Method for forming an expansion sleeve for an expansion dowel

An expansion sleeve (2) for an expansion dowel (1) has an axially extending expansion region (8) with axially extending slots (5) forming tabs between these slots. To enlarge the surface of the expansion sleeve (2) for assuring the attainment of high anchoring values, the axially extending slots (5) are formed free of any gaps. The gap-free slots (5) can be formed by extrusion including radially pressing together the tabs between the slots (5).

BACKGROUND OF THE INVENTION 
The present invention is directed to a method of forming expansion dowels 
with at least an axially extending expansion region provided with axially 
extending slots and a bore tapering inwardly in the expansion region 
towards a leading end of the dowel. 
Expansion dowels of this general type are anchored in a foundation, such as 
concrete, rock, masonry and the like by radially widening an expansion 
sleeve. Such radial widening determines the anchoring values to be 
achieved, since a connection is created between the expansion sleeve and 
the foundation affording on one hand a frictional lock and in certain 
cases a positive locking feature. The extent of a frictionally locked 
connection is in particular influenced by the amount of the surface 
available for this purpose on the expansion sleeve, that is, a small 
surface on the expansion sleeve available for friction locking affords 
lower anchoring values. 
An expansion dowel is known from DE-PS 21 52 729 having a radially 
widenable expansion sleeve. The expansion region of the expansion sleeve 
has axially extending slots for affording the radial widening with tabs 
formed between the slots. The expansion sleeve is radially widened by 
driving an expansion member into the bore in the expansion sleeve which 
tapers inwardly toward its leading end, so that the tabs move radially 
outwardly. After the radial widening has occurred, that is, when the 
expansion dowel has been completely set, a member, such as a bolt, a 
threaded rod or the like can be fastened in the trailing end of the 
expansion sleeve by load engaging means in the shape of a thread located 
at the trailing end directed away from the expansion region. 
The above-mentioned known expansion dowel can be provided with four axially 
extending slots. These slots are formed by a machine cutting operation so 
that they have a specific width transversely of the axial direction, 
depending on the tool used, such as the side milling cutter. Since the 
width of the axially extending slots depends on the width of the removing 
tool used, for economic reasons the width of the slots is the same for all 
sizes of expansion dowels. As a result, a considerable share of the 
surface of the expansion dowel is consumed by the axially extending slots, 
particularly in the case of smaller diameter expansion dowels. Such share 
of the surface is not available for affording the connection with the 
foundation, whereby the achievable anchoring values are reduced. 
Therefore, with smaller diameter expansion dowels, the share of the 
surface available for providing a connection with the foundation is 
reduced by up to 20%. This situation is further exacerbated, since in the 
radial expansion step the axially extending slots are widened. 
SUMMARY OF THE INVENTION 
Therefore, it is a primary object of the present invention to provide a 
method of forming expansion dowels which results in high anchoring values. 
In accordance with the present invention, initially the axially extending 
slots are formed after which the slots are closed largely by pressing 
together tabs formed between the slots in the expansion sleeve. 
The originally produced axially extending slots are closed for the most 
part due to the radially pressing together of the tabs of the expansion 
sleeve formed between the axially extending slots, as proposed in the 
invention. For purposes of the invention slot widths in the range of 0 to 
0.2 mm are considered to be closed. In addition to closing the axially 
extending slots and the resulting enlargement of the surface of the 
expansion section of the sleeve, the shape of the bore within the sleeve 
tapering inwardly toward the leading end is created when the tabs are 
radially pressed together. 
The material of the expansion sleeve required for forming the tapering bore 
can be obtained according to another feature of the invention when the 
expansion sleeve is first radially widened and then the axially extending 
slots are closed and the outer shape of the expansion sleeve is returned 
to its basically cylindrical form by the radially inward pressing of the 
tab located between the slots. 
In the method of the present invention the slots can be formed in a known 
way by machining. Due to the radially pressing together of the tabs 
remaining between the axially extending slots, even wide slots are closed 
in an adequate manner, so that a surface of the expansion sleeve affording 
high anchoring values is achieved. An incompletely closed section at the 
end of the axially extending slot formed in this manner has no significant 
effect upon the anchoring value. 
