EP1893369A1

EP1893369A1 - Dry-spray products for protecting centrifuge casting molds of cast iron pipes

Info

Publication number: EP1893369A1
Application number: EP06726108A
Authority: EP
Inventors: Thomas Margaria; Roland Siclari
Original assignee: Pechiney Electrometallurgie SAS
Current assignee: Ferropem SAS
Priority date: 2005-03-22
Filing date: 2006-03-21
Publication date: 2008-03-05
Also published as: MY147531A; KR20070114295A; US7896961B2; CN101142042A; BRPI0609204A2; ZA200706786B; FR2883495A1; US20080115691A1; WO2006100375A1; FR2883495B1

Abstract

The invention concerns a powdery product, of the type known as dry spray, for protecting centrifuge casting molds of cast iron pipes, comprising the usual components for this type of use, as well as an adjuvant for improving the flowability characteristics of said product when it is being deposited and make them less dependent on its physical or physico-chemical characteristics. Said adjuvant can be in particular silicone oil, potassium siliconate or micro-silica of density less than 0.1, as well as a mixture in any proportions of one or more of those.

Description

Products of the "dry-spray" type for the protection of casting molds centrifuged cast iron pipes

Field of the invention

The invention relates to a product in the form of powder, for the protection of casting molds cast iron pipes manufactured by centrifugal casting; the casting molds used are commonly referred to as "shells".

State of the art

Unless otherwise stated, all values relating to chemical compositions are expressed as a percentage by mass.

The coatings used for the protection of centrifugal casting shells of cast iron pipes can consist of inoculants and powdered refractory materials, as well as mixtures of silica and bentonite, put in place by projection of an aqueous suspension. Such coatings are described, for example, in US Patent 4,058,155 to "Pont-A-

Monsoon "and are known as" wet-spray ".

It is also customary to use dry powders sprayed onto the shell before pouring the cast iron, powders then referred to as "dry-spray". Whatever the technique used for their deposit, these products are used for several purposes, including:

- To obtain a release agent effect, ie facilitating the extraction of the pipe from the mold after solidification, - To obtain a thermal barrier effect limiting the rise in temperature of the shell and thus contributing to increasing its lifetime ,

- Obtain an anti-puncture effect that is to say limiting the risk of occurrence of pitting on the surface of the pipes,

- Obtain an ultimate inoculating effect on the cast iron so as to control the metallurgical structure of the pipe. It is well known that insufficient inoculation results in carbide formation, significant cooling shrinkage and rapid demoulding, a guarantee of high productivity. But the parts thus obtained require a subsequent heat treatment which can be expensive. Depending on the case, it may be preferable to inoculate more, even if it means slowing the production rate to avoid the final heat treatment, or, on the contrary, to inoculate little, to increase productivity, and to heat-treat the cast iron part downstream.

The inoculating power of the "dry-spray" can therefore be positioned within fairly wide limits; however, the other effects requested on the product are subject to more constant requirements.

The products used as "dry-spray" are therefore generally composed of a mixture of several components including:

An inoculant of greater or lesser effectiveness, which can typically constitute 30 to 100% of the product; can be used for this purpose, for example, ferro-silicon type alloys containing 0.1 to 4% aluminum and calcium, and possibly other elements that may provide the cast iron with an additional or complementary metallurgical effect .

Powders of elements or alloys that specifically confer an anti-pitting effect: they may be typically the elements or alloys of reducing elements of column 2 of the Mendeleev classification.

An inert mineral filler, for example silica, which can constitute up to 70% of the product.

Patent FR 2612097 of "Foseco", in particular, describes the use, as treatment agent, of Fe-Si-Mg-type alloys whose particles are electrically charged by friction.

They are usually deposited on the shell immediately before casting of the cast iron by a distribution system which generally comprises:

- One (or several) storage container (s), - An apparatus making it possible to define the quantity to be deposited and the instant of this deposit,

- A system for transporting the powder to the inside of the shell.

