GB2240288A

GB2240288A - A thick-walled, small diameter metal tubing

Info

Publication number: GB2240288A
Application number: GB9101528A
Authority: GB
Inventors: Masayoshi Usui
Original assignee: Usui Kokusai Sangyo Kaisha Ltd
Current assignee: Usui Kokusai Sangyo Kaisha Ltd
Priority date: 1990-01-25
Filing date: 1991-01-24
Publication date: 1991-07-31
Anticipated expiration: 2011-01-24
Also published as: GB9101528D0; JPH03223585A; GB2240288B; KR940009341B1; DE4102051A1; KR910014640A

Abstract

A thick-walled, small diameter metal tubing consists of a thick-walled metal tube and a coating layer of polytetrafluorethylene, in intimate contact with the inner surface thereof.

Description

C C-j - 2's a 1 THICK-WAILLED- SMALL DIAMETER HWAL TUBING The present

invention relates to a thick-walled metal tubing which has an outside diameter of less than about 20 mm which is typically, though not exclusively, for use as a passage for supplying a fuel such as an alcohol.

Metal tubing of this kind has been proposed by the present applicant in Japanese Utility Model Publication No. 19184/1984. As shown in Figure 4, this tubing comprises an outer tube 11, and inner tube 12, providing a fluid passage surface 13 inside the outer tube 11, and a spread layer 14 f itted between the outer tube 11 and the inner tube 12. The inner tube 12 is made of a special steel such as stainless steel, chromiummolybdenum steel, or manganese steel such that its tensile strength and wall thickness are limited. The spread layer 14 is made of a metal such as copper, aluminium, tin, lead, or zinc, or from a resin. Thus, the prior art tubing consists of several tubes of metals.

Where a normal Diesel fuel is used in a Diesel engine, as the rotational speed of the engine is increased to increase the power output of the engine, the inside pressure of f luid becomes high. This tends to cause cavitation erosion on the surface of the fluid passage. The prior tubing is resistant to cavitation erosion almost satisfactorily but is not highly resistant to cavitation erosion in some applications, for example, where methyl alcohol or an alcohol fuel consisting of 1 2 methyl alcohol and light oil is used. In the conventional tubing described above, the fluid passage surface 13 is formed by the inner tube 12 which is made of a special steel and surrounded by the quite thin spread layer 14. During the final step of the manufacture of the tubing consisting of the superimposed metal layers, the tubing is finished by sizing it.

At this time, looseness tends to occur between the superimposed metal layers. As a result, the resistance to pressure deteriorates. When the engine vibrates, cracks may be produced in the tubing or the mechanical strength may be adversely affected. Another problem arises from the fact that the inside tube 12 is made of a special steel. This known tubing is expensive to fabricate.

It is an object of the present invention to provide a thickwalled small diameter metal tubing which can satisfactorily prevent cavitation erosion even if an alcohol fuel is used, avoids the aforementioned looseness and cracks, has sufficient mechanical strength, and is economical to fabricate.

This object is achieved by a thick-walled small diameter metal tubing, the'tubing comprising a tube consisting of at least one layer of metal, a coating layer made from polytetrafluoroethylene and in intimate contact with the whole inner surface of the tube, and a fluid passage surface formed by the inner surface of the coating layer.

A. r M- -,' Polytetrafluoroethylene is sold under the trade name eflon.

1 1 3 In the tubing of the present invention, the inner surf ace forming the fluid passage surface is formed by a coating layer made from polytetraf luoroethylene that is smooth, -slippery, and resilient. Therefore, the energy of bubbles causing cavitation erosion is dispersed and moderated. Also, because of the wet strength, resilience, and low coefficient of friction of polytetrafluoroethylene, cavitation erosion on the fluid passage surface can be effectively prevented whether an alcohol f uel is used or not. Furthermore, when the tubing is finished by sizing it, looseness does not occur on the coating layer.

Therefore, the mechanical strength of the tubing is so high that no cracks are produced in it. In addition, the use of a coating layer made from polytetrafluoroethylene reduces the manufacturing costs. Further, the wall thickness of the tube f orming the main component of the tubing can be reduced. This permits the number of drawing steps to be reduced. Moreover, the weight of the tubing can be reduced.

