Patent Publication Number: US-2018042394-A1

Title: Method for producing an upholstery spring, upholstery spring, mattress, and upholstered furniture

Description:
The present invention relates to a method for producing an upholstery spring, in particular for upholstered furniture or mattresses, an upholstery spring, a mattress and upholstered furniture. 
     DE 10 2013 103 644 discloses a spring of a spring core which is made of wire and can be used, for example, for mattresses or upholstered furniture. The spring consists of a helically wound spring steel wire that deforms when loaded. Such springs have proven to be useful in the manufacture of upholstered furniture and mattresses, wherein the springs are heat-treated in production in order to make them tougher. A heat treatment of this type prevents a drop in individual springs and the resulting depressions such as troughs in cushions or mattresses. However, it can only be determined with great effort whether adequate heat treatment was performed. As a rule, a check is not possible for the end user. 
     It is therefore the object of the present invention to provide a method for producing an upholstery spring, in which it is possible to ensure in a simple manner that adequate heat treatment has been carried out. Furthermore, a mattress and upholstered furniture with such an upholstery spring should be provided. 
     In order to achieve this object, the method for producing an upholstery spring provides that a heat-sensitive colour indicator is applied at least in sections to a spring steel wire before, during or after the bending of the spring steel wire, and then the spring steel wire is heated to at least the changeover temperature of the colour indicator before the upholstery spring is completed. By applying the heat-sensitive colour indicator it is ensured that the heat treatment of the spring steel wire can be rendered visually visible. By means of a corresponding colour change, it is recognizable for the manufacturer of upholstered furniture and mattresses as well as for the end customer whether a heat treatment was made which makes the spring steel wire tougher. As a result, an important quality criterion can be visually emphasized for upholstery springs. 
     Preferably, the spring steel wire is heated to above 280° C. during the heat treatment. For heat treatment, the spring steel wire can, for example, be heated to a temperature of between 290° C. to 310° C., wherein the duration of the heat treatment can be configured depending on the spring steel wire used, but the temperature above 290° C. must be reached at least briefly. The changeover temperature of the colour indicator is therefore also preferably at least 250° C., in particular between 290° C. and 310° C. The positive effects by the heat treatment occur at these temperatures. 
     For effective production of the upholstery spring, the colour indicator can be applied by an immersion bath. The coating can occur in a purely electrochemical manner or galvanically by applying a voltage. The colour indicator preferably has a thickness between 0.05 to 1 μm, in particular 0.10 and 0.80μm, so that the colour indicator is applied to the spring steel wire only in small amounts. 
     Preferably, a copper-containing coating is applied as a colour indicator, which does not adversely affect the mechanical properties of the upholstery spring. The copper-containing coating can also essentially consist entirely of copper, which is applied to the spring steel wire with a low layer thickness. It is also possible to use suitable copper alloys in order to set a certain transition temperature. In the case of the colour change, the copper-coloured coating is then darker or lighter, depending on the temperature reached, which is clearly visible. 
     In a further embodiment of the invention, the colour indicator is applied to the spring steel wire only in some areas, which is particularly material-saving. The colour indicator can, for example, be applied only to a central region of the upholstery spring, which deforms upon loading, so that the colour indicator at least indicates whether the deforming region has been heat-treated. Then the end rings of an upholstery spring which are arranged at opposite sides can remain uncoated. Of course, it is also possible to completely coat the upholstery spring with the colour indicator. 
     According to the invention, an upholstery spring is also provided, which is used in particular in a mattress or a piece of upholstered furniture. It is possible for a mattress or a piece of upholstered furniture that a viewing window is provided in a cover for the upholstery spring or a unit comprising a plurality of upholstery springs so that an end customer can also recognize whether the upholstery spring has been correspondingly heat-treated. 
    
    
     
       The invention is explained in more detail below with reference to an exemplary embodiment shown in the attached drawings, wherein: 
         FIG. 1  shows a photographic view of an upholstery spring with a coating of a colour indicator according to the invention before and after the heat treatment, and 
         FIG. 2  shows a conventional upholstery spring without a colour indicator. 
     
    
    
       FIG. 2  shows an upholstery spring without a coating of a heat-sensitive colour indicator. 
     It can be seen that the spring steel wire from which the upholstery spring is made has the same colour everywhere and it is not optically apparent whether a heat treatment has been carried out with this upholstery spring in order to make the spring steel wire tougher. 
     On the left side in  FIG. 1 , an upholstery spring according to the present invention is shown. The upholstery spring is helically wound in a middle region between two end rings arranged in parallel and is coated in this central region with a heat-sensitive colour indicator. As can be seen from the view, the central region has a different colour from the two uncoated end rings of the upholstery spring. The middle region is clearly darker, which is caused by the colour change of the heat-sensitive colour indicator as a result of the heat treatment. On the right side, an upholstery spring with colour indicator and without heat treatment is illustrated. It can be seen clearly that the colour is uniform. As a heat-sensitive colour indicator, a copper-containing coating was applied to the wire electrochemically in a thickness of between 0.15 μm to 0.75 μm. For this purpose, the wire was passed through an immersion bath and a voltage was applied to the spring steel wire, so that the copper-containing material was deposited on the surface. By means of this method, the layer thickness and the coated regions can be adjusted comparatively exactly. 
     In this case, the colour indicator can be applied to the still undeformed spring steel wire, so that the latter can be deformed into the shape of an upholstery spring only after coating. Preferably, a complete coating is then applied. However, it is also possible first to form the spring steel wire into an upholstery spring and at least partially coat the already formed spring steel wire. 
     After applying the colour indicator, the bent spring steel wire was subjected to a heat treatment, wherein the bent spring steel wire is heated to a temperature between 210° C. to 250° C. By heating to this temperature, the colour indicator was activated so that an optically recognizable colour change was made in the middle region. 
     In the exemplary embodiment shown, only the middle region of an upholstery spring is coated with a colour indicator, wherein it is also possible to apply the colour indicator completely to the upholstery spring. Through the coating of the colour indicator in sections, it is easier to visually recognize the colour change by the heat treatment. In addition, it is possible to provide the coating only in the area of the upholstery spring, which deforms upon loading, i.e. in particular the region between the two end rings. 
     The upholstery spring can be bent to form different spring types. Thus, the upholstery spring can be used as a Bonell spring, a pocket spring, an open coil or as a different type of spring. The upholstery springs can also be combined into a plurality of upholstery springs and then processed into mattresses or upholstered furniture. 
     In order to enable the end customer to check whether high-quality upholstery springs have been used in the mattress or the upholstered furniture, at least one transparent viewing window or one formed by a recess can be provided in the cover so that an optical check is possible as to whether the upholstery spring is heat-treated.