Instead of machining the axial extending slots, additional advantages are 
gained in the inventive method if the slots are produced by extrusion. 
Such a procedure assures an uninterrupted run of the fibers affording 
retention of high strengths. 
Preferably, the axially extending slots are formed by pressing a male die 
into the axially extending expansion sleeve blank having a cylindrically 
shaped inside and outside surface, the material displaced by axially 
extending ribs flows outwardly so that the expansion sleeve has an 
increased length. In a following step the expansion region containing the 
axially extending slots is widened toward the leading end of the dowel. 
Subsequently, the outside surface of the expansion sleeve is returned to 
its initial cylindrical shape. In this operation, the widened expansion 
region is pressed radially inwardly so that the spacing between the tabs 
located between the axially extending slots is eliminated. Accordingly, a 
section of the bore is obtained tapering inwardly toward the leading end 
in the step of radially inwardly pressing the expansion region. 
The axially extending slots can also be formed by shearing, however, such 
an operation does not afford any flow of the material and the course of 
the fibers in the expansion region is interrupted. Another characteristic 
of the invention obtained in forming the expansion sleeve of an expansion 
dowel involves, in addition to the axially extending slots, a partial 
section of the bore tapering inwardly to the leading end of the sleeve, so 
that high anchoring values can be obtained. This characteristic is 
obtained by providing the axially extending slots free of any lateral 
spacing between the tabs formed by the slots for at least a portion of the 
length of the slots. 
As used herein, the expression free of any spacing between the sides of the 
axially extending slots, that is between the tabs formed between the 
slots, means that a considerable length of the slots is closed. If 
extrusion is used in the inventive method for forming the expansion region 
of the sleeve, it is possible to provide the entire length of the axially 
extending slots free of any spacing between the tabs formed between the 
slots. If the slots are formed by the chip-removing machining operation, 
such as a milling cutter, a part at the end of the slots may not be 
completely closed in the steps of radially pressing the tabs together. 
Since the portion of the slots which is not completely closed in relation 
to the remaining closed length of the slots is relatively short, there is 
no negative effect on the anchoring values achieved. 
The various features of novelty which characterize the invention are 
pointed out with particularity in the claims annexed to and forming a part 
of this disclosure. For a better understanding of the invention, its 
operating advantages and specific objects attained by its use, reference 
should be had to the drawing and descriptive matter in which there is 
illustrated and described a preferred embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION 
In FIG. 1 an expansion dowel 1 is illustrated formed of an axially 
extending expansion sleeve 2 with a cylindrically shaped outside surface 
and an expansion member 3. As viewed in FIG. 1 the lower end of the sleeve 
2 is its leading end and the upper end is its trailing end, in other 
words, when used in a bore in a foundation the leading end is inserted 
first into the bore. Expansion sleeve 2 has an axially extending radially 
widenable expansion region 8 with four axially extending slots 5 with tabs 
located between the slots with the axially extending edges of the tabs 
being in contacting relationship, so that the slots do not form any gaps. 
The slots 5 are spaced uniformly around the circumference of the expansion 
sleeve. Expansion sleeve 2 has a load engagement means in the form of an 
inside thread 4 at its trailing end and in spaced relation from the 
expansion region 8. The axially extending slots open to the leading end of 
the sleeve and extend axially for at least a portion of the axial length 
of the sleeve 2. The sleeve has a central bore 6 extending between the 
leading end and the trailing end and the surface of the bore in the 
expansion region tapers inwardly toward the leading end in a 
conically-shaped manner. In other words, the bore tapers inwardly in the 
axially extending region 8 of the expansion slot 5. The expansion member 3 
is located within the bore and at its leading end is at least partially 
cone-shaped corresponding to the cone-shaped section of the bore. The 
outside surface of the expansion sleeve 2 is substantially smooth and has 
a circumferentially extending chamfer 7 at the leading end. 
FIG. 2 is a schematic illustration of the method of forming the axially 
extending slots 28, 38 of the expansion sleeves 10, 20, 30 in an extrusion 
operation. The steps of the method are designated as stations 1, 2, 3 and 
only the portions of the inventive method involving the expansion sleeve 
10, 20, 30 are displayed which are involved in the formation of the 
axially extending slots 28, 38. 
