Armature insert

A metal insert is provided for use in forming an elastomer-tipped armature to a precise length. The insert is formed as an elongated member with a central hole passing through its length, and an elastomer element is molded within the hole. A circumferential groove is formed in the exterior surface of the insert to create a weakened "hinge" point in the insert wall such that, as mold elements for forming the elastomer element engage opposing ends of the insert, the insert may be compressed longitudinally at the groove to thereby decrease the overall length of the completed armature to within a predetermined tolerance.

BACKGROUND OF THE INVENTION 
The present invention relates generally to elastomer-tipped metallic 
armatures and, more particularly, to an insert for use in an armature 
construction in which the length of the elastomer portion of the armature 
may be precisely controlled during the manufacture thereof. 
Elastomer-tipped metallic armatures of various configurations are commonly 
used in electric solenoid assemblies used in fluid control applications. A 
typical armature is formed with a cylindrical metal body or insert which 
has a cavity or hole formed lengthwise in one end or which may extend 
through the entire length of the insert. An elastomer element is mounted 
within the hole and may extend beyond the end of the metal insert or it 
may have an end surface which is recessed behind the end surface of the 
insert. The elastomer tip formed at the end of the armature insert 
provides an effective means for forming a seal with another surface of the 
solenoid assembly to prevent fluid leaks, as well as forming a resilient 
contact surface for avoiding excessive wear between the sealing surfaces 
of the solenoid. 
In many applications, the effectiveness of the solenoid assembly in 
operating in a leak-free manner depends on precisely controlling the 
length of the armature and, in particular, controlling the length of the 
elastomer element during the manufacture of the armature. The armature is 
conventionally formed by fabricating the metal insert, such that the 
length of the insert falls within certain specified tolerances and, 
subsequently, mounting the insert in a mold for molding and bonding the 
elastomer element in place within the insert. Finally, the elastomer 
element is ground down to place the overall armature length within the 
required tolerances for its application. 
The armature construction described above suffers from the limitations 
imposed by the accuracy to which the elastomer grinding operation can be 
performed, which controls the tolerance limits within which the armature 
length can be maintained. In addition, if the armature design requires 
that the elastomer element be molded with the ends recessed from the ends 
of the metal insert, it may be difficult or impossible to grind the 
elastomer element down to the proper length dimensions. 
Thus, there is a need to provide an armature construction by which the 
length of the armature of a solenoid assembly can be more precisely 
controlled and, in particular, there is a need for an armature 
construction in which the length of the elastomer element may be simply 
and precisely controlled. 
SUMMARY OF THE INVENTION 
In accordance with the present invention, a metal insert is provided for 
forming an elastomer-tipped metallic armature in which an elastomer 
element is molded within a hole formed within the metal insert, and in 
which the length of the elastomer element, as well as the armature, may be 
controlled within a predetermined tolerance during the molding operation. 
In the preferred embodiment, variations in the lengths of the metal inserts 
within their tolerance limits may be compensated for by causing the mold 
sections forming the elastomer elements to slightly compress the metal 
inserts lengthwise during the molding operation, such that the mold 
sections are permitted to move together to within a predetermined distance 
regardless of variations in the length of the inserts. Thus, the elastomer 
elements are formed to an accurate predetermined length during the molding 
operation without requiring an additional grinding step. 
Also in the preferred embodiment, the metal insert is provided with a 
groove formed around the periphery of the insert such that a weakened 
"hinge" location is formed where the insert wall may crimp inward in 
response to a force applied axially to the ends of the insert. 
Other objects and advantages of the invention will be apparent from the 
following description, the accompanying drawings, and the appended claims.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
The invention will now be described with reference to FIG. 1 which shows an 
elastomer-tipped armature generally designated 10, and which incorporates 
an insert 12 of the preferred embodiment of the present invention. The 
armature 10 is useful as a plunger member in an electric solenoid assembly 
to provide an effective means for forming a seal with associated surfaces 
of the solenoid assembly and thus controlling the flow of fluids through 
the assembly. 
The insert 12 of the preferred embodiment, as seen in FIGS. 1 and 2, is 
formed as an elongated cylinder having a hexagonal exterior surface 14 
with circular end portions 16, 18, however, it should be noted that the 
exterior may be formed with any one of a variety of other shapes such as a 
square, circle, triangle or other shape. The insert 12 further includes 
means defining a hole 20 through the length thereof such that a 
cylindrical interior wall is formed within the insert 12. Opposite end 
portions 24, 26 of the interior wall of the insert 12 are formed having 
the same diameter, and a longitudinally centrally located interior portion 
28 of the insert 12 between the end portions 16, 18 is formed with a 
smaller diameter than the interior end portions 24, 26. The central 
portion 28 of the insert 12 is connected to the end portions 24, 26 by 
portions 30, 32 which taper in from the end portions 24, 26 to the central 
portion 28. 
