WO2013190340A1

WO2013190340A1 - Method and casting insert for producing tillage tools having self-edging and self-toothing properties

Info

Publication number: WO2013190340A1
Application number: PCT/HU2013/000049
Authority: WO
Inventors: Balázs FÖLDI
Original assignee: HÜLSMANN, Mónika
Priority date: 2012-06-19
Filing date: 2013-05-27
Publication date: 2013-12-27
Also published as: HU230028B1; EP2861365A1; HUP1200377A2; WO2013190340A4

Abstract

The invention relates to a method for producing self-edging and self-toothing till¬ age tool, the method comprising providing a coating member (5) made of hard metal by producing a casting insert (3) having a layer formed by said coating member (5) and providing a mould pattern for the tillage tool, the pattern has at least one pocket having the form of the of casting insert (3), placing the casting insert (3) into the pocket and creating a mould, removing the pattern from the mould while leaving casting insert (3) in the mould, closing the latter and filling the mould cavity with steel melt having a composition of C from 0.20 to 0.30 m%, Si 0.30 to 0.50 m%, Mn 1.35 to 1.90 m%, balance is Fe and unavoidable impurities, by a temperature between 1440 " C and 1520 ° C and the casting is allowed to cool.

Description

METHOD AND CASTING INSERT FOR PRODUCING TILLAGE TOOLS HAVING SELF-EDGING AND SELF-TOOTHING PROPERTIES

This invention relates to a method for producing a self-edging and self-toothing tillage tool having a front surface and a cultivating edge extending along the front surface, providing the tool front surface by a hard metal coating element, and to a casting insert for producing a self-edging and self-toothing tillage tool.

In this description the term 'tillage tool' usually refers to a device that serves to till or work the surface of the earth's crust or a near surface range of the earth by direct contact to the earth or soil worked by the agricultural cultivation and mining, building construction and civil engineering, e.g. a share of a plow, a cultivator tine, a panbreaker, edges or nails of front loader spoons of loading and backhoe loaders, scraper, deep tillage tools, or open pit quarry tools. Among these tools the share of the plow has a paramount importance. Plowing is the basic operation of the agricultural cultivation. The means for plowing is the share of the plow, which is essentially not changed in centuries of use, but nowadays it is the main cause of land degradation spreading now worldwide in dangerous proportions as a direct threat for food production along with other environmental factors, even self-generating dangerous environmental factors.

The first (and at the same time decisively) disadvantageous feature of the traditional share is that its cutting edge becomes blunted after a relatively short use, and requires an exponentially increasing traction power in soils with high drag. In the bottom of the furrow remains a very hard, compacted surface (detrimental furrow underside), which is becoming stronger and harder during the many years of cultivation and separates the upper growing layer (about 30 cm) and the underlying layers being sometimes as hard as concrete. This phenomenon is known as "plow sole illness". This phenomenon shows a declining trend as regards the soil fertility, water management, plant roots, and beyond these, the powderiness of the soil (desertification) in progress of time.

To solve the problem resulted in this phenomenon has been apparently unavoidable for centuries, but some worldwide spread half-way measures were created in agricultural engineering. The blunt share of the plow was initially beaten to be sharp- ened, and in the last couple of decades, spread the hard metal built-up edged and self- sharpening and self-toothing shares. A common feature of all these applications is that these methods are applied in the plowshares retrospectively, that is in the share already used or just produced, involving drastic subsequent heat input and thus give rise to a huge quality deterioration exactly in the most delicate structure of edge zone of the share. Although they are more durable, quickly bunted again and thus damaging the soil for a longer time, demanding more and more traction power, which increases the cost of cultivation through increased energy consumption as well. This would significantly increase the emission of pollutants, global-scale environmental effects of which cause worries nowadays.

The share for the plow has been produced by difficult and expensive forging for ages. Lately, welding of carbide inserts layers, for example plates, or build-up of hard metal welding inserts by other applying methods each involving extreme heat introduction have been proposed on different parts of the share, which are hardly improve the wearing lifetime, but are very expensive methods.

