US 3804324 A
A centrifuging chamber, with a motor therebeneath to drive the centrifuging elements is formed interiorly of a housing, the housing sidewalls, internal structural features of the housing, and support elements for the motor being of structurally hard foamed, or cured foam material, preferably polyurethane cured foam. Where necessary, a metal mesh or grid preferably steel, can be embedded in the housing structure, by foaming the material around the steel reinforcement.
Description (OCR text may contain errors)
United States Patent Sinn et al.
TABLE TOP, NOISE SUPPRESSED CENTRIFUGE Inventors: Hartmut Sinn; Hans Stallmann,
both of Osterode, Germany Herseus-Christ Gmbl'i, Osterode, Germany Filed: 06. 6, 1972 Appl. No.2 295,559
Foreign Application Priority Data June 27, 1972 Germany 2240336 US. Cl. 233/24, 233/1 R, 233/1 C, 220/71, 248/20 Int. Cl B04b 7/02 Field of Search 233/1 R, 1 B, 1 C, 26, 233/23 R, 24, 113; 312/352; 220/71, 83; 248/15, 18, 20
References Cited UNITED STATES PATENTS 3/1973 Allen 233/l B Apr. 16, 1974 2,448,196 8/1948 Shee 233/24 1,824,722 9/1931 Jones 233/23 R 3,244,363 4/1966 116111 233/28 2,878,992 3/1959 Pickels et al 233/26 x 3,078,007 2/1963 Veres et al 220/71 2,699,289 1/1955 A116 et al. 233/26 FOREIGN PATENTS OR APPLICATIONS 1,123,042 6/1956 France 233/1 R Primary Examiner-George H. Krizmanich Attorney, Agent, or FirmFlynn & Frishauf 5 7 ABSTRACT A centrifuging chamber, with a motor therebeneath to drive the centrifuging elements is formed interiorly of a housing, the housing sidewalls, internal structural features of the housing, and support elements for the motor being of structurally hard foamed, or cured foam material, preferably polyurethane cured foam. Where necessary, a metal mesh or grid preferably steel, can be embedded in the housing structure, by foaming the material around the steel reinforcement.
20 Claims, 3 Drawing Figures PATENIEU 1 61974 3.804,32A
sum 2 OF 2 Fig.2
TABLE TOP, NOISE SUPPRESSED CENTRTFUGE The present invention relates to a centrifuge, and more particularly to the housing structure for a centrifuge which is so designed that vibration and noise are substantially reduced, while permitting ease of manufacture and wide latitude to the designer of the housing Centrifuges, particularly table top model centrifuges frequently have a metal housing. Metal has the disadvantage that a number of separate components or parts must be assembled, or welded together, which causes substantial manufacturing expense. Centrifuges with metal housings also are very noisy. Metal additionally has the disadvantage that the designer of the housing is limited by cost and working considerations in proposing housing designs.
It has been proposed to make housings for table top centrifuges and the like from thermoplastic material. Thermoplastics permit manufacture of the housing by injection, or casting processes. The shape and design of the housing can be varied within wide limits. Unfortunately, plastic housings as proposed, in which the plastic is cast, or injected, or extruded, still are very noisy, and the costs for the molds to make the housings are high.
It is an object of the present invention to provide a table top centrifuge which is low in cost, and which has a substantially better noise level than previously known apparatus.
SUBJECT MATTER OF THE PRESENT INVENTION Briefly, the housing of the centrifuge has a bottom, and a cover which is made of structural hard foam material, preferably polyurethane hard foam, such as cured polyurethane.
Structural hard foam and particularly polyurethane hard foam has the advantage that the tools and fixtures to make the housing, that is, for the foam, and the molds therefor. can be made inexpensively, the molds being made of epoxy or aluminum, or the like. The foaming process itself is substantially cheaper than plastic injection, or molding processes, and the designer has wide latitude and freedom in designing the housing since there are few limitations on the shape and arrangement of the structure that can be made by foam processes.
