阅读说明：本技术 一种长叶柄复合材料叶片的制作模具 (Manufacturing die for long-petiole composite material blade ) 是由 李冬冬 曹孝君 侯冬梅 刘嘉 宋丽丽 于 2020-11-20 设计创作，主要内容包括：本发明公开了一种长叶柄复合材料叶片的制作模具,叶柄模具在叶柄上下中心的平面分割成上、下叶柄模,叶柄模腔分割成上、下叶柄模腔；叶身模具在叶身前后缘最大轮廓线的连线形成的曲面分割成上、下叶身模,叶身模腔分割成上、下叶身模腔；上、下叶柄模、上、下叶身模的前、后壁上设置有至少一个启模机构和多个固定机构,合模后,二者由固定机构固定在一起,定位销Ⅰ和Ⅱ分别位于定位孔Ⅰ和Ⅱ、定位孔Ⅲ和Ⅳ内；叶柄和叶身模具组装后,半圆凸台插在半圆凹槽内,由位于定位销孔和定位销槽内的定位销定位,由固定在多对螺栓孔内的螺栓固定。本发明结构简单,制作容易、周期短,制作成本低,其制造的叶片易脱模,精确度高,废品率低。(The invention discloses a manufacturing die of a long petiole composite material blade, wherein the petiole die is divided into an upper petiole die and a lower petiole die on the plane of the upper center and the lower center of a petiole, and a petiole die cavity is divided into an upper petiole die cavity and a lower petiole die cavity; the blade body mould is divided into an upper blade body mould and a lower blade body mould on a curved surface formed by the connection line of the maximum contour lines of the front edge and the rear edge of the blade body, and the blade body mould cavity is divided into an upper blade body mould cavity and a lower blade body mould cavity; the front and rear walls of the upper and lower blade handle molds, the upper and lower blade body molds are provided with at least one mold opening mechanism and a plurality of fixing mechanisms, after the molds are closed, the mold opening mechanism and the fixing mechanisms are fixed together by the fixing mechanisms, and the positioning pins I and II are respectively positioned in the positioning holes I and II and the positioning holes III and IV; after the petiole and the blade body are assembled, the semicircular lug bosses are inserted into the semicircular grooves, are positioned by the positioning pins positioned in the positioning pin holes and the positioning pin grooves, and are fixed by the bolts fixed in the plurality of pairs of bolt holes. The invention has simple structure, easy manufacture, short period and low manufacture cost, and the manufactured blade is easy to demould, high in precision and low in rejection rate.)

1. The utility model provides a preparation mould of long petiole combined material blade which characterized in that: comprises a petiole mould and a blade body mould;

the petiole die comprises an upper petiole die and a lower petiole die; the petiole die cavity is completely matched with the petiole profile and is divided into an upper petiole die and a lower petiole die on the plane of the upper center and the lower center of the petiole, and the petiole die cavity is divided into an upper petiole die cavity and a lower petiole die cavity; the opposite surfaces of the upper and lower blade handle dies are respectively provided with at least one positioning hole I and at least one positioning hole II, and after die assembly is carried out, the positioning pin I is positioned in the positioning holes I and the positioning holes II; the front wall and the rear wall of the upper petiole die and the lower petiole die are provided with at least one stripping mechanism and a plurality of fixing mechanisms uniformly, and the stripping mechanism and the fixing mechanisms are fixed together by the fixing mechanisms after die assembly;

the blade body mould comprises an upper blade body mould and a lower blade body mould; the blade body mould cavity is completely matched with the blade body profile, and is divided into an upper blade body mould cavity and a lower blade body mould cavity on a curved surface formed by the connecting line of the maximum contour lines of the front edge and the rear edge of the blade body; the end walls of the upper blade body mould and the lower blade body mould at one end of the blade handles are provided with semicircular accommodating grooves of the blade handles, and the semicircular accommodating grooves can be combined into an accommodating groove which is completely matched with the profile of the blade handles; at least one positioning hole III and at least one positioning hole IV are respectively arranged on the opposite surfaces of the upper blade body die and the lower blade body die, and after die assembly is carried out, a positioning pin II is positioned in the positioning holes III and IV; the front wall and the rear wall of the upper blade body mould and the lower blade body mould are provided with at least one mould opening mechanism and a plurality of fixing mechanisms uniformly, and after the moulds are closed, the mould opening mechanism and the fixing mechanisms are fixed together by the fixing mechanisms;

