JPH06198713A - Screw for extrusion or injection molding and its manufacture - Google Patents

Abstract

PURPOSE:To provide a screw for extrusion or injection molding wherein long service life is realized and a manufacturing method thereof by constituting a part for forming the screw of material having high wear resistance and constituting an attachment part of material having high toughness and not causing a crack and breakage. CONSTITUTION:The chemical component of a screw incorporates by weight percentage 1.0-2.5% C, <=2.0% Si, <=2.0% Mn, 9.0-18.0% Cr, at least one kind of element selected from a group consisting of four kinds of elements of <=8.0% W, <=4.0% Mo, <=7% V and <=7% Nb and at least one kind of element selected from a group consisting of three kinds of elements of <=3% Ni, <=10.0% Co and <=3.0% Cu and the balance consisting of inevitable impurities and Fe. Hardness of a part or all parts of an attachment part 2 is regulated to lower hardness in comparison with hardness of base material of the main part in a part for forming the screw.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a screw for extrusion or injection molding of plastics and the like and a method for producing the same.

[0002]

2. Description of the Related Art Molding of plastics is roughly classified into injection molding and extrusion molding, and a screw is used for both of them. The screw has a mounting portion at one end thereof fitted into a drive source to be fixed, and a screw forming portion from a position slightly apart from the mounting portion to the other end is inserted into the cylinder. It is rotationally driven as a cantilever structure, and in the case of injection molding, a rapid axial pressing motion is also applied. Therefore, particularly in the case of injection molding, a large stress is applied to the mounting portion, and since the mounting portion is engraved with the key groove and the spline, cracking and breakage are likely to occur. Further, in order to improve the wear resistance of the screw forming part in particular, it is effective to set the overall hardness higher, but if the hardness is too high, accidents such as breakage easily occur. . In addition, in order to prevent cracks and breakage of the shaft, the hardness of the entire screw is set to a low level, and in order to improve the wear resistance of the screw forming part or the corrosion resistance, nitriding and overlay welding of the screw forming part, Some have been subjected to surface treatment such as thermal spraying.

[0003]

As described above, these screws have high wear resistance in the screw forming portion.
Sufficient toughness to withstand cracks and breakage is required for the mounting portion at the end. However, if the entire screw is made to have a high hardness, breakage and cracks are more likely to occur, and surface treatment of the screw forming portion requires extra steps and costs. The present invention provides a screw for injection molding, which has a predetermined wear resistance in a screw forming portion, and has sufficient toughness to prevent cracks and breakage in a mounting portion, and an injection molding screw, and a manufacturing method thereof. To aim.

[0004]

DISCLOSURE OF THE INVENTION The inventors of the present invention have proposed a novel method for manufacturing a plastic screw by taking advantage of the feature that the screw forming portion has a high hardness, while also cracking or breaking the key groove or spline corner of the mounting portion. I examined the means to prevent. As a result, the screw as a whole, for example, a component with a high hardness of HRC55 or higher is selected, and after heat treatment for quenching and tempering, the mounting part is tempered again to lower the screw forming part. It has been found that the hardness can suppress the occurrence of cracks or breakage from the key groove or the spline corner of the mounting portion.

That is, according to the present invention, in an extrusion or injection molding screw having a screw forming portion and a mounting portion integrally in the longitudinal direction, the chemical component of the screw is C 1.0 to 2.5% by weight and Si 2.0. % Or less, Mn 2.0% or less, Cr 9.0 to 18.0%, W 8.0% or less, Mo 6.0%
Hereinafter, at least one selected from the group consisting of four elements of V 7% or less and Nb 7% or less, and the group of three elements of Ni 3% or less, Co 10.0% or less, and Cu 3.0% or less. It is characterized in that it contains an element and the balance consists of inevitable impurities and Fe, and the hardness of a part or the whole of the mounting portion is lower than that of the base metal of the main portion of the screw forming portion. Screw for extrusion or injection molding,
In the screw manufacturing method similar to the above, the heat treatment is characterized by quenching and tempering the entire heat-treated screw for injection molding, and then re-tempering a part or all of the mounting portion. It is a method for manufacturing a screw for extrusion or injection molding.

