JP2005324462A - Screw for thermoplastic resin molding - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a screw for thermoplastic resin molding which is of a screw channel shape to be easily machined, can inhibit the generation of carbide or a deterioration product by preventing a molten resin from residing, and has an insignificant decrease in the discharge level. <P>SOLUTION: In this screw, a concave curved surface with a radius exceeding the height of a flight, is formed on the flight profile, on the extrusion direction side, of a screw channel where the flight is helically formed. Preferably, in the section of the screw channel including a screw shaft of the screw, the radius of the concave curved surface having a radius where the concave curved surface runs through a flight angle part and comes into contact with the base of the screw channel, is 2.5 to 4.0 times the height of the flight. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a thermoplastic resin molding screw for use in an extrusion molding machine or an injection molding machine, and is particularly suitable as a thermoplastic resin molding screw such as a vinyl chloride resin that easily undergoes thermal decomposition.

Conventionally, in a molding machine with a built-in screw, if the molten resin is exposed to heat for a long time or is exposed to a high temperature even temporarily, the molten resin deteriorates or carbonizes and adheres to the screw groove. However, it is known that once the deteriorated substance is fixed, the deteriorated substances are fixed and deposited one after another.
In addition, when molding a resin molded product that is easily pyrolyzed, such as vinyl chloride resin, the carbonized or decomposed resin in the molded product becomes a foreign substance in the molded product in a relatively short period of operation. It becomes mixed and becomes a defective product.

Since the amount of this carbide or deteriorated product increases in proportion to the operating time, if the proportion of defective products increases to some extent, it is necessary to stop the molding machine and remove the extrusion screw from the extruder barrel and clean it. It becomes.
When the extrusion screw is extracted and seen, as shown in FIG. 2, the carbides and the deteriorated product e are fixed to the corners d1 and d2 between the bottom surface b of the screw groove a and the side surface of the flight c of the screw groove a. Observed.

  The cross-sectional shape of the screw groove a is such that a small-diameter curved surface is formed at the corners d1 and d2 between the bottom surface b of the screw groove a and the flight side surface c of the screw groove a, but has a substantially right-angled corner. The most carbides and deteriorated substances e were fixed along the corners d1 between the bottom surface b of the screw groove a and the side surface of the flight c facing the rear end side in the extrusion direction. It is considered that foreign matters such as carbides and deteriorated products mixed in the molded product are mixed into the molded product by peeling off the fixed carbides and deteriorated products in this way. The direction of extrusion is the direction of arrow X.

  On the other hand, in a molding machine with a built-in screw, as an invention for suppressing the thermal decomposition of the molten resin, “the flight is a screw shaft for molding a thermoplastic resin provided in a spiral shape, and the flight faces the tip side of the screw shaft. "A screw shaft for molding a thermoplastic resin, characterized in that a convex curved surface is provided at the base of the side surface" is known (for example, see Patent Document 1).

JP 2001-26046 A (Claims, FIG. 1)

  In the thermoplastic resin molding screw shaft described in Patent Document 1, as shown in FIG. 1 of Patent Document 1, a convex curved surface is provided at the root of the flight side surface facing the front end side of the screw groove in the extrusion direction. However, if this convex curved surface is formed at the base of the flight side facing the rear end side of the screw shaft in the extrusion direction, it is thought that the formation of carbides or deteriorated products can be reduced. I tried to make a prototype.

However, if the convex curved surface described in Patent Document 1 is to be formed at the base of the flight side surface facing the rear end side of the screw groove in the extrusion direction, it is difficult to process the screw groove because it is a convex curved surface. There was a problem that the production was expensive and the equipment cost was high.
Further, when the convex curved surface is provided, the cross-sectional area of the screw groove is reduced, so that there is a problem that the discharge amount is reduced as compared with a screw having the same outer diameter.

  Therefore, the present invention provides a screw for molding a thermoplastic resin that has a screw groove shape that is easy to process, can prevent the retention of molten resin, can suppress the generation of carbides and deteriorated materials, and has a small decrease in discharge amount. With the goal.

In the thermoplastic resin molding screw according to claim 1, a concave curved surface having a radius exceeding the flight height is formed on a flight side surface facing a rear end side in the extrusion direction of a screw groove formed by forming a flight spirally. It is formed.
The thermoplastic resin molding screw according to claim 2 is the thermoplastic resin molding screw according to claim 1, wherein the concave curved surface passes through a flight corner in a screw groove cross section including a screw shaft of the screw. , Provided so as to have a radius in contact with the bottom surface of the screw groove.

