Abstract:
The present invention relates to a method of sealing disk drive housing castings and the resulting housings. More specifically, as sealant is transferred between a sealant storage tank and an autoclave, the sealant is filtered to remove debris or other impurities from the sealant. By filtering a sealant, multiple casting treatment cycles can be performed using the same sealant without the quality of the sealant suffering.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This Application claims the benefit of U.S. Provisional Application Nos. 60/700,150 and 60/700,151, both of which were filed Jul. 18, 2005, the entire disclosures of which are hereby incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to inert gas-filled disk drives, and more particularly to methods of making sealed disk drive castings for purposes of retaining low density gas within an enclosure formed by the castings, including transferring disk drive casting sealant between a storage tank and autoclave as part of the manufacturing process. 
     BACKGROUND OF THE INVENTION 
     Hard disk drives incorporate magnetic storage disks and read/write heads that are capable of reading data from and writing data onto the rotating storage disks. Data is typically stored on each magnetic storage disk in a number of concentric tracks on the disk. The read/write heads, also referred to as read/write transducers or read/write elements, are integrated within a slider. The slider, in turn, is part of an actuator assembly which positions the heads relative to the surface of the storage disks. This may be at a predetermined height above the corresponding storage disk or, in some instances, in contact with the surface of the storage disk. The actuator assembly is typically positioned by a voice coil motor which acts to position the slider over a desired track. One or more read/write heads may be integrated within a single slider. In the case of non-contact sliders, a cushion of air is generated between the slider and the rotating disk. The cushion is often referred to as an air bearing. 
     Hard disk drives are an efficient and cost effective solution for data storage. Depending upon the requirements of the particular application, a disk drive may include anywhere from one to a plurality of hard disks and data may be stored on one or both surfaces of each disk. While hard disk drives are traditionally thought of as a component of a personal computer or as a network server, usage has expanded to include other storage applications such as set top boxes for recording and time shifting of television programs, personal digital assistants, cameras, music players and other consumer electronic devices, each having differing information storage capacity requirements. 
     A primary goal of disk drive assemblies is to provide maximum recording density on the storage disk. In order to provide greater storage capacity on a storage disk, track widths have become increasingly more narrow. However, decreasing the width of tracks makes it more difficult for the read/write heads to accurately read and write information to and from the narrowing tracks. Not only is it difficult to physically position the read/write element over a narrow width track, but it is increasingly difficult to maintain the read/write element over the track at an optimal position for accurate data transfer. Air turbulence created by the spinning disks, disk flutter and spindle vibrations, temperature and altitude can all adversely effect registration of the read/write element relative to the tracks. Moreover, increasing the speed of the rotating disks to achieve increased data access times increases air turbulence, which increases misregistration between the read/write element and the tracks on the storage disks (track misregistration or TMR). Higher rotational speeds can also increase disk flutter and spindle vibrations further increasing TMR. Higher rotational speeds can also increase spindle motor power and idle acoustics. 
     Accuracy can be further adversely affected if the read/write heads are not maintained within an optimum height range above the surface of the storage disk. Thus, a related goal is to increase reading efficiency or to reduce reading errors, while increasing recording density. Reducing the distance between the magnetic transducer and the recording medium of the disk generally advances both of those goals. Indeed, from a recording standpoint, the slider is ideally maintained in direct contact with the recording medium (the disk) to position the magnetic transducer as close to the magnetized portion of the disk as possible. Contact positioning of the slider permits tracks to be written more narrowly and reduces errors when writing data to the tracks. However, since the disk rotates many thousands of revolutions per minute or more, continuous direct contact between the slider and the recording medium can cause unacceptable wear on these components. Excessive wear on the recording medium can result in the loss of data, among other things. Excessive wear on the slider can result in contact between the read/write transducer and the disk surface resulting, in turn, in failure of the transducer, which can cause catastrophic failure. 
     Similarly, the efficiency of reading data from a disk increases as the read element is moved closer to the disk. Because the signal to noise ratio increases with decreasing distance between the magnetic transducer and the disk, moving the read/write element closer to the disk increases reading efficiency. As previously mentioned, the ideal solution would be to place the slider in contact with the disk surface, but there are attendant disadvantages. In non-contact disk drives there are also limitations on how close a read/write element may be to the surface of a disk. A range of spacing is required for several reasons, including the manufacturing tolerances of the components, texturing of the disk surface and environmental conditions, such as altitude and temperature. These factors, as well as air turbulence, disk flutter and spindle vibration, can cause the read/write element flying height to vary or even cause the read/write element to contact the spinning disk. 
     Disk drives are assembled in a clean room to reduce contamination from entering the drive prior to final assembly. Thus, the air that is trapped within the drive once it is finally sealed is filtered room air. Accordingly, seals used in disk drives between the housing components, such as the base plate and cover, are designed to prevent contaminants from entering the drive. Such seals are not designed to prevent internal air and other gases from exiting through the seal and out of the drive. Loss of gas in this manner is anticipated and accommodated by use of a filtered port to maintain equalized air pressure within the drive compared to that of air pressure outside of the drive. 
     As an alternative to air-filled drives, advantages may be achieved by filling disk drives with gases having a lower density than air. For example, helium has a lower density than air at similar pressures and temperatures and can enhance drive performance. As used herein, a low density gas or a lower density gas means a gas having a density less than that of air. When compared with air, lower density gases can reduce aerodynamic drag experienced by spinning disks within the drive, thereby reducing power requirements for the spindle motor. A low density gas-filled drive thus uses less power than a comparable disk drive that operates in an air environment. Relatedly, the reduction in drag forces within the low density gas-filled drive reduces the amount of aerodynamic turbulence that is experienced by drive components such as the actuator arms, suspensions and read/write heads. Reduction in turbulence allows drives filled with low density gas to operate at higher speeds compared with air-filled drives, while maintaining the same flying height and thereby maintaining the same range of read/write errors. Low density gas-filled drives also allow for higher storage capacities through higher recording densities due to the fact that there is less turbulence within the drive which allows the tracks to be spaced more closely together. 
