AU1145399A

AU1145399A - Method of producing a float, a fuel-resistant float and a use for pressed together particles produced by extrusion

Info

Publication number: AU1145399A
Application number: AU11453/99A
Authority: AU
Inventors: Gunter Rauchhaus
Original assignee: Mannesmann VDO AG
Current assignee: Mannesmann VDO AG
Priority date: 1997-09-12
Filing date: 1998-09-07
Publication date: 1999-04-05
Anticipated expiration: 2018-09-07
Also published as: ATE228646T1; DE19740058A1; KR20010023814A; AU738611B2; EP1012543A1; ES2188026T3; BR9812642A; WO1999014564A1; CN1270668A; CN1130551C; EP1012543B1; DE59806464D1; DE19740058C2

Abstract

The invention concerns a float (2) sensing a motor vehicle fuel tank level, comprising a plurality of plastic particles (7, 8) compressed together and foamed by extrusion in a free space. Said particles comprise a very large proportion of inclusions (9, 10) of pore-forming agent with respect to the plastic material thereby having a particularly reduced specific weight. The float (2) can consequently be produced from particularly economical plastic material.

Description

3609 PCT Description Method of producing a float, a fuel-resistant float and a use for pressed together particles produced by 5 extrusion The invention relates to a method of producing a float from a fuel-resistant plastic, in which a pasty composition of plastic in the liquid state is mixed 10 under high pressure with a blowing agent or a substance giving off the blowing agent and is subsequently made to solidify, to a fuel-resistant float of a filling level sensor for a fuel tank of a motor vehicle and to a use for pressed together particles produced by 15 extrusion. Fuel-resistant floats for filling level sensors in fuel tanks of motor vehicles are often produced from nitrophyl, since this material has the low relative density necessary for this purpose and the chemical and 20 physical resistance to fuels. What is disadvantageous about the known float is that nitrophyl is very expensive on account of its complex production. The idea of replacing nitrophyl by the particularly inexpensive plastic POM (polyoxymethylene) 25 has already been considered. For producing a float from this material, until now a pasty mixture of plastic and blowing agent has been introduced into a mold corresponding to the float. During this process, the blowing agent makes the plastic expand until it 30 completely fills the mold. After making the composition solidify or set, the finished float can be demolded. However, the known method can only be used to produce from POM a float with a relative density of at 35 least 0.5, so that it - only just floats in the fuel (relative density 0.7). This is not acceptable, however, in the case of a float for a fuel tank of a motor vehicle, since even slight forces acting on the float cause it to be submerged in the fuel. Such a - 2 - 3609 PCT float could, for example, sink to the bottom of the fuel tank when the motor vehicle drives through a depression in the ground, and consequently falfify the filling level indication. 5 The invention is based on the problem of further developing the method mentioned at the beginning of producing a float, so that a very low-cost float with a particularly low relative density can be produced with it. Furthermore, a very low-cost float 10 with a particularly low relative density is to be provided. In addition to this, an advantageous use' is to be found for pressed together particles produced by extrusion. The first-mentioned problem is solved according 15 to the invention by extruding the composition in [sic] a free space and subsequently producing the float from the solidified extruded composition. As a result, the method according to the invention does not require a mold for the expanding of 20 the float. By extruding the pasty composition into the free space, the blowing agent (for example C02) can expand the plastic much more strongly than in a closed mold, because occlusions of particular magnitude and in particularly high numbers are created in the 25 subsequently solidifying plastic. The size and number of the occlusions can be controlled by means of the gas pressure prevailing in the free space. Floats produced according to the invention have a particularly low relative density. They can therefore 30 be produced from a plastic which is of a particularly low cost and is heavier than nitrophyl. For example, the float produced from POM in the method according to the invention has a relative density of 0.2 - 0.25. A further advantage of the method according to the 35 invention is that particularly little plastic is required for producing the float. This leads to a further reduction in the costs for the float. According to an advantageous development of the invention, a multiplicity of floats can be produced at - 3 - 3609 PCT particularly low cost if the pasty composition is extruded into a strand and pieces corresponding to the shape of the float are subsequently cut out from the solidified strand. 5 With the method according to the invention, floats of virtually any desired shape can be produced if the pasty composition is extruded in the form of small drops and subsequently solidifying particles are cohesively bonded together to form the shape 10 corresponding to the float. In this process, the blowing agent causes the drops to expand until they solidify to form the particles. The particles produced as a result have a closed surface and a multiplicity of occlusions from the blowing agent. Since the particles 15 may be of virtually any desired shape, the float produced as a result has occlusions of great magnitude and in very high numbers from the blowing agent and consequently a particularly low relative density. During the bonding together of the particles to form 20 the intended shape, pockets of air are also trapped between the particles, which has the consequence of a further reduction in the relative density of the float produced by the method according to the invention. The particles could, for example, be bonded 25 together by a fuel-resistant adhesive. However, with many plastics permanent adhesion is not possible. According to an advantageous development of the invention, particles produced from a thermoplastic can be bonded together particularly reliably and 30 permanently if the particles are pressed into the intended shape in a warm state. According to another advantageous development of the invention, a multiplicity of floats can be produced in a particularly low-cost continuous process 35 if the particles are bonded to form a strand and pieces corresponding to the shape of the float are subsequently cut out from the strand. As a result, there is no need for a mold corresponding to the float.

