U.S. patent application number 11/357555 was filed with the patent office on 2006-08-10 for part for supporting an item of equipment, comprising support ribs, and method of molding said part.
Invention is credited to Stephane Talaucher, Gilbert Terranova.
Application Number | 20060175504 11/357555 |
Document ID | / |
Family ID | 32749754 |
Filed Date | 2006-08-10 |
United States Patent
Application |
20060175504 |
Kind Code |
A1 |
Talaucher; Stephane ; et
al. |
August 10, 2006 |
Part for supporting an item of equipment, comprising support ribs,
and method of molding said part
Abstract
The support part has support ribs for holding an item of
equipment, in particular an electric motor for a motor vehicle. A
mold consisting of at least two cores is provided. These cores are
brought toward one another in a direction (D) such that they are in
contact with one another along a parting plane. The mold is filled
with a moldable material and the cores are moved apart from one
another in the given direction (D). The support ribs are provided
on the molded part with an angle of inclination with respect to the
given direction (D). The ribs follow the parting plane. A clearance
is provided in the region of the parting plane between the cores in
order to form the ribs during molding.
Inventors: |
Talaucher; Stephane;
(Bonnelles, FR) ; Terranova; Gilbert; (Le Perray
En Yvelines, FR) |
Correspondence
Address: |
Valeo Climate Control Corp.;Intellectual Property Department
4100 North Atlantic Boulevard
Auburn Hills
MI
48326
US
|
Family ID: |
32749754 |
Appl. No.: |
11/357555 |
Filed: |
February 17, 2006 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10787271 |
Feb 26, 2004 |
|
|
|
11357555 |
Feb 17, 2006 |
|
|
|
Current U.S.
Class: |
248/309.1 |
Current CPC
Class: |
B29C 33/005 20130101;
F04D 29/601 20130101; H02K 5/04 20130101; B29L 2031/3005 20130101;
B29C 39/36 20130101; B29C 45/44 20130101; B29C 39/026 20130101;
H02K 5/00 20130101; H02K 5/24 20130101; B29C 39/34 20130101 |
Class at
Publication: |
248/309.1 |
International
Class: |
A47F 5/00 20060101
A47F005/00 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 28, 2003 |
FR |
03 02484 |
Claims
1. Support for holding an item of equipment, in particular an item
of equipment for a motor vehicle, comprising a casing of molded
plastic (2) having a peripheral wall (4) on which support ribs (16,
18) are provided for holding the item of equipment, the peripheral
wall (4) defining a housing of given axis (X-X) for receiving the
item of equipment, wherein the ribs (16, 18) are inclined with
respect to the axis (X-X) of the reception housing.
2. Support part according to claim 1, wherein the ribs (16, 18) are
formed on the inside of the casing.
3. Support part according to claim 1, wherein the ribs (16, 18)
each have a salient edge (68) that is able to make contact with the
item of equipment.
4. Support part according to claim 1, wherein the ribs (16, 18) are
grouped in pairs having opposite inclinations.
5. Support part according to claim 2, wherein the ribs (16, 18) are
grouped in pairs having opposite inclinations.
6. Support part according to claim 2, wherein the number of ribs
(16, 18) is between 4 and 12.
7. Support part according to claim 1, wherein the ribs (16, 18)
have the shape of a helix (32).
8. Support part according to claim 3, wherein the ribs (16, 18)
have the shape of a helix (32).
9. Support part according to claim 8, wherein the ribs (16, 18)
have the shape of a straight line segment (35) connecting two
points (34, 36) situated on a helix (32).
10. Support part according to claim 8, wherein the shape of the rib
(16, 18) corresponds to the shape of a salient edge (68) that the
rib has.
11. Support part according to claim 8, wherein the angle of
inclination of the helix (32) is between 1.degree. and
15.degree..
12. Support part according to claim 1, wherein the ribs (16, 18)
have a cross section selected from the group comprising triangular,
square, rectangular, semi-circular or elliptical shapes, or a
combination of these shapes.
13. Support part according to claim 2, wherein the ribs (16, 18)
have a cross section selected from the group comprising triangular,
square, rectangular, semi-circular or elliptical shapes, or a
combination of these shapes.
