The foam float is broadly used in flow meters, liquid face controllers, automatic level sensors, etc. , of various kinds of equipments such as automobiles, motorcycles, agricultural machines, heaters, carburetors, moisturizers, and compressors.

NBR (nitrile-butadiene rubber) has many properties that are advantageous for use as LPG foam floats, such as oil resistance, water resistance, LPG resistance, and ability to withstand a pressure of 25 kg/cm2. Such NBR floats may generally be used in automobiles for which gasoline or LPG is used for fuel, as well as in various kinds of flow meters.

However, since the foam float is damaged at a pressure of 50 kg/cm2 or more and because fuel permeates into the foam float when it is immersed into LPG, its functions are lost and it is not appropriate for a high pressure of 25 kg/cm2 or more.

On the other hand, gases have been recognized as clean and convenient fuels to substitute for petroleum, and they are currently utilized as the most popularized life fuels in the world. LPG automobiles are also continuously developed, and the number of vehicles is also rapidly increased.

A level gauge of a storage tank for the LPG should withstand the pressure of 50 kg/cm2 or more. However, as mentioned above, existing foam floats made of NBR can withstand the pressure up to only about 30 kg/cm2. For this reason, a float made of iron is used for these LPG storage tanks, instead.

On the other hand, a float made of iron is a hollow product. If a small leak or pinhole is created in the sphere, the LPG permeates into it and the coupled parts with their assembly are separated, which is the reason the float can not be used in many cases.

On the contrary, since there are inner walls between independent foams in its structure of the existing foam float made of NBR, its functions can be maintained even if a small leak or a hole exists. However if the foams are small and uniform, the density is increased and the specific gravity is increased accordingly, which could not satisfy the requirement that the foam float for a LPG high-pressure tank should be light and strong.

Also, mounting of an overfill-prevention device (OPD) in a LPG gas storage container is oftentimes obligatory. When the container is filled at about 80%, the float is raised and the filling work is stopped. In this way, a valve of the overfill-prevention device prevents overfilling of the gas container in advance for safety. At that time, the float should also be able to withstand a high pressure of 50 kg/cm2 or more.

In addition, in a float for a large-capacity storage tank, since its required buoyancy is large, the volume has to be large at the same specific gravity. If the volume of the float was large, a uniform heat transfer of the inside and the outside could not be realized and a dense structure could not be obtained. Also, in a vulcanization process, since a high temperature of 180°C or higher was given only to the outside, an excessive vulcanization (over cure) is caused on the surface, so that the surface is cracked or burnt and the inside was in a non- vulcanized (under cure) state. Thereby, it is difficult to obtain intended hardness and pressure resistance.

Thus, in order for the foam float to withstand a high pressure, the structure of the float should be dense and strong, and since the specific gravity of the LPG is about 0.5, the foam float should be as light as a specific gravity of about 0.3 smaller than that. However, in the manufacture of the foam float, decreasing the weight while increasing the pressure resistance is very difficult because these are mutually contradictory phenomena.

Current domestic technologies can handle a pressure of about 30 kg/cm2. If the float is at a high pressure of 50 kg/cm2 or more, it is distorted and a liquid permeates into it.

Summary The presently described apparatus and method alleviates the problems and deficiencies of the prior art by providing a pressure-resistant foam float for a LPG gas, which can withstand a high pressure of 50 kg/cm2 or more, and its manufacturing method. In one embodiment, the foam float has a specific gravity below about 0.4. In another embodiment, the foam float has a specific gravity between about 0.28 and 0.35.

RGP-0237-PCT 3 In another embodiment, the pressure-resistant foam float of the present invention is characterized by the fact that a mixture powder comprising approximately: 39-46 wt% phenol resin, 30-40 wt% carbon black, 3.5-5 wt% zinc oxide, 1.0-1. 5 wt% stearic acid, 35-43 wt% sulfur, 6.0-7. 0 wt% azodicarbonamide (AC), 3.5-4. 5 w% foaming aid, 0.5-1. 0 wt% L-7, and 1.5-2. 0 wt% CZ is put in a range of 120-150 parts by weight into NBR at 100 parts by weight.

The above-discussed and other features and advantages of the apparatus and method for providing a pressure-resistant foam float for a LPG gas will be appreciated and understood by those skilled in the art from the following detailed description and drawings.

Brief Description Of The Figures Referring now to the drawings, wherein like elements are numbered alike in the several FIGURES: Figure 1 is a 50-time enlarged photomicrograph showing a state after the primary molding process in an exemplary pressure-resistant foam float.

