HOT MELT APPLICATOR WITH ANTI-DRIP MECHANISM

Abstract: A hot melt applicator (110) has a feeding mechanism (154) for advancing a block (136) of solid material toward a melting chamber (118), and the feeding mechanism (154) includes a retraction device for shifting the block (136) a slight distance in a rearward direction to a retracted position subsequent to the dispensing operation. The feeding mechanism has a release device (197) for enabling the block (136) to float freely after moving to the retracted position in order to provide additional room for molten material in the melting chamber (118) upon thermal expansion of the material.

Description: This invention relates to a mechanism for feeding solid blocks of hot melt material toward a melting chamber of a hot melt applicator. Hand-held hot melt applicators as well as stationary hot melt applicators have a melting chamber that is adapted to receive and melt a forward end portion of an elongated, solid block of hot applied adhesive, sealant or similar material. The melting chamber has an outlet which dispenses molten material to a work site as additional portions of the block are fed into the melting chamber. During use of many types of conventional hand-held hot melt adhesive applicators, thumb pressure is applied against the trailing end of the block of adhesive to advance the block toward the melting chamber while the fingers of the same hand grasp a handle of the applicator. In recent years, however, applicators having a feeding mechanism for guiding the blocks of solid adhesive toward the melting chamber have become available. As one example, the applicator described in U.S. Patent No. 4,621,748 has a feeding mechanism with a drive member that, when depressed by an operator's thumb, moves a drive rack toward a position interleaved with a series of teeth formed in the block of adhesive in order to engage and shift the block forward toward the melting chamber. A common problem of conventional hot melt adhesive applicators is the tendency for molten adhesive to drip from the nozzle for some time after the operator has relieved the forward pressure on the block. In such situations, the operator must move the applicator to prevent excess adhesive from reaching the work site, and position the nozzle of the applicator over a drip pan to prevent damage to the work area. Even more serious, however, is the potential for the molten adhesive to burn the user while dripping from the nozzle after the intended dispensing operation. One solution proposed to overcome the problem of post-dispensing adhesive dripping is the provision of a check valve placed within the nozzle of the applicator. However, it is difficult to select a satisfactory, reliable spring for such a check valve because an overly stiff spring increases back pressure and hinders precise hand control of the dispensing operation while the block is fed into the melting chamber, while an overly weak spring may not close the valve in all instances. Certain hot melt applicators have a feeding mechanism that is operable to retract remaining solid portions of the adhesive block after a dispensing operation. As one example, some stationary hot melt applicators have a feeding mechanism with a pair of fixed axis drive rollers which continuously engage and indent one side of the block. The drive rollers are connected to a reversible motor that initially moves the block toward the melting chamber to dispense molten adhesive, and then away from the melting chamber to suck back molten adhesive from the nozzle tip and provide room in the chamber for subsequent thermal expansion of a portion of the adhesive which remains in the chamber. As another example, U.S. Patent No. 4,379,516 describes a hand-held applicator with a clamping member that releasably grips a block of adhesive as the block is advanced, and the member is molded with a pair of resilient wings which retract the member along with the block at the end of a dispensing operation. Rearward movement of the clamping member shown in U.S. Patent No. 4,379,516 ceases when the wings push the member into a position of contact with a rear wall of the applicator. However, the distance that the afore-mentioned devices retract the block at the end of a dispensing operation must be carefully selected. If the retraction distance is too small, insufficient space for subsequent thermal expansion may result and the pressure of the expanding adhesive may force molten adhesive from the nozzle. On the other hand, if the retraction distance is too large, the forward end of the block may cool excessively and additional time or energy will be necessary before molten adhesive can replace the voids in the heat block and the dispensing operation can resume. Moreover, if the retraction distance is too large, oxidation of the adhesive may be accelerated and an undue amount of air bubbles may