But the wear is not always harmful, because if we can control properly, it will not blunt but sharpens the tool. This can be achieved by building up spaced apart hard metal layers in a right angle to line of the cutting edge, resulted in sharpening and toothing the share of the plow, cultivator, ripping tool, etc. by the soil on the plowing or tilling during its whole lifetime, forming a wavy cutting edge. Such a self-sharpening- and self toothing plough share is described in Hungarian patent no. HU 224 132. This approach eliminates simultaneously all the disadvantages of known shares having straight edges, however, it raises another question.

According to the solution of HU 224 132 mentioned above, the surface of the cast, or forged or rolled steel ploughshare is partially provided with a hard metal coating, but the disclosure does not describe how such coating can be applied. According the prior art methods, the hard metal coating or layer is applied subsequently to the ploughshare by means of a welding equipment or flame spraying or an inductive method, or a hard metal piece having suitable form is welded into a recess formed on the surface, but other methods are not known. These methods each have the disadvantage that a layer, applied e.g. by flame-spraying is very thin, that is it wears off rapidly, or the welded hard metal inserts often detach from the share or fall out of the recess formed on the share when plowing. A further disadvantage is the high local heat input, which adversely affects the metallurgical structure of the material of the shareplough. Therefore, the object of the invention is to develop a method for producing a self-edging and self-toothing tillage tool, preferably a ploughshare, provided by hard metal elements to prevent hard metal elements from rapid wear off or detach, thereby increasing the lifetime of the tool, e.g. ploughshare, as well as providing a simpler and more economical solution for applying hard metal elements in comparison with welding and flame spraying.

Above objects have been achieved by providing a method according to the invention for producing a self-edging and self-toothing tillage tool having a front surface and a cultivating edge extending along the front surface, the method comprising a step of providing the tool front surface by a hard metal coating element, the method further comprising the steps of:

making a casting insert by providing a coating member made of hard metal on a mild steel plate, and

producing a tillage tool pattern for casting said tool provided by at least one pocket having the form of the hard metal coating member, and making a first half of a divided casting mould by means of said pattern, and

placing the casting insert having the hard metal coating member into the pocket of the mould, and

producing a second half of the casting mould, and

- removing the pattern from the mould, and closing the mould,

and filling the mould cavity with steel melt having a composition of C 0.20 to 0.30 m%, Si 0.30 to 0.50 m%, Mn 1.35 to 1.90 m%, balance is Fe and unavoidable impurities, by a temperature between 1440 ° C and 1520 ⁰ C and allowing the casting to cool.

Said step of making the casting insert comprises: providing a coating member as a layer made of a hard metal powder containing Ni or Co base metal and one or more carbide(s) selected from the group consisting of chrome-, titanium-, wolfram-, tantalum-, niobium-carbide, on a mild steel plate by flame-spraying or induction smelting, and cutting up a hard plate thus obtained into pieces having the shape of said casting insert.

Said step of making the casting insert comprises: providing a coating member as a layer made of a hard metal powder containing Ni base metal and chrome-carbide, on a mild steel plate.

Advantageously, providing a coating member as a layer having a thickness be- tween 1 mm and 10 mm applied onto the mild steel plate. Preferably providing a Ni based layer having a thickness between 1 ,2 mm and 1 ,8 mm applied onto the mild steel plate.

Preferably attaching a cleaner hook to the mild steel plate.

Filling the mould cavity with steel melt having a composition of C from 0.25 to 0.27%, Si 0.34 to 0.37%, n 1.57 to 1.67%, the rest is Fe and unavoidable impurities.

Casting of the steel melt is carried out at a temperature between 1440 ⁰ C and

1490 °.

Dressing off the casting, while removing the mild steel plate of the casting insert from the front surface of the casting.

The objective of the present invention is achieved also by providing a casting insert for producing a self-edging and self-toothing tillage tool, that contains a mild steel plate layer, and a coating member layer made of a hard metal powder containing Ni or Co base metal and one or more carbide(s) selected from the group consisting of chrome-, titanium-, wolfram-, tantalum-, niobium-carbide, deposited on a surface of the mild steel plate.

The coating member layer has a thickness between 1 mm and 10 mm.

