Device for lubricating the tie rods of an injection molding machine

A device for lubricating the tie rods in the die closing unit of an injection molding machine, consisting of a tubular shell which forms an annular chamber around the tie rod and a lubricant absorbing fleece body occupying said chamber, the shell being constituted by two identical half shells which are joined along longitudinal edges provided with matching flexible tongue-and-groove formations, for the forcible radial snap assembly between shell-straddling wall portions of the guided part of the die closing unit.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to injection molding machines, and, more 
particularly, to the die closing unit of an injection molding machine and 
to a device for lubricating the tie rods of such a die closing unit. 
2. Description of the Prior Art 
The prior art in the field of injection molding machines encompasses a 
number of different machine types, with an assortment of different die 
closing units. These die closing units, with few exceptions, have in 
common that they use two or four parallel tie rods to provide the guidance 
for the movable die half and its supporting structure during the die 
closing and opening movements. The accuracy and rigidity of this guidance 
is of great importance, both for a consistant quality of the machine 
output and for the longevity of the die closing unit. An important factor 
in maintaining this accuracy and longevity is a reliable supply of 
lubricant for the tie rods and the cooperating slide bushings. 
It is well known to arrange for a supply of lubricant to a reciprocating 
guide assembly by having an annular lubricant holding chamber arranged 
inside a sleeve, between axially spaced guide bushings. Such an 
arrangement is shown, for example, in U.S. Pat. No. 4,094,621 which 
discloses a die closing unit for an injection molding machine featuring a 
heavy movable die carrier frame which is guided for opening and closing 
movements on four tie rods. The die carrier frame, consisting of axially 
spaced transverse walls which are connected by four hollow guide sockets 
and reinforcing ribs, has short guide bushings arranged in both ends of 
each guide socket. The intermediate length portions of the guide sockets 
thus form chambers which, when periodically filled with lubricant, provide 
a good lubricant supply. 
Another tie rod lubrication system is disclosed in U.S. Pat. No. 3,833,204, 
where two tie rods which carry an injection unit are lubricated with 
hydraulic fluid. Tubular piston rods, surrounding a length portion of the 
two tie rods, form annular lubricant holding chambers into which lubricant 
is continuously fed from the pressure spaces of the associated injection 
cylinders, via helical lubricating grooves arranged in the tubular piston 
rods. 
The first-mentioned lubrication system has the shortcoming of being limited 
to a grease lubricant, with its disadvantage of not freely flowing to the 
place where it is consumed. It therefore requires frequent refills under 
pressure. The second prior art solution is limited to tie rods which 
support a tubular piston rod, or tie rods which double as piston rods, 
where a hydraulic pressure space providing a ready supply of hydraulic 
fluid is available. 
SUMMARY OF THE INVENTION 
Underlying the present invention is the objective of providing a 
lubricating device for the tie rods of an injection molding machine which, 
while providing a reliable supply of lubricant, requires only minimal 
changes in the structure of the die closing unit and, accordingly, is very 
inexpensive. 
The present invention proposes to attain this objective by suggesting a 
lubricating device for the tie rods of an injection molding machine which 
features a tubular shell which, together with the tie rod itself, forms an 
annular lubricant holding chamber, with a lubricant absorbing body, 
preferably a fleece body, occupying this annular chamber. 
In a preferred embodiment of the invention, the tubular shell consists of 
two identical injection molded half shells of plastic material with 
cooperating longitudinal tongue-and-groove profiles which make it possible 
for the half shells to be snapped together, around the tie rod and 
surrounding fleece body. 
The invention further suggests that this lubricating shell be arranged 
between two axially spaced guide bushings of a movable part of the die 
closing unit, whereby the bushings also provide convenient centering 
shoulders for the two half shells. However, instead of axially confining 
the lubricating shell of the invention between spaced guide bushings, it 
is also possible to axially couple the lubricating shell to the extremity 
of a guide bushing, by providing a clamping engagement, or appropriate 
cooperating radial protrusions and recesses, such as a groove-and-collar 
configuration, for example, on the extremities of the half shells and 
guide bushings. The radial snap-mounting capability of the lubricating 
shell allows for a variety of coupling configurations. 