be present in the extruded adhesive. The present invention concerns an applicator for dispensing molten material from an elongated block of solid thermoplastic material, and includes a frame and a melting chamber which is connected to the frame and which is adapted to receive and melt a portion of a block of solid material. A feeding mechanism is coupled to the frame for selectively advancing the block from an initial position toward a melting position partially within the melting chamber, and the feeding mechanism includes a retraction device for moving the block away from the melting chamber to a retracted position located between the initial position and the melting position after the portion of the block has melted. The feeding mechanism further includes a release device for enabling essentially free-floating, longitudinal movement of the block during thermal expansion of material within the melting chamber after the block has moved to the retracted position. The release device includes a sleeve having a resilient portion for frictional contact with the block such that the sleeve is movable with the block as the block is advanced a certain distance, and such that the block is also movable relative to the sleeve as the block continues to be advanced past said certain distance. The release device includes spring means for urging the sleeve and the block therewith in a rearwardly direction. The sleeve is essentially free-floating together with the block for movement relative to the frame after the block has been moved to the retracted position. Once the block is broken loose from its melting position, the build-up of excessive pressures of molten material within the melting chamber is normally prevented since thermal expansion of the forward end of the retracted block within the melting chamber causes the block to push itself rearwardly as necessary to compensate for the increased volume of the material. Consequently, the molten material does not unduly bear against the check valve in the nozzle of the applicator and post-dispensing dripping of molten material from the nozzle is largely avoided regardless of the distance that the solid block is initially retracted by the retraction device. Fig. 1 is a side elevational view of an applicator according to the present invention; Fig. 1a is a side elevational view of the applicator shown in Fig. 1 except that an actuator of the applicator has been depressed to advance a block of solid adhesive toward a melting chamber, and wherein a portion of the applicator is broken away in section; Fig. 2 is an enlarged, fragmentary, end elevational view of the applicator shown in Fig. 1 except that the block of adhesive has been removed; Fig. 3 is an enlarged, side cross-sectional view of a feeding mechanism alone of the applicator shown in Figs. 1-3 and taken along lines 3-3 of Fig. 2; Fig. 4 is a bottom view of the feeding mechanism taken along lines 4-4 of Fig. 3 except that a control body of the mechanism has been shifted to open a pair of gripping arms; Fig. 5 is an enlarged plan view of a portion of the applicator shown in Fig. 1a with the retraction mechanism illustrated in section to show the gripping arms in a closed position for advancing the block of adhesive toward the melting chamber; Fig. 6 is a view somewhat similar to Fig. 5 except that the feeding mechanism has been moved away from the melting chamber as shown in Fig. 1 and the arms have opened to release their grip from the block of adhesive; Fig. 7 is a fragmentary, enlarged, side cross-sectional view of a portion of the feeding mechanism shown in Figs. 5-6; and Fig. 8 is a front, top and side perspective view of part of the feeding mechanism illustrated in Fig. 7. An applicator 110 for dispensing molten thermoplastic material is shown in Figs. 1 and 1a and includes a molded frame 112 that presents a depending handle 114 and an upper portion which encases a heating block 116 (Fig. 1a). The heating block 116 has an internal melting chamber 118 in the shape of a truncated cone, and the chamber 118 has an inlet 120 on one end and tapers at its opposite end to an outlet 122 that leads to an internal passageway of an adjacent nozzle assembly 124. As illustrated in Fig. 1a, the nozzle assembly 124 has an internal check valve 126 which includes a stem 128 having an enlarged head 130. A compression spring 132 is received around the stem 128 remote from the head 130 and bears against an aperatured plate connected to the stem 128 to bias the latter to the left viewing Fig. 1a toward a position to bring the head 130 in sealing contact with internal walls of a nozzle tip 134. During a dispensing operation, pressure of molten thermoplastic adhesive within the melting chamber urges the head 130 toward an open position to enable the molten adhesive to flow from the melting chamber 118, through the outlet 122, around the stem 128 and