     The die casting process, as well as other methods of manufacturing housing components, often results in the components having a porosity (small pock mark-shaped craters or pits) at the surface and within the body of the component (small voids in the grain structures of the material). This porosity can inhibit or prevent an adequate seal between two abutting surfaces of two different components when there are pits or craters on the abutting surfaces and, similarly, can prevent an adequate seal of openings in a component, such as an opening in a base plate for a spindle motor, when the act of forming the opening exposes air pockets in the body of the component. Additionally, surface porosity can inhibit or prevent adequate sealing between an assembly of two parts that includes an epoxy or adhesive material at the interface. Porosity within the body of the components can also allow low-density gas to permeate through the walls of the enclosure. Porosity of these kinds must be accounted for when making a low-density gas filled disk drive. 
     To achieve hermetic sealing, some components of the disk drive, usually the die castings, can be treated with a sealant that is intended to reduce the porosity of the components, thereby reducing the amount of gas allowed to escape the disk drive. Most sealant treatment methods typically employ an autoclave or similar vessel for holding die castings and a means for sealant storage within the autoclave or via a discrete tank. In the case where a discrete storage tank is used, the autoclave is closed and sealed and a vacuum is pulled into the autoclave. A transfer valve between the storage tank and autoclave is opened and sealant is forced from the storage tank (at atmospheric pressure) to the autoclave (at vacuum pressure) where the pressurized environment forces the sealant into the surface cavities. The large pressure gradient, sometimes as large as 14.7 psia, between the storage tank and autoclave also causes the sealant to flow at a relatively high velocity resulting in a turbulent flow. As a consequence of the turbulent flow, the sealant begins to foam and encapsulate air. 
     Once the castings are fully submerged in the sealant, the transfer valve between the autoclave and storage tank is closed. The vacuum pressure in the autoclave is maintained for a predetermined period of time, and then atmospheric air is vented into the autoclave to force the sealant into the evacuated pores and crevasses in the castings. While the sealant is being forced into the pores of the casting, vacuum pressure is created in the storage tank. 
     After the sealant has been allowed to substantially penetrate pores and crevasses of the castings, the transfer valve between the autoclave and storage tank is opened. At this point there is atmospheric or increased pressure in the autoclave and vacuum pressure in the storage tank. Due to this pressure difference between the autoclave and storage tank, sealant is moved back to the storage tank at a relatively high velocity again resulting in foaming of the sealant due to turbulent flow. When the sealant is returned to the storage tank, the transfer valve is closed again and atmospheric air can be reintroduced to the storage tank. The autoclave is then opened and the castings are removed. The autoclave then waits in stand-by mode until another impregnation cycle is desired. 
     A problem with the impregnation cycle described above is the turbulent flow of sealant between the autoclave and storage tank causes the sealant to cavitate and create gas bubbles. When the sealant is impregnated into the castings, the gas bubbles may also be trapped therein. If the gas bubbles burst during the pressurized sealing process additional sealant will fill the void left by the burst bubble. However, if a gas bubble subsequently remains in a casting pore or crevasse, after the casting has been removed from the autoclave, an unsealed surface void remains which may ultimately lead to leakage of gas from the disk drive. The warranted life of an average disk drive may be decreased significantly if too much low density gas is allowed to exit the disk drive. As the life of the disk drive decreases, so does the potential market value of the disk drive. 
     In addition, the existence of dissolved or suspended air in the sealant further impedes the ability of the sealant to penetrate pores and crevasses of the casting. This condition can lead to variations in sealant penetration uniformity over the casting. The addition of bubbles to the sealant also decreases the permeability of the sealant. Thus, under turbulent flow conditions, the permeability of the sealant degrades as it is moved between the storage tank and autoclave, ultimately resulting in a lower quality sealant. Of course, the bubbles can be removed from the sealant, but this “de-gassing” process is time consuming and decreases the efficiency of the overall disk drive manufacturing process. 
     Another problem with the impregnation cycle of the prior art is that debris and other particulate matter may be introduced to the sealant as it passes between and sits in the autoclave and storage tank. The sealant is initially bought as a relatively “clean” product, meaning that it has few impurities. However, as the sealant is reused and moved between the autoclave and storage tank, the cleanliness of the sealant may become compromised. Any particles or debris that are carried to the autoclave with the castings or while the autoclave is open, or are otherwise introduced to the sealant during the impregnation process will likely remain in the sealant. It is important to maintain a clean sealant because if the impurities are trapped in a pore or crevasse of the casting and later become dislodged a passageway for gas to exit the disk drive may be created. 
     SUMMARY OF THE INVENTION 
     In one embodiment, a method of sealing disk drive housing components, such as aluminum die-cast base plates and covers, is disclosed. The preferred process comprises setting an autoclave pressure and a sealant storage tank pressure to substantially the same pressure. Thereafter, the process continues by opening a transfer valve or similar type of separation mechanism between the autoclave and storage tank. Once the transfer valve has been opened, the pressure in the storage tank is slightly and controllably increased resulting in a small pressure differential between the autoclave and storage tank. The small pressure gradient results in a laminar flowing of the sealant from the storage tank to the autoclave. It is preferable to maintain laminar flow of the sealant as it transfers from the storage tank to the autoclave in an attempt to minimize the amount of gas created and captured by the sealant. A higher quality of sealant will result if the occurrence of gas bubbles in the sealant can be reduced. Essentially, the original permeability of the sealant (i.e., the permeability of the sealant at the time of purchase) can be maintained more easily if turbulent flow can be avoided. 
