JPH0210872B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention relates to a method for manufacturing a surface-hardened body that requires surface hardening treatment, such as a screw for an injection molding machine.

(Prior technology) There are an extremely large number of products that require surface hardening, such as screws in injection molding machines, and ceramic coatings are applied to the surface of the base material to prevent wear and corrosion of the base material. has been done.

The screw of an injection molding machine, which is a typical example of a case requiring surface hardening, has the necessary fatigue strength to sufficiently withstand the torsional stress during screw rotation and the compressive stress during injection, and is also wear resistant and corrosion resistant. It is necessary to select a material that satisfies conditions such as excellent quality. Therefore, conventionally, a screw made of special alloy steel such as chromium molybdenum steel is hardened and then hard chrome plated or electroless nickel plated.

However, injection molding of extremely abrasive and corrosive materials is increasing due to the expansion of the range of applications of plastic molded products, higher functionality through improved resins, and the development of composite materials containing inorganic materials. Therefore, in these cases, a more special alloy steel is used, or a screw whose surface is coated with ceramic is used.

(Problem to be solved by the invention) However, when special alloy steel is used, it is not only very expensive, but also does not completely prevent wear and corrosion, but only slightly extends the life of the screw. It was hot.

In the case of a screw coated with ceramic, more favorable results were obtained in terms of manufacturing cost and life than when using special alloy steel. However, the conventional manufacturing process for this type of ceramic coating product was as follows: base material processing → ceramic coating → firing → finishing processing → polishing. During finishing, the ceramic coating has a hardness of Hv1800.
The polishing process requires a grinding wheel with a cutting edge made of artificial diamond or natural diamond, which requires a great deal of time and effort, which has become a major problem.

(Means for Solving the Problems) The present invention has been made in view of the above circumstances, and its purpose is to provide a new method for easily manufacturing ceramic-coated hardened surfaces. The purpose is to provide a method.

The present invention for the above-mentioned purpose includes a step of processing a tempered base material to a size slightly smaller than the final finished size, a step of coating the surface of the base material with ceramic so that it is slightly larger than the final finished size, and a step of processing the base material after being coated to a size slightly larger than the final finished size. A process of pre-firing the ceramic particles so that they have an appropriate bonding strength, a process of processing the surface of the base material after the pre-baking to the final finished dimensions, and a process of main firing so that the ceramic particles have a strong bonding force. and a base material surface finishing step after main firing. In addition, there is a process in which the tempered base material is processed to a size slightly smaller than the final finished size, a process in which the surface of the base metal is coated with ceramic so that it is slightly larger than the final finished size, and a process in which the coated base material is coated with ceramic particles as appropriate. a step of pre-firing the surface of the base material after the pre-firing to the final finished dimensions; and a step of impregnating a chromium compound into the pores of the ceramic on the surface of the processed base material. This method is characterized by comprising a step of main firing so that the ceramic particles have strong bonding strength, and a step of finishing the surface of the base material after the main firing.

(effect) Let's talk about the action.

In the present invention using the above method, the ceramic layer is not processed to the final finished size in a completely sintered state that is difficult to process, nor is it in a brittle state that is simply dried after coating, but after pre-sintering in which the particles are properly bonded. Since the machining is carried out under low conditions, machining is easy and the coating layer does not peel off due to machining.

(Example) Preferred examples embodying the present invention will be described below in detail with reference to the drawings.

FIG. 1 is an explanatory cross-sectional view of an in-line screw type injection molding machine, in which a torpedo 3 is screwed onto the tip of the screw body 2a of the injection molding machine 1, and this groove is inserted into the groove 3a of the torpedo 3. A ring-shaped non-return valve 4 having a width narrower than 3a is loosely fitted, and a claw 4b of the non-return valve 4 extending toward the tip of the screw 2 is engaged with a corresponding recess 3b of the torpedo 3. , the check valve 4 is rotated together with the rotation of the screw.

The injection molding machine 1 melts and kneads the resin material inserted through the hopper 1a, and melts and kneads the resin material inserted into the screw body 2.
The concave structure 3a of the torpedo 3 is transferred by the rotation of a.
The molten resin passes through the gap between the outer circumferential surface and the inner circumferential surface of the check valve 4, and is accumulated in front of the screw 2.
When the is moved forward, the molten resin flows into the check valve 4.
is moved backward, and the end surface 4a of the check valve 4 comes into contact with the front end surface of the screw body 2a, closing the gap, preventing backflow of the molten resin, and injecting the molten resin from the nozzle 5. Furthermore, there is a small gap between the outer circumferential surface of the check valve 4 and the inner circumferential surface of the injection cylinder, which prevents the molten resin from flowing back.

2b is a thread on the screw body 2, and a gap between the threads 2b forms a transfer groove 2c for transferring the resin.