  The thermoplastic resin molding screw according to claim 3 is the thermoplastic resin molding screw according to claim 1 or 2, wherein the radius of the concave curved surface is 2.5 to 4.0 times the flight height. The thermoplastic resin molding screw according to claim 4 is the thermoplastic resin molding screw according to claim 1 or 2, wherein the radius of the concave curved surface is 0.25 to 0.40 of the screw diameter. It is what has been doubled.

  The thermoplastic resin molding screw according to claim 5 is the thermoplastic resin molding screw according to any one of claims 1 to 4, wherein the concave curved surface is provided in a metering zone or a compression zone of the screw. It is what has been. The thermoplastic resin molding screw according to claim 6 is the thermoplastic resin molding screw according to any one of claims 1 to 5, wherein the screw is for an injection molding machine.

In the thermoplastic resin molding screw according to the first aspect, since the concave curved surface having a radius exceeding the flight height is formed on the flight side facing the rear end side of the screw groove in the extrusion direction, Curved surface processing can be easily performed, and a screw can be manufactured at low cost. Further, since the concave curved surface is used, it is possible to minimize a decrease in the discharge amount.
Furthermore, by using a concave curved surface, the retention of the molten resin can be suppressed, so that the generation of carbides and deteriorated products can be reduced, and the proportion of defective molded products due to the mixing of these foreign substances can be reduced. Moreover, since generation | occurrence | production of a carbide | carbonized_material and a deteriorated material can be reduced, the cleaning frequency of a screw can be reduced significantly and the operation rate of an installation can be improved.

  In the thermoplastic resin molding screw according to claim 2, in the screw groove cross section including the screw shaft of the screw, the concave curved surface passes through the flight corner and has a radius in contact with the screw groove bottom surface. Therefore, a curved surface in which the concave curved surface is smoothly continuous can be formed on the bottom surface of the screw groove, and the retention of the molten resin can be effectively eliminated.

  In the thermoplastic resin molding screw according to claim 3, since the radius of the concave curved surface is set to 2.5 to 4.0 times the flight height, the screw groove is formed on the flight side surface facing the rear end side in the extrusion direction of the screw groove. The resulting staying portion can be efficiently eliminated by the concave curved surface, and the generation of carbides and deteriorated products can be suppressed for a long time.

  In the thermoplastic resin molding screw according to claim 4, since the radius of the concave curved surface is set to 0.25 to 0.40 times the screw diameter, the flight height is set to 10% of the screw diameter. When applied to the screw, the stagnant portion generated on the side surface of the flight toward the rear end side of the screw groove in the extrusion direction can be effectively eliminated by the concave curved surface, and generation of carbides and deteriorated products can be suppressed for a long time.

Moreover, since the concave curved surface is provided in the metering zone or the compression zone of the screw, the thermoplastic resin molding screw according to claim 5 suppresses the retention of the molten resin and extends the discharge amount over a long period of time. Can be maintained.
When the thermoplastic resin molding screw of the present invention is used as a screw for an injection molding machine of a thermoplastic resin that is easily pyrolyzed, a greater effect can be obtained.

Next, the best mode for carrying out the present invention will be described based on an embodiment shown in the drawings.
FIG. 1 is a partial plan view showing in part a cross section an example of a thermoplastic resin molding screw of the present invention.
In the figure, reference numeral 1 denotes a thermoplastic resin molding screw, in which a flight 2 is formed in a spiral shape, and a screw groove 3 is formed between the flights 2 and 2. A concave curved surface 4 having a radius exceeding the height of the flight 2 is formed on the side surface of the flight 2 facing the rear end side of the screw groove 3 in the extrusion direction. In the figure, the direction of arrow A is the front end side in the extrusion direction.

  The concave curved surface 4 only needs to have a radius that exceeds the height of the flight 2, but preferably passes through the corner of the flight 2 in contact with the screw groove bottom surface 5 in the screw groove cross section including the screw shaft. More preferably, the radius of the concave curved surface 4 is 2.5 to 4.0 times the height of the flight 2.