     In accordance with at least one embodiment, as the sealant passes from the storage tank to the autoclave, the sealant is filtered. An in-line filter or other type of sealant purification mechanism may be placed in the conduit connecting the storage tank and autoclave. As the sealant flows from the storage tank to the autoclave it passes through the filter, and debris that has been introduced to the sealant can be removed. The filter may comprise a number of filters, each of which filters a sequentially smaller particle size from the sealant. In an alternative embodiment, the filter comprises a single debris filter that is able to remove matter of a particular size or greater. 
     Sealant is flowed into the autoclave until the castings are substantially submerged in the sealant. After the sealant has reached a predetermined level in the autoclave, the transfer valve between the storage tank and autoclave is closed thereby separating the autoclave and storage tank. After the transfer valve is closed, an increased and controlled pressure is introduced into the autoclave. The increase in pressure causes the sealant to further penetrate the pores and crevasses of the castings. It is desirable to allow the sealant to penetrate the castings such that the pores and crevasses are substantially sealed. As the pores and crevasses of a casing are sealed, the chances of gas escaping from a disk drive made with the castings are reduced. 
     Once the castings have been substantially impregnated with the sealant, the sealant is transferred back from the autoclave to the storage tank. The sealant is transferred back to the storage tank under laminar conditions thus reducing the amount of gas and air created and encapsulated by the sealant. Also, as the sealant is transferred back to the storage tank it is filtered. The filtering of the sealant helps remove debris that may have been introduced to the sealant by the castings or the autoclave. The filter used to remove debris and other particulate matter from the sealant may be the same filter that was used to remove debris as the sealant transferred to the autoclave. Alternatively, the sealant may be transferred back to the storage tank via a different transfer line having a different filter that is used to filter a specific type of matter that is more likely to be introduced to the sealant by the autoclave/castings. 
     The above-described process may be repeated if it is desired to twice impregnate the castings. In an alternative embodiment, the castings may be treated with the sealant only once. A description of a casting treatment process is described in U.S. patent application Ser. No. 10/839,608 to deJesus et al., the entire disclosure of which is hereby incorporated herein by this reference. The process described in the &#39;608 patent application described twice impregnating the castings to ensure that substantially all of the pores/crevasses of the castings are filled with the sealant. 
     Variations in the process will occur to persons of skill in the art. Various types of sealant can be used, although the preferred epoxy is methacrylate. As can further be appreciated, the process can be used in any other application where it is desired to maintain a laminar flow of fluid between two separate locations. The process described herein is not necessarily confined to treatment of disk drive parts. 
     These and other advantages will be apparent from the disclosure of the invention(s) contained herein. The above-described embodiments and configurations are neither complete nor exhaustive. As will be appreciated, other embodiments of the invention are possible using, alone or in combination, one or more of the features set forth above or described in detail below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a base plate for a hard disk drive; 
         FIG. 2  is a perspective view of the opposite side of the base plate shown in  FIG. 1 ; 
         FIG. 3  is a perspective view of a cover for a disk drive; 
         FIG. 4  is a perspective view of the opposite side of the cover shown in  FIG. 3 ; 
         FIG. 5  is a cross-section of a portion of a base plate; 
         FIG. 6  is a schematic diagram depicting one embodiment of a sealant system used to transfer sealant to/from an autoclave; 
         FIG. 7  is a flow diagram depicting one embodiment of the sealant processing method; 
         FIG. 8  is a flow diagram depicting a method of adding sealant during the impregnation process; 
         FIG. 9  is a valve state chart for continuous sealant processing using an automated controller; 
         FIG. 10  is a valve state chart for moderately delayed, short-term standby processing using an automated controller; 
         FIG. 11  is a valve state chart for preparation for a long-term standby using an automated controller; 
         FIG. 12  is a valve state chart for resuming sealant processing after a long-term standby using an automated controller; 
         FIG. 13  is a valve state chart for manually controlling continuous sealant processing; 
         FIG. 14  is a valve state chart for manually controlling moderately delayed, short-term standby processing; 
         FIG. 15  is a valve state chart for manually preparing for long-term standby; and 
         FIG. 16  is a valve state chart for manually resuming sealant processing after a long-term standby. 
     
    
    
     DETAILED DESCRIPTION 
     A conventional hard disk drive housing is comprised of a base plate  12  and cover  14  as shown in  FIGS. 1-4 . The base plate generally includes an inner chamber  16  defined by a perimeter wall  18  and an inside bottom surface  20 . The inside bottom surface  20  has a first portion  22  generally defining where the actuator assembly (not shown) is mounted. An opening  24  is formed in the first portion to accommodate a multi-pin connector (not shown) for interconnecting the actuator assembly and read/write heads to the printed circuit board (not shown) mounted to the outside bottom surface  26  of the base plate ( FIG. 2 ). A second portion  28  of the inside bottom surface defines where the disk stack is mounted. In the illustrated embodiment, the second portion is elevated compared to the first portion and further includes a central recess  30  to accommodate a spin motor (not shown). The perimeter wall  18  includes a generally planar upper surface  32  which abuts a complementary surface  34  of the cover ( FIG. 3 ). A plurality of aligned apertures  36  in the base plate and cover receive fasteners (not shown) to attach the cover to the base plate. The apertures in the base plate are typically threaded, as are the fasteners. The inside edge of the upper planar surface  32  forms a recess or shoulder  38 . In a low density gas-filled drive, a metal seal (not shown), such as a C-shaped seal, is positioned in the recess  38  to form a uniform seal between the cover and base plate. The base plate may also include openings or apertures  42  to accommodate electrical connections between the spin motor and printed circuit board. 