the upper blade body die and the lower blade body die are respectively provided with a semicircular boss around the outer side of the excircle of the semicircular accommodating groove on the end wall at one end of the blade handle; the upper and lower blade handle molds are respectively provided with semicircular grooves matched with the semicircular bosses on the end walls opposite to the upper and lower blade body molds; a plurality of pairs of bolt holes, positioning pin holes on the lower blade handle die and positioning pin grooves on the lower blade body die are arranged on the opposite surfaces of the upper and lower blade handle dies and the upper and lower blade body dies; after the petiole and the blade body are assembled, the semicircular lug bosses are inserted into the semicircular grooves, are positioned by the positioning pins positioned in the positioning pin holes and the positioning pin grooves, and are fixed by the bolts fixed in the plurality of pairs of bolt holes.

2. The mold for making a long petiole composite blade according to claim 1, wherein: the blade body mould also comprises cutting blocks I and II matched with the molded surfaces of the leading edge and the trailing edge of the end surface of the blade root and a cutting block III matched with the molded surface of the tip end surface of the blade; the lower blade body die is provided with grooves I and II matched with the cutting blocks I and II on two sides of a semicircular accommodating groove on the upper end face of the end wall at one end of the blade handle respectively, and a groove III matched with the cutting block III is arranged on the upper end face of the end wall at the other end of the blade handle; after the die is closed, the grooves I, II and III are blocked by the cutting blocks I, II and III between the upper blade body die and the lower blade body die.

3. The mold for making a long-petiole composite blade according to claim 1 or 2, wherein: the mold opening mechanism comprises an upper angular plate opening module fixed on the front or rear walls of the upper petiole mold and the upper blade body mold by screws, a lower angular plate opening module fixed on the corresponding positions on the front or rear walls of the lower petiole mold and the lower blade body mold by screws, and a mold opening long bolt; the upper corner-shaped plate opening module is provided with a threaded hole matched with the long bolt for opening the mould; the mold opening long bolt is in threaded connection with the threaded hole of the upper corner plate opening module, and the lower end of the mold opening long bolt is positioned on the upper end face of the lower corner plate opening module.

4. The mold for making a long petiole composite blade according to claim 3, wherein: the fixing mechanism comprises an upper angle plate pressurizing block fixed on the front or rear wall of the upper petiole die and the upper blade body die by screws, and a lower angle plate pressurizing block, a pressurizing long bolt and a nut which are fixed on the corresponding positions on the front or rear wall of the lower petiole die and the lower blade body die by screws; the upper and lower angular plate pressurizing blocks are provided with unthreaded holes, and nuts are welded and fixed at the lower ends of the unthreaded holes on the lower end surfaces of the lower angular plate pressurizing blocks; the long pressurizing bolt penetrates through the unthreaded holes of the upper and lower angular plates and the pressing block and is then in threaded connection with the nut.

5. The mold for making a long petiole composite blade according to claim 4, wherein: and positioning sleeves I, II, III and IV and positioning pin sleeves are arranged in the positioning holes I, II, III and IV, the positioning pin holes and the positioning pin grooves of the upper and lower blade handle molds and the upper and lower blade body molds.

6. The mold for making a long-petiole composite blade according to claim 1 or 2, wherein: the fixing mechanism comprises an upper angle plate pressurizing block fixed on the front or rear wall of the upper petiole die and the upper blade body die by screws, and a lower angle plate pressurizing block, a pressurizing long bolt and a nut which are fixed on the corresponding positions on the front or rear wall of the lower petiole die and the lower blade body die by screws; the upper and lower angular plate pressurizing blocks are provided with unthreaded holes, and nuts are welded and fixed at the lower ends of the unthreaded holes on the lower end surfaces of the lower angular plate pressurizing blocks; the long pressurizing bolt penetrates through the unthreaded holes of the upper and lower angular plates and the pressing block and is then in threaded connection with the nut.

7. The mold for making a long petiole composite blade according to claim 6, wherein: and positioning sleeves I, II, III and IV and positioning pin sleeves are arranged in the positioning holes I, II, III and IV, the positioning pin holes and the positioning pin grooves of the upper and lower blade handle molds and the upper and lower blade body molds.

