GB2028960A

GB2028960A - Improvements in and relating to adhesive bonding in reinforced sheets

Info

Publication number: GB2028960A
Application number: GB7928469A
Authority: GB
Original assignee: Fruehauf Corp
Current assignee: Fruehauf Corp
Priority date: 1978-08-09
Filing date: 1979-08-15
Publication date: 1980-03-12
Also published as: AU4987979A; BR7905058A; NL7906048A; DE2932027A1; JPS5555062A; FR2433153A1

Abstract

A metal sheet reinforced with bow cross section members 4 for the walls or roof of a vehicle, and a method of making the sheet. Each member 4 is of channel form having opposite side flanges 8 and 10. Two beads of adhesive 24 to 30 are applied side-by-side on each flange, one bead 24 and 28 being a hot melt adhesive and the other 26 and 30 of room temperature curing type. The sheet and channel members are pressed together to spread the beads and form adhesive layers. Each flange 8 or 10 is provided with a rib 12 to 14 of predetermined height which controls the thicknesses of the adhesive layers to optimise the thicknesses thereof for bonding strength and allow a predetermined bead size to be used which will spread completely to cover the bonding surfaces of the flanges without excess.

Description

SPECIFICATION Improvements in and relating to reinforced metal sheets The invention relates to reinforced metal sheets and especially to reinforced metal sheets suitable for a wall or the roof of a vehicle.

In constructing lorry and trailer bodies it is known to join metal structural members to metal sheet members by means of an adhesive, typically, a heat-curable adhesive. For example, the roof sheet of a trailer body may be joined to the roof bow member by fixing the roof bows in proper relation to each other, applying a catalyzed heatcurable adhesive to the bonding surfaces of the roof bows, placing the roof sheet in proper position on the roof bows and clamping the whole assembly together, and then subjecting the assembly to a heat-curing cycle by, for example, maintaining it at a temperature of 1 800F for a period of twenty minutes.

The bonding strength of such a heat-curable adhesive is sufficient to provide the necessary structural integrity of the assembly but the technique is time consuming owing to the need to incorporate the heat-cure cycle and it requires a rather complex clamping system to hold the parts in place until cure is effected.

It has therefore been found desirable to employ a method for making such a structural assembly wherein two disparate types of adhesive in sideby-side relationship are employed. One adhesive is a hot melt adhesive that provides an initial bond within seconds so that the assembly can be manipulated without fear of damage and the other adhesive is a room temperature curing adhesive which provides a bond strength of the requisite structural integrity.

A problem arising from the adhesively secured reinforcing member is that when the member is pressed into contact with the metal sheet, if insufficient pressure is applied, the adhesive layers are not spread over the entire bonding surfaces, and therefore maximum bonding potential is not utilised. On the other hand, if too much pressure is applied, the adhesive layers are expressed from between the bonding surfaces, thereby wasting adhesive.

An object of the present invention is to improve the manufacture of lorry and trailer roofs and wall which employ metal sheet members that are joined to structural reinforcing members by adhesives.

The invention provides a reinforced sheet for the roofs or walls of vehicles, comprising a metal sheet, at least one reinforcing bow member having an elongate main body portion provided with a pair of laterally outwardly extending side flanges longitudinally coextensive with the body portion on either side thereof, each flange presenting a face parallel to the sheet and having a longitudinally extending rib dividing that face into a pair of side-by-side bonding surfaces, each rib being in contact with the sheet to determine the separation of the bonding surfaces from the sheet, with each bonding surface, the adjoining rib, and the adjacent portion of the surface of the sheet defining a predetermined volume between them, a layer of hot melt adhesive between one bonding surface on each flange and the surface of the sheet, and a layer of cured room-temperature curing adhesive between the other bonding surface on each flange and the sheet, each adhesive layer being of a volume substantially the same as its respective said predetermined volume so that the adhesives substantially completely fill the said predetermined volumes without excess.

The invention also provides a vehicle including, as a wall or roof member, a reinforced sheet in accordance with the invention.

The invention further provides a method of making a reinforced sheet for use as a wall or roof construction for vehicle bodies, comprising providing a sheet which is to be reinforced, providing a bow member having a main body portion provided with a coplanar opposed longitudinal side flanges, each flange presenting a longitudinally extending face divided into two side-by-side bonding surfaces by a longitudinally extending rib of a height such that when the ribs are in contact with the sheet each bonding surface is spaced away from the surface of the sheet by a predetermined amount, applying a bead of hot melt adhesive on one bonding surface of each flange and a bead of room temperature curing adhesive on the other bonding surface of each flange in an amount sufficient substantially completely to fill the volume between each such bonding surface and the surface of the sheet without excess, pressing the bow against the sheet to cause the ribs to abut the sheet and so to spread the beads of adhesive to fill the volumes between each bonding surface and the surface of the sheet, and holding the bow member and the sheet together in fixed relative positions until at least the hot melt adhesive has set.

