JPH0835001A - Method for injection molding large-sized articles - Google Patents

Abstract

PURPOSE:To enable production of large-sized articles with a small-sized injection molding machine by packing pellets of a plasticized state dividedly twice into metal molds of a socket and spigot system set with parting lines apart from each other. CONSTITUTION:The upper metal mold 20 and lower metal mold 22 of the metal molds 18 are held in positions where the molds are fitted to each other by the socket and spigot system in the state of slightly parting the parting lines of the metal molds from each other. The pellets formed by pelletizing ceramics and metallic powder with an agar binder are packed into a hopper 2. The inside of the heating barrel of the injection molding machine 10 is set at the softening temp. of the agar binder. While the pellets are plasticized, the pellet melt of the amt. smaller than the prescribed amt. are injected into the cavity of the metal molds 18. The metal molds 18 are clamped and while the metal molds 18 are cooled, the melt is injected under pressurization and is filled into the remaining gaps of the cavity of the metal molds 18.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a molding method for making a large-sized sintered part by injection molding of ceramic or metal powder.

[0002]

2. Description of the Related Art In the injection molding method of ceramics and metal powders, in the conventional injection molding using a plastic binder, degreasing in the subsequent step becomes an obstacle, and a large part, for example, having a thickness of about 5 mm or more, or weighing 50 g. It is said that molding of parts such as the above is very difficult, and in some cases even impossible. However, the agar binder previously disclosed by the same applicant as the applicant of the present application
According to the injection molding method according to JP-A-4-88101, JP-A-4-337002, and US Pat. No. 5,258,155, such degreasing in the subsequent step does not pose a problem.
That is, the agar used for the agar binder is a natural polysaccharide extracted from seaweed typified by agar, 92 to 9
Dissolves in water at 6 ° C and turns into a sol state, 37-42 ° C
It has the property of exhibiting a reversible sol-gel reaction that solidifies into an elastic gel state. By using this agar as a binder for injection molding of ceramics and metal powders,
Pellets obtained by homogeneously kneading ceramic or metal powder and agar binder exhibit fluidity when heated and solidify when cooled, so that powder injection molding is possible like conventional plastic binders.

The agar binder contains 80% in the binder.
Contains ~ 85 WT% water. Therefore, when heated under mild heating conditions, the agar binder evaporates water up to 100 ° C and becomes a porous spongy body with high porosity. Sintering of non-oxide ceramics and metal powders is often performed under vacuum, but under such vacuum the boiling point of water drops to 60-70 ° C, at which temperature the agar softens. By the very weak force, the hydrogen ion bond releases the water bonded to the network structure and becomes porous.

When the agar is further heated after the water has completely evaporated, the agar starts to undergo a condensation reaction while browning, and as is clear from the chemical structural formula of the polysaccharide which is the main component of the agar,
A large number of (-H) ions and (-OH) ions are H.
₂ O, then the oxygen atoms connecting the 6-membered ring structure react with the carbon atoms of the 6-membered ring structure to form CO ₂ gas,
Evaporate through the previously formed pores. This reaction is 27
Finish at 0-280 ° C.

Paraffin waxes, which are contained in a plastic binder in an amount of 10 to 15%, are heated to a molten state, exude out of the molded body, and are thermally decomposed and gasified. At this time, the thermoplastic plastic contained in the plastic binder is softened, and when heated rapidly, the paraffin wax gasifies and foams the plastic before bleeding out of the molded body, cracking the molded body, It will be deformed or expanded. In order to obtain the desired porous state, the rate of temperature rise must be slower than the aforementioned evaporation of water. Further, the paraffin wax containing only 10 to 15% has a larger molecular weight that must be thermally decomposed than the water containing 80 to 85%, and it takes a long time.

After the paraffin wax is completely gasified, the thermoplastic is pyrolyzed to hydrocarbon monomers or oligomers, but unless extremely mild heating conditions cause foaming and gas entrapment, similar to paraffin wax. It causes cracking, deformation and expansion. Furthermore, the reaction ends at elevated temperatures of 400-500 ° C.

