Injection molding method for producing a plastic tank integrated with an inspection window, a plastic tank, and a power tool including such a plastic tank

Abstract

A method for producing a plastic tank for a power tool includes: providing a molding tool with a transparent sight glass (26); and injecting liquefied plastic onto the molding tool to form a tank wall (34), wherein the liquefied plastic engages the sight glass (26) at an overmold interface; and allowing the injected plastic to solidify, thereby forming a bond with the sight glass (26), the sight glass (26) having at least one liquefied precursor ridge (44a, 44b, 64a, 64b) extending from a face of the sight glass (26) along the overmold interface; and wherein the liquefied plastic is injected onto the overmold interface to at least partially liquefy the liquefied precursor ridge (44a, 44b, 64a, 64b).

Description

Technical Field

[0001] The present invention relates to a method for producing a plastic tank for a power tool, a plastic tank, and a power tool comprising such a plastic tank.

Background Art

[0002] Fuel tanks for modern handheld power tools are made of plastic. There are many different requirements for fuel tanks. By way of example, the fuel tank needs to be mechanically strong and easily refillable and check the current fuel level. The fuel tank also needs to meet some safety standards. By way of example, the fuel tank needs to be leak-proof at high pressure. The gas pressure can be substantially quite different between the inside of the tank and the ambient air pressure outside the tank. In some cases, the difference can be as high as 30 - 40 kPa.

[0003] Generally, the current fuel level is communicated to the operator via a transparent fuel level inspection window. The tank body is generally made of glass- or carbon fiber-reinforced plastic for mechanical strength, but the fuel window is made of transparent plastic. The transparent fuel level inspection window is generally attached to the fuel tank by ultrasonic welding. To ensure that the window is fuel-tight, the window is kept as small as possible and welded to the tank along a weld that extends generally within a single plane. Those limits are mainly set by the size and shape of the ultrasonic welding sonotrode, which is necessary to define a suitable waveguide for sending welding power across the entire interface between the tank body and the window in a single welding step. The drawback of those limits is the lighting conditions and the posture of the handheld power tool that can limit the visibility of the fuel level.

[0004] Patent Document 1 discloses a method for manufacturing a fuel tank. However, there is also a need for an improved fuel tank and a method for producing such an improved tank.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

[0006] The object of the present invention is to solve or at least mitigate some or all of the above problems. For this purpose, a method for producing a plastic tank for a power tool is disclosed. The tank comprises a tank wall and a transparent or translucent inspection window disposed within a window aperture in the tank wall, the inspection window enabling visual inspection of the content level within the tank. The method comprises providing a molding tool comprising one of the tank wall and the inspection window. The method comprises injecting liquefied plastic onto the molding tool to form the other of the tank wall and the inspection window. The liquefied plastic engages with the one of the tank wall and the inspection window at an overmold interface therebetween. The method enables the injected plastic to solidify, thereby forming a bond with the one of the tank wall and the inspection window. In such a method, the one of the tank wall and the inspection window comprises at least one pre-liquid precursor ridge extending from a face of the one of the tank wall and the inspection window and along the overmold interface, and the liquefied plastic is injected onto the overmold interface to at least partially liquefy the pre-liquid precursor ridge. A method is provided, characterized in that the dimensions of the pre-liquid precursor ridge enable it to be heated by the injected plastic and liquefy, thereby enabling the material of the tank wall and the material of the inspection window to be mixed along the pre-liquid precursor ridge. Thereby, the interface between the tank wall and the inspection window is made to have high mechanical strength and good tightness against leakage. Such liquid tightness is particularly desirable for tanks containing flammable volatile liquids such as chainsaw fuel. Liquefaction can result, for example, as a result of melting or passing through the glass transition temperature. It may be preferred that at least the pre-liquid precursor ridge, optionally the whole of the one of the tank wall and the inspection window, is a thermoplastic material. However, the process also results in improved tightness for the molding of thermosetting resins, especially in combination with the short cycle times between successive molding shots for building up the tank. According to a plurality of embodiments, the overmold interface may extend along the edge of the inspection window or the window aperture. Alternatively, the overmold interface may be located at a distance from an edge of either of the one of the tank wall and the inspection window.The method gives complete design freedom regarding the placement, size, and shape of inspection windows within the tank wall, thereby enabling the design of a tank that facilitates the confirmation of the liquid content level. The tank wall may be opaque. Alternatively, it may be translucent or transparent. According to multiple embodiments, the power tool can be a hand-held power tool. The power tool can be portable and may be carried by an operator with one or both hands during operation, or may be equipped with wheels so as to be rolled on the ground by the operator during operation. The power tool can be a power tool for outdoor use, such as a garden or forest tool.

