Venting unit for a rubber article forming mold having vents

A venting unit is inserted in a press fit within the air vent of a rubber article forming mold and is comprised of a cylindrical body member with an axial bore having a reduced outer end section forming an air inlet open to the mold cavity. Received for reciprocal axial movement within the bore between an inlet closed position in abutting engagement with the outer end section and an inlet open position removed from the outer end section is a heat absorbing piston or disc. The opposite or inner end section of the bore receives a vented plug in a press fit to form a radially inwardly projected shoulder and a spring is held in compression between the disc and the shoulder of the vented plug. During expansion of the rubber article, pressurized air in the mold cavity urges the disc to its inlet open position and is vented to the atmosphere. As the rubber article reaches its final form, venting of air is completed and any uncured rubber in the air inlet contacts the disc to set the rubber within the confines of the air inlet. The rubber in the air inlet forms a part of the molded article which, upon its removal from the mold, will exhibit only a minimal surface irregularity.

BACKGROUND OF THE INVENTION 
The invention relates generally to venting units for venting air from a 
rubber article forming mold and, more specifically, to venting units 
having a yieldable valve element for venting air from a tire mold. 
In the forming of vehicle tires, it is desirable that the tire side wall be 
free of any projected rubber pins, impressions, depressions, or other 
surface irregularities. The forming of the pins or needles is usually the 
result of the uncured tire band, in the final forming operation of the 
tire, being forced into the air release vents or passages which have 
terminal ends open to the inner surface of the tire forming cavity of the 
mold. For economical purposes, the pins are not removed and thus give to 
the tire an unfinished or hairy appearance. 
A number of attempts have been made to avoid surface irregularities on the 
tire side wall by the use of valve units. In British Pat. No. 922,788, 
issued Apr. 3, 1963, a valve body is movably mounted in a vent for 
movement to a vent closing position by the expansion of the band against 
the cavity side wall. 
The release of air from the mold cavity through vents in U.S. Pat. No. 
3,842,150, is controlled by valves that are actuated in response to a 
selective application of pressure on the valves. Appreciable time and 
expense is involved in the manufacture of the valves and in the control 
system for synchronizing the flow of variable pressure air through the 
valves with the steps in the tire forming operation. 
In U.S. Pat. No. 4,492,554, the venting unit for the tire mold is engaged 
and moved by an expanding tire band to a vent closing position to form a 
smooth surface continuous with the inner surface of the tire forming 
cavity and is yieldably urged to a vent opening position by a spring 
means. Frequent cleaning of the venting units, however, is required to 
ensure their proper operation resulting in down time losses of the molding 
equipment. 
SUMMARY OF THE INVENTION 
The venting unit of this invention is readily applicable to commercially 
available and existing tire forming machines without requiring any 
appreciable machining of the mold to accommodate the venting units which 
are adaptable to be inserted in a press fit within the mold cavity end 
portion of an air vent. The venting unit of this invention is economical 
in cost and efficient in operation over a long service life, without 
requiring frequent cleaning of the mold cavity or air vents or trimming of 
pins from the finished tire. Because pins or other visible rubber portions 
are not formed, the venting unit can be used in air vent passages that are 
curved or angular which would prevent a separated pin or residual portion 
from traveling through the air vent passage. 
Each venting unit includes a tubular cylindrical body member having a 
reduced diameter air inlet at the outer end thereof of an axial length 
less than the reduced diameter. A heat absorbing disc or piston is movable 
within the body member between a position closing the air inlet and a 
position opening the air inlet to permit venting of air through the 
venting unit. A vented plug is received at the inner end of the body 
member and a spring within the body member in compression between the disc 
and the plug yieldably urges the disc toward the inlet closing position 
therefor. Upon expansion of the uncured rubber article, the resultant 
pressurized air in the mold cavity initially moves the disc to the inlet 
open position to be vented from the mold. Upon completion of the venting 
of air, the spring urges the disc to the inlet closed position. Expanding 
uncured rubber that fills the inlet contacts the disc, the heat absorbing 
capacity and thermal conductivity of which acts to set the rubber to 
prevent its expansion outside the confines of the air inlet.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT 
With reference to FIG. 1, there is illustrated a metal mold 10 for molding 
a pneumatic tire 12, the mold 10 including a tread portion 14 and a side 
wall portion 16. The mold is of a usual two-piece construction used in a 
tire forming machine such as described in U.S. Pat. No. 4,492,554. The 
mold 10 is formed with a plurality of vents 18 each of which is open at 
one end to the atmosphere and at its other end to the mold cavity 20. The 
vents 18 release from the mold cavity 20 air that would otherwise be 
trapped therein as the uncured rubber tire band is forced against the 
cavity wall. A plurality of venting units 22 of this invention prevent 
excessive rubber protrusions or surface irregularities from forming in the 
air vents during the molding operation. For this purpose, and as shown in 
FIG. 1, a venting unit 22 is received in a press fit within the cavity or 
outer end portion of an air vent 18. 
