JP3056487U - Screw for special resin of injection molding machine - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To obtain a stable plasticized state by eliminating variations in charge time when plasticizing a special resin by using a conventional screw in which crests and valleys are smoothly buffed. SOLUTION: In a screw for an injection molding machine, a surface roughness of a counter pressure surface of a peak portion in a feed zone is set to a maximum height (Rmax) of 4S to 10S.

Description

[Detailed description of the invention]

[0001]

[Technical field to which the invention belongs]

 The present invention relates to a screw for an injection molding machine, and more particularly to a screw for an injection molding machine for a special resin material such as nylon 66/6.

[0002]

[Prior art]

 The screw used in the injection molding machine has, in terms of its functions, a feed zone in which the raw resin supplied to the heating cylinder in which the screw is inserted is transported while preheating, and a compression zone in which the raw resin is compressed and heated to plasticize and melt. And a metering zone that kneads and homogenizes the molten resin plasticized in the compression zone and extrudes it from the tip.

In the conventional screw described above, the surface roughness of the entire screw body except for the top surface of the peak is buffed to a maximum height (Rmax) of 0.8S to 1.2S. .

[0004] However, when a special resin material such as nylon 66/6 is plasticized by the conventional screw for an injection molding machine, a large variation may occur in the charging time. The charging time is the time from when the molten resin is conveyed to the front of the metering zone and stored inside the heating cylinder, until the screw retreats a predetermined distance, the amount of molten resin is measured, and the screw stops. . According to the results of the inventors' continuous molding of a 10.7-g connector with nylon 66/6 resin using a 300-mm injection molding machine with a screw diameter of 22 mm and a clamping force of 50 tons, the average charge time was 2. 807 seconds, its standard deviation was 0.366, the maximum was 4.9 seconds, the minimum was 2.3 seconds, and the difference was 2.6 seconds.

[0005] The large variation in the charging time in the plasticization does not make the temperature of the plasticized molten resin uniform, and greatly affects the viscosity thereof. In other words, if the charging time is long, the temperature of the molten resin tends to be overheated, and the viscosity is reduced, causing burrs in the mold. On the other hand, if the charging time is shortened, the molten resin temperature does not rise sufficiently and the molten resin is injected into the mold in an incompletely melted state, causing the underfill to occur.

[0006] Therefore, the inventors repeatedly performed a molding test on such a special resin, particularly a nylon 66/6 resin, using screws having various shapes and surface roughness, and judged the plasticized state based on a change in charge time. did. As a result, it was found that the quality of the transfer of the raw material resin in the screw feed zone had a large effect on the variation in charging time. In particular, they found that the raw material resin that had begun to melt adhered to the counter-pressure surface at the peak of the feed zone, hindering the resin flow and making the charging time unstable.

[0007]

[Problems to be solved by the invention]

 The purpose of this invention is to make the special resin for the injection molding machine stably pass through the feed zone, thereby minimizing the variation of the charging time and obtaining a molded product with stable quality. It is to provide a screw for resin.

[0008]

[Means for Solving the Problems]

 That is, the present invention relates to a screw for a special resin of an injection molding machine in which the surface roughness of the counter pressure surface of the peak portion in the feed zone is 4S to 10S at the maximum height (Rmax).

[0009]

[Embodiment of the invention]

 The present invention will be described in detail with reference to the drawings. FIG. 1 shows a screw 1 of an injection molding machine, which comprises a screw body 2 and a check valve 3 screwed to the tip of the screw body 2. The screw main body 2 forms a groove 7 including a ridge 8 forming a screw and a valley 11 existing between the ridges 8. The top surface 10 of the ridge 8 is machined to have an outer diameter slightly smaller than the inner hole diameter of the heating cylinder in order to fit the screw 1 into the inner hole of the heating cylinder not shown. The surface roughness of the processed surface on the top surface 10 is about 1.6S. The depth of the valley 11 from the top surface 10 becomes shallower from the root (the right end in the drawing) of the screw 1 toward the tip. That is, there is an outlet for raw resin at the base of the screw 1 and the feed zone 4 starts. Feed zone 4 has a deep valley and metering zone 6 has a shallow valley. The compression zone 5 is located between the feed zone 4 and the metering zone 6, and its valley has a tapered shape gradually decreasing from the feed zone 4 toward the metering zone 6, and is smoothly connected to the valleys of the front and rear zones. I have.