8. The mold for making a long petiole composite blade according to claim 3, wherein: and positioning sleeves I, II, III and IV and positioning pin sleeves are arranged in the positioning holes I, II, III and IV, the positioning pin holes and the positioning pin grooves of the upper and lower blade handle molds and the upper and lower blade body molds.

9. The mold for making a long-petiole composite blade according to claim 1 or 2, wherein: and positioning sleeves I, II, III and IV and positioning pin sleeves are arranged in the positioning holes I, II, III and IV, the positioning pin holes and the positioning pin grooves of the upper and lower blade handle molds and the upper and lower blade body molds.

Technical Field

The invention belongs to the technical field of long-petiole composite material blade manufacturing, and relates to a manufacturing die of a long-petiole composite material blade.

Background

The blade is used as an important part in a cooling fan, the types of the blade are more and more, the structure is more and more complex, and the requirements on the production and the processing of the blade are more and more high. The mould is as the important instrument of production blade, its structure is also more and more complicated, blade mould in the past is when designing, the phenomenon that the blade shaping can appear expanding in the mould is considered, so the design has the loose piece on the mould, before the blade demolding, take out the loose piece is whole, just so can be with the whole drawing of patterns of blade, the blade drawing of patterns is loaded down with trivial details, die fixing and drawing of patterns are all very complicated, the cycle length, the blade preparation time is long, and because the loose piece is more, it is high to require preparation cooperation precision, in case the error is great, cause the blade preparation precision poor, the rejection rate is high. The die can be designed and processed in a long time, and the later die maintenance is time-consuming and labor-consuming, so that the production cost of the product is greatly improved. The existing blade develops towards the direction of light weight and good rigidity, a composite long petiole blade appears, and for the composite long petiole blade, a petiole and a blade die are manufactured separately, so that the manufacturing mode is more complex.

Disclosure of Invention

The invention aims to solve the problems in the prior art and provide a mold for manufacturing a long-petiole composite material blade, which has the advantages of simple structure, easiness in manufacturing, short manufacturing period, low manufacturing cost, easiness in demolding of the manufactured blade, high accuracy and low rejection rate.

In order to achieve the purpose, the technical solution of the invention is as follows: a manufacturing mold of a long-petiole composite material blade comprises a petiole mold and a blade body mold;

the petiole die comprises an upper petiole die and a lower petiole die; the petiole die cavity is completely matched with the petiole profile and is divided into an upper petiole die and a lower petiole die on the plane of the upper center and the lower center of the petiole, and the petiole die cavity is divided into an upper petiole die cavity and a lower petiole die cavity; the opposite surfaces of the upper and lower blade handle dies are respectively provided with at least one positioning hole I and at least one positioning hole II, and after die assembly is carried out, the positioning pin I is positioned in the positioning holes I and the positioning holes II; the front wall and the rear wall of the upper petiole die and the lower petiole die are provided with at least one stripping mechanism and a plurality of fixing mechanisms uniformly, and the stripping mechanism and the fixing mechanisms are fixed together by the fixing mechanisms after die assembly;

the blade body mould comprises an upper blade body mould and a lower blade body mould; the blade body mould cavity is completely matched with the blade body profile, and is divided into an upper blade body mould cavity and a lower blade body mould cavity on a curved surface formed by the connecting line of the maximum contour lines of the front edge and the rear edge of the blade body; the end walls of the upper blade body mould and the lower blade body mould at one end of the blade handles are provided with semicircular accommodating grooves of the blade handles, and the semicircular accommodating grooves can be combined into an accommodating groove which is completely matched with the profile of the blade handles; at least one positioning hole III and at least one positioning hole IV are respectively arranged on the opposite surfaces of the upper blade body die and the lower blade body die, and after die assembly is carried out, a positioning pin II is positioned in the positioning holes III and IV; the front wall and the rear wall of the upper blade body mould and the lower blade body mould are provided with at least one mould opening mechanism and a plurality of fixing mechanisms uniformly, and after the moulds are closed, the mould opening mechanism and the fixing mechanisms are fixed together by the fixing mechanisms;

the upper blade body die and the lower blade body die are respectively provided with a semicircular boss around the outer side of the excircle of the semicircular accommodating groove on the end wall at one end of the blade handle; the upper and lower blade handle molds are respectively provided with semicircular grooves matched with the semicircular bosses on the end walls opposite to the upper and lower blade body molds; a plurality of pairs of bolt holes, positioning pin holes on the lower blade handle die and positioning pin grooves on the lower blade body die are arranged on the opposite surfaces of the upper and lower blade handle dies and the upper and lower blade body dies; after the petiole and the blade body are assembled, the semicircular lug bosses are inserted into the semicircular grooves, are positioned by the positioning pins positioned in the positioning pin holes and the positioning pin grooves, and are fixed by the bolts fixed in the plurality of pairs of bolt holes.

