Abstract A process and apparatus for programming the wall thickness of thermoplastic parison extrusions for subsequent conversion to blow-molded plastic articles. The apparatus for forming the parison includes a mandrel or core pin and a die assembly wherein the mandrel is made from a material having predictable and repeatable elastic properties and has enclosed therein a piston and piston rod. The piston rod extends the full length of the mandrel and is connected to the piston on the rod''s opposite end. The piston is contained in a chamber that is connected to a hydraulic fluid source. The wall thickness of the formed parison is changed by varying the size of the extrusion orifice through expansion or contraction of the mandrel produced by the application of release of hydraulic pressure on the top of the piston. The die assembly is particularly suited for extrusion of parisons from heat sensitive thermoplastic material such as polyvinyl chloride since no sliding surfaces are utilized which are known to trap and cause degradation of heat sensitive thermal plastics.
In an apparatus for controlling the extrusion of plastic parisons, the combination comprising: a. a cam having a peripheral surface conforming to the desired wall thicknesses of the extruded parison; b. cam drive means; c. means coupled to said cam to generate an electrical signal proportional to the shape of said cam; d. means for controlling fluid pressure actuated by the means of subparagraph (c); e. means for supplying fluid pressure to the means of subparagraph (d); f. means coupled to the means of subparagraph (d) for boosting the pressure of the fluid from the means of subparagraph (e); and g. means coupled to the means of subparagraph (f) for varying the wall thickness of said extruded plastic parisons.
Claim 2
Dependent Claim
119 words
In an apparatus for controlling the extrusion of plastic parisons, the combination comprising: a. a cam having a peripheral surface conforming to the desired wall thicknesses of the extruded parison; b. cam drive means; c. means coupled to said cam to generate an electrical signal proportional to the shape of said cam; d. means for controlling fluid pressure actuated by the means of subparagraph (c); e. means for supplying fluid pressure to the means of subparagraph (d); f. means coupled to the means of subparagraph (d) for boosting the pressure of the fluid from the means of subparagraph (e); and g. means coupled to the means of subparagraph (f) for varying the wall thickness of said extruded plastic parisons.
Claim 3
Dependent Claim
27 words
In the apparatus of claim 1 means coupled to the output of the means for subparagraph (d) for supplying corrective action to the means for subparagraph (c).
Claim 4
Dependent Claim
54 words
In the apparatus of claim 1 wherein the means of subparagraph (c) is a linear potentiometer, the means of subparagraph (d) is an electrically controlled servo control valve, the means for subparagraph (F) is a hydraulic pressure booster assembly, and the means of subparagraph (g) is a die assembly for extruding said plastic parison.