The coating member layer has a thickness between 1.2 mm and 1.8 mm.

A cleaner hook is fixed to the mild steel plate.

The coating member layer has a HV hardness between 900-1000 (47-52 HRC). The invention is illustrated hereinafter in details with reference to the accompanying drawings, disclosing its preferred embodiments. In the drawings:

Fig. 1 is a flow chart of the method according to the invention,

Fig. 2 illustrates the casting mold in a step of the invention, after the first mould half is provided, showing the casting inserts placed in the pockets of the mould,

Fig. 3 shows a metallographic section prepared in a cross section of the ploughshare provided by a casting insert according to the invention, with the mild steel plate removed,

Fig. 4 shows a metallographic section prepared in a cross section of the ploughshare provided by a casting insert according to the invention, with the mild steel plate,

Fig. 5 is a metallographic picture showing the interface between the insert member and the steel base material, and Fig. 6 shows a casting insert comprising an insert member prepared on a mild steel plate, in side elevational view.

A self-sharpening and self-toothing tillage tool, in the exemplary embodiment a share of a plough, is produced by steel casting by means of the method according to the invention. In this description the term 'tillage tool' usually refers to a device that serves to till or work the surface of the earth's crust or a near surface range of the earth by direct contact to the earth or soil worked by the agricultural cultivation and mining, building construction and civil engineering, e.g. a share of a plow, a cultivator tine, a panbreaker, edges or nails of front loader spoons of loading and backhoe loaders, scraper, deep tillage tools, or open pit quarry tools.

In Figure 1 a flow-chart according to the invention is shown. The process step 1 consists of preparing a mould pattern 1 of a self-edging and self-toothing tillage tool, in the exemplary embodiment a share E of a plough, in a way well known in the art, an example - of course not limited - of which is shown in Fig. 2. The mould pattern 1 may be an undivided-indexing plate type, or a divided, or divided and moulding plate mounted one, designed for manual or machinery application, depending on quantity to be produced, and can be made of metal - i.e. aluminum - wood or even plastic material (such as Teflon) as well. Making of the mould pattern 1 only takes place of course in case of no mould pattern is available, or not in the desired design, perhaps more mould pattern 1 is required. During the making the moulding pattern 1 , at least one and preferably several pockets are formed in the front surface 2 of the pattern 1 of the share E, each suitable for receiving a coating member 5 and having a shape thereof, as depicted in Figure 2,with casting inserts 3 placed in the pockets. Core marks are formed in the patter 1 for bores designed to mounting the plough share, as usual in mould pattern making.

The casting insert 3 comprising the hard metal coating member 5 is made from a hard plate prepared by flame powder spraying or induction smelting in such a way, that applying a powder layer containing a mixture of a metal belonging to the Fe group (e.g. Ni or Cr) and hard metal carbide (e.g. chrome-, titanium-, wolfram-, tantalum-, niobium-carbide), preferably e.g. a Ni base hard metal carbide (e.g. chrome-carbide or tungsten-carbide) onto the surface of a mild steel plate 6 by means of flame spraying or induction smelting, and cutting up, preferably by laser cutting, the hard plate thus obtained into pieces having the shape and size of said coating member 5. The casting insert 3 according to the invention is formed by a mild steel plate 6 and a hard metal layer consisting of a Ni-based hard metal of chrome-carbide or tungsten-carbide applied on one surface of the plate 6. The hardness of pure chrome carbides (Cr3C2, Cr7C3, Cr23C6) is between HV 1300 and HV 2100 (67-109 HRC), so these are very hard materials. The hardness of said layer is slightly smaller that the pure chrome car- bide, it is approx. between HV 900-1000 (47-52 HRC), which is an appropriately high value. The Ni-based chrome carbide layer should be applied onto the mild steel plate 6 in a thickness preferably of between 1 mm and 10 mm, primarily depending on the local thicknesses of the casting, since the heat extraction of the casting insert 3 significantly affects its proper fluxing with the material of the casting. The thicker and heavier the casting, the more thicker hard metal layer can be smelted perfectly. It was found that a Ni-base chrome-carbide layer has a preferred thickness of between 1.2 mm and 1.8 mm for the plowshare E. Figure 3 shows a metallographic section prepared in a cross section of the ploughshare provided by a casting insert 3 according to the invention, with the mild steel plate 6 removed. Figure 6 shows a casting insert 3 in side elevational view. The mild steel plate 6 located on the hard metal insert member 5 of the 3 casting insert (Figure 4) can be easily removed. A cleaner hook of arbitrary form (not shown) can be fixed to the mild steel plate 6, which holds the casting insert 5 in proper position in the moulding sand.

