EP1057936A2

EP1057936A2 - Method and apparatus for melting road marking paint

Info

Publication number: EP1057936A2
Application number: EP00111055A
Authority: EP
Inventors: Satoshi Miyagawa; Masanori Takada; Osamu Tajima; Toshifumi Kinugasa
Original assignee: Miyagawa Kogyo Co Ltd; Sumitomo Corp; Nikko Co Ltd; Nikko KK
Current assignee: Miyagawa Kogyo Co Ltd; Sumitomo Corp; Nikko Co Ltd; Nikko KK
Priority date: 1999-06-02
Filing date: 2000-06-02
Publication date: 2000-12-06
Also published as: EP1057936A3; JP2000336615A

Abstract

A paint melting tank is provided with an electric heating device, e.g. an electric heater. Paint in the paint melting tank is melted with the electric heating device while being stirred with a stirring machine by electric power supplied from a generator. A control unit has a stirring speed control device for variably controlling the speed of the stirring machine automatically or by manual operation according to the stirring load on the stirring machine, thereby efficiently stirring the paint while avoiding suspension of the apparatus due to an overload.

Description

The present invention relates to a method and apparatus for melting paint used to mark traffic lines on roads.
Road marking paint is a solid matter, e.g. powder, at an ordinary temperature. When it is to be actually used, the paint is melted by heating. Conventionally, a paint melting tank is mounted on the deck of a truck, together with a gas burner for heating the paint melting tank, and a combustible gas cylinder for supplying gas to the gas burner. The truck is driven to a predetermined site, where a powder paint is cast into the paint melting tank and melted by heating with the gas burner. The melted paint is transferred to a marking device for marking traffic lines. Then, traffic lines or the like are marked on the road with the paint.
However, there have conventionally been cases, while the truck is driven to the predetermined site, wherein the paint is melted by heating it with the gas burner of an apparatus for melting road marking paint. Thus, the conventional practice was in a danger of fire or the like and has a problem to be solved in terms of safety.
In view of the above-described circumstances, an object of the present invention is to provide a method and apparatus for melting a road marking paint, whereby the paint can be safely melted during transportation by truck to prevent a danger of fire or the like.
The present invention provides a road marking paint melting method including the steps of casting a road marking paint into a paint melting tank provided with an electric heating device, and heating the paint in the paint melting tank to a predetermined temperature with the electric heating device while stirring the paint, thereby melting the paint.
Preferably, the paint is stirred in such a manner that the stirring speed is low in the early stages of melting of the paint and is increased during the time when the paint is in the course of melting, and after the paint has been completely melted, the stirring speed is reduced to a low level.
In addition, the present invention provides an apparatus for melting a road marking paint. The apparatus includes a paint melting tank having a stirring machine installed therein, an electric heating device for heating the paint melting tank, a control unit for controlling the drive of the electric heating device and the stirring machine and a generator for supplying driving electric power to the electric heating device and the stirring machine.
Preferably, the control unit has a stirring speed control device for variably controlling the revolutionary speed of the stirring machine automatically or by manual operation according to the stirring load on the stirring machine.
Preferably, the stirring speed control device has an inverter for controlling the revolutionary speed of the stirring motor for the stirring machine and a current detector for detecting the load current value of the stirring motor. The stirring speed control device further has a controller for outputting a control signal to the inverter so that the load current value detected by the current detector will not exceed an upper-limit current set value.
According to the road marking paint melting method of the present invention, a road marking paint is electrically melted and heated to an optimum working temperature in a paint melting tank provided with an electric heating device, e.g. an electric heater. Therefore, since the road marking paint melting method according to the present invention does not use a gas burner as used in the conventional method, it is safe from danger of fire or the like. In addition, the stirring speed is varied according to stirring load conditions varying for each phase of the paint melting process. i.e. in the early stages of the paint melting operation and during the time when the paint is melting and after the paint has been completely melted. Thus, it is possible to avoid undesired suspension of the stirring motor or the like due to an overload or an overcurrent and also avoid an over-capacity operation of the generator. Moreover, it is possible to stir the paint uniformly and to improve the stirring efficiency.
According to the road marking paint melting apparatus of the present invention, a paint melting tank is provided with an electric heating device, e.g. an electric heater, a stirring machine, a control unit, and a generator to electrically heat the paint in the tank to a desired temperature while appropriately stirring it. Thus, the apparatus is safe because a gas burner is not used, and it is possible to improve the stirring efficiency. Moreover, a complete set of melting devices, including a generator, can be mounted on the deck of a truck, for example, and operated on the truck. Therefore, the paint can be safely heated even when the truck is being driven. Accordingly, the operating efficiency can be improved.
In addition, the road marking paint melting apparatus has a stirring speed control device for variably controlling the speed of the stirring machine, thereby allowing the speed of the stirring machine to be variably controlled automatically or manually according to the stirring load. Therefore, the stirring can be appropriately performed in conformity to different conditions in each phase of the paint melting process, i.e. in the early stages of the paint melting operation and during the time when the paint is melting and after the paint has been completely melted, as stated above.
In addition, the road marking paint melting apparatus is provided with an inverter for controlling the number of revolutions of a motor for the stirring machine and a current detector for detecting the load current value of the stirring motor, together with a controller therefor. Accordingly, it is possible to prevent the stirring motor from being overloaded and to automatically maintain an optimum stirring speed according to the viscosity condition of the paint. Thus, the stirring efficiency can be further improved.
The above and other objects, features and advantages of the present invention will become more apparent from the following description of the preferred embodiments thereof, taken in conjunction with the accompanying drawings.
Fig. 1 is a diagram schematically showing one embodiment of the road marking paint melting apparatus according to the present invention as mounted on a truck.
Fig. 2 is an enlarged vertical sectional view of a paint melting tank and devices associated therewith in the apparatus shown in Fig. 1.