As shown in FIG. 2, which is an enlarged cross-sectional view taken along the line II-II in FIG. 1, the peak 8 includes a counter pressure surface 12 on the screw root side, a pressure surface 13 on the screw tip side, and a top surface 10. . Since the screw 1 rotates counterclockwise when viewed from the root, the raw resin supplied from the drop port is conveyed forward by receiving a force from the pressure surface 13 of the peak portion 8.

With respect to the surface roughness expressed by the maximum height (Rmax) of the conventional screw body 2, the top surface 10 is about 1.6S as described above, but all other parts are 0.8S to 1.S. 2S buffing. The reason why the surface roughness is improved is that the molten resin does not adhere to the screw surface and is easily peeled off. However, in special resin materials, such as nylon 66/6, the material is already crystalline in feed zone 4 due to its crystallinity, having a well-defined melting temperature and melting rapidly at that temperature. Melting occurs and adheres to the counter pressure surface 12 where no conveying force is generated. In such a situation, the raw resin gradually accumulates on the adhered molten resin, the cross-sectional area of the groove 7 becomes smaller, and the passage of the resin is prevented, resulting in a longer charging time. After this situation continues for a certain period of time, it is considered that the molten resin adhered at a stretch is conveyed at a stretch and the charge time is shortened.

[0012] Therefore, as a result of studying and trying various measures for preventing the adhesion of the molten resin to the counter pressure surface 12, stabilization of the charging time was achieved by using the rough surface 9 as the counter pressure surface 12 in the feed zone 4. It was found that it can be achieved. Further, the surface roughness of the rough surface 9 is preferably 6S in the case of nylon 66/6, and when roughened to 10S or more, conversely, the molten resin easily adheres to the rough surface by the anchor effect, and when the roughness is 4S or less, the surface becomes rough. It turned out that the effect was not exhibited. The same was true for other types of resins.

Next, an embodiment using the screw of the present invention will be described. The raw material resin is nylon 66/6, and a connector weighing 10.7 g was continuously formed by injection molding with a screw diameter of 22 mm and a mold clamping force of 50 tons by 300 shots. The average charge time was 2.646 seconds, the standard deviation was 0.187, the maximum was 3.3 seconds, the minimum was 2.5 seconds, and the difference was 0.8 seconds. Comparing these values with the above-mentioned conventional example, it can be clearly understood that the screw of the present invention is extremely effective in stabilizing plasticization.

[0014]

[Effect of the invention]

 As described above, according to the screw of the present invention, the charging time can be stabilized, and a stable and uniform molten resin can be obtained. Can be produced continuously over a long period of time.

[Brief description of the drawings]

FIG. 1 is a plan view showing an example of a special resin screw of an injection molding machine according to the present invention.

FIG. 2 is an enlarged cross-sectional view showing details of a mountain portion of a special resin screw of the injection molding machine taken along line II of FIG.

[Explanation of symbols]

 1 ... Screw 2 ... Screw body 3 ... Check valve 4 ... Feed zone 5 ... Compression zone 6 ... Metering zone 7 ... Groove 8 ... Mountain part 9 ... …… Rough surface 10… Top surface 11… Valley 12… Anti-pressure surface 13… Pressure surface

Claims (1)

[Utility model registration claims] 1. A screw for a special resin of an injection molding machine, wherein a surface roughness of a counter pressure surface of a peak portion in a feed zone is 4S to 10S at a maximum height (Rmax).