JP2001049274A - Grease for ball screw in driving device of motor-driven injection molding machine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lubricating grease which prevents premature failure of ball screws to be used in the driving system of a motor-driven injection molding machine. SOLUTION: In the driving system of a motor-driven injection molding machine, a grease composed of a urea based substance as the thickening agent and a mineral oil or a synthetic oil having a base oil viscosity (40 deg.C) of 300 mm2/s as the base oil is used as the ball screw lubricant, and the incorporation consistency of this grease is rendered not less than 300. This grease is particularly applied to the balls constituting ball screws which have a ball diameter of not smaller than 5/8 in.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to grease for a ball screw used in a drive system of an electric injection molding machine.

[0002]

2. Description of the Related Art As shown in FIG. 2, for example, a ball screw has a screw groove a of a ball screw shaft A and a screw groove b of a ball nut B.
Are formed by arranging balls c for rolling bearings in a coil-shaped space formed by opposing them. The ball c protruding from one end of the ball nut B passes through a return tube d in the main body of the ball nut B or a hole (not shown) as shown in FIG. And is returned to one end of the ball nut B again through the coiled space. Due to such a structure, the coefficient of friction is extremely small as compared with a general sliding contact screw, and the screw has high efficiency. In FIG. 2, e is a return tube holder for fixing the return tube d to the ball nut B main body, f is a shim plate for adjusting the interval between the ball nuts B, and g is a labyrinth seal provided at one end of the ball nut B. , H are keys for positioning the ball nuts B together.

A ball screw used in an injection molding machine is conventionally used under a higher load than a machine tool or the like which is used for a high load, has a high rotation speed, and frequently repeats forward and reverse rotations. For this reason, there is a problem that the balls are damaged due to interference between the balls, and as a result, the screw shaft is damaged.

Heretofore, commercially available lithium-based grease for high-load applications has been used for lubricating ball screws for injection molding machines used under such high loads. These greases are generally used because the viscosity of the base oil is about 100 to 200 mm ² / s, the mixing consistency of the grease is around 300, and the retention of the grease in the nut is good. . Grease for lubrication has been improved in various ways for injection molding machines, but even the most durable grease can cause damage to the ball in a few hours in endurance tests, depending on use conditions. I'm checking. This is less than one thousandth of the life expectancy according to the prior art. This phenomenon is caused by the fact that the diameter of the ball constituting the ball screw is 5/8 inch or more, and especially the maximum ball diameter currently used is 3/4.
This is remarkable in a ball screw using an inch.

[0005]

SUMMARY OF THE INVENTION In view of the above-mentioned problems of the prior art, an object of the present invention is to prevent early damage of a ball screw used in a drive system of an electric injection molding machine, and particularly to provide a novel lubricating grease. I do.

[0006]

In a drive system of an electric injection molding machine, as a lubricant for a ball screw, a urea thickener is used as a thickener, and a mineral oil having a base oil viscosity of 300 mm ² / s (40 ° C.) or more is used as a base oil. Grease composed of synthetic oil was used, and the mixing consistency of the grease was set to 300 or more. In the above, the base oil viscosity of the base oil is 400 to 500 mm ² /
s (40 ° C.). In the above, the mixing consistency of grease is 320 to 40
0. In the above, the ball diameter of the ball constituting the ball screw is 5/8 inch or more.

[0007]

FIG. 1 is a schematic view of an injection molding machine using a ball screw. In FIG. 1, reference numeral 11 denotes a heating cylinder, and an injection nozzle 11a is disposed at a front end (left side in the figure) of the heating cylinder 11. Heating cylinder 1
A screw 12 is provided inside 1 so as to be able to move forward and backward (moving in the left-right direction in the figure) and to be rotatable. The screw 12 has a screw head 12 at the front end.
a, and extends rearward (to the right in the drawing) in the heating cylinder 11, and a bearing box 13 is fixed to a rear end (to the right in the drawing). A spiral flight 12b is formed around the screw 12, and a groove 14 is formed between the flights 12b.

[0008] A resin supply port (not shown) is formed at a set location in the heating cylinder 11, and a hopper (not shown) is fixed to the resin supply port. When the screw 12 is located at the forefront (left side in the drawing) in the heating cylinder 11, the resin supply port is
4 is formed at a position corresponding to the rear end. Therefore,
When the screw 12 is rotated during the weighing process, the resin in the form of pellets is supplied to the screw 12 from the inside of the hopper, and the resin enters the heating cylinder 11 and the groove 14 is formed.
The screw 12 is moved backward and the screw 12 is retracted.

