JPS6250484A - Production of surface hardened body of screw or the like for injection molding machine - Google Patents

Abstract

PURPOSE:To easily produce a surface hardened body having high accuracy at a low cost by working a tempered base material, coating the surface thereof with ceramics, temporarily calcining the coating and subjecting the material to finished working to the final size then to normal calcining and surface finishing. CONSTITUTION:The tempered base material is worked to the size slightly smaller than the final finish size and thereafter the surface of the base material is coated with the ceramics to the size slightly larger than, the final finish size. The coated base material is temporarily calcined to the extent that the above-mentioned ceramic particles have suitable binding strength and thereafter the base material surface is worked to the final finish size. The base material is then immersed into a soln. of a chromic compd., etc., as necessary, to impregnate said compd. into the ceramic pores. The base material is subjected to the normal calcining to form the thoroughly calcined body securely bound with the ceramic particles; further the base material is subjected to surface finishing such as finishing by polishing. The surface hardened body of a screw for an injection molding machine, etc., is thus obtd.

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.

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

The screw of an injection molding machine, which is a typical example that requires surface hardening, has the necessary fatigue strength to withstand the torsional stress caused by one rotation of the slurry and the compressive stress during injection, as well as wear resistance and corrosion resistance. It is necessary to select a material that satisfies conditions such as excellent properties.

Therefore, conventionally, screws have been used that are made of special alloy steel such as chromium-molybdenum steel and then plated with hard chrome or electroless nickel.

However, as the range of applications for plastic molded products expands, injection molding of extremely abrasive and corrosive materials is increasing due to 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. Met.

In the case of the screw coated with ceramic, more favorable results were obtained in terms of manufacturing cost and life than when using the special alloy Ioka.

However, the conventional manufacturing process for this type of ceramic coating product is base material processing → ceramic coating - firing -
Because it was done using a procedure called finishing and polishing,
Machining cannot be performed immediately after coating, and the ceramic coating has a hardness of Hv1800 during finishing, which requires polishing using a grindstone with an artificial diamond or natural diamond cutting edge. Therefore, a large amount of time and effort is spent on processing, which is a big 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 the size 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 appropriate bonding strength, a process of processing the surface of the base material after the calcining to the final finished dimensions, and a process of immersing it in a compound solution as necessary. This method is characterized by a method for manufacturing a surface-hardened body such as an injection molding machine screw, which comprises a subsequent 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, processing to the final finished size is not performed in a completely sintered state where the ceramic layer is difficult to process.
Even if it is in a brittle state that has just been dried after coating, machining is easy because the particles are properly bonded after pre-calcination, and the coating layer will not peel off during processing (Example) Below, preferred embodiments embodying the present invention will be described 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 a screw body 2a of an injection molding machine 1, and a concave groove 3a of this torpedo 3 is attached.
A ring-shaped check valve 4 narrower than the groove 3a is loosely fitted into the groove 3a, and a claw 4b of the check valve 4 extends toward the tip of the screw 2, and a recess 3b of the torpedo 3 corresponding to the claw 4b.
The non-return valve 4 is rotated together with the rotation of the screw.

The injection molding machine 1 melts and kneads the resin material inserted from the hopper 1a, transfers it by rotation of the screw body 2a, and transfers the resin material to the outer peripheral surface of the concave groove 3a of the torpedo 3 and to the backflow prevention valve 4.
The molten resin passes through the gap with the inner circumferential surface and is stored in front of the screw 2. When the screw 2 is advanced forward, the molten resin causes the check valve 4 to retreat, and the end surface 4a of the check valve 4 closes to the screw body 2a. It comes into contact with the tip surface, closes the gap, prevents the molten resin from flowing back, and injects 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.

Reference numeral 2b denotes threads 1 of the screw body 2, and gaps between the threads 2b form transfer grooves 2c for transferring the resin.

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

The screw body 2a is made of tempered chromium molybdenum steel, which is 0.03 to 0.0
It has been processed to be 13mm smaller.

The screw 2 is coated with a ceramic coating as described above or by other methods, and is made to have dimensions slightly larger than the final finished dimensions.

Next, the coated screw 2 was heated to 350°C to 40°C.
Preliminary firing is performed at 0°C so that the particles are appropriately bonded (hardness: 11v80-300).

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 made of natural materials such as normal sandstone, granite, slate, and pseudostone, which are not as hard as diamond grindstones. Grinding can be done with a whetstone or an artificial whetstone using an artificial abrasive.

Therefore, it is processed to the final finished size by grinding under the condition after pre-firing, 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 make a completely fired body (hardness II ν 1000 ~1800).

In this example, the impregnation and firing were repeated 13 times since the pores could not be completely filled by impregnating with the chromium compound twice. This fills the pores in the ceramic layer,
A denser coating layer is obtained.

Finally, if necessary, polishing or lapping is performed to make the surface even smoother and to prevent resin from adhering to the surface.

In this example, both end edges 2d of the thread 2b are formed into curved surfaces with a radius of 0.2n+m or more so as not to form acute angles, and the thickness of the coating is set to 30 to 13 mm.
Since the thickness is 0 μm, it is possible to prevent peeling and damage caused by the brittleness of ceramics and the difference in coefficient of thermal expansion. In addition,
The thickness of the ceramic layer 6 is preferably 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 valve 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 embodiments, the case of a screw head with a check valve was described, but even in the case of a straight type screw head, a ceramic coating can be applied in the same manner as described above, and the same effects can be achieved.

(Effects of the Invention) According to the present invention related to the above manufacturing method, it is possible to easily mold and manufacture a surface-hardened product of a 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.

Although the present invention has been variously explained above with reference to preferred embodiments, the present invention is not limited to these embodiments, and it goes without saying that many modifications can be made without departing from the spirit of the invention. It is.

[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...thread, 2C...transfer groove, 2d...edge, 3...torpedo, 3
a...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 it is slightly larger than the final finished size, and the coated base material. A process of pre-sintering the material so that the ceramic particles have appropriate bonding strength, a process of processing the surface of the base material after the pre-sintering to the final finished size, and a process of immersing it in a compound solution as necessary. A method for manufacturing a surface-hardened body such as a screw for an injection molding machine, which comprises a step of main firing so that the ceramic particles have a strong bonding force after the final firing, and a step of finishing the surface of the base material after the main firing. 2. The method for manufacturing a surface hardened body such as an injection molding machine screw according to claim 1, wherein the impregnating step is a step of impregnating a chromium compound into the ceramic pores on the surface of the processed base material. 3. The method for manufacturing a surface hardened body such as a screw for an injection molding machine according to claim 1 or 2, wherein the base material surface finishing step is a polishing step.