The above quenching and tempering heat treatment is preferably carried out after the rough processing of the screw forming portion is completed. In this case, finishing processing such as polishing is required after the heat treatment. Roughing of the mounting part may be performed before or after the re-tempering process. In the re-tempering process, only the mounting portion may be reheated. This temperature is a convenient condition because the hardness can be easily lowered from the hardness after the quenching and tempering heat treatment by heating the tempering temperature higher than the tempering temperature performed before that. However, the temperature of the re-tempering treatment is not limited to the above-mentioned conditions, and may be less than the tempering temperature performed immediately after quenching as long as the time is long.
The point is to select the temperature and time at which the effect of re-tempering can be obtained.

The manufacturing method of the present invention comprises a cold work tool steel, a high speed work tool steel, a hot work tool steel, a heat resistant steel, a stainless steel, etc., as a plastic screw material capable of obtaining a sufficiently high hardness.
It is a material that is subjected to quenching and tempering treatment or solution treatment and aging treatment, and is applicable to all high hardness materials that become less harder as they are heated to higher temperatures. Therefore, in the quenching treatment of the present invention, the solution treatment and the tempering treatment can be read as an aging treatment, and a re-tempering treatment or a re-aging treatment suitable for the material can be applied.

[0008]

The screw of the present invention has a chemical composition of C, Si,
Mn and Cr as essential elements, and (W, Mo, V, Nb)
Group, 1 or 2 selected from the group of (Ni, Co, Cu)
It contains additive elements of one kind or more, and the balance is Fe and inevitable impurities. When the above-mentioned additional elements are two or more kinds, they may be a combination of elements in the same group or a combination of elements in two groups. The screw material of the present invention is manufactured by a melting method or a powder metallurgy method.

Next, the action of each element and the reason for limitation will be described. C
Combines with Cr, Mo, W, V, Nb, etc. to form carbides, and the rest strengthens the matrix, but if it is less than 1.0%, the wear resistance is insufficient due to the small amount of carbides, and 1.65 by the melting method. On the other hand, if it exceeds%, on the contrary, the amount of carbide becomes too large and the mechanical properties deteriorate. However, when manufacturing by the powder metallurgy method, 2.
The amount of C can be increased up to 5%, and in this case, it can be a screw suitable for applications such as super engineering plastics, which particularly require wear resistance at high temperatures and resistance to temper softening. Si is used as a deoxidizing agent and at the same time it is effective in improving wear resistance, but if it exceeds 2.0%, the workability in hot and cold deteriorates, so it is made 2.0% or less.

Mn, like Si, is used as a deoxidizing agent and at the same time it has an effect of improving hardenability, but if it exceeds 2.0%, the transformation temperature is also lowered to make it difficult to reduce the annealing hardness. Therefore, the upper limit was set to 2.0%. Cr forms a solid solution in the matrix to increase the corrosion resistance and the hardenability, as well as increase the high temperature tempering softening resistance, and the balance forms carbides to contribute to the improvement of wear resistance. Cr is an essential element for corrosion resistance,
When Mo, W, V and Nb are the main constituents of carbide,
Since the quenching temperature is as high as that of high speed tool steel, Cr must be at least 9.0% in order to prevent this and from the viewpoint of corrosion resistance. However, in the case of the melting method, the Cr-based carbides tend to aggregate, and from the viewpoint of resistance to softening, it is better to keep the content of the screw component system of the present invention at about 14%. Therefore, the upper limit is set to 18.0% because the improvement in properties is small despite the cost and workability deterioration.

Since W, Mo, V and Nb are finely precipitated as MC and M ₂ C type carbides by heat treatment, they greatly contribute to the improvement of heat resistance, softening resistance and abrasion resistance. These elements can be added individually or in combination, but the upper limits of W, Mo, V, and Nb are 8.0% or less, 6% or less, and 7%, respectively, mainly because the hot workability deteriorates. Below, and below 7.0%. Ni, Co,
The three elements of Cu may be selected as one group and one or more elements may be added. Of these, Co forms a solid solution in the matrix and contributes to improvement in heat resistance and softening resistance. It also contributes to the improvement of corrosion resistance against sulfuric acid. If it exceeds 10%, excessive addition makes it difficult to obtain the hardness during quenching and tempering, so the upper limit was made 10.0%.