It is noted that other powders, e.g. tungsten-carbide powders, that can be used instead of chrome-carbide powders are harder (65-75 HRC) than that it should be for plowshare E, and for this reason it is difficult to align the differences in wear factors of the steel base material and the given hard metal, and these are much more expensive than chrome-carbide as well. Taking the wear factor of the unalloyed structural steel (e.g. MSZ A-38) to be 100, wear factors account of those hard metals are between 0.1 and 3.0. The hardness and the wear factor are not always linearly depending properties. In our case, there are abrasive effects that depend on the abrasive material as well. These are various composition of minerals, and the case of soil (biomass) with varying amounts of mixtures of various organic and inorganic materials.

For the process according to the invention, a first half, preferably upper half of a divided casting mould is made making by means of a ploughshare E moulding 1 pattern provided by at least one, but preferably several pocket, so that said pattern 1 and a moulding box are placed onto a moulding plate and fill the box with moulding mixture and compacting the latter. The molding mixture may be any mixture used in steel foundry, usually a mixture of quartz sand, preferably zircon sand, and a binder, e.g. bentonite and water, water glass, preferably a resin (furan resin) and a curing agent (hardener) etc.

After the upper half of the mold has been completed the mold is inverted, and fit the casting inserts 3 each having a coating member 5 in the so that the 5 coating member comes under the front surface 2 of the pattern 1 and the mild steel plate 6 comes above the front surface 2 of the pattern 1. Dividing surface of the half mold can be repaired as needed.

Then the other moulding box is placed onto the completed upper half of the mold by using box pins, misleading pins fitted to the mold form to another form box, and then filling the box with moulding mixture and compacting the latter. After inverting the finished mold, it is separated, and the mold pattern 1 removed from the mold cavity. After removal of the mold pattern, casting inserts 3 fixed by e.g. cleaner hooks remain in the lower half of the mold. Thereafter, the casting mold halves must be put together, and the two mold halves is fixed by means of suitable load and /or box locks.

Mold cavity of prepared casting mold 1 is then filled with steel melt. Since the presence of the casting insert 3 significantly affects the flowability of the steel melt in the mold cavity, and thermodynamical effects acting on the contact surface of the steel melt and the casting insert 3 make possible the perfect and continuous fusion of the casting insert 3 and the steel in a narrow range, a steel melt according to the invention having special composition and proper casting temperature must be used in the case of a casting provided by coating members 5, e.g a plowshare E. The thin plate-like tillage devices, especially the plowshare E, are delicate castings as regards steel casting procedures, as their thickness is no more than 12-15 mm, and only 4-5 mm close to the edge. That is why the composition and casting temperature of the steel must be opti- mized taking account the desired mechanical properties of a plowshare E casting provided with thin casting inserts 3 being essentially local cooling elements. Hence, a steel having a composition of adequate strength and appropriate viscosity on the casting temperature is required. Another aspect is that the appropriate steel has low costs, preferably not containing expensive alloying elements and in order to maintain proper flowability its manganese content does not exceed a minimum quantity required for fer- rite-perlite formation, otherwise the amount of austenite and hard Mn₃C structural constituents and the melt viscosity increase as well.

Tests were performed in order to determine the steel composition best meeting above requirements and it has been found that low alloyed steels having a composi- tion C 0.20 to 0.30%, Si 0.30 to 0.50%, Mn 1.35 to 1 , 90%, or preferably C 0.25 - 0.27%, Si 0.34 - 0.37%, Mn 1.57 -1.67% are considered to give satisfactory results, when the casting procedure takes place at a temperature between 1440 °C. and 1520 °C and more preferably at a temperature between 1460 °C and 1490 °C. At temperatures below 1440 °C the viscosity of steel melt relatively large to completely fill the cav- ity of the mold along the edge of the plowshare E, and casting inserts do not fuse with the steel. At temperatures above 1520 °C, shrinkage can occur even in very thin castings, especially in the middle ranges cooling down slowly, where - as the Mn content decreases the critical cooling rate of formation of martensite - hard martensite may be formed in a thin casting.