Figure 2 is a 50-time enlarged photomicrograph showing a state after the secondary molding process in an exemplary pressure-resistant foam float.

Figure 3 is a 50-time enlarged photomicrograph showing a state when no posttreatment process was applied to an exemplary pressure-resistant foam float.

Figure 4 is a 50-time enlarged photomicrograph showing a state when a posttreatment process was applied to an exemplary pressure-resistant foam float.

Figure 5 is a graph showing a weight change rate in accordance with the kind of carbon of an exemplary pressure-resistant foam float.

Figure 6 is a graph showing a weight change rate in accordance with the posttreatment of an exemplary pressure-resistant foam float.

Figure 7 is a graph showing a weight change rate in accordance with the secondary molding time of an exemplary pressure-resistant foam float.

* Explanation of symbols of the main parts of the figures A Exemplary pressure-resistant foam float.

B Comparative standard

RGP-0237-PCT 4 Detailed Description Of Exemplary Embodiments Reference will now be made in detail to exemplary embodiments, examples of which are illustrated in the accompanying drawings.

The present disclosure describes, in one exemplary embodiment, a light high-quality foam float for a high pressure containing independent foams which had no external change at a high pressure of 50 kg/cm2 or more and showed a weight change of 3 wt% or less when immersed into a LPG over a long term.

In one embodiment, an exemplary foam float for a LPG gas that has lots of small independent foams, has a large cell wall strength between the foams, exhibits little weight change when immersing it into a LPG mainly composed of propane and butane, is light, and can withstand a high pressure of 50 kg/cm2 or more is provided.

One exemplary pressure-resistant foam float is characterized by a mixture powder comprising approximately: 39-46 wt% phenol resin, 30-40 wt% carbon black, 3.5-5 wt% zinc oxide, 1.0-1. 5 wt% stearic acid, 35-43 wt% sulfur, 6.0-7. 0 wt% azodicarbonamide (AC), 3.5-4. 5 w% foaming aid, 0.5-1. 0 wt% L-7, and 1.5-2. 0 wt% CZ put in a range of 120-150 parts by weight into NBR at 100 parts by weight; In one embodiment, the above-mentioned carbon black has a particle size of 400-550 gm, and the above-mentioned sulfur is composed of particulates with a mesh of 350-450; In another embodiment, the specific gravity is 0.28-0. 35, and the weight change rate at 50 kg/cm2 or more is 3 wt% or less.

Also, one embodiment may be characterized by the fact that the above-mentioned mixture is passed through an ordinary process, molded at 115-125°C for 800-1,000 sec, remolded at 160-180°C for 2,400-2, 600 sec, and cooled, and the above-mentioned molded product is posttreated at 60-80°C for 24 h.

NBR as a main component in the pressure-resistant foam float of is manufactured by the copolymerization of butadiene (BD) and acrylonitrile (AN), and since it gives a polarity to the polymer by-C=N group of the acrylonitrile, provides oil resistance and the rubber elasticity, and raises the glass transition point (Tg). The properties can be adjusted by the change of their copolymerization ratio or the mixture prescriptions. If the content ratio of the acrylonitrile (AN) is 28%, the oil resistance is similar to that of chloroprene rubber, but the

RGP-0237-PCT 5 glass transition point is lowered. If the content ratio is 48%, the oil resistance is considerably improved. But, since the glass transition point is close to normal temperature, it is not appropriate for a rubber usage. Therefore in one exemplary embodiment, the content ratio of the acrylonitrile (AN) is about 28-48%.

Also in one exemplary embodiment, the mixture being added to the NBR as a basic substance may be at a ratio of NBR : mixture (1: 1.2-1. 5). In particular, phenol resin may be added at 39-46 wt% based on the total weight of the mixture to increase the NBR strength, to improve the swelling resistance, and to improve the impact resistance. If the phenol resin is added at less than 39 wt% as the above-mentioned lower limit, the hardness may not be sufficient, and if it is added at more than 46 wt% as the above-mentioned upper limit, the impact resistance may be weak. Thus, in one embodiment, the phenol resin is added in the above-mentioned range.

Also, carbon black has an influence on the size and hardness of cells and largely improves the tear strength, tensile strength, and wear resistance of the float, and in one embodiment, it should be charged in a range of 30-40 wt% for a mutual affinity with other components and an optimum bonding. Also, when its average particle size is 400-500 m, uniform foams smaller than 150, um or less that has been ordinarily applied can be obtained, which may be preferable (see Figure 5). Sulfur increases an elastic force and reduces the residual permanent deformation size, and in one embodiment, it is recommended that the sulfur be charged at 35-43 wt% in terms of composition of the entire mixture and chemical bonding. When the sulfur is composed of particulates with a mesh of 350-450, the inferiority of pores generated in the float can be removed. Thus, the size of the particulates may be important.