The products of the prior art have several drawbacks related to the difficulty of obtaining a homogeneous distribution on the inner surface of the mold, which results in accumulations in preferential areas, and in contrast to the lack or insufficiency of product quantity in other areas.

This has the direct effect of structural heterogeneities of the cast iron as well as surface defects of the cast pipe or product inclusions within the same pipe. Another consequence over time is a heterogeneity of wear of the inner surface of the mold that the product must protect, with its impact on the surface of the cast iron pipe.

Object of the invention

The subject of the invention is a powder product, for the protection of molds for centrifugally casting cast iron pipes by dry spraying said product onto the inner surface of said mold, comprising an alloy or a mixture of metal alloys (s) inoculating (S) optionally powders of reducing elements or alloys with an anti-pitting effect, optionally an inert mineral filler, characterized in that it further comprises at least one adjuvant intended to improve the flowability characteristics of said product.

Preferably the flowability is such that the flow time of 50 g of product through the hole of diameter 4 mm of a funnel whose walls form an angle at the top of 60 degrees, is between 17 and 27 seconds for a particle size having a loop at 300 μm between 99 and 100% and a loop at 63 microns between 10 and 35%. According to another preferred embodiment, the flow time with respect to the same product without said adjuvant is reduced by 5 to 10 s if said same product without said adjuvant flows through the hole of diameter 4 mm, and is between 20 and 27 s if said same product without said adjuvant does not flow through said hole. According to an advantageous embodiment, the adjuvant is silicone oil; according to another mode, it is potassium siliconate, and according to yet another mode, microsilica of density less than 0.1.

It may also be a mixture in any proportions of one or more of the aforementioned adjuvants. Finally, according to a preferred embodiment, the mass proportion of adjuvant in said product is between 0.02 and 0.2%.

Description of the invention The products of the prior art used as "dry-spray" in the manufacture of cast iron pipes by continuous centrifugal casting have some disadvantages. In particular, the inert mineral filler added to the mixture contributes to increase the risk of clogging of the molds and formation of inert mineral inclusions in the cast iron, which may reveal surface defects on the pipes.

- The flowability of the powder must correspond to an optimum between a good distribution capacity, and homogeneity of distribution on the internal footprint of the shell, and the need that after deposition on said footprint, it no longer flows , in particular before the front of liquid iron when it is poured into said shell.

The latter also has a hammered surface, consisting of a succession of cups, one of whose roles is to retain the powder so that it is not driven by the front of liquid iron. If the flowability of the powder is too great, this precaution is insufficient. Moreover, the characteristics of the systems for handling, dosing and dispensing said powder are different from one user to another, which in practice results in the fact that the characteristics of the powder and the equipment are not always optimized for each other.

- The choice of the particle size distribution of said powder is also dictated in particular by requirements as to its behavior during its interaction with the liquid iron in the shell so that it fulfills the previously described roles.

- The said powders, also called "inotubes" or "inopipes", are therefore fine and therefore:

- They are very sensitive to the storage conditions which can modify the flowability in the absolute and as to its homogeneity during their final use,

- Small variations in manufacturing conditions (moisture, friability of the material, etc.) can also result in global changes and / or heterogeneities in their flowability.

- The consequences of such a variation in flowability are as follows: - Because the deposit is more or less retained by the cups created by the abovementioned hammering of the surface of the shell, it may have irregularities. This defect can result in particular by the sliding of the product towards the bottom of the shell, the latter being generally inclined typically of 6%. These variations in flow can also affect the powder distribution systems, giving rise to various problems in use (blockages, blockages, etc.) and irregularities in the deposit of the product on the shell, also causing irregularities in its properties. associated effects. - These irregularities of effects result in various types of defects on the final product in cast iron, such as: localized pitting, carbide rate in the thickness of the pipe too important, etc.

A lack of product in certain areas of the shell, for example, will result locally in a lack of inoculation with presence of carbides on the surface and thus increased abrasion and wear of the shell.