In a preferred embodiment, the invention further suggests that the 
cooperating tongue-and-groove profiles of each half shell extend over the 
full axial length of the shell and that the tongue profile is shaped to 
have a base portion of uniform thickness, but outwardly inclined, 
adjoining a radially inwardly inclined, tapered entry portion, while the 
matchingly shaped groove profile is flanked by radially flexing lip 
portions. In the mounted position, the two half shells form a closed 
longitudinal joint on the inside of the tongue-and-groove configuration, 
while leaving a longitudinal gap on the outside thereof, so that the half 
shells can be readily pried apart, if necessary.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to FIGS. 1 and 2 of the drawing, which give an overall view of a 
push-type die closing unit of an injection molding machine, it can be seen 
that the die closing unit is designed for die opening and closing 
movements along a horizontal movement axis. The guidance for these 
horizontal movements is provided by four horizontal tie rods 15 whose axes 
are identically spaced from the longitudinal center axis of the unit and 
coincide with the four corners of a square. The forward end portions of 
the four tie rods are seated in a transversely extending stationary die 
carrier plate 29, the opposite end portions of the tie rods being 
similarly seated in a transversely extending cylinder head plate 35. The 
threaded extremities of the tie rods 15 are held in place and axially 
preloaded against the plates 29 and 35 by means of clamping heads 39. The 
stationary plates 29 and 35 and the four tie rods extending between them 
thus form a rigid support structure. 
The four tie rods 15 support and guide a movable die carrier frame 16. To 
the rear side of this frame is connected the piston rod 34 of a hydraulic 
drive cylinder 32 which extends rearwardly from the cylinder head plate 
35, along the center axis of the die closing unit. On the piston rod 34 is 
seated a double-acting drive piston (not shown). 
The movable die carrier frame 16 consists of a transversely extending die 
mounting wall 16a on its forward side and a likewise transversely 
extending pressure transfer wall 16b which is spaced axially rearwardly 
from wall 16a and rigidly connected thereto by means of four Y-shaped 
pressure transfer ribs 16c. As can be seen in FIG. 2, the four tie rods 15 
are positioned between the leg portions of the Y-shaped pressure transfer 
ribs 16c, but separated from them by a gap. 
The injection molding die itself is shown as consisting of two die halves 
36 and 37 which meet at the die separation plane 40, the stationary die 
half 37 being mounted on the stationary die carrier plate 29, and the 
movable die half 36 being attached to the die mounting wall 16a of the 
movable die carrier frame 16. The die closing unit of FIG. 1 further shows 
the position of a horizontal injecting unit 30, in alignment with an axial 
sprue channel, and the position of a vertical injecting unit 31, in 
alignment with a radial sprue channel which coincides with the die 
separation plane 40. In the open center space of the movable die carrier 
frame 16 is further arranged a known hydraulic ejecting device. 
The die opening and closing action of the hydraulic drive cylinder 32 and 
its piston rod 34 produces a horizontal reciprocating movement of the 
movable die carrier frame 16 on the four tie rods 15 from the closed 
position which is shown in FIG. 1 to an open position to the left thereof. 
During this reciprocating movement, the movable die carrier frame 16 is 
precisely guided on the four tie rods 15, engaging each rod with two guide 
bushings 17 and 17a, as shown in FIG. 3. There, it can also be seen that 
the guide bushings 17 and 17a are arranged in the two transverse walls 16a 
and 16b, respectively, of the die carrier frame 16. 
In the space between the guide bushings 17 and 17a of each guide rod 15 is 
arranged a tie rod lubricating device (FIG. 3) which consists essentially 
of a tubular shell 10 surrounding the tie rod 15 with a radial gap, and an 
absorbant lubricant supply body 20 occupying the annular chamber which is 
formed by the gap between the shell 10 and the tie rod 15. The absorbant 
lubricant supply body, preferably a fleece body, such as a felt sleeve, 
for example, stays in frictional engagement with the tie rod 15 during the 
reciprocating movements of the die carrier frame 16, thereby applying a 
thin film of lubricant to the surface of the tie rod 15. The absorbancy of 
the lubricant supply body makes it possible to utilize lubricants of low 
viscosity, including lubricating oils, without wasting the latter through 
excessive initial application, after the lubricant supply has been 
replenished. 
As can be seen in FIG. 3, the shell 10 occupies the entire axial space 
between the guide bushings 17 and 17a, engaging inwardly protruding end 
portions of the two guide bushings with centering collars 18 on the shell 
extremities. The centering collars 18 are part of radially inwardly 
reaching axial shoulder portions 19 on the extremities of the shell 10 
which thereby also serve to axially contain and position the fleece or 
felt sleeve 20. This means that the tie rod lubricating device is not only 
concentrically centered around the tie rod 15, but also axially confined 
between the guide bushings 17 and 17a of the movable die carrier frame 16, 
giving it a firm position. 
As can be seen in FIGS. 4 and 5, the tubular shell 10 of the invention 
consists of two identical half shells 11 which are attached to one another 
by means of a tongue-and-groove configuration. This attachment takes place 
in a simple snap action. For this purpose, each half shell 11 has on one 
longitudinal edge a longitudinal tongue formation 11b and on the opposite 
edge a longitudinal groove formation 24. The tongue 11b of one half shell 
engages the groove 24 of the other half shell. In the assembled condition, 
the two half shells 11 form a longitudinal joint along an axial center 
plane a--a, whereby the flanks 22 and 23 on the longitudinal edges abut 
against one another to form a leak-tight enclosure. 
