JP2000229341A - Check valve for injection molding machine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the check valve capable of being maximally enhanced in corrosion resistance, abrasion resistance and strength while reducing an abrasion-resistant material to the utmost and low in cost. SOLUTION: A check valve 2 for an injection molding machine arranged between a screw head 3 and a screw shaft portion 4 so as to be movable in a screw shaft direction has a check valve main body formed by bonding a hard layer 6 forming the contact surface with the screw head 3 and comprising a thermet material to a base material 5 comprising a steel material and the length ratio of the hard layer 6 is set to 10-20% with respect to the length of the check valve main body.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a check valve provided between a screw head and a screw shaft of an injection molding machine and for preventing backflow of molten resin, and more particularly to wear resistance, corrosion resistance and strength. The present invention relates to a check valve for an injection molding machine which has excellent characteristics.

[0002]

2. Description of the Related Art Since components such as a screw and a check valve of an injection device of an injection molding machine are constantly in contact with a high-temperature, high-pressure molten resin, measures against corrosion and wear are important. In particular, in recent years, with the expansion of use of engineering plastics (hereinafter referred to as engineering plastics), corrosion and wear caused by flame-retardant materials and inorganic fillers added to resins for the purpose of improving the performance of engineering plastics have become a major problem. . In addition, the molding pressure has become higher to reduce the thickness of engineering plastic products in order to reduce the weight, and component parts have been required to have high strength.

Conventionally, to improve the corrosion resistance and abrasion resistance of parts used in an injection molding machine, as a conventional technique, materials of a screw head, a check valve and a spacer are made of ceramics having excellent corrosion resistance and abrasion resistance. [Japanese Unexamined Patent Publication (Kokai) No. 64-24718] and those using ceramics in portions requiring wear resistance [Japanese Unexamined Patent Publication (Kokai) No. 62-130].
No. 818 publication].

[0004] However, although ceramics are excellent in corrosion resistance and wear resistance, they have the disadvantage of poor toughness. Therefore, in order to improve both wear resistance and strength, the check valve needs to have wear resistance. 1/4 of the check valve length on the side surface
There has been proposed a check valve excellent in both wear resistance and strength by providing a wear-resistant material layer in which a hard substance is added in an amount of 10 to 50% by weight in the range of １ ／ to 1/2 (Japanese Patent Application Laid-Open No. 9-155938). .

FIG. 8 shows a check valve disclosed in Japanese Patent Application Laid-Open No. 9-155938. In the figure, 1 is a screw, 10 is a screw head detachably attached to the tip of the screw 1, and 20 is a pusher attached to the tip of the screw 1 by the screw head 10. The check valve includes a friction ring 30 and a check ring 40. The friction ring 30 is １ ／ of the axial length from the side in contact with the backflow prevention ring 40.
The length d is formed by the sintering method so that the wear resistant material layer has a half length d and the remaining portion has a two-layer structure of the strength material layer.

Similarly, for the backflow prevention ring 40,
From the side in contact with the friction ring 30 with respect to the length in the axial direction, the length d 'is sintered so that the length d' is a two-layer structure of a wear-resistant material layer and the remaining part is a strength material layer. It is formed by a method.

[0007]

However, the conventional check valve shown in FIG. 8 has high strength even under high pressure and excellent wear resistance, but has a wear resistance of at least 1/4 of the length of the check valve. Requires a layer of wearable material and many wear-resistant materials,
There is a disadvantage that the cost is increased.

Accordingly, an object of the present invention is to solve the above-mentioned problems of the prior art and to maximize the corrosion resistance, wear resistance and strength while minimizing the use of wear-resistant materials. It is another object of the present invention to provide a low-cost check valve for an injection molding machine.

[0009]

In order to achieve the above object, an invention according to claim 1 is directed to an injection molding machine which is disposed between a screw head and a screw shaft so as to be movable in a screw axial direction. In the check valve, a hard layer formed of a cermet material forming a contact surface that contacts the screw head,
A check valve main body formed by joining a base material made of a steel material, wherein a ratio of a length of the hard layer to a length of the check valve main body is 10 to 20%. It is assumed that.

As described above, in the invention according to the first aspect, the ratio of the length of the hard layer to the length of the check valve main body is 10 to 20.
%, But the basis is as follows.

[0011] The strength of the check valve against breakage is largely related to the shape and the longitudinal elastic modulus of the hard layer. This is presumably because, when a hard layer is formed in a portion of the check valve that requires wear resistance, the magnitude of the stress generated at the boundary between the base material and the hard layer varies depending on the shape of the hard layer.