     The cover  14  also includes an inner chamber  44  defined by the perimeter wall  46 . The inside bottom surface  48  may include one or more additional recesses  50  to accommodate the components mounted to the base plate such as the actuator assembly and disk stack. In addition, the cover may include a thickened portion  52  inside of the perimeter wall for purposes of locating an aperture  54  extending through the cover. Once the drive components are fully assembled within the base plate and the cover is attached to the base plate, the aperture  54  may be used as a port to fill the drive with low density gas. It should be appreciated that this aperture may be formed at other locations on the cover or base plate. 
     With reference now to  FIG. 6 , a system used to treat base plates and covers made by a casting process will be described in accordance with at least some embodiments of the present invention. The system generally comprises an autoclave  104 , a storage tank  108  and a first conduit  112  providing a fluid communication between the autoclave  104  and storage tank  108 . The autoclave  104  and storage tank  108  may include any type of pressure chamber that can be sealed and have a pressure applied within the chamber that differs from the pressure outside the chamber. 
     The conduit  112  connecting the autoclave  104  and storage tank  108  comprises a first end  116  that connects to the autoclave  104  and a second end  118  connected to the storage tank  108 . The first end  116  may have a gage  117  connected thereto to measure certain parameters associated with the conduit  116  or any substance traveling through the conduit  112 . The gage  117  may comprise a thermometer, a pressure gage, a strain gage, flow meter, or the like. 
     The second end  118  of the conduit  112  may comprise two fluid paths  120 ,  124 . The first fluid path  120  may be used to transmit sealant from the storage tank  108  to the autoclave  104 . The first fluid path  120  may comprise a manual valve MV 3 , a process valve V 3  that is automatically controlled, and a filter  122 . The filter  122  may be designed to remove particulate matter from the sealant as it passes through the first fluid path  120 . The filter  122  may remove debris from the sealant that is greater than or equal to a predetermined size. On the other hand, the filter  122  may also be designed to remove particles from the sealant based on physical and/or chemical properties like magnetic properties, optical properties, and chemical composition. 
     In accordance with at least one embodiment of the present invention, the filters  122 ,  126  comprise a series of filters that remove increasingly smaller particles. In other words, a first in the series of filters removes particles of a first relatively large size. Thereafter, the sealant flows through a second in the series of filters that removes particles of a second size that is somewhat smaller than the first size. A third filter in the series of filters can then remove particles of smaller size than the second filter. Up to N filters may be placed in series to help filter as much debris from the sealant as possible. 
     The second fluid path  124  also comprises a manual valve MV 7 , a process valve V 7 , and/or a filter  126 . The valves in the second fluid path  124  may be actuated to allow sealant to flow from the autoclave  104  to the storage tank  108 . As sealant passes through the second fluid path  124  it gets treated by the filter  126  that removes debris or the like that may have been introduced to the sealant while the sealant was in the autoclave  104 . The second end  118  may further comprise a valve MV 1  that controls flow of sealant from the storage tank  108  into the conduit  112  and vice versa. Furthermore, the second end  118  may comprise another valve MV 2  that controls sealant flow to the drain. Generally, the sealant is transferred between the storage tank  108  and autoclave  104  multiple times and is reused on many batches. However, after a certain amount of time, the sealant may have lost some beneficial properties and should therefore be disposed of in an appropriate member, via the drain. 
     The autoclave  104  may comprise a number of censors CS 1 , CS 2 , and CS 3  each of which are capable of measuring fluid levels within the autoclave  104 . The sensor CS 1  is operable to measure and identify when the fluid levels within the autoclave  104  have reached a maximum threshold. Likewise, the sensor CS 2  is operable to measure and identify minimum fluid levels within the autoclave  104 . The minimum threshold measured by sensor CS 2  represents the minimum amount of fluid required to substantially surround the castings with sealant, and will indicate to the process operator that additional sealant must be added prior to any subsequent impregnation cycle. The sensor CS 3  is used to determine when the autoclave  104  is substantially drained of sealant and the removal of castings is permissible. The sensor CS 3  may be connected to a sensor canister  128  that represents the lowest point of the autoclave  104 . When the sensor canister  128  is empty or at least partially empty, the sensor CS 3  can determine that the autoclave  104  is empty. A valve MV 12  may be connected to the sensor canister  128  if any fluid therein needs to be drained and cannot be transferred via the conduit  112 . 
     The storage tank  108  may also comprise one or more sensors CS 4  that is operable to measure the fluid levels within the storage tank  108 . When fluid levels within the tank reach or go below the sensor CS 4  then fluid flow is discontinued between the storage tank  108  and autoclave  104 . If the fluid levels have not at least reached the sensor CS 2  then an indicator light or alarm will notify the process operator that more sealant must be added to the storage tank via the fill port  144  prior to any subsequent impregnation cycle. Sealant may be poured into the fill port  144  and the valve  142  connected thereto may be actuated to allow the sealant to flow into the storage tank at a relatively slow rate. 
