SE452859B - SHALL OR ROD-FORMED FORM, IN PARTICULAR WITH COMPLIED FORM, WHICH FORMULA IS PROVIDED FOR NOT TO BE IN A MACHINE, EXCEPT A COMBUSTION ENGINE, AND SET TO MAKE THE FORMAL - Google Patents

Description

35 452 859 with a remaining mandrel or core. Thus, SE-A-8300603-1 describes a method of producing mechanical parts with a heat-insulated gas duct (in practice only inlet ducts to an engine combustion chamber should be considered) by thermal spraying of a very thin first layer (thickness approx. 0, 1 - 0.2 mm) of a soft metal, such as zinc, tin, lead) copper or light metal, on a sand core. A second layer with a thickness of 0.5 - 2.5 mm of a metal or metal alloy, such as simple and inexpensive carbon steel, is applied by thermal spraying to the first layer, whereupon a third layer, which serves as a heat barrier and consists of a ceramic materials are applied, for example by thermal spraying. Then the sand core with the applied three layers is placed in a mold for casting the machine part in a conventional manner.

After casting, the spirit core is removed, so that the three layers form a channel lining in the machine part.

In this known method, however, there is a risk of crack formation during thermal spraying of the different layers, which have different thermal expansion properties. Furthermore, the first layer, which forms the inner surface of the machine part, is not corrosion-resistant and is also not suitable for, for example, exhaust ducts. The melting point of the soft metal is too low to allow such use in an internal combustion engine. Thus, the exhaust gas temperature is normally 850 ° C, while the melting point of zinc is about 420 ° C.

The object of the invention is to obviate the disadvantages and limitations of the known methods and to enable simple production of shell or tubular objects, even with complicated geometry, by thermal spraying of a heat and corrosion resistant metal alloy. A further object is to enable the casting of such an object into a cast body with one or more channels or cavities formed by cast shell or tubular objects according to the invention. 10 20 25 30 35 452 859 The main purpose is stated with an object resp. a production method in accordance with the following claims 1 and 7. Other suitable features are stated in claims 2 ~ 6 resp. 8.9.

Thus, in the manufacture of such an article, it is essential that the core body against which a first, relatively thin layer has been sprayed be removed before further material is applied by spraying. It is particularly suitable that the core body is made of casting sand, which, for example by heating, can lose its dimensional stability and be discharged from the thin tube or shell. Continued fitting can then be carried out to the desired thickness, without the risk of cracking due to stresses, which inevitably arise if the core body is left behind.

Conveniently, the thermal spraying of the second layer can be controlled so that this second layer contains more oxides and / or pores than the first layer, whereby desired properties, in particular poorer thermal conductivity, are obtained in this second layer. Of course, it is also possible to apply a third layer, either between the other two or as a layer sprayed on top of the second layer. Such a, preferably relatively thin third layer can e.g. be used as a diffusion barrier for carbon or nickel. It can also be used to improve the mechanical properties at high temperatures.

The invention is explained in more detail below with reference to the accompanying drawing, which illustrates an embodiment.

Pig. 1 schematically shows a sand core; Fig. 2 shows the sand core with a sprayed, thin first layer; Fig. 3 shows the desired tubular object after removal of the sand core and spraying of a relatively thick second layer on the first layer.

In a manner known per se, a core body 1 is thus made of casting sand with phenolic resin as binder. As shown in Fig. 1, this core body 1 has an external configuration corresponding to the desired tubular object internal configuration, and in addition holder portions 1a, 1b at each end for clamping the core body. In the exemplary embodiment, the desired object consists of an exhaust duct in a cylinder head for an internal combustion engine.

In accordance with Fig. 2, a relatively thin and substantially pore-free layer 2 of a metal alloy containing about 5% Al, 22% Cr and the remainder mainly Fe is sprayed onto this core body 1.

(Concentrations refer to% by weight). Any porosity must consist of closed pores. When the layer thickness is at least 0.5 mm, preferably about 1 millimeter, the spraying is stopped, whereupon the sand core 1 is removed by heating the sprayed sand core in an oven at about 600 ° C for 2-3 hours and the sand is then discharged from the barrel. tubular metal alloy layer 2.