One form of reinforced sheet constructed in accordance with the invention will now be described, by way of example, with reference to the accompanying drawings, in which: Fig. lisa perspective view of the metal sheet and the reinforcing member before they are brought into register with each other; and Fig. 2 is a transverse section of the assembled reinforced sheet.

Referring to Fig. 1 of the accompanying drawings, the metal sheet 2 shown therein is of a type conventionally employed as a wall or roof member for a lorry or a trailer body and, as is also conventional, this sheet is reinforced by bow members of which one is shown and is indicated generally by the reference numeral 4. Each reinforcing or bow member 4 has an elongate channel-shaped body 6 and a pair of lateral flanges 8 and 10 that extend along the whole length of, and are integral with, the body 6 of the bow member 4. Each of the flanges 8 and 10 is provided along its outer face with a central, longitudinal rib 12 or 14, respectively, of the same predetermined height.The rib 1 2 divides the outer surface of the flange 8 into two bonding surfaces 1 6 and 18, respectively, and the rib 14 divides the outer surface of the flange 10 into two bonding surfaces 20 and 22, respectively.

During the assembly of the reinforced sheet, there is deposited onto each of the bonding surfaces 16, 1 8, 20 and 22 a corresponding bead of adhesive 24,26,28 and 30, respectively. All of the adhesive beads 24, 26, 28, and 30 are of substantially the same cross-sectional area and they are deposited along the entire lengths of the bonding surfaces 16, 18,20 and 22, respectively.

The adhesive beads 24 and 28, which are deposited onto the bonding surfaces 16 and 20, respectively, are of a hot melt type. They should be based on elastomers formulated to provide relatively long open times of at least fifteen seconds and tackifiers may be added to provide good pressure sensitive properties. These adhesives are applied at a temperature of 3000F -4000F (149OCTh2040C) and typically will be polybutadiene elastomers, poly-isopropenestyrene copolymer elastomers, polyester elastomers and the like. At the same time as the adhesive beads 24 and 28, are deposited on the bonding surfaces 1 6 and 20, respectively, the adhesive beads 26 and 30 are deposited onto the bonding surfaces 18 and 22, respectively.The adhesive beads 26 and 30 are of a catalysed, room-temperature-curing type of adhesive and should provide low temperature flexibility and strength, high peel strength, that is to say, at least 30 psi (2.109 kilograms per square centimetre), and high lap shear strength, that is to say, at least 150 psi (10.55 kilograms per square centimetre); they should cure at low temperatures, that is to say, under 1 000F (380C) and should be more than 80%, preferably, 100%, solids. They may be onepart or two-part adhesives such as thiokol base (polysulfide), silicone, modified epoxy and urethane types.

The bow member 4 and the metal sheet 2 are than pressed together and the assembly shown in Fig. 2 is realised. The adhesive beads 24, 26, 28 and 30 are compressed and thus forced to spread into layers of adhesive 32, 34, 36 and 38, respectively. The bonding surfaces 16, 18,20 and 22 on the flanges 8 and 10 are spaced a small distance from the opposite bonding surfaces 40, 42, 44 and 46, respectively, on the metal sheet 2 by the ribs 12 and 14, to form cavities of predetermined volume. The volume of each cavity is substantially the same as that of the corresponding adhesive layer 32, 34, 36 or 38 so that the cavities are completely filled without excess. In this way, the maximum available bonding surface is utilised and there is no waste of adhesive.

Fig. 2 shows the finished structural assembly of the bow member 4 and sheet 2 which are initially joined and finally held by the hot melt adhesive layers 32 and 36. This initial bond allows the assembly to be handled before the high strength room temperature curing adhesive has cured without fear of destroying the assembly, and thereby saves time and expense as compared with the use of conventional means.

