Abstract:
A method and apparatus are used to balance an open blade fan of the kind used with trucks, diesel engine driven generator sets, and the like. An apparatus is used to spin the fans and a vibration sensor senses vibrations and a light beam is used to indicate the location to attach a balancing weight. The fan is spun again and the vibrations measured and additional weights are attached at different specified locations until the measured vibrations are below a predetermined level. The fan includes a plastic body with integral, plastic fan blades which is attached to a central metal hub plate with configured weights attached to matching configured portions of the plastic body. The preferred weights are clips with barbs that pierce the plastic body. The metal hub plates are electrostatically painted to provide a uniformly thick coating with good adhesion. An ultraviolet light additive is provided in the plastic body with the fan blades being reinforced with glass particles and rendered UV resistant by the UV additive.

Description:
FIELD OF THE INVENTION 
     This invention relates to an open blade fan for use with a fan clutch such as used in diesel powered trucks, stationary generator sets, etc., and to a method of balancing and to making same. 
     New emissions standards in Europe and new emission standards to become effective in the year 2002 in the United States require substantial reduction in emissions of hydrocarbons from diesel engines. Current proposals and modifications to diesel engines involve running the diesel engines at higher operating temperatures to reduce emissions. Thus, a greater amount of heat is generated by these diesel engines and this necessitates a greater air flow across the radiator to drop the radiator liquid temperature. Usually, manufacturer specifications specify for a given diesel engine application the volume of air flow needed to drop the cooling liquid&#39;s temperature 1° C. across the radiator at given conditions. In some instances, the current open blade fans may be using as much as 60 HP at 2400 rpm to generate about 20,000 cfm to cool engines operating at the current diesel engine temperature conditions. For the newer and hotter temperature engines, the air flow requirement may be as much as 35,000 cfm rather than 2400 cfm for the same truck, diesel generator sets, etc. 
     A typical approach in the prior art is to use the same fan and to run it at a higher speed than 2400 rpm to obtain the desired 35,000 cfm; but increase of fan speed requires an increase in horsepower and generates more noise. Of course, operating at substantially higher speeds often results in requiring greater strength for the fan to withstand higher forces and stresses because of spinning the fan mass at higher speed. There is a need to balance such fans so that they do not vibrate excessively while spinning. 
     Open blade fans used with fan clutches are subject to deterioration and a shorter life if they are not properly balanced. Because a truck fan is being driven at high rotational speeds and may be driven by an engine in a truck that may be bouncing over a rough highway, the fan is subject to various forces and vibrations that add stress to the rotating fan blades. Particularly, plastic fan blades being subjected to high ambient heat, as in desert areas and high engine heat outputs beneath a truck hood, can deteriorate and have a shorter life if subjected to high stresses due to vibrations caused by the fan being out of balance. Conversely in very cold, frigid climates and in winter, the plastic of the plastic fan blades tends to become more brittle and it is undesirable to stress these fan blades with high stresses due to fan blade vibration from out-of-balance fan blades. 
     One conventional manner of balancing open fan blade types of fans having plastic blades is to sever a piece of a fan blade plastic and then spin the fan and observe whether or not there is an improvement in ran balance. If the first saw cut of plastic failed to achieve the desired cut, then a second cut of plastic is made. Obviously, such a trial-and-error method of balancing a fan requires a skilled operator and is very subjective. A shortcoming of cutting plastic from fan blade tips in order to balance the fan blade rotation is that the shortened blade has a greater clearance with the surrounding shroud. From a fan efficiency standpoint, it is undesirable to increase the distance between the fan blade tip and the shroud housing. 
     Another prior method of balancing plastic fans of this type was to locate the center of balance in a central metal hub plate which is located at the center or hub of the fan and to which the plastic fan blades are attached. Having located the center of balance on the metal hub plate, a new mounting hole can be made at this center of balance and a circular series of bolt-receiving holes can be made about the newly-centered hole to locate the fan rotational axis at the center of the new central mounting hole. Such a secondary operation is time consuming and expensive, and results in fan blade tips that are not equally spaced from the rotational axis thereby increasing the distance between the shortest fan blade tip from the shroud with a concomitant decrease in fan efficiency. 
     Another problem with plastic, open blade fans of this kind having a central metal plate is the use of electro-plating techniques to coat the central metal hub plated with a corrosion-resistant coating. It has been found that electroplated coats may be uneven with heavy plate areas and lightly plated areas. Thus, the lightly coated areas are subject to corroding particularly in bad corrosive environments to which a truck or generator fan may be exposed. Also, these heavy spots and lighter spots of corrosion-resistance coating tend to throw the fan off balance. Some fan blades are spray painted with uneven coats of paint that also allow corrosion at lightly coated areas. Uneven paint coatings may also add to the fan balancing problem. Thus, there is a need for a new and improved manner of coating the metal fan hub plates that provide an improved, more uniform coating to resist corrosion and that also doesn&#39;t add to the fan balancing problem. 