14. Support part according to claim 4, wherein the ribs (16, 18)
have a cross section selected from the group comprising triangular,
square, rectangular, semi-circular or elliptical shapes, or a
combination of these shapes.
15. Support part according to claim 6, wherein the ribs (16, 18)
have a cross section selected from the group comprising triangular,
square, rectangular, semi-circular or elliptical shapes, or a
combination of these shapes.
16. Support part according to claim 7, wherein the ribs (16, 18)
have a cross section selected from the group comprising triangular,
square, rectangular, semi-cincular or elliptical shapes, or a
combination of these shapes.
17. Support part according to claim 1, wherein the cross section of
the ribs is constant, increasing or decreasing, or has a
combination of these forms.
18. Support part according to claim 2, wherein the cross section of
the ribs is constant, increasing or decreasing, or has a
combination of these forms.
19. Support part according to claim 4, wherein the cross section of
the ribs is constant, increasing or decreasing, or has a
combination of these forms.
20. Support part according to claim 6, wherein the cross section of
the ribs is constant, increasing or decreasing, or has a
combination of these forms.
21. Support part according to claim 7, wherein the cross section of
the ribs is constant, increasing or decreasing, or has a
combination of these forms.
22. Support part according to claim 2, wherein the ribs (16, 18)
are continuous.
23. Support part according to claim 4, wherein the ribs (16, 18)
are continuous.
24. Support part according to claim 7, wherein the ribs (16, 18)
are continuous.
25. Support part according to claim 1, wherein the ribs are formed
by a series of bosses (64, 66) arranged along a line (32) that is
inclined with respect to the axis (X-X) of the housing.
26. Support part according to claim 2, wherein the ribs are formed
by a series of bosses (64, 66) arranged along a line (32) that is
inclined with respect to the axis (X-X) of the housing.
27. Support part according to claim 25, wherein the bosses (64, 66)
are arranged along a helical line (32).
28. Support part according to claim 25, wherein the bosses (64, 66)
are arranged along a straight line segment (35) connecting two
points (34, 35) situated on a helix (32).
29. Support part according to claim 27, wherein the bosses (64, 66)
have points of contact defining salient edges (68) of the ribs.
30. Method of molding a support part (2) comprising support ribs
(16, 18) for holding an item of equipment, the step comprising:
providing a mold consisting of at least two cores (38, 40);
bringing the two cores (38, 40) toward one another in a given
direction (D) such that, once positioned, the latter are in contact
with one another along a parting plane; filling the mold with a
moldable material; moving the cores (36, 38) apart from one another
in the given direction (D), wherein the support ribs (16, 18) are
provided on the molded part with an inclination (.alpha.) with
respect to the given direction (D); the cores (16, 18) are shaped
such that their parting plane follows the ribs (16, 18), and a
clearance (62) is provided in at least one of the cores (38, 40) in
the region of their parting plane in order to form the ribs, during
molding, by the filling of this clearance (62) with the molded
material.
31. Method according to claim 30, wherein the cores (38, 40) are
shaped such that their parting plane forms salient edges (68) of
the ribs (16, 18).
32. Mold for implementing the method according to claim 30,
comprising an upper core (38) having a cylindrical central portion
(42) and peripheral protrusions (46), and a lower core (40) having
a cylindrical central portion (44) and peripheral protrusions
(48).
33. Mold for implementing the method according to claim 31,
comprising an upper core (38) having a cylindrical central portion
(42) and peripheral protrusions (46), and a lower core (40) having
a cylindrical central portion (44) and peripheral protrusions
(48).
34. Mold according to claim 32, wherein each peripheral protrusion
(46) of the upper core (38) has an outer cylindrical face (50), an
inner cylindrical face (54) and radial faces (58) connecting the
outer cylindrical face (50) and the outer cylindrical face (54),
and in that each peripheral protrusion (48) of the lower core (40)
has an outer cylindrical face (52), an inner cylindrical face (56)
and radial faces (60) connecting the outer cylindrical face (52)
and the inner cylindrical face (56).