[0007] According to multiple embodiments, one of the tank wall and the inspection window can be the inspection window. In such an embodiment, it is clear that the other of the tank wall and the inspection window is the tank wall. In an alternative embodiment, one of the tank wall and the inspection window can be the tank wall, and the other of the tank wall and the inspection window can be the inspection window.

[0008] According to multiple embodiments, the at least one pre-liquefaction ridge can define a closed loop around the inspection window or window aperture. Thereby, an increase in liquid tightness can be obtained. According to multiple embodiments, the at least one pre-liquefaction ridge can be continuous. Thereby, an increase in liquid tightness can be obtained. Alternatively, the ridge can be intermittent. For example, it can be formed by a row of closely spaced pre-liquefaction protrusions.

[0009] According to multiple embodiments, the at least one pre-liquefaction ridge can comprise a plurality of pre-liquefaction ridges. Having two or more pre-liquefaction ridges reduces the risk of leakage due to any defect in a single pre-liquefaction ridge. For example, the overmold interface can comprise two, three, four, five, or six pre-liquefaction ridges.

[0010] According to a plurality of embodiments, the plurality of pre-liquefaction ridges may include a first set of ridges on the first side of one of the tank wall and the inspection window, and a second set of ridges on the second side of one of the tank wall and the inspection window, where the second side faces the first side. The first and second sides may correspond to the inner and outer surfaces of the tank. Each set of ridges may include one, two, three, or more pre-liquefaction ridges.

[0011] According to a plurality of embodiments, the second side may face towards the inside of the tank, and the first side may face towards the outside of the tank. Such an arrangement can increase the liquid tightness of the tank to a similar extent regardless of whether the tank maintains excessive pressure or underpressure compared to the external ambient pressure. According to a plurality of embodiments, the surfaces with ridges on the first and second sides may be generally parallel locally to the plane of the tank wall adjacent to the overmold interface.

[0012] According to a plurality of embodiments, injecting liquefied plastic onto the molding tool to form the other of the tank wall and the inspection window enables the liquefied plastic to flow on a molding tool having a molding surface that generally coincides in position with the outer surface of one of the tank wall and the inspection window at the overmold interface, and may include making the outer surface of the tank wall generally coincide in position with the outer surface of the inspection window at the overmold interface. Such an arrangement makes it difficult for the inspection window to collect dust such as sawdust, thereby facilitating inspection. The molding surface may be generally in the same plane as the outer surface of one of the tank wall and the inspection window at the overmold interface, such that there is generally no step at the interface between the outer surface of the tank wall and the outer surface of the inspection window.

[0013] According to multiple embodiments, the overmold interface may comprise an outer overmold interface portion facing towards the outside of the tank, and the outer overmold interface portion is offset towards the inside of the tank as compared to the outer surface of the tank wall and the one of the inspection windows adjacent to the overmold interface. Thereby, the overmold aligns the outer surface of the tank wall relatively close to the outer surface of the inspection window. The overmold interface portion facing towards the outside of the tank may comprise one or more pre-liquefaction ridges as defined above.

[0014] According to multiple embodiments, the tank wall and the inspection window may be joined in the present embodiment, and the overmold interface of the one of the tank wall and the inspection window forms the protrusion of the present embodiment, and the other of the tank wall and the inspection window is overmolded on the protrusion to form the groove of the present embodiment, and the groove surrounds the at least one pre-liquefaction ridge. The method may further comprise the shrinkage of the other of the tank wall and the inspection window during solidification. Thereby, a particularly liquid-tight joint can be obtained.

