JPH03210959A - Manufacture of ceramic-made female screw part - Google Patents

Abstract

PURPOSE:To form a female screw part, which intensely sticks to a casting base material and can surely prevent electrical corrosion with excellent corrosion resistance by inserting ceramic thermal sprayed layer, which is obtd. by dissolving and removing a steel-made screw with strong acid, as internal chill with molten metal for casting after forming the ceramic thermal sprayed layer on surface of the steel-made screw. CONSTITUTION:After degreasing and cleaning the surface of steel-made bolt B, by executing blast treatment, the surface is finely roughened and the ceramic thermal sprayed layer 1 is formed with a thermal spraying gun except both end parts thereof. In this case, as the ceramic thermal sprayed layer 1 is formed along male screw shape of a bolt B, the male screw-like ruggedness is formed on the outer circumference of ceramic thermal sprayed layer into chloric acid or nitric acid, only the steel-made bolt B is dissolved and removed, and only the ceramic thermal sprayed layer 1 is allowed to remain as sleeve-state and in this, a bolt B' is screwed and while preventing entering of the molten metal into the sleeve, this is inserted with the molten metal of Mg alloy or Al alloy in the mold 2 as internal chill and by removing the bolt B', the light alloy casting having ceramic-made female screw is manufactured.

Description

[Detailed Description of the Invention] Industrial Application Field This invention applies a ceramic spray layer transfer technology to
The present invention relates to a method for manufacturing a female thread in a cast product.

Conventional technology As a transfer technology for a ceramic sprayed layer, for example, Jitsuhei 1
-11962 and Japanese Patent Application Laid-open No. 63-306258 disclose that ceramic spraying or coating is applied to the surface of a sand core, etc., for the purpose of insulating the cylinder head or inner wall of the cylinder block of an engine. A transfer technique has been disclosed in which a ceramic layer formed on the surface of a child etc. is adhered to the base material side during casting. This transfer technology is also applied to metal-based materials. For example, in Japanese Patent Publication No. 64-5990, a thermal sprayed metal layer is formed on the surface of the core during casting in order to improve the sliding properties. A technique for transferring to the base material side is disclosed.

On the other hand, in automobile parts that use Mg alloys, such as disc wheels, if a solvent such as moisture is present in the area where the steel bolt or hub contacts the Mg alloy wheel body, the steel may Due to the difference in ionization tendency from the Mg alloy, a current flows locally and corrodes the M1 alloy side, which is likely to cause so-called electrolytic corrosion. Therefore, in order to prevent this electrolytic corrosion, the mesh side is plated to reduce the difference in ionization tendency from the base metal, or the bolts are fastened with insulating washers made of ceramic or the like interposed.

Problems to be Solved by the Invention However, the above-mentioned transfer of the ceramic layer to the cylinder head or cylinder block, etc., takes advantage of the surface roughness of the sprayed layer during ceramic spraying to transfer the molten metal (A7 alloy or Mg alloy).
This is a casting technique that takes advantage of the anchoring effect and wettability caused by slight penetration. Therefore, it cannot be said that the ceramic layer transferred by this conventional method has strong adhesion strength to the base material.For example, when this transfer technique is applied when a large force is applied to the interface between the metal base material and the ceramic layer, There is a risk that the ceramic layer may fall off.

Therefore, in such cases, there is a method of forming irregularities on the surface of the ceramic sprayed layer by machining etc. to prevent this falling off and strengthen the adhesive force with the base metal side, but the ceramic sprayed layer is hard. Therefore, machining is difficult, machining costs are excessive, and the overall cost of parts increases.

In addition, if prevention of electrolytic corrosion is a problem because bolts are fastened using a combination of dissimilar metals such as Mg alloy or A1 alloy and steel, a member made of ceramic or resin may be interposed in the contact area. There are ways to prevent corrosion, but when bolts are fastened, sufficient fastening strength cannot be obtained at that part. Further, even when a ceramic bulk, which is a rough shape material preformed into a cylindrical shape or the like according to the purpose of use, is press-fitted, it is necessary to machine a female thread into the hard ceramic material after press-fitting.

In this way, when replacing the female threaded part of Mg alloy or A1 alloy with a different material (ceramics, etc.), there are problems in terms of strength (peeling and falling off), as well as increased cost due to threading of the inner diameter. .

The present invention was made in view of the above circumstances, and an object of the present invention is to provide a method for easily and inexpensively manufacturing a durable ceramic female threaded portion.

