NITROPHYL® Design Guide

Design your liquid level sensors with the high reliability of Rogers NITROPHYL® closed cell foam

NITROPHYL floats, with a closed-cell, homogeneous structure, offer high reliability and resistance to the attack of many fluids, including: hydrocarbon fuels like gasoline, LPG and jet fuel oils and various other fluids, solvents, and chemicals. The material, a nitrile rubber ebonite formulation, can be molded into intricately shaped floats for a variety of liquid level sensing applications.

NITROPHYL floats are well proven in both automotive and industrial applications. They are used in automotive fuel and oil level sensors, carburetors, and in general liquid level sensing applications, such as underground storage tanks, metering devices and automatic relief valves. The marine and small engine industries also use NITROPHYL floats extensively.

Design Versatility and Reliability

Moldable into complex shapes.
A closed-cell material, NITROPHYL material is not hollow.
Unlike hollow floats, they are not subject to sudden failure.
Easily machined.
Bar magnets can be easily inserted.
Resistant to most fuels, oils, aqueous solutions, solvents and chemicals.
Ring magnets and metal or plastic inserts can be molded in.

NITROPHYL floats can be molded into complex shapes and sizes, with or without inserts and can be machined by all conventional methods without impairing flotation properties.

Molded blocks or cylinders can be machined for small production runs or prototypes (Refer to the NITROPHYL Float Machining Instructions for further details). Large floats can be assembled from separately molded floats bonded together. Inserts or ring magnets can be molded in or cemented in after molding.

NITROPHYL material is transformed from a solid material to a hard, cellular structure by a two-step molding process. The outside layers, which are in contact with the hot surfaces of the cavity, produce a hard, smooth outer surface. The inside acquires a closed-cell structure. This distinctly different shell or "skin" protects the cell structure and adds to the mechanical strength of the part. NITROPHYL floats are also abrasion-resistant and capable of reproducing cavity details with sharp resolution in a wide range of sizes.

In many liquid level sensors the cylindrical float, with embedded permanent magnets, is a popular design. Following the level of the liquid, these floats actuate reed switches installed at critical points inside a non-magnetic central guide.

Density

NITROPHYL floats are available in two general density ranges: 10-12 pounds per cubic foot (160-190 Kg/m3) and 18-20 pounds per cubic foot (285-320 Kg/m3). Custom molded floats can be produced in densities from 10-40 pounds per cubic foot (160-640 Kg/m3). Density can be held to +/- 10% per cubic foot in most cases, although some situations may require wider limits. Closer control can be designed-in when necessary for satisfactory performance of a level sensing system.

Design Considerations for NITROPHYL Floats

Operating Temperatures
NITROPHYL floats are recommended for continuous service from -70°F to +220°F (-57°C to +104°C). By special processing, floats can be conditioned to operate in a +300°F (149°C) environment.

Operating Pressures
NITROPHYL floats can resist pressure up to 300 psi (2068kPa), or higher, depending on: shape and size of the float, density, operating temperature, and the fluid in which it is used.

For applications with higher operating pressures, we suggest using our high density material, 18-20 pounds per cubic foot (285-320 Kg/m3) which is more resistant to weight gain under these conditions.

Initial testing of our new, NITROPHYL-M material shows it has improved resistance in higher pressure applications. (Refer to the NITROPHYL-M data sheet for further details.)

If a NITROPHYL float will be machined for a high pressure application, we also suggest coating the machined surfaces with a two-part epoxy. The molded "skin" on a NITROPHYL float helps resist liquid absorption in pressures of 200 psi (1379kPa) or more. In low operating pressures, a machined surface should have little impact on the performance of the material.

Inserts
Ring magnets, inserts, or guiding devices are frequently molded into our floats. Generally made of metals or high temperature plastics, they may take various shapes: tubes, rods, or parts stamped from flat stock. Non-metallic components need to withstand a molding temperature of 375°F (191°C).

