Claims:WE CLAIM:

1. An elastomer composition to increase a load bearing capacity and a compressibility for a desired stiffness of a polymeric spring formed by the elastomer composition, the elastomer composition comprising:
- a synthetic elastomer 100 phr in weight;
- a metallic oxide cross linking agent ranging from 5 to 7 phr in weight;
- an acid-schwinger ranging from 4 to 5 phr in weight;
- an internal lubricator ranging from 0.5 to 1 phr in weight;
- an anti-oxidant ranging from 0.75 to 1.5 phr in weight;
- an anti-ozonant ranging from 0.75 to 1.5 phr in weight;
- a protective wax ranging from 0.4 to 1.2 phr in weight;
- a reinforcing carbon black ranging from 7 to 70 phr in weight;
- a semi-reinforcing filler ranging from 9 to 33 phr in weight;
- a Plasticizer ranging from 6 to 39 in weight;
- a softener ranging from 0.5 to 3 phr in weight;
- a coupling agent ranging from 1 to 3 phr in weight;
- an adhesion promoter ranging from 2.3 to 3.5 phr in weight;
- a stabilizer ranging from 0.5 to 0.9 phr in weight
- a co-crosslinking agent ranging from 0.3-0.5 phr in weight;
- anti-scorching agent ranging from 0.1 to 0.4 phr in weight; and
- anti retarder agent ranging from 0.1 to 0.4 phr in weight.

2. The elastomer composition according to claim 1, wherein the synthetic elastomer is Poly-chloroprene.

3. The rubber composition according to claim 1, wherein the metallic oxide cross linking agent is ZnO.

4. The elastomer composition according to claim 1, wherein the acid-schwinger is MgO.

5. The elastomer composition according to claim 1, wherein the internal lubricator is stearic acid.

6. The elastomer composition according to claim 1, wherein the antioxidant is Pilflex-13.

7. The elastomer composition according to claim 1, wherein the antiozonant is selected from a group consisting of Vulcanox, Navguard 445.

8. The elastomer composition according to claim 1, wherein the protective wax is selected from a group consisting of MC, Antilux11.

9. The elastomer composition according to claim 1, wherein the Reinforcing Carbon Black structure grades consists of equal proportions of HAF (N339), FEF (N550) and MT (N990).

10. The elastomer composition according to claim 1, wherein the semi-reinforcing filler is selected from precipitated silica and fumed silica.

11. The elastomer composition according to claim 1, wherein the plasticizer is selected from a group consisting of Aromatic oil and DOP oil.

12. The elastomer composition according to claim 1, wherein the coupling agent is Si69/ TSPET.

13. The elastomer composition according to claim 1, wherein the adhesion promoter is HMMA/ DBC and one of C.I. or wood resin and RF/ RK/ RS.

14. The elastomer composition according to claim 1, wherein the stabilizer is selected from a group consisting of NA22 and ETU.

15. The elastomer composition according to claim 1, wherein the co-crosslinking agent is selected from a group consisting of MBT and MBTS.

16. The elastomer composition according to claim 1, wherein the anti-scorching agent is PVI.

17. The elastomer composition according to claim 1, wherein the anti-retarding agent is PVS.

18. The elastomer composition according to claim 1, is moulded in the form of a cylindrical structure to further increase the load bearing capacity of the polymeric spring.

19. The elastomer composition according to claim 18, wherein the cylindrical structure is made tapered to have a concave shape in a middle portion along an axial length of the cylindrical structure.

20. The elastomer composition according to claim 18, wherein the cylindrical structure is provided with annular ring structures on its surface along an axial length of the cylindrical structure, such that the annular rings are perpendicular to the axis of the cylindrical structure.