     In accordance with at least some embodiments of the present invention, sealant is transferred between the storage tank  108  and autoclave  104  under laminar conditions. In other words the speed with which the fluid is transferred between the tanks is maintained such that no substantial creation and/or trapping of gas bubbles occurs within the conduit  112 . As used herein laminar flow of sealant is understood to include any non-turbulent streamline flow of fluid in parallel layers (laminae). In typical applications, using a resin sealant like methacrylate having specific fluid properties, the tube diameter will be sufficiently sized to maintain laminar fluid flow during sealant transfer for a specific fluid flow rate. In applications where the tube diameter has been previously determined, the fluid transfer flow rate will be adjusted to achieve and maintain laminar fluid flow. In applications where the original resin sealant is replaced by a different resin sealant having different fluid properties, the fluid transfer flow rate will be adjusted to achieve and maintain laminar fluid flow. The continued reuse of resin sealant may allow one or more of the fluid properties to change within an acceptable and pre-determined tolerance band. In this case, the fluid transfer flow rate may be adjusted to maintain laminar fluid flow. 
     To facilitate laminar flows of sealant between the autoclave  104  and storage tank  108  the system comprises a pressure regulation system  130 . The pressure regulation system includes a first side  132  for controlling pressure in the autoclave  104  and a second side  138  for controlling pressure in the storage tank  108 . The first side  132  comprises a meter valve  133  that is connected to an analog pressure meter  134 . If pressure readings are desired for the autoclave side, the meter valve  133  is opened and a pressure can be read on the meter  134 . The first side  132  also includes a pressure transmitter  136  that is separated from the autoclave  104  by a meter valve  135 . If remote pressure readings are desired for the autoclave side, the meter valve  135  is opened. Valve MV 4  is a maintenance access valve. In the event that it is desired to relieve the pressure inside the autoclave  104  or allow atmospheric air into the autoclave  104 , maintenance valve MV 4  can be opened thereby venting the autoclave  104  to the atmosphere. 
     Similar to the autoclave side  132 , the storage tank side  138  may comprise a meter valve  139  connected to a pressure transmitter  140  and a meter valve  141  connected to an analog pressure meter  142 . The storage tank  108  pressure may also be opened up to the atmosphere by the actuation of the maintenance access valve MV 5  that can either allow atmospheric air into the storage tank  108  if the tank is at an absolute pressure below 1 atmosphere or allow pressurized air out of the storage tank  108  if the tank is at an absolute pressure above 1 atmosphere. The storage tank  108  may further be connected to a centrifuge line  166  that leads from an excess sealant recovery centrifuge. The flow of sealant from the centrifuge is controlled either manually by valve MV 6  or automatically by process valve V 6 . 
     Between the autoclave side  132  and the storage tank side  138  is a middle portion  146 . The middle portion may be used to pull vacuum pressure on one or both the autoclave  104  and storage tank  108 . The middle portion  146  comprises a meter valve  147  and a meter  148  that is capable of supplying a pressure reading of the middle portion  146 . The middle portion  146  is separated from the autoclave side  132  by a manual valve MV 8  and/or an automatic process valve V 1 . The middle portion  146  is separated from the storage tank side  138  by a manual valve MV 9  and/or an automatic process valve V 2 . On each side of the middle portion  146  there is a number of throttling valves V 4 , V 5 , MV 10 , MV 11 ,  150 , and  153 , reducing bushings  149 ,  152 , and muffler/filters  151 ,  154 . The configuration of throttling valves, bushings, and muffler/filters on the autoclave side of the middle portion  146  is used to vent the autoclave  104  in a controlled manner such that the pressure difference between the autoclave  104  and storage tank  108  can be changed slowly, thereby maintaining a laminar flow of sealant. Moreover, the throttling valves on the autoclave side of the middle portion  146  are used to vent atmospheric pressure to the autoclave  104  in a controlled manner to induce sealant to flow into pores of castings held in the autoclave  104 . Likewise, the configuration of throttling valves, bushings, and muffler/filters on the storage tank side of the middle portion  146  is used to the vent the storage tank  108  in a controlled manner to the atmosphere. 
     Also connected to the middle portion  146  is a vacuum line  156 . The vacuum line  156  connects a vacuum pump  162  and filter/separator  158  to the middle portion  146 . Valve  160  is used to drain condensation from the filter/separator, and valve  164  is for maintenance access. Vacuum can be drawn on one or both of the autoclave  104  and storage tank  108 . In one embodiment, the vacuum line  156  may be separated from the autoclave  104  by having at least one of the valves MV 8  and V 1  closed. The vacuum line  156  is also separated from the storage tank  108  by having at least one of the valves MV 9  and V 2  closed. Then a vacuum can be created in the vacuum line  156 . If it is desired to transfer vacuum pressure to one of the autoclave  104  and storage tank  108 , then the lines between the middle portion  146  and desired pressure chamber  104 ,  108  are opened by actuation of the corresponding valves. 
     In certain impregnation line configuration, incorporating in-line filtration between the autoclave and storage tank may not be an option. In fact, some configurations may not employ a storage tank  108  at all and therefore sealant is maintained in the autoclave  104  at all times. To facilitate such constraints, a recirculation loop  164  may be provided for the autoclave  104  and a recirculation loop  176  may be provided for the storage tank  108 . 
     For applications where sealant is transferred between the autoclave  104  and storage tank  108 , a connection is made near the bottom of the autoclave  104 . Another connection is made below the level of sensor CS 2 . Between these connects are located shut off valves, VA and VB, a recirculation pump  168 , and a filter or series of filters to remove particulate matter and other debris from the sealant. With the autoclave  104  filled with sealant to a level between sensor CS 1  and sensor CS 2 , valves VA and VB are opened and sealant if drawn through the bottom connection of the autoclave  104 , pumped to an appropriate pressure to pass laminarly through the filter(s)  172 , and delivered back to the autoclave  104  through the top connection. The location of each connection may be specifically determined to ensure that when the autoclave  104  is properly filled, optimal filtering performance of the sealant in the recirculation loop  164  is achieved and maintained. Drawing sealant from the lowest point of the autoclave  104  helps remove particulates that may settle to the bottom of the autoclave  104 . Returning filtered sealant below the level of sensor CS 2  helps ensure that the sealant is delivered below the top of the sealant pool, which helps to minimize sealant aeration. 