The invention will now be described by way of example only with reference to the accompanying drawings Figures 1 to 4 in which:- Figure 1 is a fragmentary plan view of a thick-walled small diameter metal tubing fabricated in accordance with the invention. and in which the tubing is used as a high-pressure fuel injection pipe; Figure 2 is an enlarged horizontal cross section taken on line II-II of Figure 1; 4 Figure 3 is a cross section similar to Figure 2, but showing another thick-walled metal tubing according to the invention; and Figure 4 is an enlarged horizontal cross section of the prior art thick- walled small diameter metal tubing consisting of several superimposed metal layers.

Referring to Figures 1 and 2, there is shown tubing in accordance with the invention. This tubing consists principally of a tube 1 having a diameter less than about 20 Mm. A coating layer 2 is formed over the entire inner surface 11 of the tube 1. The coating layer 2 consists of a tube or layer of polytetraf luoroethylene (PM) In manufacturing the tubing. a tube of PTFE is formed along the inner surface 11 of the tube 1 such that the tube of PTFE makes intimate contact with the inner surface 11, or molten powdered PTFE is sprayed against the inner surf ace 1 1 of the tube 1 by f lame spray coating to form the coating layer 2. The inner surface 21 of the coating layer 2 forms a fluid passage surface 3.

Figure 3 shows a tubing similar to the tubing shown in Figures 1 and 2 except that a relatively thin-walled. metal tube 4 made of stainless steel or the like is added. This metal tube 4 is superimposed or wound on the tube 1.

In each tubing, the'coating layer 2 may consist of a tube of A le polytetraf luoroethylene and a layer of polytetraf luoroethylene formed by flame spraying.

The present applicant used an alcohol fuel consisting of 80 v.d.% of methyl alcohol and the remaining percentage of light oil. Also, an alcohol fuel consisting totally of alcohol was used. Fluid passage surfaces were formed with a stainless steel tube and a polytetrafluoroethylene tube of the same thickness for comparison purposes. Experiments have revealed that the novel tubings are free from cavitation erosion for at least twice as long as comparative examples of prior art tubing.

According to the present invention an adhesive agent 4 such as epoxy resin adhesive can be applied between the inner surface of the tube 1 and the outer surface of the coating layer 2 so as to further improve in the intimate contact of the tube with the coating layer.

As described thus far, in the inventive thick-walled metal tubing having a small diameter, the coating layer 2 made from polytetrafluoroethylene is in intimate contact with the inner surface 21 forming the fluid passage surface 3.

Therefore, because of the characteristics of PTFE i.e., wet strength, resilience, and low coefficient of friction, cavitation erosion on the fluid passage surface 3 can be effectively prevented for a long time in applications where 6 alcohol f uels are used, as well as in normal application where Diesel fuels are used. Also. looseness can be prevented during sizing process. The novel tubing is so mechanically strong that no cracks occur in it. Furthermore, the tubing is economical to manufacture. As the thickness of the wall of the tube is reduced, the number of drawing steps is reduced.

Additionally, the weight of the tubing can be reduced. In this way, the novel thick-walled metal tubing of a small diameter yields quite useful advantages.

11 7

Claims

CLAIMS:

1. Thick-walled small diameter metal tubing comprising: a thick-walled metal tube consisting of at least one layer; and a coating layer which is in intimate contact with the whole inner surface of the tube and made from polytetrafluoroethylene, the inner surface of the coating layer forming a fluid passage surface.

2. The thick-walled metal tubing of claim 1, wherein said coating layer is a tube of polytetrafluoroethylene which Is formed along the tube so as to make intimate contact with the thick-walled metal tube.

3. The thick-walled metal tubing of claim 1, wherein said coating layer is formed by spraying powdered polytetrafluoroethylene against the inner surface of the tube by flame spraying.

4. The thick-walled metal tubing of claim 1, wherein said coating layer consists of a tube of polytetraf luoroethylene and a layer of polytetrafluoroethylene formed by flame spraying.

5. The thick-walled metal tubing of claim 1, wherein an adhesive agent is applied between the inner surface of the tube and the outer surface of the coating layer.

6. Thick-walled small diameter metal tubing substantially as described herein and as shown in Figures 1 to 3.

Published 1991 at 7be Patent Office, State House. 66/71 High Holborn. LondonWC I R47P. Further copies may be obtained from Sales Branch. Unit 6. Nine Mile Point, Cwnifeltnfach. Cross Keys. Newport NPI ?HZ. Printed by Multiplex techniques ltd. St Mary Cray. Kent.