[0015] According to multiple embodiments, the protrusion may extend locally substantially parallel to the tank wall adjacent to the present embodiment. Thereby, similar tank tightness can be obtained regardless of whether the tank is maintaining excessive pressure or underpressure. Further, a relatively wide overmold interface can be used in which no substantial ridge occurs around the tank window, which can thereby further increase the liquid tightness and / or reduce the tendency of dust accumulation on the inspection window. Here, the term "locally" should be construed as each section of the protrusion that is substantially parallel to the closest portion of the tank wall.

[0016] According to multiple embodiments, the inspection window may have a generally convex outer surface and a generally concave inner surface. Such a shape is particularly well-suited for dealing with high internal pressures with maintained liquid tightness.

[0017] According to multiple embodiments, providing a molding tool comprising one of the tank wall and the inspection window may comprise injecting liquefied plastic onto the molding tool to form one of the tank wall and the inspection window. Such an arrangement simplifies and speeds up production. According to certain embodiments, the molding tool may be rotated between different respective injection nozzles to inject respective materials for one and the other of the tank wall and the inspection window. As an alternative to molding one of the tank wall and the inspection window with the same molding tool, one of the tank wall and the inspection window may be manufactured with another tool or using any other method before being moved to the molding tool for molding the other of the tank wall and the inspection window.

[0018] According to multiple embodiments, providing a molding tool comprising one of the tank wall and the inspection window may further comprise retracting at least one core of the molding tool after forming one of the tank wall and the inspection window to expose at least a portion of the overmold interface. Thereby, the other of the tank wall and the inspection window may be more easily overmolded on two opposing sides to form the present embodiment to the overmold interface.

[0019] According to multiple embodiments, the at least one liquefied precursor ridge may extend from the surface of one of the tank wall and the inspection window to a ridge height above the surface of 0.1 mm to 1 mm. Thereby, along the liquefied precursor ridge, a high degree of mixing of the material of the tank wall and the material of the inspection window is ensured. According to further embodiments, the at least one liquefied precursor ridge extends from the surface of one of the tank wall and the inspection window to a ridge height above the surface of 0.2 mm to 0.6 mm.

[0020] According to multiple embodiments, when viewed in a cross-section perpendicular to the path along which the at least one pre-liquidation precursor ridge extends, the at least one pre-liquidation precursor ridge may have a width of less than 0.3 mm at a height that is half of its height measured from the said surface of either the tank wall or the inspection window. Thereby, a high degree of mixing of the materials of the tank wall and the inspection window along the pre-liquidation precursor ridge is ensured. According to further embodiments, the ridge may have a width of less than 0.2 mm at a height that is half of its height measured from the said surface of either the tank wall or the inspection window.

[0021] According to multiple embodiments, the wall thickness of the tank wall may be 1 mm to 3 mm. Alternatively or in addition, the thickness of the inspection window may be 1 mm to 3 mm. The ratio of the ridge height to the tank wall thickness and / or the inspection window thickness may be, for example, 1:1.5 to 1:10.

[0022] According to multiple embodiments, when viewed in a cross-section perpendicular to the path along which the at least one pre-liquidation precursor ridge extends, the at least one pre-liquidation precursor ridge may have a ridge top that forms an acute angle. Thereby, a high degree of mixing of the materials of the tank wall and the inspection window along the pre-liquidation precursor ridge is ensured. According to further embodiments, the ridge top may form an angle of less than 70 degrees, less than 50 degrees, or 20 to 40 degrees. According to some embodiments, the ridge may have a triangular shape when viewed in cross-section.

[0023] According to multiple embodiments, the tank wall and the inspection window may be formed of a thermoplastic material having generally the same glass transition temperature. According to multiple embodiments, the tank wall and the inspection window may be formed of the same base polymer, with only the dye content and, optionally, any other filler materials such as fiber reinforcements being different. Generally, the material of the tank wall may be reinforced by, for example, glass or carbon fibers, while the material of the inspection window may be generally non-reinforced. The base polymer may be semi-crystalline. According to other embodiments, the other of the tank wall and the inspection window may be formed of a non-thermoplastic polymer and may be cured, for example, by cross-linking after injection.

