Electric heating – Heating devices – Combined with pressure application means
Reexamination Certificate
2000-11-13
2001-11-06
Walberg, Teresa (Department: 3742)
Electric heating
Heating devices
Combined with pressure application means
Reexamination Certificate
active
06313440
ABSTRACT:
SCOPE OF THE INVENTION
The present invention relates to a method and apparatus used to prepare and form weld connections between thin walled articles which may in themselves be subject to distortion or deformation when subjected to critical pressures or loading. The method more preferably involves the softening of the contact surface of the workpiece by means of a heat applying application device which is moved into engagement with the contact surface of the workpiece.
BACKGROUND OF THE INVENTION
When two components are connected by means of bonding, gluing or welding, the elasticity of the components, namely their ability to bend or yield to pressure, often constitutes a significant problem in terms of the quality of the connection. The quality and integrity of the connection can be reduced, particularly in the case of extrusion-blown hollow plastic bodies, due to the inconstant positioning of one of the components during the melting and pressing process. Leaky weld connections can lead to serious consequences in the context of applications where weld connections of a high quality are required, as for example in the manufacture of plastic fuel tanks which require high tolerance limits as far as the location of the connecting surfaces is concerned. In the context of such applications, the compensation of tolerance limits for the positioning of the contact surfaces with help of a welding system is required.
German Patent No. DE 35 37 670 C2 to Oxenfarth, which issued on Mar. 3, 1988, discloses a conventional process and corresponding device for use in forming a plastic weld connection. A minimum-force sensor mechanically determines the position of the contact surface on a workpiece such as a hollow plastic container (e.g. a fuel tank of a vehicle). Once the workpiece position is determined, a welding head or other heat applying device is moved by the sensed distance into contact with the workpiece to soften and melt a portion to which a second component is to be welded. This process assures safe welding of the second component, which for example may be a vent connection or filler neck onto the workpiece in spite of high tolerance limits as far as the dimensions of the workpiece are concerned. Therefore, the use of thicker materials to ensure complete welds, and which is almost impossible in the case of thin-walled hollow bodies, is not required to effect the connection. This procedure, however, neglects the forces that melting head apply to the workpiece and which can cause distortion or bending of workpiece surfaces, leading to incomplete welds.
DE-PS 39 22 066 discloses a further development of the state of the art used to achieve improved welds. This reference discloses a method to compensate for position changes and deformation of the part of a workpiece to which a second component is to be connected by readjusting the position and contact pressure of a heating element, as well as the position and contact pressure of the second component to be connected to the workpiece. For this purpose, the position of the contact surface on the workpiece is also determined by a minimum-force mechanical sensor. The result of the measuring process is then used to readjust a piston which presses the component to be added against the heating device and the heating device against the workpiece.
Published Japanese Patent Abstract No. 04 234633 to Yokoyama Takahito (published Aug. 24, 1992) discloses a holder used to position a polyethylene joint on a tank, following melting and heating of contact surfaces. The holder includes a compression spring used to bias a melted surface of the joint against a melted surface of the tank.
Published Japanese Patent Abstract No. 08 112861 to Imagawa Kanji (published May 7, 1996) discloses a heating device used to heat weld together two sheets. The heating device includes a heating part which is biased by means of a spring to project downwardly through an opening, into contact with the sheets which are to be welded.
The determination of the position of the workpiece surface using an additional sensing device constitutes a disadvantage in that it is not sufficiently accurate, as the method requires the establishment of additional reference surfaces on a potentially elastically deformable surface of the workpiece or component. In addition, the reference surfaces are often not feasible for manufacturing related reasons, or are located too far from the relevant connecting position, thus distorting the result.
Plastic welding units that are exclusively equipped with load-sensitive sensors such as load cells can compensate for the disadvantages of external sensing equipment but are often expensive and are not sufficiently sensitive for design-related reasons. Additionally, the impression depth achieved by the partial melting of the component or workpiece surface is not adequately determined.
SUMMARY OF THE INVENTION
The invention is therefore based on the need to develop an improved device and a process for the formation of weld connections of constant quality as between a workpiece and a second component which is to be connected thereto. More preferably, the present invention seeks to achieve the formation of high quality plastic weld connections where either the workpiece and/or the component may be elastically deformable upon the application of a predetermined minimum force thereto.
The inventor has appreciated an improved method of forming a plastic weld connection between a workpiece which can be shaped or deformed by application of mechanical force and a second component to be connected thereto. The method preferably involves the softening of the contact surface of the workpiece by application of heat, however, other means of joining components to the workpiece, such as gluing, sonic welding or the like are also possible. The process broadly comprises the steps of positioning of an application device adapted to melt, glue or weld the contact surface of the workpiece, activating the application device to prepare the contact portion of the workpiece while repositioning of the application device in relation to the workpiece during preparation of the contact portion. The method is further characterized by the fact that the repositioning comprises a defined displacement of the application device in relation to the contact surface of the workpiece, and which is independent of a determination of the position by means of measuring.
The present invention also overcomes the disadvantages of the prior art by providing a device for the preparation and formation of a weld connection between a workpiece which can be distorted or deformed upon the application of predetermined mechanical force and a second component which is to be connected thereto. The apparatus preferably includes a hot plate used in the softening or partial melting of the contact surface of the workpiece when applied thereto. The apparatus is characterized by the fact that it is adapted to reposition the hot plate during melting without measuring of the position of the contact surface, and most preferably during displacement of the hot plate while it is applied to the contact surface of the workpiece as deformation and melting of the contact surface occurs.
The invention preferably relates to a process for the preparation and formation of a plastic weld connection between a deformable thermoplastic workpiece which may be distorted by the application of a mechanical force and a second thermoplastic component to be connected thereto. In a preferred embodiment, the method includes a step of softening or partial melting of the contact surface of the workpiece by application of heat. More preferably, the process includes the following steps: positioning a heat applying device at the contact surface, activating the heat applying device, and continuously repositioning the heat applying device in relation to the workpiece during the softening of the workpiece.
Additionally, the present invention relates generally to a plastic welding device for the preparation and formation of a weld connection between a workpie
Oxenfarth Hans-Josef
Weber Wolfgang
KVT Technologies Inc.
Patel Vinod D.
Riches, McKenzie & Herbert
Walberg Teresa
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