21. The elastomer composition according to claim 1, wherein the elastomer composition, the elastomer composition comprises:
- a synthetic elastomer 100 phr in weight;
- a metallic oxide cross linking agent 5 phr in weight;
- an acid-schwinger 4 phr in weight;
- an internal lubricator 0.5 phr in weight;
- an anti-oxidant 0.95 phr in weight;
- an anti-ozonant 0.95 phr in weight;
- a protective wax 0.5 phr in weight;
- a reinforcing carbon black 12 phr in weight;
- a semi-reinforcing filler 10 phr in weight;
- a Plasticizer 10 in weight;
- a softener 0.5 phr in weight;
- a coupling agent 1 phr in weight;
- an adhesion promoter 3 phr in weight;
- a stabilizer 0.6 phr in weight
- a co-crosslinking agent 0.4 phr in weight;
- anti-scorching agent 0.15 phr in weight; and
- anti retarder agent 0.15 phr in weight.

, Description:FIELD OF THE INVENTION

[001] The present invention relates in general to polymeric springs and more particularly, to a elastomer or rubber composition for improving the properties of a polymeric spring.

BACKGROUND OF THE INVENTION

[002] Springs are widely used in many industries for their dynamic and mechanical properties. For example, large springs are used in the automotive industry and smaller springs are used for electronic and mechanical devices. In most of the applications, steel springs are used because of their quality of fabrication, stiffness, strength, and mass production ability. However, steel springs tend to be relatively heavier and disadvantageous to be used in certain applications where weight and size are a limitation. For example, in applications such as automobiles, airplanes, and railway cars, it is critical to reduce the weight of various components to reduce the overall weight and compactness of the system.

[003] Other drawbacks of steel springs include their limited corrosion resistance, fatigue strength, high coefficient of thermal expansion, magnetic properties, and electrically conductive nature which can pose problems in application where these properties are undesired.

[004] One approach to obviate some of the drawbacks of steel springs is to form single helical springs from composite materials. Single helical springs formed of composite materials have been developed, to take advantage of light weight characteristics of plastic materials. However, these types of springs fail to provide sufficient stiffness and compressibility to replace steel springs. A single helical spring is a torsion bar wrapped into a helical form, and the stiffness of a torsion bar is determined by the shear modulus of elasticity of the material. As the shear modulus of composite materials is much smaller than the shear modulus of steel, the stiffness of a single helical composite spring is much less than that of a single helical spring made of steel.

[005] Other forms of elastomer springs are also known for suspension systems, these generally comprise a block of rubber generally of cylindrical form having opposed flat end faces which in use are subjected to compression. In order to obtain required compression characteristics for rubber springs of substantial length, it is usually arranged that the spring should compress in such manner as to form a plurality of bulges or convolutions along its length. This allows the compressive, and other forces in the material, to be distributed along the length of the spring, rather than being over-much concentrated in one region. For this purpose the exterior of the rubber spring has commonly been provided with circumferential depressions or waists at one or more transverse planes along the length of the spring.

[006] Polymeric springs (also refereed in this document as ‘elastomer springs’) have different spring properties based on the rubber composition used to make the elastomer springs. Typically, polymeric springs provide force/ deflection curves which vary depending on the material or specific hardness and configuration of the spring. For a polymeric spring, the term "stiff" refers to that portion of the force versus deflection curve that has relatively high spring rate, whether constant slope or generally rising rate and is characteristic of progressively increasing resistance to compressive deformation. Similarly, the term "soft" refers to and is characteristic of relatively lower spring rate or less resistance to compressive deformation, whether increasing, decreasing or none at all.

[007] Polymeric compression/ tension springs pose challenges in controlling the spring rate. Stiffness or hardness is reflected by the load-deflection curve of a polymeric spring. A high spring rate is identified with stiffness of the spring being the relationship of a load and the deflection caused by it as exemplified by the tangent to the deflection curve at that particular load. A high spring rate is therefore denoted by a steep tangent, a steep deflection curve and a hard spring; conversely a low spring rate denotes a soft spring i.e. a greater deflection.

[008] The ‘load bearing capacity’ of a polymeric spring is the maximum load it can handle without losing its elastic properties during static or dynamic load, and the ‘compressibility’ is the ability of the polymeric spring to change in dimensions or deflection on application of force on the polymeric spring without losing its elastic properties. A polymeric spring which can undergo large change in dimensions on application of force is said to have good compressibility. The stiffness is the slope of the force-deflection curve at any point.

