FR2628675A1 - MOLDING DEVICE WITHOUT MOLDING BARS, PARTICULARLY FOR OBTAINING O-RINGS - Google Patents

Abstract

The invention relates to a molding device for obtaining O-rings without mold barbs. The feed orifices 26 in material to be molded do not open out at the level of the parting line 22. The axes of the feed orifices are offset from 15degre (s) to 90degre (s) with respect to the parting line and positioned in the Upper half-mold 10. The invention also relates to the seals obtained using this device.

Description

The present invention relates to a transfer molding device.

  O-rings and more particularly such a device which makes it possible to manufacture rubber O-rings without molding barbs, characterized in that the supply is axially offset with respect to the joint plane. The invention also relates to

  the O-rings obtained using this device.

  The molding of rubber objects is carried out, in the usual way by compression molding, by transfer molding or by injection molding. Transfer molding consists of placing unvulcanized rubber in a pot, the bottom of which can be placed in communication with a mold cavity via feed orifices. A hydraulic piston exerts pressure on the unvulcanized rubber over it to pass it from the pot into the mold cavity via the feed orifices. The pressure is maintained and it is heated for a sufficiently long period and to a

  sufficient temperature for the rubber to vulcanize.

  Once vulcanization is complete, the mold is opened. and

the formed object is removed from the mold.

  Molding without barbs is a form of transfer molding in which the part of the mold adjacent to the joint plane is subjected to a conventional process such that, when the mold is closed, this part of the mold adjacent to the joint plane allows air to escape without letting the rubber escape at the same time. Thus, the molded object has practically no molding barbs. Furthermore, usually the barbs are removed when the base

  transfer is separated from the bottom of the pot.

  O-rings are conventionally manufactured by a compression molding method which leaves molding barbs along their outside and bottom diameters. It has been found that the main sealing surface of the O-ring is either its inside diameter or its outside diameter but, more often, its outside diameter. It has been found that the molding barbs left by the compression molding method applied obstruct and, in some cases, prevent sealing along the outside diameter of the joint. It has also been found that O-rings made by compression molding are rejected in automatic loading machines because of the molding barbs left along the inside and outside diameters. Automatic loading machines are common pieces of equipment which use the part of the O-ring at or near the joint plane to align said O-ring in order to orient it for installation. If the O-ring has barbs

molding, it is rejected.

  Applicants have discovered that if an O-ring is molded in a mold without molding barbs, all of whose feed ports have their axes offset from the joint plane, a superior seal is obtained along the inside and outside diameters of the seal and the rejection problem associated with

  automatic loading is virtually eliminated.

  The method proposed by the present invention also solves a number of other problems associated with

  O-rings made by compression molding.

  The filling faults caused by the insufficient quantity of rubber in the mold cavity are reduced to a minimum thanks to the present invention. This is because all the unvulcanized rubber is introduced from a common pot above the footprint

of the mold.

  The bad aggregation coming from a pre-vulcanized rubber or due to the presence of an excessive quantity of internal or external lubricant of the mold, when a compression mold is used, is virtually eliminated because these lubricants are not not normally employed in the present invention and that rubber

  is not sandwiched between the two half-molds.

  There are no large or thick molding barbs due to the presence of an excessive amount of material in the mold cavity because the mold, in the case of the present invention, is closed before the material

enters the imprint.

  The bonded molding barbs, due to the rubber which escaped from the imprint * do not form because the

  The present invention does not produce molding barbs.

  The casting lines that are common in compression molding are virtually eliminated with the

present invention.

  The bubbles that are caused by air entrapment during compression molding are also

  virtually eliminated by the present invention.

  The set-up and offset that occurs in compression molding does not occur in the case of the present invention since all mold impressions are machined in pairs and placed on mold plates. In addition, each individual impression -4 is self-positioning to ensure alignment.

  The invention will be better understood thanks to the description

  which follows, given with reference to the drawings of the attached boards in which: - Figure 1 shows a cross section of a mold according to the present invention; - Figure 2 shows the cross section of the mold of Figure 1 with rubber in the molding pot; - Figure 3 shows a cross section of another mold according to the present invention and - Figure 4 is a top view of a lower impression plate receiving several molds according to the

present invention.

  Figure 1 shows a section of a mold without molding barbs produced according to the present invention. The upper half-mold 10 fits on the lower half-mold 12. The lower half-mold 12 is placed in a lower impression plate 14 while the upper half-mold 10 is placed in a plate upper cavity 16. The lower cavity plate 14 and the lower half-mold 12 are both placed against the lower mold plate 18. When the upper half-mold 10 is brought into contact with the lower half-mold 12, a mold imprint 20 is formed. The upper and lower half-molds 10 and 12 are subjected to a usual process at the joint plane 22, so that air can escape from the mold cavity 20 when the two half-molds 10 and 12 are in contact with each other. To ensure correct relative positioning of the half-molds 10 and 12, a self-positioning ring 24 is provided for each -5-

pair of half-molds 10 and 12.

  A feed orifice 26 passes through the upper half-mold 10 and is in communication with the impression of

mold 20.

  The molding pot intended to receive the rubber is formed when a pot plate 28 is brought into contact with the upper face of the upper impression plate 16, as shown in FIG. 2. The molding pot formed is shown in FIG. 2 with rubber 30 inside. The mold is equipped with a piston 32 which engages in a sleeve of the pot plate 28 so as to be able to exert pressure on the rubber 30. The piston 32 is a conventional mechanical piston. A heat source (not shown), in association with a piston plate 34 and the bottom plate 18, is used to vulcanize the rubber

  after its injection into the imprint 20.

