Alloyed rotary excavating tooth coating and process

Abstract

The application relates to the technical field of rotary digging tooth preparation, and discloses an alloy rotary digging tooth coating and a process, which comprises a tooth body, the tooth body is provided with an alloy reinforcing coating area on a conical surface, the alloy reinforcing coating area comprises a plurality of reinforcing frames in a hexagonal structure, each reinforcing frame is connected with adjacent reinforcing frames on the periphery to form a honeycomb structure, each reinforcing frame is provided with an enhancing layer in a hexagonal structure, and an adapter layer in a triangular structure is formed between each adjacent reinforcing frame; wherein the reinforcing frame is prepared from the following raw materials in weight: 10-30 parts of pig iron, 1-4 parts of metal manganese and 0.2-0.6 parts of metal titanium; the enhancing layer is prepared from the following raw materials in weight: 0.45-0.6 parts of metal silver, 5-10 parts of metal tin and 0.12-0.55 parts of metal titanium; and the adapter layer is prepared from the following raw materials in weight: 1-4 parts of metal nickel and 4-6 parts of metal cobalt. The rotary digging tooth is not easy to be damaged for a long time, and the service life of the rotary digging tooth is greatly improved.

Description

Technical Field

[0001] This invention relates to the technical field of rotary drilling tooth preparation, specifically to an alloy rotary drilling tooth coating and process. Background Technology

[0002] Rotary drilling teeth are a key working component of rotary drilling rigs. Their roots connect to the drill bit, and their tapered surfaces and carbide tips form the rotary drilling working face. Due to the intense interaction between the rotary drilling teeth and the workpiece during operation, the tapered surfaces of the teeth are prone to wear and eventual failure.

[0003] To address the above technical problems, Chinese patent document (publication number CN218669231U) discloses an alloy rotary drilling tooth for hard rock excavation, comprising a rotary drilling tooth body, the rotary drilling tooth body comprising a base layer, a first reinforcing layer fixedly connected to the surface of the base layer, a second reinforcing layer fixedly connected to the surface of the first reinforcing layer, a protective layer fixedly connected to the surface of the second reinforcing layer, the protective layer comprising a high-temperature resistant layer, a first corrosion resistant layer fixedly connected to the surface of the high-temperature resistant layer, and a second corrosion resistant layer fixedly connected to the surface of the first corrosion resistant layer.

[0004] The above technical solution improves the strength of the rotary drilling teeth by using a base layer, a first reinforcing layer, and a second reinforcing layer, and improves the corrosion resistance and wear resistance of the rotary drilling teeth by using a high-temperature resistant layer, a first corrosion-resistant layer, and a second corrosion-resistant layer. However, since the base layer, the first reinforcing layer, and the second reinforcing layer are usually clad onto the surface of the conical surface of the rotary drilling teeth using a cladding technique, a large amount of heat is introduced into the base layer, the first reinforcing layer, and the second reinforcing layer during the cladding process, resulting in the accumulation of thermal stress inside the base layer, the first reinforcing layer, and the second reinforcing layer. Therefore, in actual construction, they are often subjected to compression and impact from the rock mass, and the base layer, the first reinforcing layer, and the second reinforcing layer are easily peeled off. Summary of the Invention

[0005] The present invention aims to provide an alloy rotary drilling tooth coating and process to solve the technical problem in the prior art where the base layer, the first reinforcing layer and the second reinforcing layer are usually clad onto the surface of the conical surface of the rotary drilling tooth using a cladding technique. During the cladding process, a large amount of heat is introduced into the base layer, the first reinforcing layer and the second reinforcing layer, resulting in the accumulation of thermal stress inside the base layer, the first reinforcing layer and the second reinforcing layer. In actual construction, they are often subjected to compression and impact from the rock mass, making the base layer, the first reinforcing layer and the second reinforcing layer easy to peel off.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: an alloy rotary drilling tooth coating, comprising a tooth body, wherein an alloy reinforcing coating area is provided on the conical surface of the tooth body, the alloy reinforcing coating area comprises a plurality of hexagonal reinforcing frames, each reinforcing frame is connected to its adjacent reinforcing frames to form a honeycomb structure, each reinforcing frame has a hexagonal reinforcing layer, and a triangular connecting layer is formed between each adjacent reinforcing frame;

[0007] The reinforcing frame comprises the following raw materials by weight: 10-30 parts pig iron, 1-4 parts metallic manganese, and 0.2-0.6 parts metallic titanium;

[0008] The reinforcing layer comprises the following raw materials by weight: 0.45-0.6 parts of metallic silver, 5-10 parts of metallic tin, and 0.12-0.55 parts of metallic titanium;

[0009] The bonding layer comprises the following raw materials by weight: 1-4 parts of metallic nickel and 4-6 parts of metallic cobalt.

