JPH0857923A - Screw having a good corrosion resistance, abrasion resistance and seizure resistance - Google Patents

Abstract

PURPOSE: To enhance protection effect for corrosive atmosphere such as a fluororesin, improve abrasion resistance and seizure resistance, and facilitate manufacture by forming a layer composed of at least nickel-phosphorus-tungsten on a working surface of a screw body. CONSTITUTION: This invention relates to a screw for injection molding or extrusion molding. Formed on a working surface of a screw body is a layer composed of at least nickel-phosphorus-tungsten. Also, a good result is obtained with a construction which comprises a coating layer of nickel-phosphorus-tungsten serving as an outermost layer, a layer of nickel-phosphorus serving as an intermediate layer, and a layer of nickel at an interface between it and the screw body. Further, it is desired that the screw body be made of a nickel based alloy. While as a method of forming a layer of nickel-phosphorus-tungsten and the like, vacuum deposition, sputtering, plating and the like may be adopted, plating treatment is preferable. A screw thus obtained is improved in corrosion resistance, abrasion resistance and seizure resistance.

Description

Detailed Description of the Invention

[0001]

The present invention has excellent corrosion resistance, abrasion resistance and seizure resistance, which are particularly suitable for injection molding and extrusion molding of fluororesins or resins containing a large amount of fillers such as glass fibers and silica particles. Related to screws.

[0002]

2. Description of the Related Art A screw for a molding machine used for injection molding or extrusion molding of a synthetic resin is intended to prevent corrosive wear or seizure with a cylinder due to the resin or an additive added to the resin at the time of hot molding. Therefore, development has been advanced in consideration of corrosion resistance, wear resistance and seizure resistance. Among them, matrix-reinforced nickel-base alloys such as those disclosed in Japanese Patent Publication No. 62-21853 have been conventionally used for fluorine resin molding screw materials because of corrosion caused by fluorine gas generated by thermal decomposition. It was However, when molding a fluororesin mixed with a high hardness filler, especially when the chevron portion of the screw is used,
Since the resin is exposed to a corrosive environment while being in contact with these resins and is subjected to a high molding pressure, the mountain portion is severely set and worn, resulting in a short life.

Also, in the molding of a fluororesin containing no filler, the matrix-reinforced screw made of a Ni-based alloy with a high Mo content has low room temperature hardness and strength, so that seizure with the inner surface of the cylinder may occur. In some cases, a twisting phenomenon occurs and the life is remarkably shortened, which hardly contributes to the saving of tool cost. For this reason,
Matrix-reinforced Ni as shown in No. 25774.
A screw has been proposed in which the hardness is increased by work hardening of a base alloy (eg, main components: Ni 60%, Cr 15%, Mo 15%) by cold drawing and the seizure resistance is improved. This has enabled some improvements, but is still insufficient for fluororesins mixed with fillers,
Since work hardening by cold drawing is mainly used, there is a limit to the size that can be manufactured, and at present, the cost of tools has not been saved despite the high cost.

Further, as a screw material having both corrosion resistance and wear resistance, the applicant of the present application has proposed a corrosion resistant and abrasion resistant screw obtained by using a powder overlay, in Japanese Patent Laid-Open No. 61-248703. In this screw, a Co-based alloy, a Ni-based alloy, or hard particles are dispersedly held on the entire surface of a mountain portion of a base material having a mountain shape that is continuous in a spiral shape on the outer periphery of the screw shaft portion and a valley portion between the mountain portions. The purpose is to build up a surface-hardened alloy with powder. However, when powder buildup is applied to the entire surface of the ridges and valleys between the ridges, the material must be selected carefully so that deformation such as bending and shrinkage of the screw does not occur, and special enforcement methods must be applied. There were many restrictions in terms of selection and workability, and there was a problem that the manufacturing cost increased.

[0005]

As described above, the matrix-reinforced type N is used against a corrosive atmosphere such as a fluororesin.
Although the i-based alloy has some effects, it has a drawback that it is inferior in wear resistance and seizure resistance. Furthermore, there is a limit in workability to harden the matrix-strengthened Ni-based alloy by cold working, and in the case of overlay welding of the surface-hardened alloy in which hard particles are dispersed, it is affected by heat. There were construction problems such as deformation. An object of the present invention is to provide a screw which has a large effect of preventing a corrosive atmosphere such as a fluororesin, is excellent in wear resistance and seizure resistance, and can be easily manufactured.

[0006]

Means for Solving the Problems As a result of studies to solve the above-mentioned problems, the inventor has formed a coating layer made of nickel-phosphorus-tungsten on the working surface of a screw to obtain corrosion resistance, wear resistance and It was newly found that a screw having excellent seizure resistance can be obtained. That is, the present invention is a screw for injection molding or extrusion molding, characterized in that the working surface of the screw body is formed with at least a layer made of nickel-phosphorus-tungsten, corrosion resistance, wear resistance, resistance A screw with excellent seizure properties.
The nickel-phosphorus-tungsten coating layer is preferably the outermost layer, the intermediate layer is nickel-phosphorus, and the interface with the screw body is a nickel layer, which are plated. Is desirable. Furthermore, it is desirable that the screw main body be a Ni-based alloy.