[009] Referring to Fig. 1, a representative force-deflection curve for polymeric springs made of two different elastomer compositions R1, R2 and steel spring ‘I’ ‘S’ is shown. Different elastomer compositions R1 and R2 were made and cylindrical models of same shape and size are using the elastomer compositions R1 and R2 to have all initial conditions same. Now the elastomer blocks R1 and R2 were compressed by applying force and the deflection is measured. is made the curve R1 shows steep increase in force with the deflection almost constant, the spring is stiff which means t it has good load bearing capacity but low compressibility. The curve R2 shows another polymeric spring made by second elastomer composition, here the deflection increases without much change in force after a certain time. The spring made by R2 is soft, which means though it has good compressibility, but the load bearing capacity is bad.

[0010] The curve ‘S’ is a straight line showing the linear spring such as steel spring behaviour in which the force and deflection is proportional and predictable, which is not the case with R1 and R2 springs. It is desirable to achieve the steel spring stiffness profile by using elastomer composition polymeric spring.

[0011] For some applications high load bearing capacity with high compressibility in a spring is required within a small space, which is not possible by use of steel springs because of its huge dimensions and weight. For high load bearing capacity in order to obtain lower spring rate and higher deflection, the length of steel spring need to be increased substantially resulting in a laterally unstable and impractical structure.

[0012] In view of the limitations inherent in the available polymeric springs, there exists a need for an improved elastomer composition for making the polymeric spring having desired load-deflection characteristics, which overcomes the disadvantages of the prior art and which can be used in a simple, compact, cost effective, reliable, secure and environmentally friendly manner.

[0013] The present invention fulfils this need and provides further advantages as described in the following summary.

SUMMARY OF THE INVENTION

[0014] In view of the foregoing disadvantages inherent in the prior arts, the general purpose of the present invention is to provide an improved combination of convenience and utility, to include the advantages of the prior art, and to overcome the drawbacks inherent therein.

[0015] A primary objective of the present invention is to provide a elastomer composition for making a polymeric spring which is simple and cost effective.

[0016] In one aspect, the present invention provides a elastomer composition to increase a load bearing capacity and a compressibility for a desired stiffness profile for a polymeric spring formed by the elastomer composition. The elastomer composition comprises synthetic elastomer, metallic oxide cross linking agent, acid-schwinger, internal lubricator, anti-oxidant, anti-ozonant, protective wax, reinforcing carbon black structure grades, semi-reinforcing filler, Plasticizer, softener, coupling agent, adhesion promoter, stabilizer, co-crosslinking agent, anti-scorching agent and anti-retarder agent.

[0017] In another aspect of the present invention, the synthetic elastomer is Poly-chloroprene.

[0018] In yet another aspect of the present invention the metallic oxide cross linking agent is ZnO.

[0019] In a further aspect of the present invention, the acid-schwinger is MgO and the internal lubricator is stearic acid.

[0020] In another aspect of the present invention, the antioxidant is Pilflex-13 and the antiozonant is selected from a group consisting of Vulcanox, Navguard 445.

[0021] In yet another aspect of the present invention, the protective wax is selected from a group consisting of Micro Crystalline, Antilux11.

[0022] In a further aspect of the present invention, the Reinforcing Carbon Black structure grades consists of equal proportions of HAF (N339), FEF (N550) and MT (N990).

[0023] In one aspect of the present invention, the semi-reinforcing filler is selected from precipitated silica and fumed silica.

[0024] In another aspect of the present invention, the plasticizers are selected from a group consisting of Aromatic oil and DOP oil.

[0025] In yet another aspect of the present invention, the coupling agent is Si69/ TESPT.

[0026] In a further aspect of the present invention, the adhesion promoter is HMMA and one of C.I. and wood resin.

[0027] In another aspect of the present invention, the stabilizer is selected from a group consisting of NA22 and ETU.

[0028] In one aspect of the present invention, the co-crosslinking agent is selected from a group consisting of MBT and MBTS.

[0029] In another aspect of the present invention, the anti-scorching agent is PVI and the anti-retarding agent is PVS.