Therefore, the present inventor conducted a structural analysis by a computer using an analysis model shown in FIG. 2 in order to obtain an optimum length of the hard layer in the check valve. In the structural analysis, the analysis model was a rectangular shape, the longitudinal cross-sectional shape of the check valve, and an axisymmetric element was used. In FIG. 2, D is the outer diameter of the check valve, L is the length of the check valve, and t is the thickness of the check valve. The length of the hard layer is indicated by l. In the structural analysis, loads and constraints equivalent to those acting upon injection were applied as boundary conditions, and the maximum principal stress was calculated by changing the length l of the hard layer in various ways.

FIG. 3 is a graph showing the results of the structural analysis. In this analysis, the value of the longitudinal elastic modulus of the cermet forming the hard layer was changed in five ways within the range of 30,000 to 55000 kgf / mm ² , and the longitudinal elastic modulus of the steel material as the base material was 21.
A value around 000 kgf / mm ² is used. In FIG.
On the vertical axis, the maximum principal stress is expressed as a ratio to the maximum principal stress generated at the time of injection when the check valve is made of a single cermet. The horizontal axis represents the ratio of the length l of the hard layer to the length L of the check valve.

First, it can be seen from FIG. 3 that when two different kinds of materials such as steel are used for the base material and cermet is used for the hard layer, the maximum principal stress that occurs is greater than that of a single material. It is a tendency. According to the structural analysis, the location where the maximum main stress occurred was inside the hard layer joint surface. Therefore, it can be seen that, when the hard layer is provided on the base material, even if the wear resistance is improved, if the maximum main stress is too large, it is likely to be damaged from the joint with the hard layer.

Therefore, the magnitude of the maximum principal stress is not so large as compared with the case of other longitudinal elastic coefficients. For example, the longitudinal elastic modulus of a middle hard cermet is 43000 kgf / mm ^2.
In the case of (1), the hard layer length is 83.5% and the maximum principal stress shows a minimum of 141%. This means that if the length of the hard layer is set to 83.5% of the length of the check valve, the maximum principal stress that can be generated is minimized, and the hard layer is less likely to be damaged. However, the cermet of the hard layer material is
Since it is an expensive material, it is preferable that the length of the hard layer is as short as possible in order to obtain an effect while suppressing the material cost. On the other hand, as can be clearly seen from FIG. 3, when the length of the hard layer is 10% or less, the value of the maximum principal stress generated tends to increase in any cermet having any longitudinal elastic modulus, and breakage occurs. It tends to be easy. On the other hand, when the length of the hard layer exceeds 20%, the maximum principal stress tends to increase. Accordingly, when the longitudinal elastic modulus is 43000 kgf / mm ² , the optimum range where the maximum principal stress is relatively small and the length of the hard layer does not increase is 12.5 to 20%.

The same applies to other longitudinal elastic moduli. When the longitudinal elastic modulus is 30,000 kgf / mm ² , the optimum hard layer length is 12.8 to 25% and the longitudinal elastic modulus is 40,000 kgf / mm ^2.
In the case of the optimal hard layer length is 12.8-20.0%,
When the longitudinal elastic modulus is 55000 kgf / mm ² , the optimal hard layer length is 10.0 to 18.0%. Therefore, as a whole, the optimum range of the hard layer length in which the effect of preventing the hard layer from being damaged without increasing the material cost is 10 to 2 times.
0.0%.

Next, a second aspect of the present invention is a check valve for an injection molding machine which is disposed between a screw head and a screw shaft portion so as to be movable in the screw axis direction. Forming a surface, Ni-B-Si-
W-WC alloy [B: 0.5 to 0.9% by weight, Si: 2.
52 to 3.96% by weight, W: 20 to 35% by weight, WC:
24.2 to 41.0% by weight, Ni: balance) and a check valve main body formed by joining a base material made of steel material to the length of the check valve main body. On the other hand, the ratio of the length of the hard layer is 12.5 to 20%.

As in the present invention, the cermet used for the hard layer includes a Ni-B-Si-W-WC alloy [B: 0.5
0.9% by weight, Si: 2.52 to 3.96% by weight,
W: 20 to 35% by weight, WC: 24.2 to 41.0% by weight, Ni: balance].

The grounds for limiting the components of the cermet material most suitable for the hard layer are as follows. W is B during high temperature sintering,
It reacts with Ni to form a double boride, NiW ₂ B ₂ , in the alloy, which contributes to increasing the cohesive strength and hardness of the alloy. With an increase in the production amount of the double boride NiW ₂ B ₂ , improvement in hardness and wear resistance is brought about. When the content of W is 20% by weight or more, an effect is exhibited in improving corrosion resistance. On the other hand,
When the W content exceeds 35% by weight, the anti-deposition property sharply decreases. This is because the amount of remaining Ni decreases,
This is probably because the bonding phase in the alloy that binds the W ₂ B ₂ particles is insufficient and microvoids are formed in the alloy.

