Expansible chamber devices – Piston – Nonmetallic portion
Reexamination Certificate
1999-12-06
2001-10-23
Ryznic, John E. (Department: 3745)
Expansible chamber devices
Piston
Nonmetallic portion
C092S212000
Reexamination Certificate
active
06305266
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method of making a piston or plunger which comprises a piston body defining a peripheral surface part thereon and a sealing member made from a deformable material and being in tight engagement with said peripheral surface part. Such pistons or plungers may co-operate with pneumatic or hydraulic cylinders or may form part of any kind of piston pump. As an example, a piston or plunger of this type may be used in shock absorbers for cars or other vehicles.
DESCRIPTION OF PRIOR ART
U.S. Pat. No. 3,212,411 discloses a piston of the above type. The known piston includes a metal piston body having annular grooves formed in an outer peripheral surface part thereof by machining. A sealing member blank made from a thin sheet of polytetrafluoroethylene (PTFE) is pressed and deformed into tight engagement with the outer peripheral surface part of the piston body and into the annular grooves formed therein by means of a heated sizing tube with a tapered entrance. After treatment in the heated sizing tube, the piston body with the sealing member formed thereon is immediately introduced into a cooling tube wherein the sealing member is maintained in a confined condition with respect to the grooved surface part of the piston member.
Thus, according to the prior art a metal piston body blank is made by a moulding process, such as by casting or metal powder sintering. In the moulding process the piston body is formed with a smooth outer peripheral surface. Subsequently, a plurality of annular, peripherally extending, axially spaced channels or grooves are formed in the piston body blank by machining, such as by turning. The need for separately forming the grooves in the peripheral surface of the piston body substantially increases the production costs of the piston or plunger.
GENERAL DESCRIPTION OF THE INVENTION
The present invention provides a method of making a piston or plunger of the above type in a more economical manner.
Thus, the present invention provides a method of making a piston or plunger which comprises a piston body defining a peripheral surface part thereon and a sealing member made from a deformable material and being in tight engagement with said peripheral surface part, said method comprising: forming the piston body, forming grooves or depressions in the peripheral surface part of the piston body, applying an annular sealing member blank around said piston body, and deforming the sealing member blank into tight engagement with the peripheral surface part and into the grooves or depressions formed therein so as to form the shape of said sealing member in situ on the piston body, and the method according to the invention is characterised in that the grooves or depressions are formed so as to extend axially in an inner and/or outer peripheral surface part of the piston body when the piston body is formed by a moulding process.
It has been found that the sealing member may be safely retained on the peripheral surface of the piston body by the engagement of the sealing member with the axially extending grooves even when exposed to the axial forces usually occurring during use. Because the grooves or depressions extend axially they may be formed while the piston body is being moulded in a simple two-part mould, and no subsequent machining is necessary.
EP 0 658 611 discloses a piston body for a shock absorber. This piston body has a peripheral surface part having axially extending grooves or channels formed therein for engaging with a sealing member. However, this prior teaches that the sealing member should be applied to the piston body by inserting the piston body into an injection moulding machine by injection moulding the sealing member on the peripheral surface part of the piston body.
The annular sealing member blank may, for example, be a disk or tube, or it may have any other suitable form, such as a strip or band or a piece of sheet material, which—in an annular shape—is applied to an outer and/or inner peripheral surface part of the piston body. When the sealing member blank is applied to an inner peripheral surface part the piston or plunger formed may be in the form of an annular guiding member surrounding and sealingly engaging with a reciprocating shaft or a piston rod. When the sealing member blank is applied to an outer peripheral surface part, the sealing member blank is preferably an annular member having an inner diameter not exceeding the maximum outer diameter of the outer peripheral surface part of the piston body.
The axially extending grooves or depressions formed in the peripheral surface part may be closed at both ends. In a preferred embodiment, however, each axially extending groove or depression has an open end. In that case the mould, in which the piston body is formed, may be divided into mould parts which may be moved between open and closed positions in the axial direction of the piston body being formed. The open ends of the grooves or depressions may be positioned at opposite ends of the piston body or at the same end of the body. As an other possibility, the axially extending channels or grooves may be parallel and helical. In this case the mould parts may be moved from their closed to their open position after moulding of a piston body by a combined axial and rotational movement.
The annular sealing member blank which is applied to the piston member may be a substantially flat member which is made or cut from sheet material, for example by punching, or which may be made by cutting slices from a tubular member. The sealing member blank need not be a disc-like member, but could also be a tubular member or may be in the form of a strip, disk or band. When the sealing member blank has been applied to the peripheral surface part of the piston body, it is exposed to radially directed forces so as to deform the blank into engagement with said peripheral surface part. Thus, an annular which should be applied to an outer piston body surface may be passed onto the piston body via a tapered member having its wide end positioned in abutting engagement with one end of the piston body, and the sealing member blank may be deformed by means of a compression tool having an opening defined therein with a diameter exceeding the maximum outer diameter of the piston body, the piston body with the sealing member blank arranged thereon being moving axially in relation to the compression tool through the opening thereof, so as to deform the sealing member blank into the grooves or depressions of the piston body.
The present invention also provides a piston or plunger comprising a piston body defining a inner peripheral surface part thereon, said surface part having grooves or depressions formed therein, and an annular sealing member made from a deformable material and being in tight engagement with said peripheral surface part and extending into said grooves or depressions, so as to retain the sealing member in position on the piston body, and the piston or plunger according to the invention is characterised in that said grooves or depressions are extending axially and has been formed in an inner and/or outer peripheral surface part by a moulding process.
The piston body may be made from metal, such as by casting, extrusion or pressure moulding and/or sintering, or the piston may be made from any other suitable material, such as hard plastic material. The sealing member is preferably made from PTFE or another suitable thermoplast. Each of the grooves or depressions may, for example, have an open end and may extend axially therefrom, and these open ends of the grooves or depressions may either be located at the same or at opposite ends of the piston body. The axially extending grooves or depressions may be parallel with the axis of the piston body being formed or may extend helically in relation to the axis of the piston body.
According to further aspect the present invention provides a piston body for a piston or plunger as described above, said piston body defining a peripheral surface part having grooves or
Jensen Leo
Tonndorff Agge Jan
Klein & Szekeres LLP
Ryznic John E.
W.S. Shamban Europa A/S
LandOfFree
Piston or plunger and a method for making the same does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Piston or plunger and a method for making the same, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Piston or plunger and a method for making the same will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2552013