Cu forms a solid solution in the matrix and contributes to the improvement of corrosion resistance. However, if it exceeds 3.0%, the hardness at the time of quenching and tempering decreases, so if it is added, it should be 3.0% or less. Ni
Is a solid solution with Cu and contributes to the improvement of corrosion resistance.
However, if it exceeds 3.0%, the hardness during quenching and tempering cannot be obtained, so the upper limit is made 3.0%. In the screw of the present invention, since the screw forming portion and the mounting portion have appropriate hardness according to the characteristics required for the respective portions, the screw forming portion exhibits sufficient wear resistance, and Since the portion has a lower hardness than the former and sufficient toughness, cracks and breakage are prevented from occurring. Therefore, it is possible to realize a long life of the screw as a whole.

The main portion of the screw forming portion in the present invention means the other portion of the screw forming portion except for a very small portion on the mounting portion side. That is, depending on the form of the screw, during the re-tempering process, the hardness of a very small part of the screw may be affected by the process and the hardness thereof may be slightly lowered. As a result of various tests, it was found that it is desirable that the hardness of the attached portion is about 25 to 50 HRC in Rockwell hardness value. If the hardness exceeds HRC50, the effect of improving toughness is small and the purpose of purposely re-tempering treatment is small.
If it is less than HRC25, it may cause fatigue of the mounting part or thread breakage. More preferably, it is HRC25-40.

Next, the manufacturing method of the present invention will be described. First, the entire screw that has been roughly processed on the screw forming part is subjected to quenching and tempering heat treatment to a high hardness suitable for the screw forming part, and then the mounting part is heated at an appropriate temperature such as a temperature higher than the tempering temperature. Bath (generally salt)
By soaking and holding, the screw forming portion has a high hardness and sufficient abrasion resistance, the mounting portion has a low hardness, and a screw in which cracking or breakage is prevented can be obtained. The rough machining of the mounting portion may be performed before or after the heat treatment. If the key groove or spline processing is performed in an annealing state, that is, before quenching and tempering heat treatment, the processing itself is easy, but for those with stepped corners, it is necessary to pay attention to heat treatment cracking. It is necessary to provide a finishing allowance corresponding to the amount of heat treatment deformation and rework later.

On the other hand, in the case where the mounting portion is processed after re-tempering, when the hardness is about HRC50 or less, there is an advantage that the cutting is easy and only one processing is required. Therefore, except when the hardness of the mounting portion exceeds about HRC50, it is usually efficient to perform the mounting portion and its key groove or spline processing after re-tempering the mounting portion with a hot bath or the like. In addition, the heating method used for the re-tempering treatment is not limited to the above heat bath, and the screw and the heating means may be used as long as the heating part and the non-heating part can be defined within a relatively short distance and the temperature distribution can be heated well. Various things such as flame, induction heating, etc. can be adopted including exercise.

In the heat treatment of the screw of the present invention, when the re-tempering treatment is performed with salt or the like, heat is transferred from the re-tempering portion to the screw forming portion, so that the mounting portion side of the screw forming portion is excessively heated. The hardness may decrease. In this case, it is effective to prevent excessive temperature rise by sending cooling air to the non-immersed portion of the screw forming portion in the salt.

[0017]

EXAMPLES Examples of the present invention will be described in detail below.
With respect to the materials according to the present invention having the alloy compositions shown in Table 1 (hereinafter abbreviated as the present invention materials) A to H and SKD11 in the tempered state, only the screw forming portion was roughly worked as shown in FIG. The two-dot chain line other than the screw forming portion shows the finished shape. The tempering characteristics of the present invention materials C, G and SKD11 are as shown in FIG. 3, and the present invention materials C and G have higher hardness than SKD11 and wear resistance,
It has high corrosion resistance.