Each venting unit 22 (FIGS. 2 and 3) consists of a cylindrical body member 
24 formed with a central bore 26 having a reduced outer end section 28 to 
form an air inlet 30 open to the mold cavity 20. 
Received within the bore 26 is a floating piston or disc 32 of a size to 
permit relative axial or longitudinal motion thereof within the bore 26. 
The diameter of the disc 32 is sufficiently less than the diameter of the 
bore 26 to permit air to pass between the outer peripheral surface of the 
disc 32 and the inner peripheral surface of the bore 26. 
A vented plug 34 is inserted in a press fit into the inner or opposite end 
of the body member 24 thereby forming a radially inwardly projected 
shoulder 36. A spring 38 is held in compression between the disc 32 and 
the shoulder 36 to yieldably urge the disc 32 into abutting closing 
engagement with the air inlet 30. 
The outer diameter of the body member 24 is of a size relative to a vent 18 
providing for its insertion in a press fit within the cavity end of the 
vent 18. The insertion is facilitated by the provision of a bevel or 
chamfer 40 formed on the leading or inner end of the body member 24. Each 
venting unit 22 is received over its full length into an associated vent 
18 so that the outer end surface or face 42 is substantially flush or 
continuous with the surface of the cavity side wall 16. 
In use, and as illustrated in FIG. 4, as the uncured rubber of the tire 12 
is expanded under pressure of approximately 300 psi to its final form 
within the mold cavity 20, pressurized air will be present in the air 
inlet 30. The pressurized air will urge the disc 32 in a direction to 
further compress the spring 38. The spring constant of the spring 38 is 
selected to permit movement of the disc 32 by the pressurized air from its 
inlet closed position in engagement with the reduced outer end section 28 
to an inlet open position wherein air will be vented through the air inlet 
30, around the disc 32, and through the vented plug 34 to the atmosphere 
as indicated by arrows. 
Upon exhaustion of air from inside the cavity, a portion of uncured rubber 
of the tire 12 at the venting unit 22 will enter the air inlet 30, as 
illustrated in FIG. 5. The uncured rubber, which is at a temperature of 
approximately 370.degree. F., will come into contact with the disc 32 
which has been moved by spring 38 against the air inlet 30 at the reduced 
outer end section 28. The temperature of the disc 32 is substantially the 
same as the cavity wall of the mold, which is typically maintained at a 
temperature of approximately 370.degree. F. Accordingly, the rubber in the 
inlet on contact with the disc 32 will be heated by the absorption of heat 
from the disc. The disc 32 has a sufficient heat capacity relative to that 
of the rubber in the air inlet 30, so that the rubber in the inlet will 
set as it comes into contact with the disc 32. This setting action will 
prevent rubber from expanding outside the confines of the air inlet 30 
into the bore 26 of the body member 24. 
On removal of the cured tire from the mold cavity 20, and as illustrated in 
FIG. 6, the volume of rubber in the air inlet 30 will adhere to the cured 
tire and be removed from the venting unit 22 and the mold cavity 20. Due 
to the reduced diameter and axial length of the air inlet 30, the 
resulting surface irregularity 44 on the surface of the cured tire will be 
very minimal so as not to impair the appearance of the tire 12. The 
appearance of surface irregularities can be further reduced by the use of 
blemish paint to coat and smooth the cavity walls prior to the tire 
molding operation. 
The air inlet 30 has a diameter of about 0.010 inches to about 0.015 inches 
and an axial length of about 0.010 inches to 0.015 inches. The disc 32 is 
high carbon, 303 stainless steel and has a diameter of 0.080 inches and an 
axial length of 0.125 inches. The spring 38 is made of 0.007 inches 
diameter stainless steel wire and exerts a force of approximately 0.8 
ounces on the disc 32. The distance between the shoulder 36 and the inner 
surface of the disc 32 in its inlet closed position is 0.125 inches. A 
typical tire mold pressure of 300 psi will result in movement of the disc 
to its inlet open position. 
Although the invention has been described with respect to a preferred 
embodiment thereof, it is to be understood that it is not to be so limited 
since changes and modifications can be made therein which are within the 
full intended scope of this invention as defined by the following claims.