In one embodiment, a foaming agent, azodicarbonamide (AC) is added in a range of 6.0-7. 0 wt%, and uniform cells smaller than an existing DPT (N, N'-dinitroso pentamethylene tetramine) can be obtained. If its amount being charged is less than the above-mentioned lower limit, foaming may not be sufficiently caused and the product shape may not be properly formed. If the amount is excessive, foaming may also continuously advance in the subsequent posttreatment process, so that an inferiority may be caused in the size. Thus, the above-mentioned range is exemplary in terms of ideal cell size and minimum residue.

RGP-0237-PCT 6 Also, as proper composition ratios with the above-mentioned components characterized in one exemplary embodiment, zinc oxide, stearic acid, L-7, CZ, and foaming aid are charged in a range of approximately 3.5-5 wt%, 1.0-1. 5 wt%, 0.5-1. 0 wt%, 1.5-2. 0 wt%, and 3.5-4. 5 wt%, respectively.

Ill the exemplary manufacture of the pressure-resistant foam float comprising these constitutional components, a basic substance of NBR may be prepared in a sheet shape by kneading, and phenol resin, carbon black, zinc oxide, stearic acid, sulfur, azodicarbonamide, foaming aid, L-7 of 0.5-1. 0, and CZ powders are well weighed within the above-mentioned range, charged into the sheet-shaped basic substance, and entirely uniformly dispersed and mixed, so that the best chemical bond between the respective raw materials is derived, thereby being able to desired properties. Also, the properties of the textile also become uniform. Thus, for this exemplary embodiment, the selection of the raw materials, the mixture ratios, and the mixture process between the raw materials may be important.

Thereafter, the sheet-shaped textile generated may be passed through a tailoring process for cutting it into an appropriate size and passed through a molding process that vulcanizes and cures the textile tailored.

In the molding process, the primary molding is a step that forms pores in the foam float at a relatively low temperature, and the secondary molding is a step that solidly cures the outer wall of the pores generated in the primary molding and forms it in a desired size and shape. Since even a slight difference in the treatment conditions along with the mixture ratio of the raw materials can change the pressure resistance and the specific gravity of the final float, the above-mentioned temperature range and time may be important (see Figures 1, 2, and 7).

In other words, if the molding temperature is low, foaming is not well realized, so that the foaming rate is low and a float in a non-vulcanized state is formed. Thereby, the hardness and the pressure resistance are lowered, and the specific gravity is high. On the contrary, if the temperature is too high, the pores of the float become large, and the continuous porosity is raised, so that inferiorities are caused during the immersion and pressurization. Therefore, the primary molding is, in one exemplary embodiment, applied at 115-125°C for 800-1,000 sec, and the secondary molding is applied at 160-180°C for 2, 400-2,600 sec.

RGP-0237-PCT 7 Then, in the exemplary pressure-resistant foam float, after the primary and secondary molding processes, the float is posttreated at 60-80°C for 24 h, so that unreacted raw materials are slowly reacted at low temperature as shown in Figure 4, unlike the case of no posttreatment of Figure 3. Thereby, the complete foams are entirely formed. As a result, the crosslinking and the cell wall curing are increased, the hardness is increased, and small and uniform foams can be obtained. Accordingly, the pressure resistance is improved (see Figure 6).

An exemplary pressure-resistant foam float with the above constitution is described through the following application example to make the characteristics be able to be more easily understood, and any person skilled in the corresponding field can understand that the present invention is not limited to it but can be modified and changed within the patent claim range without departing from the scope of the present invention.

In the following application example, percentage (%) is based on weight.

Example 1 Several mixtures comprised of 39% phenol resin, 40% MT (medium thermal) carbon black with a particle size of 450, um, 3.5% zinc oxide, 1.5% stearic acid, 42% sulfur particulates with a mesh of 400,6. 5% azodicarbonamide (AC), 3.5% foaming aid, 0.8% L-7, and 1.7% CZ powders were prepared in advance.

First, NBR at 100 parts by weight was well kneaded, and while discharging it in a sheet state, the mixture of the above-mentioned each container was put on it and uniformly mixed so that the same effect might be exhibited in the same lot.