B is an element forming a double boride NiW ₂ B ₂ with W and Ni. When the amount of B added is 0.5% by weight or less, the formation of double borides NiW ₂ B ₂ is reduced, so that sufficient hardness cannot be obtained. The hardness of the alloy increases as the amount of B added increases, but when it exceeds 0.9% by weight, the eutectoid force rapidly decreases, and the balance between the hardness and the eutectoid force is lost.

Si forms a solid solution in the Ni phase, which is the bonding phase of the alloy, and strengthens the alloy by solid solution. The effect does not appear if the amount of Si is small. On the other hand, since the solid solubility limit of Si in Ni is fixed, if the amount of Si is large, a brittle Ni-Si compound is formed in the binder phase, and the strength is reduced. The range of the amount of Si in which the effect of solid solution strengthening of the alloy was obtained was 2.52 to 3.96.

According to a third aspect of the present invention, in a check valve for an injection molding machine disposed movably in a screw axial direction between a screw head and a screw shaft portion, a contact surface for contacting the screw head is formed. And Ni-B-Si-Mo-
WC alloy [B: 1.0 to 3.0% by weight, Si: 2 to 5% by weight, Mo: 10 to 20% by weight, WC: 24.2 to 4%
1.0% by weight, Ni: balance), and a check valve main body formed by joining a base material made of a steel material, wherein the rigidity is determined with respect to the length of the check valve main body. The length ratio of the layer is 12.5 to 25% by weight.

As in the present invention, the cermet used for the hard layer includes a Ni-B-Si-Mo-WC alloy [B: 1.
0 to 3.0% by weight, Si: 2 to 5% by weight, Mo: 10 to 10% by weight.
20% by weight, WC: 24.2 to 41.0% by weight, Ni:
The remainder is excellent.

The basis for limiting the components of this cermet alloy is as follows. B reacts with Ni and Mo to form Ni
_{2 B, Ni 3 B, MoB} , to produce a boride such as Mo ₂ NiB _2. These borides enhance the wear resistance and anti-depositing power of the alloy. However, if the B content is small, sufficient amount of boride is generated, so that sufficient hardness cannot be obtained. Therefore, the preferred range is 1.0 to
3.0% by weight.

Si, together with B, lowers the sintering temperature of the alloy, and is effective in metallurgically bonding the steel without deteriorating the steel at the time of sinter joining with the base steel. The effect appears from 2% by weight or more, but if it exceeds 5% by weight, densification of the alloy is hindered and the strength is rapidly reduced. Therefore, the upper limit is 5% by weight.

Mo produces MoB, Mo ₂ NiB ₂ ,
It increases the wear resistance of the alloy and improves the corrosion resistance of the binder phase mainly composed of Ni. In addition, the crystal grains of the alloy are refined to increase the anti-deposition property. The above effect becomes remarkable when the content of Mo is 10% by weight, but when the content exceeds 20% by weight, undesirably, the cohesive strength is decreased and the sintering temperature is increased.

WC is finely dispersed in the alloy and enhances the wear resistance and the anti-deposition property of the alloy. The effect becomes remarkable when the content of WC is 25% by weight. However, when the content exceeds 35% by weight, a large number of micropores are generated in the alloy, resulting in poor sintering and lowering the coercive force.

According to a fourth aspect of the present invention, in any one of the check valves, the ratio of the length of the hard layer to the thickness of the check valve body is 60 to 90%. It is assumed that.

According to the present invention, in addition to the length of the hard layer with respect to the length of the check valve body, the optimum range of the hard length with respect to the wall thickness is determined. Here, FIG. 4 is a graph showing an analysis result of the maximum principal stress when the hard layer length 1 is changed with respect to the thickness t of the check valve. When the longitudinal elastic modulus of the cermet is 43000 kgf / mm ^2, a structural analysis is performed using a rigid layer length 1 / check valve length L of 16% and a non-return valve outer diameter D as a constant analysis model. It is a thing. In FIG. 4, the horizontal axis represents the ratio of the hard layer length 1 to the check valve wall thickness t. On the vertical axis, the hard layer length 1 /
Longitudinal elastic modulus 430 of cermet with check valve length L = 16%
In the composite check valve of 00 kgf / mm ² , the maximum principal stress obtained by the structural analysis in FIG.