FIG. 2 is an enlarged sectional view showing the outer peripheral surface of the screw main body 2a. 6 is a ceramic layer coated on the outer peripheral surface of the screw body. This ceramic layer 6 is made by chamfering both end edges 2b and 2d of the screw thread 2b of the screw main body 2a with a radius of 0.2 mm or more, and applying silica-alumina-based ceramic to the outer peripheral surface by dipping, spraying, or brushing. Therefore, it is coated in a single layer or in multiple layers.

The screw main body 2a is made of tempered chromium molybdenum steel, and is made of tempered chromium molybdenum steel, which is
Processed to be 0.03~0.13mm smaller.

The screw 2 is coated with a ceramic coating as described above or by another method, and the screw size is slightly larger than the final finished size.

Next, the coated screw 2 was heated to 350°C.
Preliminary firing is performed at ~400℃ so that the particles are properly bonded (hardness Hv80~300).

In this pre-fired state, the ceramic layer is not completely fired and is not in a brittle state that has just been dried after coating, so it is not as hard as a diamond grinding stone, such as ordinary sandstone, granite, slate, or ash. Grinding can be done with natural whetstones or artificial whetstones using artificial abrasives.

Therefore, after pre-firing, it is processed to the final dimensions by grinding, and then the pores of the ceramic are impregnated with a chromium compound, and the main firing is performed at 450°C to 500°C to create a completely fired product (hardness Hv1000). ~
1800).

Note that since the pores cannot be completely filled with a single impregnation with a chromium compound, impregnation and firing were repeated 13 times in this example. This fills the pores in the ceramic layer and provides a denser coating layer.

For example, an aqueous solution of chromic acid is used to impregnate the chromium compound. By impregnating with this chromic acid aqueous solution, chromium oxide (CrO ₃ ) can be impregnated into the pores of the ceramic layer.

Note that depending on the application, the chromium compound impregnation step may be omitted.

Finally, if necessary, smooth the surface further,
Finished by polishing or wrapping to prevent resin from adhering.

In this embodiment, both end edges 2d, 2d of the thread 2b
The curved surface is formed with a radius of 0.2 mm or more to avoid sharp angles, and the thickness of the coating is set to 30 to 130 μm to prevent peeling and breakage caused by the brittleness of ceramic and the difference in thermal expansion coefficient. Can be done. Note that the thickness of the ceramic layer 6 is
The preferred thickness is about 60 μm.

On the other hand, the check valve 4 at the tip of the screw 2 rotates together with the rotation of the screw, which may cause galling or wear between the screw and the inner peripheral surface of the injection cylinder.
Therefore, it is also possible to chamfer both edges of the outer peripheral surface of the check valve 4 and apply a ceramic coating to the outer peripheral surface in the same manner as described above. This makes it possible to further improve the screw strength.

In the above embodiment, a screw head with a check valve is described, but even in the case of a straight type screw head, ceramic coating can be applied in the same manner as described above, and the same effects can be obtained.

(Effects of the Invention) According to the present invention related to the above-mentioned manufacturing method, it is possible to easily mold and manufacture a surface-hardened ceramic coating base material having excellent wear resistance and corrosion resistance, while also achieving high precision. It has remarkable effects such as reducing manufacturing costs and improving productivity.

[Brief explanation of drawings]

FIG. 1 is an explanatory sectional view of the injection molding machine, and FIG. 2 is a partial sectional view of the screw body. 1... Injection molding machine, 2... Screw, 2a...
Screw body, 2b...screw thread, 2c...transfer groove, 2d...end edge, 3...torpedo, 3a...
...Concave groove, 3b...Concave portion, 4...Return prevention valve, 4a
...End face, 4b...Claw, 5...Nozzle, 6...Ceramic layer.

Claims (1)

[Claims] 1. Processing the tempered base material to a size slightly smaller than the final finished size, coating the surface of the base material with ceramic so that the base material is slightly larger than the final finished size, and the coated base material. A process of pre-firing the ceramic particles so that they have an appropriate bonding strength, a process of processing the surface of the base material after the pre-baking to the final finished dimensions, and a process of main firing so that the ceramic particles have a strong bonding force. and a base material surface finishing step after main firing. 2. The method for manufacturing a surface hardened body such as a screw for an injection molding machine according to claim 1, wherein the base material surface finishing step is a polishing step. 3 Processing the tempered base material to a size slightly smaller than the final finished size, coating the surface of the base material with ceramic so that it is slightly larger than the final finished size, and coating the coated base material with appropriate ceramic particles. A step of pre-firing to have bonding strength, a step of processing the surface of the base material after the pre-firing to the final finished size, a step of impregnating a chromium compound into the ceramic pores on the surface of the processed base material, A method for producing a surface hardened body such as a screw for an injection molding machine, which comprises a process of main firing so that ceramic particles have strong bonding strength, and a step of finishing the surface of the base material after the main firing. 4. The method for manufacturing a surface hardened body such as a screw for an injection molding machine according to claim 3, wherein the base material surface finishing step is a polishing step.