The invention relates to heating jaw and a method of

manufacturing said heating jaw.

Background of the invention

In film and shrink wrapping machines, special heating jaws have been used for long for sealing together plastic films during the wrapping process. Such heating jaws are typically manufactured by assembling a metallic body and a heating element. In order to improve the heat transfer between the heating element and the metallic body, a heat transfer paste is provided in the groove into which the heating element is provided. However, such heat transfer pastes are not

environmentally friendly.

Furthermore, since the heating element and the metallic body are typically manufactured from different materials, heat expansion affects the different parts differently, and this can cause separation and bad heat transfer.

Summary of the invention

The present invention tries to mitigate the problems of the prior art heating jaws through the manufacturing method according to claim 1. In this method, according to one aspect of the invention, a heating jaw (10) is manufactured by performing the steps of a) placing a heating element (20) inside a mould, and b) pouring molten metal into said mould, such that the metal forms a tight grip around said heating element (20) when solidifying.

According to another aspect of the invention, a heating jaw is provided being manufactured according to the manufacturing method, and comprising a heating element (20) being embedded in a body (40) of cast metal. Further aspects of the

manufacturing method and the heating jaw are given by the dependent claims.

Brief description of the drawings

The invention will be further described with reference to a preferred embodiment, as shown in the drawings in which:

Fig. 1 shows a side view of a heating jaw according one aspect of the invention,

Fig. 2 shows a partial view of an end of the heating jaw, in cross-section, according to one aspect of the invention, Fig. 3 shows an end view of the heating jaw,

Fig. 4 shows a heating jaw in cross-section, according to one aspect of the invention, and

Fig. 5 shows a pipe holder for manufacturing a heating jaw according to one aspect of the invention.

Detailed description of the invention

The present invention will now be described by reference to the drawings, which show exemplary non-limiting embodiments. In Fig. 1, a heating jaw 10 is shown from the side. The heating jaw 10 comprises a heating element 20, in the form of a heating pipe, pipe holders 30, a body 40, a bulge 50 of vulcanized rubber around the area where a wire 60 is

connected to the heating element 20, and guide pins 70. The heating element enters at a first end of the body 40 of the heating jaw 10, and stops short of a second end thereof, as indicated with dashed lines in Fig. 1. The second end of the heating jaw is provided with a first hole 81 for a

thermometer (not shown) of some known sort, and a second hole 82 being threaded, as can be seen in Figs. 2 and 3, for allowing a screw to secure the thermometer in place with the use of some spring plate or similar (not shown) , in a way known per se. As can be seen in Fig. 3, the hole 81 for the thermometer is placed close to a tip 42 of the body 40, in order not to drill into the heating element 20.

The heating element 20 and the pipe holders 30 are typically made from stainless steel. The body 40 is made from cast aluminium such as EN AB-44300. The guide pins 70

projecting from the body 40 are typically also made from cast aluminium, and are typically integrated with the body. One of the guide pins 70 is provided with a mounting hole 71, being slightly elongated. This allows the heating jaw 10 to be securely mounted to a jaw holder (not shown) .

The heating jaw 10 is manufactured by placing a heating element 20 in pipe holders 30, of which three are used in the heating jaw 10 seen in Fig. 1. The pipe holders 30 are provided with an angled leg 31, which allow them to be securely attached to a casting mould. The heating element 20 is hence placed inside the casting mould, by placing the pipe holders 30 in therefore arranged receptacles on the mould. The mould is then closed and liquid aluminium is poured into the mould, from one end thereof. The mould is open at the other end, allowing air to exit the mould. The mould is equipped with pockets which will form the guide pins 70 during moulding. Many such pockets are provided in the mould, and the wanted configuration can be selected by filling some with correspondingly shaped blocks (where no guide pin is wanted) . In this way, one mould can be used for moulding heating jaws of different configurations.

Once the aluminium has solidified sufficiently, the mould is removed and the heating jaw is ready for additional treatment. The outer surface of the body 40 is machined with a CNC mill, which removes any impurities and provides the body 40 with an accurate outer dimension. At this time, projecting ends of the pipe holders 30 are machined off flush with the outer surface of the body 40, see Fig. 4. In the end, the body 40 comprises a main section 41 and a tip 42, having an outermost flat portion 43, corresponding to the main sealing surface. The surface 44 facing another heating jaw in use is machined to a slight angle, allowing a knife to pass between a pair of heating jaws, even when some dirt are building up on the knife. The machining of the body 40 may also comprise sand blasting or similar, for providing a surface with desired smoothness.

The body 40 of the heating jaw 10 is then at least partly subjected to plasma electrolytic oxidation, or plasma

coating, and is then coated with PTFE, such as Teflon.

Typically, the main section 41 and the tip 42 of the body are treated, while the guide pins 70 are untreated.

The heating element 20 is typically straight during the moulding process, and is subsequently bent approximately 90 degrees, outside the body 40, as can be seen in Fig. 1. The wire 60 is then connected to the heating element 20 and a bulge 50 of rubber is vulcanized over the joint, in order to give protection from dirt and/or moisture.

The resulting final heating jaw 10 now has a heating element 20 which is tightly bonded to the body 40, ensuring good heat transfer from the heating element 20 to the body 40. Furthermore, as the aluminium solidifies during cooling, the aluminium contracts and creates a compression around the heating element. This ensures a tight connection also when the heating jaw 10 is heated up.

According to one aspect of the invention, the mould is heated to a predetermined temperature during the moulding process, to control the cooling process. The mould may be heated to different temperatures in different areas, being controlled by a control system, in way known by the skilled person . Even though it is stated that the body 40 of the heating jaw 10 is manufactured from cast aluminium, it is evident to a person skilled in the art that another molten metal can be used, being suitable for casting.

Typically, the heating jaw is manufactured by chill casting or gravity die casting, but also press casting or die casting can be used. This latter casting technology is above all used for items with thin-walled features, but it would work excellently also for this heating jaw. However, moulds for press casting are typically more expensive than

corresponding moulds for chill casting.

All features described in connection with any aspect of the invention can be used with any other aspect of the invention .

Whilst the invention has been described with reference to a preferred embodiment, it will be appreciated that various modifications are possible within the scope of the invention.

In this specification, unless expressly otherwise

indicated, the word 'or' is used in the sense of an operator that returns a true value when either or both of the stated conditions is met, as opposed to the operator 'exclusive or' which requires that only one of the conditions is met. The word 'comprising' is used in the sense of 'including' rather than in to mean 'consisting of'. All prior teachings

acknowledged above are hereby incorporated by reference.