Using structural hard foam has the additional advantage with respect to extruded or cast plastic that the structural hard foam has high mechanical strength, which is absolutely necessary when used with centrifuges. which are apt to substantially vibrate. Structural hard foam and particularly polyurethane hard foam acts as a noise dampening device, so that centrifuges having such materials as the housing are substantially less noisy than centrifuges having housings of metal or cast, or extruded plastic.
The invention will be described by way of example with reference to the accompanying drawings, wherein:
FIG. I is a general perspective view of the centrifuge housing;
FIG. 2 is a longitudinal cross-sectional view through the housing illustrating the centrifuge within the housing; and 1 FIG. 3 is a magnified detail of a portion of FIG. 2 at the location indicated by the arrow Ill on FIG. 2.
The housing 1 for the centrifuge has sidewalls 2,, a bottom wall 4 and a removable cover 3. The lower part of sidewalls 2 has depressions 5, forming handles, molded therein, only one such depression being visible in FIG. 1. The front wall of the centrifuge 1 has a portion removed therefrom to permit access to a control;
panel 7. The cover 3 is formed with an aperture, or opening 8 to permit insertion of the users fingers so that the cover 3 can be lifted easily. A hinge 34', only schematically indicated in FIG. 2, connects the cover, 3 to one of the sidewalls 2. The bottom 4 has reinforcements 35 therein through which screws 26 extend which engage in matching projections at the lower edge of the sidewalls 2 to interconnect the bottom 4 and the sidewalls. Only one such interconnection is shown in FIG. 2 for simplicity.
The cover 3, sidewalls 2 and the bottom 4. of the housing 1 are all made of hard foamed polyurethane, for example completely cured polyurethane. As seen in FIG. 2, the interior portion within the sidewalls is. subdivided to form a centrifuging chamber, the subdividing wall 9 being formed as a unitary molding with the sidewalls. The subdividing wall 9, forming the centrifuging chamber has a central opening 30 in which a motor 10 is secured. Motor 10, shown schematically, is connected to an attachment projection 11, forming part of the internal projecting wall subdividing'the centrifuging chamber from the remaining interior of the centrifuge, and held therein by meansof rubber bushings 12. The upper portion of the motor 10 has a cap 13 thereon which covers the remainder of the opening 30. The centrifuging rotor 15 is secured to the motor shaft of the motor 10, above the motor structure itself.
The housing 1 is reinforced and stiffened, particularly in the region of the centrifuging chamber C by molding a reinforcement 33 into the sidewall. Reinforcement 33, molded into sidewall 2 at least in the region of the centrifuging chamber 3 is preferably formed as a perforated steel jacket, or steel plate, or the like, although it may equally well be mesh, grid-like or have similar structure. It is completely embedded within the foamed plastic, the foaming process being carried out around the perforated plate 33, so that it will be completely covered and noise, due to vibration of the metal, will be inhibited, since the metal itself is insulated from noise generated to the interior of the centrifuging chamber C. The lower part of the sidewall is formed with an inner extension 18 to define a chamber 22 which is accessible from the outside by means of an opening 19 in the bottom 4 of the housing. The chamber 22 is particularly provided to retain an electrical connecting cord (not shown) for the centrifuge, when the centrifuge is not used, or for storage or packing and transport.
The centrifuge itself is based on rubber legs 20 which may preferably be in the form of suction cups. The instrument panel 7 is connected to a projection 21 forming part of the separating wall 9, and molded unitarily therewith. The electrical portion of the centrifuge, except for the motor 10, is in the space E beneath the centrifuging chamber C. The particular elements of the electrical connection, controls, and the like have been omitted for better illustration of the structural parts of the centrifuge. Only a single switch knob 7 is shown,
having a shaft 31 extending towards a switch interiorly of chamber E, and not specially shown.