     Additionally, it has been found that, in some instances, fan blade deterioration may have been due to exposure of the plastic blades to ultra-violet light from sun rays. For example, if the plastic fan blades are used in a generator set in a very sunny desert location, the plastic of current fan blades may be adversely affected by prolonged exposure to high-intensity UV light. Thus, there is a need to provide a UV plastic fan for use in such environments. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, there is provided, as contrasted with the prior art, a new and improved plastic, open blade fan for use with trucks, diesel engine driven generator sets, etc. In accordance with another important aspect of the invention, an open blade, plastic fan is balanced with a new and improved method that comprises a spinning of the fan blade about its rotational axis and sensing vibrations from the spinning fan; stopping rotation of the fan; specifying locations on the plastic fan body to receive a clip weight; and attaching the clip weight to the plastic body at the specified locations, preferably by clipping of the clip weight to the plastic of the plastic fan body. Preferably, the method includes the providing of clip weights with integral barbs, hooks, or the like, that can be pushed into the plastic with barbs or hooks resisting a throwing off of the weights at high rotational speeds of the fan. In this illustrated and described embodiment of the invention, the fan body is provided with a circular array of integral molded ribs and metal channel-shaped clip weights are pushed over the ribs at the selected locations with integral barbs on the channel-shape clip weights piercing the plastic of the ribs. Herein, the plastic ribs have an outer contour, such as a rounded surface, and the weights have a complimentary shape to allow intimate contact across substantially an entire, inner concave surface of the channel-shaped clip and the outer, convex, rounded surface of the plastic rib. This helps in balancing and in retention of the clip weights on the ribs at high rotational speeds of the fan. 
     In accordance with another aspect of the invention, the metal hub plate of the plastic fan is provided with an improved corrosion-resistant coating and a more uniform thickness of coating for assisting in the balancing of the fan. This is achieved by using an electrostatic spray coating of the metal plate with a substantially uniform, electrical charge on the metal plate to attract the coating particles to the plate in a uniform manner that results in a more uniform thickness of coating on the metal plate. The preferred coating is an electrostatic paint. This eliminates thinly coated areas that allow corrosion, good adhesion of the paint to the metal, and a balanced uniformly thick coating that assists in the balancing of the fan. The metal plates are electrostatically painted before being molded in situ with the plastic fan body. 
     In accordance with the preferred embodiment of the invention, the fan body is made of plastic that has improved resistance to deterioration by UV light from sunlight. This is achieved by adding to the plastic a UV addition prior to molding the fan blades and the fan blade body. That is, the preferred UV additive is blended into the bulk plastic by the plastic suppliers. Herein, the preferred UV fan blades are made of nylon that is reinforced by glass particles and rendered UV-resistant by a UV additive to the plastic. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a fan blade assembly embodying the invention; 
     FIG. 2 is a perspective view of a metal hub plated used in the fan blade assembly of FIG. 1; 
     FIG. 2A is a cross-sectional view taken along the line  2 A— 2 A of FIG. 1 showing a uniform coating on opposite sides of the metal plate; 
     FIG. 3 is a diagrammatic view of a laser light beam locating spots to attach weights in order to balance the fan blade assembly; 
     FIG. 4 is an enlarged, fragmentary view of clip weights attached to ribs on the fan blade assembly to balance the latter; 
     FIG. 5 is a perspective view of a preferred clip weight; 
     FIG. 6 is a side elevational view of the weight clip of FIG. 5; 
     FIG. 7 is a side view of the weight clip; 
     FIG. 8 is an enlarged cross-sectional view showing the integral barbs on the clip weights; 
     FIG. 9 is a perspective view of the fan blade, spinning machine; and 
     FIG. 10 is a cross-sectional view taken through a channel-shaped weight clipped to a plastic, rounded rib on the fan blade assembly. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     As shown in the drawings for purposes of illustrations the invention is embodied in a fan blade assembly  10  (FIG. 1) having a plurality of fan blades  12  projecting radially outwardly from a central hub  14 , which is located at a rotational axis  16  for the fan assembly. Herein, the illustrated fan is used on large trucks or diesel generator sets for moving substantial volumes of air to cooling the engine. The illustrated fan blade assembly has a plastic body  18  in which is molded, in situ, a steel hub plate  20  located at the central hub base of the fan blade assembly and having a central mounting opening or hole  22 . A plurality of bolt receiving holes  24  encircle the central hole  22  to allow the fan to be secured as by bolts to a driver such as an on/off clutch. The preferred hub plate is configured to be connected to the plastic body to resist separation therefrom when spinning the fan blade assembly at high speed. To this end, the hub plates, which is shown in FIG. 2, has an outer series of small holes  30  and inner series of small holes  32  into which liquid plastic is introduced during the molding of the plastic body which, upon curing, results in small cylindrical pieces of plastic extending through the holes to unite the plastic fan body and hub plate without the use of fasteners and with plastic on both sides of the metal plate at a plastic hub piece  18   a  of the plastic fan body  18 . 