35. Mold according to claim 32, wherein the radial faces (58, 60)
are planar or helical.
36. Mold according to claim 33, wherein the radial faces (58, 60)
are planar or helical.
37. Mold according to claim 34, wherein the radial faces (58, 60)
are planar or helical.
38. Mold according to claim 32, wherein it comprises a clearance
(62) in at least one of the cores (38, 40) in the region of their
parting plane in order to form the ribs (16, 18) during
molding.
39. Mold according to claim 34, wherein a clearance (62) is formed
by a connecting face connecting an outer cylindrical face (50) and
a radial face (58) of the upper core (38) and/or by a connecting
face connecting an outer cylindrical face (52) and a radial face
(60) of the lower core (40).
40. Mold according to claim 34, wherein a clearance (62) is formed
by a connecting face connecting an outer cylindrical face (50) and
a radial face (58) of the upper core (38) and/or by a connecting
face connecting an outer cylindrical face (52) and a radial face
(60) of the lower core (40).
Description
FIELD OF THE INVENTION
[0001] The invention relates to a support part for holding an item
of equipment, in particular an item of equipment for a motor
vehicle, comprising a casing of molded plastic having a peripheral
wall on which support ribs are provided for holding the item of
equipment, the peripheral wall defining a housing of given axis for
receiving the item of equipment.
BACKGROUND AND SUMMARY OF THE INVENTION
[0002] Furthermore, the invention relates to a method of molding a
support part having support ribs for holding an item of equipment,
in particular an item of equipment for a motor vehicle, comprising
the steps consisting in:
[0003] providing a mold consisting of at least two cores;
[0004] bringing the two cores toward one another in a given
direction, such that they are in contact with one another along a
parting plane;
[0005] filling the mold with a moldale material; and
[0006] moving the cores apart from one another in the given
direction.
[0007] The invention relates more particularly to support parts
manufactured in industry, for example parts for supporting items of
equipment for a motor vehicle, such as electric motors driving a
blower and intended for a motor vehicle heating-ventilating and/or
air-conditioning apparatus or alternatively for a motorized fan
unit arranged behind a radiator for cooling the engine of the motor
vehicle. These parts frequently consist of a cylindrical casing of
molded plastic having, on the inside, a series of support ribs for
holding the item of equipment, for example the electric motor.
[0008] To ensure that the item of equipment is held firmly, it is
necessary for the inside diameter defined by the ends of the ribs
to be greater than the outside diameter of the supported item of
equipment. It is additionally necessary for there to be clamping or
negative clearance between the outside diameter of the item of
equipment and the ribs.
[0009] On account of the fact that the support parts are obtained
by molding, it is necessary to provide a draft angle for the mold
to allow the part to be withdrawn from the mold. This draft is
found on the ribs, which consequently have a variation in diameter
from one end to the other. This variation in diameter depends, on
the one hand, on the draft angle and, on the other hand, on the
length of the part. The larger the draft angle and the longer the
part, the greater the variation in diameter.
[0010] To ensure that the item of equipment is correctly held at
each of its two ends, it is consequently necessary for there to be
clamping at the more flared end of the ribs. It is therefore
necessary, as stated above, for the outside diameter of the item of
equipment to be supported, for example the electric motor, to be
greater than the diameter defined by the ends of the ribs at the
end where these ribs have the greatest diameter. It goes without
saying that, at the other end, that is to say at the end where the
diameter of the ribs is tightest, clamping is greater still.
[0011] This variation in clamping has several drawbacks. First of
all the item of equipment is not held uniformly over its whole
length. The item of equipment is held better at one end than at the
other. Moreover, in one end portion of the support part, there is a
first manufacturing tolerance, whereas in another end portion,
there is a second manufacturing tolerance which is different from
the first. This results in an overall tolerance that is the sum of
the two aforementioned tolerances and is therefore much too wide,
sometimes leading to a situation where it is impossible to mount
the item of equipment in the support part.