[0030] In one aspect of the present invention, the polymeric spring is moulded in the form of hollow or solid cylindrical structure to further increase the load bearing capacity of the polymeric spring.

[0031] In another aspect of the present invention, the cylindrical structure is made tapered to have a concave shape in a central portion along an axial length of the cylindrical structure.

[0032] In yet another aspect of the present invention, the cylindrical structure is provided with annular ring structures on its surface along an axial length of the cylindrical structure, such that the annular rings are perpendicular to the axis of the cylindrical structure.

[0033] These together with other aspects of the invention, along with the various features of novelty that characterize the invention, are pointed out with particularity in the description annexed here to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and the specific objects attained by its uses, reference should be made to the accompanying drawings and descriptive matter in which there are illustrated exemplary embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The advantages and features of the present invention will become better understood with reference to the following more detailed description taken in conjunction with the accompanying drawings in which:

[0035] FIG. 1 illustrates a representative force-deflection curve for polymeric springs made of different elastomer compositions R1, R2 and Ideal or steel spring ‘S’; according to state of the art;

[0036] FIG. 2 illustrates a force-deflection curve of metallic spring ‘S’ and polymeric spring ‘RF-1’ made by elastomer composition of the present invention, according to one embodiment of the present invention;

[0037] FIG. 3 illustrates a schematic diagram of a polymeric spring made by elastomer composition of the present invention, according to one embodiment of the present invention;

[0038] FIG. 4 illustrates a schematic diagram of a polymeric spring made by elastomer composition of the present invention, according to another embodiment of the present invention; and

[0039] FIG. 5 illustrates a schematic diagram of a polymeric spring made by elastomer composition of the present invention, according to yet another embodiment of the present invention;

[0040] Like reference numerals refer to like parts throughout the several views of the drawings.

DETAILED DESCRIPTION OF THE DRAWINGS

[0041] In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be apparent, however, to one skilled in the art that the present invention may be practiced without these specific details.

[0042] As used herein, the term ‘plurality’ refers to the presence of more than one of the referenced item and the terms ‘a’, ‘an’, and ‘at least’ do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced item.

[0043] Reference herein to “one embodiment” or “another embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the invention. The appearances of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments mutually exclusive of other embodiments. Further, the diagrams representing one or more embodiments of the invention do not inherently indicate any particular order nor imply any limitations in the invention.

[0044] The elastomer composition of the present invention is used to increase a load bearing capacity and a compressibility for a desired stiffness profile for a polymeric spring formed by the elastomer composition. The elastomer composition comprises synthetic elastomer 100 phr in weight, metallic oxide cross linking agent ranging from 5 to 7 phr in weight, an acid-schwinger ranging from 4 to 5 phr in weight, an internal lubricator ranging from 0.5 to 1 phr in weight, an anti-oxidant ranging from 0.75 to 1.5 phr in weight, an anti-ozonant ranging from 0.75 to 1.5 phr in weight, a protective wax ranging from 0.4 to 1.2 phr in weight, a reinforcing carbon black ranging from 7 to 70 phr in weight, a semi-reinforcing filler ranging from 9 to 33 phr in weight, a Plasticizer ranging from 6 to 39 in weight, a softener ranging from 0.5 to 3 phr in weight, a coupling agent ranging from 1 to 3 phr in weight, an adhesion promoter ranging from 2.3 to 3.5 phr in weight, a stabilizer ranging from 0.5 to 0.9 phr in weight, a co-crosslinking agent ranging from 0.3-0.5 phr in weight, anti-scorching agent ranging from 0.1 to 0.4 phr in weight and anti-retarder agent ranging from 0.1 to 0.4 phr in weight.

[0045] The above elastomer composition of the present invention provides Shore °A Hardness ranging from 30-90.

[0046] Synthetic elastomer is the base polymer resin of high molecular weight monomers/ oligomers chains to polymerization of matrix for polymer backbone formations. In one embodiment of the present invention, the synthetic elastomer used is Poly-chloroprene (CR), other synthetic polymer resin like NBR/ H-NBR/ X-NBR, SBR, BR/ PBR, IIR, EPM; EPDM, CO; ECO, AEM, ACM, CSM, EVA, SL/ MQ; PMQ, VMQ; PVMQ, FVMQ, FKM, FFKM, TH/ T, TF/ FEP, CP/ PU, AU;EU, blend with each other or with NR or mix with composite material in compatible ratio along with suitable crosslink sulphur or metal oxide or peroxide or irradiation curing system), In one preferred embodiment of the present invention, the synthetic rubber is Neoprene (CR) elastomer.

