JPS6246019A - Injection molded bearing and its molding method - Google Patents

Abstract

PURPOSE:To prevent deformation of a sliding surface in a bearing when it is fitted into a housing, by providing a damping part, elastically deformed when the bearing is fitted into the housing, in the peripheral surface of a bearing main unit. CONSTITUTION:A bearing 20, forming in its center a bearing height 21, provides its internal peripheral surface 21a to serve as the slide holding surface of a rotary shaft. While the bearing 20 provides in its peripheral part a large number of impact protrusions 22 extended tilting by a predetermined angle gamma with respect to a connection (a) of a bearing main unit peripheral circle C2. Elasticity of these impact protrusions 22 causes the bearing 20, when it is fitted into a housing, to absorb deformation of a bearing main unit, generated by an interference between an external shape of the bearing and a bearing fitting hole of the housing, by opening and closing only the damping protrusions 22. Accordingly, the bearing, when it is fitted, prevents unreasonable force from acting on a sliding surface, thus the bearing promotes high accuracy of its sliding surface.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is a q/l extrusion molded bearing A3 J for rotationally holding a lightweight industrial product made by injection molding ultra-high molecular weight polyethylene as a raw material.
:Related to Bison's injection molding method.

[Conventional technology and its problems]

Ultra-high molecular weight polyethylene with a molecular weight of 2 million to 6 million is extremely suitable as material F1 for small industrial parts such as bearings and gears because it has excellent chemical resistance, impact resistance, and cold resistance, as well as self-lubricating properties. ing.

Injection molding, compression molding, and extrusion molding are conceivable methods for molding small industrial parts using ultra-high molecular weight polyethylene, but as mentioned above, ultra-high molecular weight polyethylene has extremely high intermolecularity, so it does not have viscosity even when heated. It shows fluidity without becoming low.

For this reason, even if injection molding is performed, it is not possible to fill every corner of the cavity with ultra-high molecular weight polyethylene, resulting in poor precision and inability to make the surface of the molded product smooth. Furthermore, when ultra-high molecular weight polyethylene is plasticized using a scryco, a high shear is applied, which may cause oxidation and cleavage of the main chain due to heating, resulting in a decrease in molecular weight and resulting in ordinary polyethylene. Therefore, bearings made of ultra-high molecular weight polyethylene have conventionally been processed by cutting. As a result, high-precision molded products with smooth sliding motion can be produced efficiently and inexpensively! I can't do it.

On the other hand, in conventional plastic bearings, the lζth sliding surface that receives the rotating shaft in the holding part and the outer peripheral part that is fitted into the housing are concentric circles, and the outer diameter of the outer peripheral part is the diameter of the rotating shaft holding part in the housing. The bearing is molded approximately 50μm"-15011m larger and is fixed by press-fitting it into the holding part of the housing. Therefore, the bearing is assembled into the housing while being compressed, and at this time, the shrinkage 11 of the bearing sliding surface
1 depends on the outer diameter of the outer periphery of the bearing and the holding part of the housing. , the ratio of the contraction amount of 1Ill + receiving sliding movement to the contraction rate λ, then this contraction rate λ
varies greatly depending on the press-fitting conditions such as the speed at which the bearing is press-fitted into the housing and the press-fitting load. For this reason,@
It has been difficult to improve the accuracy of the curved bearing sliding surface due to the effects of the bearing itself, the accuracy of the holding part of the housing, the shrinkage rate, etc.

[Purpose of the invention]

In view of the above, the present invention provides an injection molded bearing made of a high-precision and inexpensive ultra-high molecular weight polyurethane resin whose sliding movement does not deform when installed in a housing, and an injection-molded bearing made of a high-precision, inexpensive ultra-high molecular weight polyurethane. The purpose of the present invention is to provide a J4 injection molding method for bearings that can be precisely injection molded.

[Structure of the invention]

The purpose of this is to have an active inner circumferential surface that slidably holds the rotating shaft, and a buffer that elastically deforms and covers the outer circumferential surface of the bearing body when the bearing is inserted into the bearing holding part of the housing. and injecting high molecular weight polyethylene, and supplying powdered ultra high molecular weight 1 polyethylene raw material to an injection cylinder in a non-oxidizing atmosphere, and adjusting the compression ratio of the screw of the injection cylinder to 1.3 to 2.0. This is achieved by melting the material in a short time with a length-to-diameter ratio of 15 to 20, and injecting the material into the mold cavity before thermal crosslinking begins.