[0007]

The nickel-phosphorus-tungsten coating layer formed on the working surface of the screw body constituting the screw of the present invention has excellent corrosion resistance to the resin or the additive added to the resin, and the hard coating layer is , Is important for exhibiting excellent wear resistance and seizure resistance. Nickel-
A vacuum vapor deposition method, an ion plating method, a sputtering method, a plating method, or the like can be used as a film forming method for the phosphorus-tungsten layer.However, in the vacuum vapor deposition method, the ion plating method, and the sputtering method, the screw body is heated during the film forming process. Due to thermal deformation and equipment restrictions due to
The plating method is practical. Of these, electroless plating is desirable because it forms a uniform film without pinholes. To form a nickel-phosphorus-tungsten film by electroless plating, for example, a nickel salt such as nickel sulfate, a tungsten salt such as sodium tungstate, or the like is used as a reducing agent such as sodium hypophosphite citrate. Can be molded.

The content of tungsten in the nickel-phosphorus-tungsten coating layer is determined by the PH value and the temperature, but if it is 10% or less, the hardness becomes 700 HV or less and a hard coating cannot be obtained. Therefore, it is preferable that the tungsten content be 10 to 21 wt% by controlling the PH in the electroless nickel plating bath to be 6 to 9.5. Preferably PH
By controlling the value of 7.5 to 8.5, the tungsten content is 20 to 21 wt% and the hardness of the film is 750 to 800 HV. Also, the thickness of the nickel-phosphorus-tungsten film is important for prolonging the life of the tool, and at least 1
It is necessary to have a thickness of at least μm, but 3 to 10 μm is suitable in view of workability and economical efficiency of electroless plating.

The above-mentioned nickel-phosphorus-tungsten layer is an essential constituent element for using the screw of the present invention, and may be directly formed on the working surface of the screw body. It is desirable to provide an undercoat layer at the interface with the body. The intermediate layer and the undercoat layer have corrosion resistance themselves, and also have the effect of enhancing the adhesion between the screw body and the nickel-phosphorus-tungsten layer, and prevent the nickel-phosphorus-tungsten layer from peeling during use. There is also a buffering effect. Intermediate layer nickel
The phosphorus film layer has a role of satisfactorily joining the outermost nickel-phosphorus-tungsten layer and the nickel layer which is the base film layer. This nickel-phosphorus film can be formed by electroless nickel-phosphorus plating using hypophosphite as a reducing agent, such as nickel chloride and nickel sulfate which are industrially used.

The hardness of the nickel-phosphorus coating layer is determined by the content of phosphorus, but if it is 8% or less, it becomes crystalline and the hardness is 400 HV or less, which is not preferable, and adhesion and appropriate hardness are obtained. Therefore, it is desirable to have an amorphous structure containing 8 to 15%, and the hardness at that time is advantageously 450 to 550 HV. The minimum thickness of the nickel-phosphorus coating layer is
Although 1 μm is required, 5-20 μm is suitable in consideration of workability and economy of electroless nickel plating. Next, the nickel layer of the base film has a role of satisfactorily joining the screw body as the base material and the nickel-phosphorus film. A film thickness of about 0.1 to 5 μm is sufficient for the nickel layer, it is not necessary to forcibly increase the film thickness, and it is preferable to form a film layer having an amorphous structure by electroless plating.

The screw body of the present invention may be made of tool steel such as high speed steel or die steel, but after being used for a long time, the above layers are damaged due to corrosion or abrasion, and the screw body is partially damaged. When exposed to, it is necessary to be careful because this part was corroded intensively. Preferably, the screw main body is made of a Ni-based alloy having a high corrosion resistance, so that even if the layer formed on the working surface of the screw main body is partially worn, the screw main body is less damaged and the film forming treatment is repeatedly used. It is possible.

[0012]

【Example】

(Example 1) As a screw main body, SKD shown in Table 1
No. 11 equivalent material, and then a nickel-phosphorus-tungsten layer as the outermost layer, a nickel-phosphorus layer as the intermediate layer, and a nickel layer at the interface of the SKD11 equivalent material by electroless plating to obtain various test pieces. The seizure resistance test piece is 8 mm diameter x 25 mm length, and the wear resistance test piece is 10 mm x 15 mm x 1
0mm, corrosion resistance test piece is 20mm × 30mm × 2mm thick. The obtained layer had a nickel layer thickness of 0.5 μm, a nickel-phosphorus layer thickness of 12.5 μm, and a nickel-phosphorus-tungsten layer thickness of 5.5 μm. As a result of ICP analysis, the nickel-phosphorus layer had a phosphorus content of 9.8 wt% and a hardness of 515 HV. The nickel-phosphorus-tungsten layer has a phosphorus content of 6.3 wt% and a tungsten content of 20.4 wt%.
The hardness was 763 HV. In addition, as a counterpart material for the seizure resistance test and the wear resistance test, as a material corresponding to the cylinder, SCM440, which is lined with the Ni-based alloy shown in Table 1, was used. The dimensions of the test piece of the mating material used were φ20 mm × 180 mmL for the seizure resistance test piece and φ8 mm × 25 mmL for the wear resistance test piece.