[0024] According to one example, at least one of, and optionally both, the tank wall and the inspection window can be made of polyamide, for example polyamide 6. The tank wall can be made of polyamide 6, for example, with 15 wt% glass reinforcement, such as glass fibers. Exemplary suitable temperatures for the liquefied plastic during injection molding are generally 200°C to 300°C, and for a specific example of polyamide 6, it can be 230°C to 285°C. Exemplary suitable temperatures for the molding tool during injection molding can be 40°C to 100°C.

[0025] According to a second aspect, some or all of the above problems are solved or at least alleviated by a plastic tank obtained by any of the methods defined above.

[0026] According to a third aspect, some or all of the above problems are solved or at least alleviated by a power tool comprising a plastic tank obtained by any of the methods defined above. The power tool can be a hand-held power tool such as a chainsaw, and / or the tank can be a fuel tank for holding fuel for the combustion engine of the power tool.

[0027] According to a fourth aspect, some or all of the above problems are solved or at least alleviated by a power tool tank comprising a tank wall and a transparent or translucent inspection window disposed within a window aperture in the tank wall, the inspection window enabling visual inspection of the liquid content level within the tank, and the tank wall and the inspection window being molded together along a molding interface, the molding interface comprising a ridge of one of the tank wall and the inspection window, the ridge being melted into the material of the other of the tank wall and the inspection window.

[0028] Note that the embodiments of the present invention can be provided by all possible combinations of the features described in the claims. Further, it is recognized that all of the various embodiments described with respect to the method can be combined with an apparatus as defined according to the second, third, and fourth aspects of the present invention, and vice versa.

[0029] Furthermore, the method can be used for the production of tanks for applications other than power tools. Therefore, according to a further aspect, and to cover any further patent applications arising therefrom, a method of producing a plastic tank, the tank comprising a first tank wall portion and a second tank wall portion, the method comprising providing a molding tool comprising the first tank wall portion, and injecting liquefied plastic into the molding tool to form the second tank wall portion, the liquefied plastic engaging the first tank wall portion at an overmold interface of the first tank wall portion, and enabling the injected plastic to be cooled and solidified, thereby forming a bond with the first tank wall portion, the first tank wall portion comprising at least one pre-liquefaction precursor ridge extending from a surface of the first tank wall portion and along the overmold interface, the method being provided such that the liquefied plastic is injected onto the overmold interface to at least partially liquefy the pre-liquefaction precursor ridge. The method can be combined with any of the embodiments defined above with reference to the first aspect, the first tank wall portion corresponding to one of the tank wall and the inspection window, and the second tank wall portion corresponding to the other of the tank wall and the inspection window.

[0030] The above and additional objects, features, and advantages of the present invention will be better understood from the following description of the preferred embodiments of the present invention and by reference to the accompanying drawings, which are non-limiting and in which like elements are denoted by the same reference numerals.

Brief Description of the Drawings

[0031]

Figure 1

Figure 2

Figure 3A

Figure 3B

Figure 4A

Figure 4B

Figure 4C

Figure 4D

Figure 5A

Figure 5B

Figure 5C

Figure 6A

Figure 6B

Figure 6C

Figure 6D

Figure 7A

Figure 7B

Figure 8

Embodiments for Carrying Out the Invention

[0032] All the drawings are schematic and not necessarily to scale, and generally show only the parts necessary to explain the embodiments, with other parts being omitted as possible. FIG. 1 shows a power tool provided as a handheld chain saw 10. The chain saw 10 includes an internal combustion engine 12 configured to rotate a saw chain 14 around a guide bar 16. A fuel tank 18 of the chain saw 10 is configured to hold fuel that is burned within the internal combustion engine 12, which is generally a two-stroke engine, and a saw chain oil tank 20 is configured to hold saw chain oil that facilitates the movement of the saw chain 14 along the guide bar 16. The fuel tank 18 includes two opaque plastic tank halves 18a, 18b that are integrally formed with and fused along a seam or joint 24 of a rear handle 22 of the chain saw 10. The first tank half 18a of the tank halves 18a, 18b includes a transparent fuel inspection window 26 that is integrally formed with the tank half 18a as will be described in detail below. The chain saw 10 further includes a front handle 28, and the rear handle 22 includes a trigger portion 30 for controlling the internal combustion engine 12.