Further preferably, the blade body mould also comprises cutting blocks I and II matched with the profiles of the leading edge and the trailing edge of the end surface of the blade root and a cutting block III matched with the profile of the tip end surface of the blade; the lower blade body die is provided with grooves I and II matched with the cutting blocks I and II on two sides of a semicircular accommodating groove on the upper end face of the end wall at one end of the blade handle respectively, and a groove III matched with the cutting block III is arranged on the upper end face of the end wall at the other end of the blade handle; after the die is closed, the grooves I, II and III are blocked by the cutting blocks I, II and III between the upper blade body die and the lower blade body die. The presence of the cutting blocks I, II and III makes the upper and lower blade body moulds easier to demould.

Further preferably, the mold opening mechanism comprises an upper angular plate opening module fixed on the front or rear wall of the upper petiole mold and the upper blade body mold by screws, a lower angular plate opening module fixed on the corresponding position on the front or rear wall of the lower petiole mold and the lower blade body mold by screws, and a mold opening long bolt; the upper corner-shaped plate opening module is provided with a threaded hole matched with the long bolt for opening the mould; the mold opening long bolt is in threaded connection with the threaded hole of the upper corner plate opening module, and the lower end of the mold opening long bolt is positioned on the upper end face of the lower corner plate opening module. The structure does not influence the arrangement of other structures of the upper die and the lower die, and is simple, and when the die is closed, the die opening long bolt is not contacted with the upper end surface of the lower angle plate die opening module, so that the die closing is not influenced; when the mold is opened, the mold opening long bolt is tightly propped against the upper end face of the lower angular plate opening module, and the upper petiole mold and the upper blade body mold are separated from the lower petiole mold and the lower blade body mold by the propping force to be opened.

Further preferably, the fixing mechanism comprises an upper angle plate pressing block fixed on the front or rear wall of the upper petiole die and the upper blade body die by screws, and a lower angle plate pressing block and a pressing long bolt and a nut fixed on the corresponding positions on the front or rear wall of the lower petiole die and the lower blade body die by screws; the upper and lower angular plate pressurizing blocks are provided with unthreaded holes, and nuts are welded and fixed at the lower ends of the unthreaded holes on the lower end surfaces of the lower angular plate pressurizing blocks; the long pressurizing bolt penetrates through the unthreaded holes of the upper and lower angular plates and the pressing block and is then in threaded connection with the nut. The structure does not influence the arrangement of other structures of the upper die and the lower die, and is simple in structure, when the dies are closed, after the upper and lower petiole dies and the upper and lower blade body dies are gradually closed by the hot press, the pressurizing long bolt is screwed on the nut, and the upper and lower petiole dies and the upper and lower blade body dies are pressurized and fixed together by the force for pressing and fixing the upper and lower angle plate pressurizing blocks together; and during demoulding, loosening the bolt until the nut is removed.

Further preferably, positioning sleeves I, II, III and IV and positioning pin sleeves are arranged in the positioning holes I, II, III and IV, the positioning pin holes and the positioning pin grooves of the upper and lower blade shank dies and the upper and lower blade body dies. The locating sleeves I, II, III and IV and the locating pin sleeves are wear-resistant parts, so that the mutual abrasion of the locating pins I, II, III and IV and the locating pins, the locating sleeves I, II, III and IV and the locating pin sleeves is avoided when the upper and lower blade shank molds are assembled and the upper and lower blade body molds are assembled, the service life is prolonged, and the locating sleeves I, II, III and IV and the locating pin sleeves are easy to replace after abrasion.

