RU2427457C1 - Method of reconditioning parts from aluminium and its alloys - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: invention relates to machine building, particularly, to reconditioning of aluminium parts and may be used in repair of machinery. Proposed method comprises cold gas dynamic surface evaporation to produce aluminium layer of thickness compensating for wear but allowing for machining allowance. Then, part is machined to roughness of Ra 2.5-1.25 and subjected to ultrasound finishing to surface roughness of Ra 0.6-0.3. Thereafter diamond-like 0.5-3.0 mcm-thick coat based on silicon hydroxycarbide is applied by condensation from plasma over entire surface being reconditioned.

EFFECT: higher wear resistance.

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Description

The technical field to which the invention relates.

The invention relates to mechanical engineering, in particular to methods for the restoration of parts from aluminum and its alloys, and can be used in the repair of machines for the restoration of parts from aluminum and its alloys.

State of the art

There is a method of restoring worn parts from aluminum and its alloys, for example, to restore pinch and bearing blocks of gear pumps of the NSh-K type. The objective of the invention is to obtain more uniform wear resistance across the thickness of the reinforcing coating of the part. The method includes surfacing in a protective gas environment, machining, hardening of the part by microarc oxidation. After microarc oxidation, the part is subjected to heat treatment at 540-550 ° C. The technical result of the invention is that, as a result of heat treatment, the method allows to reduce the drop in microhardness of the coating and the intensity of its wear when moving away from the border with the metal and, as a result, to increase uniform wear resistance by hardening thickness by 18-20% (see patent RU 2196035 C2, IPC 7 В23Р 6/00, published on January 10, 2003).

The disadvantage of this method is the duration of the recovery process and the difficulty in choosing the type of electrolyte, the concentration of its components and the calculation of the surface treatment of the part depending on the thickness and hardness of the coating.

The known method, which includes surfacing in a protective gas environment, machining, hardening a part by microarc oxidation in an alkaline electrolyte and impregnating the hardening coating with oil, while microarc oxidation is carried out in an electrolyte containing 7 g / l sodium hydroxide and 15 ... 16 g / l potassium liquid glass using the anodic-cathodic mode at a cathodic current density of 32 A / dm ² , the ratio of the cathodic and anodic currents of 1.05 ... 1.07, the final anode voltage of the formation of a strengthening coating 400 ... 420 V and the final cat a single voltage of 85 ... 100 V, and the impregnation of the hardening coating of the part is carried out with MK-22 aviation oil with a kinematic viscosity of 1.9 ... 2.1 ^. 10 -5 m ² / s, heated to a temperature of 150 ... 160 ° C. The technical result of the invention is to increase the oil absorption of the reinforcing coating formed by the MAO by increasing its bulk porosity, as well as reducing the running time of the restored and hardened parts (see patent RU 2252122 C1, IPC 7 В23Р 6/00, C25D 11/18, publ. 05/20/2005).

The disadvantage of this method is the duration of the recovery process and the difficulty in choosing the type of electrolyte, the concentration of its components and the calculation of the surface treatment of the part depending on the thickness and hardness of the coating.

The closest in technical essence and the achieved positive effect and accepted by the authors for the prototype is a method of restoring worn parts from aluminum alloys, for example, to restore with hardening of the wells of gear pump housings of the NSh or NSh-U type. In the method for reconditioning the wells of gear pumps made of aluminum alloys, the increment of the reconditioned wells of the housings is carried out by compression with heating to a temperature of 510 ° С and completion of compression at a temperature of at least 440 ° С, and microarc oxidation is carried out in an electrolyte containing 8 g / l of liquid glass at a density current 25 A / DM ² and the duration of the oxidation of 1.5 hours. EFFECT: reduced wear rate, increased wear resistance of gear pump housing wells, as well as increased productivity during restoration of housing wells by reducing the hardening time (see patent RU 2236335 C2, IPC 7 В23Р 6/00, published on September 20, 2004).

The disadvantage of this method is the difficulty in choosing the type of electrolyte, the concentration of its components and the calculation of the surface treatment of the part depending on the thickness and hardness of the coating.

Disclosure of invention

The technical result that can be achieved using the present invention is to obtain a coating of the required thickness and high wear resistance on parts made of aluminum and its alloys.

The technical result is achieved using a method of restoring parts from aluminum and its alloys, including the increment of the restored aluminum parts, while preliminary cold gas-dynamic spraying of the surface is carried out with a layer of aluminum with a thickness that compensates for wear and with an allowance for subsequent processing, followed by machining, until surface roughness of the restored surface Ra 2.5-1.25, non-abrasive ultrasonic finishing with a feed of 0.16-0.08 mm / rev to obtaining a surface roughness of Ra 0.6-0.3 and applying a diamond-like coating of 0.5-3 microns based on silicon oxycarbide on the entire surface.