[0033] FIG. 2 shows the first tank half 18a as seen from the inside. The tank half is integrally formed with a rear handle portion 22a and a front bottom plate 32 of the chain saw 10 (FIG. 1). A tank wall 34 that defines an actual fuel container wall of the tank half 18a includes a refill opening 36, which is closed by a tank refill cap 38 in the view of FIG. 1. The view of FIG. 2 also shows the inspection window 26, which is joined to the tank wall 34 along a mounting edge 40 that extends around the inspection window 26.

[0034] The perspective views of FIGS. 3A and 3B show the inspection window 26 in detail, together with its position within the inspection window aperture 27 in the tank half 18a. The inspection window 26 comprises a transparent inspection area 42 surrounded by a mounting edge 40. The inspection area 42 is higher than the mounting edge 40 and is arranged such that the outer surface 41 of the inspection area 42 is generally flush with the outer surface 43 of the tank wall 34. Two outer pre-liquidation ridges 44a, 44b (the function of which will be further described below) extend along the mounting edge 40 and define a closed loop around the inspection area 42.

[0035] Figures 4A to 4D schematically show a method of producing the tank half 18a of FIGS. 1, 2, 3A and 3B by two-shot injection moulding. Starting with FIG. 4A, the moulding apparatus 46 comprises a first resin injection device 48a connected to inject resin into a first injection mould 50a and a second resin injection device 48b connected to inject resin into a second injection mould 50b. An ejector mould support 52 holds a first ejector mould 54a in a first ejector mould position and a second ejector mould 54b in a second mould position. For the sake of brevity, only the first ejector mould 54a will be described in detail, and it will be appreciated that the description of the second ejector mould 54b is the same or is even omitted. The ejector mould support 52 is movable along an axis A between the position shown in FIG. 4A where the mould cavities are open and the position shown in FIG. 4B where the mould cavities are closed. Further, the ejector mould support 52 is rotatable about the axis A to enable the first ejector mould 54a and the second ejector mould 54b to change positions relative to each other. Each ejector mould 54a, 54b comprises a respective fixed ejector mould part 56 held in a stationary position relative to the ejector mould support 52 and a respective retractable core 58 which can be retracted into the ejector mould support 52 to change the shape of the respective ejector moulds 54a, 54b. The first ejector mould 54a is shown with the core 58 in a non-retracted position, while the second ejector mould 54b is shown with the core in a retracted position.

[0036] Figure 4B shows the first molding shot. At the position of Figure 4B, the first molds 50a, 54a are closed so as to define the first molding cavity 60, and the first resin injection device 48a injects the first composition 49a of a transparent liquefied thermoplastic resin into the first molding cavity 60 to form the inspection window 26. The inspection window 26 can be cooled and solidified before the mold is opened.

[0037] Figure 4C shows the molding apparatus 46 after the molding cavity 60 (Figure 4B) is opened and the first protruding mold 54a is rotated to the second mold position that has hitherto been held by the second protruding mold 54b. Further, the core 58 is retracted to expose two opposing side surfaces of the mounting edge 40 of the inspection window 26. Thereby, the mounting edge 40 forms the overmold interface of the two side surfaces for the next molding shot, which is shown in Figure 4D.

[0038] In the view of Figure 4D, the second injection molding mold 50b and the first protruding mold 54a are closed to define the second molding cavity 62, and the second resin injection device 48b injects the second composition 49b of a liquefied opaque fiber-reinforced thermoplastic resin into the second molding cavity 62 to form the tank wall 34. As shown, the first resin injection device 48a and the injection molding mold 50a can be used together with the second protruding mold 54b to form the next inspection window in the same step. After overmolding the tank wall 34 onto the inspection window 26 and enabling the composite tank half formed in this way to be cooled and solidified, the tank half is removed from the apparatus 46.