It is preferable that the radius of the concave curved surface 4 is 2.5 to 4.0 times the height of the flight 2 depending on the molding conditions such as the type of thermoplastic resin, molding temperature and screw rotation speed. Although the velocity distribution of the molten resin flowing in the inside is different, a concave portion having a slow flow velocity is generated on the side surface of the flight 2 facing the rear end side of the screw groove 3 in the extrusion direction. This is because the radius of the curved surface 4 is in a range smaller than 2.5 to 4.0.
When the radius is smaller than 2.5 times the height of the flight 2, the molten resin stays, the molten resin is easily fixed to the concave curved surface 4, and the carbide or deteriorated material is mixed into the molded product within a short time. It will be. Further, if the radius is larger than 4.0 times the height of the flight 2, there is no fear of stagnation, but the cross-sectional area of the screw groove 3 is reduced accordingly, and the extrusion amount is reduced.

  Further, in the case of a general screw, the height of the flight is about 1/10 of the outer diameter of the screw, so that the radius of the concave curved surface 4 is 2.5 to 4.0 times the height of the flight 2 because it is concave. This is the same as the radius of the curved surface 4 being 0.25 to 0.40 times the screw diameter.

The screw 1 includes a solid transport section (feed zone) for feeding and transporting thermoplastic resin raw material, a compression zone for feeding the raw material in a semi-molten state, and a metering zone for extruding a completely melted raw material by a certain amount. However, in the screw of the present invention, the concave curved surface 4 may be provided in the metering zone or the compression zone.
The concave curved surface 4 is preferably provided over the entire length of the compression zone and the metering zone.

When the screw 1 shown in the figure is used for injection molding, the screw shape is 50 mm in outer diameter, the pitch of flight 2 is 50 mm, the ratio L / D between the screw length L and the screw outer diameter D is 21, and the height of flight 2 Was 5 mm, and the radius of the concave curved surface 4 was 17 mm.
By an injection molding machine equipped with the screw 1, a vinyl chloride resin was molded at a molding resin temperature of 190 ° C. and a plasticizing ability of 45 kg / h. The number of foreign matters that were confirmed to be mixed was 4 / month, and the screw 1 should be cleaned once every two months.

  On the other hand, an injection molding machine using a conventional screw having the same dimensions as the screw shown in FIG. 1 except that the corners d1 and d2 shown in FIG. As a result, the number of foreign matters was as high as 30 / month, and the production efficiency of non-defective products was poor. In addition, the screw had to be cleaned once every two weeks, and the equipment operation rate was poor.

  As described above, in the thermoplastic resin molding screw of the present invention, the proportion of defective products due to the mixing of foreign matters such as carbides can be reduced. In addition, the operating rate of the equipment has improved because less screw cleaning is required.

  In the present invention, a concave curved surface having a radius exceeding the flight height is formed on the flight side surface facing the rear end side of the screw groove in the extrusion direction, and on the flight side surface facing the front end side of the screw groove in the extrusion direction, If a concave curved surface having a radius exceeding the flight height is formed, the retention of the molten resin can be more effectively suppressed, and foreign matter can be further reduced.

It is a partial top view which shows an example of the thermoplastic resin molding screw of this invention in a partial cross section. It is a fragmentary top view which shows an example of the conventional screw in a partial cross section.

Explanation of symbols

1 Screw for thermoplastic resin molding 2 Flight 3 Screw groove 4 Concave surface 5 Screw groove bottom

Claims (6)

  A thermoplastic resin molding characterized in that a concave curved surface having a radius exceeding the flight height is formed on a side surface of the flight facing the rear end side in the extrusion direction of the screw groove formed by forming the flight spirally. screw.   2. The thermoplastic resin molding screw according to claim 1, wherein the concave curved surface has a radius in contact with a bottom surface of the screw groove through a flight corner in a screw groove cross section including a screw shaft of the screw.   The thermoplastic resin molding screw according to claim 1 or 2, wherein a radius of the concave curved surface is 2.5 to 4.0 times a flight height.   The thermoplastic resin molding screw according to claim 1 or 2, wherein a radius of the concave curved surface is 0.25 to 0.40 times a screw diameter.   The thermoplastic resin molding screw according to any one of claims 1 to 4, wherein the concave curved surface is provided in a metering zone or a compression zone of the screw.   The thermoplastic resin molding screw according to any one of claims 1 to 5, wherein the screw is for an injection molding machine.

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