Applicator for molten thermoplastic adhesives

A hot melt applicator for dispensing, in rapid succession, small discrete, uniform quantities of molten thermoplastic material, to enable a dotted line of such material to be formed on a workpiece surface, said applicator comprising:

• A. a body consisting of superimposed secured together body elements defining
• 1. an elongated pump chamber having an inlet near one end thereof, and
• 2. an outlet passage extending substantially straight down from said end of the pump chamber through the lowermost of said superimposed body elements to the exterior of the body, the upper end portion of said outlet passage comprising an outlet valve chamber communicated with the pump chamber at said end thereof, said outlet valve chamber having relatively closely spaced top and bottom walls and said outlet passage having a small volume as a whole and having at its outlet end a cross section substantially smaller than that of the pump chamber so that capillary action and atmospheric pressure prevent any molten thermoplastic therein from escaping therefrom when the outlet passage is sealed at its upper end;
• B. a plunger having a close sliding fit in the pump chamber;
• C. plunger actuating means operatively connected with the plunger to impart charging and discharging strokes to the plunger to successively draw molten thermoplastic into said pump chamber through the inlet, and expel such thermoplastic from said chamber and through the outlet passage;
• D. a ball valve element in said outlet valve chamber, said ball valve element being movable axially of the outlet passage between a closed position sealing the inner end portion of the outlet passage from communication with the pump chamber during the charging stroke of the plunger and an open position permitting flow of molten thermoplastic from the pump chamber through the outlet passage during the discharging stroke of the plunger;
• E. biasing means urging the ball valve element towards its closed position, said biasing means comprising a thin flat leaf spring having a captive end portion and a free end portion;
• F. coacting opposing surfaces on the lowermost and adjacent one of said superimposed body forming elements having the captive end portion of the leaf spring clamped therebetween to thereby secure the leaf spring in position with its free end portion extending into the outlet valve chamber and engaging said ball valve element and with the flat faces of its free end portion substantially parallel to and between said relatively closely spaced top and bottom walls of the outlet valve passage and normal to the axis of said outlet passage so that the outlet valve chamber can have a small volume but can nevertheless accommodate flexing of the free end portion of said leaf spring incident to opening and closing movement of said ball valve element.

An applicator by which molten thermoplastic adhesive from a source thereof at low pressure can be dispensed in rapidly successive small, discrete, uniform quantities, said applicator comprising:

• A. body means having a substantially flat bottom face and having therein
• 1. a bore opening to said bottom face and providing a pump chamber,
• 2. an inlet chamber communicable with the pump chamber and in which a small supply of molten adhesive can be retained, there being an inlet through another face of the body means by which said inlet chamber can be connected with a remote source of molten adhesive under low pressure, and
• 3. passage means leading from the inlet chamber to said bottom face, said passage means terminating in a counterbore which opens to said bottom face in spaced relation to the pump chamber and which provides an inlet valve chamber, and
• 4. said body means having in its said bottom face an elongated leaf spring groove which extends lengthwise in one direction from said counterbore and which is laterally spaced from said pump chamber;
• B. a closely fitting plunger reciprocable in the pump chamber;
• C. plunger actuating means operatively connected with the plunger to reciprocate the same successively in a first direction to draw molten adhesive from the inlet chamber into the pump chamber and in the opposite direction to expel molten adhesive from the pump chamber;
• D. a first ball check valve element in said inlet valve chamber movable to and from a closed position preventing flow of molten adhesive from the inlet valve chamber towards the inlet chamber;
• E. a first flat, elongated leaf spring located in said groove and having a free end portion engaged with the first valve element, for biasing the same towards its closed position;
• F. an upper plate-like member secured in flatwise underlying relationship to said bottom face of the body means, said upper plate-like member having substantially flat top and bottom faces and
• 1. having a small diameter bore coaxial with the pump chamber and a coaxial counterbore opening to its bottom face that provides an outlet valve chamber,
• 2. having in its upper face a substantially L-shaped groove that communicates the inlet valve chamber with the pump chamber, one leg of said groove terminating at the pump chamber and the last-mentioned bore, the other leg thereof being in register with a part of said groove in the body means, to provide a spring chamber in which said one end portion of the first leaf spring is flatwise movably received, the other end portion of said leaf spring being confined in said spring chamber by the flat upper surface of the upper member, and
• 3having in its lower face a shallow, elongated groove that extends lengthwise from said counterbore in the upper plate-like member;
• G. a second ball check valve element in said counterbore that is in the upper plate-like member, movable between a closed position blocking flow of molten thermoplastic upwardly into the pump chamber and an open position permitting flow downwardly out of the pump chamber;
• H. a second elongated, flat leaf spring, located in said groove in the bottom surface of the upper plate-like member and having a free end portion engageable with said second valve element for biasing the same towards its closed position;
• and
• I. a lower plate-like member having a substantially flat top surface and secured in flatwise underlying relation to the upper plate-like member, said lower plate-like member
• 1. having a small diameter outlet passage therethrough that is coaxial with the pump chamber, and
• 2 having in its upper surface an elongated shallow groove to which said outlet passage opens and which registers with said groove in the lower face of the upper plate-like member to provide a spring chamber in which said one end portion of the second leaf spring is movably received, the other end portion of said second leaf spring being held in place by the flat upper surface of the lower plate-like member.