A cut was prepared for examination of microstructure of the casting, which has been etched by a solution of 2% HN03 in ethanol for visualize the structure, and the microscopic test was carried out by a metallurgical microscope of the type Epytip 2, at magnifications of 250x and 500x. The microstructure was found of essentially ferrite- perlite type, with perlite grains of varying particle size and distribution, and with a con- tinuous ferrite web on the contacting surface. The texture of the casting was Wiedmanstatten pin type, typically featurizing a fast cooling. The 250x and 500x magnification photomicrographic records of the cut are shown in Fig.5.

Since the material of casting insert 3 is Ni-based chrome-carbide and the elements Ni, Cr and Mn are equally substitutional position in the crystal lattice of the iron, a perfect coalescence was observed on the interface of the casting insert 3 and the steel melt (Fig. 5) under said conditions. A transition zone featurizing the diffusion of structural elements is not shown at the interface, the interface is sharp, but a cohesive contact can be observed at 500x magnification between the two materials in a narrow, partially fused zone. This ensures that the casting insert 3 does not fall out of the sur- face of plowshare E casting during plowing.

During steel casting production method of tillage tools, e.g plowshares E in the illustrated embodiment, according to the invention, the finished and cooled casting is dressed off, while removing the mild steel plate 6 of the casting insert 3 from the front surface 2 of plowshare E. Removal of the mild steel plate 6 can be done by a proper hand tool in a single motion, and the result is shown in Fig. 3. Alternatively, the casting may be cleaned by wheel blast equipment, wherein the mild steei plate 6 abraded from the surface of the insert member 5. It should be noted that a tillage tool, e.g. a plowshare E produced by the process according to the present invention can be perfectly used for tilling with a non removed mild steel plate 6, since the mild steel plate 6 wears off after a few minutes of plowing, removal of the mild steel plate 6 is indicated only by trade appear and visual appreciation of the plowshare E.

For implementing the method according to the invention is suitable any steel foundry by minimal investment, the moulding pattern 1 of the plowshare E provided by pockets can be prepared in a short time. Omission of aggressive hard metal build up welding procedure and the use of the method according to the present invention is believed to be a breakthrough in the field of manufacturing tillage tools, e.g. tools for groundworks machines, particularly plowshares E.

The method according to the invention is suitable for mass production of all types of tillage cultivation devices with a blade and edge, especially for plowshares E by steel casting procedure. The plowshares E produced by the processes of the prior art, that is forging and wearing member build up welding, contain other and more expensive alloying elements in smaller amounts, but in our experience the operating properties, especially wearing rate of the plowshare E are not influenced essentially by these alloying elements. These alloying elements give certain over-strength properties for the plowshare E, which are not necessary, because - although their total weight loss is somewhat less while tilling - the speed of dulling is high, so that the costs, that is the price of the plowshare E, is unnecessarily increased. 75 to 80% of the original weight of these prior art plowshares E eventually becomes scrap.

Therefore, the advantage of the method according to the invention as compared to the solutions of the prior art is primarily to prevent the hard metal elements arranged on the edge of the tillage tools from fast wearing or flaking away, thereby increasing the lifetime of cultivating implement, such as ploughshare E, and offers a simpler and more economical solution as compared to the welding and direct flame spray- ing to fix the hard metal elements. The tillage tools will last longer, while the volume of waste decreases significantly. A further advantage of the method and casting insert 3 according to the invention is that the chemical composition of a plowshare E produced in a steel foundry does not depend on commercial quality rolled steel goods for forging a great quantity of tools having a single and same composition only, since the quality of the base material can be changed in a steel foundry as desired, and can be produced also in small quantities, as well as conforming wearing factors to hard metal elements. Thus, tillage tools with specific designs best suited to abrasive properties of plow-lands with variable composition can be made, which has been inconceivable till now. With the method according to the invention the hard metal - as opposed to and instead of harm- ful and expensive welding - is combined with tillage tools in the best way, in a single operation, such as the composition of the cast steel can be chosen as the most appropriate one, either in batches or in desired volume of production as well.