The die is divided into the petiole die and the blade body die, the petiole die is divided into the upper petiole die and the lower petiole die, the blade body die is divided into the upper blade body die and the lower blade body die, all parts are respectively machined by the machine tool, the machining operation is simple, the manufacturing period is short, the accuracy is high, the rejection rate is low, and the machining cost of the die is saved. After the blade is manufactured, the die is placed on a horizontal workbench with adjustable height difference or only the horizontal workbench of the petiole die part can adjust the height difference, then the upper petiole die and the upper petiole die are taken down by using a die opening mechanism and hoisting equipment, the horizontal workbench of the petiole die part is lowered to a height larger than that of the lower petiole die, the lower petiole die is gradually separated from the petiole by gravity, the cutting blocks are arranged, the petiole is separated, then the cutting blocks I, II and III of the lower petiole die are taken down, and then the whole blade can be taken out from the lower petiole die by using the hoisting equipment. Because the lower petiole die of the invention is gradually separated from the petiole by gravity, the lower petiole die does not need to be designed with die drawing inclination and cutting blocks for demoulding, the manufacturing precision of the right-angled part of the petiole is ensured, the design is simple, the processing period is short, and the cost is low.

In a word, the die has the advantages of simple structure, easy manufacture, short manufacturing period, low manufacturing cost, easy demoulding of the manufactured blade, high precision, low rejection rate and low manufacturing cost. Is particularly suitable for manufacturing the composite long-petiole blade.

Drawings

FIG. 1 is a front view of the present invention;

FIG. 2 is a left side view of the present invention;

FIG. 3 is a top view of the present invention;

FIG. 4 is a cross-sectional view AA in FIG. 3;

FIG. 5 is a cross-sectional view BB of FIG. 3;

FIG. 6 is a front view of the upper petiole die of the present invention;

FIG. 7 is a cross-sectional view CC of FIG. 6;

FIG. 8 is a bottom view of the upper petiole die of the present invention;

FIG. 9 is a right side view of the upper petiole die of the present invention;

FIG. 10 is a front view of the lower petiole die of the present invention;

FIG. 11 is a cross-sectional view DD of FIG. 6;

FIG. 12 is a left side view of the lower petiole die of the present invention;

FIG. 13 is a top view of the lower petiole die of the present invention;

FIG. 14 is a front view of the upper airfoil mold of the present invention;

FIG. 15 is a bottom view of the upper airfoil mold of the present invention;

FIG. 16 is a view in the direction E of FIG. 15;

FIG. 17 is a view from direction F of FIG. 15;

FIG. 18 is a front view of the lower blade shell mold of the present invention;

FIG. 19 is a top view of the upper airfoil mold of the present invention;

FIG. 20 is a view from direction H of FIG. 19;

FIG. 21 is a view from direction I of FIG. 19;

FIG. 22 is a schematic view showing the automatic detachment of the lower petiole mold according to the present invention.

Detailed Description

The invention is further described with reference to the following figures and specific embodiments.

As shown in fig. 1 to 22, the present embodiment includes a petiole mold and a body mold.

The petiole die comprises an upper petiole die 1 and a lower petiole die 2. The petiole mold, in which the petiole mold cavity is completely matched with the profile of the petiole 23, is divided into upper and lower petiole molds 1 and 2 on a plane 7 at the upper and lower centers of the petiole, and the petiole mold cavity is divided into upper and lower petiole mold cavities 27 and 30. And positioning holes I28 and II 32 are respectively arranged on the opposite surfaces of the upper and lower petiole dies 1 and 2, and after die assembly is carried out, the positioning pin I20 is positioned in the positioning holes I28 and II 32. The front wall and the rear wall of the upper petiole die 1 and the lower petiole die 2 are respectively provided with a die opening mechanism and two fixing mechanisms which are uniformly arranged, and the die opening mechanism and the two fixing mechanisms are fixed together by the fixing mechanisms after die assembly.

The airfoil mold includes upper and lower airfoil molds 15 and 16. The blade body mold with the blade body mold cavity completely matched with the molded surface of the blade body 24 is divided into an upper blade body mold 15 and a lower blade body mold 16 on a curved surface 14 formed by a connecting line of the maximum contour lines of the front edge and the rear edge of the blade body, and the blade body mold cavity is divided into an upper blade body mold cavity 34 and a lower blade body mold cavity 40. The end walls of the upper blade body die 15 and the lower blade body die 16 at one end of the blade handles are provided with semicircular blade handle accommodating grooves 37 and 8 which can form an accommodating groove completely matched with the profile of the blade handles; two opposite corners of the opposite surfaces of the upper blade body die 15 and the lower blade body die 16 are respectively provided with a positioning hole III 36 and a positioning hole IV 43, and after die assembly, the positioning pin II 21 is positioned in the positioning holes III 36 and the positioning holes IV 43. Two mold opening mechanisms and three fixing mechanisms are uniformly arranged on the front wall and the rear wall of the upper blade body mold 15 and the lower blade body mold 16, and after the mold is closed, the two mold opening mechanisms and the three fixing mechanisms are fixed together by the fixing mechanisms.

