GB2355427A

GB2355427A - An injection moulded ventilation flap and a method of moulding

Info

Publication number: GB2355427A
Application number: GB9925112A
Authority: GB
Inventors: Patrice Gouritin; Rodolphe Legay
Original assignee: Draftex Industries Ltd
Current assignee: Laird Holdings Ltd
Priority date: 1999-10-22
Filing date: 1999-10-22
Publication date: 2001-04-25
Anticipated expiration: 2019-10-22
Also published as: GB2355427B; GB9925112D0

Abstract

There is provided a movable flap for a vehicle ventilation system, the flap being formed from a foamed thermoplastics material in a single injection moulding operation, and comprising a generally planar body (10,12) the major faces of which form flow surfaces over which fluid flows when the flap is in use, the flow surfaces being substantially smooth such that the flow over the surfaces is substantially laminar. The flap may include soft sealing lips (14) produced by overmoulding and having a Shore A hardness of between 3 and 90.

Description

2355427 A VENTILATION FLAP AND A METHOD OF MOULDING A VENTILATION FLAP

This invention relates to a movable flap for a vehicle ventilation system and to a method of moulding such a movable flap.

According to a first aspect of the invention there is provided a movable flap for a vehicle ventilation system, the flap being formed from a foamed thermoplastics material in a single injection moulding operation, and comprising a generally planar body the major faces of which form flow surfaces over which fluid flows when the flap in use, the flow surfaces being substantially smooth such that the flow over the surfaces is substantially laminar.

According to a second aspect of the invention there is provided a method of moulding a movable flap for a vehicle ventilation system, comprising the steps of forming a mould for injection moulding, the mould having generally smooth, un- ribbed major surfaces which correspond to generally smooth flow surfaces of the flap and the mould also having regions of smaller volume which correspond to thinner fixing regions of the flap, mixing a blowing agent with a thermoplastics material, cooling the mould walls, and injecting the material into the mould to produce an injection moulded flap formed from a single foamed thermoplastics material.

2 Movable flaps embodying the invention will now be described by way of example with reference to the drawings in which:

Figure 1A is a schematic cross-section of a prior art two-part flap; 5 Figure 1B is a schematic cross-section of another prior art flap;

Figure 2 is a schematic cross-section of a flap in accordance with the invention; Figure 3 is a schematic perspective view of a flap in accordance with the invention; and Figure 4 is a schematic perspective view of a flap in accordance with the invention including sealing lips. 15 With reference to Figure IA, a prior art flap typically consists of an injection moulded shell 2 which has strengthening ribs 4. The ribs are required to ensure that the shell 2 is sufficiently rigid to resist flexion forces caused by rotation of the flap, without significant bending (which would be detrimental to good sealing). 20 However, where the flap is required to divert air flows for example, it is necessary that

3 air flows over the upper side A and also over the lower side B. A problem with this arrangement is that as air flows over both the sides of the flap, the air flow is disrupted by the ribs 4. The result is turbulent air flow over the flap which reduces flow rates and causes noise.

This problem also occurs in the flap of Figure 1B which has ribs 4' on both sides A' and 13'.

To overcome this problem (with reference to Figure 1A), a common solution is to include a second part 6 of the flap which is secured to the underside of the shell 2. The second part 6 forms a closed cavity which encases the strengthening ribs 4. In this way, the flap presents smooth surfaces to air flowing over the sides A and B of the flap. However, this approach requires several moulding operations and an 15 assembly operation and thus the cost of manufacture is relatively high.

An alternative approach is to manufacture the flap from sheet metal. However this is also expensive in manufacture and the flap is undesirably heavier than a plastic flap.

A third alternative is to mould the flap from solid plastics. This produces a generally rigid flap but makes the flap heavy. Also, a solid plastics flap is relatively expensive 4 to make by injection moulding because of long cycle times and shrinkage problems.

With reference to Figure 2, in accordance with this invention, the flap is made from a foamed thermoplastics material. The central portion 10 of the flap has a cellular construction and is encased by a generally non-foamed or solid skin 12. The flap is produced by injection moulding with a thermoplastics and blowing agent mixture.

The skin 12 is produced by cooling the walls of the mould prior to injection. This causes the surface of the flap to set before cells have been formed in the molten plastic by the blowing agent. In this way, a smooth outer surface is produced. Furthermore, the flap is rigid and lightweight and can be moulded with a shorter cycle time than a solid plastics flap.

Preferably, sealing lips 14 are produced by overmoulding. The lips are preferably soft and have a Shore A hardness in the range of from 3 to 90 and preferably of less than 25.

With reference to Figure 3, the external appearance of a typical flap is shown. Both the upper surface C and the lower surface D are smooth. A fixing region 16 is also formed in the same injection operation. By arranging for the mould to produce thinner areas for the fixing regions, the density of the moulded material is increased. This produces more rigid and harder areas for fixing and for movement of the flap.

Typical materials for the parts 10 and 12 of the flap (typically termed "flap insert") are polypropylene, polyamide or ABS with or without fillers such as talc or fibre.

Thus, the invention provides a flap which has smooth surfaces on both sides, which is rigid and cheap to manufacture and which integrates mechanical functions such as hinges and operating levers into the flap in a single moulding operation.

The term "flap" as used herein is intended to cover a flap such as that shown in Figure 3 and also the combination of a "flap insert" and a sealing part 18 as shown in Figure 4.

6

Claims

1. A movable flap for a vehicle ventilation system, the flap being formed from a foamed thermoplastics material in a single injection moulding operation, and comprising a generally planar body the major faces of which form flow surfaces over which fluid flows when the flap is in use, the flow surfaces being substantially smooth such that the flow over the surfaces is substantially laminar.

2. A flap according to claim 1, wherein the flap has a skin formed by a substantially non-foamed surface layer of the thermoplastics material.

3. A flap according to claim 1 or claim 2, including at least one fixing member for fixing and/or moving the flap, the or each fixing member being formed as a higher density region of the foamed thermoplastics material.

4. A flap according to any preceding claim, further comprising a soft lip formed on the body and arranged for sealing against an edge of an aperture in the vehicle ventilation system, the lip having a Shore A hardness of between 3 and and preferably of less than 25.

5. A flap according to any preceding claim, wherein the thermoplastics material 7 is foamed using a blowing agent.

6. A method of moulding a movable flap for a vehicle ventilation system, comprising the steps of; a) forming a mould for injection moulding, the mould having generally smooth, un-ribbed major surfaces which correspond to generally smooth flow surfaces of the flap and the mould also having regions of smaller volume which correspond to thinner fixing regions of the flap, b) mixing a blowing agent with a thermoplastics material, C) cooling the mould walls, and d) injecting the material into the mould to produce the injection moulded flap of claim 1 formed from a single foamed thermoplastics material.

7. A method according to claim 6, further comprising the step of overmoulding a soft sealing lip onto the flap, the sealing lip having a Shore A hardness of between 3 and 90 and preferably of less than 25.

8. A flap constructed and arranged as described herein with reference to the drawings.