FR2474949A1 - Composite metal tube with internal lining of tungsten carbide - which resists heat, abrasion, and corrosion - Google Patents

Abstract

A former tube is covered with a metal layer (I) by deposition welding, which is then used to apply an outer layer (II) of a metal or alloy which is easy to machine. The assembly is next located in an outer tube by brazing or shrink-fitting; and the former tube is removed by machining, so layer (I) forms the bore of a composite tube. Layer (I) pref. consists of tungsten carbide grains bonded by a brazing alloy contg. Ni, Cr, B, and Si, whereas layer (II) is pref. brass, which is machined to a desired external dia. before being brazed. Only a limited amt. of grinding is required to produce a desired bore dia. for (I).

Description

DESCRIPTION
Improvement in the production of composite tubes including in particular protective internal coatings improving their characteristics in terms of resistance to abrasion, chemical corrosion or resistance to high temperatures.

The present invention makes it possible to produce interior coatings of tubes without practically any limitation as to the geometry of the tubes usually required in the context of current industrial requirements.

These coatings can be obtained by currently known methods of metallization, welding, deposits obtained by chemical reaction or by electrolysis.

The present invention relates in particular to metal tubes internally coated with hard alloys resistant to abrasion wear and used in t presses for the extrusion of plastics or rubber.

 The production of metallic or non-metallic composite tubes with an internal coating, having improved characteristics, are carried out by various techniques (metallization, welding, vapor phase deposits, chemical reaction deposits, etc.) in which the inside the support tube.

 We thus know the techniques of welding or rather of brazing at high temperature where we introduce by metallization or any other technique an alloy adapted inside a metal tube with the required qualities, then to bring it to temperature to obtain a metallurgical connection between the alloy inside and the outside tube. Various variants exist for heating: inside an oven, by induction.

 The regularity of the deposit being obtained as a general rule, by a rotation of the tube causing the centrifugation of the alloy. The devices making it possible to achieve this result are complicated, particularly to avoid excessive deformation of the tubes.

We immediately see the limitations of these processes
1 - Alloy melting at a temperature below
support tube.

2 - Alloy with phy characteristics
sico-chemical self-etching, so that the
metallurgical bond be correctly realized
read.

3 - Risk of significant deformation.

There are also known metallization techniques using conventional equipment, namely metallizing gun with chemical flame supplied by metallic wires, metallization beads or by powder of metallic alloy or ceramic and so-called plasma gun supplied with powders. metallic or ceramic alloys or a combination thereof.

 The main difficulty lies in the need to introduce the jet of molten particles inside the tube.

The devices sometimes implemented to overcome these drawbacks frequently cause a reduction in the performance of the coatings thus obtained (deflected jet nozzle, in particular in the case of metallizing guns with wires or cords).

Finally, it should be mentioned that Plasma devices, due to their design, lend themselves very poorly to metallization inside bores.

The method according to the invention makes it possible to avoid the drawbacks due to the need to work inside a tube. 11 indeed makes it possible to work outside initially on an intermediate piece which will disappear at the during the subsequent treatment. The realization of the coating under these conditions obviously poses no particular difficulty.

According to a first variant, the method will consist in producing, by traditional electric arc or flame welding, a deposit on a metal cylinder (1) of the alloy (2) which it is desired to have then inside the tube. however, that the diameter (D) of this intermediate part will be very close to the final internal diameter, sought for the final part. (Fig. 1)
The process according to the invention takes on a very particular interest, when the reloading thus produced presents great difficulty in being re-machined or rectified. This is particularly the case with reloading, comprising a large concentration of molten tungsten carbide. In this case, the method according to the invention consists in carrying out, in a second step, also a reloading by welding, of an easily re-machinable alloy, for example brass (3). Finally, the brass is re-machined to obtain a geometrically defined cylindrical surface. Fig. 3)
The cylinder thus obtained is then fitted inside the final tube. (4)
The two cylinders can be assembled using various techniques. In our case, we have brazed with a silver alloy with induction heating (Fig. 5)
The silver solder (6) has a great fluidity which is particularly advantageous in this case, so that, by a capillary effect, the gap between the two tubes is perfectly filled. (Inductor 5)
After the two tubes have been assembled, the bore is machined until the surface is flush with the surface. In the event of a surface filling containing a large proportion of tungsten carbide, finishing must be carried out , Island. (Fig 6)
In this specific case, the quantity to be machined of tungsten carbide reloading will be extremely limited. We imagine that, even in the case where the cylinder to be coated, is of large size and where direct reloading could have been carried out by welding on the cylinder (4), the expense for grinding is considerable. It is indeed necessary to eliminate the irregularities of the deposit by welding and this has the consequence of re-machining 3 to 4 mm of a tungsten carbide-based reloading .

 Experience shows that the cost of such an operation is considerable.

 According to a second variant, the method will consist in carrying out on a metal cylinder (i) Fig 7, a metallization with a plasma torch for recharging (2) of tungsten carbide of Imm thickness approximately The cylinder having, as in the preceding example, the characteristic of '' have an outside diameter very close to the final inside diameter, sought in the bore.

Secondly, a soft alloy (3) will be metallized on the first metallization (brass, copper, nickel
As before, this alloy will be remanufactured to obtain a geometrically defined surface, (Fig 3) The adjustment of the two tubes produced can be made by brazing or any other technique, depending on the service conditions of the part.

Claims (2)

R F V E N D T G # T I O N J Process for producing composite metal tubes comprising a protective inner reload improving the characteristics of the tube with regard to its resistance to abrasion, chemical corrosion and high temperatures. These are made by known welding or metallization techniques. 10) Process characterized by mid transfer, of a reloading carried out inside a first tube, on a second final tube with the interpositsmn of a soft alloy intermediate between the reloading and the tube to be protected.  20) Method according to claim I allowing the realization of inner tube recharging using a composite alloy., Comprenaltit grains of molten tungsten carbide bonded by a brazing nickel, chromium, boron and silicon, and comprising a sub -layer of soft brass alloy. The two tubes are assembled by brazing, with an alloy of great fluidity and heated by induction. 30) The assembly of the two tubes can be achieved by wedging obtained by hooping the outer tube on the inner tube. To achieve this assembly, it will be necessary to machine the outer tube internally to a smaller dimension than the internal part. The outer tube will then be heated homogeneously, preferably by induction to obtain an increase in its dimensions allowing the assembly of the two parts. When cooling, the contraction of the external tube will cause significant tightening on the internal part.