[0039] Figure 5A shows the inspection window 26 before the overmolding step of Figure 4D, Figure 5B is an enlarged cross-sectional view taken along B-B of the inspection window 26 shown in Figure 5A, and Figure 5C is a further enlarged view of the drawing of Figure 5B. Starting from the view of Figure 5B, the outer surface 41 of the inspection area 42 is slightly convex, while the inner surface 45 of the inspection window 26 is concave to a corresponding extent. As described above, the outer surface 41 of the inspection area 42 is higher than the outer surface 63 of the mounting edge 40 in the outward direction away from the inside of the tank 18 (Figure 1). More specifically, the outer surface 63 of the mounting edge 40 is offset by an offset step 47 towards the inside of the tank 18 compared to the outer surface 41 of the inspection area 42. The inner surface of the inspection window 26 provides a corresponding offset portion 49 so that an inspection window 26 of generally uniform thickness can be obtained across the inspection area 42. The first set 44 of liquefaction precursor ridges 44a, 44b extends from the outer surface 63 of the mounting edge 40. The first set 44 of liquefaction precursor ridges 44a, 44b is higher than the surface 63 of the mounting edge 40 in generally the same direction as the plane perpendicular to the outer surface of the inspection area 42. The second set 64 of liquefaction precursor ridges 64a, 64b extends from the inner surface 65 of the mounting edge 40, where the outer and inner directions should be interpreted in relation to the outside and inside of the tank 18 (Figure 1). In the second molding shot shown in Figure 4D, the mounting edge 40 is overmolded on two opposing sides to cover both sets 44, 64 of liquefaction precursor ridges, thereby forming the present embodiment. When overmolding, the second composition of the resin is injected onto the overmolding interface to at least partially melt the liquefaction precursor ridges 44, 64, thereby allowing the material of the tank wall 34 (Figure 1) and the material of the inspection window 26 to be mixed along the liquefaction precursor ridges 44, 64. This makes the interface between the tank wall and the inspection window have high mechanical strength and good tightness against leakage. The enlarged view of Figure 5C shows the liquefaction precursor ridge 44a in detail. The liquefaction precursor ridge 44a extends from the outer surface 63 of the mounting edge 40 (Figure 5B) to a ridge height H of about 0.4 mm and forms an upper acute angle α of about 35°. At a height half of the height H, the width W of the liquefaction precursor ridge 44a is about 0.13 mm.

[0040] Figure 6A shows the first tank half 18a after the second molding shot of Figure 4D, and Figure 6B shows a cross-section taken along B-B of Figure 6A. Figure 6C is an enlarged view of a portion of the drawing of Figure 6B, and Figure 6D is a further enlarged view of a portion of the drawing of Figure 6C. As shown in Figure 6C, the mounting edge 40 of the inspection window 26 forms the protrusions of the present embodiment, and the tank wall 34 forms a groove. Thereby, when the tank wall 34 is overmolded onto the mounting edge 40 of the inspection window 26, any shrinkage that occurs during the solidification of the tank wall 34 contributes to maintaining the liquid tightness of the present embodiment. The protrusions extend along a direction generally parallel to the tank wall 34.

[0041] Figure 6D shows the seam or joint between the inspection window 26 and the tank wall 34 after the solidification of the tank wall 34. Here, the liquefaction precursor ridges 44a, 44b, 64a, 64b dissolve into the material of the tank wall 34 and define a liquid-tight seam. Figure 6D also schematically shows the sizes of the liquefaction precursor ridges 44a, 44b, 64a, 64b with respect to the tank wall thickness T1 and the inspection window thickness T2, both of which can be approximately 1.5 mm as an example. The offset portion 47 between the outer surface 63 (Figure 5B) of the mounting edge 40 (Figure 5B) and the outer surface 41 of the inspection area 42 (Figure 5B) enables the overmolding of the outer surface 43 of the tank wall 34 that is generally aligned with the outer surface 41 of the inspection window 26.

[0042] Figures 7A and 7B show, with increased magnification, a second embodiment of the interface between the tank wall 34 and the inspection window 26. The second embodiment is the same as the embodiment described in detail above, except that the edge of the boundary between the tank wall 34 and the inspection window 26 does not form the present embodiment. This can simplify the two-shot molding process to reduce the need for any retractable core of the extractor mould.