Fig. 3 is a block diagram showing the way in which devices of one embodiment of the apparatus shown in Fig. 1 are connected to each other.
Fig. 4 it a block diagram showing the way in which devices of another embodiment of the apparatus shown in Fig. 1 are connected to each other.
Fig. 5 is a block diagram showing one example of a stirring speed control device shown in Fig. 4.
One embodiment of the present invention will be described below in detail with reference to the accompanying drawings.
A road marking paint melting apparatus 1 has a cylindrical paint melting tank 2. The paint melting tank 2 has a paint casting inlet 3 in the top thereof and a molten paint outlet 4 in the bottom thereof. The paint melting tank 2 further has an outlet gate 5 that can be opened and closed as desired.
An electric heater 6 as an electric heating device is disposed to surround the peripheral and bottom walls of the paint melting tank 2. A heat-insulating material is bonded to the outer periphery of the electric heater 6 to construct a heating and heat-insulating structure. It should be noted that the electric heater 6 may be a wire-like or plate-like heater disposed on the peripheral and bottom walls of the paint melting tank 2 as shown in Fig. 2. Alternatively, a rod-shaped heater may be inserted directly into the paint melting tank 2 or fitted in a stirring shaft 10 (described later). It is also possible to adopt a heating method. e.g. induction heating or high-frequency beating, in place of the electric heater 6 as an electric heating device for the paint melting tank 2.
A temperature sensor 7 for detecting the paint temperature is disposed at a predetermined position on the paint melting tank 2. The paint temperature detected with the temperature sensor 7 is compared with a predetermined set value of paint temperature, which is set with a temperature setting device (not shown) in a control unit 13 (described later). On the basis of the result of the temperature comparison, the electric power supplied to the electric heater 6 is controlled so that the paint is heated to the predetermined set temperature.
A stirring machine 8 has stirring blades 11 secured to a stirring shaft 10 of a motor 9 for stirring. The motor 9 is installed on a top cover 2a of the paint melting tank 2. The stirring blades 11 are inserted in the paint melting tank 2. It should be noted that the stirring blades 11 are only required to operate such that in the early stages of melting, the stirring blades 11 stir a solid paint to allow it to melt even more easily, and after the paint has been melted, the stirring blades 11 stir the molten paint uniformly. Accordingly, the stirring blades 11 may be plate-shaped blades as shown in Fig. 2. Alternatively, the stirring blades 11 may be rod-shaped blades or propeller blades.
A generator 12 (see Figs. 1 and 3) generates electric power for energizing the electric heater 6 and for driving the stirring machine 8. The generator 12 is disposed next or close to the paint melting tank 2.
A control unit 13 (see Figs. 1 and 3) controls the supply of electric power from the generator 12 to the devices 6 and 9, thereby controlling the drive of each device. More specifically, as shown in Fig. 3, the control unit 13 is connected to the electric heater 6, the temperature sensor 7, the electric or hydraulic motor 9 for stirring, and the generator 12. The control unit 13 has a temperature setting device (not shown) for setting a paint temperature. In addition, it is preferable for the control unit 13 to have, as shown in Fig. 3, a timer 14 for controlling the timing of supplying the electric power to the electric heater 6, and an inverter (frequency converter) 15 as a stirring speed control device capable of variably controlling the number of revolutions of the stirring motor 9 appropriately according to the stirring load on the stirring machine 8.
When the inverter 15 is provided as a stirring speed control device as stated above, the stirring speed can be changed appropriately by variably setting the inverter 15 by manual operation as described later. It is also possible to change the stirring speed by variably setting the inverter 15 automatically, instead of manual operation, using an automatic variable speed control circuit 21 including the inverter 15 as shown in Figs. 4 and 5.
In Fig. 5, the automatic variable speed control circuit 21 has a current detector 22 for detecting the load current value (or load power value) of the motor 9 for stirring. The current detector 22 is connected to a controller 24 through an A/D converter 23. The controller 24 is connected with an upper-limit current value setting unit 25 for setting an upper limit of the load current value and a frequency setting unit 26 for setting a frequency for speed setting to the inverter 15.
Next, a method of melting a paint by using the above-described road marking paint melting apparatus 1 will be described.
First, the road marking paint melting apparatus 1 (including the generator 12 and the control unit 13) is mounted on the deck of a truck 16 as shown in Fig. 1. To melt a paint by heating, the generator 12 is driven first to make the apparatus ready to supply electric power to each device. Next, a predetermined amount of powder or solid paint is cast into the paint melting tank 2 from the inlet 3. When a beating operation is carried out by using a timer, the timer 14 in the control unit 13 is set. It will be convenient if the timer 14 is set by taking into consideration the time required for the truck 16 to reach the application site, for example. It should be noted that when there is no timer 14, the heating switch of the electric heater 6 is turned on appropriately at the time of starting the use of the apparatus.
When the heating switch of the electric heater 6 is turned on, electric power generated from the generator 12 is supplied to the electric heater 6 of the paint melting tank 2 to start heating the paint. The temperature of the paint in the paint melting tank 2 is detected sequentially with the temperature sensor 7, and the electric heater 6 is on-off controlled by the control unit 13 so that the detected temperature value becomes equal to the set temperature.
The temperature of the paint in the paint melting tank 2 gradually rises, and eventually the paint begins to melt. At this time, the operator drives the motor 9 for stirring with hand or automatically to rotate the stirring blades 11, thereby starting to stir the paint. More specifically, in a case where only the inverter 15 is provided as a stirring speed control device, as shown in Fig. 3, if the inverter 15 is operated with hand, the operator actuates the knob of the inverter 15 with hand while confirming the stirring load (load current value) of the stirring machine 8, and sets the inverter 15 at an appropriate speed for stirring. Accordingly, in the early stages of the paint melting operation, the stirring machine 8 is rotated at a low stirring speed, thereby avoiding breakage of the stirring blades 11, which might otherwise be caused by an overload or overcurrent due to the condition of the paint, which is still solid, and also promoting melting of the paint. When the paint is in the course of melting or a powder paint is added to the molten paint, the stirring speed is increased appropriately, thereby further promoting stirring and allowing the paint to be stirred uniformly. After the paint has been completely melted, the stirring speed is reduced back to the low level, thereby preventing the paint from burning. In addition, it is possible to maintain the uniformly stirred condition of the paint. Thus, efficient stirring can be carried out by adjusting the stirring speed appropriately on the basis of the operator's experience.