[0018]

[Table 1]

After roughing the screw forming portion, the whole was heat treated by quenching and tempering under the heat treatment conditions shown in Table 2. Table 2 also shows the approximate hardness at this time. Next, as shown in FIG. 1, a re-tempering treatment was carried out by immersing 0.5Hr in a salt at 750 ° C. vertically from the end on the mounting side to a point 180 mm long. During immersion, the screw forming part etc. should be exposed to the atmosphere,
The temperature of the lowermost end of the exposed portion was monitored with a radiation thermometer, and it was confirmed that the surface temperature was 500 ° C or lower, which was lower than the tempering temperature.

[0020]

[Table 2]

FIG. 4 is a diagram showing, among the surface hardness distributions after the above-mentioned re-tempering, the hardness distributions of the materials C, G and SKD11 according to the present invention, particularly in the hardness changing portion. As can be seen from the figure, the surface hardness on the screw forming side is the same as the material C of the present invention.
Has a Rockwell hardness of about HRC62, and the present invention material G has HRC6.
Maintaining high hardness of about 2.5, SKD11 is about HRC58,
Further, the hardness of the mounting portion could be softened to HRC32 to 40.4 (the hardness of the screw forming portion and the mounting portion of other steels of the present invention are shown in Table 3). Finally, the entire finishing process was performed.

Next, Table 3 shows the trial results of the screw in which the mounting portion was re-tempered as described above, in comparison with those in which the conventional re-tempering was not performed. Table 3 also shows the hardness of the screw forming part and the hardness of the mounting part. No matter which steel is used, if the hardness of the mounting portion is appropriately reduced by the present invention as described above, there is no crack or breakage accident even after 24 months of use, but the mounting portion is re-fired. In the non-backed type, SKD11 had a breakage of 8 months, and A to H steels had a breakage of 6 months to 12 months from the spline or the key corner. From Table 3, the screw to which the present invention is applied has no cracks or accidental breakage accidents from the key groove or the spline, the life can be extended more than twice, and the final screw life is regarded as normal wear. It can be seen that it can be stably ended.

[0023]

[Table 3]

[0024]

As described above, in the screw of the present invention, the mounting portion is adjusted to the hardness according to the toughness required of the portion, so that the screw forming portion can efficiently and completely perform its performance. Cracks and breakages are prevented until it is fully used, and the screw forming portion is made to have high hardness with an emphasis on wear resistance, so that the wear resistance life can be fully exhibited. Since the screw of the present invention has a structure in which the hardness is adjusted for each part, it is not necessary to raise the hardness of the whole to improve the wear resistance and to risk breaking such as breakage. It is possible to omit an extra process such as lowering the surface treatment and performing surface treatment. However, it goes without saying that the screw of the present invention includes a screw forming portion having a high hardness and a surface of which is surface-treated.

[Brief description of drawings]

FIG. 1 is a diagram illustrating a re-tempering method according to an embodiment.

FIG. 2 is a diagram illustrating the overall shape of a screw used in a trial test.

FIG. 3 is a diagram showing the relationship between the tempering temperature and hardness of SKD11 and improved steel A.

FIG. 4 is a diagram showing a change in hardness between a screw forming portion and a mounting portion.

[Explanation of symbols]

 1 screw molding part, 2 mounting part, 3 salt

Claims (2)

[Claims] 1. A screw for extrusion or injection molding, which has a screw forming portion and a mounting portion integrally in the lengthwise direction, wherein the chemical component of the screw is from C 1.0 to about 1.0% by weight.
2.5%, Si 2.0% or less, Mn 2.0% or less, Cr 9.0 to 18.0%,
And W 8.0% or less, Mo 6.0% or less, V 7% or less, Nb
Group consisting of 4 elements of 7% or less, and Ni 3% or less, C
o Contains at least one element selected from the group consisting of three elements of 10.0% or less and Cu 3.0% or less, and the balance consists of unavoidable impurities and Fe. A screw for extrusion or injection molding, which has a hardness lower than that of the base material of the main part of the screw forming part. 2. In a method for manufacturing an extrusion or injection molding screw having a screw forming portion and a mounting portion integrally in the length direction, the heat treatment includes quenching and tempering the entire heat treated screw for molding. Then, a method of manufacturing a screw for extrusion or injection molding, which is characterized in that a part or all of the mounting part is subsequently re-tempered.