The cover 3 has an air deflection or air guide plate 23 secured at its underside. The central region 24 of the air deflection plate 23 is close to the lower side of the cover 3. The region 24 is surrounded by a second region 25, which is ring-shaped and which is relieved with respect to the cover 3, that is, projects more inwardly into the centrifuging chamber C, so that a larger distance between the air deflection plate 23 and the cover 3 will result. The edge 26 is bent over towards the lower portion of the housing cover 3. The distance from the lower face of cover 3 is small, and may be similar to that of the central region 24. Wall 26 of the air guide plate 23, and a projecting edge 27 on the cover 3 are so arranged that they overlap each other. The finger opening 8 is in the region of the ring-shaped space 28, and is defined by the lower portion of the housing cover 3 and the inwardly set region 25 of the air deflection plate 23. This arrangement of the air deflection plate 23 with respect to the cover, and particularly the ring-shaped space ensure air circulation within the centrifuging chamber C in a desired measured amount. Air can enter through an opening 32 formed in the bottom 4 of the housing, pass into the centrifuging chamber through a gap between the motor cap 13 and the bottom of the separating wall 9, circulate through the centrifuging chamber C and escape through the gap between the air deflection plate 23 and the cover 3, finally to be exhausted through the finger opening 8.
The ring-shaped space 28 is preferably subdivided into noise dampening chambers, by forming ribs 29 extending from the plate-like cover 23 into space 28, and uniformly molded thereto (see PK]. 2); alternatively, they can be molded on the air deflection plate 23 which is preferably an extruded or molded plastic part.
The centrifuge therefore includes a housing which is a single unitary molded element of hard foam, preferably polyurethane, reinforced if desired. The single molded foam construction is inexpensive and permits manufacture of the centrifuge in the most desirable form since even complicated structures can readily be foamed. Utilizing structural, hard foam results in a sturdy, yet noise dampening arrangement, which is unitary, and thus strong. The outside, esthetic appearance can be selected easily, and such convenience features as finger grips can readily be molded in. Additionally, space can be provided in the form of separate chambers for accessories, the electrical cable, or the like, since structural polyurethane hard foam is easily molded to any desired shape. Perforating the reinforcement 33 decreases the noise level of the machine in operation and ensures excellent embedding of the reinforcement within the foam. Steel grids are also suitable for this purpose.
At high centrifuging speeds of the rotor, the motor, as well as surrounding parts and the surrounding air will heat due to air friction and air turbulence. Operation of the centrifuge will, therefore, draw air in through the air cooling path, previously described, so that ventilation and air flow through the centrifuging chamber are ensured. Experiments have shown that the air guide plate 23, shaped as described, provide for effective ventilation with low noise level. The most desirable dis tance between the air guide plate and the lower face of the housing 3 can readily be determined by a few experiments for different sizes and types. and speeds of centrifuging. The spacing itself can readily be adjusted by placing intermediate washers between the attach ment means for the plate 23 to the cover 3, for example screws or the like. These washers, likewise, may be made of foamed or other plastic material. Resonance of the plate 23, or of the cover is effectively inhibited by forming reenforcement vanes or ribs on the cover, on the plate 23, or both, so that the ring-shaped space 28 will be subdivided into a plurality of noise suppression chambers.
The molds used may be of inexpensive materials such as epoxy, aluminum, zince alloys, or other customary mold materials for molding plastics.
The structural hard foam material, in the sense of the present invention, is a foamed synthetic substance having an overall density of about 400 1,200 kg/m preferably in the range of about 500 800 kg/m". Plastic materials which are almost completely, or completely formed with closed cells at their outer surfaces are particularly useful; the closed cell outer surface may have a thickness of about one-fifth or less, preferably about one-tenth of the overall thickness of the wall to be foamed, when the wall thickness is roughly in the order of one or several centimeters. The core of such a wall has a higher proportion of open cells and thus is porous. Preferably, the pores are fine, sothat it could be called a fine pored structure. Taking a cross-section through such a wall of hard foam material reveals a structure similar to a sandwich (with respect to structural aspect, since the substance, chemically, is the same, since the surface layer is made of the same material as the core). A smooth, continuous variation appears between the closed-pore tough surface layer and the open, and also closed cells or pores within the material. The density of the outer layer is close to the upper limits of the ranges above given, whereas the density of the core material is close to the lower limit of the range above given. Such a structural wall is stiff and useful for the structure of the present invention, although the overall weight is low.