Next, in Figs. 4 and 5, an operation of variably controlling the stirring speed automatically, instead of manual operation, by using the automatic variable speed control circuit 21 including the inverter 15 will be described. After stirring of the paint by the stirring machine 8 has been started, the controller 24 constantly compares a load current value detected with the current detector 22 with an upper-limit current set value, which has been set and stored in the upper-limit current value setting unit 25. When the detected load current value exceeds the upper-limit current set value, the controller 24 automatically outputs a lower frequency signal to the frequency setting unit 26 to reduce the stirring speed. When the detected load current value is not more than the upper-limit current set value, the controller 24 automatically sets an optimum frequency, which has been arbitrarily set and stored, to the frequency setting unit 26.
Thus, when the temperature of the paint is low and the stirring load is heavy, the stirring machine 8 is rotated at low speed. In the course of melting the paint, during which the temperature of the paint rises, the stirring machine 8 is automatically rotated at high speed. After the paint has been completely melted, the stirring speed is reduced back to the low speed. Consequently, the stirring machine 8 can be rotated at an optimum speed at all times. Thus, it is possible to avoid undesired suspension of the inverter 15 and the generator 12 due to an overload and to improve the stirring efficiency.
In a case where the apparatus is not provided with any device for controlling the speed of the motor 9 for stirring, the operator should preferably drive the stirring machine 8 with hand at an appropriate timing according to his/her judgment. Alternatively, it is preferable to drive the stirring machine 8 automatically by the timer setting at an appropriate timing after a predetermined period of time has elapsed after the start of heating.
When the temperature of the paint in the paint melting tank 2 has reached a desired temperature, line marking on a road is started. At this time, an application device (not shown) for marking traffic lines or the like is placed to face the outlet 4 of the paint melting tank 2, and the outlet gate 5 of the paint melting tank 2 is opened to pour a predetermined amount of molten paint into the application device from the outlet 4. Then, predetermined traffic lines or the like are marked on the road with the application device.
The use of an electric heating device to heat the paint in the paint melting tank 2 allows the paint to be safely melted during transportation by truck without a danger of fire or the like, and eliminates the need to watch the paint melting operation continuously before and during transportation and at the application site, which has been needed in the case of the conventional method using a gas burner to heat the paint melting tank. If the stirring speed control device is provided, the stirring speed can be reduced in the early stages of the paint melting operation so that an overload will not occur. Accordingly, it is possible to avoid undesired suspension of the apparatus.
As has been stated above, according to the road marking paint melting method of the present invention, a road marking paint is cast into a paint melting tank provided with an electric heating device, e.g. an electric heater, and the paint is melted and heated to an optimum working temperature with the electric heating device. Thus, the road marking paint melting method according to the present invention does not use a gas burner as used in the conventional method. Therefore, the present invention is safe from danger of fire or the like.
In the early stages of the paint melting operation. stirring is carried out at low speed, thereby avoiding breakage of the stirring blades, which might otherwise be caused by an overload due to the condition of the paint. which is still solid, and an over-capacity operation of the generator and also promoting melting of the paint. When the paint is melting or a powder paint is added to the molten paint, the stirring speed is increased appropriately, thereby further promoting stirring and allowing the paint to be stirred uniformly. After the paint has been completely melted, the stirring speed is reduced back to the low level, thereby preventing the paint from burning. In addition, it is possible to maintain the uniformly stirred condition of the paint.
The road marking paint melting apparatus according to the present invention uses an electric heating device, e.g. an electric heater, in place of a gas burner, as a device for melting the paint in the paint melting tank. The supply of electric power to the electric heating device is on-off controlled with a control unit automatically or by manual operation to heat the paint cast in the paint melting tank to a desired temperature. Therefore, the road marking paint melting apparatus is safe from danger of fire or the like. During heating of the paint, the paint is stirred by appropriately driving a stirring machine in the paint melting tank with the control unit. Accordingly, in the early stages of melting, the solid paint is allowed to melt even more easily, and after it has been melted, the paint is stirred uniformly. Thus, the stirring efficiency can be improved.
In addition, the road marking paint melting apparatus has a generator for supplying driving electric power to the electric heating device and the stirring machine. A complete set of devices described above can be mounted on the deck of a truck and operated on the truck. Accordingly, the paint can be safely heated even when the truck is being driven, and the operating efficiency can be improved.
In addition, the road marking paint melting apparatus has a stirring speed control device for variably controlling the speed of the stirring machine, thereby allowing the speed of the stirring machine to be variably controlled automatically or by manual operation according to the stirring load. Therefore, it is possible to avoid breakage of the stirring blades and an over-capacity operation of the generator, promote melting of the paint, stir the paint uniformly and prevent the paint from burning by controlling the stirring speed such that the stirring speed is low in the early stages of the paint melting operation, high during the time when the paint is in the course of melting, and low again after the paint has been completely melted, as stated above.
In addition, the road marking paint melting apparatus has an inverter for controlling the number of revolutions of a motor for the stirring machine. The load current value of the motor for the stirring machine is detected with a current detector, and the frequency setting of the inverter is performed so that the load current value will not exceed an upper-limit current set value, Thus, the stirring machine is driven to stir at an optimum speed according to the viscosity condition of the paint. Accordingly, an optimum stirring speed can be automatically maintained at all times according to the viscosity condition of a paint to be melted without overloading the motor for the stirring machine, and the paint can be stirred with high efficiency.
It should be noted that the present invention is not necessarily limited to the foregoing embodiments but can be modified in a variety of ways without departing from the gist of the present invention.

