NIVEAU A BULLE ET PROCEDE DE FABRICATION

SPIRIT LEVEL AND MANUFACTURING PROCESS FOR PRODUCING IT

Abrégé anglais

The spirit level comprising a body is made up of
a preferably T or I section with a housing in which an air
unit is fixed. According to the invention, the body is
produced in thermosetting resin and the air unit is
integrated into the section.

Revendications

1
WE CLAIM:
1. A spirit level comprising a body with a recess in which at least one air
element is fixed,
characterised in that the body is made from a thermosetting resin having a
glass
particle filler to give the thermosetting resin its required rigidity and
comprising
specifically predetermined burrs only on the top parts of the level.
2. A spirit level according to claim 1, characterised in that the
thermosetting
resin is a polyester resin having a glass particle filler.
3. A spirit level according to claim 1 or 2, characterised in that the
thermosetting resin has a glass fibre filler.
4. A spirit level according to claim 1 or 2, characterised in that the
thermosetting resin has a glass ball filler.
5. A spirit level according to claim 1 or 2, characterised in that the
thermosetting resin has glass ball filler on the outer surface of the
injection molding
and a fibre filler in its core.
6. A spirit level according to any one of the preceding claims, characterised
in that an air element is partially covered by a frame having a window at a
level of
a bubble and masking an edge of the air element and of the profile.
7. A spirit level according to any one of the preceding claims, characterised
in that the thermosetting resin is dyed in its mass.
8. A spirit level according to claim 1, characterised in that the body has the
form of a T-profile.
9. A spirit level according to claim 1, characterised in that the body has the
form of an I-profile.
10. A manufacturing process for producing the spirit level according to any
one of the preceding claims, by injection of a thermosetting material having
glass
particle filler, characterised in that the air element is fixed by means of
withdrawable
pins to a part of an injection mold and in that the injection mold brought to
a melting
temperature of the material is partially cooled in a zone of the air element
location.
11. A process for the production of the spirit level of claim 1, characterised
by
use of a mold in three or four parts, one or two partially forming a base
plate and

2
the other two closing above the base plate to form a top part of a profile
with
insertion of the air element.
12. A process for the production of the spirit level of claim 9, characterised
in
that complete closure of an injection mold is effected only after the
injection mold
has been filled with the thermosetting resin containing a filler, resulting in
formation
of specifically predetermined flashes only on top parts of the level.

Description

CA 02057365 2002-05-07
CA 2 057365-1
SPIRIT LEVEL AND MANUFACTURING PROCESS
FOR PRODUCING IT
This invention concerns a spirit level and a
manufacturing process for producing such a spirit level
comprising a body with a recess in which at least one bubble
block is fixed.
A spirit level is a precision instrument, the
manufacturing and adjustment of which must be handled with
great care. The body of a modern spirit level is often an
aluminum section. This section can be a hollow or I- or T-
shaped section. Aluminum has the advantage of being rigid
enough to ensure the necessary precision, but it is quite
expensive and requires a surface treatment for its
protection or colouring.
Plastic sections have been suggested as an alternative
to an aluminum spirit level body, but plastic materials that
lend themselves to low-cost manufacturing cannot give a
spirit level base the required rigidity. That is the reason
why composite spirit levels have been developed having a
core and a base plate in the form of an aluminum section
over which a plastic structure is molded to accommodate the
air element and manipulate the spirit level. In that case,
the plastic structure includes a cut-out where the air
element is housed. Adjustment of the exact orientation of
the air element against the base plate is achieved by

