JPS5926224A - Detecting method of anomalous point of extruded hollow pipe of thermoplastic resin - Google Patents

Abstract

PURPOSE:To detect the anomalous points, e.g., pin holes, etc., in particular, of a hollow pipe by a simplified method in which a conductive inner layer is formed in a thermoplastic extruded pipe and voltage is applied between the electrode of a sparking tester and the inner layer. CONSTITUTION:A pipe corresponding to an inner layer is molded by extruding a conductive resin from an extruder 4, land an outer layer 2 is formed on the inner layer by extruding a thermoplastic resin from an extruder 5 connected in tandem to the extruder 4. The hollow pipe 1 so molded is cooled in a water tank 6 while being pulled by a withdrawer 7, and the inner layer 3 is earthed and then passed through a linked ball type sparking tester 8. Since potential is given to the linked ball type electrode of the sparking tester 8 in such a way as to cause sufficient potential difference to occur in the inner layer 3, sparks take place at pin holes, if any, in the outer layer 2, and therefore, the pin holes can be easily detected.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for detecting abnormalities in thermoplastic extruded hollow pipes.

Hollow pipes made of thermoplastic resin are widely used as electrical conduits, control pipes, insulated pipes, etc. in place of metal pipes or knitted pipes because they are easy to process and inexpensive.

Such hollow pipes are generally formed using an extruder and are prone to clogging or pinholes in the walls, and detection of such defects is generally relatively difficult or impossible. In other words, conventional methods for detecting such defects include blowing compressed air into one end of the pipe and checking whether air comes out from the opposite end.Although it takes time, it is possible to check if the pipe is clogged. However, it is impossible to completely detect pinholes.

An object of the present invention is to provide a simple method for detecting abnormal points, particularly pinholes, in thermoplastic hollow pipes.

According to the present invention, the inside of the thermoplastic hollow pipe is formed using a conductive resin, a conductive inner layer is provided over the entire length, and the presence of a pin pole is electrically detected.

An embodiment of the present invention will be described below based on the drawings.

FIG. 1 is a cross-sectional view of a hollow pipe 1 used in the present invention, and this hollow pipe is composed of an outer thermoplastic resin layer 2 made of, for example, low-density polyethylene on the outside and an electrically conductive resin inner layer 3 on the inside. The material of the conductive resin inner layer 3 may be, for example, ethylene vinyl acetate (EVA) mixed with carbon.

FIG. 2 is a schematic diagram of a device for continuously extruding a hollow pipe 1 and inspecting pinholes. Second
In the figure, an extruder 4 extrudes the conductive resin to form an inner layer 3.
A pipe corresponding to the
The outer layer 2 is formed by extruding and coating the thermoplastic resin using an extruder 5 connected in tandem with the outer layer 2. The hollow pie goo thus formed is taken up by a taking machine 6 and passed through a water tank 6 to cool it, and after the inner layer 3 is grounded or a potential of one polarity is applied, a Jiyuzu sphere sparking tester 8 is used. Let it pass. The bead-like electrode of the sparking tester 8 is given a potential that creates a sufficient potential system for the inner layer 3, and if there is a pinhole or the like in the outer layer 2, a spark will occur at that point. Its presence can be easily detected.

As an example, Ml-2.0, which is an EVA base mixed with 30% carbon, has a conductivity of 8. An inner layer 3 with a wall thickness of 0.1 mm was made by using a conductive resin of 2゛gin'α in an extruder 4, and then a low density polyethylene with a density of 0.92 and Ml-1.0 was used in an extruder 5. A hollow pipe L having an outer layer 2 with a wall thickness of 1.5 mm was made, and after cooling, a part 30n1 with no electrical defects was used as a sample for a sparking test! , 20 holes with target diameter t) and I mm were made at intervals of 11 m, and 6000 V was applied between the inner layer 2 and a sparking tester 8 with an electrode length of 300 mm, and the hole was 50 m 7
When the pinholes were passed through the pinholes at a speed of 10 minutes, easy-to-identify sparks were generated in all 20 holes, making it extremely easy to detect pinholes.

As described below, the abnormal point detection method of the present invention is characterized by applying a voltage between the conductive inner layer of the hollow pipe and the sparking tester, and the number of conductive inner layers is arbitrary. The conductive inner layer may also be provided by means other than extrusion. In addition to polyethylene, any thermoplastic resin such as vinyl chloride, nylon, etc. can be used for the outer layer.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a hollow pipe suitable for the method of the invention;
FIG. 2 is a schematic diagram of an apparatus for carrying out the method of the invention. l...Hollow pipe, 2...Outer layer, 3...Inner layer, 4
, 5... Extruder, 6... Water tank, 7... Taking machine, 8
...Jiyuzu sphere sparking tester. 1 rhinoceros

Claims (1)

[Claims] (1) Forming a conductive inner layer on a thermoplastic extrusion pipe,
A method of detecting abnormal points in a pipe by applying voltage between the electrode of a sparking tester and the inner layer.