     In accordance with the present invention, a new and improved method of balancing the fan blade assembly comprises spinning the fan blade about its rotational axis  16  and sensing vibrations from the spinning fan and then stopping rotation of the fan; specifying locations on the plastic fan body to receive clip weight  35  (FIGS.  4  and  5 ); and attaching the clip weight  35  to the plastic body at the specified locations  38  (FIG.  3 ). The preferred method of attaching the clip weights  35  to the body comprises a clipping of the weights to the plastic by pushing integral barbs  40  (FIGS. 5-8) on the metal weights into the plastic body so that the barbs resisting a throwing off of the weights at high rotational speeds of the fan. 
     In accordance with the present invention, each of the fan blades  12  has its outer radial edge or tip  12   a  spaced radially from the central rotational axis  16  at equal distances or lengths when the fan has been balanced with the weights  35 . This is in contrast to the prior art method of trimming the blade tips to balance the fan. The use of the weights allows each of the fan blades to have the same radial clearance distance  43  (FIG. 1) with an encircling, conventional shroud  45  which surrounds the fan blades. In the prior art technique of clipping the blade ends, the radial clearance distance  43  will be larger for the clipped blades than for the unclipped blades. In other described method of balancing the fan blade assembly, the center of balance (not shown) was located for each fan assembly and a mounting hole ( 22 ) was made at this center of balance, but this center of balance axis of the new mounting hole was offset from a central physical axis defined by the intersection of radial lines through the fan blades. Thus, the center-of-balance axis in the metal plate is eccentric to an imaginary axis for the plastic fan blades from which the tips of the fan blades are equally spaced. With the mounting hole at the center of balance, which is eccentric to the imaginary axis for the blade tips, the blade tips will be spaced at unequal distances from the shroud. In the present invention, the clearance distance  43  is kept very small to increase air flow efficiency with the clearance space being substantially equal for each fan blade, which is not true for the above-described balancing methods. 
     In the preferred method, the fan body is provided with integral molded portions shaped to receive the clip weights  35  in the form of integral ribs  42 . Herein, the ribs  42  have an outer contour, such as a rounded surface  44  (FIG. 10) and the clip weights  35  are channel-shaped with an interior surface  46  that is rounded to engage intimately the similarly radiused, curved rib surface  44 . That is, the channel-shaped, clip weight has an inner concave surface  46  mated to the outer convex, rounded surface  44  of the plastic rib. The plastic ribs also have a pair of substantially parallel sidewalls  48  on opposite sides of the outer rounded surface  44  and the channel-shaped clip weight has a pair of parallel sidewalls  50  that are abutted against these rib sidewalls  48 . 
     The illustrated and preferred clip weights  35  are formed of metal such as steel and have a predetermined weight. By way of example only, one preferred weight clip is about one inch in length and about 0.525 inch in height at upper end  35   a  and an inclined web or top wall  35   b  inclined at 23° to the horizontal. The width is about 0.36 inch between the outer vertical surface  50   a  of the parallel legs  50 . The steel stock size is about 0.040 inch in thickness. The weight of this clip is 61 grains. A smaller size clip is about 0.560 inch in length and has a height of 0.400 inch at the upper end  35   a . The length of the top wall  35   b  is 0.69 inch in this instance. It measures about 0.25 inch between the outer vertical surface  50   a  of its parallel legs  50 . The steel stock size 0.050 inch and the barb has its point located 0.075 inch from the outer vertical surface  50   a  of the leg from which it is upstruck. The barbs are upstruck about a line  35   c  inclined and parallel to the top wall, as best seen in FIG.  7 . Manifestly, the size, weight and shape of the weights  35  may be varied from those illustrated and described herein. The lower edges  35   d  of the clip weights  35  may be provided with small pieces  35   e  to puncture into the plastic fan body to resist for or aft sliding of the clip weight. Herein, the puncture pieces  35   e  are about 0.250 inch in width and project downwardly about 0.010 inch from the lower edge  35   d . Manifestly, the size, shape and location of nieces to penetrate the plastic may be varied from that described herein and fall within the scope of the invention. More than one weight may be attached to the series of ribs  42 ; there being six weights  35  attached to six consecutive ribs  42  on the fan body shown in FIG.  4 . Often the clip weights are spaced from one another with one or more ribs having no weights thereon between other ribs having weights thereon. 
