JPH0720646B2 - Hollow body manufacturing method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for molding a hollow body. More specifically, it relates to a method for molding a multidimensional hollow body by an injection molding method.

[Prior Art] As a processing technology for making hollow products typified by bottles and cans made of synthetic resin, blow is performed by blowing air into a hollow parison (with or without a bottom) in a mold. A molding method (extrusion blow molding method, injection blow molding method, stretch blow molding method) is known.

Further, with the development of a multipurpose blow molding machine having an approximate mold tilting mechanism and a mold swinging device, three-dimensional shaped industrial parts have also been molded. Furthermore, a powder molding method mainly for large containers has been established.

However, in all of the methods for processing these hollow bodies, since the mold is a single-sided mold (only on the cavity side), problems remain in wall thickness accuracy, surface finish accuracy, dimensional accuracy, and the like. In terms of materials used, there are many problems such as restrictions on the properties of the material such as flow characteristics and melt elasticity, and especially for engineering plastics, many restrictions.

Gas-assisted injection molding has been developed as a method for molding hollow bodies by injection molding. However, the molding method is a technique developed mainly for the purpose of preventing sink marks and warpage of the thick portion of the hollow product. Therefore, it is used in products that do not require special specifications for the hollow part itself, and all products whose main purpose is to mold a specific hollow part are only in the trial production stage.

On the other hand, the extrusion molding method has a problem that the hollow body to be molded is limited to a linear body. As a result of intensive studies and research to solve the above problems, the present inventor has completed a manufacturing method for producing a multidimensional hollow body having an extremely smooth surface state by using an injection molding machine.

[Problems to be Solved by the Invention] The present invention is not limited by the resin to be used, and has a uniform hollow portion size, and the inner surface of the hollow portion and the outer surface of the molded body have a very smooth surface state and have many complicated shapes. The purpose is to produce a dimensional hollow product using an injection molding machine.

[Means for Solving the Problem] The method for producing a hollow body of the present invention has a mold which has a pressure port and a discharge port and corresponds to the outer shape of the hollow body when the hollow body is produced by an injection molding method. A molten thermoplastic resin in an amount larger than the required amount of the hollow body is injected into the cavity, and then a floating core having a size capable of passing through the mold cavity is pushed by a pressurized fluid from a pressure port of the mold cavity. Meanwhile, the molten resin injected into the mold cavity is advanced along the mold cavity to the discharge port, and the pressure of the pressurized fluid is maintained until the entire molten resin is solidified in the mold cavity. There is.

[Operation] A floating core (with a spherical shape) is installed in advance at one end in the mold cavity, and the amount of molten resin slightly larger than the hollow product required in the direction of pressing the floating core Inject by shot method.

Then, while the center portion of the injected molten resin is in a molten state, the pressurized fluid pushes the floating core.
Then, the floating core moves to the discharge port at the other end of the mold cavity while pushing out the molten central portion having a relatively low viscosity and pressing the molten resin against the inner surface of the mold cavity. As a result, a hollow body having a uniform hollow portion size and a smooth inner surface is produced. This manufacturing method is
This is an epoch-making manufacturing method that can make not only a simple U-shape but also a cross-shaped hollow body in one step.

Also, the extra resin pushed out by the floating core is reused with sprues and runners, so
No resin loss occurs.

[Example] As a specific example, a long pipe product having a complicated bend will be described below. Such pipe products are used, for example, for passing various fluids in engine rooms such as automobiles.

1 is a partially cutaway perspective view showing an embodiment of a mold for molding a pipe product by the manufacturing method of the present invention, and FIG. 2 is an explanatory view of a molding process using the mold of FIG. FIG. 3 is a partially cutaway perspective view of a pipe product manufactured by the manufacturing method of the present invention, and FIGS. 4 to 5 are partially cutaway perspective views showing other examples of hollow bodies manufactured by the manufacturing method of the present invention. It is a figure.

In FIG. 1, the mold (1) is composed of an upper mold (1a) and a lower mold (1b). A mold cavity (2) that matches the shape of the pipe product is formed on the mating surfaces of the upper mold (1a) and the lower mold (1b). The upper mold (1a) has an injection injection port (3) selected by a usual method. A pressure port (4) communicating with the outside is formed at one end of the mold cavity (2), and a discharge port (5) communicating with the outside is formed at the other end.

A spherical floating core (6) having a diameter smaller than the inner diameter of the mold cavity is movably arranged in the pressure port (4). An orifice (hereinafter referred to as a core stopper) (7) having an inner diameter smaller than the diameter of the floating core (6) is formed in the discharge port (5).

Next, the manufacturing process will be described with reference to FIGS.

Molten resin (8), which is slightly larger than the required amount of the hollow product, is injected from the injection port (3) into the mold cavity (2) by the short shot method or the full shot method (see FIG. 1).

The molten resin (8) is not particularly limited as long as it is a thermoplastic resin used in general injection molding, and for example, a thermoplastic resin such as polyethylene or polypropylene is used. Engineering plastics such as polycarbonate and polyacetal can also be used because they have no restrictions on fluidity or melt elasticity.

The filling pressure of the molten resin (8) is appropriately set according to the molten resin to be used, but when the ABS resin is filled by an injection molding machine, it is generally performed in the range of 50 to 100 kg / cm ² .

When the molten resin (8) is filled, the floating core (6) is then pushed into the molten resin (8) by the pressurized fluid (9) from the pressure port (4).
Then, as shown in FIG. 2, the floating core (6) moves along the central portion of the resin (8) which is still in a molten state, that is, the portion having a relatively low viscosity and toward the discharge port (5). . At that time, the floating core (6) pushes the molten resin in front of the floating core against the inner surface of the mold cavity (2) while pushing out the remaining molten resin from the discharge port (5). Therefore, after the floating core (6) has passed through the central portion, a resin having a uniform thickness remains on the inner surface of the mold cavity (2), and a hollow portion (a hollow portion or a cavity portion having an inner diameter substantially equal to the diameter of the floating core (6)). (Also referred to as a penetrating portion) (10) is sequentially formed.