A heater (not shown) is provided around the heating cylinder 11 so that the heating cylinder 11 can be heated by the heater and the resin in the groove 14 can be melted. Therefore, the screw 12
When the screw is rotated backward by a predetermined amount (moved to the right in the figure), the screw head 12a is moved forward by 1 degree.
The molten resin for the shots accumulates.

Next, during the injection step, the screw 12
When the resin is moved forward (moved to the left in the figure) without rotating, the resin accumulated in front of the screw head 12a is injected from the injection nozzle 11a, and is filled in a cavity space of a mold (not shown). By the way, behind the heating cylinder 11, a drive unit 15 for rotating and moving the screw 12 forward and backward is provided. The driving unit 15 includes a frame 16,
A motor 17 for weighing is provided so as to be movable with respect to the motor, and a motor 18 for injection is fixed to the frame 16. The motor 18 for injection and the screw 12 are arranged on the same axis.

The frame 1 has the screw 1
2, a guide bar 19 extending parallel to the guide bar 1 is provided.
The metering motor 17 moves along 9. To this end, a support plate 20 is provided so as to be slidable with respect to the guide bar 19, and a weighing motor 17
Is attached. A drive pulley 22 is provided on an output shaft 21 of the weighing motor 17, and a driven pulley 24
Are fixed, and a timing belt 25 is stretched between the driving pulley 22 and the driven pulley 24.
The drive pulley 22, the driven pulley 24, and the timing belt 25 constitute transmission means for connecting the bearing box 13 and the weighing motor 17.

On the other hand, the injection motor 18 includes a stator 26 fixed to the frame 16 and the stator 2.
6, the rotor 27 is disposed on the inner peripheral side of the rotor 2.
7 is rotatably supported by the frame 16.
Therefore, the hollow rotor shaft 2 is attached to the rotor 27.
8 are fitted and fixed, and both ends of the rotor shaft 28 are supported on the frame 16 by bearings 29 and 30, respectively.

Further, bearings 31, 32 are provided in the bearing box 13, and the bearings 31, 3
2, the screw 12 and a ball screw shaft 33 as a transmission shaft are relatively rotatably connected to each other.
A ball nut 35 fixed to the ball screw shaft 33 via a load meter 34, and a screw portion 33a formed at a front portion of the ball screw shaft 33.
And are screwed together. In addition, the screw part 33a constitutes a movement direction conversion part that converts a rotational movement into a linear movement.

Accordingly, in the measuring step, when the measuring motor 17 is driven, the rotation of the measuring motor 17 is transmitted to the driving pulley 22, the timing belt 25, the box body 23 and the screw 12 in this order, and the screw 12 When rotated, the resin is transferred to the screw head 12a.
Is moved forward. In this case, since the screw 12 and the ball screw shaft 33 are relatively rotatably connected via the bearing box 13, the box body 23
Is not transmitted to the ball screw shaft 33, but the pressure of the resin in the heating cylinder 11 is transmitted to the ball screw shaft 33 via the bearing box 13. Therefore, the ball screw shaft 33 retreats while rotating, and accordingly, the screw 12 retreats. When the screw 12 is retracted, back pressure is applied to the screw 12 against the pressure of the resin.

On the other hand, in the injection motor 18, by supplying a current of a predetermined frequency to the stator 26, the screw 12 can be advanced without rotating. Therefore, the rotor shaft 28
An annular locking member 36 is fixed substantially at the center of the inner surface of the ball screw shaft. A spline 37 formed on the inner periphery of the locking member 36 and a spline 33b formed on the outer periphery of the rear half of the ball screw shaft 33 are engaged. I agree. The spline 33b
Thus, a rotation transmitting unit that transmits the rotation of the injection motor 18 is configured.

Accordingly, in the injection step, when the injection motor 18 is driven, the rotation of the injection motor 18 is transmitted to the rotor shaft 28, the locking member 36, and the ball screw shaft 33 in this order. And the ball nut 35
Is fixed to the frame 16, so that the ball screw shaft 3
3 advances while rotating, and advances the screw 12.
At this time, the radiation output applied to the timing belt 25 is transmitted to the load meter 34 via the bearing box 13 and detected by the load meter 34.