[0012] It is for this reason that attempts have been made to reduce
as far as possible the difference in diameter between the two ends
of the ribs of the support parts that are currently known. In the
prior art, this result is currently achieved by reducing the draft
angle. However, it is not possible in practice to drop below a
draft angle of less than 1.degree.. By way of example, a draft
angle for a length of 55 mm represents a variation of 0.96 mm in
the radius of the rib.
[0013] Moreover, it is known to place the parting plane of the two
cores at the center of the part so as to halve the influence of the
length of the ribs. This method makes it possible to reduce the
variations in the diameter of the ribs by a factor of two. The
drawbacks mentioned above are lessened but nevertheless remain.
[0014] The invention aims to eliminate these drawbacks by producing
a support part having draft-free ribs.
[0015] Moreover, it concerns a method of molding the support part,
and also a mold for implementing this method.
[0016] To this end, the invention provides a support part for
holding an item of equipment, in particular an item of equipment
for a motor vehicle, of the type defined above, in which the ribs
are inclined with respect to the axis of the reception housing.
[0017] By virtue of these features, the ribs have a zero draft
angle. The diameter of the circle defined by the ends of the ribs
is constant from one end of the molded part to the other. Clamping
of the supported item of equipment is constant over its whole
length, the item of equipment therefore being held better. In
addition, it is not necessary to increase the clamping at one end
in order for the item of equipment to be held at the other end. The
manufacturing tolerances are therefore more reliable, without
possible spread. The vibration of the item of equipment, when it is
a motor, is thus better tolerated and does not cause the item of
equipment to become uncoupled from its support.
[0018] It should be noted that the peripheral wall of the support
part, on which wall the ribs are provided, has a non-zero draft.
However, this in no way constitutes a drawback because the
supported item of equipment is not in contact with it.
[0019] According to another feature of the invention, the ribs are
formed on the inside of the casing and they each have a salient
edge that is able to make contact with the item of equipment.
[0020] Advantageously, the ribs are grouped in pairs having
opposite inclinations. This feature makes it easier to remove the
cores from the mold. The number of ribs is advantageously between 4
and 12.
[0021] In one specific embodiment, the ribs have the shape of a
helix. Their draft is then strictly equal to zero. In another
specific embodiment, the ribs have the shape of a straight line
segment connecting two points situated on a helix. The draft is
then not strictly zero, but it is negligible. The angle of
inclination of the helix is preferably between 1.degree. and
15.degree..
[0022] The shape of the ribs corresponds above all to the shape of
a salient edge that the rib has. In fact, it is this salient edge
that comes into contact with the item of equipment that is housed
in the support part. The ribs may have a cross section selected
from the group comprising triangular, square, rectangular,
semi-circular or elliptical shapes, or a combination of these
shapes.
[0023] The cross section of the ribs may be constant, increasing or
decreasing. It is also possible to combine these various
possibilities.
[0024] In one specific embodiment, the ribs are continuous.
[0025] In another specific embodiment, the ribs are formed by a
succession of bosses arranged along a line that is inclined with
respect to the axis of the housing.
[0026] In this case, the bosses may be arranged along a helical
line or, alternatively, along a straight line segment connecting
two points situated on a helix. In all cases, it is advantageous
for the bosses to have points of contact defining salient edges of
the ribs.
[0027] The invention also concerns a method of molding a support
part as defined above, in which the support ribs are provided on
the molded part with an inclination with respect to the given
direction, in which the cores are shaped such that their parting
plane follows the ribs, and in which a clearance is provided in at
least one of the cores in the region of their parting plane in
order to form the ribs, during molding, by the filling of this
clearance with molded material.
[0028] Advantageously, the cores are shaped such that their parting
plane forms salient edges of the ribs.
[0029] In order to implement the method, use is advantageously made
of an upper core having a cylindrical central portion and
peripheral protrusions, and a lower core having a cylindrical
central portion and peripheral protrusions.
[0030] Each peripheral protrusion of the upper core has an outer
cylindrical face, an inner cylindrical face and radial faces
connecting the outer cylindrical face and the outer cylindrical
face, whereas each peripheral protrusion of the lower core has an
outer cylindrical face, an inner cylindrical face and radial faces
connecting the outer and inner cylindrical faces.