Since the floating core moves along the mold cavity (2) in this way, a good hollow portion is formed even in a complicated multidimensional shape.

The shape of the floating core (6) may be, for example, a conical shape, a shell shape or a hemispherical shape when forming a cavity having a circular cross section like the pipe product of this embodiment,
Spheres are particularly preferred for forming multidimensional shapes.

The material of the floating core (6) may be any material that is hard and has heat resistance, such as copper, brass, stainless steel, iron and aluminum.

The pressurized fluid (9) is not particularly limited as long as it is clean and has an appropriate temperature, and for example, gas such as air and nitrogen gas, and liquid such as water and oil are used. An inert gas such as nitrogen gas is particularly preferable because it is pressed into a high temperature and high pressure environment.

When the pressurized fluid (9) is added, the molten resin (8) in the mold cavity (2) should have a certain viscosity difference between the surface and the interior of the floating core (6). It is preferable to control the temperature distribution in order to obtain a desired hollow portion.

The pressure of the pressurized fluid (9) may be appropriately selected depending on the shape of the molded product, the resin used, and the temperature control method.

When the floating core (6) reaches the discharge port (5), it comes into close contact with the core stopper (7), and the hollow portion (10) is almost sealed while being pressurized from the inside. The pipe product (11) is manufactured by cooling the resin in that state (see FIG. 3). Since the resin is pressed against the mold cavity (2) by applying pressure from the hollow portion, the surface condition of the finished product is smooth and there is no sink or warp.

Since the resin extruded by the floating core (6) is accumulated in the storage tank (12) provided at the discharge port (5) and then reused as a material for the product together with the sprue and runner, there is no material loss.

Further, by changing the diameter of the floating core (6) with respect to the inner diameter of the mold cavity (2), a pipe product having a desired wall thickness can be obtained.

In this example, the case of manufacturing a bent pipe product was illustrated, but the manufacturing method of the present invention is not limited to this, and it is possible to change the shape of the mold cavity and the floating core, respectively. For example, the hollow body (21) shown in FIG. 4 has a hollow section (22) having a rectangular cross section, or the hollow body (23) shown in FIG. 5 has a hollow section (24) having a triangular cross section. A hollow body having a desired cross-sectional shape, such as that shown, can be manufactured. Furthermore, a hollow body or a spiral-shaped hollow body in which the hollow portion crosses three-dimensionally,
It is also possible to manufacture multidimensional hollow bodies of other shapes. In that case, a plurality of pressurizing ports (4) and discharge ports (5) may be provided, respectively, if necessary.

According to the manufacturing method of the present invention, the hollow portion formed in one portion, which cannot be achieved by the blow molding method, and the same or more meat as in the case of general injection molding formed in the other portion. Since it is possible to coexist with a portion having a thickness, it is possible to simultaneously integrally form a protrusion such as a bracket or a rib on the outer peripheral portion of the product other than the parting line.

Examples of products that can be manufactured by the manufacturing method of the present invention include various pipes for water and sewerage, pipes and ducts used in automobiles, air conditioners, various vending machines, and pure water pipes for IC production. There are shower handles, hollow handles, and parts that require partial reinforcement on the outer circumference, such as shelves and cases.

[Effects of the Invention] The manufacturing method of the present invention allows a good hollow portion to be formed even though it is injection-molded by allowing the resin to penetrate through the floating core, and has the following effects. is there.

The shape and size of the hollow part of the hollow body can be easily changed, there is no restriction on the resin used as the material of the hollow body, there are no sink marks or warps, and the shape of the hollow part is uniform with a smooth outer surface condition. , Product thickness, and smooth inner surface of the hollow part can be easily obtained, and protrusions and spiral shapes integrally formed on the outer peripheral part of the hollow body,
High degree of freedom in terms of design because it is easy to obtain a multi-dimensional hollow body such as a shape in which the hollow portions intersect. It is easy to manufacture hollow body products with different hollow thicknesses because the shape and dimensions of the hollow portion are constant. It has the effect of being capable.

[Brief description of drawings]

1 is a partially cutaway perspective view showing an embodiment of a mold for manufacturing a pipe product by the manufacturing method of the present invention, and FIG. 2 is an explanatory view of a molding process using the mold of FIG. 1, FIG. 3 is a partially cutaway perspective view of a pipe product manufactured by the manufacturing method of the present invention, and FIGS. 4 to 5 are partially cutaway perspective views showing other examples of hollow bodies manufactured by the manufacturing method of the present invention. It is a figure. (Main symbols in the drawing) (2): Mold cavity (4): Pressurization port (5): Discharge port (6): Floating core (8): Molten resin (9): Pressurized fluid (10), (22 ), (24): Hollow part (11): Pipe product (21), (23): Hollow body

Claims (1)

[Claims] 1. When manufacturing a hollow body by an injection molding method, the amount of the hollow body is larger than a required amount inside a mold cavity having a pressure port and a discharge port and corresponding to the outer shape of the hollow body. A quantity of molten thermoplastic resin is injected, and then a floating core of a size that can pass through the mold cavity is pushed by a pressurized fluid from a pressure port of the cavity, and the molten resin injected into the mold cavity is filled with the molten resin. A method for producing a hollow body, which proceeds to a discharge port along a mold cavity, and maintains the pressure of a pressurized fluid until the entire molten resin is solidified in the mold cavity.