The tongue-and-groove configuration of the half shells 11 features, as part 
of the shape of the connecting tongue 11b, a base portion 11c of uniform 
thickness d which is inclined at an angle of approximately 10.degree. 
against a tangent plane e to the periphery of the shell 10, at the point 
where it intersects the plane a--a at right angles. This outwardly 
inclined base portion 11c adjoins a tapered entry profile 11d, consisting 
of an end face 28 which is substantially parallel to plane a--a, an inner 
face 25 which is substantially perpendicular to plane a--a, and an outer 
face 26 which is inclined opposite to the inclination of the base portion 
11c, at an angle of approximately 30.degree. to the tangent plane e. This 
somewhat kinked shape of the connecting tongue 11b is matched by a similar 
shape of the connecting groove 24, so that, during the snap-action entry 
of the tongue 11b into the groove 24, the lip portions 11e and 11f on the 
inner and outer sides of the groove 24 are forcibly spread apart in the 
radial sense, until the "hump" of the tongue 11b snaps into the matchingly 
shaped recess of the groove 24. 
In order to facilitate the separation of the two half shells 11 from each 
other, they further feature two longitudinal tool gaps 27 adjacent to the 
plane a--a of their longitudinal joint. The gaps 27 are formed by flank 
portions 22a on the outer side of the half shell edges which carry the 
tongue formations 11b, the flank portions 22a being recessed peripherally, 
away from the edge flank 23 of the opposite edges. The latter coincide 
with plane a--a. 
Each half shell is further provided with a centrally located eye protrusion 
11a with a radially oriented threaded bore 12 which stops short of the 
inner wall of the half shell, leaving a thin wall, so that the threaded 
bore 12 of one half shell can remain open to the outside, while a suitable 
refill nipple 14 is screwed into the threaded bore 12 of the other half 
shell, where the thin wall at the bottom of the bore has been broken out, 
or drilled through, to form a bore 13. For lubricating devices which have 
a comparatively long shell, it may be advisable to provide two axially 
spaced refill nipples. 
It can thus be seen that the two half shells are identical injection molded 
parts which, because they require no machining operations, are very 
inexpensive. In addition, they are extremely easy to assemble and to take 
apart, if necessary. In order to improve the durability of the half 
shells, especially of their tongue-and-groove formations, it is suggested 
that the plastic material used in the injection molding process be a 
high-polymer, glass-fiber reinforced compound. 
It has been found that a single replenishment of the lubricant supply body 
with lubricant will give satisfactory lubricating service over hundreds of 
hours of operation. If, after a period of extended service, it becomes 
necessary to remove and clean the felt sleeve 20, this can be done by 
simply prying apart the half shells with a tool, or a pair of tools, that 
simultaneously engage both longitudinal gaps 27. Following washing or 
replacement of the felt sleeve 20, the half shells 11 are then simply 
snapped back together, under radial pressure, whereupon the device is 
replenished with lubricant. 
It should be understood that the lubricating device of the invention, while 
shown and described as being axially confined between two guide bushings, 
is not limited in its applications to this convenient case alone. 
Obviously, it is also possible to arrange such a guide rod lubricating 
device ahead or behind any rod guide assembly, provided the shell of the 
lubricating device is held in place adjacent to the guide bushing or guide 
bore, as the case may be. A guide bushing is preferable, because it offers 
a simple way of connecting the shell of the lubricating device to the 
extremity of the bushing, by using cooperating connecting formations on 
the bushing and shell. The radial assembly of the two half shells allows 
for a wide variety of suitable connecting configurations. For instance, 
the guide bushing may have a shallow annular groove near its extremity, or 
it may have a localized depression, or a radial bore. In each case, the 
half shells would have matching radial protrusions in the form of either a 
radial collar, or a localized radial protrusion, or a pin-like protrusion, 
to match the bore, respectively. The opposite extremity of the tubular 
shell would preferably have a shoulder portion which centers and guides 
the shell on the guide rod itself. 
While the present invention has been described as applied to the die 
closing unit of an injection molding machine, it should be quite obvious 
that its usefulness is not limited to this kind of application, but that 
the device can be used for a variety of other applications, where one 
member of a straight-line guide assembly is a guide rod and the other 
member embraces that guide rod. It should therefore be understood that the 
foregoing disclosure describes only a preferred embodiment of the 
invention and that it is intended to cover all changes and modifications 
of this example of the invention which fall within the scope of the 
appended claims.