FIG. 3 illustrates the nature of the structural hard foam material, being a magnified representation of a small portion of the housing cross-section, at the location designated on FIG. 2 by the arrow Ill. The cells of the foam, as shown in the middle of the housing wall, or rather the voids, generally communicate with each other, although only some of the passages between cells appear, of' course, in the particular cross-sectional plane. As the surface of the housing wall is approached, however, the void bubbles are more and more fully closed off from each other by an intervening skin, so that for a certain depth from the surface skin of the wall there is a closed-cell structure in which there is no communication between the voids of individual foam cells. The showing of the foam cells inFlG. 3 is not to scale, the cells being magnified relative to the wall thickness for purposes of illustration. I
Walls at the lower limit of thickness, that is, in the region of about 1 centimeter or less may also be used, al' though such walls may only have closed cells throughout their cross-sectional area, that is, closed cells appear not only at the outer surfaces but also within the zone of the core of the wall. If the wall has a thickness in the order of several millimeters, then the density of the material may be fairly uniform throughout the cross-sectional thickness thereof. The density, that is, the weight per unit volume, can be predetermined by changing the relative proportion of the components in use, or changing the proportion of propellants when injecting the mold. A higher injection speed (more material per unit time) results in a lower density; lower injection speed results in a higher density.
Apparatus useful in the process of making structures are spiral, or worm injection molding apparatus, pistontype injection molding apparatus with preplasticizing by means of worms or the like.
Examples of materials:
EXAMPLE 1 Two reactive components are used, namely polyols and biisocyanate, or higher function isocyanates, in a proportion of about 1:1, as well as tertiary amines, as activators to control the reaction and halogenated hydrocarbons as propellants, such as,
for example monofluortrichlormethane difluordi'chlormethane trifluortrichlorethane.
Fillers or dyes such as'titandioxide, barium sulfate and kaolin may be added.
The liquid starting material components from which the structural elements are made are processed as follows:
l. Pre-mixing of the polyols with propellant;
2. Measuring quantity and mixing of the foamable pre-mixture with the isocyanates;
3. Filling of the reaction mixture into a mold about 3l5 seconds; 4. Foaming and hardening of the mixture within the mold about 5-15 minutes;
5. Removal from the mold.
If desired, the following steps may follow:
6. Cooling and post-hardening;
7. Further treatments, such as enameling, painting,
coating with lacquer or the like.
The components are preferably mixed in a proportional mixer. During filling of the reaction mixture into the mold, by injection molding, the mold is preferably temperature controlled both during the injection as well as during'the foaming and hardening step. Temperature control can readily be obtained by passing liquids such as water, or proper temperature, through cavities or chambers in the mold. The pressure used during 1 foaming of the starting substances is in the approximate range of 2.5 5 kp/cm I fluid circulation system connected to the molds.
Removal of the molds is improved when separating substances such as wax or metallic soaps are used.
A sample body of l m surface and 1 cm thickness, with an average density of 73S kg/m, after six hours submerged in distilled water (a test in accordance with I DIN 53455) had the following characteristics:
Weight Thickness Rupture Rupture Temp. Change Change Tension Torque 20C 2.38% L357! 6 about i a about 6.44%
l03 ltp/cm EXAMPLE 2 Polystyrol-granulate and butylstearate were premixed for about two minutes. A solid propellant, such as for example azodicarbonamide was added similar to the method of dry-dyeing, the azodicarbonamide of the type of later developing gas. A mixing time of 10 minutes is adequate.
The mixture is plastisized in a cylinder, or in a worm of the injection molding machine-The melt, at the nozzle at the end of the cylinder will have a temperature of about 230 C. The propellant dissociates under this temperature while developing gas. The speed of the.
worm was between 30-80 rpm, the worm operating under dynamic pressure.
The injection pressure at the nozzle of the cylinder was a few atmospheres. The mold was cooled with water cooling, and the foamed, hardened structural element could be removed after a few minutes of cooling and hardening time.