[0010] In practical operation, this invention involves machining multiple hexagonal annular grooves on the conical surface of the rotary drilling tooth body. Each annular groove has the same width and depth, and the ends of adjacent annular grooves are connected, forming a honeycomb structure on the conical surface of the rotary drilling tooth body. The laser head of a laser is aimed at the annular groove and uniformly feeds the mixed material of the reinforcing frame into it. The laser head emits a laser beam with a circular spot whose diameter is equal to the width of the annular groove. The laser beam continuously melts the mixed material of the reinforcing frame along a predetermined trajectory. The reactants produced by melting fill the annular groove and protrude outward, so that part of the reinforcing frame is embedded in the annular groove, and the other part protrudes from the conical surface of the rotary drilling tooth body.

[0011] After the reinforcement frame is processed, a hexagonal groove is formed inside the reinforcement frame. The laser head of the laser is aimed at the hexagonal groove and the above-mentioned reinforcement layer mixture is evenly fed into the hexagonal groove. The above-mentioned reinforcement layer mixture is intermittently melted according to a predetermined trajectory, and the reaction product generated by melting fills the hexagonal groove.

[0012] Meanwhile, after the reinforcement frame is processed, a triangular groove is formed between adjacent reinforcement frames. The laser head of the laser is aimed at the triangular groove and the mixed raw material of the above-mentioned connecting layer is evenly fed into the groove. The mixed raw material of the connecting layer is intermittently melted according to a predetermined trajectory, and the reactants generated by melting fill the triangular groove.

[0013] In this design, the reinforcing frame is infiltrated into the pig iron using a combination of manganese and titanium in the aforementioned proportions. This alters the metallographic structure of the pig iron, making it more uniform and dense, overcoming the defects of a porous pig iron structure, improving its impact resistance, and enhancing the wear resistance of the reinforcing frame. The reinforcing layer is infiltrated into the tin using a combination of titanium and silver in the aforementioned proportions, and is confined within the reinforcing frame. Simultaneously, the connecting layer, using nickel and cobalt in the aforementioned proportions, increases the strength of the reinforcing frame's edges. Therefore, this invention enhances the corrosion resistance of the rotary drilling teeth, increases their strength, improves their wear resistance, and enhances their stability through the reinforcing frame, reinforcing layer, and connecting layer. It has a wide range of applications, making the rotary drilling teeth less prone to damage even after prolonged use, thus significantly extending their service life.

[0014] Furthermore, the reinforcing frame comprises the following raw materials by weight: 10 parts pig iron, 1 part manganese metal, and 0.2 parts titanium metal; the reinforcing layer comprises the following raw materials by weight: 0.45 parts silver metal, 5 parts tin metal, and 0.12 parts titanium metal; and the connecting layer comprises the following raw materials by weight: 1 part nickel metal and 4 parts cobalt metal.

[0015] Furthermore, the reinforcing frame comprises the following raw materials by weight: 30 parts pig iron, 4 parts manganese metal, and 0.6 parts titanium metal; the reinforcing layer comprises the following raw materials by weight: 0.6 parts silver metal, 10 parts tin metal, and 0.55 parts titanium metal; and the connecting layer comprises the following raw materials by weight: 4 parts nickel metal and 6 parts cobalt metal.

[0016] Furthermore, the reinforcing frame comprises the following raw materials by weight: 20 parts pig iron, 3 parts manganese metal, and 0.4 parts titanium metal; the reinforcing layer comprises the following raw materials by weight: 0.5 parts silver metal, 7 parts tin metal, and 0.33 parts titanium metal; and the connecting layer comprises the following raw materials by weight: 3 parts nickel metal and 5 parts cobalt metal.

