Die venting apparatus in molding of thermoset plastic compounds

In molding of plastic materials, particularly thermoset compounds, venting of dies is essential to obtain well molded parts, and this invention discloses improved venting of dies in molding of thermoset plastic compounds wherein a vent path 4 vents from the die into a vent well 3, said vent well comprises a wedge shape having a transition angle of 10.degree. to 35.degree. and a vent extension 6 extending from said vent well 3, to the atmosphere.

SUMMARY OF THE INVENTION 
When dies for molding of thermoset plastic are not adequately vented, the 
resultant moldings are marked by inadequate fill of the die, and may have 
so-called burned spots, and indications of so-called short fill due to gas 
entrapment. 
An object of this invention is to disclose die venting means to insure 
adequate fill of the die. 
Another object of this invention is to disclose die venting means 
comprising a vent well outside of the molding die. 
Another object of this invention is to disclose die venting means, 
comprising a vent well outside of the die and connected thereto by a vent 
path to fill said vent well, and means comprising a knock out pin to eject 
the material in said vent well. 
Another object of this invention is venting of dies in molding of thermoset 
plastic compounds, comprising a vent path and vent well connected thereto, 
said vent well comprising a wedge shape, and a transition angle of 
10.degree. to 30.degree. going into said wedge shape, a knock out pin in 
contact with said wedge shape, and vent extension from said wedge to 
atmosphere. 
Another object of this invention is to disclose venting of a die in molding 
of thermoset plastic compounds, comprising a vent well outside of the die, 
said vent well connected to said die by means of a vent path. 
Another object of this invention is to disclose venting of a die in molding 
of thermoset plastic compounds, comprising a die, die vent and a vent well 
connected thereto by means of said vent and vent extension from said vent 
well and means to eject cured compound from said vent well. 
INFORMATION DISCLOSURE OF RELEVANT ART 
Relevant art considered pertaining to this present invention is as follows. 
U.S. Pat. No. 2,178,744--Method of Making a Golf Ball--This patent 
discloses straight vents opposite the fill gate of the molding, which 
vents are merely straight holes to vent the air out of the die during fill 
of the die with the thermoplastic material, then plugs are inserted into 
the vents to develop more pressure in the die. This would not be usable in 
molding of thermoset compound. 
U.S. Pat. No. 3,377,662--Metal Mold Having Vent Plug Means For Shaping a 
Plastic Article And Vulcanizing a Rubber Article. This patent discloses a 
vent means comprising a cylinder and a removal plug with grooves thereon. 
This patent then does not touch this present application. 
U.S. Pat. No. 3,822,857--Synthetic Resin Plug for Vent Hole of Mold. This 
patent covers plugs with micro holes for die venting. This present Rose 
invention does not involve such as is disclosed in this patent. 
U.S. Pat. No. 4,126,291--Injection Mold For Elongated Hollow Articles. This 
patent pertains to molding of elongated hollow articles and vents in a 
manner comprising spiral flats ground on vent pin. 
U.S. Pat. No. 4,140,470--Transfer Molding Venting System. "Venting" of this 
patent concerns a filter means to allow flow of gases but not elastomeric 
materials being molded. This does not concern the present Rose invention. 
U.S. Pat. No. 4,359,443--Venting Arrangement For Matched Molds And Method. 
The venting of this patent involves a gasket between the mold halves with 
vents being tubes through the gasket. 
This present invention of Rose does not involve a gasket between the mold 
halves or tubes to serve as vents.

DESCRIPTION OF INVENTION 
Referring now to the drawings, FIGS. 1 and 3, the cured compound 12 of 
molding 1, is shown in die cavity 2. Vent path 4, vent well 3, and vent 
extension 6, exhausting to the atmosphere, all contain cured compound 12. 
Knock out pin 5 pushes cured compound out of vent well 3 when molding 1 is 
ejected from the die. 
For illustration vent path 4 is located opposite gate 7, connected to 
runner 8, as shown in FIG. 2. In FIG. 2, knock out pin 5 location is 
shown. 
The vent well 3 construction comprises a wedge of triangular shape in 
elevation, FIGS. 1 & 3, wherein bottom vent well angle 9 is of about 
60.degree., vent well angle 10 is 90.degree. and, transition angle 11 of 
vent path to vent well is about 30.degree.. As angle 11 varies, so will 
angle 9. 
.theta. is an obtuse angle, which when subtracted from 180.degree. gives 
the acute or transition angle of vent path to vent well angle 11. 
Vent wall 13 is vertical and is to be parallel to the long axis of knock 
out pin 5. 
An example of vent dimension is as follows: 
Assuming the weight of the molding to be 100 gms, vent path 4 of about 
0.0127 mm thick by about 2.38 mm long, from die well to transition angle 
11 of vent path 4 to vent well 3. The width of said vent path 4 and vent 
well 3 and vent extension 6 is about 4.76 mm maximum. The depth of vent 
well 3 is 4.76 mm and vent extension 6, at about 0.051 mm in thickness, 
and about 4.76 mm wide. The transition angle 11 is 30.degree., and .theta. 
angle is 150.degree.. 
The angle .theta. is 150.degree., then 180.degree. minus 150.degree. gives 
a transition angle 11 of 30.degree.. 
The transition angle 11 may vary depending on amount of material and type 
of material being forced into the die. This transition angle of between 
10.degree. to 35.degree., and preferably not over 30.degree. is to be 
determined by trail of molding as those acquainted with the art of molding 
will readily realize. 
Removal of the vented compound from the vent well, vent path and vent 
extension, by action of the knock out pin 5 always insures an open vent on 
each fill cycle of the die. 
This invention is based on the wedge shape of the vent well 3 and vent 
extension 6, exhausting to the atmosphere. The transition angle 11, of 
vent path to vent well can vary from 10.degree. to 35.degree., with the 
preferred angle to be less than 35.degree. preferably not over 30.degree.. 
The transition angle 11 referred to above means the angle at which the 
wedge shape drops off of horizontal to form the above mentioned wedge, or 
it can be considered the angle at which the wedge shape varies from the 
plane of the die land area. To express the angle in a different way, the 
angle .theta. is 180.degree. minus the transition angle or 180.degree. 
minus .theta. is the transition angle. 
The "die land area" is, in molding of plastics, on a plane known as "seal 
off" surface on mating of the die male and female sections, and as shown 
in the drawing FIG. 3, the die land area is on a horizontal plane, and the 
angle at which the wedge shape drops off of the horizontal is the 
transition angle. 
It is to be pointed out that vent top A-B is to extend straight out from 
the die 2 so that knock out 5 on being activated, forces material out of 
the vent well 3. 
In FIGS. 1 and 2, note that the cavity 2 is on the knock out side of vent 
well 3, however the invention is not limited to this configuration as the 
knock out pin 5 of the vent well 3 could just as easily be mounted on the 
male or punch side of the cavity 2 as those acquainted with the molding 
art would be well aware. 
The knock out pin 5 as shown in FIGS. 1 & 3, has a flat top which makes 
contact with the cured compound 12 extending from vent well 3 into knock 
out pin hole 14. 
For clarity in the description of this invention, only the vent arrangement 
is shown. The punch or male section of the die is not shown as this is 
well known in the art.