  Once the mold is closed, the unvulcanized rubber 30 is placed in the pot formed by the upper parts, both of the upper half-mold 10 and of the upper impression plate 16, and of the sleeve of the pot plate 28 The piston 32 is brought into contact with the unvulcanized rubber 30 to force the latter through the feed orifices 26 into the cavity of the mold 20. A conventional hydraulic system is used (not shown)

  to close the mold and to move the piston 32.

  As shown in Figures I and 2, the axis of the supply port 26 is offset from the plane

seal 22.

  Figure 3 shows an alternative embodiment of the mold according to the present invention. In this variant the axis of the supply orifice 26 is offset by approximately

relative to the joint plane 22.

  - 6 - It is preferable that the axis of the supply orifice it offset by about 15 to 90 relative to the joint plane; it is even more preferable that it is about 30 to 90 and, even better, that it is about 45 to 90. Good results have been obtained with feed orifice axes offset by about 45 relative to the joint plane. The best results have been obtained with the feed orifice positioned in the half-mold

higher 10.

  As specialists will understand, a mold produced according to the present invention will include a plurality of cavities 20. FIG. 4 represents a top view of a part of the lower mold plate 14 in which half of the mold cavity 20 is shown with a self-positioning ring 24. Each cavity 20 has 5 feed orifices. The number of supply ports depends on the viscosity of the tool used. The actual position of the half-molds on the mold plate is chosen to obtain a setting

optimum place.

  The number of feed orifices in communication with each mold cavity should preferably be between 1 and 13, better between 3 and 9 and better still between 3 and 7. Good results have been obtained with 5 feed orifices. O-rings are commonly made of rubber and more particularly of synthetic rubber such as ethylene propylene diene monomer (EPDM), fluorocarbon, silicone, fluorosilicone, nitrile or neoprene. Generally, any thermosetting material can be used in the application of the present invention. Natural rubber can also be used. Good results have been obtained with the manufacture of O-rings in EPDM

according to the present invention.

  The vulcanization time and temperature for a process of this kind are those usually used and depend on the material used. Good results have been obtained with EPDM at a vulcanization temperature of approximately 182 C and for a vulcanization time of approximately

3 minutes.

  The method and the mold proposed by the present invention are suitable for the production of O-rings of any size. Good results have been obtained with O-rings with a diameter of about 0.39 cm to about 5.1 cm. Commonly, the O-ring has a cross section of about 0.10 cm

at 0.53 cm.

  The size of the feed orifices, as well as their number, depends on the viscosity of the rubber used. Preferably, the feed orifices have diameters between 0.038 and 0.127 cm and good results have been obtained with feed orifices with diameters between 0.038 and 0.076 cm. The diameter of the supply ports is measured at the entry point

in the mold imprint.

  The manufacture of an O-ring according to the present invention takes place according to the following method: firstly, the mold is closed and the press locks the half-molds together. Unvulcanized rubber is placed in the upper pot and subjected to the action of a piston which forces it through the feed orifices into the mold cavity. When the downward pressure of the piston is counterbalanced or balanced by the back pressure exerted by the mold cavity, the piston comes to rest and the mold is heated to vulcanize the rubber. Usually, the transfer pressure is between 100 and 350 kg / m2, approximately, and vulcanization time is approximately 3 minutes. The pressure and the vulcanization time vary depending on the characteristics of the rubber used. Once the vulcanization time has elapsed, the action of the hydraulic pressure on the half-molds is released and the mold

  is extracted and then opened for removing the O-ring from the mold.

  Of course, the invention relates not only to what

  is specifically set out in the claims but

  also all variants and modifications of the described embodiment which remain in accordance with the spirit

  and the scope of the invention.

Claims (8)

  1) Molding device without molding barbs comprising a mold cavity formed by an upper half-mold and a lower half-mold, said upper half-mold and said lower half-mold being in contact with each other at level of a joint plane and one or more supply orifices for injecting a thermosetting material into said mold impression, characterized in that the supply orifice (s) are positioned with their   axes offset from said joint plane.   2) Molding device according to claim 1, characterized in that each feed orifice has its axis offset from about 15 to about 90 relative to on the parting line.   3) Molding device according to claim 1, characterized in that each feed orifice has its axis offset from about 30 to about 90 relative to on the parting line.   4) Molding device according to claim 1, characterized in that each supply orifice   - opens into the upper half-mold.    ) Molding device according to claim 4, characterized in that each feed orifice has its axis offset by about 15 to about 90 relative to on the parting line.   6) molding device according to claim 5, characterized in that it comprises between 1 and 13   fingerprint feed holes.   y1o d2628675) Molding device, without molding barbs, for O-rings comprising: a) a mold for manufacturing an O-ring, comprising a mold cavity, this being formed by an upper half-mold and a half lower mold, said upper half-mold and said lower half-mold being in contact with each other at a joint plane, and b) at least one supply orifice in communication with said cavity mold for injecting thermosetting material, said feed orifice having its axis offset from the plane seal.   8) Molding device according to claim 7, characterized in that each supply orifice has its axis offset from about 15 to about 90 relative to on the parting line.   9) molding device according to claim 7, characterized in that each supply orifice has its axis offset from about 45 to about 90 relative to the joint plane,) molding device according to claim 7, characterized in that each supply port   opens into the upper half-mold.   11) Molding device according to claim 10, characterized in that each supply orifice has its axis offset from about 15 to about 90 relative to on the parting line.   A4l 12) Molding device according to claim 11, characterized in that it comprises between 1 and 13 orifices fingerprint feed.