[0017] An alloy rotary drilling tooth coating process includes the following steps:

[0018] Step 1: Mix the raw materials of the reinforcing frame according to the formula to form the reinforcing frame mixed raw material; mix the raw materials of the reinforcing layer according to the formula to form the reinforcing layer mixed raw material; mix the raw materials of the connecting layer according to the formula to form the connecting layer mixed raw material; process multiple hexagonal annular grooves along the height direction on the conical surface of the rotary drilling tooth body, with each end of each annular groove connected to the adjacent annular groove, so that multiple hexagonal annular grooves surround the conical surface of the rotary drilling tooth body to form a honeycomb structure;

[0019] Step 2: After Step 1 is completed, the laser head of the laser is aligned with the annular groove and the above-mentioned reinforcing frame mixed material is uniformly fed into it. The above-mentioned reinforcing frame mixed material is continuously melted along a predetermined trajectory to form a reinforcing frame. The reactants generated by melting fill the annular groove and protrude outward, so that part of the reinforcing frame is embedded in the annular groove and the other part protrudes from the conical surface of the rotary drilling tooth body.

[0020] Step 3: After the reinforcement frame is processed in Step 1, a hexagonal groove is formed inside the reinforcement frame. The laser head of the laser is aligned with the hexagonal groove and the above-mentioned reinforcement layer mixture is evenly fed into the groove. The above-mentioned reinforcement layer mixture is intermittently melted along a predetermined trajectory to form a reinforcement layer. The reactants generated by melting fill the hexagonal groove.

[0021] Step 4: After the reinforcement frame is processed in Step 1, a triangular groove is formed between the ends of adjacent reinforcement frames; after the reinforcement layer is processed in Step 3, the laser head of the laser is aligned with the triangular groove and the above-mentioned connecting layer mixture material is uniformly fed into it. The above-mentioned connecting layer mixture material is intermittently melted according to a predetermined trajectory to form a connecting layer, and the reactants generated by melting fill the triangular groove.

[0022] Step 5: After completing the machining of the connecting layer in Step 4, the reinforcing frame, the reinforcing layer, and the connecting layer work together to fuse onto the conical surface of the rotary drilling tooth body.

[0023] Furthermore, in step one, the width and depth of each annular groove are equal. This facilitates the rapid filling of the annular groove by the molten reactants.

[0024] Furthermore, in step two, the laser head emits a laser beam, and the laser beam is a circular beam with a diameter equal to the width of the annular groove.

[0025] Furthermore, in step two, the thickness of the reinforcing frame protruding from the conical surface of the rotary drilling tooth body is 2mm.

[0026] Furthermore, in step five, the thickness of the reinforcing layer and the connecting layer is 2 mm.

[0027] Compared with the prior art, the present invention also has the following technical effects:

[0028] This invention involves machining multiple hexagonal annular grooves on the conical surface of the rotary drilling tooth body, then cladding reinforcing frames within these grooves. Simultaneously, a strong reinforcing layer is clad within the reinforcing frames, and a connecting layer is clad within the triangular grooves formed between adjacent reinforcing frames. Compared to existing technologies, this invention provides a more stable connection between the reinforcing frames and the rotary drilling tooth body through an embedded method. Furthermore, the portion of the reinforcing frame protruding from the tooth body surface, in conjunction with the reinforcing layer and connecting layer, forms a honeycomb structure surrounding the conical surface of the rotary drilling tooth body. This achieves a combination of a high-hardness, wear-resistant layer and a high-toughness substrate, effectively preventing thermal stress failure while ensuring the wear resistance of the rotary drilling tooth. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the structure of an alloy rotary drilling tooth coating according to the present invention. Detailed Implementation

[0030] The following detailed description illustrates the specific implementation method:

[0031] The reference numerals in the accompanying drawings include: reinforcing frame 1, reinforcing layer 2, and connecting layer 3.

[0032] Example 1

[0033] An alloy rotary drilling tooth coating includes a tooth body, an alloy reinforcing coating area is provided on the conical surface of the tooth body, the alloy reinforcing coating area includes a plurality of hexagonal reinforcing frames 1, each reinforcing frame 1 is connected to the adjacent reinforcing frames 1 on its periphery to form a honeycomb, each reinforcing frame 1 has a hexagonal reinforcing layer 2, and a triangular connecting layer 3 is formed between each adjacent reinforcing frame 1.