[0047] The cross-linking agent is used to crosslink two polymer chains. In one embodiment of the present invention, the metallic oxide cross linking agent is ZnO.

[0048] In one embodiment of the present invention, the acid-Schwinger used is MgO and the internal lubricator used is stearic acid.

[0049] The function of protective agents such as antioxidant and antiozonants is to protect the polymeric spring from environmental Oxygen and Ozone attack on unsaturated double bonds or free radical/ free ions present into polymer matrix during service life as non-staining/ staining mode. In one embodiment of the present invention, the antioxidant used is Pilflex-13.

[0050] In one preferred embodiment of the present invention, the antiozonant is selected from a group consisting of Vulcanox, Navguard 445.

[0051] The protective wax is used in the elastomer composition to protect the polymer from external harsh environment, by forming a thin masking layer on the polymer matrix material. In one embodiment of the present invention, the protective wax is selected from a group consisting of M.C., Antilux11.

[0052] The adhesion promoter agent enhances the adhesion/ tackifier properties of polymer matrix for adhesiveness with metal/ other rigid substrates. In one embodiment of the present invention, the adhesion promoter agent is selected from HMMA/ DBC and one of C.I. or wood resin and RF/ RK/ RS.

[0053] The reinforcing carbon black is used to enhance/ reinforce the mechanical strength/ holding properties of polymer matrix around 4 to 5 times of Base polymer matrix. In one embodiment of the present invention, the Reinforcing Carbon Black structure grades consists of equal proportions of HAF (N339), FEF (N550) and MT (N990).

[0054] The semi-reinforcing filler is added in the elastomer composition to incorporate viscosity control, increase the volume and rigidity of polymer material and reduce the cost. In one embodiment of the present invention, the semi-reinforcing filler is selected from precipitated silica and fumed silica.

[0055] The plasticizers is used as lubricant for ease of processability by adjusting the viscosity and enhances the flexibility/softness of the polymer matrix by parallel short chains formations. In one embodiment of the present invention, the plasticizer is selected from a group consisting of Aromatic oil and DOP Oil.

[0056] The process improving agents are added for enhancing the processability, dimensional stability, glassiness/ non-stickiness, flow property of polymer matrix during the process of polymer formation. In one embodiment of the present invention, the coupling agent used is Si69/ TESPT and the stabilizer is selected from a group consisting of NA22 and ETU.

[0057] In one embodiment of the present invention, the co-crosslinking agent is selected from a group consisting of MBT and MBTS.

[0058] The anti-scorching agent is a pre-vulcanization inhibitor. It provides predictable scorch control in most Sulphur and other vulcanization and improved quality performance through marginal storage or stock recovery, single-stage mixing, higher processing and/ or curing temperatures. It is used to control the reaction initiation rate for material storage safety and quality production before/ during processing. In one embodiment of the present invention, the anti-scorching agent is PVI.

[0059] The anti-retarder agent is a post vulcanization stabilizer, A single-stage mixing, higher processing and/ or curing temperatures, It is used to control the reaction termination rate for optimal saturation for quality production and prevent reversion/ degradation during processing/ latent curing. In one embodiment of the present invention, the elastomer composition includes anti- retarder agent as PVS.

[0060] In one preferred embodiment of the present invention, the elastomer composition includes synthetic elastomer 100 phr in weight, a metallic oxide cross linking agent 5 phr in weight, an acid-schwinger 4 phr in weight, an internal lubricator 0.5 phr in weight, an anti-oxidant 0.95 phr in weight, an anti-ozonant 0.95 phr in weight, a protective wax 0.5 phr in weight, a reinforcing carbon black 12 phr in weight, a semi-reinforcing filler 10 phr in weight, a Plasticizer 10 in weight, a softener 0.5 phr in weight, a coupling agent 1 phr in weight, an adhesion promoter 3 phr in weight, a stabilizer 0.6 phr in weight, a co-crosslinking agent 0.4 phr in weight, anti-scorching agent 0.15 phr in weight and anti-retarder agent 0.15 phr in weight.

