Reciprocating piston pump surface treatment process

Abstract

A process for treating rods and cylinders for use in reciprocating piston pumps is provided which yields a substantial increase in wear over the chrome coatings of the prior art. A base material of stainless steel 17-4ph is heat treated in the range generally from H-900 to H-1150. Once the material is pretempered, an ion nitriding process is applied. With this process, the hardness can be increased from the standard 17-4 hardness of RC-44 max to a desired hardness of RC-65 to 75.

Description

BACKGROUND OF THE INVENTION

[0002] Reciprocating piston pumps (primarily double-acting but also single-acting) have been used for pumping paints and similarly viscous abrasive materials for many years. To date, the most successful traditional finishing of the cylinders and rods in such products are to chrome-finish surfaces of those parts.

SUMMARY OF THE INVENTION

[0003] It is an object of this invention to provide rods and cylinders for use in reciprocating piston pumps which provide a substantial increase in wear over the chrome coatings of the prior art.

[0004] Towards this end, for a base material, a stainless steel of a grade known as 174ph. The base material is then heat treated in the range generally from H-900 to H-150. Non-standard heat treatment temps such as H-950 can also be used. Once the material is pretempered, the ion nitriding process is then applied. With this process, the hardness can be increased from the standard 17-4 hardness of RC-44 max to a desired hardness of RC-65 to 75. These hardnesses can be controlled to within 0.001 of the thickness effective case depth and go as deep as 0.010 on the 17-4 material. These hardnesses are the equivalent or higher than the best chrome coatings available.

[0005] These and other objects and advantages of the invention will appear more fully from the following description made in conjunction with the accompanying drawings wherein like reference characters refer to the same or similar parts throughout the several views.

A BRIEF DESCRIPTION OF THE DRAWINGS

[0006] FIG. 1 is an exploded view of a pump capable of using the instant invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0007] Towards this end, for a base material for rod 201 and cylinder 206, a stainless steel of a grade known as 17-4ph is used. The base material is then heat treated in the range generally from H-900 to H-1150. Non-standard heat treatment temps such as H-950 can also be used. Once the material is pretempered, the ion nitriding process is then applied. With this process, the hardness can be increased from the standard 17-4 hardness of RC-44 max to a desired hardness of RC-65 to 75. These hardnesses can be controlled to within 0.001 of the thickness effective case depth and go as deep as 0.010 on the 17-4 material. These hardnesses are the equivalent or higher than the best chrome coatings available.

[0008] The ion nitriding process (which is generally well known) is not a coating and will not flake off or have poor adhesion to the base material. Using an ion nitriding process also eliminates one grinding operation and the wear surface of the part is whatever the 17-4 material has been prefinished to. Accordingly, the surface does not have small microcracks covering the entire surface, as was the case with prior art coatings and finishes. This eliminates potential premature failures due to erosion through the surface cracks. Most importantly, use of this process provides an increase in pump life of up to four times over the standard part finishes such as chrome.

[0009] In another variant of the life improving process, a chromium nitride coating is provided which is capable of providing an equivalent or better life at a 50-60% cost reduction. These coatings are provided on a base 17-4ph material with again a hardness in the range of H900 to H1150. The chrome nitriding is actually a PVD coating which has a hardness of 60-65RC with a thickness of approximately 3 to 5 mils. Such chrome nitriding is also void of all surface cracks present in traditional chrome and because of this premature failure is nonexistent providing very consistent and predictable life curves. The process can also eliminate one finish grind operation and provide a uniform thickness.

[0010] It is contemplated that various changes and modifications may be made to the surface treatment without departing from the spirit and scope of the invention as defined by the following claims.

Claims

1. In a reciprocating piston pump for use with paints and coatings, said pump having at least one of a piston rod and cylinder, the improvement comprising treating at least one of said rod and cylinder with an ion nitriding process.

2. The reciprocating piston pump of claim 1 wherein the base material for at least one of said rod and cylinder is a 17-4ph stainless steel.

3. The reciprocating piston pump of claim 1 wherein the base material for at least one of said rod and cylinder is treated via ion nitriding to a hardness of about RC-65 to 75.

4. The process of treating at least one of a reciprocating piston pump rod and cylinder formed of a base material and comprising the steps of: heat treating the base material to a hardness of about H-900 to H-1150; and ion nitriding said material to a hardness of about RC-65 to 75.