Process for making chemical resistant pump diaphragm

Details Process for making chemical resistant pump diaphragm Process for making chemical resistant pump diaphragm

1999-11-15

2004-06-08

Lee, Edmund H. (Department: 1732)

Plastic and nonmetallic article shaping or treating: processes

With printing or coating of workpiece

Coating or impregnating workpiece before molding or shaping...

C264S250000

Reexamination Certificate

active

06746637

ABSTRACT:

BACKGROUND
This invention relates generally to a process for making a chemical resistant pump diaphragm, and more particularly, to a process for making a two layer bonded thermoplastic elastomer pump diaphragm. Air driven diaphragm pumps are well known in the art. There are many types of pump apparatus which employ compressed air through an actuator valve to drive double diaphragms. Some examples of such devices can be found described in U.S. Pat. Nos. 4,247,264, D294,946, D294,947, and D275,858, all issued to James K. Wilden. An actuator valve used with such air driven diaphragm pumps is disclosed in U.S. Pat. No. 3,071,118, also issued to James K. Wilden.
Common to the aforementioned patents describing air driven diaphragm pumps is the presence of an air chamber housing having a center section and concave discs facing outwardly from the center section, liquid chamber housings, an inlet manifold and an outlet manifold. Check valves are also positioned in both the inlet passageways and the outlet passageways. The check valve chambers are defined with ribs or other restrictions typically cast into the components to maintain the check valves in position. Seats are provided which may be inserts or integral with the components depending on material and fabrication techniques. Diaphragms located between the air chambers and water chambers reciprocate back and forth under the influence of air pressure directed alternately to one side or the other of the pump. This action in combination with the check valves provides for the pumping of a wide variety of materials.
Typically, the diaphragms can be formed from rubber, which can also be reinforced by fabric or other fillers. However, because certain application require the pumping of materials which can contain chemicals which can be corrosive to the rubber compounds, it can be necessary to either coat the rubber diaphragms with a protective material or form the diaphragm from a substance which is resistant to chemicals. One manner of providing protection from chemicals which is well known in the art is to attach a Teflon™ shield to a rubber diaphragm. The Teflon™ shield can also provide protection against high temperatures. However, Teflon™ shields can be relatively expensive. It is also known to form diaphragms from other materials besides rubber. Such materials can have high tensile strength, thermal stability, elasticity and fatigue resistance. Some examples are polyester based materials such as Hytrel™, Santoprene™ and Sarlink™. These polymers can be utilized to form diaphragms more simply, such as by injection molding, and also less expensively than fabric reinforced rubber diaphragms. A Hytrel™ diaphragm is described in an English language abstract of French patent No. FR 2422086. However, such polymer diaphragms still lack chemical resistance and would require a Teflon™ shield similarly to rubber diaphragms if they are to be exposed to certain chemicals.
It is also known to bond together two types of materials having different degrees of hardness, as described in U.S. Pat. No. 5,816,133 to Schoenmeyer. However, in Schoenmeyer, the two types of material are not actually different materials. They both have the same base polymer, and the only difference is the percentage of rubber filler in each. Hence, that patent describes that the first layer of material is inject and permitted to harden prior to the second layer being injected onto the first layer. It is stated that when the second layer is injected onto the first layer that the two layers “weld” together because the base materials of each layer has the same melt temperature. Regarding the composition of the diaphragm in that patent, it is believed to be Santoprene™. Basically one type of the Santoprene™ material is harder, i.e. less rubber than the second type of Santoprene™ material being used. Thus, there is the identical base polymer, except one has a lower rubber content than the other, which means that material is a little softer than the other. In any case, both layers contain the same base polymer which is what permits the welding of the interface of the two layers. Additionally, both layers contain rubber, which means that neither layer can provide chemical protection for the diaphragm. If there is any rubber content at all, the chemical resistance of the diaphragm is only as good as the chemical resistance of the rubber content, which is typically insufficient. Regarding the application for the type of diaphragm in Schoenmeyer, the hard layer can be provided to work against the fluid pressure, whereas the softer layer can be for flexibility and to help support the hard layer. In contrast to a air driven double diaphragm pump wherein the diaphragms actually flex back and forth, the diaphragm in the Schoenmeyer patent does not flex. Rather, it is subjected to a rolling type of application. Typically, in pumps which use this type of diaphragm, such as bilge pumps for boating applications, there is a wobble plate positioned against the top portion of the diaphragm. In operation, this wobble plate is “wobbling,” i.e. lifting one, lowering a second, and lifting the other third, as it pumps. There are typically three chambers pumping water out. The diaphragm in the Schoenmeyer patent was developed in order to withstand pressure, e.g. hydraulic pressure, not for chemical resistance. Because of the rubber content, if the Schoenmeyer diaphragm were to be used in a chemical environment, a Teflon™ shield would still be needed. However, in regard to chemical resistance, there can be alternative materials to Teflon™ which can provide adequate chemical resistance for diaphragms. For example, a material called Arnitel™ is also known to provide resistance to chemicals similarly to Teflon™. Yet, Arnitel™ can be less resistant to high temperatures than Teflon™. Nevertheless, many applications can require chemical resistance but not involve high temperatures, and thus can be suitable for Arnitel™. Moreover, Arnitel™ can be injection molded for simplicity of production and is less expensive than Teflon™.
Accordingly, there is a need for a pump diaphragm which can be produced simply and less expensively than fabric reinforced rubber and which can be provided with chemical resistance more simply and less expensively than providing a Teflon™ shield.
SUMMARY
The invention provides a two layer flexible pump diaphragm wherein one layer is chemical resistant. One layer can be produced from a polymer, such as, for example Hytrel™, Santoprene™, or Sarlink™ which can be injection molded for ease of production and cost efficiency. Such materials can also provide high tensile strength, thermal stability, elasticity and fatigue resistance. The diaphragm can be produced by a two part injection molding and can utilize a common mold portion and two different mold portions which can mate with the common portion. The common mold portion can be used in both molding operations. The first part of the molding process can include injecting molten Arnitel™ material into a cavity having the form of the diaphragm to be produced. The Arnitel™ portion can provide the desired chemical resistance for the two part diaphragm. As many Arnitel™ portions can be molded initially as desired depending on the number of diaphragms to be produced. After curing, the Arnitel™ diaphragm portions can painted with an adhesive which can be used to bond the two parts of the diaphragms together. To create the two part diaphragm, the cooled Arnitel portion which has been painted with the adhesive can be placed back into the common mold portion which can then be mated up with the second mold portion. Molten Sarlink™ or Hytrel™ material can then be injected into the mold cavity against the Arnitel™ portion. The adhesive can be activated by the heat of the molten material and thereby bond the Sarlink™ or Hytrel™ material to the Arnitel™ to create the final two part diaphragm. Additional finishing steps, such as drilling fastener holes can be performed after the diaphragm is hardened.
Other details, objects, and advantages of the invention

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