Abstract:
A hose for carrying liquid, such as hot met adhesive, within a predetermined elevated temperature range. The hose includes a tube for carrying liquid therethrough. The tube is encased in a reinforcing layer with an outer surface. A heater wire, which has an inner core encased in a protective casing, is wound around the reinforcing layer such that the protective casing is in direct contact with the outer surface of the reinforcing layer. Preferably, the protective casing is made from polytetraflouroethylene (PTFE). A thermal insulation layer is disposed around the heater wire and the reinforcing layer to act as a barrier to heat loss from the hose.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention generally relates to hoses for carrying heated liquids, such as hot melt adhesives.  
         BACKGROUND OF THE INVENTION  
         [0002]    Various processes involve the transmission of a heated liquid a liquid dispensing device to a desired location such as onto a substrate. For example, hot melt adhesives are frequently applied to products and product packaging. Generally, the hot melt adhesives are applied by a dispensing gun which is connected via a hose to a supply tank. Hot melt adhesives are generally solid at room temperature and, accordingly, must be heated prior to their application so that they can flow from the supply tank, through the hose, and to the dispensing gun. To melt and subsequently maintain the hot melt adhesive at the appropriate temperature, components such as the supply tank, the hose, and the dispensing gun are selectively heated by individual heating devices associated with each component. To monitor the temperature of the hot melt adhesive throughout the application process, each component further includes some form of temperature sensing device which is associated with at least one of the heating devices. A controller operates the heating device in response to signals from the temperature sensing device to maintain the hot melt adhesive within a predetermined temperature range.  
           [0003]    In heated hoses such as the one disclosed in U.S. Pat. No. 4,455,474, the inner tube of the hose is typically made from a polymeric material such as polytetraflouroethylene (PTFE) or Teflon® because of its ability to withstand the relatively high temperatures of the hot melt adhesive pumped through the hose. U.S. Pat. No. 4,455,474 is assigned to Nordson Corporation, Westlake, Ohio, the same assignee as the present invention and its disclosure is hereby incorporated fully herein by reference. As PTFE will not withstand the relatively high pressures at which the hot melt adhesive is pumped, i.e., on the order of 200 psi, the PTFE tube is typically encased within a stainless steel braiding. The stainless steel braiding generally has a relatively rough outer surface. Thus, any component wound around and directly contacting the stainless steel braiding may experience abrasion as the entire hose flexes and the wound component moves relative to the stainless steel braiding.  
           [0004]    To minimize the risk of abrasion by the stainless steel braiding, the stainless steel braiding is wrapped with at least two layers of a protective tape, such as silicon tape. The silicon tape provides a relatively smooth surface over which other operative elements of the hose, such as heating and temperature sensing devices, can be wrapped without experiencing appreciable abrasion. For example, the heating device is often an electrical resistance heater comprised of two or more bare electrically conductive resistance heating wires collectively wrapped by a layer of tape, such as Kapton® tape. The Kapton® tape serves primarily to consolidate the individual bare wires into a unitary group and this unitary group is then wrapped around the layers of silicon tape. In this instance, the silicon tape over the stainless steel braiding is essential because the Kapton® tape is not abrasion resistant. Without the protective layer of silicon tape, the stainless steel braiding would quickly abrade the Kapton® tape, allowing the bare wires to contact the stainless steel braiding and causing the electrical resistance heater to short out. Unfortunately, once the heating device shorts out, replacement of the entire hose is generally necessary.  
           [0005]    Using a protective tape between the stainless steel braiding and the heating device has several drawbacks. One drawback is the expense and time required to place the protective tape over the stainless steel braiding. Another drawback is that the protective tape acts as a thermal insulation layer between the heating device and the hot melt adhesive. Furthermore, the addition of the protective layers increases the diameter of the hose and may affect its flexibility.  
           [0006]    In light of the drawbacks discussed above, it would be desirable to provide a heated hose that includes an protective cover or casing that is not susceptible to abrasion when placed in contact with a reinforcing layer such as a stainless steel braided cover. Advantageously, the normally present protective tape should be eliminated resulting in reduced manufacturing costs and energy requirements.  
         SUMMARY OF THE INVENTION  
         [0007]    The present invention is directed to a hose which overcomes the drawbacks associated with previous hoses connecting supply tanks to adhesive dispensing guns. In the preferred embodiment, the hose includes a tube for carrying liquid therethrough. Preferably, the tube is made from polytetraflouroethylene. The tube is encased in a reinforcing layer which has an outer surface. Preferably, the reinforcing layer is a metallic braided cover and more preferably a stainless steel braided cover. A heater wire, which has an inner core contacted in surrounding relation by a protective casing, is wound around the reinforcing layer such that the protective casing is in direct contact with the outer surface of the reinforcing layer.  
           [0008]    Preferably, the protective casing is made from one or more abrasion resistant materials including self-lubricating polymers such as polytetraflouroethylene (PTFE), polyamides, polyethene, and ultrahighmolecular-weight polyethylene (UHWMPE) and/or non-self-lubricating polymers such as acetals. A thermal insulation layer is disposed around the heater wire and the reinforcing layer to act as a barrier to heat loss from the hose.  
