JPS6134972B2 - - Google Patents

Description

Detailed Description of the Invention The present invention relates to a method for manufacturing hollow profiles such as pipes, etc. When extrusion molding hollow profiles such as pipes with internal diameter regulation using the conventional inside mandrel sizing method, long-term molding is required. Sometimes, low molecular weight components, additive components, or monomers in the molding resin precipitate on the surface of the inside mandrel, causing poor sizing. That is, as shown in FIG. 1, in the conventional extrusion molding of hollow profiles, the inside mandrel sizing method involves bringing a molten resin into contact with the surface of a cooled inside mandrel 1, cooling it, solidifying it, and regulating the size and shape. At the start of this molding,
The tips of the die 12' and the core 9', that is, the lip 1
The distance from a point called 4' to the inside mandrel 3' is easy to change. Therefore, in general, in normal manufacturing conditions, the distance between the inside mandrel 3' and the lip 14' is zero or very small, so the die 12' on the surface of the inside mandrel 3' that does not come into contact with the molten resin. An exposed portion is formed nearby, and when this exposed portion 11' is cooled, low molecular weight components, monomers, or additive components generated between the core 13' and the inside mandrel 3' are precipitated on the exposed portion 11', and this precipitation As the amount of material gradually accumulates, it enters the gap between the molten resin and the inside mandrel 3', resulting in a thick wall in that area, or the molten resin stops flowing, resulting in a large change in wall thickness and In some cases, the molding (or resin) stops completely and the molded product breaks. As a countermeasure to this, it is possible to use resins with low molecular weight components, monomers, and volatile components, but it is not possible to completely eliminate the precipitates, and the selection of resins is limited, and the amount of precipitates is low. The content of density polyethylene is about 2 to 100 ppm, and some copolymer resins exceed 500 ppm. As another countermeasure, even if a method of removing the precipitate using a vent type extruder or a solvent is used, about 2 to 10 ppm of precipitates remain, resulting in a problem of sizing defects. The present invention solves the problem of such sizing defects in terms of equipment, and will be described in detail below with reference to the drawings. FIG. 2 is a schematic diagram showing the molding system of the present invention, in which the molten resin is extruded from the extruder 1, passes through the die head 2, is cooled on the surface of the inside mandrel 3, solidifies, and regulates the shape and size. This is a system in which the profile 4 is collected by a collection machine 5. In the drawing, 6 is a cooling pipe for supplying cooling water for cooling the inside mandrel 3, 7 is a cooling pipe for discharging the cooling water, and 8 is an air pipe for discharging volatile components. As shown in FIG. 3 in the above molding system, the present invention provides a heat insulating fixing ring 10 between the inside mandrel 3 and the core 9 in the die head 2 so that no gap or step is created between the inside mandrel 3 and the inside mandrel 3. As a result, the portion of the inside mandrel 3 that is not in contact with the molten resin, that is, the exposed portion 11 is minimized. The amount of separation, that is, the exposed portion 11, varies depending on the molding speed, molding temperature, material, wall thickness, thickness, etc. of the inside mandrel 3, but the better the thermal conductivity of the inside mandrel 3, the thinner the wall thickness of the inside mandrel. For example, when brass is used as the material for the inside mandrel 3, it is preferably in the range of 0 to 15 mm, preferably 3 to 5 mm. Also, the length of the heat insulating fixing ring 10 is determined in advance from the die 1 of the die head 2.
2 and the point S where the molten resin coming out from the lip 13 which is the tip of the core 9 contacts the inside mandrel 3
(hereinafter referred to as the sizing starting point S). Ideally, the amount of the exposed portion 11 of the inside mandrel 3 is zero as described above, but this exposed portion 11 is set to several mm, and the core 9 The length obtained by subtracting the distance from the sizing start point S is the length of the heat insulating fixing ring 10. Here, a good material for the heat insulating fixing ring 10 is polytetrafluoroethylene, which has low thermal conductivity, heat resistance, and is easy to process.This heat insulating fixing ring 10 covers the cooling pipe 6 as shown in the drawing. It is preferable to attach it so that it does not come into contact with the molten resin. Next, it is preferable that the inside mandrel 3 near the sizing start point S be made thinner to facilitate cooling as shown in FIG. Furthermore, in order to cool the inside mandrel 3, it is preferable that the cooling pipe 6 is also wrapped with a heat insulating material inside the tie head 2 to prevent precipitates from condensing or falling on the cooling pipe 6 inside the die head 2.
Here, the heat insulating material may be any material with low thermal conductivity that is stable depending on the molding temperature and does not deform due to the molding temperature, such as fluoride resin, asbestos cement material, etc.
Porcelain, glass fiber board, etc. can be used. The present invention is a manufacturing method as described above, in which a heat insulating fixing ring is provided between the sizing start point and the die head to prevent a gap or step from occurring between the inside mandrel and the inside mandrel. Volatile components such as low molecular weight components, unreacted components, and additives in the molten resin generated between the point and the die head do not condense and cause sizing defects, and it is easy to control the position up to the sizing starting point. , excellent moldability. Furthermore, at the start of molding, there is no conductive heat from the head or radiant heat from the parison, so the heat insulating fixing ring is also cold, so even if the resin comes into contact with it, it is unlikely to stick, and even if it does, it will be easy to separate. Therefore, it can be easily molded. Therefore, with the apparatus of the present invention, the conventional yield of 97 to 98% was increased to about 99.8%. Examples of the present invention will be shown below. Example Low density polyethylene (MI=1.0, d
= 0.91), molding speed: 6m/m, average wall thickness 420μ, die inner diameter 42φ, core outer diameter 40φ
Using an inside mandrel for a 30φ brass pipe, I obtained the following results. 【table】

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing a conventional hollow profile manufacturing method, FIG. 2 is a schematic diagram showing a molding system of the present invention, and FIG. 3 is a schematic diagram showing an embodiment of the present invention. 4 is a schematic diagram showing a manufacturing method showing another embodiment. 1... Extruder, 2... Die head, 3, 3'... Inside mandrel, 4... Hollow profile, 5
...Taking machine, 6...Cooling pipe, 7...Discharge cooling pipe, 8
...Air pipe, 9,9'...Core, 10...Insulating fixing ring, 11,11'...Exposed portion, 12,12'...Die, 13,13'...Rip, S...Sizing starting point.

Claims (1)

[Claims] 1 In a method of manufacturing a hollow profile using the inside mandrel sizing method that regulates the inside diameter, a heat insulating fixing ring is provided between the inside mandrel and the die head to prevent gaps and steps from forming between the inside mandrel and the die head. A method for manufacturing a hollow profile characterized by providing a heat insulating material and reducing the exposed portion of the inside mandrel.