The essence of the method consists in applying a porous aluminum coating 1 to the reconditioned part 2 with the formation of surface 3 by the method of cold gas-dynamic spraying and applying a powder material - A-20-11, with a thickness that compensates for wear and with an allowance for subsequent processing, with a powder supply of 0.3- 0.4 g / s.

After cold gas-dynamic spraying, machining is performed with increased accuracy by surface formation 4 with a roughness Ra 2.5-1.25.

After machining, a non-abrasive ultrasonic surface treatment is performed with a frequency of 20-24 kHz and a transverse feed of 0.16-0.1 mm / rev, which not only reduces surface roughness 5 by crushing the microroughness vertices to Ra 0.6-0.3 , but also additionally strengthens the surface of the part to a depth of 100 microns with the formation of a hardened layer 6.

After that, the reconditioned part is hardened with the help of the plasma plasma hardening. A layer 7 of silicon oxycarbide with a surface 8 of thickness 0.5 ... 3 μm is applied.

This method allows to obtain a surface superior to the surface of the method taken as a prototype for all requirements and indicators, such as hardness, wear resistance, roughness.

Brief Description of the Drawings

Figure 1 shows the base metal with a porous aluminum coating deposited by the installation.

In Fig.2 - the same as in Fig.1, after milling processing.

In Fig.3 - the same as in Fig.2, after non-abrasive ultrasonic finishing.

In Fig.4 - the same as in Fig.3, with a diamond-like coating based on silicon oxycarbide.

The implementation of the invention

Examples of specific performance of the method for the restoration of parts from aluminum and its alloys

Example 1. Restoration of aluminum parts of oil pumps type NSh

To restore aluminum parts of oil pumps of the NSh type, a porous aluminum coating 1 is applied to the restored part 2 with the formation of surface 3 by the method of cold gas-dynamic spraying with a powder material - A-20-11, with a thickness that compensates for wear, and with an allowance for subsequent processing, with a powder supply of 0 , 2 g / s. The resulting surface after cold gas-dynamic spraying does not satisfy, because due to the unevenness of the coating, it has a large porosity, waviness and roughness and requires subsequent processing.

After cold gas-dynamic spraying, machining is performed with increased accuracy with a feed of 0.32 mm / rev and surface formation 4 with a roughness of Ra 6.3. The resulting surface after milling processing satisfies the waviness, but requires further processing to increase surface strength and reduce roughness.

After turning, a non-abrasive ultrasonic finishing is performed with a feed of 0.32 mm / rev and the formation of a surface 5 with a frequency of 20-24 kHz, which not only reduces the surface roughness by crushing the microroughness vertices to R _a = 1.25, but also strengthens it the surface of the part to a depth of 100 microns, with the formation of a surface layer 6.

Then, to improve the physicomechanical properties of the part and increase the service life of the parts, the reconditioned part is hardened using plasma finishing hardening, the entire surface of the part is treated in one pass, lasting 1.54 minutes to obtain a layer of silicon oxycarbide 7 with a surface 8 of thickness 0.1 microns. The applied coating obtained by condensation from an arc or high-frequency plasma, a silicon-containing base composition of SiC - SiO ₂ , being a dielectric, forms a film barrier that prevents the setting of contact surfaces. In addition, this coating has a certain corrosion resistance and heat resistance, forming a residual stress on the surface of σ = -45MPa, and with a microhardness of 82-84 HRC. When forming a hardening film coating, it practically repeats the profile of the substrate. Increasing the hardness of the coated surface complicates the plastic deformation of the surface layer of the part, eliminates micro-cutting and promotes the elastic interaction of the rubbing surfaces, which is most favorable for increasing wear resistance, the friction coefficient is 0.12.

The resulting surface does not satisfy in the following indicators:

- Due to the low feed rate of 0.2 g / s of powder material A-20-11, when spraying the surface, the spraying time is significantly increased.

- Due to the feed of 0.32 mm / rev, a roughness of Ra 6.3 is formed during machining.

- Due to a feed of 0.32 mm / rev, a roughness of Ra 1.25 is formed during non-abrasive ultrasonic finishing.

- Due to the small number of passes and processing time, we get a diamond-like coating based on silicon oxycarbide of small thickness, insufficient to increase wear resistance.

Example 2. The restoration of the aluminum parts of oil pumps of the NSh type is carried out analogously to example 1, but the processing modes are changed:

- Cold gas-dynamic spraying is carried out with a feed of 0.5 g / s of powder material A-20-11.

- Mechanical produce processing with a feed of 0.05 mm / rev with the formation of a roughness Ra of 0.63.

- Non-abrasive ultrasonic finishing hardening is performed with a feed of 0.05 mm / rev with the formation of a roughness Ra of 0.063.