ID)

- 4 - 3609 PCT The float is generally machined and drilled through for receiving a lever wire of the filling level sensor. This may cause a number of occlusions to be damaged and to fill with fuel. According to another 5 advantageous development of the invention, filling of the occlusions with fuel can be avoided if the float is coated with a fuel-resistant plastic. As a result, the occlusions of the float are reliably sealed. Since only a small quantity of plastic is required for the 10 coating, the use of a high-grade, and consequently cost-intensive, plastic nevertheless leads only to an insignificant increase in the production costs of the float. The coating may, for example, be produced by dipping the float in liquefied plastic or by spraying. 15 A further advantage of this design is that only the plastic used for the coating requires a permanent chemical and physical resistance to fuel. The second-mentioned problem, that is of providing a very low-cost float with a particularly low 20 relative density, is solved according to the invention by the float having bonded together particles expanded by extrusion. This design has the effect that the float according to the invention has a particularly high 25 ratio of occlusions in relation to the plastic, so that it has a much lower relative density than known floats expanded in a closed mold. ThankS to the invention, the float produced from extruded particles of POM has, for example, a relative density of 0.2 - 0.25. 30 Furthermore, by virtue of *the high ratio of occlusions in relation to the plastic, the float according to the invention requires very little plastic and, what is more, can be re-used at particularly low cost (recycling). 35 The float according to the invention is reliably protected against fuel penetrating into the occlusions if it has an outer skin of fuel-resistant plastic.

- 5 - 3609 PCT To solve the third-mentioned problem, that is the advantageous use of pressed together particles produced by the extrusion process, according to the invention a fuel-resistant float of a filling level 5 sensor for a fuel tank of a motor vehicle is produced from these particles. As a result, the pressed together particles, which can be produced with a particularly low relative density by extrusion, are used as floats. Since a very small quantity of a 10 particularly inexpensive plastic can be used for this purpose, use of the particles produced by the extrusion process and pressed together leads to a particularly low-cost float. The invention allows numerous embodiments. To 15 illustrate its basic principle further, one of these is described below and is represented in the drawing, in which: Figure 1 shows a float according to the invention, arranged in a fuel tank, 20 Figure 2 shows an enlarged representation of the float in a section along the line II-II from Figure 1. Figure 1 shows a float 2 according to the invention, arranged in a fuel tank 1 of a motor 25 vehicle. The float 2 is arranged on a lever wire 4, which is pivotably mounted in a carrier part 3 fastened on a tank wall and follows the surface or the filling level of the fuel 5 in the fuel tank 1. The position of the lever wire 4, and consequently the position of 30 the float 2, is sensed in a known way by a displacement or angle transducer 6, arranged on the carrier part 3, and is fed to an evaluating and indicating unit (not shown). In a sectional representation along the line 35 II-II from Figure 1, Figure 2 shows that the float 2 has a multiplicity of plastic particles 7, 8 pressed together in a warm state. These in each case have a closed surface and a multiplicity of occlusions 9, 10 from a blowing agent. To simplify the drawing, the - 6 - 3609 PCT occlusions 9, 10 are represented in the case of two particles 7, 8 as representative of all the particles 7, 8. The blowing agent may be, for example, CO 2 and the plastic may be POM. The relative density of the 5 float 2 depends substantially on the ratio of the size and number of occlusions 9, 10 in relation to the quantity of plastic. Furthermore, between the particles 7, 8 there are pockets of air 11, 12, which contribute to the particularly low relative density of 10 the float 2. In order that no fuel 5 can penetrate into the pockets of air 11, 12, the float 2 has a thin outer skin 13 of plastic. However, it is possible to dispense with this in the case of an embodiment - not shown - of the float 2 according to the invention in 15 which the pockets of air 11, 12 are largely sealed off by particularly firm pressing of the particles 7, 8. 7o

Claims

1. A method of producing a float from a fuel resistant plastic, with which a pasty composition of 5 plastic in the liquid state is prepared under high pressure with a blowing agent or a substance giving off the blowing agent and is subsequently made to solidify, wherein the composition is extruded into a free space and the shape of the float is produced from the 10 solidified extruded composition.

2. The method as claimed in claim 1, wherein the pasty composition is extruded into a strand and pieces corresponding to the float are subsequently cut out from the solidified strand. 15

3. The method as claimed in claim 1, wherein the pasty composition is extruded in the form of small drops and subsequently solidifying particles are cohesively bonded together to form the shape corresponding to the float. 20

4. The method as claimed in at least one of the preceding claims, wherein the particles are pressed into the intended shape in a warm state.

5. The method as claimed in at least one of the preceding claims, wherein the particles are bonded to 25 form a strand and pieces corresponding to the shape of the float are subsequently cut out from the strand.

6. The method as claimed in at least one of the preceding claims, wherein the float is coated with a fuel-resistant plastic. 30

7. A fuel-resistant 'float of a filling level sensor for a fuel tank of a motor vehicle, wherein it has a multiplicity of particles (7, 8) bonded together, expanded into a free space by extrusion and solidly bonded together to form the float shape. 35

8. The float as claimed in claim 7, which comprises an outer skin (13) of fuel-resistant plastic.

9. A use for a body consisting of pressed together particles produced by extrusion as a fuel-resistant - 8 - 3609 PCT float of a filling level sensor for a fuel tank of a motor vehicle.