the head 130 and out a small opening formed in the end of the nozzle tip 134 to the work site. The heating block 116 carries a pair of electrical resistance heating elements (not shown) that extend in a direction slightly inclined relative to the central axis of the melting chamber 118. Thus, as a forward end portion of a block of solid thermoplastic adhesive 136 is moved through the inlet 120 and into the melting chamber 118, the forward end portion melts and the molten adhesive is forced toward the outlet 122 as additional portions of the solid adhesive block 136 are directed into the chamber 118. The elongated block of adhesive 136 is formed with a series of coaxial cylindrical tooth portions 138, each of which is spaced apart from adjacent cylindrical portions 138 by square portions 140 which have uniform diagonal dimensions about equal to the diametrical dimensions of the cylindrical portions 138. The adhesive block 136 is essentially identical to the block of adhesive described in U.S. Patent No. 4,774,123, issued September 27, 1988. The frame 112 includes a rearwardly extending rack 142 that is shown in Figs. 1-2 and 5-6. Opposite vertical sides of the rack 142 are formed with a series of upright, spaced apart teeth 144 along with a horizontally extending channel 146 that can be best observed by reference to Fig. 1a. In addition, the rack has an open bottom, trapezoidal shaped channel 148 (Fig. 2) that extends in a horizontal direction parallel to the two side channels 146. As can be seen in Fig. 2, the top of the rack 142 has a longitudinally extending, rounded trough which supports the adhesive block 136 as the latter moves through a cylindrical sleeve 150 (Figs. 1 and 1a) and toward the inlet 120 of the melting chamber. The sleeve 150 carries a number of spaced apart, ring-shaped cooling flanges 152 to substantially prevent melting of portions of the adhesive block 136 that are adjacent the inlet 120 but outside of the melting chamber 118. The sleeve 150 also functions to align the adhesive block 136 during its travel through the inlet 120 and into the melting chamber 118. A feeding mechanism 154 is movably coupled to the rack 142 of the frame 112 for selectively advancing the adhesive block 136 toward the melting chamber 118. The feeding mechanism 154 includes a slide 156 which has a generally inverted U-shaped configuration, and a domed top portion of the slide 156 extends around the top of the adhesive block 136. A pair of lower, opposed, depending legs of the slide 156 each include a horizontally extending guide 158 which slides along one of the side channels 146 of the rack 142. The feeding mechanism 154 also includes a control body 160 that has an upper, trapezoidal-shaped key 162 that is complemental in cross-sectional configuration to the transverse shape of the trapezoidal channel 148 as can be appreciated by reference to Fig. 2. The key 162 extends in a horizontal direction parallel to the longitudinal axis of the rack 142, and is slidable along the length of the channel 148. Below the key 162, the control body 160 has a generally inverted U-shaped configuration (see, e.g., Fig. 3) that is presented by a front depending tab 164 and a rear depending tab 166 spaced behind the tab 164 in a direction along the length of rack 142. The control body 160 is movably connected to the slide 156 by a pair of arms 168, 168 which are shown in Figs. 2-6. The arms 168 are each pivotally connected to opposed, U-shaped portions of the slide 156 by means of a vertical pin 170 (Figs. 3-4) which extends through the coil of a wire torsion spring 172 that bears against adjacent portions of the slide 156 and the respective arms 168. Each of the arms 168 has a front portion with a pair of spaced apart, upright teeth 174 (Figs. 5-6) that are complemental in shape to the recesses between adjacent tooth portions 138 of the adhesive block 136. The arms 168 are swingable about pins 170 from a closed position that is illustrated in Fig. 5 with the teeth 174 in firm, gripping contact with the adhesive block 136, and to an open position as is shown in Fig. 6 wherein the arms 168 have disengaged and thus released their grip from the block 136. The springs 172 bias the arms 168 to the closed position. Referring now to Figs. 2-3, the arms 168 each have a depending, L-shaped leg 176 with a lowermost, inwardly extending portion that is pivotally connected to an upper link 178, 178 (Fig. 2) and a corresponding lower link 180, 182. In turn, links 178, 180, 182 are pivotally coupled to a rearwardly extending flange portion of the control body 160. Movement of the control body 160 in rearward direction relative to the slide 156 causes the links 178, 180, 182 to pull inwardly on the legs 176 and thereby pivot the respective arms 168 about pins 170 and cause the arms 168 to open as shown in Figs. 4 and 6 to disengage the adhesive block 136. On