CA 02057365 2002-05-07
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screws. In the case of a perfect alignment, the air element
is glued to the plastic structure.
This manufacturing process is long and tedious but the
saving of aluminum compensates for the high manufacturing
cost.
For this reason, the object of the invention is to
create a spirit level of the type described above as well as
to attain a simple and inexpensive manufacturing process
that ensures the required precision and a low manufacturing
cost.
The subclaims describe preferred embodiments of the
invention.
According to the invention, the thermosetting resin of
the spirit level can be coloured. Thus, even when it is
prone to scratches, the section continues to have a clean
appearance.
Necessary handling during the manufacturing process are
limited to a minimum.
Other features and advantages of the invention can be
seen more clearly in the following description, given only
as an example but not restricted hereto, as well as the
attached drawing in which
Fig. 1 is a perspective view of an embodiment of the
spirit level and of the invention, and
Fig. 2 is a perspective view of the injection mold for
manufacturing a spirit level according to the invention.
The spirit level 1 shown in Fig. 1 is mainly composed
of three parts: the base plate 2, the core of the body 3 and
the air element 5. The base plate 2 forms one piece, called
section, with the core of the body 3. The section has a

CA 02057365 2002-05-07
- 3 -
cut-out showing a housing 4 for the air element 5. This
housing 4 is located exactly in the middle of the body's
core to improve the contact between the lateral faces and
the bottom of the air element 5. The section is enlarged in
the cut-out area so as to have the width of the air element
5.
Starting at element 5 positioned above the centre of
the base plate 1, the core 3 of the sectional body is
chamfered toward the ends of the spirit level.
The body of the spirit level shown in Fig. 1 is cast in
a mold for casting by injection as shown in Fig. 2. The
material to be cast is a polyester resin loaded with glass
particles. These glass particles may either be long fibres
or relatively short fibres or even glass marbles. The
section of the glass particles' shape depends on the
requirements placed on the spirit level or the ease of the
manufacturing process.
The glass particles integrated in the resin give the
thermosetting resin its required rigidity.
The thermosetting resin can be loaded with glass balls
on the outside faces of the injected piece and loaded with
core fibres.
Another essential feature of the invention is that the
air element is permanently fixed to the spirit level's
section during cooling of the resin in the injection mold.
Therefore, further adjustment is unnecessary.
As shown in Fig. 2, the injection mold 6 used to
manufacture the spirit level 1 of the invention is composed
of three parts: one base part 7, or alternatively two parts,
and two lateral parts 8,9, that close up over the first one.

CA 02057365 2002-05-07
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The injection mold 7 is schematically drawn to illustrate
some essential features of the invention. These are the
means for fixing an air element to one of the inside faces
of at least one of the lateral parts 8,9 of the injection
mold 7. The air element 5 is then set by these fixing means
10, i.e. by a set of small pins put in openings in at least
one of the lateral parts of the injection mold 7 at the
level of the lateral faces 8,9 and the base of the air unit
5. These externally removable pins are taken out of the
mold before the resin is completely hardened. The injection
mold 7 is partially cooled around the air element housing
area so that injected resin temperatures do not rise to a
point that could be destructive for the material forming the
air element unit. This material is often transparent, shock
resistant plastic, for example Altuglas (registered trade-
mark). The material to be cast is injected when the mold is
not yet completely closed. This method presents the
following advantages:
The risk of cavities forming inside the material to be
cast is reduced because the material repels the air
contained in the partially open injection mold 7. Moreover,
since the injection mold 7 is completely closed after the
injection of the resin, burrs form. Burrs of a
predetermined shape can be easily polished with a planing
tool.
After the cooling of the thermosetting resin, the
spirit level 1 is removed from the injection mold 7. The
air element 5 is well joined to the section. To improve the
visual appearance of the spirit level 1 and hide contact
areas between the lateral faces or the base of the air

CA 02057365 2002-05-07
element and the housing 4 in the section's core 3, it is
possible to provide a frame 11 for the air element 5 with a
case that still shows the central parts of the top surface
and the lateral surfaces of the air element 5.
Since the air element 5 is carefully inserted into the
injection mold 7, the adjustment of the spirit level 1 is no
longer necessary and because it is joined to the section, a
disturbance is no longer possible. The air elements 5 are
completely immobilized and foolproof. The manufacturing
process is very simple which leads to very low costs. The
thermosetting resin ensures the required sturdiness and
costs much less than aluminum.
The invention is not limited to the embodiments
described above and a person skilled in the art will be able
to modify it without going beyond the scope of the
invention, in particular with respect to the number of base
plates.

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