Although the invention has been described in detail in relation to the plowshare E, the invention may be used with other soil cultivating tools, such as cultivator tines, subsoil looseners, etc., but it can be used on nails or edges of buckets of dredgers or backhoe loaders.

Claims

1. Method for producing a self-edging and self-toothing tillage tool having a front surface (2) and a cultivating edge extending along the front surface (2), the method comprising a step of providing the tool front surface (2) by a hard metal coating element (5) characterized in that the method further comprising the steps of:

making a casting insert (3) by providing a coating member (5) made of hard metal on a mild steel plate (6), and

producing a tillage tool pattern (1 ) for casting said tool provided by at least one pocket having the form of the hard metal coating member (5), and making a first half of a divided casting mould by means of said pattern, and

placing the casting insert (3) having the hard metal coating member (5) into the pocket of the mould, and

producing a second half of the casting mould, and

- removing the pattern (1) from the mould, and closing the mould,

and filling the mould cavity with steel melt having a composition of C 0.20 to 0.30 m%, Si 0.30 to 0.50 m%, Mn 1.35 to 1.90 m%, balance is Fe and unavoidable impurities, by a temperature between 1440 ⁰ C and 1520 ⁰ C and allowing the casting to cool.

2. The method according to claim 1 , characterized in that said step of making the casting insert (3) comprises: providing a coating member (5) as a layer made of a hard metal powder containing Ni or Co base metal and one or more carbide(s) selected from the group consisting of chrome-, titanium-, wolfram-, tantalum-, niobium-carbide, on a mild steel plate (6) by flame-spraying or induction smelting, and cutting up a hard plate thus obtained into pieces having the shape of said casting insert (3).

3. The method according to claim 2, characterized in that said step of making the casting insert (3) comprises: providing a coating member (5) as a layer made of a hard metal powder containing Ni base metal and chrome-carbide, on a mild steel plate (6).

4. The method according to claim 3, characterized in that providing a coating member (5) as a layer having a thickness between 1 mm and 10 mm applied onto the mild steel plate (6).

5. The method according to claim 3, characterized in that providing a Ni based layer having a thickness between 1 ,2 mm and 1 ,8 mm applied onto the mild steel plate (6)·

6. The method according to any of claims 1-5, characterized in that attaching a cleaner to the mild steel plate (6).

7. The method according to any claims of 1-6, characterized in that filling the mould cavity with steel melt having a composition of C from 0.25 to 0.27%, Si 0.34 to 0.37%, Mn 1 .57 to 1.67%, the rest is Fe and unavoidable impurities.

8. The method according to any claims of 1-7, characterized in that casting of the steel melt is carried out at a temperature between 1440 ⁰ C and 1490 °.

9. The method according to claim 8, characterized in that dressing off the casting, while removing the mild steel plate (6) of the casting insert (3) from the front sur- face (2) of the casting .

10. Casting insert (3) for producing a self-edging and self-toothing tillage tool, characterized in that contains a mild stee! plate (6) layer, and a coating member (5) layer made of a hard metal powder containing Ni or Co base metal and one or more carbide(s) selected from the group consisting of chrome-, titanium-, wolfram-, tantalum- , niobium-carbide, deposited on a surface of the mild steel plate (6).

1 1. Casting insert (3) according to claim 10, characterized in that the coating member (5) layer has a thickness between 1 mm and 10 mm.

12. Casting insert (3) according to claim 1 1 , characterized in that the coating member (5) layer has a thickness between 1.2 mm and 1.8 mm.

13. Casting insert (3) according to any claims of 10-12, characterized in that a cleaner is fixed to the mild steel plate (6).

14. Casting insert (3) according to any claims of 10- 3, characterized in that the coating member (5) layer has a HV hardness between 900-1000 (47-52 HRC).