〔Example〕

Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a sectional view of an injection molding machine according to the present invention. The injection molding machine of the present invention has a cylinder 2 in which a screw 1 is disposed, a hopper 4 for supplying raw material 3 into the cylinder, and a molding cavity 5 inside which the tip of the cylinder 2 faces. The mold 6 and the cavity 5
The main parts are a vacuum tank 7 and a rotary pump 8 for evacuating the air.

A vibrator 9 for supplying an atmospheric gas such as a gas line is connected to the hotter 4, and the raw material 3 supplied into the cylinder 2 is melted and covered in an oxidizing atmosphere. The lower part of the hopper 4 is provided with an adjustment plate 10 which has circular or rectangular shaped sleeves 1 to 10a for adjusting the supply M of the material 113.

On the other hand, the compression ratio of the screw 1 rotated by the vane motor 11 is suitably 2.3 or less, especially 1.3 to 2.0, and L/D (+-varnish screw length, r)
Niscri-1-diameter) is 10 to 25, especially 15 to 20
is preferred. J: Dasukuri] --'s bit P is P-π
It is determined by o tan θ (θ: angle of flight),
If the value of θ is not indicated, it is 10° to 18°, especially 11.
The angle is preferably 5° to 14.5°.

When the compression ratio is 2.31 mE, more pressure than necessary is applied to the ultra high molecular weight polyethylene raw material, which causes it to remain in the cylinder, and when crosslinking begins, it shows no fluidity.
Rinaru. Further, if the compression ratio is 1.3 or less, it is insufficient to melt the surface of the powder of ultra-high molecular polyethylene.

Regarding the ratio 1-/D of the length I- of the screw 1 and its diameter [), if 1-/D is 20 or more, there is a risk that the ultra-high molecular weight M polyethylene will remain in the cylinder for an unnecessarily long time. , 1-/D is less than 15, the precision of heating control of ultra-high molecular weight polyethylene becomes insufficient.

The screw pitch is determined by the flight angle O, and θ determines the magnitude of the torque applied to ultra-high molecular weight polyethylene. If 0 is less than 10 degrees, sufficient torque can be obtained but it is unnecessary. Adds a long residence time and frictional energy to the ultra-high polymer polygoblen powder. In addition, if θ is 18° or more, ultra-high molecular weight Borini
- to Jiren for 1 minute. 'K If the torque cannot be applied and a load is placed on the vane motor, the specified screw rotation speed cannot be obtained, and the engine may remain in the cylinder for a long period of time.
By leaving the 11th station, it is inappropriate.

Furthermore, use a backflow prevention ring on the screw head, cut the flight to the tip, and set the diameter of the screw to be 0.1 to 0.2 inches smaller than the inner diameter of cylinder 2.

Further, the rear half of the cylinder 2 is a feeder section 2a.

The Air half is a compression part 2b, the tip part is a nozzle part 2C,
The length of the heat radiation fins 12 formed in the feeder portion 2a is preferably 1/4 to 1/3 of the total length of the cylinder 2.

The ultra-high molecular weight poly(1-bun)
As the compression ratio increases, the polyethylene powder rubs against each other and generates heat. This state of <1 occurs when the screw reaches the [Shib 1] pressure zone, and at this point 2b, the powder is first softened by external heating, and before that, zone 2a is softened. Therefore, we must avoid heating as much as possible, dissipate the heat generated by friction, and prevent crosslinking.

If the heat dissipation fins 12 are not provided, the heating control in the compression part 2b will be impossible, and the polyethylene powder will be crosslinked. And the compression part 2b, the nozzle part 2
A heater 13 is disposed at C to instantly melt the raw material 3.

In addition, FIG. 2 is a plan view of the cavity, FIG. 3 is a vertical cross-sectional view of the mold, and FIG. 4 is a cross-sectional view of the mold.As can be seen from these figures, one section of the mold 6 is Runway 14 in mold 6a
A cavity 5 for bearing molding is formed on the U surface of the other mold 6 [), and the circumferential width of this cavity 5 is 5M to 10 mm Pl! J and f communicate with the annular vacuum path 15 through a hole 16. The length of this hole 16 is 1 to 20 mm.
In particular, it is appropriate to write 3 to 7 thm. Further, a seal ring 17 is provided at the joint between the molds 6a and 6b, so that the degree of vacuum during mold assembly 1h can be maintained. In addition, during molding, the temperature of the mold 6 is 30 to 130 °C, especially 6
It is preferable to set the temperature to 0°C/120°C.