[0031] The radial faces may be, in particular, planar or
helical.
[0032] Advantageously, the mold comprises a clearance in at least
one of the cores in the region of their parting plane in order to
form the ribs during molding.
[0033] This clearance is preferably formed by a connecting face
connecting an outer cylindrical face and a radial face of the upper
core and/or by a connecting face connecting an outer cylindrical
face and a radial face of the lower core.
BRIEF DESCRIPTION OF THE DRAWINGS
[0034] Other features and advantages of the invention will also
become apparent on reading the following description of exemplary
embodiments given by way of illustration with reference to the
appended drawings, in which:
[0035] FIG. 1 is a perspective view of a part produced according to
the invention for supporting an item of equipment, in this example
an electric motor;
[0036] FIG. 2 is a plan view of the support part depicted in FIG.
1;
[0037] FIG. 3 is a view in section on III-III of the support part
of FIG. 1;
[0038] FIG. 4 is a three-dimensional diagram illustrating the
inclination of the support ribs, with respect to the axis of
rotation, of a support part produced according to the
invention;
[0039] FIG. 5 is a three-dimensional diagram depicting a pair of
associated ribs;
[0040] FIGS. 6 and 7 are perspective views depicting two positions
of the cores used in the method of the invention;
[0041] FIG. 8 is a plan view of the cores depicted in FIGS. 6 and
7;
[0042] FIG. 9 is an enlarged detail of FIG. 8;
[0043] FIG. 10 is a partial perspective view of another embodiment
of a support part molded according to the invention; and
[0044] FIG. 11 is a partial view in section of a support part, a
rib of which is in contact with an item of equipment housed in the
support part.
DETAILED DESCRIPTION OF THE PREFFERED EMBODIMENTS
[0045] FIG. 1 shows a perspective view of a support casing 2 for an
electric motor. The casing 2 is a molded part obtained by molding a
plastic, for example a polypropylene, a talc-filled polypropylene,
a polyurethane, or a polyoxymethylene. The support part 2 has a
peripheral wall 4 (or skirt) of axis X-X (see FIGS. 2 and 3) that
bounds an open housing that is able to receive an electric motor
(not shown). In the example, three ledges 6 arranged respectively
at 120.degree. to one another (FIG. 2) enable the electric motor to
be retained in the housing. However, the number of ledges is not
restricted to this value and could be greater than three. On the
outside, the peripheral wall 4 has three tabs 8 arranged at
120.degree. to one another, and a stud 10 on each of these tabs.
This enables the casing 2 to be fixed to the chassis of a motor
vehicle.
[0046] This electric motor is, for example, a motor intended for
the motorized fan unit that is fitted in a motor vehicle
heating-ventilating/air-conditioning installation.
[0047] Three support grooves 12 formed at 120.degree. to one
another in the peripheral wall 4 enable the support to be uncoupled
from the remainder of the installation. Three clips 14 arranged
between the grooves 12 retain the electric motor after it has been
put in place. Ribs 16 and 18 are formed on the inside on the
peripheral wall 4. As can be seen in FIG. 2, which is a plan view
of the support part depicted in FIG. 1, the number of these ribs is
in this case six, namely three ribs 16 and three ribs 18.
Generally, it is possible to have from two pairs to six pairs of
ribs, i.e. from four to twelve ribs. The ribs 16 are inscribed in a
right-handed helix, whereas the ribs 18 are inscribed in a
left-handed helix. The inclinations of the ribs 16 and 18 with
respect to the axis of rotational symmetry X-X of the casing 2 are
therefore opposite. Consequently, the ribs are grouped in pairs
(one rib 16 and one rib 18) of opposite inclinations.
[0048] An area 20 in the form of an isosceles trapezoid that widens
progressively downward (as shown in FIG. 3) is thus bounded between
two ribs 16 and 18. In the same way, areas 22 in the form of
isosceles trapezoids that widen progressively upward are bounded,
on the peripheral wall 4, between the ribs 16 and 18 of two
neighboring pairs of ribs. These trapezoidal areas 20 and 22 have a
draft angle to allow them to be removed from the mold.
