the recess in the area thereof by means of pressure air.