Then a second layer 3 is sprayed on the outside of the first, self-supporting thin layer 2. In the absence of a core body, the first layer 2 was allowed to expand and shrink freely under the influence of temperature variations, without risk of stresses and subsequent cracking. The thickness of this second layer can be at least 1 mm. The spraying can be performed without interruption for cooling or cooling.

Different methods of spraying are conceivable. Preferably, the first, relatively thin layer 2 is sprayed with a wire-fed flame sprayer, which gives a dense layer. If a surface layer of high purity is sought (small amounts of oxides and pores), the layer can be applied by plasma spraying. The second layer 3 can be conveniently applied with a powder-fed flame sprayer to obtain a suitable amount of pores and oxides. A total amount of 5 - 25%, preferably about 15%, of pores and oxides is sought.

However, the second layer 3 does not have to have the same material composition as the first layer 2, but can e.g. consists of other metal alloys with high heat resistance.

However, with regard to the thermal stresses that can arise in the material, it is an advantage if the layer consists of the same material and differs only in terms of perosity and oxide content.

In addition, a thin third layer can be laid either between or on top of the two above-mentioned layers. The third layer can i.a. act as a membrane layer or diffusion barrier.

The article and the method of production according to the invention have several advantages. The geometric shape can be chosen as desired, as well as material and wall thickness. Thus, very thick layers (second layer 3) can be applied after the core body has been removed. Furthermore, the manufacturing method is relatively fast (metal can be sprayed on a red-hot surface) and the handling is fairly simple. The cassation is very lawful due to the eliminated risk of cracking. Also subsequent work steps, e.g. casting, is facilitated and can be performed with great precision. The avoidance of ceramic materials also facilitates the recycling of scrap.

Claims (9)

452 859 PATENT CLAIMS A shell or tubular article, in particular with a complicated shape, which article is intended to be in a machine oath, in particular in an internal combustion engine, and has a first, inner layer (2) of one thermally against a core body (1) sprayed metal alloy and a second, thicker layer, consisting of a thermally sprayed metal alloy on the outside of the first layer (2), characterized in that the first layer (2) consists of a high temperature and corrosion resistant metal alloy with a thickness of 0.5 - 1.5 mm, and that the second layer (3) likewise consists of a high temperature resistant metal alloy, which contains more oxides and / or pores than the first layer (2) and thereby serves as a heat barrier, wherein the second layer (3) for avoiding spot formation is sprayed after removal of said core body (1). An article according to claim 1, characterized in that the second layer (3) has substantially the same material composition as the first layer (2). An article according to claim 1 or 2, characterized in that the porosity and oxide content of the second layer (3) exceeds 10%. An article according to any one of claims 1 to 3, characterized in that at least the first layer (2) consists of 1 - 12% Al, 10 - 30% Cr, optionally small amounts of one or more elements in the group Si, Mn, Co, Y, HE, possibly small amounts of oxides and nitrides and reeten Fe. 5. An article according to any one of claims 1 - 4, characterized in that the thickness of the second layer (3) is greater than 1 mm, preferably about 2.5 mm. 452 859 6. An article according to any one of the preceding claims, characterized by a third layer between or on top of the other two layers and substantially thinner than these. A method of making a shell or tubular article according to any one of the preceding claims, wherein the article is made by thermal spraying of a high temperature and corrosion resistant metal alloy, characterized in that said first layer (2) is formed by thermal spraying against a core body (1), the external dimensions of which correspond to the internal dimensions of the finished article, whereupon the core body (1) is removed and said second, thicker layer (3) is applied externally to the first layer (2) by thermal spraying, so that the internal article of the finished article surface is formed by the pre-layer (2). 8. A method according to claim 7, characterized in that the core body (1) is made of casting sand. 9. A method according to claim 7 or 8, characterized in that the thermal spraying is regulated so that the second layer <3) contains more oxides and / or pores than the first layer (2).