     In a similar fashion, if a storage tank  108  is utilized with the autoclave  104 , the above-described recirculation configuration can be optionally or additionally incorporated with the storage tank  108 . Specifically the bottom connection of the recirculation loop  176  is made to the bottom of the storage tank  108  and the top connection is made below the top surface of the sealant pool in the storage tank  108 . To pull sealant from the storage tank  108 , valves VC and VD are opened and pump  180  is activated to pull sealant from the bottom of the storage tank  108 . The sealant is passed through the filter(s)  184  and at least a portion of particulate debris therein is removed. Thereafter, the sealant is returned to the storage tank  108  at the top connection below the top level of the sealant pool. 
     The recirculation loop  164 ,  176  can be engaged at defined intervals between impregnation cycles, and during short and long-term stand-by process modes. These intervals can be determined based on the efficiency of the filter(s)  172 ,  184 , cleanliness and quality of the castings being sealed, and volume of castings going through an impregnation process. When not being utilized, the shut off valves VA, VB, VC, and/or VD are closed to isolate the filtration loop  164 ,  176  from the normal impregnation process to protect the pump  168 ,  180  and filter(s)  172 ,  184  from the extreme vacuum pressures achieved during the impregnation process. 
     Turning to  FIG. 7 , a flow chart generally describing the preferred method of impregnating disk drive housing components according to one embodiment of the present invention is shown. The process applies to base plates and cover plates made by a casting process. The casting process results in components having voids or porous grain structure in the material. The size of the pores will vary depending upon the casting process. The size of the pores may be referred to as the porosity of the material. Exemplary embodiments of a base plate and cover are shown in  FIGS. 1-4 . Additionally, the preferred embodiment is described in association with aluminum casting components. It should be appreciated that the process would work with components made from other materials such as steel, zinc and magnesium. 
     As a threshold step, it is preferable that the disk drive housing components be created from a process that minimizes porosity within the components. For example, base plates and covers are typically made by a casting process using aluminum. Castings which meet the American Society of Testing and Methods (ASTM) E505, Category A, provide suitable low porosity components. Such castings have porosity in external part surfaces which does not exceed 0.127 millimeters in diameter. Internal pores may be larger. A desired level of porosity which does not exceed 0.127 millimeters in diameter may be achieved using chill block cooling or vacuum-assist methodology for die casting for type A380 or 383 aluminum. 
     Once the components have been cast, one or more of the castings are set in the autoclave  104  (step  200 ). The castings may be placed in a holder as described in the &#39;608 application, which is incorporated by reference herein. After the castings are suitably positioned within the autoclave  104 , the autoclave  104  is closed and sealed (step  204 ). 
     With the autoclave  104  sealed, a vacuum is created in the autoclave (step  208 ). The vacuum is created in the autoclave  104  because the storage tank  108  is presumably maintained at vacuum pressure. In the event that the storage tank  108  initially has an internal pressure that differs from that of a vacuum, the pressure within the autoclave  104  is adjusted to substantially match that of the storage tank  108 . However, it is advantageous to maintain a vacuum within the storage tank  108 , which helps to de-gas the sealant as it sits in the storage tank  108 . The sealant may be degassed as it sits in either the autoclave  104  or storage tank  108  under absolute pressure conditions that are substantially less than atmospheric pressure conditions. 
     Once the internal pressures of the autoclave  104  and storage tank  108  have been adjusted to substantially equal one another, the one or both of the transfer valves V 3  and MV 3  are opened (step  212 ). Opening the transfer valve between the autoclave  104  and storage tank  108  creates a fluidic connection between the respective chambers. Since the pressures in the two chambers are equal, fluid transfer from the storage tank  108  to the autoclave  104  will generally be motivated only by the hydrostatic pressure head of the sealant in the storage tank  108 . Eventually, fluid transfer will cease when the sealant levels in both the autoclave  104  and storage tank  108  equalize. In order to achieve the desired laminar flow rate of sealant from the storage tank  108  and autoclave  104 , atmospheric pressure is vented into the storage tank  108 , thereby increasing the relative pressure between the storage tank  108  and the autoclave  104  (step  216 ). Atmospheric pressure is vented into the storage tank in a controlled manner by the actuation of the pressure release throttling valve V 5  or MV 11 . As a pressure gradient is created between the chambers the sealant begins to flow through the first fluid path  120 . As the sealant flows through the first fluid path  120  it passes through the filter  122  and particulate debris of a predetermined size and/or having certain physical/chemical properties is removed from the sealant (step  220 ). 
     In step  224  it is determined if the castings have been sufficiently submerged in sealant. In the event that the fluid level has not yet reached a minimum threshold, the method returns to step  216  and venting of the storage tank  108  continues. In other words, sealant is flowed from the storage tank  108  to the autoclave  104  until the sensor CS 2  senses fluid levels. As can be appreciated by one of skill in the art, the sealant may continue to be flowed until it reaches the sensor CS 1  or the flowing may be stopped somewhere in between the levels measured by CS 1  and CS 2 . In an alternative embodiment, the flowing may be stopped when the fluid levels in the storage tank  108  reach sensor CS 4 . 