In constructing an armature 10, an interior element 34 formed of an 
elastomeric material is positioned within the hole 20 in the insert 12 and 
is in sealing contact with the interior insert walls 24, 26, 28. The 
elastomer element 34 is preferably molded in place and extends through the 
length of the insert 12 up to a point adjacent to and slightly recessed 
from each of the ends 16, 18 of the insert 12. The elastomer element 34 
forms a resilient contact surface for forming a seal with another surface 
of the solenoid assembly, such as a cylindrical orifice member which fits 
into the end portions of the hole 20 formed in the insert 12, to form a 
leak-free seal. In addition, the resiliency of the elastomer element 34 
provides a relatively soft contact point for avoiding wear of sealing 
surfaces of the solenoid assembly associated with the armature 10. 
During the operation of molding the elastomer element 34 in place, an end 
of the insert 12 is held against movement by a first mold element and a 
second mold element is displaced along the longitudinal axis of the insert 
12 to engage the opposite end of the insert 12. Typically, in prior art 
molding operations, the second mold element is displaced until it contacts 
the insert, at which time the insert would resist and prevent further 
movement of the mold, and at this point the elastomer element would be 
molded in place. Thus, in prior art operations the distance from the 
second mold element to the opposing end of the insert, and therefore the 
length of the elastomer element, would vary depending on variations within 
the tolerance of the length of the insert. 
The effectiveness of the solenoid assembly in properly acting to control 
fluid flows is closely related to the precision with which the length of 
the elastomer element 34 is held to a small tolerance. To this end, the 
insert 12 is provided with a circumferential groove 36 formed in the 
hexagonal exterior wall 14 and located approximately midway between the 
two ends 16, 18 of the insert 12 and adjacent to the smaller diameter 
interior portion 28. In this manner, a weakened or "hinge" portion 38 of 
the insert wall is formed which has a decreased resistance to longitudinal 
forces applied to the ends 16, 18 of the insert 12. The weakened portion 
38 of the insert 12 facilitates the precise control of the length of the 
elastomer element 34 during the molding operation by permitting the insert 
12 to be compressed in the longitudinal direction. 
In the preferred embodiment, the circumferential groove 36 is formed as a 
V-shaped recess with opposing walls 40, 42 of the recess forming a 
90.degree. angle, with the innermost portion of the groove 36 having a 
circumference 44 substantially equal to the circumference of the inner 
wall of the insert 12 at the larger diameter end portions 24, 26 of the 
hole 20. 
As can be seen from the above description, the weakened portion of the wall 
formed by the groove of the present insert eliminates the problem 
associated with the variations in the lengths of the inserts. As the mold 
elements contact the insert of the present invention, the width of the 
groove decreases and the insert wall crimps inward slightly at the 
location of the groove such that the insert does not present sufficient 
resistance to the relative displacement of the mold elements to prevent 
them from moving after contacting the insert. Thus, the mold elements may 
be set to move to within a precise predetermined distance of each other, 
and consequently, the elastomer element is molded to a precise length 
within the insert. In addition, the longitudinal compressive force applied 
by the mold elements also acts to control the length of the insert more 
precisely. 
In an alternative embodiment, as can be seen in FIG. 3, an armature 110 
having an elastomer element 134 is formed using an insert 112 similar to 
that shown in FIG. 1 except that a groove 136 is provided having walls 
140, 142 which slope down to a flat bottom 144 which is formed by a 
surface which is substantially parallel to the longitudinal axis of the 
insert 112. In addition, the groove bottom 144 may have a circumference 
which is approximately equal to the circumference of the inner wall of the 
insert 112 at the larger diameter end portions 124, 126 of the hole 120. 
FIG. 4 shows another embodiment of the present invention in which an 
armature 210 is formed with an insert 212 having a hole 220 for receiving 
the elastomer element 234, wherein the hole 220 passes through only a 
portion of the length of the insert 212. In this embodiment, the hole 220 
is of a constant diameter and the groove 236 is formed as a semi-circular 
recess at a point along the length of the insert which is adjacent to the 
hole 220. A thin-walled weakened portion 238 is formed at the location of 
the groove 236 to decrease the resistance of the insert 212 to a 
longitudinal compressive force in the same manner as the previous 
embodiments. 
As can be seen from the above embodiments, an insert is provided with a 
groove which may be formed in a variety of configurations. The shape of 
the groove is selected such that a compressive force applied to opposite 
ends of the insert will result in a decrease in the width of the groove 
and an inward crimping of weakened portion of the wall forming the smaller 
diameter portion of the hole. Thus, the main consideration in determining 
the shape and depth of the groove is the effectiveness of the groove in 
forming a weakened "hinge" area at which the length of the insert can be 
decreased during the molding of the elastomer element. 
While the form of apparatus herein described constitutes a preferred 
embodiment of the invention, it is to be understood that the invention is 
not limited to this precise form of apparatus, and that changes may be 
made therein without departing from the scope of the invention which is 
defined in the appended claims.