[0034] The reinforcing frame 1 comprises the following raw materials by weight: 10 parts pig iron, 1 part manganese metal, and 0.2 parts titanium metal; the reinforcing layer 2 comprises the following raw materials by weight: 0.45 parts silver metal, 5 parts tin metal, and 0.12 parts titanium metal; the connecting layer 3 comprises the following raw materials by weight: 1 part nickel metal and 4 parts cobalt metal.

[0035] Example 2:

[0036] An alloy rotary drilling tooth coating includes a tooth body, an alloy reinforcing coating area is provided on the conical surface of the tooth body, the alloy reinforcing coating area includes a plurality of hexagonal reinforcing frames 1, each reinforcing frame 1 is connected to the adjacent reinforcing frames 1 on its periphery to form a honeycomb, each reinforcing frame 1 has a hexagonal reinforcing layer 2, and a triangular connecting layer 3 is formed between each adjacent reinforcing frame 1.

[0037] The reinforcing frame 1 comprises the following raw materials by weight: 30 parts pig iron, 4 parts manganese metal, and 0.6 parts titanium metal; the reinforcing layer 2 comprises the following raw materials by weight: 0.6 parts silver metal, 10 parts tin metal, and 0.55 parts titanium metal; the connecting layer 3 comprises the following raw materials by weight: 4 parts nickel metal and 6 parts cobalt metal.

[0038] Example 3:

[0039] An alloy rotary drilling tooth coating includes a tooth body, an alloy reinforcing coating area is provided on the conical surface of the tooth body, the alloy reinforcing coating area includes a plurality of hexagonal reinforcing frames 1, each reinforcing frame 1 is connected to the adjacent reinforcing frames 1 on its periphery to form a honeycomb, each reinforcing frame 1 has a hexagonal reinforcing layer 2, and a triangular connecting layer 3 is formed between each adjacent reinforcing frame 1.

[0040] The reinforcing frame 1 comprises the following raw materials by weight: 20 parts pig iron, 3 parts manganese metal, and 0.4 parts titanium metal; the reinforcing layer 2 comprises the following raw materials by weight: 0.5 parts silver metal, 7 parts tin metal, and 0.33 parts titanium metal; the connecting layer 3 comprises the following raw materials by weight: 3 parts nickel metal and 5 parts cobalt metal.

[0041] The alloy rotary drilling tooth coating process described in Examples 1-3 includes the following steps:

[0042] Step 1: Mix the raw materials of the reinforcing frame according to the formula to form the reinforcing frame mixed raw material; mix the raw materials of the reinforcing layer according to the formula to form the reinforcing layer mixed raw material; mix the raw materials of the connecting layer according to the formula to form the connecting layer mixed raw material; process multiple hexagonal annular grooves along the height direction on the conical surface of the rotary drilling tooth body, with each end of each annular groove connected to the adjacent annular groove, so that multiple hexagonal annular grooves surround the conical surface of the rotary drilling tooth body to form a honeycomb structure;

[0043] Step 2: After Step 1 is completed, the laser head of the laser is aligned with the annular groove and the above-mentioned reinforcing frame mixed material is uniformly fed into it. The above-mentioned reinforcing frame mixed material is continuously melted along a predetermined trajectory to form a reinforcing frame. The reactants generated by melting fill the annular groove and protrude outward, so that part of the reinforcing frame is embedded in the annular groove and the other part protrudes from the conical surface of the rotary drilling tooth body.

[0044] Step 3: After the reinforcement frame is processed in Step 1, a hexagonal groove is formed inside the reinforcement frame. The laser head of the laser is aligned with the hexagonal groove and the above-mentioned reinforcement layer mixture is evenly fed into the groove. The above-mentioned reinforcement layer mixture is intermittently melted along a predetermined trajectory to form a reinforcement layer. The reactants generated by melting fill the hexagonal groove.

[0045] Step 4: After the reinforcement frame is processed in Step 1, a triangular groove is formed between the ends of adjacent reinforcement frames; after the reinforcement layer is processed in Step 3, the laser head of the laser is aligned with the triangular groove and the above-mentioned connecting layer mixture material is uniformly fed into it. The above-mentioned connecting layer mixture material is intermittently melted according to a predetermined trajectory to form a connecting layer, and the reactants generated by melting fill the triangular groove.