The cavity 5 has the shape of a bearing according to the present invention, and a circular protrusion 5 ah is provided in the center thereof, which corresponds to a bearing sliding surface for receiving a rotating shaft. A large number of grooves 5b, 5b, . . . 5b are formed on the outer periphery of the cavity 5 and extend at a predetermined angle with respect to the tangent to the virtual outer circumferential circle C1, and the tips of these grooves 5b communicate with the inner end of the hole 16. １ノ(-there.

A method for molding ultra-high molecular weight poly-1-dylene using the injection molding machine described above will be described below.

First, powdered ultra-high molecular weight polyethylene of culm with a particle size of 30 μ to 100 tt is placed in the hopper 4. 13, a predetermined amount is supplied. Unlike ordinary poly-1-dylene, the ultra-high molecular weight polyethylene is not in the form of pellets but in powder form, and the coefficient of friction between the particles is small. The amount of supply can be determined. Adjusting the raw material supply M to the feeder section 2a will avoid a relative decrease in the compression ratio of the screw 1, and as a result, when plasticizing the ultra-high molecular weight polyethylene, the compression ratio will be abnormally increased. This can prevent the original F3+ from staying in the cylinder 2.

Then, the ultra-high molecular polyethylene supplied into the cylinder 2 is instantaneously heated from the feeder section 2a to the compression section 2b and melted (only the surface) at the nozzle section 2G. here,
Since nitrogen gas is supplied into the hopper 4, the inside of the cylinder 2 is maintained in a non-oxidizing atmosphere, thereby preventing a decrease in molecular weight due to oxidation. Furthermore, ultra-high molecular weight polyethylene has the characteristic that once it is melted, crosslinking immediately begins. Therefore, if the material is instantaneously melted in the compression part and injected into the cavity 5 from the nozzle part as in this embodiment, it can be poured while it still has fluidity.

Crosslinking of the raw material injected into the cavity 5 starts immediately, and by promoting this crosslinking, the raw material does not re-melt even in the high temperature cavity. Furthermore, the cavity 5 is filled with molten ultra-high molecular weight polyethylene up to the tip of the projection of the bearing.

A bearing 20 shown in FIG. 5 is formed by the cavity 5, and a bearing height 21 is formed at the center of the bearing 20, and the inner circumferential surface 21a serves as a sliding holding surface for the rotating shaft. As mentioned above, ultra-high molecular weight polyethylene with molecules M1 of 2 million to 6 million has self-lubricating properties, so that the rotating shaft slides smoothly within the sliding surface.

The outer circumferential portion of the bearing 20 has a connection a of the outer circumferential circle C2 of the bearing body.
A large number of impact protrusions 22, 22, . Since this buffer protrusion 22 has elasticity, only the buffer protrusion 22 opens or closes when the bearing 20 is fitted into the housing, and the interference between the outer shape of the bearing and the bearing fitting hole of the housing is J.
: Absorbs deformation of the bearing body. Therefore, the sliding surface of the bearing is not subjected to unreasonable cracks when the bearing is fitted, and the precision of the bearing circular surface can be improved.

The outer diameter D2 including the buffer protrusion on the outer periphery of the bearing is 3ml.
~70mm, the inner diameter d of the inner circular surface of the bearing is 1ml11~50I
IIIll is formed. The difference n/D2 between the number n of the buffer protrusions 22 and the outer diameter D is set to 2 to 50I1m, and particularly preferably 5 to 20. Further, the outer diameter D2 is 20 to 250 μm larger than the inner diameter of the housing, and the diameter D1 of the bearing body is 50 to 2000 μm larger than the inner diameter of the housing.
mMold into small pieces. The inclination angle γ of the buffer protrusion 22 with respect to the tangential direction of the inner circumference is 5° to 60°, preferably 30° to 45°.
°. In addition, the thickness t of the buffer protrusion is 0.3 to 2111
Set to 111.

The shape of the buffer protrusion may be such that it is located on the outer periphery of the bearing 30 body and has an inverted trapezoidal cross section forming a groove, as shown in FIG. That is, a large number of buffer protrusions 31, 31...31 having an inverted trapezoidal cross section are formed on the outer periphery of the main body of the bearing 30. Enlarged outer peripheral portion 31a of
deforms elastically to absorb deformation of the bearing body during fitting.

Now, the outer shape including the buffer protrusion 31 of the bearing is D2 (radius γ2
), the diameter of the outer peripheral surface of the bearing body is Dl, the diameter of the internal sliding surface that engages with the rotating shaft is d (radius γ1), and the buffer protrusion 31
The protrusion length in the radial direction is t, and the protrusion length t is 1 of the outer shape.
It is set in the range of ~30%, and 5 to 20% is particularly good.