the other hand, movement of the control body 160 in a forward direction relative to the slide 156 moves the links 170, 180, 182 to aligned positions transverse to the length of the rack 142 and thus spreads the legs 176 apart to cause the arms 168 to swing in an opposite direction about pins 170 to a closed position wherein the teeth 174 firmly grip the adhesive block 136 in the manner shown in Fig. 5. The link 180 includes a projection 184 that is received on a shoulder 186 (Fig. 4) formed in the lower link 182 when the control body 160 is urged in a forward direction (toward the melting chamber 118) and the arms 168 have moved to their closed position as shown in Fig. 5. The projection 184 and shoulder 186 function as a stop to prevent the arms 168 from moving past their closed position when the control body 160 is moved forwardly so that the arms 168 do not toggle past their closed position and begin to open. As shown in Figs. 1-2, an elongated actuator 192 is movably connected at its lower end to the handle 114 of frame 112 by horizontal pivot pin 194. The pin 194 extends through a coil of a torsion spring 196 (Figs. 1a-2) that urges the actuator 192 in a counter-clockwise arc viewing Figs. 1-1a. An upper end of the actuator 192 is received in the space between the front tab 164 and the rear tab 166 of the control body 160. A housing 101 is located rearward of the feeding mechanism 154 and has four depending legs 102 (Figs.7-8) that snap in place between teeth 144 of rack 142 to securely hold the housing 101 in place. The housing 101 may be positioned at any one of a number of locations along the length of the rack 142 and functions as a stop for rearward movement of slide 156. The housing also provides a selective limit for the length of the stroke of the slide 156. The housing 101 has a generally inverted U-shaped configuration and carries two pins 103 which extend parallel to the rack 142. A generally cylindrical sleeve 105, made of synthetic resinous material, is integrally molded with a pair of elongated wings 107 which extend away from each other, and each wing 107 has a hole through which a respective pin 103 extends. Consequently, the sleeve 105, guided by pins 103, is movable relative to the housing 101 in directions parallel to the length of the rack 142 either toward or away from the melting chamber of the applicator 110. The cylindrical central portion of the sleeve 105 is formed with a number of resilient, forwardly extending short portions or tabs 109 as well as two somewhat longer tabs 111. The tabs 109, 111 are biased inwardly toward the central axis of the adhesive block 36 and provide a limited amount of resistance to movement of the block 36 relative to the sleeve 105 as explained in more detail below. In the use of the applicator 110, the actuator 192 is depressed to close the arms 168 of the feeding mechanism 154 and advance the slide 156 with the block 136 toward the melting chamber as shown in Fig. 5. As a result, the block 136 is advanced from its initial position to its melting position to dispense molten adhesive from the nozzle tip 134. As the block 136 advances, the tabs 109, 111 engage the block 136 with enough frictional force to cause the sleeve 105 to move forward toward the melting chamber with forward movement of the block 136 and compress springs means comprising a pair of springs 113 which are received around the pins 103 between the wings 107 and the housing 101. Once the springs 113 are fully compressed and the sleeve 105 has reached its extent of possible forward movement relative to the housing 101, continued forward presssure of the slide 156 on the block 136 overcomes the frictional force presented by the tabs 109, 111, enabling the springs 113 to shift the sleeve 105 relative to the block 136 in a rearward direction. The tabs 109, 111, however, are molded with an inherent, resilient, radially inward bias and thus grab the next rearward cylindrical portion 138 of the block 136, thereby causing the sleeve 105 to again move forwardly with further advancement of the block 136 toward the melting chamber. The longer tabs 111 are of a length relative to the shorter tabs 109 such that the sleeve 105 retracts only one-half of the distance between adjacent cylindrical portions 138 whenever the sleeve 105 moves rearwardly. Otherwise, elimination of the longer tabs 111 would cause the sleeve 105 to retract essentially the full distance between adjacent cylindrical portions 138 as the short tabs 109 jump from one portion 138 to the next. Once forward pressure on the actuator 192 is released, the spring 196 causes the top of the actuator 192 to bear against the rear tab 166 and the arms 168 immediately open and disengage the block 136. Thereafter, the spring 196 continues to urge the control body 160 in a rearward direction and thus enables the body 160 and the slide 156 to move relative