- Finishing plasma hardening is carried out in 4 passes of 2.5 minutes each with the application of a diamond-like layer based on silicon oxycarbide with a thickness of 3 μm.

The resulting surface does not satisfy in the following indicators:

- Due to the large supply of 0.5 g / s of powder material A-20-11, over-spraying of the powder significantly increased during surface spraying.

- Due to the feed of 0.05 mm / rev during machining, the processing time is significantly increased.

- Due to the feed of 0.05 mm / rev during non-abrasive ultrasonic finishing, the processing time is significantly increased.

- Due to the large number of passes and the long processing time, the surface overheats.

Example 3. The restoration of the aluminum parts of oil pumps of the NSh type is carried out analogously to example 1, but the processing modes are changed:

- Cold gas-dynamic spraying is carried out with a feed of 0.3 g / s of powder material A-20-11.

- Machining is carried out with a feed of 0.16 mm / rev with the formation of a roughness of Ra 2.5.

- Non-abrasive ultrasonic finishing hardening is carried out with a feed of 0.16 mm / rev with the formation of a roughness of Ra 0.6.

- Finishing plasma hardening is carried out in 2 passes of 1.8 minutes each with the application of a diamond-like layer based on silicon oxycarbide with a thickness of 0.5 μm.

The resulting surface satisfies the following indicators:

- The supply of 0.3 g / s during surface spraying satisfies us both in time and in the consumption of powder material A-20-11.

- Due to the feed of 0.16 mm / rev during machining, the maximum allowable roughness Ra 2.5 was obtained for subsequent non-abrasive ultrasonic treatment.

- Due to the feed of 0.16 mm / rev during non-abrasive ultrasonic finishing, an acceptable roughness of Ra 0.6 is obtained.

- Due to two passes of 1.8 minutes each, the minimum allowable thickness of a diamond-like coating of 0.5 μm based on silicon oxycarbide was obtained.

Example 4. The restoration of aluminum parts of oil pumps type NSH is carried out analogously to example 1, but change the processing modes:

- Cold gas-dynamic spraying is produced with a supply of 0.4 g / s of powder material A-20-11.

- Machining is carried out with a feed of 0.1 mm / rev with the formation of a roughness Ra of 1.25.

- Non-abrasive ultrasonic finishing hardening is performed with a feed of 0.1 mm / rev with the formation of a roughness of Ra 0.3.

- Finishing plasma hardening is carried out in 3 passes of 2.1 minutes each with the application of a diamond-like layer based on silicon oxycarbide with a thickness of 3 μm.

The resulting surface satisfies the following indicators:

- The supply of 0.4 g / s during surface spraying led to a reduction in spraying time and a slight overspending of the powder material A-20-11 in comparison with example 3.

- The feed of 0.1 mm / rev during machining slightly increased the processing time, but improved the roughness Ra 1.25 for subsequent non-abrasive ultrasonic processing.

- The feed of 0.1 mm / rev during non-abrasive ultrasonic finishing slightly increased the processing time, with obtaining an optimal roughness Ra of 0.3.

- Due to 3 passes of 2.1 minutes each, the maximum possible thickness of 3 μm of a diamond-like coating based on silicon oxycarbide was obtained with a slight heating of the workpiece.

This method allows to obtain a surface superior to the surface of the method taken as a prototype, according to all requirements and indicators, such as hardness, wear resistance, roughness.

Table Physico-mechanical properties of the working surfaces of aluminum parts during restoration by the method taken as a prototype, and the proposed method Indicator Prototype The proposed method Stresses in the surface layer, MPa -310 -45 Microhardness, HRC 69 ... 71 82 ... 84 The total thickness of the hardened layer, mm 0.12 0.103 Wear resistance of a surface in comparison with a surface of a serial deposit, times 2 ... 3 3.2 ... 4.1

The sequence of technological operations for the restoration of aluminum parts of gear pumps of the NSh type is selected so that each subsequent operation improves the properties of the previous operation and ultimately helps to give the surface completely new qualitative properties that other methods do not have.

The proposed method in comparison with the prototype and other known technical solutions has the following advantages:

- universality;

- ease of implementation;

- increased wear resistance of the resulting coating;

- the possibility of repeated use for the same restored parts.

Claims (1)

The method of restoring parts from aluminum and its alloys, including cold gas-dynamic spraying of the surface with the application of a layer of aluminum with a thickness that compensates for wear, and with an allowance for subsequent processing with subsequent machining to obtain a roughness of the restored surface Ra 2.5-1.25, non-abrasive ultrasonic finish processing to obtain a surface roughness of Ra 0.6-0.3 and applying a diamond-like coating with a thickness of 0.5-3 microns based on silicon oxycarbide by plasma condensation throughout the recovery avlivaemoy workpiece surface.

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