The height of the protruding ribs 12 and 1 4 on their respective flanges 8 and 10 is such as to ensure that, when the sheet 2 and bow member 4 are assembled as shown in Fig. 2, the thickness of the adhesive layers 32, 34, 36 and 38, respectively, is that at which the adhesive layers exhibit an optimum bonding strength. The relationship between the height of each of the ribs 12 and 1 4 and the width of each of the bonding surfaces 1 6, 1 8, 20 and 22, respectively, is such that, associated with each of the bonding surfaces, there is formed a cavity and each cavity contains a quantity of adhesive of substantiallythe same volume as that of the cavity. The volume of adhesive used is dictated by the cross sectional area of the adhesive beads 24,26, 28 and 30.In order that adhesive beads of a reasonable size can be employed, the volume of the cavities must be sufficiently large to accept beads of a cross sectional area which are practical to obtain. The volume of these cavities is controlled by the width of their associated bonding surfaces 1 6, 1 8, 20 and 22, respectively, and, for simplicity, the bonding surfaces 16, 18,20 and 22 are all of equal width so that the adhesive beads 24, 26, 28 and 30 deposited thereon can all be of equal cross sectional area.

Preferably, the height of the ribs 12 and 1 4 is of the order of 0.020 of an inch (0.0508 cm) and the size of the adhesive beads 24,26,28 and 30 is of the order if - of an inch (0.635 cm) in diameter.

This allows adhesive beads of conveniently obtainable size to be employed and ensures that, when the beads are compressed into the adhesive layers, their thickness is within a range which exhibits an optimum bonding strength.

If the ribs 12 and 14 are of the order of 0.020 of an inch (0.0508 cm) high and the adhesive beads 24, 26, 28 and 30 are of the order of - of an inch (0.635 cm) in diameter, then the width of each of the bonding surfaces 16, 18,20 and 22 must be of the order of 2.45 inches (6.234 cm) so that the volume of the cavities is substantially equal to that of the adhesive deposited therein.

Claims

1. A reinforced sheet for the roofs or walls of vehicles, comprising a metal sheet, at least one reinforcing bow member having an elongate main body portion provided with a pair of laterally outwardly extending side flanges longitudinally coextensive with the body portion on either side thereof, each flange presenting a face parallel to the sheet and having a longitudinally extending rib dividing that face into a pair of side-by-side bonding surfaces, each rib being in contact with the sheet to determine the separation of the bonding surfaces from the sheet, with each bonding surface, the adjoining rib, and the adjacent portion of the surface of the sheet defining a predetermined volume between them, a layer of hot melt adhesive between one bonding surface on each flange and the surface of the sheet, and a layer of cured room-temperature curing adhesive between the other bonding surface on each flange and the sheet, each adhesive layer being of a volume substantially the same as its respective said predetermined volume so that the adhesives substantially completely fill the said predetermined volumes without excess.

2. A reinforced sheet as claimed in claim 1, wherein the main body portion of the bow member is of channel shaped configuration, with the flanges extending from the rims of the channel.

3. A reinforced sheet as claimed in claim 1, wherein the rib is of a predetermined height such that when the rib is in contact with the metal sheet the space between each bonding surface and the surface of the sheet is of a thickness such that the adhesive layers exhibit substantially optimum bonding and for shear strength.

4. A reinforced sheet substantially as hereinbefore described with reference to, and as shown in Figs. 1 and 2 of, the accompanying drawings.

5. A vehicle including, as a wall or roof member, a reinforced sheet as claimed in any one of claims 1 to 4.

6. A method of making a reinforced sheet for use as a wall or roof construction for vehicle bodies, comprising a sheet which is to be reinforced, providing a bow member having a main body portion provided with coplanar.oppo5ed longitudinal side flanges, each flange presenting a longitudinally extending face divided into two side-by-side bonding surfaces by a longitudinally extending rib of a height such that when the ribs are in contact with the sheet each bonding surface is spaced away from the surface of the sheet by a predetermined amount, applying a bead of hot melt adhesive on one bonding surface of each flange and a bead of room temperature curing adhesive on the other bonding surface of each flange in an amount sufficient substantially completely to fill the volume between each such bonding surface and the surface of the sheet without excess, pressing the bow member against the sheet to cause the ribs to abut the sheet and so spread the beads of adhesive to fill the volumes between each bonding surface and the surface of the sheet, and holding the bow member and the sheet together in fixed relative positions until at least the hot melt adhesive has set.

7. A method as claimed in claim 7, wherein the bow member is heated to a sufficient temperature to ensure that the hot melt adhesive does not set before the bow member is in contact with the metal sheet.

8. A method of making a reinforced sheet substantially as hereinbefore described with reference to the accompanying drawings.