As shown in FIG. 4, the analysis result obtained by examining the relationship with the maximum principal stress by changing the check valve thickness t indicates that:
It has been found that the value of the maximum principal stress can be reduced by increasing the check valve thickness t. In addition, the increase in the check valve thickness t results in a reduction in L / D [molded body height / molded body outer diameter] of the hard layer molded body from the viewpoint of moldability, resulting in improved moldability. On the other hand, since the amount of the cermet material powder to be filled increases, the production cost increases. Therefore, a suitable check valve thickness t that balances good moldability with increased powder loading.
Can be determined to be 60 to 90%.

Further, in the invention according to claim 5, the ratio of the length of the hard layer to the outer diameter of the check valve main body is 11.10.
3% or more.

In the present invention, in addition to the length of the hard layer with respect to the length of the check valve body, the optimum range of the hard length with respect to the outer diameter of the check valve body is determined. Here, FIG.
It is a graph which shows the analysis result of the maximum principal stress at the time of changing the hard layer length 1 with respect to the check valve outer diameter D. As in this case, the longitudinal elastic modulus of the cermet is 43000 kgf / mm ²
4, the hard layer length 1 / check valve length L is 16%, and the hard layer length 1 / check valve thickness t = 65.
Structural analysis was performed using a 2% constant check valve inner diameter as an analysis model. In FIG. 5, the horizontal axis represents the ratio of the hard layer length 1 to the check valve inner diameter. On the vertical axis, the length of the hard layer 1 / the thickness of the check valve t = 6
Assuming that the maximum principal stress obtained by the structural analysis of FIG. 4 in the 5.2% composite check valve is 1, the maximum principal stress is represented by a ratio to the maximum principal stress.

As shown in FIG. 5, from the analysis results obtained by examining the relationship with the maximum principal stress by changing the check valve outer diameter D,
It has been found that the value of the maximum principal stress can be reduced by reducing the check valve outer diameter D. In addition, from the viewpoint of molding the hard layer molded body, the amount of the cermet material powder to be filled decreases with a decrease in the check valve outer diameter D, which directly leads to cost reduction. Therefore, the hard layer length l with respect to the check valve outer diameter D
The preferred range is that the effect of reducing the maximum principal stress can be seen.
It can be determined that it is 1.3% or more.

[0034]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of a check valve for an injection molding machine according to the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a sectional view showing a check valve for an injection molding machine according to an embodiment of the present invention. 2 shows a check valve. The check valve 2 is arranged so as to be movable in the screw axis direction at a screw head 3 which is a tip end of the screw and at a screw shaft portion 4. When the molten resin is measured, the check valve 2 is pushed forward by the pressure of the molten resin as shown in FIG.
Contact The main body of the check valve 2 includes a base material 5 made of a steel material and a hard layer 6 made of a cermet, and the hard layer 6 forms a surface in contact with the screw head 3. ing.

The ratio of the length l of the hard layer to the length L of the main body of the check valve 2 is 10 to 20%. Sufficient strength is ensured so as not to occur.

FIG. 6 is a view showing a method of forming the hard layer 6. The molding is performed by a uniaxial pressure molding method (press molding method) using a mold 7, a core rod 8, an upper punch 9a, and a lower punch 9b. The dimensions of the mold 7 are determined in consideration of the amount of shrinkage generated during sintering of the hard layer molded body 11 and the allowance for grinding during finishing.

First, cermet powder is filled in a space formed by the mold 7, the core rod 8, and the lower punch 9b. Then, the upper punch 9a is inserted from above the mold 7, and pressure is applied at about 65 MPa by the upper and lower punches 9a and 9b to form the hard layer molded body 11. Thereafter, the hard layer molded body 11 is taken out of the mold 7 and sintered at 1170 ° C. in a vacuum furnace at a pressure of 4 to 7 Pa. After sintering, a portion to be a bonding surface with the substrate 5 is ground.

Next, as shown in FIG. 7, a brazing material 12 (preferably, BNi-2) is sandwiched between the hard layer 6 obtained by firing and the base material 5 and placed in a vacuum furnace. Perform quenching. Then, after being rapidly cooled in the furnace, the substrate 5
In order to impart toughness, tempering is performed. Finally, the outer diameter, the inner diameter, and both end faces are ground to predetermined dimensions to manufacture the check valve 2.

After finishing after joining and quenching, by further performing a nitriding treatment, the hardness of the base material 5 can be reduced to about HV1100 [HRC70] without deteriorating the performance of the cermet for forming the hard layer 6. It is possible to increase up to.