           [0009]    Various additional advantages, objects and features of the invention will become more readily apparent to those of ordinary skill in the art upon consideration of the following detailed description of the presently preferred embodiments taken in conjunction with the accompanying drawings. 
       
    
    
     DETAILED DESCRIPTION OF DRAWINGS  
       [0010]    [0010]FIG. 1 is a diagrammatic perspective view of the hose of the present invention connecting a supply tank to a dispensing gun;  
         [0011]    [0011]FIG. 2 is a side elevational view of one section of the hose of FIG. 1 illustrating a portion of the wrapping sequence during the manufacture of the hose;  
         [0012]    [0012]FIG. 3 is a side elevational view of another section of the hose of FIG. 1 illustrating a further portion of the wrapping sequence during the manufacture of the hose; and  
         [0013]    [0013]FIG. 4 is a side elevational view of still another section of the hose of FIG. 1 illustrating the final wrapping sequence during the manufacture of the hose. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0014]    With reference to FIG. 1, an adhesive dispensing system  10  includes a hose  12  constructed in accordance with the principals of the present invention. The adhesive dispensing system further includes a melt unit, sometimes also referred to as an applicator, as shown schematically at  14  and a dispensing unit  16  with hose  12  connected therebetween. The melt unit  14  includes a reservoir or supply tank  18  which holds a thermoplastic material, such as a hot melt adhesive  20 . The melt unit  14  also incorporates a controller  22 , heaters  24  for melting and liquifying the adhesive  20 , and a pump  26  which is coupled to the supply tank  18  for pumping the liquified adhesive  20  from the supply tank  18 . A typical melt unit  14  would include any number of those manufactured by Slautterback Corporation or by Nordson Corporation, such as for example, the Nordson® 3000 series applicators. In addition, hose  12  of this invention may be used with other types of melting or liquifying apparatus, including premelters, drum and pail melters, etc.  
         [0015]    The dispensing unit  16  may include a manifold or service block  28  coupled to an adhesive dispensing gun  30 . The adhesive dispensing gun  30  selectively dispenses adhesive  20  onto a substrate  32  such as, for example, a nonwoven web used in the construction of a diaper or the flaps of a box or carton for sealing the flaps closed. Alternatively, a heated hand gun may be used to dispense the hot melt adhesive  20  onto the substrate  32 .  
         [0016]    Pump  26  is selectively controlled to pump adhesive  20  from supply tank  18 , through hose  12  and to adhesive dispensing gun  30 . Controller  22  monitors the temperature of adhesive  20  in the supply tank  18 , the hose  12 , and the manifold  28  and selectively controls heater  24  to maintain the adhesive  20  in the supply tank  18 , the hose  12 , and the manifold  28  within a predetermined temperature range.  
         [0017]    The hose  12  has an inlet end  34  and a discharge end  36 . The inlet end is coupled to the melt unit  14  and more specifically to a discharge outlet  38  which is coupled to pump  26 . Discharge end  36  of hose  12  may be coupled directly to manifold  28 . A wire harness  40 , which extends generally from inlet end  34 , has a connector  42  which couples to a connector  44  of melt unit  14 . Connector  44  is operatively connected to controller  22  for providing electrical power and/or control. A selectively detachable cable  46  is connected between a connector  48  associated with discharge end  36  and manifold  28 . As will be discussed in greater detail below, cable  46  serves to operatively connect controller  22  and heater  24  to manifold  28 .  
         [0018]    Hose  12  is comprised of several different layers and components. A section of hose  12  is shown in FIG. 2 in the initial stages of assembly. A tube  60  forms the operative core of the hose  12  through which the adhesive  20  actually flows at a pressure of up to several hundred psi. Tube  60  is preferably made from a material capable of withstanding relatively high temperatures such as polytetraflouroethylene (PTFE). Because tube  60  is made from PTFE, it is unable to withstand high fluid pressure. Accordingly, tube  60  must be reinforced by a reinforcing layer, such as encasing it from end to end in a braided cover  62 . Braided cover  62  should be made from high strength material to provide tube  60  with sufficient strength to resist the high fluid pressure as well as to provide flexibility. Preferably, the braided cover  62  is made from stainless steel. Because of its braided construction, braided cover  62  has a generally rough outer surface, especially compared to the smooth outer surface of tube  60 .  
         [0019]    Hot melt adhesive is generally a solid at room temperature. Furthermore, the viscosity of hot melt adhesive is temperature dependent. If the adhesive is allowed to cool below a critical flow temperature, the adhesive will not flow or dispense properly and may ultimately solidify and/or clog the adhesive dispensing system  10 . To counter this, a heater wire  64  is helically wound directly over the outside surface of the stainless steel braided cover  62 . The heater wire  64  and the number of wraps per unit length are selectively operative to maintain the adhesive within a predetermined temperature range in order that the adhesive flows and dispenses properly.  