Means for Solving the Problems As a means for solving the above-mentioned problems, the present invention provides a method for forming a female thread in a cast product by applying ceramic spraying to the surface of a male threaded member that is screwed into the female thread to be manufactured. a step of forming a sprayed layer with thread-like irregularities on the outside; a step of melting the male thread member to leave only the sprayed ceramic layer; and a step of casting the remaining sprayed ceramic layer. It is characterized by

When forming a female thread in a cast product, first, ceramics is sprayed on the outside so as to coat the surface of a male thread member such as a steel bolt that is screwed into the female thread to be manufactured. A sprayed layer having a thread-like uneven shape is formed to a predetermined thickness. Next, only the male threaded member is dissolved by a process such as immersing the male threaded member on the surface of which the sprayed layer has been formed in a chemical solution.

When melted, only a sleeve-shaped thermal sprayed layer with a female thread formed on the inside and a thread-like uneven shape on the outside remains. Then, after setting the remaining ceramic sprayed layer inside the mold to prevent molten metal from penetrating inside,
By pouring the metal and encasing it, a highly durable ceramic internal thread is formed in the cast product.

Embodiments Hereinafter, embodiments of the present invention will be described with reference to FIGS. 1 to 8.

First, a steel bolt B, which has been previously degreased and plastered, is rotatably supported in a predetermined position, and this bolt B is
While rotating, ceramic spraying is performed using a spray gun on all surfaces except both ends (see FIG. 2) to form a ceramic sprayed layer 1 having a thickness of 2 pupils or less (see FIG. 3). The bolt B used here has the same type of thread as the bolt B' that will be screwed into the female threaded portion to be manufactured. Moreover, since the ceramic sprayed layer 1 formed on the surface of the bolt B is formed along the male thread shape of the bolt B, the outer circumferential surface of the ceramic sprayed layer 1 is formed with male thread-like irregularities.

Next, the coated bolt B on which the ceramic sprayed layer 1 was formed,
When only the steel bolt B is melted by immersing it in hydrochloric acid or nitric acid (see Figure 4), only the ceramic sprayed layer 1 remains undissolved and remains in the form of a sleeve.
An internal thread is formed using the mold as a mold, and the outside is formed into an uneven shape along the shape of the internal thread (see Fig. 5).

After washing and drying, a bolt B' (a bolt with the same type of thread as the melted bolt B) is screwed into the sleeve-shaped ceramic sprayed layer 1 to prevent molten metal from penetrating inside the sleeve. After fixing the ceramic sprayed layer 1 with this bolt B' screwed in at a predetermined position in the cavity 3 of the mold 2, Mg alloy or A
Casting is performed by injecting a molten metal such as 1 alloy, and the ceramic sprayed layer 1 is cast into the product (see FIG. 7). At this time, since male thread-shaped unevenness is formed on the outside of the sleeve-shaped ceramic sprayed layer 1 along the uneven shape of the female thread,
Bonds strongly with molten metal.

Then, after removing it from the mold, bolt B was screwed in.
′ is removed, and an insulating material such as an asbestos plate with a thickness of about IM is attached to the part of the bolt B′ that becomes fastening dust, so that the ceramic coating is lifted from the surface of the base material when the bolt is fastened, and ceramic spraying is applied. The female threaded portion consisting of layers is completed.

Next, we will discuss Example 1 in which a female threaded portion was actually manufactured using the method of this example, and as a comparative example, a female threaded portion was actually manufactured using a ceramic bulk using a conventional method. This will be explained using an example.

[Example 1] A sprayed layer is formed on the surface of a Mlo steel bolt with a thread pitch of 1.5 mm and a length of 40 nm using a plasma spraying device using zirconia powder. The thermal spraying conditions at this time were a current of 500 A, a gas flow rate of nitrogen at 401/min, hydrogen at 7.5 A'/min, a powder supply rate of 90 g/min, and a spraying distance of 100 m. The surface of the bolt was coated with a ceramic sprayed layer.

Next, the head of the formed coated bolt was cut leaving one plate thick, and then immersed in hydrochloric acid to dissolve the bolt.

After screwing MIO bolts with a thread pitch of 1.5 mm and a length of 40 mm into the obtained sleeve-shaped ceramic sprayed layer, Mg alloy (Its MC-5; M9-0.
A test piece with a diameter of 20 mm and a length of 50 mm was cast using 1~G, 5Mn -9,9~10.7^Q) as if casting a ceramic sprayed layer.

Next, as Comparative Example 1, a ceramic bulk (using alumina) was cast with M and alloy in the same manner as in Example 1, and then female thread processing was performed to manufacture a test piece. A comparison was made.