     After the sealant has reached an acceptable level in the autoclave  104  (or a suitable level in the storage tank  108 ), one or both of the transfer valves V 3  and/or MV 3  are closed (step  228 ). Thereafter, a vacuum is maintained in the autoclave  104  for a predetermined period of time, thus letting the sealant settle in the autoclave (step  232 ). During this time, the fluid levels of the sealant are monitored (step  236 ). In step  240 , it is determined if more sealant is required to reach an acceptable level. In the event that more sealant is required, then sealant is added to the storage tank  108  via the fill port  144  prior to any subsequent impregnation cycle (step  244 , as will be described in further detail with reference to  FIG. 8 ). Once fluid levels have reached an adequate threshold, the autoclave  104  is sealed (step  248 ). The steps involved in this particular procedure may be completed in parallel while a current impregnation cycle is commencing and completing. 
     With the autoclave  104  sealed and separated from other components in the system, atmospheric pressure is vented into the autoclave  104 , which induces sealant into openings and pores of the castings (step  252 ). The impregnation process may be performed for a predetermined amount of time, or may be performed until the sealant has reached a second predetermined level below the starting level of the sealant. In the preferred embodiment, the submersed castings are maintained at an increased pressure for approximately ten minutes to twenty minutes. 
     In step  256  it is determined if the impregnation is complete. In the event that casting impregnation is not yet complete, the method returns to step  252  and more pressure is vented into the autoclave  104 . In an alternative embodiment, the venting of air into the autoclave  104  is continued until the internal pressure of the autoclave  104  is substantially equal to the internal pressure of the storage tank  108 . This new internal pressure of the autoclave  104  and/or storage tank  108  is generally higher than the initial internal pressure of the autoclave  104  and/or storage tank  108 . In a preferred embodiment, the internal pressure of the autoclave  104  and storage tank  108  are at atmospheric pressure at the end of the casting impregnation. 
     When the impregnation has been completed, the middle portion  146  is vented along with the vacuum lines  156  (step  260 ). Thereafter, one or both of the transfer valves V 7  and MV 7  are opened thereby creating a fluidic connection between the autoclave  104  and storage tank  108  via the second fluid path  124  (step  264 ). With the transfer valve open, a vacuum is created in the storage tank  108  via the vacuum pump  162  (step  268 ). This results in the creation of a pressure gradient that induces a laminar flow of sealant from the autoclave  104  to the storage tank  108 . As the sealant exits the autoclave  104 , air is vented into the autoclave  104  replacing the exiting sealant, further helping maintain laminar flow (step  272 ). 
     As sealant flows through the second fluid path  124 , the sealant is filtered by the filter  126  (step  276 ). As noted above, the filter  122 ,  126  may comprise a number of filters in series that remove foreign debris of decreasing size. 
     In step  280  it is determined if the autoclave  104  is empty. This particular step may be performed by referencing the sensor CS 3 . If the autoclave  104  is not yet empty, then the method returns to step  268  and more sealant is removed from the autoclave  104 . After the autoclave  104  has been satisfactorily emptied, the autoclave  104  is sealed off from the storage tank  108  by closing one or both of the transfer valves that were previously opened (step  284 ). A substantial vacuum now exists in the storage tank  108  and thus the de-gassing of the sealant can continue. However, the autoclave  104  has an internal pressure that is about equal to one atmosphere. With the autoclave  104  and storage tank  108  separated, the autoclave  104  can be opened and the castings can be removed and taken to the next step in the disk drive manufacturing process (step  288 ). 
     As can be appreciated, once treated castings have been removed, new castings can be placed in the autoclave  104  and the process can start over again. In an alternative embodiment, a moderate delay between cycles can be realized. During a moderate delay, it is preferable to turn the vacuum pump  162  off and vent the vacuum lines  156 , so that unnecessary damage can be avoided. Also, if necessary, additional sealant can be added to the storage tank  108  via the fill port  144 . When the process is ready to begin again, a vacuum may be pulled on the storage tank  108  and the method can return to step  200 . 
     In an alternative embodiment, a long-term standby mode may be employed between impregnation cycles. In this embodiment, the vacuum  162  is turned off and the vacuum lines  156  are vented. Thereafter, the valve MV 1  is closed to seal the storage tank  108  from conduit  112 . Thereafter the transfer valves between the autoclave  104  and storage tank  108  (with the exception of valve MV 1 ) are opened allowing the sealant to be drained into a clean container. The sealant flows under the hydrostatic pressure of the sealant fluid height. The sealant is then poured back into the storage tank  108 . Once the sealant reaches a predetermined level (i.e., the level measured by sensor CS 3 ), the transfer valves are closed. To re-start the process, the transfer valve is opened and a vacuum is pulled on the storage tank  108 . 
     With reference now to  FIG. 8 , a method of adding sealant to the storage tank  108  will be described in accordance with at least some embodiments of the present invention. The method begins when it is determined that sealant needs to be added to the system. The transfer valve between the autoclave  104  and storage tank  108  is closed (step  300 ). Thereafter, the autoclave  104  is opened and the castings are removed from the autoclave  104  (step  304 ). Then, the vacuum lines  156  are vented and the vacuum pump  162  is turned off (step  308 ). With the vacuum lines  156  and middle portion  146  at atmospheric pressure, atmospheric pressure is vented into the storage tank  108  (step  312 ). With the storage tank  108  at atmospheric pressure it is safe to open the fluid fill port  144 , thus the fill port  144  is opened (step  316 ) and sealant is poured into the storage tank  108  (step  320 ). Thereafter, the fill port  144  is closed and a vacuum is created within the storage tank  108  (step  324 ). With additional sealant added and the storage tank  108  back to vacuum pressure, the method returns to step  200  and the impregnation cycle is ready to begin (step  328 ). 