The upper and lower blade body molds 15 and 16 are provided with semicircular bosses 35 and 41 on the end wall at one end of the blade shank respectively around the outer sides of the outer circles of the semicircular accommodating grooves 37 and 8. The end walls of the upper and lower blade handle molds 1 and 2 opposite to the upper and lower blade body molds 15 and 16 are respectively provided with semicircular grooves 45 and 44 matched with the semicircular bosses 35 and 41; and a plurality of pairs of bolt holes and positioning pin holes 31 on the lower shank die 2 and positioning pin grooves 42 on the lower body die 16 are provided on the opposite surfaces of the upper and lower shank dies 1, 2 and the upper and lower body dies 15, 16. After the petiole and blade body dies are assembled, the semicircular bosses 35 and 41 are inserted into the semicircular grooves 45 and 44, positioned by the positioning pins 22 positioned in the positioning pin holes 31 and the positioning pin grooves 42, and fixed by bolts fixed in the pairs of bolt holes. The upper and lower shank dies 1, 2, which are provided with a plurality of pairs of bolt holes, are provided with grooves 33 for accommodating bolts.

Preferably, the mold opening mechanism comprises an upper angle plate opening module 4 fixed on the front or rear wall of the upper petiole mold 1 and the upper blade body mold 15 by screws 6 and spring washers, and a lower angle plate opening module 5 and a mold opening long bolt 3 fixed on the front or rear wall of the lower petiole mold 2 and the lower blade body mold 16 by screws 6 and spring washers. The upper corner plate opening module 4 is provided with a threaded hole matched with the mold opening long bolt 3; the mold opening long bolt 3 is in threaded connection with a threaded hole of the upper corner plate opening module 4, and the lower end of the mold opening long bolt is located on the upper end face of the lower corner plate opening module 5.

Preferably, the fixing mechanism comprises an upper angle plate pressurizing block 9 fixed on the front or rear wall of the upper petiole die 1 and the upper blade body die 15 by screws, a lower angle plate pressurizing block 12 fixed at a corresponding position on the front or rear wall of the lower petiole die 2 and the lower blade body die 16 by another screw 11, a pressurizing long bolt 10 and a nut 13; the upper and lower angle plate pressurizing blocks 9, 12 are provided with unthreaded holes, and nuts 13 are welded and fixed at the lower ends of the unthreaded holes on the lower end surfaces of the lower angle plate pressurizing blocks 12; the long pressurizing bolt 10 is threaded on the nut 13 after passing through the unthreaded holes of the upper and lower angular plate pressurizing blocks 9 and 12.

Preferably, the blade body mould further comprises cutting blocks I25 and II 26 matched with the leading edge and trailing edge profiles of the end faces of the blade root and a cutting block III 19 matched with the profile of the tip end face. The lower blade body die 16 is provided with grooves I38 and II 39 matched with the cutting blocks I25 and II 26 respectively on two sides of the semicircular accommodating grooves 37 and 8 on the upper end face of the end wall at one end of the blade handle, and is provided with a groove III 46 matched with the cutting block III 19 on the upper end face of the end wall at the other end. After closing, the grooves I38, II 39 and III 46 are blocked by the cutouts I25, II 26 and III 19 between the upper and lower blade molds 15 and 16.

Preferably, the positioning holes I28, II 32, the positioning holes III 36, IV 43, the positioning pin holes 31 and the positioning pin grooves 42 of the upper and lower blade shank dies 1, 2 and the upper and lower blade body dies 15, 16 are internally provided with positioning sleeves I, II, III, IV and wear-resistant positioning pin sleeves.

There are, of course, many other embodiments of the invention and modifications and variations of this invention that will be obvious to those skilled in the art may be made without departing from the spirit and scope of the invention, but it is intended to cover all such modifications and variations as fall within the true spirit and scope of the invention.