Various changes and modifications may be made within the inventive concept.
1. Centrifuge having a housing including sidewalls, a bottom wall, and a removable cover for the housing and comprising also;
means defining a centrifuging chamber (C) within the housing;
a centrifuging rotor-(l5) rotatably mounted in the chamber; and motor means (10) mounted in the housing to drive the rotor in the chamber; 2
wherein the housing sidewalls, the bottom wall, and the cover comprise hard structural plastic foam material of a sandwich structure comprising outer skins of closed cell structure and an intermediate core of at least partly open cell, porous structure, said outer skins being of substantially higher density than said intermediate core.
2. Centrifuge according to claim 1, wherein the. hard foam material comprises hardened polyurethane foam.
3. Centrifuge according to claim 1, wherein the sidewalls of the housing and the means defining the centrifuging chamber are a unitary foam molding of hard structural plastic foam material.
4. Centrifuge according to claim 1, wherein the housing is formed with internal projections forming attachment means (ll, 2]) for the motor, said attachment means being part of a unitary molding comprising said housing and said attachment means (11, 2f).
5. Centrifuge according to claim 4, wherein the centrifuge comprises electric switching and circuit elements (7) and the housing is formed with a mounting means for said elements, said mounting means being part of the unitary molding comprising said housing, said attachment means and said mounting means.
6. Centrifuge according to'claim 1, wherein said sidewalls have gripping depressions (5).
7. Centrifuge according to claim 1, comprising an internal portion located adjacent the lower portion of the sidewalls and the bottom wall and defining a separate chamber (22), said chamber being open (19) interiorly of the centrifuge to permit access from the chamber to the motor, said chamber permitting storing of electrical connecting cables for the centrifuge motor, or of accessories, within the housing of the centrifuge.
8. Centrifuge according to claim 1, comprising reinforcement means (33) embedded in at least one of the sidewalls and located at least in the region of the centrifuging chamber (C).
9. Centrifuge according to claim 8, wherein the reinforcing means comprises a metal insert.
10. Centrifuge according to claim 9, wherein the metal insert is a steel insert.
11. Centrifuge according to claim 9, wherein the metal insert is perforated or grid or mesh-like.
l2. Centrifuge according to claim 1, wherein the cover (3) is formed with an elongated opening (8) to permit removal of the cover and provide for ventilation of the centrifuging chamber (C) and an air deflection plate (23) covering said opening is mounted at the side of the cover facing the chamber (C).
13. Centrifuge according to claim 12, wherein the air deflection plate (23) is shaped to have a small distance from the cover in a central region (24) thereof;
a greater distance from the cover at side regions (25) thereof;
and little distance from the cover at marginal regions (26) there of so that the air deflection plate and the cover will conjointly define a ring-shaped space (28), the opening (8) within the cover being located in the region of the ring-shaped space (28).
l4. Centrifuge according to claim 13, wherein the cover (3) has a projecting edge portion (27) overlapping the marginal regions (26) of the air deflection plate (23).
15. Centrifuge according to claim 13, wherein the cover is plate-like to form a cover plate, and internally projecting ribs (29) are located in the ring-shaped space (28) extending from at least one of said plates (3, 23) towards the other plate to subdivide the ringshaped space in a plurality of noise dampening chambers.
l6. Centrifuge according to claim 13, wherein the air deflection plate comprises a thermoplastic extrusion.
l7. Centrifuge according to claim 1, wherein said skins of said sandwich structure have a thickness of l millimeter or more.
18. Centrifuge according to claim 1, wherein said hard structural plastic foam material has an overall density in the range between 400 and 1,200 kglm l9. Centrifuge according to claim 1, wherein said hard structural plastic foam material has an overall density within the range between 500 and 800 kglm 20. Centrifuge according to claim 1, wherein said hard structural plastic foam material has a closed cell skin portion having a thickness of about one-tenth of the overall thickness of the sidewalls of said housing and wherein said wall thickness is within the range of l to several centimeters.