The steps of shaping an expansion sleeve blank into the inventive expansion 
sleeve involves female extrusion dies 11, 21, 31 and pressing rams 12, 13, 
22, 23, 32, 33 insertable into the female extrusion dies. The female 
extrusions dies 11, 21, 31 are guided and held in a receiving member 9. 
Upper top guides 14, 24, 34 are located on the upper side of the receiving 
member 9 and guides 15, 25, 35 are located on the lower side of the 
receiving member for guiding the pressing rams 13, 23, 33. The upper 
pressing guides 12, 22, 32 are axially displaceable in the upper guides 
14, 24, 34. The lower guides 15, 25, 35 are axially displaceable for 
directing the lower pressing rams 13, 23, 33 into the female extrusion 
dies 11, 21, 31. 
Female extrusion die 11 at station 1 has a central cylindrically-shaped 
receiving bore 17 in which an expansion sleeve blank 10 is positioned so 
that its trailing end rests against the end face 12a of the upper pressing 
ram 12 extending partly into the receiving bore 17. The lower pressing ram 
13 is driven into the leading end of the expansion sleeve 10 and the ram 
13 has radially outwardly projecting and axially extending ribs 18 on its 
outside surface. When the pressing ram 13 is driven into the expansion 
sleeve blank 10, its axially extending ribs 18 form axially extending 
slots, not shown, in the expansion sleeve blank 10. Material displaced in 
this extrusion step flows outwardly providing an increased length of the 
expansion sleeve blank 10. The axially extending slots divide the axially 
extending expansion region 16 into individual tabs. 
The next step of the method takes place at station 2 and is formed on the 
expansion sleeve 20. As inserted into the female extrusion die 21, the 
expansion sleeve 20 has a cylindrically-shaped outside surface and is 
supported within a receiving bore 27 in the female extrusion die 21 and is 
conically widened as the pressing ram 23 is forced into the bore 27 by the 
guide 25 due to the conically widened section 26 of the receiving bore 27. 
In station 2 the trailing end of the expansion sleeve 20 bears against the 
end face 22a of the upper pressing ram 22 which extends partly into the 
upper end of the receiving bore 27. 
At station 2 the end of the lower pressing ran 23 is conically-shaped 
conforming to the conical shape of the lower end of the bore 27. As the 
lower pressing die 23 is forced into the lower end of the receiving bore 
27 the lower or leading end of the expansion sleeve 20 is compressed and 
the tabs 29 located between the slots 28 are compressed so that the 
material forming the tabs flows outwardly into the conically-shaped 
widened region of the receiving bore 27. As a result, the expansion sleeve 
20 experiences an axial shortening and conical widening of the expansion 
region 28 due to the pressing action of the ram 23. 
Another step of the method is carried out at station 3. The expansion 
sleeve 20 formed at station 2 is now identified as expansion sleeve 30 in 
station 3 and is pressed into the female die 31 by the lower pressing ram 
33 with the die 31 having a cylindrically-shaped receiving bore 37. In 
this step of the method, the previously widened expansion region 26 is 
compressed radially inwardly affording a substantially 
cylindrically-shaped outside surface for the expansion sleeve 30. The bore 
in the expansion sleeve has an axially extending section in the expansion 
region provided with a conically-shaped surface tapering inwardly towards 
the leading end of the sleeve. In the end position shown at station 3 
within the receiving bore 37 of the female die 31, the trailing end of the 
expansion sleeve bears against the end face 32a of the upper pressing ram 
32 projecting partly into the receiving bore 37. The axially extending 
slots 38, previously formed in the extrusion step at station 1 are pressed 
together, so that there is no gap formed between the adjacent tabs 39 when 
the leading expansion region is pressed inwardly within the receiving bore 
37. In station 3 the width of the axially extending slots 38 is in the 
range of 0 to 0.2 mm. 
The deformation of the expansion sleeve 2, 10, 20, 30 can be effected by 
cold extrusion or semi-cold extrusion at temperatures in the range of 
200.degree. to 300.degree. C. 
While a specific embodiment of the invention has been shown and described 
in detail to illustrate the inventive principles, it will be understood 
that the invention may be embodied otherwise without departing from said 
principles.