Also, the area of the bearing holding hole in the housing that contacts the bearing is S. If the surface area of the internal layer moving part is 81 and J”, then 3
=ax3. Here, the range of a is γ 1 γ 1 In particular, γ 1 γ 1 Next, specific examples will be described.

First, ultra-high molecular weight polyethylene (manufactured by Mitsubishi Petrochemical Industries) having an intermolecular molecular weight of 3,000,000 was put into the hopper 4 of the injection molding machine according to the present invention, and the INl'l supply amount adjusting slits 1 to 10a at the bottom of the popper were fully opened. Here the diameter of the screw is 25m
The total compression ratio was 11111, the ratio L/D between the length L of the screw and its diameter was 20, and the rotational speed of the screw was i s o rpm. In addition, the temperature of the nozzle part 2c (open nozzle) of the cylinder is 220°C, the temperature of the compression ratio 2b is 170°C, and the temperature of the feeder 2a is 70°C to 100°C when measured during molding without heating. It is clear that In addition, Popper 4 has 1. O,fl
Nitrogen gas was introduced at a rate of 1/min.

On the other hand, the temperature of the molds 6a and 6b was set at 100° C., and the pressure in the cavity was reduced to 0.5 atm. A mold is formed for manufacturing the bearing shown in Fig. 6, and the outer diameter of the molded product bearing [) = 9 + a
m, main body outer diameter [)1=7m111. Inner sliding phase (7)
The diameter d = 411un, the number of buffer protrusions n-32,
Molding was performed using a two-point gate (gate diameter 0.4 mm).

Further, the molding conditions were as follows: injection time: 1.5 seconds, holding pressure time: 5 seconds, cooling time: 15 seconds, interval: 3 seconds, and total cycle: 24.5 seconds.

When we compared the inner diameter of the surrounding inner peripheral surface of the bearing thus obtained before and after mounting it on the housing, we found that there was almost no change.

〔effect〕

As explained above, according to the injection molding method for a bearing according to the present invention, ultra-high molecular weight polyethylene is instantly melted,
Since this molten raw material is immediately injected into the cavity, a high precision bearing can be manufactured easily. Since the obtained bearing has self-lubricating properties, it does not require lubrication and can be used in a vacuum or underwater.

In addition, according to the shape of the bearing according to the present invention, there is no influence on the inner circumferential surface of the bearing caused by the buffer projection on the outer circumference of the bearing and the interference between the bearing holding part of the rehousing and the outer diameter of the bearing. This has the effect that the precision of use is reduced to the precision of the molded product itself, making it possible to obtain a bearing with high viscosity.

[Brief explanation of drawings]

Fig. 1 is a longitudinal cross-sectional view of an injection molding machine according to the present invention, Fig. 2 is a plan view of a cavity in the mold, Fig. 3 is a longitudinal cross-sectional view of the mold, and Fig. 4 is a cross-sectional view of the mold. , FIG. 5, and FIG. 6 are a quarter-half plan view and an overall plan view of the bearing, which is a molded product. 1...Screw, 2...Cylinder, 2a...
Feeder part, 2b... compression part, 2C... nozzle part,
3... Ultra-high molecular weight polyethylene raw material, 4... Hopper, 5... Cavity, 6... Mold, 15... Vacuum path, 16... Hole, 22.31... Buffer protrusion . Figure 2 Figure O

Claims (1)

[Claims] 1. It has a sliding inner circumferential surface that slidably holds the rotating shaft, and the outer circumferential surface of the bearing body is elastically deformed when the bearing is inserted into the bearing holding part of the housing. 1. An injection molded bearing characterized in that the buffer portion is formed by injecting high molecular weight polyethylene. 2. The injection molded bearing according to claim 1, wherein the buffer portion comprises a plurality of buffer protrusions inclined at a predetermined angle with respect to a tangent to the outer circumferential surface of the bearing body. 3. The injection molded bearing according to claim 1, wherein the buffer portion is formed of a plurality of buffer protrusions having an inverted trapezoidal cross section formed on the outer periphery of the bearing body. 4. Powdered ultra-high molecular weight polyethylene raw material is supplied to an injection cylinder in a non-oxidizing atmosphere, the compression ratio of the screw of the injection cylinder is set to 1.3 to 2.0, and the length to diameter ratio is set to 15 to 2.0. 20 to melt it in a short time,
A bearing injection molding method characterized in that this raw material is injected into a mold cavity before heating crosslinking begins.