[0046] Step 5: After completing the machining of the connecting layer in Step 4, the reinforcing frame, the reinforcing layer, and the connecting layer work together to fuse onto the conical surface of the rotary drilling tooth body.

[0047] The laser cladding process parameters are: power 2000W, scanning speed 3mm / s, defocusing amount 15mm, and protective gas flow rate 20L / min.

[0048] Comparative Example 1: A prior art method for hard rock excavation using alloy rotary drilling teeth (publication number CN218669231U).

[0049] Comparative Example 2:

[0050] The difference from Examples 1-3 is that the reinforcing frame 1 and the connecting layer 3 are missing in the alloy reinforcing coating area. The reinforcing layer 2 is mixed with the raw materials in Example 1 and sputtered onto the conical surface of the rotary drilling tooth body by a laser.

[0051] Comparative Example 3:

[0052] The difference from Examples 1-3 is that the reinforcing layer 2 is missing in the alloy-reinforced coating area.

[0053] Experiment 1:

[0054] According to GB / T230.1-2009 "Rockwell Hardness Test for Metallic Materials", the rockwell hardness tester of model HR-150D was used to test the hardness of the rotary drilling teeth of each embodiment and the comparative example.

[0055] Experiment 2:

[0056] According to GB / T229-2007 "Charpy Impact Test Method for Metallic Materials", the impact strength of the rotary drilling teeth in each embodiment and comparative example was tested using a JB30A pendulum impact testing machine.

[0057] The test results for Experiment 1 and Experiment 2 are detailed in Table 1.

[0058] Table 1

[0059] Hardness (HRC) <![CDATA[Impact strength (J / m 2 )]]> Example 1 74 3.7 Example 2 72 3.6 Example 3 70 3.4 Comparative Example 1 45 1.6 Comparative Example 2 57 2.4 Comparative Example 3 66 3.1

[0060] According to the comparison of the data of Example 1 and Comparative Example 1 in Table 1, compared with the existing rotary drilling teeth, the rotary drilling teeth prepared in this application have improved hardness and impact strength, thereby extending the service life of the rotary drilling teeth of this application.

[0061] According to the comparison of the data of Example 1 and Comparative Example 2 in Table 1, by infiltrating titanium metal and titanium metal into pig iron in a specific ratio, the hardness and impact resistance of the rotary drilling teeth are improved at the same time. This proves that the addition of titanium metal and manganese metal in a specific ratio greatly improves the density of the rotary drilling teeth obtained by smelting pig iron as the main raw material. The rotary drilling teeth can withstand multiple collisions without deformation or damage.

[0062] According to the comparison of the data of Example 1 and Comparative Example 3 in Table 1, by controlling the combination of titanium and silver infiltrating into tin, titanium increases the strength of the rotary drilling teeth, silver enhances the wear resistance of the rotary drilling teeth, and tin improves the stability of the rotary drilling teeth, which is beneficial to extending the service life of the cast iron pot.

[0063] The above are merely embodiments of the present invention. Commonly known technical solutions and / or characteristics are not described in detail here. It should be noted that those skilled in the art can make various modifications and improvements without departing from the technical solution of the present invention, and these should also be considered within the scope of protection of the present invention. These modifications and improvements will not affect the effectiveness of the implementation of the present invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. An alloy rotary drilling tooth coating, characterized in that, The tooth body includes an alloy-reinforced coating area on its conical surface. The alloy-reinforced coating area includes multiple hexagonal reinforcing frames. Each reinforcing frame is connected to its adjacent reinforcing frames to form a honeycomb structure. Each reinforcing frame has a hexagonal reinforcing layer inside. A triangular connecting layer is formed between each adjacent reinforcing frame. The reinforcing frame comprises the following raw materials by weight: 10-30 parts pig iron, 1-4 parts metallic manganese, and 0.2-0.6 parts metallic titanium; The reinforcing layer comprises the following raw materials by weight: 0.45-0.6 parts of metallic silver, 5-10 parts of metallic tin, and 0.12-0.55 parts of metallic titanium; The bonding layer comprises the following raw materials by weight: 1-4 parts of metallic nickel and 4-6 parts of metallic cobalt.