         [0020]    Heater wire  64  of the present invention is comprised of an electrically conductive core  66  encased in a protective casing or coating  68 . The conductive core  66  may be a single strand or solid core, or it may be comprised of a number of strands. The conductive core  66  illustrated in FIG. 2 has only one strand encased in protective casing  68 . If additional strands or filaments are utilized to comprise conductive core  66 , they may be encased or encapsulated by a single protective casing  68 . Alternatively, multiple single core wires  64  may be wrapped around cover  62 . In accordance with the principles of the present invention, the protective casing  68  is constructed from material which is highly resistant to abrasion. Abrasion resistant materials suited for use as the protective cover  68  for heater wire  64  include self-lubricating polymers such as polytetraflouroethylene (PTFE), polyamides, polyethene, and ultrahigh-molecular-weight polyethylene (UHWMPE) and non-self-lubricating polymers such as acetals. Other polymers filled with PTFE, graphite or molybdenum disulfide (MoS 2 ) may also be used. The preferred manner of manufacturing the heater wire  64  is by extruding casing  68  in surrounding relation to core  66  or otherwise coating core  66  with casing  68 .  
         [0021]    Because the protective casing  68  is abrasion resistant, the heater wire  64  can be wrapped directly over the outer surface of steel braided cover  62  without the need for the usually intervening protective layer. During assembly of hose  12 , the heater wire  64  is wrapped from the inlet end  34  to the discharge end  36  and then wrapped back towards the inlet end  34 . As a result, heater wire  64  has two leads which exit the hose  12  around inlet end  34 , traverse wire harness  40  and connect to connector  42 . Tape (not shown) may be used to hold the heater wire  64  in place as it is wrapped around the steel braided cover  62 . As such, heater wire  64  is operatively connected to controller  24 .  
         [0022]    A temperature sensing device  70  is also helically wound in direct contact with steel braided cover  62 . The temperature sensing device  70  measures the temperature of the adhesive flowing through the tube  60 . The temperature sensing device  70  could be a resistance temperature device (RTD), a thermocouple, or any other suitable temperature sensing device for measuring temperature. The temperature sensing device illustrated in FIG. 2 is an RTD with first and second RTD leads  72 ,  74  shown as dashed lines. To facilitate assembly, a layer of tape  76  is used to secure the RTD leads  72 ,  74  to the steel braided cover  62 . Temperature sensing device  70  measures the temperature of the adhesive along a discrete portion of the hose  12  generally near the discharge end  36  of hose  12 . Like the two leads of the heater wire  64 , first and second RTD leads  72 ,  74  exit the hose  12  around inlet end  34 , traverse wire harness  40  and connect to connector  42 . As such, temperature sensing device  70  is operatively coupled to controller  22 .  
         [0023]    With reference to FIG. 3, hose  12  is shown in a more advanced stage of assembly relative to FIG. 2. A single layer of double stick tape  80  is wrapped around the heater wire  64 , the temperature sensing device  70  and the steel braided cover  62 . Advantageously, the double stick tape is constructed of fiberglass to provide some thermal insulation for the tube  60 . A thermal insulation layer  82  is then wrapped over the double stick tape  80 . As illustrated, the thermal insulation layer  82  has a 50% overlap such that the thermal insulation layer  82  forms two complete layers over the double stick tape  80 . Thermal insulation layer  82  may be applied without overlap such that only a single layer is present.  
         [0024]    With thermal insulation layer  82  in place, five electrical leads  84 ,  86 ,  88 ,  90 ,  92  are helically wound around thermal insulation layer  82  and extend between connector  42  of wire harness  40  and connector  48  at the discharge end of hose  12 . Electrical lead  84  is a ground wire which serves as a ground for the dispensing unit  16 . Electrical leads  86 ,  88  are two leads which operatively couple heater  24  to a heating element (not shown) internally located in manifold  28 . Similarly, electrical leads  90 ,  92  are two leads which operatively couple controller  22  to a temperature sensing device (not shown) internally located in manifold  28 . Although electrical leads  84 ,  86 ,  88 ,  90 ,  92  are shown in FIG. 3 wrapped over thermal insulation layer  82 , they could be wrapped under the thermal insulation layer  82 .  
         [0025]    With reference to FIG. 4, a layer of tape  94 , such as electrical tape, is wrapped around the thermal insulation layer  82  and the electrical leads  84 ,  86 ,  88 ,  90 ,  92 . A plastic braided cover  100  extends the entire length of the hose  12  to provide protection for the interior layers described above. Cuffs  102 ,  104  are placed over inlet end  34  and discharge end  36 , respectively, to protect the interior layers from potentially damaging substances such as water.  
         [0026]    While the present invention has been illustrated by a description of various preferred embodiments and while these embodiments have been described in considerable detail in order to describe the best mode of practicing the invention, it is not the intention of applicant to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications within the spirit and scope of the invention will readily appear to those skilled in the art.