[0013]

[Table 1]

Example 2 Various test pieces were prepared using Hastelloy C shown in Table 1 as the screw body, and the same surface treatment as in Example 1 was performed. In the obtained composite layer, a nickel layer having a thickness of 0.5 μm, a nickel-phosphorus layer having a thickness of 11.3 μm as an intermediate layer, and a nickel-phosphorus-tungsten layer having a thickness of 5.3 μm as an outermost layer were sequentially formed. The result of the ICP analysis was the same composition as in Example 1, and the hardness of the outermost layer was 750 HV. (Example 3) Using Inconel 718 shown in Table 1 as a screw body, various test pieces were prepared and subjected to the same surface treatment as in Example 1. The resulting composite layer has a thickness of 0.
A nickel layer having a thickness of 5 μm and a nickel-phosphorus-tungsten layer having a thickness of 5.2 μm were formed as the outermost layer, and no nickel-phosphorus layer as an intermediate layer was formed. The result of the ICP analysis is the same composition as in Example 1, and the hardness of the outermost layer is 75.
It was 0HV.

(Comparative Example 1) Various test pieces were prepared from the material equivalent to SKD11 shown in Table 1 as the screw body. The prepared test piece was a sample that was not surface-treated. (Comparative Example 2) As a screw main body, Hastelloy C shown in Table 1 was used as a material, and various test pieces were prepared. With respect to the test pieces corresponding to the screws of the above-described examples, the wear resistance and the corrosion resistance were independent, and the seizure resistance was the test piece and the cylinder material as the mating material. For seizure resistance, use a reciprocating friction wear tester with a lubricating oil between the fixed test piece (screw) and the sliding test piece (cylinder material), sliding speed 30m / min, stroke 130mm, load Was increased by 10 kg for 50 cycles each, and the optimum load was 300 kg. The load at the time of seizure was measured from the chart paper.

For abrasion resistance, a sample of 10 mm × 15 mm × 10 mm was pressed against # 400 emery abrasive paper with a load of 2 kg to obtain 480 m
After sliding the distance of, the amount of wear of the test piece corresponding to the screw was measured. Regarding the corrosion resistance, the weight reduction ratio (weight reduction / weight before immersion) was measured after immersion in 20% hydrofluoric acid, 20% hydrochloric acid and 20% sulfuric acid aqueous solution at 25 ° C. for 24 hours.
The results of these tests are shown in Tables 2 and 3. Regarding the seizure resistance, as is clear from Table 2, the composite coating layers of Examples 1, 2, and 3 having the nickel-phosphorus-tungsten coating as the outermost layer were the most excellent. As for the wear resistance, as is clear from Table 2, the outermost layer is made of nickel-
Examples 1, 2 and 3 with a phosphorus-tungsten coating
The composite film layer of 1 was the best. As for the corrosion resistance, as is clear from Table 3, each sample was generally good for 20% hydrochloric acid and 20% sulfuric acid, but for 20% hydrofluoric acid, the outermost layer of nickel- The composite coating layers of Examples 1, 2 and 3 having the phosphorus-tungsten coating were the best.

[0017]

[Table 2]

[0018]

[Table 3]

[0019]

As described above, the screw comprising the composite layer having the nickel-phosphorus-tungsten coating as the outermost layer of the present invention has high corrosion resistance to an aqueous solution of hydrofluoric acid, good abrasion resistance, and excellent resistance to abrasion. Since it has excellent seizure properties, it is sufficiently durable to be used as a screw for a fluororesin and is advantageous in reducing tool costs.

[Brief description of drawings]

1 is a scanning electron microscope metallographic photograph showing a cross-sectional structure of a composite nickel layer of Example 2, showing a magnification of 4,000. FIG.

[Explanation of symbols]

A: nickel-phosphorus-tungsten layer, B: nickel-
Phosphorous layer, C: Nickel layer

Claims (4)

[Claims] 1. A screw for injection molding or extrusion molding, characterized in that a layer of at least nickel-phosphorus-tungsten is formed on the working surface of the screw body, which is corrosion resistance, wear resistance, and corrosion resistance. A screw with excellent seizure properties. 2. A screw for injection molding or extrusion molding, wherein an outermost layer of nickel-phosphorus-tungsten and an intermediate layer of nickel-are formed on a working surface of the screw body.
A screw with excellent corrosion resistance, wear resistance, and seizure resistance, characterized in that a nickel layer is formed at the interface between the phosphorus layer and the screw body. 3. The screw excellent in corrosion resistance, wear resistance, and seizure resistance according to claim 1, wherein the layer formed on the working surface of the screw body is a plated layer. 4. The screw excellent in corrosion resistance, wear resistance and seizure resistance according to claim 1, wherein the screw body is a Ni-based alloy.