[0049] FIG. 4 depicts a view in space that shows the inclination of
the ribs 16, 18 with respect to the longitudinal axis X-X of the
peripheral wall 4. The circle 24 schematically represents the
diameter of the peripheral wall. The axis X-X is perpendicular to
the plane of the circle 24 and it passes through the center of this
circle. The straight line 26 is parallel to the axis X-X and it
intersects the circle 24 at a point 28. The straight line 30 is
tangential to the helix 32 of axis X-X. It makes an angle .alpha.
with the straight line 26.
[0050] The ribs 16 and 18 may advantageously have a helical shape
and they each have a salient edge intended to come into contact
with the item of equipment, in this case the shell of the electric
motor. In other words, each of the salient edges of the ribs 16 and
18 consists of a segment of a helix 32 having an angle of
inclination .alpha. with the parallel 26 to the axis X-X of the
peripheral wall of the molded part. Of course, the direction of the
helices is different. The helix depicted in FIG. 4 is a right helix
that corresponds to the ribs 16. The salient edges of the ribs 18
follow the profile of an identical helix, preferably having
(although this is not essential) the same inclination a but the
opposite direction (left helix). Two oppositely directed helices 16
and 18 are thus grouped in pairs as depicted in FIG. 5.
[0051] In another embodiment of the method of the invention, the
salient edges of the ribs 16 and 18 consist of a straight line
segment 35 connecting two points 34 and 36 situated on the helix
32. This embodiment is simpler because the ribs are then
rectilinear. The shape of the base of the ribs is not decisive as
long as it is not detrimental to the support part's being removed
from the mold. What is important here is the shape of the salient
edge of the rib, which may be pointed to a greater or lesser
extent.
[0052] FIGS. 6 and 7 illustrate the molding method of the
invention. In this method, use is made of a mold consisting of two
cores, namely an upper core 38 and a lower core 40. The cores 38
and 40 are depicted in part in FIGS. 6 and 7. The upper core 38 has
a cylindrical portion 42 and the lower core 40 has a cylindrical
portion 44. Peripheral protrusions 46 are attached to the
cylindrical central portion 42 of the upper core 38, and peripheral
protrusions 48 are attached to the cylindrical central portion 44
of the lower core 40. In the example, there are three protrusions
for each of the cores, but this number could be lower or
higher.
[0053] The protrusions 46 of the upper core 38 have an outer
cylindrical face 50 and an inner cylindrical face 54 and radial
faces 58 that connect the outer cylindrical face 50 and inner
cylindrical face 54.
[0054] The peripheral protrusions 48 of the lower core 40 have an
outer cylindrical face 52 and an inner cylindrical face 56 and
radial faces 60 that connect the outer cylindrical faces 52 and
inner cylindrical faces 56.
[0055] The radial faces 58 and 60 are inclined with respect to the
axis X-X of the part to be molded by an angle a equal to the angle
of inclination of the ribs. They may be planar or helical. More
precisely, what is being referred to here is the area of connection
between the outer cylindrical wall and the radial wall of each
protrusion, as will be seen later.
[0056] As can be seen in FIG. 6, and also in FIG. 8, which depicts
a plan view of the cores, the shapes of the cores 38 and 40 are
designed so that they fit into one another. In other words, the
three peripheral protrusions 46 of the upper core and the three
peripheral protrusions 48 of the lower core fit into one another
perfectly, their radial faces coming into contact with one another
so as to reconstitute a complete cylinder without there being any
play between these faces, except within the rib-molding areas.
Since the angles of inclination of the faces are identical, these
faces are in perfect contact with one another and form a parting
plane for the cores, except within the rib-molding areas.
[0057] As can be seen in FIG. 8 and more particularly in FIG. 9,
clearances 62 are formed in the peripheral protrusions 46 and 48.