     As can be seen in  FIGS. 9-16 , valve state diagrams indicate the status of each valve depicted in the system between steps. Specifically,  FIG. 9  depicts a valve state diagram for continuous processing of castings using a programmable logic controller (PLC) that can receive inputs from the various sensors of the system and actuate valves based on those inputs. During the continuous processing, valves MV 1 , MV 3 , MV 7 , MV 8 , MV 9 , MV 10 , and MV 11  are open. Valves V 6 , MV 2 , MV 4 , MV 5 , MV 6 , and MV 12  are closed. The rest of the valve positions are depicted in sequential order where step A corresponds to process steps  200 - 208 , step B corresponds to steps  212 - 220 , step C corresponds to steps  224 - 244 , step D corresponds to steps  248 - 260 , step E corresponds to steps  264 - 280 , and step F corresponds to steps  284 - 288 . Additional steps that may be added to the process described above include steps G and H. Step G is an alternative to step F prior to returning the system to step A that provides for the addition of sealant to the storage tank  108 . Step H is the preparation of the system after the addition of sealant prior to returning to step A. 
       FIG. 10  depicts a valve state diagram for the process where a delay of moderate length is used between cycles. The valve state diagram of  FIG. 10  corresponds to such a process that is automatically controlled. Steps A-E of  FIG. 10  generally correspond to steps A-E of  FIG. 9 . The difference with a moderate delay between cycles occurs at step F where the system is prepared for a moderate delay. Thereafter, step G is used to prepare the system for another cycle after a moderate delay has been endured. 
       FIG. 11  depicts a valve state diagram in preparation for a long-term standby between impregnation cycles. The valve state diagram of  FIG. 11  corresponds to such a process that is automatically controlled. Step A in  FIG. 11  corresponds to an alternative to step F of  FIG. 9  where the system is prepared for a long-term standby, where the vacuum pump is opened and the storage tank  108  and autoclave  104  are vented to atmospheric air. Step B in  FIG. 11  corresponds to closing the transfer valve MV 1  between the storage tank  108  and conduit  112  then draining any sealant remaining in the autoclave  104 , conduit  112 , and sensor canister  128  into a clean container and pouring it back into the storage tank  108 . Step C in  FIG. 11  corresponds to closing transfer valves and opening the storage tank  108  and autoclave  104  to atmospheric pressure. 
       FIG. 12  depicts a valve state diagram for preparing to begin an impregnation cycle after a long-term standby has been endured. The valve state diagram of  FIG. 12  corresponds to a process that is PLC controlled. Step A in  FIG. 12  corresponds to closing the ventilation valves to the autoclave  104  and storage tank  108  and opening the transfer valves between the autoclave  104  and storage tank  108 . Step B in  FIG. 12  occurs when the storage tank fluid level reaches the level corresponding to sensor CS 3 . Thereafter, a vacuum is pulled on the storage tank  108  in step C of  FIG. 12 . At this point process cycle returns to step A and another impregnation cycle can begin. 
       FIG. 13  depicts a valve state diagram for continuous processing of castings using a manual actuation of valves. During the manually controlled continuous processing, valves V 1 , V 2 , V 3 , V 4 , V 5 , V 7 , and MV 1  are opened and valves V 6 , MV 2 , MV 4 , MV 5 , MV 6 , and MV 12  are closed. As noted above, during the automatic process control, the sensors can be used as inputs to monitor fluid levels. During manual control, the sensors may be used to turn on indicator lights or other feedback mechanisms. In an alternative embodiment, area corresponding to the placement of the sensors may be used as view ports for a user to visually confirm the fluid level in the autoclave  104  and/or storage tank  108 . The steps A-H of  FIG. 13  generally correspond to steps A-H of  FIG. 9  except that manual valves are used to complete the steps rather than automated valves. 
       FIG. 14  depicts a valve state diagram for the process where a delay of moderate length is used between cycles. The valve state diagram of  FIG. 14  corresponds to such a process that is manually controlled. Steps A-G of  FIG. 14  generally coincide with steps A-G of  FIG. 10  except that manual valves are used to complete the steps rather than automated valves. 
       FIG. 15  depicts a valve state diagram in preparation for a long-term standby between impregnation cycles. The valve state diagram of  FIG. 15  corresponds to such a process that is manually controlled. Steps A-C of  FIG. 15  generally correspond to steps A-C of  FIG. 11  with manual valves implementing the steps rather than automated valves. 
       FIG. 16  depicts a valve state diagram for preparing to begin an impregnation cycle after a long-term standby has been endured. The valve state diagram of  FIG. 16  corresponds to a process that is manually controlled. Step A of  FIG. 16  corresponds to step C of  FIG. 12  where the manual valves implement the step rather than automated valves. 
     The foregoing discussion of the invention has been presented for purposes of illustration and description. The foregoing is not intended to limit the invention to the form or forms disclosed herein. In the foregoing Detailed Description for example, various features of the invention are grouped together in one or more embodiments for the purpose of streamlining the disclosure. This method of disclosure is not to be interpreted as reflecting an intention that the claimed invention requires more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive aspects lie in less than all features of a single foregoing disclosed embodiment. Thus, the following claims are hereby incorporated into this Detailed Description, with each claim standing on its own as a separate preferred embodiment of the invention. 
     Moreover, though the description of the invention has included description of one or more embodiments and certain variations and modifications, other variations and modifications are within the scope of the invention, e.g. as may be within the skill and knowledge of those in the art, after understanding the present disclosure. It is intended to obtain rights which include alternative embodiments to the extent permitted, including alternate, interchangeable and/or equivalent structures, functions, ranges or steps to those claimed, whether or not such alternate, interchangeable and/or equivalent structures, functions, ranges or steps are disclosed herein, and without intending to publicly dedicate any patentable subject matter.