A dispenser having a discharge orifice and by which molten thermoplastic fluid can be delivered from a source thereof to a zone of use in successive small, discrete, uniform quantities, said dispenser comprising:

• A. a body having
• 1. opposite faces,
• 2. a bore having one of its ends opening to one of said opposite faces, said bore providing a pump cylinder with a mouth defined by said end of the bore, and
• 3. an inlet compartment having
• a. an entrance through which molten thermoplastic fluid enters the dispenser from a source thereof, and
• b. an exit opening to said face of the body at a point spaced from but adjacent to the mouth of the pump cylinder;
• B. a plunger reciprocable in the pump cylinder to draw fluid into the cylinder from the inlet compartment during its charging stroke and to expel fluid from the cylinder during its discharing stroke;
• C. a passage-forming assembly secured to said face of the body to coact with the plunger in delivering fluid to the pump cylinder and discharging the same through the discharge orifice of the dispenser, said assembly comprising
• 1. a pair of inner and outer overlying plates, the former being contiguous to said face of the body,
• 2. means on the outer plate providing the discharge orifice of the dispenser,
• 3. means at the interface of said inner plate and said face of the body defining
• a. an inlet valve chamber in open communication with the mouth of the pump cylinder and with the exit of said inlet compartment, and
• b. an inlet valve seat with a port therethrough, and an outlet valve seat with a port therethrough, the former being between the exit of the inlet compartment and the inlet valve chamber, and the latter providing an exit from said inlet valve chamber,
• 4. means at the interface between said inner and other plates defining an outlet valve chamber that has open communication with the discharge orifice and that communicates with the inlet valve chamber through the port of said outlet valve seat,
• 5. a ball in each of said valve chambers, and
• 6. first and second leaf springs, each having an anchored end portion and a free end portion,
• the first leaf spring having its anchored end portion clamped between the inner plate and said face of the body with its free end portion projecting into the inlet valve chamber and engaging the ball therein, to yieldingly hold the same on its respective seat, and
• the second leaf spring having its anchored end portion clamped between the inner and outer plates with its free end portion extending into the outlet valve chamber and engaging the ball therein, to yieldingly hold the same on its respective seat,
• the orientation of the inlet and outlet valve chambers and their respective valve seats being such that during the charging stroke of the plunger the ball in the outlet valve chamber is drawn onto its seat enabling fluid to be drawn into the pump cylinder, while during the discharging stroke the disposition of the balls with respect to their seats is reversed enabling fluid to be forced from the pump cylinder and out of the discharge orifice;
• and
• D. means for reciprocating the plunger.