These clearances 62 are each formed by a connecting face connecting
an outer cylindrical face 50 and a radial face 58 of a protrusion
46 of the upper core 38 or by a connecting face connecting an outer
cylindrical face 52 and a radial face 60 of a protrusion 48 of the
lower core 60. As an alternative, it is possible for these
clearances to be provided on only one of the cores. These
clearances leave a gap that will be filled by the molded material
at the time of molding so as to form the ribs 16 and 18. Of course,
the shape of the clearances 62 corresponds to the shape of the ribs
that it is desired to obtain.
[0058] In the example shown, the clearances 62 bound a volume of
triangular cross section such that, after molding, the ribs will
have a corresponding shape, that is to say a triangular cross
section. If it is desired to obtain another rib shape, for example
a semi-circular or elliptical, etc., shape, the shape of the
clearances 62 must be tailored to this profile.
[0059] Since the ribs 16 and 18 are arranged along the parting
plane, it will be understood that it is not necessary to design in
a draft angle. The upper core 38 and the lower core 40 separate
from one another while releasing from the ribs. The angle of
inclination of the radial planar faces 58 and 62, for example
between 1.degree. and 15.degree., naturally facilitates removal
from the mold.
[0060] When the salient edges of the ribs have a helical shape that
follows the profile of the helix 32 (FIG. 4), the draft angle is
completely zero. When, by contrast, the radial faces are
rectilinear, there is a small space between the profile of the
helix and the straight line segment 35. There is then a very small
draft. For example, for a radius of 32.5 mm and an angle .alpha. of
7.degree. and a length of 50 mm for the ribs 16 and 18, the maximum
variation in the circle defined by the ends of the ribs 16 and 18
is less than 0.15 mm over the radius of this circle.
[0061] However, the use of a circular or square cross section
generates a very small draft angle of the planar surface described
by the cross section along the helix. The draft angle applies in a
direction D in which the cores are brought toward one another or
moved apart from one another, which limits the effect of the draft
angle.
[0062] Prior to molding, the cores 38 and 40 forming the mold are
brought toward one another in the direction D, which coincides with
the longitudinal axis X-X of the support part to be molded. After
molding, the cores are moved apart from one another in the same
direction D as schematically represented by the arrows 53 and 55
(FIGS. 6 and 7).
[0063] FIG. 10 depicts an alternative embodiment of the method and
of the part obtained by the method. In this embodiment, the
peripheral wall 4 of the part to be molded does not have continuous
ribs, as in the preceding embodiment, but a series of bosses 64
forming a discontinuous rib. The bosses 64 are arranged along the
parting plane between the upper and lower cores, in a similar
manner to the ribs of the preceding embodiment. They are produced
by molding, by filling molded plastic into cutouts (not shown)
formed in the peripheral protrusions 46 and 48. It goes without
saying that the shape of these cutouts (not shown) corresponds to
the shape of the bosses 64 that it is desired to obtain.
[0064] In the same way as for the ribs, the bosses 64 may have a
wide variety of profiles as long as they provide points of contact
that can form the salient edges of the ribs. These bosses may have
a triangular, square, rectangular, elliptical or semi-circular
cross section or a combination of these shapes. Their rectangular
cross section preferably has a length of 10 mm and a width of 5
mm.
[0065] The bosses 64 may be arranged exactly along the profile of
the helix 32 (FIG. 4), or else they may be arranged along a
rectilinear straight line segment 35 joining two points of the
helix. However, the arrangement of the bosses must be designed so
as to make molding possible, which rules out the superposition of
demolding areas. The length of the bosses is preferably below 10
mm. This length makes it possible to retain a slight variation in
the radius of the circle defined by their ends.
[0066] In the example shown, the bosses 64 are teardrop-shaped,
which is advantageous for removal from the mold. Also depicted in
FIG. 10 is an alternative form of a boss 66 having a semi-circular
cross section and two rounded ends. All these forms make it
possible to provide continuous and constant clamping of the
electric motor while generating a slight variation in the diameter
of the circle defined by the end of the bosses.
[0067] FIG. 11 shows a rib 16 of triangular cross section having a
salient edge 68 and an opposite base that is attached to the
cylindrical wall 4 of the support part 2. The salient edge 68 comes
into contact with an item of equipment 70, in this case the shell
of an electric motor.
* * * * *