[0043] Figure 8 shows a method of producing the plastic tank half 18a described in detail above. In the first step 801, the inspection window 26 is formed by injecting a first composition of liquefied plastic onto a first protruding mold 54a (FIG. 4B).

[0044] In the second step 802, the tank wall 34 is formed by injecting a second composition of liquefied plastic onto a first protruding mold 54a (FIG. 4D), thereby overmolding and partially liquefying the liquefied precursor ridges 44, 64 (FIG. 5B).

[0045] In the third step 803, the second composition of the injected plastic is enabled to solidify together with the partially liquefied liquefied precursor ridges 44, 64, thereby joining between the tank wall 34 and the inspection window 26.

[0046] The present invention has been mainly described above with reference to several embodiments. However, as will be readily recognized by those skilled in the art, other embodiments other than those disclosed above are equally possible within the scope of the present invention as defined in the appended claims. By way of example, according to the embodiments described above, the tank wall is overmolded onto the inspection window. As an alternative, the inspection window may be overmolded onto the tank wall. In such embodiments, the mounting edge along the inspection window aperture of the tank wall may comprise one or more liquefied precursor ridges. Further, according to the method described in detail above, the inspection window is formed within the same molding tool as the tank wall. It is clear that this is not essential. The inspection window is first formed in a first mold. Thereafter, the inspection window is removed from the first mold and placed in a second mold for overmolding with the tank wall. This may be done manually or automatically by a robot.

[0047] In the claims, the term "comprising" does not exclude other elements or steps, and the indefinite articles "a" or "an" do not exclude a plurality.

Claims

1. A method of producing a plastic tank (18) for a power tool (10), wherein the plastic tank (18) comprises a tank wall (34), a transparent or translucent inspection window (26) disposed within a window aperture in the tank wall (34), and a circular refill opening (36) for refilling fuel, and the inspection window (26) enables visual inspection of the content level within the plastic tank (18), the method comprising providing a molding tool (54a) comprising either the tank wall (34) or the inspection window (26), the method comprising injecting liquefied plastic (49b) onto the molding tool (54a) to form the other of the tank wall (34) and the inspection window (26), the liquefied plastic (49b) engaging with either the tank wall (34) or the inspection window (26) at an overmold interface of either the tank wall (34) or the inspection window (26), the method comprising enabling the injected plastic (49b) to solidify, thereby bonding between either the tank wall (34) and the inspection window (26), In a method of producing a plastic tank (18) for a power tool (10), either the tank wall (34) or the inspection window (26) comprises at least one liquefied precursor ridge (44a, 44b, 64a, 64b), the liquefied precursor ridge (44a, 44b, 64a, 64b) extending from a surface (63, 65) of either the tank wall (34) or the inspection window (26) along the overmold interface, and the liquefied plastic (49b) is injected onto the overmold interface to at least partially liquefy the liquefied precursor ridge (44a, 44b, 64a, 64b), The method is characterized in that the inspection window (26) is formed to include a curved portion facing along an arc of the refill opening (36).

2. The method according to claim 1, wherein either the tank wall (34) or the inspection window (26) is the inspection window (26).

3. The method according to claim 1 or 2, wherein the at least one liquefied precursor ridge (44a, 44b, 64a, 64b) defines a closed loop around the inspection window (26) or the window aperture (27).

4. The method according to any one of claims 1 to 3, wherein the at least one pre-liquidation precursor ridge (44a, 44b, 64a, 64b) is continuous.

5. The method according to any one of claims 1 to 4, wherein the at least one pre-liquidation precursor ridge (44a, 44b, 64a, 64b) is a plurality of pre-liquidation precursor ridges (44a, 44b, 64a, 64b).

6. The plurality of pre-liquidation precursor ridges (44a, 44b, 64a, 64b) includes a first set of ridges (44) on a first side surface (63) of either the tank wall (34) or the inspection window (26), and a second set of ridges (64) on a second side surface (65) of either the tank wall (34) or the inspection window (26), the second side surface (65) facing the first side surface (63). The method according to claim 5.

7. The method according to claim 6, wherein the second side surface (65) faces towards the inside of the plastic tank (18), and the first side surface (63) faces towards the outside of the plastic tank (18).