From the above, a molded body using an agar binder does not crack, deform or expand even when directly placed in a sintering furnace and heated, and a degreasing step is not required, but a molded body of a plastic binder does not contain a binder. It requires a long degreasing step to decompose.

However, such ceramic or metal powder injection molding method is basically an application of the plastic injection molding technique, and the injection capacity of the ceramic or metal powder using an agar binder is increased. It is considered that a large-sized injection molding machine having a large mold clamping force and a large injection capacity should be used when molding a large-sized large component.

[0009]

Therefore, if a large component having a large injection capacity is to be molded by the ceramic or metal powder injection molding method, as a matter of course, the apparatus to be used becomes expensive and the installation is required. There is a problem that the area becomes large. In addition, in recent years, the trend of high-mix low-volume production of products has been increasing more and more, and there is also a problem that the depreciation cost of the molding machine increases and the cost of the product increases for large-scale products with a small production quantity per lot. are doing.

Therefore, when it becomes possible to manufacture a large-sized part by the injection molding method of ceramics or metal powders, the mechanical characteristic value is remarkably improved as compared with the large-sized part by the conventional sintering method, and the selection of the material is made. Although the advantage of widening is known, the above-mentioned problems greatly hinder the production of large parts by injection molding of ceramics and metal powders, which has not been widely implemented. is there. The present invention solves such a problem.

[0011]

The present invention improves a ready-made small injection molding machine, and by improving the molding method, a large-sized part can be manufactured by using the small injection molding machine used so far. Made it possible to mold. More specifically, in order to reduce the production cost of large parts, a pair of molds are placed apart by the spigot method, and the molds are pelletized with an agar binder. While holding the above, while injecting the pellet melt into the mold cavity while plasticizing the pellets, the mold melt is clamped and the mold cavity is cooled. Then, pressure injection molding is performed until the cavities are completely filled.

[0012]

[Function] In the mold of the spigot system set apart from the parting line, the ceramic and metal powder pelletized with the agar binder are in a plasticized state, and initially, a pellet having a volume smaller than the predetermined amount is pushed, After the mold is clamped, the pellets are pressure-injected while cooling the mold until the remaining voids are filled to mold large parts.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGS. 1 and 2, 3 and 4, 5 and 6
Are the first to the third when carrying out the method of the present invention.
The state of the apparatus in the process of is shown. In the figure, an injection molding machine 10 known per se has a hopper 12, and pellets supplied from the hopper 12 are supplied by a screw 14 into a mold 18 through an injection nozzle 16. The mold 18 is composed of an upper mold 20 and a lower mold 22.

In the first step, which is the preparatory step shown in FIGS. 1 and 2, the heater temperature in the heating cylinder of the injection molding machine 10 is set to 94 ° C. to 96 ° C. which is the softening temperature of the agar binder. On the other hand, the hopper 12 is previously filled with pellets obtained by pelletizing ceramic and metal powders with an agar binder. In addition, a heating medium circulation pipe (not shown) provided inside the upper mold 20 and the lower mold 22
A heating medium at 0 ° C to 70 ° C is flown, and the temperature of these molds is preferably maintained at 50 ° C or higher.
Further, as shown in FIG. 2, the mold 18 has a mold clamping position detection sensor (not shown) set so that the parting lines of the upper mold 20 and the lower mold 22 are located at some distances from each other. I'll do it. As a result, the volume of the injection molding portion inside the mold 18, that is, the cavity 24 is finally maintained in a state of being larger than the volume of the intended injection molded product. Therefore, the mold 18 is held at a position where the upper and lower molds 20 and 22 are fitted to each other by a so-called spigot system.

In the second step, which is the continuous plasticizing and filling step shown in FIGS. 3 and 4, the filling nozzle 16 of the injection molding machine 10 is pressed against the mold 18, and the ceramics and the metal charged in the hopper 12 are charged. The pellets obtained by pelletizing the powder with an agar binder are continuously plasticized by the screw 14 and supplied into the cavity 24. The continuous plasticizing filling amount at this time is the upper and lower molds 20 and 2 shown in FIG.
The amount is such that the inside of the cavity 24 is completely filled as shown in FIG. 6 when 2 is pushed down and clamped as shown in FIG. Therefore, the amount of plasticization is controlled by the relationship between the size of the screw 14, the number of rotations, and the time.
This means that in the conventional injection molding method, the pellets are plasticized, the screw is lowered backward while calculating the required amount, and after the weighing is finished, the injection pressure is applied to the plasticized pellets inside the cavity 24 at once. To push
In the case of a molded product with a large cavity 24 volume, a large injection molding machine with a large mold clamping pressure was required,
It's a completely different place.