Claims

A road marking paint melting method comprising the steps of:

casting a road marking paint into a paint melting tank provided with electric heating means: and

heating the paint in said paint melting tank to a predetermined temperature with said electric heating means while stirring said paint, thereby melting said paint.
A road marking paint melting method according to claim 1, wherein said paint is stirred in such a manner that a stirring speed is low in early stages of melting of said paint and increased during a time when said paint is in the course of melting, and after said paint has been completely melted, the stirring speed is reduced to a low level.
An apparatus for melting a road marking paint, said apparatus comprising:

a paint melting tank;

a stirring machine having at least stirring blades disposed in said paint melting tank;

electric heating means for heating said paint melting tank;

a control unit for controlling drive of said electric heating means and said stirring machine: and

a generator for supplying driving electric power to said electric heating means and said stirring machine.
An apparatus according to claim 3, wherein said control unit has stirring speed control means for variably controlling a speed of said stirring machine automatically or by manual operation according to a stirring load on said stirring machine.
An apparatus according to claim 4, wherein said stirring machine has a stirring motor for rotating said stirring blades,

said stirring speed control means having at least:

an inverter for controlling a number of revolutions of said stirring motor;

a current detector for detecting a load current value of said stirring motor; and

a controller for outputting a control signal to said inverter so that the load current value detected with said current detector will not exceed an upper-limit current set value.