Conversely, an excess of product will cause lack of dissolution by melting and as a result of surface defects of the pipe may lead to its disposal.

To overcome these drawbacks, the Applicant has therefore sought to improve the flowability of the powder to facilitate operations prior to its deposit and the deposit itself, while avoiding negative effects after deposit in the shell, ie by ensuring a low flowability when the cast iron is poured into said shell.

This result has been obtained thanks to additives that improve the cold flowability, that is to say until it is deposited, the powder. A judicious choice of said adjuvant allowed, when the powder is then deposited on hot shells, typically between 250 and 300 ° C, to cancel this increase in flowability, the temperature of the powder rising by the very fact of contact with the hot shell.

These adjuvants, the effect of which is described in the examples below, may be potassium siliconate, but other adjuvants with a similar behavior as to their effect on flowability are also usable, such as, in particular, silicone oil, micro silica with a density typically of less than 0.1 (usual density for the so-called "chemical" micro silica) or a mixture in any proportions of one or more of these products. The following tests were carried out with 0.06% of adjuvant, but the usual proportion in industrial conditions can be between 0.02 and 0.2%.

The particle size of the powder product according to the invention is less than 580 μm and preferably 250 μm. Examples:

The flowability characteristics of a powder for "inotubes" are determined by various tests including in particular the flow time of a given quantity through a standardized funnel, the measurement of the shear properties under load and in particular according to the known method. under the name "Jenike test", the flow time under load which consists of measuring the maximum load at which the product can flow through a hole of given diameter, etc ...

In the examples below the flowability characteristics were determined by the flow time of 50 g of powder through the 4 mm diameter hole of a funnel whose walls form an angle at the top of 60 degrees.

In all cases, the particle size has a passing at 300 microns between 99 and 100%.

The flow hierarchy thus obtained is the same if one uses a test of the type of flow under load as mentioned above. Typically, said adjuvants make it possible to obtain a flow time for the "inotube", whose particle size has a 63 μm pass from 10 to 35%, between 17 and 27 s.

Example No. 1:

A mixture was prepared from the following constituents:

76% of ferro-silicon with 65.5% Si, 1.3% Ca and 0.95% Al, in powder with a particle size of less than 300 μm,

4% of fluorspar powder with a particle size of less than 150 μm,

20% silicon-calcium alloy known as "CaSi", 30.3% Ca, powder of particle size less than 300 microns.

The measurement of the particle size shows that it has a 63 μm pass of 23%.

The flow time is 28 s.

Used as a "dry spray" as a reference test, this product has given satisfactory results: the pipes are practically free from pitting; the few bites present are shallow and allow to meet the specifications; the carbide content is 8% and there is a thickness of ferritic cast iron of 35 μm in the outer surface of the pipe.

Example N ° 2: The product described in Example No. 1 was stored in canvas bags known as "big bags" under a shed for 2 months.

After this storage:

-The measurement of the particle size shows that it still has a 63 μm loop of 23%,

-The product does not flow through the 4mm diameter hole.

Used in "dry-spray", this product has given less good results: the pipes have pits in many areas and the scrap rate is much higher than in Example 1. The carbide content is 12% on average, but it is characterized by a greater dispersion than in Example 1. As a consequence, the time of the subsequent annealing for absorbing the carbides must be increased. No ferritic pig iron was found on the outer surface of the pipe.

Example No. 3

The same mixture was prepared as in Example 1 but with the addition of 0.06% of a 40% solution of potassium siliconate in water homogeneously during the mixing operation. The measurement of the particle size shows that it has a 63 μm pass of 23%.

The flow time is 21 s.

Used in "dry-spray", this product has given very good results: the pipes are completely free of punctures; the degree of carbides is 8% and a thickness of ferritic cast iron of 35 μm has been noted on the external surface of the pipe.

Example 4:

The product described in Example No. 3 was stored in a "big bag" under a shed for 2 months.

After this storage:

-The measurement of the particle size shows that it still has a 63 μm passing 23%. -The flow time is 27 s.