First, connect both test pieces with a 5T bolt (M10 x 1.5
, a tightening torque of 270 to 420 kg-cm, and a standard tightening torque of 321.5 kg-cm), and repeated evaluations of loosening and tightening were performed 20 times. The tightening torque is 320 kg-
It was set to cn.

As a result, in the case of the test piece of Comparative Example 1, the ceramic bulk rotated together with the bolt in the second test, so the evaluation was discontinued. On the other hand, in the test piece of Example 1, no abnormality was observed until the 20th test was completed. This is considered to be because, in the case of the test piece of Example 1, the uneven outer periphery of the sleeve-shaped ceramic member forming the female threaded portion was strongly adhered to the base material.

[Example 2] Next, the thickness of the ceramic sprayed layer was set to 1m, 2m+, 3cm
, 4w were formed, and the same evaluation as in Example 1 was conducted.

As a result, when the thickness of the ceramic sprayed layer is 3 m,
The ceramic sprayed layer crumbled and adhered to the bolt side on the second time, and when the thickness was 4 mm, on the second time. This is because if the ceramic sprayed layer becomes too thick, the strength of the sprayed layer itself is low and cannot withstand the predetermined torque. On the other hand, when the thickness of the ceramic sprayed layer was set to 2 or less, no abnormality was observed until the end of 20 times. Therefore, the optimum thickness of the ceramic sprayed layer used for casting is 2 mm or less.

[Example 3] In addition, the test piece of Example 1 and a case where a female threaded portion was formed without forming any ceramic layer (Comparative Example 2) were screwed together with the same type of steel bolt. I compared it.

It was exposed for 240 hours (10 days) to a 25° C. atmosphere sprayed with 4% salt water at 95% humidity.

As a result, in the case of Comparative Example 2, significant corrosion (possibly due to electrolytic corrosion) was observed at the boundary between the steel bolt and the Mg alloy. On the other hand, in the case of Example 1,
Almost no corrosion was observed.

This is because in the case of Example 1, a ceramic layer exists around the threaded part of the steel bolt, and a ceramic layer and an asbestos plate are also provided in the fastening pressure part, and the steel bolt is made of an Mg alloy. It is thought that electrolytic corrosion was prevented because there was no contact with the base material at all.

Therefore, according to the method for manufacturing a ceramic female threaded portion of this embodiment, it is possible to form a bolt fastening portion for an Mg alloy or Aj alloy member that is durable and free from electrolytic corrosion. Further, the female thread portion can be formed at a lower cost than when the female thread portion is formed using ceramic bulk.

In this embodiment, the case where the base material is Mg alloy or A1 alloy has been described, but the same method can be applied to the case where the base material is other light alloy or casting metal.

DETAILED DESCRIPTION OF THE INVENTION As described in detail, the method of the present invention is a method for forming a female thread in a cast product by applying ceramic spraying to the surface of a male thread member that is screwed into the female thread to be manufactured, thereby forming a thread-like shape on the outside. The process involves forming a sprayed layer with unevenness, melting the external threaded part to leave only the ceramic sprayed layer, and casting the remaining ceramic sprayed layer, so that the base metal is strongly coated. It is possible to easily and inexpensively manufacture a female ceramic threaded portion that can be bonded, has durability, and reliably prevents electrolytic corrosion.

[Brief explanation of drawings]

Figures 1 to 8 show examples of the method of the present invention. Figure 1 is a process diagram showing the manufacturing process of a ceramic female threaded part, and Figure 2 is a process diagram for explaining the working method of the thermal spraying process. Figure 3 is a cross-sectional view of the covered bolt, Figure 4 is a schematic diagram for explaining the method of melting with an acid, and Figure 5 is a diagram of the sleeve-shaped ceramic sprayed layer after the bolt has been melted. 6 is a sectional view showing a state in which a bolt for preventing molten metal adhesion is screwed into a sleeve-shaped ceramic sprayed layer, FIG. 7 is a schematic diagram for explaining the pouring process, and FIG. It is a sectional view showing a completed internal thread part. 1... Ceramic sprayed layer, 2... Mold, 3...
・Cavity, B, B'...Steel bolt.

Claims (1)

[Claims] A method for forming a female thread in a cast product includes a step of applying ceramic spraying to the surface of a male thread member that is screwed with the female thread to be manufactured to form a sprayed layer with thread-like irregularities on the outside. A method for manufacturing a female ceramic threaded part, comprising the steps of: melting a threaded member to leave only a sprayed ceramic layer; and casting the remaining sprayed ceramic layer.