[0061] The above elastomer composition of the present invention provides Shore °A Hardness of 45 with a tolerance of 5 on both sides.

[0062] The elastomer composition of the present invention (also referred in the present description as ‘RF’) is tested by making a sample and tested as per the ASTM standards to obtain a stress-strain curve. Cylindrical model having same shape and size like the models of the elastomer compositions R1, R2 is made and all initial conditions are kept same. Now the elastomer models made from RF is compressed/ tension by applying force and the deflection is measured and the curve is plotted. The sample is tested for iterative loading and one mean curve is selected to represent the properties of the elastomer composition in the form of stress-strain curve ‘RF’ as shown in FIG.1. It is observed that the elastomer composition of the present invention ‘RF’ gives better stiffness profile and better compressibility as compared to the elastomer compositions ‘R1’, ‘R2’ and is much near to the Ideal/ steel material profile ‘S’.

[0063] This elastomer composition ‘RF’ is used to make a polymeric spring. The stress-strain curve obtained is fed as property of material into a Finite Element Analysis simulation. In one embodiment of the present invention, the polymeric spring is moulded in the form of a cylindrical structure as shown in FIG. 3 to further increase the load bearing capacity of the polymeric spring. A cylindrical shaped hollow & solid polymeric spring is made from using the properties of elastomer composition ‘RF’ and load and boundary conditions are applied on it and analysed to obtain the force deflection curve. It is observed that the polymeric spring formed by elastomer composition of the present invention ‘RF-1’ gives better stiffness profile and is much closer to the steel spring profile ‘S’ as shown in the graph of FIG. 2.

[0064] The cylindrical shape of the polymeric spring is further optimized to achieve required dimensions and properties for the polymeric spring made from the elastomer composition of the present invention. In one embodiment of the present invention, the cylindrical structure is made tapered to have a concave shape in a central portion along an axial length of the cylindrical structure as shown in FIG.4. In another embodiment of the present invention, the cylindrical structure is provided with annular ring structures on its surface along an axial length of the cylindrical structure, such that the annular rings are perpendicular to the axis of the cylindrical structure as shown in FIG.5.

[0065] It is to be noted that the shapes of the polymeric spring made from the elastomer composition of the present invention as shown in FIGs. 3,4 and 5 are some of the shapes and are not limitations for the polymeric spring shapes. Though not disclosed, but a number of other shapes with or without additions of some metallic or composite parts as reinforcement is also part of the present invention if the polymeric spring is made with the elastomer composition of the present invention.

[0066] The polymeric spring made by elastomer composition of the present invention provide advantages as below:
- Reduced Weight: The weight of the polymeric spring is reduced up to 50% as compared to the steel spring.
- Better compressibility: The elastomer composition of the present invention has made it possible to use rubber to make a spring which can provide compressibility up to 60% under heavy load applications
- Corrosion Free: The polymeric spring is corrosion free for entire life of the spring
- Field Repairable Assemblies: Safe and convenient installation of polymeric makes the system repairable on site
- Stable geometries: The optimized shapes of the polymeric springs provide stable geometry with higher compressibility and reduced bulging
- Extrusion based manufacturing: The shapes of the springs can be produced by extrusion process for reduced manufacturing cost

[0067] Although a particular exemplary embodiment of the invention has been disclosed in detail for illustrative purposes, it will be recognized to those skilled in the art that variations or modifications of the disclosed invention, including the rearrangement in the configurations of the parts, changes in steps and their sequences and similar function ingredients or skipping the one or more parts may be possible. Accordingly, the invention is intended to embrace all such alternatives, modifications and variations as may fall within the spirit and scope of the present invention.

[0068] The foregoing descriptions of specific embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teaching.

[0069] The foregoing description of the specific embodiments will so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the appended claims.