Used in "dry-spray", this product has given satisfactory results: the pipes are practically free of punctures: the few punctures present are shallow and allow to respect the specifications; the carbide content is 10% and a thickness of ferritic cast iron of 35 μm has been noted on the external surface of the pipe.

Example N ⁰ 5:

A mixture was prepared from the following constituents:

76% of ferro-silicon with 65.5% Si, 1.3% Ca and 0.95% Al, in powder with a particle size of less than 300 μm.

4% powdered fluorspar with a particle size of less than 150 μm. 20% Ca-Si at 30.3% Ca, in powder with a particle size of less than 200 μm.

The measurement of the particle size shows that it has a loop at 63 μm of 31%.

The flow time is 35 s.

Used in "dry-spray", this product has given unsatisfactory results: the pipes have punctures and some do not comply with the specifications; the carbide content is 12% and there is a thickness of ferritic cast iron of 15 microns on the outer surface of the pipe.

Example No. 6

The same mixture as in Example 5 was prepared, but with the addition of 0.06% of a 40% solution of potassium siliconate in water homogeneously.

The measurement of the particle size shows that it has a loop at 63 μm of 31%.

The flow time is 25 s. Used in "dry-spray", this product has given satisfactory results: the pipes are virtually free of punctures: the few punctures present are shallow and allow to meet the specifications; the degree of carbides is 8% and a thickness of ferritic cast iron of 35 μm has been noted on the external surface of the pipe.

It can be seen that, thanks to the adjuvant, the flow time is reduced by 7 and 10 seconds for the mixtures which, without adjuvant, flow through the hole of diameter 4 mm (Examples 3 and 6 compared respectively to Examples 1 and 5) and is brought to 27 s in the case of a mixture which, without adjuvant, does not flow through said hole (Example 4 compared to Example 2). More generally, it can be remembered that this time is reduced from 5 to 10 s, if the mixture without adjuvant flows through the hole of diameter 4 mm, and is between 20 and 27 s if the mixture without adjuvant does not flow. not through said hole.

Moreover, the adjuvant makes it possible to make the flowability characteristics of the product little dependent on its physical or physico-chemical characteristics, which is observed in particular by comparison between the flow times before and after storage of the "inotubes" of the examples. 3 and 4, while products without adjuvant are significantly sensitive (Examples 1 and 2).

Claims

claims

1. Powdered product, for the protection of centrifugal casting molds cast iron pipes by dry spraying said product on the inner surface of said mold, comprising an alloy or a mixture of metal alloy (s) inoculant (s), optionally powders of reducing elements or alloys with an anti-pitting effect, possibly an inert mineral filler, characterized in that it further comprises at least one adjuvant intended to improve the flowability characteristics of said powdered product.

2. Product according to claim 1, characterized in that said adjuvant is chosen so that the flowability is such that the flow time of 50 g of product through the hole of diameter 4 mm of a funnel whose walls form an angle at the top of 60 degrees, is between 17 and 27 seconds for a particle size having a loop to 300 microns between 99 and 100% and a passing at 63 microns between 10 and 35%.

3. Product according to claim 2, characterized in that said adjuvant is chosen so that the flowability is such that the flow time with respect to the same product without said adjuvant is reduced from 5 to 10 s if the same product without said adjuvant flows through the hole of diameter 4 mm, and is between 20 and 27 s if said same product without said adjuvant does not flow through said hole.

4. Product according to one of claims 1 to 3, characterized in that the adjuvant is silicone oil.

5. Product according to one of claims 1 to 3, characterized in that the adjuvant is potassium siliconate.

6. Product according to one of claims 1 to 3, characterized in that the adjuvant is microsilica of density less than 0.1.

7. Product according to one of claims 1 to 3, characterized in that the adjuvant is a mixture in any proportions of silicone oil, potassium siliconate and / or microsilica of density less than 0.1 .

8. Product according to one of claims 1 to 7, characterized in that the mass proportion of adjuvant in said product is between 0.02 and 0.2%.