2. The alloy rotary drilling tooth coating according to claim 1, characterized in that: The reinforcing frame comprises the following raw materials by weight: 10 parts pig iron, 1 part manganese metal, and 0.2 parts titanium metal; the reinforcing layer comprises the following raw materials by weight: 0.45 parts silver metal, 5 parts tin metal, and 0.12 parts titanium metal; the connecting layer comprises the following raw materials by weight: 1 part nickel metal and 4 parts cobalt metal.

3. The alloy rotary drilling tooth coating according to claim 1, characterized in that: The reinforcing frame comprises the following raw materials by weight: 30 parts pig iron, 4 parts manganese metal, and 0.6 parts titanium metal; the reinforcing layer comprises the following raw materials by weight: 0.6 parts silver metal, 10 parts tin metal, and 0.55 parts titanium metal; the connecting layer comprises the following raw materials by weight: 4 parts nickel metal and 6 parts cobalt metal.

4. The alloy rotary drilling tooth coating according to claim 1, characterized in that: The reinforcing frame comprises the following raw materials by weight: 20 parts pig iron, 3 parts manganese metal, and 0.4 parts titanium metal; the reinforcing layer comprises the following raw materials by weight: 0.5 parts silver metal, 7 parts tin metal, and 0.33 parts titanium metal; the connecting layer comprises the following raw materials by weight: 3 parts nickel metal and 5 parts cobalt metal.

5. An alloy rotary drilling tooth coating process according to any one of claims 1-4, characterized in that: Includes the following steps: Step 1: Mix the raw materials of the reinforcing frame according to the formula to form the reinforcing frame mixed raw material; mix the raw materials of the reinforcing layer according to the formula to form the reinforcing layer mixed raw material; mix the raw materials of the connecting layer according to the formula to form the connecting layer mixed raw material; process multiple hexagonal annular grooves along the height direction on the conical surface of the rotary drilling tooth body, with each end of each annular groove connected to the adjacent annular groove, so that multiple hexagonal annular grooves surround the conical surface of the rotary drilling tooth body to form a honeycomb structure; Step 2: After Step 1 is completed, the laser head of the laser is aligned with the annular groove and the above-mentioned reinforcing frame mixed material is uniformly fed into it. The above-mentioned reinforcing frame mixed material is continuously melted along a predetermined trajectory to form a reinforcing frame. The reactants generated by melting fill the annular groove and protrude outward, so that part of the reinforcing frame is embedded in the annular groove and the other part protrudes from the conical surface of the rotary drilling tooth body. Step 3: After the reinforcement frame is processed in Step 1, a hexagonal groove is formed inside the reinforcement frame. The laser head of the laser is aligned with the hexagonal groove and the above-mentioned reinforcement layer mixture is evenly fed into the groove. The above-mentioned reinforcement layer mixture is intermittently melted along a predetermined trajectory to form a reinforcement layer. The reactants generated by melting fill the hexagonal groove. Step 4: After the reinforcement frame is processed in Step 1, a triangular groove is formed between the ends of adjacent reinforcement frames; after the reinforcement layer is processed in Step 3, the laser head of the laser is aligned with the triangular groove and the above-mentioned connecting layer mixture material is uniformly fed into it. The above-mentioned connecting layer mixture material is intermittently melted according to a predetermined trajectory to form a connecting layer, and the reactants generated by melting fill the triangular groove. Step 5: After completing the machining of the connecting layer in Step 4, the reinforcing frame, the reinforcing layer, and the connecting layer work together to fuse onto the conical surface of the rotary drilling tooth body.

6. The alloy rotary drilling tooth coating process according to claim 5, characterized in that: In step one, the width and depth of each annular groove are equal.

7. The alloy rotary drilling tooth coating process according to claim 5, characterized in that: In step two, the laser head emits a laser beam, and the laser beam is a circular beam with a diameter equal to the width of the annular groove.

8. The alloy rotary drilling tooth coating process according to claim 5, characterized in that: In step two, the thickness of the reinforcing frame protruding from the conical surface of the rotary drilling tooth body is 2mm.

9. The alloy rotary drilling tooth coating process according to claim 5, characterized in that: In step five, the thickness of the reinforcing layer and the connecting layer is 2 mm.

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