Next, in the third step, which is the mold clamping step shown in FIGS. 5 and 6, the mold clamping is performed so that the parting lines of the upper and lower molds 20 and 22 are aligned with each other. This time
It is desirable to further inject a small amount of plasticized pellets to apply injection pressure inside the cavity 24 shown in FIG. In addition, when the molded product is an extremely large article or an article having a complicated shape, in the initial injection step, a pellet melt having a capacity smaller than the cavity capacity of the mold is injected, and the mold is clamped, A two-stage injection and filling process is required in which the pellet melt is finally injected to completely fill the remaining cavitating space while cooling the mold. In some cases, in the initial injection step, a pellet melt having a capacity smaller than the cavity capacity of the mold is injected, the mold is clamped, the mold is cooled, and then the mold is reused. In some cases, it is effective to inject the pellet melt into the remaining space of the cavitation and perform mold clamping again so that the melt can reach the end of the cavitation. After the melt reaches the end of the cavity, cooling water is circulated through a cooling medium circulation pipe (not shown) provided inside the molds 20 and 22 to apply a holding pressure to eliminate the sink mark of the molded product. While cooling, the mold temperature is cooled until the solidification temperature of the pellets made of the agar binder falls below 40 ° C to 42 ° C. When the finished product is completely cooled, the mold is opened and the finished product is ejected and pushed up with a pin to take it out. The finished product molded in this way is then sintered by known means. In this way, by utilizing the characteristics of the agar binder having a very large temperature difference between the softening temperature (94 to 96 ° C) and the solidifying temperature (40 to 42 ° C or less), the injection capacity can be reduced by a small injection molding machine. It is possible to mold large parts.

[0017]

EFFECTS OF THE INVENTION Since a component having a large injection capacity can be molded by a small injection molding machine, the cost of purchasing the machine is low and the installation place of the molding machine may be small.

[Brief description of drawings]

FIG. 1 is an explanatory view of an injection molding machine showing a process before a mold is attached to an injection molding machine and a molded product is molded.

FIG. 2 is a diagram showing a fitted state of a mold when the injection molding machine is in the state of FIG.

FIG. 3 is an explanatory view of the injection molding machine in a continuous plasticizing and filling step.

FIG. 4 is a view showing a fitted state of a mold when the injection molding machine is in the state of FIG.

FIG. 5 is an explanatory view of the injection molding machine in a mold clamping step after filling.

FIG. 6 is a view showing a fitted state of a mold when the injection molding machine is in the state of FIG.

[Explanation of symbols]

10: Injection molding machine 12: Hopper 14: Screw 16: Nozzle 18: Mold 20: Upper mold 22: Lower mold 24: Cavity

Claims (2)

[Claims] 1. A pair of inlay-type molds are installed with a separating distance of a predetermined distance, the molds are maintained at a temperature above the plasticizing temperature of ceramic and metal powder pelletized with an agar binder, and pellets. A large-sized machine consisting of injecting a predetermined amount of melt into the cavity of the mold while plasticizing the mold, cooling while clamping the mold, and injecting the melt into the mold under pressure as necessary. A method of injection molding an article. 2. A pair of metal molds of inlay type are installed with a separating distance of a predetermined distance, the metal molds are held at a temperature above the plasticizing temperature of ceramic and metal powder pelletized with an agar binder, and pellets. Injecting a melt with a volume smaller than a predetermined amount into the cavity of the mold while plasticizing the mold, and then cooling the mold while clamping the mold, the cavity is completely filled in the remaining cavity. Pressurizing the melt until it is full,
A method of injection molding a large article consisting of.