8. Injecting the liquefied plastic (49b) onto the molding tool (54a) to form the other of the tank wall (34) and the inspection window (26) includes allowing the liquefied plastic (49b) to flow on a molding tool having a molding surface, the molding surface being such that the outer surface (43) of the tank wall (34) is generally aligned with the outer surface (41) of the inspection window (26) at the overmold interface, and the outer surface (41) of either the tank wall (34) or the inspection window (26) at the overmold interface. The method according to any one of claims 1 to 7.

9. The overmold interface includes an outer overmold interface portion (63) facing towards the outside of the plastic tank (18), the outer overmold interface portion (63) being offset towards the inside of the plastic tank (18) compared to the outer surface (41) of either the tank wall (34) or the inspection window (26) adjacent to the overmold interface. The method according to any one of claims 1 to 8.

10. The tank wall (34) and the inspection window (26) are joined in the present embodiment, and one of the overmolding interfaces of the tank wall (34) and the inspection window (26) forms a protrusion of the present embodiment, and the other of the tank wall (34) and the inspection window (26) is overmolded on the protrusion to form a groove of the present embodiment, and the groove surrounds the at least one liquefaction precursor ridge (44a, 44b, 64a, 64b). The method according to any one of claims 1 to 9.

11. The protrusion extends locally substantially parallel to the tank wall (34) adjacent to the present embodiment. The method according to claim 10.

12. The inspection window (26) has a generally convex outer surface (41) and a generally concave inner surface (45). The method according to any one of claims 1 to 11.

13. Providing a molding tool (54a) comprising one of the tank wall (34) and the inspection window (26) comprises injecting liquefied plastic (49a) onto the molding tool (54a) to form one of the tank wall (34) and the inspection window (26). The method according to any one of claims 1 to 12.

14. Providing a molding tool (54a) comprising either one of the tank wall (34) and the inspection window (26) further comprises retracting at least one core (58) of the molding tool (54a) after forming either one of the tank wall (34) and the inspection window (26) to expose at least a portion (64, 65) of the overmolding interface. The method according to claim 13.

15. The at least one liquefaction precursor ridge (44a, 44b, 64a, 64b) extends from the surface (63, 65) of either one of the tank wall (34) and the inspection window (26) to a ridge height (H) above the surface (63, 65) of 0.1 mm to 1 mm. The method according to any one of claims 1 to 14.

16. The at least one pre-liquefaction precursor ridge (44a, 44b, 64a, 64b) has a width (W) of less than 0.3 mm at a height that is half of its height (H) above one of the surfaces (63, 65) of the tank wall (34) and the inspection window (26) when viewed in a cross-section perpendicular to the path along which the pre-liquefaction precursor ridge (44a, 44b, 64a, 64b) extends. The method according to any one of claims 1 to 15.

17. The wall thickness (T1) of the tank wall (34) is from 1 mm to 3 mm. The method according to any one of claims 1 to 16.

18. The at least one pre-liquefaction precursor ridge (44a, 44b, 64a, 64b) has a ridge top that forms an acute angle (α) when viewed in a cross-section perpendicular to the path along which the pre-liquefaction precursor ridge (44a, 44b, 64a, 64b) extends. The method according to any one of claims 1 to 17.

19. The tank wall (34) and the inspection window (26) are formed of a thermoplastic material having generally the same glass transition temperature. The method according to any one of claims 1 to 18.

20. A plastic tank (18) obtained by the method according to any one of claims 1 to 19.

21. A power tool (10) comprising the plastic tank (18) according to claim 20.

22. A power tool tank (18) comprising a tank wall (34), a transparent or translucent inspection window (26) disposed within a window aperture (27) in the tank wall (34), and a circular refill opening (36) for refilling fuel, wherein the inspection window (26) includes a curved portion facing along an arc of the refill opening (36) and enables visual inspection of the liquid content level within the power tool tank (18), and the tank wall (34) and the inspection window (26) are integrally molded along a molding interface, and the molding interface includes a ridge (44a, 44b, 64a, 64b) of one of the tank wall (34) and the inspection window (26), and the ridge is dissolved in the material of the other of the tank wall (34) and the inspection window (26). Power tool tank (18).

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