The above-mentioned mixtures were respectively molded at 120°C for 800 sec to form pores, and one group of the above-mentioned samples was remolded at 170°C for 2,400 sec (samples 1 and 3). Another group was molded at the same temperature for 2,200 sec (sample 4), and another group was molded at the same temperature for 3,000 sec (sample 5), so that pores with desired sizes and shapes were formed.

Then, the molded products of the samples 1,3, 4, and 5 were cooled, and except for the sample 3, the samples 1, 4, and 5 of three groups were posttreated at 60°C for 24 h.

RGP-0237-PCT 8 Apart from it, for comparison, a mixture with the same constitutional components as those of the above-mentioned mixtures except for substituting the MT as a carbon black by the same amount of SRF (semi-reinforcing furnace) with a particle size of 100/mi was prepared, molded in the same matter as that of the above-mentioned sample 1, and posttreated (sample 2).

Of the performances of the molded products obtained, the specific gravity was measured. As a result, the specific gravity was satisfactorily 0.35 or less in all the molded products.

Also, in order to confirm the pressure resistance of each sample and the performances during the immersion, the following methods were applied to each test. The liquid in which the float was actually used was LPG, however a hydraulic test was carried out due to the danger in terms of handling. In the hydraulic test, the weight of the samples was measured, and these samples were put into a hydraulic tester. After the bolt of the tester was completely fastened, the pressure was set to a desired value by slowly pressurizing, and the tester was held for 15 min. Then, the samples were drawn out, and the liquid of the surface was removed. Then, the appearance abnormality and the weight change rate were measured. In an immersion test, the samples were immersed for 72 h into hexane at normal temperature, and the weight change rate was measured. As a result, the results shown in Tables I and II were respectively obtained.

Table I Weight 30 kg/cm2, 15 min 40 kg/cm2, 15 min 50 kg/cm2, 15 min before Weight Change Weight Change Weight (g) Change test (g) (g) rate (g) rate (%) rate (%) (%) Sample 9.2921 9. 2975 0. 06 9. 3009 0. 09 9. 3080 0. 17 1 Sample 9.2903 9. 2963 0. 06 9. 3157 0. 27 9. 3732 0. 89 2 Sample 9.2629 9. 2744 0. 07 9. 2798 0. 13 9. 2898 0. 24 3 Sample 9.2536 9. 2608 0. 07 9. 1917 0. 16 9. 2133 0. 39 4 Sample 5.5997 11. 8944 112. 53 Sample damage Sample damage 5

Test condition: After pressurizing for 15 min in water at normal temperature, the surface liquid was completely removed, and the weight was measured.

(The numerical values of each sample 1-5 were average values of five values each.) Table II Weight before test (g) N-hexane Weight (g) Change rate (%) Sample 1 9. 2760 9. 2902 0. 15 Sample 2 9. 2742 9. 2945 0. 22 Sample 3 9. 2751 9. 2948 0. 21 Sample 4 9. 2704 9. 2666 0. 17 Sample 5 5. 5481 5. 5592 0. 20

* Test condition: After immersing for 72 h in hexane at normal temperature, the surface liquid was removed, and the weight was measured.

(The numerical values of each sample 1-5 were average values of five values each.) From the above results, it could be confirmed that a slight difference in the time and temperature of the posttreatment and molding, the content of the constitutional components, and the particle size of the carbon black had a significant influence on the pressure resistance and the specific gravity. In other words, as shown in Table I and Figure 5, the pressure resistance of the sample 2 was more or less lower than that of the sample 1, and in the sample 3 to which no posttreatment was applied, the weight change rate at high pressure was very severer than that of the sample 1 to which the posttreatment was applied. When the secondary molding temperature was lower than the temperature range being prescribed in the present invention, the pressure resistance was low, while if the secondary molding temperature exceeded the upper limit of the above-mentioned range, product inferiorities were caused.

As mentioned above, according exemplary embodiments of the pressure-resistant foam float, the weight is little changed at a high pressure of 50 kg/cm2 or more, lots of small independent foams exist, and the cell wall strength between the foams is large. Even if the float is immersed over a long term in LPG, since the weight change is little and the specific gravity is about 0.28-0. 35, the float is lighter than the LPG and is always floated on the fuel.

Also, the float can withstand a high pressure of 50 kg/cm2 or more. Thus, this foam float can be optimally used as a foam float for LPG gas.

It will be apparent to those skilled in the art that, while exemplary embodiments have been shown and described, various modifications and variations can be made to the apparatus and method for self-compensation of a laser tracker disclosed herein without departing from the spirit or scope of the invention. Accordingly, it is to be understood that the various embodiments have been described by way of illustration and not limitation.