to the adhesive block 136 and back toward the position illustrated in Fig. 1. Once the slide 156 is next to the stationary housing 101, a trailing end of each arm 168 comes into contact with a respective, inclined wall 115 of the housing 101 and the walls 115 thereafter insure that the arms 168 stay in their open position as shown in Fig. 6 until the next time that the actuator 192 is depressed. About the same time, the compressed springs 113 shift the sleeve 105 and cause the sleeve 105 to move the block 136 rearwardly to the retracted position shown in Fig. 6 since the tabs 109, 111 are in gripping engagement with the block 136. As soon as the block 136 has been retracted, the block 136 is essentially free-floating and may move further in a rearward direction as its forward end enlarges due to thermal expansion within the melting chamber over a period of time. The springs 113 are shown in Fig. 6 in their fully extended normal orientation, and the wings 107 may move rearwardly along the pins 103 within the spaces designated 117 (Fig. 6) of the housing 101 as may be necessary to compensate for thermal expansion of the block 136. The possible length of free-floating movement of the wings 107 in space 117 is equivalent to the distance 119 shown in Fig. 6 between the rear surfaces of the wings 107 and the facing wall of a rear portion of the housing 101. A release device 197 of the feeding mechanism 154 includes the spring 196, the sleeve 105 and the clearance spaces 117. Once the feeding mechanism 154 breaks loose the block 136 from its dispensing or melting position and the block 136 is retracted, the block 136 is free to move in a longitudinal direction. During the next dispensing operation, the teeth 174 of the arms 168 grasp the adhesive block 136 at a location which is spaced rearward of the location where the teeth 174 engaged the block 136 during the previous dispensing operation. In this manner, the teeth 174 move in ratchet-like fashion relative to the block 136 so that after a number of dispensing operations the block 136 has moved a substantial distance even though the stroke of the top of the actuator 192 during each individual dispensing operation is significantly smaller.

Claims: An applicator (110) for dispensing molten material from an elongated block (136) of solid material comprising: a frame (112); a melting chamber (118) connected to said frame and adapted to receive and melt a portion of an elongated block of solid material; a feeding mechanism (154) coupled to said frame for selectively advancing said block from an initial position toward a melting position partially within said melting chamber; said feeding mechanism including a retraction device for moving said block away from said melting chamber to a retracted position located between the initial position and the melting position after said portion of said block has melted, said feeding mechanism including a release device (197) for enabling essentially free-floating longitudinal movement of said block during thermal expansion of material within the melting chamber after said block has moved to said retracted position, wherein said release device includes a sleeve (105) having a resilient portion (109,111) for frictional contact with said block such that said sleeve is movable with said block as said block is advanced a certain distance and such that said block is also movable relative to said sleeve as said block continues to be advanced past said certain distance, and wherein said release device includes spring means (113) for urging said sleeve and said block therewith in a rearwardly direction, said sleeve being essentially free-floating together with said block for movement relative to said frame after said block has moved to said retracted position. The applicator of claim 1, wherein said release device includes a housing (101) carrying said sleeve and said spring means, said housing being movable to any one of a number of fixed locations on said frame in directions toward or away from said melting chamber. The applicator of claim 2, wherein said housing includes a wall (115), and wherein said feeding mechanism includes an arm (168) movable toward and away from a location in contact with said block, and wherein said wall is engagable with said arm for retaining said arm in a location out of contact with said block once said block has been moved to said retracted position. The applicator of claim 1, wherein said resilient portion comprises a tab (109,111) biased toward said block for frictional contact with said block.

Inventors: OSTER, CRAIG D., QUINN, GERALD W., WILSON, RODNEY J., OSTER, CRAIG D., C/O MINNESOTA MINING AND, QUINN, GERALD W., C/O MINNESOTA MINING AND, WILSON, RODNEY J., C/O MINNESOTA MINING AND
Applicants: MINNESOTA MINING AND MANUFACTURING COMPANY
Application year: 1990
Main classification: B05C17
IPC codes: B05C5, B05C17