The ball screw shaft 33 moves back and forth by a stroke S in the axial direction.

As the grease for ball screw lubrication in the electric injection molding machine as described above, a urea-based thickener and a high-viscosity grease of mineral oil or synthetic oil as base oil are used. As the thickener, a urea-based one such as a diurea-based one or a triurea-based one having a small characteristic change up to 100 ° C. is selected. The base oil may be either mineral oil or synthetic oil.
Base oil viscosity of 300 mm ² / s or more is selected. In particular, the base oil has a base oil viscosity of 400 to 500 mm ² /
It is desirable to use s (40 ° C.). Further, it is desirable to adjust the mixing consistency of grease to be 300 or more, and particularly to adjust the mixing consistency to be 320 to 400. The extreme pressure additive is appropriately Mo, Z
An n, Cu, Ni, B type or the like is adopted.

The early damage of the ball screw adopted by the injection molding machine is caused not only by the small stroke reciprocation under a high load, which has been conventionally considered, but also by the self-weight of the large-diameter ball itself and its inertia. Various endurance tests by the inventor of the present invention have revealed that during the high-speed response operation peculiar to the molding machine, the balls do not roll well and are easily clogged, and the sliding of the balls strongly influences greatly. In the grease of the present invention, the urea-based strong holding film, commonly called a urea film, and the strong adhesion to the metal by the high-viscosity base oil cause lubrication between the balls at the time of interference between the balls during a high-speed rising operation. The membrane is held firmly,
It was found that lubrication was difficult to cut. Further, in the conventional grease, it is difficult for grease to enter into a relatively large-area contact portion between the large-diameter balls or between the large-diameter balls and the screw shaft or the nut groove, so that the lubrication is easily caused. However, by setting the mixing consistency to 320 to 400,
It was found that lubrication was difficult to cut.

[0020]

According to the present invention, by maintaining the lubricating film on the ball surface firmly during the high-speed response operation, the balls are prevented from directly contacting with each other, and the early galling damage unlike the conventional one is less likely to occur. , And the life can be predicted.

In fact, when a durability test was carried out on a molding machine under operating conditions assumed to be severe within the range of the specification of the molding machine, it was found that the conventional durable grease for injection molding machines (base oil viscosity 200 mm ² / s, (40 ° C)),
It was confirmed that the grease of the present invention had a durability of several hundred times or more, while the surface of the ball was scuffed in several hours at a penetration consistency of 300.

By using the grease of the present invention,
This makes it possible to improve the oil film retention during a high-speed response operation unique to an injection molding machine, particularly when a large-diameter ball (3/8 inch or more) is used.

[Brief description of the drawings]

FIG. 1 is a schematic view of an electric injection molding machine.

FIG. 2 is a perspective view of a known ball screw.

[Explanation of symbols]

 1 Tapered section 11 Heating cylinder 11a Injection nozzle 12 Screw 12a Screw head 12b Flight 13 Bearing box 14 Groove 15 Drive section 16 Frame 17 Metering motor 18 Injection motor 19 Guide bar 20 Support plate 21 Output shaft 22 Drive pulley 23 Box body 24 Driven pulley 25 Timing belt 26 Stator 27 Rotor 28 Rotor shaft 29 ・ 30 Bearing 31 ・ 32 Bearing 33 Ball screw shaft 33a Screw part 34 Load cell 35 Ball nut 36 Locking member 37 Spline

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Claims (4)

[Claims] 1. In a drive system of an electric injection molding machine, a lubricant for a ball screw is composed of a urea-based thickener and a mineral oil or a synthetic oil having a base oil viscosity of 300 mm ² / s (40 ° C.) or more as a base oil. Using grease, the mixing consistency of the grease is 3
A grease for a ball screw in a drive unit of an electric injection molding machine, wherein the grease is at least 00. 2. The base oil has a base oil viscosity of 400 to 500 mm.
^The grease for a ball screw in a drive unit for an electric injection molding machine according to claim 1, wherein the grease is ² / s (40 ° C). 3. The grease has a penetration consistency of 320-4.
The grease for a ball screw in the drive unit for an electric injection molding machine according to claim 1, wherein the grease is 00. 4. The grease for a ball screw in a drive unit for an electric injection molding machine according to claim 1, wherein the ball diameter of the ball constituting the ball screw is 5/8 inch or more.