The bond between the NITROPHYL float and the insert is mechanical in nature. Prepare the insert either by having a knurl or groove in tubes and rods, or by providing stamped parts with some configuration for the float material to mold around. A molded-in component can take substantial loads while remaining securely attached, even under severe vibration conditions.

Rogers can assist in the design of the inserts to assure compatibility, sufficient bonding, and the lowest possible cost. Inserts can be supplied to, or consigned to Rogers for molding, or we can purchase the inserts directly from one of our approved suppliers. Most customers prefer we purchase the inserts to assure quality for the entire final assembly.

Figure 1 shows how we would suggest dimensioning a float with a molded-in ring magnet.

Notes:

Material: Rogers NITROPHYL material
Density: Material - lb/cu Ft. "J", "K"
Magnet: Properties to be determined
0.02 max flash permissible
0.04 max radius due to nonfill on sharp corners
Dimensions and tolerances are in inches

Cementing/Bonding

Components may also be attached by applying cement in molded or machined recesses. The most reliable bond is achieved when the skin is machined off the surface of the float. Although requiring secondary operations, machining standard parts can offer cost advantages where tooling costs are high, when the size of the component lowers the productive capacity of the mold, or when the quantities used do not justify the cost of dedicated tooling.

Type of Area	Dimension Range	Typical Tolerance
Exterior Dimensions	0 - 1.00" 1.00" - 2.00" 2.00" above	±0.010" ±0.020" ±0.030"
Internal Features	0 - 1.00" 1.00" - 2.00" 2.00" above	±0.015" ±0.020" ±0.030"
Drilled Holes	0 - 0.100" 0.100" - 0.200"	±0.007" ±0.010"

Design Considerations

In designing custom molded floats, we suggest the following typical tolerances:

Molding flash: Like other molded products, NITROPHYL floats have characteristic flash lines where the mold is parted. Typically we request a maximum of 0.030" (0.76mm) for flash that is not included in the other dimensions. We can work with designers to locate the parting lines in an area that is not detrimental to the application.
Molded wall thickness should be a minimum of 1/4"(6.4mm).
Exceptionally large floats can be assembled from small, separately molded parts.
Mold mismatch allowances should be a maximum of 0.015" (0.38)mm.
Holes less than 0.180"(4.6mm) in diameter and over an inch long are impractical to mold in. Small holes can be drilled without affecting the performance of the float.
Holes greater than 0.180"(4.6mm) in diameter can be molded in.
The simplest, most cost effective part to produce with our process is a cylinder with sharp corners.
Radii on the ends of cylinders are not required by our process and add to the tooling cost.
A draft angle for demolding is not required by the NITROPHYL float molding process.
Avoid features that could interfere with part removal from the mold (normal to the parting line).
Cavity markings are typically 0.120" (3.0mm) high characters.
The coefficient of thermal expansion for NITROPHYL material is approximately 50 parts per million per degree centigrade.

Design Assistance

The process of molding NITROPHYL floats is very different from that of typical injection molding. Space, pressure, and density requirements may need adjusting to provide optimum float performance for each application. We are available for design assistance and encourage early involvement in the design process. Helping design the part with you can minimize tooling costs and produce the most cost effective float for each application.

NITROPHYL Bulletin #1: Compatibility with Various Liquids.

We can provide some guidance for setting up test procedures and putting together product specifications.

Rogers assures that environmental issues are addressed

No ozone depleting chemicals (ODC's) or CFC's are used in our process.
NITROPHYL material is recyclable with other rubber type components such as automobile tires.
We normally use recyclable corrugated cardboard cartons for packaging our floats, but we also utilize reusable containers supplied to us at our customer's request.
Our facility has an on-site Environmental Coordinator to assure the strictest compliance to environmental regulations.
Our facility's recycling of metal, paper, cardboard, and wood has reduced our landfill waste by 75%.
The remaining waste is incinerated at a trash-to-energy plant to produce electricity.

For more information on NITROPHYL floats or to discuss an application, contact a technical representative.