Wheel body

The present invention relates to a wheel body for carriages or other vehicles which are used, inter alia, in roller-coasters and other installations of amusement parks.

According to the prior art, wheels or wheel bodies for carriages or other vehicles used, inter alia, in roller-coasters and other installations of amusement parks, are fabricated from an aluminium alloy. Because of the good castability of the latter, Al-Si alloys are often used for this application. Carriages or other vehicles used in the roller-coasters and other installations of amusement parks comprise not only wheels for forward movement of the vehicle on the installation, but also wheels by which the vehicle in the installation bears against a guide.

These guide wheels do not make continuous contact with the guide, instead the contact between the guide wheel and the guide is subject to interruptions. When the contact between a guide wheel and the guide is broken, the speed of rotation of the wheel will decrease. When the contact between the guide wheel and the guide is subsequently restored, the guide wheel will be subject to large acceleration. In order to be able to sustain the acceleration and the changing stresses which occur when the contact between the guide wheel and the guide is broken and restored, a guide wheel is ideally made from a ductile material. In order, moreover, to be able to absorb more effectively the shock which occurs when the wheel makes contact with the guide, the running tread of the wheels is preferably provided with a running tread of plastic. A second effect of such a plastic running tread being fitted is that noise is reduced. In the prior art it is customary to provide the wheels used in roller-coasters and comparable installations with a running tread of polyurethane rubber, fixed in an exothermal reaction in a vulcanization process. In that exothermal reaction the temperature may increase to up to 160°C.

A first important drawback of the wheels which are used in roller-coasters and comparable installations according to the prior art is that the Al-Si alloys used have relatively low elongation at rupture, less than 10%. Because of the enormous mechanical stresses to which the wheels are subjected, there is a risk that the wheels may break spontaneously without much deformation during overloading or after having been damaged. Certainly, given that the roller-coasters and comparable installations are most commonly used in an environment where many people are present, this means that life-endangering situations can thus be created.

A second important drawback of the wheels which are used in roller-coasters and comparable installations according to the prior art is that the mechanical characteristics of the Al-Si alloys used are adversely affected under the influence of thermal stress in the region of 160°C. This means that each time a running tread of polyurethane is applied to the wheel by means of an exothermal reaction in the vulcanization process, the mechanical characteristics of the wheel will change. In the prior art the maximum number of times a wheel is allowed to be provided with a new running tread of polyurethane rubber is therefore restricted to a limited number of times, for example five times.

The object of the invention is to provide a wheel body for carriages or other vehicles which are used, inter alia, in roller-coasters and other installations of amusement parks, which do not have the drawbacks of the prior art. This object is achieved in the present invention by the wheel body according to the present invention being made of a casting alloy which, expressed in percentages by weight, comprises the following elements:

Al > 94.000

Mg > 4.500

Si < 0.100

Cu < 0.015

Fe < 0.100

Mn < 0.007

Ti < 0.025

Zn < 0.050

Sn < 0.010.

In this context it is advantageous for the wheel body according to the present invention to be made of a casting alloy which, expressed in percentages by weight, comprises the following elements:

94.0 < Al < 95.0

4.5 < Mg < 5.0

0.005< Si < 0.05

0.001< Cu < 0.01

0.001< Fe < 0.01

0.001< Mn < 0.01

0.001< Ti < 0.01

0.001< Zn < 0.01

0.001< Sn < 0.01.

The advantage of using the abovementioned Al-Mg casting alloy is that this alloy has an elongation at rupture which is greater than 14% and a fatigue limit at a load above 60 N/mm². "FEM" studies have shown that the highest stress achieved in said wheel design for a roller-coaster is at most about 31 N/mm². This is far below the fatigue limit load of 60 N/mm². This means that an assessment of the service life of the wheels for use in roller-coasters and the like is not applicable and that the wheels, in principle, have an unlimited service life. If the length of a ride is 660 to 1600 metres and if the usage is 25 rides per hour for eight hours per day, wheels in a roller-coaster are subject to at least 0.3 to 0.7 million load changes. Wheels used for that purpose, which comprise alloys according to the prior art, will be subject to fatigue damage after at most 10 to 100 days of service. Wheels used for that purpose according to the present invention are not subject to fatigue damage. Another effect of the presence of a large elongation at rupture is, that the wheel body is able to deform without breaking. This means that deformation of the wheel body can manifest itself without the wheel breaking immediately and hazardous situations being produced.

It is advantageous for the wheel body according to the present invention to be fitted with a running tread of plastic such as polyurethane.

Surprisingly, the mechanical characteristics of the Al-Mg alloy which is used for the wheel body according to the present invention proved not to change after repeated thermal stress in a temperature range of from 0 to 180°C. This means that applying a running tread of plastic, for example of polyurethane, in an exothermal reaction in which the temperature increases up to, for example, 160°C, does not affect the mechanical characteristics of the alloy which is used for the wheel bodies according to the present invention. This means that the application of a new running tread of polyurethane can, in principle, be repeated an infinite number of times without adversely affecting the mechanical characteristics.

The present invention further relates to a method for fabricating a wheel body wherein, in a first step, a wheel body is fabricated by means of a casting process from a casting alloy which comprises the following elements, indicated in percentages by weight:

Al > 94.000

Mg > 4.500

Si < 0.100

Cu < 0.015

Fe < 0.100

Mn < 0.007

Ti < 0.025

Zn < 0.050

Sn < 0.010,

said wheel body, in a second step, being fitted with a running tread of plastic such as polyurethane.

In this context it is advantageous for the casting alloy to comprise the following elements, indicated in percentages by weight:

94.0 < Al < 95.0

4.5 < Mg < 5.0

0.005< Si < 0.05

0.001< Cu < 0.01

0.001< Fe < 0.01

0.001< Mn < 0.01

0.001< Ti < 0.01

0.001< Zn < 0.01

0.001< Sn < 0.01.

It is further advantageous for the wheel body according to the present invention to be fabricated in a sand casting process.

In the prior art, wheel bodies for carriages used in roller-coasters and comparable installations of amusement parks are, as said before, usually made of an Al-Si alloy. Such wheels or wheel bodies are generally fabricated by means of a gravity die-casting process. The alloy which is used for the wheel bodies or wheels according to the present invention can advantageously be fabricated by means of a casting process in sand. After the fabrication of the wheel bodies themselves it is possible, by means of an exothermal reaction in a vulcanization process, for a running tread of plastic such as polyurethane rubber to be applied to the wheel bodies, the temperature increasing in the process to at most 160°C. As already stated above, this does not affect the mechanical characteristics of the Al-Mg alloy used.

An advantageous embodiment of the wheel body according to the present invention is illustrated in the accompanying figures.

Figure 1 schematically shows a cross-section of the wheel according to the present invention.

Figure 2 schematically shows a plan view from above of the wheel from the present invention.

Figures 1 and 2 show that the wheel comprises a wheel body which comprises a hub 1, a rim 2 and a number of stiffening ribs 3. Fixed to the wheel body is a plastic running tread 4 by which the wheel makes contact with a guide 5.