[0040]

Next, an embodiment of a check valve for an injection molding machine according to the present invention will be described. Ni- as cermet material
The powder of the B-Si-W-WC alloy was blended into the composition described above, mixed and pulverized by a rotary ball mill, and then dried to prepare an alloy powder. The substrate 5 has SKD61.
Was used. Then, the above-mentioned press forming step, sintering step, joining step, quenching at 1070 ° C. for 30 minutes, 600
After a tempering step and a finishing step at 180 ° C. for 180 minutes, a check valve having a hard layer length of 9 mm, a hard layer thickness of 13.0 mm and an outer diameter of 79.9 mm was finally manufactured.

In the check valve thus manufactured, the hardness was HRC65 in the hard layer and HRC48 in the base material. Table 1 shows the results of various tests performed on the characteristics of the hard layer.

[0042]

[Table 1] Here, the corrosion resistance test was carried out by immersing in a 20% by volume HCl solution and measuring the corrosion loss after 5 hours. In the wear resistance test, a specific wear amount was measured under the following test conditions using an Ogoshi quick wear tester. Friction speed 2.0m / sec Friction distance 600m Final load 18.6kgf Counterpart material SKD11 (HRC58) When the manufactured check valve was installed in an injection molding machine and operated, it was compared with the conventional screw material made of SKD61. As a result, the wear amount of the end face of the hard layer in contact with the screw head was reduced to 1/5, and no damage such as cracks occurred. The production cost was about 75% of that of the conventional product.

[0043]

As is clear from the above description, according to the present invention, the shape and dimensions of the hard layer can be optimized in order to enhance the corrosion resistance, wear resistance and strength of the check valve. It is possible to provide a low-cost check valve which is excellent in wear resistance, corrosion resistance, and fatigue strength and is low in cost.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an embodiment of a check valve for an injection molding machine according to the present invention.

FIG. 2 is a view showing a modeled check valve for performing a structural analysis on a check valve for an injection molding machine according to the present invention.

FIG. 3 is a diagram showing a result of a structural analysis on a relationship between a hard layer length and a maximum principal stress with respect to a check valve length.

FIG. 4 is a view showing a result of a structural analysis on a relationship between a hard layer length and a maximum principal stress with respect to a check valve thickness.

FIG. 5 is a view showing a result of a structural analysis on a relationship between a hard layer length and a maximum principal stress with respect to a check valve outer diameter.

FIG. 6 is an explanatory view of a step of forming a hard layer of a check valve.

FIG. 7 is a view for explaining the joining between the base material of the check valve and the hard layer.

FIG. 8 is a sectional view showing a conventional check valve for an injection molding machine.

[Explanation of symbols]

 2 Check valve 3 Screw head 4 Screw shaft 5 Base material 6 Hard layer

Claims (5)

[Claims] 1. A check valve for an injection molding machine disposed movably in a screw axis direction between a screw head and a screw shaft portion, wherein the check valve is formed of a cermet material and has a contact surface that contacts the screw head. A check valve body formed by joining a layer and a base material made of a steel material, wherein the ratio of the length of the hard layer to the length of the check valve body is 10 to 20%. A check valve for an injection molding machine. 2. A check valve for an injection molding machine disposed movably in a screw axis direction between a screw head and a screw shaft portion, wherein a check surface for contacting the screw head is formed,
B-Si-W-WC alloy [B: 0.5 to 0.9% by weight,
Si: 2.52 to 3.96% by weight, W: 20 to 35% by weight, WC: 24.2 to 41.0% by weight, Ni: balance) and a base material made of steel. For the injection molding machine, wherein the ratio of the length of the hard layer to the length of the check valve body is 12.5 to 20%. Check valve. 3. A check valve for an injection molding machine, movably disposed in a screw axis direction between a screw head and a screw shaft portion, wherein a contact surface for contacting the screw head is formed,
B-Si-Mo-WC alloy [B: 1.0 to 3.0% by weight, Si: 2 to 5% by weight, Mo: 10 to 20% by weight, W
C: 24.2 to 41.0% by weight, Ni: balance) and a check valve main body formed by joining a base material made of a steel material, and a length of the check valve main body. A check valve for an injection molding machine, wherein the ratio of the length of the hard layer to the length is 12.5 to 20%. 4. The injection molding according to claim 1, wherein the ratio of the length of the hard layer to the thickness of the check valve body is 60 to 90%. Check valve for machine. 5. The check valve for an injection molding machine according to claim 4, wherein the ratio of the length of the hard layer to the outer diameter of the check valve body is at least 11.3%. .