     In the preferred method, the fan blade assembly  10  is mounted on a rotational hub  48  (FIG. 3) of a spinning machine  50  (FIG. 9) that has a frame and housing  52  in which is disposed a motor and controls for spinning the driving hub  48  and attached fan at the selected rotational speed. A clear plastic cover  54  is pivotally mounted on the machine to allow positioning of a fan blade assembly  10  on the hub and removal of the fan blade assembly after specifying rib locations to receive the clips. A vibration sensor  58  on the machine senses vibrations on the rotating fan blade body  10  and an indicator  60  (FIGS. 3 and 9) such as a laser light beam  62  (FIG. 3) specifies the location  38  and rib  42  to receive a weight clip. The illustrated machine has a laser beam generator  63  (FIGS. 3 and 4) which emits the laser beam  62  to locate a rib  42  on the hub while the fan blade assembly is stationary and mounted in the machine. The fan blade assembly may have to be spun several times and then stopped and another weight clip attached at a newly located rib at the end of each spinning cycle. When the vibration sensor  45  no longer senses a predetermined amount of vibrations being present in the spinning fan, then the balancing and spinning is terminated. The vibration sensor and laser light beam indicator are known technology and the illustrated machine is commercially available from Ravens Engineering. 
     By way of example only, the fan blade assemblies  10  described herein range in size from 24 inches to 38 inches in diameter and come with 6, 7, 8, 9 or 10 blades (12) and run at various rpm up to a maximum of 2400 rpm. Typically, the fan volume ranges in 20,000 cfm to 35,000 cfm and are driven using a maximum of about 45 to 60 horsepower from the diesel motor drive. 
     In accordance with an important aspect of the invention, the central metal plate  20  is provided with a very even, corrosion-resistant coating  70  (FIG. 2A) on opposite faces  71  of the metal plate. This is achieved by electrostatically spray painting the metal plate with charged particles of paint that are electrically charged opposite to the charge on the metal plate. This positive and negative charge relationship controls the thickness of the coating and the coating of the metal plate uniformly across the entire faces  71  of the metal plate. In contrast thereto, the usual coating techniques involving non-electrostatic painting or involving the use of electro-plating techniques leave uneven coats with heavy plated areas and lightly plated areas on the plate surface  71 . 
     The non-uniform coating of the conventional techniques used heretofore and the resulting heavy and light spots of coating resulted in an off-balance of the fan adding to the balancing problem. 
     In accordance with another important aspect of the invention, the plastic fan blade assembly  10  has enhanced resistance to deterioration due to exposure to sunlight, particularly the UV rays in sunlight. In addition to being used in vehicles such as trucks, these fan blade assemblies  10  are often used with heavy construction equipment and diesel electric generator sets to cool the liquid in the radiators of such equipment and generators of electricity. To this end, the plastic material, which is preferably nylon filled with about 30% glass to provide additional strength, has added thereto a UV additive. That is, the producer of the bulk plastic, in this instance BASF Corporation, located in New York, U.S.A., adds the UV additive and blends it into the nylon and glass bulk plastic which is then shipped to the fan molder who then molds the fan blade assembly  10 . Thus, the blades and plastic hub are UV resistant when exposed to sunlight. In deserts or other hot areas, the plastic fan blade assembly may have prolonged exposure to intense sunlight and hence exposed to considerable UV light waves. 
     From the foregoing, it will be seen that there is a new and improved fan blade assembly that is balanced by an improved balancing method and by attached weights. The use of a spinning technique and clipping of weights to plastic portions shaped to receive the weights provide a less expensive and better way to balance the fan blade assembly. The use of an electrostatic application of coating to the metal plate hub results in a uniform coating on both sides of the metal plate. The preferred coating is a paint that is uniform in thickness across both sides of the metal plate to assist in balancing the spinning fan assembly and to provide uniform protection over the entire metal plate to corrosive elements being applied to fan during its life. Also, in accordance with the invention, the plastic of the fan blade assembly has a UV additive therein to resist deterioration due to prolonged exposure to sunlight and UV wave length rays in the sunlight. 
     It will be appreciated that although various aspects of the invention have been described with respect to specific embodiments, alternatives and modifications will be apparent from the present disclosure, which are within the spirit and scope of the present invention as set forth in the following claims.